Electrochemical Properties of (111)-Oriented n-Si Surfaces Derivatized with Covalently- Attached Alkyl Chains

Abstract

The electrochemical properties of alkyl-terminated, (111)-oriented, n-type Si surfaces, prepared via a twostep halogenation/alkylation procedure, were analyzed in contact with CH 3 OH-1,1′-dimethylferrocene +/0 (Me 2 Fc +/0 ) solutions. Current density-potential and differential capacitance-potential measurements of these surfaces in contact with CH 3 OH-Me 2 Fc +/0 indicated that the electrochemical properties of the alkyl-terminated surfaces were very similar to those of the H-terminated Si surface. The alkyl overlayers did not shift the Si band edges or induce significant surface recombination, but they did provide an additional electrical series resistance to charge transfer across the Si/liquid interface. The efficacy of alkyl overlayers in preventing photooxidation and photocorrosion of n-silicon surfaces was measured in contact with CH 3 OH-Me 2 Fc +/0 solutions to which a known amount of water had been added. Under these conditions, the alkyl-terminated surfaces consistently showed excellent current density-potential characteristics and displayed lower oxidation rates than the H-terminated surface, indicating that stability toward oxidation had been achieved without any significant compromise in the electrochemical qualities of the silicon surface.

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

“…This behavior is in accord with the stability toward oxidation of alkyl-terminated Si(111) photoanodes under illumination. 25,26 The inhibition of oxidation enabled the measurement of interfacial electron-transfer processes that were in accord with the ideal model of electron transfer at the semiconductor/liquid interface. The current density for an electron-transfer process from the conduction band of an n-type semiconductor to an acceptor species, A, in solution, is given by …”

Wet chemical routes to the assembly of organic monolayers on silicon surfaces via the formation of Si–C bonds: surface preparation, passivation and functionalization

“…1). [75][76][77][78] Hydrogenated silicon surfaces are attractive to work with because of their ease of preparation, 78 their relative stability in air 79,80 and during brief water ring procedures, 31,76 and their lack of appreciable reactivity toward a range of common solvents (including acetonitrile, 81 diethyl ether, 46 chlorobenzene, 82 hexane, 83 toluene 84 and mesitylene 85,86 preparation of covalent organic layers by wet chemical methods. 87 Notable exceptions to the typically straightforward conditions are [2+2] and [4+2] cycloaddition reactions under 'dry' UHV conditions.…”

“…This method generally results in ordered, 144 electrically and chemically well-passivated alkyl Si (111) 82,109,114,124,[144][145][146][147][148][149][150] and Si(100) 102 surfaces (Fig. 6).…”

Preparation of air-stable, low recombination velocity Si(111) surfaces through alkyl termination

“…Crystalline Si has been functionalized previously at atmospheric pressure with organic layers through the use of alkyl Grignard and alkyl lithium reagents, 6 alkenes, [7][8][9] and phenyldiazonium salts, 10 while the reaction chemistry of porous Si has been developed yet further to include use of alkynes 11,12 and organohalides. 13 The electrochemical properties of some of these surfaces have been reported, 14,15 but to date there appears to be no information on the electrical properties of such systems. We report herein that crystalline Si functionalized through a twostep, wet-chemistry-based chlorination/alkylation procedure 6 has an extremely low surface recombination velocity.…”