INELASTIC ELECTRON-TUNNELING SPECTRA OF NEUTRAL AND BASIC ZINC DITHIOPHOSPHATES ON NATIVE ALUMINUM-OXIDE SURFACES

Inelastic electron tunneling (IET) spectra of pure neutral and basic i sopropyl, isobutyl, and Pt-octyl phenyl ZnDTPs are reported. These pur e compounds were specially synthesized in order to examine the IET spe ctra of the neutral and basic ZnDTP salts separately. This is of inter est since the commercial ZnDTPs, whose spectra were reported previousl y, consist of mixtures of neutral and basic ZnDTP salts for all types of primary, secondary, and aryl ZnDTPs used today. Thus, an examinatio n of each representative pair was made, i.e. isobutyl (primary), isopr opyl (secondary), and p-t-octyl phenyl (aryl), in order to investigate these structural modifications on the IET spectra and relate the data to the adsorption characteristics. Generally, the conclusions drawn a re in agreement with those from precious work on commercial ZnDTPs. Ar yl ZnDPTs dissociate on adsorption, and do not retain the P = S group. Alkyl ZnDTPs retain the P = S group an adsorption. Differences among the neutral and basic forms of the pure alkyl ZnDTPs investigated in t his work were found. An unusual OH absorption frequency was observed i n rite IET spectrum of the basic isobutyl ZnDTP, corresponding to a st rongly hydrogen-bonded OH group, possibly due to a surface zinc hydrox ide phase. The lowest frequency for the P = S group, adsorbed on the s urface, was found for the neutral isopropyl ZnDTP, suggesting this spe cies was more strongly bonded to the surface than the other ZnDTPs exa mined in this work.