REAL-TIME ELECTRONIC MONITORING OF ADSORPTION-KINETICS - EVIDENCE FOR2-SITE ADSORPTION MECHANISM OF DICARBOXYLIC-ACIDS ON GAAS(100)

We show that the chemisorption of dicarboxylic acids on GaAs (100) is described well by a two-site mechanism, in contrast to benzoic acid ad sorption which fits to a one-site mechanism. We do so by using a novel electrical method for direct measurement of adsorption kinetics. In t he method we measure the current through a GaAs/(Al, Ga)As-based devic e, where the bare surface between two contacts is used as the adsorpti on domain. The results, which are in agreement with FTIR absorption eq uilibrium data, are obtained in ambient notwithstanding the notorious instability of GaAs surfaces under such conditions. We conclude that t hese acids chemisorb on the GaAs surface and that binding is significa ntly stronger for the di-than for the monocarboxylic acids.