Dissociative Adsorption of Water on an H₂O/GaAs(100) Interface: In Situ Near-Ambient Pressure XPS Studies

Abstract

Dissociative water adsorption on a GaAs(100) surface is demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under near-ambient conditions. These in situ XPS studies enable us to monitor the evolution of water dissociation on GaAs under elevated pressures and temperatures for the first time. In pressure-dependent XPS studies, the GaAs surface was exposed to room-temperature water vapor at pressures ranging from UHV to 5 mbar. With an increase in H 2 O pressure, enhancement of oxygenation and hydroxylation of surface Ga atoms is observed. In addition, strong XPS signals are also detected that originate from water molecules that are molecularly adsorbed onto the GaAs surface and hydrogen-bonded to surface OH species. Peak broadening and shifts in the As 2p XPS spectra are correlated with the signal increase resulting from surface HO−Ga species, suggesting the formation of surface H−As bonds. In temperature-dependent XPS studies, the GaAs surface was annealed from room temperature up to 773 K at a water vapor pressure of 0.1 mbar. The temperature increase leads to desorption of weakly adsorbed water molecules or their dissociation, resulting in surface Ga oxidation. However, no changes in chemical state of the surface As atoms are observed at higher temperatures.

Comparison of the Stability of Functionalized GaN and GaP

“…This was supported by the shifting of the O1 s spectra from 533 eV (corresponding to -OH termination) to 531 eV (corresponding to -O-type bonding). [5,62,65] Subsequent soaking forms gallium-rich oxide species for etchants not capped with hydrogen peroxide, whereas those capped continue to form gallium-deficient sub-oxides.…”

“…[17,43,73,74] Given enough time, gallium oxides would have limited subsequent leaching because by simply soaking the surface, it becomes more gallium-rich. Despite the reported insolubility of gallium oxide formations, the fact that water spontaneously dissociates when in contact with these materials [63,65] ultimately controls the degree of stability that appears similar to one another.…”

How Indium Nitride Senses Water

“…at 533.6 eV on the other hand represents molecular water at the InN surface due to previous exposure to humidity. 21,22 A decrease in the spectral weight of peak 'iii' results from continuous desorption of water by the X-ray beam. This resulted in a shift of the main O 1s core level (peak 'i'), as well as the main peaks in the In 4d ( Fig.…”

Adsorption and dissociation of H2O on the Ga-rich GaAs(001)-(4×2) surface: DFT and DFT-D computations with a Ga7As8H11 cluster model

“…The corresponding adsorption and decomposition mechanisms were elucidated experimentally and theoretically [4,5]. As to the interactions of H 2 O with the GaAs surfaces, different mechanisms were obtained with different GaAs surfaces and experimental conditions [6][7][8][9][10][11][12][13][14]. The dissociation of H 2 O on the GaAs surface was found due to the formation of the Ga-O bond [7,[11][12][13][14].…”

“…As to the interactions of H 2 O with the GaAs surfaces, different mechanisms were obtained with different GaAs surfaces and experimental conditions [6][7][8][9][10][11][12][13][14]. The dissociation of H 2 O on the GaAs surface was found due to the formation of the Ga-O bond [7,[11][12][13][14]. For example, Chung and coworkers [13] studied the adsorption, desorption, and decomposition mechanisms of H 2 O on the GaAs(0 0 1)-(4 Â 2) surface with the temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and Auger electron spectroscopy (AES).…”