bluuebunny/crossref_metadata_2025 huggingface dataset:
Y1Ba2Cu3O7/MgO/Y1Ba2Cu3O7 edge Josephson junctions
Authors: Robertazzi R. P. , Koch R. H. , Laibowitz R. B. , Gallagher W. J.
Published: July 2002

Josephson edge junctions have been fabricated using thin sputtered films of MgO (8–32 Å) to produce a weak connection between high Tc electrodes. The current voltage characteristics of these junctions can be well modeled by the resistively shunted junction (RSJ) equation and they possess excellent Josephson properties, exhibiting strong magnetic field modulation and microwave response at 10 and 100 GHz up to 82 K. The best high-temperature (T≳70 K) operation has been obtained with devices which have critical current densities in excess of 105 A/cm2 at 4.2 K, and junction critical current resistance products IcRn≂0.15 mV at 60 K. Experiments indicate that improvements in device quality are expected as the base electrode junction surface is improved.
Tera-hertz GaAs metal-semiconductor-metal photodetectors with 25 nm finger spacing and finger width
Authors: Chou S. Y. , Liu Y. , Fischer P. B.
Published: July 2002

We have fabricated metal-semiconductor-metal (MSM) photodetectors with the smallest finger spacing and finger width of 25 nm on molecular beam epitaxy grown GaAs. Direct current measurement shows that they have low dark current and high sensitivity. Monte Carlo simulations demonstrate that for a MSM photodetector with 25 nm finger spacing and width, the full width at half maximum impulse response is as short as 0.25 ps and the 3 dB bandwidth is 0.4 THz. They also show that by eliminating holes, the bandwidth can be over 1.8 THz. Furthermore, the detector capacitance was calculated, indicating that by reducing the ratio of finger width to finger spacing the detector capacitance can be decreased.
GaAs microcavity quantum-well laser with enhanced coupling of spontaneous emission to the lasing mode
Authors: Horowicz R. J. , Heitmann H. , Kadota Y. , Yamamoto Y.
Published: July 2002

We have observed low-threshold lasing in a GaAs single quantum-well vertical microcavity. At 4 K the quantum-well emission linewidth is reduced, and the coupling efficiency β of the spontaneous emission to the lasing mode is improved. The laser threshold pump power obtained for a 200 Å GaAs quantum well pumped by a continuous wave Ti:sapphire laser was 5 mW, corresponding to 85 μW absorbed power. We have compared the experimental results with the theoretical prediction, and estimated the value of β to be 10−2.
Near-infrared cathodoluminescence imaging of defect distributions in In0.2Ga0.8As/GaAs multiple quantum wells grown on prepatterned GaAs
Authors: Rich D. H. , Rajkumar K. C. , Chen Li , Madhukar A. , Grunthaner F. J.
Published: July 2002

The defect distribution in a highly strained In0.2Ga0.8As/GaAs multiple-quantum-well (MQW) structure grown on a patterned GaAs substrate is examined with cathodoluminescence imaging and spectroscopy in the near infrared. By spatially correlating the luminescence arising from the MQW exciton recombination (λ≊950 nm) with the longer wavelength (1000≲λ≲1200 nm) luminescence arising from the defect-induced recombination, we demonstrate that it is possible to determine the regions of highest film quality in both the mesa and valley regions. The present approach enables a judicious determination of the optimal regions to be used for active pixels in InGaAs/GaAs spatial light modulators.
Competition between transport and recombination in photocurrent spectra of semiconductor superlattices
Authors: Grahn H. T. , Fischer A. , Ploog K.
Published: July 2002

Photocurrent spectra of semiconductor superlattices with different barrier widths display a crossover from a maximum to a minimum at the excitonic transition energies. For strong coupling a maximum of absorption results in a maximum in the photocurrent spectra. If the coupling is strongly reduced, the absorption maximum transfers into a minimum in the photocurrent spectra. This effect complicates the deduction of transition energies and oscillator strengths from photocurrent spectra.
Isothermal capacitance transient spectroscopy measurements on polycrystalline diamond/hydrogenated amorphous silicon heterojunctions
Authors: Kiyota Hideo , Okushi Hideyo , Okano Ken , Akiba Yukio , Kurosu Tateki , Iida Masamori
Published: July 2002

A deep level in boron-doped polycrystalline diamond films located approximately 0.6 eV above the valence-band edge has been found using isothermal capacitance transient spectroscopy (ICTS) measurements. p-n heterojunctions between polycrystalline diamond and hydrogenated amorphous silicon were used in the study. The density and the hole-capture cross section of the deep level traps were determined from the temperature dependence of ICTS spectra and found to be 2×1016 cm−3 and 1×10−17 cm2, respectively.
Γ-X intervalley tunneling in InAs/AlSb resonant tunneling diodes
Authors: Carnahan R. E. , Maldonado M. A. , Martin K. P. , Nogaret A. , Higgins R. J. , Cury L. A. , Maude D. K. , Portal J. C. , Chen J. F. , Cho A. Y.
Published: July 2002

We present an experimental study of intravalley and intervalley transport in an InAs/AlSb/InAs/AlSb/InAs double barrier resonant tunneling diode at liquid helium temperatures. This work reports the first observation of intervalley tunneling through an InAs Γ-point quasibound state confined by AlSb X-point barriers. The incident energy of tunneling electrons was tuned by a transverse magnetic field (0<B<17 T). Self-consistent calculations of the current-voltage relation and a model that includes a transverse wave vector contribution to the magnetic field behavior of the resonances are used to describe the experimental results. From this, we determine that the device current is composed of Γ-point InAs electrons tunneling through X-point AlSb barriers (with large longitudinal effective mass) as well as Γ-point AlSb barriers.
Voltage-tunable multiple quantum well photodetector vertically integrated with voltage-tunable multiple quantum well filter
Authors: Goossen K. W. , Cunningham J. E. , Santos M. B. , Jan W. Y.
Published: July 2002

We present a n-i[multiple quantum well (MQW)]-p-i(MQW)-n device wherein the bottom MQW functions as a voltage-tunable photodetector and the top MQW functions as a voltage-tunable filter, allowing enhanced detectivity at the exciton wavelength compared to photon energies below or above the band gap. Thus this device more closely approximates a true single wavelength, voltage-tunable photodetector. We achieve about 2–1 selectivity over a tuning range of 14 nm with 12 V operation.
Epitaxial C60 films on CaF2 (111) grown by molecular beam deposition
Authors: Fölsch S. , Maruno T. , Yamashita A. , Hayashi T.
Published: July 2002

Epitaxial C60 films grown by molecular beam deposition onto CaF2(111) surfaces are investigated by reflection high-energy electron diffraction at deposition temperatures of 30–300 °C and coverages corresponding to average thicknesses of 1–50 nm. Over this entire temperature range, C60 forms an incommensurate overgrowth of stacked hexagonal layers exhibiting a characteristic nearest-neighbor spacing of 0.98 nm. Below 170 °C, unidirectional growth occurs in accordance with the crystallographic directions of the substrate. At higher deposition temperatures, however, two equivalent, rotated domain orientations are observed which are characterized by a significantly lower degree of lattice mismatch.
Dielectric loss in thin films of an aromatic polyimide
Authors: Aboelfotoh M. O. , Feger C. , Castellano A. , Kaufman R. , Molis S.
Published: July 2002

The dielectric response of thin aromatic polyimide films with thicknesses ranging from 40 nm to 3 μm has been measured in the frequency range of 104–108 Hz. The dielectric loss shows a frequency-independent behavior regardless of film thickness, which is attributed to the dipolar response of the dielectric lattice. Film morphology is found to affect the magnitude of the dielectric loss but not its frequency dependence.
Modeling the current-voltage characteristics of silver-sheathed Bi-Sr-Ca-Cu-O tapes
Authors: Gurevich A. , Pashitski A. E. , Edelman H. S. , Larbalestier D. C.
Published: July 2002

Measurements of voltage-current (V-I) characteristics and critical currents of 2212 and 2223 Ag-clad Bi-Sr-Ca-Cu-O tapes at 0<B<7 T and 4.2 and 77 K are presented. We show that the V-I curves are nonlinear at I<Ic and become linear above the critical current I≳Ic due to the effect of the Ag cladding. It is shown that the V-I curves can be well described by a simple universal formula, which enables one to extract Ic(T, B) and the flux creep rate s(T, B) from the resistive measurements, taking into account the effects of voltage criterion, strong nonlinearity of V(I) and I<Ic and the dependence of the resistivity of Ag upon T and B. For a 2212 tape, Ic(B) is shown to decrease as B−α with α=0.15 at 4.2 K, and exponentially at 77 K. For a 2223 tape, Ic(B) displays a power law dependence with α=0.1–0.3 at 4.2 K, whereas at 77 K Ic(B) can be well described by the formula I0b−1/2(1−b), where b=B/B*, and B* is the irreversibility field. The results are interpreted in terms of strong bulk pinning modified by thermal fluctuations.
Prediction of unusual electronic properties of Si quantum films
Authors: Zhang S. B. , Zunger Alex
Published: July 2002

Direct pseudopotential band structure calculations of thin Si(001) films reveal a number of features that are unexpected on the basis of conventional quantum confinement models: (i) The energies of some valence-band states exhibit oscillations when the number of monolayers in the film changes from even to odd, (ii) certain film wave functions have a cosine (rather than sine) envelope function, and (iii) the energy of the highest occupied film state remains pinned at a constant value for all even-layered film. We demonstrate a simple alternative to the effective-mass model which explains these results.
Electric field effect on the artificial grain boundary of bicrystal YBa2Cu3O7−δ films
Authors: Nakajima Kensuke , Yokota Kazuki , Myoren Hiroaki , Chen Jian , Yamashita Tsutomu
Published: July 2002

An ability of the artificial grain boundary of bicrystal YBa2Cu3O7−δ thin films is demonstrated as the field effect channel of high Tc field effect devices. The influence of field application on the channel resistance is examined with a metal-insulator-semiconductor-type structure, in which a channel is arranged across the grain boundary. The field-induced change in the resistance of the grain boundary is enhanced up to around 5% by lowering temperature below Tc of adjoining YBa2Cu3O7−δ grains. The enhancement is explained not only by an increase in the dielectric constant of the gate insulator (SrTiO3) but also by a reduction in the carrier density nearby the grain boundary. The latter is indeed a benefit to high Tc field effect devices.
Modulation doping and observation of the integral quantum Hall effect in PbTe/Pb1−xEuxTe multiquantum wells
Authors: Springholz G. , Ihninger G. , Bauer G. , Olver M. M. , Pastalan J. Z. , Romaine S. , Goldberg B. B.
Published: July 2002

In Pb1−xEuxTe layers grown by molecular beam epitaxy a drastic reduction of electron mobility is observed for increasing Eu content. This is exploited for the investigation of the electronic properties of the two-dimensional electron gas in PbTe/Pb1−xEuxTe quantum wells (x=4.7%). In such structures we report the observation of the integer quantum Hall effect with a dominance of the odd filling factors due to the large spin splitting in the lead salts.
Highly sensitive YBa2Cu3O7 dc SQUID magnetometer with thin-film flux transformer
Authors: Grundler D. , David B. , Eckart R. , Dössel O.
Published: July 2002

We have designed and fabricated a thin-film flux transformer by a YBa2Cu3O7/SrTiO3 (YBCO/STO) multilayer process. The flux transformer consists of a 20-turn input coil of 10 μm linewidth and a single-turn pickup loop surrounding an area of 7.5 by 7.5 mm2. All device levels are patterned by standard photolithography and Ar-ion-beam etching. The flux transformer has been combined in flip-chip configuration with the square washer of a low-noise YBCO dc SQUID. The dc SQUID magnetometer exhibits a magnetic field sensitivity of 1.4 nT/Φ0. The intrinsic white flux noise level of 70μΦ0/√Hz at 77 K is mainly dominated by the SQUID corresponding to a magnetic field resolution of the magnetometer of 100 fT/√Hz for frequencies above 40 Hz. At 1 Hz we measured 200 fT/√Hz. Biomagnetic measurements were performed in a magnetically shielded chamber.
Quasi-one-dimensional electron gas and its magnetic depopulation in a quantum wire prepared by overgrowth on a cleaved edge of AlGaAs/GaAs multiple quantum wells
Authors: Motohisa J. , Sakaki H.
Published: July 2002

We have succeeded in the formation of a quasi-one-dimensional electron gas on an edge surface of an AlGaAs/GaAs multiple quantum well (MQW) structure with well width of 100 nm. The sample was prepared by the exposure of a cleaved surface of an MQW substrate and subsequent overgrowth of a doped AlGaAs layer on the edge. The existence of electrons on the edge surface and their one dimensionality are, respectively, evidenced by the angular dependence of magnetoresistance and the magnetic depopulation effect.
Hall effect under null current conditions
Authors: Mani R. G. , von Klitzing K.
Published: July 2002

In a double boundary geometry, it is shown that dual independent Hall effects may be realized simultaneously by injecting two currents into the device, and the Hall effect on each boundary reflects only the current injected via the same boundary. A study of the magnetoresistance shows, however, that branch dissipation may be reduced through the optimal orientation of the injected currents. The results help clarify the signature edge currents in experiment by demonstrating that a Hall effect may be generated under null (net) current conditions.
Hydrogen desorption kinetics from epitaxially grown Si(100)
Authors: Greenlief C. Michael , Liehr Michael
Published: July 2002

The kinetics for the desorption of H2 from silicon are examined. The hydrogen coverage is generated during silicon epitaxy using SiH4 in a rapid thermal chemical vapor deposition reactor. The hydrogen coverage could be ‘‘frozen out’’ completely on the surface by the rapid cooldown and pump down of the reactor up to temperatures of about 845 K. The activation energy for the desorption of hydrogen is 49±3 kcal mol−1 and the pre-exponential for desorption is 8×1013±1 s−1. The presence of defect sites due to quenching the growth may influence the subsequent desorption kinetics of H2.
Boron-controlled solid phase epitaxy of germanium on silicon: A new nonsegregating surfactant
Authors: Klatt J. , Krüger D. , Bugiel E. , Osten H. J.
Published: July 2002

10-nm-thick germanium layers have been grown on Si(100) with boron as a surfactant with three different growth procedures, and investigated with reflection high-energy electron diffraction, transmission electron microscopy, and secondary ion mass spectroscopy. We obtained smooth and completely closed epitaxial germanium layers only by depositing the boron on top of the amorphous germanium layer followed by a post-annealing step. The surface energy anisotropy of the germanium will be affected by the presence of boron in this equilibrium process. The islanding observed in all other growth processes can be understood by taking into account that boron is a typical nonsegregating material in Ge below 600 °C and a surfactant acts mainly due to its presence in the growing front.
Reflectivity measurements of femtosecond carrier and field dynamics in semiconductors
Authors: Keil U. D. , Dykaar D. R. , Kopf R. F. , Darack S. B.
Published: July 2002

Carrier and field dynamics in a photoconductive switch are investigated by voltage modulated reflectivity. Measurements are performed with single, femtosecond pulsed and cw probe beams, and with pulsed pump and probe beams. We investigate the spatial dependence of the reflectivity changes and show that for mode-locked probe light the signal at the positive electrode completely dominates the response. The comparison of above and below bandgap excitation and reflectivity changes resolves the contributions of carrier-induced field changes and those due to the modulation of the applied field. Photoconductive switches on p- and n-doped substrates show that field enhancement at the Schottky barriers has only secondary influence. We explain the results in terms of a two-dimensional field distribution which produces the largest field gradient and hence acceleration of carriers at the electrodes and that the higher mobility of electrons accounts for the dominant signal appearing at the positive electrode.
Carbon tetrabromide carbon doping of molecular beam epitaxial (GaAs) films
Authors: Hoke W. E. , Weir D. G. , Lemonias P. J. , Hendriks H. T.
Published: July 2002

GaAs films were doped with carbon up to a hole concentration of 1.3×1020 cm−3 using CBr4 vapor. The material quality of the heavily doped films was found to be better than that obtained using evaporated carbon. Improvements at the highest doping levels include better surface morphology, higher hole mobilities, significantly stronger photoluminescence, and near unity substitutional incorporation. Doping pulses created using CBr4 exhibited abrupt transitions. From the results it is suggested that the material quality of the films doped with evaporated carbon are degraded at high doping levels due to surface combination of reactive carbon species.
Plasma nitrogen doping of ZnTe, Cd1−xZnxTe, and CdTe by molecular beam epitaxy
Authors: Baron T. , Tatarenko S. , Saminadayar K. , Magnea N. , Fontenille J.
Published: July 2002

The p-type doping of ZnTe, CdTe, and Cd1−xZnxTe (CZT) using a nitrogen dc plasma source during growth by molecular beam epitaxy is demonstrated. For ZnTe, doping levels as high as 1020 cm−3 were achieved. In CZT alloys, a progressive decrease of the maximum doping level is observed for decreasing Zn content. Using pulse doping methods, a doping level of p≊3×1018 cm−3 is obtained for a 12% Zn CZT layer. For CdTe layers, the highest level achieved is p≊1017 cm−3. The progressive acceptor compensation phenomenon is discussed with emphasis on the role of the lattice distortion on the nitrogen incorporation mechanisms.
Broad fullerene-ion beam generation and bombardment effects
Authors: Horak P. D. , Gibson U. J.
Published: July 2002

We report the generation of a large, moderate current density beam of fullerenes from a Kaufman ion source, and initial results on the use of the beam for ion assisted deposition of MgF2 and for growth of hard amorphous carbon films. A 50–100 μA/cm2 beam of fullerenes approximately 3.0 cm in diameter was generated; singly and doubly ionized fullerenes were observed after passage through a mass analyzer, with little or no indication of breakdown of the fullerenes. The beam energy was varied over the range 100–700 eV, and continuous beam operation was maintained for approximately 30 min on an initial charge of 150 mg of fullerenes. Low friction, wear resistant coatings were generated from fullerene-ion bombardment of fullerene neutrals, and optical degradation of MgF2 films bombarded during growth was observed.
Detection of anisotropy in the reversible transverse susceptibility
Authors: Chang Ching-Ray , Yang Jyh-Shinn
Published: July 2002

A model of reversible transverse susceptibility is proposed. It is based on the Stoner–Wohlfarth coherent rotation model, but with a macroscopic mean field interaction included to represent mutual interaction between particles. Unlike previous predictions, our calculated results show that the determination of the magnetic anisotropy field strength by means of the location of the peak in the transverse susceptibility curve works only in a weakly interacting particle system. For a strongly correlated system, nucleation does not start at the anisotropy field; therefore, it can be concluded that the peak detection method of anisotropy in transverse susceptibility should fail in this system.
p-type conduction in Mg-doped GaN and Al0.08Ga0.92N grown by metalorganic vapor phase epitaxy
Authors: Tanaka T. , Watanabe A. , Amano H. , Kobayashi Y. , Akasaki I. , Yamazaki S. , Koike M.
Published: July 2002

Temperature dependences of the hole concentration and Hall mobility in Mg-doped GaN and Al0.08Ga0.92N grown by metalorganic vapor phase epitaxy were measured by the van der Pauw method over a wide temperature range from 100 to 500 K. Assuming that the effective mass of holes in Al0.08Ga0.92N is equal to that of GaN, the activation energy of the Mg shallow acceptor in Al0.08Ga0.92N is estimated to be about 35 meV deeper than that in GaN.
Generation and inhibition of domain movement in semi-insulating GaAs:Cr
Authors: Ellin H. C. , Grunnet-Jepsen A. , Solymar L.
Published: July 2002

Electric-field domains in semi-insulating GaAs:Cr are investigated both by imaging the locally induced birefringence using a transverse electro-optic configuration and by measuring the dc current flowing through the crystal. It is shown that the formation of domains may be controlled by optical means.
High efficiency submicron light-emitting resonant tunneling diodes
Authors: Buhmann H. , Mansouri L. , Wang J. , Beton P. H. , Eaves L. , Henini M.
Published: July 2002

We have fabricated GaAs/AlAs p-i-n double-barrier resonant tunneling diodes with lateral dimensions down to 0.5 μm. There are significant differences in the electroluminescence spectra of these diodes as compared with large area diodes fabricated from the same heterostructure. In particular, a red shift of the quantum well emission line is observed together with an additional spectral line which is attributed to spatially indirect recombination. Furthermore, there is a strong increase in the low-temperature electroluminescence efficiency for the smallest devices.
Light emission from thermally oxidized silicon nanoparticles
Authors: Zhang D. , Kolbas R. M. , Milewski P. D. , Lichtenwalner D. J. , Kingon A. I. , Zavada J. M.
Published: July 2002

Light emission characteristics from silicon nanoparticles consisting of a crystalline core encased in an amorphous oxide shell are presented. The particles were thermally oxidized in the open atmosphere at 800 °C for times from 5 to 160 min in order to decrease the Si core dimensions. Photoluminescence spectra, at low excitation levels, reveal that the light emission shifts to shorter wavelengths as the oxidation time is increased. At high excitation levels, photoluminescence spectra show little or no shift. These results indicate that there are at least two mechanisms involved with light emission from Si nanoparticles, one associated with quantum size effects and another which is independent of size distribution.
Simple technique for picosecond electrical pulse injection into arbitrary circuits
Authors: Dykaar D. R. , Darack S. B.
Published: July 2002

We demonstrate a new external photoconductive excitation source. Low-temperature grown GaAs is used as a picosecond electrical pulser. A simple fabrication technique results in probes suitable for wafer scale probing of arbitrary circuits.
Factors determining the composition of strained GeSi layers grown with disilane and germane
Authors: Tweet D. J. , Tatsumi T. , Hirayama H. , Miyanaga K. , Terashima K.
Published: July 2002

Growth rates and compositions are reported for GeSi alloy films and superlattices epitaxially grown on both Ge(100) and Si(100) substrates using disilane and germane source gases in an ultrahigh vacuum chemical vapor deposition chamber. Although the growth rate changes rapidly with temperature the composition is nearly independent of it. Specifically, we find that the order of the adsorption reaction for disilane and germane is the same, resulting in the composition being determined by the partial pressures and by the ratio of the adsorption reaction rate constants. This ratio depends very weakly on temperature, if at all, and appears to vary slightly with the layer composition.
On the dark current noise of quantum well infrared photodetectors
Authors: Wang Daniel , Bosman Gijs , Li Sheng S.
Published: July 2002

Dark current noise measurements on a bound to miniband transition quantum well infrared photodetector were carried out at 77 K to either prove or disprove the correctness of three different, recently published noise expressions. The noise data indicate that the bound electron generation rate varies exponentially with applied voltage.
Comparison of ultrathin SiO2 films grown by thermal oxidation in an N2O ambient with those in a 33% O2/N2 ambient
Authors: Bong Kang Sug , Kim Sun-Oo , Byun Jeong-Soo , Kim Hyeong Joon
Published: July 2002

An N2O ambient allowed the oxidation rate to be substantially low while forming an oxynitride layer at the early stage of oxidation, and also provided nitrogen atoms to the oxide film during further oxidation. Both the formation of an oxynitride layer in the interface of SiO2 and Si substrate and a nitrogen incorporation in the grown oxide film were determined by wet chemical etching and x-ray photoelectron spectroscopy analysis of the grown oxide film. The electrical properties of the N2O oxide films were determined and compared with those of the oxide films grown in a pure or 33% O2/N2 ambient. The superiority in electrical properties appeared to be caused by the formation of the oxynitride layer in the interface of SiO2 and Si substrate.
Determination of the GaN/AlN band offset via the (-/0) acceptor level of iron
Authors: Baur J. , Maier K. , Kunzer M. , Kaufmann U. , Schneider J.
Published: July 2002

A characteristic infrared luminescence spectrum, dominated by a zero-phonon line at 1.30 eV, has been observed on AlN polycrystalline material. It is assigned to the spin-forbidden internal 3d–3d transition 4T1(G)→6A1(S) of Fe3+Al(3d5). By photoluminescence excitation spectroscopy the (-/0) acceptor level of iron in AlN could be located at EV+3.0 eV. The corresponding value for iron in GaN is EV+2.5 eV. From these values, the valence-band offset in AlN/GaN heterojunctions is predicted as ΔEV=0.5 eV, the conduction-band offset as ΔEC=2.3 eV.
Low specific resistance (<6×10−6 Ω cm2) TiC ohmic contacts to n-type β-SiC
Authors: Parsons J. D. , Kruaval G. B. , Chaddha A. K.
Published: July 2002

An array of transfer length measurement (TLM) structures was formed on an electrically isolated n+β=SiC (111) epilayer. The n+β-SiC epilayer was in situ doped with a nitrogen concentration of 2×1019 cm−3. The specific contact resistance (pc), sheet resistance (Rs), contact resistance (Rc), and transfer length (LT) were calculated from resistance (RT) versus contact spacing (d) measurements obtained from 10 TLM structures. The linear curves used for these calculations were fit to the RT versus d data by calculating the standard error of linear regression of RT on d; where, the average correlation coefficient with a straight line was 1.0000 and the average standard error of linear regression of RT on d was 0.26 Ω. The resulting average values were: pc=5.4×10−6 Ω cm2, Rs=22 Ω/⧠, Rc=1.45 Ω, and LT=5.0 μm. The TiC contacts, epitaxially grown by chemical vapor deposition, could not be scratched with a tungsten carbide scriber, nor could they be delaminated from the β-SiC surface.
Spiral growth of GaAs by molecular beam epitaxy
Authors: Hsu C. C. , Xu J. B. , Wilson I. H. , Andersson T. G. , Thordson J. V.
Published: July 2002

Steps of monolayer height (0.28 nm) were observed by atomic force microscopy on a GaAs surface grown by molecular beam epitaxy. The monolayer terrace width between steps was found to be as large as 1000 nm in some areas. Surface reconstruction affects the surface diffusion process during growth and the shape of the step edges. Growth spirals were observed. Spirals originate from screw dislocations. The growth mechanism is according to the Burton–Cabrera–Frank theory.
Electroluminescence from Er-doped GaP
Authors: Wang X. Z. , Wessels B. W.
Published: July 2002

The electroluminescent properties of the Er-doped GaP light-emitting diodes prepared by metalorganic vapor phase epitaxy and diffusion were investigated. Strong characteristic Er3+ intra-4f-shell emission at 0.80 eV is observed over the temperature range of 12–300 K. The electroluminescence intensity is only weakly temperature dependent, decreasing less than 40% as the temperature increases from 20 to 300 K.
Transparent conducting thin films of GaInO3
Authors: Phillips Julia M. , Kwo J. , Thomas G. A. , Carter S. A. , Cava R. J. , Hou S. Y. , Krajewski J. J. , Marshall J. H. , Peck W. F. , Rapkine D. H. , Dover R. B. van
Published: July 2002

GaInO3 is recently identified transparent conducting material which is structurally and chemically distinct from indium tin oxide [R. J. Cava, J. M. Phillips, J. Kwo, G. A. Thomas, R. B. van Dover, S. A. Carter, J. J. Krajewski, W. F. Peck, Jr., J. H. Marshall, and D. H. Rapkine, Appl. Phys. Lett. 64, 2071 (1994)]. We have used both dc reactive sputtering in the on- and off-axis geometries and pulsed laser deposition to grow films of this material. Layers of pure GaInO3 as well as those partially substituted with Ge for Ga or Sn for In have been studied. Both growth techniques are capable of producing films with conductivity ∼400 (Ω cm)−1 and transmission as high as 90% throughout the visible spectrum for ∼1-μm-thick films. The growth techniques differ in the morphology of the films produced as well as in the degree of dopant incorporation that can be achieved. A post-growth anneal in H2 can help produce an optimized oxygen content and a reduction of resistivity. Hall measurements indicate a carrier concentration up to 4×1020 cm−3 for all films and a Hall mobility up to 10 cm2/(V s). Doping appears to be due both to oxygen vacancies and aliovalent ion substitution.
Novel design of a resonant photoacoustic spectrophone for elemental carbon mass monitoring
Authors: Petzold A. , Niessner R.
Published: July 2002

An improved design of a resonant photoacoustic spectrophone is reported for aerosol absorption measurements by using a near-infrared laser diode (λ=802 nm; P=450 mW) in combination with a double-pass configuration for excitation of azimuthal modes and right-angle mounting of two electret microphones for signal detection. As a result of the new spectrophone setup a small-sized portable sensor system for real-time in situ elemental carbon monitoring is presented. The detection limit is estimated to 4.5×10−8 cm−1 or 1.5 μg elemental carbon per m 3.
Epitaxial regrowth of n+ polycrystalline silicon at 850 °C, induced by fluorine implantation
Authors: Moiseiwitsch N. E. , Marsh C. , Ashburn P. , Booker G. R.
Published: July 2002

A study is made of fluorine implantation into n+ polycrystalline silicon (polysilicon), with the aim of producing completely epitaxially regrown polysilicon emitters at lower temperatures. Polysilicon-on-silicon sheet resistance measurements are made to obtain an indication of the amount of polysilicon regrowth, and cross-section transmission electron microscope examinations to directly observe the regrowth. Samples given a fluorine implant, followed by a 1000 °C/10 min preanneal, show 50% epitaxial regrowth of the polysilicon after an emitter drive-in of only 850 °C/30 min. In contrast, in the absence of fluorine, negligible regrowth occurs even after an emitter drive-in of 850 °C/480 min.
Optically induced quasi-phase matching in strontium barium niobate
Authors: Kewitsch Anthony S. , Towe Terrence W. , Salamo Gregory J. , Yariv Amnon , Zhang Min , Segev Mordechai , Sharp Edward J. , Neurgaonkar Ratnakar R.
Published: July 2002

We observe dynamic ferroelectric domain gratings in strontium barium niobate (SBN) induced by photorefractive space charge fields. The optically induced modulation of the spontaneous polarization attains a maximum of 1%. Quasi-phase matched second harmonic enhancements are observed above the ferroelectric-paraelectric phase transition due to the glassy ferroelectric nature of SBN. We find that the second harmonic power is significantly enhanced by recording gratings in optically fatigued rather than electrically poled crystals.
Metalorganic molecular beam epitaxy of heavily carbon-doped InP using tertiarybutylphosphine as a carbon auto-doping source
Authors: Oh Je-Hwan , Shirakashi Jun-ichi , Fukuchi Fumihiko , Konagai Makoto
Published: July 2002

Metalorganic molecular beam epitaxy (MOMBE) of heavily carbon-doped InP was performed by using elemental In and tertiarybutylphosphine (TBP). In this study, TBP was employed as both phosphorus and carbon source, and carbon-doping characteristics in MOMBE growth of InP using TBP were discussed. The electron concentration of carbon-doped InP could be controlled in three orders of magnitude (n=1016–1019 cm−3) by only varying the growth temperature. In the growth temperature region investigated, two distinct growth temperatures dependencies of the electron concentration of carbon-doped InP epilayers were observed. It was also found that the carbon incorporation is affected by the TBP cracking temperature. As the TBP cracking temperature increases, the electron concentration increased at fixed growth temperature and also showed less dependence on growth temperature. Moreover, under higher TBP cracking temperature condition, the overall carbon incorporation may be dominated by the more atomiclike decomposed species.
High field transport in an edge overgrown lateral superlattice
Authors: Kurdak Ç. , Zaslavsky A. , Tsui D. C. , Santos M. B. , Shayegan M.
Published: July 2002

We have realized by cleaved edge overgrowth a two-dimensional electron gas system in a one-dimensional lateral superlattice consisting of 100 periods of 120 Å GaAs/20 Å AlGaAs. These devices exhibit nonlinear I–V, including negative differential resistance, at high electric fields. We demonstrate, by monitoring the changes in the two-dimensional electron density, that the nonlinear I–V is due to high field induced electron trapping.
Hot-electron microcalorimeters as high-resolution x-ray detectors
Authors: Nahum M. , Martinis John M.
Published: July 2002

Measurements are presented on a novel microcalorimeter for the detection of x rays. This detector uses a normal metal film deposited on a thin membrane to absorb x-ray photons. The subsequent temperature rise of the electrons is measured from the current–voltage characteristics of a normal-insulator-superconductor tunnel junction, where part of the absorber forms the normal electrode. A superconducting-quantum-interference-device is used as a low-noise high-bandwidth readout for the junction. We have measured an energy resolution of 22 eV full width at half-maximum and a time constant of 15 μs for a detector operating at 80 mK and having a 0.5 μm thick Au absorber with an area of 100×100 μm2.
Optimization procedure for the cooling of liquid 3He by adiabatic demagnetization of praseodymium nickel
Authors: Parpia J. M. , Kirk W. P. , Kobiela P. S. , Rhodes T. L. , Olejniczak Z. , Parker G. N.
Published: July 2002

The construction and performance of a single stage nuclear demagnetization apparatus utilizing 0.267 mole of praseodymium nickel material is described. An optimization procedure to minimize entropy production during the demagnetization of the hyperfine enhanced material has been developed which enabled the cryostat to cool a liquid-3He sample to a temperature of 350 μK. The effects of measured heat leaks and inferred eddy-current heating are accounted for satisfactorily in a model of this procedure.
Headspace attachment for a Varian model 3700 gas chromatograph
Authors: Keeley Dean F. , Meriwether John R.
Published: July 2002

A headspace analysis attachment for a Varian model 3700 gas chromatograph is described. The attachment differs from most commercial headspace attachments in the size sample bottle that it can accommodate. Graphical data obtained using the attachment is given.
Variable mixing frequency method for accurate and convenient measurement of ultrasonic velocity
Authors: Kojima Akira , Tozaki Ken-ichi , Akao Fumio
Published: July 2002

A simple and convenient method for the accurate measurement of ultrasonic velocity is presented using a commercially available pulsed ultrasonic oscillator and receiver. The principle of operation of the present method belongs to the variable frequency method. The cw signal by the rf signal generator is provided not only for the purpose of the superposition of the same frequency rf pulse transmitted through the specimen in the form of the ultrasonic pulse, but also for the purpose of the triggering of the pulsed ultrasonic oscillator via a frequency divider. The phase matching of the cw signal of the signal generator with the rf pulse, which was generated by the ultrasonic oscillator, is detected sensitively by the video signal on the oscilloscope. The through-transmission technique makes it easy to measure the ultrasonic velocity of a highly attenuated signal, as in case of the critical phenomena.
Motor control and data-acquisition system: Automatic control of x-ray cameras
Authors: Starke Martin M. , Corcoran Daniel W. , Bilello John C.
Published: July 2002

A unique motor control and data-acquisition system has been developed to automate experiments. The system is capable of controlling 16 stepping motors while collecting, analyzing, and graphically displaying data. The system has been applied to automatically finding x-ray rocking curves and Bragg angles in x-ray topography. The Stony Brook motor control system has been successfully applied to the automated control of double crystal and Berg–Barrett cameras.
First encouraging experience with a new type of belt material for electrostatic accelerators
Authors: Arndt P.
Published: July 2002

A new belt material has been tested and installed in our HVEC-CN-type Van de Graaff with very good results. The accelerator has been running with this belt for several months up to design voltage of 6 MV. So far no indication of deterioration of the belt has been observed.
Rebuilding ion pump elements for longer life
Authors: Berners Edgar D.
Published: July 2002

Used ion pump elements can be rebuilt to give approximately twice the normal life, with a small decrease in pumping speed.
Recent work on very-low-velocity superconducting accelerating structures
Authors: Shepard K. W.
Published: July 2002

A superconducting resonant cavity containing a 10-cm active length, interdigital accelerating structure has been demonstrated to work at accelerating gradients above 5 MV/m. The 48.5-MHz, four-gap accelerating structure is designed for particle velocities 0.007c≤V≤0.014c, and is the first of several structures intended to form a low-velocity positive-ion injector linac for the ATLAS accelerator.
Waveform display for slowly varying signals
Authors: Zhou-jing Yang , Blackburn James A. , Smith H. J. T.
Published: July 2002

Slowly changing signals will appear on an oscilloscope as a moving dot. A circuit is described which permits such waveforms to be fully displayed in real time. The oscilloscope screen functions as a window across which the signal scrolls at a user selectable rate.
Diode-array coupled time-resolved transmission grating spectrometer
Authors: Ikeda N. , Tanaka K. A. , Okada K. , Mochizuki T. , Yamanaka C.
Published: July 2002

A new type of sub-keV x-ray (0.1–1.2 keV) spectrometer diode array time-resolved transmission grating spectrometer (DATTS) with a fast time response (≤270 ps) has been developed to measure transient soft x-ray spectra from laser-produced plasmas. DATTS, the combination of the transmission grating (TG) and fast biplanar diodes, offers many advantages over the conventional x-ray diagnostics. Among the advantages are flexibility of the energy windows, fast time response, large dynamic range, and the capability of measuring absolute x-ray energy. All of these measurements have not been possible with a single diagnostic. The performance of the DATTS was compared with the data taken with the x-ray diode system, showing excellent agreement in the sub-keV x-ray energy range.
Tunable diode laser spectroscopy using the IBM PC
Authors: Glenar D. A. , Hill A.
Published: July 2002

This paper describes a dual-beam, tunable diode laser (TDL) spectrometer built for gas-phase vibrational spectroscopy studies. It employs a commercially available cryogenic cooler and control electronics and can incorporate Pb-salt diode lasers with operating wavelengths from 7 to 12 μm. The instrument optics have been largely assembled using inexpensive reflecting components. An IBM personal computer with enhanced graphics and high-speed data-acquisition unit permits dual-channel sweep averaging (normally done with expensive, commercial hard-wired units) as well as on-line spectral line parameter calculations. Such an arrangement puts this type of laser spectroscopy capability within reach of undergraduate physics and chemistry programs.
Molecular beam stabilized CO2 laser
Authors: Gough T. E. , Gu X. J. , Isenor N. R.
Published: July 2002

A method for stabilizing a cw CO2 laser using a molecular beam absorption signal as an external reference is described. The laser may be stabilized at line center or at any offset within the Doppler width by Stark tuning the absorption frequency. A time-domain fractional frequency stability of σ(τ)=2.03×10−10τ−1.3 was measured with another CO2 laser independently stabilized on the Lamb dip of the 4.3-μm fluorescence.
Speckle interferometer for thermal expansion measurements
Authors: Costa G. P. , Mangini S. , Ottonello P. , Piano E.
Published: July 2002

This paper describes a real-time speckle interferometer specially designed to measure the thermal expansion of a large class of intermetallic compounds for which surface optical treatments are difficult or even impossible. The instruments’ 5% accuracy, experimentally checked over the range 300–900 K, makes it a more accurate and cheaper alternative to the x-ray devices commonly used for the above-mentioned compounds. Moreover, the extreme simplicity of the optical setup allows an almost immediate alignment procedure and therefore makes the instrument suitable for routine measurements. The advantages of simultaneous measurements in different spots of the sample surface are also outlined. A comparison with standards, together with the measured expansion anomaly of an intermetallic compound (Ce24Co11) are presented.
Application of infrared scanners and inverse heat conduction methods to infrared computerized axial tomography
Authors: Kassab A. J. , Hsieh C. K.
Published: July 2002

An infrared scanning system was used along with inverse heat conduction methods in IR computerized axial tomography (IR CAT scan). The method consists of scanning the exposed surfaces of an object with an unknown inner boundary geometry and reconstructing section views of the object using the surface temperature data and the boundary condition prescribed along the inner boundary as input in an analysis. The mathematical theory and operational procedures of IR CAT scan are developed, and they are applied to the successful reconstruction of a section of a test model with a Dirichlet condition prescribed along the inner boundary. The sensitivity of the method to erroneous input temperature data is discussed. The mathematical theory of the IR CAT scan method developed in this paper is general and can be applied to other situations when Neumann or Robin conditions are prescribed along the inner boundary.
Simple method to generate combined luminance and chromaticity differences at threshold levels
Authors: Gorraiz Juan , Horvath Helmuth , Habenreich Thomas
Published: July 2002

We developed a rapid and simple measuring system for contrast thresholds for a human observer, based on simultaneously presenting eight negative, different contrasts against a uniform background on a screen. This experimental method allows: (1) a continuous variation of the presented contrasts and (2) generation of very small chromaticity differences parallel to the luminance differences.
Piezoelectric Q switching of a CO2 laser
Authors: Marcus S. , Stein D. T.
Published: July 2002

Reactive Q switching of a CO2 laser by means of a piezoelectrically actuated end reflector is reported. The high-frequency response of the piezoelectric transducer was maintained by optically polishing the transducer’s surface directly instead of employing a separate mirror. Submicrosecond pulses at rates in excess of 100 kHz were obtained. This technique is especially appropriate for generating high pulse rates in low-power lasers, as no lossy intracavity elements are required.
Magnetic energy analyzer with a microchannel plate calibrated using cellulose nitrate film
Authors: Hirano Katsumi , Yamamoto Toshikazu , Okabe Yushiro , Shimoda Katsuji
Published: July 2002

A time-resolved measurement of an impulsive ion source has been carried out by developing a detector consisting of a magnetic energy analyzer and a microchannel plate (MCP) with multianodes. A method to calibrate the electron multiplication factor of the MCP for charged particles using a solid-state nuclear track detector (SSNTD) is presented. The method has been successfully used for the energy analysis of the deuteron beam produced by the plasma focus. The method is applicable not only for deuterons but also for any other energetic charged particles.
Synchronization of transient digitizers to random events
Authors: Vojnovic B.
Published: July 2002

A circuit is described which synchronizes the timebase of a transient waveform digitizer to a randomly occurring trigger signal synchronous with the experiment information which is to be digitized. The method described overcomes the triggering ambiguity of the recorder and, therefore, uncertainties in time origin of the recorded signals. Pretrigger information is still preserved accurately except for a±1 sample period uncertainty prior to the trigger event. The design is based around a 200-MHz sample rate digitizer and uses a clock generator, which can be synchronized within one period to an external event. The same technique is applicable to slower clock rates and up to ∼500 MHz.
Inductance effects on resonator dielectric measurements
Authors: Deri R. J. , Migliuolo M.
Published: July 2002

The effect of residual series inductance on dielectric measurements with transmission line resonators is analyzed in detail. The analysis is useful for determining when errors due to such inductance are important, and outlines the calibration approach which minimizes inductance errors. The results also suggest a method for resonator calibration with varactor diodes.
Temperature-jump apparatus and measuring system for synchrotron solution x-ray scattering experiments
Authors: Hiragi Yuzuru , Nakatani Hiroshi , Kajiwara Kanji , Inoue Hideo , Sano Yoh , Kataoka Mikio
Published: July 2002

A rapid temperature-jump (T-J) device was designed for the kinetic measurements of small-angle x-ray scattering from solutions of biological macromolecular systems. The dead time of the apparatus is reduced to a few hundred milliseconds. The structural change of biological macromolecules in solutions can be monitored in the time scale of a few hundred milliseconds by the synchrotron small-angle x-ray scattering with a combination of a CAMAC data-acquisition system and the present T-J apparatus.
Tunable diode laser infrared spectroscopy of the metal/liquid interface
Authors: Wragg J. L. , White H. W. , Sutcu L. F.
Published: July 2002

A tunable diode laser infrared spectrometer has been constructed which can measure in situ vibrational spectra of liquids interacting with metal surfaces. The spectrometer uses a zinc selenide photoelastic modulator and commercially available diode lasers to make single-beam, single-pass measurements of molecular vibrations attributable to monolayer concentrations of molecules chemisorbed or physisorbed on metal surfaces. It also measures bulk spectra of liquids from a single reflection in an attenuated total reflection mode. With a suitable sample cell it would be possible to investigate liquids or gases at wide ranges of temperature, pressure, pH, etc.