Spectral investigations of surface ordering in ultrathin molecular films

Surface molecular ordering in ultrathin molecular films is investigated. Th e optical transmission spectra of molecular films ranging in thickness from 2 to 13 smectic layers (6.7-43 nm) in the region of the electronic absorpt ion bands in the smectic A phase of cyanobiphenyl CB9 are measured. The thi ckness and temperature dependences of the permittivity are determined. It i s found that the orientational ordering of the molecules depends on the fil m thickness. The penetration depth of the surface molecular orientational o rder does not exceed two smectic layers (< 7 nm). (C) 1999 American Institu te of Physics. [S1063-7761(99)02205-2].