Development of Optical Fibre Chemical Probes by Oblique Angle Deposition

265 Pages·2012·13.67 MB·English

Development of
Optical Fibre Chemical Probes
by Oblique Angle Deposition
A thesis submitted for the degree of
Doctor of Philosophy
by
Sasani Jayawardhana
Centre for Atom Optics and Ultrafast Spectroscopy and
Faculty of Engineering and Industrial Sciences
Swinburne University of Technology
Melbourne, Australia
September 16, 2011
“Do not believe in anything simply because you have heard it. Do not believe in
anything simply because it is spoken and rumored by many. Do not believe in anything
merely on the authority of your teachers and elders....... But after careful observation
and analysis, when you find that anything agrees with reason and is conducive to the
good and benefit of one and all, then accept it and live up to it.”
- Lord Buddha (563-483 B.C)
Abstract
An optical fibre chemical sensor based on the technique of surface-enhanced Raman
scattering(SERS)hasbeendeveloped. SERSreliesonthecloseinteractionbetweenthe
target analyte and a nanostructured metal surface. This nanostructure was fabricated
using the method of oblique angle deposition (OAD) under thermal evaporation. The
deposition was carried out by holding the sample surface at an oblique angle to the
metal vapour flux, which results in a columnar morphology of the thin film. The
viability of thermal OAD for SERS substrates was initially determined by the use
of a planar silicon wafer with a thermal oxide layer. It was found that a vapour
deposition angle of 86○ provided the optimum nanostructure for SERS performance,
using thiophenol (C H SH) as a test analyte. Strict control of the evaporation current
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was required to minimise radiant heating inside the evaporation chamber, as any
increase in the temperature resulted in a high variability in the SERS response across
different deposition runs. This appeared to be due to increased adatom diffusivity
on the nanorod surface triggered by the thermal energy, which in turn resulted in
morphological changes of the nanostructure. Controlling the heating by regulating the
evaporation current produced a highly reproducible SERS substrate which exhibited a
repeatabilityof 10%basedonrelativestandarddeviation(RSD).Thisinsightwasused
≲
to extend the technique to the tip of a standard multi-mode optical fibre. The earlier
results were verified by further tests, and the SERS activity was found to increase
with film thickness, with a maximum activity at a nanorod length of 260 28 nm.
±
Although the OAD nanorod structures fabricated on the fibre tip exhibited excellent
SERS activity in direct excitation, the signal collection efficiency was found to be
reduced down to between 8% and 1%, in the remote excitation where the substrate was
excited by coupling light through the fibre. The main reason for this discrepancy was
revealed to be due to an incomplete overlap between the confocal light collection area
and the spatial distribution of the scattered light in the fibre core. Other factors such
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as optical coupling between the microscope objective and optrode sensor, waveguide
distribution across the fibre core and transmission losses associated with the OAD
layer were also found to contribute to the decrease in signal collection efficiency in the
remote interrogation. Nevertheless, the appropriate selection of collection optics and
optical fibre could result in a more efficient signal collection in the optrode sensor.
The possibility of using the intensity of the Raman band (430 cm−1) of the silica as
an internal standard to normalize the collected analyte signal was demonstrated. This
provided a mechanism to account for the variability in the analyte signal arising due
to the waveguide properties and optical misalignment. The potential for using the
OAD substrate as an environmental sensor was investigated in the context of detecting
atrazine, which is a common herbicide and water contaminant. In addition, issues
relating to surface contamination of OAD substrates due to amorphous carbon were
also investigated.
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Acknowledgments
Even though this thesis comes forward as one person’s work, it is not a fair statement.
This work, years of it, would not have been possible without the enormous support
that I received from those who were around me and who truly deserve to be mentioned.
My wonderful husband - Yasas, thanks for believing in me throughout all these
years. Always grateful for your constant encouragement and understanding, despite
this page being as far as you would read in this thesis. My parents for your love and
unwavering support you have shown me over the years, in whatever I decide to take
on.
My supervisors - Dr Paul Stoddart and A/Prof. Alex Mazzolini, for guiding me
along the path of science while giving me room to grow. I’m truly indebted to Paul for
being there throughout, setting aspirational goals, cracking the tough nuts along the
way and tolerating my antics with his good humour. It was a true pleasure working
with you.
The folks in the Applied Optics group as part of Centre for Atom Optics and
Ultrafast Spectroscopy (CAOUS), recently joined hands with the Biointerfaces group
at the Industrial Research Institute Swinburne (IRIS). A special thanks to Prof. Peter
Cadusch for all his mathematical magic. Thanks to Keith Gibbs for times spent
pondering on arcane physics matters over cups of tea; Prof. Sally Macarthur, Dr
Scott Wade, Dr Peter Mahon and Dr Chris Easton for all those useful discussions.
Thanks to all the students past and present - Chiara, Alex, Elena, Akanaxa, Will and
Dori for all the help in and outside the lab. Thanks to Andrea and Jiawey for help
with all things chemical and a special mention to my ‘predecessor’ Dr Daniel White
for teaching me the instrumentation and setting me off on my project.
Many thanks to the Director of CAOUS, Prof. Peter Hannaford for nurturing
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a friendly environment to work in. Tatiana Tchernova for all help with paperwork
and cheering us up with her stories; and of course Mark ‘the magnificent’ Kivinen, our
workshop supervisor for making all the obscure items that I kept requesting, sometimes
even before I could get a signed job request form, in triplicate.
The folks at RMIT University - Dr Gorgi Kostovski, Dr Sharath Sriram and Dr
Madhu Bhaskaran for their enthusiastic support in all work done in collaboration;
Yuxun Cao, Dr Vijay Sivan and Paul Jones for their help with the dicing machine.
Mircea Petre at OptoTech (Pty) Ltd, for his zealous help with lasers and optics.
Dr Colin Cook at the Department of Primary Industries, for his help with preparing
and testing atrazine solutions.
Dr Finlay Shanks, at Monash University for trusting me with the Raman
microscopes.
Dr Matteo Altissimo at the Melbourne Centre for Nanofabrication for his eager
assistance with the use of the plasma cleaner.
Dr Robert Jones at La Trobe University for his assistance with surface analysis
using X-ray Photoelectron Spectroscopy.
Dr Bob Irving, Dr Peter Binks and Dr Sarah Morgan at NanoVentures Australia,
for providing financial support for the project.
Thanks to Ben Cumming for entrusting me ‘the key’, that made things all that
more convenient. And definitely not forgetting to thank the rest of the fellow students;
Evelyn, Eva, Chris, Smitha and Gethin who were around day in and day out, sharing
the ups and downs of life as a PhD student along with tea times and quiz times that
made long working days very much enjoyable.
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Declaration
I, Sasani Jayawardhana, declare that this thesis entitled:
“Development of optical fibre chemical probes by oblique angle
deposition”
is my own work and has not been submitted previously, in whole or in part, in
respect of any other academic award.
Sasani Jayawardhana
Centre for Atom Optics and Ultrafast Spectroscopy
Faculty of Engineering and Industrial Sciences
Swinburne University of Technology
Melbourne, Australia
Dated this day, September 16, 2011
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Glossary
AFM Atomic Force Microscope
CCD Charge Coupled Device
EF SERS Enhancement Factor
EM Electromagnetic
FON Film-on-Nanosphere
FWHM Full-width half-maximum
GCMS Gas Chromatography - Mass Spectroscopy
GLAD Glancing Angle Deposition
GRIN Graded-Index
HCl Hydrochloric Acid
HJY Horiba Jobin-Yvon Modular Raman Microscope
IR Infra-red
KJL Kurt J. Lesker Coating Unit
LSPR Localised Surface Plasmon Resonance
n Refractive Index
NA Numerical Aperture
NRS Normal Raman Spectroscopy
NSL Nanosphere Lithography
OAD Oblique Angle Deposition
PPA Phenylphosphonic Acid
ppb Parts-per-billion
ppm Parts-per-million
PVD Physical Vapour Deposition
SAM Self-assembled Monolayer
SEF Surface-enhanced fluorescence
SEM Scanning Electron Microscope
SERRS Surface-enhanced resonance Raman Spectroscopy
SERS Surface Enhanced Raman Spectroscopy
TERS Tip-enhanced Raman Spectroscopy
UV Ultra-violet
XPS X-Ray Photoelectron Microscopy
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