Control of the Stability, Electron-Transfer Kinetics, and pH-Dependent Energetics of Si/H₂O Interfaces through Methyl Termination of Si(111) Surfaces

Abstract

Methyl-terminated, n-type, (111)-oriented Si surfaces were prepared via a two-step chlorination-alkylation method. This surface modification passivated the Si surface toward electrochemical oxidation and thereby allowed measurements of interfacial electron-transfer processes in contact with aqueous solutions. The resulting semiconductor/liquid junctions exhibited interfacial kinetics behavior in accord with the ideal model of a semiconductor/liquid junction. In contrast to the behavior of H-terminated Si(111) surfaces, current density vs. potential measurements of CH 3 -terminated Si(111) surfaces in contact with an electron acceptor having a pH-independent redox potential (methyl viologen 2+/+ ) were used to verify that the band edges of the modified Si electrode were fixed with respect to changes in solution pH. The results provide strong evidence that the energetics of chemically modified Si interfaces can be fixed with respect to pH and show that the band-edge energies of Si can be tuned independently of pH-derived variations in the electrochemical potential of the solution redox species.

Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes

“…However, the band edge positions can remain unchanged by coating the semiconductor with a pH-insensitive organic group. 40 Moreover, the band edges can be directly tuned without altering the semiconductor by forming a dipolar structure at the interface, which is caused by the specific adsorption of ions from the electrolyte. 41 1.3.10.…”

Atomic layer deposition for electrochemical energy generation and storage systems

“…7,48 It has been shown that surface grafted molecular layers can tune the band edge position of semiconductor photoelectrode. 49,50 ALD is an excellent process for chemically modifying substrates with sub to monolayers of different molecules. 7,9 This, in principle, can provide beneficial applications in grafting designed functional molecules for tuning surface dipole properties, band edges, and surface state density of the electrodes.…”

Porous Silicon-based Electrochemical Biosensors

“…As will be seen below, the presence of silica layers at solid/liquid interface confers sensitivity to pH variations. The functionalisation steps, which substitutes silica with other chemical groups may lead to the loss of pH sensitivity and hence to the impossibility to use it for the realisation of potentiometric biosensor (Hamann and Lewis 2006). This is not, in any case, a problem for other types of signal transduction.…”