Electron-beam-induced disordering of the Si(001)-c(4 x 2) surface structure

An electron beam (EB) irradiation effect on the Si(001)-c(4 x 2) surface was investigated by using low-energy electron diffraction. Quarter-order spots become dim and streaky by EB irradiation below approximately 40 K, indicating a disordering in the c(4 x 2) arrangement of buckled dimers. A quantitative analysis of decreasing rates of the spot intensity at various conditions of beam current, beam energy, and substrate temperature leads to a proposal for a mechanism of the disordering in the buckled-dimer arrangement in terms of electronic excitation, electron-phonon coupling, and carrier concentration.     

Oxidation of step edges on Si(001)-c(4x2)

The initial oxidation process of the ultraclean Si(001)-c(4x2) surface is studied using scanning tunneling microscopy at low temperature. At the early stage of oxygen adsorption, reactions with Si atoms at SB steps are dominant over those at terraces by more than 2 orders of magnitude, and they proceed in two distinct stages to high oxidation states. Guided by the ab initio calculations, the oxidation structures at each stage are proposed. The extreme reactivity of the step edge is due to the presence of rebonded adatoms with dangling bonds and weak rebonds, and their proximity allows the formation of -Si-O- chain structures along the step edge, unlike those on the Si(111) surface.     

InP(001)-(2 x 1) surface: a hydrogen stabilized structure

The InP(001)(2 x 1) surface has been reported to consist of a semiconducting monolayer of buckled phosphorus dimers. This apparent violation of the electron counting principle was explained by effects of strong electron correlation. Combining first-principles calculations with reflectance anisotropy spectroscopy and LEED experiments, we find that the (2 x 1) reconstruction is not at all a clean surface: it is induced by hydrogen adsorbed in an alternating sequence on the buckled P dimers. Thus, the microscopic structure of the InP growth plane relevant to standard gas phase epitaxy conditions is resolved and shown to obey the electron counting rule.     

Atomic structure of a (2 x 1) reconstructed NiSi2/Si(001) interface

Nickel disilicide/silicon (001) interfaces were investigated by aberration corrected scanning transmission electron microscopy (STEM). The atomic structure was derived directly from the high spatial resolution high angle annular dark field STEM images without recourse to image simulation. It comprises fivefold coordinated silicon and sevenfold coordinated nickel sites at the interface and shows a 2 x 1 reconstruction. The proposed structure has not been experimentally observed before but has been recently predicted theoretically by others to be energetically favored.     

Electronic bond rupture of Si-Dimers on Si(001)-(2x1) induced by pulsed laser excitation

A scanning tunneling microscopy study has revealed that 532 nm laser pulses of fluences well below melt and ablation thresholds induce electronic bond rupture of Si-dimers on the Si(001)-(2x1), resulting in the formation of single dimer-vacancies followed by progressive growth into vacancy clusters. The rate of bond rupture on the intrinsic (2x1) structure shows super-linearity with respect to excitation intensity, and saturates as the number of vacancies reaches a few percent, relative to total dimer sites. The mechanism of laser-induced bond rupture is discussed based on these results. PACS 61.80.Ba; 61.82.Fk; 68.35.Bs; 79.20.La