Inherent charge transfer layer formation at La0.6Sr0.4FeO3∕La0.6Sr0.4MnO3 heterointerface
Hiroshi KumigashiraDaisuke KobayashiR. HashimotoAkira ChikamatsuM. OshimaN. NakagawaTsuyoshi OhnishiMikk LippmaaHiroki WadatiA. FujimoriK. ÔnoM. KawasakiHideomi Koinuma
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Abstract:
We have investigated the Mn3d spectral function in La0.6Sr0.4FeO3(LSFO)∕La0.6Sr0.4MnO3(LSMO) heterointerfaces as well as of La1−xSrxMnO3 films using Mn2p−3d resonant photoemission spectroscopy. The strong enhancement of the Mn3d spectra at the Mn2p−3d threshold enables us to extract the Mn3d spectra of LSMO layers in the vicinity of the interface with the LSFO overlayers. We have found that the spectral intensity of eg↑ states near the Fermi level is gradually reduced with increasing LSFO overlayer thickness and is finally saturated at 5–7ML. The close similarity in reduction of the intensity of the eg↑ states between the LSFO∕LSMO interface and hole-doped LSMO films indicates the occurrence of charge transfer at the interface between the LSMO and LSFO layers.Keywords:
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The electronic structure at the interface between bathocuproine (BCP) and a metal was studied by ultraviolet photoemission spectroscopy (UPS). For Ag, Al, Mg, and Ca, interface states were observed near the Fermi level. On the other hand, no interface states were observed for Au. The intensities of the interface states increase with decreasing metal work function. It is suggested that the interface states play an important role in electron transport at the interface. It was found that the energy difference between the BCP vacuum level and the metal Fermi level is almost constant. This phenomenon is similar to the Schottky barrier pinning observed at a metal/semiconductor interface. The cause of this phenomenon is discussed.
Inverse photoemission spectroscopy
Vacuum level
Ultraviolet photoelectron spectroscopy
Fermi energy
Ultraviolet
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The electronic structures of pristine and Cs-doped CuPc films are investigated using photoemission spectroscopy and inverse photoemission spectroscopy (IPES). The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital can be directly observed by IPES and ultraviolet photoemission spectroscopy simultaneously. We found that the Fermi-level position in organic film can be modified by Cs doping. The observed onset of the LUMO of the CuPc film is shifted by Cs doping to less than 0.2 eV above the Fermi level. The result indicates that the energy alignment and charge injection properties of the organic materials can be modified by a simple doping process.
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Inverse photoemission spectroscopy
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Organic semiconductor
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Ultraviolet photoemission spectroscopy has been employed to provide information on the valence band of the Heusler alloy. The contribution of the d bands of Mn and Cu to the density of states has been investigated by means of 3p to 3d resonant enhancement. The valence band extends to 6 eV below the Fermi level, with a main peak at a binding energy of 3.2 eV and a shoulder extending to the Fermi edge. Resonant photoemission indicates that the Mn 3d character extends across the full width of the band. An experimental photoemission spectrum obtained at a photon energy of 40 eV has been compared with a calculated spectrum derived from a theoretical band structure. The main difference occurs in the region 1 - 2 eV below the Fermi level. The calculated spectrum exhibits a peak at a binding energy of 1.5 eV, comprising contributions from both the Cu and Mn 3d bands. There is no evidence of a similar feature in the experimental spectrum.
Inverse photoemission spectroscopy
Density of states
Ultraviolet
Photon energy
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The surface reactions that occur when adatoms of La are deposited onto the high-temperature superconductor YBa2Cu3O6.9 have been studied using high-resolution synchrotron radiation photoelectron spectroscopy and inverse photoelectron spectroscopy. These adatoms lead to the depletion of oxygen from the substrate as La-O forms at low coverage. The process of oxygen withdrawal quickly becomes kinetically limited as the thickening overlayer impedes mass transfer. At the same time, Cu atoms released from the disrupted, no-longer- superconducting substrate outdiffuse into, and segregate to the top of, the growing La overlayer. The complex reacted interface, therefore, exhibits phases which are likely to be superconducting, insulating, and metallic.
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The interface formation of Cr/NH3/GaAs(100) and its temperature dependence using synchrotron radiation photoemission and resonance photoemission spectroscopies have been investigated. We observed that at T=90 K the initial deposition of Cr stimulated nitridation of the GaAs substrate and subsequent interface reaction was characterized by Cr-induced substrate disruption. Annealing of the thus formed interface to room temperature and above caused further Cr–GaAs reaction. The metallicity of the Cr overlayer was examined using constant initial-state spectroscopy (CIS) of Cr 3d with Ei=1.7 eV below the Fermi level. The CIS spectra showed a maximum at the photon energy hν=50.0 eV followed by a second broad maximum centered at hν=56–58 eV depending on the stage of the interface formation. As the nominal Cr coverage increases from 1 to 10 Å, the valence band photoemission spectra show a shift of the Cr 3d band toward the Fermi level. At the same time, the second maximum in CIS gradually dominates over the first, suggesting the evolution of the Cr overlayer to a more metallic state. The sensitivity of the second maximum in its peak position and intensity to the density of states near the Fermi level indicates that this maximum likely results from many body electron interactions. The results show that CIS can provide valuable information about the transition of a thin overlayer to a metallic state.
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Inverse photoemission spectroscopy
Density of states
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Ultraviolet
Inverse photoemission spectroscopy
Ultraviolet photoelectron spectroscopy
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Photoemission spectroscopy is used to study chemistry and band bending at the Ca-GaAs(110) interface as a function of metal coverage. An intermediate position of the Fermi level (EF ) resulting from the formation of adsorbate-induced states and native defects is found at low coverage at 0.75–0.9 eV above the top of the valence-band maximum (VBM). An additional abrupt shift of EF leading to a final position 0.55 eV above VBM takes place when metallicity develops in the overlayer. The results for this interface supports Schottky-barrier models based on gap states induced or modified by the metal.
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Band bending
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Chemisorption
Electron spectroscopy
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Ultraviolet
Inverse photoemission spectroscopy
Ultraviolet photoelectron spectroscopy
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Fermi level (Ef ) movement and overlayer metallization at room temperature (RT) and 110 K low-temperature (LT) Cs/GaAs (110) interfaces are studied using photoemission. Initial p-type GaAs band bending is attributed to the surface donor states that originate from Cs atom chemisorption. The Ef stabilization at RT and LT is interpreted in terms of defects and the metal-induced gap states and the interplay between them. For the latter to dominate, fewer defects and establishment of overlayer metallicity are necessary.
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Chemisorption
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