bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamics of tetragonal zirconia formation in a nanolaminate film
Authors: Aita C. R. , Wiggins M. D. , Whig R. , Scanlan C. M. , Gajdardziska-Josifovska M.
Published: July 2002

Zirconia–alumina transformation-toughening nanolaminates were fabricated by reactive sputter deposition. The average crystallite size and volume fraction of each zirconia polymorph were determined by x-ray diffraction. The volume fraction of tetragonal zirconia, the phase necessary for transformation toughening, was found to strongly depend upon the zirconia layer thickness. An end-point thermodynamics model involving hemispherical cap zirconia crystallites was developed to explain this phenomenon. In excellent agreement with experimental results, the model predicts that unity volume fraction of tetragonal zirconia is produced in the nanolaminate when the zirconia layer thickness is less than the radius at which a growing zirconia crystallite spontaneously transforms to the monoclinic phase.
Theoretical investigation of CoSi2/Si1−xGex detectors: Influence of a Si tunneling barrier on the electro-optical characteristics
Authors: Chu D. P. , Peeters F. M. , Kolodinski S. , Roca E.
Published: July 2002

We present a theoretical investigation of the influence of a non-reacted Si layer on the transport and optical properties of CoSi2/Si1−xGex Schottky barrier diodes grown from Co/Si/Si1−xGex systems. The presence of this layer reduces the effect of the lowering of the Schottky barrier height which would be expected in a CoSi2/Si1−xGex. However, due to the small thickness of this Si layer, the charge carriers are able to tunnel through it. This tunneling process allows for a significant lowering of the Schottky barrier height and therefore an extension of the detection regime into the infrared.
Improved hydrogen depth profiles with in-chamber annealing of hydrogenated amorphous silicon thin films
Authors: Rüther R. , Livingstone J. , Dytlewski N. , Cohen D.
Published: July 2002

We have undertaken a study on the influence of deposition temperature and an in-chamber annealing treatment on the hydrogen depth profiles of sputter-deposited hydrogenated amorphous silicon (a-Si:H) thin films. Our results show that for higher temperature deposition (285–300 °C), which leads to a lower degree of hydrogen incorporation, very steep hydrogen distribution profiles resulted. The hydrogen content at the film–substrate interface of such films can be ∼2/3 of that at the film’s surface. It is believed that a strong hydrogen outdiffusion from the bulk took place during film growth at those relatively high temperatures. When an in situ in-chamber annealing treatment was carried out just after deposition and before samples reached room temperature, hydrogen distribution through the film thickness showed a more homogeneous profile. Moreover, the resultant films appeared to be more dense when samples were subjected to this treatment in an atomic hydrogen atmosphere.
Enhanced Raman conversion by a two-longitudinal-mode beam in the para-hydrogen Raman laser
Authors: Takasaki Takuya , Tsunemi Akira , Nagasaka Keigo , Suda Akira , Tashiro Hideo
Published: July 2002

Using a longitudinally mode-controlled transversely excited atmospheric CO2 laser, we studied the conversion characteristics of single-, two-, and multimode pump pulses in a para-H2 Raman laser. In the small signal region, two- and multimode pump pulses showed higher Raman conversion efficiencies. In the saturation region, however, output energies pumped with single- and two-mode pulses exceeded those pumped with multimode pulses. Consequently, the two-mode pumping was the most efficient within the limit of pump energies used in the experiment. The results are explained in relation to the mode-mixing effect for the correlated pump and Stokes beams.
Formation mechanism of crystallites in the as-deposited mixed-phase low pressure chemical vapor deposition silicon thin films
Authors: Kim J. H. , Lee J. Y. , Nam K. S.
Published: July 2002

Transmission electron microscopy study on the microstructure of silicon thin films, deposited at temperature ranges of 565 °C∼600 °C and at 200 mTorr by low pressure chemical vapor deposition and annealed at 570 °C, was carried out so that the formation mechanism of crystallites observed in as-deposited mixed-phase silicon thin films could be proposed. Crystallites were observed only at the Si/SiO2 interface in the as-deposited silicon thin film deposited at 570 °C for 28 min. Their size was about 20 nm and they had an irregular shape. Areal density of crystallites in the as-deposited film was about 4 × 1010/cm2, but that in the film deposited as an amorphous phase and annealed at 570 °C for 2 h was about 2×109/cm2. No remarkable crystal growth occurred in the film deposited at 570 °C for 28 min and then annealed at 570 °C for 1 h. Two kinds of crystallites were observed in the film annealed at 570 °C for 3 h. The first, observed only at the Si/SiO2 interface, had an irregular shape, and the second, grown through the entire thickness of the film, had an elongated elliptical shape. On the basis of above results, it was proposed that crystallites observed in as-deposited silicon thin films were formed not because silicon films deposited as an amorphous phase had been annealed during the deposition process, but because silicon films were deposited as a crystalline phase at the initial stage of the deposition process and then deposited as an amorphous phase after the initial stage of the deposition process.
The estimation of the true area of contact between microscopic particles and a flat surface in adhesion contact
Authors: Podczeck F. , Newton J. M. , James M. B.
Published: July 2002

The true area of contact between pharmaceutical powder particles and flat surfaces of various materials in adhesion contact has been calculated. The centrifuge technique has been used to measure the adhesion force between the particles and the surfaces after application of a defined press-on force, which caused plastic deformation of the surface asperities. It was found that in most cases the true area of contact is less than 15% of the apparent area of contact, and for irregular particles the true area of contact is less than 10% of the apparent area of contact. Principal Component Analysis indicated that there is a strong proportionality between the work of adhesion, the indentation hardness and the surface roughness on one side, and the reduced Young’s modulus at the contact points between the surfaces and the adhesion force measured on the other side. A model equation could be proposed that allows an approximate prediction of the adhesion force from the four physical properties of the materials in contact.
Isotropic soft magnetic properties of CoFeAlCu films with (111) orientation
Authors: Cai Jian-Wang , Kitakami Osamu , Shimada Yutaka
Published: July 2002

The dynamic behavior of the magnetization for (111)-oriented films with cubic crystalline structures has been studied theoretically, and the permeability for such textured films has been confirmed to be isotropic. Meanwhile, Co-rich CoFeAlCu films with high saturation magnetization (4πMs=15.8 kG) and low magnetostriction (λs=1.3×10−6), prepared by the dc sputtering method, are found to exhibit perfect fcc (111) orientation with grain size of about 400 Å. A fairly good isotropic magnetic softness has been attained for CoFeAlCu films with Zr underlayers even in the as-sputtered state with Hc of about 1.5 Oe in every measuring direction. After annealing in a rotating magnetic field at 380 °C for 2 h, the magnetic softness is further improved with Hc as low as 0.85 Oe, and the permeability is isotropic in the film plane and as high as 500–600. The perfect (111) orientation of the CoFeAlCu films leads to the isotropic softness, which is consistent with the theoretical prediction.
Electrical characterization of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited silicon dioxide metal–oxide–silicon structures
Authors: Ang S. S. , Shi Y. J. , Brown W. D.
Published: July 2002

The electrical characteristics of rapid thermal nitrided and re-oxidized low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide metal–oxide–silicon (MOS) structures were investigated. Both nitridation temperature and time affect the properties of the MOS structures as revealed by capacitance–voltage characteristics. Nitridation at 1000 °C for 15 s followed by re-oxidation for 60 s at 1000 °C in an oxygen/nitrogen ambient was found to be superior to the same nitridation for 60 s with no re-oxidation. Typical values of fixed charge and interface state densities for devices subjected to nitridation and re-oxidation in a mixture of oxygen and nitrogen were 4×1010 cm−2 and 7×1010 eV−1 cm−2, respectively. Avalanche electron injection using electric fields of 3–3.5 MV/cm produced positive shifts in flatband voltage for devices nitrided at 1000 °C for 15 s followed by re-oxidation, whereas samples nitrided at 1000 °C for 60 s without the re-oxidation yielded negative shifts in flatband voltage. An electron barrier height of 2.4 eV was found for these nitrided samples. These results strongly suggest that device quality MOS dielectrics for high-voltage power MOS field-effect-transistors can be realized by nitridation/re-oxidation of LPCVD oxide.
Optical constants of Pb1−xSnxTe alloys
Authors: Suzuki Norihiro , Adachi Sadao
Published: July 2002

The optical constants, such as the complex dielectric function, complex refractive index, absorption coefficient, and normal-incidence reflectivity, of Pb1−xSnxTe alloys have been determined using spectroscopic ellipsometry in the 1.15–5.5 eV photon-energy range at room temperature. The dielectric-function spectra [ε(E)] and their second-derivative spectra [d2ε(E)/dE2] were analyzed using a simplified model of the interband transitions. The composition dependence of the critical-point parameters and high-frequency dielectric constant has been obtained from these analyses.
Detection and comparison of localized states produced in poly-Si/ultra-thin oxide/silicon, structures by plasma exposure or plasma charging during reactive ion etching
Authors: Fonash Stephen J. , Ozaita Milagros , Awadelkarim Osama O. , Preuninger Fred , Chan Y. D.
Published: July 2002

An approach using two terminal current measurements obtained in a cyclic current–voltage sweeping procedure, is shown to be very useful in detecting damage in poly-Si/ultra-thin SiO2/substrate Si gate structures subjected to dry etching. The current peaks seen in this approach, are shown to be due to displacement currents and to have different features depending on whether the capacitor structures were subjected to plasma charging currents, or plasma photon/particle exposure during etching. A model is presented relating these features to localized states at or near the SiO2/substrate interface.
Structural relaxation and stress reduction in hydrogenated silicon oxide films
Authors: Takahashi Hiroki , Nishiguchi Akihiro , Nagata Hirotoshi , Kataoka Haruki , Fujishima Masahide
Published: July 2002

Ar/H2 sputtering of a SiO2 target can produce thick silicon oxide films with significantly reduced internal stresses compared with those of conventional films prepared by an Ar/O2 sputtering method. As an origin of the stress reduction, we proposed previously the structural relaxation model of the Si–O–Si network via partial Si–H termination. This model is experimentally supported here by the Raman spectroscopy measurements which show a large decrease of planar three- and four-fold ring-type defects in the hydrogenated Si–O–Si network structure.
Electronic structure of dual gate quantum wire
Authors: Yang R. , Ruden P. P.
Published: July 2002

The electronic structure of a novel nanometer scale semiconductor quantum wire structure [S. Y. Chou and Y. Wang, Appl. Phys. Lett. 63, 788 (1993)] has been calculated self-consistently. The structure has two control parameters, the voltage applied to a split gate and the voltage applied to a wire gate. The influences of both the split gate and the narrow wire gate which is placed inside the gap of the split gate, on the electronic structure of the system are examined. We show that varying the voltage on either the split gate or the wire gate changes the induced quantum wire confinement potential profile, the energy level spacing, the channel electron density, and the effective channel width. Results for the ballistic conductance of the device as a function of the two control voltages are extracted from the electronic structure calculations and are found to be in satisfactory agreement with experimental data.
Ionized impurity scattering rate for full band Monte Carlo simulation in heavily doped n-type silicon
Authors: Jung H. K. , Ohtsuka H. , Taniguchi K. , Hamaguchi C.
Published: July 2002

Both the ionized impurity scattering rate and its angular dependence in n-type silicon were theoretically calculated using a full band model, in which a wave-vector- and frequency-dependent dielectric function was used instead of the dielectric constant of 11.7ε0. The number of grid points was determined from the relation between the wave vector and screening length to ensure the validity of the ionized impurity scattering rate. The results show that (1) the calculated overlap integral is small compared with the one used in a nonparabolic band model and (2) the screening effect is strong especially for low energy electrons. The validity of the scattering rate was tested by comparing electron mobilities obtained by a full Monte Carlo simulation with experimental data.
Minority carrier magneto-oscillations in the bipolar quantum well resonant tunneling transistor
Authors: Clark K. P. , Kirk W. P. , Seabaugh A. C. , Kao Y. C.
Published: July 2002

Magneto-oscillations due to a minority carrier two-dimensional electron gas (2DEG) in the base of a bipolar quantum well resonant tunneling transistor at liquid helium temperatures are reported, we believe, for the first time. These are attributed to a high-density 2DEG formed in the 20 nm undoped setback layer between the base and emitter. The 2DEG density has a nonmonotonic dependence on the emitter/base junction bias, increasing to a maximum at flatband conditions, then decreasing at higher bias. Associated lateral electron diffusion dominates recombination such that the current gain can increase 1000 times in a 6 T magnetic field.
Accurate base and collector current modeling of polysilicon emitter bipolar transistors: Quantification of hole surface recombination velocity
Authors: Kizilyalli I. C. , Rambaud M. M. , Ham T. E. , Stevie F. A. , Kahora P. M. , Zaneski G. , Thoma M. J. , Boulin D. M.
Published: July 2002

We present predictive and accurate modeling of base and collector currents in poly-Si emitter bipolar transistors Ref. . Using a standard 0.8 μm bipolar complementary metal–oxide–semiconductor technology process flow Ref. , numerous experiments are performed. The base and emitter doping profiles are varied intentionally over a wide range in a controlled manner, so as to extract a self-consistent set of apparent band-gap narrowing, minority-carrier mobility, intrinsic concentration parameter, and Auger recombination rate that is valid for simultaneously modeling bipolar transistor base and collector currents. The standard nature of the fabrication process technology chosen for this study allows the results to be more generally applicable. The doping concentrations for physical device simulations are taken directly from secondary-ion-mass spectrometry measurements. These profiles are then verified using spreading resistance measurements and capacitance–voltage measurements. It is shown that the measured base and collector currents for all experiments at room temperature can be fit simultaneously using Klaasen’s unified apparent band-gap narrowing and mobility model Ref. . The emitter poly-Si/epi-Si interface (surface) hole recombination velocity is derived as a function of the emitter implant dose (arsenic concentration in the emitter) consistent with the model mentioned above. Sensitivity of the simulation results to model parameters is shown. It is further shown that the emitter implant dose can be used as a bipolar transistor optimization parameter.
Basic processes accompanying solid-phase reactions on the silicon surface
Authors: Italyantsev A. G.
Published: July 2002

A model of the basic processes accompanying solid-phase reactions (SPR) on the Si surface has been developed based on general physical considerations. The model considers these processes in various structures, including M–Si, Si–SiO2, and Si–Si3N4. Analytical expressions have been derived to estimate values of the elastic stresses, steady-state crystal supersaturation by point defects, and SPR activation energy. Data related to the type of point defect generated during SPR have been obtained. A rule to predict the sequence of phase formation in systems with a polyphase constitution diagram is proposed. In particular it is shown that the steady-state crystal supersaturation by self-interstitials during thermal oxidation of Si ranges from 2.4 to 4.4 at 1200 °C. However, the supersaturation by vacancies during the metal silicide formation varies in range from 102 to 107 depending on the reaction type and temperature. The analytical results have been compared with experimental data on the enhanced diffusion of impurities, growth of oxidation stacking faults, and growth parameters of metal silicide layers, and have shown good agreement.
Impact ionization model for full band Monte Carlo simulation in GaAs
Authors: Jung H. K. , Taniguchi K. , Hamaguchi C.
Published: July 2002

The impact ionization rate in GaAs is derived from a first principle’s calculation which includes realistic band structure and a wave-vector- and frequency-dependent dielectric function. The impact ionization rate is highly anisotropic at low electron energy, while it becomes isotropic at higher energy range in which impact ionization events frequently occur. The calculated impact ionization rate is well fitted to a modified Keldysh formula with two sets of power exponents of 7.8 and 5.6, indicating very soft threshold characteristics. Using a full band Monte Carlo simulation which includes the empirical phonon scattering rate based on first principles theory, we derived the impact ionization coefficient. The calculated impact ionization coefficients agree well with available experimental data. Our isotropic model shows better agreement with reported experimental data than a previous anisotropic model, especially in low electric field. The mean energy of secondary generated electrons is found to be expressed as two sets of linear functions of the primary electron energy.
On the theory of barrier-δ-doped quantum well Ge0.3Si0.7/Si/Ge0.3Si0.7 grown on Ge0.3Si0.7 (001)
Authors: Xu Zhi-Zhong
Published: July 2002

The electronic band structures and electronic density distributions of barrier-δ-doped quantum well Ge0.3Si0.7/Si/Ge0.3Si0.7 grown on Ge0.3Si0.7 (001) are self-consistently calculated in effective mass approximation. The dependencies of the electronic charge transfer on the δ-doping impurity concentration, δ-doping position (spacer layer width), well width, and temperature are studied in detail.
The study of nonequilibrium Fe–Ti alloys prepared by high-energy mechanical deformation
Authors: Macrí P. P. , Enzo S. , Cowlam N. , Rose P. , Principi G. , Gupta R.
Published: July 2002

We have studied the nature of the solid-state amorphization induced by mechanical deformation (ball milling) in the case of the Fe2Ti phase [mechanical milling (MM)] and that of the iron and titanium phases mixed in the atomic proportion Fe67Ti33 [mechanical alloying (MA)]. Neutron and x-ray diffraction, combined with Mössbauer spectroscopy at room temperature, of samples mechanically treated for different times indicate that the MM of the Fe2Ti compound leads to a highly fragmented and disordered (micro)crystalline phase. No changes of the Fe2Ti (MgZn2-type) structure are observed in the mechanically and thermally treated Fe2Ti alloys. Conversely, the MA of the pure elements shows a partial amorphization reaction. The chemical short-range order observed in the neutron-diffraction data indicates that a true alloying of the elements occurs. In addition, the thermograms of the MA specimens are different from those of the equivalent MM products. In fact, the phases observed after annealing at 600 °C of the specimens MA 2 and 4 h are a mixture of α-iron and of disordered Fe–Ti intermetallic. A fully amorphous structure is obtained after annealing the samples MA treated for 8 and 16 h.
Theoretical gain of [hhk]-oriented quantum wire lasers
Authors: Yamaguchi A. Atsushi , Usui Akira
Published: July 2002

Optical gain in quantum wire (QWI) lasers are theoretically investigated as functions of wire crystallographic direction taking valence band anisotropy into account. Calculations for GaAs cylindrical QWI with infinite barriers are performed by using the 4×4 Luttinger–Kohn Hamiltonian. Considering the structural optimization of QWI lasers from the viewpoint of crystallographic direction, we find that a [111]-QWI lasers is the most suitable low-threshold laser and that a [1,−1,0]-QWI laser on a (110) substrate is the most suitable polarization-stab-ilized vertical-cavity surface-emitting laser.
The Staebler–Wronski effect and the thermal equilibration of defect and free carrier concentrations
Authors: Dawson R. M. A. , Fortmann C. M.
Published: July 2002

Light-induced changes in the photo-, σph, and dark, σd, conductivities of undoped hydrogenated amorphous silicon (a-Si:H) and amorphous silicon–carbon are investigated as functions of deposition and measurement temperature. Previous work described the temperature dependence of the annealed state σph and σd of a series of intrinsic a-Si:H materials deposited over a range of substrate temperatures, 200 °C<Ts<380 °C, and a thermal equilibrium framework for the high temperature behavior of the relationship between concentrations of dangling bond defects (DBs) and free carriers. The annealed-state results are extended to the light-degraded state where elevated temperatures ensure equilibration of the free carrier and DB concentrations as suggested by the thermal equilibrium framework. Both σd and σph in the light-degraded-equilibrium state decrease compared to the annealed state while the ratio, σd/σph, remains unchanged. From this result, relationships between the Fermi level and the ratio of positively and negatively charged DBs are derived in terms of the thermal equilibrium framework equations.
High quantum efficiency Schottky diode photodetector on the base of ultrathin GaAs-on-Si film
Authors: Joshkin V. A. , Pavlenko V. N. , Kvit A. V. , Oktyabrsky S. R.
Published: July 2002

A new type of a Schottky diode photodetector based on the ultrathin (10 nm) low-temperature grown GaAs-on-Si heterolayer was fabricated and studied. Properties of the heterostructure and electrical characteristics of the photodetector were determined using low-temperature photoluminescence, high-resolution transmission electron microscopy, capacitance–voltage, current–voltage, and spectral responsivity measurements. The high responsivity of the photodetector (corresponding to external quantum efficiency of 0.8–0.9) is explained by effective carriers separation in the GaAs layer and by the carrier multiplication effect at the GaAs/Si interface.
Dependence of structural and magnetic properties on deposition angle in electron-beam evaporated Co/Pt multilayer thin films
Authors: Moon Ki-Seok , Shin Sung-Chul
Published: July 2002

The effects of deposition angle on the structural and magnetic properties of e-beam evaporated Co/Pt multilayer thin films prepared on tilted substrates were examined. It was found that the [111] crystallographic orientations of the multilayer thin films were not aligned with columnar growth orientations and that they remained normal to the substrate planes, irrespective of deposition angle, even though the deposition angle was severely oblique up to 60°. Interestingly enough, the magnetic easy axis orientation was nearly aligned with the substrate normal,J. Appl. Phys. irrespective of deposition angle, which suggested that surface anisotropy was a major reason for the perpendicular anisotropy in Co/Pt multilayer thin films.
Measurement of the crystalline anisotropy in sputtered single-crystal FeTaN thin films
Authors: Varga L. , Doyle W. D.
Published: July 2002

FeTaN single-crystal thin films were grown in order to investigate the dependence of the crystalline anisotropy constant, K1, on the Ta and nitrogen content. Films with 5 and 10 wt % Ta and different nitrogen contents were prepared by dc sputtering on MgO(100) substrates at elevated temperatures. The film/substrate orientation was (100)∥(100) and [100]∥[110]. The values of K1 were determined by measuring the in-plane angular dependence of the ferromagnetic resonance spectra and agreed very well with the values obtained from torque measurements, indicating that the total volume was biaxial cubic material. The hysteresis loops were characteristic of biaxial anisotropy and the anisotropy fields estimated from magnetization curves were consistent with the resonance and torque data. In Fe, K1 was (4.8±0.1)×105 ergs/cc in good agreement with the bulk value. In FeTa, K1 decreased to (4.4±0.1)×105 and (3.5±0.1)×105 ergs/cc for 5 and 10 wt % Ta content, respectively, and further to (2.7±0.1)×105 and (2.1±0.1)×105 ergs/cc in (Fe95Ta5)N depending on the nitrogen content. The nitrogen addition to Fe90Ta10 resulted in the formation of epitaxial (FeTa)4N which is an fcc structure with a negative K1 of (−1.5±0.2)×105 ergs/cc.
Explosive compaction of Magnequench Nd–Fe–B magnetic powders
Authors: Guruswamy S. , McCarter M. K. , Shield J. E. , Panchanathan V.
Published: July 2002

Magnequench NdFeB powders having high and low rare earth contents were explosively compacted to obtain cylindrical magnets. The magnetic properties were found to be isotropic and were superior to conventionally consolidated isotropic magnets. The (BH)max was 14.7 MGOe and the remanence was 8.7 kG for the explosively compacted magnet with lower rare earth content. X-ray diffraction patterns confirm the explosively compacted magnet to be crystalline and the predominant phase to be the 2-14-1 phase. Transmission electron microscopy examination showed a microstructure to consist of 20–25 nm size equiaxed grains consistent with the magnetic measurements.
Sputtered hexagonal Ba-ferrite films for high-density magnetic recording media
Authors: Morisako Akimitsu , Matsumoto Mitsunori , Naoe Masahiko
Published: July 2002

Ba-ferrite (BaM) thin films were prepared by both a facing targets sputtering (FTS) system and dc magnetron sputtering (DCMS) at room temperature. They were successively annealed to crystallize. The films prepared by FTS system were crystallized at 650 °C, while those prepared by DCMS system were crystallized at 700 °C. Saturation magnetization, coercivity, and squareness ratio of the films prepared by FTS are 210 emu/cc, 3.3 kOe, and 0.7 in perpendicular direction, respectively, after the annealing at 650 °C. It was found that oxidized Fe is partially reduced to metallic Fe by high-temperature annealing.
NiBr2⋅3H2O, a lower dimensional antiferromagnet
Authors: DeFotis G. C. , Goodey J. R. , Narducci A. A. , Welch M. H.
Published: July 2002

The trihydrate of nickelous bromide, NiBr2⋅3H2O, is examined magnetically for the first time. A Curie–Weiss fit, χM=C/(T−θ), to the susceptibility between 70 and 300 K yields g=2.31±0.01 (S=1) and θ=6.6±0.5 K. Systematic curvature in χ−1 vs T is evident below 70 K. Despite the positive θ, NiBr2⋅3H2O appears to order antiferromagnetically at Tc=3.82±0.05 K, somewhat below a maximum in χ(T) at T(χmax)=6.17±0.10 K, with χmax=0.0900±0.0005 emu/mol. The ratio Tc/T(χmax)=0.62±0.01 suggests lower magnetic dimensionality. Between 4 and 12 K an acceptable fit with a two-dimensional Heisenberg model can be made, with g=2.58±0.01, J/k=−1.36±0.02 K (assuming Ĥex=−2J∑i≳jŜi⋅Ŝj), and a correction for interlayer exchange z′J′/k=−0.99±0.02 K. Well above Tc the susceptibility is analyzed assuming axial and rhombic crystal field distortions, i.e., D[Ŝ2z−S(S+1)/3] and E[Ŝ2x−Ŝ2y] spin Hamiltonian terms, with exchange included in a mean field approximation: g=2.33±0.02, D/k=57.3±5.0 K, E/k=−24.9±3.0 K, and zJ/k=5.28±0.20 K. The parameters are provisional lacking single-crystal data, but the zero-field splitting is clearly quite large. Magnetization versus field isotherms depart only slightly from linearity for fields above 10 kG, and show a small hysteresis, even for temperatures above Tc. It is likely that ferromagnetically coupled NiBr2NiBr2Ni... chains are present, and that there are antiferromagnetic interactions between chains, such that strongly coupled layers occur, with weaker interactions between layers.
Rotational hysteresis and self-organized criticality in magnetic recording media
Authors: Templeton T. L. , Arrott A. S.
Published: July 2002

Collective magnetic dipoles are written into sections of commercial magnetic recording tapes by application of high fields at angles θset with respect to the tape axis. The media is rotated 2000 times about the tape normal in a lower magnetic field Hm in the plane of the tape. The magnetization along the direction of Hm is measured in steps of Δθ=π/5. Harmonic analysis of the angular dependence of the magnetization is used to discover how the dipole term depends on cycle number n, Hm, the direction of rotation, and θset. The data are analyzed using μd(n)=μd(∞)+[μd(1)−μd(∞)]n−γ. This dipole disappears on rotation for an infinite number of cycles in fields Hm≳Hcrit. For Hm<Hcrit, μd(∞) depends on Hm much as Ms(T) depends on temperature. For Hm close to Hcrit, γ becomes as small as 0.1 for which 1010 cycles would be required to produce 90% of the change.
Electrical conductivity in ferromagnetic perovskite structures
Authors: Zhang Shufeng
Published: July 2002

A spin-polaron Hamiltonian is proposed to study the electrical conductivity in perovskite structures. A crossover from the metallic conduction at low temperatures to the hopping-type conduction at high temperature is calculated within the proposed model Hamiltonian. It is found that most of the experimental observations on resistivity and colossal magnetoresistance can be well explained with the assumption of the existence of spin clusters.
Transport properties and magnetic behavior of La1−xSrxMnO3 single crystals (abstract)
Authors: Anane A. , Dupas C. , Le Dang K. , Renard J. P. , Veillet P. , de Leon Guevarra A. M. , Millot F. , Pinsard L. , Revcolevschi A.
Published: July 2002

Single crystals of La1−xSrxMnO3 with x ranging from 0.06 to 0.42 have been investigated by various techniques: resistivity and magnetoresistance, superconducting quantum interference device magnetometry, and 55Mn nuclear magnetic resonance. In addition, for two Sr concentrations, x=0.13 and 0.25, the I(V) characteristic of the oxide-metal junction has been measured versus temperature. Semiconductor-metal transition occurring just below the Curie temperature Tc was observed for x≥0.175 whereas, for x≤0.15, the crystals exhibits only semiconducting behavior, in agreement in the previous studies. These transport properties are closely connected with the electron transfer mediated by the double exchange interaction between Mn3+ and Mn4+, as revealed by 55Mn spin-echo experiments. A cusp in the magnetoresistance (MR) was observed near Tc for the crystals with x≥0.13 with typical maximum resistivity ratio R(0)/R(10 T)≊10; for the sample with x=0.1, the huge MR persists well below Tc≊140 K, which is probably due to a noncollinear spin configuration. The I(V) characteristic of the oxide-aluminum junction is strongly dependent on temperature and applied magnetic field. In the semiconducting phase, a nonlinear behavior reminiscent to that of a strongly doped dirty semiconductor is observed.
The influence of a transverse-effective-mass difference on the current at an abrupt heterojunction
Authors: Searles S. , Pulfrey D. L.
Published: July 2002

The issue of momentum conservation, and its effect on tunneling, at an abrupt heterojunction interface between semiconductors of different transverse effective mass is considered. A thorough derivation is provided of the equations needed to calculate the electron tunnel current in forward bias. Quantitative results are presented for the current in a variety of effective-mass-difference scenarios, including that of the AlGaAs/GaAs case. The circumstances are identified in which the effective-mass difference causes the current to differ significantly from the value computed when following the usual practice of assuming the effective masses are equal.
Laser-induced ignition of single crystals of the secondary explosive cyclotrimethylene trinitramine
Authors: Ramaswamy A. L. , Field J. E.
Published: July 2002

The interaction of laser radiation from a Nd/glass laser with single crystals of cyclotrimethylene trinitramine (RDX) secondary explosive and RDX slices (cleaved from larger crystals of RDX) has been studied by high-speed framing photography with microsecond interframe times. Decomposition and deflagration were recorded following ignition at localized regions or ‘‘hot spots.’’
Low-temperature Mössbauer study of the mechanically alloyed FexMn0.7−xAl0.3 (0.4≤
x
≤0.5) series
Authors: González J. M. , Giri Anit K. , Pérez Alcázar G. A. , Zamora Ligia E.
Published: July 2002

Results are presented concerning the magnetic properties at low temperatures of mechanically alloyed samples of the FexMn0.7−x Al0.3 (0.4≤x≤0.5) series. According to these results the samples were characterized as having a broad spectrum of relaxation times related to the occurrence of clustering. Also, in the particular case of the x=0.40 sample, we were able to detect a reentrant spin glass freezing transition.
The spin-glass state of Y1−xUxPd3
Authors: Lopez de la Torre M. A. , Fernandez J. Rodriguez , McEwen K. A.
Published: July 2002

We have performed a detailed study of the magnetization of Y0.6U0.4Pd3 (Tf∼10 K), which shows thermal, transport, and magnetic properties typical of a spin-glass system. Strong irreversibility is observed among our zero-field-cooled and field-cooled measurements in fields as large as 30 kOe. Thus, the freezing temperature displays an unusual weak dependence with field. We observe a very slow temporal dependence of the magnetization below the freezing temperature. The nonlinear susceptibility coefficients extracted from our data show an increase by a factor of approximately 20 when approaching the freezing temperature from above, but do not show a true divergence at Tf, and a scaling analysis does not seem to be possible. We compare these results with those expected for classical spin glasses, and propose a possible mechanism for the onset of frustration below x=0.45 in Y1−xUxPd3.
Magnetic circular x-ray dichroism in Co/Pt multilayers (abstract)
Authors: Koide T. , Nakajima N. , Shidara T. , Miyauchi H. , Kawabe H. , Fukutani H. , Fujimori A. , Iio K. , Katayama T. , Suzuki Y.
Published: July 2002

A Co/Pt multilayer is one of the most attractive candidates for next-generation high-density magneto-optical recording media. With a decreasing Co layer thickness, the direction of the easy axis of magnetization changes from in-plane to out-of-plane. We have measured core-level MCD of Co/Pt multilayers. Six Co/Pt multilayer samples were prepared which had Co layer thicknesses from 3 to 14 Å. The MCD experiments were made using circularly polarized undulator radiation.

The spectra were taken separately for the energy regions around the Co M2,3 (and Pt O3) and Pt N6,7 (and Pt O2) edges. The dichroic signals in reflectivity were recorded for two opposite directions of an external magnetic field of 2 T. We have also measured the reflectivity spectra down to 4 eV and have made Kramers–Kronig analyses to obtain the dielectric tensor. The dielectric tensor element which represents absorption MCD shows a dramatic change at the Co M2,3 edges. The MCD spectra of thinner Co-layer samples are more asymmetric than those of thicker ones. This shows that the orbital magnetic moment of Co is enhanced as the Co layer thickness decreases. The MCD spectra become sharper and narrower with a decreasing Co layer thickness. This feature strongly reflects a band narrowing of the Co 3d state at or around the Co/Pt interfaces. The MCD spectra at the Pt N6,7 edges show little dependence on the Co layer thickness. This can be explained by assuming that Pt atoms only at the interfaces are responsible for the MCD signals, since the surface density of Pt atoms is equal for all the samples. Combining the result at the Co M2,3 edges with that at the Pt N6,7 edges leads to the conclusion that perpendicular magnetic anisotropy mainly depends on the electronic structure of Co at Co/Pt interfaces and that Pt atoms at the interfaces play a partial role in magnetic anisotropy.
NMR study of the local inhomogeneities in the soft magnetic alloy Co74.26Fe4.74Si2.1B18.9 (abstract)
Authors: Iannarella L. , Kim C. , O’Handley R. C. , Guimarães A. P.
Published: July 2002

Results of a pulsed NMR study of the soft ferromagnetic amorphous alloy Co74.26Fe4.74Si2.1B18.9 in the as-cast and the heat treated (at 410 °C for 12 minutes) states re reported. The measurements were performed at 4.2 K. Very intense resonances lines are observed in the frequency region 10–110 MHz (range of the present study), for both as-cast and heat treated samples. The NMR signal intensity depends on the rf power level; this suggests the existence of several magnetic regions with different local anisotropies. We identify NMR lines in two frequency ranges: (a) 10–50 MHz, which probably come from 57Fe, 11B, and 29Si nuclei in Fe–Si-like regions and 57Fe in Co(Fe) solid solutions; and (b) for frequencies above 50 MHz, lines from 59Co (and probably 11B) in Co-rich crystalline-like environments with short-range order as in Co2B, in the range 70–110 MHz. In the higher frequency region, the NMR spectra suggest that the environments are similar to Co3B and to Co(B) solid solutions. For the heat treated sample, lines above 95 MHz disappear for lower rf power levels; also, this sample shows lines around 75 MHz narrower than those for the amorphous alloy. These results give evidence of the concentration inhomogeneity of the samples, both in the as-cast and heat-treated forms.
Synthesis and magnetic properties of rare earth–iron–chromium phases and their nitrides
Authors: Kalogirou O. , Psycharis V. , Gjoka M. , Niarchos D. , Fuerst C. D.
Published: July 2002

Synthesis, structural, and magnetic properties of R3(Fe,Cr)29 intermetallic compounds (R=Ce,Nd) and their nitrides are reported. The Ce3(Fe,Cr)29 sample was single phase while the R=Nd ingot contained significant contamination by secondary phases. X-ray analysis reveals the monoclinic Nd3(Fe,Ti)29-type structure with space group A2/m. The unit cell dimensions for the parent R=Ce compound are a=10.513(2) Å, b=8.478(1) Å, c=9.657(1) Å, β=96.75(1)°, and V=854.70 Å3. In the case of Ce a relative unit cell expansion of 6.5% is observed upon nitrogenation. The Curie temperature is 326 K for Ce and 432 K for Nd and becomes 612 and 633 K for Ce–nitride and Nd–nitride, respectively. The room temperature magnetization at 5 T is 58.2 A m2/kg for Ce and 104.1 A m2/kg for Nd and increases after nitrogenation to 109.8 and 127.2 A m2/kg for Ce and Nd, respectively. The average hyperfine field of the R=Ce compound at 85 K is 19.2 T. X-ray diffraction measurements on a magnetically aligned powder of Ce3(Fe,Cr)29 indicate that the magnetocrystalline anisotropy of the iron sublattice is most likely an in-plane type. Mössbauer spectrum analysis provided evidence that the Cr enters the dumbbell sites.
Capillary instabilities in solid thin films: Lines
Authors: McCallum Matthew S. , Voorhees Peter W. , Miksis Michael J. , Davis Stephen H. , Wong Harris
Published: July 2002

The linear morphological instability of a line of film on a substrate has been examined for contact angles between 0 and π. The base state of the line is an infinitely long cylinder with cross-sectional shape a segment of a circle. We assume that mass flows by diffusion along the film surface and that local equilibrium holds. We find that for non-zero contact angles there is a finite range of perturbation wavenumbers in the axial direction which correspond to instability and will potentially lead to agglomeration of the line of film. All unstable perturbations are of the varicose (sausage) type. The presence of the substrate is stabilizing; the range of unstable wavelengths is always less than that of a freely-suspended circular cylinder with the same volume and decreases to zero width at zero contact angle. The maximum growth rate of the instability varies strongly with the contact angle and approaches zero as the contact angle approaches zero. Our results agree qualitatively with the experimentally observed wavelength and growth rates of the instability.
Growth and electrical characterization of Si delta-doped GaInP by low pressure metalorganic chemical vapor deposition
Authors: Wang Chien-Jen , Feng Ming-Shiann , Chan Shih-Hsiung , Chang Chun-Yen , Wu Janne-Hua , Sze Simon Min
Published: July 2002

The growth and electrical characterization of Si delta-doped GaInP grown by low-pressure metalorganic chemical vapor deposition are reported in this article. It was found that the sheet carrier density saturated as a function of doping time or flow rate. Because of the limitations of Hall-effect measurements, the saturation was explained as the result of electron population in satellite L valley. The mobility enhancement was observed for the delta-doped structure with an enhancement factor of 2–3. A sharp capacitance–voltage profile with a full width at half-maximum of 30 Å was obtained. Depletion-mode Si delta-doped GaInP field-effect transistors with a gate length of 2 μm and gate width of 50 μm were fabricated and showed good device pinch-off characteristics. The extrinsic maximum transconductance of 92 mS/mm was obtained and a broad plateau transconductance profile was observed to confirm the electron confinement in the V-shape potential well of a delta-doped GaInP layer.
Metamagnetic transition in PrCo13−xSix
Authors: Tang Weihua , Liang Jingkui , Rao Guanghui , Yang Fuming
Published: July 2002

Alloys of PrCo13−xSix (1.5≤x≤4.0) have been prepared by arc melting and subsequent annealing. X-ray powder diffraction proved that the alloys crystallized in the cubic NaZn13-type structure for x=1.5, and in the tetragonal NaZn13-derivative one for x≥2.0. Their Curie temperatures are almost independent of the Si content. Their magnetization curves exhibit a binary-step characteristic. The ac susceptibility curve indicates that there exists a magnetic transition below room temperature. The anomalous binary-step magnetization curves and the ac susceptibility curves versus temperature suggest a metamagnetic transition.
Cr(CoPtCr,CoPtx) layered film studies for hard bias applications
Authors: Tsoukatos A. , Gupta S. , Marx D.
Published: July 2002

Cr\(CoPtCr,CoPt) films were deposited on oxidized Si 〈100〉 substrates via dc magnetron sputtering. Process parameters, such as deposition rates, number of bilayers, and bias voltage, were varied to achieve the hard magnetic properties without thermal processing of the films. Coercivities in the range of 2000 Oe, with corresponding squareness of about 0.8–0.9, and remanent magnetization in the range (3–3.6) memu/cm3, were achieved by identification of the optimum conditions.
Analytic investigation of the glow discharge anode region in elevated-pressure electronegative gases
Authors: Islamov R. Sh.
Published: July 2002

An analytic model for a three-component electronegative plasma has been developed within the framework of a diffusion–drift approximation. Anode fall voltage and anode sheath thickness are found for elevated-pressure glow discharge. The predicted voltage–current dependencies are compared to available experimental and numerical results for dc glow discharges in air at pressures of 40–100 Torr. Electronegative ions increase the anode fall voltage at high current densities, including the values for anode spots, and reduce the anode fall voltage at low current densities, but pass through a minimum at a critical value of their concentration.
Absorption of a single quantum well
Authors: Shrinivasan J. , Narasimhan K. L. , Arora B. M.
Published: July 2002

In this communication we show that we can distinguish the absorption of a single quantum well from that of the substrate in a quantum well structure by using photothermal deflection spectroscopy (PDS). This technique uses the phase of the PDS signal, in addition to the amplitude. The method is applied to single and multiple quantum wells grown on InP substrates.
A self-consistent model for quantum well infrared photodetectors
Authors: Thibaudeau L. , Bois P. , Duboz J. Y.
Published: July 2002

We present the results of a new model for the simulation of quantum well infrared photodetectors (QWIPs) both in dark conditions and under illumination. This model takes into account the elementary mechanisms involved in the detection process (injection at the contacts, balance between capture and emission in each well) in a self-consistent way. The main feature emerging from the model is the redistribution of the electric field along the structure in order to maintain current conservation. The calculated dark current, electrical noise, responsivity, and detectivity of different QWIP structures are compared with experimental measurements and the agreement is found to be fairly good. This model may be considered as a step toward more powerful simulation tools for QWIPs.
Trends in the emitter-base bias dependence of the average base transit time through abrupt heterojunction bipolar transistors
Authors: Kumar T. , Cahay M. , Roenker K.
Published: July 2002

The average base transit time is computed using a current impulse response technique for three typical abrupt Npn heterojunction bipolar transistors as a function of the emitter-base bias, VBE. This technique is based on a hybrid model of carrier transport incorporating a quantum-mechanical analysis of carrier injection at the emitter-base junction and a Monte Carlo analysis of base transport. For typical AlGaAs/GaAs and InP/InGaAs structures, the base transit time first increases with VBE, reaches a maximum, and then decreases towards a value close to the one predicted using a semi-Maxwellian injection of carriers into the base at an energy equal to the emitter-base conduction band spike. For a typical InAlAs/InGaAs structure, the average base transit time is found to decrease with an increase in VBE. For all structures, we show that there is a correlation between the bias dependence of the average base transit time and the bias dependence of the average number of collisions per carrier (calculated for carriers transmitted across the base).