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The neutralization of 3 keV Li+ ions scattered from Si(lll) is measured as a function of doping density, dopant type, and hydrogen coverage. When the surfaces are saturated with hydrogen to unpin the Fermi level, the neutral fractions decrease for lightly doped samples but become anomalously large for highly doped n-type Si. A simple model that includes the many-body band-gap narrowing effect predicts the neutralization to good accuracy using a tunneling mechanism similar to the free-electron gas jellium model normally employed for ion/metal interactions, but excluding levels in the gap. [ABSTRACT FROM AUTHOR]

The high-Tc cuprate Bi-2212 is sputtered with 500 eV Ar+ ions, and changes to the surface composition are investigated with low energy (2 keV) Na+ ion scattering. It is shown that ion bombardment leads to the development of a Bi-O overlayer, differing in structure from the underlying material and making the surface highly resistant to further sputtering-induced changes. In contrast, sputtering and ion-scattering simulations would suggest that atoms from lower layers should be present at the surface as a consequence of the kinematics of the sputtering process. It is thus concluded that the Bi-O layer forms because the surfactant effects of Bi reduce the surface energy. [ABSTRACT FROM AUTHOR]

The conductivity of an Al0.24Ga0.76As/GaAs quantum well was studied as a function of the surface charge generated by electron bombardment of the sample in the absence of an externally applied surface electric field. Under a suitable rate of electron irradiation, it was possible to completely shut off the conductive channel, implying a surface density $n=2.5 \times 10^{11}\,\mbox{el/cm}^2 $. Light illumination quenches the increase of the resistivity, apparently due to photoemission from the metastable surface states. Upon turning off the electron bombardment the surface charge on adsorbed layers of xenon and water at 8 K decays in room temperature darkness with a lifetime τ= 0.30 ±0.02 s. The average charging efficiency, is μ0 ≃0.001. Surface charging is shown to be an effective method for contactless gating of field effect devices. [ABSTRACT FROM AUTHOR]

The surface charge generated on an Al0.24Ga0.76As/GaAs quantum well sample by electron bombardment was monitored by measuring the change in the conductivity of the channel. Upon turning off the electron bombardment the surface charge on adsorbed layers of xenon and water at 8 K decays in room temperature darkness with a lifetime τ=0.30±0.02 s. The average charging efficiency, μ0, defined as the ratio of the charge collected by the surface to the beam current times the charging time, is μ0≃0.001. Surface charging proves to be an effective method for contactless gating of field effect devices. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive investigation of schreibersite inclusions within iron-poor and iron-rich meteorites, and of the associated intrinsic low-temperature oxidation products observed after exposure to terrestrial weathering. First, a thermodynamic equilibrium modeling of the oxidation of schreibersite was carried out and showed that oxidation is mostly limited to the surface in the absence of other ions and/or water. This oxidation occurs rapidly (less than a few weeks) and is mediated by the atmosphere, forming primarily iron oxides and iron phosphates. Second, detailed analyses of meteorite schreibersite inclusions and synthetic schreibersite surrogates (Fe3P and Fe2NiP) were performed using surface characterization techniques such as micro-Raman spectroscopy, atomic force microscopy (AFM), electrostatic force microscopy (EFM), electron microprobe analysis (EPMA), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Such thorough analyses are required as many prebiotic reactivity studies performed use meteoritic samples that have been somewhat exposed to Earth weathering. We find that, while the meteorite samples have not been introduced directly into water, they all bear significant oxidation signatures that appear to be similar for both short-term and long-term natural weathering corrosion processes. In addition, we find that synthetic schreibersite samples have similar surface and sub-surface chemistry and are reasonable chemical proxies for natural schreibersite. The thorough analytical studies detailed in this paper provide a chemical model for schreibersite oxidation products. [ABSTRACT FROM AUTHOR]