Structure of steps on As-passivated Si(111):Ab initiocalculations and scanning tunneling microscopy

Abstract

The structures of terrace steps on As-covered Si͑111͒ are examined using ab initio calculations. In scanning tunneling microscope ͑STM͒ images, two orientations of steps are found to terminate As-covered Si islands after annealing: ͓112͔ and ͓112͔. Total energy calculations and simulations of STM images yield detailed information on the atomic structures of the steps: In the lowest-energy configuration for both orientations, surplus As atoms replace any exposed Si atoms at the steps. The As atoms rearrange to establish a threefold coordination. For ͓112͔ steps the atom positions of the relaxed configuration are very close to the ideal bulk positions, but for ͓112͔ steps the terminating As atoms form dimers in front of the steps. The different atomic structures of the two step orientations clearly show up in the simulated STM images for negative bias ͑occu-pied states imaged͒, the STM images for positive bias ͑unoccupied states͒ are much less distinctive. All features of existing experimental positive-bias STM images can be explained by an analysis of the electronic local density of states. With the calculated step energies we construct a phase diagram for the equilibrium shape of As-covered islands. In the accessible range of As chemical potentials between As bulk and As 4 molecules, we expect either triangular islands terminated by ͓112͔ steps or hexagons with long edges of ͓112͔ orientation and short ones with ͓112͔ orientation.

Scanning tunneling microscopy contrast in lateral Ge-Si nanostructures onSi(111)−3×3-Bi

“…A shape of the spectra closely resembles the LDOS calculated for Si͑111͒-ͱ 3 ϫ ͱ 3-As surface in Ref. 39.…”

Nature of contrast in Ge/Si(111) layers in scanning tunneling microscopy in the presence of Bi and Sb surfactants

“…We performed test calculations of the spectra of the local density of electronic states of the surfaces of well stud ied systems Si(100) 2 × 1 and As/Si(111). Our results are in good agreement with the data reported in [12,26], where the realistic positions of the tip over the sur face were used to simulate the scanning tunneling spectroscopy spectra.…”

Mechanism of twin-reduced III-V epitaxy on As-modified vicinal Si(111)

“…), also metastable structures with mixed step heights and facet formation can occur. In addition, also the presence of adatoms, or the formation of clusters or islands on the As-passivated surface was reported [53,63,64].…”

“…Note that DH steps can be further distinguished between vertical and horizontal DH steps [52]. The former are, however, not stable under As treatment (due to "overhanging" As) [53]. We therefore only consider the horizontal type in this work.…”

“…The presence of excess Si on top of the Asmonolayer stemming from a Si-As exchange process seems to be a common explanation for the source of adatoms. Antons et al [53] performed ab initio molecular dynamics calculations showing that for vicinal Asterminated Si(111) TBBS are energetically favored over DBBS. In both cases As-As bonds at the step edge are more stable than Si-As configurations.…”