bluuebunny/crossref_metadata_2025 huggingface dataset:
High voltage polycrystalline thin-film transistor with variable doping slots in the offset region
Authors: Xu Y. Z. , Cross R. , Manhas Meenakshi , Clough F. J. , DeSouza M. M. , Narayanan E. M. S. , Flores D. , Rebello J. , Vellvehi M. , Millan J.
Published: July 2002

Performance of a high voltage polycrystalline Si thin-film transistor (TFT) with variable doping slots in the offset region is demonstrated in this letter. In the proposed structure, the width of the doping slots and the gaps increase from the drain toward the gate edge. Compared to offset-drain (OD) TFT fabricated on the same substrate, the proposed structure exhibits an increase in on current by a factor of 15 at 0.1 V drain bias and by an order at 10 V drain bias. The device also shows a more saturate drain characteristic. The blocking capability is 152 V, which is almost the same as the OD TFT and is attributed to the voltage sharing across the doping slots.
Measuring ferroelectric polarization component parallel to the surface by scanning nonlinear dielectric microscopy
Authors: Odagawa Hiroyuki , Cho Yasuo
Published: July 2002

A scanning nonlinear dielectric microscope (SNDM) probe, called the ε311-type probe, and a system to measure the ferroelectric polarization component parallel to the surface have been developed. This is achieved by measuring the ferroelectric material nonlinear dielectric constant ε311 instead of ε333, which is measured in conventional SNDM. Experimental results show that the probe can satisfactorily detect the direction of the polarization parallel to the surface. Moreover, we propose an advanced measurement technique using a rotating electric field, which can be applied to measure three-dimensional polarization vectors.
Single electron transistors with high-quality superconducting niobium islands
Authors: Dolata R. , Scherer H. , Zorin A. B. , Niemeyer J.
Published: July 2002

Deep submicron Al/AlOx/Nb tunnel junctions and single electron transistors with niobium islands were fabricated by electron beam gun shadow evaporation. Using stencil masks consisting of the thermostable polymer polyethersulfone and germanium, high quality niobium structures with good superconducting properties and a gap energy of up to 2ΔNb=2.5 meV were achieved. The I(U) characteristics of the transistors show special features due to tunneling of single Cooper pairs and significant gate modulation in both the superconducting and the normal state.
Near-field optical photoluminescence microscopy of high-density InAs/GaAs single quantum dots
Authors: Eah Sang-Kee , Jhe Wonho , Arakawa Yasuhiko
Published: July 2002

We performed low-temperature near-field optical photoluminescence (PL) microscopy of a high-density (>100 μm−2) sample of single InAs/GaAs quantum dots (QDs) with very high spatial resolution. Six single QDs of different emission energies are spatially resolved with an apertured fiber probe of 200 nm diam by taking the complete PL spectrum at each point, while the scanning area is 250×250 nm2.
Adsorbate-induced one-dimensional long-range modulation of an epitaxial insulator film
Authors: Ernst W. , Eichmann M. , Pfnür H. , Jonas K.-L. , von Oeynhausen V. , Meiwes-Broer K. H.
Published: July 2002

Using low-energy electron diffraction and scanning tunneling micrsocopy, we found that epitaxial NaCl films grown on Ge(100) with thicknesses up to (at least) 15 monolayers can be modulated with a period of six lattice constants and an amplitude directed mainly normal to their surface. The (6×1) periodicity on the NaCl films is induced by a preadsorbed Na layer at very low coverages (Θ≈0.06), that form chain structures with a sixfold periodicity in one dimension. At 10 monolayers thickness of NaCl a modulation amplitude of 0.28 Å was obtained.
Polaronic quasiparticle injection in organic copper (II) phthalocyanine/Bi2Sr2CaCu2O8+δ tunnel junctions
Authors: Kim Sunmi , E Jungyoon , Lee Kiejin , Ishibashi Takayuki , Sato Katsuaki , Friedman Barry
Published: July 2002

We report the current transport properties of an organic conductor/superconductor tunnel junction as a high-Tc superconducting three terminal device. The organic copper (II) phthalocyanine (Cu–Pc) layer was used for a polaronic quasiparticle (QP) injector. The junction was investigated in the dark and under ultraviolet radiation. The injection of polaronic QP from the Cu–Pc interlayer into a superconductor Bi2Sr2CaCu2O8+δ (BSCCO) thin film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. The tunneling spectroscopy of a Cu–Pc/BSCCO junction exhibited a zero bias conductance peak, which may be interpreted as Andreev reflection at a Cu–Pc/d-wave superconductor junction.
Modeling of Q-switched semiconductor lasers based on type-II quantum wells: Increasing the pulse energy and peak power
Authors: Khurgin Jacob B. , Vurgaftman Igor , Meyer Jerry R.
Published: July 2002

We propose a semiconductor laser (λ≈1.25 μm) whose active region is a type-II multiple-quantum-well structure (AlGaInAs/AlGaAsSb/AlInAs on InP) to lengthen the free-carrier lifetime. Simulations project an order-of-magnitude enhancement of the Q-switched energy per pulse without increasing the pump current.
Simple nondestructive extraction of the vertical channel-impurity profile of small-size metal–oxide–semiconductor field-effect transistors
Authors: Mattausch Hans Jürgen , Suetake Masami , Kitamaru Daisuke , Miura-Mattausch Mitiko , Kumashiro Shigetaka , Shigyo Naoyuki , Odanaka Shinji , Nakayama Noriaki
Published: July 2002

An improved method for extracting the vertical channel-impurity profile [Nsub(x)] of metal–oxide–semiconductor field-effect transistors (MOSFETs) from measured threshold–voltage dependence on bulk–source voltage is proposed. Previous restriction to slowly varying Nsub(x) is overcome by approximating Nsub(x) as a simple analytic function. Application to advanced MOSFETs with steep pileup or retrograded channel profiles and channel length down to 100 nm becomes possible. Extracted analytic profiles are additionally useful for modeling of Nsub(x)-dependent MOSFET phenomena, e.g., the reverse-short-channel effect.
Role of defect centers in recombination processes in GaN monocrystals
Authors: Joshi N. V. , Cros A. , Cantarero A. , Medina H. , Ambacher O. , Stutzmann M.
Published: July 2002

A confocal fluorescence microscopic study was carried out on GaN monocrystals grown by molecular beam epitaxy and doped with Mn. The samples were irradiated with mid band gap radiation (488 nm) rather than ultraviolet, and it was found that a strong yellow radiation was emitted by defect centers. Three-dimensional images clearly reveal not only the size and the form of the illuminating defect centers but also their orientations with respect to the plane on which these defects were grown. This is a direct evidence for the radiative recombination at the defect centers when excited by the midgap radiation.
Nitrogen-doped GaAsP light-emitting diodes with junctions grown by hydride vapor-phase epitaxy
Authors: Sato Tadashige , Imai Megumi
Published: July 2002

Nitrogen-doped GaAsP light-emitting diodes (LEDs) with grown junctions have been fabricated on GaP substrates using hydride vapor-phase epitaxy. A p+/p-layer structure was employed to reduce light absorption and to optimize the carrier concentration at the junction. The carrier concentration in the p layer of the structure plays the important role of improvement of the luminous intensity, and is optimized at 3×1017 cm−3. The LEDs were 20% brighter than those commercially available with diffused junctions. Reliability studies showed good stability through 168 h of operation, enough to suggest they could be used as commercial products.
Subwavelength-sized aperture fabrication in aluminum by a self-terminated corrosion process in the evanescent field
Authors: Haefliger D. , Stemmer A.
Published: July 2002

We present a simple, one-step process to fabricate apertures of high quality for scanning near-field optical microscope probes based on aluminum-coated silicon-nitride cantilevers. An evanescent optical field at the glass–water interface is used to heat up the aluminum at the tip apex due to light absorption. The heat induces breakdown of the passivating oxide layer and corrosion of the metal. Apertures with a protruding silicon-nitride tip of up to 30 nm height and minimal diameter of 38 nm are fabricated. The diameter is predefined by the lateral dimension of the silicon-nitride tip while the tip height is controlled by the penetration depth of the evanescent field. The corrosion process proves to be self-terminating, yielding highly reproducible tip heights. Near-field optical resolution in the transmission mode of 85 nm is demonstrated.
Photoluminescence study of hydrogen passivation in InAs1−xNx/InGaAs single-quantum well on InP
Authors: Ke Y. Y. , Ya M. H. , Chen Y. F. , Wang J. S. , Lin H. H.
Published: July 2002

It is well known that nitrogen incorporation into III–V compounds will degrade the quality of materials. In this letter, we show that the incorporation of atomic hydrogen into InAsN/InGaAs quantum wells can effectively passivate defects and lead to enhancement of photoluminescence intensity near the band edge. After hydrogenation, the change of the optical properties is quite different from that of the annealing with nitrogen treatment. For instance, the linewidth becomes wider after hydrogenation, while the linewidth is narrower after nitrogen annealing. Through a detailed study of the photoluminescence spectra, we show that the passivation of defect bonds is the main reason for the improved optical behavior for hydrogenation, while the interdiffusion is responsible for the change after nitrogen annealing.
Phonons on GaN(110)
Authors: Tütüncü H. M. , Miotto R. , Srivastava G. P. , Tse J. S.
Published: July 2002

We present results of adiabatic bond-charge model calculations for the vibrational properties of the GaN(110) surface using electronic and structural data obtained from a first-principles pseudopotential method. It is found that in order to relate the energy locations of optical phonon modes on this surface with corresponding modes on nonnitride III–V(110) and II–VI(110) surfaces, it is necessary to consider scaling of results with the lattice constant in addition to the reduced mass.
Infrared electroluminescence from an organic ionic dye containing no rare-earth ions
Authors: Suzuki Hiroyuki
Published: July 2002

This paper reports the electroluminescence (EL) characteristics of a single-layer light-emitting diode (LED) with an organic functional layer, which is composed of an organic ionic emissive dye, IR1051, an electron transporting material, 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, and poly(N-vinylcarbazole). The LED exhibits IR EL in the 0.9–1.5 μm range, which is ascribable to IR1051 with reference to steady-state absorption and photoluminescence measurements. The present study demonstrates a class of IR EL materials containing no rare earth ions and compatible with silicon-based photocircuits.
Hall mobility enhancement caused by annealing of Si0.2Ge0.8/Si0.7Ge0.3/Si(001) p-type modulation-doped heterostructures
Authors: Myronov M. , Phillips P. J. , Whall T. E. , Parker E. H. C.
Published: July 2002

The effect of post-growth furnace thermal annealing (FTA) on the Hall mobility and sheet carrier density measured at 9–300 K in the Si0.2Ge0.8/Si0.7Ge0.3/Si(001) p-type modulation-doped heterostructures was studied. FTA treatments in the temperature range of 600–900 °C for 30 min were performed on similar heterostructures but with two Si0.2Ge0.8 channel thicknesses. The annealing at 600 °C is seen to have a negligible effect on the Hall mobility as well as on the sheet carrier density. Increases in the annealing temperature resulted in pronounced successive increases of the mobility. For both samples the maximum Hall mobility was observed after FTA at 750 °C. Further increases of the annealing temperature resulted in a decrease in mobility. The sheet carrier density showed the opposite behavior with an increase in annealing temperature. The mechanism causing this behavior is discussed. Structural characterization of as-grown and annealed samples was done by cross-sectional transmission electron microscopy.
Properties of superconducting MgB2 single crystal grown by a modified flux method
Authors: Cho Yong Chan , Park Sang Eon , Jeong Se-Young , Cho Chae-Ryong , Kim Bong Jun , Kim Young Cheol , Youn Hwa Shik
Published: July 2002

We report on the growth of MgB2 single crystals with a large thickness of about 100 μm and a clear hexagonal prismatic morphology. On the low-field magnetization curve M(T), a superconducting transition was observed at 39 K. Using the x-ray diffractometer equipped with a microprobe, we obtained Laue patterns of MgB2 single crystal from a piece of the grown crystal and investigated the impurities introduced during the growing process using Auger electron spectroscopy.
Optical properties of ZnO thin films: Ion layer gas reaction compared to sputter deposition
Authors: Rebien M. , Henrion W. , Bär M. , Fischer Ch.-H.
Published: July 2002

Zinc oxide films prepared by the recently developed ion layer gas reaction (ILGAR) technique and by rf magnetron sputtering are compared with respect to their linear optical properties. Spectral ellipsometry as well as reflectance and transmittance measurements in the UV-visible-near infrared range were employed to deduce the complex refractive index. The band gap energy, Urbach energy, and packing density were determined. The results are compared to literature data of single crystals and thin films.
Common-emitter current–voltage characteristics of a Pnp AlGaN/GaN heterojunction bipolar transistor with a low-resistance base layer
Authors: Kumakura Kazuhide , Makimoto Toshiki , Kobayashi Naoki
Published: July 2002

We fabricated a Pnp AlGaN/GaN heterojunction bipolar transistor and investigated its common-emitter current–voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The Al mole fraction in an AlGaN emitter layer was 0.18. The thickness of the GaN base layer was 0.12 μm and its Si doping concentration was as high as 1×1019 cm−3, so its base resistance decreased two orders of magnitude compared with the reported Npn nitride heterojunction bipolar transistors. The transistor showed good saturation current–voltage characteristics and the maximum common-emitter current gain of 28 was obtained for collector current of −2×10−5 A at room temperature.
Room-temperature, ground-state lasing for red-emitting vertically aligned InAlAs/AlGaAs quantum dots grown on a GaAs(100) substrate
Authors: Liu H. Y. , Sellers I. R. , Airey R. J. , Steer M. J. , Houston P. A. , Mowbray D. J. , Cockburn J. , Skolnick M. S. , Xu B. , Wang Z. G.
Published: July 2002

The effect of the growth temperature on the properties of InAlAs/AlGaAs quantum dots grown on GaAs(100) substrates is investigated. The optical efficiency and structural uniformity are improved by increasing the growth temperature from 530 to 560 °C. The improvements of InAlAs/AlGaAs quantum-dot characteristics could be explained by suppressing the incorporation of oxygen and the formation of group-III vacancies. Furthermore, edge-emitting laser diodes with six quantum-dot layers grown at 560 °C have been fabricated. Lasing occurs via the ground state at 725 nm, with a room-temperature threshold current density of 3.9 kA/cm2, significantly better than previously reported values for this quantum-dot systems.
Effects of H2 impregnation on excimer-laser-induced oxygen-deficient center formation in synthetic SiO2 glass
Authors: Ikuta Yoshiaki , Kajihara Koichi , Hirano Masahiro , Kikugawa Shinya , Hosono Hideo
Published: July 2002

We examined the effect of H2 impregnation on defect formation upon F2 laser (7.9 eV) and ArF excimer laser (6.4 eV) irradiation. It was revealed that H2 impregnation enhanced the formation of oxygen-deficient center (Si–Si bond) as well as suppressed the formation of E′ center and nonbridging oxygen hole center. A Si–Si bond gives an intense absorption band peaking at 7.6 eV, which contributes the absorption at the wavelength of F2 laser light. These results indicate that H2-free SiO2 glass, which is clearly inappropriate for KrF and ArF excimer laser optics, is more suitable for F2 laser optics than H2-impregnated glass.
Stability of interfacial dislocations in (001) silicon surfacial grain boundaries
Authors: Rousseau K. , Rouvière J. L. , Fournel F. , Moriceau H.
Published: July 2002

Ultrathin (001) silicon films bonded onto (001) silicon wafers, which form “surfacial grain boundaries” have been investigated by transmission electron microscopy. The samples were obtained by bonding one silicon-on-insulator (SOI) structure with one silicon wafer. After the removal of the SOI substrate, the remaining top thin film was further reduced by a thermal oxidation. Samples with a given film thickness selected in the 200 nm to 10 nm range were obtained. For very thin films, the thinning procedure can induce a mobility of the interfacial dislocations. To keep the interfaces stable, we have replaced the thermal oxidation thinning by a low-temperature chemical etching.
Time-resolved photoluminescence of quaternary AlInGaN-based multiple quantum wells
Authors: Ryu Mee-Yi , Chen C. Q. , Kuokstis E. , Yang J. W. , Simin G. , Khan M. Asif , Sim G. G. , Yu P. W.
Published: July 2002

Time-resolved photoluminescence (PL) dynamics has been studied in AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by a pulsed metalorganic chemical vapor deposition (PMOCVD) procedure. The PL decay kinetics was found to be sensitive to the emission energy and temperature. The PL decay time increases with decreasing emission energy, which is a characteristic of localized carrier/exciton recombination due to alloy fluctuations. Its temperature dependence shows radiative recombination to be the dominant process at low temperatures, indicating a high quality of PMOCVD grown quaternary AlInGaN MQWs and establishing them as promising structures for the active region of deep ultraviolet light emitting diodes.
Three-dimensional self-assembly by ice crystallization
Authors: Im Sang Hyuk , Park O Ok
Published: July 2002

Three-dimensional self-assembly of colloidal particles by ice crystallization is observed in a water based-colloidal suspension. When water containing polystyrene beads freezes and is crystalized into ice, the polystyrene beads are extruded outward from the ice regions. Consequently, the concentration of polystyrene beads increases rapidly and they are assembled together into a regular structure. As ice crystallization proceeds, a color appears abruptly. This indicates that the polystyrene beads have been assembled three dimensionally. The generated three-dimensional structure is confirmed by scanning electron microscopy images and the existance of a photonic band gap measured by an ultraviolet-visible spectrophotometer. The sample fabricated by this method is compared with a sample made by conventional vertical deposition.
Erbium doped nanostructured tin–silicate glass–ceramic composites
Authors: Chiodini N. , Paleari A. , Brambilla G. , Taylor E. R.
Published: July 2002

Er-doped tin–silicate glass–ceramic composites were synthesized from Si, Er and Sn molecular precursors by following a sol–gel method. Optical spectroscopy and electron microscopy showed that the resulting material is composed of an amorphous silica network that encloses submicrometric SnO2 crystalline clusters. Analysis of the luminescence properties shows that Er ions are, at least partially, trapped in the crystalline phase. Raman spectra show that nanostructured tin–silicate composites act as low phonon energy hosts for rare earth ions and are thus suitable for photonic applications.
Lineshape analysis for optical transitions in III-V semiconductors using a sequential simplex procedure
Authors: Estrera J. P. , Duncan W. M. , Slaughter S. R.
Published: July 2002

A computer lineshape analysis for optical transitions in III-V semiconductors is presented. The routine utilizes the Nelder–Mead version of the sequential simplex optimization procedure embodied in a pascal program that can be executed on a personal computer. The sequential simplex routine allowed the optimum fitting of experimental data with a function or group of functions with n-independent parameters. The routine was successfully applied to two types of optical spectra. First, convolved Gaussian and asymmetric Gaussian bands in low temperature (4.2 K) Fourier-transformed photoluminescence spectra of lattice-matched InxGa1−xAs on InP substrates were fit. As a result of applying the sequential simplex routine to the InxGa1−xAs/InP system, three optical transitions (excitonic band, donor-to-acceptor pair band, and defect/impurity or exciton LO replica band) were identified in all spectra and a fourth transition was found in some samples. A second application of the routine was the fitting of the Aspnes third derivative lineshapes (TDLS) to room temperature, low electric field photoreflectance spectra of high purity GaAs. In applying the routine to photoreflectance spectra, it was found that the two-dimensional critical point, n=3 form of the TDLS best fit the photoreflectance spectra of high-purity GaAs at room temperature. In both applications of the sequential simplex routine, the lineshape analysis contributed valuable insight into the nature of the optical phenomena occurring in the analyzed material.
Temporal behavior of NO laser emission from the photodissociation of ClNO and BrNO
Authors: del Barrio J. I. , Rebato J. R. , Tablas F. M. G.
Published: July 2002

We have studied the temporal behavior of the NO laser emission produced from the photodissociation of ClNO and BrNO. No J shifting has been observed except in the 7→6 band of 2Π3/2 from ClNO. In both cases laser starts from an intermediate lasing vibrational level, triggering higher and lower transitions that end with the lowest observed band.
Stimulated two-photon processes: Effects of the radiation frequencies ratio on the gain spectrum induced by a focused pump
Authors: Gingras Michel , Denariez-Roberge Marguerite-Marie
Published: July 2002

It is shown that the calculated gain spectrum of the radiation generated by a two-photon process, evaluated from a high-order approximation solution of the wave equation, is larger than the one obtained from a zero-order approximation. The difference between the two approximations becomes very important when the ratio of the frequency of the generated radiation to that of a focused pump is large and/or when the pump power is low.
Electron field emission from intentionally introduced particles on extended niobium surfaces
Authors: Noer R. J. , Niedermann Ph. , Sankarraman N. , Fischer O/.
Published: July 2002

Field emission properties of microscopic particles of graphite, sulfur, and MoS2 deposited on nonemitting Nb surfaces under ultrahigh vacuum conditions are described. Both graphite and MoS2 particles are shown to emit strongly, with field enhancement factors of the order of 100, in contrast to sulfur particles, which emit only weakly. The emission characteristics are measured locally on the individual sites, and emitting particles are further characterized by microfocus Auger spectroscopy and scanning electron microscopy. Their behavior upon heat treatment was studied, with the main result that both for graphite and MoS2 particles the emission disappears after heating to 1200 °C. The properties of the artificially created emitters are compared with those of naturally occurring field emitters.
Modified image method: Application to the response of layered ohmic conductors to active electromagnetic sources
Authors: Bergeron Clyde J.
Published: July 2002

The standard image method is modified in order to extend its range of applicability to the near-space regime (h∼λ the screening length) for all electromagnetic screening phenomena in conducting matter which are governed by Helmholtz’s equation. The modified method assumes a single image of a near inducing source and that the effective location of the image plane and surface screening distribution that satisfy the electromagnetic boundary conditions is one screening length below the free surface of the conductor. For applications in which the primary source and detector distance from the conducting free surface is much greater than the appropriate screening length, the modified image method (MIM) reduces to the standard form. An additional ad hoc modification for the case of induced ohmic screening is introduced into Wait’s multilayer correction function Q which is used in the definition of the complex screening length for the MIM model. This results in an extended range of agreement (both as to amplitude and phase )between the complex image fields produced by the MIM model and the secondary field produced by induced currents in the layered conducting half-space as originally formulated by Sommerfeld. This suggests the use of MIM, at least as a first-order tool, for rapid real-time inverse calculations of the structure parameters, conductivities, and thickness of the layers. The good agreement between MIM and the standard theory for a two-layer model occurs over a range of values for the parameters that define the conducting structure and the geometry of the source and sensor coils which are relevant to airborne active electromagnetic source (AEM) coastal bathymetry, sea ice thickness measurements, and studies of salt water intrusions of river deltas and marshes. The success of this application of the MIM model in the near-field regime for ohmic screening suggests the applicability of MIM in calculating the near-field electrostatic and superconducting response of conducting matter as well.
Transversely excited atmospheric-pressure copper-vapor laser
Authors: Im Kiegon , Sung Nackchin , Kim Jin J.
Published: July 2002

We report the results of the measurements of the performance parameters of the transversely excited atmospheric-pressure (TEA) copper-vapor laser (CVL). A specific laser energy density of 36 μJ/cm3 was achieved in an excited volume of 0.6×1×20 cm3. This corresponds to a specific power density of 3.6 kW/cm3 for a 10-ns pulse. Because of the high buffer gas pressure that can be used in the TEA-CVL, containment of the copper vapor in the heated zone can be maintained for an extended period, making a sealed system possible.
Transmittance of liquid-crystal cells: A comparison
Authors: Anjaneyulu Y. , Yoon D. W.
Published: July 2002

A liquid-crystal window has been considered as an optical shutter to control solar energy. Transmittance of dynamic-scattering, twisted-nematic, and phase change guest-host (PCGH) cells having 6, 9, and 12 μm thicknesses has been measured and compared. A PCGH cell with black dye exhibits an anomalous transmission dip in the region of cholesteric to nematic or vice versa phase transformation for incident incoherent light of λ<500 μm. We attribute this dip to voltage-induced inhomogeneities generated during the phase transition. Transmittance controllability as high as 50% has been achieved with a 6-μm-thick PCGH cell with one polarizer. A comparison of the transmittances of the three types shows that PCGH material is a suitable candidate for large size window fabrication.
Fluctuations and nonuniformity of the ion beam current and electron flow in a long-pulse, applied B
r magnetically insulated ion diode
Authors: Nakagawa Yoshiro , Enomoto Tamotsu
Published: July 2002

The low-frequency fluctuations (10–200 MHz) and spatial nonuniformity (2–20 mm) of ion beam currents and electron flow have been studied for a long-pulse (insulation time ∼1 μs) intense ion beam source. The total ion current was ≳5 kA, the ion energy was ∼70 keV, and the total ion output was ∼1×1016/pulse. The fluctuations and nonuniformity of the electron flow were measured using x-ray emission from the anode and magnetic probes. Those were closely correlated to the fluctuations and nonuniformity of the ion beam. With a high-current, low-voltage diode, measurements indicated that the ion beam characteristics were caused by a low-frequency instability. One possible candidate for this instability is the cathode-plasma filamentation which has been found using an image converter carnera.
Electron dislocation drag at low temperatures
Authors: Galligan J. M. , Goldman P. D. , Motowidlo L. , Pellegrino J.
Published: July 2002

Measurements of the influence of a magnetic field on the stress of plastic deformation for a number of materials are presented. These measurements are given for copper, some copper alloys, zinc, cadmium, lead, and bismuth. The measurements, carried out at a number of temperatures between 1.8 and 40 K, show that this change in stress has a monotonic and an oscillatory dependence upon the magnetic field. The oscillatory dependence on field has a temperature dependence which is consistent with a 1/T3 dependence. We also show that the oscillations are strain rate dependent as well as strain dependent. These results are compared with the inertial model of dislocation motion and the agreement is quite good. Measurements of the orientation dependence of the magneto-oscillations allows us to assess the relative velocities of screw and edge dislocations, showing that, at low temperatures, screw dislocation move faster than do edge dislocations. Agreement is also found between the present measurements of the Fermi surface extrema and acoustic measurements. Finally the temperature where the dislocations no longer act as underdamped oscillators is compared with theory.
Interfacial CuAl2 precipitate nucleation and growth during the deposition of Al-4% Cu-1.5% Si alloys
Authors: Thomas M. E. , Keyser T. K. , Goo E. K. W.
Published: July 2002

A series of experiments was performed to evaluate the effects of varying substrate temperature on the vertical distribution of Cu in S-Gun■ sputtered films of Al-4% Cu-1.5% Si. Films having a thickness of 1 μm were sputtered onto substrates of SiO2 and Ti:W alloy films which were heated to temperatures between 25 and 360  °C. Rutherford backscattering and AES depth profile data indicated that a large fraction of the Cu was present near the substrate interface when deposited at elevated temperatures. Films prepared on substrates at room temperature exhibited little segregation. Placement of a Ti:W alloy barrier between the Al–Cu–Si film and the SiO2 substrate did not affect the Cu distribution. Cross-sectional transmission electron micrographs of samples prepared at 360  °C revealed the presence of Cu-rich precipitates approximately 4000 Å in size at the substrate interface. Precipitates formed in the room-temperature deposited films were approximately 1500 Å in size. These results suggest that, if sufficient thermal energy is available, Cu-rich precipitates which nucleate at the substrate interface will grow rapidly by depleting adjacent film regions of copper. The deduced driving force behind this phenomena is the desire of the system to reduce its precipitate surface to volume ratio and consequently free energy via an Ostwald ripening process. A surface diffusion mechanism is proposed to explain the interfacial precipitate nucleation and growth for the alloys deposited under cold substrate conditions.
Transitional behavior of pulsed dc losses in superconducting solenoids with self-fields greater than B*
Authors: Broach J. Thomas , Lee W. David , Eaton Russell
Published: July 2002

Losses were calorimetrically measured for five multilayer superconducting solenoids carrying pulsed dc transport currents. The solenoids, which were wound from commercial NbTi multifilamentary wire, had self-fields of B*<B<15 B*, where B* is the calculated field for full penetration of the filament. Loss measurements were taken as a function of peak current at a fixed frequency of 10 Hz and as a function of frequency (1–10 Hz) at a peak current of 30 A. The data do not agree with existing full or partial penetration loss models. The range of magnetic fields between the dominance of either full or partial penetration was found to be wider than expected. A model proposed by Ashkin predicted such a region and his technique for loss calculation agrees with the data.
Electrostatic electron cyclotron resonance maser (linear theory)
Authors: Liu Shenggang , Zhang Shichang , Yang Zhonghai , Cheng Xiaodong , Ouyang Zhengbiao
Published: July 2002

The linear theory of electrostatic electron cyclotron resonance maser (EECRM) is given in this paper. Starting from the fundamental concept, we obtained the perturbed equation of relativistic electron motion in an electrostatic centrifugal system, and the dispersion equation for both TEmn and TMmn modes of the EECRM have been derived with detailed discussion for the infinitely thin beam layer. The nonrelativistic case has also been studied. Digital calculations show that the dispersion curves of the EECRM are similar in shape to that of the conventional electron cyclotron resonance maser (MECRM) and the magnitude of growth rate of the EECRM is comparable with that of MECRM. Although the dispersion equation of EECRM contains a special kind of singularity [ω−k∥v∥−(m±(2−β2⊥)1/2) ω0 =0], the relevant instability within the parameter region of our calculations in this paper has not yet been found; this problem remains to be studied in the future.
Theory of a variable aperture phase conjugate mirror with application to an optical cavity
Authors: Bochove Erik
Published: July 2002

A new model for phase conjugate mirror reflectivity is derived and applied to a laser cavity with phase conjugate mirror. We find that by matching the phases of transverse cavity and phase conjugate mirror modes, the phase aberration correction ability of the mirror can be significantly improved.
Physical and optical properties of R-Zn-Ba-Yb-Th fluoride glasses
Authors: Shelby James E. , Lapp Josef C. , Suscavage Michael J.
Published: July 2002

The effect of glass composition on the density, refractive index, thermal expansion coefficient, glass transformation temperature, viscosity, and crystallization temperatures of R-Zn-Ba-Yb-Th fluoride glasses (R=Li or Na) was measured as BaF2 was replaced by RF. The optical spectra of these glasses were also measured. Values of each of the physical properties decreased with increasing alkali fluoride concentration. In every case, lithium had a larger effect than did sodium on the value measured for a given property. These results indicate that the substitution of an alkali fluoride for barium fluoride results in a decrease in the degree of linkage of the vitreous network.
Ion beam annealing during high current density implants of phosphorus into silicon
Authors: Cannavó S. , La Ferla A. , Rimini E. , Ferla G. , Gandolfi L.
Published: July 2002

The damage left by high current density∼10 μA/cm2 implants of 120-keV P+ into 4-in. (500-μm-thick) and 5-in. (600-μm-thick) Si wafers of 〈100〉 orientation has been measured by 2.0-MeV He backscattering in combination with the channeling effect technique. The fluences ranged between 1 and 7.5×1015/cm2. The amount of disorder is highest at 1×1015/cm2 and then decreases with fluence. The annealing of the amorphous layer takes place by the movement of two and one amorphous–single crystal interfaces for the 500- and 600-μm-thick wafers, respectively. The experimental data are compared with a beam annealing model based on the temperature-rise profile, the amount of point defects generated by the ion in the collision cascade volume, and the assumption of a regrowth process governed by an activation energy of 0.25 eV.
Atom and acceptor depth distributions for aluminum channeled in silicon as a function of ion energy and crystal orientation
Authors: Wilson R. G. , Jamba D. M. , Chu P. K. , Hopkins C. G. , Hitzman C. J.
Published: July 2002

Acceptor depth distributions measured using differential capitance-voltage profiling, and atom depth distributions measured using secondary ion mass spectrometry are reported for aluminum implanted in the random and the 〈100〉, 〈110〉, and 〈111〉 directions of the silicon crystal in the ion energy range from 5 to 300 keV, and show agreement between the two measurements for selected energies and with one prior work. Values of range parameters, maximum channeling ranges, and electronic stopping Se are reported.
Crazing and fracture in polystyrene studied by acoustic emission
Authors: Koenczoel L. , Hiltner A. , Baer E.
Published: July 2002

Acoustic emission (AE) has been coupled with slow crack propagation experiments in polystyrene to probe the mechanisms of damage and fracture. The single AE active mechanism recorded during slow crack growth is probably caused by failure of the craze fibrils in the craze zone at the propagating crack tip. The AE event rate and the AE energy release rate varied linearly with the crack speed indicating that the AE depends only upon the amount of fracture surface created independent of the crack speed. Since the duration of the AE was less than 1% of the total time of the experiment, it is concluded that crack propagation is discontinuous even at the highest crack speeds investigated.
Effect of thermal treatment on the impact strength of polycarbonate
Authors: Hornberger Lee E. , Fan Gloria , DeVries K. L.
Published: July 2002

Thermal treatment of polymers has been found to have a pronounced effect on the residual stress state and the impact properties of these materials. Researchers have found that compressive residual stresses can be used to bring about a transition from a brittle to higher-energy absorbing impact failure in polycarbonate and have subsequently proposed that this transition is predominately a function of the local stress state at the notch tip. In this study the impact strength of polycarbonate has been measured as a combined function of the residual compressive stress in the material, the thickness of the material, the radius of the notch tip and the location of the notch relative to the residual stress field. The transition in the energy absorption capability of the material was found to be highly dependent on these local variables at the notch tip.
Yukawa potentials for atomic negative ions
Authors: Ganas P. S. , Arakelian T.
Published: July 2002

For the purpose of calculating bound-state properties (e.g., energy levels) and scattering properties (e.g., cross sections) of atomic systems, we seek a precise independent-particle model (IPM) for electrons in atomic negative ions from Z=3 up to Z=85. The IPM potential is a combination of two Yukawa potentials whose strengths and ranges are functions of two adjustable parameters. The parameters are varied until the inner energy levels are close to the experimental energy levels of neutral atoms, and the last electron eigenvalue is precisely equal to the electron affinity of negative ions. Systematic trends in the parameters are determined.
Performance of and excited state densities in a linear thyratron
Authors: Kushner M. J. , Fisher C. H. , Demboski J. S. , Petr R. A.
Published: July 2002

A prototype of a new class of thyratrons having a linear geometry is described and measurements of excited state densities in the thyratron plasma using hook method spectroscopy are presented. The linear thyratron is conceptually scalable to high currents by lengthening it in the axial dimension without changing any other critical scaling dimension (such as the cathode-control grid distance). The prototype linear thyratron is a tetrode having a 3 cm×10 cm slotted dispenser cathode with an effective area of 80 cm2. The thyratron has separately switched 25 kV and 10 kA, with a maximum dI/dt of 1.3×1011 A s−1. Using helium as the working gas, maximum excited state densities of 6×1012 cm−3 were measured for the 23P state.
Characterization of the heavily doped emitter and junction regions of silicon solar cells using an electron beam
Authors: Luke Keung L. , Cheng Li-Jen
Published: July 2002

The electron-beam-induced-current (EBIC) technique is applied to the investigation of heavily doped emitter and junction regions of silicon solar cells via the beam specimen configuration in which the junction is parallel to the surface and the beam is perpendicular to it. It is demonstrated that this technique is very well suited to the investigation of the emitter and junction regions. Even though the experimental EBIC data are collected under three-dimensional conditions, it is shown analytically with the help of two numerical examples that the solutions obtained with one-dimensional numerical modeling are adequate. EBIC data for bare and oxide-covered emitter surfaces are measured and compared with theory. Good agreement is obtained when a cell quality factor of 0.89 is assumed, thus suggesting that ∼11% of the collected carriers recombined in the cell depletion region. This result is similar to Possin’s finding that there was evidence for ∼10% of recombination in the junctions of some of his silicon diodes with very shallow junctions [J. Appl. Phys. 50, 4033 (1979)]. It appears that further improvement of the solar cell conversion efficiency is possible if we can consistently make cells with an unity cell quality factor. The improvement in collection efficiency when an emitter surface is covered with an ∼100-A SiO2 film varies with beam energy. For a cell with a junction depth of 0.35 μm the improvement is ∼54% at 2 keV.
Thermal stability and aging effect of hydrogen-implanted bubble garnet films
Authors: Imura R. , Sugita Y.
Published: July 2002

Aging and thermal stability have been studied for a hydrogen-implanted bubble garnet by measuring the effective anisotropy field change Δ(Hk−4πMs) and the lattice strain (Δa⊥/a) in the normal direction to the film. After annealing, a large decrease of Δ(Hk−4πMs) has been observed due to the out-diffusion of hydrogen. It has been found that a larger Δ(Hk−4πMs) is kept after annealing in samples with SiO2 deposited on the garnet surface. The relaxation process of (Δa⊥/a) corresponding to Δ(Hk−4πMs) shows two activation energies EA (0.8 eV and 1.6 eV) for H+2 -implanted samples. A fast relaxation process (EA =0.8 eV) is peculiar to the H+2 -implanted samples due to the out-diffusion of hydrogen and has not been observed for He+ or Ne+ implanted samples. From the aging test, it has been established that the lifetime t is about 5000 years to assure 99% stability of Δ(Hk−4πMs) at 100 °C for samples stabilized at 400 °C after SiO2 deposition.
Cell performance and defect behavior in proton-irradiated lithium-counterdoped n+p silicon solar cells
Authors: Weinberg I. , Goradia C. , Stupica J. W. , Swartz C. K.
Published: July 2002

Lithium-counterdoped n+p silicon solar cells were irradiated by 10-MeV protons and their performance determined as a function of fluence. It was found that the cell with the highest lithium concentration exhibited the higher radiation resistance. DLTS studies of deep level defects were used to identify two lithium related defects. Defect energy levels otained after the present 10-MeV irradiations were found to be markedly different than those observed after previous 1-MeV electron irradiations. However, the present DLTS data are consistent with our previous suggestion of a lithium–oxygen interaction which tends to inhibit formation of an interstitial boron–oxygen defect.
Quality factor of the piezoelectric thin film on semiconductor composite resonator resulting from radiation into the semiconductor wafer
Authors: Shick D. V. , Stevens D. S. , Tiersten H. F.
Published: July 2002

The composite resonator consists of a uniform thin layer etched in a small well-defined region of a semiconductor wafer to form a diaphragm, upon which is deposited a thin piezoelectric film along with the electrodes to form a resonant region directly on the wafer. Although the composite resonator, which operates in an essentially thickness-extensional mode, can be constructed to employ energy trapping, almost all existing experimental work in the literature is for the case when trapping is not present. All previous analytical work expressly ignores radiation into the bulk semiconductor except one treatment, which unrealistically ignores the junction between the etched diaphragm and the bulk semiconductor. In this work an analysis of the composite resonator driven into essentially thickness-extensional vibrations by the application of a voltage to strip electrodes is performed. The analysis includes all radiating plate waves in the thick portion of the semiconductor. The solution consists of a sum of terms satisfying all differential equations and boundary conditions on major surfaces exactly and uses the appropriate variational principle of linear piezoelectricity to satisfy the remaining conditions approximately. For the case of the aluminum–nitride film on gallium arsenide the Q is calculated for both the configuration in which the film ends at the edges of the electrodes and in which it continues to the edges of the etched diaphragm when trapping is not present and for the latter configuration when trapping is present. The calculations show that when trapping is not present the Q is a very rapidly varying function of the ratio of the composite resonator thickness to the wafer thickness and that the range of variation is very large, i.e., between one and two orders of magnitude. The calculations also reveal that when trapping is present the Q is always much larger and its range of variation much smaller than when trapping is not present.
Resistivity of AuIn2+δ thin films
Authors: Bright A. A. , Wetzel J. T.
Published: July 2002

The resistivity and residual resistance ratio of 31-nm films of AuIn2+δ have been measured for a series of precision vacuum-deposited films covering the range of −0.04≤δ≤0.12. Both the resistivity and the resistance ratio exhibit a strongly peaked dependence on δ around δ=0. The results are analyzed in terms of the Mayadas–Shatzkes theory of scattering in thin films which includes the effects of both surface and grain boundary scattering. The dominant contribution to the resistivity is due to grain boundary scattering. The grain boundary scattering coefficient is unusually large compared to published results on single-phase metal films. These findings are interpreted in relation to the structure of the films and to the presence of second-phase material (AuIn or In) in the grain boundaries.
Low-temperature dielectric properties of SrTiO3 glass-ceramics
Authors: Swartz S. L. , Bhalla A. S. , Cross L. E. , Clark C. F. , Lawless W. N.
Published: July 2002

The low-temperature dielectric properties of strontium titanate aluminosilicate glass-ceramics, in which perovskite SrTiO3 is the primary crystalline phase, have been investigated. These glass-ceramics exhibited dielectric constant peaks at temperatures below 100 K; the magnitude of these peaks, along with their frequency and temperature dependencies, were strongly dependent on the crystallization conditions. In heavily crystallized glass-ceramics, two low-temperature, relaxation-type loss mechanisms were identified, at temperature ranges near 50 and 100 K. The magnitude of the dielectric loss peak increased with increasing frequency for the lower temperature (50 K) mechanism and the magnitude of the loss peak decreased with increasing frequency for the higher temperature (100 K) mechanism. Arrhenius activation energies were calculated to be 0.054 and 0.17 eV for the lower and higher temperature loss mechanisms, respectively. The higher temperature loss mechanism was further analyzed by the Cole–Cole method, and a relaxation strength of 41 was calculated. It was proposed that the dielectric constant and loss peaks were related to ferroic phenomena occurring in the SrTiO3 phase, caused by interactions of the SrTiO3 with the glass-ceramic matrix.