Ellipsometric study of peptide layers – island-like character, depolarization and quasi-absorption

Highlights: • Ellipsometric data of differently adhering peptides on silicon are analyzed. • Transparent, absorbing and discontinuous layer approaches are compared. • Different models provide similar peptide thickness, but optical properties differ. • Strategies are presented which can help to find the appropriate model. • Depolarization can provide useful information about the sample structure. - Abstract: In this work, the ellipsometric measurements of small molecular size polypeptides deposited onto silicon are analyzed. Results of ellipsometric evaluation procedures based on transparent layer, absorbing layer and discontinuous layer approaches are compared. Although these models result in similar fitting quality and can predict the amount of the deposited material, the gained optical properties can be rather different due to the different assumptions of the models. To choose the physically correct results, independent measurements as atomic force microscopy or transmission measurement of peptide solutions are necessary. It is shown that the measured ellipsometric depolarization can provide also useful information about the sample properties.