A 14

Surface Science 276 (1992) 353-359 North-Holland

X-ray study of step morphology on a W(ll0) surface in air S.M. Jeong, H.W. Kim, C.Y. Kiln, S.M. Chung, K.B. Lee and J.W. Chung Department of Physics and Center for A&~anced Materials Physics, Pohang Institute of Science and Technology, Pohang 790-330, South Korea

Received 10 December, 1991; accepted for publication 9 June 1992

Using a surface sensitive X-ray scattering technique, we demonstrate that an atomic-scale surface step structure can be investigated with a sample in air. This is made clear by the observation of distinct step peaks precisely at the positions expected from the surface step geometry using a vicinal Mo(031) surface. The technique was then adopted to probe step structures on a W(I10) surface. It is found that the fine structure of a crystal truncation rod (CTR), where the vertical component of the momentum transfer varies, reveals distinct step peaks. These step features are interpreted in terms of a simple 1D model of a step structure, which shows that the surface contains steps with step heights of 1.4, 2, 4, and 7 atomic layers along the [001] direction. Results of a lineshape analysis of the in-plane and out-of-plane scans are discussed in terms of the height-height correlation lengths.

Surface Science 276 (1992) 360-368 North-Holland

High energy resonance electronic states inside a W - P d ( l l l ) tunnel junction Leszek Jurczyszyn, Maria St~licka Institute of Experimental Physics, University of Wroctaw, ul. Cybulskiego 36, 50-205 Wroctaw, Poland

and Leonard Dobrzynski Equipe lnternationale de Dynamique des Interfaces, Laboratoire de Dynamique des Cristaux Moleculaires, Unit# de Formation et de Recherche en Physique, Universit# de Lille I, 59655 l~lleneuve d'Ascq Cedex, France Received 26 February 1992; accepted for publication 16 June 1992

Distributions of density-of-states have been calculated between the electrodes of a W - P d ( I l l ) tunnel junction. The effect of the inclusion of the Pd lattice potential is discussed in detail. A comparison is also made between the results obtained using the cut-off interface potential barrier and the results of Jones, Jennings and Jepsen.

Surface Science 276 (1992) 369-387 North-Holland

Collective excitations of a quasi-one-dimensional electron gas: nonlocal response theory R.H. Yu Department of Physics, Central Washington University, Ellensburg, WA 98926, USA

and

A15

J.C. Hermanson Department of Physics, Montana State University, Bozeman, MT59717, USA

Received 4 December 1991; accepted for publication 8 May 1992

Self-consistent calculations of the subband electronic structure of semiconductor quantum wires are reported. The sample parameters were chosen to match the GaAs/AIGaAs heterostructure recently fabricated by molecular-beam epitaxy and ion milling by Weiner et al. The Schr'6dinger and Poisson equations were solved simultaneously in a rectangular waveguide geometry, using Fermi statistics for electrons at finite temperature. Calculated energy levels, wave functions, charge density, and potential differ from the predictions of the simple square well and harmonic oscillator models because of the influence of accumulation and depletion regions. The subband energies depend on the free-carrier density and the temperature as well as the band bending. Based on the self-consistently determined subband structure, the dynamical structure factor was evaluated using a noniocal description of dielectric response in the random-phase approximation at finite temperature. We obtain intersubband as well as intrasubband plasmons and discuss their dispersion relations, localization, and line shapes. The dynamical structure factor of our model quasi-one-dimensional electron gas displays unique line shapes and dispersion relations which are in sharp contrast with the results expected for higher-dimensional electron gases. Two well-defined spectral features, which are almost free of Landau damping, are found, The calculated shift of the intersubband resonance frequency, caused by the depolarization effect, agrees well with previous experiments.