Investigation on the nature of the chemical link between acetylenic organosilane self-assembled monolayers and Au(1 1 1) by means of synchrotron radiation photoelectron spectroscopy and scanning tunneling microscopy

The nature of the chemical link between self-assembled monolayers (SAMs) formed by two polyunsaturated linear organosilanes on Au(1 1 1) 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-1-tridecene-6,12-diyne 1 (R-CC-Si(CH3)3) and 13-dimethylsilyl-1-tridecene-6,12-diyne 2 (R-CC-Si(CH3)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(1 1 1) and hence the adsorption geometry from upright standing (silane 1) to horizontal lying (silane 2). Analysis of the Au 4f7/2 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.