Thermal decomposition of an ultrathin Si oxide layer around a Si(001)-(2 x 1) window

We examine the thermal decomposition of an ultrathin Si oxide layer around a Si(001)-(2 x 1) window opened by electron-beam-induced selective thermal decomposition. The decomposition progresses at the oxide/Si(001)-(2 x 1) boundary and follows two rate-limiting steps with activation energies of 4.0 and 1.7 eV. We propose that the former and latter energies correspond to the reaction of Si monomer with the oxide and the desorption of the SiO into the vacuum, respectively.     

Primary processes of laser-induced selective dimer-layer removal on Si(001)-(2x1)

Excitation with nanosecond-laser pulses at fluences well below the melt threshold removes Si dimers on the Si(001)-(2x1) surface and induces atomic-Si desorption through an electronic mechanism. The rate of this photoinduced reaction depends superlinearly on the excitation intensity, and is enhanced resonantly at the photon energy where the optical transition injects holes into the dimer backbond surface-band state. The results reveal the crucial role of surface holes and their nonlinear localization in the bond rupture of Si dimers on this surface.     

Enhanced terrace stability for preparation of step-free Si(001)-(2 x 1) surfaces

We show that depositing Si while annealing patterned Si(001)-(2 x 1) substrates at sublimation temperatures enhances terrace stability, permitting larger step-free areas to be produced in a given time than possible by annealing alone. We confirm this enhanced terrace stability using real-time low-energy electron microscopy observations, and quantitative microscopic modeling of step dynamics. Our measurements can be used to estimate the lateral variation in adatom concentration across large terraces, and to estimate an adatom diffusion length lambda approximately 10-30 microm at 1000 degrees C.     

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.     

Interaction of H2 with Si(001)-(2 x 1): solution of the barrier puzzle

The sticking probability of H2 on Si(001) is immeasurably small at room temperature, indicating the presence of a large energy barrier to adsorption. Surprisingly, the final state energy distributions of H2 molecules desorbing from Si(001) show no signs of having traversed such a barrier, in apparent contradiction with microscopic reversibility. Here we report experimental and theoretical evidence resolving this long-standing puzzle. Adsorption and desorption proceeding along two distinct, microscopically reversible pathways can explain all observations.     

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     

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.