Thermal annealing effect of alkanethiol monolayers on Au(111) in air

We present a systematic study on the effect of air annealing on the structures of alkanethiol (CH3(CH2)(n-1)SH) self-assembled monolayers (SAMs) on Au(1 1 1) with chain length n = 7, 10, 18. partial desorption of the monolayers has been observed by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) at relatively low annealing temperatures. By increasing the annealing time at appropriate temperatures, the structures of SAMs transform from densely packed (root3 x root3)R30 degrees phase to c(4 root3 x 2 root3)R30 degrees phase, and then slowly to striped (p x root3) phases with p = 4 and 5. Through the relative carbon content measurement by XPS and the stripe spacing measurement by STM, we propose a different stripe phase structure than those observed for SAMs grown by gas-phase deposition or by vacuum annealed solution-grown samples. (C) 2001 Elsevier Science B.V. All rights reserved.