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57 %\title{\bf Characterisation of nanostructured thin films}
58 %\author{Sam Moore\\ School of Physics, University of Western Australia}
63 B.Sc. (Hons) Physics Project \par
64 {\bf \Large Thesis} \par
66 School of Physics, University of Western Australia \\
69 \section*{Characterisation of Nanostructured Thin Films}
70 {\bf \emph{Keywords:}} surface plasmons, nanostructures, spectroscopy, metallic-blacks \\
71 {\bf \emph{Supervisers:}} W/Prof. James Williams (UWA), Prof. Sergey Samarin (UWA) \\
76 \section*{Acknowledgements}
82 \item Workshop (for producing electron gun mount?)
83 \item Peter Hammond (?)
86 \section{Introduction}
88 \item Waffle about motivation for the project
90 \item Metal-Black films may have application for ... something.
92 \item Radiometer vanes, IR detectors
93 \item Number of applications where high absorbance into IR is required
94 \item These have all been studied before though.
96 \item The electron spectra of metal-blacks have not yet been examined.
97 \item Remarkable difference between Metal-Black films (bad vacuum) and normal metal films (UHV)
99 \item No (detailed/satisfactory) explanation (that I can find...) for difference
101 \item Talk about plasmonic based computing? Moore's law? Applications to thin film solar cells?
104 \item Specific aims of project
106 \item Surface density of states / band structure of Black-Au films using TCS (The main aim)
107 \item Identification of plasmonic effects in Black-Au films (?) (If they even exist!)
109 \item Identify plasmonic effects in Au and Ag films with Ellipsometry (this is fairly simple to do)
111 \item Combination of Ellipsometry and TCS to characterise thin films (not just Black-Au)
113 \item Ie: How can one technique be used to support the other?
116 \item Structure of thesis
119 \section{Overview of Theory}
120 Summarise the literature, refer to past research etc
122 \subsection{Electron Spectra of a Surface}
124 \item Description of the near surface region
126 \item All real solids occupy finite volumes in space.
127 \item The surface of a solid is important because interactions between the solid and its surroundings occur in the near surface region.
128 \item Characterised physically by:
130 \item Termination of periodic crystal lattice
131 \item Violation of geometric order
132 \item Distortion of interatomic distances and hence interaction forces
133 \item There is a transition ``near surface'' region between bulk and surface properties, roughly 5 atomic distances.
135 \item Potential seen by an electron at a surface can differ greatly from the bulk
136 \item $\implies$ the electron spectra of the near surface region differs from the bulk spectra
137 \item Simplest case: Step potential at surface
139 \item Metal & Semiconductor
145 \item The Electron Spectra
147 \item Electron Spectra describes the energy eigenstates for an electron in a Bulk or Surface potential
148 \item Characterised by
150 \item Energy dispersion $E(\vect{k})$
152 \item Dependence of Energy on electron wave vector
153 \item Obtained theoretically by solving Scrhrodinger's Equation
154 \item For a free electron gas, $E = \frac{\hbar^2 k^2}{2m}
155 \item Periodic potential in bulk solid leads to band gap structure of $E(\vect{k})$
156 \item Periodic potential $\implies$ E is periodic. Only needs to be defined in first Brillouin zone.
158 \item Density of States $N(E)$
160 \item $N(E) = \frac{\Delta N}{\Delta E} = \frac{1}{4\pi^3}\int_S\left(\der{E}{k}\right)^{-1} dS$
161 \item Integral is in momentum space over the isoenergetic surface of energy $E$
162 \item For a free electron gas, $N(E) = $
170 \item Tamm States: Periodic potential in solid, free space outside, jump at surface
172 \item Energy eigenvalues lie in the forbidden band of the bulk spectra
173 \item Attenuation of eigenvalues from surface to vacuum, oscillation of state within surface
174 \item Max electron density occurs on the crystal surface
176 \item Shockley states: Potential of surface and bulk cells equal
178 \item Corresond to free valences (dangling bonds) at the surface
181 \item Tamm and Shockley states arise from two extreme models (large change and small change respectively between bulk and surface). In reality, a combination of Tamm and Shockley states appear.
185 \item Properties of surface region
187 \item Difference between potential of surface and bulk
189 \item Change between the two limits in the ``near-surface'' region
191 \item Theoretical models for the potential, 1D vs 3D
193 \item Simplest case is a step potential.
194 \item Various improvements on this model, discussed in Komolov's book.
196 \item Possibly adapt CQM project to model these potentials, if I get time
199 \item Limitations of theoretical models
201 \item Real surface is not a step potential
202 \item Adsorption of foreign particles onto the surface also plays a large role in determining the electron spectrum.
205 \item Main reference: Komolov "Total Current Spectroscopy"
206 \item "Solid State Physics" textbooks and "Electron Spectroscopy" textbooks
209 \subsection{Plasmonics}
210 I really think I should actually find plasmonic effects before writing too much about them...
212 \item Charge density oscillations
213 \item Surface and bulk plasmons
215 \item Review article from T.W.H Oates et al about using Ellipsometry to characterise plasmonic effects
218 \subsection{Metallic-Black Thin Films}
220 \item How they are made (bad vacuum, in air or a noble gas)
222 \item If made in air, there are usually tungsten oxides present (from filament). Refer to paper by Pfund.
224 \item Structural difference between Black-Au and ``Shiny'' (need a better term) Au
226 \item Can include electron microscopy images?
227 \item An actual photograph of a Black-Au film? Not necessary?
229 \item Pfund (earliest publisher, preparation and general properties)
230 \item Louis Harris (most research in 50s and 60s)
232 \item L. Harris mostly did transmission spectroscopy in the far infra red (well beyond the ellipsometer and Ocean Optics spectrometer ranges)
233 \item The really crappy measurements I did with the Ocean Optics spectrometer seem to agree with these measurements
235 \item L. Harris' $\lambda$ has a range of 1nm to $100\mu$m; my measurements are only to $1\mu$m
236 \item Agreement in first $1\mu$m anyway
237 \item I should probably re-do those measurements with a less crappy setup, if I actually want to use them
239 \item Harris related the optical properties to the structure of the film (condensor strands) via the electronic properties
241 \item Plasmonic effects - Deep R. Panjwani (honours thesis)
243 \item Not sure if I can use an honours thesis as a reference.
244 \item Concluded that surface plasmon resonance in Black-Au film on solar cells lead to increase in solar cell efficiency
245 \item Used simulation that modelled Black-Au film as spherical balls to show E field increased by plasmon resonance
247 \item Was this model appropriate? Black-Au is more ``smoke'' or ``strand'' like according to other references. Images also do not show ``blob'' like structure.
249 \item Need to read this reference more thoroughly
253 \section{Experimental Techniques}
255 \subsection{Preparation of samples}
257 \item Black-Au - 1e-2 mbar vacuum
258 \item ``Shiny'' - 1e-6 / 1e-7
259 \item Current of ~3.5A through W wire filament spot welded onto Ta strips in turn spot welded to Mo posts
260 \item Voltage through filament is ~1 V; quote the power?
261 \item Filament isotropically coats sample with desired material.
262 \item Possibly get a curve of Au thickness estimated with Ellipsometry vs exposure time?
264 \item Probably too much work and too unreliable
265 \item Maybe do it, but only use 2/3 data points
270 \subsection{Total Current Spectroscopy}
272 \item Overview of technique
274 Total Current Spectroscopy (TCS)
277 \item Low energy beam of electrons incident on sample
278 \item Measure slope of resulting I-V curve
279 \item Relate to density of states and electron band structure (Komolov chapter 3.2)
281 \item Description of apparatus
283 \item Electron gun and filament
284 \item Electron gun control box
285 \item ADC/DAC control box and data processing
287 \item Photographs vs Diagrams
289 \item Prefer diagrams to photographs
290 \item Especially for the ADC/DAC control box circuit. Because it looks like a horrible mess.
294 \subsection{Ellipsometry and Transmission Spectroscopy}
296 \item Overview of techniques
297 \item Description of apparatus (use VASE manual)
298 \item Ocean Optics spectrometer? Usable?
299 \item Application of Ellipsometry to finding plasmonic effects
301 \item Surface plasmons = E oscillation parallel to surface $\implies$ only $p$ component of light excites plasmons
305 \section{Experimental Results and Discussion}
306 \subsection{TCS Measurements}
309 \item TCS for Si + Au
310 \item TCS for Si + Black-Au
311 \item Affect of preparation pressure on TCS for Si + Black-Au
312 \item Repeat for Si + Ag and Si + Black-Ag (?)
315 \subsection{Ellipsometric Measurements}
317 \item Ellipsometry to estimate thickness of SiO2 layer on Si
318 \item Estimate thickness of Au/Ag on Si+SiO2
319 \item Ellipsometric measurements of Si+Black-Au/Ag
321 \item Modelling procedures to characterise Black-Au/Ag
323 \item Ellipsometric measurements of Glass+Black-Au/Ag (?)
324 \item Transmission spectra of Glass+Black-Au/Ag from earlier in year (?)
327 \section{Achievements}
329 \item Deposition of thin films of Au and Black-Au in vacuum chamber
330 \item Ellipsometric and spectroscopic measurements on these films
331 \item Repurpose vacuum chamber for sample preparation and TCS experiments
332 \item Designed and built electronics for TCS experiments
334 \item Electron gun control box
337 \item Wrote software for data aquisition and data processing
340 \section{General notes}
343 \item Optimise setup of gun
345 \item Emission current. How much does it vary, why does it vary.
346 \item Why does Is/Ie curve shift with successive sweeps? Does sweep modify sample's surface?
347 \item Is sample holder acceptable? Are ceramic washers accumulating charge?
348 \item How do I tell when the setup is optimised...
349 ``The setup was optimised by looking for an S curve''. Very scientific.
350 \item The gun was focused on the phosphor screen... and then I turned it around, changing the distance from the gun to the sample. Brilliant.
352 \item Obtain TCS spectra for Si that compares well with literature
354 \item How to relate TCS spectrum to $n(E)$ and $E(\vect{k})$
356 \item Prepare Au films, obtain TCS spectra that compares with literature
357 \item Obtain TCS spectra of Black-Au films
358 \item Use results to compare properties of films with results from other methods in the literature
361 \item Oscilloscope measurements of inputs to ADC channels under controlled conditions
363 \item Expected values are +/-3mV due to ADC channel, +/-300mV due to 610B, +/-1mV due to 602
364 \item 610B and 602 will probably be worse because they are ancient
365 \item There is about 200mV of noise between the GND of the ADC box and the electron control box.
366 \item How to reduce ground loops? Not much I can do. Rack is now also grounded to water pipe, but this doesn't seem to make a difference.
368 \item Stupid 50Hz AC noise... how to reduce with filters and/or averaging
370 \item Create circuit diagrams for Electron gun circuit
371 \item Create circuit diagrams for ADC/DAC box
373 \item Simulate behaviour of circuit
374 \item Use of instrumentation amplifier on ADC5 to make off-ground measurements
375 \item Use of low pass filter on ADC5
377 \item Include references to all datasheets, etc
380 \item Base pressure with rotary pump? Was 1e-3 after 30 minutes at start of year, but probably introduced leaks since then
381 \item Lowest pressure achieved with turbo pump is 1.1e-7 mbar as of 25/07.
382 \item Viton gaskets on some seals. Copper on other.
385 \item View window (large, view of sample \& sputtering filaments)
386 \item Rotation manipulator \& sample mount
388 \item Filament flanges 1 (used earlier in year, not anymore) and 2
389 \item Inlet with leak valve (for introducing gases into chamber)
390 \item Vent valve on turbo pump
391 \item Electron gun flange
392 \item View window (small, view of back of electron gun)
398 \bibliographystyle{unsrt}
399 \bibliography{thesis}