Relaxation of the Mo(112) and W(112) surfaces

Relaxation of the Mo(112) and W(112) surfaces has been simulated within DFT in local density approximation. It has been found that the surface relaxation, which can be described as a 14% contraction of the topmost surface layer with a small (0.1%) shift of surface atomic rows, results in a strong decrease of the surface energy with respect to the bulk truncated crystal surfaces (from 0.2 to 0.17 eV/Å2 for the Mo(112) and from 0.36 to 0.33 eV/Å2 for the W(112)). The surface relaxation is accompanied by the redistribution of the surface density of states, associated with the transformations of surface states.     

Reactions of atomic oxygen with the D-covered Si(1 0 0) surfaces

We have studied D abstraction by O on the D/Si(1 0 0) surfaces using a continuous as well as pulsed O-beams. Both D₂ and D₂O molecules are detected during O-exposure. The D₂ desorption is found to take place more efficiently on the monodeuteride/dideuteride surface than on the monodeuteride surface. The pulsed beam experiments exhibit occurrence of both a slow and a fast D₂ desorption. The D₂ desorption is found to obey the second-order rate law in on the monodeuteride surfaces and 3.5th-order rate law on the monodeuteride/dideuteride surfaces. The D₂O desorption is found to be governed also by the second-order rate law, however regardless of D coverage even on the monodeuteride/dideuteride surfaces. Possible mechanisms for the O-induced desorption from the D/Si(1 0 0) surfaces are discussed.     

Novel mesoscale defect structure on NiO(1 0 0) surfaces by atomic force microscopy

Cleaved NiO(1 0 0) surfaces were imaged with atomic force microscopy (AFM) to determine defect concentrations and morphology. Random 〈0 1 0〉 and 〈0 0 1〉 oriented steps, which have been previously characterized, were the most common defect observed on the cleaved surface and formed with step heights in multiples of 2.1 Å, the Ni-O nearest-neighbor distance, and terrace widths in the range of 25-100 nm. In addition, the surface showed novel mesoscale (∼0.5-2 μm) square pyramidal defects with the pyramid base oriented along 〈1 0 0〉 symmetry related directions. Upon etching, the pyramidal defects converted to more stable cubic pits, consistent with (1 0 0) symmetry related walls. The square pyramidal pits tended to cluster or to form along step edges, where the weakened structure is more susceptible to surface deformations. Also, a small concentration of square pyramidal pits, oriented with the base of the pyramid along 〈0 1 1〉, was observed on the cleaved NiO surfaces. For comparison purposes, chemical mechanical polished (CMP) NiO(1 0 0) substrates were imaged with AFM. Defect concentrations were of comparable levels to the cleaved surface, but showed a different distribution of defect types. Long-ranged stepped defects were much less common on CMP substrates, and the predominant defects observed were cubic pits with sidewalls steeper than could be accurately measured by the AFM tip. These defects were similar in size and structure to those observed on cleaved NiO(1 0 0) surfaces that had been acid etched, although pit clustering was more pronounced for the CMP surfaces.     

Longitudinal spin polarization and symmetries in low-energy-electron diffraction: Experiment and theory for Pt(111)

In low-energy electron diffraction from Pt(111), the longitudinal component of the spin polarization vector and its transverse component normal to the scattering plane were measured by a Mott detector and found to agree very well with corresponding theoretical results. Rotation diagrams of the longitudinal and transverse components exhibit only a three-fold symmetry in contrast to the six-fold symmetry, which time reversal invariance dictates for intensities.     

Structural analysis of the c(4 × 2) reconstruction in Si(0 0 1) and Ge(0 0 1) surfaces by low-energy electron diffraction

The c(4 × 2) structures in (0 0 1) surfaces of Si and Ge have been studied by low-energy electron diffraction (LEED). Using a proper cleaning method for the Si surface, we were able to observe clear c(4 × 2) LEED patterns up to incident energy of ∼400 eV as well as the Ge surface. Extensive experimental intensity-voltage curves allowed us to optimize the asymmetric dimer model up to the eighth layer (including the dimer layer) in depth in the dynamical LEED calculation. Optimized structural parameters are almost the same for the Si and Ge except for the height of the buckled-up atom of the asymmetric dimer. For the Ge surface, the structural parameters are in excellent agreement with those obtained by a previous theoretical calculation. The tilt angle and bond length of the dimer are 18 ± 1 (19 ± 1)° and 2.4 ± 0.1 (2.5 ± 0.1) Å for the Si(0 0 1) (Ge(0 0 1)), respectively.