bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acoustic wave amplification in quantum semiconductor structures
Authors: Rodrigues C. , Amato M. A. , Nunes O. A. C. 
Published: July 2007

AbstractA microscopic theory of acoustic wave amplification is presented for an ideal, periodic array of quantum wells (superlattice) in the presence of an applied electric field. The effect of the external field is to produce a drift velocity of the charge carriers in the superlattice heterostructure such that when this drift velocity exceeds the acoustic wave velocity, the confined electrons can lose energy to the acoustic wave and an acoustic amplification rather than attenuation occurs. It is shown that for these quantum semiconductor structures provided they can be tailored, acoustic wave amplification can occur at much larger rate and at much lower electric fields as compared with the bulk structure.
An effective transfer matrix approach for semi‐infinite ferromagnetic systems
Authors: Zhao Ping‐Bo , Teng Yong‐Ping , Li Bo‐Zang , Pu Fu‐Cho 
Published: July 2007

AbstractAn effective transfer matrix approach for the Ising model is proposed. Taking a semi‐infinite ferromagnetic system as an example, its surface magnetic order is calculated. The results also show that the discontinuity of the surface magnetization will not appear in our treatment.
Annealed Ising model with competing interactions on a bethe lattice
Authors: Haroni A. A. , Paraskevaidis C. E. 
Published: July 2007

AbstractFrustration effects which appear in an annealed Ising‐type system with two types of magnetic atoms (a = A, B) on the sites of a Bethe lattice with branching ratio 2 are studied. Competing magnetic interactions between nearest neighbors (J) and next‐nearest neigbors (J′ J″) in the presence of an external magnetic field are considered. The distribution of the magnetic atoms on the sites of the Bethe lattice‐is determined, aside from the magnetic interactions, by spin‐independent interactions Ū, Ū′ U″ and by the chemical potential applied to the system. An iterative scheme for the renormalized effective nearest‐neighbor (magnetic) couplings and the effective fields is applied. This scheme reduces the study of an N‐layer Bethe lattice to the study of a cluster consisting of four lattice points. The effective fields along with the effective nearest‐neigbor couplings of the central cluster contain all the information for the thermodynamic state of the system. The phase diagrams of these systems contain, besides the ferromagnetic and the paramagnetic, a) a four‐cycle antiferromagnetic (AF‐2) phase and b) a modulated phase (M) consisting of commensurate and incommensurate regions. In the case of strong coupling between magnetic atoms of different species, the phase diagrams are enriched by the presence of a modulated antiferromagnetic (MAF) region. The information of modulation persists even within the ferromagnetic phase.
Fluctuation properties and charge resolution of the superconducting SET electrometer in the regime of cooper‐pair tunneling
Authors: Hädicke A. , Krech W. 
Published: July 2007

AbstractSingle‐charge tunneling through a voltage‐biased SSS transistor with a capacitively coupled gate and an electromagnetic environment is considered. The dc Cooper‐pair current in the blockade region of quasiparticle tunneling is studied. Basing on a two‐level approximation, which can be used in the realistic case of low temperatures and small environment resistances, the mean dc Cooperpair current, the noise power spectrum, and the charge resolution are calculated as functions of the driving voltage and the external charge on the island.
Polycrystalline heterojunction solar cells: A device perspective
Authors: Phillips J. E. , Birkmire R. W. , McCandless B. E. , Meyers P. V. , Shafarman W. N. 
Published: July 2007

AbstractAnalysis of high efficiency, thin film, small grain, polycrystalline, heterojunction CdTe and CuInSe2based solar cells can help explain the high quantum efficiencies and the resulting short circuit current (Jsc) as well as the forward diode current that controls the open circuit voltage (Voc). This analysis shows that minority carrier recombination at the metallurgical interface and at grain boundaries is greatly reduced by the proper “doping” of the window and absorber layers thereby increasing Jsc. Additional analysis and measurements show that the Voc in present state of the art solar cells is controlled by the magnitude of the forward diode current which appears to be caused by recombination in the space charge region of the absorber layer. This also shows that any quantitative modeling of these devices which relates the device performance to the bulk electronic properties of the material should consider the additional geometric dimension introduced by the polycrystallinity because of grain boundary effects.
Sub‐micron silicon structures for thin film solar cells
Authors: Nebel C. E. , Dahlheimer B. , Schöniger S. , Stutzmann M. 
Published: July 2007

AbstractThe realization of a lateral structured thin solar cell based on silicon is introduced and advantages such as increased internal electric fields, light diffraction into the bulk of the absorber, and improved light trapping are discussed. The key process for the realization of such a solar cell is the interference laser recrystallization of amorphous silicon which has been applied to produce stripe, grid, and dot arrays. The experimental set‐up of the laser recrystallization is presented, and a detailed description of electronic properties of laser recrystallized, boron doped silicon films is given.
InAs‐GaAs quantum dots: From growth to lasers
Authors: Bimberg D. , Ledentsov N. N. , Grundmann M. , Kirstaedter N. , Schmidt O. G. , Mao M. H. , Ustinov V. M. , Egorov A. Yu. , Zhukov A. E. , Kopev P. S. , Alferov Zh. I. , Ruvimov S. S. , Gösele U. , Heydenreich J. 
Published: July 2007

AbstractInjection lasers based on InAsGaAs and InGaAsGaAs quantum pyramids (QPs) with a lateral size ranging from 80 to 140 Å, are realized. The structures with relatively small dots (≈80 Å) exhibit properties predicted earlier for quantum dot (QD) lasers such as low threshold current densities (below 100 A cm−2) and ultrahigh characteristic temperatures (T0 = 350 to 425 K). For temperatures of operation above 100 to 130 K T0 decreases and the threshold current density increases (up to 0.95 to 3.3 kA cm−2 at room temperature) due to carrier evaporation from QPs. Larger InAs QPs (≈140 Å) providing better carrier localization exhibit saturation of the ground state emission and enhanced nonradiative recombination rate at high excitation densities. The radiative lifetime shows a weak dependence on the dot size (80 to 140 Å) being close to ≈1.8 to 2 ns, respectively. A significant decrease in radiative lifetime is realized in vertically‐coupled quantum dots formed by a QP shape‐transformation effect. The final arrangement represents a three‐dimensional tetragonal array of InAs islands inserted in a GaAs matrix each composed of several vertically merging InAs parts. The first injection lasing in such an array is achieved.
Electronic energy bands and lattice dynamics of pure and lithium‐intercalated InSe
Authors: Balkanski M. , Da Costa P. Gomes , Wallis R. F. 
Published: July 2007

AbstractA discussion of the electronic energy bands and lattice dynamics of pure and lithium‐intercalated InSe is presented. After a review of the structure of this material and its polytypes, experimental results on both optical absorption and photoluminescence are compared for the pure and lithiumintercalated cases. A similar comparison is made for experimental Raman spectra. Electronic energy band calculations based on the tight‐binding method are presented. The results indicate that InSe containing lithium has an impurity band just below the conduction band edge. The phonon dispersion curves of pure and lithium‐intercalated InSe have been calculated using the rigid ion model and the results compared with the Raman spectra. Normal modes associated with lithium impurity atoms are identified. A set of conclusions is presented.
Black gold deposits as absorbers for far infrared radiation
Authors: Becker W. , Fettig R. , Gaymann A. , Ruppel W. 
Published: July 2007

AbstractThermal infrared sensors with maximal sensitivity and minimal response time require radiation absorbing layers with small heat capacity and high absorbance. In the near infrared these conditions are well met by black gold layers. In order to examine the question whether black gold layers are suitable absorbers as well in the far infrared, their reflectance is measured in a wave number range from k = 14 to 650 cm−1, corresponding to a range in wavelength λ = 1/k between 15 and 710 μm. The samples are prepared at various residual gas pressures. The influence of tempering on the absorbance and the spectral absorption behavior at low temperatures is discussed. The experimental results may be accounted for by a dielectric function according to the Bergman formalism. The spectral dependence of the absorption coefficient and the real and imaginary parts of the refractive index following from it are presented.
The derivation of particle statistics: Some clarifying remarks
Authors: Landsberg P. T. , Canagaratna S. G. 
Published: July 2007

AbstractA recent paper published in this journal suggests that some clarifying remarks about the derivation of particle statistics are in order. These are given here in a somewhat more general context than is usual. In particular, we show that the statistics for electrons in semiconductors can, of course, not be used unamended for localised states. In addition, a combinatorial method of writing the grand partition function for particles in bands is here related to a more usual procedure.
Raman scattering and lattice vibrations in tetragonal CdAs2 crystals
Authors: Weszka J. , Balkanski M. , Raukhman A. M. , Marenkin S. F. 
Published: July 2007

AbstractRaman scattering (RS) in CdAs2 semiconducting crystals has been studied. The RS spectra have been recorded in the backscattering configuration with the λ = 514.5 nm line of an ion argon laser at 50 mW output level, at room temperature. The recorded RS spectra have brought some evidence of the quasi‐molecular character of the crystal lattice dynamics. The phonon modes at frequencies within the interval 180 to 270 cm−1 are attributed to the arsenic atom‐chain oscillations. There is some evidence of correlation splitting to occur for these high‐frequency phonons. The modes at frequencies inferior to about 180 cm−1 are attributed to the ones with important contribution of cadmium atoms and they resemble external modes in molecular crystals.
Anisotropy and spin resonance in cubic and wurtzite structure semiconductors
Authors: Bria D. , Zorkani I. , Nougaoui A. , Karteuser E. 
Published: July 2007

AbstractA theory is presented which permits the determination of the integrated absorption coefficient corresponding to the electric spin resonance for electrons bound to donors in cubic and wurtzite‐type semiconductors. The anisotropy effect of the effective Bohr radius is included in the determination of this coefficient. The results of the theory are compared with relevant data on Cd0.9Mn0.1Se. The fit of theory to the experimental results yields values for the strength γ of the spin‐orbit interaction equal to 2.40 × 10−10 cm, the transverse Bohr radius at* = 43.5Å, and the anisotropy parameter ϵ = at*/al* = 0.998.
Collisional broadening effect in vacuum emission of hot electrons from SiO2: The role of non‐polar optical phonon scattering
Authors: Reggiani L. , Fitting H.‐J. , Hingst Th. , Köhn J. , Beauvivre S. , Varani L. 
Published: July 2007

AbstractThe energy distribution function of hot electrons emitted from a 13 nm SiO2 layer is measured through vacuum emission experiments up to 4 eV. The results evidence the presence of carriers in an energy region well above the ballistic threshold. A Monte Carlo simulation of carrier transport in the presence of non‐polar scattering and collisional broadening is in qualitative agreement with the experiments thus providing a value of 3.1 × 109 eV/cm for the deformation potential and a direct indication of collisional broadening effect in high‐field transport of electrons in SiO2.
Investigation on the bisoliton mechanism of high‐temperature superconductors
Authors: Zhang Ling‐Yun , Li Bo‐Zang , Lin Jia‐Tih , Pu Fu‐Cho 
Published: July 2007

AbstractMicroscopic parameters in the Davydov model are calculated on the basis of the bisoliton idea. The energy gap is obtained from combining the condition for the solution of Davydov's equation with the condensation energy of the superconductive state in zero field, and some characteristic parameters of high‐temperature superconductors such as coherence length, penetration depth, and density of critical current for a thin film in weak magnetic field are given. It is also proved that lattice displacement in Davydov's equation satisfies the φ4 field form. The critical temperature and the coefficient of linear specific heat of high‐temperature superconductors are studied from the statistics of lattice kinks. The agreement between theoretical and experimental values for YBaCuO oxide ceramics suggests that the bisoliton model gives a reasonable explanation of high‐temperature superconductivity.
Optical absorption, photoluminescence, and thermally stimulated luminescence of CsCl: Tb crystals
Authors: Selvan P. Christober , Selvasekarapandian S. , Neelamegam P. 
Published: July 2007

AbstractOptical absorption, photoluminescence, and thermoluminescence emission studies are made on CsCl:Tb3+ crystals at room temperature. The presence of impurities is confirmed by the characteristic OA band at 360 nm. Photoluminescence of these crystals shows characteristic Tb3+ emissions due to transitions from the 5D3 and 5D4 levels to various levels of the 7F septet. The glow curve studies clearly show the participation of terbium ions in the thermoluminescence process. The new 415 K glow peak, not observed in pure CsCl, is ascribed to the terbium ion in the vicinity of F centers. All the TL glow peaks give the characteristic emissions of Tb3+ in addition to the emission due to the recombination of the F electron with V‐type centers.
Raman scattering from polar modes in KTiOPO4 single crystals
Authors: Mohamadou B. , Kugel G. E. 
Published: July 2007

AbstractA detailed investigation of Raman light scattering was performed in potassium titanyl phosphate (KTiOPO4) using various scattering geometries. The modifications of the Raman frequencies and intensities were discussed in terms of change of selection rules. The directional dependence of the mixed mode frequencies is calculated on the basis of earlier infrared results and by using the model of Shapiro and Axe. The results of calculations show an excellent agreement between the theoretically predicted and the measured frequencies obtained in the particular case of right‐angle Raman scattering and allow an accurate assignment of the Raman structures.
Solution of the incompatibility problem in linear three‐dimensional anisotropic media for an isotropic incompatibility tensor
Authors: Michelitsch Th. , Wunderlin A. 
Published: July 2007

AbstractA solution of the incompatibility problem in three‐dimensional anisotropic elasticity is derived for the case that the incompatibility tensor has isotropic symmetry. To that end an infinitely extended linear elastic anisotropic medium is assumed. Under these conditions the internal stresses are obtained by pure differentiations from the corresponding fourth‐order stress function tensor. This result is then used to express the internal stress tensor as a convolution of the incompatibility tensor and the elastic Green's function tensor.
Transient photocurrents under optical bias in time‐of‐flight experiment with amorphous films of As2Se3: Sn and As2S3: Sb2S3
Authors: Iovu M. S. , Shutov S. D. , Toth L. 
Published: July 2007

AbstractRelaxation of pulsed photocurrents under optical bias is studied in amorphous films of ternary glassy alloys As2Se3:Snx (x = 0 to 3.5 at%) and (1−y)(As2S3):y(Sb2S3) (y = 0 to 0.55) by the time‐of‐flight technique. In the frame of a multiple‐trapping model it is shown that by adding tin and Sb2S3 to the glass formers As2Se3 and As2Se3 respectively, the hole drift mobility is strongly increased (up to 200 times), while small amounts of tin (about 1 at%) hamper the recombination. Optical bias causes the drift mobility to increase many times with its activation energy being decreased. The obtained results indicate the variation in occupation of deep localized centres and explain the known effect of photosensitivity enhancement when ternary chalcogenide glassy alloys are used in layer structures for optical information storage.
Resonant tunneling through single GaAlAs barriers
Authors: Chaabane H. , Bourgoin J. C. 
Published: July 2007

AbstractThe current‐voltage characteristics of molecular beam epitaxy grown GaAlAs barriers, imbedded in n+ type doped GaAs, have been recorded in the range 77 to 300 K and analyzed. Below ∼130 K and for high enough electric fields, oscillations appear on these characteristics that can be quantitatively accounted for by the phenomenon of resonant tunneling. The fit between theory and experiment allows to deduce the band discontinuity (250 meV), equal to the expected value for electron tunneling into the T band. Defects have then been introduced by irradiation to evaluate the concentration of scattering centers necessary to destroy these oscillations. The band offset becomes 380 meV when defects are present which indicates that defect scattering induces tunneling into the x band.
A model for thin film texture evolution driven by surface energy effects
Authors: Knuyt G. , Quaeyhaegens C. , D'Haen J. , Stals L. M. 
Published: July 2007

AbstractA model was developed in order to calculate the texture evolution of a growing film with large atomic diffusion on the surface. The tendency for lowest surface energy was taken as the driving force for the evolution. The orientation dependent surface energy y was approximated by a function with a sharp minimum in two crystallographic directions. The texture evolution was calculated, starting from various initial situations. With realistic assumptions it was found that a texture without preferential orientations evolved to a bimodal texture, and finally to a situation with only lowest y planes parallel to the substrate. For some initial situations a texture turn over from one crystallographic direction to another one can be expected. In all cases a sharpening of the angular distribution of the texture is found near the directions of a local minimum for y. For sufficiently large times the mean top diameter of the columns always increases with layer thickness. The calculated effects describe well a number of experimentally observed phenomena.
Matrix elements of the electron‐phonon interaction in the rigid electron density displacement approximation
Authors: Novysh B. V. , Dorozhkin N. N. , Gololobov E. M. , Anishchik V. M. 
Published: July 2007

AbstractWe present a method for electron‐phonon matrix element calculations based on a rigid displacement of in‐sphere electron densities. This method may be viewed as an extension of the famous rigid muffin‐tin approximation. At the same time it allows one to take into account the long‐range Coulomb interactions, the collective character of ion displacements in phonon modes, and effects due to the anisotropy of electron densities inside the muffin‐tin spheres. Non‐muffin‐tin corrections are shown to cause electron‐ion scattering selection rule variations.
Surface impedance of SSWR in thin metallic films for parallel configuration
Authors: Chan Ngoc , Fraitova D. 
Published: July 2007

AbstractSSWR (standing spin‐wave resonance) spectra for parallel configuration were calculated analytically for the case of metallic thin films, including surface anisotropy (of equal value at both surfaces). Landau‐Lifshits damping, and electrical conductivity effects. The analytical formulae for the surface impedance and for the microwave magnetic fields propagating in the film are derived, symmetrical and antisymmetrical cases of spin‐wave mode excitation are treated following Wolf's method.
Band model approach to the theory of the dynamic susceptibility and spin waves in superlattices
Authors: Swirkowicz R. 
Published: July 2007

AbstractThe transverse dynamic susceptibility of periodic layered systems is calculated within the framework of the multiband model by using the equation of motion method. The presented formalism can be applied to systems with ferro‐or antiferromagnetic coupling between the layers. Numerical calculations are performed for the superlattice composed of ferromagnetic and nonmagnetic materials. Spin waves are investigated and the magnon spectrum is found.
2H NMR studies of the antiferrodistortive phase transition in betaine phosphite and betaine phosphate
Authors: Freude P. , Michel D. 
Published: July 2007

AbstractSingle crystals of betaine phosphite and betaine phosphate were investigated in the antiferrodistortive and paraelastic phases. The comparison of the data obtained in these phases indicates an order‐disorder type of phase transition. It could be shown that the two betaine molecules, which can be distinguished by 2H NMR, are located in the high‐temperature phase in the mirror plane only in a statistical sense and tilt by about ±7.8° in opposite direction out of this mirror plane below the phase transition.
Medium‐range structural ordering and macroscopic interactions in 1 to 2 mm thin two‐dimensional platelets of borate glasses
Authors: Ram S. , Haldar S. 
Published: July 2007

AbstractA locally ordered microstructure of interconnected planar boroxol rings (basis structural units) in 1 to 2 mm thin 2D (two‐dimensional) platelets of a ternary borate glass, with cation ratio B3+/Ba3+(Fe3+) ≈0.94, exhibits an up to 57 cm−1 increase in the infrared characteristic B‐O stretching vibration frequencies (BOSF) with respect to those in a powder (or bulk) of confined particle (or domain) size of μm scale. At 500 to 850°C, the planar network forms a planar α‐β interface with thermally induced phase separation (β) of Ba2+ and Fe3+ cations in the network. These cations are interconnected by the network structure in α‐β thermodynamic equilibrium. As a result, they are easily mobile to grow up to several μm long acicular BaFe12O19 crystals, over the network in the basis morphology (elongated hexagonal crystal unit cell of c/a ratio ≈3.94) of the BaFe12O19 nuclei driven by the heat flow released in the nucleation and growth processes along the α‐β interface coplanar with the network. The BaFe12O19 crystallites, which are precipitated over the network, firmly adhere to the network by strong electromagnetic macroscopic interactions. The crystallized glass, which no longer has such a regularly interconnected network configuration, therefore measures similarly high (or even higher) values of the BOSF as in a highly ordered network.
Local ordering and thermodynamic properties of bismuth‐tellurium alloy
Authors: Hussain L. A. , Akinlade O. , Uhuegbu C. C. 
Published: July 2007

AbstractA quasi‐lattice model is used to explain the concentration dependence of the free energy of mixing, heat of mixing, excess entropy of mixing, chemical short‐range order parameter, and concentration‐concentration fluctuation in the long‐wavelength limit for Bi‐Te molten alloys. The results show that the molten alloys form a complex of the form Bi2Te3, with chemical ordering throughout the whole concentration range with a peak at a concentration of 0.50.