Addimer Chain Structures: Metastable Precursors To Island Formation On Ge-Si(001)-(2 X N) Alloyed Surface
Surface Science(2007)
摘要
We have identified addimer chain structures as metastable precursors to compact epitaxial islands on the (2 x n) reconstructed SiGe wetting layer, using polarity-switching scanning tunneling microscopy (STM). These chain structures are comprised of 2-12 addimers residing in the troughs of neighboring substrate dimer rows. The chain structures extend along equivalent < 130 > directions across the substrate dimer rows in a zigzag fashion, giving rise to kinked and straight segments. We measure a kink-to-straight ratio of nearly 2:1. This ratio corresponds to a free energy difference of 17 +/- 4 meV, favoring the formation of kinked segments. The chain structures convert to compact epitaxial islands at elevated temperatures ( >= 90 degrees C). This conversion suggests that the chain structures are a precursor for compact island formation on the SiGe wetting layer. We digitally process filled- and empty-state STM images to distinguish chain structures from compact islands. By monitoring the populations of both species over time, the chain-to-island conversion rates are measured at substrate temperatures ranging from 90 to 150 degrees C. The activation energy for the conversion process is measured to be 0.7 +/- 0.2 eV with a corresponding pre-exponential factor of 5 x 10(4 +/- 2) s(-1). (c) 2006 Elsevier B.V. All rights reserved.
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关键词
addimer chain structures,compact epitaxial islands,C-dimer,polarity-switching scanning tunneling microscopy,(2 x n) silicon-germanium alloy,surface kinetics
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