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Title: Adsorption of alkali metals on Ge(001)(2×1) surface

Abstract

Ab initio total energy calculations have been performed for Na, K and Rb adsorption on Ge(001)(2?1) surface. It was found that the adsorption site of AM is AM size dependent. Structural analysis showed that the Ge-Ge dimer bond becomes stronger with increasing AM size. As the coverage increases from 0.5 to 1 ML it turns out that no depolarization effect occurs upon Na adsorption, while this effect become more important with increasing AM size. We also found that for all adsorption systems investigated the germanium surface is metallic and semiconducting for the coverage of 0.5 and 1 ML, respectively.

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
877578
Report Number(s):
PNNL-SA-46784
Journal ID: ISSN 0009-2614; CHPLBC; 8208; KC0201020; TRN: US200608%%427
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemical Physics Letters; Journal Volume: 417; Journal Issue: 1-3
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ADSORPTION; GERMANIUM; SURFACE PROPERTIES; RUTHERFORD BACKSCATTERING SPECTROSCOPY; SODIUM; POTASSIUM; RUBIDIUM; DIMERS; Alkali metals; Surface Adsorption; Ge(001) surface; Environmental Molecular Sciences Laboratory

Citation Formats

Xiao, H Y., Zu, Xiaotao, Zhang, Yanfeng, and Gao, Fei. Adsorption of alkali metals on Ge(001)(2×1) surface. United States: N. p., 2006. Web. doi:10.1016/j.cplett.2005.09.103.
Xiao, H Y., Zu, Xiaotao, Zhang, Yanfeng, & Gao, Fei. Adsorption of alkali metals on Ge(001)(2×1) surface. United States. doi:10.1016/j.cplett.2005.09.103.
Xiao, H Y., Zu, Xiaotao, Zhang, Yanfeng, and Gao, Fei. Mon . "Adsorption of alkali metals on Ge(001)(2×1) surface". United States. doi:10.1016/j.cplett.2005.09.103.
@article{osti_877578,
title = {Adsorption of alkali metals on Ge(001)(2×1) surface},
author = {Xiao, H Y. and Zu, Xiaotao and Zhang, Yanfeng and Gao, Fei},
abstractNote = {Ab initio total energy calculations have been performed for Na, K and Rb adsorption on Ge(001)(2?1) surface. It was found that the adsorption site of AM is AM size dependent. Structural analysis showed that the Ge-Ge dimer bond becomes stronger with increasing AM size. As the coverage increases from 0.5 to 1 ML it turns out that no depolarization effect occurs upon Na adsorption, while this effect become more important with increasing AM size. We also found that for all adsorption systems investigated the germanium surface is metallic and semiconducting for the coverage of 0.5 and 1 ML, respectively.},
doi = {10.1016/j.cplett.2005.09.103},
journal = {Chemical Physics Letters},
number = 1-3,
volume = 417,
place = {United States},
year = {Mon Jan 09 00:00:00 EST 2006},
month = {Mon Jan 09 00:00:00 EST 2006}
}
  • First-principles calculations based on DFT-GGA method have been performed on rubidium adsorption on Si(001)(2?1) surface. The atomic and electronic structures of Si(001)(2?1)-Rb have been calculated and compared with those of Cs adsorption (J.Chem. Phys.122 (2005) 174704). It turns out that the saturation coverage of Rb is one monolayer rather than half a monolayer, similar to that of Cs adsorption. Comparison of Rb on Si(001)(2?1) with Cs adsorption showed that at saturation coverage larger alkali metal (AM) atom leads to stronger AM-AM interaction and weaker AM-Si interaction. However, for low coverage of 0.25 and 0.5 ML the Rb-Si interaction is surprisinglymore » weaker than Cs-Si interaction. Further detailed analysis suggested that this is a consequence of depolarization effect with decreasing AM size below 1 ML coverage. For the saturation coverage the dispersion curves show that the surface is of semi-conducting character. This result does not support the direct and inverse angle-resolved photoemission investigation where a metallization is observed at saturation coverage.« less
  • Synchrotron-radiation-excited angle-resolved photoelectron spectra of the Ge(001)-(2 x 1) reconstructed surface reveal two surface states 0.6 and 1.3 eV below the bulk valence-band maximum at the GAMMA point of the surface Brillouin zone. These two states are similar to those observed previously for Si(001) and GaAs(001) surfaces. The dispersion of the Ge bands with k/sub parallel/ is qualitatively in agreement with the calculations of Chadi using his asymmetric dimer model for Si(001)-(2 x 1).
  • Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2[times]1 by cyclic gas-source molecular beam epitaxy from Si[sub 2]H[sub 6] has been investigated using [ital in] [ital situ] reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy, electron-energy-loss spectroscopy, and scanning tunneling microscopy, combined with post-deposition high-resolution cross-sectional transmission electron microscopy. The layers were deposited using repetitive cycles consisting of saturation Si[sub 2]H[sub 6] dosing at room temperature, followed by annealing for 1 min at 550 [degree]C. Film growth was observed to proceed via a mixed Stranski--Krastanov mode. Single-step-height two-dimensional growth was obtained for nominal Si depositionmore » thicknesses [ital t][sub Si] up to [congruent]1.5 monolayers (ML). However, the upper layer remained essentially pure Ge which segregated to the surface through site exchange with deposited Si as H was desorbed. At higher [ital t][sub Si], the Ge coverage decreased slowly, the surface roughened, and two-dimensional multilayer island growth was observed for [ital t][sub Si] up to [congruent]7.5 ML, where bulk reflections in RHEED patterns provided evidence for the evolution of three-dimensional island formula.« less
  • Si{sub 1{minus}x}Ge{sub x} layers with {ital x} ranging from 0 to 0.30 were grown on Si(001)2{times}1 substrates at temperatures ranging from 450 to 950thinsp{degree}C by gas-source molecular-beam epitaxy (GS-MBE) from Si{sub 2}H{sub 6} and Ge{sub 2}H{sub 6}. In the low-temperature surface-reaction-limited growth regime, the deposition rate R{sub SiGe} increases with increasing Ge concentration due to an enhancement in the hydrogen desorption rate resulting in a correspondingly higher steady-state dangling bond density. In the high-temperature impingement-flux-limited regime, where the steady-state hydrogen coverage approaches zero, R{sub SiGe} is controlled by the Si{sub 2}H{sub 6} and Ge{sub 2}H{sub 6} reactive sticking probabilities {italmore » S} which decrease with increasing Ge{sub 2}H{sub 6} flux but are not strongly temperature dependent. S{sub Si{sub 2}H{sub 6}} and S{sub Ge{sub 2}H{sub 6}} range from 0.036 and 0.28 on Si(001) to 0.012 and 0.094 during growth of Si{sub 0.82}Ge{sub 0.18} at T{sub s}=800thinsp{degree}C. In both growth regimes, large changes in R{sub SiGe} require only modest increases in incident Ge{sub 2}H{sub 6} to Si{sub 2}H{sub 6} flux ratios, J{sub Ge{sub 2}H{sub 6}}/J{sub Si{sub 2}H{sub 6}}, due to Ge segregation which is strongly coupled to the steady state hydrogen coverage. The Ge to Si ratio in as-deposited films increases linearly, while S{sub Ge{sub 2}H{sub 6}}/S{sub Si{sub 2}H{sub 6}} remains constant, with increasing J{sub Ge{sub 2}H{sub 6}}/J{sub Si{sub 2}H{sub 6}}. Hydrogen desorption and Ge segregation rates, together with Si{sub 2}H{sub 6} and Ge{sub 2}H{sub 6} reactive sticking probabilities, were quantitatively determined from D{sub 2} temperature-programmed desorption (TPD) measurements. The combined results from film growth kinetics and TPD studies, together with the assumption of linear superposition, were then used to develop a predictive model, with no fitting parameters, for R{sub SiGe}(T{sub s},J{sub Si{sub 2}H{sub 6}},J{sub Ge{sub 2}H{sub 6}}) during Si{sub 1{minus}x}Ge{sub x} GS-MBE. {copyright} {ital 1998 American Institute of Physics.}« less
  • The surface structure of (2 x 1)S/Ge(001) was determined using the angle-resolved photoemission extended-fine-structure technique in the normal-emission direction. By comparison of the experimental data with curved-wave, multiple-scattering calculations, quantitative information about the local adsorption geometry was obtained. In particular, adsorption in a twofold bridge site, with a S-Ge bond length of 2.36 +- 0.05 A, was found. The twofold S bridge appears most likely to occur between two partially intact symmetric Ge-Ge dimers, with the Ge dimer laterally displaced by 0.10 +- 0.05 A from the bulk position. This result therefore provides evidence for S bonding to strong danglingmore » bonds in the original dimers of the clean Ge(001) surface. There is, however, no evidence of significant surface contraction or expansion in the substrate layers, in contrast to the (2 x 2)S/Ge(111) case.« less