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1.
  • Fang, AP, et al. (författare)
  • Theoretical study of electromagnetically induced transparency in Er3+: YAlO3 crystal
  • 2003
  • Ingår i: Physica B: Condensed Matter. - 0921-4526. ; 328:3-4, s. 204-210
  • Tidskriftsartikel (refereegranskat)abstract
    • By using the density matrix theory of interaction between light and matter, and relevant parameter calculations of the relaxation rate, the dipole matrix elements and the ion density for a three-level ladder model, we have discussed theoretically the possibility to realize electromagnetically induced transparency (EIT) in Er3+:YA1O(3) crystal. (C) 2002 Elsevier Science B.V. All rights reserved.
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2.
  • Gershenson, M. E., et al. (författare)
  • Quantum interference effects in percolated metal networks
  • 1994
  • Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; , s. 1109-1110
  • Konferensbidrag (refereegranskat)abstract
    • Quantum corrections (QC) to the resistivity due to weak localization (WL) and electron-electron interaction (EEI) have been measured for percolated metal networks with percolation coherence length z comparable to the quantum length scales-the phase-breaking length L and the thermal diffusion length LT. Far from the percolation metal-insulator transition (MIT) the `macroscopic' disorder is averaged over the quantum lengths (L,LTz) and the QC are of the universal two-dimensional (2D) type with R=R(z), where R(z) is the resistance per square at scales larger than z. A crossover 2D1D in the dimensionality of the QC and the Nyquist phase-braking mechanism is observed near the MIT, where zL,LT
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3.
  • Hedin, Lars, et al. (författare)
  • Extrinsic and intrinsic processes in EXAFS
  • 1989
  • Ingår i: Physica B. - : Elsevier BV. - 0921-4526. ; 158, s. 344-346
  • Konferensbidrag (refereegranskat)abstract
    • The author extends the ideas of Bardyszewski and Hedin (1987) to treat EXAFS. He summarises the theory, adds new viewpoints and extends the theory.
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4.
  • Koblischka, M. R., et al. (författare)
  • Paramagnetic Meissner response of an artificially granular YBCO thin film
  • 2000
  • Ingår i: Physica B: Condensed Matter. - 0921-4526. ; 284-288, s. 599-600
  • Konferensbidrag (refereegranskat)abstract
    • Field-cooling measurements on an YBa2Cu3Oy thin film, patterned into a hexagonal close-packed lattice of disks with a diameter of 50 m reveal a paramagnetic Meissner response (PME) when cooled in fields below 1 mT. In contrast to previous investigations on Nb and melt-cast Bi-2212, the PME in this artificial granular film is attributed to field trapping in the space between the disks
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5.
  • Lipinska-Kalita, KE, et al. (författare)
  • High-pressure studies of titanium pyrophosphate by Raman scattering and infrared spectroscopy
  • 2003
  • Ingår i: Physica B: Condensed Matter. - 0921-4526. ; 337:1-4, s. 221-229
  • Tidskriftsartikel (refereegranskat)abstract
    • High-pressure investigations of titanium pyrophosphate, TiP2O7, in diamond anvil cell have been performed at room temperature using in situ Raman scattering and Fourier transform infrared spectroscopy (FTIR). The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. The pressure-stimulated alterations in the spectral profile, the position, and the intensity of the stretching and bending modes Of PO4 tetrahedral structural units have been investigated up to 42.8 and 49.4 GPa for Raman and infrared-active modes, respectively. The spectral changes pointed mostly to the densification and partial amorphization of the crystal lattice. FTIR spectra confirmed that the investigated compound, TiP2O7, compressed smoothly up to the highest investigated pressures. The spectroscopic studies did not indicate an unambiguous structural transformation matching to a pressure-driven phase transition. The reversibility to ambient pressure structure upon decompression was implied by FTIR but was not confirmed by Raman spectroscopy. The mode Gruneisen parameters were calculated for the various Raman and infrared-active vibrational modes. The results obtained are consistent with our previous high-pressure synchrotron radiation-based X-ray diffraction investigations. (C) 2003 Elsevier B.V. All rights reserved.
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6.
  • Mortensen, K., et al. (författare)
  • Shear devices for in situ structural studies of block-copolymer melts and solutions
  • 1995
  • Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 213, s. 682-684
  • Tidskriftsartikel (refereegranskat)abstract
    • Structural studies of soft material while exposed in situ to stretch or shear provide a new experimental technique which gives important insight into polymer dynamics. Such devices can be used for making single-domain block-copolymer and colloidal mesophases, and to study various growth mechanisms. In addition, combined structure and shear instruments can give detailed insight into the influence of fluctuations. Two types of shear device, the Couette cell and a parallel plate device, are presented, and some applications are shown.
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7.
  • Agren, P., et al. (författare)
  • Hysteretic current-voltage characteristics and Coulomb blockade in 1D-arrays of Josephson junctions
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 280:04-jan, s. 414-415
  • Tidskriftsartikel (refereegranskat)abstract
    • The IV characteristics (IVC) of 1D-arrays of small capacitance Josephson junctions with E-C similar to E-J have been measured. The IVC show Coulomb blockade of Cooper pair tunneling and exhibit a pronounced hysteresis which appears to be dual to the well-known resistively shunted junction behavior of ordinary Josephson junctions. A dual serially resistive junction model is used to qualitatively explain the measured data.
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8.
  • Andersen, O., et al. (författare)
  • Piezospectroscopic analysis of the hydrogen-carbon complexes in silicon
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 139-142
  • Tidskriftsartikel (refereegranskat)abstract
    • We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen-carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen-carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.
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9.
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10.
  • Andersson, K., et al. (författare)
  • Synchronous Cooper pair tunneling in a 1D-array of Josephson junctions
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1816-1817
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied 1D-arrays of Josephson junctions with a gate capacitively coupled to the middle of the array. The SQUID shape of each junction enables tuning of the Josephson coupling energy, El. By adding a signal to the gate with a radio-frequency f we create a step in the I-V characteristics at the value I = 2ef: The step is clearly visible as a peak in the differential resistance dI/dV and can be seen in the whole frequency range studied (10-90 MHz).
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11.
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12.
  • Axnas, J., et al. (författare)
  • Magnetoconductivity of polycrystalline Hg,Tl-1223
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1009-1010
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetoconductivity of polycrystalline Hg1-xTlxBa2Ca2Cu3O8+delta With x = 0 and 0.2 has been measured above T-c and analysed in terms of superconducting fluctuations. Such studies are numerous and successful for Y- and Bi-based materials, but still rare for Hg- and Tl-based materials. Results for the coherence lengths and the role of the Maki-Thompson contribution are briefly discussed.
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13.
  • Bergsten, T., et al. (författare)
  • Hall resistance in two-dimensional arrays of Josephson junctions
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1818-1819
  • Tidskriftsartikel (refereegranskat)abstract
    • We have measured the Hall resistance in two-dimensional arrays of ultrasmall aluminium Josephson junctions. We found that the Hall resistance was periodical with respect to an external magnetic field applied perpendicular to the plane of the array. We also found that the Hall resistance was affected by an applied voltage to a nearby gate electrode, but not by a gate plane silting underneath the array.
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14.
  • Buyanova, Irina A., et al. (författare)
  • Strain relaxation in GaNxP1-x alloy : Effect on optical properties
  • 2001
  • Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 308-310, s. 106-109
  • Tidskriftsartikel (refereegranskat)abstract
    • By using scanning electron microscopy and cathodoluminescence (CL), a decrease in radiative efficiency of GaNP alloy with increasing N content is seen due to the formation of structural defects. The defect formation is attributed to relaxation of tensile strain in the GaNP layer, which is lattice mismatched to GaP substrate. Several types of extended defects including dislocations, microcracks and pits are revealed in partly relaxed GaNxP1-x epilayers with x=1.9%, whereas coherently strained layers exhibit high crystalline quality for x up to 4%. According to the CL measurements, all extended defects act as competing, non-radiative channels leading to the observed strong decrease in the radiative efficiency. From CL mapping experiments, non-uniformity of strain distribution around the extended defects is partly responsible for the broadening of the photoluminescence (PL) spectra recorded in the macro-PL experiments. © 2001 Elsevier Science B.V. All rights reserved.
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15.
  • Coomer, B.J., et al. (författare)
  • Interstitial aggregates and a new model for the I1/W optical centre in silicon
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 505-508
  • Tidskriftsartikel (refereegranskat)abstract
    • The properties of di-interstitial (I2), tri-interstitial (I3) and tetra-interstitial (I4) structures in silicon were studied by employing first principles local-density-functional (LDF) theory. A tri-interstitial defect can account for many of the fundamental properties of the I1/W-optical center which is observed in irradiated, annealed silicon. Energy comparisons between di-interstitial defects reveal four low-energy structures within 0.5 eV of each other.
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16.
  • Coomer, B.J., et al. (författare)
  • The divacancy in silicon and diamond
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 520-523
  • Tidskriftsartikel (refereegranskat)abstract
    • First-principles studies of the divacancy (V2) in both silicon and diamond are reported. We demonstrate that the contrasting experimental spin-density localisation of both systems can be explained through the one-electron pictures arising from opposing distortions
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17.
  • Coutinho, J., et al. (författare)
  • Over-coordinated oxygen in the interstitial carbon-oxygen complex
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 305-308
  • Tidskriftsartikel (refereegranskat)abstract
    • The interstitial carbon-oxygen complex is one of the most prominent defects formed in e-irradiated Cz-Si containing carbon. Stress alignment investigations have shown that the oxygen atom only perturbs the carbon interstitial but the lack of a high frequency oxygen mode has been taken to imply that the oxygen atom is over-coordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts, along with the piezoscopic stress-energy tensor support the trivalent model, thus providing evidence for oxygen over-coordination.
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18.
  • Davidsson, P, et al. (författare)
  • Vortex mapping on gold covered conventional type II superconductors using the very low temperature tunnelling microscope
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196:Part 1, s. 375-376
  • Tidskriftsartikel (refereegranskat)abstract
    • We have used a dilution refrigerator cooled STM for investigating the vortex state in lead-bismuth alloy 4000Aofilms. The vortices were recognized by the decreasing dynamic conductance near the gap voltage when the instrument was operated in its normal feed back mode. A clean surface suitable for tunneling was maintained by a 75Aolayer of gold deposited on top of the sample film. The temperature was kept at 80 mK and magnetic fields between 0 and 0.2 T were used.  
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19.
  • DJURBERG, C, et al. (författare)
  • RELAXATION OF THE FIELD COOLED MAGNETIZATION IN 2D CU(MN) FILMS
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 303-304
  • Tidskriftsartikel (refereegranskat)abstract
    • The relaxation of the field cooled magnetisation of a multilayered 2D Cu(Mn) spin glass film has been investigated in a SQUID-magnetometer. The sample is cooled in a constant magnetic field (10 Oe) from a high temperature, where the magnetisation is at equilibrium, to a temperature below the freezing temperature, T(f). At constant temperature, the magnetisation is then found to increase with time at temperatures near T(f), showing an initial decrease followed by an increase at long time scales at intermediate temperatures and only decreases with time at lower temperatures. The behaviour, including the surprising downward relaxation away from the thermodynamic equilibrium magnetisation, is qualitatively interpreted in terms of a spin glass domain model.
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20.
  • Eberlein, T.A.G., et al. (författare)
  • Self-interstitial clusters in silicon
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 454-457
  • Tidskriftsartikel (refereegranskat)abstract
    • Although there have been made many calculations for structures of the self-interstitial in Si and small aggregates of interstitials, In, there have been relatively few attempts to relate these defects with experimental data. Here, we discuss the assignments of the self-interstitial to the AA12 EPR centre and the di-interstitial to the P6 EPR centre.
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21.
  • Fabrega, Lourdes, et al. (författare)
  • Vortex dynamics and vortex phase diagram in artificial oxide superlattices
  • 1996
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 222:4, s. 379-384
  • Tidskriftsartikel (refereegranskat)abstract
    • DyBa2Cu3O7/(Y1-xPrx)Ba2Cu3O7 multilayers are model materials to study the nature of the vortex system in high-temperature superconductors and its dynamics. Indeed, by changing in such structures the thickness of the superconducting and the alloy layers, and the composition of the alloy, we can control at wish the critical temperature, the anisotropy and the pinning strength. Additionally, finite thickness effects may be studied. We review here our results on the study of the flux motion and phase diagram in coupled multilayers, displaying an intermediate anisotropy between those of YBa2Cu3 O-7 and Bi2Sr2CaCu2O8. Transport measurements with an applied field H/c allow to identify the solid and liquid phases in the mixed state, and reveal the presence of a field-induced crossover in the thermally activated dynamics of both phases, which lead us to draw a possible mixed state phase diagram for these artificial superconductors and correlate it to the existing results for other HTS.
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22.
  • Festin, Örjan, et al. (författare)
  • Zero-field vortex dynamics in YBCO thin films
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284-288:Pt. 1, s. 963-964
  • Tidskriftsartikel (refereegranskat)abstract
    • The dynamics of spontaneously generated vortices in epitaxial YBCO films have been investigated in the superconducting transition region by means of flux noise measurements. The investigated samples differ with respect to film thickness and sample quality and the influence of these parameters on the flux noise spectra is discussed.
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23.
  • Fransson, Jonas, et al. (författare)
  • On the non-orthogonality problem in the description of quantum devices
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 272:1-4, s. 28-30
  • Tidskriftsartikel (refereegranskat)abstract
    • An approach which allows to include the corrections from non-orthogonality of electron states in contacts and quantum dots is developed. Comparison of the energy levels and charge distributions of electrons in 1D quantum dot (QD) in equilibrium, obtained within orthogonal (OR) and non-orthogonal representations (NOR), with the exact ones shows that the NOR provides a considerable improvement, for levels below the top of barrier. The approach is extended to non-equilibrium states. A derivation of the tunneling current through a single potential barrier is performed using equations of motion for correlation functions. A formula for transient current derived by means of the diagram technique for Hubbard operators is given for the problem of QD with strongly correlated electrons interacting with electrons in contacts. The non-orthogonality renormalizes the tunneling matrix elements and spectral weights of Green functions.
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24.
  • Geller, Michael, et al. (författare)
  • Theory of electron–phonon dynamics in insulating nanoparticles
  • 2002
  • Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 316-317, s. 430-433
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss the rich vibrational dynamics of nanometer-scale semiconducting and insulating crystals as probed by localized electronic impurity states, with an emphasis on nanoparticles that are only weakly coupled to their environment. Two principal regimes of electron--phonon dynamics are distinguished, and a brief survey of vibrational-mode broadening mechanisms is presented. Recent work on the effects of mechanical interaction with the environment is discussed.
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25.
  • Ghiringhelli, G., et al. (författare)
  • Probing the singlet character of the two-hole states in cuprate superconductors
  • 2002
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 312, s. 34-35
  • Tidskriftsartikel (refereegranskat)abstract
    • Using spin-resolved resonant photoemission we have probed the singlet vs. triplet character of the two-hole state in the layered cuprates Bi2Sr2CaCu2O8+delta La2-xSrxCuO4 and Sr2CuO2Cl2. The combination of the photon circular polarization with the photoelectron spin detection gives access to the character of the photoemission final states, which correspond to the two-hole configurations localized at a (CuO4) site. In particular, the lowest energy state is found to have a very high singlet character in all the measured compounds. This can be considered as a strong indication of the existence and stability of the so-called Zhang-Rice singlets in the layered cuprates.
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26.
  • Godlewski, M., et al. (författare)
  • In-plane and in-depth nonuniformities in defect distribution in GaN and InGaN epilayers
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 102-105
  • Tidskriftsartikel (refereegranskat)abstract
    • The in-plane and in-depth characteristics of the GaN and InGaN epilayers grown by the metalorganic chemical vapour deposition (MOCVD) on three different substrates (sapphire, SiC and bulk GaN) are evaluated. Relatively large intensity fluctuations of "edge" GaN and InGaN emissions are observed and are related to the details of the micro-structure of the GaN and InGaN films studied. The experiments indicate a nonuniform defect distribution in all types of the MOCVD films studied. In particular, the decoration of structural defects with impurities, an increased defect accumulation at the interfaces and a surprisingly small influence of the micro-structure on the in-plane homogeneity of the yellow band cathodoluminescence emission are observed. © 2001 Elsevier Science B.V. All rights reserved.
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27.
  • Han, Shunhui, et al. (författare)
  • Thermodynamic fluctuation in doped BiSrCaCuO superconductors with 110K phase
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196, s. 1513-1514
  • Tidskriftsartikel (refereegranskat)abstract
    • The resistivity has been carefully measured for four sintered samples of Pb and Pb/Sb doped Bi-Sr-Ca-Cu-O superconductors with the 110 K phase from zero resistance temperature up to 300 K. The thermodynamical fluctuation have been fitted on the form DELTAsigma is-proportional-to epsilon(x) (epsilon=(T-T(c))/T(c)) in the regions -4 < In epsilon < -2. By choosing T(c) in different ways, it is shown that consistent results only could be obtained when T(c) is defined according to the Lawrence-Doniach theory.
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28.
  • Haviland, David B., et al. (författare)
  • Quantum-phase transition in 1D Josephson junction arrays
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1808-1809
  • Tidskriftsartikel (refereegranskat)abstract
    • One-dimensional arrays of small capacitance SQUIDs have been studied experimentally. The effective Josephson coupling between neighboring electrodes is tunable in situ. The arrays can be tuned from a Josephson-like state, with low resistance and sharp critical current, to a Coulomb blockade state, with infinite resistance and sharp threshold voltage. A quantum phase transition occurs at the crossover between these two types of behavior, which is evident from an analysis of the temperature dependence of the zero bias resistance.
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29.
  • Hermansson, J., et al. (författare)
  • Complexes of the self-interstitial with oxygen in irradiated silicon : A new assignment of the 936 cm-1 band
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 302-303, s. 188-192
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Three vibrational infrared absorption bands at about 936, 944 and 956 cm-1 appear commonly in spectra of Czochralski-grown silicon irradiated at low temperatures. All three bands have earlier been assigned to local vibrational modes related to oxygen in the complex of the silicon and the oxygen interstitials (IOi). However, it is shown that such an assignment of the 936 cm-1 band clearly is inconsistent with many facts and observations and that the band is most likely due to oxygen vibrations in the Si interstitial pair and interstitial oxygen complex, I2Oi. © 2001 Published by Elsevier Science B.V.
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30.
  • Holm, William, et al. (författare)
  • Negative magnetoresistance in an yba2cu3O7-delta thin-film
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 2309-2310
  • Tidskriftsartikel (refereegranskat)abstract
    • Negative magnetoresistance was observed in a thin YBa2Cu3O7-delta film which could be correlated with the presence of magnetic impurities. After empirical compensation for this effect the fluctuation conductivity was well described by the Aronov-Hikami-Larkin theory.
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31.
  • Holm, William, et al. (författare)
  • Study of magnetoresistance in oriented yba2cu3O7-delta thin-film
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194, s. 2291-2292
  • Tidskriftsartikel (refereegranskat)abstract
    • The magnetoresistance of a c-axis oriented YBa2Cu3O7-delta thin film has been measured in magnetic fields, B, up to 12 T. The magnetic field was oriented both perpendicularly and parallel to the basal plane. The temperatures ranged up to epsilon = (T-T(c))/T(c) almost-equal-to 1/3 for B parallel-to c, while for B perpendicular-to the range was limited to epsilon less-than-or-equal-to 0.16. Analysis of the data in terms of superconducting fluctuations described by the Aronov-Hikami-Larkin theory is discussed.
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32.
  • Hong, V. V., et al. (författare)
  • Nitrogenation studies of Nd2Fe17 alloys
  • 2003
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 327:04-feb, s. 404-409
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present investigation, the kinetics of nitrogenation of Nd2Fe17 alloys were studied in order to optimize the magnetic properties of the pure Nd2Fe17 alloy by the introduction of nitrogen interstitials. The nitrogenation kinetics was followed in the temperature interval 1173-1473K by the use of the thermogravimetric (TG) technique. The nitrogenated alloys were prepared from a Nd2Fe17 master alloy by heat treating in different partial pressures of nitrogen under well-controlled conditions. The results of the TG experiments showed that there was an initial incubation time before the onset of nitrogenation. The length of the incubation period was found to be a function of temperature and the partial pressure of nitrogen in the gas. The nitrogen used was of high purity (99.9999% N-2). The gas purification system adopted in the present work could effectively remove traces of reducing as well as oxidizing impurity gases in the system. In order to remove the traces of CO, CH4 and H-2, (as well as other hydrocarbons) if present, the gas was passed through a column of Cu turnings kept at 973 K. The lower portion of the Cu column was surface oxidized. The reducing gases got oxidized passing through this column and CO2 and H2O were formed. Further, the oxygen impurity in the gas (ca. 10(-2) Pa) could react with the remaining reducing gases. These products were absorbed by columns of ascarite and dehydrite, respectively. Remaining oxygen impurity in the gas could then be removed by passing the gas through a furnace containing Mg turnings at 773 K. The rate of nitrogen uptake after this period was found to increase with increasing temperature. After an initial rapid nitrogenation period, the reaction rate was found to slow down, possibly due to nitrogen atoms diffusing into the bulk. The reaction was found to be rapid, and the incubation time was conspicuously absent, when nitrogen gas was used without the purification steps mentioned earlier. Oxygen impurity in the gas was found to have a strong influence on the reaction kinetics. Heat capacity measurements, as well as magnetic hysteresis measurements, were also conducted. The heat capacity of the Nd2Fe17 master alloy, as well as that of the nitrogenated alloys, Was determined in the temperature interval 293-773 K by the use of the differential scanning calorimetric technique. From the experimental heat-capacity data the Curie temperatures of the alloys were derived. Compared to the master alloy, significantly increased Curie temperatures were obtained for the nitrogenated alloys. The magnetic measurements were conducted at 300 K by the use of a quantum design magnetometer. The results obtained indicate that the nitrogenated alloys were soft magnets as no large hysteresis loop was found to exist.
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33.
  • Hourahine, B., et al. (författare)
  • Evidence for H2* trapped by carbon impurities in silicon
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 197-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Local mode spectroscopy and ab initio modelling are used to investigate two trigonal defects found in carbon-rich Si into which H had been in-diffused. Isotopic shifts with D and 13C are reported along with the effect of uniaxial stress. Ab initio modelling studies suggest that the two defects are two forms of the CH2* complex where one of the two hydrogen atoms lies at an anti-bonding site attached to C or Si, respectively. The two structures are nearly degenerate and possess vibrational modes in good agreement with those observed.
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34.
  • Hourahine, B., et al. (författare)
  • Optically active hydrogen dimers in silicon
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 176-179
  • Tidskriftsartikel (refereegranskat)abstract
    • First-principles calculations are used to explore the structure and properties of several defects which are prominent luminescent centers in Si. The trigonal defects B41 and B711, which are known to contain two hydrogen atoms in equivalent and inequivalent sites, respectively, are attributed to a hexavacancy containing two H atoms in different configurations. It is suggested that the J luminescence centers arises from a stable hexavacancy without hydrogen atoms
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35.
  • Johannson, J., et al. (författare)
  • Coulomb blockade in anodised titanium nanostructures
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1796-1797
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the electrical transport properties of narrow titanium (Ti) wires which are thinned by anodic oxidation. At temperatures below 1 K the current-voltage (IV) characteristics of the resulting Ti/TiOx nanostructures exhibit a zero current state due to the occurrence of Coulomb blockade. An indium gate electrode is placed on top of the anodised region, and the modulation of the conductance as a function of the gate voltage is investigated.
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36.
  • Jones, R., et al. (författare)
  • Thermal double donors in Si and Ge
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 8-12
  • Tidskriftsartikel (refereegranskat)abstract
    • Three experiments appear to cast doubt on self-interstitial-free models of the family of thermal donors, based on oxygen defects of increasing size. These are (a) the rapid transformation of TDD(N) into TDD(N+1) with activation energies considerably lower than that of oxygen diffusion, (b) the lack of any appreciable spin-density on oxygen in TDD(N)+, and (c) the observation of only two oxygen related vibrational modes associated with each donor. However, we show that the oxygen-only model of the donors is compatible with experiment for a structure involving an insulating core with normal oxygen coordination, surrounded by over-coordinated oxygen atoms which are responsible for the donor activity. It is also shown that the calculated stress-energy tensors for the early donors are in good agreement with the measurements.
  •  
37.
  • Kemerink, Martijn, et al. (författare)
  • Exchange interaction in degenerate p-type quantum wells
  • 1998
  • Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 256, s. 503-506
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed comparison between a magneto-transport experiment on a p-type GaAs/AlGaAs quantum well and model calculations is presented. It is shown that for all magnetic fields the Shubnikov-de Haas (SdH) trace is strongly influenced by the exchange interaction, in contrast with n-type structures where this interaction is only important in high magnetic fields. As a consequence, the effective hole masses that are extracted from the temperature dependence of the SdH oscillations are not a good measure of the single-particle hole mass, and can be regarded as meaningless. (C) 1998 Elsevier Science B.V. All rights reserved.
  •  
38.
  • Koptioug, Andrei, 1956-, et al. (författare)
  • Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions
  • 1990
  • Ingår i: Physica. B, Condensed matter. - : Esevier. - 0921-4526 .- 1873-2135. ; 164:1-2, s. 200-204
  • Tidskriftsartikel (refereegranskat)abstract
    • It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.
  •  
39.
  • Kubatkin, S E, et al. (författare)
  • Movement of scattering centers in a point contact induced by a scanning tunneling microscope
  • 1994
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 194-196:Part 1, s. 991-992
  • Tidskriftsartikel (refereegranskat)abstract
    • A new method is introduced to study transport in a mesoscopic sample. The electric field from an STM-tip is used to locally influence a mesoscopic object. We detect abrupt changes in the mesoscopic signal both as a function of the tip position and tip-sample voltage. They could be interpreted as due to spatial shifts or changes in the activity of scattering centers in the sample.  
  •  
40.
  • Lindstrom, J.L., et al. (författare)
  • Interaction between self-interstitials and the oxygen dimer in silicon
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 284-289
  • Tidskriftsartikel (refereegranskat)abstract
    • Interactions between the oxygen dimer (O2i) and silicon self-interstitials (I) and vacancies (V) have been studied in Czochralski-grown silicon (Cz-Si) crystals using infrared absorption and deep level transient spectroscopies. The focus in this report is on reactions of O2i with I. The first step in this interaction is found to be the formation of a self-interstitial-dioxygen centre (IO2i) with oxygen-related local vibrational mode (LVM) bands at 922 and 1037 cm-1. During the second formation step, another centre, I2O2i, with LVM bands at 918 and 1034 cm-1 is suggested to appear. A Si-related band at about 545 cm-1 is also assigned to both the IO2i and I2O2i centres. The IO2i centre is found to be electrically active with an acceptor level at Ec - 0.11 eV. The both defects, IO2i and I2O2i, are stable at room temperature and anneal out at about 400 and 550 K, respectively. © 2001 Elsevier Science B.V. All rights reserved.
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41.
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42.
  • Lundqvist, Björn, et al. (författare)
  • Vortex dynamics for in- and out-of-plane magnetic fields in oxygen deficient single crystals of YBa2Cu3O7-delta
  • 2000
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284:Part. 1, s. 705-706
  • Tidskriftsartikel (refereegranskat)abstract
    • The resistive transition into a glassy vortex state in oxygen deficient single crystals of YBa2Cu3O7-delta (YBCO) has been studied for magnetic fields 0 less than or equal to B less than or equal to 12 T along the crystallographic c-axis, parallel to the ab plane, and also with a small misalignment of 1 degrees from the ab plane. Angular sweeps of the magnetic field reveal a sharp dip in the resistivity for B \textbackslash\textbackslash ab, which is attributed to intrinsic pinning of vortices between the planes. For Bile the vortex glass line is well described by B-g(T)= B-0[(1 - T/T-c)/(T/T-c)](alpha), where B-0 is anisotropy dependent and alpha approximate to 1.0-1.2. For B \textbackslash\textbackslash ab the behaviour is significantly different, and at high magnetic fields a change to a field-independent vortex solid-to-liquid transition is observed. This behaviour disappears for small misalignments between B and ab.
  •  
43.
  • Marcinkevicius, Saulius, et al. (författare)
  • Changes in carrier dynamics induced by proton irradiation in quantum dots
  • 2002
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 314:04-jan, s. 203-206
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of proton irradiation on carrier dynamics were investigated by time-resolved photoluminescence on different InGaAs/GaAs quantum-dot (QD) structures varying in QD surface density and substrate orientation, as well as thin InGaAs quantum wells. The carrier lifetimes in the dots are much less affected by proton irradiation than in the wells. Decrease in lifetimes of only 40 percent at the highest proton dose are observed in some of the QDs, whereas an similar to20 to similar to40-fold decrease is observed in the wells. Similar trends were observed for all quantum dot samples.
  •  
44.
  • Markevich, V.P., et al. (författare)
  • Local vibrational mode bands of V-O-H complexes in silicon
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 300-304
  • Tidskriftsartikel (refereegranskat)abstract
    • H2 molecules, which are introduced into moderately doped silicon crystals by high-temperature in-diffusion from H2 gas ambient followed by fast cooling to room temperature, are found to interact effectively with the defects induced by irradiation of the crystals with fast electrons. In Czochralski-grown silicon crystals, the interaction of the mobile H2 molecules with vacancy-oxygen defects (A centers) leads to the creation of V-O-H2 complexes. This complex gives rise to infrared (IR) absorption lines at 943.5, 2126.4, and 2151.5 cm-1. Ab initio calculations showed that the most stable configuration of V-O-H2 consists of one oxygen and two hydrogen atoms sharing a vacancy site. It is suggested that the interaction of the V-O-H2 complexes with interstitial oxygen atoms results in the formation of V-O2-H2 complexes, which are responsible for the IR absorption line at 891.5 cm-1.
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45.
  •  
46.
  • Mattsson, J., et al. (författare)
  • Temperature dependence of free energy barriers in a Cu(7 at. % Mn) spin glass
  • 1994
  • Ingår i: Physica B: Condensed Matter. - : Elsevier BV. - 0921-4526. ; 194-196:1, s. 305-306
  • Tidskriftsartikel (refereegranskat)abstract
    • Time dependent zero-field-cooled magnetisation measurements have been performed in order to determine the temperature dependence of the free energy barriers, B(T), in the spin glass Cu(7 at% Mn). The results have been analysed using the temperature dependence of the free energy barriers predicted in the droplet model, B( T)∝Δ( T) Lψ where L is the size of the droplet. It is found that as T→0 K, Δ (T)→constant, yielding activated dynamics in agreement with the droplet model. As T→ Tg, Δ (T) decreases but stays finite at Tg. This result is in contrast to the current droplet model where Δ (T)→0 when T→ Tg.
  •  
47.
  • Murin, L.I., et al. (författare)
  • Early stages of oxygen clustering in hydrogenated Cz-Si : IR absorption studies
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 302-303, s. 180-187
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The formation kinetics of small oxygen clusters in hydrogenated Si has been studied by means of infrared absorption measurements. Hydrogen was introduced into the crystals by in-diffusion from H2 gas at 1200-1300°C. The samples were heated at temperatures in the range of 280-370°C for different durations. At initial stages of heat-treatment, enormous generation rates of the oxygen dimer have been observed in hydrogenated samples. This indicates highly enhanced diffusion of the interstitial oxygen atoms. The maximum achievable concentration of the dimers is found to be limited by their dissociation rate even at temperatures of about 300°C, while in as-grown crystals the capture processes are known to be dominant in this temperature region. An explanation of this phenomenon is presented. © 2001 Published by Elsevier Science B.V.
  •  
48.
  • Murin, L.I., et al. (författare)
  • Isotopic effects on vibrational modes of thermal double donors in Si and Ge
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 290-293
  • Tidskriftsartikel (refereegranskat)abstract
    • The local vibrational modes of thermal double donors in Si and Ge are investigated by FTIR and ab initio modelling. At most, two oxygen modes are detected from each donor, which exhibit regular shifts with increasing donor number. By using mixtures of 16O and 18O, it is found that in Si the upper band does not yield any new modes suggesting that any oxygen atom is decoupled from any other. However, the lower frequency bands exhibit unique mixed modes proving for the first time that oxygen atoms are coupled together and in close spatial proximity. Ab initio calculations demonstrate that the modes and their isotopic shifts are consistent with a model involving two parallel chains of oxygen atoms linking second neighbour Si atoms, terminated by O-atoms close to the normal position for interstitial O. © 2001 Elsevier Science B.V. All rights reserved.
  •  
49.
  • Narayan, V., et al. (författare)
  • Calculation of the temperature dependence of hot electron scattering in heavily p-doped GaAs using a high-temperature approximation to the dielectric function
  • 2002
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 324:1-4, s. 393-402
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a high-temperature approximation to the dielectric function within the random phase approximation, we calculate hot electron scattering rates, as a function of temperature and doping density, in p-doped GaAs. The dielectric function of the holes contains contributions from intraband excitations and interband excitations. The former reduces to an analytic form within the two pole approximation (which used Boltzmann statistics), whereas the latter was calculated numerically. The collective excitation mode of the holes was defined by intraband excitations, since at very small wavevectors, the interband excitations vanish. However, at low temperature the interband excitations were found to be the dominant Landau damping mechanism, which strongly suppressed the plasmon at moderate doping levels. At high temperature the excitations from the heavy to light band were partially suppressed, and the plasmon was not overwhelmingly Landau damped by either interband or intraband excitations. At room temperature, an analytic dielectric function where the interband excitations have been neglected, may be used to accurately calculate hot electron mean free paths. This approximation was found to become more accurate with lower doping levels, but was not appropriate at low temperature. © 2002 Elsevier Science B.V. All rights reserved.
  •  
50.
  • Nguyen, Son Tien, 1953-, et al. (författare)
  • Electron-paramagnetic-resonance studies of defects in electron-irradiated p-type 4H and 6H SiC
  • 1999
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 655-658
  • Tidskriftsartikel (refereegranskat)abstract
    •  Defects in p-type 4H and 6H SiC irradiated by 2.5 MeV electrons were studied by electron paramagnetic resonance (EPR). Two anisotropic EPR spectra, labeled I and II, were observed in both 4H and 6H SiC. These spectra demonstrating triclinic symmetry of the center can be described by an effective electron spin S=1/2. The angle α between the direction of the principal gz of the g-tensors and the c-axis is determined as 63° and 50° for spectra I and II, respectively. In the 6H polytype, a third also similar EPR spectrum was detected. Based on their similarity in the electronic structure (electron spin, symmetry, g values), annealing behavior and temperature dependence, these spectra are suggested to be related to the same defect occupying different inequivalent lattice sites in 4H and 6H SiC. A pair between a silicon vacancy and an interstitial is a possible model for the defect.
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