-\chapter{Introduction}
+\chapter{Introduction} \label{chapter_introduction}
-% TODO: Broad general sweeping statements about thin films
+Interest in the optical properties of nanostructured thin films can be traced back to the 19th century. In the 1857 Bakerian Lecture, Michael Faraday discussed a range of unusual optical effects exhibited by thin films of Au and other metals subjected to different treatements \cite{faraday1857}. The role of metallic nanoparticles of gold in producing the colours of stained glass was first investigated by Garnet in 1904 \cite{garnet1904} using Rayleigh's theory for scattering of light from spherical particles. A few years later, Gustav Mie developed a more complete theory of light scattering for spherical nanoparticles; Mie's theory is still widely used accross many disciplines \cite{mei1908} \cite{wriedt2008}.
-Motivation:
-\begin{itemize}
- \item The properties of solids can be understood in terms of an infinite periodic lattice
- \item In reality, every solid must have a finite spatial extent. The surface is extremely important because it is the interface for all physical/chemical interactions with the solid and its environment.
- \item Thin films can have extremely complicated and interesting properties.
- \item The characterisation of thin films is important research in electronics as the surface to volume ratio increases.
- \item Most recent research has been into constructing ``meta-materials'' which can be exploited for nanoscale applications. Eg: plasmonic based circuitry.
- \item Somehow link to metallic-black films (?)
-\end{itemize}
+Many of the properties investigated by Faraday are now understood in terms of the behaviour of the electron gas in a metal, and in particular the ability for thin metal films to support plasmonic resonance effects. A plasmon is a quasiparticle which describes the collective oscillation of conduction electrons in a metal. The behvaiour of plasmons is well understood in terms of classical models for a free electron gas; in the Lorentz model electrons are treated as damped harmonic oscillators. When light is incident on a metal, the electrons may collectively resonate in response to the sinusoidal forcing field.
+Recently there has been much interest in the exploitation of plasmonic effects in nanoscale devices for a bewildering array of applications from improvement of photovoltaic solar cell efficiency \cite{atwater2010,linic2011} to biosensing \cite{maksymov2011}, and even the potential for plasmonic based computing devices \cite{maksymov2010}. %The extremely rapid developement of the field of plasmonics during the last decade has been stimulated by advances in nano-fabrication technology \cite{}.
-\emph{More about metallic-black films}
+A fascinating phenomena first observed in the 1930s \cite{pfund1930} is the tendency for metal films deposited in high pressure\footnote{Of the order of $10^{-2}$mbar} atmospheres to appear completely black at visible wavelengths. Such films have found use in a range of optical applications as near perfect black bodies with very low thermal mass \cite{pfund1930,harris1948,harris1952,harris1953}.
-So called metallic-black films are the result of deposition of metal elements at a relatively high pressure (of the order of $10^{-2}$ mbar). The films are named due to their high absorbance at visible wavelengths; they appear black to the naked eye. There is a remarkable contrast between such films and films deposited under low pressure (less than $10^{-6}$mbar), which are typically highly reflective and brightly coloured.
+Recently, so called ``black metal'' films have been found to enhance the efficiency of thin film solar cells; this is consistent with the presence of plasmonic effects in the films \cite{panjwani2011}.
-% First mentions and early research; Pfund
-This phenomenom has been known since the early 20th century, with the first papers on the subject published by Pfund in the 1930s \cite{pfund1930}, \cite{pfund1933}. Pfund established the conditions for formation of metallic-blacks \cite{pfund1930}, and showed that the transmission spectrum of metallic black films is almost zero in visible wavelengths, but increases to a plateau in the far infrared \cite{pfund1933}. More extensive research on the structural and optical properties of these films by Louis Harris and others during the 1940s and 1950s \cite{harris1948}, \cite{harris1952}, \cite{harris1953}.
+\begin{comment}
+Just several months ago, an ``artificially blackened'' plasmonic meta-material termed has been produced with similar applications in mind to those of the ``traditional'' black metal films. This technology has largely been motivated by the difficulty of theoretically modelling the traditional Black metal samples. \cite{sondergaard2012}.
+\end{comment}
-% Research by Harris concluding ``condensor'' like structure
-Harris et al. have produced experimental results of the transmission of metallic-black films from visible wavelengths to the far-infrared \cite{}. By modelling the film as a layer of metallic strands, acting as ``condensors'', Harris et al. arrived at an expression for the electron relaxation time of [element]-black \cite{}, leading to a a transmission spectrum in good agreement with experimental results.
+The aim of this project has been the preparation and characterisation of thin metal film samples, with a focus on black metal films. We have also investigated the possibility for plasmonic behaviour in Black metal films. We have prepared samples for subsequent study with both electronic and optical spectroscopic techniques.
-% Mckenzie
-Mckenzie has established that the presence of oxygen effects the optical and electrical properties of metallic-blacks \cite{mckenzie2006}.
+The remainder of this report will be organised as follows: in chapter \ref{chapter_overview} we will present an overview of past research into the characterisation of black metal films, followed by a brief explanation of plasmonic behaviour based on the Lorentz model. Chapter \ref{chapter_techniques} will give an overview of the two main experimental techniques employed during this study (Total Current Spectroscopy and Ellipsometry). In chapter \ref{chapter_results} we will present results and discussion of experiments, which will be followed with the conclusions of this study.
-% More recent research
-More recently, it was shown that Au-black coatings increased the efficiency of thin film solar cells \cite{}. In this study, a simulation approximating an Au-black film as a layer of semi-spherical structures showed plasmonic behaviour which lead to an increase in electric field behind the film.
-
-
-% Artificially ``blackened'' thin films
-Metallic-black films have proven useful in applications requiring efficient absorption of light, including the. Recently there has been interest in artificial ``blackening'' of metal surfaces in ways which simplify the characterisation of the surfaces for practical applications.
-
-Sondergaard et al. have produced metallic-black surfaces capable of suporting surface plasmon modes \cite{sondergaard2012}. These films exhibit similar optical properties to the previously considered ``evaporated'' metallic-black surfaces.
-
-% What I will be doing with metallic-black films
-This project will employ several techniques, including:Total Current Specroscopy; Ellipsometry and Optical Spectroscopy to investigate the difference between metallic films deposited at low pressure, and high pressure (metallic-blacks).
-
-This report will be organised as follows...
-You just read the introduction, which comes first. After that we talk about theory and then experimental stuff.
+\subsubsection*{A Note on Terminology}
+There is some possibility for confusion when referring to metal films evaporated at high pressure, which appear black at visible wavelengths, and metal films evaporated at low pressure, which are typically highly reflective. In the remainder of this report, we will refer to the former as ``black metal'' films and the latter simply as ``metal'' films (regardless of whether the film is thick enough for the colour to be visible to the naked eye).
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