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Published November 30, 2006 | public
Journal Article

Scanning Tunneling Microscopy of Ethylated Si(111) Surfaces Prepared by a Chlorination/Alkylation Process


Scanning tunneling microscopy (STM) and computational modeling have been used to study the structure of ethyl-terminated Si(111) surfaces. The ethyl-terminated surface was prepared by treating the H-terminated Si(111) surface with PCl_5 to form a Cl-terminated Si(111) surface with subsequent exposure to C_2H_5MgCl in tetrahydrofuran to produce an alkylated Si(111) surface. The STM data at 77 K revealed local, close-packed, and relatively ordered regions with a nearest-neighbor spacing of 0.38 nm as well as disordered regions. The average spot density corresponded to ≈85% of the density of Si atop sites on an unreconstructed Si(111) surface. Molecular dynamics simulations of a Si(111) surface randomly populated with ethyl groups to a total coverage of ≈80% confirmed that the ethyl-terminated Si(111) surface, in theory, can assume reasonable packing arrangements to accommodate such a high surface coverage, which could be produced by an exoergic surface functionalization route such as the two-step chlorination/alkylation process. Hence, it is possible to consistently interpret the STM data within a model suggested by recent X-ray photoelectron spectroscopic data and infrared absorption data, which indicate that the two-step halogenation/alkylation method can provide a relatively high coverage of ethyl groups on Si(111) surfaces.

Additional Information

© 2006 American Chemical Society. Received 12 June 2006. Published online 9 November 2006. Published in print 1 November 2006. The authors acknowledge the National Science Foundation, Grants CHE-0604894 (N.S.L.) and NSF-CCF-05204490, the MARCO Materials Structures and Devices Focus Center (J.R.H. and W.A.G), and the Department of Energy for support of this research. L.J.W. thanks the NSF for a graduate fellowship.

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