bluuebunny/crossref_metadata_2025 huggingface dataset:
String structure over the Brownian bridge
Authors: Léandre Rémi
Published: July 2002

We give the definition of a line bundle over the Brownian bridge by using its section. This allows us to define a Hilbert space of sections of a line bundle over the Brownian bridge associated to the transgression of a representative of an element of H3(M;Z). We consider the case of a string structure over the Brownian bridge: this allows us to define a Hilbert space of spinor fields over the Brownian bridge, when the first Pontryaguin class of the spin bundle over the manifold is equal to 0.
Geometry, stochastic calculus, and quantum fields in a noncommutative space–time
Authors: Vilela Mendes R.
Published: July 2002

The algebras of nonrelativistic and of classical mechanics are unstable algebraic structures. Their deformation towards stable structures leads, respectively, to relativity and to quantum mechanics. Likewise, the combined relativistic quantum mechanics algebra is also unstable. Its stabilization requires the noncommutativity of the space–time coordinates and the existence of a fundamental length constant. The new relativistic quantum mechanics algebra has important consequences on the geometry of space–time, on quantum stochastic calculus, and on the construction of quantum fields. Some of these effects are studied in this paper.
Optical spectroscopy of disorder in molecular chains (
J
-aggregates)
Authors: Malyukin Yu. V. , Tovmachenko O. G. , Katrich G. S. , Kemnitz K.
Published: July 2002

The form of the exciton absorption band for 1D molecular chains and their luminescence are investigated in glass matrices of various composition and in Langmuir–Blodgett (LB) films under selective excitation. It is shown that the exciton absorption band for 1D chains is always asymmetric. The shape of the low-frequency edge of their absorption band changes from the Gaussian to the Lorentzian depending on the method of obtaining of 1D chains due to a change in the diagonal and off-diagonal disorder in molecular chains. Under selective excitation of 1D molecular chains, the effect of considerable luminescence band narrowing is not observed. This is associated with statistical properties of the exciton absorption band and with relaxation processes in the materials under investigation in the excited state.
Order breaking in Dean flow
Authors: Le Guer Yves , Peerhossaini Hassan
Published: July 2002

The idea of combining large vortical structures in the flow with the dynamical behavior of open systems to enhance heat transfer and mixing has led to the design and construction of an experimental apparatus to study order breaking in such systems. The apparatus consists of a succession of curved channels in which the curvature plane rotates 90° between each two adjacent curved elements. In this paper, the basic idea and the design concepts are described in detail. Some preliminary results are also presented.
The stability of imploding detonations in the geometrical shock dynamics (CCW) model
Authors: DeVore C. Richard , Oran Elaine S.
Published: July 2002

The stability of cylindrically and spherically imploding detonations is examined within the theoretical framework of geometrical shock dynamics. The linearized Chester–Chisnell–Whitham (CCW) equations describing the accelerating detonation wave are solved both analytically and numerically to track the evolution of the distorted wave front. As is the case for the corresponding nonreactive shock problem, for harmonic mode numbers greater than unity the perturbation amplitudes decrease as the implosion proceeds, but not as rapidly as the implosion radius itself. Thus, the detonation is relatively unstable in this model, and indeed is more unstable than the imploding shock of the same initial strength. The latter result is due primarily to the slower acceleration of the detonation wave as it implodes, relative to the nonreactive shock wave.
Vorticity amplification and annihilation in a potential vortex
Authors: Williams Marc H.
Published: July 2002

An analytical solution is given that describes the transient growth and decay of an axial disturbance in a line vortex flow. The solution serves two functions. First, it illustrates the essential mechanisms whereby vorticity is amplified by swirl and annihilated by viscous diffusion. Second, it provides a nontrivial test case, involving significant small-scale structure, for numerical solutions of the general incompressible Navier–Stokes equations at high Reynolds numbers.
Gyrokinetic theory of perpendicular cyclotron resonance in a nonuniformly magnetized plasma
Authors: Lashmore-Davies C. N. , Dendy R. O.
Published: July 2002

The extension of gyrokinetic theory to arbitrary frequencies by Chen and Tsai [Phys. Fluids 26, 141 (1983); Plasma Phys. 25, 349 (1983)] is used to study cyclotron absorption in a straight magnetic field with a perpendicular, linear gradient in strength. The analysis includes the effects of magnetic field variation across the Larmor orbit and is restricted to propagation perpendicular to the field. It yields the following results for propagation into the field gradient. The standard optical depths for the fundamental O-mode and second harmonic X-mode resonances are obtained from the absorption profiles given in this paper, without invoking relativistic mass variation [see also Antonsen and Manheimer, Phys. Fluids 21, 2295 (1978)]. The compressional Alfvén wave is shown to undergo perpendicular cyclotron damping at the fundamental minority resonance in a two-ion species plasma and at second harmonic resonance in a single-ion species plasma. Ion Bernstein waves propagating into the second harmonic resonance are no longer unattenuated, but are increasingly damped as they approach the resonance. It is shown how the kinetic power flow affects absorption profiles, yielding information previously obtainable only from full-wave theory. In all cases, the perpendicular cyclotron damping arises from the inclusion of magnetic field variation across the Larmor orbit.
The Bohm criterion and the field singularity at the sheath edge
Authors: Riemann K.-U.
Published: July 2002

In the asymptotic limit of a small Debye length (λD→0) the analysis of the plasma boundary layer leads to a two-scale problem of the space-charge sheath and the quasineutral presheath. Usually the presheath solution ends at the sheath edge with a field singularity indicating the scale transition in the potential variation. Recently, two special presheath solutions were published in which this typical field singularity is missing [Phys. Fluids 23, 803 (1980); Phys. Fluids 31, 1748 (1988)]. In this Brief Communication a kinetic investigation of the plasma sheath transition under quite general conditions is presented. It is shown that the (generalized) Bohm criterion is fulfilled with the equality sign. A sheath edge without field singularity is possible only for a few special cases.
Status of global energy confinement studies
Authors: Kaye S. M. , Barnes Cris W. , Bell M. G. , DeBoo J. C. , Greenwald M. , Riedel K. , Sigmar D. , Uckan N. , Waltz R.
Published: July 2002

Empirical scaling expressions, reflecting the parametric dependence of the L-mode energy confinement time, have been used not only as benchmarks for tokamak operation and theories of energy transport, but for predicting the performance of proposed tokamak devices. Several scaling expressions based on data from small and medium sized devices have done well in predicting performance in larger devices, although great uncertainty exists in extrapolating yet further, into the ignition regime. Several approaches exist for developing higher confidence scaling expressions. These include reducing the statistical uncertainty by identifying and filling in gaps in the present database, making use of more sophisticated statistical techniques, and developing scalings for confinement regimes within which future devices will operate. Confidence in the scaling expressions will be increased still further if the expressions can be more directly tied to transport physics theory. This can be done through the use of dimensionless parameters, by better describing the edge and core confinement regimes separately, and by incorporating transport models directly into the scaling expressions.
Excitation of strong Langmuir turbulence in the ionosphere: Comparison of theory and observations*
Authors: DuBois D. F. , Hansen Alfred , Rose Harvey A. , Russell David
Published: July 2002

The predictions of models of strong Langmuir turbulence (SLT) are compared with recent space- and time-resolved radar observations of the power spectra of turbulence induced in the ionosphere by powerful high-frequency (HF) waves. Distinct signatures of caviton dynamics, not predicted by the weak turbulence approximation, are seen in the observations. An improved model of the low-frequency fluctuations for equal electron and ion temperatures is presented as well as a discussion of density profile modification by the induced turbulence.
Relativistic backward-wave oscillators operating near cyclotron resonance
Authors: Vlasov A. , Nusinovich G. , Levush B. , Bromborsky A. , Lou W. , Carmel Y.
Published: July 2002

Microwave sources based on backward-wave oscillators (BWO’s) driven by relativistic electron beams are capable of producing high-power coherent radiation in the cm and mm wavelength region. When the axial magnetic field used in these devices to confine the electron beam satisfies the condition of cyclotron resonance there is a significant modification in the behavior of BWO due to beam coupling to cyclotron modes. In this paper a time-dependent, self-consistent theory of BWO’s is developed, taking into account a possible cyclotron interaction. The analysis of the system near the cyclotron resonance yields the power drop due to the cyclotron absorption effect observed in many BWO experiments. In addition, the theory predicts that there exists a region of magnetic field strength, where an increase in power and efficiency is possible. Depending on the value of the magnetic field and beam coupling to cyclotron mode various regimes of BWO operation are possible, including stable single-frequency oscillations, self-modulation, and a succession of microwave bursts.
Microwave radiation by a relativistic electron beam propagation through low-pressure air
Authors: Jordan S. , Baranga A. Ben-Amar , Benford G. , Tzach D. , Kato K.
Published: July 2002

Intense relativistic electron beams fired into air at varying pressures display a wide range of microwave signatures. These experiments held beam current, energy, and pulse length constant while varying gas pressure. Our observing window is 10 to 40 GHz. At low pressures (<10 mTorr) exponential spectra result, consistent with beam reflexing or virtual cathode oscillations. Above 20 mTorr the spectrum flattens and suggests collective emission at the beam-generated plasma frequencies. Power falls linearly with pressure above 20 mTorr, until electron-Neutral collisions damp the emission at a few Torr. However, weak 10 GHz emission appears at full atmospheric pressure.
Effects of trapped alpha particles on ballooning modes in tokamaks
Authors: Spong D. A. , Sigmar D. J. , Cooper W. Anthony , Hastings D. E. , Tsang Kang T.
Published: July 2002

The effects of a trapped, precessing alpha particle population on ballooning modes are examined for a large aspect ratio, shifted circular flux surface tokamak equilibrium. The alphas are modeled in the deeply trapped limit and with a Maxwellian distribution in energy. The resulting kinetic ballooning equation is solved numerically, and the dependence of the eigenvalues and stability boundaries on shear, background pressure gradient, and ratio of hot-to-background tempera- tures (and densities) is investigated. In the low-frequency regime (ω ≪ ωdH =alpha precessional drift frequency), the alpha component has a stabilizing influence, while in the intermediate frequency range (ω≲ωdH) the alphas destabilize ballooning modes through interaction with the trapped particle precessional drift resonance. Parameter ranges which should be typical of alpha production in near term tokamak devices such as the Tokamak Fusion Test Reactor (TFTR) [Phys. Rev. Lett. 52, 1492 (1984)] are considered.
Spontaneous thermocapillary interaction of drops, bubbles and particles: Unsteady convective effects at low Peclet numbers
Authors: Lavrenteva O. M. , Leshansky A. M. , Nir A.
Published: July 2002

Mass and heat transfer between two adjacent droplets and the surrounding viscous fluid induce local variations in the surface properties of the drops. These may result in a self-induced surface flow and a subsequent motion of the droplets toward or away from each other. Previous studies of this spontaneous thermocapillary interaction were conducted under the limiting assumptions that inertia, convective effects, and interfacial deformation were negligible. In the present paper the effect of convective transport on the spontaneous interaction of droplets at small nonzero Peclet numbers is examined. It is shown that at large separation distances the motion maintains its quasi-steady nature and the correction to the approach velocity is of O(Pe). When the droplets are at closer proximity the temporal changes of the domain are dominant. They result in the appearance of a Basset type history term in the expansion of concentration field and, hence, in the force balance equation. The correction to the approach velocity is of O(Pe1/2) and it depends on the initial position and the evolution in time of the interaction process.
Recombination lifetime of carriers in GaAs-GaAlAs quantum wells near room temperature
Authors: Arakawa Yasuhiko , Sakaki Hiroyuki , Nishioka Masao , Yoshino Junji , Kamiya Takeshi
Published: July 2002

The lifetime τ of carriers in undoped GaAs-GaAlAs quantum well structures was studied at room temperature by using the photoluminescence phase shift method. We have found that τ is inversely proportional to the carrier concentration under the excitation levels of 1016–1018 cm−3. The comparison of these results with both the theory of band-to-band recombination and the measured dependence of τ on the carrier concentration at 77 K suggests that the carrier recombination near room temperature is dominated by this band-to-band recombination process. We also discussed the dependence of τ on the quantum well thickness.
Measurement of the band gap of GexSi1−x/Si strained-layer heterostructures
Authors: Lang D. V. , People R. , Bean J. C. , Sergent A. M.
Published: July 2002

We have used photocurrent spectroscopy to measure the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy. A dramatic lowering of the indirect band gap, relative to that of unstrained bulk Ge-Si alloys, is observed. Our results for 0≤x≤0.7 are in remarkably good agreement with recent calculations of the effects of misfit strain on the band edges of coherently strained Ge-Si heterostructures. At x=0.6, the gap is lower than that of pure Ge.
Antiphase disorder in epitaxial GaAs films grown on CaxSr1−xF2 (100) with higher crystallographic symmetry
Authors: Tsutsui Kazuo , Ishiwara Hiroshi , Furukawa Seijiro
Published: July 2002

Antiphase disorder in the top layer of GaAs/Ca0.5Sr0.5F2/GaAs(100) semiconductor-on-insulator structure was revealed by preferential chemical etching. The domains were rotated by 90° with respect to each other on the (100) surface. The origin of this antiphase disorder is considered to be the growth of the twofold symmetrical crystal of GaAs(100) on the fourfold symmetrical crystal of CaxSr1−xF2(100).
One-dimensional transport in quantum well wire-high electron mobility transistor
Authors: Yuh Perng-fei , Wang K. L.
Published: July 2002

A novel one-dimensional electron gas field-effect transistor (FET) is proposed with the advantages of higher electron mobility and higher carrier concentration than conventional two-dimensional electron gas FET. The FET structure, device operation, and the low-field mobility of impurity scattering, which takes the screening effect into account, are discussed.
Detection of phonons with a scanning tunneling microscope
Authors: Smith Douglas P. E. , Binnig Gerd , Quate Calvin F.
Published: July 2002

A well defined spectrum of peaks in d2I/dV2 vs V has been obtained with a tunneling microscope immersed in liquid helium. The positions of the peaks correspond closely to the energies of the phonons of the graphite sample and the tungsten tip. We propose that electrons coupling to the bulk phonons near the tip to sample gap cause the observed increases in the tunneling conductance. Spectroscopic imaging at a phonon energy shows spatial variations of the vibrational spectra on an atomic scale.
Crystal structure of sputter-synthesized CoNx thin films
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

This letter discusses the synthesis of CoNx films using rf diode reactive sputtering. It describes the properties of crystal structures in CoNx thin films and in particular, the post-annealing effects on the crystal structures of CoNx. The CoNx films have the crystal structures of ε-Co(hcp), α-Co(fcc), α′-Co(fcc) as a superstructure of α-Co, γ-Co3N(hcp), and δ-Co2N(orthorhombic). The crystal structures have topotaxial relationships with each other, and exist in a wider composition range than in bulk.
Photoassisted oxidation of amorphous SiOx
Authors: Devine R. A. B. , Auvert G.
Published: July 2002

The oxidation in air of substoichiometric films of SiOx by scanned, cw laser irradiation at 500 nm has been studied as a function of incident power density up to a maximum of 5.3 MW/cm2. Results obtained on substrates having widely different thermal conductivities suggest that the oxidation is thermally stimulated. Observed Auger electron spectra and measured refractive indices in oxidized films are characteristic of amorphous SiO2.
Lateral solid phase epitaxy in selectively P-doped amorphous Si films
Authors: Ishiwara Hiroshi , Tanaka Makoto , Furukawa Seijiro
Published: July 2002

A selective doping method of P atoms is proposed in lateral solid phase epitaxy (L-SPE) of amorphous Si films, in which L-SPE mainly proceeds along the P-doped regions and active devices are fabricated in the undoped regions. It was found that diffusion of P atoms into the undoped region was negligible during L-SPE growth at 600 °C for about 20 h. Usefulness of this method was demonstrated by fabricating metal-oxide-semiconductor field-effect transistors in the films, in which the P-doped regions were used as the source and drain regions and the undoped region was used as a channel between them.
Exact analytical solution to diffusion equation for ion-implanted dopant profile evolution during annealing
Authors: Moroi D. S. , Hemenger P. M.
Published: July 2002

Exact solution in analytical form to the dopant diffusion equation for an arbitrary initial implanted profile is obtained with a judicious choice of variables. The diffusivity can be an arbitrary function of the dopant concentration and the temperature of a sample, provided only that their gradients at the front surface of an ion-implanted semi-infinite semiconductor wafer are zero. As an example, we derive a closed-form expression for the annealed concentration profile for the special case in which the diffusivity is a product of a certain power of the concentration and an arbitrary function of the temperature, the initial dopant concentration profile is a truncated Gaussian, and the temperature dependent part of the diffusivity is initially a Gaussian. The present calculation is a generalization of the data fitting analysis of ion-implanted dopant profile evolution during annealing by R. Ghez, A. S. Oehrlein, T. O. Sedgwick, F. F. Morehead, and Y. H. Lee [Appl. Phys. Lett. 45, 881 (1984)].
dc characterization of the AlGaAs/GaAs tunneling emitter bipolar transistor
Authors: Najjar F. E. , Radulescu D. C. , Chen Y.-K. , Wicks G. W. , Tasker P. J. , Eastman L. F.
Published: July 2002

AlGaAs/GaAs tunneling emitter bipolar transistors (TEBT’s), grown by molecular beam epitaxy, have been fabricated. Device structures with two different tunneling barrier Al mole fractions and each for two different barrier thicknesses were characterized at room temperature. A differential current gain of 410 was achieved using a single 50 Å AlAs tunneling barrier. Devices with either thinner barriers (20 Å) or Al0.38Ga0.62As barriers had lower gains. Al0.24Ga0.76As/GaAs heterojunction bipolar transistors and GaAs homojunction bipolar transistors without tunneling barriers were also fabricated and characterized, for comparison. The performance of the homojunction devices was improved in all cases by inserting the tunneling barrier. The variations of the base and collector currents were measured for all devices and, for the TEBT’s they showed a functional dependence on the interfacial barrier Al mole fraction and thickness, which was attributed to carrier tunneling through the barrier. Furthermore, the above characteristics exhibit a clear electron-to-hole preferential tunneling.
Interactions of amorphous TaxCu1−x (x=0.93 and 0.80) alloy films with Au overlayers and GaAs substrates
Authors: Oh Jae E. , Woollam John A. , Pouch John J.
Published: July 2002

Amorphous Ta93Cu7 and Ta80Cu20 alloy films are prepared by co-sputtering of pure Ta and pure Cu targets with a rotating sample holder table. To investigate the possible application of these materials as diffusion barriers for the Au-GaAs system, vacuum annealings are made in the temperature range from 200 to 800 °C. Resistivity change, x-ray diffraction, and Auger electron spectroscopy measurements are performed to find the chemical and metallurgical stabilities of these materials in this system. The reaction temperature for TaxCu1−x in contact with GaAs lies between 500 and 700 °C. For Au in contact with TaxCu1−x the reaction occurs at about 600 °C. Amorphous Ta93Cu7 shows different interdiffusion characteristics with surrounding elements than does Ta80Cu20.
GaAs/AlGaAs distributed feedback transverse junction stripe laser grown by molecular beam epitaxy
Authors: Mitsunaga K. , Noda S. , Kojima K. , Kameya M. , Kyuma K. , Hamanaka K. , Nakayama T.
Published: July 2002

GaAs/AlGaAs transverse junction stripe lasers with a distributed feedback structure were fabricated. The cw threshold current was 27 mA at 20 °C. The laser operated in a pure single longitudinal mode at the wavelength of 867 nm.
Inclined epitaxy of (411) beta silicon carbide on (511) silicon by chemical vapor deposition
Authors: Shigeta Mitsuhiro , Nakanishi Kenji , Fujii Yoshihisa , Furukawa Katsuki , Hatano Akitsugu , Uemoto Atsuko , Suzuki Akira , Nakajima Shigeo
Published: July 2002

Epitaxial growth of β-SiC on Si(511) substrates has been carried out. Single-crystalline β-SiC films without warpage and cracking are grown by chemical vapor deposition. The epitaxial orientation of the film is determined using x-ray precession camera. The orientation is inclined as SiC(411)//Si(511) coincident with the [011̄] axis, which should be compared with the parallel epitaxial growth on Si(100) or Si(111).
Technique for the direct synthesis and growth of indium phosphide by the liquid phosphorus encapsulated Czochralski method
Authors: Inada Tomoki , Fujii Takashi , Eguchi Minoru , Fukuda Tsuguo
Published: July 2002

The direct synthesis and growth of InP have been successfully performed by the newly developed liquid P encapsulated Czochralski technique. We have developed a way to use liquid P both as a source element for the synthesis instead of P gas, and also as an ‘‘encapsulant’’ for the Czochralski growth instead of B2O3. The existence of two distinct layers, liquid P and molten InP, has been discovered during the process. Grown single crystals showed a carrier concentration of as low as 5×1015 cm−3.
Magnetotransport and luminescence measurements in an n-type selectively doped InGaAs/GaAs strained quantum well structure
Authors: Fritz I. J. , Schirber J. E. , Jones E. D. , Drummond T. J. , Dawson L. R.
Published: July 2002

A selectively doped, n-type, single strained quantum well (SSQW) structure, consisting of an 8-nm-thick In0.25Ga0.75As layer sandwiched between thick GaAs layers, has been grown by molecular beam epitaxy. Low-field Hall-effect measurements from 4 to 300 K and field-dependent magnetotransport measurements at 4 K show that conduction through the doped GaAs layers competes with conduction from the two-dimensional electron gas confined by the InGaAs quantum well. Photoluminescence measurements at 4 K yield a band-gap energy of 1.30 eV and confirm the transport measurement of carrier density in the InGaAs conducting channel. Analysis of the parallel-conduction process yields channel carrier density and mobility which are consistent with data on strained-layer superlattices (SLS’s) not exhibiting parallel conduction. Comparison of the SSQW and SLS results demonstrates that heavily doped SSQW structures require narrow doping spikes to avoid parasitic current paths.
Above barrier doublets in GaAs/AlxGa1−xAs superlattices
Authors: Song J. J. , Yoon Y. S. , Jung P. S. , Fedotowsky A. , Schulman J. N. , Tu C. W. , Brown J. M. , Huang D. , Morkoç H.
Published: July 2002

Doublets from optical transitions with energies greater than the barrier energy gap were observed by photoluminescence excitation spectroscopy in a series of GaAs/AlxGa1−xAs superlattices. The well width and the aluminum concentration in the barrier regions were fixed at 150 Å and 22%, respectively. The barrier widths ranged from 70 to 180 Å. The doublets arise from transitions between the first unconfined heavy-hole and conduction subbands. The separation of the doublet is found to be a sensitive function of the barrier width. It corresponds to the energy difference between the transition at the Brillouin zone center and at the Brillouin zone boundary along the superlattice growth direction. Good agreement was found between the experimental data and theoretical calculations. The sensitivity of the energy splitting to the width of the barrier provides a useful analytical tool in determining this quantity, in much the same way that the confined transition energies relate to the well width.
Mobility degradation in a quantum well heterostructure of a GaAs/AlGaAs prototype
Authors: Arora Vijay K. , Mui David S. L. , Morkoç H.
Published: July 2002

Mobility degradation of a quasi-two-dimensional electron gas in a high electric field as shown to arise from the asymmetry in the distribution function of electrons. The critical field for the onset of appreciable mobility degradation is given by ε*=kBT/el=vsat/2μ0, where T is the lattice temperature, l the mean free path, μ0 the low field ohmic mobility, and vsat the saturation velocity. High mobility materials are vulnerable to mobility degradation particularly at low temperature. The effective electron temperature in a protruded distribution undergoes a transition from quadratic to linear behavior as the electric field is increased. This behavior is consistent with the most recent experimentally observed behavior of GaAs/AlGaAs heterostructures and can be usefully applied to the design of devices operating at high electric field.
New insights on nucleation of tungsten on insulators during selective chemical vapor deposition
Authors: Wilson R. H. , Williams A. G.
Published: July 2002

Selective deposition of tungsten on metals and silicon in the presence of insulators is important in several very large scale integrated circuit applications. The results of experiments investigating this selectivity are reported. The influence of the total area and composition of the selective growth surface on the nucleation of tungsten on adjacent insulators are illustrated. Specifically, nucleation is shown to occur preferentially in close proximity to the area of tungsten growth. The extent of nucleation on silicon dioxide compared to silicon nitride or phosphorus-doped glass is dependent on the composition of the surface on which the initial selective tungsten growth occurs. The qualitative observations presented here form the basis for further quantitative investigations.
Observation of enhanced laser emission and new laser transitions in triple cascade operation of an optically pumped cw HCOOH submillimeter laser
Authors: Stimson P. A. , James B. W. , Falconer I. S. , Whitbourn L. B. , Macfarlane J. C.
Published: July 2002

We report an investigation of the enhancement of the output power and the observation of new cw lasing transitions for an optically pumped formic acid laser when the resonator length is adjusted so that it is simultaneously resonant for adjacent rotational cascade transitions. Cascade operation was found to be a particularly useful technique for increasing the power of the second transition of a cascade sequence. New cw transitions were observed at 418 μm (the third member of the 394 μm, 406 μm cascade), 447 μm (the third member of the 419 μm, 432 μm cascade), and 460 μm (the third member of the 433 μm, 446 μm cascade).
Phase conjugation of mode scrambled optical beams: Application to spatial recovery and interbeam temporal information exchange
Authors: Yahalom Ram , Kyuma Kazuo , Yariv Amnon
Published: July 2002

Coupling of temporal information between two beams is demonstrated using a combination of a multimode fiber and a photorefractive passive phase conjugation mirror. It is shown that the polarization and spatial properties are fully recovered but temporal information is exchanged. The theoretical explanation for these phenomena and possible applications are discussed.
Electrical properties of thermally stable LaB6/GaAs Schottky diodes
Authors: Uchida Yoko , Yokotsuka Tatsuo , Nakashima Hisao , Takatani Shinichiro
Published: July 2002

Electrical properties of LaB6/GaAs(001) Schottky diodes have been studied by current-voltage measurements. The diodes were made by depositing LaB6 on chemically etched GaAs and molecular beam epitaxy prepared GaAs-c(4×4) surfaces by electron beam evaporation. The barrier height and ideality factor show appropriate values for metal-semiconductor field-effect-semiconductor application and do not change much by high-temperature annealing. These results provide firm evidence that LaB6 is a very promising candidate for self-aligned gate material of GaAs integrated circuits.
Measurement of the ZnSe:MnSe:ZnSe heterojunction valence-band discontinuities
Authors: Asonen H. , Lilja J. , Vuoristo A. , Ishiko M. , Pessa M.
Published: July 2002

UV-photoemission spectroscopy was used to measure directly the valence-band discontinuity ΔEv for both sides of a MnSe layer which was sandwiched between two ZnSe layers by the molecular beam epitaxy method. ΔEv is 0.16±0.05 eV for each interface; the valence-band edge Emaxv of the wider gap MnSe semiconductor lies within the ZnSe gap. The interface-pinning position of the Fermi level appears at 1.74 eV above Emaxv of ZnSe. It is concluded that interfacial electrostatic dipoles are small compared to the observed shift in Emaxv of MnSe, which lends a qualitative support to Tersoff’s model [Phys. Rev. Lett. 52, 465 (1984); Phys. Rev. B 30, 4874 (1984)] of heterojunction band offsets.
Phase-locked operation of coupled pairs of grating-surface-emitting diode lasers
Authors: Hammer J. M. , Carlson N. W. , Evans G. A. , Lurie M. , Palfrey S. L. , Kaiser C. J. , Harvey M. G. , James E. A. , Kirk J. B. , Elia F. R.
Published: July 2002

Grating-surface emission from phase-locked monolithic pairs of grating-surface-emitting diode lasers has been observed for the first time. Near-diffraction-limited far fields of 0.06°, spectra and power versus current plots of the coherent emission from the three second-order distributed Bragg reflectors which form the laser cavity for two collinear gain sections are presented. The results suggest that linear arrays of grating-surface emitters can be formed by connecting additional gain-grating sections in series.
Grain growth observation of 〈100〉 textured germanium film by transmission electron microscopy
Authors: Ogura Atushi , Terao Hiroshi
Published: July 2002

Grain growth of 〈100〉 textured Ge films on amorphous SiO2 substrates during 900 °C isothermal annealing was observed by transmission electron microscopy. An rf sputtering technique was used to deposit the films. By using initially 〈100〉 textured film, grain growth (∼1.5 μm diameter) occurs and is enhanced (∼2 μm diameter) by square-wave-shape grooves fabricated on a SiO2 surface, although initial films are relatively thick (0.6 μm). On the other hand, this grooving edge also has an effect of interrupting the grain growth. These grain growths can be explained by the minimization of the energy required for grain rotation (rotational energy) during grain coalescence.
Rapid thermal processing to improve the epitaxy of (100) silicon on (11̄02) sapphire
Authors: Pfeiffer Loren , Phillips Julia M. , Luther K. E. , West K. W. , Batstone J. L. , Stevie F. A. , Maurits J. E. A.
Published: July 2002

The heteroepitaxial quality of (100) Si films on (11̄02) sapphire substrates (SOS) as measured by Rutherford backscattering (RBS) and x-ray pole figure analysis is improved by a rapid thermal anneal (RTA) after deposition which brings the Si temperature above 1350 °C for at least several seconds. For a 6000-Å (100) SOS film the (100) aligned to random RBS yield improves from 10% and 54% at the front and back interfaces, to as low as 3.2% and 13% after the RTA. The microtwin volume shows a corresponding decrease to under 1% from the as-grown value of 2.7%. A model based on isothermal solid phase epitaxial regrowth from the untwinned material near the front surface is proposed to account for these results.
Temporal evolutions of frequency resolved radiations from a Raman regime free-electron laser
Authors: Ohigashi Nobuhisa , Morita Masanobu , Mima Kunioki , Miyamoto Syuji , Imasaki Kazuo , Kuruma Shinichiro , Nakai Sadao , Yamanaka Chiyoe , Taguchi Toshihiro , Murai Akira
Published: July 2002

In pulse power driven free-electron laser experiments for a diode voltage 300–600 kV, a maximum electron beam current 730 A, with a 110-ns width of beam voltage pulse and a helical wiggler with a pitch of 2 cm, the temporal evolution of radiation spectra is observed. The frequency variations are explained theoretically by using instantaneous values of beam voltages and currents. In the calculation we take account of the variation in the beam cross section of the beam voltage drop and the wiggler field. The spatial growth rate of the radiation power was also measured. The observed growth rate is 1 dB/cm and the saturation level is 250 kW with the spector peak at 58 GHz.
Graphite picosecond optoelectronic opening switch
Authors: Chauchard E. A. , Lee Chi H. , Huang C. Y.
Published: July 2002

Highly oriented pyrolytic graphite, a conductive material in the dark, is found to exhibit a high resistivity when illuminated by intense laser light. Its operation as an opening switch with a switching time under 1 ns is demonstrated.
Growth and characterization of silicon molecular beam epilayers on GaP (111) substrates
Authors: Jiang Weidong , Zhou Guoliang , Chen Keming , Sheng Chi , Zhang Xiangjiu , Wang Xun
Published: July 2002

Silicon molecular beam epitaxy on thermally cleaned GaP(111) substrates has been prepared at 450 °C with the growth rate of 0.2 Å/s. The P segregation on the surface of Si epilayer beyond the thickness of 1500 Å has been observed. The surface of epilayer has the same (1×1) periodicity as that of the substrate when the thickness of the epilayer is less than 500 Å. Above 500 Å, the surface shows a (3×3) reconstruction. It is suggested that both (1×1) and (3×3) geometries are P-stabilized surface structures.
Abruptness of Au-Si contacts with thin CoSi2 interlayers
Authors: Xu F. , Aldao C. M. , Vitomirov I. M. , Weaver J. H.
Published: July 2002

High-resolution synchrotron radiation photoelectron spectroscopy has been used to study Au/Si and Au/CoSi2/Si interface formation at room temperature. Our results show Au-Si intermixing, the absence of a well defined Au-Si compound, and surface segregation of small amounts of Si to the Au surface. An interlayer formed by the deposition of ≤3 Å of Co has relatively small effect on this Au-Si atomic profile. Intermixing is abruptly quenched, however, when the Co deposition exceeds 3.5 Å, and a Au film free of Si can grow on the CoSi2 layer. These results demonstrate the effectiveness of CoSi2 layer as a barrier against Au-Si intermixing and identify the critical coverage of Co needed to passivate the Si surface.
Degradation in GaAs/AlGaAs double-heterostructure light-emitting diodes
Authors: Ogawa Junko , Tamamura Kohshi , Akimoto Katsuhiro , Mori Yoshifumi
Published: July 2002

Degradation of GaAs/AlGaAs double-heterostructure light-emitting diodes under accelerated aging tests has been investigated through cathodoluminescence measurements. We observed an increase in intensity of the band-edge emission and a decrease in that of defect-related deep level emision for the cladding layers. As for the active layer, a decrease was observed in the intensity of the band-edge emission. These results suggest that defects migrate gradually from the cladding layer into the active layer.
Implications for a short wavelength laser experiment based on a theory of quasi-channeling phenomenon for electrons
Authors: Makowitz Henry
Published: July 2002

The theory of electron and positron channeling and radiation production in crystals has been extended to macroscopic-scale systems. The new theory, named QCP theory (quasi-channeling phenomenon), examines macroscopic systems that exhibit periodicity along the axis of beam propagation, specifically, periodic electrostatic fields; the dimensions of the field periodicity (lz) are much greater than typical interatomic lattice spacing (lL), e.g., lz≫lL, but much smaller than a typical wiggler wavelength lw, e.g., lw≫lz. The feasibility of a laser based on this predicted new phenomenon is examined in this letter. Differences between the properties of the proposed quasi-channeling radiation and radiation produced by wigglers and free-electron lasers (FEL’s) are discussed. System lengths a factor of 103 shorter than FEL’s are expected, with favorable scaling for below 500 eV laser photon output energies. A 500-eV QCP laser system with a gain of 1 and a length of 1 m is predicted, based on extrapolations of existing storage-ring technology.
New probe of thin-film microstructure
Authors: Mizrahi Victor , Suits F. , Sipe J. E. , Gibson U. J. , Stegeman G. I.
Published: July 2002

We demonstrate that second harmonic generation is a sensitive probe of thin-film deposition conditions.
Correlation between the elastic and structural properties of thin-film tungsten silicide layers from surface acoustic wave analysis
Authors: Crean G. M. , Golanski A. , Oberlin J. C. , Perio A.
Published: July 2002

Thin, silicon-rich tungsten silicide layers, deposited using the co-sputtering technique and annealed within the temperature range 750–950 °C, were investigated using the acoustic material signature technique, transmission electron microscopy, and the Rutherford backscattering technique. The effective elastic constants were determined from the dispersion curves calculated using a Tiersten model [J. Appl. Phys. 40, 2 (1969)] and fitted to the experimental dispersion data. It is shown that for the annealing temperatures used the elastic properties of thin silicide films are correlated with the annealing temperature-dependent content of the excess silicon present within the grain boundaries.
Comparison of interface positive charge generated in metal-oxide-silicon devices by high-field electron injection and x-ray irradiation
Authors: Mott D. B. , Buchner S. P.
Published: July 2002

Interface positive charge induced in thin oxides (582 Å thick) of metal-oxide-silicon devices by Fowler–Nordheim injection and x-ray irradiation was evaluated based on measurements of room-temperature annealing characteristics. Results showed that in the low-dose regime, the dose dependence of the density and distribution of the positive charge was different for the two forms of stress. However, at higher doses, the positive charge density produced by both methods increased monotonically while its spatial extent decreased and became more localized at the interface. These latter results are attributed to a buildup of negative charge in the oxide that neutralizes the positive charge furthest from the interface, whereas the differences at low dose are due either to the different character of the positive charge generated by the two techniques or to the much smaller electron density present during irradiation than injection.
AlGaAs/GaAs distributed feedback lasers with first-order grating fabricated by metalorganic chemical vapor deposition
Authors: Hirata Shoji , Tamamura Koshi , Mori Yoshifumi , Kojima Chiaki
Published: July 2002

Distributed feedback AlGaAs/GaAs lasers with first-order grating (1295 Å) were fabricated and successfully operated under continuous wave conditions at room temperature. A coupling coefficient of 115 cm−1 and a threshold current of 47 mA were obtained. A stable single-mode oscillation was maintained up to 100 °C.
Holographic interferometry using iron-doped lithium niobate
Authors: Magnusson R. , Mitchell J. H. , Black T. D. , Wilson D. R.
Published: July 2002

Holographic interferometry using crystals of iron-doped lithium niobate is reported. The interferograms presented are produced via double-exposure Fourier transform holography in heavily doped crystals without applied electric fields. Flow-field visualization is used as an example application area.
Heteroepitaxial growth of CdTe on InSb by metalorganic chemical vapor deposition
Authors: Sugiura O. , Tanaka Y. , Shiina K. , Matsumura M.
Published: July 2002

Heteroepitaxial growth of CdTe on an InSb (111)B substrate has been investigated using the metalorganic chemical vapor deposition method under a total vapor pressure of about 1 Pa. By cracking diethyltellurium thermally at 670 °C, CdTe films were deposited in a wide substrate temperature range from 120 to 450 °C. Single-crystal films grown at 250 °C showed a good surface morphology.
Effects of ZnSe epitaxial growth on the surface properties of GaAs
Authors: Olego D. J.
Published: July 2002

The epitaxial growth of ZnSe induces changes in the surface properties of GaAs: surface barrier height, surface recombination velocity, and Fermi level pinning. These changes were investigated with Raman and photoluminescence spectroscopies in ZnSe-GaAs heterostructures with ZnSe layer thickness D ranging from 50 to 5000 nm. The ZnSe layers were grown by molecular beam epitaxy on (100)n-type GaAs substrates. Barrier heights smaller than 0.1 eV together with lower recombination velocities were obtained for pseudomorphic ZnSe layers with no misfit dislocations at the interface (D≤150 nm). When D exceeds the critical layer thickness and misfit dislocations are present at the interface the barrier height gradually increases with D. The barrier height and the pinning position of the Fermi level depend on the surface density of the dangling bonds generated by the misfit dislocations.
Observation of quantum interference effects and SQUID operation in a bulk sample of YBa2Cu3Oy at 77 and 4.2 K
Authors: Pegrum C. M. , Donaldson G. B. , Carr A. H. , Hendry A.
Published: July 2002

We have studied the response of a bulk sample of YBa2Cu3Oy to an applied static magnetic field B and a 20-MHz rf field. At both 77 and 4.2 K we found clear evidence of behavior within the sample that was characteristic of a superconducting quantum interference device. At 77 K, the absorption of rf power was a periodic function of B, characterized by several superposed periods in the range 8×10−8 to 9×10−6 T. At 4.2 K only one period, of 4.8×10−7 T, was evident. By applying flux feedback we could lock to minima in the response, and in this mode of operation as a magnetometer the field spectral density S1/2B was 1.5×10−10 T Hz−1/2 at 77 K and 5.8×10−10 T Hz−1/2 at 4.2 K.
Reproducible liquid phase epitaxial growth of InGaAsP buried heterostructure lasers
Authors: Logan R. A. , Temkin H. , Blaha J. P. , Strege K. E.
Published: July 2002

Buried heterostructure lasers are formed using double heterostructure planar layers which are masked and etched to define laser mesas, with final regrowth by liquid phase epitaxy. Controlled melt etching of the exposed wafer surface is introduced just prior to the liquid phase epitaxial regrowth to form etched mesa buried heterostructure lasers. The melt etching uses an In-InP melt undersaturated by only ∼0.2 °C and does not degrade the dimensional shape of the etched mesas. This process is shown to dramatically improve the growth reproducibility and results in excellent device characteristics. This closely controlled removal of the mesa sidewall just prior to epitaxy is also expected to contribute to increased laser reliability.
Oxide conductive coated cathodes for a sealed-off CO2 laser
Authors: Hsieh Tai-Chiung , Lan Yuan-Liang
Published: July 2002

Cold cathodes coated with oxide conductive materials, such as indium tin oxide and tin oxide, were applied to dc gas discharges of a sealed-off CO2 laser. Laser power enhancement and stable gas discharge, two areas of laser performance, were affected, in contrast to the uncoated metallic cathode. Mass spectrometric study revealed a correlation of laser power enhancement and an increase in the CO2 content associated with these coated cathodes.
Interfacing multispectral sensors to real time processors based on neural network models
Authors: Bandara K. M. S. V. , Coon D. D. , Karunasiri R. P. G.
Published: July 2002

Experiments have been carried out to demonstrate and study the interfacing of silicon sensors to silicon devices which represent first stage elements of an artificial neural network. Sensor outputs (network inputs) are photocurrents associated with infrared, visible, or ultraviolet light. First stage linear coding of input current into the pulse rate of a stereotypical neuronlike spiketrain output has been achieved with a dynamic range of more than 106. For 1 pA inputs, the estimated noise referred to input is 10 fA. Network elements are shown to obey equations of the same form as equations which occur in nonlinear neural network models recently analyzed by Hopfield [Proc. Natl. Acad. Sci. 81, 3088 (1984)] and previously studied by Sejnowski [J. Math. Biology 4, 303 (1977)].
Chemical structure of nitrogen in amorphous silicon matrix
Authors: Singh Jagriti , Budhani R. C.
Published: July 2002

Direct evidence of substitutional doping of nitrogen in ion beam deposited hydrogenated amorphous silicon, from analysis of infrared spectra and Si-2p core level shape measured with x-ray photoelectron spectroscopy (XPS), is presented. For the first time the XPS technique has been used to deduce the upper limit for substitutional solid solubility of the impurity.
Low-temperature nitridation of fluorinated silicon dioxide films in ammonia gas
Authors: Aritome S. , Morita M. , Tanaka T. , Hirose M.
Published: July 2002

A new technique of growing nitrided oxide at low temperatures has been developed. Fluorine-enhanced thermal oxidation of silicon in O2+NF3 at temperatures below 800 °C and subsequent annealing of the fluorinated oxide in pure ammonia gas at the same temperature result in the formation of nitrided oxide. The dielectric breakdown strength of the fluorinated oxide is improved by the nitridation. Also, the nitrided oxide acts as a protective layer against alkaline ion contamination.
Narrowband, single line, 1 μs XeF laser
Authors: Kimura W. D. , Guyer Dean R. , Seamans J. F. , Ford D. H.
Published: July 2002

A narrowband (5 GHz) electron beam pumped XeF oscillator/amplifier, lasing at 353.2 nm over a 1-μs pulse duration, has been demonstrated. Line selection, bandwidth narrowing, and near-diffraction-limited output are achieved by using an echelle grating and an intracavity solid étalon in a stable oscillator configuration. The amplifier features an off-axis design and yields output energies ≳0.8 J. The oscillator and amplifier are located in the same gas chamber and are transversely pumped by the same electron beam. A Fabry–Perot interferometer together with a streak camera is used to verify narrowband operation over the entire pulse duration.