Imaging ellipsometry is presented as a technique for quantification and visualization of the lateral thickness distribution of thin ͑0-30 nm͒ transparent layers on solid substrates. The main advantage of imaging ellipsometry is that every point on a surface is measured at the same time with a high lateral resolution. The method is based on the use of combined null and off-null ellipsometry at an incident angle close to the pseudo-Brewster angle of a high index substrate such as silicon. In the present experimental setup, a xenon lamp, a collimator, and a wavelength-selective filter provide an expanded collimated probe beam with a diameter of 25 mm. Other major components in the system are a polarizer, a compensator, and an analyzer. In this way, a 15ϫ30 mm 2 image of a sample surface can be focused onto a charge-coupled-device video camera and transferred to a computer for further evaluation by image processing. Thickness measurements are performed for calibration purposes with ordinary null ellipsometry. The imaging ellipsometer has an accuracy of better than 0.5 nm at a lateral resolution of 5 m in the present configuration, but improvements of at least a factor of 5 can be foreseen. Several aspects of the ellipsometric imaging system are illustrated in selected applications including continuous protein thickness distributions, stepped silicon dioxide thickness distributions, and visualization of protein patterning of surfaces. The latter can be used in a biosensor system as illustrated here by antigen-antibody binding studies.

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Porous silicon Fabry-Pérot optical filters with reflectivity peaks in the visible and near infrared spectral range have been manufactured electrochemically and characterized with variable angle spectroscopic ellipsometry. Generalized ellipsometry and the Bruggeman effective medium approximation were employed to study the anisotropy of the samples including determination of the tilt of the optic axis relative to the sample normal. At a wavelength of 700 nm, the difference between the real parts of the ordinary and extraordinary indexes of refraction of the low and high index sublayers were 0.05 and 0.07, respectively. In addition, the effect of temperature on the spectral redshifts caused by capillary condensation of water and toluene vapors in the porous material are investigated. It is demonstrated that a temperature decrease causes the spectral shifts to occur at lower partial pressures, indicating a more effective vapor capture at lower temperatures. Finally, it is shown that this phenomenon can be used to increase the ellipsometric response to very low vapor concentrations and thus improve the sensitivity of the technique in gas sensor applications.

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Optical properties of porous silicon superlattices are investigated using variable angle spectroscopic ellipsometry. Different phenomena such as in-depth inhomogeneities and interface transition regions are resolved and studied using various optical models. The optical properties of the samples are modified irreversibly by thermal oxidation yielding a blueshift of the reflectance. A reversible redshift of the spectra is obtained by vapor adsorption and liquid penetration into the superlattice. Moreover, existence of different specific internal surface areas and pore size distributions in the low and high index sublayers of the material is proposed.