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Published April 13, 2006 | public
Journal Article

Transmission Infrared Spectroscopy of Methyl- and Ethyl-Terminated Silicon(111) Surfaces

Abstract

Transmission infrared spectroscopy (TIRS) has been used to investigate the surface-bound species formed in the two-step chlorination/alkylation reaction of crystalline (111)-oriented Si surfaces. Spectra were obtained after hydrogen termination, chlorine termination, and reaction of the Cl−Si(111) surface with CH_3MgX or C_2H_5MgX (X = Cl, Br) to form methyl (CH_3)- or ethyl (C_2H_5)-terminated Si(111) surfaces, respectively. Freshly etched H-terminated Si(111) surfaces that were subsequently chlorinated by immersion in a saturated solution of PCl_5 in chlorobenzene were characterized by complete loss of the Si−H stretching and bending modes at 2083 and 627 cm^(-1), respectively, and the appearance of Si−Cl modes at 583 and 528 cm^(-1). TIRS of the CH_3-terminated Si(111) surface exhibited a peak at 1257 cm^(-1) polarized perpendicular to the surface assigned to the C−H symmetrical bending, or "umbrella" motion, of the methyl group. A peak observed at 757 cm^(-1) polarized parallel to the surface was assigned to the C−H rocking motion. Alkyl C−H stretch modes on both the CH_3- and C_2H_5-terminated surfaces were observed near 2900 cm^(-1). The C_2H_5-terminated Si(111) surface additionally exhibited broad bands at 2068 and 2080 cm^(-1), respectively, polarized perpendicular to the surface, as well as peaks at 620 and 627 cm^(-1), respectively, polarized parallel to the surface. These modes were assigned to the Si−H stretching and bending motions, respectively, resulting from H-termination of surface atoms that did not form Si−C bonds during the ethylation reaction.

Additional Information

© 2006 American Chemical Society. Received: August 16, 2005; In Final Form: November 9, 2005. Publication Date (Web): March 21, 2006. L.J.W. thanks the NSF for a Graduate Research Fellowship, and D.J.M. thanks the Link Foundation for an Energy Fellowship. We gratefully acknowledge the NSF, grants CHE-0213589 at Caltech and CHE-0415652 at Rutgers, for support of this work.

Additional details

Created:
August 19, 2023
Modified:
October 25, 2023