| 1. |
- Söderholm, S, et al.
(författare)
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A photoemission spectroscopy and X-ray absorption study of Bi(2)Sr(2)CaCu(2)O(8) single crystal with adsorbed Cs: On the origin of states affected by electron doping and evidence for spatially resolved electron doping
- 1996
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 8, s. 1307-1320
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Tidskriftsartikel (refereegranskat)abstract
- The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of 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 1s, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O 1s, 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 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.
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| 2. |
- Andersson, Garbriella, et al.
(författare)
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Effects of varying compressive biaxial strain on the hydrogen uptake of thin vanadium (001) layers
- 1999
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 11:35, s. 6669-6677
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen uptake of asymmetric Fe/V (001) superlattices with LFe/LV = 3/16 monolayers and 3/10 monolayers was investigated by resistometric methods. The hydrogen distribution and the enthalpy of solution were simulated using a diffusion model and calculated H-H interaction energies. It was found that the strain state of the V lattice strongly influenced the H-H interaction. The hydrogen-depleted interface region in the V layers was populated at lower concentrations than in previously studied symmetric samples, which implied that the energy difference between interior and interface regions was lowered. The V-H binding energy was found to be up to 60 meV higher than in the symmetric superlattices.
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| 3. |
- Carlberg, M H, et al.
(författare)
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Self-interstitial structures in body-centred-cubic W studied by molecular dynamics simulation
- 1999
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 11:34, s. 6509-6514
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a simulation study of the detailed structure of an interstitial in a body-centred-cubic (bcc) metal, tungsten (W), using molecular dynamics and the embedded-atom method. Several distinct configurations can be discerned, including the well-known split-interstitial [011] dumb-bell. The [111] crowdion is also observed, as is a set of similar, one-dimensional, defect configurations. These are grouped into a proposed classification scheme, in which the traditional crowdion is revealed as part of a whole family. The defect energies of the various configurations are computed, and comparisons are made with bce iron (Fe) results. The [011] dumb-bell is the energetically most favourable configuration in W. It is found to have a radius of approximately one W lattice constant, 3.16 Angstrom.
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| 4. |
- Hanson, Maj, et al.
(författare)
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The influence of particle size interactions on the magnetization susceptibility of nanometre-size particles
- 1995
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 7, s. 9269-9277
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Tidskriftsartikel (refereegranskat)abstract
- We studied the magnetic properties of frozen magnetic liquids containing amorphous Fe1-xCx particles. By varying the particle size and concentration, we could separate single particle effects from interactions. In samples containing particles with median diameters 5.0 nm and 3.8 nm and with spontaneous saturation magnetizations 7.1 kA m-1 and 9.2 kA m -1, effects of particle interactions are observed. For 3.2 nm no interactions were observed. In samples with negligible interactions the superparamagnetic blocking temperature increases with the particle size. The effective anisotropy constant increases with decreasing particle size, implying that the anisotropy is enhanced by surface effects.
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| 5. |
- Hanson, Maj, et al.
(författare)
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Zero-field cooled magnetization of amorphous Fe1-xCx particles - field dependence of the maximum
- 1995
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 7, s. 9263-9268
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Tidskriftsartikel (refereegranskat)abstract
- We measured the zero-field cooled magnetization, MZPC of a frozen magnetic liquid with amorphous Fe1-xCx particles. MZFC has a maximum at Tp approximately=20 K, which is interpreted as due to blocking of superparamagnetic relaxation in single particles. The maximum shifts towards higher temperatures with increasing measuring field. The shift is explained by the nonlinear field dependence of the magnetization of particles with a size distribution. At temperatures below Tp the magnetic particles have a coercivity and remanence in good agreement with those expected for an ensemble of non-interacting uniaxial particles with a random distribution of easy axes.
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| 6. |
- Lundberg, Tomas, et al.
(författare)
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Analysis of electron transport in a two-dimensional structure using quantal trajectories
- 1998
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 10:25, s. 5583-5594
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Tidskriftsartikel (refereegranskat)abstract
- Ballistic and dissipative electron transport through a two-dimensional geometry is studied in the de Broglie-Bohm quantal trajectory model. The dissipative effect, incorporated to simulate inelastic scattering, is introduced via an imaginary potential term in the Hamiltonian. The relation between the conductance and the local behaviour of the quantal trajectories is discussed. The vortex-like structure of the de Broglie-Bohm trajectories in the vicinity of wavefunction nodes is studied.
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| 7. |
- Soderholm, S, et al.
(författare)
-
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
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 8:9, s. 1307-1320
-
Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Vos, M., et al.
(författare)
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Determination of the energy-momentum densities of aluminium by electron momentum spectroscopy
- 1999
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 11:18, s. 3645-3661
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Tidskriftsartikel (refereegranskat)abstract
- The energy-resolved momentum densities of thin polycrystalline aluminium films have been measured using electron momentum spectroscopy (EMS), for both the valence band and the outer core levels. The spectrometer used for these measurements has energy and momentum resolutions of around 1.0 eV and 0.15 atomic units, respectively. These measurements should, in principle, describe the electronic structure of the film very quantitatively, i.e. the dispersion and the intensity can be compared directly with theoretical spectral momentum densities for both the valence band and the outer core levels. Multiple scattering is found to hamper the interpretation somewhat. The core-level intensity distribution was studied with the main purpose of setting upper bounds on these multiple-scattering effects. Using this information we wish to obtain a full understanding of the valence band spectra using different theoretical models of the spectral function. These theoretical models differ significantly and only the cumulant expansion calculation that takes the crystal lattice into account seems to describe the data reasonably well.
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| 9. |
- Syväjärvi, Mikael, et al.
(författare)
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Anisotropy of dissolution and defect revealing on SiC surfaces
- 1999
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 11:49, s. 10041-10046
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Tidskriftsartikel (refereegranskat)abstract
- Micropipes and dislocations in silicon carbide single crystals are revealed by chemical etching. Micropipes are shown to be interconnected with other structural defects and the reason for this is discussed. The Si and C faces are attacked by molten KOH preferentially and isotropically, respectively. The mechanism is discussed in relation to the different surface free energies on the Si and C faces. The revealing of micropipes is more pronounced on the Si face. The hexagonal pattern of micropipes are revealed by rapid etching provided by a large undersaturation at the surface. It is shown that etching from a melt gives a disintegration of the SiC crystal at the micropipe via spiral dissolution which is due to etching near equilibrium conditions. The temperature dependence of the etch rate follows an Arrhenius dependence with an apparent activation energy of about 12-15 kcal mol(-1) derived from measuring etch rate and weight loss.
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| 10. |
- Syväjärvi, Mikael, et al.
(författare)
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Step-bunching in 6H-SiC growth by sublimation epitaxy
- 1999
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 11:49, s. 10019-10024
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Tidskriftsartikel (refereegranskat)abstract
- Thick 6H-SiC epitaxial layers grown by sublimation epitaxy have been investigated concerning step-bunching. The macrostep appearances on the surfaces were studied for both (0001) Si and (000 (1) over bar) C faces. The surface structure on the Si face is less regular compared with the C face. Data on the steps have been collected and the step height shows a linear relation with the step width.
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