Thermal annealing effect of alkanethiol monolayers on Au(1 1 1) in air

We present a systematic study on the effect of air annealing on the structures of alkanethiol (CH3(CH2)n−1SH) 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 (3×3)R30° phase to c(43×23)R30° phase, and then slowly to striped (p×3) 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.