bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct writing in Si with a scanning tunneling microscope
Authors: van Loenen E. J. , Dijkkamp D. , Hoeven A. J. , Lenssinck J. M. , Dieleman J.
Published: July 2002

Using the W tip of a scanning tunneling microscope, indentations with diameters of 2–10 nm have been made directly in Si (110) and Si (001) surfaces. It is possible to create and image (‘‘write and read’’) arbitrary lines and bit patterns reproducibly with a single tip, without degrading its sharpness. The method does not require ideally flat surfaces and the indentations, when made in Si and kept in ultrahigh vacuum, are stable in time.
Control factor of native oxide growth on silicon in air or in ultrapure water
Authors: Morita M. , Ohmi T. , Hasegawa E. , Kawakami M. , Suma K.
Published: July 2002

Native silicon (Si) oxide growth on Si (100) wafers in air and in ultrapure water at room temperature requires coexistence of water and oxygen in the air and ultrapure water ambients. The growth rate data on n-, n+-, and p+-Si (100) in air indicate layer-by-layer growth of an oxide. The growth rate on n-Si (100) in ultrapure water may be governed by a parabolic law. For native oxide growth in ultrapure water, the number of Si atoms dissolved in ultrapure water is over one order of magnitude larger than the number of Si atoms contained in the grown native oxide film. The structural difference between the native oxide film in air and in ultrapure water is also discussed.
Minimum fluence for laser blow-off of thin gold films at 248 and 532 nm
Authors: Baseman Robert J. , Froberg Nan M. , Andreshak Joseph C. , Schlesinger Zack
Published: July 2002

The minimum 248 nm, 25 ns, and 532 nm, 15 ns laser fluences required to blow off thin gold films from optical quartz have been measured as a function of film thickness. The films apparently blow off when the gold-quartz interface reaches the normal boiling point of gold. Even though the initial reflectivities at the two wavelengths are very different, the actual laser fluences required to blow off the films are very similar. While the reflectivities above the melting point appear to be very low, as expected, large decreases in the reflectivity at 532 nm may also occur prior to film melting.
Strained InGaAs/InP quantum well lasers
Authors: Temkin H. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

Quantum well lasers based on strained InxGa1−xAs/InP were grown by atmospheric pressure metalorganic vapor phase epitaxy. Buried-heterostructure lasers with the active layer consisting of three quantum wells, each ∼50 Å thick, placed in a continuously graded waveguide, exhibit threshold currents as low as 15 mA, high quantum efficiency (24%), and power output (∼100 mW), independent of composition. Changing the In concentration from x=0.48 to 0.62 results in the lasing wavelength shift from 1.45 to 1.62 μm. These wavelengths are in excellent agreement with the calculated energies of the electron–heavy hole exciton transition.
Intense laser-induced electron emission from prepoled lead-lanthanum-zirconium-titanate ceramics
Authors: Geissler K. , Gundel H. , Riege H. , Handerek J.
Published: July 2002

A sample of lead-lanthanum-zirconium-titanate (PLZT 9/65/35) has been exposed to 6-ns-long laser pulses of 266 nm wavelength. The maximum output pulse energy of the laser beam was 300 μJ, the output power density on the sample 5×105 W/cm2, and the beam diameter 3 mm. By applying a moderate extraction voltage of several kilovolts, intense electron beam pulses are emitted from the free sample surface. Their time structure corresponds to the time structure of the laser pulse. Electron beam current intensities of up to 0.1 A and 2 A/cm2 and total charges of 1 nC (corresponding to 20 nC/cm2 ) were measured with a simple Faraday cup. In the range where the parameters of laser intensity and of extraction voltage could be varied their influence on the emitted electron beam current amplitude was determined.
Amorphous silicon phototransistors
Authors: Kaneko Yoshiyuki , Koike Norio , Tsutsui Ken , Tsukada Toshihisa
Published: July 2002

An amorphous silicon field-effect phototransistor is fabricated using a processing technology compatible with conventional amorphous silicon-silicon nitride thin-film transistors. The phototransistor has an offset structure between the source and gate electrodes, where light is absorbed to produce a photocurrent. In an electron accumulation mode, the photocurrent is greater than the dark current by three orders of magnitude. In addition, the phototransistor is found to have output characteristics showing good saturation. Typical photoconductive gain of this saturation current is 17.
High-purity GaSb epitaxial layers grown from Sb-rich solutions
Authors: Anayama C. , Tanahashi T. , Kuwatsuka H. , Nishiyama S. , Isozumi S. , Nakajima K.
Published: July 2002

Undoped GaSb crystals with mirror-like surfaces were obtained by liquid phase epitaxy from Sb-rich solutions. The background carrier concentration strongly depended on the growth temperature. By growing crystals below 600 °C, we can obtain a GaSb crystal with a background carrier concentration under 1016 cm−3. Photoluminescence studies showed that native defects related to Sb vacancies were significantly reduced in the GaSb crystal.
Effect of the vibration-translation transfer rate on laser-induced frequency chirp in a long-pulse CO2 laser
Authors: Chou H. P. , Willman B. , Leung K. , Theophanis G. , Hasson V.
Published: July 2002

A frequency sweeping (chirping) mechanism governed by the lasing gas pressure and composition has been observed in a long-pulse TE CO2 laser for the first time. The mechanism was detected in heterodyned data obtained from photomixing the pulsed laser output with a cw local oscillator. A theory has been developed which links this chirp-governing mechanism to the vibration-translation (V-T) transfer rate from the lower laser level to the ground state. This new theory extends the existing theories on chirp in pulsed CO2 lasers into the long-pulse regime.
Intense charged-particle emission in a diffuse vacuum discharge
Authors: Gundel H. , Riege H.
Published: July 2002

The effects of plasma-assisted emission of electrons from a cathode and of ions from an anode are used in experiments to generate intense particle beams in a vacuum gap. The plasma is produced by sputtering of the electrons and ions impinging on the electrode surfaces. When the initial electron beam, which is generated by ferroelectric emission, reaches a current density of about 1 A/cm2, a homogeneous vacuum discharge takes place provided an electric field of the order of 10 kV/cm is applied between the anode and the cathode. The vacuum gap is short circuited and the sum of the electron and ion beam currents is determined by the charging voltages and by the parameters of the external electric circuit. Beam currents of electrons and ions are extracted through holes or grids in the corresponding electrodes.
Diagnostics of high-frequency discharges in CH4/H2 by time- and space-resolved optical emission spectroscopy
Authors: Kokubo Terukazu , Tochikubo Fumiyoshi , Makabe Toshiaki
Published: July 2002

The diagnostic technique of the rf glow discharge at 13.56 MHz is developed by using the spatiotemporally resolved optical emission spectroscopy. New experimental evidence that the temporal excitation rate at the sheath peaks in phase with the maximum of the total current is obtained in a parallel-plate geometry at 13.56 MHz in CH4(10%)/H2 under a typical condition of the plasma chemical vapor deposition of amorphous carbon film at room temperature.
Long-wavelength infrared detection in a Kastalsky-type superlattice structure
Authors: O Byungsung , Choe J.-W. , Francombe M. H. , Bandara K. M. S. V. , Coon D. D. , Lin Y. F. , Takei W. J.
Published: July 2002

The first successful demonstration of long-wavelength infrared (LWIR) detection with a Kastalsky-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is centered near 10 μm in very good agreement with the theoretical response band provided that electron-electron interactions are taken into account. The detector operates at significantly lower bias voltage than photoconductive multiple quantum well LWIR detectors. This could lead to important advantages in applications to photovoltaic detector arrays. The response at 83 K is about 50% of the response at 24 K. Optimization of the response, operating temperature, or bias voltage has not been carried out.
Cathodoluminescence study of erbium in La1−xErxF3 epitaxial layers on Si(111)
Authors: Müller H. D. , Schneider J. , Lüth H. , Strümpler R.
Published: July 2002

Erbium-substituted La1−xErxF3 lanthanum trifluoride epitaxial layers have been grown on Si(111) substrates by molecular beam epitaxy (MBE). Strong near-infrared luminescence, peaked at 1.54 μm, was observed from such films under electron beam excitation. This cathodoluminescence arises from the intra-4f-shell transitions 4I13/2→4I15/2 of Er3+(4f11). The infrared spectra reveal that MBE-grown LaF3 layers on Si(111) crystallize in the hexagonal tysonite structure, typical for bulk LaF3 single crystals.
Generation of diamond nuclei by electric field in plasma chemical vapor deposition
Authors: Yugo S. , Kanai T. , Kimura T. , Muto T.
Published: July 2002

Generation of diamond nuclei has been realized on a silicon mirror surface in plasma chemical vapor deposition. Prior to the normal diamond growth process, a predeposition process of several minutes duration was introduced in which a high methane fraction in the feed gas was used and in which a negative bias voltage was applied to the substrate. This resulted in an enormous enhancement of the generation of diamond nuclei. For the onset of diamond nucleation the minimum voltage was −70 V and the minimum methane fraction in the methane-hydrogen feed gas was 5%. Density of a diamond nuclei as high as 1010/cm2 was attained with this method.
Epitaxial thin films of YBa2Cu3O7−x on LaAlO3 substrates deposited by plasma-enhanced metalorganic chemical vapor deposition
Authors: Chern C. S. , Zhao J. , Li Y. Q. , Norris P. , Kear B. , Gallois B. , Kalman Z.
Published: July 2002

High quality epitaxial YBa2Cu3O7−x (YBCO) superconducting thin films (0.3 μm thick) were grown on the closely lattice and thermal expansion matched substrate, LaAlO3, which has low dielectric loss. The YBCO layers were prepared, in situ, by a microwave plasma-enhanced metalorganic chemical vapor deposition process. The films, which had mirror-like smooth surfaces, were deposited at a substrate temperature of 730 °C with a partial pressure of 2 Torr of N2O. The electrical resistance and magnetic susceptibility versus temperature of the as-deposited films show metallic behavior in the normal state and sharp superconducting transitions with Tc (R=0) of 88 K. Critical current densities measured on patterned bridges were 5×105 A/cm2 at 78 K for the films deposited on LaAlO3. X-ray diffraction measurements indicate that films grow epitaxially in the plane of the substrate with axis perpendicular to the substrate surface.
Low-field flux pinning in twinned and detwinned single crystals of YBa2Cu3O7−x
Authors: Swartzendruber L. J. , Kaiser D. L. , Gayle F. W. , Bennett L. H. , Roytburd A.
Published: July 2002

Flux trapping in single crystals of YBa2Cu3O7−x before and after twin removal has been measured for vortices parallel and perpendicular to the c axis. The results show clearly that, for low applied magnetic fields, twins contribute significantly to flux pinning over the temperature range 60 to 85 K when the vortices are parallel to the twin boundaries (i.e., parallel to the c axis).
Metal-induced dislocation nucleation for metastable SiGe/Si
Authors: Higgs V. , Kightley P. , Goodhew P. J. , Augustus P. D.
Published: July 2002

A new mechanism of misfit dislocation nucleation is demonstrated. Deliberate contamination with approximately 0.003 monolayers of Cu and subsequent annealing at 600 °C is shown by transmission electron microscopy, photoluminescence, and defect etching to produce dislocation half loops in a 1.1 μm layer of Si0.93Ge0.07 on a silicon substrate.
Gas source iodine n-type doping of molecular beam epitaxially grown CdTe
Authors: Rajavel D. , Summers C. J.
Published: July 2002

Highly conductive n-type CdTe films were grown by molecular beam epitaxy by iodine doping, utilizing ethyliodide as the dopant precursor. The room-temperature electron concentration increased from 8×1016 to 3×1018 cm−3 for dopant flow rate from 10−5 to 10−2 sccm and the films exhibited very high electron mobilities. The structural and optical properties were determined by x-ray double crystal rocking curve and photoluminescence measurements. Secondary ion mass spectroscopic analysis indicated a high degree of electrical activity, and sharp dopant profiles. These results demonstrate that iodine is highly effective for the n-type doping of CdTe.
Defects in amorphous silicon probed by subpicosecond photocarrier dynamics
Authors: Stolk P. A. , Calcagnile L. , Roorda S. , Sinke W. C. , Berntsen A. J. M. , van der Weg W. F.
Published: July 2002

The photocarrier dynamics in pure nonhydrogenated amorphous silicon (a-Si) have been studied with subpicosecond resolution using pump-probe reflectivity measurements. The photocarrier lifetime increases with the annealing temperature from 1 ps for as-implanted a-Si to 11 ps for a-Si annealed at 500 °C. The lifetime in annealed a-Si can be returned to the as-implanted level by ion irradiation. These observations indicate that a-Si can accommodate a variable number of defect-related trapping and recombination centers. The saturated defect density in as-implanted a-Si is estimated to be ≊1.6 at. %. Comparison with Raman spectroscopy suggests that various kinds of structural defects are present in a-Si.
Subpicosecond gain dynamics in InGaAsP optical amplifiers: Experiment and theory
Authors: Mark J. , Mo/rk J.
Published: July 2002

Pump-probe measurements on bulk InGaAsP optical amplifiers are compared with numerical calculations based on simplified density matrix equations. We find that the gain dynamics is well described by the combined effect of carrier heating, spectral holeburning, and two-photon absorption.
Fatal electromigration voids in narrow aluminum-copper interconnect
Authors: Rose J. H.
Published: July 2002

The shape and crystallography of fatal electromigration voids in near-bamboo Al-2 wt % Cu thin-film conductors were studied with transmission electron microscopy. Fatal voids were typically slit shaped and intragranular. Voids formed with {111} faces and with the slit length parallel to a 〈022〉 direction. The void faces were inclined and resided in grains of varying surface crystallographic orientation. Void morphology was independent of initial precipitate condition.
χ(3) components of single-crystalline vanadyl phthalocyanine film
Authors: Hoshi Hajime , Kohama Keiichi , Fang Shaoli , Maruyama Yusei
Published: July 2002

Single-crystalline vanadyl phthalocyanine film has been grown by the molecular-beam epitaxy technique. The χ(3) components, χ111 and χ1111, have been determined by third-harmonic generation using a fundamental Nd:YAG laser source. The relation, χ1221∼0.8χ1111, reveals that the nondiagonal component significantly contributes to the nonlinear optical response, which originates in two-dimensional π-electron system of this molecule.
Polythiophene field-effect transistor with polypyrrole worked as source and drain electrodes
Authors: Koezuka H. , Tsumura A. , Fuchigami H. , Kuramoto K.
Published: July 2002

The field-effect transistor has been fabricated, where polythiophene works as a semiconductor and a couple of polypyrrole layers act as a source and/or a drain electrode. The modulation ratio of the channel current with gate voltages has reached ca. 105, which is the largest one among organic FETs. This large modulation has been attributed to the depression of the channel current at no gate bias. It has been elucidated that the depression is caused by the barrier against hole transport formed inside the polythiophene layer and near the interface with polypyrrole.
Single-crystal Al growth on Si(111) by low-temperature molecular beam epitaxy
Authors: Miura Y. , Fujieda S. , Hirose K.
Published: July 2002

Al films were formed by low temperature molecular beam epitaxy on Si(111) surfaces. The substrates were pretreated in a NH4F solution to obtain a nearly atomically flat surface by anisotropic etching. Planview transmission electron microscopy observation demonstrates that single-crystal Al films are successfully grown on the 7×7 surface structure. Such single-crystal growth is arrested on a disordered or hydrogen-terminated surface.
Synthesis of preferred-oriented HgBa2CaCu2O6+δ thin films
Authors: Wang Y. Q. , Meng R. L. , Sun Y. Y. , Ross K. , Huang Z. J. , Chu C. W.
Published: July 2002

Superconducting preferred-oriented films of HgBa2CaCu2O6+δ of a thickness of ∼1 μm have been successfully synthesized. The process involves reacting rf-magnetron sputtered films of Ba2CaCu2Ox in a controlled Hg atmosphere at ∼800 °C for ∼5 h, followed by oxygenation. The films so obtained show a relatively sharp superconducting transition up to ∼120 K, as determined magnetically, which is similar to that of bulk Hg-1212.
Ultraviolet photon induced stimulation of surface reaction during growth of hydrogenated amorphous silicon: Estimation of the lifetime of film precursors
Authors: Suzuki Atsushi , Ganguly Gautam , Matsuda Akihisa
Published: July 2002

The effect of ultraviolet (UV) photons for the improvement of photoconductivity in hydrogenated amorphous silicon (a-Si:H) films has been investigated by intermittent deposition and UV laser irradiation procedures. It is found that UV photons stimulate precursor reaction on the growth surface effectively, and this results in improved photoelectronic properties of a-Si:H. Moreover, lifetime of precursors on the growth surface is estimated to be on the order of seconds under UV photon irradiation at room temperature.
Spatially resolved studies of the microwave properties of superconducting devices
Authors: Quenter D. , Stehle S. , Doderer T. , Krülle C. A. , Huebener R. P. , Müller F. , Niemeyer J. , Pöpel R. , Weimann T. , Ruby R. , Barfknecht A. T.
Published: July 2002

Low temperature scanning electron microscopy (LTSEM) offers the possibility for spatially resolved investigations of microwave properties of single Josephson junctions, superconducting striplines, resonators, and complex cryoelectric circuits during their operation. The spatial resolution of about 1 μm is at least two orders of magnitude better than the typical wavelength (≳100 μm in the elements) in the frequency range of interest (50–500 GHz). We demonstrate that LTSEM is a well suited tool for the experimental investigation of superconducting microwave devices and cryoelectronic circuits.
Electroabsorption of InAsP/InP strained multiple quantum wells for 1.3 μm waveguide modulators
Authors: Hou H. Q. , Cheng A. N. , Wieder H. H. , Chang W. S. C. , Tu C. W.
Published: July 2002

We report the electroabsorption property of InAsP/InP strained multiple quantum wells (MQWs), grown by gas-source molecular beam epitaxy, for 1.3 μm modulator applications. Very sharp excitonic absorption at room temperature was observed. Electroabsorption measurements performed for a ring-shaped p-i-n diode, consisting of 10-period InAs0.41P0.59(100 Å)/InP(150 Å) strained MQWs, reveal a significant red shift of the absorption peak with increasing reverse biases due to the quantum-confined Stark effect. This large energy shift (e.g., ∼18 meV at an external field of 57 kV/cm) is well accounted for in the ‘‘effective well-width’’ model. The change of the absorption coefficient at a 22 meV detuning is as large as 3510 cm−1 with a small residual absorption, which can be very useful for 1.3 μm waveguide modulators.
Relationship between implantation damage and electrical activation in gallium arsenide implanted with Si+
Authors: Haynes T. E. , Morton R. , Lau S. S.
Published: July 2002

The relationship between implantation damage and electrical activation has been investigated in GaAs implanted with 100-keV 30Si+ to doses of 5×1013/cm2 and 2×1014/cm2, using low and moderate beam currents at room temperature (RT) and at slightly elevated temperatures. For a given Si+ dose, the damage, measured by ion channeling immediately after implantation, was varied by more than a factor of 2 over the range of conditions studied. A strong negative correlation was established between this damage and the electrical activation obtained after high-temperature annealing, i.e., an increase in the initial damage led to a decrease in the sheet-carrier concentration. The results demonstrate a scheme for increasing the sheet-carrier concentration beyond that typically obtained for high-dose Si in GaAs, namely, by using a slightly elevated implant temperature (∼90 °C for a beam current of 1 μA/cm2). In addition, the initial damage is shown to consist of two components; one that is stable at RT and another that is not. The sheet-carrier concentration was found to be affected only by that component of the damage that is stable at RT, although both components were reduced by increasing the implant temperature or by reducing the dose rate.
Carrier heating in InGaAsP laser amplifiers due to two-photon absorption
Authors: Mo/rk J. , Mark J. , Seltzer C. P.
Published: July 2002

The carrier dynamics in an InGaAsP quantum-well laser amplifier excited by an ultrashort optical pulse is investigated experimentally as well as theoretically. For operation in the absorption region, a transition from pump induced cooling to pump induced heating of the carriers is observed for increasing pump pulse energy and is attributed to the generation of hot carriers through two-photon absorption. The results further support the interpretation of the carrier dynamics in the perturbative regime.
Fluid dynamics and dust growth in plasma enhanced chemical vapor deposition
Authors: Haaland Peter , Ibrani Sokol , Jiang Hao
Published: July 2002

A paradox arises with the observation of large dust particles in a low-pressure plasma enhanced chemical vapor deposition reactor. Neutral drag forces in an axisymmetric flowing afterglow reactor permit micrometer sized dust grains to form by trapping them for long times in regions with high concentrations of film precursors. A summary of the relevant mechanical and electrostatic forces on dust grains shows that collisions with neutral gas reconcile the growth rate, residence times, and relatively large diameters of the observed dust particles.
Optical and electrical properties of titanium dioxide films with a high magnitude dielectric constant grown on p-Si by metalorganic chemical vapor deposition at low temperature
Authors: Kim T. W. , Jung M. , Kim H. J. , Park T. H. , Yoon Y. S. , Kang W. N. , Yom S. S. , Na H. K.
Published: July 2002

Metalorganic chemical vapor deposition of titanium dioxide (TiO2) on p-Si(100) using titanium isopropoxide and nitrous oxide via pyrolysis at relatively low (∼500 °C) temperature was performed to produce high quality TiO2/p-Si interfaces and to fabricate TiO2 insulator gates with a dielectric constant of high magnitude. Scanning electron microscopy shows that the surfaces of the TiO2 films have very smooth morphologies. From the x-ray diffraction analysis, the grown layer was found to be a polycrystalline film. Raman spectroscopy showed the optical phonon modes of a TiO2 thin film. The stoichiometry of the TiO2 film was investigated by Auger electron spectroscopy. Room-temperature current-voltage and capacitance-voltage measurements clearly revealed metal-insulator-semiconductor behavior for the samples of the Ag/TiO2/p-Si. The interface state density at the TiO2/p-Si interface was approximately high 1011 eV−1 cm−2 at the middle of the Si energy gap, and the dielectric constant determined from the capacitance-voltage measurements was as large as 73. These results indicate the TiO2 layers grown at relatively low temperature can be used for high density dynamic memory.
Temperature dependence of growth rate for diamonds grown using a hot filament assisted chemical vapor deposition method at low substrate temperatures
Authors: Yamaguchi A. , Ihara M. , Komiyama H.
Published: July 2002

Diamond particles were deposited using a hot filament-assisted chemical vapor deposition (HFCVD) method in which the substrate temperature ranged from 210 to 700 °C. The size of the diamond particles measured as a function of time showed that a diamond grows via two periods of incubation and growth. Compared with an activation energy of 10–25 kcal/mol for substrate temperatures higher than 600 °C as reported in literature, the growth rate for a diamond grown using a HFCVD method was much less dependent on the substrate temperature for that temperature range investigated in our study. The apparent activation energy, determined from the Arrhenius plot of the substrate temperature versus diamond growth rate, decreased from 5 to 1 kcal/mol with decreasing temperature.
Correlation between nucleation site density and residual diamond dust density in diamond film deposition
Authors: Ihara Manabu , Komiyama Hiroshi , Okubo Tatsuya
Published: July 2002

Diamond was deposited on substrates pre-etched with diamond powder using either a microwave plasma chemical vapor deposition method or a hot-filament-assisted chemical vapor deposition method. Density of residual diamond dust (i.e., number of diamond particles per unit area on the surface of a substrate) on the pre-etched substrates was determined using field emission scanning electron microscopy, and ranged from 3.3×107 to 6.6×1010 ♯/cm2. The diamond nucleation-site density (i.e., number of nucleation sites per unit area on the surface of a substrate) ranged from 1.5×106 sites/cm2, typical of the deposition on a substrate etched with diamond paste, to 1.1×1010 sites/cm2, sufficient to create nanostructured diamond films. We found that the nucleation site density was about 10% of the residual dust density. Our results also show that the residual diamond dust is the main source of nucleation sites for diamond growth on diamond-etched substrates.
Improvement of grain size and deposition rate of microcrystalline silicon by use of very high frequency glow discharge
Authors: Finger F. , Hapke P. , Luysberg M. , Carius R. , Wagner H. , Scheib M.
Published: July 2002

The influence of the plasma excitation frequency on the growth conditions and the material properties of microcrystalline silicon prepared by plasma enhanced chemical vapor deposition at low deposition temperature is investigated. It is found that an increase of the plasma excitation frequency leads to a simultaneous increase of the growth rate, the grain size, and the Hall mobility of microcrystalline silicon. This is attributed to an effective selective etching of disordered material creating more space to develop crystalline grains, while also more species for faster growth of the crystallites are available.
Role of hydrogen ions in plasma-enhanced chemical vapor deposition of hydrocarbon films, investigated by in situ ellipsometry
Authors: von Keudell A. , Jacob W. , Fukarek W.
Published: July 2002

Ion bombardment during plasma-enhanced chemical vapor deposition of hydrocarbon films mainly governs the properties of the films. The range of this ion-induced modification of the optical properties of hydrocarbon films was determined in situ by monochromatic ellipsometry. The hydrocarbon films were deposited by an electron cyclotron resonance methane plasma onto silicon substrates and additional rf bias was applied to vary the kinetic energy of the impinging ions. The ion-induced modification of the film properties was investigated by means of a double layer consisting of a polymerlike film with low optical absorption and a hard carbon film with high absorption on top. The deposition of this double layer was monitored in situ by ellipsometry during the growth and during the erosion of this film system in an oxygen plasma at floating potential. From these data it is possible to determine with high accuracy the range of the ion-induced modification of the optical properties. This layer ranges from 6 Å at 30 V dc self-bias to 40 Å at 100 V dc self-bias, which is consistent with TRIM.SP calculations for the bombardment of polymerlike films by hydrogen ions.
Giant magnetoresistance in epitaxial Nd0.7Sr0.3MnO3−δ thin films
Authors: Xiong G. C. , Li Q. , Ju H. L. , Mao S. N. , Senapati L. , Xi X. X. , Greene R. L. , Venkatesan T.
Published: July 2002

The magnetoresistance of epitaxial Nd0.7Sr0.3MnOδ thin films has been studied. A giant magnetoresistance, with more than 4 orders of magnitude change in resistance (−ΔR/RH≳106%), was obtained at ∼60 K and a magnetic field of 8 T. This giant magnetoresistance (GMR) ratio is about one order of magnitude larger than the highest value reported previously which was observed in La–Ca–Mn–O film. We have also obtained a large GMR ratio with −ΔR/RH≳3000% for H=5 T in an in situ Nd0.7Sr0.3MnOδ thin film, a much larger effect than the previous results in doped manganese oxide films in which a large GMR ratio was obtained only in postannealed samples. Our results also show that the GMR effect in these films can be strongly influenced by the thin-film preparation conditions.
A distinct recombination regime in amorphous silicon diodes under double injection
Authors: Han Daxing , Wang Keda
Published: July 2002

Room temperature electroluminescence efficiency as a function of forward bias voltage, VF, shows that there are two recombination regions in device quality a-Si:H diodes. The recombination threshold voltage, Vt1, is 0.48–0.49 V. The transition voltage, Vt2, is 0.7–0.8 V. When Vt1<VF<Vt2 the electric field strongly enhances the luminescence efficiency, when VF≳Vt2 the luminescence efficiency is almost independent of the electric field. The increase of the EL efficiency in the low injection regime depends on the competition of radiative and nonradiative recombination.
Simple method to determine thickness of thin silicon dioxide film
Authors: Singh Awatar
Published: July 2002

The depth of the rocking mode infrared absorption peak at 450 cm−1 from IR response at 500 cm−1 has been observed to be a linear function of silicon dioxide thickness grown on silicon wafers. At the critical oxide thickness of 100 A°, the depth becomes zero, i.e., the IR response is flat. With further decrease of oxide thickness, the absorption peak changes sign and for oxide-free silicon, the absorption minima is shifted by about 2% from the IR response at 500 cm−1. Such IR response has been successfully used for determining oxide thicknesses in the range of 100–1200 A° with ±50 A° accuracy.
Heterodyne interferometric laser probe to measure continuous ultrasonic displacements
Authors: Monchalin Jean-Pierre
Published: July 2002

A heterodyne Michelson interferometer-type laser probe has been designed and constructed. The probe is used to measure subangstrom continuous ultrasonic displacements from rough surfaces. The probe optical and electronic design ensure optimal use of the available laser intensity, immunity from ambient vibrations, and ease of calibration.
Apparatus to measure chemical wear of carbon brushes
Authors: Kosky P. G. , Peters H. C. , Spiro C. L. , Lamby E. J. , McKee D. W.
Published: July 2002

It has been inferred for several years that the wear of a carbon brush at a sliding interface of a dc machine is influenced by chemical factors. Previously, the difficulties of isolating and measuring chemical factors in such circumstances have discouraged specific verification. An apparatus is described that hermetically seals a selected polarity brush and uses an artificial atmosphere of humidified oxygen and argon to simulate air. By monitoring the ratio of mass spectrometric peaks of CO+2 to 36Ar+, a consistent rise is observed in the amount of CO2 present. The amount of carbon thus gasified exceeded 25% of the total carbon lost.
Ultralow repetition rate shutter mechanism for thyratron triggered pulsed lasers
Authors: Viswanathan R. , Hussla Ingo
Published: July 2002

An electronic controller for an electromechanical shutter is described. The synchronization pulse output from a thyratron-triggered pulsed laser is used to keep the shutter open and to unblock the optical path followed by the laser beam for specific selected laser pulses. Effectively, ultralow repetition rates down to 0.001 Hz are obtained when the pulsed laser is operated at normal repetition rates between 0.5 and 2 Hz.
Versatile data-acquisition system based on the Commodore C-64/C-128 microcomputer
Authors: Lee H. E.
Published: July 2002

A low-cost multichannel data-acquisition system based on the Commodore C-64 or the C-128 microcomputer is described. The hardware supports up to 16 input channels at 13-bit resolution. The sampling rate of the analog-to-digital converter is 25/s. Features of the supporting software include both numeric and multicolor graphic screen output, printer output with user’s comments, and disk storage of the digitized signals. The graphic display has a 320×200-pixel grid and can be displayed in 16 colors. Input readings may be scheduled using the internal computer clock for data collection over an extended period. Easy construction using low-cost components makes this an attractive laboratory data-acquisition system.
Fractional fringe Fabry–Perot interferometer diagnostic for low-density plasmas
Authors: Dooling J. C. , York T. M.
Published: July 2002

A high-resolution Fabry–Perot interferometer (FPI) has been developed to diagnose plasma with low electron line densities. The technique is based on the fact that a cavity which is undergoing a small oscillation in length will periodically pass through a point of maximum sensitivity; in the present work the duration of this condition is about 100 μs. Line densities of approximately 1015 cm−2 were examined; this corresponded to shifts on the order of one-thousandth of a fringe. A scanning FPI was used to tune in one axial mode of a 632.8-nm He–Ne laser with a linewidth of 2.0×10−5 nm. The plasma was generated in an arc discharge formed in 50-mT air with electron densities of about 1014 cm−3. A double Langmuir probe was used as the reference diagnostic. In this case, sensitivities to electron densities were 2–5 times greater than could be achieved with a standard double-pass device; order of magnitude improvements can be made with refinements.
Fluorescence spectrometer for a single electrodynamically levitated microparticle
Authors: Arnold S. , Folan L. M.
Published: July 2002

A spectrometer for measuring the fluorescence emission from a single trapped aerosol particle is described. This device consists of a particle generator, an electrodynamic levitator, an excitation source, and detection optics and electronics. Provision is made to cool the sample chamber, and spectra can be obtained in real time. Typical spectra from particles containing organic laser dyes are presented.
ATLAS cryogenic system
Authors: Nixon Jack M.
Published: July 2002

The Argonne Tandem Linac-Accelerating System (ATLAS) superconducting heavy-ion linac is cooled by forced flow of liquid helium supplied by a 300- and a 180-W refrigerator. Outgoing flow is recondensed between heat loads by heat exchange with return flow. Control valves limit line pressure by diverting flow to return stream heat exchangers. Heater controls can maintain constant pressure or level in two helium Dewars, or constant flow for increasing or decreasing liquid level. A power meter reads excess refrigeration capacity. A stable, constant pressure liquid-nitrogen system utilizes flash loss cold gas in the refrigerators, and supplies stable low-pressure nitrogen for general cooling and shielding.
Two-photon excitation spectrometer for dilute gases
Authors: Kohler Bryan E. , Spiglanin Thomas A.
Published: July 2002

A two-photon excitation spectrometer which can be used with dilute molecular gases is described. The spectrometer is based on a standing wave tunable dye laser synchronously pumped by a mode-locked Ar+ laser. Two-photon excitation is enhanced in two ways. First, excitation is carried out intracavity at a focus produced by a pair of spherical mirrors. Second, nonlinear absorption is further enhanced by temporal compression of the laser power through mode locking the Ar+ pump laser and synchronously pumping the dye laser. The performance of the synchronously pumped intracavity focused (SPIF) dye laser spectrometer is analyzed by measuring the two-photon excitation spectrum of naphthalene vapor and comparing it with previously measured spectra. Two-photon excitation spectra of naphthalene measured with SPIF have signal-to-noise ratios that significantly surpass those of spectra found in the literature. It is estimated that for 1 Torr of gas whose fluorescence yield is unity, a two-photon absortivity of order 10−56 cm4 s photon−1 molecule−1 would produce a photon count rate of 1 Hz. This high sensitivity is partly due to the stability of the cw design of the dye laser and the high intracavity powers. This stability and the ease of its operation makes SPIF an especially useful spectroscopic tool.
Safety and efficiency ideas for electrostatic accelerators
Authors: Pepmiller Philip L.
Published: July 2002

This paper deals with rather simple devices and procedures for improving the safety and efficiency of accelerator facilities.
Operation of the Stony Brook tandem/linac accelerator system
Authors: Noé John W.
Published: July 2002

The Stony Brook nuclear structure laboratory operates the first superconducting linac based on a lead-on-copper resonator technology. Heavy ions up to mass A≂100 from the FN tandem Van de Graaff are boosted to energies of 5–10 MeV per nucleon for a variety of nuclear structure and reaction studies. We review the first 2 1/2 years of linac operating experience, with emphasis on resonator performance, system limitations, and future improvements.
First accelerated beam in the Chalk River tandem accelerator superconducting cyclotron (TASCC) facility
Authors: Bigham C. B. , Burn N. , Davies W. G. , Heighway E. A. , Hepburn J. D. , Hoffmann C. R. , Hulbert J. A. , Ormrod J. H.
Published: July 2002

The Chalk River TASCC facility consists of a 13-MV tandem accelerator injecting into a four sector k=520 (ME/q2) superconducting cyclotron that is designed to accelerate all ions from lithium (up to 50 MeV/u) to uranium (up to 10 MeV/u). This report describes the first stages of commissioning in which an iodine-127 beam was accelerated by the tandem to an energy of 71 MeV, injected into the cyclotron and accelerated to a final energy of 1.2 GeV.
Introduction to low-velocity superconducting accelerating structures and recent work at ASI and Caltech (invited)
Authors: Delayen J. R.
Published: July 2002

The characteristics and design parameters of low-velocity superconducting resonators for the acceleration of heavy ions are reviewed and discussed. Recent results obtained on lead-plated split-ring and half-wave resonators are also presented.
NPL superconducting linac control system
Authors: Swanson H. E. , Howe M. A. , Jackson L. W. , LaCroix J. M. , Readdy H. P. , Storm D. W. , Van Houten L. P.
Published: July 2002

The control system for the Nuclear Physics Lab (NPL) linac is based on a Microvax II host computer connected in a star network with nine satellite computers. These satellites use single-board versions of DEC’s PDP 11 processor. The operator’s console uses high-performance graphics and touch-screen technology to display the current linac status and as the means for interactively controlling the operation of the accelerator.
Versatile macroscale heat flow calorimeter for the study of chemical processes
Authors: Stockton Gerald W. , Ehrlich-Moser Susan J. , Chidester Dale H. , Wayne Richard S.
Published: July 2002

A novel macroscale calorimeter has been designed and fabricated for the purpose of evaluating the thermodynamic and kinetic properties of chemical reactions, especially those associated with industrial manufacturing processes. This calorimeter includes provisions for isothermal and temperature-programmed operation over a wide range of temperatures, simultaneous or sequential addition of several reagents, and variable-rate agitation. The metal reaction vessel can be removed from the main housing of the calorimeter, permitting the use of vessels made from various materials for optimum corrosion resistance. Heat transfer takes place only through the base of the vessel, ensuring that the thermal efficiency remains independent of the sample volume. A novel computer control algorithm provides precise control of the reaction temperature, as well as low-noise measurement of heat flux. The observed detection threshold is 50 mW and a heat flux of several hundred watts can be dissipated. Provisions for simultaneous measurement of other properties, such as pH, make the calorimeter especially useful for small scale piloting of chemical processes.
Achieving pulse-echo overlap with scopes having no intensity modulation
Authors: Pathak L. , Palanisami K.
Published: July 2002

Modification of the pulse-echo-overlap equipment to make it compatible with any ordinary scope, which does not have an intensity modulation facility, is described.
Quadruple thickness monitor with double backup
Authors: Strauven H. , De Wijngaerdt E. , Spinnewijn J. , Verbeke O. B.
Published: July 2002

A quadruple thickness monitor, based on quartz oscillators, in order to control the co-evaporation of quaternary alloys, is described in detail. Saturated crystals can be changed without interrupting the vacuum. The system is satisfactory in very high vacuum (no degassing at 10−8 Torr) and can be adapted to ultrahigh vacuum.
Thin-film x-ray analysis using the Read camera: A refinement of the technique
Authors: Tao K. , Hewett C. A.
Published: July 2002

The accuracy of lattice parameter determinations by Read camera x-ray diffraction is shown to be strongly dependent on camera alignment. Alignment of the Read camera eliminates the main sources of error. Further improvement in analysis was achieved by constructing a collimator with a rectangular cross section. Analysis and testing showed that the rectangular collimator enhances the efficiency, resolution, precision, and peak-to-background intensity ratio for x-ray analysis of thin films using the Read camera.
Polychromatic x-ray beam produced by a wiggler: A new dimension in x-ray diffraction at megabar pressures
Authors: Vohra Yogesh K. , Duclos Steven J. , Brister Keith E. , Ruoff Arthur L.
Published: July 2002

The wiggler provides a substantially higher flux of photons through a given collimator at high energies than is available from the bending magnet at the Cornell High Energy Synchrotron Source. This opens a new dimension in ultrapressure x-ray diffraction studies. Examples are shown in which a good diffraction pattern of gold at 112 GPa (1.12 Mbar) was obtained in 13 s and in which the diffraction pattern for primitive hexagonal silicon at 35 GPa using the beam from the wiggler contains twice as many peaks as is the case for the beam from the bending magnet.
Origin of scintillation in cerium-doped oxide crystals
Authors: Korzhik M. V. , Trower W. P.
Published: July 2002

We propose here a model of the scintillation from complex oxide single crystals doped with Ce3+ ions to explain the correlation observed between scintillation light yield and intrinsic luminescence of the matrix.
Two-wavelength infrared interferometer/polarimeter system for CIT
Authors: Ma C. H. , Hutchinson D. P. , Vander Sluis K. L.
Published: July 2002

The results of a feasibility study of a two-wavelength infrared interferometer/polarimeter system for measurements of electron density and plasma current profiles in the Compact Ignition Tokamak (CIT) are presented. The system utilizes CO2 lasers at a wavelength of 10.6 μm, and water-vapor lasers at 28 μm. Both magneto-optic and electro-optic polarization-modulation techniques have been used to determine the sensitivity and time response of the polarimetry at 10.6 μm. Measurement of a simulated plasma Faraday rotation demonstrated a sensitivity of approximately 0.01° for a CO2 laser polarimeter with an electro-optic CdTe crystal modulator.
A 25-W longitudinal, discharge-heated copper vapor laser
Authors: Wang T. C. , Yang C. Y. , Lee W. S. , Hwang Y. Y. , Shea M. W. , Luoh F. B. , Chen C. H. , Chen M. , Luo H. H.
Published: July 2002

A longitudinal, discharge-heated copper vapor laser with an internal diameter of 4.2 cm and a length of 150 cm has been constructed. At the charging voltage of 14.5 kV, buffer gas pressure of 20 Torr, pulse repetition rate of 6.5 kHz, and laser tube temperature of 1450 °C; the laser offers an average power of 25 W with excellent stability and requires a minimum amount of maintenance.
Magnetization loop tracer for superconductors
Authors: Haugdahl J. B. , Andrien B. A.
Published: July 2002

A recently developed, sensitive M/H hysteresis loop tracer can be used to detect and characterize superconductive materials under dynamic conditions. Entire sets of nested loops are obtained in seconds. The superconducting diamagnetic hysteresis loops are discussed and compared with ferromagnetic hysteresis loops and eddy current loops.
Novel alignment techniques used in multiphoton ionization experiments for laser plasma beat wave
Authors: Amiranoff F. , Benkheiri P. , Dyson A. , Gregory C. , Jacquet F. , Marques J. R. , Matthieussent G. , Mine Ph. , Montes B. , Poilleux P. , Stenz C.
Published: July 2002

This paper describes the techniques used to create a fully ionized plasma by the multiphoton ionization of gases at pressures of a few Torr to give an initial electron density precision of better than a few percent, necessary for beat-wave experiments. A gas containment vessel has been constructed using high vacuum techniques with a temperature control system to maintain the fill gas pressure constant. Novel alignment techniques are used that do not require an alignment target placed in the vessel. This involves the use of a rotating pencil beam to determine the focusing of the optics.
An ultrasonic, continuous wave, computer-controlled, reflection bridge spectrometer
Authors: Sundfors R. K.
Published: July 2002

An ultrasonic, continuous wave, computer-controlled, reflection bridge spectrometer has been developed with off-the-shelf components. This spectrometer can be used for measurements of the velocity of sound and acoustic attenuation, sampled-cw acoustic modes, and nuclear acoustic resonance. The frequency range of the spectrometer is from 5 to 400 MHz with only phase shifter, band-pass filter, and sample probe tuning changes. Sensitivity of the spectrometer over a wide range of power from 0.01 μW to 1 W in a 50-Ω system is as good as that of marginal oscillators used in nuclear acoustic resonance. The spectrometer can be used to measure ultrasonic phase velocity to within ±0.0001% and the ultrasonic attenuation to within ±0.1% for a low attenuating composite resonator kept at a constant temperature.
Generation of single longitudinal mode in a pulsed passively Q-switched Nd:YAG laser
Authors: Hariri A. , Soltanmoradi F. , Nayeri M.
Published: July 2002

It is shown that a single longitudinal mode in a passively Q-switch Nd:YAG laser can be obtained by adjusting an intracavity saturable absorber gelatin film (BDN) to work as a mirror in a three-mirror Fabry–Perot resonator. With a 0.13-mm-thick gelatin film of 40% unsaturated transmission, a temporally smooth single-laser pulse of ∼10 ns duration has been obtained.
An automated light scattering system scanning in two spherical angles
Authors: Wen Xin , Schnitzer Mark J. , Meyer Robert B.
Published: July 2002

We have designed and built a light scattering system that can detect scattered light in two spherical angles with scanning ranges more than 270° about the vertical axis and 100° about a horizontal axis. The detector and the sample holder are automated by high-precision stepping motors with a minimal angular increment 0.01° or 0.02°. A novel modular design in the detector allows the experimenter to examine the image of the scattering object and the direction of the scattered light while the detector is fixed at the measurement position. The angular resolution of the system is smaller than 0.19° in both azimuthal and polar directions. This setup has been successfully applied to study the static and dynamic properties of the ordered phases in colloidal solutions.