| 1. |
- Johansson, Leif, 1945-, et al.
(författare)
-
Synchrotron radiation studies of the SiO2/SiC(0001) interface
- 2004
-
Ingår i: JOURNAL OF PHYSICS-CONDENSED MATTER ISSN (0953-8984). - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; , s. S3423-S3434
-
Konferensbidrag (refereegranskat)abstract
- Two questions thought to have a significant effect on SiC-MOS device characteristics are treated. The existence of carbon clusters or carbon containing by-products and the existence of sub-oxides at the SiO2/SiC interface. Results of photoemission studies using synchrotron radiation of the interface of the Si-terminated surface of n-type SiC(0001) crystals are presented. The results show that no carbon clusters or carbon containing by-product can. be detected at the interface of in situ or ex situ grown samples with an oxide layer thickness larger than similar to10 Angstrom. The presence of sub-oxides at the SiO2/SiC interface was predicted in a theoretical calculation and has been revealed in Si 2p core level data by several groups. These results were not unanimous; significant differences in the number of sub-oxide and shifts were reported. A study also including the Si 1s core level and Si KLL Auger transitions was therefore made. These data show the presence of only one sub-oxide at the interface, assigned to Si1+ oxidation states. The SiO2 chemical shift is shown to exhibit a dependence on oxide thickness, similar to but smaller in magnitude than the thickness dependence earlier revealed for SiO2/Si.
|
|
| 2. |
- Magnuson, Martin, et al.
(författare)
-
Resonant soft x-ray Raman scattering of NiO
- 2002
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:13, s. 3669-3676
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant soft x-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single-impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p x-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9\underline L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.
|
|
| 3. |
- Beutler, A., et al.
(författare)
-
Identification of a laterally mobile state during CO adsorption
- 2000
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:6, s. 765-772
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated CO adsorption at 300 K on ∼ 1.5 atomic layer thick Pd films on a Mo(110) surface by high-resolution core level photoemission. We describe how high-resolution core level spectroscopy may be utilized to study the influence of laterally mobile states on the sticking probability of molecules on such a laterally heterogeneous surface. The present Pd films are laterally heterogeneous in the sense that the additional ∼ 0.5 atomic Pd layer forms mesoscopic one-layer thick islands on top of the first Pd layer. At 300 K, CO chemisorbs on these two-layer thick islands but not on the one-layer parts of the film. The rate at which these two-layer islands are filled by CO molecules as the surface is exposed to CO is found to be consistent with a picture where CO molecules that initially impinge on the one-layer parts of the surface enter a laterally mobile state and diffuse to the two-layer islands and adsorb there. This mobile state is in many respects similar to a classical precursor state.
|
|
| 4. |
- Csontos, Dan, et al.
(författare)
-
Scattering-matrix formalism of electron transport through three-terminal quantum structures: formulation and application to Y-junction devices
- 2002
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 14:47, s. 12513-12528
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a formalism for the calculation of electron transport through three-terminal junction devices, which have received attention due to their recently demonstrated non-linear electrical properties. The formalism, which is based on the scattering-matrix method, takes quantum interference effects fully into account. Furthermore, the formalism provides numerical stability in the calculations as well as large flexibility in the modelling of arbitrary potential profiles due to the common basis approach used in the formulation. The method is used to calculate the transport properties for Y-shaped three-terminal ballistic junction (TBJ) structures with configurations typical of recently performed experiments. Quantum interference effects are shown to strongly influence the transport characteristics of TBJ structures due to complex scattering of the electrons in the cavity-like coupling window between the three arms of the device. The theoretical approach presented in this paper provides a flexible tool for the study of such quantum interference effects, which may play an important role in the design and functionality of future nanoscale devices based on three-terminal junctions.
|
|
| 5. |
- Darnton, N., et al.
(författare)
-
Hydrodynamics in 2 1/2 dimensions : Making jets in a plane
- 2001
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:21, s. 4891-4902
-
Tidskriftsartikel (refereegranskat)abstract
- We show that a careful analysis of the Navier-Stokes equation in the low Reynolds number limit has two distinct solutions, one valid for a deep, thin curtain of flow and the other for a thin wide flow. We derive a solution to the latter situation and use the results to develop a new way to control fluid flows in thin, wide sheet flow.
|
|
| 6. |
- Goss, J.P., et al.
(författare)
-
Small aggregates of interstitials and models for platelets in diamond
- 2000
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10257-10261
-
Tidskriftsartikel (refereegranskat)abstract
- By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties
|
|
| 7. |
- Irbäck, Anders
(författare)
-
A minimalistic all-atom approach to protein folding
- 2003
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 15:18, s. 1797-1807
-
Tidskriftsartikel (refereegranskat)abstract
- Using simple sequence-based potentials, the folding properties of a designed three-helix-bundle protein, an alpha-helix and a beta-hairpin are studied. The three-helix-bundle protein is modelled using 5-6 atoms per amino acid and is found to undergo a first-order-like folding transition in which chain collapse and helix formation cannot be separated, which is in-accord with experimental data. The other two sequences are studied using a model that contains all atoms and are indeed found to make an alpha-helix and a beta-hairpin, respectively, for exactly the same choice of parameters. The calculated melting curves are, moreover, in reasonable quantitative agreement with experimental data, for both peptides. The melting curves are found to be quite well described by a simple two-state model, although the energy distributions lack a clear bimodal shape.
|
|
| 8. |
- Johansson, Emil, et al.
(författare)
-
Hydrogen uptake and optical properties of sputtered Mg-Ni thin films
- 2004
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16, s. 7649-
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrogen uptake and distribution in wedged Mg–Ni films, with composition ranging from Mg0.85Ni0.15 to Mg0.55Ni0.45, were investigated. Upon hydrogen loading at 298 K these films undergo a transition from a mirror-like metallic to a semiconducting transparent state. After exposure to a hydrogen pressure of 1 bar, the samples exhibit large variation in optical appearance, ranging from a pale yellowish (Mg rich side) to a brownish shade (Ni rich side). The change in the effective optical band gap Egeff as a function of sample composition and hydrogen concentration was determined; it showed changes from 3.6 eV in the Ni poor domain to 2.4 eV in the Ni rich domain. Composition analysis using the 15N nuclear resonance method showed close to homogeneous hydrogen distribution throughout the film and close to linear increase in the hydrogen uptake with increasing Mg content. The thermal stability of the films is limited; annealing above 393 K results in significant redistribution of the constituents. Mg is enriched at the surface, reacting with Pd and thereby degrading the capping layer through the formation of Mg6Pd and MgO, as determined by x-ray diffraction, x-ray photoelectron spectroscopy and Rutherford backscattering studies. This redistribution results in a severe decrease of the hydrogen uptake rate, as monitored by in situ resistivity measurements.
|
|
| 9. |
- Lapushkin, I, et al.
(författare)
-
A self-consistent investigation of the semimetal-semiconductor transition in InAs/GaSb quantum wells under external electric fields
- 2004
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 16:26, s. 4677-4684
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the phase transitions in InAs/GaSb quantum wells sandwiched between two wide-gap AlSb barrier layers under an external electric field perpendicular to interfaces. The Schrodinger and the Poisson equations are solved self-consistently to derive the subband dispersions, the potential profile, the electron charge distribution in the InAs layer, and the hole charge distribution in the GaSb layer. The Burt-Foreman envelope function theory and the scattering matrix method are used to solve the Schrodinger equation in the framework of the eight-band k (.) p model, including the spin-splitting of subbands in our calculation. We have found that in a thick InAs/GaSb quantum well, which has been investigated experimentally by Cooper et al (1998 Phys. Rev. B 57 11915), under low external electric fields, two electron levels stay below the highest hole level at zero in-plane wavevector k(parallel to) = 0. Then, the anticrossings of electron and hole levels produce several minigaps in the inplane dispersions, inside which the states of other subbands exist. As a result, the system is in a sernimetal phase. With increasing external electric field, the semimetal phase changes to semiconductor phase with only one hybridization gap. When all electron levels become higher than the hole levels at higher electric fields, the system has a semiconducting gap.
|
|
| 10. |
- Linse, Per
(författare)
-
Mean force between like-charged macroions at high electrostatic coupling
- 2002
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 14:49, s. 13449-13467
-
Tidskriftsartikel (refereegranskat)abstract
- Interactions between two like-charged macroions in the presence of their counterions confined in a cylindrical cell have been investigated by Monte Carlo simulations. The mean force and the potential of mean force (pmf) as a function of the macroion separation have been determined at conditions at which short-range attractions become significant. As the electrostatic coupling is increased, the nature of the mean force changes from being purely repulsive to bein attractive at short separations and finally attractive at all separations. At a sufficiently large electrostatic coupling, the attractive mean force is promoted by an increase of the macroion charge to counterion charge ratio and by an increase of the macroion volume fraction (assuming a not too concentrated solution). At the onset of an attractive force, nearly all counterions are localized at the macroion surfaces, but the counterions still display a two-dimensional fluid structure. The pmfs determined from the cylindrical cell model agreed qualitatively very well with those obtained from simulations of corresponding fluids, suggesting that higher-order macroion correlations are of less importance. Finally, it is argued that the attractive component of the mean force originates from spatial correlations between counterions residing near different macroions.
|
|
