Configuration of pentacene (C22H14) films on Si(100)-2 x 1 studied by NEXAFS

Pentacene films on Si(1 0 0)-(2 x 1) surface at 300 K were investigated using near edge X-ray absorption fine structure (NEXAFS) at the carbon K-edge. NEXAFS spectra show that pentacene molecules are chemisorbed on the Si(1 0 0)-(2 x 1) surface for monolayer with flat-laying and predominantly physisorbed on the Si(1 0 0)-(2 x 1) surface for multilayer films with an upright molecular orientation. Absorption angle of pentacene molecules were measured through pi* transition. The angles between the double bond and the silicon surface were 35-55 degrees, 65 degrees and 76 degrees at monolayer, 24 and 48 mn pentacene deposited on the Si(1 0 0) surface, respectively. We observed that the intermediate flat-laying phase is favored for monolayer coverage, while the films of molecules standing perpendicular to the Si(1 0 0) surface are favored for multilayer coverage. (c) 2007 Published by Elsevier B.V.