posted on 2015-07-22, 00:00authored byKeith
T. Wong, Youn-Geun Kim, Manuel P. Soriaga, Bruce S. Brunschwig, Nathan S. Lewis
Atomically
flat, terraced H–Ge(111) was prepared by annealing
in H2(g) at 850 °C. The formation of monohydride Ge–H
bonds oriented normal to the surface was indicated by angle-dependent
Fourier-transform infrared (FTIR) spectroscopy. Subsequent reaction
in CCl3Br(l) formed Br-terminated
Ge(111), as shown by the disappearance of the Ge–H absorption
in the FTIR spectra concomitant with the appearance of Br photoelectron
peaks in X-ray photoelectron (XP) spectra. The Br–Ge(111) surface
was methylated by reaction with (CH3)2Mg. These
surfaces exhibited a peak at 568 cm–1 in the high-resolution
electron energy loss spectrum, consistent with the formation of a
Ge–C bond. The absorption peaks in the FTIR spectra assigned
to methyl “umbrella” and rocking modes were dependent
on the angle of the incident light, indicating that the methyl groups
were bonded directly atop surface Ge atoms. Atomic-force micrographs
of CH3–Ge(111) surfaces indicated that the surface
remained atomically flat after methylation. Electrochemical scanning–tunneling
microscopy showed well-ordered methyl groups that covered nearly all
of the surface. Low-energy electron diffraction images showed sharp,
bright diffraction spots with a 3-fold symmetry, indicating a high
degree of order with no evidence of surface reconstruction. A C 1s
peak at 284.1 eV was observed in the XP spectra, consistent with the
formation of a C–Ge bond. Annealing in ultrahigh vacuum revealed
a thermal stability limit of ∼400 °C of the surficial
CH3–Ge(111) groups. CH3–Ge(111)
surfaces showed significantly greater resistance to oxidation in air
than H–Ge(111) surfaces.