Growth kinetics, structure, and morphology of para-quaterphenyl thin films on gold(111).

Abstract

The adsorption, desorption, and growth kinetics as well as the thin film morphology and crystal structure of p-quaterphenyl (4P) grown under ultrahigh vacuum conditions on single crystalline Au(111) have been investigated. Thermal desorption spectroscopy (TDS) reveals two distinct first-order peaks attributed to monolayer desorption followed by a zero-order multilayer desorption. The saturation coverage of the full 4P monolayer has been quantitatively measured with a quartz microbalance to be 8 x 10(13) molecules/cm2. Using low energy electron diffraction the structures of the 0.5 and 1 ML (monolayer) adsorbates have been studied, showing highly regular arrangements of the 4P molecules, which are affected by the (111) surface structure. At the transition from 0.5 to 1 ML a structural compression of the overlayer has been observed. The behavior of thicker 4P films has been investigated by combined TDS-XPS (XPS-x-ray photoelectron spectroscopy). A temperature-induced recrystallization process at about 270 K has been observed for a 7 nm thick 4P film grown at 93 K, corresponding to a transition from a disordered layerlike growth to a crystalline island growth. Ex situ optical microscopy and atomic-force microscopy investigations have revealed needle-shaped 4P islands. Applying x-ray diffraction the crystalline order and epitaxial relationship of the 4P films with 30 nm and 200 nm mean thicknesses have been determined.