bluuebunny/crossref_metadata_2025 huggingface dataset:
Line tension of extended double kinks in thin films
Authors: Twigg M. E.
Published: July 2002

We derive an expression for the dislocation line tension in thin-film structures for double-kink (dislocation dipole) extension of a threading dislocation. From these calculations, we conclude, that for a double kink that is a distance of more than three times the vertical dipole separation from the free surface, the effect of the free surface on the double-kink line tension is insignificant. We consider the specific case of a double-kink bounding a 60-nm-thick Si0.7Ge0.3 strained layer grown on a silicon substrate and buried under a silicon cap. For this specific configuration, line tension is seen to increase with cap thickness (which is equivalent to distance of the double kink from the surface) only up to a cap thickness of 100 nm.
Reactively sputtered TiN as a diffusion barrier between Cu and Si
Authors: Wang Shi-Qing , Raaijmakers Ivo , Burrow Brad J. , Suthar Sailesh , Redkar Shailesh , Kim Ki-Bum
Published: July 2002

The properties of 100-nm-thick Ti55N45 and Ti45N55 films as diffusion barriers between silicon substrates and thin Cu films were studied by sheet resistance measurements, Rutherford backscattering spectrometry, Auger electron spectroscopy, secondary-ion mass spectrometry, transmission electron microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry, and diode leakage current measurements. For unpatterned Si/titanium nitride/Cu samples, all the layers were intact and there was no indication of interdiffusion by conventional depth profiling techniques up to 700 °C for Ti55N45 and 900 °C for Ti45N55 after 30 s rapid thermal anneal in N2, respectively. Leakage current measurements did not show deterioration of diode junction (with junction depth of 0.25 and 0.30 μm) up to 650 °C for Ti55N45 and 800 °C for Ti45N55. The improvement in failure temperature of the N-rich Ti45N55 diffusion barrier is a result of the lower defect density and a more stable feature furnished by nitrogen stuffed at the defects.
Oxygen enhancement induced by ionic implantation in scandium diphthalocyanine thin films
Authors: Robinet S. , Gauneau M. , Salvi M. , Clarisse C. , Chaplain R.
Published: July 2002

Secondary ion mass spectrometry correlated with ionic implantations has allowed us to determine oxygen bulk concentration in scandium diphthalocyanine thin films. This concentration, around 2×1020 atom cm−3, increases by a factor 20–25 in implanted areas. This oxygen enhancement is observed for oxygen implantation but as well for xenon, caesium, or iodine implantation, and therefore is not dependent on the nature of the implanted atoms. The oxygen concentration saturates in the damaged region but its quantity depends on the energy loss and on the fluence; the larger the damaged layer, the larger the region where the enhancment takes place. The phenomenon will be tentatively related to the creation of free radicals induced by bond breaking occurring during the implantation process.But, other explanations including more severe degradations of the molecular material cannot be dismissed.
Effect of misfit strain on physical properties of InGaP grown by metalorganic molecular-beam epitaxy
Authors: Ozasa Kazunari , Yuri Masaaki , Tanaka Shigehisa , Matsunami Hiroyuki
Published: July 2002

The effects of misfit strain on physical properties (lattice parameters, photoluminescence, and electron mobility) are discussed for In1−xGaxP epilayers with a constant thickness of around 0.75 μm grown by metalorganic molecular-beam epitaxy on GaAs(001) substrates. The elastic accommodation of misfit strain is observed in the analysis of lattice parameters and energy-band-gap shift. Tensile strain is relaxed more easily than the compressive strain. Theoretical predictions of critical thickness for elastic-strain accommodation and of energy-band-gap shift agree well with experimental results. The energy-band-gap shift and electron mobility are relatively insensitive to dislocations generated by relaxation of the misfit strain.
Modeling of electron-beam-controlled semiconductor switches
Authors: Brinkmann R. P.
Published: July 2002

The subject of this paper is the mathematical modeling of a recently proposed class of electron-beam-controlled high-power semiconductor switches that are able to overcome the space-charge limitation of conventional electron bombarded semiconductor devices by utilizing the secondary ionization effects of cathodoluminiscence and bremsstrahlung. Current densities of several kA/cm2 at forward voltages some 10 V can be controlled with an electron beam of 100 keV and 1 A/cm2; holdoff voltages of more than 100 kV/cm and dark currents as small as 10 μA/cm2 are possible. The concept has several possible applications: Its fast and repetitive closing and opening under load makes it suitable for inductive energy storage applications; its linear characteristics suggests a use as a high-power modulation device.
Comparison of coolants for achieving short-wavelength recombination lasing
Authors: Thornhill J. W. , Apruzese J. P. , Giuliani J. L. , Roelant D.
Published: July 2002

A promising approach for reducing the operating wavelength of x-ray lasers is the generation of population inversions via recombination in rapidly cooling plasmas. We have examined the relative merits of radiative and hydrodynamic cooling in a freely expanding plasma. The specific lasing scheme studied is recombination in heliumlike silicon, but the general results apply to other elements and ionization stages which are capable of generating gain in the soft x-ray region. We find that the higher radiative cooling rates obtained by mixing the silicon lasant with a high atomic number coolant are more than offset by the reduced expansion cooling brought on by the higher mass density associated with the high-Z elements. Specific results are presented for hydrogen, carbon, aluminum, and selenium coolants mixed with silicon lasant. The present results do not apply to magnetically confined lasant plasmas where high-Z radiators might be valuable.
The relation of the performance characteristics of pseudomorphic In0.53+xGa0.47−x As/In0.52Al0.48As (0≤x≤0.32) modulation-doped field-effect transistors to molecular-beam epitaxial growth modes
Authors: Pamulapati J. , Lai R. , Ng G. I. , Chen Y. C. , Berger P. R. , Bhattacharya P. K. , Singh J. , Pavlidis D.
Published: July 2002

We have examined the growth and device characteristics of In0.53+x Ga0.47−x As/ In0.52 Al0.48 As (0≤x≤0.27) pseudomorphic modulation-doped field-effect transistors on InP substrates. In situ reflection high energy electron diffraction oscillation studies were carried out to study the growth of pseudomorphic InGaAs on GaAs and InP substrates. The data from these measurements and a theoretical formalism based on energy minimization suggest that in the pseudomorphic growth regime increased strain causes growth modes to change from two-dimensional layer-by-layer to a three-dimensional island mode. The resulting interface roughness is used as a parameter to explain the observed trends in channel mobility and device performance. It is also shown that altered growth techniques, such as migration enhanced epitaxy, in which the surface reconstruction may be changed, can restore the layer-by-layer growth mode for large amounts of strain in the pseudomorphic layer.
Analytic theory of current drive by an exact solution of kinetic equation
Authors: Khan T. P.
Published: July 2002

The phenomenon of current drive under the action of radio-frequency traveling waves into a tokamak is analytically studied by solving the two-dimensional Fokker-Planck equation first treated by Fisch. The runaway rate, the number of runaway electrons, the electron current density, and power density are obtained analytically and are compared with the results of one-dimensional analytic treatment.
First design and characterization of HgZnTe optical waveguides
Authors: Azema A. , Gaucherel P. , Roustan J. C. , Granger R. , Triboulet R.
Published: July 2002

Infrared waveguides have been made by isothermal evaporation diffusion of HgTe on a ZnTe substrate and characterized at 10.6 μm by m-lines analysis. Refractive index profiles deduced from this analysis are correlated to the composition ones measured with a microprobe. As a result, we obtain the refractive index of the alloy as a function of the zinc concentration ranging from 0.2 to 1. Direct measurement of the substrate refractive index gives a value 2.60 to 2.65, results in slight disagreement with the previous data.
Independence of peak current from emitter spacer layer width in AlGaAs/GaAs resonant tunneling diodes
Authors: Koenig E. T. , Huang C. I. , Jogai B.
Published: July 2002

The peak current for the negative differential resistance region of AlGaAs/GaAs resonant tunneling diodes is shown to behave independently of the width of a low-doped emitter spacer layer if an isolated accumulation region forms upstream from the first AlGaAs barrier. The effect of the voltage drop across the emitter spacer layer is shown to be minor. These results appear to confirm that electron transport through these resonant tunneling diodes is a two-step process. In addition, a radial dependency of device performance attributed to molecular beam epitaxy growth conditions is noted.
Raman analysis of anodic films on mercury cadmium telluride
Authors: Hill I. R. , Chang W. H. , Lau W. M
Published: July 2002

Raman spectroscopy has been used to characterize anodic films grown on n-Hg0.8Cd0.2Te from alkaline media. The spectral results, when compared with those from several reference chemicals, provide unambiguous identification of the anodic film as a 1:1 mixture of amorphous cadmium and mercury tellurites. Since the anodic film is transparent to visible light, Raman spectroscopy was also used to probe nondestructively the substrate surface under the film. The results indicate that the substrate surface was depleted in cadmium.
High-γ inverse Čerenkov acceleration in resonant media
Authors: Steinhauer L. C. , Kimura W. D.
Published: July 2002

Inverse Čerenkov acceleration (ICA) is a novel approach to electron acceleration involving the interaction of laser light with a polarizable gaseous medium. This technique may achieve very high acceleration gradients and tends to be best suited for the role as an energy booster for electrons of GeV energy or higher. A generic optimization study of ICA is performed to identify the desired properties of the ideal gaseous medium, in particular a medium in which the laser light frequency is near a resonance of the medium. Several factors that can limit the effectiveness of the interaction are taken into account. It appears that acceleration gradients exceeding 1 GeV/m are possible at low gas pressures that minimize problems with electron-beam emittance growth.
Temperature-dependent ultraviolet absorption spectra of group IIIb and Vb compounds used in photo-assisted chemical vapor deposition
Authors: Okabe Hideo , Emadi-Babaki M. K. , McCrary V. R.
Published: July 2002

The ultraviolet (UV) absorption cross sections from 185 to 320 nm have been measured for four group IIIb and two Vb alkyl compounds. These are trimethylaluminum (TMAl), trimethylgallium (TMGa), triethylgallium (TEGa), ethyldimethylindium (EDMIn), trimethylarsenic (TMAs), and tertiarybutylphosphine (TBP). In the case of ethyldimethylindium (EDMIn) and tertiarybutylphosphine (TBP), the UV absorption spectra have not been previously recorded. The UV absorption cross sections were measured at 193, 222, and 248 nm; wavelengths that are readily achieved with commercially available excimer lasers. The UV spectra of the group IIIb compounds show a weak long-wavelength absorption followed by a strong absorption, while those of the group Vb compounds show a sharp cutoff in the long-wavelength end of a strong absorption. TMGa, TEGa, and TMAs exhibit a decreasing absorption with increasing temperature. However, with an increase of temperature, the absorption of TMAl increases rapidly and the absorption extends towards longer wavelengths, reflecting dissociation of the dimer into monomer at higher temperatures. A simple molecular orbital model by Walsh is used to interpret the UV spectra of these metal alkyl compounds.
BF2 implanted polycrystalline silicon gates with and without CoSi2: Microstructure and work functions
Authors: Lindenberger S. , Georgiou G. E. , Hillenius S. J. , Luftman H. , Baiocchi F. A. , Sheng T. T. , Field R. L.
Published: July 2002

The microstructure and metal-silicon work function was evaluated for polycrystalline Si (poly-Si) films (∼3500 Å) implanted with BF2, with and without a CoSi2 superlayer. The poly-Si implant doses were 2, 4, and 6×1015 cm−2, activated at 800–950 °C, for various times. The work function is observed to be dependent upon the BF2 dose, the anneal time, the anneal temperature, and independent of the presence of a thin CoSi2 superlayer subsequently sintered on the poly-Si. The work function is not affected by additional implants into a CoSi2 superlayer. The measured work function for this material is shifted to more positive values by penetration of boron from the gate, into the oxide and possibly into the substrate during a ≳900 °C activation cycle. The major correlation of CoSi2/poly-Si interface roughness is with poly-Si grain size. The interface becomes smoother as the poly-Si grain size becomes smaller. Similarly, the maximum extent of CoSi2 asperities is less for Co sintered on BF2 implanted poly-Si when the poly-Si is activated at 900 °C (smaller grain size) rather than at 950 °C. Within statistical limitations of cross-section transmission electron microscopy and sensitivity limitations of Rutherford backscatterings, CoSi2 asperities do not extend close enough to the (4000-Å-thick) poly-Si/SiO2 interface to affect complimentary metal-oxide-semiconductor device characteristics.
Mössbauer study on structural changes in sputtered Fe-Al-Si thin films
Authors: Miyazaki Masahiro , Ichikawa Masashi , Komatsu Takayuki , Matusita Kazumasa , Nakajima Kensuke
Published: July 2002

The sendust alloy films of Fe74.3Al9.8Si15.9 with a thickness of 1 μm were deposited on crystallized-glass substrates by rf planar magnetron sputtering, and the microscopic structural changes in the films due to the annealing were investigated with a conversion electron Mössbauer spectroscopy (CEMS). The films annealed at 500 °C exhibited excellent soft magnetic properties as for recording-head materials. The CEMS studies revealed that the disordered structure of α-type in as-sputtered films transformed into the ordered structure of DO3-type at the temperature of 500 °C. The structure of the films annealed at 400 °C deviated largely from the DO3 ordered structure, and the DO3 ordered structure was gradually destroyed by annealing above 600 °C. The magnetic and electrical properties in the films were well explained with the microscopic structural changes clarified through the Mössbauer spectra.
Oxidation of Si and TiSi2 thin films in rf oxygen plasma
Authors: Pérez-Casero R. , Perrière J. , Enard J. P. , Straboni A. , Vuillermoz B. , Climent A. , Martínez-Duart J. M.
Published: July 2002

We have investigated the oxidation of silicon and titanium disilicide in a rf oxygen plasma at floating potential in the 400–900 °C temperature range. Rutherford backscattering spectrometry and nuclear reaction analysis have been used to determine the kinetics of oxide growth and the elemental depth distribution in the oxide layers. For both oxides formed on Si and TiSi2 we have evidenced two different regimes in the growth, depending upon the temperature. The transition temperature between these two regimes is about 600 °C. In the case of TiSi2 oxidation, in addition to a different mechanism of growth, the nature of the oxide depends on temperature: almost pure SiO2 for T≳600 °C and a TiO2-SiO2 mixture for T<600 °C. The low temperature regime gives rise to an unexpected high oxide growth rate with respect to the behavior at high temperatures.
Far-field pattern of a coherently combined beam from large-scale laser diode arrays
Authors: Kwon Jin H. , Lee Ja H. , Williams Michael D.
Published: July 2002

The far-field pattern of a large-scale amplifier array (LSAA) consisting of a large number (2000) of diode laser amplifiers is numerically simulated, and the power collection efficiencies are determined. Random distributions of phase mismatches, misorientations, and element failures in the LSAA system are considered. Phase mismatches and misorientations of the element amplifiers are found to be the most critical parameters of those affecting the power-collection efficiency. Errors of 0.2λ and 25% for phase and diffraction angle, respectively, cause a 10% reduction in power-collection efficiency. The results are used to evaluate the concept of space-laser power transmission. It was found that an overall transmission efficiency of 80% could be realized with a 5-m-diam. receiver at a distance of 10 000 km when an LSAA transmitter 6 m in diam. is aimed with state-of-the-art pointing accuracy.
Electron-fluid model for dc size effect
Authors: Jaggi R.
Published: July 2002

The ensemble of conduction electrons is treated as a fluid whose collective motion is described by the Navier–Stokes and Maxwell equations. Under simplifying conditions, Ohm’s law is generalized for the stationary case. The profile of the current density is shown. Geometry-dependent effective conductivities are derived for circular cylinders and plates with rectangular and square cross sections, in good agreement with size effect experiments. A compilation of the fitting parameters, bulk resistivity, and adherence length used for Cu, Ga, and CoSi2 is presented in the temperature range 300→0 K for dimensions between 1 nm and 2 mm.
An analysis of the two electron satellite spectrum of GaAs in high magnetic fields
Authors: Driessen F. A. J. M. , Lochs H. G. M. , Olsthoorn S. M. , Giling L. J.
Published: July 2002

We report the observation of 2p0,−1, 2s0, 3d−1,−2, 3p−1, and 4f−3 structures in the ‘‘two electron’’ satellite photoluminescence of excitons bound to the (hydrogenic) shallow donors Ge and Se/Sn in high purity metalorganic vapor-phase epitaxy grown GaAs. The attribution is based upon selective excitation of the different principal donor bound exciton (D0,X) lines at magnetic fields of 7 T at T=1.5 K, combined with a careful analysis of the behavior of the hydrogen atom in a magnetic field. The results are interpreted in terms of high magnetic field quantum numbers and in terms of shapes of hydrogen wavefunctions in strong magnetic fields. One of the samples used in this work is so pure that for the first time donors have been identified from the relatively broad n=2 two electron satellite involving the (D0,X) ground state at zero field.
A numerical data analysis of thickness modes in arbitrary coupling piezoelectric plates
Authors: Strashilov V. L. , Boyanov B. I.
Published: July 2002

A numerical method for the analysis of thickness modes in piezoelectric plates with full account of the electromechanical coupling is presented. Numerical data for the main electroacoustical characteristics of some highly efficient piezoelectric crystals are given. Some inconsistencies with the available theoretical models are discussed.
Kinetics of laser-photochemical deposition by gas-phase dissociation
Authors: Ward Timothy L. , Kodas Toivo T. , Jackson Robert L.
Published: July 2002

The effects of reaction and transport kinetics on deposition resulting from laser-induced gas-phase photodissociation were investigated using numerical and analytical models. Deposition rates and deposit profiles for a laser beam focused onto a substrate in a chamber were determined assuming production of metal atoms in the gas phase by a single-photon dissociation mechanism and free-molecular and diffusive transport to chamber surfaces. The predictions of the model computations were compared to experimental and theoretical results from the literature. The effect of total pressure on deposition rates and profiles depends strongly on the sticking coefficient. With a sticking coefficient of unity, deposition rates and profiles do not depend strongly on the total pressure or transport regime. However, when the sticking coefficient is 0.01, the deposit profile flattens dramatically at pressures below about 1 atm. The conditions and consequences of gas-phase reactant depletion due to diffusional limitations were also demonstrated. The extent of gas-phase reactant depletion can be predicted by a single dimensionless group; however, transport of the reaction product must also be considered to predict deposition rates. At high laser power or total pressure, reactant depletion leads to reduced deposition rates and flatter deposit profiles, and severe depletion can produce volcano-shaped deposits.
Uniaxial stress effects on the AlAs/GaAs double-barrier heterostructures
Authors: Lu S. S. , Meng C. C. , Williamson F. , Nathan M. I.
Published: July 2002

We have measured the current-voltage characteristics of GaAs-AlAs-GaAs-AlAs-GaAs double-barrier heterostructures grown by molecular beam epitaxy on (100) oriented substrates under longitudinal uniaxial stress along 〈100〉 (parallel to current) direction and transverse uniaxial stress along 〈011〉 (perpendicular to current) direction at 77 K. For longitudinal stress measurement, the peak-to-valley current ratio due to Γ conduction electrons and the peak voltage (the voltage where the current peaks) decrease essentially with longitudinal stress and the negative differential resistance (NDR) disappears at a stress that depends on the dopings and dimensions of the heterostructures. However, it is surprisingly recovered at very high stress and the peak voltage reappears at a lower voltage, which is quite in contrast with the previous report for hydrostatic pressure studies. The observed shifts of the peak voltage, the decrease of the peak current, and hence the disappearance of the NDR are consistent with pressure-induced increase of the effective mass. The recovery of Γ-NDR is explained by the more rapid reduction of Xl (momentum conserving longitudinal X valleys) nonresonant current due to the increase of reflections at GaAs/AlAs interfaces under very high uniaxial stress, where there are potential wells rather than barriers for Xl current. A distinct NDR near- zero bias (∼40 mV) appears when the externally applied uniaxial stress is high enough. This has been attributed by Mendez and Chang [Surf. Sci. 229, 173 (1990)] to the resonant tunneling between two-dimensional electron gases. Our experiment shows that this tunneling is via momentum conserving longitudinal X-valleys (Xl). For transverse stress measurement, there is no evidence of this feature up to 7 kbar.
Electromigration failure
Authors: Lloyd J. R.
Published: July 2002

Electromigration failure is modeled as a nucleation and growth process, where void nucleation is due to the generation of a nonequilibrium vacancy concentration from an electromigration induced mass flux divergence. Following nucleation, voids grow until equaling the width of the conductor, causing an open circuit. It is seen that if the failure process is dominated by the nucleation stage, a j−2 dependence on lifetime is observed. In this model, electromigration lifetimes are predicted without resort to adjustable parameters with reasonable accuracy.
Electromagnetic perturbation on acoustic shear waves generated by magnetostriction
Authors: Lanotte L. , Luponio C. , Porreca F.
Published: July 2002

The problem of coupling between mechanical shear waves and electromagnetic waves propagating in magnetostrictive materials has been stressed. The system of the acoustic field equations and the Maxwell ones has been combined with the piezomagnetic constitutive relations to obtain z-propagating x-polarized transversal standing wave characterized both by particle displacement, Ux(z,t), and magnetic field, Hx(z,t). Attention has been paid on the separation of the purely acoustic wave from the hybrid one to the scope to evaluate their difference in velocity D. Generally, the latter is very small (1/105) but it cannot be neglected in new technological materials exhibiting low magnetoelastic coupling coefficients. The difference D has been theoretically obtained for magnetoelastic waves generated in transversally isotropic samples versus the permeability and the magnetoelastic coupling coefficient. Moreover, it has been possible to check the electromagnetic disturbance behavior as a function of the bias field by using our experimental results.
Infrared study of oxygen precipitates in Czochralski grown silicon
Authors: Borghesi A. , Geddo M. , Pivac B.
Published: July 2002

Oxygen precipitation in the bulk of silicon wafers was investigated by using micro-Fourier transform infrared spectroscopy. It was found that even at 1100 °C annealing (in single step) SiO2 precipitates are formed in platelet shape, in the bulk, giving rise to characteristic absorption peak in the infrared spectrum at 1230 cm−1. Complete mapping of wafer cross section demonstrated that these precipitates are not distributed homogeneously but are agglomerated in irregularly shaped clusters and are easily detectable up to distance of about 100 μm from the back surface and from the epi-substrate interface.
A model current spectral density for hot-carrier noise in semiconductors
Authors: Kuhn Tilmann , Reggiani Lino , Varani Luca
Published: July 2002

Analytical expressions are presented for the spectral density of current fluctuations derived from a rigorous theoretical analysis which can be applied at any electric-field strength. The main peculiarities of these spectra are discussed from an analytical point of view and in terms of the physical processes involved at increasing electric fields. Then, two different expressions are provided for an analytical fitting of spectra based on physical parameters related to a rigorous eigenvalue expansion of the correlation functions. These model spectra are in good agreement with the experiments and the results of Monte Carlo simulations for the case of p-type Si at 77 K.
Application of bipolar transistor structures to optical waveguide modulators and switches
Authors: Okada Yoshitaka , Tada Kunio
Published: July 2002

Basic experimental results obtained with a GaAs/AlGaAs double-heterojunction bipolar transistor (DHBT) waveguide structure carrier-injected optical intensity modulator/switch are fully described. Typical common-emitter dc current gain obtained with a 0.25-μm-thick base/waveguide was ∼40, and the switching times have been determined as 1.5 ns. Optical on/off modulation ratios of up to 2.1:1 have been demonstrated at an input base current of as small as 3 mA for a device with emitter/waveguide width of 7 μm and length of 190 μm. Design and analysis of the optical switching characteristics expected for a reflection-type X-crossing optical switch of DHBT waveguide structure are also presented on the basis of these experimental results.
High-power stable chemical oxygen iodine laser
Authors: Shimizu K. , Sawano T. , Tokuda T. , Yoshida S. , Tanaka I.
Published: July 2002

A high-power chemical oxygen iodine laser system has been developed with industrial applications in mind. The present system shows fairly high efficiency, good stability, and reasonably good beam quality applicable to practical applications. Highly efficient power transmission through optical fibers has been demonstrated.
Systematics of positive secondary ion mass spectrometry relative sensitivity factors for Si and SiO2 measured using oxygen and argon ion bombardment
Authors: Novak S. W. , Wilson R. G.
Published: July 2002

We have measured normalized positive ion yields of more than 20 elements implanted into SiO2 and compare them with positive ion yields of the same elements sputtered from Si by oxygen and argon ion bombardment. All measurements were made using similar instruments and similar primary ion beam conditions; thus, we compare secondary ion emission from an unoxygenated matrix (Si using argon ion bombardment), from a partially oxygenated matrix (Si using oxygen ion bombardment), and from a fully oxygenated matrix (SiO2). Plots of the logarithm of secondary ion yield or secondary ion mass spectrometry relative sensitivity factor (RSF) versus ionization potential of the sputtered impurity elements exhibit primary linear trends for these three conditions, the slopes of which decrease with increasing oxygenation. A trend line of opposite slope for impurity elements that have ionization potential greater than about 10.5 eV is observed in each case. This latter trend moves to lower values of yield (higher RSF) with increasing oxygenation, perhaps as the result of competition from electronegative elements with oxygen in forming element–Si bonds. These observed changes are primarily the result of increasing the oxygen content in the surface of the Si.
Growth and characterization of single-heterostructure AlGaAs/InGaP red light-emitting diodes by liquid-phase epitaxy
Authors: Lu Shoei-Chyuan , Wu Meng-Chyi , Lee Chong-Yi , Yang Ying-Chuan
Published: July 2002

High quality Te-doped Al0.7Ga0.3As/Mg -doped In0.5Ga0.5P on p-type GaAs substrate single-heterostructure light-emitting diodes have been reproducibly fabricated by liquid-phase epitaxy using a supercooling technique. The growth conditions and properties of the undoped and Mg- and Zn-doped In0.5Ga0.5P layers are described in detail. The strongest photoluminescence peak intensity occurs at a hole concentration of 1×1018 cm−3 of the Mg-doped layer. Diodes fabricated from the heterostructure are characterized by electron-beam-induced current, current-voltage measurement, electroluminescence, light output power, and external quantum efficiency. By appropriately controlling the hole concentration of the Mg-doped In0.5Ga0.5P active layer and the electron concentration of the Te-doped Al0.7Ga0.3As window layer, the p-n junction can be precisely located at the metallurgical junction as measured by the electron-beam-induced current technique. A forward-bias turn-on voltage of 1.5 V with an ideality factor of 1.65 and a breakdown voltage as high as 20 V are obtained from the current-voltage measurements. The emission peak wavelength and the full width at half maximum of electroluminescence spectra are around 6650 and 250 Å at 20 mA, respectively. The light output power of the uncoated diodes is as high as 150 μW at a dc current of 100 mA and an external quantum efficiency of 0.085%–0.10% is observed.
Interactions of surface plasmons with surface acoustic waves and the study of the properties of Ag films
Authors: Sun X. , Shiokawa S. , Matsui Y.
Published: July 2002

Experimental and theoretical studies on the interactions of surface plasmons with surface acoustic waves have been carried out. Surface acoustic waves were generated on the hypotenuse face of a LiNbO3 prism at f0=85 MHz and 3f0=255 MHz, respectively, which acted as ‘‘dynamic’’ gratings for the conversion of incident light into surface plasmons. The experiment results demonstrated excellent agreement with theoretical calculations based on Fresnel’s formulas for a layered structure and the theory for light diffraction in association with surface acoustic waves. Furthermore, interesting changes in the interaction spectra were observed that have been related to the Ag film’s oxidization. From these observations, variations in Ag film properties have been evaluated.
Magnetic anisotropy induced by cold rolling in Co and Co-Fe alloys
Authors: Tanaka T. , Takahashi M. , Kadowaki S. , Wakiyama T.
Published: July 2002

The roll reduction and concentration dependences of the uniaxial magnetic anisotropy induced by cold-rolling, Kur, were investigated for hexagonal Co and Co-Fe alloys. The maximum value of Kur was 3×105 erg/cm3 at 10%–20% roll reduction for Co and Co-1.5% Fe. The easy direction was perpendicular and parallel to the rolling direction for the alloys containing less than 1.2% Fe and more than 1.2% Fe at room temperature, respectively. The easy direction of Kur changed at 260 °C for Co. The texture produced by cold-rolling was detected by Schulz’s method. The induced anisotropies were evaluated by using the Ku1, Ku2, and the x-ray reflected intensities. The calculated values and easy direction agreed well with the experimental results. The origin of Kur for hexagonal Co and Co-Fe alloys is clearly explained by formation of rolling texture.
An experimental study of the influence of oxygen on silicide formation with tungsten deposited from tungsten hexafluoride
Authors: Zhang S.-L. , Smith U. , Buchta R. , Östling M.
Published: July 2002

Tungsten disilicide (WSi2) was formed by annealing tungsten films deposited by low-pressure chemical vapor deposition on 〈100〉-silicon substrates. The influence of oxygen on the silicidation rate was studied. Si wafers with different oxygen content in the form of Czochralski, float-zone, and epitaxial wafers were used. Oxygen was also ion implanted into either the silicon substrate or the as-deposited tungsten film. The Rutherford backscattering technique was used to follow the progress of the silicidation. The silicidation rate was found to be dependent on the oxygen content of the Si substrates. The rate was lowest for Czochralski substrates and highest for float-zone substrates. Secondary ion mass spectroscopy was used to study the oxygen and fluorine profiles in the films prior to and after silicidation. Growth of WSi2 was found to be retarded concurrently with a pile-up of fluorine at the tungsten side of the W/WSi2 interface and a gettering of oxygen from the annealing atmosphere at the interface. Growth of WSi2 was then transferred to the tungsten surface. Oxygen implantation into silicon and tungsten, respectively, reduced the rate of silicide formation. Oxygen implantation into tungsten altered the distribution of fluorine and suppressed WSi2 growth at the tungsten surface. The observations led to a conceptual model, which ascribes the retardation in the growth of the inner WSi2 to a‘‘poisoning’’ effect caused by the increase of oxygen and fluorine levels at the interface.
Evolution of the microstructure of rapidly solidified Nd-Fe-B permanent magnets
Authors: Chu Tsung-Yao , Rabenberg L. , Mishra R. K.
Published: July 2002

Nd-Fe-B permanent magnets prepared by rapid solidification have been extensively characterized by transmission electron microscopy at all stages of their development. Grains in the as-spun ribbons range in size up to several micrometers in their largest dimension. Excess Nd is trapped within some of the larger grains during solidification; this excess Nd separates from the lattice during subsequent processing, forming Nd-rich, coherent, precipitates. During consolidation of the ribbons, the surface oxide films are broken, creating intimate metallurgical bonds and allowing grain growth to occur across the original ribbon interfaces. The bulk of the grains in the final magnet are plate shaped, having a c axis in common and parallel to the axis of die upsetting; these grains are surrounded by the Nd-rich grain-boundary phase.
Ferromagnetism of Ni(SCN)2(C2H5OH)2
Authors: DeFotis G. C. , Harlan E. W. , Remy E. D. , Dell K. D.
Published: July 2002

The magnetic properties of Ni(SCN)2(C2H5OH)2 have been studied, the first Ni(II) system in the general family of compounds M(SCN)2(ROH)2 (where M=divalent Mn, Fe, Co, or Ni and R=CH3, C2H5, i- or n-C3H7) to be examined at low temperatures. In contrast to previously studied Mn(II) and Co(II) members of this family, which exhibit predominant antiferromagnetism, the present compound is ferromagnetic. The susceptibility of a polycrystalline sample is of Curie–Weiss form only above 75 K, with ḡ = 2.175 ± 0.01 and S=1 and with θ=24.1±1.0 K. The initial susceptibility is well accounted for by an asymptotic critical law, χ0 = Γ[T/Tc − 1]−γ, in the reduced temperature range 0.147–0.013, with Tc = 13.081 ± 0.01 K, γ=1.354±0.02, and Γ=0.0925±0.003 emu/mol. The γ value is between 3D-XY and 3D-Heisenberg model predictions. The susceptibility in the paramagnetic regime well above Tc is analyzed including the effects of axial and rhombic crystal field distortions, represented by D[Ŝ2z − S(S + 1)/3] and E[Ŝ2x − Ŝ2y] terms in the spin Hamiltonian, and incorporating exchange interactions in a mean-field approximation. An excellent fit is obtained with g=2.175, D/k=−64.3±5 K, E/k=23.1±4 K, and zJ/k=19.4±1 K. The magnitude of D is the largest we know of in a Ni(II) compound. The three spin states of the 3A crystal field ground term are strongly split, probably contributing to the relatively low value of Tc compared to zJ/k. Some two-dimensional character in the exchange, as has been found for other members of this family of compounds, may also contribute.
Magnetic structure of KMnPO4⋅H2O
Authors: Visser D. , Carling S. G. , Day P. , Deportes J.
Published: July 2002

The compound KMnPO4⋅H2O adopts the NH4CoPO4⋅H2O structure, in which distorted MII octahedra form corner-sharing sheets, separated by layers of K+ ions. Within a layer, the divalent metal ions form an approximately square lattice. In the range 75–300 K the magnetic susceptibility of KMnPO4⋅H2O follows the Curie–Weiss law, with C=4.73(6) emu K mol−1, θ=−61(2) K. Below 75 K, the susceptibility deviates from this simple model, showing a broad susceptibility maximum with T(χmax) ∼ 27(2) K, which suggests the presence of two-dimensional magnetic interactions. Below about 18 K, magnetization measurements at 0.068 T indicate a weak ferromagnetic moment, with domain effects apparent below 9 K. High-resolution powder neutron-diffraction profiles have been measured at room temperature and 1.7 K. No change in crystal structure is found between these two temperatures, and all additional magnetic reflections in the low-temperature profile were indexed on the nuclear cell. The space group is Pmn21, and Bertaut’s theorem clearly demonstrates that only two magnetic structures in which ferro- and antiferromagnetic moments coexist are possible. The antiferromagnetic structure has been unambiguously refined, however, the canting was too small to be resolved with the available data.
Magneto-optical properties of MnBiAl thin films
Authors: Shen J. X. , Kirby R. D. , Sellmyer D. J. , Wang Y. J.
Published: July 2002

Mn-Bi-Al thin films were produced by sequential evaporation of the constituents, followed by an anneal at 300 °C. The temperature and composition dependencies of the Kerr rotation angle, absolute reflectivity, and magnetic anisotropy were measured. The results show that, up to 30 at. % Al concentration, the thin films retain the pure MnBi hexagonal structure. Further, for suitable Al content, the films have the same large Kerr rotation as MnBi. Pure MnBi films exhibit perpendicular anisotropy at room temperature and in-plane anisotropy for temperatures below 142 K. In contrast, the Al-doped films prepared here have perpendicular anisotropy down to at least 85 K. The increased coercivities of the Al-doped films are attributed to the occupation of grain-boundary and interstitial sites of the NiAs-type hexagonal structure by the Al atoms.
Threshold fields for low-frequency oscillations and chaos in parallel pump instabilities in YIG films
Authors: Srinivasan G.
Published: July 2002

The applied static magnetic field dependence of the frequency of auto-oscillations and threshold microwave magnetic fields for the onset of such oscillations, subharmonic bifurcations, and chaos have been investigated for parallel pump instabilities in YIG films. The measurements at 9.47 GHz on (111) single crystals with thickness in the range 13–110 μm were performed for the static and microwave fields parallel to the film plane. Auto-oscillations at 50–500 kHz were seen for static fields H in the range 100–1200 Oe. The frequency of oscillation fosc was an order of magnitude smaller than values predicted by theory. No noticeable dependence of fosc on the film thickness was observed. A period doubling bifurcation and chaos were observed almost over the entire static field range. The variations of threshold fields for auto-oscillations, period doubling, and chaos with H were found to resemble the so-called ‘‘butterfly’’ curve for parallel pumping.
Magnetic properties of the Y2Fe14B0.5C0.5 compound
Authors: Zhao Z. G. , Sun X. K. , Chuang Y. C.
Published: July 2002

Y2Fe14B0.5C0.5 has the same tetragonal structure as Y2Fe14B with space group P42/mnm. Magnetic properties of the Y2Fe14B0.5C0.5 compound have been studied using an extraction magnetometer with a maximum field of 6 T, in the temperature range from 1.5 to 300 K. By means of fitting the hard magnetization curves, the magnetocrystalline anisotropy constants K1, K2, and K3 were determined. It was found that although the magnetocrystalline anisotropy field (μ0Ha) increases abnormally with increasing temperature as in the case of Y2Fe14B, the dependence of anisotropy constants on temperature is quite different from that of Y2Fe14B. K1 and K3 decrease slightly with increasing temperature. K2 increases abnormally with increasing temperature, which contributes to the abnormal dependence of anisotropy field on temperature. In addition, the substitution of carbon for boron leads to a reduction of 3d-3d interaction and spontaneous magnetization. In contrast, uniaxial anisotropy is increased by the addition of carbon below room temperature.
Spin fluctuations and covalence in neutron Bragg scattering from YBa2Cu3O6 and La2CuO4
Authors: Kaplan T. A. , Mahanti S. D.
Published: July 2002

A puzzle is pointed out concerning the low-temperature behavlor of La2CuO4 and YBa2Cu3O6, the insulating ‘‘parents’’ of the high-Tc superconductors, and indicate a possible solution. The measured ordered magnetic moment is about 0.64 μB per Cu, in agreement with the value calculated on the basis of the Heisenberg Hamiltonian. But this calculation is within a nearly purely ionic or localized picture of the Cu d hole, the reduction from 1.1 μB (g≊2.2) being entirely due to spin fluctuations. Thus the almost perfect agreement leaves no room for the moment reduction due to covalence or 3d-2p hybridization, expected to be large in these oxides. A possible explanation might lie in the fact that an ostensibly symmetry-based argument relating the calculated moment (in the symmetry-unbroken state) to that measured is not valid, as has recently been shown.
Magnetic and electrical properties of reentrant Ce(Fe1−xAlx)2
Authors: Eynon John , Ali Naushad
Published: July 2002

The intermetallic compound CeFe2 undergoes a transition from paramagnetic to ferromagnetic ordering at the Curie temperature Tc = 227 K. Upon substitution of Al at the Fe sites, the system Ce(Fe1−xAlx)2 undergoes a reentrant transition at Tf < Tc, below which the ferromagnetic structure is destroyed. As Al concentration is increased, Tf is raised and Tc is lowered, reducing the temperature range of ferromagnetic order. Results are presented for resistivity, ac susceptibility, magnetization, and thermal-expansion experiments for x≤0.15 in the temperature range 4–290 K. At Tf there is a dramatic drop in ac susceptibility and magnetization as well as a local minimum in the resistivity. This local minimum, and subsequent rise to a peak in resistivity can be explained in terms of spin-glass freezing. Thermal-expansion experiments indicate that the low-temperature transition is not of the first order.
Analysis of Kerr rotation from Cu/Co, Pd/Co, and Pt/Co superlattices
Authors: Moog E. R. , Zak J. , Bader S. D.
Published: July 2002

Numerical simulations of the Kerr signals from Cu/Co, Pd/Co, and Pt/Co superlattices show, in general, a scaling of the signal with the amount of Co in the superlattice. Experimentally, however, the signal from Pt/Co superlattices at ∼4 eV is larger than that from bulk Co, despite the lesser total amount of Co. This is due to the magnetization induced in the Pt by the Co. Comparison of the Pd/Co and Pt/Co results with experiment indicates that the magnetization induced in the Pt by the Co plays a more important role in the magneto-optic activity than does the induced magnetization of Pd.
Magnetic and structural properties of permalloy-tantalum multilayer thin films
Authors: Hill E. W. , Li J. P. , Birtwistle J. K.
Published: July 2002

This work describes a detailed investigation into the magnetic and structural properties of permalloy-tantalum multilayered thin films produced by vacuum evaporation. Their microstructure was investigated using high-resolution TEM and the magnetic properties were measured with vibrating-sample and vibrating-reed magnetometers. The results show a reduction in coercivity for the multilayer films which is independent of the number of layers but depends strongly on the magnetic layer thickness. The tantalum layer is shown to be continuous and microcrystalline down to 25-Å thickness, but the interface between the layers is irregular and may give rise to additional magnetostatic coupling as the tantalum layer thickness is reduced.
Effects of film growth mode on magnetic exchange coupling in trilayer structures (abstract)
Authors: Kay E. , Donath M. , Scholl D. , Siegmann H. C.
Published: July 2002

In situ temperature-dependent spin-polarized cascade electron spectroscopy is used to study exchange coupling processes between a magnetic substrate and a magnetic overlayer separated by a nonferromagnetic spacer layer. Relative Auger intensities of the overlayer/substrate configurations as a function of overlayer coverage together with a model by Ossicini are used to evaluate the degree to which these trilayer structures grow by a continuous layer growth mode. Measurement of the spin polarization and Auger spectroscopy are used during film growth as criteria of chemical film purity. Evidence will be given to show that the oscillatory magnetic coupling behavior as a function of Cr thickness of a NiFe/Cr/NiFe trilayer changes significantly depending on the deposition temperature, which may be associated with microstructural changes. Competing coupling mechanisms are thought to account for this behavior. Data will also be presented to suggest how trace quantities of residual gas sorbates, presumably acting as surfactants, can dramatically alter the magnetization behavior of ultrathin films. Significant increases in magnetization of a 5-Å Fe overlayer film in a Fe/Ta/Fe trilayer structure were observed and are attributed to changes in wetting characteristics at the Fe/Ta interface which cause morphological changes in the film structure. Conversion of weakly interacting magnetic islands to a long-range ferromagnetic continuous film medium exhibiting remanence and a steady-state Brillouin functional M(T ) behavior is thought consistent with these observations. The possible significance of these kinds of observations to some conflicting data in the literature will be mentioned.