Advanced Materials Characterization
Research on the characterization of advanced materials is being undertaken
as a joint project of national institutes
in Tsukuba (NIRIM, NIMCR, ETL and NRLM) at a beamline which has
a 27-pole wiggler/undulator. Its purpose is the advanced analysis
of materials, in particular, in-situ structure analysis during
the synthesis process, which may involve the use of
high temperature/pressure, molecular beam epitaxy(MBE) and surface reactions.
Understanding the process of synthesis of materials is important
in designing of materials with exotic properties and functions.
The structure of Ge epitaxial overlayers grown by MBE on Si(001) has
been studied by in-situ surface-sensitive XAFS. The osciilatory
intensities of reflection high energy electron diffraction (RHEED)
during the growth of Ge overlayers are used to control the number
of Ge layers.
The Ge K-EXAFS spectra for Ge overlayers on Si(001) have been obtained
by detecting the Ge fluorescence signal in a total reflection geometry
where only the sub-surface (5nm) region is probed. The figure indicates
the elongated dimer structure for 1ML Ge on Si(001). Detailed
analysis of the EXAFS profiles indicates evidence for a surface
site exchange induced by site-selective strains for 2ML Ge on Si(001).
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