Formation of Organic Monolayers on Silicon via Gas-Phase Photochemical Reactions

Abstract

A new method for the formation of molecular monolayers on silicon surfaces utilizing gas-phase photochemical reactions is reported. Hydrogen-terminated Si(111) surfaces were exposed to various gas-phase molecules (hexene, benzaldehyde, and allylamine) and irradiated with ultraviolet light from a mercury lamp. The surfaces were studied with in situ Fourier transform infrared spectroscopy, high-resolution electron energy loss spectroscopy, and scanning tunneling microscopy. The generation of gas-phase radicals was found to be the initiator for organic monolayer formation via the abstraction of hydrogen from the H/Si(111) surface. Monolayer growth can occur through either a radical chain reaction mechanism or through direct radical attachment to the silicon dangling bonds.

Modulation of flat-band voltage on H-terminated silicon-on-insulator pseudo–metal–oxide–semiconductor field effect transistors by adsorption and reaction events

“…8,20 Decyl monolayers were formed via a recently reported gas phase photochemical route. 21 H-terminated samples were quickly transferred to a small vacuum chamber with a sorption pump (base pressure <10 À4 Torr). The chamber was equipped with a UV transparent sapphire port allowing 60% transmission at 190 nm as measured by a spectrophotometer.…”

“…[28][29][30] In order to use the W-MOS-FET technique to probe the changes induced by alkyl monolayer formation, we have chosen to employ a recently developed gas phase photochemical alkylation process. 21 In this process, the absorption of 185 nm UV photons in the primary alkene CH 3 (CH 2 ) k CH ¼ CH 2 (g) induces photolysis, forming the reactive radical fragments needed to generate dangling bonds on the H-terminated surface (initiation). A radical chain reaction involving the direct reaction of the alkene itself with these dangling bonds can then propagate on the surface, forming the methyl terminated monolayer Si-(CH 2 ) kþ2 CH 3 .…”

Recent Applications of Molecular Structures at Silicon Anode Interfaces

“…SAMs can also refer to layers of molecules on sphere surfaces such as nanoparticles [76]. Monolayers have a broader scope than SAMs, as the preparation of monolayers may not always strongly depend on self-assembly processes [77]. This section discusses monolayer-type coatings on silicon anodes, which are layers of organic molecules chemically bonded on the Si surface.…”

Exclusively Gas-Phase Passivation of Native Oxide-Free Silicon(100) and Silicon(111) Surfaces

“…40,41 Initial attempts included gas-phase hydrosilylation reactions aiming for high surface coverage 42−44 and mechanistic understanding. 45 These pioneering efforts employed standard liquid-phase fluoride etching for native-oxide removal 42, 43 and a specialized in-situ-synthesized H-terminated nanoparticle substrate. 44 On a longer run, gas-phase reactions could provide many additional advantages, including reagent−solvent economy, cleanliness, 46 better etching selectivity resulting in wider material compatibility, 40,41 as well as procedural simplicity.…”