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Title: Evolution of a Symmetry Gap and Synergetic Quantum Well States in Ultrathin Ag Films on Au(111) Substrates.

Abstract

Using first-principles calculations within density functional theory, we carry out a comprehensive study of how a symmetry gap around the Fermi level develops towards its bulk value as the thickness of Ag films grown on a Au(111) substrate increases. We show that, contrary to prevailing assumptions, the symmetry gap in ultrathin Ag films can be substantially wider than the gap of the Au substrate along the [111] direction. As a result, the first and second quantum well states (QWS) are confined within the Ag films only when the film thickness reaches about 10 and 19 monolayers, respectively. We further show that, when ultrathin Au films are grown on Ag(111) slabs of comparable thicknesses, synergetic QWS spanning across the whole (Au + Ag) systems are established. These results are discussed in comparison with high-resolution photoemission measurements.

Authors:
 [1];  [2];  [3];  [3];  [3];  [3];  [4]
  1. Georgia Institute of Technology
  2. Fudan University, China
  3. Universitat Wurzburg, Germany
  4. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931734
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: European Physics Letters; Journal Volume: 78; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; FERMI LEVEL; DENSITY FUNCTIONAL METHOD; PHOTOEMISSION; QUANTUM WELLS; SUBSTRATES; SYMMETRY; THICKNESS; THIN FILMS; SILVER; GOLD

Citation Formats

Huang, Li, Gong, Xingao, Gergert, E., Forster, F., Bendounan, A., Reinert, F., and Zhang, Zhenyu. Evolution of a Symmetry Gap and Synergetic Quantum Well States in Ultrathin Ag Films on Au(111) Substrates.. United States: N. p., 2007. Web. doi:10.1209/0295-5075/78/57003.
Huang, Li, Gong, Xingao, Gergert, E., Forster, F., Bendounan, A., Reinert, F., & Zhang, Zhenyu. Evolution of a Symmetry Gap and Synergetic Quantum Well States in Ultrathin Ag Films on Au(111) Substrates.. United States. doi:10.1209/0295-5075/78/57003.
Huang, Li, Gong, Xingao, Gergert, E., Forster, F., Bendounan, A., Reinert, F., and Zhang, Zhenyu. Mon . "Evolution of a Symmetry Gap and Synergetic Quantum Well States in Ultrathin Ag Films on Au(111) Substrates.". United States. doi:10.1209/0295-5075/78/57003.
@article{osti_931734,
title = {Evolution of a Symmetry Gap and Synergetic Quantum Well States in Ultrathin Ag Films on Au(111) Substrates.},
author = {Huang, Li and Gong, Xingao and Gergert, E. and Forster, F. and Bendounan, A. and Reinert, F. and Zhang, Zhenyu},
abstractNote = {Using first-principles calculations within density functional theory, we carry out a comprehensive study of how a symmetry gap around the Fermi level develops towards its bulk value as the thickness of Ag films grown on a Au(111) substrate increases. We show that, contrary to prevailing assumptions, the symmetry gap in ultrathin Ag films can be substantially wider than the gap of the Au substrate along the [111] direction. As a result, the first and second quantum well states (QWS) are confined within the Ag films only when the film thickness reaches about 10 and 19 monolayers, respectively. We further show that, when ultrathin Au films are grown on Ag(111) slabs of comparable thicknesses, synergetic QWS spanning across the whole (Au + Ag) systems are established. These results are discussed in comparison with high-resolution photoemission measurements.},
doi = {10.1209/0295-5075/78/57003},
journal = {European Physics Letters},
number = 5,
volume = 78,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • A Ag[sub 8]/Au[sub 3]/Ag[sub [ital x]] double quantum well is grown on Au(111) to form two Ag quantum wells coupled through a thin Au barrier layer, and the electronic structure of this system is examined with angle-resolved photemission. As the thickness of the outer well ([ital x], in monolayers) is varied, the measured binding energies of the quantum-well states show an avoided-crossing behavior, in good agreement with a model calculation based on Bloch wave functions. The results demonstrate the effect of electronic translayer coupling.
  • Quantum-well states have been observed with angle-resolved photoemission for Ag overlayers with thicknesses up to 40 monolayers epitaxially grown on Au(111). These states are observed within an energy window of 1 eV. The complementary system, Au on Ag(111), exhibits no such states. The results can be explained in terms of the band-structure mismatch between Au and Ag. The coherence length of the states and quasibound quantum-well resonances will be discussed.
  • Angle-resolved photoemission has been employed to examine the electronic properties of a lattice-matched, epitaxial system prepared by depositing first a thin Au(111) layer on a Ag(111) substrate, and then a Ag(111) overlayer. The Au layer acts as a potential barrier for electron motion in the system. The Ag overlayer can be regarded as a quantum well, but in our experiment, the Au barrier is rather thin, and there is substantial coupling between the valence electrons in the Ag overlayer and the continuum states in the substrate. Nevertheless, well-defined quantum-well resonances are observed for Au barriers as thin as two atomicmore » layers. These resonances can be understood as a result of partial trapping of valence electrons in the Ag overlayer. A calculation which takes into account the band structure and surface properties is carried out, and the results are in good agreement with the experiment. Initial- and final-state features in the spectra are identified by comparison with theoretical models. The effects of lattice match or mismatch at the interface will be discussed. {copyright} {ital 1996 The American Physical Society.}« less
  • We present surface x-ray-diffraction results from Pb films grown on pretreated Si(111) substrates at 110 K. Time-resolved data show that the films follow a metastable layer-by-layer growth mode. The resulting film roughness is small, allowing for a thickness-dependent study of the film layer structure and its distortion (strain) relative to the bulk. The strain arises as a result of quantum confinement of the electrons in the film, which leads to charge distortions similar to Friedel oscillations. The charge distortions in turn lead to lattice distortions, for which two models are derived based on a free-electron gas confined to a quantummore » well. Extended x-ray-reflectivity data show evidence of quasibilayer distortions in the film, which are well described by the free-electron models. Oscillations in the relaxations of the Pb layers closest to the film boundaries as a function of thickness are also observed. Calculations of the net expansion or contraction of the films as a function of thickness are made that also exhibit quasibilayer variations and are consistent with the results of previous studies.« less