Near-Ideal Complete Coverage of CD3 onto Si(111) Surfaces Using One-Step Electrochemical Grafting: An IR Ellipsometry, Synchrotron XPS, and Photoluminescence Study

Abstract

A one-step electrochemical grafting process using Grignard reagents has been performed to achieve a complete monolayer methyl-terminated Si(111) surfaces. Anodic treatment (0.5 mA/cm2 for 300 s) has been applied to atomically flat H-terminated Si(111) surfaces in methylmagnesium bromide (CH3MgBr), methylmagnesium iodide (CH3MgI), and methyl-d3-magnesium iodide (CD3MgI) to obtain methylated Si(111) surfaces. Infrared spectroscopic ellipsometry (IRSE) clearly reveals a vibrational shift of the symmetric “umbrella” mode characteristic for methyl groups (CH3 and CD3) with a preferential z-orientation. Additionally, X-ray photoelectron spectroscopy using synchrotron radiation (SXPS) shows a well-defined splitting of the Si 2p core level spectra from the methylated Si(111) surfaces. This splitting is more pronounced for the CD3-terminated Si(111) surfaces. Moreover, the C 1s spectra also confirm the well-defined structure of the CD3-terminated Si(111) surfaces by the presence of C–D vibrational stretching features. Photoluminescence (PL) measurements reveal better surface passivation in the case of CD3-terminated Si(111) surfaces. Finally, the quality of the surfaces depends strongly on the counterions. Grignard reagents containing iodine show the best performance in the formation of complete monolayer methylated Si(111) surfaces.