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

Antons, A.; Voigtländer, B.; Berger, R.; Schroeder, K.

doi:10.1103/PhysRevB.73.125327

Journal Article

PreJuSER-53407

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

Antons, A. ; Berger, R. ; Schroeder, K.FZJ* ; Voigtländer, B.FZJ*

2006
APS College Park, Md.

Physical review / B 73(12), 125327 (2006) [10.1103/PhysRevB.73.125327]

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Please use a persistent id in citations: http://hdl.handle.net/2128/1583 doi:10.1103/PhysRevB.73.125327

Abstract: The structures of terrace steps on As-covered Si(111) are examined using ab initio calculations. In scanning tunneling microscope (STM) images, two orientations of steps are found to terminate As-covered Si islands after annealing: [11 (2) over bar] and [(11) over bar2]. 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 [11 (2) over bar] steps the atom positions of the relaxed configuration are very close to the ideal bulk positions, but for [(11) over bar2] 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 (occupied states imaged), the STM images for positive bias (unoccupied states) 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 [11 (2) over bar] steps or hexagons with long edges of [11 (2) over bar] orientation and short ones with [(11) over bar2] orientation.

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