bluuebunny/crossref_metadata_2025 huggingface dataset:
Weak ferromagnetism in NiCO3
Authors: Plumier R. , Sougi M. , Lecomte M. , Saint-James R.
Published: July 2002

Magnetization curves and neutron diffraction experiments performed at various temperatures on a powdered specimen of NiCO3 point out a Curie temperature TC =24.25 K. Down to 20 K, the spontaneous magnetization follows a (TC −T)1/2 relation. No good agreement exists between the observed and calculated dependencies of the magnetization on T and H on both sides of TC when the calculated values are obtained from an extension correct up to terms in H3 of Dzyaloshinsky’s theory of weak ferromagnetism. On the other hand, the relation m(T,H)= f(H)e−1/2(TC−T) is found to give excellent agreement with the experiments at T<TC and in a range ΔT/TC ≂20%.
Large-diameter plasma columns produced by surface waves at radio and microwave frequencies
Authors: Chaker M. , Moisan M.
Published: July 2002

Up to now, the production of plasma columns through the propagation of electromagnetic surface waves had been reported essentially in the microwave range (200 MHz–10 GHz), with tube diameters that extend from 0.5 to 40 mm. Such plasmas can be obtained at much lower frequencies, at least down to 27 MHz. We also present larger plasma column diameters, up to 124 mm, as well as column lengths up to 6 m. The surface wave dispersion and the axial electron density distribution observed under these new conditions are well described by the cold plasma model.
Optical detector using superconducting BaPb0.7Bi0.3O3 thin films
Authors: Enomoto Youichi , Murakami Toshiaki
Published: July 2002

This paper describes a highly sensitive optical detector using a perovskite-type superconductor, BaPb0.7Bi0.3O3 (BPB) thin film. Optical signals create quasiparticles and induce changes in the superconducting energy gap. These changes are measured by tunnel junctions which are formed along the grain boundaries in the BPB polycrystalline thin film. The detector sensitivity is about 104 V/W in the 1–8-μm wavelength range, and the detector is found to be capable of responding up to 1.3 GHz at the 1.3-μm wavelength. Consequently, this BPB detector is well suited in infrared spectrometer and optical-communications system applications.
Low-temperature phase diagram of the Ga-As-Sb system and liquid-phase-epitaxial growth of lattice-matched GaAsSb on (100) InAs substrates
Authors: Mani H. , Joullie A. , Karouta F. , Schiller C.
Published: July 2002

The liquidus and solidus in the Ga-rich corner of the Ga-As-Sb system were determined by experiments using liquids of constant antimony concentration xLSb =0.0615. Evidence was obtained for a quite asymmetric solid-phase miscibility gap. A theoretical phase diagram has been calculated on the basis of simple solution model. This diagram predicts the equilibrium conditions for the liquid-phase epitaxy of lattice-matched ternary layers on InAs substrates in the growth temperature domain 500–600 °C, but it gives a symmetric solid-phase miscibility gap that is inconsistent with our experimental data. The actual conditions for exact lattice matching were experimentally determined by measurements on liquid-phase-epitaxial layers grown by the supercooling method on (100)-oriented InAs. Flat and uniform mirrorlike epilayers were obtained using slight initial supercoolings (3–10 °C) within the range of relative lattice mismatch from −0.05% to +0.1%, which corresponds to positive mismatch (alayer>asubstrate) at the growth temperature (∼550 °C). The growth kinetics of the lattice-matched ternary alloy, which has the composition GaAs0.09Sb0.91, appear to be governed by solute diffusion in the liquid. If it is assumed that As and Sb have the same diffusion coefficient, a value of 6.8×10−5 cm2 s−1 for this coefficient is obtained by fitting the experimental data.
Subthreshold response of rf SQUIDs to a general external perturbation
Authors: Bulsara Adi R.
Published: July 2002

We consider a rf SQUID subjected to an external magnetic flux that includes dc, periodic, and stochastic components. Using a previously developed linearization technique, the response of the SQUID (below its hysteresis threshold) to this force is determined as a function of the internal parameters of the device. The measurement process, wherein the flux sensed by the SQUID is coupled to a tank circuit, is also considered. The results obtained, using the linearization technique referred to above, are compared with previously reported work on this subject. It is seen that, while not exact, this technique allows one to compute, analytically, the response (measured as an autocorrelation function or its associated spectral density) very accurately below the SQUID hysteresis threshold.
Penumbral neutron imaging—optimization and simulation
Authors: Nugent K. A. , Luther-Davies B.
Published: July 2002

This paper describes the optimization of the penumbral neutron imaging camera. The optimum parameters are qualified by practical considerations and the resulting camera is tested using a full Monte Carlo simulation. It is shown that an object emitting only 1.3×1010 neutrons/resolution element should be imageable. This result is confirmed by simulations of three different object shapes which indicate that the shape of the core of a compressed inertial confinement fusion pellet may be determined by this technique. It is further shown that these results correspond to the lowest possible imageable yield for any coded-aperture technique using the parameters assumed here. Finally, an alternative aperture and detector arrangement is briefly described which may lower the imageable yield by more than an order of magnitude.
Amorphous silicon deposition rates in diode and triode discharges
Authors: Gallagher A.
Published: July 2002

The relative rates of radical deposition on discharge electrodes and substrate surfaces are calculated for two-and three-electrode discharges. The reaction rate, diffusion coefficient, screen-electrode transparency, and surface sticking coefficient are parameters in the general solution. The parameters are then chosen to describe typical silane discharges used for a-Si:H photovoltaic production, and the effect of screen transparency and other parameters on substrate deposition rates is evaluated. We then show that a measurement of deposition rate versus screen–substrate spacing in a three-electrode discharge has been misinterpreted as due to gas reactions, whereas it is primarily due to screen deposition. Finally, we note some possibilities for measuring deposition parameters and for varying the mix of depositing species.
Activation energy for electromigration failure in Al–Cu conductor stripes covered with polyimide
Authors: Lloyd J. R. , Steagall R. N.
Published: July 2002

The activation energy for electromigration failure was determined for Al-4% Cu conductor stripes covered with polyimide. The activation energy was measured to be 0.88 eV, which is substantially higher than that measured previously for similar systems under glass. The difference in the activation energies is attributed to the possible presence of hydrogen in the Al–Cu grain boundaries.
Inertial confinement fusion ion temperature measurements using a single-hit detector array
Authors: Cable M. D.
Published: July 2002

Neutron time-of-flight techniques have been used to diagnose fuel ion temperatures of inertial confinement fusion plasmas. A new technique for making this measurement using an array of ‘‘single-hit’’ detectors operating in single-particle counting mode is described. This technique has some potential advantages over previous methods (faster timing, better energy resolution, good sensitivity) and can possibly be further developed to allow detailed measurements of neutron energy spectra to give other diagnostic information, such as fuel areal density (〈ρR〉).
Analytic model of Applied-B ion diode impedance behavior
Authors: Miller P. A. , Mendel C. W.
Published: July 2002

An empirical analysis of impedance data from Applied-B ion diodes used in seven inertial confinement fusion research experiments was published recently. The diodes all operated with impedance values well below the Child’s-law value. The analysis uncovered an unusual unifying relationship among data from the different experiments. The analysis suggested that closure of the anode-cathode gap by electrode plasma was not a dominant factor in the experiments, but was not able to elaborate the underlying physics. Here we present a new analytic model of Applied-B ion diodes coupled to accelerators. A critical feature of the diode model is based on magnetic insulation theory. The model successfully describes impedance behavior of these diodes and supports stimulating new viewpoints of the physics of Applied-B ion diode operation.
Interaction between magnetic and compositional order in Ni-rich NicFe1−c alloys (invited)
Authors: Staunton J. B. , Johnson D. D. , Gyorffy B. L.
Published: July 2002

We have developed a first-principles electronic theory of concentration fluctuations in spin polarized binary alloys. It is a mean field theory of the state of compositional order and it is based on the local spin density (LSD) approximation for describing the electrons. The usual averages over the statistical mechanical ensemble are carried out with the aid of the self-consistent Korringe–Kohn–Rostoker coherent-potential approximation (SCF-KKR-CPA). To illustrate the main consequences of the theory we study the compositional short-range order in the NicFe1−c alloy system. We find that the ordering energy is almost entirely of magnetic origin.
Stabilization of precession-free rotors supported by magnets
Authors: Sasaki Shosuke
Published: July 2002

Two types of precession-free rotors are proposed which are characterized by a magnetic suspension and by a precession damper. The type-I rotor is composed of a contactless rotor with a magnetic precession damper, and the type-II rotor is composed of a rotor with a mechanical precession damper. The classical equations of motion for these rotors are studied and solved. Then the solutions for the rotating motion of both rotors show that the inclination of the figure axis decreases spontaneously. Namely, these rotors have very stable rotation. The type-II rotor is produced in the laboratory, and a revolution of 120 000 rpm is obtained in a preliminary experiment.
Gallium- and arsenic-induced oscillations of intensity of reflection high-energy electron diffraction in the growth of (001) GaAs by chemical beam epitaxy
Authors: Chiu T. H. , Tsang W. T. , Cunningham J. E. , Robertson A.
Published: July 2002

The observations of a damped intensity oscillation using reflection high-energy electron diffraction during the growth of GaAs by chemical beam epitaxy using triethylgallium and arsine are reported. It is experimentally demonstrated that the As flux can be instantly shut off without any memory effect by measuring the Ga-induced intensity variation and the subsequent As-induced oscillations. The Ga deposition, free of any background As contamination, makes possible the direct determination of metal-alkyl adsorption and pyrolysis efficiency on the hot substrate surface. At 530 °C a (4×6) diffraction pattern is observed when Ga is deposited alone. The appearance of this (4×6) reconstruction along with the associated intensity behavior indicates that the first monolayer of Ga grows two-dimensionally. This can be understood qualitatively in terms of the simple kinematic model involving only surface roughness. These observations support a two-dimensional growth mechanism in the growth process. Furthermore, the ability to control submonolayer deposition of pure Ga coupled with the in situ electron-diffraction monitoring technique presents a new growth configuration of atomic layer epitaxy to be realized by chemical beam epitaxy.
Ion energy measurement at the powered electrode in an rf discharge
Authors: Kuypers A. D. , Hopman H. J.
Published: July 2002

Ion energy measurements have been performed with an electrostatic parallel plate energy analyzer at the powered electrode of a 13.56–MHz rf discharge. Considerable splitting of the ion energy distributions is observed due to rf oscillations. Plasma potential, sheath thickness, and total ion current are derived from the observed energy profiles. Low-pressure operation of the plasma at several mTorr permits a collisionless sheath approximation and gives rise to well-defined energy spectra.
Acoustic emission along the hysteresis loops of various ferro- and ferrimagnets
Authors: Guyot M. , Merceron T. , Cagan V.
Published: July 2002

For the first time, the acoustic emission (AE) along a hysteresis loop has been investigated at variable magnetizing field frequency (10−2 up to 102 Hz) on three very different magnetic materials: polycrystalline YIG, amorphous FeNiBSi ribbon and mumetal. For all the samples the AE activity is hysteretic; in the very-low-frequency range it shows two sharp minima around the coercive field values ±Hc and a smooth decrease when approaching the saturation, as we have reported in a previous paper. At increasing frequency, the AE minima at Hc vanish progressively and in some cases are even replaced by broad maxima, as already reported in the literature. Such an effect could be attributed to the complex situation occurring when increasing the frequency, due either to the measurement technique or to physical phenomena such as echoes. However, we cannot exclude the possible influence of dynamical changes of the microprocesses which originate the AE. That leads us to the conclusion that AE is better investigated in quasistatic conditions.
Large surface anisotropies in ultrathin films of bcc and fcc Fe(001) (invited)
Authors: Heinrich B. , Urquhart K. B. , Dutcher J. R. , Purcell S. T. , Cochran J. F. , Arrott A. S. , Steigerwald D. A. , Egelhoff W. F.
Published: July 2002

Large uniaxial anisotropies associated with interfaces are observed for ultrathin films (3-28 ML) of bcc Fe(001) grown epitaxially on Ag(001) single-crystal substrates and for epitaxial sandwiches of fcc Fe(001) grown with three layers of Fe using Cu as substrate and coverlayers. The uniaxial anisotropy is well described by a pseudosurface anisotropy term as theoretically predicted, yet that theory also predicts large in-plane anisotropies that are not observed. Adequate treatment of spin-orbit coupling in magnetic theories remains a challenge. Comparisons of ultrathin films of bcc Fe(001) on Ag(001) with different coverlayers of Ag or Au show subtle differences in magnetic behavior as studied by ferromagnetic resonance (FMR) and Brillouin light scattering (BLS). The FMR measurements were carried out at 9.6, 36.6, and 73 GHz microwave frequencies. The BLS measurements were performed using a six-pass Fabry–Perot interferometer. The power of the techniques of molecular-beam epitaxy (MBE) for producing well-characterized interfaces is stressed. Growths at 140 K are compared with those at 300 K to show the limited role of interdiffusion. Oscillations in the intensity of reflection high-energy electron diffraction (RHEED) are exploited in the characterization of growth. Comparison of the properties of films grown on perfect iron whisker surfaces with results for mosaic single-crystal substrates show that, while the former are much to be preferred for growth studies, the latter are really adequate for magnetic studies.
Valence-band mixing effects on the gain and the refractive index change of quantum-well lasers
Authors: Ahn D. , Chuang S. L. , Chang Y.-C.
Published: July 2002

The effects of valence-band mixing on the gain and on the refractive index change of the quantum-well laser and the effect of an applied electric field perpendicular to the quantum wells for gain switching are studied theoretically. Our calculations are based on the multiband effective-mass theory (k⋅p method) and the density-matrix formalism with the intraband relaxation taken into account. First, we calculate the nonparabolic valence-band structure by the finite difference method after making a unitary transformation of the Luttinger-Kohn Hamiltonian. The calculated gain for our model shows remarkable differences in both spectral shape and peak amplitude as compared with those for the conventional model of the parabolic valence band. The peak gain is reduced considerably and the gain spectrum is more symmetric in our model compared with that for the conventional model. The refractive index change shows a negative increment in the active region for both the TE and TM polarizations resulting in the antiguidance. However, the TM polarization shows more negative change which would result in the suppression of the TM modes as compared with the TE modes. As another example, the perpendicular electric field effects on the quantum-well laser with lateral current injection are also calculated. A red shift and a reduction of the gain spectrum are shown when an electric field is applied. This may have applications as a tunable and high-speed switching quantum-well laser.
High-temperature behavior of an InP wafer heated locally by a Nd:YAG laser beam
Authors: Kawamura Tsutomu , Kitajima Hiroshi
Published: July 2002

An InP wafer has been locally heated by a Nd:YAG laser beam to between 600 and 1060 °C (melting point) in air. When the temperature gradient is very steep, explosive disordering takes place in the irradiated region of the InP wafer, prior to the formation of InPO4 polycrystals at above 900 °C. If the specimen is heated above the melting point of InP, In2O3 polycrystals are instantaneously generated around the tiny cylindrical hole made by burning through the InP wafer. It is inferred that the explosive disordering plays an important role in the rapid formation of these polycrystals. On the other hand, if the specimen is heated in a thin refractory film coated state, the above-mentioned alterations can be largely suppressed and the trace of the anisotropic thermal vibration of InP crystal lattice near the melting point can be clearly recorded in in situ observation of x-ray diffraction photographs.
Electrical and optical properties of gold-doped n-type silicon
Authors: Weman H. , Henry A. , Begum T. , Monemar B. , Awadelkarim O. O. , Lindström J. L.
Published: July 2002

Different measurement techniques, both electrical and optical, were utilized in this work to characterize gold diffusion in n-type, float-zoned silicon in the temperature range 600–1150 °C. In the lower temperature region (≤750 °C), the gold diffusion is observed by the introduction of the Au acceptor state at 0.53 eV below the conduction band, and is correlated to the electrical behavior of the samples deduced from Hall effect and resistivity data. Also, the effects of Au diffusion on the free-carrier concentration and mobilities are discussed. It was shown that high temperatures and long times for gold diffusion change the conductivity type in the samples from n to p. In the samples that converted to p type, a limiting room-temperature resistivity of 2.0×103 Ω cm was attained, when the conduction is mainly influenced by the Au-related deep electronic states in the band gap. In this case, the diffusion mechanism is also investigated by secondary ion mass spectroscopy data determining the equilibrium Au solubility, which is close to the equilibrium solubility of interstitial gold. Low-temperature photoluminescence measurements have shown that the intensity of the lines often attributed to dislocations, increases significantly by gold diffusion in the lower temperature region. At higher diffusion temperatures, a decrease of the dislocation-related lines was found, associated with formation of gold-related precipitates. Introducing an inhomogeneous internal stress distribution in the Si matrix, these precipitates cause line shifts as well as line broadenings of the free exciton, the phosphorus bound exciton, and the electron-hole droplet photoluminescence emissions. The concentration of substitutional phosphorus is found to decrease with increasing diffusion temperatures.
An electron trap related to phosphorus deficiency in high-purity InP grown by metalorganic chemical vapor deposition
Authors: Yamamoto Norio , Uwai Kunihiko , Takahei Kenichiro
Published: July 2002

Deep levels in high-purity InP crystal grown by metalorganic chemical vapor deposition (MOCVD) have been measured by deep level transient spectroscopy. While no electron traps are observed in the samples grown at 600 °C with a [PH3]/[In(C2H5)3] of 170, three electron traps with activation energies of 0.80, 0.44, and 0.24 eV were observed in the samples grown at 500 °C with the same [PH3]/[In(C2H5)3]. The 0.44-eV trap, whose capture cross section is 1.5×10−18 cm2, observed at a low [PH3]/[In(C2H5)3] shows a decrease in concentration as [PH3]/[In(C2H5)3] is increased, and becomes less than 5×1012 cm−3 at a [PH3]/[In(C2H5)3] of more than 170. The comparison of annealing behavior of this trap in MOCVD InP and that in liquid-encapsulated Czochralski InP suggests that the 0.44-eV trap is related to a complex formed from residual impurities and native defects related to a phosphorus deficiency such as phosphorus vacancies or indium interstitials. This trap is found to show configurational bistability similar to that observed for the trap in an Fe-doped InP, MFe center.
Adhesion and deformation of metal/polyimide layered structures
Authors: Faupel F. , Yang C. H. , Chen S. T. , Ho P. S.
Published: July 2002

Adhesion and interfacial failure of Cr, Cu, and Cu/Cr films on a thin pyromellitic dianhydride-oxydianiline polyimide substrate have been investigated using a recently developed stretch deformation technique. This method directly measures the energy required to separate the interface from the difference in the load versus elongation curves between film/substrate and substrate structures. The failure mode was observed in combination with morphological studies by in situ optical microscopy and scanning and transmission electron microscopies. The stress distribution in the sample upon stretching has been computed by a finite element analysis. The difference in the stress relief modes, film fracture, and delamination behavior for Cu versus Cr films is discussed. The important role of crack formation in the metal overlayer for initiating failure is demonstrated. The effects due to the addition of a brittle Cr interface layer between polyimide and Cu on the buildup of stress and the onset of failure have also been investigated.
Substrate-induced peak in the photoluminescence of heavily doped epitaxial GaAs
Authors: Szmyd D. M. , Majerfeld A.
Published: July 2002

A peak at 1.38 eV is observed in the 300-K photoluminescence of n+ and p+ epitaxial GaAs. This peak appears as a shoulder of the principal band-to-band emission. The shoulder is an artifact produced by the substrate and should not be interpreted as an additional optical transition. It is demonstrated that the subband-gap luminescence, which arises from the band-gap reduction caused by the heavy doping, travels through the transparent semi-insulating substrate, reflects off the back surface, and is emitted from the epilayer. The shoulder intensity is enhanced by the scattering of light off the back surface. Thick substrates with polished back surfaces are optimum for reducing the shoulder peak.
Large differences of critical current density in thin films of superconducting YBa2Cu3O7−x
Authors: Mogro-Campero A. , Turner L. G. , Hall E. L.
Published: July 2002

Thin films of YBa2 Cu3 O7−x with three types of c-axis alignment have been prepared by evaporation: unaligned films on oxidized silicon with zero-resistance transition temperatures as high as 88 K (the highest value reported for thin films of this superconductor on this substrate), films with regions aligned along each of the three 〈100〉 directions of the (100) SrTiO3 substrate, and films with the c-axis perpendicular to the (100) SrTiO3 plane. Typical values of critical current density (A cm −2 ) at 77 K are 102 , 3×104 , and 106, respectively. The temperature dependence of the critical current density is similar for the three types of films; it increases linearly with decreasing temperature, which is suggestive of a flux creep-limited model.
Semi-insulating properties of Fe-doped InP grown by hydride vapor phase epitaxy
Authors: Iyer S. , Macrander A. T. , Karlicek R. F. , Lau S.
Published: July 2002

Epitaxial layers grown by hydride vapor phase epitaxy using N2 as a carrier gas were studied. Charge transport measurements at temperatures as high as 416 K and as low as 38 K were made on layers grown on (100)-, (311)B-, (511)B-, and (110)- oriented substrates. Resistivities in the range 4×106–2×1010 Ω cm were obtained in all cases except for growth on (311)B surfaces. In that case resistivities were in the range 1×103–5×107 Ω cm. Detailed fitting to I-V data was done using a two trap model, and a good fit was obtained if traps lying at 0.68 and 0.30 eV below the conduction band were included. The deeper lying trap concentration which gave the best fit was in the range 1–8×1015 cm−3. This level corresponds to the Fe3+⇄Fe2+ transition which is usually observed in semi-insulating bulk and MOCVD grown Fe-doped InP and which compensates the background donors. A concentration lying in the range 2–20×1018 cm−3 must be used for the 0.30-eV trap to produce a good fit. The presence of this trap at such a large concentration also explains our observations that the Fermi level moves up in the band gap as the temperature is decreased. We speculate that this trap is N impurity related. Secondary-ion-mass spectrometry results rule out the possibility that the 0.30-eV trap is Fe related. Low-temperature photoluminescence spectra typical of Fe-doped InP were obtained and revealed a broad band at 1.1 eV. Such a band has been commonly reported for bulk InP:Fe and is usually assigned to an Fe related deep level. Our results suggest that this assignment may not be correct for our material.
Fast ion conduction in β-Ag3SI1−xBrx solid solutions
Authors: Beeken R. B. , Menningen K. L.
Published: July 2002

Polycrystalline solid solutions of Ag3SI1−xBrx were prepared from the melt and characterized in the superionic β phase by x-ray diffraction and electrical conductivity. Alloy lattice parameters decrease linearly from x=0.0 to x=1.0 within experimental uncertainty. Room-temperature conductivity of Ag3SI is enhanced with the substitution of bromide for iodide while a corresponding, though smaller, effect is observed in Ag3SBr as iodide is substituted for bromide. The transition temperature separating the superionic β phase and the covalent γ phase in these alloys attains a minimum at x=0.80.
Particulate generation in silane/ammonia rf discharges
Authors: Anderson Harold M. , Jairath Rahul , Mock Joseph L.
Published: July 2002

The rate of particle generation in a SiH4/NH3 rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode. Measurements of the bulk quantity of particles produced in the discharge reveal that the mode of coupling (capacitive or dc) as well as the electrode temperature significantly affects particle generation rates. Laser light scattering measurements made as a function of the plasma power density indicate that particle generation abruptly ceases at a threshold value sufficient to induce spark breakdown at the cathode. Based on these observations, it is shown that particle growth in plasmas can be modeled entirely as a heterogeneous process. The initiation of particle growth is shown to be consistent with an electron surface desorption model involving vibrational excitation of surface clusters. Propagation of growth in the gas phase is shown to be consistent with an eliminative ion-molecular condensation reaction, and the pressure dependence of this mechanism is exploited to estimate a value for the rate constants for SiH4 and NH3 condensation in SiN:H particle growth.
An x-ray photoelectron spectroscopic analysis of plasma deposited silicon nitride films
Authors: Chiang J. N. , Hess D. W.
Published: July 2002

The effect of deposition conditions on the structure and composition of plasma deposited silicon nitride films was studied using x-ray photoelectron spectroscopy. Plasma deposited silicon nitride films were transferred directly from the deposition chamber into a surface analysis system, thereby permitting analysis of as-deposited films without modification due to ion sputtering. Plasma deposited silicon nitride films with N:Si ratios from 1.8–0.3 were deposited using SiH4, NH3, N2, and H2 as the source gases. The N:Si ratio in the films increased with increasing nitrogen concentration in the gas phase. Changes in the deposition power or the substrate temperature also influenced the N:Si ratio. Large differences in the film structure were observed for plasma deposited silicon nitride films formed with NH3 compared to N2 with respect to deposition temperature variations.
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u emission and mass spectroscopic measurement of chemical species responsible for diamond growth in a microwave plasma jet
Authors: Mitsuda Yoshitaka , Tanaka Ken-itsu , Yoshida Toyonobu
Published: July 2002

Chemical species responsible for diamond growth were examined by in situ methods using a microwave plasma jet from Ar-H2-CH4/C2H2. Irrespective of the reactants, diamond was successfully deposited, and morphology was likely to depend only upon the carbon equivalent concentration in the gas phase. Emission spectroscopy revealed that the C2 radical was the main emissive species in the plasma, and that its vibration temperature was estimated to be about 5000 K with little dependence on the axial position. Moreover, emission from just above the substrate showed a considerably lower concentration ratio of H atom to C, including radicals, than the case of low-pressure microwave plasma. On the other hand, mass spectroscopy mainly detected CH4 and C2H2 in the species impinging on a substrate. The importance of kinetic processes in a boundary layer was strongly emphasized.
Beryllium δ doping of GaAs grown by molecular beam epitaxy
Authors: Schubert E. F. , Kuo J. M. , Kopf R. F. , Luftman H. S. , Hopkins L. C. , Sauer N. J.
Published: July 2002

Spatial localization of Be in δ-doped GaAs within few lattice constants (<20 Å) is achieved at low growth temperatures for concentrations N2DBe <1014 cm−2 as indicated by capacitance-voltage profiles and secondary ion mass spectroscopy. At elevated growth temperatures and at higher Be concentrations, significant spreading of the dopants occurs and is explained by (i) Fermi-level pinning-induced segregation, (ii) repulsive Coulomb interaction of dopants, and (iii) diffusion. The highest Be concentration achieved at low growth temperatures exceeds 2×1020 cm−3 and is limited by repulsive dopant interaction. It is shown that the repulsive Coulomb interaction results in a correlated, nonrandom dopant distribution. The diffusion coefficient of Be in GaAs is determined and is found to be much lower than previously reported.
Mössbauer spectra study of Nd2Fe14−xGaxB and Nd2Fe11.5−xCo2.5GaxB compounds
Authors: Xie J. Q. , Wu C. H. , Chuang Y. C. , Yang F. M.
Published: July 2002

A Mössbauer study of Nd2Fe14−xGaxB and Nd2Fe11.5−xCo2.5GaxB confirmed that, in Nd2Fe14−xGaxB with x<1, preferential occupation of the k2 site by Ga atoms occurs, and that when x≥1, Ga atoms preferentially occupy the k1 as well as j1 sites in addition to the k2 sites. In Nd2Fe11.5−xCo2.5GaxB, the Ga atoms preferentially occupy the j2 site, and also appear at the j1 sites when x≥1. Based on these findings, the different effect of Ga on the Curie temperature in these two compound series can be interpreted satisfactorily. The fact that in these compound series the a axis is little changed whereas the c axis remarkably increases with increasing Ga substitution can also be explained.
Native defects in the AlxGa1−xSb alloy semiconductor
Authors: Ichimura M. , Higuchi K. , Hattori Y. , Wada T. , Kitamura N.
Published: July 2002

Defect concentrations in AlxGa1−xSb which is in equilibrium with a liquid phase are calculated. When the liquid phase is Ga rich, a Ga antisite (Ga2−Sb) or an Al antisite (Al2−Sb) is dominant, and the concentrations of vacancies are much smaller than the antisite concentrations. Ga2−Sb is dominant in GaSb equilibrated with a Sb-rich solution, but the concentration of Sb antisites comes close to that of Ga2−Sb as temperature is lowered. For x larger than 0.6, a group-III vacancy is the predominant defect in the case of Sb-rich solutions. Calculated net acceptor concentrations agree well with those determined experimentally. A complex defect composed of GaSb and a Ga vacancy, which have been taken as the dominant residual acceptor, is expected to be negligible.
Applying Steinberg’s model to the Hugoniot elastic limit of porous boron carbide specimens
Authors: Brar N. S. , Rosenberg Z. , Bless S. J.
Published: July 2002

Plate-impact experiments were performed on boron carbide specimens, having different porosities, in order to measure their Hugoniot elastic limit (HEL) values. The measurements were performed with commercial manganin gauges embedded at the back surface of the specimen and backed by a thick Plexiglas disk. The measured values show an almost linear decrease in the HEL values between 194 kbar (For the fully dense material) to 96 kbar for a specimen with 16.3% porosity. These values were compared with a theoretical model [suggested by D. Steinberg (LLL report LLL-UCID-16946, 1975)] which accounts for the dependence of the HEL on porosity, and the agreement is shown to be good.
A model for the high-temperature transport properties of heavily doped n-type silicon-germanium alloys
Authors: Vining Cronin B.
Published: July 2002

A model is presented for the high-temperature transport properties of large-grain-size, heavily doped n-type silicon-germanium alloys. Electron and phonon transport coefficients are calculated using standard Boltzmann equation expressions in the relaxation time approximation. Good agreement with experiment is found by considering acoustic phonon and ionized impurity scattering for electrons, and phonon-phonon, point defect, and electron-phonon scattering for phonons. The parameters describing electron transport in heavily doped and lightly doped materials are significantly different and suggest that most carriers in heavily doped materials are in a band formed largely from impurity states. The maximum dimensionless thermoelectric figure of merit for single-crystal, n-type Si0.8Ge0.2 at 1300 K is estimated at ZT≂1.13 with an optimum carrier concentration of n≂2.9×1020 cm−3.
Calculation of the ferromagnetic resonance linewidth of barium ferrite
Authors: Marshall S. P. , Sokoloff J. B. , Lu F. , Perry C. H.
Published: July 2002

Two microscopic models have been proposed to explain the large intrinsic linewidth of barium ferrite. The first is a two-magnon scattering process due to an intrinsic disorder associated with the unique trigonal bipyramidal site in the crystal. [E. Tsantes and L. M. Silber, J. Appl. Phys. 63, 3350 (1988)]. The second is the Kasuya–LeCraw relaxation process [S. P. Marshall, J. B. Sokoloff, and C. Vittoria, IEEE Trans. Magn. MAG-25, 3491 (1989)]. Both of these processes involve modulation of the single-ion anisotropy. Analytical calculations using simplified models for the acoustic magnon and phonon spectra fail to account for the linewidths characteristic of barium ferrite. In order to understand both of these relaxation processes as they relate to barium ferrite, we have calculated the full phonon spectrum for this crystal based on the rigid-ion model. The calculated reflectivity compares well with the infrared reflectivity data that we have taken. Using phonon modes that we have calculated and the magnon modes calculated previously [S. P. Marshall and J. B. Sokoloff, J. Appl. Phys. 67, 2017 (1990)], we have calculated the ferromagnetic resonance linewidth on the basis of the Kasuya–LeCraw mechanism and two-magnon scattering by fluctuating 2b-site ions. We find that the trigonal-site disorder scattering mechanism is able to account for the observed magnitude of the linewidth.
Modeling of the transverse mode suppressor for dielectric wake-field accelerator
Authors: Gai Wei , Ho Ching-Hung
Published: July 2002

An analytical model is given for the transverse mode suppressor of dielectric wake-field accelerators. The calculated results are compared with recent experimental data.
Defect production in Si(100) by 19F, 28Si, 40Ar, and 131Xe implantation at room temperature
Authors: Bai G. , Nicolet M-A.
Published: July 2002

We used x-ray double-crystal diffractometry and MeV 4He channeling spectrometry to study quantitatively the damage produced in Si(100) at room temperature by 230-keV 19F, 230-keV 28Si, 250-keV 40Ar, or 570-keV 131Xe implantation. The measured defect concentration and the perpendicular strain have the same depth profile, and both are depleted near the surface compared to the Frenkel pair concentration calculated from computer simulation. The perpendicular strain is proportional to the defect concentration with a coefficient of B∼0.01 common to all implanted species. The maximum value of the perpendicular strain and of the defect concentration rises nonlinearly with the dose for all species. The damage produced by different implanted species depends on the dose in approximately the same way save for a scaling factor of the dose. In the regime of low damage, the strain and the defect concentration rise linearly with increasing dose. The slope of this rise with dose increases with the square of the Frenkel pairs produced per unit dose of incident ions, as calculated from computer simulations. This fact means that stable defects produced by room-temperature implantation in Si(100) cannot be predicted by a linear cascade model.
Etching roughness for (100) silicon surfaces in aqueous KOH
Authors: Palik E. D. , Glembocki O. J. , Heard I. , Burno P. S. , Tenerz L.
Published: July 2002

The quality of vertical roughness produced by the etching of Si in aqueous KOH has been studied by varying several experimental parameters such as molarity, time of etching, temperature, and stirring. We note that at room temperature, unstirred etching is smoother at low and high molarities, and etch rate and roughness both peak near 5–6 M. With no stirring, roughness increases as a function of etch time, then levels off. With stirring, roughness decreases, especially around the peak etch rate near 5–6 M. For a fixed molarity like 5 M, unstirred etching becomes smoother with increasing temperature even as the etch rate increases rapidly. Such results suggest that masking by hydrogen bubbles or silicate etch products is the principle origin of vertical roughness. Bubble properties as a function of molarity and stirring (as determined from electrolysis experiments) are used to suggest a pseudo-masking model to explain some roughness properties.
Correlation factors for diffusion in binary random alloys with fcc structure
Authors: Franke P. , Dieckmann R.
Published: July 2002

Tracer correlation factors have been calculated by simulating the diffusion of atoms and defects on a computer using a Monte Carlo technique. The correlated motion of the atomic species by a vacancy mechanism have been investigated for a binary random alloy with fcc structure. The tracer correlation factors for the atoms, fA and fB, and for the vacancies, fV, are calculated as functions of the jump frequencies, and the mixing ratio of A and B atoms for vacancy concentrations of cV = 0.001 and 0.1. The results are compared with theories and Monte Carlo simulations from the literature. Substantial discrepancies with previous Monte Carlo studies are observed. It is concluded that the correlation factors given in the literature are systematically too high because the jump sequences in those calculations were too short.
Picosecond gain and saturation measurements in a KrF laser amplifier depumped by amplified spontaneous emission
Authors: Harvey E. C. , Hooker C. J. , Key M. H. , Kidd A. K. , Lister J. M. D. , Shaw M. J. , Leland W. T.
Published: July 2002

The input/output characteristic of a large aperture (270-mm diam) electron-beam-pumped KrF laser amplifier is obtained for pulses of 6- and 40-ps duration. The off-resonance absorption coefficient is estimated by measurement of loss at 268 nm. The gain-to-loss ratio is found to decrease from 8 to 6 as the specific pump rate is increased from 0.3 to 0.65 MW cm−3. Gain depumping due to amplified spontaneous emission (ASE) is treated by a simple 1D code and found to give good agreement with experiment. A 3D code incorporating wall reflections gives even better agreement. The spatial distribution of gain and ASE is recorded using visible and ultraviolet imaging.
Investigation of electron density and velocity distribution in high-pressure discharges for excimer laser pumping using laser Thomson scattering
Authors: Uchino K. , Kubo Y. , Muraoka K. , Sakoda T. , Yamakoshi H. , Kato M. , Takahashi A. , Maeda M.
Published: July 2002

Thomson scattering from plasmas in high-pressure discharges for rare-gas halide excimer laser pumping was observed using an yttrium-aluminum-garnet laser with a second harmonic generator, combined with a double-monochromator to reject large signal from Rayleigh scattering. The results showed the electron velocity distribution to be Maxwellian which was different from prediction of computer simulations, while variation of electron density and temperature with time and gas composition was consistent with results of computer simulations.
Characterization of sputtered yttria-stabilized zirconia thin film and its application to a metal-insulator-semiconductor structure
Authors: Miyahara Yuji
Published: July 2002

An rf-sputtered yttria-stabilized zirconia (YSZ) thin film was characterized as to its structural and electrical properties. Then a metal-insulator-semiconductor (MIS) structure incorporating it as a part of a multi-insulator was investigated particularly for use in a field-effect transistor (FET)-type oxygen sensor. The YSZ film deposited on a Si3N4 film was found to be a cubic structure based on x-ray diffraction and reflective high-energy electron diffraction analyses. As cracks were formed at 800 °C, annealing treatment of the film should be carried out below that temperature. The leakage current of the sputtered YSZ film was smaller than 2×10−7 A/cm2 in the applied voltage range 0–5 V, which was comparable to that of the calcia-stabilized zirconia film used for a potentiometric oxygen sensor. The dielectric constant of the sputtered YSZ film was 16±2 at 105 Hz. The minimum loss tangent was 0.01. The frequency dispersion of the dielectric constant and loss tangent were improved by annealing treatment at temperatures lower than 400 °C. The capacitance-voltage (C-V) characteristics of the MIS structure incorporating the YSZ film showed hysteresis and positive shifts of the flatband voltages as compared with those of the MIS structure without the YSZ film. The hysteresis was considered to be due to the movement of charged species such as oxygen ions and/or electrons in the YSZ film, which would cause an unstable response of the FET-type oxygen sensor.
A new theory of the plasma-filled diode
Authors: Kares Robert J. , Geary James L. , Grossmann John M.
Published: July 2002

The behavior of a planar plasma-filled diode (PFD) is examined in the limit in which the mass of the plasma ions is allowed to approach infinity. In this limit the plasma ions are immobilized and act as a fixed, spatially uniform background of positive charge. Using a one-dimensional, electrostatic particle-in-cell simulation of a PFD coupled to an external LC circuit, it is shown that the PFD still has a low-voltage conduction phase followed by a high-voltage opening phase in this limiting case. An analytic theory is developed that describes the operation of the diode in the immobile ion case, and this theory is shown to be in good agreement with the simulation results. A simple expression is also derived that gives an upper bound on the current that may be conducted before opening as a function of the density of immobile ions. Finally, it is shown that essentially the same process that determines the behavior of the PFD in the immobile ion limit also controls the operation of the PFD in the case where the ions have finite mass and are free to move under the influence of the diode electric fields.
Complexing in silicon induced by surface reactions: Electron paramagnetic resonance detection of a 6-platinum cluster
Authors: Höhne M. , Juda U.
Published: July 2002

Complexing of 5dn impurities from supersaturated solutions in silicon occurs during thermal processing at intermediate temperatures subsequent to fast or retarded quenching. Doping of silicon with 5dn transition-metal ions in a wet chlorine-containing atmosphere provides the formation of various complex defects, which differ from those formed after doping under protecting conditions. As an example a 6-platinum cluster of trigonal symmetry is presented. The analysis of electron-paramagnetic-resonance data uniquely reveals six geometrically equivalent platinum ions strongly interacting with probably two silicon atoms. A tentative model assumes the introduction of hydrogen during the high-temperature surface reaction. Passivation of the platinum acceptors might be the condition for the formation of the clusters at intermediate temperatures. The formation of similar clusters at appropriate temperatures would explain the higher thermal stability of high-temperature passivation, recently reported.
Low energy ion etching of aluminum oxide films and native aluminum oxide
Authors: Day M. E. , Delfino M. , Salimian S.
Published: July 2002

Aluminum oxide films were etched using low energy argon ions generated by a microwave electron cyclotron resonance (ECR) source argon plasma. The argon ion energies were controlled by biasing substrates placed on a 13.56 MHz capacitively coupled electrode. Reactively sputtered aluminum oxide films were used to study the relationship between the dc bias applied to these substrates and the etch rate of their films. In situ x-ray photoemission spectra of the Al 2p and O 1s transitions showed that the ECR plasma was effective in completely removing native aluminum oxide and adventitious hydrocarbon in 1 min at ion energies as low as 100 eV. This preclean technology did not change the dielectric breakdown distribution of antenna structures with 12-nm-thick gate oxide capacitors.
Metal-oxide-semiconductor field-effect transistor characteristics as influenced by carrier mobility variation along the channel
Authors: Pellegrini Gianfranco , Anderson Richard L.
Published: July 2002

The electrical characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) are calculated within the gradual channel approximation by taking into account that the carrier mobility varies with position along the channel from source to drain due to the variation of electric field in the channel normal to the gate and by considering velocity saturation effects. It is found that for a typical buried channel p-channel MOSFET the increased low-field mobility with position from source to drain more than offsets the decreased mobility due to carrier saturation effects. For short-channel devices saturation effects predominate.
Delta-H plot evaluation of remanence behavior in barium ferrite tapes and disks
Authors: Harrell J. W. , Richards David , Parker Martin R.
Published: July 2002

Remanence studies in recent years have used the characteristics of the Henkel plot and the delta-M plot in the interpretation of interaction field effects in particulate magnetic media. Studies of these two plots in ordered BaFe coatings, however, indicate that both plots give inadequate description of interaction field effects. An alternative to the delta-M plot is the delta-H plot in which, essentially, the (normalized) susceptibility curves for the isothermal remagnetization and dc demagnetization processes are differenced horizontally (rather than vertically as in the delta-M plot). It is shown here that the delta-H plot is a more direct way of examining the interaction fields. Simulated delta-H plots are presented based on a recent mean field model by Che and Bertram and are compared with measurements made on oriented BaFe coatings.