bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of gas phase reactions in silicon chemical vapor deposition from monosilane
Authors: Scott B. A. , Estes R. D.
Published: July 2002

A simple flow reactor experiment is described which measures the gas phase reaction contribution to silicon chemical vapor deposition from SiH4. The approach uses the fact that the rate constant for SiH4 homogeneous decomposition exhibits a linear total pressure dependence in the low-pressure chemical vapor deposition (LPCVD) regime. Gas phase reaction channels are found to be significant even under silicon LPCVD conditions.
Periodic morphological modification developed on the surface of polyethersulfone by XeCl excimer laser photoablation
Authors: Niino Hiroyuki , Nakano Masashi , Nagano Shozaburo , Yabe Akira , Miki Tetsuro
Published: July 2002

Periodic and stable micropatterns appeared on the surface of amorphous polyethersulfone etched with an excimer laser at 308 nm in ambient air and a vacuum. The control of such radiative conditions as fluence and incident angle enables us to modify the spacing and pattern of the microstructures. A topographical investigation with scanning electron microscopy and an experiment with x-ray photoelectron spectroscopy to determine its composition is reported.
New high-efficiency quasi-continuous operation of an ArF(B→X) excimer lamp excited by microwave discharge
Authors: Kumagai Hiroshi , Obara Minoru
Published: July 2002

A quasi-continuous ArF(193 nm:B→X) fluorescence of over 8 ms pulse duration with 100 Hz operation frequency was observed in a microwave-discharge-pumped ArF lamp. The average ArF fluorescence power was 29 W obtained with an intrinsic efficiency of 4.4% with a 655 W average microwave power deposition. A peak ArF fluorescence power of 53 W with a power efficiency of 5.5% was also obtained.
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u detection of methyl radicals in laser chemical vapor deposition environment by resonance ionization spectroscopy
Authors: Okada Tatsuo , Andou Hiroyuki , Moriyama Yoshio , Maeda Mitsuo
Published: July 2002

The resonance ionization spectroscopic technique was developed for in situ detection of nonfluorescent radicals in a laser chemical vapor deposition environment. The technique was applied to measure the temporal change of methyl radical densities generated in an Ar and acetone gas mixture by an ArF laser photolysis, and the decrease of radical densities was explained by the self-recombination reaction.
Helical distributed feedback free-electron laser
Authors: Akiba Tatsuro , Tanaka Katsuya , Mokuno Masaaki , Miyamoto Shuji , Mima Kunioki , Nakai Sadao , Kuruma Shinichiro , Imasaki Kazuo , Yamanaka Chiyoe , Fukuda Masahiko , Ohigashi Nobuhisa , Tsunawaki Yoshiaki
Published: July 2002

Results of the implementation of a distributed feedback (DFB) reflector in a free-electron laser (FEL) are described. The reflector was positioned in the interaction region of the FEL waveguide in order to produce narrow bandwidth features in the output spectrum. Both the DFB and wiggler were of helical configuration. The energy, current, and pulse width of the electron beam were 1.5 MeV, 100 A, and 50 ns. By employing the DFB structure the intensity of the two specific frequencies may be increased by factors of 3 and 5. These frequencies are in good agreement with those predicted by theory. Temporally radiation waveforms exhibit a double peak, revealing a sensitivity of the oscillation condition to beam energy.
Heavy carbon doping in metalorganic chemical vapor deposition for GaAs using a low V/III ratio
Authors: Kushibe Mitsuhiro , Eguchi Kazuhiro , Funamizu Masahisa , Ohba Yasuo
Published: July 2002

Heavily carbon-doped GaAs was obtained by low-pressure metalorganic chemical vapor deposition by using trimethylgallium and arsine with a low V/III ratio. The hole concentration became as high as 2×1019 cm−3 without using intentional doping source gases when the V/III ratio was decreased to 2.4. The hole concentration coincided with the carbon concentration measured by secondary-ion mass spectroscopy. The epilayer surface tended to be rough when the V/III ratio was decreased below 10. However, when the V/III ratio was lowered to 2.4, the epilayer surface became completely mirror-like.
Epitaxial Y1Ba2Cu3O7−y/Y1−xPrxBa2Cu3O7−y heterostructures
Authors: Venkatesan T. , Inam A. , Dutta B. , Ramesh R. , Hegde M. S. , Wu X. D. , Nazar L. , Chang C. C. , Barner J. B. , Hwang D. M. , Rogers C. T.
Published: July 2002

For a variety of device applications, junction devices in particular, we have demonstrated a heterostructure system of Y1Ba2Cu3O7−y/Y1−xPrxBa2Cu3O7−y which maintains epitaxy over the entire Pr composition range x=0–1. We have grown both trilayer and multiperiod superlattices which show nearly single crystalline helium ion backscattering minimum yields of <6% in the topmost layer. X-ray diffraction measurements indicate c-axis orientation by a transverse scan across (005) line with a full width at half maximum of 0.6° and 0.4° on MgO and SrTiO3 substrates, respectively. Scanning Auger electron depth profiles and cross-sectional transmission electron micrographs indicate abrupt Pr/Y interfaces within one unit cell and virtually no disruption of the layered structure at the interface. These results indicate the potential for the growth of excellent heterostructures and superlattices of the high-temperature superconductors.
High-temperature superconducting microbolometer
Authors: Stratton T. G. , Cole B. E. , Kruse P. W. , Wood R. A. , Beauchamp K. , Wang T. F. , Johnson B. , Goldman A. M.
Published: July 2002

A superconducting microbolometer employing a DyBaCuO film deposited upon a silicon microstructure was found to have a responsivity of 800 V/W at 89 K and a response time of 1 ms.
Y1Ba2Cu3O7−x thin films grown on sapphire with epitaxial MgO buffer layers
Authors: Berezin A. B. , Yuan C. W. , de Lozanne A. L.
Published: July 2002

We have developed a process for growing as-deposited Y1Ba2Cu3O7−x (YBCO) thin films on R-plane sapphire substrates with an intermediate layer of epitaxial MgO. The orientation of the layers has YBCO (001) parallel to MgO (100) which is parallel to the substrate normal. These films are superconducting by 88.5 K and exhibit Jc=1×106 A/cm2 at 77 K and 2.5×107 A/cm2 at 4.2 K. The MgO layers may be grown at temperatures as low as 370 °C and are very stable in air. Little or no diffusion occurs between the substrate and the two layers as measured by Auger profiling.
Performance of a narrow band microwave filter implemented in thin-film YBa2Cu3O7−δ with ohmic contacts
Authors: Kalokitis D. , Fathy A. , Pendrick V. , Belohoubek E. , Findikoglu A. , Inam A. , Xi X. X. , Venkatesan T. , Barner J. B.
Published: July 2002

Using in situ deposited thin-film Y1Ba2Cu3O7−δ on LaAlO3 substrates, we have developed a pseudo-interdigital three-pole stripline filter with a minimum passband loss under 3.5 dB at 9.5 GHz and 77 K. The passband is very narrow, having a bandwidth of only 50 MHz (0.5%). The filter occupies a volume of less than 0.1 cm3. An equivalent copper filter produced a loss of 18.5 and 28 dB at 77 and 300 K, respectively. The input and output coupling is achieved by ex situ sputtered Au thin-film contacts defined on the Y1Ba2Cu3O7−δ by a lift-off technology and ultrasonically bonded to hermetic K connectors. Some of the major concerns in the realization of narrow band filters such as air gaps between high dielectric constant substrates and uniformity of the substrate’s dielectric constant are addressed.
Time-resolved photoluminescence spectroscopy from erbium-doped Ga0.55Al0.45As
Authors: Benyattou T. , Seghier D. , Guillot G. , Moncorge R. , Galtier P. , Charasse M. N.
Published: July 2002

Time-resolved photoluminescence (PL) spectroscopy has been performed on erbium-doped Ga0.55Al0.45As. We have investigated the 4I13/2→4I15/2 optical transition. The measured fluorescence lifetime is around 1.2 ms which is similar to values found for other erbium-doped III-V compounds. Studies as a function of temperature indicate nonradiative transitions characterized by thermal activation of 40 meV. With the help of two beam experiments we have confirmed the existence of Auger losses during the PL excitation and a model of the excitation process is proposed that accounts for the experimental results.
Novel metalorganic chemical vapor deposition system for GaN growth
Authors: Nakamura Shuji , Harada Yasuhiro , Seno Masayuki
Published: July 2002

A novel metalorganic chemical vapor deposition (MOCVD) system, which has two different flows, has been developed. One flow carries a reactant gas parallel to the substrate, and the other an inactive gas perpendicular to the substrate for the purpose of changing the direction of the reactant gas flow. The growth of a GaN film was attempted using this system, and a high quality, uniform film was obtained over a 2 in. sapphire substrate. The carrier concentration and Hall mobility are 1×1018/cm3 and 200 cm2/V s, respectively, which are the highest for GaN films grown directly on a sapphire substrate by the MOCVD method.
Synthesis of in-plane aligned a-axis YBa2Cu3O7−δ thin films
Authors: Young K. H. , Sun J. Z.
Published: July 2002

We report the successful synthesis of superconducting YBa2Cu3O7−δ (YBCO) (100) thin films with alignment of the in-plane c axis. These films were grown on single crystal NdGaO3 (110) substrates. The twofold symmetry of the substrate surface is believed to lead to anisotropic alignment of the in-plane c axis of the epitaxial YBCO (100) film. X-ray diffraction studies indicate that over 80% of the film grew epitaxially with the YBCO [100] perpendicular to the substrate surface, and YBCO [001] aligned along one pseudo-cubic axis of the NdGaO3. The superconductivity onset of the film was measured to be 89 K by ac susceptibility.
Wet etching of gold films compatible with high T
c superconducting thin films
Authors: Eidelloth W. , Sandstrom R. L.
Published: July 2002

We report a wet etch process for selective patterning or removing gold (Au) layers on top of high Tc YBa2Cu3O7 (YBCO) thin-film structures. As an etchant for Au, an aqueous solution of potassium iodide (KI) and iodide (I) was chosen. This etchant does not degrade YBCO or any commonly used substrate materials (SrTiO3, MgO, zirconia, and NdGaO3). This KI and I solution gives convenient etch rates of 200–300 Å/min and easily stops on the YBCO due to its high selectivity. Using this wet chemical etching process, we have fabricated structures with better than 1 μm resolution. We have found this etchant to be very useful for secondary electron microscopy analysis of high Tc device structures.
Identification of epitaxial Y2O3 inclusions in sputtered YBa2Cu3O7 films: Impact on film growth
Authors: Catana A. , Broom R. F. , Bednorz J. G. , Mannhart J. , Schlom D. G.
Published: July 2002

Y2O3 inclusions with typical sizes between 100 and 300 nm3, densely distributed (1016 cm−3) in sputtered YBa2Cu3O7 (YBCO) films on SrTiO3 substrates, have been identified by high-resolution electron microscopy. The precipitates exhibit either cuboid or needlelike shapes and grow epitaxially within and on top of YBCO. The dominant orientation relationship corresponds to a situation where the two-dimensional lattices are nearly coincident in the interfacial (001) plane. These precipitates may contribute to the generation of screw and edge dislocations. In addition, they provide a large number of potential pinning sites for magnetic flux lines, which may contribute to the observed high critical current densities.
Low-temperature formation of epitaxial Tl2Ca2Ba2Cu3O10 thin films in reduced O2 pressure
Authors: Lee W. Y. , Garrison S. M. , Kawasaki M. , Venturini E. L. , Ahn B. T. , Boyers R. , Salem J. , Savoy R. , Vazquez J.
Published: July 2002

Epitaxial Tl2Ca2Ba2Cu3O10 films on (100) LaAlO3 are prepared by post-annealing 2Tl:2Ca:2Ba:3Cu precursor films at 830–860 °C in ≂0.03–0.15 atm of O2. These films (0.2–1.1 μm thickness) are smooth and shiny to the eye, and have a sharp zero resistance and onset diamagnetic transition temperature of 117–121 K. Transport critical current densities of 1.6×106 A/cm2 at 77 K and ≂105 A/cm2 at 100 K are obtained for a 0.38-μm-thick film in magnetic fields up to 100 Oe. Strong flux pinning at low temperatures is inferred from the weak-field dependence of the critical current density calculated from magnetic hysteresis loops. At 5 K, the best film has a magnetic critical current density of 9×106 A/cm2 in zero field, decreasing gradually to 1.5×106 A/cm2 in a 5-T field.
Epitaxial growth of alkaline earth fluoride films on HF-treated Si and (NH4)2Sx-treated GaAs without in situ cleaning
Authors: Hung L. S. , Braunstein G. H. , Bosworth L. A.
Published: July 2002

HF-treated Si and (NH4)2Sx-treated GaAs were used as substrates for epitaxial growth of CaF2 and BaF2 films without in situ cleaning. The fluoride layers grown on the chemical-treated substrates exhibit good crystalline quality and smooth surfaces. With fluorides on Si, minimum ion channeling yields are about 3%–5%, comparable with the best data reported in the literature using thermal etching or sputtering for substrate cleaning. CaF2 and BaF2 films grown on GaAs(100) exhibit the same (100)-lattice orientation as the underlying GaAs substrate and no misoriented crystallites are observed. Pole figure measurements on BaF2 show that the crystallites are in close registry with the principal axes of the GaAs.
Distribution of radiation defects in submicron subsurface crystal layers
Authors: Chaplanov Victor A. , Nefedov Aleksey A.
Published: July 2002

The degradation of the structure of a silicon surface irradiated with high-energy (6 MeV) electrons has been studied by x-ray asymptotic Bragg diffraction. The results of the investigation of the spatial distribution of radiation defects in subsurface layers with atomic scale resolution are presented. The thickness of the distorted layer on the Si-crystal surface is close to 6 nm. The interplanar distance in this layer was decreased, which means that the main radiation defects in the subsurface region are vacancylike. Previous oxidation of silicon has prevented the distortion on the real Si-surface. Interstitial atoms, which have been created under oxidation, have recombined with radiation defects. It has resulted in suppressing the subsurface distortions. The reasons for the observed effects are discussed.
Hydrodynamic analysis of submicrometer n+nn+ diodes for microwave generators
Authors: Gruzhinskis V. , Starikov E. , Shiktorov P. , Reggiani L. , Saraniti M. , Varani L.
Published: July 2002

We present a theoretical investigation on the electrical behavior of submicrometer n+nn+ diode microwave generators. To this end we adopt a mixed scheme which uses space-homogeneous and stationary Monte Carlo simulations to provide the input parameters for a hydrodynamic analysis of the diode performances. Comparison between GaAs and InP made devices working at 400 K give similar results by predicting generation frequencies up to 700 GHz for an active region length of 0.2 μm.
Charge transfer and low-temperature electron mobility in a strained Si layer in relaxed Si1−xGex
Authors: Stern Frank , Laux Steven E.
Published: July 2002

Calculated results for charge transfer and low-temperature electron mobility in strained silicon grown epitaxially on relaxed Si1−xGex are presented versus the thickness of an undoped spacer layer and other structural and materials parameters. The indicated conduction band offset for Si on relaxed Si0.7Ge0.3 is 180±15 meV. Scattering by the remote doping impurities that supply the carriers is found to be the dominant scattering mechanism in high-mobility samples. Samples with enhanced interface scattering are expected to have a stronger temperature dependence of mobility.
Bombardment energies of O2+ in low pressure reactive ion etching
Authors: Janes Joachim , Huth Christoph
Published: July 2002

Quadrupole mass spectroscopy has been used to resolve the energy distributions of O2+ on the substrate plane of a parallel plate reactive ion etching reactor. Energy spectra show pronounced structures caused by charge exchange collisions in the plasma sheath in combination with rf modulation. Additionally, continuous distributions are found which are attributed to the effect of elastic scattering of ions.
Photoinduced hydrogen loss from porous silicon
Authors: Collins R. T. , Tischler M. A. , Stathis J. H.
Published: July 2002

In this letter we show that UV illumination of porous silicon causes a decrease in its luminescence efficiency. Infrared measurements allow us to associate the efficiency decrease with a loss of hydrogen from the silicon surface. We also find that the rate at which the luminescence intensity degrades increases rapidly when the illumination energy exceeds a threshold near 3.0 eV. We conclude that the decrease in photoluminescence efficiency occurs as a result of optically induced hydrogen desorption and discuss possible explanations for the energy threshold.
Deposition of dense hydrocarbon films from a nonbiased microwave plasma
Authors: von Keudell A. , Möller W. , Hytry R.
Published: July 2002

An electron cyclotron resonance plasma was used to prepare C:H layers from methane. The temperature dependence of the deposition rate was investigated at substrate temperatures ranging from room temperature to 700 K, at a gas pressure of 1.6 Pa. Despite low ion energies corresponding to the plasma potential, transparent hard coatings were obtained at elevated temperature with a density up to 2 g cm−3. A deposition model is proposed which describes the growth from an adsorbed layer, including surface reactions with radicals and atomic hydrogen as well as the direct incorporation of ions. Two different deposition processes can be identified, yielding polymerlike films in the temperature range up to 450 K and dense hydrocarbons above this temperature. The observed temperature dependence of the film properties such as H/C ratio, index of refraction, and density is consistent with the predictions of the model.
Strain-compensated InGaAs/GaAsP/GaInAsP/GaInP quantum well lasers (λ∼0.98 μm) grown by gas-source molecular beam epitaxy
Authors: Zhang G. , Ovtchinnikov A.
Published: July 2002

We report on the first strain-compensated InGaAs/GaAsP/GaInAsP/GaInP separate-confinement-heterostructure quantum well lasers emitting at about 0.98 μm. The laser structure was grown by gas-source molecular beam epitaxy. The lasers exhibited low threshold current densities and high characteristic temperatures. It was found that the structural and optical quality of a strain-compensated InGaAs/GaAsP multiple-quantum well (MQW) was superior to that of an InGaAs/GaAs MQW when the number of quantum wells was large. This was due to the presence of tensile strain in GaAsP which balanced compressive strain in InGaAs so that the InGaAs lattice does not relax. As a result, much fewer defects were formed in InGaAs/GaAsP than in InGaAs/GaAs. Thus strain-compensated InGaAs/GaAsP MQW structures are desirable for device applications which require many quantum wells.
Origin of 1/f noise in Y1Ba2Cu3O7−x step-edge dc SQUIDs
Authors: Grundler D. , Eckart R. , David B. , Dössel O.
Published: July 2002

We have fabricated Y1Ba2Cu3O7−x step-edge junction dc superconducting quantum interference devices (SQUIDs) and characterized their noise performance. The current-voltage characteristics of our SQUIDs are of resistively shunted junction type with critical current densities jc of about 104 A/cm2 and maximum flux to voltage transfer functions δV/δΦ of 20 μV/Φ0 at 77 K. We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the frequency dependent noise in our devices results from critical current fluctuations of the Josephson junctions. A bias current reversing technique is effective in suppressing this noise contribution. A flux noise Φn of 80 μΦ0/Hz1/2 at 1 Hz and 77 K was measured on a dc SQUID with an inductance Ls of 60 pH.
Atomic-scale planarization of SiO2/Si(001) interfaces
Authors: Niwa Masaaki , Udagawa Masaharu , Okada Kenji , Kouzazki Takashi , Sinclair Robert
Published: July 2002

Atomically flat silicon-oxide interfaces were obtained after preparing the Si(001)-2×1 reconstructed surface in ultrahigh vacuum (UHV) followed by native oxide growth and then conventional thermal oxidation. When the surface is prepared with conventional wet cleaning prior to oxidation, the flat interfaces initially tend to become rough and then smoother with increasing oxide thickness. In comparison with the conventional interfaces, UHV surface planarization is significant up to oxide thicknesses of about 8 nm. This thickness range will be extremely important for future ultralarge-scale integrated circuits (ULSIs).
Transient four-wave mixing on (InGa)As/InP multiple quantum wells using a femtosecond optical parametric oscillator
Authors: Albrecht T. F. , Sandmann J. H. H. , Feldmann J. , Stolz W. , Göbel E. O. , Nebel A. , Fallnich C. , Beigang R.
Published: July 2002

We present femtosecond four-wave mixing (FWM) experiments on unstrained, thin (InGa)As/InP multiple quantum wells in the spectral region around 1175 nm. These experiments became feasible by employing a stabilized femtosecond optical parametric oscillator which generates tunable 160 fs pulses in the near-infrared. The dephasing time of the heavy-hole exciton is determined to be 1.2 ps at low temperature, corresponding to a homogeneous linewidth of 1.1 meV. In addition, a beating of the FWM signal with a time period of 1.3 ps corresponding to an energy spacing of 3.2 meV is observed. We attribute this to the simultaneous excitation of localized excitons and excitons bound to an impurity or defect, which are not spectrally resolved in the linear optical spectra due to considerable inhomogeneous broadening.
A novel hysteresis loop and indirect exchange coupling in Co/Pt/Gd/Pt multilayer films
Authors: Takanashi K. , Kurokawa H. , Fujimori H.
Published: July 2002

We have investigated the magnetization behavior of Co/Pt/Gd/Pt multilayers in order to study the indirect exchange coupling between Co and Gd through Pt. A novel hysteresis loop has been observed for the samples with Pt layer thicknesses larger than 10 Å. This loop is considered to be due to the combined effect of the antiferromagnetic coupling between Co and Gd layers and the large magnetic anisotropy acting on the Co layer magnetization. The magnetization data suggest that the coupling strength oscillates with the Pt layer thickness.
Accelerated photobleaching of nonlinear optical polymer for the formation of optical waveguide
Authors: Zyung Taehyoung , Hwang Wol-Yon , Kim Jang-Joo
Published: July 2002

The photobleaching process in nonlinear optical polymer thin film is shown to be accelerated by the addition of a photosensitizer. Photobleaching time has been effectively reduced by a factor of 3–5. Refractive indices of both unbleached and fully bleached film with benzyldimethylketal (BDK) is higher than those of the film without BDK. Nonlinear optical properties of the optical copolymer with photosensitizer were little affected by the addition of the photosensitizer. Optical loss of the waveguide formed by the technique is comparable to that of waveguide without photosensitizer.
Electrical characterization of arsenic-ion-implanted semi-insulating GaAs by current-voltage measurement
Authors: Lin Gong-Ru , Chen Wen-Chung , Chang C.-S. , Pan Ci-Ling
Published: July 2002

The characteristics of an amorphous GaAs film by implanting dense arsenic ions into semi-insulating GaAs substrate have been studied. The specific contact resistance of the sample at room temperature is found to be 1.1×10−1 Ω cm2. This indicates that the conduction-band electron concentration is less than 1013 cm−3. The activation energy at temperature above 360 K and the density of states are, respectively, 0.6 eV and 1027 m−3 eV−1 as estimated from the slope of Arrhenius plot. Fitting of the Arrhenius plot also suggests that the carrier transport at metal/semiconductor junction of this material below 360 K is dominated by the variable-range hopping conduction mechanism which depends on deep level defects.
Preparation of (100)-oriented metallic LaNiO3 thin films on Si substrates by radio frequency magnetron sputtering for the growth of textured Pb(Zr0.53Ti0.47)O3
Authors: Yang Ching-Chyuan , Chen Ming-Sen , Hong Tian-Jue , Wu Chii-Ming , Wu Jenn-Ming , Wu Tai-Bor
Published: July 2002

Highly (100)-oriented LaNiO3(LNO) thin films were grown on Si, SiO2/Si, Pt/SiSiO2/Si, as well as glass substrates by rf magnetron sputtering deposition at substrate temperatures ranging from 150 to 500 °C. As-deposited LNO films are metallic; those prepared at substrate temperature ∼150–250 °C have a resistivity of 0.4–0.5 mΩ cm and can be used as the bottom electrode for the fabrication of integrated ferroelectric capacitors on Si. A subsequent deposition of sol-gel derived Pb(Zr0.53Ti0.47)O3 (PZT) thin film on the LNO-coated substrate was also found to have a significant (100)- and (001)-oriented texture. The ferroelectric capacitor fabricated from these films displays a good P–E hysteresis characteristic.
Nonlinear optical properties of textured strontium barium niobate thin films prepared by metalorganic chemical vapor deposition
Authors: Nystrom M. J. , Wessels B. W. , Lin W. P. , Wong G. K. , Neumayer D. A. , Marks T. J.
Published: July 2002

Highly textured strontium barium niobate thin films were deposited in situ by low pressure metalorganic chemical vapor deposition. [001]-oriented strontium barium niobate films on single crystal (100) magnesium oxide substrates were obtained at a growth temperature of 800 °C. Second-harmonic generation of 1.064 μm incident light was measured on the thin films. The nonlinear optical susceptibility of the films was as high as 8.7 times that of quartz (∼3.0 pm/V), which is comparable to the bulk value.
Random telegraphic signals in silicon bipolar junction transistors
Authors: Neugroschel Arnost , Sah Chih-Tang , Carroll Michael S.
Published: July 2002

Random telegraphic signals (RTS) are observed in the forward-biased dc base current of electrically stressed silicon bipolar transistors. The RTS noise in the base current is shown to originate from random trapping of electrons at the stress-created oxide and interface traps located over the oxide-covered emitter-base junction space-charge region. The observed pulse width (∼0.1–100 s), the uniform height of the pulses (∼1% of dc base current), and their dependencies on temperature and VBE (emitter/base bias voltage), exp(qVBE/nkT) with n=2, are interpreted by the two-step model consisting of electron tunneling between the oxide and interface traps, and the recombination of Si band electrons and holes at the interface traps.
Ge/Pd (Zn) Ohmic contact scheme on p-InP based on the solid phase regrowth principle
Authors: Wang L. C. , Park Moon-Ho , Deng Fei , Clawson A. , Lau S. S. , Hwang D. M. , Palmstro/m C. J.
Published: July 2002

A contact metallization scheme of Ge/Pd(Zn), based on the solid-phase regrowth principle, has been developed for the formation of Ohmic contact on p-InP. Typical contact resistivities of low 10−4 to low 10−5 Ω cm2 can be obtained after annealing at temperatures higher than 400 °C. Cross-sectional transmission electron microscopy study confirmed the solid-phase regrowth process in the InP substrate. Precipitates of trapped materials during solid phase regrowth have also been observed. A solid phase regrowth model is proposed to rationalize the electrical and metallurgical properties. This solid phase regrowth process is expected to form low resistance Ohmic contact on other In-based compound semiconductors.
Silicon pn junction imaging and characterizations using sensitivity enhanced Kelvin probe force microscopy
Authors: Kikukawa Atsushi , Hosaka Sumio , Imura Ryo
Published: July 2002

We observed the surface potential of silicon pn junctions using a Kelvin probe force microscope whose sensitivity was about five times better than that of a conventional one. It was achieved by three major improvements: electrostatic force detection using the second cantilever resonance, cantilever Q-value enhancement by operating in a vacuum, and direct cantilever resonance frequency detection using the frequency modulation technique. It was demonstrated that the surface potential of the pn junctions made by thermal diffusion varies gradually compared to those made by ion implantation, possibly reflecting their gradual dopant concentration profile.
Near-infrared two-color pyrometer for determining ignition temperatures of metals and metal alloys
Authors: Nguyen Ke , Branch Melvyn C.
Published: July 2002

A two-color pyrometer has been designed, constructed, and used to measure the ignition temperatures of metals and metal alloys. Cylindrical metal and metal alloy specimens were ignited by a focused cw CO2 laser beam in a cool, static, pure oxygen environment. The pyrometer operates in the near-infrared at two narrow spectral regions, with a nominal bandwidth of 10 nm centered at 0.9051 and 1.06 μm, and has a temperature range from 1000 to 4000 K. In the present design the temperature of a spot, ∼0.5 mm in diameter, can be recorded with a maximum time resolution of 25 μs and with an accuracy of a few percent. Results of CO2 laser ignition of cylindrical specimens of 6061 aluminum alloy and 302 SS in a pure oxygen environment were obtained from the two-color pyrometer and were compared with those obtained from a thermocouple placed inside the specimen near the laser-irradiated surface.
Feedback system for the characterization of nonideal Schottky diodes with high series resistance
Authors: Cibils Roberto M. , Buitrago Román H.
Published: July 2002

In this work we describe a simple measurement system that allows us to obtain the characteristic parameters (the ideality factor n, the saturation current Is, and the series resistance R), for nonideal Schottky barrier diodes with high series resistance. The principal features of this new system are: analog processing of the measured signal (in order to avoid large errors coming from digital differentiation) and the easy interpretation of the shape of the I0-VA curves obtained.
Measurement of small strains in a noisy environment
Authors: Tillack M. S. , Kazimi M. S. , Lidsky L. M.
Published: July 2002

A simple technique is demonstrated for measuring strains in an electromagnetically noisy environment using electrical strain gauges. For applications in which strains are produced electromagnetically in current-carrying structures, the noise signal can be much larger than the strain signal. Furthermore, the noise signal is at precisely the same frequency as the strain signal, making standard methods of synchronous signal detection difficult. This problem has been surmounted by modulating the detection circuit sensitivity. Bridge circuit modulation has been shown to effectively decouple the strain signal from the noise, even at very low strain levels of ∼10−8 m/m.
High-voltage trigger pulser for split dc discharges in waveguide lasers
Authors: Nedvidek F. J. , Kucerovsky Z. , Brannen E.
Published: July 2002

A device to initialize discharges in multisection waveguide lasers is described.High-voltage pulses from the trigger circuit ionize the laser mixture via electrodes attached to the outside wall of the waveguide. cw discharges have been started in CO2 waveguide laser sections for various gas mixtures at operating pressures of up to 450 Torr.
Power crowbar with an air-core transformer
Authors: Harper G. C. , Ribe F. L.
Published: July 2002

An air-core power crowbar transformer has been successfuly applied to a passively crowbarred theta-pinch plasma physics experiment with a large (1-MA), fast-rising (0.5-μs) solenoid current. Without the power crowbar, the current falls exponentially from its peak value with a decay time of 20 μs. With the power crowbar, the current remains at its peak value for ∼30 μs before falling. As described here, it can be built with materials that are lightweight and inexpensive. For applications similar to this one, these two features make the air-core power crowbar transformer simpler and less expensive than one with a ferrite or ferromagnetic core.
New technique for measuring the heat of solid deformation
Authors: Lyon R. E. , Farris R. J.
Published: July 2002

A calorimetric technique has been developed to simultaneously measure the heat and work of solid deformation. The physical construction of the instrument is similar to previously reported deformation calorimeters which operate as null or compensating devices, utilizing features of differential gas thermometry and hot-wire methods of measuring thermal conductivity. The present method combines the quick response time and high sensitivity of such devices with a direct measurement principle which greatly simplifies data acquisition. Theory and operation of the instrument are discussed and some data on a polyurethane elastomer are presented.
Low-temperature acoustic system for inducing nonthermal ultrasonic damage on biological targets
Authors: Himberger Douglas E. , Malinin George I. , Mayer Walter G.
Published: July 2002

A novel insonification system, intended for the verification of the existence and assessment of single-frequency, nonthermal vibrational effects of ultrasound on biological targets, is described. The induction of vibration-triggered damage was made possible by insonifying suitable targets immersed in liquid nitrogen with continuous-wave ultrasound at approximately 3, 5, and 7 MHz, while monitoring the ultrasonic intensities (2–24 mW/cm2) by acoustic and acousto-optic methods. The extent and nature of vibration-induced damage in recovered samples may then be assessed by a variety of analytical procedures.
High-resolution time-of-flight mass spectrometry impulse-field focusing pulse generators
Authors: Miller R. L. , Browder J. A. , Sanzone G.
Published: July 2002

Experiments have shown that the unit mass resolution of conventional Wiley–McLaren time-of-flight (TOF) mass spectrometers can be significantly improved using the technique of impulse-field focusing (IFF). Details of the circuitry used to test the IFF theory are presented. Generators of electrical pulses with nanosecond rise times and 100-V amplitudes are described.
Word programmer for NMR
Authors: Danese Giovanni , Dotti Domenico , Jian Huang Guo , Braschi Enrico , Confrancesco Pacifico , Villa Marco
Published: July 2002

A NMR programmer is described which is built around a logic idea and a set of specifications, rather than availability of special or new integrated circuits. We begin by discussing what a quintessential Touring machine can do to solve the problem of outputting words (or pulses) with the resolution of the system clock over arbitrarily long time intervals. We then illustrate a simple realization of this machine, with 4096 program lines, 25-ns resolution, two 16-bit output lines, the possibility of nesting loops down to the 256th level, and a component cost in the 102 $ range. A software ‘‘human’’ interface has been developed in an IBM-PC compatible (MS-DOS) environment, which simplifies the task of debugging the entire NMR spectrometer, and that of designing new experiments. While certainly overspecified for all traditional solid-state NMR experiments, our programmer may meet the requirements of recently suggested selective excitation and imaging experiments in liquids.
Fast microcomputer-based data acquisition system for thermal desorption spectroscopy
Authors: O’Connor Tom , Schreifels John A.
Published: July 2002

Thermal desorption experiments are controlled by an IBM-XT personal computer interfaced to the ISAAC-2000 data acquisition system.
CAMAC interface for digitally recording infrared camera images
Authors: Dyer G. R.
Published: July 2002

An instrument has been built to store the digital signals from a modified imaging infrared scanner directly in a digital memory. This procedure avoids the signal-to-noise degradation and dynamic range limitations associated with successive analog-to-digital and digital-to-analog conversions and the analog recording method normally used to store data from the scanner. This technique also allows digital data processing methods to be applied directly to recorded data and permits processing and image reconstruction to be done using either a mainframe or a microcomputer. If a suitable computer and CAMAC-based data collection system are already available, digital storage of up to 12 scanner images can be implemented for less than $1750 in materials cost. Each image is stored as a frame of 60×80 eight-bit pixels, with an acquisition rate of one frame every 16.7 ms. The number of frames stored is limited only by the available memory. Initially, data processing for this equipment was done on a VAX 11-780, but images may also be displayed on the screen of a microcomputer. Software for setting the displayed gray scale, generating contour plots and false-color displays, and subtracting one image from another (e.g., background suppression) has been developed for IBM-compatible personal computers.
Temporal development of hard and soft x-ray emission from a gas-puff Z pinch
Authors: Choi P. , Dangor A. E. , Deeney C. , Challis C. D.
Published: July 2002

Previous time- and space-resolved x-ray measurements on a small gas-puff Z pinch indicated the presence of bursts of energetic electron beam and related ‘‘hot spots’’—high-temperature, high-density plasma regions. Spectra taken from these hot spots are consistent with a plasma of electron density about 1022–1023 cm−3 and electron temperature of 500 eV. Here we present time correlation of the hard x-ray emission from the anode with large fluctuations in İ and with short bursts of intense soft x rays. These soft x-ray bursts originating from the hot spots are shown always to be preceded by hard x-ray emissions. Using suitable apertures, the plasma is shown to be a source of hard x rays, <2.5 Å. This is confirmed by x-ray pinhole photographs. By varying the Z of the anode the electron beam associated with hard x-ray emission is found to be of low energy (10 keV) agreeing with previous measurements. In particular a plastic, PTFE (Teflon), is shown to be a suitable material for the anode, with superior lifetime performance compared with conventional metallic substances.
Green light 2ω as an x-ray streak camera fiducial
Authors: Nilson D. G. , MacGowan B. J.
Published: July 2002

The fiducial system for the multiple optical and x-ray streak cameras on the two Nova target chambers is intended to allow cross comparison of time-resolved data from laser plasmas to an accuracy of ±50 ps. Development of the system has led to the discovery that Al-coated fiber optics incorporated into the x-ray photocathode can be made to produce photoelectrons when irradiated by ∼1 μJ of 2ω light. The low loss and dispersion of 2ω light in fused silica fibers are significant advantages over our original intention of using 3ω light. Results indicating input and output pulse lengths and required energies to produce photoelectrons will be discussed.
Use of graphite in Langmuir-calorimeter probe heads
Authors: Kilpatrick S. , Manos D. , Stangeby P. , Ritter R.
Published: July 2002

Graphite has become an important material in magnetically confined fusion devices, being used for components such as limiter blades, divertor plates, and Faraday shields. Langmuir-calorimeter probes on the tokamak fusion test reactor (TFTR) and the Princeton large torus (PLT) have utilized graphite in probe heads, active elements, protective shields, and in an epoxy compound for various applications. Most recently, all-graphite edge probes have been used successfully on these machines. The advantages and disadvantages of using this material as a collecting element and a heat resistant support are discussed, with reference to its survivability and usefulness in the TFTR environment. A three-dimensional finite difference thermal analysis of a TFTR graphite calorimeter is presented which calculates its temperature response to selected power inputs. This was used to estimate power densities at the edge of TFTR plasmas.
Analysis of highly asymmetric radiation loss profiles in TFTR
Authors: Schivell J. , Bush C. E.
Published: July 2002

The profiles are measured in the tokamak fusion test reactor (TFTR) with two bolometer arrays, one of which looks in at the plasma horizontally and one vertically. Under some conditions the profiles have large, localized features. The most common are a bright band of radiation near the inner wall (usually referred to as a ‘‘marfe’’) and a wide bright layer that occurs when the plasma is in contact with the inner bumper limiter. The asymmetric profiles have been analyzed in three ways: by inspection, by separating the excess over the normal part of the profile, and by a 2-D reconstruction procedure in which the cross section is divided into zones tailored to our specific geometry. Inspection shows the motion of the bright band and its development into a bright shell. Integration of the excess yields the power in the band. This power rises smoothly and dramatically as a function of density as one nears the high-density limit. However, it needs to be taken into account in profile Abel inversion even at modest densities. The 2-D reconstruction yields, among other results, the intensity and the thickness of the inner-bumper layer. These are typically 300 kW/m3 and approximately 0.1 m. The reconstruction is not accurate enough to be used as a substitute for Abel inversion.
Spectra from a cooling Planckian source
Authors: Zahrt John D. , Shirk Donald G.
Published: July 2002

During the study of spectra with non-Planckian shape, we investigated the effects of thermal transients on the recorded spectrum of a Planckian source. We assumed that the response time of the detector is long compared to the time rate of change of the Planckian temperature and that the source always emits as a Planckian at the instantaneous temperature. Several temperature–time models have been studied. The results are conveniently expressed in terms of the exponential integral and related functions. In particular, for a source starting at temperature Θ and cooling linearly, the spectrum is narrower (FWHM) and shifted to lower energy than a Planckian spectrum at temperature Θ. The results of this ‘‘Gedanken’’ experiment show that it is possible to generate a non-Planckian shaped spectrum from a thermally evolving Planckian source.
Facility for non-LTE studies of a magnetically rotated arc
Authors: Frierson R. V. , Eddy T. L. , Put’ko V. F.
Published: July 2002

A facility is described for the spectroscopic diagnostics of an electric arc in a rotating magnetic field. The magnetic field is used to convert the arc into a ‘‘surface of revolution’’ which internally provides a more uniform and controllable plasma for particle treatment or plasma chemistry applications. The magnetic field also enhances the spectral lines indicating a non-LTE condition. A high-frequency, two phase amplifier and phase shifter are used to generate the rotating mag- netic field in the coil. Present operating conditions are 0–300 G at 500–2000 Hz and 100–1000 A.
Fiber-optic current sensor with heterodyne detection
Authors: Chandler G. I. , Forman P. R. , Jahoda F. C. , Klare K. A.
Published: July 2002

The toroidal plasma current in the ZT-40M experiment (100–380 kA) has been measured using a fiber-optic sensor. This sensor consists of six turns of permanently twisted, single-mode fiber which was wound poloidally around the experiment. By modifying the laser output to a rotating linear polarization, amplitude-independent single output heterodyne detection is possible.1 The signal is proportional to the B field produced by the plasma current so integration of the data is not required to obtain the current. Comparison with the existing Rogowski coil consistently shows less than 1% difference. Present efforts are directed toward simplifying the design to minimize optical alignment and to implement real-time digital data reduction. The fiber current sensor has demonstrated accuracy comparable with existing techniques. In addition, it possesses broad frequency response, it eliminates insulation, electromagnetic interference, and ground loop problems and can easily be installed on existing plasma experiments. This work is supported by U.S. DOE.
Development of a FIR interferometer for ATF: Part I—High-power FIR laser development
Authors: Casson W. H. , Hutchinson D. P.
Published: July 2002

A FIR interferometer system for the Advanced Toroidal Facility (ATF) at Oak Ridge National Laboratory has been developed with some major modifications to previous designs used at ORNL. Due to the highly elliptical cross section of the plasma and the projected plasma densities, a 15-channel interferometer was designed to operate at 119 μ. The large number of channels necessitated the construction of a high-power FIR laser with a fundamental mode Gaussian output over 500 mW. Also, laser stability has been significantly improved. The final design of the pump laser is modular to the extent that any single optical component can be removed and replaced without changing the optical alignment. The FIR cavity was modified by changing to a smaller bore, using gold-coated end mirrors, and using curved internal reflectors. The addition of buffer gas to the cavity provided a significant improvement in output power. Research supported by the Office of Fusion Energy, U.S. DOE, under Contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.
Slitless intensified readout gated spectrometer
Authors: Gerassimenko Michel
Published: July 2002

A spectrometer has been developed to meet the requirements of the x-ray laser effort at Lawrence Livermore National Laboratory (LLNL). The instrument takes advantage of the intrinsically small divergence and size of the lasing source by putting it, the grating, and the detector on the Rowland circle. This design obviates the need for a slit but makes the target chamber an integral part of the spectrometer. Sensitivity is maximized by intercepting the entire laser footprint, by keeping the angle of incidence upon the grating at about 70° to the normal, and by single-photon detection capability at the detector plane. Signal to background is greatly improved by gating the spectrometer at the subnanosecond level, using three stripline structures deposited on the microchannel plate detector. The sum of incident and diffracted angles is kept constant. By using simple spacers and custom ruled gratings any energy in the 65–200 eV range is accessible.
Database tools for enhanced analysis of TMX-U data
Authors: Stewart M. E. , Carter M. R. , Casper T. A. , Meyer W. H. , Perkins D. E. , Whitney D. M.
Published: July 2002

A commercial database software package has been used to create several databases and tools that assist and enhance the ability of experimental physicists to analyze data from the Tandem Mirror Experiment-Upgrade (TMX-U) experiment. This software runs on a DEC-20 computer in M-Divisions’s User Service Center at Lawrence Livermore National Laboratory (LLNL), where data can be analyzed off line from the main TMX-U acquisition computers. When combined with interactive data analysis programs, these tools provide the capability to do batch-style processing or interactive data analysis on the computers in the USC or the supercomputers of the National Magnetic Fusion Energy Computer Center (NMFECC) in addition to the normal processing done by the TMX-U acquisition system. One database tool provides highly reduced data for searching and correlation analysis of several diagnostic signals within a single shot or over many shots. A second database tool provides retrieval and storage of unreduced data for use in detailed analysis of one or more diagnostic signals. We will show how these database tools form the core of an evolving off-line data analysis environment on the USC computers.