| 1. |
- Qvarford, M, et al.
(author)
-
Photoemission and x-ray absorption study of superconducting and semiconducting Ba1-xKxBiO3 single crystals
- 1996
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:9, s. 6700-6707
-
Journal article (peer-reviewed)abstract
- Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence band photoelectron spectroscopy and O K edge x-ray absorption spectroscopy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but the intensity near the Fermi level, was lower in the experimental spectrum as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-metal transition of this system is of a different nature than that of the hole doped cuprate high-T-c superconductors. The core level photoemission spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry resulting in a resolved high binding energy shoulder in the Bi 4f spectrum. The origin of this feature is discussed.
|
|
| 2. |
- Wigren, C., et al.
(author)
-
Sm- and Yb-induced reconstructions of the Si(111) surface
- 1993
-
In: Physical Review B. - 0163-1829. ; 48:15, s. 11014-11019
-
Journal article (peer-reviewed)abstract
- Low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy results from the submonolayer Sm- and Yb-induced surface structures are presented. Several similar metal-induced surface reconstructions are found to exist for Yb and Sm on Si(111) for low submonolayer coverages: 3×2, 5×1, and 7×1. At higher submonolayer coverage, Yb induces a 2×1 reconstruction while Sm induces a (3 × 3) R30°-like reconstruction. Yb is found to be divalent in all structures, whereas the Sm valence increases with increasing coverage. In the 3×2 structure only divalent Sm is present, in the 5×1 and 7×1 structures a small amount of trivalent Sm appears, and, finally, in the (3 × 3) R30°structure approximately half of the Sm atoms are trivalent. The surface Fermi-level position in the band gap for the different Sm and Yb reconstructions has been measured. The difference in valence stability between Sm and Yb is suggested to be the cause of the difference in the high-coverage structures found and the differences in pinning level for the two elements observed for the 5×1 and 7×1 structures. © 1993 The American Physical Society.
|
|
| 3. |
- Andersson, C B M, et al.
(author)
-
Bulk and surface electronic structure of InAs(110)
- 1998
-
In: Surface Science. - 0039-6028 .- 1879-2758. ; 398:3, s. 395-
-
Journal article (peer-reviewed)abstract
- The InAs(110) cleavage surface has been investigated by angle-resolved photoelectron spectroscopy. A separation between the In 4d(5/2) bulk component and the valence band maximum of 16.8 eV is found to be consistent with normal emission spectra. Experimental energy band dispersions, E-i(k), for the four bulk valence bands are established along the Sigma-line of the bulk Brillouin zone. A bulk band structure calculation utilizing the augmented plane-wave method is made. The experimental and calculated E-i(k) dispersions are found to be in good agreement with each other. E-i(k(parallel to)) dispersions for two surface-related structures are established along the lines <(Gamma)over bar>-(M) over bar and (Y) over bar-(M) over bar of the surface Brillouin zone. (C) 1998 Elsevier Science B.V.
|
|
| 4. |
- Nyholm, R., et al.
(author)
-
ELECTRONIC AND STRUCTURAL-PROPERTIES OF THE CU-BI2CASR2CU2O8 INTERFACE
- 1991
-
In: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 180:1-4, s. 120-123
-
Journal article (peer-reviewed)abstract
- The formation of the Cu-Bi2CaSr2Cu2O8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi2CaSr2CuO8 and Cu is manifested by the formation of metallic Bi. From the intensity variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.
|
|
| 5. |
- Nyholm, R., et al.
(author)
-
SYNCHROTRON-RADIATION SOFT-X-RAY PHOTOEMISSION-STUDY OF LEAD ON BI2CASR2CU2O8
- 1992
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:10, s. 6488-6494
-
Journal article (peer-reviewed)abstract
- In this paper we present a study of the interaction of Pb with a clean single-crystal Bi2CaSr2Cu2O8 superconductor surface based on photoemission and low-energy electron diffraction (LEED). Deposition of Pb on a Bi2CaSr2Cu2O8 Crystal kept at room temperature gives rise to the formation of metallic Bi and oxidized Pb at the interface. This behavior could not be observed when the crystal was kept at 100 K during Pb deposition. For all investigated Pb overlayers on a cold crystal (100 K), surface-sensitive photoelectron spectroscopy revealed the growth of a covering metallic Pb overlayer film. The growth at 100 K, contrary to the growth at room temperature, preserved the original LEED 5 X 1 pattern even for Pb depositions corresponding to a 24-angstrom thick overlayer indicating epitaxial growth. Furthermore, a rigid 0.4-eV shift of the valence band and the Bi 5d core levels is observed upon initial Pb deposition and is tentatively attributed to electron doping.
|
|
| 6. |
- Qvarford, M, et al.
(author)
-
Doping dependence of the O 1s is core-level photoemission in bi-Sr-Ca-Cu-O superconductors
- 1996
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:22, s. 14753-14756
-
Journal article (peer-reviewed)abstract
- The O 1s core level of three different Bi-Sr-Ca-Cu-O superconductors has been studied by means of high-resolution x-ray-photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS). The O 1a XPS spectra could be decomposed into three components that were unambiguously assigned to the emission from the three different oxide layers in the crystal structure. These are, in order of increasing binding energy, Cu-O-2, Sr-O, and Bi-O. Furthermore, the component assigned to the Cu-O-2 layers exhibits a shift which depends on the hole doping as monitored by the XAS spectra.
|
|
| 7. |
|
|
| 8. |
- QVARFORD, M, et al.
(author)
-
X-RAY-ABSORPTION AND RESONANT-PHOTOEMISSION STUDY OF CA IN THE HIGH-TEMPERATURE SUPERCONDUCTOR BI2SR2CACU2O8
- 1992
-
In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 46:21, s. 14126-14133
-
Journal article (peer-reviewed)abstract
- The electronic structure of Ca in the high-temperature superconductor Bi2Sr2CaCu2O8 has been studied by x-ray-absorption spectroscopy and resonant-photoemission at the Ca L2,3 absorption edge. In the x-ray-absorption spectrum no edge structure is seen at the energy corresponding to the Ca 2p3/2 core-level binding energy, in agreement with the very low Ca density of states at the Fermi level predicted by band-structure calculations. Furthermore, the crystal-field splitting of the Ca 3d level, which is characteristic of ionic Ca compounds, is clearly observed in the x-ray-absorption spectrum. The photoemission spectra display strong resonant enhancements of the Ca 3s and 3p core levels as well as strong changes in the intensity and the line shape of the Ca L2,3M2,3M2,3 Auger structure at the Ca L2,3 threshold, showing the localized nature of the 3d states in core ionized Ca. The 3d induced spectator shift of the Ca L2,3M2,3M2,3 complex is fairly small as compared to what has been reported for CaF2, indicating that the screening of the normal Auger final state by the charge carriers in the surrounding Cu-O2 layers is quite efficient. From the Ca L2,3M2,3M2,3 data it is also suggested that, at the Ca L2 threshold, the excited 3d electron participates in a Coster-Kronig-type decay resulting in a 2p3/2 core hole followed by a normal L3M2,3M2,3 Auger decay.
|
|
| 9. |
- Soderholm, S, et al.
(author)
-
A photoelectron spectroscopy and x-ray absorption study of Bi2Sr2CaCu2O8 single crystal with adsorbed Cs : On the origin of the states affected by electron doping and evidence for spatially resolved electron doping
- 1996
-
In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 8:9, s. 1307-1320
-
Journal article (peer-reviewed)abstract
- The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of Bi2Sr2CaCu2O8 has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O Is, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O Is, Cu 2p and Ca 2p edges. The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu-O layer. It is evident from bulk- and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of Bi2Sr2CaCu2O8 locally through spatially resolved electron doping. When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi-O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.
|
|
