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Phys. Rev. B 75, 165403 (2007) [5 pages]

Formation and evolution of a self-organized hierarchy of Ge nanostructures on Si(111)-(7×7): STM observations and first-principles calculations

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H. F. Ma, Z. H. Qin, M. C. Xu, D. X. Shi, and H.-J. Gao*
Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

Sanwu Wang†
Department of Physics and Engineering Physics, University of Tulsa, Tulsa, Oklahoma 74104, USA

Sokrates T. Pantelides‡
Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA and Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

Received 30 October 2006; revised 29 January 2007; published 5 April 2007

We report scanning-tunneling-microscopy observations and first-principles calculations for the formation and evolution of self-organized Ge nanostructures on Si(111)-(7×7) surfaces for Ge coverages up to 0.5 ML. We show that individual Ge atoms initially form a triangular lattice. At higher coverages, Ge nanoparticles 1 nm in diameter gradually form in both the faulted and unfaulted half unit cells with an initial preference in the faulted halves, ultimately driving ordered hexagonal arrays. The underlying 7×7 surface periodicity, the triangular single-Ge lattice, and the nanoparticle hexagonal superstructures coexist. Charge transfer from Si adatoms to Ge nanoparticles is shown to play a key role in the self-organization.

© 2007 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevB.75.165403
DOI:
10.1103/PhysRevB.75.165403
PACS:
68.43.−h, 68.47.Fg, 73.22.−f, 81.16.Rf

*Electronic address: hjgao@aphy.iphy.ac.cn

†Electronic address: sanwu-wang@utulsa.edu

‡Electronic address: pantelides@vanderbilt.edu

 
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