| 1. |
- Andersson, Ove, et al.
(författare)
-
Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ of C60 shows anomalies near 260 K and 90 K which are associated with the well-established phase transition and glass transition, respectively. Both transition temperatures increase with pressure, at the rates 120 K GPa-1 and 62 K GPa-1, respectively. With increasing temperature, λ of the simple cubic (sc) phase increased below 170 K (glasslike behavior) but decreased above. The glasslike behavior of λ is probably due to a substantial amount of lattice defects. Possible reasons for the change of sign of dλ/dT near 170 K are discussed. In the face centered cubic (fcc) phase (T≳260 K at atmospheric pressure) λ was almost independent of temperature, a behavior which is far from that of an ordered crystal (λ∝T-1 for T≳Debye temperature). This result can be attributed to the molecular orientational disorder of the fcc phase. The relaxation behavior associated with the glassy state and its unusually strong dependence on thermal history are discussed briefly, and data which support a previously reported relaxation model are presented. At room temperature, the density dependencies of λ, (∂ lnλ/∂ lnρ)T, were 5.5 and 9.5 for the fcc and sc phases, which are values typical for an orientationally disordered phase and a normal crystal phase, respectively.
|
|
| 2. |
- Magnuson, M., et al.
(författare)
-
Angular-dependent resonant-photoemission processes at the 2p thresholds in nickel metal
- 1999
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 60:4, s. 2436-2440
-
Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved valence-band resonant-photoemission of nickel metal has been measured close to the 2p core-level thresholds with synchrotron radiation. The well-known 6-eV correlation satellite has an intensity enhancement of about two orders of magnitude at resonance. The angular dependence of the photoemission intensity has been studied as function of photon energy and provides unambiguous evidence for interference effects all the way up to the resonance maximum. The observation of different angular asymmetries, β, for the valence band and the satellite is discussed in connection to the origin of the resonant-photoemission process and the character of the satellite.
|
|
| 3. |
- Magnuson, Martin, et al.
(författare)
-
Energy dependence of Cu L2,3 satellites using synchrotron excited x-ray-emission spectroscopy
- 1997
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 56:19, s. 12238-12242
-
Tidskriftsartikel (refereegranskat)abstract
- The L2,3 x-ray emission of Cu metal has been measured using monochromatic synchrotron radiation. The self-absorption effect in the spectra is shown to be very small in our experimental geometry. From the quantitative analysis of spectra recorded at different excitation energies, the L3/L2 emission intensity ratio and the partial Auger width are extracted. High-energy satellite features on the L3 emission line are separated by a subtraction procedure. The satellite intensity is found to be slowly increasing for excitation energies between the L3, L2, and L1 core-level thresholds due to shake-up and shake-off transitions. As the excitation energy passes the L2 threshold, a step of rapidly increasing satellite intensity of the L3 emission is found due to additional Coster-Kronig processes.
|
|
| 4. |
- Magnuson, Martin, et al.
(författare)
-
Resonant Auger spectroscopy at the L2,3 shake-up thresholds as a probe of electron correlation effects in nickel
- 1998
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:7, s. 3677-3681
-
Tidskriftsartikel (refereegranskat)abstract
- The excitation energy dependence of the three-hole satellites in the L3-M45M45 and L2-M45M45 Auger spectra of nickel metal has been measured using synchrotron radiation. The satellite behavior in the nonradiative emission spectra at the L3 and L2 thresholds is compared and the influence of the Coster-Kronig channel explored. The three-hole satellite intensity at the L3 Auger emission line reveals a peak structure at 5 eV above the L3 threshold attributed to resonant processes at the 2p53d9 shake-up threshold. This is discussed in connection with the 6-eV feature in the x-ray-absorption spectrum.
|
|
| 5. |
- Winter, Johannes, et al.
(författare)
-
Charge transfer in alkali-metal-doped polymeric fullerenes
- 1996
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54, s. 17486-17492
-
Tidskriftsartikel (refereegranskat)abstract
- We present room-temperature Raman measurements of pressure-polymerized C60 and compare them with the spectra of RbC60 in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized C60 and the rubidium-doped orthorhombic compound, have the same overall structure and the AC60 compounds can be considered as the doped species of the C60, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency Hg(7) and Hg(8) modes. The low values for the coupling constants compared to the ones in the K3C60 can explain the lack of superconductivity in the AC60 compounds.
|
|
| 6. |
|
|
| 7. |
- Andersson, Magnus, et al.
(författare)
-
Vortex solid-to-liquid transition in DyBa2Cu3O7-delta/(Y0.45Pr0.55)Ba2Cu3O7-delta multilayers
- 1996
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:1, s. 675-681
-
Tidskriftsartikel (refereegranskat)abstract
- Current-voltage (I-V) characteristics of a coupled multilayer system consisting of thin (24 Angstrom) superconducting layers of DyBa2Cu3O7-delta each separated by 96 Angstrom of (Y0.45Pr0.55)Ba2Cu3O7-delta have been studied in the mixed state. Analyses of vortex glass scaling and signs of the clean system melting transition in the dynamics of our multilayers both suggest that the vortex system is close to three-dimensional for magnetic fields up to several T. Therefore, the theoretically predicted crossover when in-plane vortex correlations become more important than out-of-plane vortex correlations (occurring at a few tenths of a T in our multilayers) does not correspond to a complete decoupling of the superconducting layers in these materials.
|
|
| 8. |
- Bjorkqvist, M, et al.
(författare)
-
NH3 on Si(111)7x7 : Dissociation and surface reactions
- 1998
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:4, s. 2327-2333
-
Tidskriftsartikel (refereegranskat)abstract
- Core-level and valence-band photoelectron spectroscopy on the dissociative adsorption of ammonia on Si(111) 7 X 7 is presented. Adsorption at room temperature produces three nitrogen 1s components, of which two are assigned to NH2 and one to NH, with an initial tendency for double dissociation. These doubly dissociated species can be connected to the development of silicon atoms coordinated with two nitrogen atoms, necessitating silicon-silicon bonds to be broken. The dominating picture evolving is thus adatoms saturated by NH2 with a NH group inserted into one backbond, and hydrogen preferentially capping restatoms. The dissociation proces is hence much more complex than generally proposed before. This is further accentuated by the fact that not all adatoms appear reacted. When annealed above 600 K the dissociation process progresses and atomic nitrogen appears at 700 K, to be the only remaining specie at 850 K. At 1200 K, further changes in the N 1s core level indicates true silicon nitride formation.
|
|
| 9. |
- Budde, M., et al.
(författare)
-
Identification of the hydrogen-saturated self-interstitials in silicon and germanium
- 1998
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:18, s. 4397-4412
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4 cm-1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5 cm-1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.
|
|
| 10. |
- Butorin, S. M., et al.
(författare)
-
Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy
- 1996
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54, s. 4405-4408
-
Tidskriftsartikel (refereegranskat)abstract
- We measured the Mn Lα,β x-ray fluorescence spectra of MnO excited by selected photon energies near the L2,3 absorption edges. The resulting resonant inelastic x-ray scattering spectra probe low-lying electronic excited states, due to dd and charge-transfer excitations. Using a two-step model and a purely atomic approximation, we reproduce both energies and varying intensities of dd excitations relative to the electronic recombination peak. Our results show that strongly varying line shapes in resonant x-ray emission need not be due to channel interference effects.
|
|
