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Abdulrahman, Nadia Abdulkarim (2014) Nanotechnology and c...
I
Nanotechnology and Chiroptical Spectroscopy
to Characterise Optically Active
Chiral Metamaterials
By
Nadia Abdulkarim Ab...
II
Abstract
Work in this thesis involves manipulating the interaction between light and
matter in order to retrieve import...
III
Contents
Abstract .......................................................................................................
IV
2.6.5. Influence of the nanofeatures size on CD spectra ......................................111
2.6.6. Compliments ne...
V
5. Chapter 5: The origin of off-resonance non-linear optical activity of Gold chiral
nanomaterials ........................
VI
9. Appendix B: List of Figures ......................................................................................29...
VII
n nano
Nd:YAG Neodymium Doped Yttrium Aluminum Garnet
OA-SHG Optically Active-Second Harmonic Generation
OR Optical Ro...
VIII
Publications
1. Induced Chirality through Electromagnetic Coupling between Chiral
Molecular Layers and Plasmonic Nano...
IX
2. The origin of off-resonance non-linear optical activety of a gold chiral
nanomaterial.
Nadia A. Abdulrahman, Christo...
X
Acknowledgements
I would like to thank my supervisor Dr. Malcolm Kadodwala for his constant
assistance and guidance duri...
XI
Appreciative thanks also go to academics in our school of chemistry, Dr. Adrian
Lapthorn and Dr. Justin Hargreaves for ...
XII
Finally I would like to thank the Iraqi government for my PhD scholarship
funding. I would also like to thank Engineer...
XIII
Author`s Declaration
I declare that, except where explicit reference is made to the contribution of
others, that this...
Chapter 1
1
Chapter 1: Introduction
1.1. Overview
Chirality, or handedness, is the key phenomenon of interest in this thes...
Chapter 1
2
the plane of the benzene ring is described as a chiral plane. In order to assign
the absolute configuration fo...
Chapter 1
3
2. The G`s nanostructures are another example of superstructural chirality. Here
we used to number the negativ...
Chapter 1
4
Figure 1: A chiral molecule is a molecule of four different groups, represented here by
1, 2, 3 and 4, these g...
Chapter 1
5
O
O
OH
O
(CH2)8
Figure 2: Chiral plane and its absolute configuration for cyclophane. a shows
the molecule wit...
Chapter 1
6
Figure 3: Our methodology to determine the chirality of our nanostructures. a
illustrates how the four arms of...
Chapter 1
7
L- gammadionL- G`s
0
200000
400000
600000
800000
1000000
0
30
60
90
120
150
180
210
240
270
300
330
0
200000
4...
Chapter 1
8
An increasing number of spectroscopic techniques that are sensitive to chirality
have emerged in recent years ...
Chapter 1
9
effect. e.g. 2,2′-dimethoxy-binaphtyl (Figure 5e) and our J-like shapes (Figure 5
f), again, more examples can...
Chapter 1
10
SEM and AFM microscopy. In chapter 4, the possibility of characterising
biomolecules adsorbed on the surface ...
Chapter 1
11
h
d
b
Figure 5: Four concepts of chirality are demonstrated here, these are:
propeller is demonstrated in a f...
Chapter 1
12
Figure 6: Five concepts of chirality are demonstrated here, these are: pseudo
chirality in a for different ex...
Chapter 1
13
1.2. Historical review
The study of optical activity and its possible applications has a long and
distinguish...
Chapter 1
14
mirror, ideally realized, cannot be brought to coincide with itself `[2ch1 pp25
, 27].
Thereafter, biological...
Chapter 1
15
1.3. References
1. Nafie L. A., “Vibrational Optical Activity Principles and Applications”, Jhon
Wiley& Sons ...
Chapter 1
16
22. Vignolini S., Yufa N.A., Cunha P. S., Guldin S., Rushkin I., Stefik M., Hur K.,
Wiesner U., Baumberg J. J...
Chapter 2
17
Chapter 2: The Nanofabrication of plasmonic
nanostructures by Electron Beam Lithography
Abstract
This chapter...
Chapter 2
18
Electron beam lithography (or E-beam writing) is one of many other
lithographical techniques, these are: The ...
Chapter 2
19
For this project, 2D plannar chiral metamaterials have been manufactured using
EBL with nanofeatures ranging ...
Chapter 2
20
5.The radiant signal domain (which our sensors are characterised under): here
the signals are quantities of t...
Chapter 2
21
< 0) and magnetic permeability (µ < 0) simultaneously (see Figure 1 which
illustrates materials classificatio...
Chapter 2
22
techniques and pathogenic detections [37,38]. Advancements in scanning
electronic and scanning atomic force m...
Chapter 2
23
Observer
Imag
e
Objec
t
Material with negative
refractive index
Ordinary
refraction
Negative
refraction
Air A...
Chapter 2
24
2.1.3. Surface Plasmons
At a definite wavelength, light can excite metal-dielectric surfaces since metals
hav...
Chapter 2
25
film, it requires having the electromagnetic waves of the incident light to be
incident on the metal surface ...
Chapter 2
26
angular frequency (2f), t is time, r is the propagation axis (x or y or z) and
j=√-1 [45].
Metal thin film
P...
Chapter 2
27
Figure 5: Surface Plasmon Polaritons (SPPs). a represents the
electromagnetic field E propagating parallel to...
Chapter 2
28
As mentioned previously, the SPPs from the nanoparticles and the
nanostructures are confined by the LSPR whic...
Chapter 2
29
different aspect ratios support plasmon mode of field polarization parallel
(Figure 8d) or perpendicular (Fig...
Chapter 2
30
enhancement at a distance gap on the order of the radius of the nanoparticle. In
addition, Giessen’s group th...
Chapter 2
31
Figure 10: Relationship between nanoparticle size and shape and LSPR
wavelength. LSPR wavelength of periodic ...
Chapter 2
32
Figure 11: SPPs enhancements are occurred as a result of near field
coupling at the separation gaps between n...
Chapter 2
33
Figure 12: SPPs enhancement occurs as a result of near field coupling at
the separation gaps between the nano...
Chapter 2
34
In either case (PSPR or LSPR), SPPs are very beneficial fields and have a number
of applications especially i...
Chapter 2
35
affinity of the system. An example for application of LSPR in biosensing
technology is the Superchiral field ...
Chapter 2
36
2.1.4. Plasmonic metamaterials
As it already mentioned, this chapter describes the nanofabrication of the
pla...
Chapter 2
37
2.2. Theory and background
2.2.1. Electron beam- substrate surface interferences
As mentioned above, electron...
Chapter 2
38
These simulations are in agreement with the view of Rai-Rechoudhury who
suggested in 1997 that the electron b...
Chapter 2
39
beam energy. The electron beam launching with high energy causes the electron
beam proximity effect to expand...
Chapter 2
40
2.2.2. Electron beam- PMMA resist interferences
PMMA resist is an organic transparent polymer synthesised by ...
Chapter 2
41
altered to high solubility value. The ionization of the resist molecules aids the
polymer chains to break int...
Chapter 2
42
exposure dose of 50, 100 and 150µC/cm2
on PMMA resist. They believe that at a
dose of 50µC/cm2
; the fragment...
Chapter 2
43
grating pitch by accelerating voltage of 30keV. Different doses (line doses) were
applied here, these are 2.0...
Chapter 2
44
Figure 20: The theoretical estimation of the scission of the time exposure domain in
molecular level. The hig...
Chapter 2
45
The effect of the accelerating voltage domain (which represents a key
objective of the electron beam interfer...
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials
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Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials

Published on: Mar 3, 2016
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Transcripts - Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials

  • 1. Glasgow Theses Service http://theses.gla.ac.uk/ theses@gla.ac.uk Abdulrahman, Nadia Abdulkarim (2014) Nanotechnology and chiroptical spectroscopy to characterise optically active chiral metamaterials. PhD thesis. http://theses.gla.ac.uk/5480/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given
  • 2. I Nanotechnology and Chiroptical Spectroscopy to Characterise Optically Active Chiral Metamaterials By Nadia Abdulkarim Abdulrahman MSc. Physical Chemistry Submitted in the fulfilment of the requirements for the Degree of Doctor of Philosophy in the School of Chemistry Collage of Science and Engineering University of Glasgow May 2014
  • 3. II Abstract Work in this thesis involves manipulating the interaction between light and matter in order to retrieve important information from adsorbed molecules, such as their structure and/or function, and henceforth, to gain insight into highly sensitive detection capabilities for biosensor applications. Such manipulation might be achieved via rationalising the surfaces of optically active metamaterials by taking full advantage of the recent growth in a variety of nanotechnology disciplines. As such, the possibility of characterising biomolecules adsorbed on the surface of chiral and achiral plasmonic metamaterials, referred to as chiral and achiral plasmonic nanostructures, have been investigated. Also, illustration and applications for the so called `Superchiral Field`, which has been generated via circular polarised light (CPL), are presented. Microscopic origin of the chiroptical second harmonic generation (SHG) signal that originates from the surface of the chiral nanostructures has been investigated. Practical visualisation via femtosecond laser beam of regions of intense plasmonic activity, i.e., hot-spot mapping, has been performed. In general, the work described in this thesis involved the use of several linear and non-linear chiroptical techniques namely as extinction (absorption and scattering), CD, ORD and SHG spectroscopy, in addition to scanning imaging namely SEM and AFM microscopy. Given that most biomolecules contain either chiral molecules or adopt chiral structures, the plasmonic nanostructures presented in this work could be used to study a wide range of biological problems, from the structure of biomolecules associated with neurodegenerative illnesses such as Alzheimer’s disease and Parkinson’s disease, to DNA and viruses. As a regard, general classifications for aspects of chirality are presented in order to emphasise the association of the samples used in this chapter with some of these aspects. All samples are fabricated via Electron Beam Lithography (EBL) in JWNC cleanroom/UK; the associated fabrication techniques, the instruments and the experimental methods are described.
  • 4. III Contents Abstract .................................................................................................................................II Contents............................................................................................................................... III Abbreviations used in this thesis........................................................................................ VI Publications...................................................................................................................... VIII Acknowledgements.............................................................................................................. X Author`s Declaration........................................................................................................ XIII 1. Chapter 1: Introduction ................................................................................................1 1.1. Overview...................................................................................................................1 1.2. Historical review.....................................................................................................13 1.3. References...............................................................................................................15 2. Chapter 2: The nanofabrication of plasmonic nanostructures by Electron Beam Lithography ..................................................................................................................17 2.1. Introduction.............................................................................................................17 2.1.1. Electron Beam Lithography .........................................................................17 2.1.2. Metamaterials ...............................................................................................20 2.1.3. Surface plasmon ...........................................................................................24 2.1.4. Plasmonic metamaterials..............................................................................36 2.2. Theory and background ..........................................................................................37 2.2.1. Electron beam-substrate surface interferences ............................................37 2.2.2. Electron beam-PMMA resist interferences .................................................40 2.2.3. Resist Development......................................................................................46 2.2.4. Forms of morphological damages ...............................................................47 2.3. Instruments .............................................................................................................51 2.3.1. VB6 UHR WFE machine ............................................................................51 2.3.2. Plassys II MEB550S E-beam Evaporator ....................................................54 2.3.3. Scanning Electron Microscope (SEM) ........................................................57 2.4. Pre-nanofabrication work........................................................................................68 2.4.1. Pattern Design ..............................................................................................68 2.4.2. Substrates preparations ................................................................................75 2.4.3. Cleaning routine ...........................................................................................76 2.5. Nanofabrication parameters....................................................................................77 2.5.1. PMMA resist ................................................................................................77 2.5.2. Resist spin coating........................................................................................81 2.5.3. The spot size, the VRU and the Dose parameters ........................................84 2.5.4. Patterns writing.............................................................................................94 2.5.5. Wet etching ..................................................................................................95 2.5.6. The Development .........................................................................................96 2.5.7. Metal deposition...........................................................................................99 2.5.8. Lifting off ..................................................................................................100 2.6. Samples validation test .........................................................................................105 2.6.1. Influence of the nanopatterns shapes..........................................................105 2.6.2. Influence of the nanopatterns chiral orientation ........................................106 2.6.3. Influence of the depth of the metallic layer ...............................................107 2.6.4. Pattern reproducibility................................................................................109
  • 5. IV 2.6.5. Influence of the nanofeatures size on CD spectra ......................................111 2.6.6. Compliments necessity...............................................................................112 2.7. Summary...............................................................................................................113 2.8. References.............................................................................................................113 3. Chapter 3: Super Chiral Fields to Sense Biomolecules on Gold chiral plasmonic nanostructures via CD spectroscopy and scanning microscopy ............................117 3.1. Introduction ..........................................................................................................117 3.1.1. Chirality and biomolecules sensing............................................................117 3.1.2. CD spectroscopy.........................................................................................118 3.2. Theory and background ........................................................................................119 3.2.1. Circular Dichroism (CD) and Optical Rotation (OR) ...............................119 3.2.2. Theoretical aspects of the Superchiral Field ..............................................130 3.2.3. Superchiral Field to sense biological molecules.........................................146 3.3. Experimental work................................................................................................148 3.4. Results and discussions.........................................................................................151 3.4.1. Sensitivity to proteins with α-helical and β- sheet secondary structures.......................................................................................151 3.4.2. Sensitivity to proteins with high order structure level (quaternary structure)............................................................................165 3.4.3. Sensitivity to different stages of fibrils growth ..........................................168 3.4.4. Adsorption of insulin and a-synuclein on the surface of our nanostructures .....................................................................................178 3.5. Conclusion ............................................................................................................180 3.6. References.............................................................................................................181 4. Chapter 4:Induced Chirality through electromagnetic field coupling between chiral molecular layer and plasmonic nanostructures ..........................................183 4.1. Introduction...........................................................................................................183 4.2. Theory and background ........................................................................................185 4.2.1. Theoretical model.......................................................................................185 4.2.2. Mechanism .................................................................................................193 4.2.3. Resonance band considerations..................................................................195 4.3. Experimental work................................................................................................195 4.4. Results...................................................................................................................204 4.4.1. Effect of material optical activity on chirality induction............................204 4.4.2. Configure extinction spectra for the crosses...............................................207 4.4.3. Configure extinction and CD spectra for FMN on quartz and the crosses substrates........................................................................................................209 4.4.4. Control measurements................................................................................210 4.4.5. Configure near-field length scale ...............................................................212 4.4.6. Configure FMN coverage densities on the crosses substrates....................213 4.4.7. Anisotropic factor (g-factor) consideration................................................214 4.5. Conclusion ............................................................................................................217 4.6. References.............................................................................................................218
  • 6. V 5. Chapter 5: The origin of off-resonance non-linear optical activity of Gold chiral nanomaterials .............................................................................................................221 5.1. Introduction...........................................................................................................222 5.2. Theory and background ........................................................................................224 5.2.1. Linear and non-linear interactions of electromagnetic waves with surfaces..................................................................................................225 5.2.2. Theoretical aspects of the second harmonic generation signal from chiral surfaces .......................................................................................227 5.2.3. The SHG signals from plasmonic surfaces ................................................235 5.3. Experimental work................................................................................................236 5.3.1. Sample characterisation..............................................................................238 5.3.2. The optics ...................................................................................................239 5.4. Results and discussions.........................................................................................245 5.4.1. The Off-Resonance Configurations............................................................245 5.4.2. Samples reference and SHG errors configurations.....................................247 5.4.3. SHG signal from the gammadion patterns .................................................249 5.4.3.1. Schematic and theoretical treatments to determine the enantiomer sensitivity from the s-out and p-out measurements...............................251 5.4.3.2. Theoretical treatments to determine electric dipole excitation-induced SHG signal from s-out measurements...................................................260 5.5. Conclusion ............................................................................................................262 5.6. References.............................................................................................................263 6. Chapter 6: Femtosecond Laser Irradiation for Hot-Spot Mapping on the surface of Chiral Metamaterials ........................................................................................... 266 6.1 Introduction...........................................................................................................266 6.2 Theory and background ........................................................................................269 6.2.1. Hot Spot Imprinting....................................................................................269 6.2.2. Electromagnetic modelling for hot spot mapping ......................................270 6.3 Experimental work................................................................................................272 6.4 Results and discussions.........................................................................................273 6.4.1. The damage morphology (or the beam spot track (BST))..........................273 6.4.2. Results are in good agreements with theoretical model .............................282 6.4.3. Hot spot mapping by using linearly polarised laser beam..........................284 6.4.4. Hot spot mapping by using circularly polarised laser beam.......................285 6.4.5. Comparison of results to the literatures......................................................287 6.5 Conclusion ............................................................................................................288 6.6 References.............................................................................................................289 7. Chapter 7: Conclusion and future work..................................................................291 8. Appendix A: List of Tables........................................................................................293 List of Tables in Chapter 2.................................................................................................293 List of Tables in Chapter 3.................................................................................................293 List of Tables in Chapter 5................................................................................................ 294
  • 7. VI 9. Appendix B: List of Figures ......................................................................................295 List of Figures of chapter 1................................................................................................295 List of Figures of chapter 2................................................................................................296 List of Figures of chapter 3............................................................................................... 304 List of Figures of chapter 4................................................................................................308 List of Figures of chapter 5.............................................................................................. 311 List of Figures of chapter 6................................................................................................313 Abbreviations used in this thesis AAmyloid  peptide AFM Atomic Force Microscope APTS 3-Amino-Propyl-Triethoxy-Silane CARS Coherent Anti- Stokes Raman Scattering CD Circular Dichroism CPL Circularly Polarised Light DNA Deoxyribonucleic acid 2D Two Dimensions 3D Three Dimensions EBL Electron Beam Lithography ECD Electronic Circular Dichroism EPL Elliptically Polarised Light FEG Field Emitter Gun FIB Focused Ion Beam Lithography FMN Flavin Mononucleotide fs femto second FWHM Full-Width Half-Maximum HSQ Hydrogen Silses-Quioxane IPA Iso-Propyl Alcohol IR Infra- Red L Left LSPR Localized Surface Plasmon Resonance MD Molecular Dynamics MIBK Methyl Iso-Butyl Ketone
  • 8. VII n nano Nd:YAG Neodymium Doped Yttrium Aluminum Garnet OA-SHG Optically Active-Second Harmonic Generation OR Optical Rotation ORD Optical Rotary Dispersion PMMA Poly Methyl Meth-Acrylate pp paper page ps picosecond R Right R4 Racemic 4 ROA Raman Optical Activity RSC Resist Spin Coating SDS Sodium dodecyl sulphate SE Secondary Elactrons SEM Scanning Electron Microscopy SERS Surface-Enhanced Raman Scattering SH Second Harmonic SHG Second Harmonic Generation SPPs Surface Plasmon Poalretions SPR Surface Plasmon Resonance UV Ultra-Violet vAC Voltages Alternating Currents vDC Voltages Direct Currents VRU Variable Resolution Unit VCD Vibrational Circular Dichroism
  • 9. VIII Publications 1. Induced Chirality through Electromagnetic Coupling between Chiral Molecular Layers and Plasmonic Nanostructures Abdulrahman N. A., Fan Z., Tonooka T., Kelly S. M., Gadegaard N., Hendry E., Govorov A. O. and Kadodwala M., Nano Lett., 2012, Vol.12, pp (977−983).
  • 10. IX 2. The origin of off-resonance non-linear optical activety of a gold chiral nanomaterial. Nadia A. Abdulrahman, Christopher D.Syme, Calum Jack, Affar Karimuallh, Laurence D.Barron, Nikolaj Gadegaard and Malcolm Kadodwala. The Royal Society of Chemistry, Nanoscale, 2013, Vol.5, pp(12651-12657).
  • 11. X Acknowledgements I would like to thank my supervisor Dr. Malcolm Kadodwala for his constant assistance and guidance during the course of my PhD. Likewise, I would like to thank my second supervisor Professor Greame Cooke; also my supervisor in the School of Engineering; Dr. Nikolaj Gadegaard and my mentor Professor Stephen Wimperis for their constant assistance, advice and support during my PhD course. A special thank should go to the head of our Chemistry school; Professor James Stephen Clark for his constant assistance, advice and support during my PhD course. Also, I would like to thank my examiners: Professor Klass Wynne (Chair in Chemical Physics in our Chemistry school) and Professor Christian Johannessen (Professor in Molecular Spectroscopy at University of Antwerp/ Belgium) for their essential suggestions and theoretical corrections. A special thank also should go to my supervisor in biochemistry section (Life Sciences), Dr. Sharon Kelly, for her constant and generous assistance during my experimental work and my thesis writing, especially for essential training on CD and UV spectroscopy, also for her essential assistance to prepare the fibrils that we used in our studies, as well, for her voluntarily assistant to proof read this thesis. Many thanks certainly should go to research assistant Dr. Christopher Syme for his essential training on SHG, Raman and ROA spectroscopy, also for his general assistance and support during my PhD course, as well as for his assistance in proof reading this thesis. I sincerely thank my colleague Dr. Martin King for his immediate assistance, reliability and constant support during my PhD course, also for his assistance to proof read several chapters in this thesis. I would also like to thank Professor Euan Hendry from University of Exeter/UK for theoretical simulations associated with electromagnetic modelling for our gammadion-like shapes. Also, I would like to thank Professor Alexander Govorov from University of Ohio/ USA for theoretical simulations and treatment for plasmonic core- chiral shell systems.
  • 12. XI Appreciative thanks also go to academics in our school of chemistry, Dr. Adrian Lapthorn and Dr. Justin Hargreaves for effective help to my experimental work and for useful advice on thesis writing. Also, my acknowledgements should go to Stuart Mackay for generous help with computer troubleshooting and IT problems. Also, I would like to acknowledge research assistant Dr. David Turton for his assistance with the sample irradiations using the femtosecond laser beam; I would also like to acknowledge research assistant, Dr. Affar Karimullah for his help with ORD measurements for SHG samples. I would also acknowledge my fellow PhD student, Calum Jack for general help. My grateful thanks should go to all JWNC staff in Electrical and Electronic Engineering at Glasgow University, especially, Dr. Stephen Thoms for advice in producing high quality nanostructures. Also, many thanks for Mrs. Hellen Mcllen, for extensive training on Plassys II, modefide evaporator, FEI and SEM microscopy. Likewise, for Mr. Robert H Harkins and Mr. Donald Nicolson, for their constant assistance and training on nanofabrication work. Many thanks to academics and research assistants in Electric and Electronic Engineering in Glasgow University, especially: Dr. Matthew Steer for generous help for training on AFM microscopy, Dr. Rasmus Pederson and Dr. Kevin Docherty for training and assistance for my nanofabrication work. Also, many thanks essentially go to Dr. Kamil Rudnicki for immediate and voluntarily help with my nanofabrication work in general, and for long term accompanying on late working in JWNC, including weekends; accompanying which was essential to satisfy safety and security policy in the JWNC cleanroom. I could not, and will never be able to, find words to thank my God, ALLAH, for his great gift; this is my family. Many thanks should go to a patient and supportive mother and father; sister and two brothers, it`s much appreciated. Without doubt, great thanks should go to my husband, Dr. Karwan Sahibqran, who suffered for a long time, on daily basis, from a student wife; likewise, my two young daughters, Sarah and Maryam, who suffered, almost five years now, from a student mum. Again, it`s much appreciated. Thanks god for having such a great gift.
  • 13. XII Finally I would like to thank the Iraqi government for my PhD scholarship funding. I would also like to thank Engineering and Physical Sciences Research Council EPSRC, BBSRC bioscience well as Medical Research Council MRC for research funding. Surely, I would like to thank Glasgow University for giving me the opportunity to finish my PhD degree within its academia, my great honour.
  • 14. XIII Author`s Declaration I declare that, except where explicit reference is made to the contribution of others, that this thesis is the result of my own work and has not been submitted for any other degree at the University of Glasgow or any other institution.
  • 15. Chapter 1 1 Chapter 1: Introduction 1.1. Overview Chirality, or handedness, is the key phenomenon of interest in this thesis. The building blocks of life such as DNA, proteins, amino acids, sugars etc. are chiral molecules whose structures are inextricably linked to function. A molecule consisting of four different groups bonded to a central atom is described as a chiral molecule; which cannot be superimposed upon its mirror image. Figure 1 illustrates this concept; the molecule can have right handed chirality referred to as d (also written as (+)- [from dextrorotatory. Latin dexter: right hand-side]) or left handed chirality referred to as l- (also written as (-)- [from laevorotatory. Latin laevus: left hand-side]). In addition, Figure 1 illustrates how the absolute configurations (the spatial orientation) of the chiral centre could be assigned, following Cahn-Ingold-Prelog system, to be either R (from rectus in Latin meaning right) or S (from sinister in Latin meaning left). In principle, the chirality observed in molecules can be attributed to four types of atomic configurations, namely: Chiral centre; Chiral axis; Chiral Helix; and Chiral plane. For Chiral centre, Figure 1 illustrates an example of this configuration which is represented by the tetrahedral C atom. For Chiral axis, when substituents spatially arranged around a fixed axis with a chiral fashion (i.e. the mirror image of the final structure cannot be superimposed on its original one) then this axis is called chiral axis. In this case it is not necessary for the substituents to differ. An example of a molecule with a chiral axis is 2,2′- dimethoxy-binaphtyl, shown in Figure 5e. A Chiral helix, can be described as a molecule with a simple helical shape. An example of this element is helicinebisquinone, shown in Figure 5c. For chiral plane: This is `a structural plane in a molecule with a group substituted in the plane that destroys a symmetry plane perpendicular to the structural plane` [1 ch3 pp75 ]. An example of this element is the cyclophane molecule, shown in Figure 2a. In this Figure, without carboxyl group, one could imagine two orthogonal symmetry planes (shown with dashed red lines) both are perpendicular (denoted by the red dot circle) on the plane of the molecule (plane of the page). However, upon attaching the carboxyl group to the benzene ring these two symmetry planes that are perpendicular to the plane of the benzene ring will be destroyed. Here,
  • 16. Chapter 1 2 the plane of the benzene ring is described as a chiral plane. In order to assign the absolute configuration for cyclophane, which follows the R/S system mentioned above, first, we should choose a reporter atom (either above or below the chiral plane) which is an atom that is attached to an atom in the chiral plane, e.g. for cyclophane, the C of methylene chain that lies above the plane of the molecule could be chosen as a reporter atom, see Figure 2b. Then, following the rules of mass priority system described in Figure 1, we should create an arc from the atom attached to the reporter to the atom of the substituted group, and see (view the arc path from the reporter atom toward the chiral plane) if the arc orientation is clockwise or anticlockwise. For cyclophane the orientation of the arc is clockwise and hence, the absolute configuration of this molecule is R, see Figure 2b below [1-5]. Molecules with opposite chirality are described as enantiomers which are indistinguishable in terms of physical properties such as density and molecular weight. However, they interact differently and hence become distinguishable, with other chiral objects [6]. As will be explained later, this is a key property of chiral molecules. In this thesis, we used 2D chiral nanostructures which support what is known as planar chirality. Figure 3 illustrates how our 2D nanostructures are assigned to be either right handed, (referred to as R) or left handed, (referred to as L). For example for the gammadions, the four arms are equal because they are made out of gold with the same thickness and dimensions, however if we number the end of each arm e.g. starting from number 1 for the first arm (this could be arbitrarily chosen) to end up with number 4 for the fourth arm and then join up these numbers with the dashed arrows we will end up with lines orientating in left-handed fashion or right-handed fashion, see Figure 3a. The actual configuration was evidenced using the CD spectra shown in Figure 73 in chapter 2. For J`s nanostructures which support what we refer to as a superstructural chirality (we chose this name in parallel to Supermolecular chirality illustrated in Figure 5) we used to number the twisted end for any J by number 1 and the other twisted end for the other J by number 2 and then we join up these numbers with the dashed arrows to end up with lines orientating in left-handed fashion or right-handed fashion, see Figure 3b. Again, this configuration was evidenced using the CD spectra shown in Figure 74 in chapter
  • 17. Chapter 1 3 2. The G`s nanostructures are another example of superstructural chirality. Here we used to number the negative tone areas (the black areas) in a way similar to that we illustrated in Figure 3c, then by joining up these numbers by the red dashed arrows shown in the same Figure we end up with lines orientating in left- handed fashion or right-handed fashion. This configuration was indirectly evidenced via SHG spectra shown in Figure 4. In this Figure we present SHG spectra for right handed gammadions (R-gammadions (red)) and left handed gammadions (L-gammadions (blue)) as well as for right handed G`s (R-G`s (red)) and left handed G`s (L-G`s (blue)). From this Figure, it is clear that the intensity of SHG signal generated via nanostructures with right handed orientation (for both: G`s and gammadions) are characterised by very similar spectra (Butterfly like shape). Also, the intensity of SHG signal generated via nanostructures with left handed orientation (again for both: G`s and gammadions) are characterised by similar spectra also. The fact that our G`s were deposited on a silicon wafer (i.e. a non-transference surface) means that only spectra that are collected from reflected light could be used to characterise it. Therefore we used the spectra of Figure 4 to evidence the handedness of our G`s since the handedness of our gammadion were clearly evidenced via CD spectra presented in Figure 73 chapter 2. Furthermore, Valve group have evidenced the handedness of these G`s with SHG spectroscopy and SHG microscopy, which are in agreement with our configurations [7].
  • 18. Chapter 1 4 Figure 1: A chiral molecule is a molecule of four different groups, represented here by 1, 2, 3 and 4, these groups are bonded to a central atom (such as tetrahedral carbon), a whole molecule cannot be superimposed upon its mirror image. Different rearrangements for 1, 2, 3 and 4 will end up with only two absolute configurations; these are: an original configuration and its mirror image. The four groups are ordered according to its priority (importance) which is assigned here by the atomic numbers (or atomic masses) of the molecules of these groups, i.e. the most important group is the group with bigger atomic number. Considering the smallest group (i.e. group no.4) being always behind this page, and via joining up the other groups by the dashed arrows shown above one would decide the chiral centre (i.e. C atom) to have a right handed orientation R (from rectus in Latin means right) which means to have a molecule being characterised as a d- or (+)- (this is a representation of an optical rotation induced by this molecule for a plane polarised incident light in a clockwise direction) or to have a left handed orientation S (from sinister in Latin means left) which means to have a molecule being characterised as an l- or (-)- (this is a representation of an optical rotation induced by this molecule for plane polarised incident light in anti-clockwise direction). Note that R/ S system is used to characterise the chiral centre (which is represented here by C atom), while d-/l- system is used to characterise whole molecule. 1 23 4 C 1 2 3 4 C R d- or (+)- /Clockwise S l- or (-)- / Anti-Clockwise Mirror e.g. 1: COOH, 2: C3H7, 3:NH2, 4: H e.g. 1: COOH, 2: C3H7, 3:NH2, 4: H
  • 19. Chapter 1 5 O O OH O (CH2)8 Figure 2: Chiral plane and its absolute configuration for cyclophane. a shows the molecule with two perpendicular (denoted by the red dot circle) planes (red dashed lines). b shows the chiral plane which is the plane of the benzene ring. Note how Carboxyl group attachment destroys the two perpendicular symmetry planes. The absolute configuration of the chiral plane could be assigned via R/S system if one viewed the arc path from the reporter atom. O 4 3 O Reporter atom 1 2 O HO (CH2)6 H2C H2C a b 4 3 Viewed from Reporter atom 21 R
  • 20. Chapter 1 6 Figure 3: Our methodology to determine the chirality of our nanostructures. a illustrates how the four arms of the gammadion could be numbered and joined up by the black arrows to end up with either right handed handedness (R) or left handed handedness (L) configuration. b illustrates how the two twisted ends of the J`s nanostructures could be numbered and then joined up by the black arrows to end up with either right handed handedness (R) or left handed handedness (L) configuration. c illustrates how the negative tone areas (the black areas) for the G`s nanostructures could be numbered and then joined up by the red arrows to end up with either right handed handedness (R) or left handed handedness (L) configuration. 1 3 4 2 12 3 4 1 2 34 R /ClockwiseL / Anti-Clockwise 1 2 1 2 Mirror a b c
  • 21. Chapter 1 7 L- gammadionL- G`s 0 200000 400000 600000 800000 1000000 0 30 60 90 120 150 180 210 240 270 300 330 0 200000 400000 600000 800000 1000000 0 50000 100000 150000 200000 250000 0 30 60 90 120 150 180 210 240 270 300 330 0 50000 100000 150000 200000 250000 SHGintensityinCountUnit φ 0 100000 200000 300000 400000 500000 600000 0 30 60 90 120 150 180 210 240 270 300 330 0 100000 200000 300000 400000 500000 600000 -200000 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 0 30 60 90 120 150 180 210 240 270 300 330 -200000 0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 SHGintensityinCountUnit φ φφ R- gammadionR- G`s Figure 4: SHG spectra for right handed gammadions(R-gammadions (red)) and left handed gammadions (L-gammadions (blue)) as well as for right handed G`s (R-G`s (red)) and left handed G`s (L-G`s (blue)). Clearly, nanostructures with right hand handedness have very comparable spectra (Butterfly like shape). Similarly, nanostructures with left hand handedness have very comparable spectra.
  • 22. Chapter 1 8 An increasing number of spectroscopic techniques that are sensitive to chirality have emerged in recent years e.g. OR, ORD, CD (or ECD), VCD and ROA (or VROA) [1-3]. Chirality is also a key property in the pathogenic detection of biological species that are associated with amyloidal diseases, such as Alzheimer’s disease and Parkinson’s disease [8]. Chirality is also of significant interest in the pharmaceutical and drug industries, particularly due to the difference in physiological activity of different enantiomers. For instance, thalidomide is a drug that was used against morning sickness and was administrated to pregnant women, however only one enantiomer had the desired therapeutic effect, while the other enantiomer linked itself to the DNA of the growing foetus and inhibited the development of limbs, causing a spate of birth defects. Also, ethambutol is a drug that was administrated to patients with tuberculosis; however its enantiomer caused blindness. Therefore, the characterisation of optically pure molecular compounds, i.e. single enantiomer molecular compounds, is essential in the pharmaceutical and drug industries [9]. In essence, the characterisation of optically pure molecular compounds means to gain insight into the chiroptical effect associated with chiral compounds. Chiral plasmonic nanostructures are potentially useful platforms to sense chiroptical effects. As such, chiral plasmonic nanostructures are of considerable interest and this is one of the main reasons for the work described in this thesis. In order to investigate the chiroptical properties of chiral molecules, one may transpose the concepts of natural chirality to artificial nanostructured surfaces. In principle, the general concepts of chirality (natural and artificial) have been termed in six classes so far, namely as: helical chirality/propellers, helical chirality/spirals, chiral coupling, supermolecular chirality, pseudo/extrinsic chirality and chiral scaffolds [7, 9-23]. The work in this thesis is associated with the first four classes only. In principle, Helical chirality/propellers is when the overall aspect shows a shape of a three-armed helix e.g. perchlorotriphenylamine (Figure 5 a), or, a shape of a four armed helix e.g. our left and right handed gammadions (Figure 5 b), likewise, examples are shown in references [9-11]. Helical chirality/spiral is when the molecule is expanded over its spiral span e.g. helicinebisquinone (Figure 5 c), as well as our G-like shapes (Figure 5 d); more examples are shown in references [7,9,12]. Chiral coupling applies when two achiral elements are coupled to exhibit a chiroptical
  • 23. Chapter 1 9 effect. e.g. 2,2′-dimethoxy-binaphtyl (Figure 5e) and our J-like shapes (Figure 5 f), again, more examples can be found in references [9, (13-15)]. Supermolecular chirality applies when at least two chiral elements are coupled to exhibit a chiroptical effect e.g. the DNA double helix, and also if molecules in 5c are stacked in a super-chiral fashion (Figure 5 g), likewise for quadric units of our right-handed G-like shapes (Figure 5 h), again, more examples are found in references [9,13,16]. Pseudo and/or extrinsic chirality is shown when the geometry of the experimental setting is arranged for a chiral environment. As such, it is required to have the wave vector ̂, the surface normal ̂, and the light polarization vector ̂ arranged together to exhibit pseudochirality, as shown by 2-docosylamino-5-nitropyridine molecules (Figure 6 a) [9, 17], or further, to exhibit extrinsic chirality which was shown in split ring nanostructures (Figure 6 b) [9, 18], and more examples can be found in references [9, 19]. Finally, chiral scaffolds are blocks consisting of chiral and achiral elements, here either the chiral molecules bind to a cluster of the nanoparticles to enhance the optical chirality of the cluster (Figure 6 c) [9, 20], or oppositely, the nanoparticles are binding to helical molecules, such as strands of DNA, to follow its chiral arrangement (Figure 6 d) [9, 21], otherwise, 3D chiral metamaterials are driven to large scale self-assembling scaffolds to have nanostructures with gyroid networks (Figure 6 e) [9, 22, 23]. Generally speaking, the work of this thesis has been presented in seven different chapters; including this one. In chapter 2, the nanofabrication work is presented. Nanofabrication work was carried out in the James Watt Nanofabrication Centre (JWNC) cleanroom facilities at Glasgow University/UK. Samples (i.e chiral and/or achiral plasmonic nanostructures) were fabricated via Electron Beam Lithography (EBL). All fabrication techniques, instruments and experimental methods are described in this chapter. In chapter 3, circular polarised light (CPL) was used to generate the so-called `Superchiral Field` by illuminating a surface of the chiral plasmonic nanostructures. The aim was to reduce the pitch length scale of the incident light to that approaching the pitch length scale of the biomolecules that are adsorbed on the surfaces of the chiral plasmonic nanostructures; this in order to enable the detection and structural characterisation of very low concentrations of biomolecules e.g. picogram quantities. Three main techniques were used for this purpose: CD spectroscopy,
  • 24. Chapter 1 10 SEM and AFM microscopy. In chapter 4, the possibility of characterising biomolecules adsorbed on the surface of achiral plasmonic nanostructures is explored. The work in this chapter is based on the far field electromagnetic field coupling between the electromagnetic field of the plasmonic surface and the electromagnetic field of the adsorbed chiral molecules, a coupling essentially to be achieved by the aid of the incident light. In chapter 5, the origin of the chiroptical second harmonic generation (SHG) signal that originates from the surface of the chiral plasmonic nanostructures upon irradiation with intense linearly polarised light has been investigated. From the work presented in this chapter, it may be concluded that the non-linear optical activity of the chiral plasmonic nanostructures share a common microscopic origin with that of aligned chiral molecules, which was established to be electric dipolar excitation. This is an unexpected result since it might have been expected that non- localised higher multipolar excitation (e.g. electric quadrupole and magnetic dipole contributions) would dominate the optical activity of such relatively large plasmonic nanostructures. Importantly, measurements were performed in off- resonance conditions for reasons discussed throughout the chapter. In chapter 6 the practical visualisation of regions of intense plasmonic activity, referred to as `hot spots` has been described. After irradiation with a femtosecond laser beam, SEM microscopy was used to map chiral plasmonic nanostructures surfaces to show which areas have been damaged, and hence reveal where the plasmonic hot spots are. Finally, in chapter 7, we derived our conclusion and hence present our anticipation for future work.
  • 25. Chapter 1 11 h d b Figure 5: Four concepts of chirality are demonstrated here, these are: propeller is demonstrated in a for perchlorotripheylamine and in b for the left and Right handed gammadions, spiral is demonstrated in c for helicinebisquinone and in d for G like shapes, chiral coupling is demonstrated in e for 2,2′-dimethoxy-binaphtyl and in f for J like shapes, finally, supermolecular chirality is demonstrated in g for molecules in c stacked in super chiral fashion and in h for quadric units of G like shapes. Grey dashed circle illustrates chiral axis. g e f a c
  • 26. Chapter 1 12 Figure 6: Five concepts of chirality are demonstrated here, these are: pseudo chirality in a for different experimental set up for 2-docosylamino-5-nitropyridine molecule, extrinsic chirality in b for different experimental set up for split rings nanostructures, chiral scaffolds in c for chiral molecules that are binding to a cluster of nanoparticles, chiral scaffolds in d for nanoparticles that are binding to helical molecules, such as strands of DNA, and finally, chiral scaffolds in e for 3D chiral metamaterials that are fabricated to gyroid networks. b e d c a C21 H45 2-docosylamino-5-nitropyridine
  • 27. Chapter 1 13 1.2. Historical review The study of optical activity and its possible applications has a long and distinguished history dating back more than 200 years. Early observations of optical activity was recorded by Arago in 1811, when he observed the rotation of plane polarised sunlight by a piece of quartz, located between two crossed polarisers, thus demonstrating the optical rotation measurements (OR) for the first time. Several years later in 1815, a French physicist called Jean Biot verified the optical rotation for several liquids varied between organic liquid like turpentine, alcoholic solution of camphor and aqueous solutions of sugars [1,2ch1 pp2 ]. He then managed to record the optical rotation for the second form of quartz, the amethyst, in 1818 which showed the opposite effect to the one used by Arago above. Furthermore, in 1832 he tested the optical rotation for tartaric acid, to pioneer the idea of optical activity as a distinguishing of a single molecule; since he couldn`t find it in molten quartz i.e. in molecule attached to its own crystal structure[2ch1 pp2 ]. Meanwhile, in 1825 Frensel discovered the circular polarised beam which was then used in 1847 by Haiding to resolve CD measurements of violet amethyst [1,2ch1 pp5 ]. A year later, in 1848, Louis Pasteur had formulated the concept of dissymmetry and that mirror image molecules shared the same formula but have a different spatial arrangement, when he successfully isolated and characterised CD measurements for enantiomeric solutions of tartaric acid crystals [2ch1 pp25 ,24,25]. With this achievement, the idea of three dimensional molecular structures had become an important breakthrough; as long as two dimensional structures are incapable to support such studies [26]. Fifty years later, in 1895, Aimé Cotton substantiated CD measurements for liquids comprised of chiral metallic complexes of copper and chromium tartarate, to reveal the relationship between the optical rotation and the wavelength of incident light for the first time, which is now known as a Cotton effect, a phenomena that was first theoretically predicted and distinct by Biot in 1812 as an optical rotary dispersion ORD [1, 2ch1 pp2 ]. By the early 20th century, CD spectroscopy was considered to be a useful tool to quantify objects with specific spatial geometry named for the first time in 1904 by Lord Kelvin as `chiral` objects, when he said: `I call any geometrical figure, or group of points, chiral, and say that it has chirality if its image in a plane
  • 28. Chapter 1 14 mirror, ideally realized, cannot be brought to coincide with itself `[2ch1 pp25 , 27]. Thereafter, biological molecules like proteins and DNA, the building block of life, began to be studied by CD spectroscopy [8]. Yet, CD measurements of biomolecules remained challenging, particularly for small molecules because of their weak response [28]. More than a century ago in 1908, Nobel laureate Gustav Mie published his solutions to Maxwell`s equations of electromagnetic scattering by homogenous and isotropic spheres, giving the first theoretical explanation for the colourful appearance of colloidal gold solutions. Effectively, it is the electromagnetic field surrounding the spherical particles which is responsible for the colours seen. This field is the result of conductive electrons oscillations which arise when excited by incident light. Recent literature refers to this principle as `Mie Theory` [29,30] and for the field in question as SPPs (explained in more details in Chapter 2). In last four decades, great efforts have been devoted to extend the scattering modelled above to spheres immersed in an adsorbing host medium [31,32]. More recently, in 2010, Cohen`s group from Harvard university, extended it to a metamaterials made out of gold, when they theorised their surface plasmonic resonance by Maxwell`s equations for the first time, to show that in a certain circumstances this field could be twisted and therefore make it chiral, so they called it `Superchiral field` (explained in more details in chapter 3) [33].
  • 29. Chapter 1 15 1.3. References 1. Nafie L. A., “Vibrational Optical Activity Principles and Applications”, Jhon Wiley& Sons Ltd., 2011, printed book. 2. Barron L. D., “Molecular Light Scattering and Optical Activity”, Cambridge University press, Cambridge, 2nd edition, 2004, printed book. 3. Berova N., Polavarapu P. L., Nakanishi K. and Woody R. W., “Comprehensive Chiroptical Spectroscopy/ Instrumentation, Methodologies, and Theoretical Simulations”, John Wiley & Sons, Inc., Hoboken, 2012 Vol.1, printed book. 4. Moss P. G., Pure & Appl. Chem., 1996 , Vol. 68, pp ( 2193-2222). 5. http://chemistry.umeche.maine.edu/CHY556.html (cited in 2014). 6. Yang N.,Tang Y. and Cohen A., Nano Today , 2009, Vol.4, pp (269-279). 7. Valev V. K., Smisdom N., Silhanek A. V., De Clercq B., Gillijns W., Ameloot M., Moshchalkov V. V. and Verbiest T., Nano Lett., 2009, Vol.9, pp (3945- 3948) 8. Hendry E., Carpy T., Johnston J., Popland M., Mikhaylovskiy R. V., Lapthorn A. J., Kelly S. M., Barron L. D., Gadegaard N. and Kadodwala M., Nature Nanotechnology, 2010, Vol.5, pp (783-787). 9. Valev V. K., Baumberg J. J., Sibilia C. and Verbie T., Advanced Materials. 2013, Vol.25, pp (2517–2534). 10. Kuwata-Gonokami M., Saito N., Ino Y., Kauranen M., Jefimovs K., Vallius T., Turunen J. and Svirko Y., Phys. Rev. Lett., 2005, Vol. 95, pp( 227401(1- 4)). 11. Valev V. K., De Clercq B., Zheng X., Denkova D., Osley E. J., Vandendriessche S., Silhanek A. V., Volskiy V., Warburton P. A. ,Vandenbosch G. A. E., Ameloot M., Moshchalkov V. V. and Verbiest T., Opt. Express, 2012, Vol.20, pp(256 -264). 12. Gansel J. K., Thiel M., Rill M. S., Decker M., Bade K., Saile V., Von Freymann G., Linden S. and Wegener M., Science, 2009 , Vol. 325, pp (1513- 1515). 13. Decker M., Ruther M., Kriegler C. E., J. Zhou J., Soukoulis C. M., Linden S. and Wegener M., Opt. Lett. 2009, Vol.34, pp (2501-2503) . 14. Huttunen M. J., Bautista G., Decker M., Linden S., Wegener M. and Kauranen M., Opt. Mat. Express, 2011, Vol.1, pp (46-56). 15. Liu N., Liu H., Zhu S. and Giessen H., Nat. Phot., 2009, Vol.4, pp (1-2). 16. Decker M., Zhao R., Soukoulis C. M., Linden S. and Wegener M., Opt. Lett., 2010, Vol.35, pp (1593-1595) . 17. Verbiest T., Kauranen M., Van Rompaey Y. and Persoons A., Phys. Rev. Lett., 1996, Vol.77, pp (1456-1459) . 18. Plum E., Liu X. X., Fedotov V. A., Chen Y., Tsai D. P. and Zhelude N. I., Phys. Rev. Lett., 2009, Vol.102, pp (113902-(1-4)) . 19. Belardini A., Larciprete M. C., Centini M., Fazio E. and Sibilia C., Phys. Rev. Lett., 2011, Vol.107, pp (257401-(1-5)) . 20. Noguez C. and Garzon I. L., Chemical Society Reviews, 2009, Vol.38, pp (757- 771). 21. Kuzyk A., Schreiber R., Fan Z., Pardatscher G., Roller E. M., Hogele A., Simmel F. C., Govorov A. O. and Lied T., Nature 2012, Vol.483, pp(311-314).
  • 30. Chapter 1 16 22. Vignolini S., Yufa N.A., Cunha P. S., Guldin S., Rushkin I., Stefik M., Hur K., Wiesner U., Baumberg J. J. and Steiner U., Advenced Optical Materials, 2012, Vol.24, pp (OP23–OP27). 23. Hur K., Francescato Y., Giannini V., Maier S. A., Hennig R. G. and Wiesner U., Angewandte Chemie International Edition, 2011, Vol.50, pp (11985-11989). 24. Flack H. D., “Louis Pasteur`s discovery of molecular chirality and spontaneous resolution in 1848, together with a complete review of his crystallographic and chemical work”, Acta Crystallographica, 2009, Vol.65, pp (371-389). 25. Gal J., “Louis Pasteur, Language, and Molecular Chirality/ Background and Dissymmetry”, Chirality, 2011, Vol.23, pp (1-16). 26. Corrêa D. H. and Ramos C. H., African J. of Biochemistry Research, 2009, Vol.3, pp (164-173). 27. Lord Kelvin, “Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light”, Clay C.J. and Sons, Cambridge University Press Warehouse, London, 1904. 28. Tang Y. and Cohen A. E., Science, 2011, Vol.332, pp (333-336). 29. Kosuda K. M., Bingham J. M., Wustholz K. L. and Van Duyne R. P., Comprehensive Nanoscience and Technology, 2011, Vol.3, pp (263-301). 30. Hergert W., Wriedt T., “The Mie Theory, Basics and Applicatons”, Springer, 2012, e-book. 31. Mundy W. C., Roux J. A. and Smith A. M., Journal of the Optical Society of America, 1974, Vol.64, pp (1593-1597). 32. Bohren C. F. and Gilra D. P., Journal of Colloid Interface Science, 1979, Vol.72, pp (215-221). 33. Tang Y. and Cohen A. E., Phys. Rev. Lett., 2010, Vol.104, pp (163901-163904).
  • 31. Chapter 2 17 Chapter 2: The Nanofabrication of plasmonic nanostructures by Electron Beam Lithography Abstract This chapter describes the nanofabrication of the plasmonic nanostructures which have been fabricated during the project. The nanofabrication work was carried out in the JWNC cleanroom in the Department of Electronic and Electrical Engineering/ School of Engineering/ Glasgow University. All the samples were fabricated via Electron beam lithography (EBL). An outline of Electron beam lithography technique is included together with a discussion of the factors which affect the interactions between the electron beam and sample surfaces. The instruments used and experimental methods employed are described. 2.1. Introduction: 2.1.1. Electron Beam Lithography Electron Beam Lithography (EBL) is the technique of using a focused electron beam as a means of drawing geometrical features on a polymer matrix of a supporting substrate. The idea is to exploit the capability of the electron beam to interact with the molecules of this matrix. This interaction can be directed to produce a specific pattern consisting of thousands of features scaled to nanometer sizes. The pattern is then revealed by the development process, which removes the exposed area of the matrix and retains the unexposed area. Then, a metallic layer is deposited on the matrix to fill up the exposed area (the patterned area) with a specific thickness layer of the metal. Eventually, the metallic pattern is revealed by the lifting off process, in which the metallic layer is removed from the unexposed area to retain the area with the metallic pattern [1 Chapter(2) pp142 , 2 Chapter(2) pp(11-12) ].
  • 32. Chapter 2 18 Electron beam lithography (or E-beam writing) is one of many other lithographical techniques, these are: The Deep UV (200-290nm), extreme UV (<200nm) photolithography and Phase-shift photolithography, the X-ray lithography, focused ion beam (FIB) lithography, scanning probe lithography and others. EBL has the advantages of: high resolution performance that approaches less than 10nm feature size; reproducibility and high quality throughout. It is a direct writing routine and does not require a mask or a template to transform the desired pattern. The only disadvantage is that the procedure is time- consuming since the writing practice is performed as a dot by dot system [3-12]. In general, EBL can be used to manufacture electronic devices like semiconductors, circuits and biosensors. The functionality in such electronics requires a very high resolution performance e.g. of the order of 10nm or less which is comparable to the size of large molecules. This can only be achieved by techniques like Electron Beam Lithography; because the spot size of the electronic beam using this technique is ~4 nm in diameter [1Chapter2 pp142 ,2Chapter(2) pp12 ,3]. Table 1 illustrates the length scales of common objects [13 chapter(1) pp1 ]. In fact, the manufacture of nanoscale patterns is challenging, especially when considering ways in which the electron beam (the writing tool) interferes with the substrate surfaces. On the other hand, the nanometer scale is small enough to be comparable with invisible dust particles. Thus, contamination by dust is the main concern in the nanofabrication industry. Therefore, the technique is usually performed within special `cleanroom environments` which are designed to ensure a dust-free working area. The maintenance of such cleanroom environments requires huge funding, efforts, expertise and a restricted entrance with special suits to maintain the cleanroom status.
  • 33. Chapter 2 19 For this project, 2D plannar chiral metamaterials have been manufactured using EBL with nanofeatures ranging between 200-1000nm. The size of such features is comparable with the scale of the wavelength of the spectroscopic light. This is important to study the interferences between the nanoscale features and the nanoscale wavelength of the spectroscopic light; which is the basis of this thesis. Some bespoke 2D plannar chiral metamaterials were used in this thesis; however all designs are presented in section 2.4.1. Wire widths of 40nm, 60nm, 80nm and 200nm have been achieved. All patterns were written by an ultrahigh resolution writing machine at the JWNC cleanroom of Glasgow University. The aim of the nanofabrication work in this chapter is to make plasmonic nanostructures that are considered to be sorts of `radiant signal domain` sensors. These sensors depend on the signal properties of the electromagnetic waves such as intensity, wavelength, polarisation and phase. From literatures, sensors; are classified into six categories [14 Chapter7 pp381 ], these are: `1.The thermal signal domain sensors: functionalised through temperature, heat and heat flow 2. The mechanical signal domain sensors: functionalised through force, pressure velocity, acceleration and position 3.The chemical signal domain sensors: measure the internal quantity of the matter such as concentrations of materials, composition and reaction rate 4. The magnetic signal domain sensors: functionalised through magnetic field intensity, flux density and magnetisation Object Typical diameter SI metric scale Grain of sand 1 mm = 1000 μm 1µm = 10-6 m 1nm = 10-9 m 1pm = 10-12 m Human hair 150 μm Red blood cell 10 μm Bacterium 1 μm Virus 20 nm DNA molecule 2 nm Uranium atom 0.2 nm = 200 pm Table 1: These are approximate sizes for some common objects with SI metric scale units.
  • 34. Chapter 2 20 5.The radiant signal domain (which our sensors are characterised under): here the signals are quantities of the electromagnetic waves, such as intensity, wavelength, polarisation and phase 6.The electrical signal domain sensors: measuring voltage, current and charge`. Historically, EBL was first demonstrated over 50 years ago following the development of Scanning Electron Microscopy (SEM) and the addition of a pattern generator and blanker plates to the column of the scanning electron microscope [1Chapter(2) pp142 ,2Chapter(2) pp12 ,15,16]. The subsequent discovery of high resolution resists like PMMA (poly methyl methacrylate), ZEP 520 (11% methyl styrene + chloromethyl acrylate copolymer (solid) + 89% anisole (solvent)) and HSQ (hydrogen silsesquioxane) has contributed significantly to this development since they represent the platform for pattern deposition [1 Chapter(2) pp142 , 17-19]. The concept of EBL was first introduced by Buck et.al in 1959 when they decided to use the contamination layer, known as a side effect in electron microscopy at that time, as an etching mask for the 100nm patterns. This layer forms as a result of polymerisation of the hydrocarbon or siloxane exiting under vacuum by the electron beam of the microscope [15]. EBL terminology came from the idiom Lithography, which is `The process of printing from a flat metal (formerly stone) surface treated so as to repel the ink except where it is required for printing`. Origin Greek ` lithos ` is stone, and `graphic` is writing or drawing [20 (Concise English Dictionary)]. Another reference defines Lithography as `A method of printing from a metal or stone surface on which the printing areas are not raised but made ink-respective while the non-image areas are made ink-repellent` [21 (Collins English Dictionary)]. 2.1.2. Metamaterials Metamaterials can be described as an array of artificially sculpted materials [22], patterned in a two or three dimensional periodic lattice, distributed over a dielectric substrate, sized in smaller than a certain wavelength, spaced by sub- micron and frequented in order larger than 100s x 100s of d nm thick features. Their advantage of possessing negative values for both dielectric permittivity (ε
  • 35. Chapter 2 21 < 0) and magnetic permeability (µ < 0) simultaneously (see Figure 1 which illustrates materials classification based on materials dielectric permittivity and materials magnetic permeability), lead to imply negative refractive index (n √ ), where `the phase velocity is opposite to the energy flux`, a unique characteristic causes to change opaque materials (with negative value for either ε or µ ) to transparent materials (with positive value for both ε or µ), which is unlikely to be found naturally. Changing opaque materials to transparent materials can be explained as follows: when electromagnetic waves reflect from the surface of an object hidden behind a metamaterial plate, the electromagnetic waves are bended negatively at the interface between A (e.g. air) and B (e.g. the metamaterial plate) (see Figure 3), and hence, a focal point is formed inside the metamaterial plate. This in turn, and similarly to the original source, acts as a new source of light. Hence, once again, the electromagnetic waves are bended negatively at the interface between B (the metamaterial plate) and A (the air), as such, a focal point is formed outside the metamaterial plate this time; which means the object behind the metamaterial plate become visible, see Figure 3. Generally speaking, due to this novel phenomena, when an electromagnetic field with a visible frequency incident the metamaterial surfaces; it will twisted in the `wrong` direction, and hence such materials are termed as `Left Handed Materials` or `Double Negative Materials` or even `Backward Wave Materials` [23-26], see Figure 2 which illustrates examples of a solution with normal refractive index (left) and a solution with negative refractive index (right). This description has provoked a considerable number of aspects to use it successfully (applications have increased within a decade) and yet are being researched, Thus, since 1999 when first manufactured by Pendry group [27] others start to employ it in a variety of schemes, like, Terahertz metamaterials [28], photonic metamaterails [29], plasmonic metamaterias [30], chiral metamaterials[31], non-linear metamaterials [32] and more [33-35]. Indeed, it is a virtue back to the theoretical model pioneered by the Russian physicist V.G Veselago in 1967 [23]. Recently, light scattering using metamaterials has become a vital concept that could be used to improve diagnostic devices like biosensors. This is because the functionality of these biosensors is highly optimised by the metamaterials optical properties [36]. Hence, the optical properties of metamatrials with plasmonic surfaces and negative refractive indices have become an important field in bio sensing
  • 36. Chapter 2 22 techniques and pathogenic detections [37,38]. Advancements in scanning electronic and scanning atomic force microscopy, also in techniques such as, electron beam lithography, CD spectroscopy and laser based tools, in addition to computing devices that enable sophisticated numerical calculations to be achieved quickly and precisely, all together are playing a key role to support such studies with adequate details. Positive µ µ > 0 Positive  > 0 Negative µ µ < 0 Negative < 0 Negative µ µ < 0 Positive > 0 Positive µ µ > 0 Negative < 0  µ Figure 1: Illustration of materials classification that is based on negative and positive dielectric permittivity  in addition to negative and positive magnetic permeability µ. DPS is double positive materials, ENG is epsilon negative materials, DNG is double negative materials and MNG is mu negative materials. DPSENG DNG MNG e.g. Dielectricse.g. Plasma e.g. metamaterials e.g. ferromagnetic materials (in the microwave region) Propagatingnon-propagating Propagating non-propagating
  • 37. Chapter 2 23 Observer Imag e Objec t Material with negative refractive index Ordinary refraction Negative refraction Air AirMetamaterial Figure 3: the electromagnetic waves are bended negatively at the interface between A (air) and B (metamaterial) and therefore, a focal point is formed inside the metamaterial, which in turn, and in the same way to the original source, acts as a new source of light. Then, once again, the electromagnetic waves are bended negatively at the interface between B (metamaterial) and A (air), hence, a focal point is formed outside the metamaterial this time; which means the object behind the metamaterials become visible [40]. Figure 2: Examples of a solution with normal refractive index (left) and a solution with negative refractive index (right). This Figure was taken from reference [39].
  • 38. Chapter 2 24 2.1.3. Surface Plasmons At a definite wavelength, light can excite metal-dielectric surfaces since metals have free electrons on their outside orbitals (e.g. visible light is able to excite gold-air and silver-air surfaces under certain experimental conditions). This is an important phenomenon as when light excites such surfaces it will induce coherent oscillations associated with the metal’s free electrons along the metal- dielectric interface. Such oscillations are known as `Surface Plasmons` or SPs and the collective of oscillations is known as `Surface Plasmon Resonance`, or SPR. For the reason that SPR propagates along metal-dielectric interface, researchers also refer to the propagating SPR as `Propagating Surface Plasmon Resonance` or PSPR. Such oscillations are usually excited on continuous metal thin film (e.g. 50nm gold film) through prism couplers that follow Kretschmann excitation configuration, Figure 4. Essentially, SPR induces quasiparticles known as ` Surface Plasmon Polaritons`, or SPPs, which arise as surface longitudinal, p- polarized, electric field waves that propagate along the metal-dielectric interface. In principle, SPPs are near fields, also known as evanescent fields, with a maximum intensity at 1/3  from the surface of its formation (Figure 5a) and exponentially decay towards the dielectric medium and inside the metal (Figure 5b). For example, for 50nm gold film, the SPPs propagate 10-100 microns along the metal-dielectric interface in the x- and y- directions and decay exponentially over a distance on the order of 200nm in the z-directions. Concerning the nanoparticle and the nanostructure surfaces, there is another variation of SPR known as `Localised Surface Plasmon Resonance` or LSPR, in which the SPR is localised around the nanoparticles (Figure 6) and the nanostructures. Importantly, the actual sizes of the nanoparticle and the nanostructure should be smaller than the wavelength of the incident light. SPPs from such surfaces are confined by the LSPR which is itself confined by the shape of the nanoparticles and the nanostructures [37,(41-44)]. The advantages of such confinements will be explained below. Generally speaking, SPPs originate when electromagnetic waves of an incident light couples to the oscillations of the surface plasmon. Such coupling requires the electromagnetic waves of the incident light to be p-polarised; it also requires having the electromagnetic waves of the incident light and the oscillations of the surface plasmon propagating at the same frequency. In addition, for continuous thin
  • 39. Chapter 2 25 film, it requires having the electromagnetic waves of the incident light to be incident on the metal surface through a dielectric medium (e.g. a prism) at an incident angle greater than the critical angle for total internal reflection (Kretschmann configuration). However, for nanoparticles and nanostructures it requires having the electromagnetic waves of the incident light to be incident on the metal surface through air (i.e. prism is not required) at a normal incident angle. In fact, all these requirements are necessary to be maintained in order to increase the K (wave vector) value of the incident light inside the optically denser medium (i.e. prism for PSPR or structure confinements for LSPR) to match the K value of the SPR. To clarify this issue, from the dispersion plot for continuous metal thin film (i.e. PSRR) shown in Figure 7, it is clear that the K value of the incident light ( dk =ω/c d ) is much smaller than the counterpart K value of the surface plasmon ( dmk = √ d m d m ), meaning that light will not be able to propagate through the plasmon. But with Kretschmann excitation configuration (in addition to other excitation configurations such as Otto excitation configuration and diffraction effect) it is possible to increase K value for the incident light to satisfy perfect matching between the wave vector of the incident light and the wave vector of the surface plasmon to generate efficient SPPs. The reason of such requirements is that the traveling waves of the SPPs only originate if the exponent term appears in equation1 as a complex term, i.e. a fraction of the incident light is absorbed. Indeed, light absorption is essential here in order to excite the free electrons of the metal which therefore excites SPR. The latter will not induce SPPs unless the bespoke wave vectors are perfectly coupled; simply because the newly generated SPPs waves need to follow this vector. This is expressed by the equation: Where E is the amplitude of the evanescent waves (SPPs) which propagate along the wave vector k. Eo is the amplitude of the incident electric field, ω is the  rjktjEE o .exp   ……………………………………………..1
  • 40. Chapter 2 26 angular frequency (2f), t is time, r is the propagation axis (x or y or z) and j=√-1 [45]. Metal thin film Prism Incident light Reflected light PSPR Figure 4: Schematic illustration for Kretschmann excitation configuration. PSPR can be excited on a metal thin film attached to the surface of a prism. PSPR can be excited if p-polarised light is incident by a certain angle called resonance angle, denoted by θi, which allows light to be absorbed by the free electrons of the metal, and hence, arising coherent oscillations represented by PSPR. The prism slows down the wave vector of the incident light to have it comparable to the wave vector of the PSPR oscillations. PSPR induce SPPs along the metal-dielectric interface. SPPs exponentially decay in the dielectric medium as well as in the metal. θi SPPs Resonance angle
  • 41. Chapter 2 27 Figure 5: Surface Plasmon Polaritons (SPPs). a represents the electromagnetic field E propagating parallel to the incident plane i.e. in x-z plane. Magnetic field H is propagating parallel to the surface i.e. in x-y plane. b represents the perpendicular field Ez decays exponentially at an order of d in the dielectric (when  represents the wavelength of the incident light) and at an order of m in the metal. With m ~ 1/3 d This Figure was taken from [46]. Figure 6: Localised Surface Plasmon Resonance. This Figure was taken from reference [47].
  • 42. Chapter 2 28 As mentioned previously, the SPPs from the nanoparticles and the nanostructures are confined by the LSPR which is itself confined by the boundary conditions of the nanoparticles and the nanostructures which vary depending on their size, shape, inter-particle spacing and the surrounding medium [48]. Such confinements coming from the fact that those different boundary conditions imply different plasmon modes. For example, in Figure 8 we show five plasmon modes from the surfaces of different nanoparticles presented by Wang et al [49]. In this Figure, spherical nanoparticles support dipolar mode, and hence SPPs with dipolar radiation is generated. Also, metal nanoshells of different thicknesses support symmetric (Figure 8b) and asymmetric (Figure 8c) plasmon modes and vary with the thickness variation. Likewise, metal nanorods of Figure 7: Dispersion plot of the surface Plasmon for continuous thin film. represents the wave vector of the dielectric medium , represents the wave vector of the surface Plasmon, represents the dielectric constant of the dielectric medium and represents the dielectric constant of the metal. Black sold line represents the propagation of the wave vector in dielectric medium, red sold line represents the propagation of the wave vector in surface Plasmon and black dashed line represents the metal-dielectric interference. dd c k    md md dm c k     d m k 
  • 43. Chapter 2 29 different aspect ratios support plasmon mode of field polarization parallel (Figure 8d) or perpendicular (Figure 8e) to the rod. However, for specific engineered nanostructures the plasmon modes are confined by the polarisation state of the incident light and the edge cut of the nanostructures. For example, if the electric wave vector of the incident light is vertically polarised (p- polarised) then it drives the SPR on the surface of the horizontal edges in a manner similar to that shown in chapter 6 Figure1. This also the case for U shape made out of gold, with two assigned edges: A and B, see Figure 9. In this Figure, for plane polarised light, LSPR could be switched off or on simultaneously at the edges depending on the polarisation state of the incident light whether it is perpendicular (Figure 9a) or parallel (Figure 9b) to A and B. Also, for circularly polarised light, LSPR could be switched off or on individually at A or B depending on the handedness of the incident CPL whether it is left handed (Figure 9c) or right handed (Figure 9d). On the other hand, LSPR wavelength (or LSPR maximum absorption) is confined by the size and shape of the nanoparticles and the nanostructures. In 2011, the Van Duyne group demonstrated a relationship between nanoparticle size and shape and LSPR wavelength. Upon changing the LSPR wavelength of periodic particle arrays via changing nanoparticle in-plane width (Figure 10 inset a) and out-of-plane height (Figure 10 inset b) they have found that increasing the in-plane width shifts the LSPR wavelength towards lower-energy wavelengths and increasing the out-of-plane height shifts the LSPR wavelength towards higher-energy wavelengths, see Figure 10. On the whole, LSPR confinement for SPPs leads to SPPs coupling within the structural gaps which not only protect the SPPs from rapid decay but also supports much more intense SPPS fields which could be guided within a specific path depending on the shape of the nanostructures. As such, for specific engineered nanoparticles and nanostructures the field lines of the adjacent SPPs might couple together to generate enhanced SPPs. For example, intense near field oscillations were observed by Chung et al. in the gap area of spherical nanoparticle dimers, see Figure 11a. This research group also observed intense near field oscillations that were developed in the nanogap area for double nanocrescents facing each other, see Figure 11b. Also, Capasso et al, observed intense near field oscillations that were developed in the nanogap area for optical antenna, see Figure 11c. Apparently, gap distance is another factor that affects the SPPs enhancement e.g. for spherical nanoparticles, Chung et al. have demonstrated a maximum
  • 44. Chapter 2 30 enhancement at a distance gap on the order of the radius of the nanoparticle. In addition, Giessen’s group theoretically predicted that SPPs can be enhanced as a result of a near field coupling at the separation gaps between the nanowires of the nanostructures, i.e. chiral nanostructures can confine the SPPs enhancements to a chiral fashion, for example, the right handed gammadion structure (Figure 12a) and the left handed helix structure (Figure 12b) can enhance the electric energy density  eU to 400 and 375, respectively. Figure 8: Different field distributions imply different surface plasmon modes. a represents dipolar plasmon mode of a metal sphere imbedded in different dielectric media. b represents symmetric plasmon mode of a metal nanoshells of different thicknesses. c represents asymmetric plasmon mode of a metal nanoshells of different thicknesses. d represents metal nanorods of different aspect ratios with plasmon mode of field polarization parallel to the rod. e represents metal nanorods of different aspect ratios with plasmon mode of field polarization perpendicular to the rod. This Figure was taken from reference [49].
  • 45. Chapter 2 31 Figure 10: Relationship between nanoparticle size and shape and LSPR wavelength. LSPR wavelength of periodic particle arrays can be changed with changing nanoparticle in-plane width (inset a) and out-of-plane height (inset b). This Figure was taken from refrence [37]. NormalisedExtinction Wavelength (nm) 120 42 426 150 70 446 150 62 497 95 48 565 120 46 638 145 59 720 145 55 747 145 50 782  a (nm) b (nm) Shape Figure 9: Illustration for SPR modes on U shape made out of gold with two assigned edges: A and B. Red arrows denote the direction of the incident light. Note that for plane polarised light, SPR could be switched off or on simultaneously at the edges depending on the polarisation state of the incident light whether it is perpendicular (a) or parallel (b) to A and B. Likewise, for circular polarised light, SPR could be switched off or on individually at A or B depending on the handedness of the incident CPL whether it is left handed (c) or right handed (d). This Figure was taken from reference [41].
  • 46. Chapter 2 32 Figure 11: SPPs enhancements are occurred as a result of near field coupling at the separation gaps between nanoparticles. a represents an intense near field oscillations in the gap area of spherical nanoparticles dimer. b represents an intense near field oscillations in the nanogap area for double nanocrescents facing each other. (a and b were taken from reference [50]. c represents an intense near field oscillations in the nanogap area for bowtie optical nanoantenna, see Figure 6c (This Figure was taken from reference [51]. 0 9 b a c
  • 47. Chapter 2 33 Figure 12: SPPs enhancement occurs as a result of near field coupling at the separation gaps between the nanowires of the nanostructures, e.g. the chiral shapes of the nanostructures confine the SPPs enhancements to a chiral fashion and hence enhance the electric energy density in the right handed gammadion structure (a) and in the left handed helix structure (b). This Figure was taken from reference [52]. a b
  • 48. Chapter 2 34 In either case (PSPR or LSPR), SPPs are very beneficial fields and have a number of applications especially in biosensing technology. An example for application of PSPR in biosensing technology is SPR spectroscopy `which measures changes in the refractive index of a monolayer attached to a metal surface`. SPR spectroscopy is a powerful optical technique for label-free biomolecular interaction detection in real time. In prism–based SPR spectroscopy [majority of SPR instruments are prism–based SPR (Kretschmann configuration)] a linearly polarised (p-polarised) light passes through a prism onto the back side of a central surface chip and then is reflected back to the detector. At a certain incident angle known as the resonance angle (defined in Figure 4), light is absorbed by the electrons in the metal film of the central surface chip causing them to resonate and hence surface plasmon resonance arises. As such, an intensity lost in the reflected beam appears as a dark band and can be seen as a dip in the SPR reflection intensity curve. Since the surface plasmon resonances are sensitive to the refractive index of the surrounding environment (because SPPs are sensitive to the refractive index of the surrounding environment) the shape and the location of the SPR dip in the reflection intensity curve can be used to gain information about the surface. In order to take an advantage of this phenomenon, probe molecules are immobilised onto the central surface chip, and hence when a flow of analyte passes over the central surface chip, molecular binding interactions can be monitored between the analyte molecules and the probe molecules. A direct consequence of the molecular binding interactions is that the angular position of the dark band will shift, and hence the SPR dip will shift as well, which means a shift in SPR reflection intensity curve will be observed; indicating molecular interaction, see Figure 13. Monitoring changing in SPR response over time allows monitoring molecular binding interactions in a real time. While analyte is continually delivered to the central surface chip, analyte molecules start to bind to the probe molecules resulting in a rapid increas in SPR response. As the number of molecules binding and dissociating become equal, the SPR response level approaches equilibrium. When no more analyte is introduced into the system the analyte molecules will continue to dissociate resulting in a decrease in SPR response. The association rate constant Ka can be extracted from the behaviour of the binding response and likewise the dissociation rate constant Kd can be extracted from the unbinding response. The ratio between these two constants yields the binding
  • 49. Chapter 2 35 affinity of the system. An example for application of LSPR in biosensing technology is the Superchiral field induced-CD spectroscopy, which measures changes in the refractive index of dielectric environment surrounding chiral plasominc nanostructures. These changes are induced once the analyte molecules lie within SPPs regions and hence induce shifts (red shift or blue shift depending on the molecular chirality of the analyte molecules) in LSPR wavelengths following the relationship shown in equation 15 chapter3. More details are presented in chapter 3. Gold thin film Prism p- polarised incident light Figure 13: Schematic illustration for SPR spectroscopy. SPR can be excited on a central surface chip when p-polarised light incident by a certain angle called resonance angle, denoted by θi, which allows light to be absorbed by the gold free electrons. Reflection from central surface chip with immobilised probe molecules is denoted by θr and reflection from central surface chip with immobilised probe molecules plus analyte molecules is denoted by by θr-analyte. SPR reflection intensity may change from θr to θr-analyte by a value of Δθ indicating analyte detection, see SPR reflection intensity curve on right. Location and value of Δθ is sensitive to SPR on the central surface chip which is itself sensitive to the refractive index of central surface chip and hence varies with analyte concentration. Rate of molecular binding interactions between probe molecules (navy angular shape) and analyte molecules (red filled circles) is monitored via SPR response with time, see SPR response curve on left. In SPR response curve, Ka and Kd denote the association and dissociation rate constants, respectively. The ratio of these two constants yields the binding affinity of the system. θ SPR reflection intensity curve SPRreflectionintensity Δθ Flow channel Probe molecules Analyte molecules Time Resonance Ka Kd SPR Central surface chip θi θr θr-analyte SPR response curve
  • 50. Chapter 2 36 2.1.4. Plasmonic metamaterials As it already mentioned, this chapter describes the nanofabrication of the plasmonic nanostructures i.e. plasmonic metamaterials. Plasmonic metamaterials are materials made out of metals, like gold or silver that have free electrons (conductive electrons) in their outer orbitals i.e. plasmon. Plasmons enable such metals to support plasmonic surfaces. A unique aspect of the plasmonic surfaces is to produce the evanescent fields; which emit photons at the same frequency as of the photons of the incident light. This provides an extra electromagnetic field source for the nearby molecules which is why they glow. This property of the surface plasmon is really useful and is being applied in a number of disciplines; a common example is their usage in biological sensors [38].In general, since the SPPs arise on metal/dielectric interfaces; and because SPPs is oscillating within a fraction of the wavelength, any small disturbance caused by external element, e.g. the adsorption of a biomolecule, could affect the homogeneity of its oscillations, and hence sense particles comparable to the length scale of spectroscopic incident light or even less. However, some circumstances should be concerned here to achieve typical consequences; for example, because the dielectric constant is frequency dependent [37], the resonance condition for gold or silver metal is justified only at visible band with water and at IR spectrum with air. Besides, the dielectric constant of the medium should be less than that for the metal [37,38,42]. Although as circumstances are not difficult to be achieved, still limit the application for a certain metals, certain solutions and certain wavelengths. From other hand, the fact that the metamaterials shapes and structures affect the surface plasmon resonance [53], this might confine researchers to design metamaterials in a way when a triple match: between the incident wavelength of spectroscopic instrument they use (like CD spectrometer), the length scale of the plasmonic surface, and the target proportions (the molecule keen to be sensed) is become possible.
  • 51. Chapter 2 37 2.2. Theory and background 2.2.1. Electron beam- substrate surface interferences As mentioned above, electron beam lithography uses a focused electron beam as a means of drawing geometrical features on a matrix of substrate. In principle, when the electronic beam strikes the surface of this matrix, which is represented by the resist film, it is believed that three possibilities might occur depending on the nature of the interaction. These are: 1. The electron beam might be forward scattered. This is when the electrons are deflected by the molecules of the resist as a consequence of elastic collisions. This causes the electron beam to be broadened gradually. The width of the electron beam increases with increasing thickness layer of the resist. It also increases with decreasing energy of the electron beam. Generally, the broadness of the electron beam creates broadened feature sizes. Thus, the width of the electron beam can be a problematic issue. Recently, S.K. Dew and his group simulated the electron beam profile as it strikes the resist layer at energies of 3keV and 10keV. This simulation is shown in Figure 14 below. According to these simulations, the broadening of the electron beam increases with decreasing accelerating voltage. It can be seen that the width of the beam increases towards the base as the thickness of the resist increases. At 60nm thickness the electron beam accelerated with 3 keV approaches a size of 50nm, while the electron beam accelerated with 10 keV approaches a size of 30nm for the same thickness[2 Chapter(2) pp13 ].
  • 52. Chapter 2 38 These simulations are in agreement with the view of Rai-Rechoudhury who suggested in 1997 that the electron beam diameter is proportional to the thickness of the resist layer and conversely with the accelerating voltage of the electron beam. This is expressed by the following equation: df = 0.9 (Rf / Vb ) Where df is the effective diameter of the electron beam due to forward scattering, the R f is the resist thickness and Vb is the electron beam voltage in kilovolt [1Chapter(2) pp158 ]. 2. More elastic collisions might be due to the electron beam being back scattered by the substrate surface. This arises when the electron beam penetrates through the resist and strikes the molecules of the substrate, like silicon. This causes the electrons to be deflected by relatively large angles and being back scattered through the resist again. In this case, the electrons will be scattered distant from their incident beam. This means the proximal region of the resist will receive a non-zero exposure dose (Figure 15), which causes `the electron beam proximity effect`, a very common problem in nanofabrication. The proximity effect varies depending on two main factors. It depends on both the substrate materials (low molecular weight substrate materials have less effectiveness than high molecular weight substrate materials) and the electron Figure 14: Simulations of two parallel beams of electrons. In a and b, the electron beam expands with increasing the thickness layer of the resist. The expansion with 3kV accelerating energy (shown in a) is almost a double of the expansion of 10KV one (shown in b). This is accrued as a result of the forward scattering by the molecules of the resist. This Figure was taken from [2 Chapter(2) pp13 ].
  • 53. Chapter 2 39 beam energy. The electron beam launching with high energy causes the electron beam proximity effect to expand microns away from the incident point. This ends up with overexposed and large features [53]. Nevertheless, the research group of Yoshihide Kato believe that increasing the electron beam energy has the advantage of reducing the proximity effect even if the pattern density is changed and hence improves the resolution [54]. In fact, two strategies can be employed to help reduce the proximity effect: a) reduce the thickness of resist layer to, indirectly, restrict the features; b) reduce the electron beam energy to confine the brightness of the electron beam and hence the resolution of the writing process [2 Chapter(2) pp13 ]. 3. In addition to the elastic collisions, the electron beam probably undergoes inelastic collisions with the molecules of the resist. This causes the outer electrons of the resist molecules to be discharged a few nanometers away from their original atoms. This is with a range of energy varied between 2 eV to 50 eV. This leads to the formation of ` Secondary Electrons` (SE) illustrated in Figure 15 below. The SE also contribute to the proximity effect mentioned above. Although their contribution is only a few nanometers, they limit the resolution of the fine detail features [1Chapter2 vpp159 , 2 Chapter(2) pp13 ]. Thought, another issue might contribute to the proximity effect; this is if the secondary electrons are characterised as `fast secondaries`. In such cases, the energy level is much higher than the normal energy levels. It might approach 1000 eV. This affects the proximity effect by a few tenths of a micron. The fast secondaries form only a small fraction of the secondary electrons [1 Chapter2 pp159 ].
  • 54. Chapter 2 40 2.2.2. Electron beam- PMMA resist interferences PMMA resist is an organic transparent polymer synthesised by the process of the polymerisation of the monomer methyl methacrylate to form the poly methyl methacrylate PMMA, chemically formulated as CH2=C(CH3)COOCH3. An analogue with ZEP and HSQ, this polymer is used in electron beam lithography as a resist layer. In principle, the writing process is performed upon either positive tone resist or negative tone resist. In positive tone resist, like PMMA and ZEP520, if the electron beam delivers enough energy to ionise the resist molecules, the low solubility of the resist molecules in the developer is O CH3OC CH3 CCH2 Poly Methyl Methacrylate PMMA Figure 15: The path of the electron beam striking silicone substrate with PMMA resist on the top. The electron beam is either forward scattered; or elastically releases secondary electrons from PMMA molecules; or backscattered. Backward scattering The secondary electrons The Electron Beam Forward scattering Silicon PMM A The Electron Beam source
  • 55. Chapter 2 41 altered to high solubility value. The ionization of the resist molecules aids the polymer chains to break into smaller chains, more soluble than the larger chains. Therefore, in the development process the exposed area of the resist with small fragments chains is removed and the unexposed area with long chains remains (Figure 16 a). In contrast, negative tone resist consists of small and soluble chains of polymers. Here the electron beam helps the small and highly soluble chains to combine together to form long and low soluble chains. This process called the `cross-linking reaction`. Because of the cross- linking reaction, in negative tone development process the exposed area is retained and the unexposed area is removed (Figure 16b). A common example for negative resist is the HSQ (hydrogen silsesquioxane) [1Chapter(2) pp(205,210) ,2Chapter(2) pp14 , (55-57)] For nanofabrication work of this project a positive tone of PMMA resist has been used. Fundamentally, the PMMA resist consists of long chain polymers, with a mass of 496 and 950kDa. Such long chains require many scissions to be fragmented into small and soluble chains. The fragmentation process is influenced by three main factors, these are: the dose of the exposure, the duration of the exposure and the accelerating voltage of the electron beam. Regarding the dose exposure domain, S.K. Dew and his group calculated the b Figure 16: Cartoons of positive tone resist (a) and negative tone resist (b). a The Electron Beam
  • 56. Chapter 2 42 exposure dose of 50, 100 and 150µC/cm2 on PMMA resist. They believe that at a dose of 50µC/cm2 ; the fragments sizes are varied between a single to twenty monomers, which give a maximum contribution of 13%. While in exposure dose of 100µC/cm2 , the fragment sizes are varied between a single to twelve monomers, which give a maximum contribution of 18%. Increasing the dose to150 µC/cm2 , the fragment sizes are varied between a single to nine monomers, with a contribution of 25%. It is clear that increasing the dose value leads to smaller fragment’s sizes (Figure 17 a). Apparently, this study was necessary to illustrate the spatial variation of the dose caused by the variation of the scattering; which caused by different fragment sizes. The spatial variation of the dose was suggested by the same group, assuming a spatial dose scattering by fragment size of less than ten monomers, and accelerated by 10keV voltage. This prediction ended up with a 3D exposure scission event shown in Figure 17 b. This theoretical calculation could also apply to other positive and negative tones resist [2 Chapter(2) pp15 ]. It can be concluded from Figure 17a that the value of the exposure dose plays a key role in the final quality of resolution, and hence the nanofabrication work. The effect of increasing the dose value is shown in Figure 18 below. This Figure shows the cross section profile of 55nm PMMA resist, patterned with a 70nm Figure 17: Theoretical simulations of the dose exposure domain on the PMMA resist. a shows three doses of 50, 100 and 150µC/cm2 with their corresponding contributions of the fragments sizes. b shows 3D spatial distribution of the dose scattered by less than ten monomer fragments sizes. This Figure was taken from [2 Chapter(2) pp15 ].
  • 57. Chapter 2 43 grating pitch by accelerating voltage of 30keV. Different doses (line doses) were applied here, these are 2.0 nC/cm, 4.5 nC/cm and 7.0 nC/cm, shown in a, b and c, respectively. An increasing in interlines width with increased dose exposure leads to broadened feature sizes and poorer resolution [2 Chapter(2) pp17 ]. The other concern is the time exposure domain. Recently, a research group led by Yoshihiko Hirai had demonstrated their theoretical estimation for the scission of the time exposure in molecular detail. They used the Molecular Dynamics (MD) simulations to analyse the atomic-scale region. They assumed a 4nm PMMA film thickness, with 10nm width, on silicon substrate. The exposed line width was 2nm and the PMMA molecular weight was 5000 (Figure 19) below. They believe that the process of fragmentation to small sizes polymer chains is proportional to the exposure time. This is because the fragment sizes in an exposure time of 7 ps were smaller than the fragment sizes of the exposure time of 3 ps. And the fragment sizes of an exposure time of 3 ps were smaller than the fragment size of the exposure time of 1ps [58]. This is shown in the Figure 20 a, b, c and d: a b c 2.0 n C/cm 4.5 n C/cm 7.0 n C/cm Figure 18: The effect of increasing the dose values on the grating of 70nm pitch on 55nm PMMA resist. The dose (line doses) values of 2 nC/cm, 4.5 nC/cm and 7.0 nC/cm are shown in a, b and c, respectively. These images were adopted from reference [2 Chapter(2) pp17 ]. 70nm Pitch Interlines
  • 58. Chapter 2 44 Figure 20: The theoretical estimation of the scission of the time exposure domain in molecular level. The highlighted molecules are the molecules experiencing fragmentation event. a, b, c and d show the effect of time exposure at 0 ps, 1ps, 3ps and 7 ps, respectively. This Figure was adopted from reference [58]. ba c d Figure 19: The model of Molecular Dynamic simulations for PMMA resist on silicon substrate. This model was used to conclude the effect of the time domain on the exposure scission, in molecular level system. This Figure was adopted from reference [58].
  • 59. Chapter 2 45 The effect of the accelerating voltage domain (which represents a key objective of the electron beam interferences with the PMMA resist) represents a further cause for concern in the technique of EBL. It has been found that increasing the accelerating voltage of the electron beam increases the absorption level for the energy by the PMMA resist. This effect was demonstrated in the same study for the model shown in Figure 19 above. Again, the Monte Carlo method was used to simulate the energy distribution absorbed by PMMA resist on silicon substrate. Three values of acceleration voltage were used in this simulation, these are: 1keV, 10keV and 100keV. It has been found that an electron beam with acceleration voltage of 1 KeV has the largest and the broadest distribution level of energy. This is due to electron scattering by the sample molecules. For 10 keV, more energy absorption and less electron beam scattering were observed. Eventually, the best level of absorption with the lowest distribution was achieved by 100 keV (Figure 21). The 100 keV supports the highest resolution of the writing process in electron beam lithography [58]. For our nanofabrication work, a 100 keV was used for all experiments. Figure 21: The Monte Carlo simulation for the effect of acceleration voltage domain. Note that by increasing the accelerating voltage; the energy level absorption increases and the energy level distribution decreases. This Figure was adopted from reference [58].