Ellipsometery is used to calculate thicknesses and optical properties (complex refractive index) of very thins films. The technique measures changes in light polarisation and so can be used to study films that are thinner than the wavelength of the light. Multilayer coatings can be examined and surface roughness modelled.
How does it work?
An ellipsometer consists of a light source, a detector and a number of polarisers. In nulling ellipsometry, elliptically polarised light is incident on a sample such that the reflected light is of minimum intensity. The configurations of the polarisers required to produce these conditions are converted into the ellipsometric parameters Δ and Ψ.
The instrument can be used to collect values of Δ and Ψ at different angles of incidence and at a range of wavelengths. A modelling procedure is used to fit values such as film thickness and refractive index to the data. An imaging function allows mapping studies over an area of the surface to be undertaken, illustrating properties such as thickness inhomogeniety.
Layer thickness; optical constants (refractive index and extinction coefficient); surface roughness; composition; optical anisotropy; multilayer thicknesses; interfacial roughness; constituent fraction; void fraction.
Sample handling requirements:
Thin film (monolayer up to approximatly 1000 nm depending on optical properties) on a substrate, several mm2.
Dr Ian Hancox, 024 76 150380 email i dot hancox at warwick dot ac dot uk
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