An IETS study of the adsorption of 2,3-dihydroxynaphthalene, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene and 1,4-dihydroxybenzene on thin-film plasma-grown aluminium and magnesium oxides

Abstract

Inelastic Electron Tunnelling Spectroscopy (IETs) has been applied to study the adsorption of 2,3-dihydroxynaphthalene, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene and 1,4-dihydroxybenzene onto plasma-grown thin-film partially hydroxylated magnesium and aluminium oxides. For both 2,3-dihydroxynaphthalene and 1,2-dihydroxybenzene on aluminium oxide it is found that adsorbate chemisorption involves reaction of the two hydroxyl groups present in the adsorbate to form a di-anion in the case of the former and both the mono- and di-anion for the latter. The tunnel spectra for both compounds on magnesium oxide indicate that the di-anion is formed. Adsorption at the oxide surfaces for these two adsorbates involves adsorbate deprotonation with the formation, at the oxide surface, of molecular water which is subsequently desorbed and pumped away during sample junction preparation. For the 1,3- and 1,4-dihydroxy systems, on both oxides, the presence of a strong ν(OH) band at ≈3650 cm −1 suggests that only one of the hydroxyl groups present in both systems is involved in adsorbate deprotonation interactions at the respective oxide surfaces, with the second hydroxyl group present contributing to the enhanced substrate oxide ν(OH) envelope observed.