Showing papers by "Fernando Flores published in 1987"

On the formation of semiconductor interfaces

Abstract: A critical review of the different theoretical models proposed for explaining the metal-semiconductor and semiconductor-semiconductor interfaces is presented. Although no attempt to present a thorough review of the experimental evidence is made, the authors discuss the most relevant information concerning those interfaces. Their discussion concentrates mainly on the models that have received more widespread acceptance: the induced density of interface states model and the defect model. A few comments on other cases are also made, and a critical evaluation of the different models is presented.

Lifetime in a two-dimensional image-potential-induced electron band

Abstract: Lifetimes in a two-dimensional image-potential-induced electron band have been evaluated. Realistic wave functions, allowing penetration of the electron into the crystal, have been used. This results in a shorter lifetime for image electrons in the (111) noble-metal faces than in the (100) faces. Our results agree well with the recent experimental data of Geisen et al.

Inelastic proton-solid collisions.

Abstract: A first-principles calculation of charge states of moving protons in Al is presented. The many-body self-energy approach combined with ordinary atomic physics has been used. We find that at high velocities, V>2V/sub 0/ or 3V/sub 0/ (Bohr velocity), the processes are atomiclike, while at intermediate velocities, 0.7V/sub 0/

A Barrier Potential Calculation for Tunneling Electrons at a Metal-Metal Interface

Abstract: The interface potential for tunneling electrons between two interface metals has been obtained as the sum of a local and a nonlocal contribution, the last one introducing image force effects. Our results show that the image potential is the dominant effect for interface distances between metal surfaces greater than 10 A. For smaller distances, local effects control the barrier height. We have calculated this barrier height for distances between 5 and 10 A and found its value ranging between 1.2 and 2.4 eV in good agreement with other independent evidence.

Raman Scattering by Electron-Hole Pairs at Metal Surfaces

Abstract: Surface Raman scattering (SRS) by electron-hole pairs at metal surfaces has been analysed theoretically and experimentally. Our analysis, performed for a planar surface, predicts for the SRS intensity a broad peak at low temperatures, due to the excitation of e-h pairs by the polariton field penetrating into the metal. At high enough temperatures that peak disappears. Experiments performed for Ag-islands films, where SRS is more easily observed, show a qualitative agreement with our theoretical analysis.

Electronic Structure of Interfaces

Abstract: A discussion of the theoretical models trying to explain the semiconductor interfaces formation is presented. Metal-semiconductor and semiconductor-semiconductor junctions are discussed. While the metal-semiconductor interface is worse known due to the uncertainties in the chemisorption sites of the metal on the semiconductor surface, heterojunctions are better understood. We discuss the results obtained with different methods used to calculate heterojunctions band offsets: the induced density of interface states model (IDISM), the selfconsistent tight-binding model (SCTBM) and the selfconsistent local density method (SCLDM) are considered; all of them yield results in good agreement with the experimental evidence. The band offset accuracy for low ionicity semiconductors is higher in the SCLDM (better than 0.05 eV) and lower in the IDISM (better than 0.20 eV), while the SCTBM yields results with an intermediate accuracy, better than 0.1 eV.

Interpolative solution for the Anderson model of an impurity.

Abstract: We present calculations for the occupation number, the specific heat, and the density of states of the Anderson model of an impurity using an interpolative approach. The results are compared with the exact solution, showing that the interpolative method can be advantageously used for a periodic Hamiltonian.

Indirect interactions between CO molecules on transition-metal surfaces and the interpretation of thermal desorption experiments

Abstract: A model is set up for the description of the chemisorption of a CO molecule on specifically Ni, Pd and Pt surfaces. This is based on the molecular 2 pi * and 5 sigma levels lying within the metal bands, the former above the Fermi level and the latter well below. Broadening of the former into a virtual bound state which can overlap the Fermi level then leads to a situation in which it is demonstrated that one can obtain strong indirect interactions between CO molecules. The amplitude and the phase of the long-range oscillatory form B cos(2KFr+Q)/r5 for separation r between the CO molecules are thereby estimated. The results of this model are then compared with an analysis made of thermal desorption as a function of coverage for CO on Pt. Immediately the strong scattering situation predicted by the above model is revealed, with a phase shift of between pi /4 and pi /2 and a large amplitude B.

Correlation between charge and current corrugations in scanning-tunneling microscopy.

Abstract: The aim of this paper is to investigate how charge and current corrugations in scanning-tunneling microscopy are compared. A Si(111) surface is analyzed and a method to calculate tunneling currents from localized states is proposed. The main result of this model is that charge corrugations are always greater than current corrugations, although they only differ significantly for large corrugations.