Physicochemical and Electrochemical Properties of Etched GaP(111)A and GaP(111)B Surfaces

Abstract

The observable chemical, electrochemical, and morphological features of GaP͑111͒ surfaces after wet chemical etching have been assessed using X-ray photoelectron spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy. HF͑aq͒, NH 4 F͑aq͒, H 2 SO 4 ͑aq͒, HCl͑aq͒, HCl-HNO 3 ͑aq͒, and dilute Br 2 in CH 3 OH ͑with and without a follow-up alkaline etch͒ are all potent etchants for GaP͑111͒ but yield distinctly different GaP͑111͒A and GaP͑111͒B surface conditions. Freshly etched GaP͑111͒B interfaces show higher residual oxide coverages and are generally rougher than similarly treated GaP͑111͒A surfaces. Differential capacitance measurements of n-GaP͑111͒A and n-GaP͑111͒B electrodes show that various etchants result in a wide range of apparent values for the conduction bandedge potentials, spanning approximately 700 mV in acetonitrile. These data show that these etched surfaces are not equivalent and that the observable physicochemical and electrochemical properties of GaP͑111͒ are strongly influenced by the choice of wet chemical etchant. Additionally, X-ray photoelectron spectra show that adsorption of ͑4-fluorophenyl͒methanethiol onto GaP͑111͒ is insensitive to surface orientation or etching method, indicating no dominant covalent interaction between organic thiols and GaP͑111͒ interfaces.

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

“…The former signal suggested phosphate-type oxides. 14,25,32 The latter signal could be seen more definitively in the difference spectrum and was assigned to with P−OH surface moieties remaining on the surface after wet etching. 24, 25 Still, in the context of the present study, we further wished to establish whether the predominant surface reactivity was more oxide-like rather than phosphinelike (i.e., bonding through bare atop P atoms).…”

Annealing of gold nanoparticles on GaP(111)B: initial stage of GaP nanowire growth

“…Therefore, we included O 2 plasma and cleaned the substrate in four different ways. This led to various oxides on it: original oxides of the ‘epi‐ready' substrate (A), fresh native oxides as aqueous HF solutions remove oxides from GaP 22, 23 (B and D), and additional oxides created by O 2 plasma via O 2 ‐diffusion 24 (C).…”

Dye Sensitization of n and p Type Gallium Phosphide Photoelectrodes

“…Prior to photoelectrochemical measurements the GaP crystal was polished for 5 min with a soft polishing cloth using 20 nm colloidal silica (Buehler, Inc) to remove the native oxide layer and rinsed with MilliQ 18 M water, followed by an etch in fresh aqua regia (HCl : H 2 SO 4 = 3 : 1 volume ratio) to remove the thin oxide layer. 8,9 Rhodamine 6G (Rh-6G) (ACROS), Rhodamine B (Rh-B) (EAST-MAN), Cresyl Violet Perchlorate (Kodak), Nile Blue A Perchlorate (Kodak) and Crystal Violet (Kodak) were used as received. Cyclic voltammetry, with 2.5 mM dyes and 50 mM supporting electrolyte (tetrabutylammonium hexafluorophosphate (Fluka)) in acetonitrile under inert atmosphere (glove box), was used measure the reduction and the oxidation potentials of the dye molecules.…”