Electrochemical stabilization of crystalline silicon with aromatic self‐assembled monolayers in aqueous electrolytes

Abstract

We report stable chemical engineering of hydrogen-terminated Si [111] surfaces in aqueous electrolytes by electrochemical grafting of aromatic monolayers. The topography and free energy of the engineered surface obtained from AFM and contact angle measurements confirmed homogeneous coating of the surface with a monolayer. Grafting of monolayers actually resulted in a clear suppression of the surface defect densities, demonstrated by photoluminescence lifetime. Changes in the surface chemical identities after grafting and post-treatments were followed by X-ray photoelectron spectroscopy (XPS). The electrochemical stability in aqueous electrolytes was assessed by impedance spectroscopy, revealing an improved stabilization of the Si/electrolyte interface by the grafted monomolecular film. This protocol was further applied for another aromatic compound, where the impact of 4-substituent functions could clearly be detected by photovoltage measurements. The chemical and electrochemical stability achieved here is promising for the successive deposition of biocompatible polymer films and lipid membranes.

Electrografting: a powerful method for surface modification

“…Hydrogenterminated Si surfaces have a finite lifetime under atmospheric conditions and in solutions; the formation of polyphenylene layer has been investigated as a means of stabilizing the surface. [620][621][622][623][624] A complete energy band diagram has been constructed for electrografted Si (111) surfaces including band bending for Si-C 6 H 4 -R (R = NO 2 , Br, OCH 3 ). 624 The measurement of the integrated photoluminescence intensity with time indicates that Si surfaces electrografted with aryl groups are much more stable than the H-terminated surface in aqueous electrolytes 622 and in air.…”