Paper NM-MoE1
Interfacial Chemistry between gas-phase molecules and GaAs surfaces: morphology dependence

Monday, December 8, 2014, 5:40 pm, Room Hau

A detailed understanding of molecular interactions at the interface of two-dimensional GaAs systems under ultra-high vacuum (UHV) conditions has been achieved over the decades. While research on the understanding of such interactions with lower-dimensional GaAs-based structures, such as one-dimensional nanowires (NWs), has not been performed despite the potential importance of these structures in developing nano-electronic devices. Moreover, surface characterization of GaAs under more realistic conditions rather than the UHV studies, are critical in any attempt to correlate surface chemistry with device properties.

Due to recent advances in the surface characterization techniques, and especially the development of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP XPS) [1], we are able to monitor in-situ surface chemistry under elevated pressures and temperatures.

In our present work, we performed NAP XPS studies for different GaAs morphologies:

the simple planar GaAs(100) crystal and a radically non-planar GaAs surface comprised of an ensemble of GaAs NWs under elevated pressures of O₂ or H₂O molecules. The evolution of O₂ and H₂O molecule dissociation on GaAs NWs was tracked under in-situ conditions as a function of temperature and gas pressure to establish whether the processes of dissociation leading to oxidation an hydroxylation depend on surface morphology. In contrast to ideally flat GaAs single crystal surfaces [2], gas molecules experienced the enhanced dissociation on GaAs NW ensembles due to an increase in the surface area ratio and the presence of stepped edges, atom vacancies, and other defects on non-flat semiconductor surfaces [3].

The research described herein was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Basic Energy Sciences, Office of Science, United States Department of Energy through grant number DE-FC02-04ER15533.

[1] D. E. Starr, Z. Liu, M. Havecker, A. Knop-Gericke, and H. Bluhm, "Investigation of solid/vapor interfaces using ambient pressure X-ray photoelectron spectroscopy. ," Chemical Society Reviews, vol. 42, 5833-5857, 2013

[2] X. Zhang, S. Ptasinska, Dissociative Adsorption of Water on an H₂o/GaAs(100) Interface-in-Situ near Ambient Pressure XPS Studies, J. Phys. Chem. C 2014, 118, 4259-4266.

[3] X. Zhang, E. Lamere, X. Liu, J. K. Furdyna, S. Ptasinska, Morphology Dependence of Interfacial Oxidation States of Gallium Arsenide under near Ambient Conditions, Appl. Phys. Lett. 2014, 10.1063/1.4874983.