First Reaction of a Bare Silicon Surface with Acid Chlorides and a One-Step Preparation of Acid Chloride Terminated Monolayers on Scribed Silicon

Methyl-terminated and acyl chloride terminated monolayers are produced when silicon is scribed under mono- and diacid chlorides, respectively. To the best of our knowledge, this is the first report of the reaction between a bare silicon surface and acid chlorides. This reaction takes place by wetting the silicon surface in the air with the acid chloride and scribing. Scribing activates the silicon surface by removing its passivation layer. We propose that scribed silicon abstracts chlorine from an acid chloride to form an Si-Cl bond and that the resulting acyl radical diffuses back to the surface to condense with the surface and form an alkyl monolayer. X-ray photoelectron spectroscopy (XPS) confirms the presence of chlorine and shows a steady increase in the amount of carbon with increasing alkyl chain lengths of the acid chlorides. Time-of-flight secondary ion mass spectrometry shows SiCl(+) species and a steady increase in representative hydrocarbon fragments with increasing alkyl chain lengths of the acid chlorides. XPS indicates that diacid chlorides react primarily at one of their ends to create acyl chloride terminated surfaces in a single step. The resulting surfaces are shown to react with various amines (piperazine, morpholine, and octylamine) and a protein. Calculations at Hartree-Fock and density functional theory levels are consistent with the proposed mechanism.