ATOMICALLY RESOLVED SCANNING-TUNNELING-MICROSCOPY IMAGES OF INP(001),(111)A, AND (111)B SURFACES IN SULFURIC-ACID-SOLUTION

Electrochemical scanning tunneling microscopy (STM) was used to study n type InP surfaces in an aqueous sulfuric acid solution. Well-defined InP(001), (111)A, and (111)B surfaces were prepared by chemical etchi ng. in 1 M HCl. Cathodic polarization of the InP electrodes effectivel y protected the surfaces from oxidation. However, when the potential w as made too negative, the decomposition of InP surfaces inhibited stab le STM imaging. Atomically flat terrace-step structures were consisten tly observed on all surfaces in 0.05 M H2SO4 under suitable cathodic p otentials. Steps observed on these surfaces corresponded to the monola yer steps with heights of 0.29 and 0.34 nm for the (001) and (111) sur faces, respectively. Atomically resolved STM images of InP electrodes were successfully obtained on the terraces for the first time. Ln situ STM revealed that all these surfaces possess a (1 x 1) structure with an interatomic distance of 0.42 nm. These results clearly demonstrate that the ideal InP(001), (111)A, and (111)B surfaces can be exposed i n H2SO4 solution by the chemical etching method.