Investigation on the nature of the chemical link between acetylenic organosilane self-assembled monolayers and Au(111) by means of synchrotron radiation photoelectron spectroscopy and scanning tunneling microscopy

摘要

The nature of the chemical link between self-assembled monolayers (SAMs) formed by two polyunsaturated linear organosilanes on Au(111) are investigated by means of synchrotron radiation induced photoelectron spectroscopy (SR-PES) and scanning tunneling microscopy (STM). The two silane derivatives studied here are 13-trimethylsilyl-l-tridecene-6,12-diyne 1 (R-C≡C-Si(CH_3)_3) and 13-dimethylsilyl-1-tridecene-6,12-diyne 2 (R-C≡C-Si(CH_3)_2H). STM clearly shows that the replacement of one methyl group of 1 by one H atom on the Si atom to give compound 2, modifying the chemical reactivity versus Au(111) and hence the adsorption geometry from upright standing (silane 1) to horizontal lying (silane 2). Analysis of the Au 4f_(1/2) and the Si 2p core levels by SR-PES confirms that, as expected, the chemical reactivity with the Au surface increases from 1 to 2. In terms of the initial state model increased surface-silane electron transfer is correlated with the horizontal surface packing.