bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of InN layers grown by MOCVD using analytical and high resolution TEM: The structure, band gap, role of the buffer layers
Authors: Ruterana P. , Abouzaid M. , Gloux F. , Maciej W. , Doualan J. L. , Drago M. , Schmidtling T. , Pohl U. W. , Richter W. 
Published: January 2006

AbstractIn this work we investigate the microstructure of InN layers grown by MOCVD on different buffer layers using TEM (InN, GaN). The large mismatch between the various lattices (InN, sapphire or GaN) leads to particular interface structures. Our local analysis allows to show that at atomic scale, the material has the InN lattice parameters and that no metallic In precipitates are present, meaning that the PL emission below 0.8 eV is a genuine property of the InN semiconductor. It is also shown that the N polar layers, which exhibit a 2D growth, have poorer PL emission than In polar layers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strain state analysis of InGaN/GaN – sources of error and optimized imaging conditions
Authors: Rosenauer A. , Gerthsen D. , Potin V. 
Published: January 2006

AbstractTransmission electron microscopy investigation of the chemical composition of Inx Ga1–x N/GaN layers by strain state analysis can lead to substantial artefacts. We evaluated simulated images in dependence of specimen thickness, specimen orientation and objective lens defocus. We observed that the measurement is in agreement with the true strain profile for certain conditions only. An analysis of error sources revealed that artefacts are mainly caused by a combination of delocalization and the composition dependence of the phases of the beams contributing to the image formation. The delocalization effect is minimized for interference of the undiffracted beam with one of the 000 ± 2 beams. The least chemical shift of the phases is obtained using the 000 + 2 beam and a strong excitation of 000 + 4. Images simulated for these conditions taking into account lattice plane bending and strain using finite‐element calculations revealed a good agreement of evaluated and true strain profiles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasmonic effects in InN‐based structures with nano‐clusters of metallic indium
Authors: Shubina T. V. , Ivanov S. V. , Jmerik V. N. , Toropov A. A. , Vasson A. , Leymarie J. , Kop'ev P. S. 
Published: January 2006

AbstractInN is a unique material with a tendency for spontaneous formation of metallic indium particles during growth. To elucidate peculiarities related to plasmonic effects, the InN films have been grown either with or without such particles by molecular beam epitaxy using different growth regimes. Studies of the films have demonstrated that their optical properties are influenced by both absorption and electromagnetic enhancement related to the metallic clusters. Basic optical parameters of InN with the metallic inclusions are considered in relation to a cluster shape and orientation with respect to the electric field vector. The origin of infrared emission is discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recombination processes with and without momentum conservation in degenerate InN
Authors: Valcheva E. , Alexandrova S. , Dimitrov S. , Lu H. , Schaff W. J. 
Published: January 2006

AbstractWe report on a theoretical approach in which the two cases of recombination with and without momentum conservation in optically excited high carrier concentration InN are considered. The calculations are used to analyze emission spectra of n‐type InN layers of electron concentrations from 7.7 × 1017to 1.4 × 1019cm–3studied in the temperature range between 9 and 100 K. The spectra peak near 0.7 eV and the applicability of the two approaches with increasing carrier concentration is estimated. Different transition mechanisms are considered in order to properly account for the observed features in the spectra. Recombination processes involving acceptor‐ and donor‐like localized states are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1−xN surfaces
Authors: Veal T. D. , Piper L. F. J. , Phillips M. R. , Zareie M. H. , Lu Hai , Schaff W. J. , McConville C. F. 
Published: January 2006

AbstractElectron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga‐content, corresponding to the band gap of InGaN. The measured InxGa1–xN band gaps (between ∼0.65 eV for x = 1 and 1.8 eV for x = 0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two‐dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga‐content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge‐profile and the subband energies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inhomogeneities in MOVPE InN
Authors: Yamamoto Akio , Miwa Hiroshi , Wang Wen Jun , Hashimoto Akihiro 
Published: January 2006

AbstractThis paper reports the in‐depth and in‐plane inhomogeneities in InN films. Samples of InN are grown on sapphire substrates without or with a buffer using the atmospheric‐pressure MOVPE. For the in‐depth inhomogeneity analysis, the conventional PL measurement using an excitation source with a different wavelength is made from both the front surface and the film/substrate interface sides of samples. The measurement reveals that samples grown for a long time without buffer contain a deteriorated layer, which shows a higher PL peak energy, near the film/substrate interface. Such a layer is never found on the surface side. The deterioration is markedly enhanced when the sample is annealed in an NH3 flow. Since the coexistence of TMI and NH3 (growth environment) suppresses the deterioration and the InN samples used in this experiment have an In‐polarity, such a deterioration is hydrogen‐related degradation on the N‐face of InN film. In‐plane inhomogeneity of InN grown with a different buffer is studied by analyzing PL and absorption data. A wider PL spectrum and a larger discrepancy between PL peak energy and absorption edge, those are observed for films grown without buffer, are well explained by taking account of a large in‐plane inhomogeneity in the samples. The existence of the large in‐plane inhomogeneity is confirmed by the near‐field PL mapping obtained by the SNOM. The SNOM analysis also shows that, although the use of the buffer improves the apparent in‐plane uniformity, such a film has a fine inhomogeneity due to small grains of the buffer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of N‐polarity InN by ArF‐laser assisted MOVPE
Authors: Yamamoto A. , Kasashima K. , Miyanishi M. , Hashimoto A. 
Published: January 2006

AbstractIn this paper, the employment of the ArF excimer‐laser assisted nitridation of sapphire substrate is studied in the ArF‐laser assisted MOVPE (la‐MOVPE) of InN. An ArF excimer laser with an energy 50 mJ/pulse and a repetition rate 20 Hz is introduced parallel to the substrate surface. The surface morphology of InN film grown on α‐Al2O3 (0001) is found to be markedly dependent on the nitridation conditions for the sapphire substrate. When no nitridation is made, the surface of grown InN film is very rough and many In droplets are found on it. A film with a mixture of rough‐surface region with In droplets and smooth‐surface region is grown on the thermally‐nitrided substrate (1000 °C for 30 min). By employing the ArF‐laser irradiation to the NH3 flow during the substrate nitridation at 1000 °C for 30 min (la‐nitridation), a smooth surface region is expanded to the entire surface of film. The smooth surface is found to be stable at growth temperature higher than 700 °C. The KOH etching of grown films reveals that the smooth surface has 5–10 time higher etching rate than the rough one. From these facts, it is concluded that the film with the smooth surface has N‐polarity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fields of deformation anisotropy exploration in multilayered (In,Ga)As/GaAs structures by high‐resolution X‐ray scattering
Authors: Yefanov O. , Kladko V. , Gudymenko O. , Strelchuk V. , Mazur Yu. , Wang Zh. , Salamo G. 
Published: January 2006

AbstractThe results of investigation of In0.3Ga0.7As/GaAs superlattice by high‐resolution X‐ray scattering are presented. The influence of lattice distortion on diffraction curves (DC) were analyzed with dynamical diffraction theory. It allowed to explain azimuth dependence of experimental diffraction curves. Anisotropic changes in the shape of InGaAs lattice unit cell were shown and measured. The influence of smooth borders between hetero‐layers were analyzed. Comparative analysis of different gradient functions on the hetero‐border influence on diffraction curves was done. Parameters of heterojunction in investigated samples were determined with the help of DC modelling. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth of InN with ammonia on sapphire
Authors: Drago M. , Vogt P. , Richter W. 
Published: January 2006

AbstractMOVPE growth of InN on sapphire substrate is reviewed focusing on the critical growth parameters. Based on our in situ spectroscopic ellipsometry results obtained during growth and the results found in the literature we suggest a strategy for successful growth of high quality InN layers. This includes nitridation of the substrate, growth parameters and suppression of layer peeling off. We find that the optimal temperature for the nitridation of the sapphire is around 1050 °C and the optimal growth temperature is always very close to the highest possible temperature which is determined by the thermal decomposition of the InN layer. The smallest accessible V/III ratio, before Indium droplets formation occurs, lies between 5000 and 10000 depending on the growth parameters. With the procedure we suggest here the growth temperature can be increased up to 580 °C with changes of the respective V/III ratio limits resulting in an improvement of the InN quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Half‐filled stripes in thet–t′–UHubbard model
Authors: Raczkowski Marcin , Oleś Andrzej M. , Frésard Raymond 
Published: January 2006

AbstractUsing a self‐consistent Hartree‐Fock approximation we investigate the relative stability of various stripe phases in the extendedt–t′–UHubbard model. One finds that a negative ratio of next‐ to nearest‐neighbor hoppingt′/t< 0 expells holes from antiferromagnetic domains and reinforces the stripe order. Therefore the half‐filled stripes not only accommodate holes but also redistribute them so that the kinetic energy is gained, and these stripes take over in the regime oft′/t≃ –0.3 appropriate for YBa2Cu3O6+δ. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiferroic bilayers of manganites and titanates
Authors: Dörr K. , Thiele C. 
Published: January 2006

AbstractIsostructural ferromagnetic and ferroelectric perovskites like manganites (La,A)MnO3 and titanates Pb(Zr,Ti)O3 are favourable candidates for layered film structures with large magnetoelectric coupling phenomena. Manganites (La,A)MnO3 have already been intensively investigated: conduction electrons have a high degree of spin polarization and are strongly coupled to lattice degrees of freedom, making electric transport sensitive to lattice distortions. Epitaxial film systems of manganites and titanates have been prepared by off‐axis pulsed laser deposition (PLD). Field effect devices of La1–x Ax MnO3 (A = Sr; Ca; Ce) and PbZr0.52Ti0.48O3 (PZT) show channel resistance modulation from both, (i) the electric field effect at the PZT‐manganite interface and (ii) the biaxial strain induced by the inverse piezoeffect of PZT. Piezoelectric substrates have been employed to dynamically control the in‐plane strain state of manganite films, revealing strain‐dependent variation of the ferromagnetic Curie temperature and the resistance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fundamentals for magnetic patterning by ion bombardment of exchange bias layer systems
Authors: Ehresmann A. , Engel D. , Weis T. , Schindler A. , Junk D. , Schmalhorst J. , Höink V. , Sacher M. D. , Reiss G. 
Published: January 2006

AbstractIn the present paper we investigate whether the ion bombardment induced magnetic modifications in exchange biased bilayers are stable in time, whether the direction of the exchange bias can be set to any arbitrary (in‐plane) direction by the ion bombardment and whether the exchange bias field can be changed in successive bombardment steps. These three fundamental characteristics are prerequisites for ion bombardment used for an efficient, practical, and stable magnetic patterning of exchange biased layer systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic microstructure of NANOPERM‐type nanocrystalline alloys
Authors: Miglierini Marcel , Kaňuch Tomáš , Švec Peter , Krenický Tibor , Vůjtek Milan , Zbořil Radek 
Published: January 2006

AbstractControlled crystallization of amorphous NANOPERM‐type Fe76Mo8Cu1B15 alloy leads to the formation of crystalline grains of about 10 nm in size. The evolution of crystallization and its impact on the resulting magnetic properties is followed by nuclear and atomic based techniques of (subatomic) structural characterization comprising Mössbauer spectrometry, X‐ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, differential scanning calorimetry, and atomic force microscopy. The amount of nanocrystalline grains identified as bcc‐Fe rises with temperature of annealing and influences magnetic states of the original amorphous precursor. Results of structural characterization are correlated with magnetic data obtained from macroscopic measurements. In the samples with low contents of nanocrystallites, a deterioration of soft magnetic properties is observed. A very good soft magnetic behaviour is regained, however, towards the end of the primary crystallization process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New magnetostatic modes in small nonellipsoidal magnetic particles
Authors: Puszkarski H. , Krawczyk M. , Lévy J.‐C. S. 
Published: January 2006

AbstractMagnetostatic normal modes are investigated here in elongated rods. The dipolar field resulting from the dipole–dipole interactions is calculated numerically in points of the axis connecting opposite rod face centers (central axis ) by collecting individual contributions to this field coming from each of the atomic planes perpendicular to the central axis. The applied magnetic field is assumed to be oriented along the central axis, and the magnetization to be uniform throughout the sample. The frequency spectrum of magnetostatic waves propagating in the direction of the applied field is found numerically by solving the Landau–Lifshitz equation of motion with the spatially nonhomogeneous dipolar field taken into account; the mode amplitude profiles are depicted as well. While energetically highest modes have bulk‐extended character, the modes forming the lower part of the spectrum are localized in the subsurface region (bulk‐dead modes ). Between these two mode types, magnetostatic modes of a new type (comb modes ) are found to occur, characterized by two clearly discernible regions: a zone of fast amplitude oscillations inside the rod, and narrow slow‐oscillation regions at the borders. Absorbing virtually no energy from an applied alternating field, comb modes will have no significant contribution to the magnetic noise. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Torque induced by spin‐polarized current in ferromagnetic single‐electron transistors
Authors: Kowalik M. , Wiśniewska J. , Barnaś J. 
Published: January 2006

AbstractWe present theoretical analysis of the current‐induced torque exerted on the magnetic moment of the central electrode (island) in a ferromagnetic single electron transistor with non‐collinear magnetic moments of the electrodes. The considerations are restricted to the sequential tunneling regime, and the charge and spin currents are calculated within the master equation approach. The torque is calculated from the net spin current absorbed by the island. The calculations are carried out in the limit of fast spin relaxation processes, when no nonequilibrium magnetic moment can build up on the island. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hall effect in the low charge‐carrier density ferromagnet UCo0.5Sb2
Authors: Tran V. H. , Paschen S. , Steglich F. , Troć R. , Bukowski Z. 
Published: January 2006

AbstractThe Hall coefficient R H of ferromagnetic UCo0.5Sb2 (T C = 64.5 K) has been measured on a single crystal in the temperature range 2–300 K and in magnetic fields up to 7 T. The values of the normal R 0 and anomalous R s) coefficients were estimated by comparing R H(B ) with magnetisation M (B ) data. The charge carrier concentration is found to decrease rapidly when the system undergoes a transition to the ferromagnetic ordered state. The charge mobility appears to fall down by as much as two orders of magnitude for temperatures from 20 K to 2 K. We ascribe this behaviour to an enormous decrease of the carrier collision time. The temperature dependencies of the Hall mean free path and mobility can be consistently interpreted within the 2D‐weak localization feature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electronic states of magnetite from photoemission spectroscopy ARUPS
Authors: Zalecki R. , Kołodziejczyk A. , Kozłowski A. , Korecki J. , Spiridis N. , Kąkol Z. 
Published: January 2006

AbstractThe valence band photoemission spectra of epitaxially grown film and bulk single crystal of magnetite were measured by the angle‐resolved ultraviolet photoemission spectroscopy (ARUPS) at 300 K and 120 K. Four main features of the electron photoemission were observed at about –1.0 eV, –3.5 eV, –5.0 eV and –6.5 eV below the chemical potential; they are rather strongly dependant on structure and preparation of surface. The three higher‐energy features showed significant energy dispersion. The ARUPS spectra were compared to the accessible band structure calculations. Special attention was paid to the leading edge of the emission at –1.0 eV of the low‐temperature spectrum where an insulating gap should be observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New orthorhombic multiferroics R1–xYx MnO3 (R = Eu, Gd)
Authors: Ivanov V. Yu. , Mukhin A. A. , Travkin V. D. , Prokhorov A. S. , Popov Yu. F. , Kadomtseva A. M. , Vorob'ev G. P. , Kamilov K. I. , Balbashov A. M. 
Published: January 2006

AbstractA tendency to form multiferroic states with a spatially modulated antiferromagnetic structure and electric polarization in pure orthorhombic manganites RMnO3 upon decreasing of the rare‐earth ionic radii has been realized in single crystals of substituted compounds Eu1–x Yx MnO3 (0.2 ≤ x ≤ 0.5) and Gd1–y Yy MnO3 (0 ≤ y ≤ 0.2). While the parent pure and slightly substituted (x ≤ 0.1) compounds exhibited a spontaneous transition from the incommensurate (IC) to the canted antiferromagnetic (CAF) state at T CA < T N = 45–50 K, the transitions from IC to commensurate ferroelectric (C/FE) phase were observed at T lock < T N for x ≥ 0.3 and y ≥ 0.05 accompanied by dielectric anomalies. Various phase transitions were observed in magnetic fields up to 250 kOe along the a ‐, b ‐, c ‐axes by magnetization, magnetostriction and electric polarization measurements. The latter indicate the existence of a spontaneous electric polarization below T lock. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymmetric magnetization reversal in exchange‐biased Co/Pt multilayers
Authors: van Dijken Sebastiaan , Czapkiewicz M. , Zoladz M. , Stobiecki T. 
Published: January 2006

AbstractA detailed study of the magnetization reversal process in [20 Å Pt/t Å Co]3/100 Å IrMn/20 Å Pt multilayers with 4 Å ≤ t ≤ 9 Å is presented. The hysteresis of as‐deposited films with t ≥ 5 Å is found to be asymmetric. This asymmetry is explained by a lateral variation in the perpendicular exchange bias direction due to the growth of IrMn onto multi‐domain Co/Pt multilayers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Double exchange model in cubic vanadates
Authors: Wohlfeld Krzysztof , Oleś Andrzej M. 
Published: January 2006

AbstractWe investigate the role of the double exchange mechanism for stability of the metallic C‐type antiferromagnetic (C‐AF) phase, which was observed experimentally in hole doped La1–x Srx VO3. The double exchange model treats localized electrons in xy orbitals as classical S = 1/2 spins, which interact by Hund's exchange J H with yz /zx electrons in partly filled t 2g orbitals. Including strong on‐site Coulomb repulsion U between t 2g electrons, and using slave boson method we demonstrate that C ‐AF and metallic phase can be stabilized due to the specific features of the hopping in degenerate and partly filled t 2g orbitals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The properties of the CDW phase in the weak coupling anharmonic Holstein–Hubbard model
Authors: Grzybowski P. 
Published: January 2006

AbstractThe anharmonic Holstein–Hubbard Hamiltonian in the case of weak effective electron–electron attraction is studied. To deal with anharmonicity of phonons, variational canonical transformations are used to derive an effective electron Hamiltonian. The properties of the charge density wave (CDW) phase, for half‐filling, are analyzed using this effective Hamiltonian. In particular, the critical temperatures, gap function, order parameter and gap ratio are calculated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Properties of the extended Hubbard model with transverse (XY‐type) spin‐exchange interaction
Authors: Czart W. R. , Robaszkiewicz S. 
Published: January 2006

AbstractThe properties of the extended Hubbard model with transverse (XY‐type) spin‐exchange intersite interaction (J ⊥) are studied. The cases of ferromagnetic and antiferromagnetic XY exchange are considered. The analysis of the model is performed for d ‐dimensional hypercubic lattices 2 ≤ d ≤ ∞, by means of the (broken symmetry) Hartree–Fock approximation supplemented, for d = ∞, by the slave‐boson mean‐field method. The effects of phase fluctuations on T c of XY phases for d = 2 lattices are estimated within the Kosterlitz–Thouless scenario. Qualitative differences between the properties of the ferromagnetic and antiferromagnetic XY phases are pointed out. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Giant magnetoresistance effect in quantum nano‐scale wires
Authors: Chudzinski P. , Krompiewski S. 
Published: January 2006

AbstractWe study transport properties of nano‐scale wires connected to ferromagnetic semi‐infinite electrodes in the ballistic regime. Systems with different geometries are considered. Our method is based on recursive Green's function technique. We fully deal with atomistic structure of the whole system, treating both the nano‐wire and the electrodes on equal footing. The results include the transmission, with parallel and antiparallel magnetization in the electrodes, and giant magnetoresistance (GMR) vs. energy. The influence of the magnetic polarization, coupling between the nano‐wire and the electrodes as well as the geometry of the device on transport properties are discussed. We emphasize the shape dependent effects and take into account also imperfect structures with some atoms removed from the central region. In addition to evolution from conductance quantization to resonant tunneling regime (upon changing the hopping parameter), it has been found that with increasing polarization other features appear due to decreasing overlap between surface density of states of propagating modes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)