Structural properties of tetracene films on Ag(111) investigated by SPA-LEED and TPD

Abstract

The adsorption of tetracene (Tc) on Ag(111) was investigated by high resolution LEED (SPA-LEED) and temperature programmed desorption (TPD). Two long-range ordered monolayer phases (a, b) were found after Tc evaporation at sample temperatures of 300K and 230K, respectively, and subsequent cooling below 230K. The metastable b phase exhibits a 44% larger coverage than the a phase, and can be transformed into the a phase by annealing. At room temperature the long-range order is lost. At submonolayer coverage, only short-range order was observed, even at low temperatures. The unit cell of the a phase contains one molecule in planar geometry. There are two molecules within the unit cell of the b phase, which are presumably tilted with respect to the surface. Multilayer growth proceeds in a pronounced Stranski–Krastanov mode, leaving a large part of the monolayer uncovered. The TPD peak of the monolayer is very broad (300–550K). The zero-order multilayer TPD peak has its onset at about ~280K and yields a desorption energy of 120–130kJmol-1.