Synthesis and characterization of well-​ordered methyl-​, ethynyl-​, and propynyl-​terminated Si(111) surfaces

Abstract

Alkyl-termination of Si(111) surfaces has been shown to effectively passivate the surface to oxidn. in air. Me groups are unique among satd. hydrocarbons in that they are capable of terminating nearly all of the Si(111) atop sites. However, secondary functionalization of methyl-terminated Si has proven challenging. Ethynyl and propynyl groups, which have Van der Waals radii similar to Me groups, contain functional groups capable of secondary reactivity. Thus, ethynyl- and propynyl-terminated Si(111) surfaces were prepd. by a two-step halogenation/alkylation procedure and characterized by transmission IR spectroscopy (TIRS), XPS, high-resoln. electron energy loss spectroscopy (HREELS), LEED (LEED), at. force microscopy (AFM), and surface recombination velocity (SRV) measurements. Vibrational spectra of ethynyl-terminated Si(111) surfaces exhibit acetylenic C-H and C≡C stretching modes that are oriented perpendicular to the surface, while spectra of propynyl-terminated Si(111) surfaces show a C-H sym. bending (umbrella) mode also oriented perpendicular to the surface. LEED patterns indicate the preservation of a 1 × 1 surface unit cell, and AFM images show the preservation of at. terraces. Ethynyl-terminated Si(111) surfaces were deprotonated with a strong base and soaked in CD_3OD to produce partially deutorated ethyne functionality on the surface, demonstrating the reactivity of the terminal alkyne moiety.