bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and grain boundary defects of recrystallized silicon films prepared from amorphus silicon deposited using disilane
Authors: Hasegawa S. , Watanabe S. , Inokuma T. , Kurata Y.
Published: July 2002

The structure of polycrystalline Si (poly-Si) films, prepared by annealing amorphous Si (a-Si) films deposited using Si2H6, has been investigated by x-ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), and electron spin resonance, as functions of deposition conditions, such as deposition temperature Td (450–580 °C) of the a-Si and annealing time under a fixed temperature of 600 °C. A dominant texture of the poly-Si films changed from a 〈100〉 texture for Td below 530 °C to a 〈111〉 for Td above 530 °C, independent of the deposition rate of the a-Si films and of the film thickness. Although the XRD grain size was independent of Td, the TEM grain size increased from 1.0 to 2.5 μm with decreasing Td. It is suggested that the increase in this TEM size is caused by enhanced lateral growth of 〈100〉 grains due to the presence of strain. The spin density Ns and the factor g were found to first increase with the annealing time, and rapidly decreased after the films were crystallized. It is also found that the value of g for the poly-Si films decreased from 2.0051 to 2.0048 with decreasing Td. Furthermore, effects of post-hydrogenation on the poly-Si films with different textures were investigated, and a structural change of the boundary regions in the poly-Si films is discussed in connection with a change in the dominant texture, through the corresponding change in g.
X-ray focusing optics. II. Properties of doubly bent crystals with an extended x-ray source
Authors: Chukhovskii F. N. , Chang W. Z. , Förster E.
Published: July 2002

Calculations and analysis of an extended x-ray source image with a 2D focusing geometry are presented. Based upon the calculations for an x-ray point source image (Paper Ia), theoretical expressions are derived which reveal the contributions from both the Bragg and the optical (Fresnel) diffractions to the intensity distribution of the image at the focal plane. That is, for a given focusing geometry, the intensity distribution of the image of an extended source consists not only of the crystal rocking curves for a bent crystal, due to the Bragg diffraction; but also of the optical diffraction, the Fresnel integral, due to the phase correlations of the thickness and the spatial extent of a doubly bent crystal. The contribution from the optical diffraction depends solely upon the bent crystal focusing geometry. The relationship between the source and the image at the focal plane is obtained, and the intensity distribution of an extended x-ray source image with a 2D bent silicon crystal is given.
Characterization of interfacial structure of InGaAs/InP short-period superlattices by high resolution x-ray diffraction and Raman scattering
Authors: Mozume Teruo
Published: July 2002

InGaAs/InP short-period superlattices (SPSLs) grown by gas source molecular beam epitaxy (GSMBE) and by gas source migration enhanced epitaxy (GSMEE) on (001)InP substrates were investigated by x-ray diffraction (XRD) and Raman scattering. XRD and Raman scattering results show that, although the average lattice mismatch relative to the InP substrate in GSMBE-grown SPSL is close to zero, there may be some lattice parameter relaxation and substrate-layer tilting caused by asymmetrical ordering of atomic layers and/or interchange between As and P atoms at interfaces. In GSMEE-grown SPSLs, layer-by-layer growth is achieved and strained interface layers are formed.
Electron traps in GaAs:Sb grown by liquid phase epitaxy
Authors: Dhar S. , Mallik Kanad , Mazumdar Mousumi
Published: July 2002

Deep level transient spectroscopy studies of GaAs:Sb layers, grown by liquid phase epitaxy reveal the existence of two electron traps with activation energies of 0.4 and 0.54 eV. High temperature annealing of the material reduced the density of the former trap while that of the latter is increased substantially. Density of the 0.54 eV trap is also found to be controlled by the Sb content in the material. These two results, together with the obtained signature of the 0.54 eV trap, suggest that it is the same as the SbGa related electron trap observed previously in GaAs:Sb materials grown by other techniques. Annealing increases the density of this trap by creating more SbGa defects as a consequence of Ga out-diffusion from the material. Photocapacitance measurements indicate the presence of a 0.75 eV electron trap in the annealed layers, which is identified with the second charge state of the SbGa electron trap.
Optical methods for determining diffusion in magnetic quantum-well structures
Authors: Stirner T. , Harrison P. , Hagston W. E.
Published: July 2002

It is shown that the occurrence of magnetic polaron formation can have an appreciable influence on the values of the diffusion constants deduced from observations of the photoluminescence in diffused magnetic quantum-well structures. Arguments are presented that show that photoluminescence excitation spectroscopy provides several independent, more accurate measurements from which the diffusion constants can be more reliably estimated.
Competition between carrier concentration and temperature influences on gain as means for improving modulation response of semiconductor laser
Authors: Tolstikhin V. I. , Willander M.
Published: July 2002

Concentration and effective temperature of carriers are established to compete in their influences on the band-edge dielectric function of an active semiconductor medium under the lasing conditions. This competition is shown as capable of suppressing the relaxation oscillations and wavelength chirping in the modulation response of a semiconductor laser, provided the carrier injection and carrier heating are combined in a suitable way. The problem of how to combine them is studied under the small-signal approximation assuming that modulation signal can be imposed on both the injection current and energy flux flowing into the active layer. All the numerical results relate to single-frequency 1.55 μm GaInAsP/InP laser.
Calculation of the structural dependence of infrared absorption in p-type strained layer SiGe/Si quantum wells
Authors: Liou Tsyr-Shyang , Wang Tahui , Chang Chun-Yen
Published: July 2002

A study of infrared absorption due to intersubband transitions in p-type Si1−xGex/Si quantum wells has been performed. The influence of the hole envelope wave-function and the subband structure on the absorption characteristics is evaluated. In the calculation, the subbands in a SiGe strained layer are computed by using a bond orbital model, which combines the k⋅p and the tight-binding methods, with a strain Hamiltonian. Both of the Poisson and the Schrödinger equations are solved self-consistently to take into account a band-bending effect. The calculated quantum efficiency in a 40 Å Si0.75Ge0.25/Si quantum well detector is compared favorably with an experimental result. The structural dependence of infrared absorption on quantum well width, doping and Ge content in a wavelength range of 3–15 μm is investigated. By varying a well width, our study reveals that a maximum absorption coefficient is obtained when the energy level of the excited-state subband is near the top of a quantum well.
Magnetic state of Fe at and near the interface between Fe–Al–Si magnetic thin films and Zn–ferrite
Authors: Komatsu Takayuki , Shimagami Keisuke , Sakemi Yoshikazu , Matusita Kazumasa , Miyazaki Masahiro
Published: July 2002

The magnetic state of Fe atoms at and near the interface between Fe74.3Al9.8Si15.9 sendust magnetic thin films and polycrystalline Zn–ferrite substrates has been examined using conversion electron Mössbauer spectroscopy. The thicknesses of sputtered films are 0.05, 0.08, 0.47, and 1.91 μm, and the annealing conditions are at 500 °C for 1 h. The sendust films/Zn–ferrite interface is very reactive, and the DO3-type ordered structure is not formed near the interface. This is the reason that excellent soft magnetic properties are not obtained for the films with a thickness of less than 0.47 μm. The presence of ferromagnetic Fe atoms with an internal magnetic field of 324 or 330 kOe is confirmed near the interface, indicating the formation of an Fe-rich phase such as Fe94Si6 and diffusions of Al and Si atoms from the sendust films to the interface. The thickness of the Fe-rich phase in the films has been estimated to be approximately 0.42 μm from the value (12.8 kG) of saturation magnetic-flux density for the film with 1.91 μm. It is found that a large part of Fe3+ ions in Zn–ferrite being at the interface is reduced to Fe2+ ions. The redox reaction at the interface has been proposed.
Structure of the interface between ErAs, a cubic semimetal and AlAs, a tetrahedral semiconductor
Authors: Tarnow Eugen
Published: July 2002

Using ab initio local density calculations, the atomic structure of the (100) interface between ErAs, a semimetal with the sodium-chloride (SC) structure and AlAs, a semiconductor with the zinc-blende (ZB) structure is investigated. Several findings emerge: (1) Eight different high symmetry SC/ZB interfaces are identified and classified. (2) Several low energy interfaces, and combinations thereof, are found for epitaxial growth and for small superlattices. The energies of these interfaces change during epitaxy pointing to importance of kinetics. Calculated structural energies and Er 〈100〉 placements are compared with experimental Rutherford backscattering measurements. (3) The AlAs ZB structure buckles the first ErAs SC layer. There is a strong correlation between the amount of buckling induced in a substrate SC layer and the energy required to add another SC layer. (4) For small superlattices a complete ZB or SC arrangement, removing the SC/ZB interfaces altogether, is sometimes energetically preferred.
Use of carbon films for passivation and environmental protection of superconducting YBa2Cu3O7−x
Authors: Tatum Julie Dreyfuss , Tsai Jack W. H. , Chopra Manoj , Chan Siu-Wai , Phillips Julia M. , Hou S. Y.
Published: July 2002

Electronic device applications of high-temperature superconducting cuprates require the production of patterned thin films that are stable and inert in various processing and operating environments; however, the superconducting rare-earth barium cuprates have been shown to decompose in water and to degrade in superconducting properties in a humid atmosphere. The thermodynamics that forms the driving force for the degradation is reviewed. Protective coatings or removable protective films can realize many applications and facilitate processing of superconducting devices. Diamondlike carbon films as well as amorphous carbon films are investigated as possible protective layers for YBa2Cu3O7−x (YBCO). Amorphous carbon (a-carbon) films deposited by evaporation are shown to protect superconducting YBCO films from degradation by humidity. The YBCO films with a-carbon coatings have been shown to have critical current densities four orders of magnitude higher than the uncoated YBCO films after 2 h at a stressing of 100% relative humidity (RH). A similar stressing for 44.5 h has conducting YBCO films but no longer has a measurable critical current density. The a-carbon coating is an effective passivation layer for short-term storage (with time <2 h and 100% RH and time ≳4 h at 50% RH) at room temperature. The critical current is shown to be a better indicator for the degree of degradation, since the transition temperature remains relatively constant as long as there is enough superconducting YBCO to provide a percolation path for the supercurrent. Degrees of degradation were also assessed by scanning electron microscopy. The versatility of these carbon films lies in that their deposition and removal by plasma oxidation at room temperature are compatible with YBCO films.
Current-density dependence of activation energy in high-T
c superconductor HgBa2Ca2Cu3O8+x
Authors: Li J. , Ding S. Y. , Zhu J. S. , Shao H. M. , Wang Y. N.
Published: July 2002

The real and imaginary parts of the ac susceptibility of high-Tc superconductor HgBa2Ca2Cu3O8+x were measured as a function of temperature in different ac fields and frequencies at a fixed dc field. The current-density dependence of activation energy was obtained in terms of nonlinear diffusion equation of vortices. The relaxation of the current density and the exponent μ of the glassy phase were deduced from the relation between the activation energy and the current density. In addition, the pinning energy and critical current density were estimated.
Influence of demagnetization in remanence curves of magnetic thin films
Authors: te Lintelo J. G. Th. , Lodder J. C.
Published: July 2002

Remanent magnetization curves of perpendicular magnetic thin films are simulated and measured. The simulations are used to investigate the theoretical influence of the strong demagnetizing field present in these films. Conclusions are drawn from this on how remanence curves should be measured and how they should be corrected for the demagnetizing influence. The experimental part consists of measurements on Fe-Alumite, Co-Pt–based multilayers, and Co-Cr. In addition the latter material is also artificially patterned into microstrips in order to investigate the influence of demagnetization on remanence curves experimentally.
Analytical and optimization procedures for determination of all elastic constants of anisotropic solids from group velocity data measured in symmetry planes
Authors: Kim Kwang Yul , Sribar Rok , Sachse Wolfgang
Published: July 2002

Analytical and optimization methods of determining all elastic constants of elastically anisotropic solids from the group velocities measured in various directions in the symmetry planes are described. The group velocities in various directions of the specimen are measured, using broadband pointlike and line-type sources in combination with pointlike detectors, and changing a source-to-detector orientation. The mixed index elastic constants of the specimen are determined using analytic formulas that relate the elastic constants to the group velocity in an arbitrary direction on the symmetry plane. It is demonstrated that given the numerous group velocity data, one can efficiently determine the elastic constants by first converting them into phase velocity data and then applying the least-squares optimization methods to the phase velocity data. Examples are provided with specimens of transversely isotropic zinc, cubic silicon, and orthotropic fiber-reinforced poly ether ether kethon.
Measurement of an elliptical fiber mode field using near-field microscopy
Authors: Butler D. J. , Horsfall A. , Nugent K. A. , Roberts A. , Bassett I. M. , Lo K. M.
Published: July 2002

Near-field scanning optical microscopy is used to determine the field structure within a noncircularly symmetric optical fiber. The output from an elliptical core fiber is measured and found to be in good agreement with the field predicted using a point matching method and fiber parameters determined from the preform.
Rapid thermal annealing of amorphous and nanocrystalline soft-magnetic alloys in a static magnetic field
Authors: Roozeboom Fred , Dirne Frank W. A.
Published: July 2002

In this paper, we report on rapid thermal annealing (RTA) of two different soft-magnetic materials in a static magnetic field: amorphous Co-Nb-Zr and nanocrystalline Fe-Nb-N. RTA of Co-Nb-Zr films was investigated in an attempt to suppress the crystallization of Co during the induction of the anisotropy, thus extending the process window of this material in video-head manufacturing. Also, RTA of Fe-Nb-N was studied in an effort to promote the nucleation of nanocrystalline Fe grains, while suppressing the grain growth of α-Fe. Using RTA in a magnetic field, Co-Nb-Zr alloys can be heated to temperatures above 525 °C, while suppressing the crystallization of hexagonal-close-packed Co. This temperature is considerably higher than that of conventional magnetic annealing in a furnace (400 °C), and thus allows us to combine annealing with other high-temperature processes during recording head manufacturing procedures, such as glass bonding in sandwich head manufacturing. Furthermore, RTA allows the formation of nanocrystalline Fe-TM-N alloys with both a high permeability and a low magnetostriction (TM is a transition metal such as Zr, Hf, Nb, or Ta). Using high processing temperatures and short processing times, both the nucleation of bcc Fe and the segregation of NbN from Fe-Nb-N can be promoted, while the undesired grain growth of Fe is reduced, thus lowering the magnetic anisotropy. Moreover, layers produced in this way have increased resistivity to wear (during tape recording) than conventionally annealed layers.
Dependence of the absorption of pulsed CO2-laser radiation by silane on wavenumber, fluence, pulse duration, temperature, optical path length, and pressure of absorbing and nonabsorbing gases
Authors: Bl/ażejowski Jerzy , Gruzdiewa Ludwika , Rulewski Jacek , Lampe Frederick W.
Published: July 2002

The absorption of three lines [P(20), 944.2 cm−1; P(14), 949.2 cm−1; and R(24), 978.5 cm−1] of the pulsed CO2 laser (0001–1000 transition) by SiH4 was measured at various pulse energy, pulse duration, temperature, optical path length, and pressure of the compound and nonabsorbing foreign gases. In addition, low intensity infrared absorption spectrum of silane was compared with high intensity absorption characteristics for all lines of the pulsed CO2 laser. The experimental dependencies show deviations from the phenomenological Beer–Lambert law which can be considered as arising from the high intensity of an incident radiation and collisions of absorbing molecules with surroundings. These effects were included into the expression, being an extended form of the Beer–Lambert law, which reasonably approximates all experimental data. The results, except for extending knowledge on the interaction of a high power laser radiation with matter, can help understanding and planning processes leading to preparation of silicon-containing technologically important materials.
Partial and perfect dislocation nucleation at the onset of stress relaxation in In0.60Ga0.40As active layers of high mobility transistors grown on InP
Authors: Peiró F. , Cornet A. , Morante J. R.
Published: July 2002

The morphology of compressive InxGa1−xAs/In0.52Al0.48As layers grown on (100)-InP substrates by molecular beam epitaxy was observed by transmission electron microscopy. A preliminary analysis of the network of misfit dislocations at the interface in layers with a thickness of 0.5 μm and xIn between 54% and 63% led to a further study of the onset of stress relaxation for layers with composition xIn=60% and thickness ranging from 5 to 25 nm. A critical thickness was found for plastic relaxation at 20 nm<tc<25 nm. Following a model of excess stress, a mechanism for the nucleation of dislocations according to the sequence 90°partial→60°perfect→30°partial is proposed.
Determination of alloy composition in modulation doped AlxGa1−xAs/GaAs heterostructure
Authors: Wang D. P. , Lo Ikai , Chern J. L. , Mitchel W. C.
Published: July 2002

We have determined the alloy composition of modulation doped AlxGa1−xAs/GaAs heterostructure by Raman scattering and photoreflectance spectroscopy at room temperature. We also demonstrated that Franz-Keldysh oscillations in photoreflectance spectroscopy can be used to evaluate the band gap of semiconductor heterostructure. The band gap measured by Franz-Keldysh oscillations of photoreflectance spectrum is 1.865 eV. The alloy composition calculated from the band gap is 0.30. From the frequency positions of ‘‘GaAs-like’’ and ‘‘AlAs-like’’ phonon modes of the Raman scattering data, the value of the alloy composition was evaluated to be 0.29 which is in good agreement with the photoreflectance result. Both values also agree with the target composition in the molecular beam epitaxy growth and the target composition is equal to 0.30.
Influence of cavity length and emission wavelength on the characteristic temperature in AlGaAs lasers
Authors: Sánchez M. , Díaz P. , Torres G. , González J. C.
Published: July 2002

The dependence of the characteristic temperature T0 on the cavity length and lasing wavelength is theoretical and experimentally analyzed. The devices are straight separate confinement heterostructure lasers with active layer thickness of 30 and 12 nm grown by low temperature liquid phase epitaxy. The recent observation that for very short lasers T0 is an increasing function of the cavity length is confirmed, and explained in terms of the threshold current cavity length dependence. The temperature dependence of the threshold current Ith gives T0 as high as 307 K for a quantum well laser with cavity length L=168 μm.
Analysis by optical absorption and transmission electron microscopy of the strain inhomogeneities in InGaAs/InP strained layers
Authors: Roura P. , Clark S. A. , Bosch J. , Peira F. , Cornet A. , Morante J. R.
Published: July 2002

Optical absorption spectra and transmission electron microscopy (TEM) observations on InGaAs/InP layers under compressive strain are reported. From the band-gap energy dispersion, the magnitude of the strain inhomogeneities, σε, is quantified and its microscopic origin is analyzed in view of the layer microstructure. TEM observations reveal a dislocation network at the layer interface the density of which correlates with σε. It is concluded that local variations of dislocation density are responsible for the inhomogeneous strain field together with another mechanism that dominates when the dislocation density is very low.
Infrared-absorption line shapes of shallow donors in cylindrical quantum-well-wire structures
Authors: Latgé A. , Oliveira Luiz E.
Published: July 2002

A theoretical study of the intraimpurity infrared-absorption properties associated to donor-doped cylindrical GaAs–(Ga,Al)As quantum-well wires is presented. Donor binding energies and envelope wave functions are calculated within a variational scheme in the effective-mass approximation, and line strengths for intradonor transitions to excited states of 2s-, 2pz-, and 3pz-like symmetries are obtained for different photon polarizations and for donor positions varying along the radial direction of the wire. The donor-related absorption coefficients are evaluated in the case of 1s→2pz and 1s→3pz transitions for z-polarized radiation, and for different donor profiles in the quantum wire.
Formation of metal-rich silicides in the initial stage of interfacial reactions in Nb/Si systems
Authors: Nakanishi Taichi , Takeyama Mayumi , Noya Atsushi , Sasaki Katsutaka
Published: July 2002

The interfacial reaction of Nb thin films on (100) Si indicates the first phase nucleation of metal-rich silicide and the occurrence of multiphases under certain annealing conditions. Nb3Si was identified as being the first nucleated phase at the annealing temperature of 550 °C, and subsequently Nb5Si3 is found to be formed by annealing at 600 °C. The multiphases of Nb3Si, Nb5Si3, and NbSi2 were observed to be formed simultaneously in the specimen annealed at 650 °C. The growth of NbSi2 by the out-diffusion of Si, which overcame the metal-rich phase, was observed at annealing temperatures over 700 °C.
Comment on ‘‘Equation of state of aluminum nitride and its shock response’’ [J. Appl. Phys. 76, 4077 (1994)]
Authors: Rosenberg Z. , Brar N. S.
Published: July 2002

A recent article by Dandekar, Abbate, and Frankel [J. Appl. Phys. 76, 4077 (1994)] reviews existing data on high-pressure properties of aluminum nitride (AlN) in an effort to build an equation of state for this material. A rather large portion of that article is devoted to the shear strength of AlN and, in particular, to our data of 1991 with longitudinal and lateral stress gauges [Z. Rosenberg, N. S. Brar, and S. J. Bless, J. Appl. Phys. 70, 167 (1991)]. Since our highest data point has an error of 1 GPa, much of the discussion and conclusions of Dandekar and co-workers are not relevant once this error in data reduction is corrected. We also discuss the relevance of our shear strength data for various issues, such as the phase transformation of AlN at 20 GPa and the general shape of Hugoniot curves for brittle solids.
Temporal evolution of the physical response during photorefractive grating formation and erasure for BSO
Authors: Murillo J. G. , Magaña L. F. , Carrascosa M. , Agulló-López F.
Published: July 2002

The time evolution of the charge carrier density, ionized donor density and space-charge field under a sinusoidal light pattern have been calculated by solving numerically the nonlinear differential equations for a photorefractive material (such as BSO). The time evolution for optical erasure starting from the steady-state solution has also been obtained. Arbitrary modulation depths have been considered for two relevant cases: pure diffussion and under an applied dc electric field of 5 kV/cm.
Positive nonlinear index of refraction in tellurium dioxide single crystals above the two-photon absorption edge
Authors: Watanabe Yuichi , Ohnishi Masato , Tsuchiya Toshio , Ueda Naoyuki , Kawazoe Hiroshi
Published: July 2002

A phase distortion method is applied to examine the optical nonlinearity in tellurium dioxide single crystal. The positive nonlinear index of refraction is observed in the crystal at above the two-photon absorption edge. While the observed positive sign is consistent with that predicted theoretically, the absolute values of both nonlinear index of refraction and two-photon absorption coefficient are larger than the theoretical values by a factor of five.
Optimization of the slow-mode plasmon polariton in light-emitting tunnel junctions
Authors: Connolly M. P. , Dawson P.
Published: July 2002

Light emitted from metal/oxide/metal tunnel junctions can originate from the slow-mode surface plasmon polariton supported in the oxide interface region. The effective radiative decay of this mode is constrained by competition with heavy intrinsic damping and by the need to scatter from very small scale surface roughness; the latter requirement arises from the mode’s low phase velocity and the usual momentum conservation condition in the scattering process. Computational analysis of conventional devices shows that the desirable goals of decreased intrinsic damping and increased phase velocity are influenced, in order of priority, by the thickness and dielectric function of the oxide layer, the type of metal chosen for each conducting electrode, and temperature. Realizable devices supporting an optimized slow-mode plasmon polariton are suggested. Essentially these consist of thin metal electrodes separated by a dielectric layer which acts as a very thin (a few nm) electron tunneling barrier but a relatively thick (several 10’s of nm) optically lossless region.
Effect of phase shifter on the characteristics of the distributed feedback laser
Authors: So Daniel W. C. , Seshadri S. R.
Published: July 2002

For both transverse magnetic and transverse electric modes, the governing equations for the guided-guided wave interaction in a dielectric thin film waveguide which is etched with a cosinusoidal surface corrugation have been developed by using a quasioptical technique. These governing equations are used to investigate the effect of the phase shifter on the characteristics of the distributed feedback laser. Phase shifters either at the center or at the ends of the laser eliminate the gain degeneracy and make the power distribution inside the laser more uniform. When the amount of phase shift is appropriately chosen, the gain margin increases and reaches a maximum value. The roles of the other parameters in achieving a single-mode operation for the laser have been investigated by means of numerical examples. It has been found that the characteristics of the distributed feedback laser with phase shifters are quite similar for both transverse magnetic and transverse electric modes.
Synthesis of actinide carbides encapsulated within carbon nanoparticles
Authors: Funasaka Hideyuki , Sugiyama Kenji , Yamamoto Kazunori , Takahashi Takeshi
Published: July 2002

Actinide carbides encapsulated with multilayered graphitic capsules have been produced by the arc burning of a composite carbon rod containing thoriated tungsten or uranium ore. The morphology of these filled nanoparticles was observed by transmission electron microscopy. The preferential encapsulation in the constituent elements of the core materials surrounded by the graphite cage was demonstrated. Furthermore, it was found that these carbon nanoparticles filled with radioactive materials have been quite stable for 1 year or more.
Iterative evaluation of thermally stimulated depolarization current peak parameters in polymers: A dipolar interaction approach to molecular dipole relaxation
Authors: Migahed M. D. , Ahmed M. T. , Kotp A. E. , El-Henawy I. M.
Published: July 2002

An approach for the dipole relaxation in polymers is treated considering the dipole–dipole interaction between the molecules. The thermally stimulated depolarization peak parameters, i.e., the activation energy E, the pre-exponential factor τ0, and the dipole interaction strength parameter q, were evaluated using the iterative technique. Good results are obtained in comparison with other methods. A linear relationship between the activation energy and the logarithm of the pre-exponential factor of the relaxation times is existing confirming the operation of the compensation law.
Methods for calculating electrostatic quantities due to a free charge in a nanoscale three-dimensional tip/base junction
Authors: Peridier Vallorie J. , Pan Li-Hong , Sullivan Thomas E.
Published: July 2002

The exact solutions for fully three-dimensional electrostatic quantities due to a free charge in a nanoscale tip/base junction, such as the scanning-tunneling microscope, are given for the problem as modeled in the prolate-spheroidal coordinate system. These exact solutions consist of summation series of integrals of conical functions, and methods for calculating these exact solutions with high accuracy are described in detail in this paper. Calculated results for the surface-charge distribution on the tip and the base due to a free electron in a nanoscale tip/base junction are also presented. This analysis has important implications for the ultimate objective of quantifying electron tunneling, from first principles, in nonplanar geometries such as sharp vacuum field emitters.
The metamagnetic and the weak ferromagnetic transitions of the Cu lattice of Ho2CuO4
Authors: Rouco A. , Obradors X. , Tovar M.
Published: July 2002

We have studied the magnetic properties of the Cu lattice of Ho2CuO4. This cuprate can only be synthesized at high pressure. It crystallizes in a structure derived from the Nd2CuO4-type structure (T′ phase), modified by local distortions in the CuO2 planes. We have measured dc magnetization versus temperature and isothermal dc magnetization versus magnetic field. These measurements were made in the range of temperature from 5 to 540 K applying magnetic fields up to ±50 kOe. ac susceptibility has also been measured in the range of temperatures from 80 to 320 K, using different frequencies between 33 and 1000 Hz and excitation fields between 1 and 10 Oe. We have found a three-dimensional antiferromagnetic (AF) ordering of the Cu lattice of Ho2CuO4 below TN=271(1) K. This AF order is accompanied by a weak ferromagnetic (WF) component, due to a small canting of the Cu spins away from perfect AF alignment. Below TN, at zero field, the interlayer AF coupling makes the WF components in neighboring CuO2 planes to be oriented antiferromagnetically and, thus, to remain almost compensated. Only above a field-induced metamagnetic transition is the weak ferromagnetism evidenced. The WF component persists above TN, in a large temperature interval, induced by the magnetic field. The magnetization of the paramagnetic (PM) Ho lattice, which follows a Curie–Weiss law with μeff=10.16(1)μB/Ho atom and θ=7.6(5) K, is superimposed to the magnetism of the Cu lattice. There exists an exchange coupling between both lattices and the PM Ho ions are polarized through an internal magnetic field due to the WF component of the Cu moments.
Domain wall motion coercivity
Authors: Jatau James A. , Torre Edward Della
Published: July 2002

This article presents a comparison of one-, two-, and three-dimensional models for domain wall motion coercivity. The effect of wall bending in two-dimensional models as compared to one-dimensional models and the additional effect of wall flexing in three-dimensional models is studied. The models are implemented numerically and calculations are carried out for soft magnetic materials. A discussion of how parameters must be chosen in lower dimensional models to obtain the correct magnitude of coercivity is included.
Recombination rate saturation mechanisms at oxidized surfaces of high-efficiency silicon solar cells
Authors: Robinson S. J. , Wenham S. R. , Altermatt P. P. , Aberle A. G. , Heiser G. , Green M. A.
Published: July 2002

Shoulders have been observed in the measured semilogarithmic current-voltage (I–V) characteristics of high-efficiency passivated emitter and rear locally diffused silicon (Si) solar cells. An improved understanding is given of the mechanism proposed to cause these nonideal I–V curves. It is shown that this mechanism is due to the electrostatic behavior of free carriers at the Si/SiO2 interface of oxidized Si devices in which the Si adjacent to the oxide is depleted (or in some cases, inverted) at equilibrium, and results in saturation of the surface recombination rate. Two-dimensional numerical computer simulations are used to investigate this mechanism and its effect on cell performance. In addition, the simulations provide a means of estimating the extent to which lateral conduction in the rear surface channel also contributes to the observed recombination saturation in these cells. It is shown that ohmic limitation of lateral conduction occurs, however, the lateral current flows are negligible in comparison to the recombination currents due to the former mechanism.
Junction current distributions and ac impedances of thin resistive films on semiconductor junctions
Authors: Baraff G. A.
Published: July 2002

Certain aspects of the blocking layer behavior in semiconductor heterojunction lasers can be modeled as a thin resistive film overlaying a semiconductor forward biased junction. The dc behavior of such a model has been studied previously by W. B. Joyce and S. H. Wemple [J. Appl. Phys. 41, 3818 (1970)]. This paper studies the ac aspects of that model, and also makes some of the dc results of Joyce and Wemple more immediately accessible.
An analysis of the Mott-Schottky behavior in ZnO-Bi2O3 based varistors
Authors: Alim Mohammad A.
Published: July 2002

A series of non-converging frequency-dependent Mott–Schottky straight lines can lead to significant errors in the calculation of the device-related parameters (such as; built-in-potential, barrier height, carrier concentration, etc.) for the ZnO-Bi2O3 based varistors. These errors are illustrated using the frequency-dependent slope of these straight lines. To avoid this problem, a method of obtaining the frequency-independent Mott-Schottky response has been devised for these devices. This method employs the well-known lumped parameter/complex plane analysis technique, and thereby resolves the complexity of the frequency-dependent Mott–Schottky response. Using this technique, it is possible to characterize the Mott–Schottky behavior of varistor materials without incorporating frequency-dependent phenomenon in the analysis. These parameters are self-consistent, and satisfy the basic/classical Mott-Schottky equation.
Comment on ‘‘Equation of state for extrapolation of high-pressure shock Hugoniot data’’ [J. Appl. Phys. 65, 3852 (1989)]
Authors: Johnson J. B.
Published: July 2002

Oh and Persson [J. Appl. Phys. 65, 3852 (1989)] proposed an equation of state to extrapolate high-pressure shock Hugoniot data to other high-pressure and high-temperature states and compared it to data. The requirement that F=−(∂E/∂V)P/(∂E/∂V)H≊1 (E is specific internal energy, V is specific volume, P is the constant pressure path and H is the constant Hugoniot path) needed to establish the equation of state appears to be in error. I have found F to vary from 0.16 to 3.59 for fifteen common materials of interest to shock physicists. Oh and Persson’s [J. Appl. Phys. 65, 3852 (1989)] comparison of their equation of state to data gives the impression of a better agreement than actually occurs because of possible errors in the transcription of data, and the use of an inappropriate Hugoniot for water. When data are correctly plotted and an appropriate water Hugoniot is used, the comparison of data to theory indicates that the equation of state loses accuracy with increasing pressure or decreasing porous initial density.
Sequential phase formation by ion-induced epitaxy in Fe-implanted Si(001)
Authors: Lin X. W. , Maltez R. , Behar M. , Liliental-Weber Z. , Washburn J.
Published: July 2002

Ion-beam-induced epitaxial crystallization (IBIEC) of Fe-implanted Si(001) was studied by transmission electron microscopy and Rutherford backscattering spectrometry. For sufficiently high Fe doses, it was found that IBIEC at 320 °C results in sequential epitaxy of Fe silicide phases in Si, with a sequence of γ-FeSi2, α-FeSi2, and β-FeSi2 with increasing Fe concentration along the implantation profile. The critical concentrations for the γ-α and α-β phase transitions were determined as ≊11 and 21 at. % Fe, respectively. The observed sequential phase formation can be correlated to the degree of lattice mismatch with the Si matrix and the stoichiometry of the silicide phases.
In situ measurement of Si-dopant concentration in GaAs during epitaxy
Authors: Braun W. , Däweritz L. , Ploog K.
Published: July 2002

Reflection high energy electron diffraction intensity oscillations are found to be shifted in phase by the predeposition of Si atoms on the (100) GaAs surface during molecular beam epitaxy. The shift is related to a change in surface reconstruction and is a linear function of the Si density. It is only observed in a narrow range of GaAs growth parameters. A different behavior is seen for (100) AlAs, which we attribute to a roughening of the growth front. The phase shift for (100) GaAs is less pronounced on the {01} streaks. This can be explained by a different surface structure near steps running along [11̄0].
Friction force microscopy study of lubricant thin films on thin-film magnetic recording media
Authors: Fujiwara Ichiro , Kamei Takahiro , Tanaka Koichi
Published: July 2002

The microscopic frictional properties of lubricant thin films on thin-film magnetic recording media [metal-evaporated (ME) tape] were investigated with a friction force microscope in order to understand the intrinsic frictional properties of the lubricant on the ME tapes. We propose the microscopic effective friction coefficient, the friction force normalized by the normal force based on the JKR theory, of the lubricant thin films, which is the critical parameter to understand microscopic friction phenomena. It is found that the microscopic effective friction coefficient of the lubricants on the ME tapes is not dependent on the surface roughness of the media, but the macroscopic friction coefficient of the lubricants is dependent on the surface roughness. This suggests that the effective friction coefficient describes the intrinsic friction properties of the lubricant materials on the ME tapes in the microscopic level. It is also found that the magnitude of the microscopic effective friction coefficient is dependent on the lubricant materials on the ME tapes and is in fair agreement with the relative intensity of the macroscopic friction coefficient for three kinds of the lubricants. This indicates that lubricants with smaller effective friction coefficients correspond to the lubricants with lower friction properties. Furthermore, concerning the two-dimensional distribution of the friction force, it is found that the friction force of the higher part of the surface grains is lower than that of the lower part of the surface grains.
Decrease of the number of the isolated emission center Mn2+ in an aged ZnS:Mn electroluminescent device
Authors: Lee Y. H. , Kim D. H. , Ju B. K. , Song M. H. , Hahn T. S. , Choh S. H. , Oh M. H.
Published: July 2002

We observed a decrease of the number of effective emission centers Mn2+ in the aged ZnS:Mn electroluminescence (EL) devices compared to the fresh EL devices using the electron-paramagnetic-resonance technique. Such phenomena can take place during the operation of the EL device, since the isolated Mn can easily diffuse into another site and forming cluster. Another possible explanation is that Mn2+ changes into Mn1+ or Mn3+ by transferring the electronic charge of the isolated Mn2+ to the neighboring Mn ions via sulfur and/or sulfur vacancy. As a result, luminance is lowered due to the decrease in the number of efficient emission centers of isolated Mn2+.
Crystallinity and average grain size of films grown by chemical vapor deposition
Authors: Kim S. K. , Lee Hong H.
Published: July 2002

Probabilities are utilized to arrive at a relationship that defines the boundary for the monocrystalline region in terms of the partial pressure of the source gas and the deposition temperature. Also derived is a relationship for the average grain size of polycrystalline film. The results are restricted to the complete or near-complete condensation case of nucleation.
A theoretical consideration of the dielectric behaviors of ferrofluid subjected to a magnetic field
Authors: Zhang Qi , Wang Jianhua , Zhu Hesun
Published: July 2002

The dielectric behaviors of a ferrofluid subjected to a magnetic field are discussed theoretically on the basis of the model of dynamically chain-growing process with increase of the magnetic field. The model, which is an expansion of the former model of stationarily chain-growing process, is put forward by defining the anisotropy of the ferrofluid as a function of the magnetic field. Thus, the dielectric constant matrix of a ferrofluid subjected to a magnetic field can be established. Some theoretical calculations about the field dependencies of both the refractive indices and the transmission coefficients in the two directions, parallel and perpendicular to the field direction, are carried out for different particle concentrations of the ferrofluid and conclusions are drawn.
Impurity photoionization in the presence of a static electric field: Phonon coupling and non-uniform electric field effects
Authors: Lamouche Guy , Lépine Yves
Published: July 2002

The modifications induced by a static electric field (Franz-Keldysh effect and Franz-Keldysh oscillations) in the photoionization cross section of semiconductor impurities are studied in presence of two factors relevant to experimental measurements: the electron-phonon polar coupling and a linear spatial variation of the applied electric field. Important for II-VI and III-V semiconductors, the electron-phonon polar coupling is treated using an approach adapted from the classical work of Huang and Rhys. Our calculations show that the Franz-Keldysh oscillations should be visible even in the presence of the electron-phonon interaction for shallow impurities. For deeper impurities, the oscillations should be visible if the electron-phonon coupling is weak, which is unlikely to happen in II-VI semiconductors. We also show that a linear spatial variation of the applied electric field leads to modifications of much smaller amplitude.
Low-pressure Cs-Ba discharge. I. Model development
Authors: Luke James R. , El-Genk Mohamed S.
Published: July 2002

A transient model of a low-pressure Cs-Ba diode which operates in a collisionless Knudsen mode is developed and benchmarked with experimental measurements. The model couples the external circuit to the plasma discharge in the diode. The model calculates the electron energy, plasma density, densities of ground state and first four excited states of neutral Cs atoms, sheath potentials, Cs coverage on the electrode surfaces, forward voltage drop, and discharge current as functions of time, as well as the current-voltage (I-V) characteristic of the diode. Calculated terminal voltage and current characteristics are in good agreement with experimental values.
Low filament temperature deposition of a-Si:H by hot-wire chemical vapor deposition
Authors: Brogueira P. , Conde J. P. , Arekat S. , Chu V.
Published: July 2002

Hydrogenated amorphous silicon, a-Si:H, is deposited from silane and hydrogen by hot-wire chemical vapor deposition using a tungsten wire filament at a temperature Tfil=1200 °C. Film properties depend on whether the films were deposited using filaments with an accumulated deposition time lower than 90 min (‘‘new’’ filaments) or longer than 90 min (‘‘old’’ filaments). The deposition rate for films deposited with ‘‘new’’ filaments is 4 times higher than that for aged filaments. For ‘‘new’’ filaments, a monotonic increase of the growth rate, rd, with the pressure is observed, as well as a maximum of rd for FH2/FSiH4 close to unity. The optoelectronic properties are controlled by the substrate temperature Tsub, and show different dependences for ‘‘new’’ and ‘‘old’’ filaments. The Urbach band tail energy, Eu, is lower for films deposited with ‘‘new’’ filaments. A kinetic growth model for hot-wire chemical vapor deposition in the Tfil∼1200 °C regime is proposed.
Third-order nonlinearities and coherent transient grating effects of narrow-gap semiconductors in the midinfrared
Authors: Hughes S. , Ciesla C. M. , Murdin B. N. , Pidgeon C. R. , Jaroszynski D. A. , Prazeres R.
Published: July 2002

Picosecond excitation-probe measurements using a far-infrared free-electron laser (CLIO) have revealed large nonlinearities for indium antimonide at 4.7 μm. A theoretical model is described to determine the cw third-order nonlinear susceptibility and the interband relaxation time of the semiconductor which were found to be −8.6×10−11 m2 V−2 and 0.3 ns, respectively. Furthermore, the observation of the associated coherent transient grating effects allows us to obtain a coherence time of the laser system (2.5 ps) and the χ(3) of the transient grating which was found to be −7.2×10−13 m2 V−2. The measurements were performed at room temperature on undoped bulk InSb.
Covering and filling of porous silicon pores with Ge and Si using chemical vapor deposition
Authors: Halimaoui A. , Campidelli Y. , Badoz P. A. , Bensahel D.
Published: July 2002

Filling of the pore network of porous silicon layers with Ge and Si has been demonstrated using a chemical vapor deposition (CVD) technique. It is shown that at low growth rate the species are deposited throughout the whole layer which can be completely filled. At high growth rate, the deposition takes place mainly on the top surface leading to pore mouth bridging. Investigation of the experimental data through a model shows that pore filling is a powerful tool for the study of the mechanisms involved in CVD processes at low temperature.