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

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 (alpha, beta) were found after Tc evaporation at sample temperatures of 300K and 230K, respectively, and subsequent cooling below 230K. The metastable beta phase exhibits a 44% larger coverage than the a phase, and can be transformed into the alpha 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 alpha phase contains one molecule in planar geometry. There are two molecules within the unit cell of the beta 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 (300-550 K). The zero-order multilayer TPD peak has its onset at about -280K and yields a desorption energy of 120-130 kJ mol(-1). (C) 2004 Elsevier B.V. All rights reserved.