Ultra thin films of anthracene on fused quartz and sapphire

Abstract

Ultra thin films of anthracene ranging in thickness from a half to several monolayers have been deposited on fuse quartz and sapphire substrates cooled down to liquid He temperatures in vacuums of 10⁻⁹ Torr. These films have been investigated by transmission spectroscopy of the first singlet–singlet absorption. The films have been examined in the incremental steps of annealing up to about 240 °K at which point noticeable sublimation begins. The films as deposited are disordered but still partially oriented. During the annealing process there is a red shift of the spectral peaks and the formation of some ’’stable ground state dimers’’ is seen. After a complete anneal the film spectra can be quantitatively related to the bulk single crystal spectra of anthracene indicating that the film consists of microcrystallites. The orientation of the microcrystallites have been found to differ for fused quartz and sapphire substrates.