Spectroscopic ellipsometry is an excellent choice if you are looking for a non-contact, non-destructive technique to characterize thin films or surfaces. This is an optical technique using linearly polarized light which is reflected from the surface. The interaction with the surface alters the polarization, which results in an elliptical signal. This signal carries information on the sample’s composition. Spectroscopic ellipsometry can characterize a wide number of surface properties in a wide range of materials.
ST Instruments provides equipment for spectroscopic ellipsometry from Horiba Scientific. They offer the UVISEL PLUS/UVISEL 2 Phase Modulated Ellipsometers and Auto-SE/Smart-SE Liquid Crystal Phase Modulated Ellipsometers.
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Spectroscopic ellipsometry measures the change in polarization caused by the interaction of the incident light with the thin film surface. Specifically, the measurement results are expressed in the amplitude ratio Ψ (psi) and the phase difference Δ (delta). These two values are used to derive different properties of the surface using a model-based approach: models of the material are used to fit the data and thus derive values like film thickness (on scales from angstrom to micron), optical constants, surface roughness, interfacial mixing, composition, crystallinity, anisotropy, depolarization and uniformity (by depth and area).
Not only visible light is used for spectroscopic ellipsometry. It is possible to use electromagnetic radiation of different wavelengths, from x-ray to far-UV and Near Infrared. Light sources may contain different wavelengths or just one (laser light). Incident light is passed through a polarizer and an optional compensator or modifier, and the reflected light passes through an analyzer (again after an optional compensator or modifier) before it reaches the detector. Using multiple wavelengths increases the amount of information that is gathered. Also, it allows a more precise determination of film thickness, as a multiple thickness values can fit the results from a single wavelength measurement.
Spectroscopic ellipsometry does not interfere in any way with the sample. It can be used in situ to monitor thin film properties. As these properties are derived from the measurements through a model of the film it is an indirect method, which is nevertheless highly sensitive, precise and reproducible. Thin films of almost any type material can be analyzed with this technique, including dielectrics, semiconductors, polymers, organic materials or metals, and it is even used to study solid-liquid or liquid-liquid interfaces. Although models are required for a full analysis, it is possible to characterize a number of optical properties even in samples of unknown material.
Measures psi and delta, (or Is and Ic) which indirectly translates into characterization via model based approach.
It is important to stress that spectroscopic ellipsometry is an indirect technique.
Derived: film thickness (angstrom to micron) optical constants, surface roughness, interfacial mixing, composition, crystallinity, Anisotropy, depolarization and uniformity (by depth and area).
Precise and reproducible, almost any thin film, very sensitive (films < 10 nm), ideal for in situ applications.
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Spectroscopic Ellipsometry is relatively inexpensive and quick method for characterization and optimization of DLC film properties to match relevant biomedical application. Spectroscopic Ellipsometry could be used to study the demineralization and the remineralization process of tooth surface. It also could be used for other medical application like development of artifi cial saliva.