Formation of ultrathin films at the solid-liquid interface studied by in situ ellipsometry

Ellipsometric investigations of self-assembled monolayers (SAMs) of alkylsi loxanes on native silicon substrates and of organothiols on gold substrates were performed under in situ conditions with the substrate in direct conta ct with the adsorbate solution. Specially designed liquid cells matched for different incidence angles were used to carry out measurements in a range of organic solvents with different refractive indices as the ambient medium . The observed shifts in the ellipsometric phase angles a upon monolayer fo rmation were found to depend very sensitively on the incidence angle and th e refractive indices of the adsorbate him and the ambient solvent, from whi ch a rather simple method for determining the refractive index of the adsor bate film, based on a variation of the ambient refractive index, was derive d. Time-resolved in situ measurements of SAM formation in different solvent s and onto different substrates yielded accurate kinetic information on the monolayer growth process and revealed hitherto unknown strong solvent effe cts on the growth rate. (C) 1999 Academic Press.