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The present work deals with localized dissolution processes (pit and pore initiation and growth) of p-and n-type (100) GaAs. Pit and pore growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized dissolution is only observed if a passivating film is present on the surface, otherwise, e.g., in acidic solutions, the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, localized dissolution (pitting corrosion) and pore formation on n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p-and a space charge layer in the case of the n-GaAs). The porous structure was characterized by scanning electron microscopy, energy dispersive x-ray analysis, and Auger electron spectroscopy, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For ntype material, atomic force microscopy investigations show that light induced roughening of the order of several hundred nanometers occurs under nonpassivating conditions. This nanometer-scale roughening however does not affect the pitting process.

The treatment of Ge(100) in an aqueous ammonium sulfide solution is investigated by means of x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. This treatment is shown to produce an S-passivated Ge(100)-(1×1) surface, where the S atoms appear to be bridge bonded to the Ge atoms. Desorption of the S is observed to occur between 460 and 750 K and results in a Ge(100)-(1×1) surface with a surface morphology similar to that of the initial sample.

It is found that an ordered and air-stable GaAs͑111͒A-͑1ϫ1͒-Cl surface can be produced by chemical etching/passivation with dilute HCl solution. The synchrotron polarization-dependent Cl K-edge x-ray absorption near-edge structure and x-ray photoelectron spectroscopy studies showed that the surface is terminated with Ga-Cl bonds oriented along the surface normal. Low-energy electron diffraction studies showed a bulklike ͑1ϫ1͒ structure on the Cl-terminated GaAs͑111͒A surface. The Cl termination eliminates surface band-gap states caused by surface oxides. Photoluminescence measurements showed a dramatic increase in the near-band radiative emission rate corresponding to reduction in the occupied surface band-gap states. A reduction of surface gap states by Cl termination was confirmed by surface photovoltage measurements.

Hydrogen gas production during corrosion of copper by water Hultquist, G.; Graham, M. J.; Szakalos, P.; Sproule, G.I.; Rosengren, A.; Gråsjö, L.Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca.