bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐Resolution Auger Spectroscopy Applied to Metals and Alloys
Authors: Kleiman G. G.
Published: July 2007

Auger electron spectroscopy (AES) is fundamentally a spectroscopy of excited states, so that the resulting information is complementary to that from X‐ray photoelectron spectroscopy (XPS). Consequently, high‐resolution AES has received a great deal of theoretical and experimental attention in recent years. In metals and their alloys, much of the interest has involved valence band spectra, which are explained in terms of the quasi‐atomic model of final‐state screening, especially in closed d‐shell metals, such as Cu and Ag. In open shell metals, such as Ni and Pd, however, the shapes of the valence band spectra are often ambiguous. Core level spectra, which might reduce uncertainties, are often complex and not readily interpretable. It is shown that the high‐energy LMM spectra of the 4d metals and their alloys are sufficiently simple in form and narrow to permit unambiguous comparisons with quasi‐atomic theories. The exploitation of the experimental systematics of the LMM Auger parameter elucidates screening mechanisms as well as the nature of d‐band holes and the extension of the analysis to the 3d and 5d metals indicates similar results. Application to metallic alloys clarifies the electronic structure changes; examples of Pd‐based alloys are presented. Consideration of the lineshapes of these spectra reveals a satellite structure which can, with considerable certainty, be identified with shake‐up processes associated with 4d‐band spectator vacancies.
Two‐Dimensional Growth of Si Grains inside Au Thin Films
Authors: Pasa Pasa A. A. , Losch W. , Bauer G. H.
Published: July 2007

The growth of Si grains inside Au thin films is studied in the Au/aSi: H bilayer system. The crystallization process is promoted at low temperatures and the samples are characterized by scanning electron microscopy (SEM) and in‐situ electrical measurements. SEM micrographs obtained on samples submitted to isothermal treatment show the appearance of Si grains on the Au thin film surface. The number of nuclei did not change during the reaction and the crystallized area shows a quadratic dependence on the treatment time, a typical behavior of an interface‐limited crystallization process. The electrical measurements allowed monitoring the crystallization process and the determination of the growth parameter n varying between 1.9 and 2.6. Comparison between the two techniques permits us to conclude that the Si grains grow two‐dimensionally inside the Au thin film.
Anharmonicity, weak localization, and reciprocal length of ultrasound attenuation
Authors: Zhernov A. P. , Chulkin E. P.
Published: July 2007

Proceeding from the concepts of localization processes in anharmonic lattices with impurity quasi‐local excitations (resonance localized scattering centers) universal anomalies in the temperature dependences of the reciprocal length of ultrasound attenuation in amorphous systems are described within the temperature range where a plateau in thermal conductivity is observable. A probability of the manifestation of the localization process in quantum crystals is also discussed.
Effect of Quantum confinement on impurity hopping in quantum wells
Authors: Keiper R. , Wang W. , Zvyagin I. P.
Published: July 2007

The problem of evaluation of the impurity hopping conductance in quantum wells is discussed, taking account of the impurity position‐dependent shifts of the binding energies and the variation of the localization radii. It is demonstrated that these effects give rise to a temperature dependence of the conductance of the form σ = σ0exp {−(T0/T)1/3}, where the parameter T0depends on the well width L. Numerical calculations using the variational principle show that this dependence is strong for strongly compensated samples in the region of L/a* ≦ 1, where a* is the effective Bohr radius.
Alternative analytical descriptions of the temperature dependence of the energy gap in cadmium sulfide
Authors: Pässler R.
Published: July 2007

Experimental data available from published literature for the temperature dependence of the energy gap in CdS (A‐gap) are fitted numerically on the basis of four different analytical models. In analogy to earlier applications to many other semiconductor materials, the conventional models due to Varshni (1967) and Viña et al. (1984) are found here also for CdS to provide some rough fits of experimental data. A high‐precision fit is shown to be given by a novel analytical expression of the form \documentclass{article}\pagestyle{empty}\begin{document}$ E_{\rm g} (T) = E_g (0) - (a/2)(\sqrt {(2)^p + \theta ^p - \theta),} $\end{document} where α is the familiar (limiting) gap shrinkage coefficient and θ tbond; ħω/k represents the effective phonon energy on temperature scale. The corresponding low‐temperature Tp‐power exponent p is found for CdS to be nearly equal to 2.5. Thus we are concerned with a fractional exponent whose magnitude is markedly larger than its conventional value of 2. The associated θ value of about 150 K suggests that the main contribution to the gap shrinkage effect in CdS should be due to acoustic phonons ranging energetically slightly below the middle of the total phonon energy spectrum.
Finite‐temperature ferromagnetism of f.c.c. cobalt
Authors: Vega A. , Nolting W.
Published: July 2007

The influence of electron correlations on the temperature dependent electronic structure of ferromagnetic f.c.c. cobalt is investigated by a many‐body evaluation of a generalized model of magnetism. The single‐particle part of the model‐Hamiltonian is taken from an LDA band structure calculation. The interaction part contains two parameters, an intraband Coulomb interaction U and an interband exchange J. With U = 3.5 eV and J = 0.3 eV the self‐consistent model solution yields a magnetic T = 0 moment of about 1.75μB and a Curie temperature of 1375 K. The magnetic behaviour finds a conclusive microscopic explanation by the temperature and density dependent quasiparticle density of states. Typical differences as well as common features in the electronic structures of Fe, Co, and Ni are worked out. Contrary to Ni, no satellite appears in Fe and Co.
Linear optical properties of the dopyballs C60−nXn (X = B or N; n = 1, 2)
Authors: Xu Qiang , Jiang Jie , Dong Jinming , Xing D. Y.
Published: July 2007

The linear optical absorption of dopyballs C60−nXn (X = B or N; n = 1, 2) is studied using the extended Su‐Schrieffer‐Heeger model and the sum‐over‐states approach. Comparing the calculated results C60−nXn with those of C60, it is shown that the substitutional doping of impurity atoms (B or N) can greatly change the optical properties of the c60 system. Many absorption peaks due to substitutional doping appear in the low frequency region. In particular, a remarkable peak is found at the low frequency end in C58X2 (1,60) isomers.
Dielectric function and plasmon excitations in silver
Authors: Fehrenbach G. M. , Bross H.
Published: July 2007

The microscopic dielectric function of silver is investigated in the framework of the time‐dependent density‐functional theory underlying a spline augmented plane‐wave band calculation. A reasonable overall agreement is found when comparing our results with experimental data. Small systematic errors in the position of the peaks can be ascribed to the local density approximation. It is shown that in the long‐wave limit a zero of the diagonal element corresponds to a plasmon excitation. The frequency of the q = 0 plasmon excitation agrees quite well with its experimental value. No plasmon excitation can be found even for small values of the propagation vector.
Structure of YBaSiON glasses by neutron diffraction
Authors: Jin J. S. , Kozuka H. , Yoko T. , Fukunaga T.
Published: July 2007

The structure of YBaSiON glasses is investigated by neutron diffraction, and their physical and chemical properties are measured. It is found from the analysis of the radial distribution functions that nitrogen atoms exist as a mixture of two‐coordinated and three‐coordinated states in the glass, and the ratio of the three‐ to the two‐coordinated nitrogens decreases as the nitrogen content increases. The relationship between structure and properties is also discussed.
Heat conduction in parahydrogen quantum crystals with very heavy neon and argon impurities
Authors: Zhernov A. P.
Published: July 2007

The experimental data on heat conduction of parahydrogen solid solutions with Ne and Ar impurities are analyzed. Specific relaxation mechanisms which may manifest themselves in strongly anharmonic crystals with resonantly scattering impurity centers are examined.
Cu2(1−z)MnzGa2Se4 alloys: Phase diagram and effects of Mn ordering on magnetic behaviour
Authors: Quintero M. , Lopez M. , Morocoima M. , Rivero A. , Bocaranda P. , Woolley J. C. , Lamarche G. , Re R. Brundel
Published: July 2007

X‐ray powder diffraction, differential thermal analysis, and magnetic susceptibility measurements on polycrystalline samples are used to determine the details of the T(z) phase diagram of the alloy system Cu2(1−z)MnzGa2Se4. At high temperatures, there is a single phase solid solution across the complete diagram in a disordered zincblende phase. However, at lower temperatures, the singlephase range is limited to relatively wide terminal fields, which are ordered structures based on a zincblende subcell. Several different ordered phases are found to occur and the values of the Curie‐Weiss constant θ are used to investigate the changes in ordering with composition. It is shown that these ordering changes cause discontinuous changes in the slope of the graphs against composition of the lattice parameters, optical energy gap, and Néel temperature values.
Surface thermal stability of nickel clusters
Authors: Chen Xiaoshuang , Zhao Jijun , Sun Qiang , Liu Fengqi , Wang Guanghou , Shen Xue Chu
Published: July 2007

Overall and surface melting of NiN clusters have been studied using Monte Carlo simulation and effective interaction model potential. Physical quantities such as internal energy per atom, specific heat, and bond length fluctuations are calculated as a function of temperature to illustrate overall and surface thermal softening of these clusters. It is found that the surface melting temperature is lower than the overall melting temperature for a Ni cluster of certain size. The results show that the surface and core atoms play different roles in the melting process. The recent experimental observations about metal cluster melting might be explained by using surface melting arising from the surface atom disorder first appearing due to an increase of temperature.
Acoustic wave amplification in quantum semiconductor structures
Authors: Rodrigues C. , Amato M. A. , Nunes O. A. C.
Published: July 2007

A 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

An 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

Frustration 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

Single‐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

Analysis 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

The 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

Injection 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

A 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

Thermal 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

A 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

Raman 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

A 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

The 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

Microscopic 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

Optical 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

A 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

A 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

Relaxation 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

The 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

A 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

We 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

SSWR (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

The 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

Single 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

A 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

A 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.
Vibrational dynamics of Pd80Si20 glass
Authors: Prasad A. , Jain K. C. , Saxena N. S.
Published: July 2007

The vibrational dynamics of Pd80Si20 glass has been studied at room temperature in terms of the phonon eigenfrequencies of longitudinal and transverse modes employing the theoretical formulations of Hubbard and Beeby as well as of Takeno and Goda. The effective interatomic pair potential in this glass is obtained using the experimental partial pair correlation functions and the hypernetted chain (HNC) equation. Long wavelength limits of the phonon modes are then used to get information on the elastic and thermal properties of the system. It has been found that the theoretical results of these properties as computed through Hubbard and Beeby's method are in good agreement with the available experimental results.
Self‐consistent green's function approach to dissipative two‐state system
Authors: Chu H. Y. , Ye Z. , Umezawa H.
Published: July 2007

We study the properties of a dissipative two‐state fermionic system embedded in a phonon bath at zero temperature. In contrast to the traditional path‐integral and canonical transformation approaches, we propose a self‐consistent Green's function approach. Our results show that the mean field theory overestimates the polarization of the system. To justify our approach, we consider a simplest case in which there is only one phonon mode. This simple model can be ‘exactly’ diagonalized. We find that the results from the self‐consistent Green's function approach agree well with the quantum mechanical diagonalization results.
Empirical tight‐binding band structure of zinc‐blende nitrides GaN, AIN, and BN
Authors: Ferhat M. , Zaoui A. , Certier M. , Khelifa B.
Published: July 2007

The electronic band structure and density of states for zinc‐blende nitrides GaN, AIN, and BN are reported using an sp3s* tight‐binding method. The large band gap found for these compounds is analyzed in terms of chemical and volume deformation effects. The calculated ionicity agrees with the Phillips scale and shows a strongly ionic character for GaN and AIN, while BN is found more covalent.
Phase diagram of three fermionic chains: A renormalization‐group study
Authors: Arrigoni E.
Published: July 2007

The weak‐coupling phase diagram of a system of three coupled spin 1/2 chains (at zero temperature) is studied as a function of fermion density and of transverse single‐particle hopping by means of a renormalization‐group analysis. We identify different phases with a different behavior of the renormalization‐group flow and interpret the effect of relevant couplings in terms of the associated bosonized Hamiltonian. A frustrated (gapped) magnetic spectrum in a large region about and at half filling is obtained in the unphysical case of periodic boundary conditions in the direction transverse to the chains. The expected spin phase diagram (as also observed in the Sr2Cu3O5 ladder compounds) is instead obtained when open transverse boundary conditions are considered. In particular, the spin modes are ungapped in a wide region about half filling and at half filling down to a critical value of the transverse hopping t⟂. A Mott transition as a function of ⟂ is thus present at half filling.
Analysis of transient phenomena in GaAs within the metastable model
Authors: Santic B. , Radic N. , Desnica U. V. , Fillard J. P.
Published: July 2007

Transients of the diode capacitance Cd, optical absorption coefficient α, and EPR signal in GaAs are studied within the framework of the metastable model. The spectral behavior of transients is studied theoretically in the 0.9 to 1.3 eV range. It is shown that the occupancy factor F (electron occupancy of EL2 defect) plays an important role in the observation of the characteristic ‘fingerprint’ signals. It significantly influences both the amplitude and the shape of the transient as well as its spectral behavior. A novel way for the determination of the value of F from the experimental results is proposed. It is discussed why the variation of F among the samples leads to the sample dependence of the results which is frequently experimentally observed. The appearance of ‘non‐quenchable’ and ‘EL2‐like’ defects is also discussed. The experimentally observed results can be modeled even with the assumption of a constant value of σ* (capture cross section for the metastable transition). The light flux intensity and the time of illumination should be specified for a meaningful comparison of various experimental results.
Surface effects on excitons in n‐period CdMnTe/CdTe superlattices
Authors: Afif K. , Diouri J.
Published: July 2007

The binding energy EB of Wannier excitons in N‐period CdMnTe/CdTe superlattices including or not a step discontinuity in the potential barrier at the interface and with varying N as well as well width is calculated by a variational method. The calculation is performed in the framework of the effective mass approximation for both heavy‐hole and light‐hole excitons. The results obtained show that EB is sensitive to those three parameters in the limit of short dimensions of the structure.
Phase diagrams of the spin‐3/2 transverse ising model with random interactions
Authors: Kerouad M. , El‐Atri A. , Ainane A. , Saber M.
Published: July 2007

The transverse spin‐3/2 Ising model with random interactions is studied using an effective field method within the framework of a single‐site cluster theory. The effective field equations are derived using a probability distribution method based on the use of generalized Van der Waerden identities, that account exactly for the single‐site kinematic relations. A model is adopted in which the nearest‐neighbour exchange couplings are described by the probability distribution law: P(Jij) = p δ(Jij‐J) + (1‐p) δ(Jij‐aJ). The critical temperature at which the longitudinal magnetization vanishes is studied as a function of p and the transverse field strength. The thermal variation of the longitudinal and transverse magnetizations and higher‐order magnetization moments are also studied.
Magnetism of the Rh13 cluster
Authors: Yang Jinlong , Deng Kaiming , Xiao Chuanyun , Wang Kelin
Published: July 2007

The electronic structure of the 13‐atom Rh cluster is studied with the structure model optimized by Estiu and Zerner using the discrete variational local‐spin density‐functional method. The magnetic moment per atom of the cluster is calculated to be 0.54μB, in good agreement with experimental measurements (0.48±0.13)μB. It confirms our previous assumption that the structural distortion of the Rh13 cluster from a perfect icosahedron to its ground state geometry decreases its magnetic moment and makes the theoretical calculation close to the experimental measurement.
Theoretical interpretation of the temperature dependence of zero‐field splitting of Ni2+ in NiSiF6 · 6 H2O
Authors: Peng Long‐Cai , Wu Ping‐Feng , Zhou Kang‐Wei
Published: July 2007

By use of a trigonal crystal‐field model and by means of the eigenvalues and eigenvectors of a d8 (C) ion, a unified calculation is given for the spectral fine structure, the EPR parameters (D, 9|, 9⟂), and the EPR absorption condition (H,v) of Ni2+ ions in NiSiF6· 6H2O at different temperatures. The theoretical results agree well with the findings. It is shown that the trigonal field parameter v, which describes the splitting degree of the t2g orbitals in a trigonal field, has approximately a linear temperature dependence, v (cm−1) = 117.3 + 0.4898 T (K). This is shown to be the physical mechanism of the temperature dependence of the zero‐field splitting parameter D. The theoretically predicted EPR absorption conditions (H,v) and a very slight temperature dependence of the g‐values also agree very well with the findings.
Spontaneous polarization behaviour in ferroelectrics
Authors: Wojtczak L. , Zasada I.
Published: July 2007

The spontaneous polarization behaviour in the vicinity of the ferro‐paraelectric phase transition is discussed. The experimental results for ferroelectrics are analyzed in the case of pyroelectric function investigations. The description in terms of the two‐point scaling hypothesis is then applied in order to explain the tail of the polarization in the paraelectric phase. The critical exponents are evaluated. The Curie temperature determined from experimental data above or below the temperature for the maximum of the pyroelectric function is considered in the model assuming that the fixed point can be related to one of the stability points for the ferro‐ or paraelectric phase, respectively. In the model presented the temperature hysteresis seems to be a natural phenomenon because of the phase transition point whose position results from the competition between fluctuations in the ferro‐paraelectric phase coexistence interval.
Electronic and vibronic structure of the nonplanar organic charge‐transfer salt m‐BDNT‐PF6
Authors: Dong J. , Yakushi K. , Yamashita Y. , Imaeda K. , Inokuchi H.
Published: July 2007

The monoclinic form of BDNT‐PF6 (m‐BDNT‐PF6) is characterized as a pseudo‐one‐dimensional half‐filled Hubbard system from the electrical conductivity, magnetic susceptibility, and single crystal optical spectra. m‐BDNT‐PF6 undergoes a spin‐Peierls transition at about 150 K. The lattice dimerization was confirmed by the evolution of the vibronic modes at low temperature. The small polaron binding energy of this compound, which was estimated through the analysis of the vibronic modes, is smaller than those of TTF, TCNQ, or CA. Hubbard parameters U and t were obtained to be 0.8 and 0.13eV by analyzing the charge‐transfer band. The optical and magnetic data are consistent with each other.
Photoluminescence spectra of CdTe/CdMnTe quantum well structures in an external magnetic field
Authors: Aguekian V. F. , Ashenford D. E. , Lunn B. , Koudinov A. V. , Kusrayev Yu. G. , Zakharchenya B. P.
Published: July 2007

The investigation of the photoluminescence spectra of CdTe/CdMnTe quantum well structures proves that the exciton localization efficiency is governed by temperature, external magnetic field, and excitation energy. The polarization of the luminescence in a magnetic field suggests that the impurity related luminescence band is due to the recombination of electron states situated near the interface.
Atomic charges in RBa2Cu3O7 superconductor lattices. Electronic structure of the copper atoms
Authors: Masterov V. F. , Seregin P. P. , Nasredinov F. S. , Seregin N. P. , Sagatov M. A.
Published: July 2007

The effective atomic charges for all sites of the RBa2Cu3O7 lattices have been found using our Mössbauer data withthe 67Cu(67Zn),133Ba(133Cs), 155Eu(155Gd) isotopes, our calculations of the lattice electric field gradient (EFG) at the lattice sites, as well as the 17O NMR data available in literature. The charges show holes placed in the chain oxygen sublattice mainly. The Cu2+ Sternheimer factor has been estimated and the Cu2+ valence EFG in YBa2Cu37 has been found. The z‐axes of the total, lattice, and valence EFG tensors for Cu(2) coincide with the crystal axis c. For Cu(1) they coincide with the axes b, a, and a, respectively.
Orthogonalizing of core bloch states for crystalline copper
Authors: Syrotyuk S. V. , Ye. Kynash Yu.
Published: July 2007

The orthonormalized core Bloch states for crystalline copper have been obtained by means of the unitary rotation matrix. This matrix depends on anoverlap matrix which is evaluated on non‐orthogonal core Bloch functions. We evaluate the orthogonalization matrix in two ways. The first one consists in evaluation of the orthogonalization matrix exactly by iteration. The second approach is perturbative. The comparison of the numerical results of these two approaches allows us to conclude that the orthogonalization of core Bloch functions for crystalline copper should be done by means of aunitary rotation matrix, which is evaluated up to fifth order with respect to the overlap matrix.
Additive double gate analysis in photoinduced current transient spectroscopy: Application to cuprous oxide
Authors: Rakhshani A. E. , Khan W. I. , Mathew X.
Published: July 2007

Photoinduced current transient spectroscopy, in its conventional doublegate version, has been used extensively in the characterization of deep levels in semiinsulating materials. The analysis of the digitally captured transient signals by the post capture double gate method is a parallel technique with much more advantages. One of the drawbacks of the latter is, of course, the excessive time needed to capture data with a high signal‐to‐noise ratio. We have shown that the capturing time can be chosen tobe relatively low and the signal‐to‐noise ratio can be improved by a post capture data analysis referred to as the additive double gate analysis. The usefulness of this approach is demonstrated by the results obtained, for the first time, on high resistivity films of cuprous oxide. Thetechnique leads to the identification and measurement of the parameters of a few deep levels. The apparent activation energies of these levels are 0.33, 0.47, 0.49, and 0.59 eV. The corresponding capture cross sections are 2 × 10−17, 7 × 10−12, 1 × 10−15 (7 × 10−13), and 4 × 10−15 cm2, respectively.
Bulk modulus and equation of state of High‐Temperature superconductors
Authors: Kumar Munish
Published: July 2007

An empirical method is used to predict the bulk modulus of high‐temperature superconductors. The variation of the unit cell volume under the effect of high pressure is investigated by the Murnaghan relation. The results obtained are found to present a good agreement with the data reportedby earlier workers.
Comparison between the endor data of different superoxide ions in alkali halides
Authors: Van Doorslaer S. , Callens F. , Maes F. , Boesman E. , Bouden D.
Published: July 2007

The ENDOR data of O−2 in RbBr and KBr are compared with the ones in KCl for which two different types of O−2 ions were reported earlier. Interactions with the nearest neighbour alkali ions could be detected. The corresponding hyperfine and nuclear quadrupole coupling tensors were determined. For all cases, the ENDOR spectra could be explained in terms of a monovacancy model, i.e. the O−2 ion is replacing a single halide ion. One of the O−2 defects in KCl was found to be completely analogous to the ones found in KBr and RbBr. The second type of O−2 ion is also replacing a single halide ion and is believed to be perturbed by a nitrogen impurity.