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Published August 3, 2006 | public
Journal Article

Chemical and Electrical Passivation of Silicon (111) Surfaces through Functionalization with Sterically Hindered Alkyl Groups

Abstract

Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using sterically bulky alkyl groups such as (CH_3)_2CH− (iso-propyl), (CH_3)_3C− (tert-butyl), and C_6H_5− (phenyl) moieties. X-ray photoelectron spectroscopic (XPS) data in the C 1s region of such surfaces exhibited a low energy emission at 283.9 binding eV, consistent with carbon bonded to Si. The C 1s XPS data indicated that the alkyls were present at lower coverages than methyl groups on CH_3-terminated Si(111) surfaces. Despite the lower alkyl group coverage, no Cl was detected after alkylation. Functionalization with the bulky alkyl groups effectively inhibited the oxidation of Si(111) surfaces in air and produced low (<100 cm s^(-1)) surface recombination velocities. Transmission infrared spectroscopy indicated that the surfaces were partially H-terminated after the functionalization reaction. Application of a reducing potential, −2.5 V vs Ag^+/Ag, to Cl-terminated Si(111) electrodes in tetrahydrofuran resulted in the complete elimination of Cl, as measured by XPS. The data are consistent with a mechanism in which the reaction of alkyl Grignard reagents with the Cl-terminated Si(111) surfaces involves electron transfer from the Grignard reagent to the Si, loss of chloride to solution, and subsequent reaction between the resultant silicon radical and alkyl radical to form a silicon−carbon bond. Sites sterically hindered by neighboring alkyl groups abstract a H atom to produce Si−H bonds on the surface.

Additional Information

© 2006 American Chemical Society. Received 5 December 2005. Published online 13 July 2006. Published in print 1 August 2006. We gratefully acknowledge the NSF, Grant CHE-021358 and the Beckman Institute for support of this work.

Additional details

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