Solvent-Dependent Assembly of Terphenyl- and QuaterphenyIdithiol on Gold and Gallium Arsenide
D Krapchetov, H Ma, AKY Jen, Daniel A. Fischer, Y-L Loo
The assembly of terphenyldithiol (TPDT) and quaterphenyldithiol (QPDT) on gold and gallium arsenide from ethanol (EtOH), tetrahydrofuran (THF), and solutions consisting of both solvents was characterized by near-edge x-ray absorption fine structure spectroscopy. The monolayer coverage and the average orientation of both TPDT and QPDT on gold are solvent independent. These molecules readily form monolayers on gold with an ensemble-average backbone tilt of 30+/-3 degree from the substrate normal. In sharp contrast, the assembly of TPDT and QPDT on gallium arsenide is extremely solvent sensitive. At high ethanol fractions, both molecules form monolayers with an ensemble-average orientation that is indistinguishable from those on gold substrates. At low ethanol fractions and in pure THF, however, these molecules are disordered on gallium aresenide and the surface coverage is poor.