Wet Chemical Functionalization of GaP(111)B through a Williamson Ether-Type Reaction

Abstract

Functionalization of crystalline gallium phosphide (GaP) (111)B interfaces has been performed through the formation of P–O–R surface bonds. The approach described herein parallels classical Williamson ether synthesis, where hydroxyl groups on etched GaP(111)B surfaces were reacted with halogenated reactants. Grazing angle total internal reflectance infrared spectra showed increased intensities for −CH2– and −CH3 asymmetric and symmetric stretches after reaction with long alkyl halides. Changes in the X-ray photoelectron spectra collected before and after reaction separately corroborated surface attachment to GaP(111)B. Static sessile drop water contact angle measurements for GaP(111)B separately showed increased hydrophobicity following surface modification with long alkyl chains. The surface functionalization reaction rate was increased by the addition of non-nucleophilic bases, consistent with surface deprotonation as the rate-limiting step. Separately, photoelectrochemical measurements conducted before and after reaction with alkyl halides at long wavelengths (λ > 545 nm) showed surface attachment decreased sub-band-gap photocurrents, implying lowered activity of surface traps. Conversely, photoelectrochemical measurements performed after functionalization of p-GaP(111)B with Coomassie Blue sulfonyl chloride showed evidence of persistent sensitized hole injection from the dye into p-GaP.