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Transmission Infrared Spectra of CH_3-, CD_3-, and C_(10)H_(21)-Ge(111) Surfaces

Knapp, David and Brunschwig, Bruce S. and Lewis, Nathan S. (2011) Transmission Infrared Spectra of CH_3-, CD_3-, and C_(10)H_(21)-Ge(111) Surfaces. Journal of Physical Chemistry C, 115 (33). pp. 16389-16397. ISSN 1932-7447. doi:10.1021/jp110550t.

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The surface chemistry of CH_3–, CD_3–, and C_(10)H_(21)–Ge(111) surfaces prepared through a bromination/alkylation method have been investigated by infrared spectroscopy. Well-ordered CH_3–Ge(111) surfaces could be prepared only if, prior to bromination, the surface was etched with 6.0 M HCl or with a two-step etch of H_2O_2 (1.5 M)/HF (5.1 M) followed by a short HF (6.0 M) etch. The etching method used to make the Ge precursor surface, and the formation of a bromine-terminated intermediate Ge surface, were of critical importance to obtain clear, unambiguous infrared absorption peaks on the methyl-terminated Ge surfaces. Polarization-dependent absorption peaks observed at 1232 cm^(–1) for CH_3–Ge(111) surfaces and at 951 cm^(–1) for CD_3–Ge(111) surfaces were assigned to the methyl “umbrella” vibrational mode. A polarization-dependent peak at 2121 cm^(–1) for CD_3–Ge(111) surfaces was assigned to the symmetric methyl stretching mode. Polarization-independent absorption peaks at 755 cm^(–1) for CH_3–Ge(111) and at 577 cm^(–1) for CD_3–Ge(111) were assigned to the methyl rocking mode. These findings provide spectroscopic evidence that the methyl monolayer structure on the alkylated Ge is well-ordered and similar to that on analogous Si(111) surfaces, despite differences in the composition of the precursor surfaces. The X-ray photoelectron spectra of CH_3–Ge(111) surfaces, however, were not highly dependent upon the etching method and showed a constant C 1s:Ge 3d ratio, independent of the etching method. The infrared spectra of C_(10)H_(21)–Ge(111) surfaces were also not sensitive to the initial etching method. Hence, while the final packing density of the alkyl groups on the surface was similar for all etch methods studied, not all methods yielded a well-ordered Ge(111)/overlayer interface.

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Brunschwig, Bruce S.0000-0002-6135-6727
Lewis, Nathan S.0000-0001-5245-0538
Additional Information:© 2011 American Chemical Society. Received: November 4, 2010. Revised: June 7, 2011. Publication Date (Web): June 16, 2011. We acknowledge the National Science Foundation, Grant No. CHE-0911682, and the Beckman Institute for support of this work. We are also grateful to Dr. Erik Johansson for helpful discussions. XPS and FTIR data were collected at the Molecular Materials Research Center of the Beckman Institute at the California Institute of Technology.
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Caltech Beckman InstituteUNSPECIFIED
Issue or Number:33
Record Number:CaltechAUTHORS:20110906-070404983
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Official Citation:Transmission Infrared Spectra of CH3–, CD3–, and C10H21–Ge(111) Surfaces David Knapp, Bruce S. Brunschwig, Nathan S. Lewis The Journal of Physical Chemistry C 2011 115 (33), 16389-16397
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25219
Deposited By: Ruth Sustaita
Deposited On:06 Sep 2011 14:42
Last Modified:09 Nov 2021 16:31

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