\item Nikita Kostylev
\item Workshop (for producing electron gun mount?)
\item Peter Hammond (?)
+ \item JA Woolam (for providing replacement alignment detector pins)
+ \item CMCA at UWA (for SEM images) (Is there a specific person I should thank?)
\end{itemize}
\section{Introduction}
+
+In this section I will give the overview of research done on metallic-black thin films, and explain the motivation for this project given the conclusions of past research.
+
\begin{itemize}
- \item Waffle about motivation for the project
+ \item {\bf Aim of Project}
+ \begin{itemize}
+ \item The aim is to employ a range of techniques for characterisation of metallic thin films
+ \item In particular, metallic-black films vs ``shiny'' (``bright'' might sound better)
+ \item TODO: Find a result (plasmonic behaviour?) so that I can say I was aiming to find it
+ \end{itemize}
+ \item {\bf Motivation for Project}
\begin{itemize}
- \item Metal-Black films may have application for ... something.
+ \item Talk about the surface playing an increasingly important role as semiconductor devices become smaller
+ \item Although metallic-black films are well known, they are extremely complicated and difficult to characterise
\begin{itemize}
- \item Radiometer vanes, IR detectors
- \item Number of applications where high absorbance into IR is required
- \item These have all been studied before though.
+ \item Fractal like structure, remarkable
+ \item Mechanism for formation is not well understood
+ (Probably due to metallic nanoparticles having insufficient energy to form a regular lattice, due to energy losses through collisions with the high pressure atmosphere... I need to find a reference for this)
\end{itemize}
- \item The electron spectra of metal-blacks have not yet been examined.
- \item Remarkable difference between Metal-Black films (bad vacuum) and normal metal films (UHV)
+ \item Metallic-black films have had numerous applications as good absorbers of optical wavelengths
\begin{itemize}
- \item No (detailed/satisfactory) explanation (that I can find...) for difference
+ \item High absorbsion coatings for radiometer vanes (Pfund)
+ \item Infra-red detectors; due to being almost transparent in the far infra-red
+ \item (Very recently; 2011), as scattering centres to increase the efficiency of thin film solar cells (Deep R Panjwani)
+ \emph{NOTE: This work was done in an honours thesis, although I believe the supervisor has also published a (much shorter) paper that I may reference if the honours thesis is not a good reference}
\end{itemize}
- \item Talk about plasmonic based computing? Moore's law? Applications to thin film solar cells?
+ \item
\end{itemize}
- \item Specific aims of project
- \begin{enumerate}
- \item Surface density of states / band structure of Black-Au films using TCS (The main aim)
- \item Identification of plasmonic effects in Black-Au films (?) (If they even exist!)
- \begin{itemize}
- \item Identify plasmonic effects in Au and Ag films with Ellipsometry (this is fairly simple to do)
- \end{itemize}
- \item Combination of Ellipsometry and TCS to characterise thin films (not just Black-Au)
+ \item {\bf Past Research}
+ \begin{itemize}
+ \item Pfund - First mentions, preparation, optical transmission, resistivity
+ \item Harris - Later work, extends Pfund's experiments, introduces theoretical discussion of structure
+ \item Some other authors repeat or extend Harris' work. Metallic-black in different atmospheres, etc.
+ \item Modern research - Tends towards ``artificially'' blackened films, which suppress light reflection through plasmonic effects.
\begin{itemize}
- \item Ie: How can one technique be used to support the other?
+ \item The goal is to develop films that exhibit similar effects to metallic-black films, but are simpler to describe theoretically. These films can then be used in applications requiring high absorbsion, as the original films
\end{itemize}
- \end{enumerate}
- \item Structure of thesis
+ \item Can't find much research on plasmons in the ``naturally'' blackened films, except Panjwani
+ \emph{NOTE: Panjwani seems to have modelled the black films as semi-spherical nanoparticles, which in the light of other research (and the SEM images) may be inaccurate}
+ \end{itemize}
+
\end{itemize}
+
\section{Overview of Theory}
-Summarise the literature, refer to past research etc
-\subsection{Electron structure of surface}
+I will use this section to introduce general concepts of solid state physics. The Experimental Methods section will concentrate on the theory of each method, and how this relates to the overall theory.
+
\begin{itemize}
- \item Overview of electron spectrum properties
+ \item {\bf What a nanostructured film is, how it differs from the bulk material}
\begin{itemize}
- \item Density of states $n(E)$
- \item Energy band structure $E(\vect{k})$
+ \item The surface of a solid is the interface for physical/chemical interactions with it's surrounding environment
+ \item The physical and chemical properties of a material are largely determined by the electron spectra at the surface
+ \begin{itemize}
+ \item Electron spectra is determined by the lattice potential
+ \item Characterised by
+ \begin{enumerate}
+ \item Band structure of energy states - due to periodic lattice potential
+ \item Density of States
+ \end{enumerate}
+ \item Surface differs from bulk due to
+ \begin{enumerate}
+ \item Termination of periodic lattice
+ \item Adsorbed particles on surface (thin films)
+ \item Relocation of lattice sites near the surface
+ \end{enumerate}
+ \item Band structure for Metal's vs Semi-conductors
+ \begin{enumerate}
+ \item Metals:
+ \item Semiconductors:
+ \end{enumerate}
+ \end{itemize}
+
+
\end{itemize}
- \item Properties of surface region
+ \item {\bf Surface Plasmons}
\begin{itemize}
- \item Difference between potential of surface and bulk
+ \item A collective oscillation of the electron gas in a metal
+ \item Surface plasmons are confined to the surface region; 2 dimensional, differs from bulk plasmons
\begin{itemize}
- \item Change between the two limits in the ``near-surface'' region
+ \item In nanostructured materials, plasmons can be localised
\end{itemize}
- \item Theoretical models for the potential, 1D vs 3D
- \begin{itemize}
- \item Simplest case is a step potential.
- \item Various improvements on this model, discussed in Komolov's book.
+ \item Bohms and Ritchie
+ \item Past studies at CAMSP and UWA
+ \item May be caused due to excitations from
+ \begin{enumerate}
+ \item Electrons - refer to next section
+ \item Photons
\begin{itemize}
- \item Possibly adapt CQM project to model these potentials, if I get time
+ \item Only light polarised in the plane of the surface can excite plasmons
+ \item Need to provide an extra wavevector to ``match'' the momenta of the photon and plasmon
+ \item Possibility for rough structure of metallic films to provide this wavevector
+ \begin{itemize}
+ \item Refer to papers on ``artificially'' blackened films
+ \item Similar topic to Nikita's thesis; look at some of his references
+ \end{itemize}
\end{itemize}
+ \end{enumerate}
+ \end{itemize}
+ \item {\bf Interactions between Electrons and Metallic Thin Films}
+ \begin{enumerate}
+ \item Electron-Surface Interaction
+ \begin{itemize}
+ \item How an incoming electron interacts with the surface as a whole
+ \item Elastic reflection from potential barrier
+ \item Phonon vibrations of lattice (quasi-elastic - low energy losses)
\end{itemize}
- \item Limitations of theoretical models
+ \item Electron-Electron Interaction
\begin{itemize}
- \item Real surface is not a step potential
- \item Adsorption of foreign particles onto the surface also plays a large role in determining the electron spectrum.
+ \item Inelastic scattering processes determined by interaction of primary electron with the electron gas
+ \item Low energy interactions (focus of low energy TCS)
+ \begin{itemize}
+ \item Outer electron transitions between valence and conduction band (result of interaction between primary electron and an individual bound electron)
+ \item Plasmon excitation (result of interaction between incoming electron and the electron gas as a whole)
+ \end{itemize}
+ \item Higher energy interactions (focus of other forms of 2nd Electron Spectroscopy)
+ \begin{itemize}
+ \item Auger processes due to excitation of inner band electrons
+ \item ``True'' secondary electrons; bound electrons given sufficient energy to leave the surface
+ \end{itemize}
\end{itemize}
- \end{itemize}
- \item Main reference: Komolov "Total Current Spectroscopy"
- \item "Solid State Physics" textbooks and "Electron Spectroscopy" textbooks
+ \item General structure of secondary electron energy distribution (not investigated by TCS)
+ \item Mention that secondary electrons have an angular distribution (not investigated by TCS)
+
+ \end{enumerate}
\end{itemize}
-\subsection{Plasmonics}
-I really think I should actually find plasmonic effects before writing too much about them...
-\begin{itemize}
- \item Charge density oscillations
- \item Surface and bulk plasmons
- \item Pines and Bohm
- \item Review article from T.W.H Oates et al about using Ellipsometry to characterise plasmonic effects
-\end{itemize}
+\section{Experimental Methods}
-\subsection{Metallic-Black Thin Films}
-\begin{itemize}
- \item How they are made (bad vacuum, in air or a noble gas)
+Here I will give overviews of each method used in the study, including:
+
+\begin{enumerate}
+ \item {\bf Scanning Electron Microscopy}
\begin{itemize}
- \item If made in air, there are usually tungsten oxides present (from filament). Refer to paper by Pfund.
+ \item Not used directly by me, so I will be very brief
+ \item Very useful for understanding the structural differences between metallic-black and metallic-bright films
\end{itemize}
- \item Structural difference between Black-Au and ``Shiny'' (need a better term) Au
+
+ \item {\bf Total Current Spectroscopy}
\begin{itemize}
- \item Can include electron microscopy images?
- \item An actual photograph of a Black-Au film? Not necessary?
+ \item Experimental setup
+ \begin{itemize}
+ \item Refer to appendices for detailed description of control circuit and electron optics
+ \end{itemize}
+ \item Formation of the signal $S(E) = \der{I(E)}{E}$, and relation to theory of {\bf Interactions between Electrons and Metallic Thin Films}
+
\end{itemize}
- \item Pfund (earliest publisher, preparation and general properties)
- \item Louis Harris (most research in 50s and 60s)
+ \item {\bf Ellipsometry}
\begin{itemize}
- \item L. Harris mostly did transmission spectroscopy in the far infra red (well beyond the ellipsometer and Ocean Optics spectrometer ranges)
- \item The really crappy measurements I did with the Ocean Optics spectrometer seem to agree with these measurements
+ \item Optical technique commonly used for characterising thin films
+ \begin{itemize}
+ \item Measures change in polarisation of light
+ \begin{enumerate}
+ \item
+ \end{enumerate}
+
+ \end{itemize}
+
+ \item Sensitive to optical properties of materials; can be used to determine optical constants of a sample
\begin{itemize}
- \item L. Harris' $\lambda$ has a range of 1nm to $100\mu$m; my measurements are only to $1\mu$m
- \item Agreement in first $1\mu$m anyway
- \item I should probably re-do those measurements with a less crappy setup, if I actually want to use them
+ \item Can relate the Ellipsometric parameters $\psi$ and $\Delta$ to the optical constants ($n$ or $\epsilon$) of the
\end{itemize}
- \item Harris related the optical properties to the structure of the film (condensor strands) via the electronic properties
+ \item {\bf Variable Angle Spectroscopic Ellipsometry}
+ \begin{enumerate}
+ \item Aquires a large amount of data automatically over different $\lambda$ and $\theta$
+ \item Using fitting algorithms, can construct multi-layered model of the surface, and determine characteristics of each layer based on known information
+ \item Can be complemented by reflection and transmission spectroscopy, performed with the same instrument
+ \end{enumerate}
\end{itemize}
- \item Plasmonic effects - Deep R. Panjwani (honours thesis)
+
+ \item {\bf Optical Spectroscopy}
\begin{itemize}
- \item Not sure if I can use an honours thesis as a reference.
- \item Concluded that surface plasmon resonance in Black-Au film on solar cells lead to increase in solar cell efficiency
- \item Used simulation that modelled Black-Au film as spherical balls to show E field increased by plasmon resonance
+ \item Brief section, may not include if the other sections are sufficient
+ \item May combine with Ellipsometry section, since the Ellipsometer is used for these measurements
\begin{itemize}
- \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.
+ \item The important concepts will already have been discussed in the Ellipsometry section
+ \item Also used OceanOptics spectrometer early in the year, but repeated the same measurements using the Ellipsometer
+ \item Will need to review results before deciding whether to include or not
\end{itemize}
- \item Need to read this reference more thoroughly
\end{itemize}
-\end{itemize}
+\end{enumerate}
-\section{Experimental Techniques}
+\section{Results and Discussion}
-\subsection{Preparation of samples}
-\begin{itemize}
- \item Black-Au - 1e-2 mbar vacuum
- \item ``Shiny'' - 1e-6 / 1e-7
- \item Current of ~3.5A through W wire filament spot welded onto Ta strips in turn spot welded to Mo posts
- \item Voltage through filament is ~1 V; quote the power?
- \item Filament isotropically coats sample with desired material.
- \item Possibly get a curve of Au thickness estimated with Ellipsometry vs exposure time?
- \begin{itemize}
- \item Probably too much work and too unreliable
- \item Maybe do it, but only use 2/3 data points
- \item Low priority
- \end{itemize}
-\end{itemize}
+In this section I will discuss the results from each of the experimental methods described above, in order.
-\subsection{Total Current Spectroscopy}
-\begin{itemize}
- \item Overview of technique
- \begin{itemize}
- \item Low energy beam of electrons incident on sample
- \item Measure slope of resulting I-V curve
- \item Relate to density of states and electron band structure (Komolov chapter 3.2)
- \end{itemize}
- \item Description of apparatus
+\begin{enumerate}
+ \item {\bf SEM}
\begin{itemize}
- \item Electron gun and filament
- \item Electron gun control box
- \item ADC/DAC control box and data processing
- \end{itemize}
- \item Photographs vs Diagrams
- \begin{itemize}
- \item Prefer diagrams to photographs
- \item Especially for the ADC/DAC control box circuit. Because it looks like a horrible mess.
+ \item Images prepared by CMCA
+ \begin{itemize}
+ \item The secondary electron current is imaged. The secondary electron current due to an Si substrate alone is substracted.
+ \item This gives an idea of the spatial distribution of the density of Au deposited on the Si substrate
+ \item TODO: Learn exactly how they are related... can I assume intensity $\propto$ density?
+ \end{itemize}
+ \item Discuss the clear difference in structure
+ \begin{itemize}
+ \item Well defined regions (metallic nanoparticles) vs ``smoke'' like connected strands
+ \end{itemize}
+ \item Perform image fourier transforms
+ \begin{itemize}
+ \item Au-Bright shows a elliptical distribution of low frequencies; indicates a preferred orientation for the Au
+ \item Au-Black shows a wider, circular distribution of low frequencies, and significantly larger high frequencies
+ \item Phase plots appear random except for some sharp lines near the centre of the FFT image (not sure how to interpret yet)
+ \item Validity of the transforms?
+ \begin{itemize}
+ \item Error is introduced due to discontinuities in the periodic extension of the image
+ \item However, since the image is a region taken out of a periodically structured surface, these should be small
+ \item No window has been applied
+ \end{itemize}
+ \item Relation of image fourier transforms to theory?
+ \begin{itemize}
+ \item I would love to be able to do this, but may not have time to understand how to do it
+ \item Can at least give a numerical approximation of fourier transform of density distribution of electron gas
+ \item Surely this can be used somehow? Approximate the structure factor of system?
+ \item Predict plasmonic behaviour?
+ \end{itemize}
+ \end{itemize}
\end{itemize}
-\end{itemize}
-\subsection{Ellipsometry and Transmission Spectroscopy}
-\begin{itemize}
- \item Overview of techniques
- \item Description of apparatus (use VASE manual)
- \item Ocean Optics spectrometer? Usable?
- \item Application of Ellipsometry to finding plasmonic effects
+ \item {\bf TCS}
\begin{itemize}
- \item Surface plasmons = E oscillation parallel to surface $\implies$ only $p$ component of light excites plasmons
- \end{itemize}
-\end{itemize}
+ \item {\bf TCS of Stainless Steel}
+ \begin{itemize}
+ \item Establishes the location of the primary electron peak for Stainless steel
+ \item Useful because it allowed me to tell when the electron gun was focused so that the beam struck both the sample holder and the sample of interest
+ \item Appears to change over time; will discuss this behaviour below in relation to Si
+ \end{itemize}
-\section{Experimental Results and Discussion}
-\subsection{TCS Measurements}
-\begin{itemize}
- \item TCS for Si
- \item TCS for Si + Au
- \item TCS for Si + Black-Au
- \item Affect of preparation pressure on TCS for Si + Black-Au
- \item Repeat for Si + Ag and Si + Black-Ag (?)
-\end{itemize}
+ \item {\bf TCS of Si substrate}
+ \begin{itemize}
+ \item Changing of TCS vs Time
+ \item I am pretty sure it is not due to a ``mistake'' in the electron gun circuit
+ \item Possibly due to adsorbsion of oxide layer on the surface
+ \item I can show that depositing a thin layer of Au has the effect of ``resetting'' the TCS, which then begins to evolve over time.
-\subsection{Ellipsometric Measurements}
-\begin{itemize}
- \item Ellipsometry to estimate thickness of SiO2 layer on Si
- \item Estimate thickness of Au/Ag on Si+SiO2
- \item Ellipsometric measurements of Si+Black-Au/Ag
- \begin{itemize}
- \item Modelling procedures to characterise Black-Au/Ag
- \end{itemize}
- \item Ellipsometric measurements of Glass+Black-Au/Ag (?)
- \item Transmission spectra of Glass+Black-Au/Ag from earlier in year (?)
-\end{itemize}
+ \item I can also show that a sudden jump in $E$ causes $I$ to tend towards an assymptote
+ \begin{itemize}
+ \item One reason why I changed to use $E$ steps of $0.4$V per second, instead of $2$ V per
+ \item I probably won't discuss this in the thesis; maybe in an appendix
+ \end{itemize}
+ \end{itemize}
+
+ \item {\bf TCS of Au}
+ \begin{itemize}
+
+ \end{itemize}
-\section{Achievements}
-\begin{itemize}
- \item Deposition of thin films of Au and Black-Au in vacuum chamber
- \item Ellipsometric and spectroscopic measurements on these films
- \item Repurpose vacuum chamber for sample preparation and TCS experiments
- \item Designed and built electronics for TCS experiments
- \begin{itemize}
- \item Electron gun control box
- \item ADC/DAC box
\end{itemize}
- \item Wrote software for data aquisition and data processing
-\end{itemize}
-\section{General notes}
-\subsection{TCS}
-\begin{itemize}
- \item Optimise setup of gun
+ \item {\bf Ellipsometry}
\begin{itemize}
- \item Emission current. How much does it vary, why does it vary.
- \item Why does Is/Ie curve shift with successive sweeps? Does sweep modify sample's surface?
- \item Is sample holder acceptable? Are ceramic washers accumulating charge?
- \item How do I tell when the setup is optimised...
- ``The setup was optimised by looking for an S curve''. Very scientific.
- \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.
+ \item {\bf General Application to thin films}
+ \begin{itemize}
+ \item {\bf Jeremy's Sample - Permalloy}
+ \begin{itemize}
+ \item Already have a good idea of the thicknesses
+ \item Can construct a model which gives good agreement with these thicknesses
+ \item Lorentz Oscillator model for the Permalloy
+ \item NOTE: I need to repeat this modelling procedure with more care
+ \end{itemize}
+
+ \item {\bf Mikhail's Sample}
+ \begin{itemize}
+ \item White Ni compared to Normal Ni
+ \end{itemize}
+ \end{itemize}
+
+ \item {\bf Metallic-Black Films}
+ \begin{itemize}
+ \item Difficult to measure Au-black directly
+ \item Measured Au on Au-black on Si
+ \begin{itemize}
+
+ \end{itemize}
+
+ \item Compare with Au-bright on Si
+ \end{itemize}
\end{itemize}
- \item Obtain TCS spectra for Si that compares well with literature
+
+ \item {\bf Optical Spectroscopy}
\begin{itemize}
- \item How to relate TCS spectrum to $n(E)$ and $E(\vect{k})$
+ \item Need to review data before deciding whether to include this section
+ \item Mostly conducted transmission spectroscopy experiments
+ \begin{itemize}
+ \item Transmission spectra of Au-Black agrees qualitatively with published spectra by Pfund and Harris
+ \begin{itemize}
+ \item However, the range of my experiments is extremely small (visible wavelengths to short infra-red) compared to Harris (visible to extremely far infra-red)
+ \end{itemize}
+ \item Can show a difference between Au-Bright on Glass and Au-Black on Glass transmission spectra
+ \item Also have some transmission spectra of Ag, agree with expected Ag transmission spectra
+ \end{itemize}
\end{itemize}
- \item Prepare Au films, obtain TCS spectra that compares with literature
- \item Obtain TCS spectra of Black-Au films
- \item Use results to compare properties of films with results from other methods in the literature
- \item Uncertainties
- \begin{itemize}
- \item Oscilloscope measurements of inputs to ADC channels under controlled conditions
+\end{enumerate}
+
+\section{Conclusion}
+
+In this section, I will hopefully find something intelligent to say about my results
+
+\section*{Appendices}
+
+Mostly to do with the practical side of setting up the TCS experiment, and therefore (sadly) of little interest to the markers.
+
+\begin{enumerate}
+ \item The TCS experiment in more detail
+ \begin{enumerate}
+ \item Electron Gun control circuit
+ \item Electron Optics - focusing the gun
\begin{itemize}
- \item Expected values are +/-3mV due to ADC channel, +/-300mV due to 610B, +/-1mV due to 602
- \item 610B and 602 will probably be worse because they are ancient
- \item There is about 200mV of noise between the GND of the ADC box and the electron control box.
- \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.
+ \item This is extremely important for optimising the resolution of TCS
+ \item Include results of 2D simulation, but for qualitative purposes only (not actually used to focus the real gun)
\end{itemize}
- \item Stupid 50Hz AC noise... how to reduce with filters and/or averaging
+ \item ADC/DAC Card for control of $E$ and measurement of $I(E)$ in TCS
+ \end{enumerate}
+
+ \item Monitoring of the Vacuum Chamber pressure
+ \begin{itemize}
+ \item This one will be short (I pointed a webcam at the pressure gauge, and wrote some software)
+ \item Include graphs of pressure over time
\end{itemize}
- \item Create circuit diagrams for Electron gun circuit
- \item Create circuit diagrams for ADC/DAC box
+
+ \item Theory
\begin{itemize}
- \item Simulate behaviour of circuit
- \item Use of instrumentation amplifier on ADC5 to make off-ground measurements
- \item Use of low pass filter on ADC5
+ \item I may use this to put more detailed theory if the {\bf Overview of Theory} section is too long
+ \item Then again, I may not have enough detailed theory to need this.
\end{itemize}
- \item Include references to all datasheets, etc
- \item Vacuum chamber
+
+ \item Software
\begin{itemize}
- \item Base pressure with rotary pump? Was 1e-3 after 30 minutes at start of year, but probably introduced leaks since then
- \item Lowest pressure achieved with turbo pump is 1.1e-7 mbar as of 25/07.
- \item Viton gaskets on some seals. Copper on other.
- \item Flanges:
+ \item I will probably just make all software available on my website and link to it
+ \item The software is not really written with ``someone else may want to use this'' in mind
+ \item The software includes:
\begin{enumerate}
- \item View window (large, view of sample \& sputtering filaments)
- \item Rotation manipulator \& sample mount
- \item Pump inlet
- \item Filament flanges 1 (used earlier in year, not anymore) and 2
- \item Inlet with leak valve (for introducing gases into chamber)
- \item Vent valve on turbo pump
- \item Electron gun flange
- \item View window (small, view of back of electron gun)
+ \item Atmel AVR Butterfly
\end{enumerate}
\end{itemize}
-\end{itemize}
+
+\end{enumerate}
-\pagebreak
-\bibliographystyle{unsrt}
-\bibliography{thesis}
+%\pagebreak
+%\bibliographystyle{unsrt}
+%\bibliography{thesis}
\end{document}
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