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-%\title{\bf Characterisation of nanostructured thin films}
-%\author{Sam Moore\\ School of Physics, University of Western Australia}
-%\date{April 2012}
-%\maketitle
-
-\begin{center}
- B.Sc. (Hons) Physics Project \par
- {\bf \Large Thesis} \par
- Samuel Moore \\
- School of Physics, University of Western Australia \\
- April 2012
-\end{center}
-\section*{Characterisation of Nanostructured Thin Films}
-{\bf \emph{Keywords:}} surface plasmons, nanostructures, spectroscopy, metallic-blacks \\
-{\bf \emph{Supervisers:}} W/Prof. James Williams (UWA), Prof. Sergey Samarin (UWA) \\
-
-
-%\tableofcontents
-
-\section*{Acknowledgements}
-\begin{itemize}
- \item Sergey Samarin
- \item Jim Williams
- \item Paul Guagliardo
- \item Nikita Kostylev
- \item Workshop (for producing electron gun mount?)
- \item Peter Hammond (?)
-\end{itemize}
-
-\section{Introduction}
-\begin{itemize}
- \item Waffle about motivation for the project
- \begin{itemize}
- \item Metal-Black films may have application for ... something.
- \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.
- \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)
- \begin{itemize}
- \item No (detailed/satisfactory) explanation (that I can find...) for difference
- \end{itemize}
- \item Talk about plasmonic based computing? Moore's law? Applications to thin film solar cells?
-
- \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)
- \begin{itemize}
- \item Ie: How can one technique be used to support the other?
- \end{itemize}
- \end{enumerate}
- \item Structure of thesis
-\end{itemize}
-
-\section{Overview of Theory}
-Summarise the literature, refer to past research etc
-
-\subsection{Electron Spectra of a Surface}
-\begin{itemize}
- \item Description of the near surface region
- \begin{itemize}
- \item All real solids occupy finite volumes in space.
- \item The surface of a solid is important because interactions between the solid and its surroundings occur in the near surface region.
- \item Characterised physically by:
- \begin{itemize}
- \item Termination of periodic crystal lattice
- \item Violation of geometric order
- \item Distortion of interatomic distances and hence interaction forces
- \item There is a transition ``near surface'' region between bulk and surface properties, roughly 5 atomic distances.
- \end{itemize}
- \item Potential seen by an electron at a surface can differ greatly from the bulk
- \item $\implies$ the electron spectra of the near surface region differs from the bulk spectra
- \item Simplest case: Step potential at surface.
-
- \end{itemize}
-
- \item The Electron Spectra
- \begin{itemize}
- \item Electron Spectra describes the energy eigenstates for an electron in a Bulk or Surface potential
- \item Characterised by
- \begin{enumerate}
- \item Energy dispersion $E(\vect{k})$
- \begin{itemize}
- \item Dependence of Energy on electron wave vector
- \item Obtained theoretically by solving Scrhrodinger's Equation
- \item For a free electron gas, $E = \frac{\hbar^2 k^2}{2m}
- \item Periodic potential in bulk solid leads to band gap structure of $E(\vect{k})$
- \item Periodic potential $\implies$ E is periodic. Only needs to be defined in first Brillouin zone.
- \end{itemize}
- \item Density of States $N(E)$
- \begin{itemize}
- \item $N(E) = \frac{\Delta N}{\Delta E} = \frac{1}{4\pi^3}\int_S\left(\der{E}{k}\right)^{-1} dS$
- \item Integral is in momentum space over the isoenergetic surface of energy $E$
- \item For a free electron gas, $N(E) = $
- \end{itemize}
- \end{enumerate}
- \end{itemize}
-
- \item Surface states
- \begin{itemize}
- \begin{enumerate}
- \item Simplest model: Step potential
- \item Tamm States: Periodic potential in solid, free space outside, jump at surface
- \begin{itemize}
- \item Energy eigenvalues lie in the forbidden band of the bulk spectra
- \item Attenuation of eigenvalues from surface to vacuum, oscillation of state within surface
- \item Max electron density occurs on the crystal surface
- \end{itemize}
- \item Shockley states: Potential of surface and bulk cells equal
- \begin{itemize}
- \item Corresond to free valences (dangling bonds) at the surface
- \end{itemize}
- \end{enumerate}
- \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.
- \item These states arise from termination of the lattice; but the surface cells are assumed undistorted
- \item In reality surface cells are distorted by relaxation and reconstruction of the surface
- \end{itemize}
-
- \item Main reference: Komolov "Total Current Spectroscopy"
- \item "Solid State Physics" textbooks and "Electron Spectroscopy" textbooks
-\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}
-
-\subsection{Metallic-Black Thin Films}
-\begin{itemize}
- \item How they are made (bad vacuum, in air or a noble gas)
- \begin{itemize}
- \item If made in air, there are usually tungsten oxides present (from filament). Refer to paper by Pfund.
- \end{itemize}
- \item Structural difference between Black-Au and ``Shiny'' (need a better term) Au
- \begin{itemize}
- \item Can include electron microscopy images?
- \item An actual photograph of a Black-Au film? Not necessary?
- \end{itemize}
- \item Pfund (earliest publisher, preparation and general properties)
- \item Louis Harris (most research in 50s and 60s)
- \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
- \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
- \end{itemize}
- \item Harris related the optical properties to the structure of the film (condensor strands) via the electronic properties
- \end{itemize}
- \item Plasmonic effects - Deep R. Panjwani (honours thesis)
- \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
- \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.
- \end{itemize}
- \item Need to read this reference more thoroughly
- \end{itemize}
-\end{itemize}
-
-\section{Experimental Techniques}
-
-\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}
-
-\subsection{Total Current Spectroscopy}
-\begin{itemize}
- \item
- \item Total Current Spectroscopy methods measure the total current of secondary electrons as a function of primary electron energy.
- \item These methods are distinguished from ``differential'' methods (such as Auger electron spectroscopy and energy loss spectroscopy) which measure the secondary electron spectrum at a fixed primary electron energy.
- \item
- \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{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.
- \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
- \begin{itemize}
- \item Surface plasmons = E oscillation parallel to surface $\implies$ only $p$ component of light excites plasmons
- \end{itemize}
-\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}