Chemical structure of dihydride phase on saturated H-chemisorbed Si surfaces

Abstract

By observing infrared absorption features including dynamic polarizations due to Si–H stretching vibrations, chemical structures were determined on H-chemisorbed single-crystal Si surfaces that were formed in solution. A technique using polarized infrared multiple internal reflections was applied. The absorption features were obtained as a function of surface H density by systematically tilting the orientation of the surfaces from (111) through (113) up to (001). For surface orientations from (111) to (113), narrow absorption peaks, which had been assigned due to the strained vertical dihydride, and (111)-terrace monohydride species were predominantly observed. But, as the surface orientation moved away from (111), narrow peaks with dynamic polarizations in the (1̄10) plane were observed for the first time. Meanwhile, the broad feature with several peaks in the whole Si–H stretching region was detected in the surface-parallel component of dynamic polarization. Because the absorption area for the surface parallel component increased monotonically with the angle, the features were concluded to be localized at the vertical-dihydride step edges along 〈1̄10〉. A complex composed of a strained horizontal dihydride and a strained monohydride provided a temporary explanation. On (001), the peaks caused by the strained vertical dihydride disappeared completely, and the predominant peaks were those observed for the first time on the other surfaces. A major part of the (001) surface was composed of the complex. The microscopic origin for the appearance of such a disordered structure is described.