bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of additives on the response of sensors utilizing semiconducting oxide on carbon monoxide sensitivity
Authors: Ratna Phani A. , Manorama S. , Rao V. J.
Published: July 2002

A carbon monoxide gas sensor based on semiconducting oxide SnO2 has been developed. The addition of small amounts of transition metal oxide, MoO3, not only makes the elements highly selective to CO but significantly enhances the sensitivity of the sensor element in terms of the magnitude of the signal as well as the response time. The sensor element has been tested for cross selectivity to other reducing gases and confirmed unambiguously to be specifically sensitive to carbon monoxide gas. The sensor elements have been tested under different operating conditions. Different analytical techniques were used to establish the mechanism of sensitivity specifically to CO.
Observation of wave front curvature inside a vertical-cavity surface-emitting laser
Authors: van Doorn A. K. Jansen , van Exter M. P. , Woerdman J. P.
Published: July 2002

By performing interferometric measurements on the fundamental transverse mode of a planar VCSEL, we have determined the wave front curvature inside the VCSEL cavity. The results show that the (apparent) position of the beam waist is 0–8 μm below the surface of the top DBR, i.e., up to 25% of the Rayleigh range. From these results we estimate the amount of index and gain guiding in the VCSEL.
Electromigration induced resistance changes in a single aluminum via
Authors: Alers G. B. , Oates A. S. , Beverly N. L.
Published: July 2002

High resolution resistance measurements have been performed on isolated aluminum vias to study resistance changes induced by electromigration. The via test structures consisted of a 1.5 μm diameter, 0.8 μm deep interconnect between two aluminum alloy metallization layers separated by a TiN layer. The TiN interlayer acts as a diffusion barrier for the electromigration process at which material may accumulate or be depleted to induce resistance changes. The resistance changes were measured with a resolution of 10−9 Ω/s for a ∼0.1 Ω via. A dc current caused both increases and decreases in the resistance, depending in the current direction, which recovered completely when the current was removed. The initial resistance changes were found to be proportional to t1/2 as would be expected for a diffusive electromigration process. Because both the geometry and diffusion barrier of these structures are well defined a quantitative analysis can be made which is found to be most consistent with copper as the initial diffusing element.
Nanoprobe-induced electrostatic lateral quantization in near-surface resonant-tunneling heterostructures
Authors: Taylor M. D. , Wetsel G. C. , McBride S. E. , Brown R. C. , Frensley W. R. , Seabaugh A. C. , Kao Y.-C. , Beam E. A.
Published: July 2002

We report experimental and theoretical evidence for electrostatic lateral confinement induced by a nanoprobe. The lateral confinement is manifest as oscillations of the differential conductance of a near-surface resonant-tunneling heterostructure in air at room temperature.
Improved laser performance at 946 and 473 nm from a composite Nd:Y3Al5O12 rod
Authors: Hanson Frank
Published: July 2002

Efficient pulsed room-temperature laser operation at 946 nm has been achieved by end-pumping Nd:YAG with multiple diode array bars. High average power operation was made possible by the use of a water-cooled composite doped/undoped Nd:YAG laser rod. A 5.7 W output at 946 nm was obtained at 500 Hz in long-pulsed operation. Over 15% efficiency based on incident pump power was measured at 300 Hz. With intracavity frequency doubling using KNbO3, 366 mW was obtained at 473 nm and 200 Hz.
In situ observation of phase transition and the transition-induced step bunching on InAs(001) surfaces by scanning electron microscopy
Authors: Yamaguchi Hiroshi , Homma Yoshikazu , Horikoshi Yoshiji
Published: July 2002

The reconstruction and the step structure change during the phase transition on an InAs(001) surface under As pressure is observed directly by using scanning electron microscopy. The domain formation corresponding to the first-order phase transition is clearly seen as predicted by Monte Carlo simulation with a lattice gas model. It is also seen that the step structure largely depends on the surface reconstruction and the misorientation direction. This gives the first observation of phase-transition-induced step bunching on a compound semiconductor surface.
Electrical and structural properties of InxGa1−xN on GaAs
Authors: Abernathy C. R. , MacKenzie J. D. , Bharatan S. R. , Jones K. S. , Pearton S. J.
Published: July 2002

InxGa1−xN (x=0.07–1.0) layers were grown on GaAs substrates by metalorganic molecular beam epitaxy. The films display strong n-type conductivity (n≳1020 cm−3) for a wide range of compositions. The use of an H2 rather than a He carrier gas produces a lower carrier concentration in the as-grown material. The InxGa1−xN is single crystal at low Ga concentrations with the lattice mismatch accommodated by a high density of stacking faults and microtwins. The InN layers contain only the cubic phase, while the ternaries contain both cubic and hexagonal phases.
Preparation of monolithic barium titanate xerogels by sol–gel processing and the dielectric properties of their sintered bodies
Authors: Kuwabara M. , Miki K. , Takahashi S. , Shimooka H.
Published: July 2002

Monolithic xerogels of crystalline barium titanate, with dimensions of ∼3 mm thick and ∼6 mm in diameter, have been produced by sol–gel processing using metal alkoxides. An excess amount of water with the H2O/Ba ratio≳100 (for hydrolysis of the barium titanate precursor alkoxides) and aging time≳8 days were necessary to produce the monolithic crystalline xerogels without breaking during drying (at 90 °C). The barium titanate xerogels as-dried, with a porosity of about 70%, have been found to consist of crystalline grains in the range of 10–20 nm. Firing the xerogels at 1000 °C in air yielded porous barium titanate ceramics with an average grain size around 50 nm and a decreased porosity around 60%. The dielectric constant (εr)–temperature (T) characteristics of these ceramics have been found to be rather flat below 120 °C with a broad peak around this temperature, and those above 120 °C showed a specific behavior of ferroelectric materials described by a Curie–Weiss equation, εr=C/(T–T0), with C≊2×104 K and T0≊230 K (−43 °C); although these values are quite different from those of ferroelectric barium titanate.
Heteroepitaxial growth of a c -axis-oriented BaTiO3/YBa2Cu3O7−σ bilayer structure by pulsed laser ablation
Authors: Zhang Jie , Chen Zhenghao , Cui Dafu , Lu Huibin , Zhou Yueliang , Li Lin , Yang Guozhen , Jiang Nan , Hao Jianmin
Published: July 2002

BaTiO3/YBa2Cu3O7−δ  bilayer structure has been epitaxially grown on a LaAlO3 (100) substrate by pulsed laser ablation with sintered YBa2Cu3O7−δ  and single crystal BaTiO3 targets. The analysis of the BaTiO3/YBCO bilayer structure by x-ray diffraction (XRD) 2θ/θ, w, and φ scans as well as high resolution electron microscopy indicates that the bilayer thin films have a high degree of c-axis-oriented epitaxial crystalline structure. The surface morphology of the thin film was observed by scanning electron microscopy.
Luminescence of low-temperature GaAs in a GaAs/In0.2Ga0.8As multiple quantum well structure
Authors: Cheng T. M. , Chang C. Y. , Huang J. H.
Published: July 2002

The luminescence of GaAs layers grown by molecular beam epitaxy at low substrate temperature (230 °C) in a GaAs/In0.2Ga0.8As multiple quantum well structure is presented. The near-band-gap emission and defect-related emission are observed for samples annealed at high temperature (800–900 °C), but are not observed for samples annealed at lower temperature (600–700 °C). The luminescence shows a strong correlation with the spacing between As precipitates based on the transmission electron microscope observations. The evolution of luminescence of annealed low-temperature (LT) GaAs can be reasonably explained by the buried Schottky model.
Effect of misorientation angles on the surface morphologies of (001) homoepitaxial diamond thin films
Authors: Lee Naesung , Badzian Andrzej
Published: July 2002

Etching and homoepitaxial growth were performed on 0.1°, 3.5°, and 11.0° off (001) diamond substrates using microwave plasma-assisted chemical vapor deposition. Etched surfaces showed a sequential morphological change from etch pits to stepped surface to flat surface with increasing misorientation angle. In homoepitaxial growth hillock formation on the (001) surface was ascribed to the lack of surface steps on the well-oriented substrate, while the growth on the misoriented surfaces proceeded via step flow along 〈110〉. Reflection high-energy electron diffraction showed that the films were single crystals and their surfaces were composed of the 2×1 and 1×2 double-domain structure.
GeSi/Si bistable diode exhibiting a large on/off conductance ratio
Authors: Zheng X. , Carns T. K. , Wang K. L.
Published: July 2002

A novel bistable phenomenon having both a high conductance on state and a high impedance off state has been observed in a forward biased delta-doped GeSi/Si tunnel diode grown by molecular beam epitaxy. The bistable characteristics are attributed to the different mobile carrier densities in the delta-doped layers, which leads to the switching of the band structure from a tunnel junctionlike alignment to a p-i-n junctionlike alignment or vice-versa. An on/off conductance ratio larger than 106 has been demonstrated for a modified diode structure. The device processing is technologically compatible to the current Si metal-oxide-semiconductor technology, making the device useful for a high speed, high density static random access memory cell.
Superior output linearity of optimized double heterostructure vertical-cavity top-emitting lasers
Authors: Tu L. W. , Schubert E. F. , Wang Y. H. , Weir B. E. , Zydzik G. J. , Cho A. Y.
Published: July 2002

Optimized double heterostructure (DH) vertical-cavity top-emitting lasers are grown by molecular beam epitaxy. Both the doping profile and the laser structure are optimized to achieve high performance. Continuous wave 2 mW output power at room temperature is obtained for nominal 10 μm diam DH vertical-cavity top-emitting injection lasers. A single fundamental longitudinal and transverse mode is maintained up to 1.7 mW. It lases in continuous waves at a temperature of 80 °C. A lasing power range of ∼0.8 mW is sustained within a 10% change in the output linearity, which is much larger than a value of less than 0.1 mW for quantum well lasers. This demonstrates that its output linearity is far more superior than the one of compared quantum well lasers, which is explained in detail.
High-repetition operation of a symmetric Mach–Zehnder all-optical switch
Authors: Nakamura S. , Tajima K. , Sugimoto Y.
Published: July 2002

The high-repetition switching capabilities of a recently developed symmetric Mach–Zehnder (SMZ) all-optical switch are experimentally investigated. Using a series of four control pulses at intervals of 100 or 25 ps, nearly full switching is achieved at the corresponding intervals. The results experimentally show that the repetition rate, as well as the switching speed, of the SMZ all-optical switch is not restricted by the slow relaxation of the utilized high-efficiency band-filling effect.
High quantum efficiency dual wavelength resonant-cavity photodetector
Authors: Srinivasan A. , Murtaza S. , Campbell J. C. , Streetman B. G.
Published: July 2002

A new dual-wavelength, resonant-cavity photodiode is described. It has previously been shown that the resonant-cavity structure can achieve high quantum efficiencies in a relatively narrow spectral region with thin absorbing regions. In this letter, a dual wavelength mirror is incorporated into the cavity to achieve operation in two wavelength regions. Peak external quantum efficiencies greater than 50% were demonstrated at 730 and 910 nm.
Phase transitions in the Pb(In1/2Nb1/2)O3–PbZrO3 system
Authors: Yasuda Naohiko , Mizuno Takuya
Published: July 2002

Phase transitions and dielectric properties of (1−x)Pb(In1/2Nb1/2)O3(PIN)-xPbZrO3(PZ) solid solution system have been examined as a function of the concentration x. Two morphotropic phase boundaries were identified: (1) pseudocubic to rhombohedral phase boundary at x=0.35 and (2) rhombohedral to orthorhombic at x=0.8. For x<0.35, a diffuse phase transition was observed. For 0.35<x<0.8, the relative permittivity ε′r showed a sharp peak at Tc. In this regime, the phase below Tc was confirmed to be ferroelectric by observation square P-E hysteresis loops. For x≳0.8, a steplike dielectric anomaly appeared at Tt (below Tc) as well as the sharp peak in the permittivity. The phase below Tt was confirmed to be antiferroelectric by the observation of double P-E hysteresis loops. The maximum permittivity of 15 000 (at 100 kHz) was observed at x=0.35
Al diffusion into GaAs from monatomic AlAs layers investigated by localized vibrational modes
Authors: Ono Haruhiko , Ikarashi Nobuyuki , Baba Toshio
Published: July 2002

Using infrared absorption spectroscopy, we investigate the thermal diffusion behavior of Al atoms from monatomic Al layers embedded in a GaAs epitaxial film. After thermal annealing, the absorption peak of the two-dimensionally localized vibrational modes at 358 cm−1 due to Al layers decreases, while the peak at 362 cm−1 due to isolated Al atoms increases. The 362 cm−1 peak height is compared with the fraction of isolated Al atoms calculated, assuming the second nearest neighbor hopping diffusion from a monatomic Al layer into GaAs matrix. We thus determine the diffusion coefficient of Al atoms in GaAs to be 2×10−19 cm2/s at 700 °C. The present study offers a simple and reliable method to investigate the impurity diffusion in crystals.
Stable glow discharge for synthesis of carbon nanotubes
Authors: Wang X. K. , Lin X. W. , Dravid V. P. , Ketterson J. B. , Chang R. P. H.
Published: July 2002

The use of a stable glow discharge for the synthesis of carbon nanotubes is reported. Bundles of buckytubes are synthesized with remarkably large diameters (up to 200 μm). The bundles are evenly spaced, parallel, and occupy the entire central region of the deposited rod. High resolution electron microscopy (HREM) images of the deposited rod produced by the glow discharge revealed higher yield and improved quality buckytubes as compared to those produced by an arc discharge. The behavior of the two deposition modes (glow and arc) has been compared and their effects on the formation of buckytubes are discussed.
New encapsulant source for III–V quantum well disordering
Authors: Rao E. V. K. , Hamoudi A. , Krauz Ph. , Juhel M. , Thibierge H.
Published: July 2002

We report here the characteristic features of a newly developed dielectric encapsulant cap layer, which after adequate thermal treatments, leads to a reproducible local alloy disorder in several III–V quantum well (QW) structures. Data are presented to demonstrate its universality, namely, its ability to promote alloy-disorder free of charge carriers either on group III or group V sublattice depending on the type of the QW structure.
X-ray image monitoring using a new soft x-ray plate: Ag/chalcogenide film
Authors: Utsugi Yasushi , Kakuchi Masami , Maezawa Hideki
Published: July 2002

A new soft x-ray plate of Ag/chalcogenide film is proposed, which offers in situ monitoring of high-resolution x-ray images. Soft x-ray exposure of synchrotron and undulator radiation causes color change in the Ag/chalcogenide film, capable of yielding a potential resolution on the order of 100 Å. In situ monitoring of the diffraction light of a He-Ne laser-beam irradiation on the film revealed the processes involved in recording x-ray images of gratings during the exposure. The reflection light caused by scanning with the laser beam provided good reconstructed images. A possible application to future x-ray holography is also described.
Soft x-ray spectroscopy of polymer resist using synchrotron radiation
Authors: Mochiji Kozo , Sooda Yasunari , Ito Masaaki , Kimura Takeshi
Published: July 2002

Soft x-ray absorption spectra and spectral sensitivity of x-ray resists are studied by using synchrotron radiation. Spectral sensitivity is successfully evaluated from the fragment yield change of the decomposed resists by changing incident x-ray wavelengths. This evaluation method is newly developed here. Using this technique, x-ray wavelength dependency for the decomposition efficiency of polymer resists poly(2-methylpentene-1-sulfone) and their decomposition characteristics are clarified. These are very important for development of more sensitive x-ray resists.
VUV-SX spherical grating monochromator for BEPC beamline 4B9B
Authors: Shu D. , Wang W. , Liu W. , Zhang Y. , Wang M. , Liu J. , He W. , Cong Z. , Xie Q.
Published: July 2002

The BEPC beamline 4B9B is intended for VUV-SX photoelectron spectroscopy and other soft x-ray applications. The beamline optical system consists of a focusing mirror system and a VUV-SX spherical grating monochromator with four gratings, which cover a large spectral range 10–1100 eV. Three laminar gratings (1100, 500, and 200 lines/mm) with a 57–m radius are used at a 174° including angle, and the other grating (600 lines/mm) with a 6-m radius is used at a 142° including angle to be suited for low-energy use. Scanning is achieved by the rotation of the grating, and a pair of stepping motor-driven slits follow the Rowland circle to improve the monochromator’s performance. The optical design and ray tracing results about this monochromator are described
Development of an optical emission spectroscopy-based method for dynamic compositional analysis of sputter deposited films from multicomponent targets
Authors: Leedy K. D. , Rigsbee J. M.
Published: July 2002

A method of calculating as-deposited elemental film composition during the actual deposition process was developed using optical emission spectroscopy of the glow discharge. These results are demonstrated by analyses of a series of thin film Ag1−xSix alloys fabricated using radio frequency sputter deposition with composite Ag+Si sputter targets. Using intensity ratios of the Si (251.6 nm), Ag (328.1 nm), and Ar (419.8 nm) emission lines after equilibration of the substrate temperature, estimates of at. % Si in the films were calculated which agreed well with post-deposition composition measurements of the films by Auger electron spectroscopy.
rf-induction plasma apparatus for generating submicron particles of metals
Authors: Barmore W. L. , Hrubesh L. W. , Keene L. E. , Raymond E. L.
Published: July 2002

A unique apparatus is described for generating submicron particles of metals over a narrow-size distribution range. Coarse particles of the metal were injected into the tail flame of an argon rf-induction plasma torch, where they were vaporized. The vapor was gas quenched, producing a metallic smoke of fine spheroidal particles. The system collection units separated the fine particles (∼0.3-μm diameter) from the heavier particles (≥1-μm diameter) while the material was finely dispersed and moving in the gas stream.
Effects of deposition conditions on transport properties of intrinsic hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide films investigated by the photomixing technique
Authors: Tang Yi , Braunstein R.
Published: July 2002

By using the photomixing technique, we have determined the electron drift mobility, lifetime, and the conduction band Urbach energy of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H) films as a function of deposition temperature (Ts, 200 °C≤Ts≤280 °C) and hydrogen dilution ratio (R,0≤R≤25), respectively. We have found that for the a-Si:H films with increasing deposition temperature, the lifetime (at 480 K) increases, both the drift mobility (at 480 K) and the Urbach energy decrease and for the a-SiC:H films with increasing hydrogen dilution ratio, both the drift mobility (at 480 K) and the lifetime (at 480 K) increase, and the Urbach energy shows a tendency to decrease. These results, together with previous results of other workers, indicate that for the a-Si:H films with increasing deposition temperature, the density of negatively charged defects increases and the density of positively charged and neutral defects decreases; and for the a-SiC:H films with increasing hydrogen dilution ratio, the density of positively charged, negatively charged, and neutral defects all show a tendency to decrease.
Optical phonons in a quantum well containing monolayers
Authors: Ridley B. K.
Published: July 2002

The continuum theory of optical-mode hybrids in multilayered structures is applied to the case of a quantum well containing a centrally placed monolayer of a semiconductor whose optical frequencies are very different from those of the host. It is shown that antisymmetric modes are strongly modified whereas symmetric modes are not modified at all. As a consequence, the intersubband scattering rate is expected to be reduced.
Area-selective formation of an organosilane monolayer on silicon oxide nanopatterns fabricated by scanning probe anodization
Authors: Sugimura Hiroyuki , Nakagiri Nobuyuki , Ichinose Nobuyuki
Published: July 2002

An organosilane monolayer was formed from a precursor vapor (trimethylchlorosilane, TMCS) onto the surface of silicon oxide (SiOx) nanopatterns surrounded by hydrogen-terminated silicon (Si–H). The nanopattern was fabricated with a resolution of 20 nm by scanning probe anodization, that is, localized anodization induced beneath the tip of a scanning probe microscope. The area-selectivity arises from the difference in the chemical reactivity of the vapor between the SiOx and Si–H surfaces. The TMCS-coated SiOx patterns showed a resistivity to chemical etching with an aqueous solution of ammonium fluoride and hydrogen peroxide. Lateral force microscopy with an organosilane-coated probe also indicated the presence of the monolayer on SiOx through a friction force contrast between the monolayer-coated and uncoated regions.
Design of an asynchronous electrostatic motor
Authors: Kobayasi Syoyu
Published: July 2002

An asynchronous electrostatic motor that works under a high-voltage pulse controller using LED-phototransistor photosensors is described. The motor produced the torque 1030-dyn-cm at 1500 V and attained the power 0.8 mW at 80 rpm in n-hexane.
Effect of surface steps and nonstoichiometry on critical thickness of strained InGaAs layers grown by molecular beam epitaxy on InAlAs/InP heterostructures
Authors: Gendry M. , Drouot V. , Hollinger G. , Mahajan S.
Published: July 2002

It is shown that critical thicknesses of In0.65Ga0.35As epilayers, grown by molecular beam epitaxy on lattice matched InAlAs/InP heterostructures, are affected by surface steps and excess arsenic, i.e., nonstoichiometry, in the overgrowth. The critical thickness is reduced in the presence of steps, but is observed to increase when the excess arsenic atoms are present in the layer. It is argued that the generation of dislocation loops required for misfit dislocations is facilitated at the step edges. The resulting misfit dislocations augment the strain relaxation produced by the glide of threading dislocations in the epilayers. On the other hand, the internal strains associated with the nonstoichiometry strengthens the lattice, thus making dislocation glide difficult which delays the relaxation process.
ERC sources for the production of highly charged ions (invited)
Authors: Lyneis C. M. , Antaya T. A.
Published: July 2002

Electron cyclotron resonance ion sources (ECRIS) using rf between 5 and 16 GHz have been developed into stable, reliable sources of highly charged ions produced from a wide range of elements. These devices are currently used as ion sources for cyclotrons, synchrotrons, and heavy-ion linacs for nuclear and relativistic heavy-ion physics. They also serve the atomic physics community as a source of low energy multiply charged ions. In order to improve their performance both with respect to maximum charge state and beam intensity, ECRIS builders are now designing and constructing sources which will operate at frequencies up to 30 GHz. In this article we review the present status of operating ECRIS, review recent experimental measurements on plasma parameters, and look at the technology and potential of sources operating at frequencies up to 30 GHz.
Bimodal roughness of heterointerface in quantum wells analyzed by photoluminescence excitation spectroscopy
Authors: Woo J. C. , Rhee S. J. , Kim Y. M. , Ko H. S. , Kim W. S. , Kim D. W.
Published: July 2002

Photoluminescence excitation (PLE) studies were performed on GaAs-Al0.25Ga0.75As quantum wells (QWs) with fractional monolayer differences. The quantized PLE peaks and their submonolayer shifts clearly show that the heterointerface of thin QWs prepared by growth-interrupted molecular beam epitaxy has islands which extend out a lateral dimension larger than 100 Å, but they themselves have the microroughness smaller than 30 Å. The result of this work using exciton as the probe provides a clear evidence supporting the bimodal roughness model.
A new InP-based heterojunction bipolar transistor utilizing an In0.53Al0.22Ga0.25As base
Authors: Wu Y. H. , Su J. S. , Hsu W. C. , Liu W. C. , Lin W.
Published: July 2002

A lattice-matched In0.53Al0.22Ga0.25As/InP heterojunction bipolar transistor has been fabricated by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). No potential spike due to zero conduction band discontinuity at the emitter-base heterojunction is obtained. Meanwhile, the larger valence discontinuity (ΔEV=460 meV) than AlGaAs/GaAs and InGaAs/InP systems provides this structure with a better hole confinement. An offset voltage as low as 50 mV along with a current gain of 85 is achieved.
An ultrahigh vacuum goniometer system equipped with a Si(Li) array detector for soft x-ray standing-wave experiments
Authors: Maeyama Satoshi , Kawamura Tomoaki , Oshima Masaharu
Published: July 2002

An ultrahigh vacuum compatible goniometer system has been developed for use in angle-scan standing-wave experiments in a soft x-ray region. This system uses a horizontal two-axis (theta and two-theta) goniometer for the x-ray diffractometer. The theta axle used for sample rotations is inserted into the vacuum chamber through a differentially pumped rotary feedthrough and is driven by a stepping motor. To detect x-ray fluorescence excited by x-ray standing waves, a three-element linear-array Si(Li) detector is equipped for this system. SKα fluorescence angular yield from monolayer-order sulfur atoms on a GaAs(111) surface could be measured for the first time by the angle-scan standing-wave experiment. This result demonstrates that this goniometer system can be used for angle-scan standing-wave experiments in the soft x-ray region.
Tunable far infrared laser spectrometers
Authors: Blake G. A. , Laughlin K. B. , Cohen R. C. , Busarow K. L. , Gwo D-H. , Schmuttenmaer C. A. , Steyert D. W. , Saykally R. J.
Published: July 2002

The state of the art in far infrared (FIR) spectroscopy is reviewed. The development of tunable, coherent FIR radiation sources is discussed. Applications of tunable FIR laser spectrometers for measurement of rotational spectra and dipole moments of molecular ions and free radicals, vibration-rotation-tunneling (VRT) spectra of weakly bound complexes, and vibration-rotation spectra of linear carbon clusters are presented. A detailed description of the Berkeley tunable FIR laser spectrometers is presented in the following article.
Thermal-wave imaging of hydrogen in metals and alloys
Authors: Mussati G. , Sala E. , Maffi S. , Razzini G. , Peraldo Bicelli L.
Published: July 2002

Ex situ photoacoustic thermal-wave imaging of hydrogen electropermeated in a titanium and stainless steel (AISI 304) foil has been performed. Both the magnitude and phase of the complex amplitude of the photoacoustic signal have been investigated. The results show a new phase (TiH2) in the case of titanium and typical blisters in the case of stainless steel; both could be imaged deeply below the sample surface.
All solid source molecular beam epitaxy growth of strained-layer InGaAs/GaInAsP/GaInP quantum well lasers (λ=980 nm)
Authors: Toivonen Mika , Jalonen Marko , Salokatve Arto , Näppi Jari , Savolainen Pekka , Pessa Markus , Asonen Harry
Published: July 2002

We report on the growth of 980-nm strained-layer InGaAs/GaInAsP/GaInP separated confinement quantum well lasers using all solid source molecular beam epitaxy. Valved cracker cells were employed for both phosphorus and arsenic. Fabricated lasers exhibited excellent performance that is comparable to similar lasers grown by gas source molecular beam epitaxy in our laboratory. A maximum output power of 450 mW and over 250 mW in single mode operation was achieved for ridge waveguide lasers with AR/HR coated facets.
Potential profile measurements using a collimated proton detector in spherical inertial-electrostatic plasma confinement
Authors: Nadler J. H. , Gu Y. B. , Miley G. H.
Published: July 2002

A collimated proton detector has been developed for spatial resolved proton measurements in inertial-electrostatic plasma confinement (IEC) fusion experiments. These are the first proton measurements used to infer potential well profiles on an IEC device. This paper describes a new technique for investigating the existence of multiple potential wells inside IEC devices. Analysis of the observed proton energy and source profile indicates that (for a 12-mA cathode current, a 30-kV cathode voltage in a 4-mTorr D2 background) predominantly beam-background fusion occurs. Computer simulation suggests that a positive space charge potential approximately half that of the applied voltage is formed inside the cathode. These results establish the first measurement of a positive potential well structure inside an ion-injected IEC device.
Nitrogen doping during atomic layer epitaxial growth of ZnSe
Authors: Zhu Z. , Horsburgh G. , Thompson P. J. , Brownlie G. D. , Wang S. Y. , Prior K. A. , Cavenett B. C.
Published: July 2002

This letter reports the growth and characterization of ZnSe:N layers by atomic layer epitaxy (ALE) using a nitrogen rf-plasma source. The ALE-grown ZnSe:N layers have been investigated in terms of in situ reflection high electron energy diffraction and ex situ capacitance–voltage profiling and photoluminescence spectroscopy. The net acceptor concentration in the ALE-grown layer has been obtained as high as 1.2×1018 cm−3 and the ALE layers of ZnSe:N show reduced number of compensating deep centers compared with the ZnSe:N grown by molecular beam epitaxy. The effects of the Fermi level at a growing surface on the generation of compensating donors with a binding energy of 57 meV are also discussed.
Detailed experimental investigation of a local defect layer used for Si solar cells
Authors: Zundel M. K. , Csaszar W. , Endrös A. L.
Published: July 2002

The structural, electronic, and optical properties of the so-called local defect layer (LDL), the key feature of the junction near the local defect layer (JNLD) Si solar cell, have been studied after each processing step using transmission electron microscopy, spreading resistance (SR), and absorption measurements. Our results show that a layer of 20–80 nm sized bubbles is formed beneath the Si surface after proton implantation and a two-step annealing process. The SR profiles reveal that the implantation-damaged Si material is almost electronically reconstituted after the second annealing step. This LDL absorbs less than 2% of the sunlight; therefore, the efficiency of a JNLD solar cell cannot be increased by more than 2% (relative) compared to an unimplanted reference cell. However, by using higher implantation doses a buried textured layer is formed which leads to an enhanced absorption and has a similar beneficial effect in solar cells as a textured surface.
Indium desorption from InAs surfaces and its dependence on As coverage
Authors: Ekenstedt M. J. , Yamaguchi H. , Horikoshi Y.
Published: July 2002

The desorption rate of In atoms from an InAs surface and its dependence on surface As coverage is reported. InAs films were grown by molecular beam epitaxy on fully strained 1 monolayer thick In0.75Ga0.25As films deposited on (001) InAs substrates. Using a sensitive technique based on reflection high-energy electron diffraction, the desorption rate for In is found to be highly dependent on the As coverage. During a sublimation process, where In from an InAs surface is desorbed, the desorption rate at 510 °C is five times greater for a group III stabilized surface than for an As-stabilized surface. The difference in desorption rate is believed to be related to changes in the In to surface bond strengths.
Metastable assisted deposition of TiN films
Authors: Baránková H. , Bárdoš L. , Berg S.
Published: July 2002

An excess heat from an exothermic reaction of metastable Ar (43P0) and Ar (43P2) atoms with N2 molecules at low contents of N2 in Ar was found to be responsible for an enhanced thermionic emission, an enhanced production of Ti target vapor, an increased ionization, and consequently for an enhanced deposition rate of TiN films in the radio frequency hollow cathode plasma jet (RHCPJ). This finding emphasizes favorable geometry of hollow cathodes, as well as an important role of metastables in plasma-assisted processes.
Dynamics of low-pressure gain-switched iodine lasers
Authors: Nicholson J. , Rudolph W. , McIver J. , Tate R. , Hager G.
Published: July 2002

The dynamics of gain-switched, low-pressure photolytic iodine lasers were investigated experimentally and theoretically as a function of pressure and buffer gas. The behavior of the pulse shape, build-up, and duration can be explained by relaxation from a nonthermalized to a thermalized velocity distribution of the gas.
Radiometry at the NIST SURF II storage ring facility
Authors: Furst M. L. , Graves R. M. , Canfield L. R. , Vest R. E.
Published: July 2002

The National Institute of Standards and Technology (NIST) in Gaithersburg, MD, is the site of the Synchrotron Ultraviolet Radiation Facility (SURF II). The synchrotron radiation from the 300 MeV electron storage ring is used for most of the NIST radiometry programs in the far ultraviolet. Continuum radiation from SURF II extends from the infrared to about 4 nm (310 eV) and is a standard source for the calibration of integrated optical systems, particularly space experiments. The SURF II facility is also used for a large portion of the NIST far ultraviolet transfer detector standards program, in which spectrally calibrated detector standards are available from 5 nm (248 eV) to 254 nm (4.9 eV). One of the most recent activities has been the development of a new apparatus designed to qualify working standards for calibration of the NIST MgF2 windowed far ultraviolet transfer standard detectors. Additionally, new radiometric quality silicon photodiodes have now been developed. These detectors offer many improvements onver NIST’s photoemissive standards.
Current transport properties of metal/hydrogenated amorphous silicon/GaSb structures
Authors: Dutta P. S. , Sreedhar A. K. , Bhat H. L. , Dubey G. C. , Kumar Vikram , Dieguez E.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) has been deposited on n- and p-GaSb by the plasma glow discharge technique. The electrical characteristics of metal/a-Si:H/GaSb structures are presented. The current transport in these structures is dictated by the barriers at the metal/a-Si:H and a-Si:H/GaSb interfaces and the series resistance of the bulk a-Si:H interfacial layer. Space charge limited current in the interfacial layer gives rise to a voltage dependent resistance and increases the forward ‘‘turn-on’’ voltage. Furthermore, these structures exhibit extremely low reverse leakage currents and high reverse breakdown voltages. Significantly, rectifying junctions of a-Si:H/p-GaSb have been achieved with barrier heights of ∼0.4 eV.
Fluorescence-photoion-coincidence spectroscopy on ICN core excited molecules
Authors: Meyer M. , Lacoursière J. , Simon M. , Morin P.
Published: July 2002

An experimental setup is presented to measure coincidence spectra between a fluorescence photon (260 nm≤λph≤600 nm) and one or two photoions after core excitation providing information about the dissociation channels leading to excited, fluorescing states. The dissociation of ICN molecules excited in the iodine 4d shell is discussed. Upon resonant excitation the intensity due to the parent ion is found to be negligibly small and the atomic fragments comprise the most important part of the fluorescence intensity. For the first time coincidences between one photon and two photoions have been measured. In general, the observed mean slopes of the double coincidence peaks are consistent with photoelectron-photoion-photoion) measurements on ICN. In the I+/CN+ channel the singly charged iodine atom is found with relatively high percentage in a different excited state than in the I+/C+ or I+/N+ channels.
Explanation of stretched exponential growth behavior
Authors: Kim Kwangjoon , Epstein Arthur J.
Published: July 2002

We show that the photoinduced defect population growth of an optically thick film may have stretched exponential time dependence if the defect does not decay nor diffuse within the time scale of the experiment. After the formulation of this simple model, low-temperature photoinduced absorption of polyaniline is described as an example.
A new pulse compression circuit for low impedance pulse power generation
Authors: Masugata Katsumi
Published: July 2002

A new type of pulse compression circuit is proposed to generate low impedance pulse power. By using the circuit, high efficiency, low load of switching device, and reduction of reflected pulse are expected and it is suitable to produce a low impedance pulse. Performance of the system is evaluated by a computer simulation and compared with a conventional circuit using a pulse forming line. Energy transfer efficiency of 94% is obtained which is 15% higher than the conventional one. The Vτ value of the switching device is reduced to 56% of that for a conventional circuit.
Long-pulsed Nd:YAG frequency-doubled laser for optical measurements of high-velocity phenomena
Authors: Uchino Masakazu , Yuan Gang , Mashimo Tsutomu
Published: July 2002

A long-pulsed neodymium-doped yttrium aluminum garnet (Nd:YAG) frequency-doubled laser with no Q-switch was constructed for optical measurements of high-velocity phenomena. The laser consists of a doubled-elliptical pump cavity with a Nd:YAG rod and two xenon flash lamps, an intracavity potassium titanyl phosphate crystal, and a high-voltage electrical-pulse source. A narrow-band-stimulated emission at the frequency-doubled 532-nm wavelength was confirmed by a spectrometer. The delay time from a trigger signal and the effective pulse duration were approximately 40 and 65 μs, respectively. The laser average output power was measured to be larger than 6 kW by a pyroelectric joulemeter. This laser may be used as a flash monowavelength light source, and also as a long-pulsed single-mode laser in the visible wavelength region using for example, an intracavity étalon and/or a brewster plate.
An accurate technique to record the angular distribution of backscattered light
Authors: Wiersma D. S. , van Albada Meint P. , Lagendijk Ad
Published: July 2002

We report on a new technique to record the angular distribution of light which is scattered from a (disordered) material around the backscattering direction. The technique is accurate over a large scanning range (500 mrad) which includes the exact backscattering direction, and the angular resolution is high (100 μrad). The technique is particularly suitable for the study of coherent backscattering from very strongly scattering random media, but it can be applied in any situation where the angular distribution of backscattered light is studied. It allowed us to measure for the first time the theoretical value of two of the enhancement factor in coherent backscattering.
Fast interfacial oxidation of amorphous Si1−xGex:H by SnO2
Authors: Edelman F. , Brener R. , Cytermann C. , Eizenberg M. , Weil R. , Beyer W.
Published: July 2002

Fast oxidation of amorphous (a) Si1−xGex:H by interfacial reaction with SnO2 was observed at the temperature range of 400–500 °C. The rate of interfacial oxidation was very significant, while a test in a dry O2 ambient at the same temperatures showed no oxidation of Si1−xGex:H beyond the native oxide. The interfacial reaction of the SiGe:H/SnO2/glass system resulted in a layered structure of silicon oxide, tin oxide, and β-Sn at the SiGe/SnO2 interface. The extent of the interfacial reaction was found to depend on the Ge content in the Si1−xGex:H films; after annealing, the resultant silicon oxide layer is thicker for the Si-rich SiGe layer than for the Ge-rich composition. On the other hand, the SnO2 layer was totally reduced by an a-Ge:H top layer after a 1 h, 500 °C annealing procedure.
Hole dominated transport in InGaAs metal semiconductor metal photodetectors
Authors: Hargis Marian , Ralph Stephen E. , Woodall Jerry , McInturff Dave
Published: July 2002

We report the direct measurement of the intrinsic photocurrent response of both top and back illuminated planar metal–semiconductor–metal structures. We directly observe the temporal dynamics of the hole transport dependence on applied bias and the initial spatial distribution using a near infrared tunable femtosecond light source and electrically biased structures. The increased hole transit time of back illuminated structures can be completely understood in terms of the hole velocity and the initial spatial distribution of the carriers. Additionally, we report the fastest directly measured 50 μm diameter InGaAs photodetector with a 26 ps full width at half maximum.
Ultrahigh frequency oscillations and multimode dynamics in vertical cavity surface emitting lasers
Authors: Buccafusca O. , Chilla J. L. A. , Rocca J. J. , Wilmsen C. , Feld S. , Leibenguth R.
Published: July 2002

We report the observation of ultrahigh frequency oscillations of up to 240 GHz in optically gain switched vertical cavity surface emitting lasers. These oscillations are shown to be produced by multimode emission through mode competition (10–30 GHz) or mode beating (above 100 GHz). Although these oscillations are not related to the intrinsic modulation bandwidth, some of them could be mistaken for relaxation oscillations, calling for careful interpretation of the results of this type of experiments. The highest frequencies observed for single mode relaxation oscillations were about 9 GHz in agreement with values of modulation bandwidth reported in the literature.
Spectral series of internal friction peaks in cold-worked metals
Authors: Marchesoni F.
Published: July 2002

We suggest that both the Bordoni and the Hasiguti peaks (of the type P1 and P3) be addressed in terms of one basic microscopic mechanism; the nucleation of multikink–antikink pairs in pinned dislocation segments. Correspondingly, the relevant activation energies are multiples of one quantum of energy, the single kink (antikink) rest energy, whence the possibility of ordering these internal friction peaks according to simple spectral series. Such a conclusion appears to be consistent with the experimental data.
Biexcitonic contribution to polarization-dependent degenerate four-wave mixing in GaAs quantum wells
Authors: Denton G. J. , Phillips R. T. , Smith G. W.
Published: July 2002

We report measurements of the polarization and time-averaged intensity of four-wave mixing signals from GaAs quantum wells as functions of the pump beam polarizations, laser photon energy, and optical injection density, the latter covering a range of higher levels than has previously been reported. Excitation of heavy-hole excitons produced a sin2 variation of the signal intensity as the pump beam polarizations changed from parallel to perpendicular, while injection of light-hole excitons led to an approximately cos2 dependence. The tuning dependence of the heavy-hole-exciton signal revealed a low-energy signal which is attributed to biexcitons. The dominance of this signal for perpendicular polarization causes the observed sin2 variation of the heavy-hole-exciton signal.
On-wafer characterization of In0.52Al0.48As/In0.53Ga0.47As modulation-doped field-effect transistor with 4.2 ps switching time and 3.2 ps delay
Authors: Zeng A. , Jackson M. K. , Van Hove M. , De Raedt W.
Published: July 2002

We report fabrication and electro-optic measurement of In0.52Al0.48As/In0.53Ga0.47As modulation- doped field-effect transistors. The devices are monolithically integrated with coplanar stripline fixtures incorporating photoconductive switches. The switching time for a 0.35 μm T-gate device is 4.2 ps and the delay is 3.2 ps. This is the fastest directly measured switching in a three-terminal device reported to date.
Iodine doping of CdTe and CdZnTe layers grown by molecular beam epitaxy
Authors: Brun-Le-Cunff D. , Baron T. , Daudin B. , Tatarenko S. , Blanchard B.
Published: July 2002

The successful n-type doping of CdTe and CdZnTe alloys by using iodine as a dopant is reported. For CdTe, doping levels as high as 6.2×1018 cm−3 can be obtained with carrier mobility around 500 cm2 V−1 s−1 at room temperature. An ionization energy of 14.8 meV has been determined for the shallow donor by Hall effect measurements. In the case of Cd1−xZnxTe ternary alloys, only a slight decrease in the carrier density is observed when increasing the Zn concentration, by contrast to doping with indium. The doping level of 5×1017 cm−3 can be achieved for a Zn concentration x as high as 0.25, demonstrating the higher efficiency of iodine doping as compared to indium doping.
Apparatus for measuring electron-impact excitation cross sections using fast metastable atoms produced via charge exchange
Authors: Boffard John B. , Lagus Mark E. , Anderson L. W. , Lin Chun C.
Published: July 2002

An apparatus for measuring absolute cross sections due to electron-impact excitation out of the metastable levels of rare-gas atoms via the optical method is described with the focus specifically on excitation out of the 2 3S metastable helium level. The metastable helium target (He*) is prepared by charge exchange between 1.6 keV He+ ions and cesium vapor. An electron beam crosses the fast metastable beam target at a right angle and the fluorescence is collected at right angles to both beams. The charge transfer reaction produces He atoms mainly in the n=2 He levels. Because the target contains a negligible ground state He fraction, we can measure excitation cross sections from excitation threshold up to an arbitrarily high energy (keV regime) which represents a major improvement over previous metastable excitation cross sections measurements. The He* target density is extremely small (∼106 atoms/cm3) yielding minuscule signal rates. We describe steps taken to maximize the signal-to-noise ratio. We discuss the implications of using a fast beam target including both the finite flight time of the excited atoms across the light gathering region and the reduction of the cascade contributions to the apparent cross sections. A discussion of the identification and elimination of various systematic effects is also given. To measure absolute cross sections, we explicitly determine the spatial distributions of both the electron and metastable beams, as well as the spatially dependent response of the fluorescence gathering region. We determine the absolute flux of fast metastable atoms using a thermal detector calibrated with a He+ ion beam. As examples, we present absolute cross sections for excitation out of the 2 3S metastable level into the 3 3D and 4 3D levels.