Physisorption of an electron in deep surface potentials off a dielectric surface

We study phonon-mediated adsorption and desorption of an electron at dielectric surfaces with deep polarization-induced surface potentials where multi-phonon transitions are responsible for electron energy relaxation. Focusing on multi-phonon processes due to the nonlinearity of the coupling between the external electron and the acoustic bulk phonon triggering the transitions between surface states, we calculate electron desorption times for graphite, MgO, CaO, (\text{Al}_2\text{O}_3), and (\text{SiO}_2) and electron sticking coefficients for (\text{Al}_2\text{O}_3), CaO, and (\text{SiO}_2). To reveal the kinetic stages of electron physisorption, we moreover study the time evolution of the image state occupancy and the energy-resolved desorption flux. Depending on the potential depth and the surface temperature we identify two generic scenarios: (i)adsorption via trapping in shallow image states followed by relaxation to the lowest image state and desorption from that state via a cascade through the second strongly bound image state in not too deep potentials and (ii)adsorption via trapping in shallow image states but followed by a relaxation bottleneck retarding the transition to the lowest image state and desorption from that state via a one step process to the continuum in deep potentials.Comment: 12 pages, 7 figure

Growth studies on Si0.8Ge0.2 channel two-dimensional hole gases

We report a study of the influences of MBE conditions on the low-temperature mobilities of Si/Si0.8Ge0.2 2DHG structures. A significant dependence of 2DHG mobility on growth temperature is observed with the maximum mobility of 3640 cm2 V−1 s−1 at 5.4 K being achieved at the relatively high-growth temperature of 640 °C. This dependence is associated with a reduction in interface charge density. Studies on lower mobility samples show that Cu contamination can be reduced both by growth interruptions and by modifications to the Ge source; this reduction produces improvements in the low-temperature mobilities. We suggest that interface charge deriving from residual metal contamination is currently limiting the 4-K mobility

Electron surface layer at the interface of a plasma and a dielectric wall

We study the potential and the charge distribution across the interface of a plasma and a dielectric wall. For this purpose, the charge bound to the wall is modelled as a quasi-stationary electron surface layer which satisfies Poisson's equation and minimizes the grand canonical potential of the wall-thermalized excess electrons constituting the wall charge. Based on an effective model for a graded interface taking into account the image potential and the offset of the conduction band to the potential just outside the dielectric, we specifically calculate the potential and the electron distribution for magnesium oxide, silicon dioxide and sapphire surfaces in contact with a helium discharge. Depending on the electron affinity of the surface, we find two vastly different behaviors. For negative electron affinity, electrons do not penetrate into the wall and an external surface charge is formed in the image potential, while for positive electron affinity, electrons penetrate into the wall and a space charge layer develops in the interior of the dielectric. We also investigate how the electron surface layer merges with the bulk of the dielectric.Comment: 15 pages, 9 figures, accepted versio

Back gating of a two-dimensional hole gas in a SiGe quantum well

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3

QUANTITATIVE NON-DESTRUCTIVE NEUTRON ACTIVATION ANALYSIS OF SILVER IN COINS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65909/1/j.1475-4754.1967.tb00617.x.pd

Scaling and the Metal-Insulator Transition in Si/SiGe Quantum Wells

The existence of a metal-insulator transition at zero magnetic field in two- dimensional electron systems has recently been confirmed in high mobility Si-MOSFETs. In this work, the temperature dependence of the resistivity of gated Si/SiGe/Si quantum well structures has revealed a similar metal- insulator transition as a function of carrier density at zero magnetic field. We also report evidence for a Coulomb gap in the temperature dependence of the resistivity of the dilute 2D hole gas confined in a SiGe quantum well. In addition, the resistivity in the insulating phase scales with a single parameter, and is sample independent. These results are consistent with the occurrence of a metal-insulator transition at zero magnetic field in SiGe square quantum wells driven by strong hole-hole interactions.Comment: 3 pages, 3 figures, LaTe

Surface electrons at plasma walls

In this chapter we introduce a microscopic modelling of the surplus electrons on the plasma wall which complements the classical description of the plasma sheath. First we introduce a model for the electron surface layer to study the quasistationary electron distribution and the potential at an unbiased plasma wall. Then we calculate sticking coefficients and desorption times for electron trapping in the image states. Finally we study how surplus electrons affect light scattering and how charge signatures offer the possibility of a novel charge measurement for dust grains.Comment: To appear in Complex Plasmas: Scientific Challenges and Technological Opportunities, Editors: M. Bonitz, K. Becker, J. Lopez and H. Thomse

IDENTIFICATION OF THE GEOLOGIC ORIGINS OF ARCHAEOLOGICAL ARTIFACTS: AN AUTOMATED METHOD OF Na and Mn NEUTRON ACTIVATION ANALYSIS

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66345/1/j.1475-4754.1967.tb00618.x.pd

Coexistence of Weak Localization and a Metallic Phase in Si/SiGe Quantum Wells

Magnetoresistivity measurements on p-type Si/SiGe quantum wells reveal the coexistence of a metallic behavior and weak localization. Deep in the metallic regime, pronounced weak localization reduces the metallic behavior around zero magnetic field without destroying it. In the insulating phase, a positive magnetoresistivity emerges close to B=0, possibly related to spin-orbit interactions.Comment: 4 pages, 3 figure