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Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission

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Abstract

It is demonstrated that it is possible to investigate details of the electronic structure of an internal atomic monolayer using soft-x-ray-emission spectroscopy. The local and partial density of states of one monolayer and three monolayers of Si, embedded deep below a GaAs(001) surface, was extracted. Clear differences to the density of states for bulk Si were observed.

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... Explaining the physical properties of MAX phases requires a thorough knowledge of orbital occupation and chemical bonding, as well as the role of phonons [15,16] and electron correlation effects [17,18]. By using bulk-sensitive and element-selective X-ray spectroscopy [19,20], it is possible to differentiate between the occupation of orbitals across and along the laminate basal plane in the interior of the MAX phases. ...
... Particularly useful aspects of the XAS technique in TFY mode and the XES/RIXS techniques of great importance for probing buried layers [19] and nanolaminates such as MAX phases containing two or more different elements are the element selectivity and the large probe and information depth obtained in fluorescence yield. This makes it possible to probe partial electronic structures from the different elements in the bulk of the materials with negligible contribution from surface contamination if the samples are freshly synthesized. ...
Article
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This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibits a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M\ \C bonds in high-density MC slabs, and relatively weak M\ \A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity , elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... Explaining the physical properties of MAX phases requires a thorough knowledge of orbital occupation and chemical bonding, as well as the role of phonons [15,16] and electron correlation effects [17,18]. By using bulk-sensitive and element-selective X-ray spectroscopy [19,20], it is possible to differentiate between the occupation of orbitals across and along the laminate basal plane in the interior of the MAX phases. ...
... Particularly useful aspects of the XAS technique in TFY mode and the XES/RIXS techniques of great importance for probing buried layers [19] and nanolaminates such as MAX phases containing two or more different elements are the element selectivity and the large probe and information depth obtained in fluorescence yield. This makes it possible to probe partial electronic structures from the different elements in the bulk of the materials with negligible contribution from surface contamination if the samples are freshly synthesized. ...
Article
This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibits a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong MC bonds in high-density MC slabs, and relatively weak MA bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity, elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... For example, in a study of Si(100) buried in GaAs (similar scheme to the layer-3 in Figure 2a), it has been demonstrated that it is in fact possible to extract detailed information about DOS. 25 By irradiating the sample with a bright source, it is possible to detect characteristic fluorescence from buried layers. The ability to probe a buried structure with respect to the chemical bonding to the surrounding matrix is applied to one monolayer (ML) of Si buried at 100 Å depth in a GaAs matrix. ...
... The measured spectral profiles of Al, Si and Ge are compared to spectra of the pure elements from Refs. [11, 13, 15] (dashed lines). The Ge spectrum (bottom) was smoothed with a binomial average of the raw data. ...
Chapter
The electronic structures of the MAX–phases Ti3AlC2, Ti3SiC2 and Ti3GeC2 were investigated by soft X–ray emission spectroscopy. These nanolaminated carbide compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk–sensitive soft X–ray emission technique is shown to be particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. A weak covalent Ti–Al bond is manifested by a pronounced shoulder in the Ti L–emission of Ti3AlC2. When Al is replaced by Si or Ge, the shoulder disappears. Furthermore, the spectral shapes of Al, Si and Ge in the MAX–phases are strongly modified in comparison to the corresponding pure elements. By varying the constituting elements, a change of the electron population is achieved causing a change of covalent bonding between the laminated layers, which enables control of the macroscopic properties of the material.
Chapter
IntroductionElectronic Structure of Nanostructured MaterialsSoft X-Ray Process and SpectroscopyChemical Sensitivity of X-Ray SpectroscopyFullerenes and Carbon NanotubesBuried Atomical Layers and InterfacesNanostructured 3d Transition Metal OxidesAcknowledgmentsReferences
Chapter
In this chapter, we introduce the basics of soft x-ray absorption (XAS) and emission spectroscopy (XES), and resonant inelastic soft x-ray scattering (RIXS) followed by description of instrumentation including beamline, ensdtation, and spectrometer. Chemical cells are designed for in-situ electronic structure study of samples in gas or liquid environment. The application of XAS, XES, and RIXS on TiO2 crystals of rutile and anatase phases have yielded characteristic fingerprints that provide the information on geometric structure, bandgap, doping effects. A number of in-situ electronic structure studies are also addressed.
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We examine the stability of pseudomorphic submonolayer Si films embedded in (001) GaAs by molecular‐beam epitaxy. Secondary ion‐mass spectrometry depth profiling reveals the presence of 10<sup>19</sup> Si‐atoms/cm<sup>3</sup> in the first 40 nm of the GaAs cap layer. The systematic investigation of samples having different cap thickness by Hall effect measurements and local vibrational mode Raman spectroscopy allows us to identify the site distribution of Si atoms in the cap layer and yields insight into the migration mechanism.
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GaAs has been grown on pseudomorphic Si (100) surfaces and (100) surfaces misoriented 4° toward [011] and [001] in order to study the quality of the GaAs on Si interface in the absence of misfit dislocations. We obtain completely two‐dimensional single‐domain GaAs epitaxy after only 80 Å of deposition as observed by in situ high‐energy electron diffraction. Transmission electron microscopy verifies that the GaAs grown on pseudomorphic Si is free of antiphase domains and other notable defects.
Article
We have measured the soft-x-ray–emission L2,3 spectra of c-Si and a-Si:H and removed the shakeup and bremsstrahlung contributions using the method of Livins and Schnatterly [Phys. Rev. B 37, 6731 (1988); 37, 6742 (1988)]. We have obtained an estimate of the real part of the self-energy describing the effect of the random potential which characterizes a-Si:H on the c-Si transition density of states (TDOS), using an approach based on Dyson’s equation. This approach also yields the TDOS of c-Si and a-Si:H outright. In addition, we resolve the spectra into L2 and L3 components using an iterative procedure and remove an estimate of the intrinsic broadening effects, and thereby obtain a second determination of the TDOS. These results and those obtained through the procedure based on Dyson’s equation agree. The TDOS obtained for c-Si compares well with calculations.
Article
Soft x-ray emission spectroscopy is for the first time applied to surfaces and adsorbates. Surface sensitivity is achieved by employing synchrotron radiation in grazing incidence for the excitation. We present O K emission from adsorbed atomic oxygen on Ni(100) and Cu(100) and molecular CO on Ni(100). The observed spectral features correspond to the occupied 2p partial density of states of the adsorbates.
  • J Englund
  • Nordgren
Englund, and J. Nordgren, Rev. Sci. Instrum. 66, 1561 (1995).
  • E G See
  • J.-E Rubensson
  • D Mueller
  • R Shuker
  • D L Erderer
  • C H Zhang
  • J Jia
  • T A Calcott
  • E Z Kurmaev
  • G Wiech
See, e.g., J.-E. Rubensson, D. Mueller, R. Shuker, D. L. Erderer, C. H. Zhang, J. Jia, and T. A. Calcott, Phys. Rev. Lett. 64, 1047 (1990); E. Z. Kurmaev and G. Wiech, J. Non-Cryst. Solids 70, 187 (1985); P. A. Bruhweiler and S. E. Schnatterly, Phys. Rev. B 39, 12 649 (1989), and references therein.
  • E G See
  • D J.-E. Rubensson
  • R Mueller
  • D L Shuker
  • C H Erderer
  • J Zhang
  • T A Jia
  • Calcott
See, e.g., J.-E. Rubensson, D. Mueller, R. Shuker, D. L. Erderer, C. H. Zhang, J. Jia, and T. A. Calcott, Phys. Rev. Lett. 64, 1047 (1990);
  • P A Bruhweiler
  • S E Schnatterly
P. A. Bruhweiler and S. E. Schnatterly, Phys. Rev. B 39, 12 649 (1989), and references therein.