SwePub - sökning: L773:1521 3951

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1.	Beenken, W J D, et al. (författare) Excited state properties of neutral and charged ter-fluorene with and without a keto-defect 2008 Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 245:5, s. 849-853 Tidskriftsartikel (refereegranskat)abstract Stimulated by the recent experimental report of optical properties of charged oligofluorenes [S. Fratiloiu et al., J. Phys. Chem. B 210, 59845993 (2006)], we have used time-dependent density functional theory (TD-DFT) to study the electronic structure of neutral and charged ter-fluorene with and without keto-defect. We have characterized the excited states by site- and space-based representations of the density matrix. For the defectless neutral species we found typical excitons, while the first excited states of the corresponding charged species represent long-range oscillations of the electron or hole along the whole oligomer. For the neutral ketonized ter-fluorene we found trapping of the excited electron. Similarly, the unpaired electron of the anion ground' state is trapped. The excited state properties of the cation; however, are insensitive to the keto-defect.
2.	Darakchieva, Vanya, et al. (författare) Assessment of phonon mode characteristics via infrared spectroscopic ellipsometry on a-plane GaN 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1594-1598 Tidskriftsartikel (refereegranskat)abstract Generalized infrared spectroscopic ellipsometry was applied to study the vibrational properties of anisotropically strained a-plane GaN films with different thicknesses. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and strain-free frequency of the GaN A,(TO) mode. These results are compared with previous theoretical and experimental findings and discussed.
3.	Grivickas, Vytautas, et al. (författare) Strong photoacoustic oscillations in layered TlGaSe2 semiconductor 2007 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:12, s. 4624-4628 Tidskriftsartikel (refereegranskat)abstract Periodic deflections of infrared probe are observed in TlGaSe2 after lateral excitation with optical pulse. The effect is explained by generation of photoacoustic dilatational wave, which propagates within the crystal. Low pulse fluence (0.01 mJ/cm(2)) is needed to induce such wave when the layer plane is excited. Acoustic wave is generated within a mu m-distance near the excited face, much shorter then the light penetration depth, 1/alpha, where alpha is the absorption coefficient. In the temperature range 105-120 K, where ferroelectric-paraelectric phase transition occur in TlGaSe2, discontinuous changes of the longitudinal sound velocity have been detected.
4.	Harati Zadeh, Hamid, 1964-, et al. (författare) Optical observation of discrete well width fluctuations in wide band gap III-nitride quantum wells 2007 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:5, s. 1727-1734 Tidskriftsartikel (refereegranskat)abstract A detailed observation of discrete well width fluctuations via localized excitons in the photoluminescence (PL) spectra of MOCVD-grown undoped GaN/Al0.07Ga0.93 N multiple quantum wells (MQWs) has been reported. Doublet excitonic features with a distance varying between 10 and 25 meV for different well widths (1.5 to 4.5 nm) are observed in the PL spectra. They are explained in terms of discrete well width variations by one c-lattice parameter, i.e. two GaN monolayers. By mapping the PL measurements across the samples with different excitation spot size, it is shown that the extension of areas with a constant well width is less than 1 μm2. TEM pictures give evidence of interface roughness, although the contrast is weak at this low Al composition. In addition we observe a long-range variation of the PL peak position across the sample, interpreted as a fluctuation in Al composition in the barriers. The residual broadening of an excitonic peak (apart from the splitting related to well width fluctuations) is about 10 meV, somewhat larger for larger well widths, and is mainly ascribed to hole localisation potentials in the QWs. Additional broadening occurs in the MQWs due to inequivalent properties of each QW within the excitation spot. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
5.	Heszler, P, et al. (författare) On the Selectivity of Nanostructured Semiconductor Gas Sensors 2007 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:11, s. 4331-4335 Tidskriftsartikel (refereegranskat)abstract Different methods are presented for improving chemical selectivity and sensitivity of semiconductor gassensors consisting of nanostructured thin films. Pure and doped WO3 nanoparticles, forming nanoporouslayers, are used as test material. The chemical selectivity is increased by applying different operating tem-peratures, using temperature modulation and pattern recognition methods, and by a fluctuation enhancedspectroscopy technique. The selectivity improvement of a fluctuation enhanced sensor is compared to thatof a classical resistive sensor.
6.	Isoya, J., et al. (författare) EPR identification of intrinsic defects in SiC 2008 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:7, s. 1298-1314 Tidskriftsartikel (refereegranskat)abstract The structure determination of intrinsic defects in 4H-SiC, 6H-SiC, and 3C-SiC by means of EPR is based on measuring the angular dependence of the 29Si/13C hyperfine (HF) satellite lines, from which spin densities, sp-hybrid ratio, and p-orbital direction can be determined over major atoms comprising a defect. In most cases, not only the assignment of the variety due to the inequivalent sites (h- and k-sites in 4H-SiC) but also the identification of the defect species is accomplished through the comparison of the obtained HF parameters with those obtained from first principles calculations. Our works of identifying vacancy-related defects such as the monovacancies, divacancies, and antisite-vacancy pairs in 4H-SiC are reviewed. In addition, it is demonstrated that the observation of the central line of the TV2a center of S = 3/2 has been achieved by pulsed-ELDOR. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
7.	Kastberg, Anders, 1963-, et al. (författare) A three-dimensional Brownian motor, realised with symmetric optical lattices 2009 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 246:5, s. 999-1005 Tidskriftsartikel (refereegranskat)abstract A three-dimensional Brownian motor is realised using lasercooled caesium atoms trapped in a system of two static, and individually symmetric, optical lattices; a so-called double optical lattice. Isotropic fluctuations, emanating from light scattering, are rectified, and the diffusion of the ensemble of atoms is biased, with a resulting constant velocity that is controllable both in direction and magnitude. The working principle of the Brownian motor can be seen as a pulsation between two different potentials, both symmetric but around different points. The correlation between interferometric spatial offsets, and imbalance in optical pumping rates, leads to a spatio-temporal asymmetry sufficient for generating a controlled, directed motion.
8.	Koseoglu, Y, et al. (författare) Synthesis, characterization and ESR measurements of CoNiO nanoparticles 2005 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 242:8, s. 1712-1718 Tidskriftsartikel (refereegranskat)abstract Powders of cobalt core with a nickel (11) oxide shell (CoNiO) have been studied by Electron Spin Resonance (ESR) technique in the temperature range of 10-300 K. A strong and broad (1300 G) single ESR peak in X-, K- and Q-band spectra has been observed at all the temperature ranges. While the resonance field remains almost constant, both the ESR line intensity and the line width were seen to increase first slowly down to T-c = 160 K. And then both the resonance field and the ESR signal intensity decrease and the line width increase with decreasing temperature. Below T. the intensity smoothly decrease down to 10 K. This kind of behavior is attributed to a typical spin-glass like behavior. Some small and relatively smooth changes at about 60 K, 90 K, 210 K, and 250 K are appeared as well. A linear dependence of resonance field to microwave frequency is observed at room temperatures and the effective g-value and internal field are theoretically found as 2,17 and 90 G, respectively. The experimental data indicate a very strong spin disorder (spin frustration) due to antiferromagnetic exchange interactions among the spins. This is attributed to the D-M anisotropy on the particle surfaces that it is expected to enhance due to increment of surface-to-volume ratio.
9.	Liu, Xinju, 1979, et al. (författare) Intersubband absorption at 1.5-3.5 µm in GaN/AlN multiple quantum wells grown by molecular beam epitaxy on sapphire 2007 Ingår i: Physica status solidi. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:8, s. 2892-2905 Tidskriftsartikel (refereegranskat)abstract Ten and twenty period multiple quantum well structures with 1.5-5.4 nm GaN wells and 1.2-5.1 nm AlN barriers were grown on sapphire by molecular beam epitaxy. Layer thicknesses were determined by X-ray diffraction measurements and simulations. Reciprocal space mapping showed that the relaxation of the quantum well layers was independent of the buffer layer thickness. Intersubband absorption was observed by Fourier transform infrared spectroscopy at λ ∼ 1.5-3.5 μm. Monolayer fluctuations in the quantum well width induced multiple peaks in spectra, which were well fitted to Lorentzian peaks of only 57 meV linewidth. Samples were very homogeneous as the absorption peak energy varied less than 1% along ∼4 cm on 2 inch wafers. The intersubband transition energies were calculated considering the conduction-band nonparabolicity, built-in fields, strain, and many-body effects. The calculation and comparison to the fitted Lorentzian peak energies indicated a moderate blueshift due to many-body effects. It was shown by both experiments and calculations that the AlN barrier width affects the intersubband transition energy.
10.	Makarova, Tatiana, 1959-, et al. (författare) Ageing effects in nanographite monitored by Raman spectroscopy 2008 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:10, s. 2082-2085 Tidskriftsartikel (refereegranskat)abstract The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated ampoules, has been studied by monitoring the evolution of the Raman spectra. Reduction of some Raman bands associated with “in-plane” structural defects, such as vacancies, dislocations or grain boundaries, and those associated with “out-of-plane” defects, such as stacking faults, is accompanied by the rise of new bands around 1180 and 2000 cm–1. The development of these bands is suppressed in nanographite samples exposed to a flux of pure anhydrous hydrogen.
11.	Makarova, Tatiana L., et al. (författare) Experimental realization of high spin states in dilutely hydrogenated fullerenes 2009 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 246:11-12, s. 2778-2781 Tidskriftsartikel (refereegranskat)abstract A novel method for preparing dilutely hydrogenated fullerenes H:C60 is presented. DFT calculations of the Raman spectra at the B3LYP/3-21G level are compared with the experimental data. Under the laser treatment these phases form a rich variety of dimeric and polymeric structures, quite in contrast to pristine C60 which forms dimers and polymers bonded through the [2 + 2] addition, and in contrast to heavily hydrogenated fullerenes which do not polymerize at all. Dilutely hydrogenated fullerenes polymerize differently, forming both double bonded structures and single bonded dimers. We have shown that dilute hydrogenation of C60 creates large amount of unpaired spins which disappear due to the formation of diamagnetic single bonded dimers.
12.	Makarova, T. L. (författare) Graphite under the magnetic force microscope 2007 Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 244:11, s. 4138-4142 Tidskriftsartikel (refereegranskat)
13.	Malinauskas, T, et al. (författare) Contribution of dislocations to carrier recombination and transport in highly excited ELO and HYPE GaN layers 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1426-1430 Tidskriftsartikel (refereegranskat)abstract Nonequilibrium carrier dynamics has been investigated in ELO and HYPE grown GaN layers in a wide temperature and excitation range by using the time-resolved picosecond FWM technique. Carrier lifetime in the samples at 300 K increased up to 2.8-5.1 ns in accordance with the decreasing threading dislocation density from 4 x 10(7) cm(-2) (ELO) to mid 106 cm(-2) in HYPE layers. At T < 100 K, the hyperbolic shape of FWM kinetics indicated carrier density dependent radiative lifetimes, which gradually decreased at lower temperatures to a few hundreds of ps. The dominance of bimolecular recombination in HVPE layers at 10-40 K was demonstrated by the exposure characteristic of FWM, that has shown a sublinear growth of carrier density with excitation, N proportional to I-1/2. Numerical fitting of the set of FWM kinetics at various T confirmed the temperature dependence of bimolecular recombination coefficient B proportional to T-1/5 and provided its value B = 2 x 10(-11) cm(3)/s at 300 K and 3.2 x 10(-9) cm(3)/s at 9 K. The measured bipolar diffusion coefficients allowed determination of carrier diffusion length of 0.8-1 mu m at 300 K and its dependence on dislocation density and temperature. (c) WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
14.	Malysheva, Lyuba, et al. (författare) Interband transmission in armchair graphene ribbons with a step-like profile of potential energy: Relevance to Kleins tunneling 2009 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 246:11-12, s. 2549-2552 Tidskriftsartikel (refereegranskat)abstract Three principal results concerning graphene-based wires and their ambipolar behavior are presented. First, it is the exact expression of the transmission coefficient for armchair graphene wires described by the tight-binding Hamiltonian with the step-like change U of site energies. Second, the exact relation between the energy of incident electrons or holes and potential U at which there is no backscattering for the given mode of the transverse motion. Third, the range of relevance of Kleins formula describing the motion of relativistic particles in the same potential profile is established. Analysis of newly derived results shows that physics of interband transitions at constant energy in graphene wires is richer than it was believed.
15.	Malysheva, Lyuba, et al. (författare) Orientation of OH terminal groups in oligo(ethylene glycol)-terminated self-assemblies : results of ab initio modeling 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:13, s. 3489-3493 Tidskriftsartikel (refereegranskat)abstract
16.	Malysheva, Liubov, et al. (författare) Tunneling through molecular wires : A comparison of the Franz two-band model with exact results 2007 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:11, s. 4244-4247 Tidskriftsartikel (refereegranskat)abstract This report concerns finding the tunneling exponential factor exp [-2 kappa(E) d], on the basis of electronic band structure of organic oligomers, which are d-long molecular wires. It is shown that energy dependence kappa(E) given by the Franz two-band model agrees remarkably well with exact model calculations, provided that the quadratic dispersion parameter is calculated from the real (non-parabolic) band structure of organic oligomers. For narrow and moderate band gaps (with respect to the band width), the approximate dependence is practically indistinguishable from that which is obtained from these exact calculations. The divergence (particularly, in the mid of the band gap) becomes appreciable and increases with an increase of the band-gap/band-width ratio. The apparent effective mass (as it is estimated from kappa(E) measured at the Fermi energy E=E-F) is defined in terms of the inherent parameters of the wire. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
17.	Monemar, Bo, et al. (författare) Recent developments in the III-nitride materials 2007 Ingår i: Physica status solidi. B, Basic research. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 244:6, s. 1759-1768 Tidskriftsartikel (refereegranskat)abstract We review a selection of recent research work on III-nitride materials, limiting the scope to bulk properties and quantum well structures. The different stages of development of the compounds AlN, GaN and InN are illustrated, with reference to the electronic properties demonstrated so far. The important alloy systems AlxGa1-xN and InxGa1-x have quite different properties, still not understood in detail for high Al and In contents, respectively. Some important unresolved issues are highlighted, and possible future directions of the materials development are indicated. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
18.	Monemar, Bo, 1942-, et al. (författare) Recombination of free and bound excitons in GaN 2008 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:9, s. 1723-1740 Tidskriftsartikel (refereegranskat)abstract We report on recent optical investigations of free and bound exciton properties in bulk GaN. In order to obtain reliable data it is important to use low defect density samples of low doping. We have used thick GaN layers (of the order of 1 mm) grown by halide vapour phase epitaxy (HVPE) with a residual doping down to <1016 cm-3 in this work. With such samples all polarisation geometries could also easily be exploited. The influence of the surface states on the photoluminescence (PL) experiments is analysed, it is concluded that surface recombination plays an important role for the free exciton (FE) recombination. The electronic structure of the FEs is discussed in detail, including the influence of spin-exchange and polariton effects, and compared with polarised PL spectra at 2 K. The detailed structure of excited states from the PL spectra is discussed, but further data are needed to fully explain all the peaks observed. The polarized FE spectra at room temperature allow a determination of the bandgap as 3.437 eV at 290 K, assuming an exciton binding energy of 25 meV. The PL transient of the A FE is very short (about 100 ps) for the no-phonon (NP) line interpreted as dominated by nonradiative surface recombination. The longitudinal-optical (LO) phonon replicas of the A FE exhibit a longer decay of about 1.4 ns at 2 K, suggested to represent the bulk lifetime of the FE. The corresponding decay time at 290 K is 9 ns in our samples, a value that might be affected by nonradiative recombination. The Si and O donor bound exciton (DBE) spectra with sharp NP lines at 3.4723 eV and 3.4714 eV respectively, are well resolved together with the so-called two-electron transitions (TETs) and several optical phonon replicas. The electronic structure of the DBE states including excited rotational states is discussed and compared with experiment. The well-resolved TET lines allow an accurate determination of the ground state binding energy of the Si donor as 30.4 meV and 33.2 meV for the O donor. The PL transients of the DBEs reveal a non-exponential decay for the NP lines. The DBE NP transient lineshape is assumed to be influenced by optical dispersion and scattering in the vicinity of exciton resonances, as well as by surface effects. The DBE decay time can most properly be deduced from the PL decay of the respective TETs and LO replicas, leading to values in the range of 1.1-1.8 ns. These values differ significantly from previous theoretical predictions, where values about two orders of magnitude shorter were obtained. A tentative discussion of the main observed features of acceptor bound excitons (ABEs), which are much less studied in GaN, is given. A decay time of about 0.9 ns for the shallowest 3.466 eV ABE is estimated, i.e. shorter than that for the shallow donor BEs. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
19.	Monemar, Bo, et al. (författare) The dominant shallow 0.225 eV acceptor in GaN 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1604-1608 Tidskriftsartikel (refereegranskat)abstract We have studied the optical signatures of the Mg acceptor in GaN, using samples that are doped with Mg during MOCVD growth. In order to reduce the defect density in the material and thus achieve narrow linewidths in optical spectra we have used thick HVPE grown GaN layers as templates in the MOCVD growth. The photoluminescence (PL) spectra show two acceptor-related bound exciton peaks at 3.466 eV and 3.455 eV respectively. In the lower photon energy range the 3.27 eV emission with its LO-phonon replicas is dominant, riding on a broad background emission peaking at about 3.1 eV. These results, together with previous data in the literature, indicate that there are two acceptors in Mg-doped GaN, one dominating the optical spectra (the 3.466 eV and the 3.27 eV emissions) and another related to the 3.455 eV and the 3.1 eV emissions. We suggest that the latter is related to the Mg acceptor, while the former is a H-related complex, not necessarily involving Mg.
20.	Nitze, Florian, 1971-, et al. (författare) Ammonia assisted growth of multiwalled carbon nanotubes 2009 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 246:11-12, s. 2440-2443 Tidskriftsartikel (refereegranskat)abstract Bamboo structured nitrogen-containing carbon nanotubes are grown on e-beam deposited thin metal films (cobalt/iron) by chemical vapor deposition. The approach uses ammonia as supporting gas to form nano catalyst particles in the pretreatment phase. Ammonia is also used as nitrogen source. The effect of ammonia on the grown structures at different temperatures (720 and 810 °C) is investigated by SEM, TEM and Raman spectroscopy. We show that ammonia promotes growth of vertically aligned CNT carpets on thicker metal films (5 nm) than usually used. At the same time ammonia is inducing a high amount of defects but this effect changes significantly with temperature. At 720 °C defects are clearly ammonia induced while at 810 °C the defects seem to be induced by a different mechanism. Furthermore, the presence of ammonia in both pretreatment phase and growth phase reduces the outer diameter of the grown nanotubes.
21.	Olevik, David, et al. (författare) Stability of carbon nanotubes to laser irradiation probed by Raman spectroscopy 2008 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:10, s. 2212-2215 Tidskriftsartikel (refereegranskat)abstract We report on a systematic study of the influence of laser irradiation on the Raman spectra of HiPco-produced single-wall CNTs. Specifically, we have examined the Raman response of bundled CNTs to: i) laser power density; ii) exposure time and iii) photon energy (1.96 and 2.33 eV). Our results show that irreversible destruction of CNTs in the bundles can occur at even low laser power density (0.15 kW/cm2). The tubes with smaller diameters are influenced first and the rate of CNT destruction increases with photon energy. Finally, we determined that when investigating destruction of CNT bundles, the use of a low laser power density is required because changes in the structure of the bundles can lead to sample temperature changes for otherwise identical measurement parameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
22.	Olovsson, Weine, et al. (författare) Core-level shifts in complex metallic systems from first principle 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:11, s. 2447-2464 Tidskriftsartikel (refereegranskat)abstract We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations.
23.	Silvera, Isaac F., et al. (författare) Calibration of the ruby pressure scale to 150 GPa 2007 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 244:1, s. 460-467 Tidskriftsartikel (refereegranskat)abstract For many years the ruby pressure standard has been the so-called quasi-hydrostatic scale of Mao, Xu, and Bell published in 1986. The calibration was determined by X-ray diffraction of metal markers in an argon pressurization medium to 80 GPa, along with simultaneous measurement of the shift of the ruby R lines. We have used data in the literature, as well as our own, mostly for ruby in quasi-hydrostatic helium, to produce a new ruby scale with calibration data that extends to 150 GPa. The new scale shows that at the highest shifts of the ruby R lines the pressures are substantially higher than on the old scale. To understand small systematic shifts of the pressures as determined from the X-ray diffraction of metal "markers" used in the calibration, a finite element analysis of quasi-hydrostatic conditions in a diamond anvil cell has been carried out.
24.	Svensson, Johannes, 1978, et al. (författare) Field emission induced deformations in SiO2 during CVD growth of carbon nanotubes 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243, s. 3524-3527 Tidskriftsartikel (refereegranskat)abstract The application of an electric field while growing carbon nanotubes with CVD can induce deformations in the SiO2 substrate. The effect is attributed to field emission from the tubes and Marangoni convection in a small molten SiO2 region underneath the tubes. Postgrowth deformation has been performed as well as large scale deformations using the collective effect of many field emitters. The porosity of one type of deformation is also examined and discussed.
25.	Toropov, A.A., et al. (författare) III-V/II-VI heterovalent double quantum wells 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:4, s. 819-826 Tidskriftsartikel (refereegranskat)abstract We report on design, fabrication by molecular beam epitaxy, and photoluminescence (PL) studies of III-V/II-VI heterovalent structures containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well (QW). The studies of temperature-dependent and time-resolved PL have provided an insight into the nature of the exciton localization potential induced by the heterovalent interface. It is found that under the resonant conditions the observed emission mostly originates from the recombination of excitons confined in type II quantum-dot-like structures, where the holes are localised within the GaAs QW due to the well width fluctuations and the electrons are localized in the plane of the ZnCdMnSe QW due to the fluctuations of the conduction band offset at the heterovalent interface, induced by random variation of the interface microscopic structure. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA,.
26.	Tuomisto, F, et al. (författare) Dissociation of V-Ga-O-N complexes in HVPE GaN by high pressure and high temperature annealing 2006 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1436-1440 Tidskriftsartikel (refereegranskat)abstract We have used positron annihilation spectroscopy to study the high-pressure annealing induced thermal recovery of vacancy defects in free-standing GaN grown by hydride vapor phase epitaxy (HYPE). The results show that the in-grown Ga vacancy complexes recover after annealing at 1500-1700 K. Comparison of the experimental positron data with ab-initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. We show that the difference between the isolated V-Ga in electron irradiated GaN and the V-Ga-O-N complexes in highly O-doped GaN is clear, and the Ga vacancy related defect complexes that start dissociating at 1500 K can be identified as V-Ga-O-N pairs.
27.	Weber, Carsten, et al. (författare) Zero-phonon line broadening and satellite peaks in nanowire quantum dots: The role of piezoelectric coupling 2009 Ingår i: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 246:2, s. 337-341 Tidskriftsartikel (refereegranskat)abstract We investigate the influence of the one-dimensional character of the phonon modes in a catalytically grown GaAs nanowire on the absorption spectrum of an embedded quantum dot, focusing on the on the contribution from the piezoelectric coupling. In general, the reduced dimensionally of the phonons leads to spectral side peaks and a zero-phonon line broadening due to the energetically lowest (acoustic) phonon mode. While the deformation potential predominantly couples to radial modes, the piezoelectric interaction can also couple strongly to modes of axial character, leading to additional absorption features. The contribution of the piezoelectric coupling to the zero-phonon line is negligible. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
28.	Winell, Sofia, et al. (författare) Cation ordering in NiFe2-xCrxO4-spinels studied by Mössbauer spectroscopy in external fields 2008 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:8, s. 1635-1640 Tidskriftsartikel (refereegranskat)abstract NiFe2-xCrxO4, 0 < ;= x < ;= 1.8, produced from appropriate oxides, has been studied using Mossbauer spectroscopy (MS) at low and ambient temperatures and in external fields up to 7 Tesla. X-ray diffraction (XRD) shows all samples to be single phase cubic spinels, where a(0) change in x, as a concave curve, with a minimum at around x=1. Analyses, based on Mossbauer spectra, show NiFe2-xCrxO4 to be a nearly perfect inverted spinel for x < ;= 0.6. However, for higher x-values the ordering is more complicated. It is shown that iron also populates the octahedral positions for x > ;= 0.8.

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