Azobenzene-containing self-assembled monolayers (SAM) have been prepared on silicon by chemisorption of 4-trichlorosilylazobenzene and mixtures of 4-trichlorosilylazobenzene (TSA) and phenyltrichlorosilane (PTS). The resulting films contain azobenzene units connected to the surface by means of a short, rigid spacer. The films have been analysed by single-wavelength ellipsometry and measurement of the water contact angle. Irradiation of the films with 360 nm ultraviolet light-induced a switching effect, which results in a decrease of the water contact angle and a change in the ellipsometric parameters. The switching could be made reversible by exposing the sample to visible light for 24 h. (C) 2003 Elsevier B.V. All rights reserved.