Taking advantage of liquid ammonia to control the surface modification of silicon electrodes

Abstract

This work shows the advantages of using a non-aqueous solvent such as ammonia, which can be used at cryogenic temperatures and can be prepared anhydrously, to control the state of a silicon electrode surface in contact with the electrolyte. Depending on the in-situ experimental conditions, it was possible to change the oxidized material surface (native oxide) to an oxide-free surface and conversely. An original technique for pretreatment of the electrodes in a solvated electron solution in ammonia was used to corroborate the results obtained with the usual treatment, HF under an inert atmosphere. The influence of a superficial oxide layer and the growth of this layer under various conditions, was studied carefully by following the variations of two experimental parameters: the flatband potential and the photocurrent onset potential. By changing the pH, in liquid ammonia, the growth of the superficial oxide layer could be completely controlled; moreover, the oxide could be obtained either by a chemical reaction with traces of water or by a photoelectrochemical route.