The interface of GaP(100) and H2O studied by photoemission and reflection anisotropy spectroscopy

Matthias M May,Roel Van De Krol,Christian Höhn,Oliver Supplie,Hans-Joachim Lewerenz,Thomas Hannappel

doi:10.1088/1367-2630/15/10/103003

Abstract

We study the initial interaction of adsorbed H2O with P-rich and Ga-rich GaP(100) surfaces. Atomically well defined surfaces are prepared by metal-organic vapour phase epitaxy and transferred contamination-free to ultra-high vacuum, where water is adsorbed at room temperature. Finally, the surfaces are annealed in vapour phase ambient. During all steps, the impact on the surface properties is monitored with in situ reflection anisotropy spectroscopy (RAS). Photoelectron spectroscopy and low-energy electron diffraction are applied for further in system studies. After exposure up to saturation of the RA spectra, the Ga-rich (2 × 4) surface reconstruction exhibits a sub-monolayer coverage in form of a mixture of molecularly and dissociatively adsorbed water. For the p(2 × 2)/c(4 × 2) P-rich surface reconstruction, a new c(2 × 2) superstructure forms upon adsorption and the uptake of adsorbate is significantly reduced when compared to the Ga-rich surface. Our findings show that microscopic surface reconstructions of GaP(100) greatly impact the mechanism of initial interface formation with water, which could benefit the design of e.g. photoelectrochemical water splitting devices.

Highlights

We will first present our findings for the Ga-rich surface of GaP(100), as its behaviour with respect to H2O exposure has been subject of several theoretical studies [12, 13]
Ga-rich, mixed dimer surface reconstruction Ga-rich samples were prepared with metal-organic vapour phase epitaxy (MOVPE) under reflection anisotropy spectroscopy (RAS) in situ control before they were transferred to UHV
The clean surface was characterized by ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS) as well as low-energy electron diffraction (LEED)

Summary

Introduction

For adsorbed hydroxyl on the Ga-rich (2 × 4) surface reconstruction, Ga–[OH]–Ga bridge configurations and Ga–OH atop configurations are expected to be energetically most favourable, with neighbouring OH groups stabilized further by hydrogen bonding [12]. Jeon et al [13] have modelled the interaction of a single H2O molecule with the Ga-rich (2 × 4) surface reconstruction of GaP(100). They found a three-step process to be most likely, where H2O is initially adsorbed in a molecular state, dissociated into HO/H and forms Ga–O–Ga bridges desorbing molecular hydrogen. The P-rich surface reconstruction is formed of buckled P–P dimers on top, which are stabilized by one hydrogen atom per dimer.

Results

Discussion

Conclusion