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 −CH 2 − and −CH 3 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.

Synthesis, Characterization, and Reactivity of Ethynyl- and Propynyl-Terminated Si(111) Surfaces

“…The fractional monolayer coverage for 4-fluorobenzyl-modified HCC-Si(111) and SiO x surfaces was estimated using a three-layer model [13][14] …”

Solar Hydrogen Production Using Molecular Catalysts Immobilized on Gallium Phosphide (111)A and (111)B Polymer-Modified Photocathodes

“…Both faces are subject to oxidative and corrosive processes; however methods have been developed to chemically protect and passivate these otherwise structurally unstable surfaces, including treatment with (NH 4 ) 2 S x , 29 alkylation or allylation with subsequent secondary functionalization of the A-side 30,31 and alkyl halide reactions with the P sites via a Williamson ether synthesis on the B-side. 32 An attachment strategy that can be utilized across multiple crystal face orientations may be useful in interfacing molecular catalysts to nanostructured materials that terminate with a range of indices, thereby permitting a relatively dense loading of catalysts and relieving the turnover frequency (TOF) of individual active sites required to achieve a selected current density. Reports describing strategies to directly integrate molecular catalysts for hydrogen production to visible-lightabsorbing semiconductors are limited, but include the following: [Fe 2 S 2 (CO) 6 ] adsorbed onto indium phosphide nanocrystals, 33 a cobaloxime-containing polymer grafted onto GaP(100), 34−37 trinuclear molybdenum cluster salts drop-cast on Si(100), 38 ferrocenophane-containing polymers deposited on Si (100) and (111), 39 Si (100) and GaP(100), 40 Negishi coupling of phosphine ligands onto Si(111) followed by metalation, 41 a metal−organic surface composed of a cobalt dithiolene polymer drop-cast onto Si(100), 42 and cobaloxime catalysts adsorbed onto a TiO 2coated GaInP 2 semiconductor.…”

“…The crystal face of GaP(100) terminates with a mixed phase of Ga and P sites, while GaP(111)­A and GaP(111)B consist of surfaces with predominantly atop Ga or atop P, respectively. Both faces are subject to oxidative and corrosive processes; however methods have been developed to chemically protect and passivate these otherwise structurally unstable surfaces, including treatment with (NH 4 ) 2 S x , alkylation or allylation with subsequent secondary functionalization of the A-side , and alkyl halide reactions with the P sites via a Williamson ether synthesis on the B-side …”

Sensitization of p-GaP with Monocationic Dyes: The Effect of Dye Excited-State Lifetime on Hole Injection Efficiencies

“…21−25 Recent developments in these research areas suggest that the design of photoelectrodes using GaP nanostructures with high aspect ratios can be used to increase the charge collection efficiencies. [21][22][23]25 Furthermore, the stability of the GaP surface can be improved by chemical modifications using covalent attachment of organic molecules 5,17,20 or by the deposition of a thin layer of metal oxides. 19 To expand light-harvesting efficiencies, the hole injection into p-GaP can be sensitized using organic dyes 17,26−28 or quantum dots 29 that absorb the light with wavelengths above 550 nm.…”