Reversible Phase Transformation on Ge (111) Surface by Potential

摘要

Reversible phase transformation on atomically flatGe (111) induced by potential in 40% NH4F solution has beenobserved with in situ scanning tunneling microscope. The abruptchange in Ge surface morphology as a function of the potential isattributed to the phase transformation, where small terraces areconverted into large terraces as the potential is changed from –1.32 to-0.98 V. Cyclic voltammograms show that the chargeunder the cathodic peak is almost the same as that under theanodic peak (4.2250L?0-4C/cm2). Combined with ex situ X-rayphotoelectron spectroscopy and secondary-ion mass spectroscopyresults, we conclude that Ge (111) surface is terminated by amonolayer hydroxide or hydride depending on the appliedpotential. The formation of hydroxide-terminated Ge (111) islikely co occur at –0.98 V, far away from the anodic peak in thecyclic voltammogram. This fact suggests that the reversible phasetransformation between monolayer hydrogen- and hydroxyl-capped Ge (111) surface is induced by potential. An atomicallyflat Ge (111) surface prepared with wet cleaning provides anattractive substrate for epitaxial growth of compound semiconductors.