bluuebunny/crossref_metadata_2025 huggingface dataset:
BiPbSrCaCuO superconductors prepared by the multiple pressing and sintering process
Authors: Wang Weiguo , Zhou Meiling , Zuo Tieyong , Huang Jian , Cai Jianguo , Zhou Xianghua , Wei Qin
Published: July 2002

Pellets of bulk density 5.5 g/cm3, Tc of 107 K, and magnetic critical current of 104 A/cm2 (77 K, 3×4×10 mm3) were achieved under the multiple pressing and sintering process in the Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06Ox bulk samples. The powder x-ray diffraction shows the existence of the single high-Tc phase. Highly textured microstructures with strong (001) reflections were confirmed by x-ray diffraction on the surface of the pellets. The internal textured microstructures were obviously observed by a scanning electron microscope. No second stage was observed, and the superconducting volume fractions of the Meissner and shielding effects were more than 70% and 90%, respectively, as observed by dc magnetic susceptibility.
Collision-induced resonant amplification of electromagnetic waves by electrons in circular orbits
Authors: Felsteiner J. , Rosenberg A.
Published: July 2002

Electrons moving in circular orbits and colliding with gas atoms interact with a circular electromagnetic mode. Applying the linearized Boltzmann equation, the known nonresonant-stimulated bremsstrahlung and the near-resonance Landau effect are obtained. We predict that resonant electrons moving with angular velocity equal to the azimuthal phase velocity of the electromagnetic wave can exchange energy with the wave if the momentum transfer cross section for an electron-atom collision is velocity dependent. Amplification is obtained if the momentum transfer cross section has a positive slope.
Radiation from a disk and loop of charge in a cylindrical pipe with multiple step changes in wall radius
Authors: Pham Tan , Schill Robert A.
Published: July 2002

A theory is developed to model diffraction and Bremsstrahlung radiation from a loop and a disk of charge in a cylindrical pipe with multiple step changes in wall radius supporting all azimuthally symmetric transverse magnetic modes. The beam kinetics are assumed a priori. A correction in phase due to the abrupt change in beam velocity is incorporated at each step change in wall radius. A longitudinal coupling impedance based on energy and power considerations is employed. Loop charge radiation from cavity and collimator geometries is examined. By suitably choosing the loop charge radius, the energy backscattered in the beam tunnel problem can be minimized. The loading effects of the cavity onto the beam is sensitive to its length.
Temperature dependence of intersubband absorption in InGaAs/InAlAs multiquantum wells
Authors: Asai Hiromitsu , Kawamura Yuichi
Published: July 2002

Intersubband absorption in In0.53Ga0.47As/In0.52Al0.48As multiquantum wells is investigated at temperatures ranging from 5 to 300 K. Two absorption peaks from the first to the second subband E21 and from the second to the third E32 are observed at 300 K. As temperature is reduced to 5 K the E32 peak disappears, while the E21 absorption intensity remains almost constant. This temperature dependence can be explained by a theoretical calculation of electron distribution in each subband.
X-ray photoemission studies of reactions of arsine with platinum, palladium, and nickel metals and metal oxides
Authors: Cheung T. T. P.
Published: July 2002

Surfaces of platinum, palladium, and nickel metals and metal oxides treated with arsine at room temperature have been studied with x-ray photoemission spectroscopy. It is found that arsine decomposes readily on platinum, palladium, and nickel metal surfaces to form arsenic alloys. The resulting electronic structures of the treated surfaces are similar to those of the alloys of platinum, palladium, and nickel with sp metals: (1) reduction in the core level line-shape asymmetry, (2) narrowing of the valence d band and shifting of the band away from the Fermi level, (3) considerable shifts of the Auger lines to lower kinetic energies, and (4) reduction of the intensity of the core-level satellites and increase of their separation from the main peaks. At room temperature, arsine reacts with PtO2 and PdO, and reduces them to Pt-As and Pd-As alloys. However, NiO does not react with arsine.
Change in density of states in a resonant tunneling structure due to a scattering center in the well
Authors: Pandey L. N. , George Thomas F. , Rustgi M. L. , Sahu D.
Published: July 2002

The change in density of states and transmission resonance energy shifts have been calculated for a double-barrier single-quantum-well heterostructure by placing a scattering center in the middle of the well and representing it by (1) a thin barrier of variable height and fixed width or (2) a delta-function potential of variable strength. It is found that the energies of the even-resonance states shift towards the higher energies and states get broader as the height of the thin barrier increases. Similar behavior is observed for the delta-function potential as the strength of the delta-function potential increases. The peak value of the density of states versus energy plot are reduced for even resonance states due to the broadening of these states. The physical processes related with these behavior are discussed. Moreover, there are no changes in the odd-resonance states because of the nature of their wave functions in the well region of the resonant tunneling structure.
Influence of ball-forming conditions on the hardness of copper balls
Authors: Onuki J. , Koizumi M. , Suzuki H. , Araki I. , Iizuka T.
Published: July 2002

Effect of ball-forming conditions on the microstructure and the hardness of balls has been investigated in order to obtain soft balls suitable for a reliable ball-bonding process using copper wire. Copper balls formed in a room-temperature shield gas are found to be harder by 6 Hv than fully annealed copper wires of the same purity. This is caused by many dislocation loops which are generated in balls due to inclusion of gaseous impurities from the atmosphere and due to rapid solidification. On the other hand, copper balls formed in a shield gas heated above 175 °C are found to be softer by the amount of 4.5 Hv than balls formed in a room-temperature shield gas. This is due to disappearance of dislocation loops caused by the reduction of solidification rate and by elimination of gaseous impurities from the balls during solidification. Impurities, especially oxygen, are found to have a strong influence on the hardening of copper balls. From these results, we conclude that copper balls formed in a shield gas heated at 175 °C are suitable for mass production.
Sb doping and electrical characteristics of ultrathin SinGem superlattices
Authors: Presting H. , Kibbel H. , Kasper E. , Jorke H.
Published: July 2002

Ultrathin strained layer SinGem superlattices (SLS) with periods of a few atomic monolayers (n-ML Si, m-ML Ge; n+m≤20) have been grown by molecular-beam epitaxy. On a 〈100〉-oriented, n+ -doped silicon substrate a buffer with a Si1−yBGeyB alloy layer has been grown applying the concept of strain symmetrisation for the subsequent SLS layer. The thickness of the SLS layer was chosen to be around 200 nm. The buffer and SLS layer have been n doped by incorporation of an antimony adlayer deposited prior to growth. A thin (20 nm), p+ -doped (B, 6×1019 cm−3 ) Si1-ycGeyc contact layer was grown on top of the SLS layer. We have fabricated mesa photodiodes (AM=1.3×10−5 cm2) by standard semiconductor processing techniques and characterized them by current-voltage (I-V) and capacitance-voltage (C-V) measurements. We compare the Sb-dopant profiles of the buffer and the SLS layer measured by secondary-ion mass spectroscopy and by C-V analysis. Due to depletion of the Sb adlayer the SinGem SLS samples exhibit a declining Sb-dopant profile in the growth direction where the integral concentration of the SLS layer is found to depend on the n/m ratio and is up to 60% lower than a reference Si homodiode grown under the same conditions. The Si0.6Ge0.4 alloy sample shows a 2–3 times lower Sb concentration than the corresponding superlattice samples with the same integral Ge content (Si6Ge4 and Si12Ge8 SLS). We conclude that the Sb incorporation in a SLS can be used as a probe for the quality of the SLS growth.
High frequency noise and the diffusion coefficient of an AlGaAs/GaAs heterostructure device with a square potential well
Authors: van Rheenen Arthur D. , Bosman Gijs , Morkoç Hadis
Published: July 2002

Measurements of the diffusion coefficient in a square well heterostructure device are reported here. We present diffusion coefficient data as a function of frequency (0.5–12.0 GHz) and as a function of the electric field strength (F<3 kV/cm). Possible explanations of the observed trends, in terms of charge transfer mechanisms are tendered.
Thermal energy charge transfer in the Zn-Ar system
Authors: Tamir Y. , Shuker R.
Published: July 2002

Charge transfer was predicted in the Zn-Ar system. We have shown experimentally the validity of this prediction and that in fact Ar+ excites the Zn+ 2P3/2,1/2 states. Moreover, we find that this process preferentially excites the J= (1)/(2) state in this mixture. This is inferred from the behavior of the intensity ratio of the transition from these two states in correlation with the intensity of the 811.5-nm line of Ar i, where the latter is a measure for Ar ionization. Our model is based on the molecular states of Zn+Ar and Ar+Zn. The model displays a plausible curve crossings leading to the preference 2P1/2 excitation.
Temperature variation of elastic nonlinearity of NaCl
Authors: Jiang Wenhwa , Breazeale M. A.
Published: July 2002

The second harmonic generation technique has been used to evaluate combinations of third-order elastic constants (TOEC) of NaCl between room temperature and liquid-nitrogen temperature. TOEC data at room temperature are compared both with theory and other experimental results. The temperature variation of C111 is somewhat larger than predicted by theory. The temperature behavior suggests that a noncentral force and other exchange interactions predominate at 0 K.
An extreme ultraviolet spectroscopic diagnostic for fluctuations of electron density and temperature in tokamak plasmas
Authors: Huang L. K. , Finkenthal M. , Bhatia A. K. , Moos H. W.
Published: July 2002

Extreme ultraviolet (XUV) spectral line emissivities, originating from resonant transitions with upper states excited mainly from ground or both ground and lowest metastable states by electron collisional excitations of highly ionized intrinsic impurities in tokamak plasmas, are linear functions of both electron density and temperature fluctuations, ñe and T̃e, when the fluctuations are small and at high frequency. Correlations between measured intensities of spectral lines can thus provide localized measurements of the fluctuations. Newly developed XUV monochromators of high throughput enable accurate and fast diagnostics of ñe and T̃e for the study of the tokamak plasma microturbulence.
Phototransmission study of strained-layer InxGa1−x As/GaAs single quantum well structures
Authors: Yuan Shu , Wang Shumin , Qian Shixiong , Li Yufen , Andersson T. G. , Chen Z-G.
Published: July 2002

We report the phototransmission measurement of strained-layer InxGa1−x As/GaAs single quantum well structures at room temperature. The spectra obtained show distinct features of excitons in the single quantum wells. Fitting of the phototransmission spectrum indicates that the excitonic transition energy modulation is the main mechanism. The phototransmission can be used as a supplement to photoreflectance due to its sensitivity and convenience.
Numerical simulations of amorphous silicon thin-film transistors
Authors: Hack M. , Shaw J.
Published: July 2002

In this paper we present results of two-dimensional numerical simulations of low voltage, high voltage, and vertical amorphous silicon transistors. The model input consists of one realistic density of states spectrum for undoped amorphous silicon, and one self-consistent set of model parameters for all devices. Our results are in good agreement with experimental data, and this good fit is based on a new model for the source and drain contacts. Our approach is to treat these contacts as consisting of a fixed resistance in series with a small potential barrier whose height is modulated by current flow. Finally we show that relatively small changes in the density of deep localized states significantly alter the simulated device characteristics.
Generalization of Bragg reflector geometry: Application to (Ga,Al)As-(Ca,Sr)F2 reflectors
Authors: Fontaine C. , Requena P. , Muñoz-Yagüe A.
Published: July 2002

Bragg reflectors based on (Ca,Sr)F2 and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular-beam epitaxy were performed. Quarter-wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack-free surface morphology were obtained.
Superconducting HoBa2Cu3Ox films on Si without a buffer layer
Authors: Tsukamoto Akira , Imagawa Kazushige , Hiratani Masahiko , Aida Toshiyuki , Miyauchi Katsuki
Published: July 2002

HoBa2Cu3Ox thin films with a zero resistivity temperature of 63 K are successively grown on a Si substrate, at a substrate temperature as low as 550 °C using reactive evaporation with microwave-discharged oxygen plasma. The films are polycrystalline and consist of grains with radii of about 100 nm without microcracks. No significant interdiffusion between the substrate and film is observed by x-ray diffraction or secondary ion mass spectrometry depth profiles. However, a transmission electron microscopy study reveals that two kinds of amorphous interlayers are formed between the film and substrate: a Ba-excess diffusion layer and a silicon oxide layer.
X-ray reflectivity of an Sb delta-doping layer in silicon
Authors: Slijkerman W. F. J. , Gay J. M. , Zagwijn P. M. , van der Veen J. F. , Macdonald J. E. , Williams A. A. , Gravesteijn D. J. , van de Walle G. F. A.
Published: July 2002

X-ray reflectivity measurements were made on Si(001) crystals containing a delta-doping layer of Sb atoms a few nanometers below the surface. The measurements show the Sb doping profile to be abrupt towards the substrate side of the sample and to decay towards the surface with a characteristic decay length of 1.01 nm.
Dynamics of electrons accelerated by strong uniform or weakly inhomogeneous electric fields in the presence of phonons
Authors: Hinata Satoshi
Published: July 2002

We have analyzed the dynamics of electrons injected into the region of strong electric field and thermal phonons, as the electron kinetic energy is essential to the initiation of dielectric breakdown. For concreteness we discuss the situation expected in SiO2 which was explored in detail by the IBM group [M. V. Fischetti, Phys. Rev. Lett. 53, 1755 (1984); M. V. Fischetti, et al., Phys. Rev. 31, 8124 (1985)] with Monte Carlo simulation. We have obtained an analytic expression for the electron energy as a function of applied electric field under the collisional equilibrium approximation, which is basically the same for higher energies as that obtained by Fischetti [Phys. Rev. Lett. 53, 1755 (1984)] with a more elaborate Monte Carlo simulation. The difference exists in the lower-energy behavior. Our result shows a sharp energy drop for electric fields below 3.5 MV/cm and a plateau below 2 MV/cm. The former provides a reason for not observing electrons in experiments when the electric field is below about 3.5 MV/cm. We have extended the collisional equilibrium picture to weakly inhomogeneous electric fields to study ‘‘overshooting,’’ which is actually ‘‘undershooting’’ in the sense that the peak energy is less than the collisional equilibrium value for the local electric field.
Electric-field-enhanced dissociation of the hydrogen-Si donor complex in GaAs
Authors: Cho Hoon Young , Kim Eun Kyu , Min Suk-Ki , Chang K. J. , Lee Choochon
Published: July 2002

The passivation and dissociation process of the hydrogen-Si donor complex in plasma-hydrogenated GaAs was presented. The temperature dependent values of dissociation frequencies νd which the first-order kinetics permit, satisfy the relation νd=5.7×1013 exp(−1.79±0.05 eV/kT) s−1 for the no-biased anneals. During electric-field-enhanced anneal experiments, we confirm that no in-diffusion from the passivated region to the bulk is observed in the temperature ranges below 150 °C, and that there is a dissociation frequency region independent of the annealing temperature. Finally, from the electric field annealing experiment on the passivated donor in n-type GaAs, it is suggested that the hydrogen atom in Si-doped GaAs exposed to the plasma hydrogen is negatively charged with the gain of free electrons and passivates the Si donor, and also that the hydrogen atom or the electron of the hydrogen-Si donor complex can be easily released by the electric field.
Electron-beam confinement by rotational stabilization in a linear wiggler free electron laser
Authors: Friedland L. , Shefer R. E.
Published: July 2002

Finite radius electron-beam transport in a linear wiggler free-electron laser with a guide magnetic field is investigated. The addition of a guide magnetic field improves the beam confinement, but also leads to a detrimental drift in the direction transverse to the wiggler magnetic field. The introduction of a rotational transformation of the wiggler magnetic field is proposed to further improve the beam confinement. It is shown that the transformation results in a stable, uniform, solid body rotation of the beam provided (a) the guide field is larger than the amplitude of the wiggler field, (b) the electron drift velocity is much smaller than the rotation speed of the wiggler field as seen by the beam, and (c) the wiggler field rotates in the direction opposite to the direction of the electron gyromotion in the guide field. Theoretical predictions of the improvement of the radial beam transport with the introduction of the rotation of the wiggler field are confirmed in numerical simulations.
Theory of electrical characteristics for metal-oxide-insulator Schottky barrier and metal-insulator-metal structures
Authors: Gupta H. M. , Morais Marta B.
Published: July 2002

The metal-insulator or metal-amorphous semiconductor blocking contact is still not well understood. Here, the intimate metal-insulator and metal-oxide-insulator contact are discussed. Further, the steady-state characteristics of metal-oxide-insulator-metal structures are also discussed. Oxide is an insulator with wider energy band gap (about 50 Å thick). A uniform energetic distribution of impurities is considered in addition to impurities at a single energy level inside the surface charge region at the oxide-insulator interface. Analytical expressions are presented for electrical potential, field, thickness of the depletion region, capacitance, and charge accumulated in the surface charge region. The electrical characteristics are compared with reference to relative densities of two types of impurities. ln I is proportional to the square root of applied potential if energetically distributed impurities are relatively important. However, distribution of the electrical potential is quite complicated. In general energetically distributed impurities can considerably change the electrical characteristics of these structures.
The suppression by pressure of negative differential resistance in GaAs/GaAlAs double barrier structures
Authors: Pritchard R. , Austing D. G. , Klipstein P. C. , Roberts J. S. , Higgs A. W. , Smith G. W.
Published: July 2002

High-pressure measurements of thermionic emission (TE) and of resonant tunneling in Ga1−xAlxAs/GaAs double barrier structures are reported, where x=1 or 0.33. For x=1, TE in a structure with a very narrow well yields a direct measurement of ∼150 meV for the Γ-X barrier height, and a shift of ∼−11 meV/kbar. For a structure with a well width of ∼70 Å and barriers of ∼40 Å, negative differential resistance (NDR) is observed, which is suppressed at a pressure of ∼8 kbar, when the height of the Γ-X barrier is approximately equal to the confinement energy of the state in the well. For x=0.33, and in samples with spacer layers, the same criterion for suppression of the NDR applies as for x=1. When spacer layers are absent, anomalies occur in the variation of the first NDR resonance with pressure, and for sufficiently large samples, the threshold for loss of NDR is much lower than expected. The anomalous behavior is related to the higher concentration of impurities in the barriers. The low-pressure threshold of the anomaly, and the dependence of the anomaly on sample size, suggest that impurity correlation may play a significant role in the suppression of NDR. At low pressures, or in the absence of anomalies, the pressure dependence of the peak and valley currents of all resonances which are always in the range −1% to −3%/kbar, indicates that the Γ profile controls the tunneling, through the pressure dependence of the effective mass.
Simulation of domain structure for magnetic thin film in an applied field
Authors: Saka Chiaki , Shiiki Kazuo , Shinagawa Kiminari
Published: July 2002

Domain structures in an applied field are simulated by minimizing the total energy in two dimensions. Wall positions and magnetization directions in the applied field are determined mainly by the balance of magnetostatic energy Es and Zeeman energy Em. On the other hand, the number of domains is determined by the balance of anisotropy energy and wall energy. Using this calculation, a soft magnetic film of low aspect ratio, such as a magnetic head core, is analyzed in the applied field. It was found that the energies Es and Em are seemed to be determined by the film shape independently of the number of domains, and the ratio of Es to Em is about 1 to −2. Moreover, the change in domain structure induced by applied field agrees with observations using a Kerr microscope. By analyzing a trapezoidal film which is similar to the thin-film head core, we can obtain the angle of the film side surface whose domain structure is stable.
Operating conventional electronic devices in the noninstantaneous multiplication (amplification) regime
Authors: Jindal R. P.
Published: July 2002

One requirement for operating a device in the noninstantaneous multiplication mode is that its response to an incident photon is the generation of a pulse of constant current. This current is allowed to have a fluctuating duration and can exhibit full shot noise. It is shown that a majority of conventional current-to-current and voltage-to-current converting devices should be operable in the noninstantaneous mode. Ideal photoconductive detectors (current-to-current converters) operated in the conventional (temporally deterministic) mode are a factor of 2 below the ideal limit on the signal-to-noise ratio set by the shot noise of the input light signal. When operated in the noninstantaneous mode these devices can be made to approach this ideal limit. The issue of resettability, i.e., the guaranteed turn off of each pulse of constant current, is examined with the help of a specific detector structure. Junction field-effect transistors are presented as an example of voltage-to-current converting devices operated in the noninstantaneous mode. The consequent improvement in the noise performance is also quantified.
Epitaxial growth of bcc-Eu/Yb superlattices
Authors: Maeda Atsushi , Satake Tohru , Fujimori Toshinari , Kuroda Haruo
Published: July 2002

A bcc-Eu metal layer having a double-domain structure was grown by the molecular-beam epitaxy (MBE) technique on a cleaved NaCl (100) surface with the epitaxial relationship that Eu (110) [100] or [110] is parallel to NaCl (100) [100]. An Eu/Yb superlattice was successfully prepared by MBE on this Eu buffer layer at a growth temperature of 260 K. The Yb layers in the prepared superlattices were found to be in the bcc phase which is stable only at high temperatures above 1071 K. It was also shown that a bcc-Yb can be epitaxially grown on the bcc-Eu layer up to a thickness of 1500 Å.
Thermodynamic investigations of solid-state Si-metal interactions. II. General analysis of Si-metal binary systems
Authors: Gong S. F. , Hentzell H. T. G.
Published: July 2002

Silicides, amorphous alloys, and metal-induced crystallization of amorphous Si are commonly encountered in solid-state reactions between Si and metals. In order to investigate the possible correlations between these phenomena, a thermodynamic analysis was made on various binary systems consisting of Si and metals. It was revealed that (1) the capability of forming silicides between Si and a transition metal results from the largely negative heat of mixing in a certain medium composition range of the two elements; (2) amorphous Si-metal alloys may form not only in the systems which form silicides, but also in some systems which do not form stable silicides; and (3) the phenomenon of metal-induced crystallization of amorphous Si occurs in a Si-rich composition range of a binary system, which is attributed to the lowering of Si—Si bonding energy, owing to the incorporation of metal species. A model describing the phenomenon is developed.
Monte Carlo study of minority electronic transport in InGaAs: Effects of phonon mode splitting and dynamically screened electron-hole interactions
Authors: Joshi R. P. , Kriman A. M. , Ferry D. K.
Published: July 2002

We present an ensemble Monte Carlo simulation of electronic transport in p-type In0.53Ga0.47As. The effects of mixed phonon modes and of dynamically screened electron-hole scattering on the velocity-field characteristics are examined. Our results show that a two phonon model yields smaller velocities at low fields and higher values beyond the intervalley transfer threshold. The dynamic screening leads to a field dependent velocity enhancement at moderate carrier densities.
Double crystal x-ray analysis of strain distribution in rapid thermal annealed, S-implanted GaAs
Authors: Fatemi M. , Thompson P. E. , Chaudhuri J. , Shah S.
Published: July 2002

Double crystal x-ray analysis has been carried out on GaAs wafers implanted with 1.15 MeV sulfur ions at a dose of 5×1014/cm2, followed by rapid thermal anneal for 10 s at temperatures between 300 and 1100 °C. A systematic reduction of strain with increased annealing temperature has been observed, as measured from the separation between the peak of the unimplanted substrate and the major peak of the strained region. Calculations of strain distribution based on existing numerical models are correlated with implantation parameters using Pearson’s type-VI distribution functions. Strain reduction after a silicon nitride encapsulation process is found to be equivalent to that after a 300 °C, 10 s rapid thermal anneal (RTA). It is also found that strain relaxation by RTA is strongly dependent on both sample size and the annealing geometry.
Electro-optical properties of films consisting of nematic liquid crystals and connected polymer microspheres
Authors: Nomura Hideshi , Suzuki Sachio , Atarashi Yuji
Published: July 2002

Thin films composed of nematic liquid crystals in polymer matrices are promising materials for use in displays and light shutters. Light scattering in these films is controlled by applied electric fields. This paper describes films consisting of nematic liquid crystal, micrometer-size polymer microspheres, and polymer binders. The microspheres are connected by a small quantity of binders, and the gaps between the microspheres are filled with the nematic liquid crystal. These films were produced using several diameters of microspheres, and the relationship between the microsphere size and electro-optical properties was investigated.
Preparation and electrical properties of ε-Ti2N thin films
Authors: Igasaki Yasuhiro , Mitsuhashi Hiroji
Published: July 2002

An ε-Ti2N film nearly free from any other phase of the Ti-N compound was deposited and the temperature dependencies of the resistivity and the Hall coefficient of the film were measured. The resistivity data were analyzed in terms of the Bloch–Grüneisen equation. The characteristic temperature θ of the film was 410.8 K, independent of the temperature ranging from 4.2 to 300 K. From a Hall measurement it was determined that the conduction carriers in the ε-Ti2N were holelike over the temperature range from 77 to 300 K.
Axial modes of acoustically coupled surface acoustic wave Fabry–Perot resonators
Authors: Schwelb Otto
Published: July 2002

The distribution of resonant frequencies in single cavity and acoustically coupled surface acoustic wave grating resonators is investigated. The axial mode distribution is calculated using the transverse resonance method. The components of the resonator are represented by equivalent circuits whose parameters can be adjusted to conform to experimental values. Results showing the effect of cavity design parameters on the distribution of the resonant frequencies in resonators of bilaterally symmetric construction are presented.
Annealing characteristics and electrical properties of 1-MeV arsenic-ion-implanted layers in silicon
Authors: Inada T. , Nishida A. , Kanazawa M. , Hasebe H.
Published: July 2002

Arsenic ions have been implanted in (100)Si at an incident energy of 1 MeV to a dose of 1×1015/cm2. Rutherford backscattering measurements with a 1.5-MeV He-ion beam have shown that a buried amorphous layer is formed in the Si substrate which is implanted at a low ion-beam current of 0.8 μA and that considerable annealing occurs when implantation is carried out at a high ion-beam current of 2 μA. The implantation-induced amorphous layer recrystallizes after annealing above 550 °C, but a high density of lattice defects still remains in the substrate even after annealing at 1000 °C. Defect observations using a cross-sectional transmission electron microscope have revealed that those defects are located at the two depths corresponding to the initial transition regions where the crystallinity is changed from the amorphous to nonamorphized states in the substrate. In addition, secondary defects also exist in a particular region inside the initial buried amorphous layer. The recrystallization of the buried amorphous layer during post-implant annealing is initiated not only from the deeper part of the substrate but also from the nonamorphized surface layer. From a series of isothermal annealing studies, it has been shown that the recrystallization rates at 550 °C are 140 and 180 Å/min on the frontside and backside of the buried amorphous layer, respectively. Electrical profile measurements, using the differential Hall method, have shown that a highly doped, buried conductive layer with a peak carrier concentration of around 2×1019/cm3 can be formed by annealing above 800 °C.
Reply to the ‘‘Comment on: ‘The pinning force between a Bloch wall and a planar pinning site in MnAlC’ ’’
Authors: Chen X.
Published: July 2002

The boundary condition requiring continuity of (A/K)1/2 (∂θ/∂z) is discussed, where A and K are the exchange and anisotropy, respectively, θ is the spin orientation at the position z. This boundary condition is the result of the minimization of domain wall energy.
Electrical properties of SiInxPyOz-InSb metal-insulator-semiconductor structures
Authors: Hattori K. , Torii Y.
Published: July 2002

The electrical properties of n-type InSb metal-insulator-semiconductor (MIS) structures have been investigated. As gate insulators, SiInxPyOz layers are formed on InSb by a new method. In the method, an In-SiOx′ double layer is formed on the InSb (111)B surface by evaporation of SiO and In. Further, a Py′Oz′ layer is deposited on the double layer. The reaction between a Py′ Oz′ layer and In-SiOx′ double layer yields a SiInxPyOz layer. The SiInxPyOz layers exhibit high resistivities ρ, i.e., ρ≊6.5× 1015 Ω cm at 100 K and 1.0×1014 Ω cm at room temperature. The hysteresis in the capacitance-voltage (C-V) and conductance-voltage (G-V)curves of InSb MIS structures at 100 K is found to be less than 0.6 V and an injection type. The surface-state density in the MIS interface is evaluated by including the effects of the nonparabolicity of the conduction band and Fermi–Dirac statistics for electrons in InSb. A typical value of the minimum surface state density is observed as 8.3× 1011 cm−2 eV−1 at about 0.05 eV below the conduction-band edge. Further, the C-V characteristics of InSb MIS structures at room temperature are discussed by including the features of the narrow band-gap semiconductor.
Angular dependence of the upper critical field and the critical current density for Y1Ba2Cu3O7−δ films
Authors: Watanabe K. , Awaji S. , Kobayashi N. , Yamane H. , Hirai T. , Muto Y.
Published: July 2002

Resistive measurements for the angular dependence of both Bc2 and Jc were performed using high-Jc Y1Ba2Cu3O7−δ films prepared by chemical vapor deposition. The angular dependence of Bc2 was described by the anisotropic Ginsburg-Landau theory with different masses for in-plane and out-of-plane. We found that the angular dependence of Bc2 largely contributes to the anisotropic Jc on the basis of the flux pinning scaling law.
Anomalous low-frequency butterfly curves for subsidiary and ferromagnetic resonance overlap at 3 GHz
Authors: Cross R. W. , Patton C. E. , Srinivasan G. , Booth J. G. , Chen M.
Published: July 2002

Subsidiary absorption butterfly curves of spin-wave instability threshold versus static in-plane field have been obtained for yttrium iron garnet (YIG) thin films at 3 GHz. The butterfly curves have been found to be rather anomalous, typically displaying a pronounced dip and a very low minimum threshold. These anomalous features are attributed to the overlap of the subsidiary absorption field region with ferromagnetic resonance (FMR). First-order instability theory was extended to include the uniform mode response near FMR. The extended theory yields good fits to the data for reasonable values of the YIG FMR linewidths. The theoretical analysis also shows a predicted flip in the azimuthal propagation angle φk for the unstable spin waves in the region of FMR overlap. With increasing field, there are predicted discontinuous changes in φk from 90° to 0° and back to 90° in the region of FMR.
The four-level transition model and the Faraday effect in ferromagnetic media
Authors: Liu Gong-qiang , Zuo Wen-de , Le Zhi-qiang
Published: July 2002

In ferromagnetic media, besides originating from the splitting of the excited state resulting from the spin-orbit interaction, magneto-optical effects also arise from the splitting of the ground state caused by both the exchange interaction and the applied field. In view of the standpoint mentioned above, it is shown by calculation that the Faraday rotation θ depends linearly on magnetization M in both the regions of T≪Tc (Curie temperature) and of high temperature for the medium with high Tc, but nonlinearly on M and T in the usual temperature region between the above two regions.
Characterization of SiO2/Si heterostructures by soft x-ray reflection
Authors: Woronick S. C. , Ng W. , Król A. , Kao Y. H. , Arnold E.
Published: July 2002

Grazing incidence x-ray reflectivity has been used to characterize four as-grown SiO2/Si(100) heterostructures with SiO2 overlayer thicknesses ranging from about 126 to 1100 Å. Root-mean-square roughness at both the top surface and buried interface is determined, as is the (complex-valued) x-ray refractive index of the SiO2 heterostructure material for photons in the energy range 400–800 eV. Knowledge of the SiO2 and Si refractive indices allows the oxygen atomic scattering factor to be deduced at these energies. Evidence that one of the four thermally grown structures may consist of more than just a single homogeneous overlayer is also examined.
Hydrogen solubility in n-type silicon doped GaAs and its effects on the material electronic quality
Authors: Caglio N. , Constant E. , Pesant J. C. , Chevallier J.
Published: July 2002

Solubility of hydrogen in silicon doped GaAs has been investigated from deuterium diffusion experiments in buried silicon doped GaAs epilayers exposed to a deuterium plasma. The presence of silicon donors in the buried layer induces an increase of the solubility of hydrogen equal to the amount of active donors. Diffusion profiles after thermal annealing provide evidence that, in the buried doped layer, hydrogen is present at least in two forms: a mobile species, which is removed under annealing at 250 °C, 20 min, and a trapped form known to be Si-H complexes from infrared spectroscopic studies. The electron mobility of the annealed neutralized samples is systematically higher than in as-grown samples, for a given active donor concentration. For plasma conditions used for the fabrication of field effect transistors having a hydrogen neutralized active region, this holds true for buried layers protected by undoped GaAs cap layers as thin as 0.1 μm, then, the defects generated by the plasma are confined on a superficial layer less than 1000 Å.
Interpretation of transmission electron microscope images of amorphous silicon/germanium and silicon/iron multilayers
Authors: Donovan P. , George B. , Bruson A. , Dufour C. , Marchal G. , Mangin Ph.
Published: July 2002

We show that the observed contrast in transmission electron microscope images of multilayer specimens composed of amorphous materials can be understood in terms of the scattering of electrons passing through the material. This leads us to develop a simple method of analyzing the image contrast to give quantitative information about the thicknesses of individual layers, which cannot be obtained by any other technique. The results of this analysis for images of silicon/germanium and silicon/iron multilayers are in good agreement with the results of small-angle x-ray scattering and the readings of quartz thickness monitors during the deposition of the layers. The accuracy of the thickness measurements we obtain from transmission electron microscope images is 7% for the average layer thickness of a single component and 10% for the thickness of individual layers when the layer thickness is about 4 nm, which is comparable to the accuracy which can be attained for crystalline layers.
Stress analysis of elastically anisotropic bilayer structures
Authors: Jou Jwo-Huei , Hsu Li
Published: July 2002

In this paper, a newly developed model for analyzing stresses and curvatures in elastically anisotropic bilayer structures is presented. This model can be applied to bilayer structures composed of a single thin film that is deposited or grows on an elastically anisotropic substrate. The thin-film materials considered can be either elastically isotropic or anisotropic. According to this model, the Young’s modulus, Poisson’s ratio, and thermal-expansion coefficient of any given thin film cannot be determined independently by simply using a single elastically anisotropic substrate in a stress measurement without making additional assumptions. By using our model and with reasonable assumptions, more reasonable values of the mechanical constants and thermal-expansion coefficient of the aluminum thin film have been recalculated from the results of Janda [Thin Solid Films 112, 219 (1984)].
Donor-related deep levels in heavily Se-doped AlxGa1−xAs
Authors: Kajikawa Y.
Published: July 2002

The effects of donor-related deep levels on the doping characteristic and photoluminescence in Se-doped AlGaAs grown by metalorganic chemical vapor deposition have been studied. The net donor concentration has been observed to increase in proportion to doping in GaAs and Al0.4Ga0.6As, showing a cube-root dependence in Al0.1Ga0.9As in the high doping concentration range. In a photoluminescence study, the emission due to self-activated (SA) centers, which are complexes comprising a donor atom and a group-III vacancy, was observed in Al0.1Ga0.9As with a stronger intensity than in GaAs. It is therefore suggested that more serious compensation in Al0.1Ga0.9As than in GaAs by SA centers is responsible for the early beginning of the cube-root dependence in Al0.1Ga0.9As. In addition, the emission energy of SA centers was studied as a function of the carrier concentration; the observation of a Burstein–Moss shift in the SA emission energy reveals that it is due to a band-to-acceptor transition. In the case of Al0.4Ga0.6As, since no SA emission was observed, the linear increase in the net donor concentration up to high density has been interpreted as being the result of the absence of SA centers. The mechanism which suppresses the formation of SA centers in Al0.4Ga0.6As is discussed in conjunction with DX centers. A new luminescence band associated with DX centers was observed in Al0.4Ga0.6As; its emission mechanism is also discussed.
Microwave photoconductive mixing in n- and p-type compensated silicon
Authors: Giessinger E. R. , Braunstein R. , Dong S. , Martin B. G.
Published: July 2002

Low-temperature photoconductive mixing measurements have been performed on n- and p-type compensated Si at a microwave beat frequency of 253 MHz. The dependence of the transport parameters (electron-hole recombination lifetime and drift velocity) on temperature and electric field obtained from this experimental technique, are discussed. At high temperatures (T≥35 K for n-type and T≥60 K for p-type), the drift velocity is determined by neutral impurity and ionized impurity, and charge carrier-phonon scattering. In the carrier freeze-out regime (T≤35 K for n-type, T≤60 K for p-type) hopping charge transport is the dominant mechanism determining the drift velocity.
Comparison of pumping a cesium beam tube with D1 and D2 lines
Authors: Dimarcq N. , Giordano V. , Théobald G. , Cérez P.
Published: July 2002

The operation of a cesium beam tube optically pumped with cesium D1 and D2 lines is theoretically and experimentally investigated. In a single laser diode configuration using the D2 line, the most efficient excitation scheme is found to be the 3→3σ(D2) scheme leading to a clock signal-to-noise ratio equal to 15 000 in a one-hertz bandwidth. In the case of the D1 line, the predicted best excitation schemes are the 4→3π(D1) and the 4→3σ(D1) schemes. However, these two configurations lead to an extra fluorescence noise presumably due to unpumped atoms. The 3→4π(D1) scheme is experimentally found to be the best with S/N performances comparable to the 3→3σ(D2) configuration. Nevertheless, in the case of the 3→3σ(D2) scheme, optical pumping efficiency decreases when the magnetic field is too low whereas 3→4π(D1) features are independent of the magnetic-field amplitude. Moreover, the well-separated fluorescence lines in the case of the D1 line allow a more accurate locking of the laser frequency on the top of the fluorescence line than in the case of the D2 line. A perfectly symmetrical microwave spectrum results when the 3→4π(D1) scheme is used.
Calculation of the quasistationary field in conductors of discontinuous cross section
Authors: Baum E. , Mrozynski G.
Published: July 2002

The calculation of the quasistationary current distribution and the magnetic field strength in conductors of discontinuous cross section needs some numerical effort. In this article, a method is derived to calculate the resultant current distribution by integrating incremental field strength distributions due to infinitesimal currents fed to one of the conductors in the common part of the conductors cross section. The method is applied for a coaxial line of axial discontinuity to demonstrate the accuracy of the approximate solution compared to the exact field distribution which can be also given for the selected example.
Optimum performance considerations for a large-aperture average power solid-state laser amplifier
Authors: Sutton S. B. , Albrecht G. F.
Published: July 2002

The effect of a gas cooling system on the efficiency of an average-power solid-state disk laser amplifier is addressed. Such a configuration has application in solid-state fusion drivers. Analytical models are discussed that identify the important parameters in specifying an optimized laser and optimized cooling system. It is shown that the penalty that the cooling and conditioning system power requirements have on the overall laser system efficiency can be easily maintained below 10%, particularly for large-aperture systems.
Experimental study of a supersonic high repetition rate H2+F2 pumped HF laser
Authors: Waichman K. , Chuchem D. , Stricker J.
Published: July 2002

Experimental study of a supersonic pulsed, H2+F2 pumped HF laser is presented. The reactants are premixed and then expanded through a supersonic nozzle into the laser cavity, whereupon the reaction is initiated by an electrical discharge at a high repetition rate. The small-signal gain of some of the laser lines was measured as a function of the distance downstream from the initiation point and as a function of the reactants concentration. The spectral content of a laser pulse was analyzed and the induction times between the initiation and the onset of lasing on different laser lines were measured. The output power was measured as a function of the discharge voltage, the discharge pulse frequency and the reactants concentration. The results are compared with the lasing characteristics of a cold reaction, H2+SF6 -pumped laser.
Sidegating characteristics of AlGaAs/GaAs heterostructures with varied AlGaAs spacer layers
Authors: Gray M. L. , Yoder J. D. , Brotman A. D.
Published: July 2002

Sidegating characteristics of molecular-beam-epitaxially grown AlGaAs/GaAs heterostructure field-effect transistors were obtained from layer structures containing varied AlGaAs spacer layer thicknesses. It is demonstrated that the sidegating effects for these wafers can be related to the leakage currents measured at the sidegate electrodes. The leakage currents were determined primarily to be a function of the resistance created by the isolation implants between the sidegate electrode and the device. Additionally, the various AlGaAs spacer layer thicknesses permitted the influence of silicon diffusion on device properties to be observed. The experimental results are compared with theoretical calculations.
Electrical transport and optical properties of zirconium nitride/aluminum nitride multilayers
Authors: Meng W. J. , Morelli D. T. , Roessler D. M. , Heremans J.
Published: July 2002

We have synthesized zirconium nitride/aluminum nitride multilayered thin films with a reactive sputtering technique. The electrical transport and optical properties of these multilayers have been examined by resistivity, Hall effect, and near-normal incidence reflectance and transmittance measurements. We show the existence of a metal-to-insulator transition and strong increase of Hall coefficient at small wavelength of composition modulation. The optical response of the multilayers is systematically modified from the behavior of the individual constituents. The measured optical response is in qualitative agreement with a simple effective-medium theory.
Possibility of ac applications of high-T
c superconductors in a flux-flow state
Authors: Ando Yoichi , Akita Shirabe
Published: July 2002

For the ac applications of high-Tc superconductors, the possibility of a ‘‘flux-flow conductor’’ is proposed. The ac loss of a high-Tc superconductor in the flux-flow state is theoretically examined. Two applications, a power transmission cable and a winding of an ac coil, are considered. The ac loss of a ‘‘flux-flow superconducting cable’’ may become smaller than that of a ‘‘critical state cable’’ in ordinary conditions, because the upper critical fields of high-Tc oxides are large. On the other hand, the ac loss of a ‘‘flux-flow ac superconducting wire’’ becomes advantageous only in a limited condition, namely, high frequency, low current density, and low magnetic field.