Confinement-induced film thickness transitions in liquid crystals between two alkanethiol monolayers on gold

We describe the use of two semitransparent gold layers of equal thickness a s substrates in the interferometric surface forces apparatus. The continuou s gold layers were evaporated onto an adhesion layer of chromium on muscovi te mica that had been exposed to water vapor plasma to introduce reactive g roups on its surface. Multiple beam interferometry was used to measure the thickness of mixed alkanethiol monolayers covalently bound to the gold and the film thickness of homeotropically oriented liquid crystals confined bet ween these monolayers. In 4 ' -n-pentyl-4-cyanobiphenyl, quasi-periodic str uctural forces with transitions comparable to the length of a liquid crysta l dimer were observed at film thicknesses below 13 nm, indicating that conf inement-induced smecticlike ordering can occur also between two surfaces wi th a root-mean-square roughness of less than or equal to1 nm. Similar trans itions could also be observed in 4 ' -n-octyl-4cyanobiphenyl.