| 1. |
- 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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| 2. |
- Karlsson, Magnus, 1967, et al.
(författare)
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Geometrically induced non-linear phenomena of the TE11-mode in a rectangular optical waveguide
- 1995
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Ingår i: Physica Scripta. - : IOP Publishing. - 1402-4896 .- 0031-8949. ; 52:3, s. 313-317
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Tidskriftsartikel (refereegranskat)abstract
- Retaining all significant terms of Maxwell equations, we derive a gener-alized governing equation for waves in a Kerr-nonlinear, rectangulai optical waveguide. As a specific example, we show that the field com-ponents of the TEn-mode in such a waveguide will achieve oscillations in both amplitude and phase during propagation. The nonlinearity appeal only in a characteristic length scale of these phenomena, whereas tht overall properties of the oscillations are determined by the waveguidt geometry.
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| 3. |
- Kawamura, J., et al.
(författare)
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Low noise NbN lattice-cooled superconducting hot-electron bolometric mixers at submillimeter wavelengths
- 1997
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 70:12, s. 1619-1621
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Tidskriftsartikel (refereegranskat)abstract
- Lattice-cooled superconducting hot-electron bolometric mixers are used in a submillimeter-wave waveguide heterodyne receiver. The mixer elements are niobium nitride film with 3.5 nm thickness and ∼ 10 μm2 area. The local oscillator power for optimal performance is estimated to be 0.5 μW, and the instantaneous bandwidth is 2.2 GHz. At an intermediate frequency centered at 1.4 GHz with 200 MHz bandwidth, the double sideband receiver noise temperature is 410 K at 430 GHz. The receiver has been used to detect molecular line emission in a laboratory gas cell.
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| 4. |
- Aleksandrovskii, A. N., et al.
(författare)
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Negative thermal expansion of fullerite C60 at helium temperatures
- 1997
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 23:11, s. 943-946
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Tidskriftsartikel (refereegranskat)abstract
- The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed
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| 5. |
- Andersson, Ove, et al.
(författare)
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Reorientational relaxation in C60 following a pressure induced change in the pentagon/hexagon equilibrium ratio
- 1995
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Ingår i: Physics Letters A. - : Elsevier Science B.V.. - 0375-9601 .- 1873-2429. ; 206:3-4, s. 260-264
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Tidskriftsartikel (refereegranskat)abstract
- The orientational structure of C60 depends on pressure and temperature. Pressurization below the glass transition temperature Tg can freeze in non-equilibrium orientational structures. The relaxation of such structures on heating through Tg has been studied through thermal conductivity measurements and the effects observed are explained in a simple model.
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| 6. |
- Andersson, Ove, et al.
(författare)
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Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
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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.
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| 7. |
- Chen, W., et al.
(författare)
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Electronic and geometric structure of clean Pt3Ti(111)
- 1994
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Ingår i: Physical Review B. - 0163-1829 .- 1095-3795. ; 50:8, s. 5620-5627
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Tidskriftsartikel (refereegranskat)abstract
- Photoemission spectra and scanning tunneling microscopy (STM) images of the clean Pt3Ti(111) surface are presented. Grazing-emission core-level spectra show that the topmost layer is pure platinum, modified compared with the Pt(111) surface. The Pt 4f levels at the surface are shifted 0.4 eV toward the Fermi level relative to bulk Pt3Ti while the Pt 4f and Ti 2p levels in the bulk are shifted 0.4 and 1.3 eV to higher binding energy relative to pure bulk platinum and titanium, respectively, Tunneling measurements show a surface with only metallic atoms and a small p(2×2) buckling. Our observations of molecularly adsorbed CO are not compatible with metallic titanium atoms at the surface and the STM data thus indirectly confirm that only platinum atoms are present in the topmost layer. Linear muffin-tin-orbital calculations of the bulk band structure and valence-band photoemission spectra reveal highly hybridized electron states between the Pt d and Ti d levels. The calculations give a minor charge transfer from Ti to Pt, 0.37 electrons per Ti atom, but the large core-level shifts reflect the stability of the alloy and the response to the excitation rather than the amount of charge transfer. The observed segregation of platinum to the surface and the altered electronic structure of the topmost layer, due to interaction with the underlying alloy, are in full agreement with earlier conclusions based on low-energy electron-diffraction measurements and on the chemical properties of the surface. © 1994 The American Physical Society.
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| 8. |
- Chen, W., et al.
(författare)
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Redox properties of titanium oxides on Pt3Ti
- 1995
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 99:34, s. 12892-12895
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and electronic structure of surface-segregated titanium oxides on Pt3Ti(111) are presented. Core level photoemission spectra at grazing emission reveal two states of oxidation: a dominant and reducible four-valent oxide together with a small amount of a three-valent oxide is produced by oxidation in 0 2 at and below 400°C; an irreducible three-valent oxide by oxidation in 02 at and above 450 °C. The ratio between the active four-valent and the inactive three-valent oxides decreases with increasing oxidation temperature. The probability for reduction by CO is almost unity for the Ti 4+ oxide, and the conclusion must be that the four-valent oxide plays an active role for catalytic reactions. Scanning tunneling measurements relate these observations to changes in the dispersion and nucleation of the oxide overlayer. The four-valent oxide grows as islands with remaining areas open for CO adsorption while the three-valent oxide spreads on and blocks the crystal surface. Photoemission spectra relate these dispersion effects to an electronic interaction between the Ti 3+ oxide and adjacent Pt atoms. The above observations are in accordance with the common picture of dispersion effects in titania-supported SMSI catalysts and prove that interfacial energies play a crucial role whether the dominant phase is metallic or an oxide.
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| 9. |
- Lundin, Anders, et al.
(författare)
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Compressibility and Structure of C70
- 1995
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 30:8, s. 469-474
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Tidskriftsartikel (refereegranskat)abstract
- The compressibility of C70 has been investigated by means of direct piston and cylinder measurements in the temperature range 150 to 365 K and up to 1 GPa. At 296 and 343 K we find a very rapid change of volume with pressure below 0.15 GPa. We tentatively interpret this as a continuous molecular reorientation with pressure, probably resulting in a transformation from a mixture of face-centred cubic (f.c.c.) and rhombohedral (r.h.) phases to mainly pure r.h. phase. At 365 K as well as at 236 K and below we see no anomalies indicating any structural or rotational anomalies in the pressure range investigated. The zero-pressure bulk modulus decreases with increasing temperature, from 13.1 GPa at 185 K to 7.9 GPa at 365 K. Our volumetric measurements confirm a recently proposed phase diagram for C70.
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| 10. |
- Lundin, Anders, et al.
(författare)
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Compressibility of C61D2 up to 1 GPa in the temperature range 175 - 345 K
- 1996
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Ingår i: Carbon. - : Elsevier Science Ltd.. - 0008-6223 .- 1873-3891. ; 34:9, s. 1119-1121
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.
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