What Is Ellipsometry

Ellipsometry is a branch of specular reflection spectroscopy which is particularly useful for characterising thin films on surfaces in situ, e.g. in the presence of supernatant liquids. It is applicable to many problems in corrosion and passivation, lubrication, the physics and chemistry of new materials, and biological chemistry. The principles behind it have been known for a long time, but it remains a rather under-used technique. This situation is now changing because of a number of factors, such as the advent of cheap computing power, and the impetus, brought about by the great economic importance of the semiconductor industry, to produce more powerful theories to interpret the results. 

Another reason for its relative neglect may be that it deals with properties that are rather unfamiliar, such as complex refractive index and the nature of polarised light, and has a mathematical basis that can seem obscure. To some extent this is the fault of ellipsometrists who have sometimes been content to talk only to other specialists in the field and have not devoted much effort to popularising the technique. Understanding what ellipsometry is and what it can do does require some acquaintance with the basic concepts, and, in particular, with three important parameters that are often ignored. 

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