bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of superconductivity in YBaCuO films by aluminum ion implantation
Authors: Hong S. H. , Miller J. R. , Ma Q. Y. , Yang E. S. , Luke G. M.
Published: July 2002

We have studied the inhibition of superconductivity in high-temperature superconductors oxide films by aluminum ion implantation. Aluminum ions, with doses ranging from 1×1015–1×1016/cm2, were implanted into epitaxial YBa2Cu3O7−x (YBCO) films with an injection energy of 100 keV. Doses of 1×1016/cm2 completely suppressed the diamagnetism of the YBCO film without the need for annealing. Lower doses of 1×1015/cm2 inhibited the superconductivity after low-temperature annealing. The results of the aluminum implantation are compared with previous silicon and boron implantations.
Infrared-optical transmission and reflection measurements on loose powders
Authors: Kuhn J. , Korder S. , Arduini-Schuster M. C. , Caps R. , Fricke J.
Published: July 2002

A method is described to determine quantitatively the infrared-optical properties of loose powder beds via directional-hemispherical transmission and reflection measurements. Instead of the integration of the powders into a potassium bromide (KBr) or a paraffin oil matrix, which would drastically alter the scattering behavior, the powders are placed onto supporting layers of polyethylene (PE) and KBr. A commercial spectrometer is supplemented by an external optics, which enables measurements on horizontally arranged samples. For data evaluation we use a solution of the equation of radiative transfer in the 3-flux approximation under boundary conditions adapted to the PE or KBr/powder system. A comparison with Kubelka–Munk’s theory and Schuster’s 2-flux approximation is performed, which shows that 3-flux approximation yields results closest to the exact solution. Equations are developed, which correct transmission and reflection of the samples for the influence of the supporting layer and calculate the specific extinction and the albedo of the powder and thus enables us to separate scattering and absorption part of the extinction spectrum. Measurements on TiO2 powder are presented, which show the influence of preparation techniques and data evaluation with different methods to obtain the albedo. The specific extinction of various TiO2 powders is presented.
Novel charge integrating pulsed I(V) technique: A measurement of Fowler–Nordheim currents through thin SiO2 films
Authors: Poler J. C. , Woodward W. S. , Irene E. A.
Published: July 2002

The design, characterization, and applications of a novel charge integrating pulsed current-voltage I(V) measurement are described. Tunneling transport through thin metal-oxide-semiconductor capacitors is measured over ten orders of magnitude of current. Short pulse widths (<1 μs) allow electrical characterization of these films under high current densities without significant charge injection. A study of the quantum interference of electrons during Fowler–Nordheim (FN) conduction is used to illustrate the measurement.
Simple device for the generation and optical levitation of single aerosol particles
Authors: Hoffmann Günter Georg , Lentz Emil , Schrader Bernhard
Published: July 2002

The construction of a simple and inexpensive device is described which allows the generation and optical levitation of single droplets.
Laser stimulated scattering microscope: A tool for investigating modified metallic surfaces
Authors: Harata Akira , Nishimura Hiroyuki , Tanaka Takayuki , Sawada Tsuguo
Published: July 2002

An instrument, based on the principle of microscopic measurements using transient reflecting gratings, has been built for investigation of modified metallic surfaces. After holographic illumination of focused light pulses of short duration, dynamic processes are observed by detecting the reflecting diffraction of the synchronously delayed probe pulse, while the sample is two-dimensionally scanned. Distribution imaging and relaxation time (or diffusivity) imaging are demonstrated for ion-implanted silicon wafers.
A time-of-flight spectrometer for low-energy neutral and ionized alkalis
Authors: Kimmel G. A. , Cooper B. H.
Published: July 2002

A time-of-flight spectrometer has been developed for measuring velocity- and angle-resolved distributions of neutral and ionized alkali atoms in the range of several electron volts to several thousand electron volts. The spectrometer is mounted on a rotating platform inside a previously existing ultra-high-vacuum scattering chamber equipped with a low-energy ion beamline. A high work function platinum foil, placed after a pair of angle-defining apertures, is used to ionize the alkali atoms, regardless of their incident charge states. After striking the platinum foil, the alkali ions are accelerated and detected with a channel electron multiplier. Velocity resolution of the scattered flux is achieved using standard time-of-flight techniques. Neutral and ionized alkali atoms are detected with the same high efficiency. The ion flux can be rejected by biasing a pair of rejection elements, and therefore absolute ratios of the neutral to total flux can be determined. Such a spectrometer can be used to probe the role of charge transfer in a number of dynamical processes at surfaces.
Diamond synthesis by capacitively coupled radio frequency plasma with the addition of direct current power
Authors: Chattopadhyay K. K. , Matsumoto S.
Published: July 2002

Diamond films were synthesized by using radio frequency (RF) power in a capacitively coupled mode with a parallel plate electrode configuration in which direct current (DC) power was also applied simultaneously. This new plasma method is superior to plain DC plasma chemical vapor deposition (CVD) techniques for diamond deposition since it is very stable and seems readily scaleable. Good quality diamond films were synthesized by this modified plasma CVD method. The effect of variation of both RF and DC parameters on the deposited diamond films is discussed.
A displacement and angle interferometer with subatomic resolution
Authors: Bergamin A. , Cavagnero G. , Mana G.
Published: July 2002

The position and angle measurements discussed in the paper are carried out by application of a displacement-angle interferometer which employs a single laser and is capable of resolutions better than 1 pm and 1 nrad. Angle and displacement values are simultaneously obtained by measuring the phase shifts between four points of the interference pattern with the use of a position-sensitive detector. Though the instrument resembles an optical lever, it is largely insensitive to beam movements, since angle values are obtained by phase rather than position measurements. The interferometer design and performance are discussed, emphasis being given to applications in x-ray/optical interferometry.
Sb-surfactant-mediated growth of Si/Si1−yCy superlattices by molecular-beam epitaxy
Authors: Pettersson P. O. , Ahn C. C. , McGill T. C. , Croke E. T. , Hunter A. T.
Published: July 2002

Si/Si0.97C0.03 superlattices were grown on Si(001) substrates by molecular beam epitaxy (MBE) to study the use of Sb as a surfactant during Si1−yCy growth. In situ reflection high energy electron diffraction (RHEED) shows that while carbon easily disrupts the two-dimensional growth of homoepitaxial Si, such disruption is suppressed for layers grown on Sb-terminated Si(001) surfaces. Cross-sectional transmission electron microscopy (TEM) reveals that for samples grown without the use of Sb, the Si/Si0.97C0.03 interfaces (Si0.97C0.03 on Si) were much more abrupt than Si0.97C0.03/Si interfaces. In the case of Sb-mediated growth, differences in abruptness between the two types of interfaces were not readily observable.
Improved optical emission of porous silicon with different postanodization processes
Authors: Pellegrini Vittorio , Fuso Francesco , Lorenzi Gabriele , Allegrini Maria , Diligenti Alessandro , Nannini Andrea , Pennelli Giovanni
Published: July 2002

Time integrated and time resolved photoluminescence measurements have been performed at room temperature on porous silicon samples prepared under identical conditions but processed after anodization in four different ways. New and simple treatments were made to reduce the structural damage due to the drying process. The results show that suitable conditions exist to substantially improve the optical emission of porous silicon samples. The observed modifications of the time integrated photoluminescence signal are related to dangling bonds produced during the drying process that are supposed to act as trap states in the electron–hole or excitons recombination mechanism. Time resolved measurements provide an evaluation of the relative density of trap states for each analyzed sample.
A high intensity sputter negative ion source with multitarget positions and target scanners
Authors: Du Guangtian
Published: July 2002

The source is based on the principle put forward by Middleton, but modified significantly to a multifunction version for variant applications. It is equipped with a spherical molybdenum ionizer, an eight-position target wheel, and a special Cs vapor nozzle. Due to the special design, target changing and scanning are carried out only by means of rotations, to simplify the mechanism and automatic control procedures. The tube for transmitting Cs vapor, as a resistance, is connected in series in the ionizer supply circuit to reach a high enough temperature for the vapor to pass. Details of the mechanical design, operation modes, and test results are given.
Developments of a wide range characterization system for high-T
c superconductors [Comment on Rev. Sci. Instrum. 63, 2044 (1992)]
Authors: Bellingeri E. , Eggenhöffner R.
Published: July 2002

An improved method is reported for measurements of I-V characteristics of high-Tc superconductors based upon the acquisition system developed by Kirkup et al. [Rev. Sci. Instrum. 63, 2044 (1992)]. The introduction of a lock-in mode of operation significantly enhances the voltage sensitivity in the range of relevance for the definition of the superconducting state. In addition, this approach permits the current direction in the sample to be reversed whenever needed.
On distributed microwave effects in semiconductor lasers and their practical implications
Authors: Wu Bin , Georges John B. , Cutrer David M. , Lau Kam Y.
Published: July 2002

Recently, it has been shown that when a semiconductor laser is directly modulated at high frequencies, the modulation signals suffer substantial loss and phase shift propagating from the wire feed point along the length of the laser. It was suggested that these distributed microwave effects lead to a further bandwidth degradation in electrical current injection over the single-pole roll-off predicted by a lumped RC model. We show, however, that this degradation is significant only when the laser is driven directly by a voltage source. In contrast, when the laser is driven, commonly, through a 50 Ω transmission line the degradation is minimal, and the total injection current is still RC limited.
Characteristics of a SiC microwave absorber for a damped cavity
Authors: Izawa M. , Koseki T. , Kamiya Y. , Toyomasu T.
Published: July 2002

Development of a SiC microwave absorber for a damped cavity is presented. The SiC studied has a resistivity of 101–102 Ω cm, which is the expected value to damp higher-order modes (HOMs) in the cavity and also has high thermal conductivity. The absorber is attached to the cavity as a part of the beam duct. Since the SiC duct receives a large amount of energy from the electron (or positron) stored beam, it is very important to estimate the dissipation power in the SiC duct and to design a cooling mechanism. The heat load problem of the SiC duct is discussed and the results of high power testing of the SiC duct are presented. The damping mechanism for HOMs is based on the power dissipation due to the resistivity of SiC. The fine control of the resistivity of SiC in fabrication is very important. The preliminary results on this problem are also presented.
A picosecond electron gun for surface analysis
Authors: Aeschlimann M. , Hull E. , Cao J. , Schmuttenmaer C. A. , Jahn L. G. , Gao Y. , Elsayed-Ali H. E. , Mantell D. A. , Scheinfein M. R.
Published: July 2002

Theoretical and experimental investigations for a new design of an ultrashort pulsed laser activated electron gun for time resolved surface analysis are described. In addition, a novel electron detection and image analysis system, as it applies specifically to time resolved reflection high-energy electron diffraction in the multiple-shot operation, are reviewed. Special attention is directed to minimize the photoelectron transit-time spread from the electron gun, in spite of an unusually long focal length and a small convergence angle of the pulsed electron beam. Both requirements are necessary to use the electron gun for diffraction techniques. The design value for the temporal resolution in the synchroscan operation is 1.3 ps. Based on a thorough theoretical investigation, a new electron gun has been designed, constructed, and tested.
Size effect in hard superconductors at unilateral excitation
Authors: Pérez-Rodríguez F. , Makarov N. M. , Yampol’skii V. A. , Lyubimova I. O. , Lyubimov O. I.
Published: July 2002

It is shown that size effect plays an important role in the ac response of hard superconductors not only at bilateral but at unilateral excitation as well. This effect manifests itself in the ac amplitude dependences of the surface impedance and absorptivity. We find that the absorptivity of a superconductor has always a prominent maximum independently of the dielectric properties of the substrate. This statement is demonstrated by theoretical calculations performed within the critical state model.
Comment on ‘‘Effect of electron temperature on negative hydrogen ion production in a low-pressure Ar discharge plasma with methane’’ [Appl. Phys. Lett. 63, 1619 (1993)]
Authors: Pinnaduwage Lal A.
Published: July 2002

The author proposes a mechanism for the efficient production of negative Hydrogen ions in a low−pressure Ar discharge plasma with methane using a novel pin−hollow cathode as reported in Appl. Phys. Lett. 63, 1619 (1993). (AIP)
Low-temperature raster system for moving crystals with application to sound-beam topography
Authors: Scheffold B. , Weis O.
Published: July 2002

Construction details of a low-temperature raster system for moving crystals with a maximum size of 14 mm × 14 mm × 14 mm over a small area of piezoelectric sound excitation are described. The pure mechanical raster system in the liquid helium is driven by two stepping motors outside the cryostat. The minimum step size is 1 μm and the maximum raster area 14 mm×14 mm. This raster system was used in sound-beam topography at a frequency of 70 GHz. For this purpose, a special quasioptical transmission line across the dewar wall was also developed which is briefly described together with the applied electromechanical transducer system.
Low cost fast switch using a stack of bipolar transistors as a pockel cell driver
Authors: Dharmadhikari A. K. , Dharmadhikari J. A. , Adhi K. P. , Mehendale N. Y. , Aiyer R. C.
Published: July 2002

A fast high voltage switch to discharge a capacitive load using a stack of bipolar junction transistors is described. The switch operating at a voltage of 3.5 kV has a fall time (90%–10%) of ∼2 ns. With a capacitive load (pockel cell) the pulse fall time increases to 6 ns. The life of the stack is >50 million shots.
Effects of spectral hole burning, carrier heating, and carrier transport on the small-signal modulation response of quantum well lasers
Authors: Tsai Chin-Yi , Tsai Chin-Yao , Lo Yu-Hwa , Spencer Robert M.
Published: July 2002

We present an analysis of the high-speed characteristics of quantum well lasers by simultaneously considering the effects of spectral hole burning, carrier heating, and carrier transport. An exact form of the small-signal modulation response is obtained. The effects of carrier dephasing time in spectral hole burning, energy relaxation time in carrier heating, and diffusion-capture-escape times in carrier transport on the modulation response of quantum well lasers are theoretically investigated.
Role of radiative and nonradiative processes on the temperature sensitivity of strained and unstrained 1.5 μm InGaAs(P) quantum well lasers
Authors: Braithwaite J. , Silver M. , Wilkinson V. A. , O’Reilly E. P. , Adams A. R.
Published: July 2002

By measuring the spontaneous emission from strained and unstrained 1.5 μm InGaAs quantum well lasers as a function of temperature we deduce the temperature dependence of the radiative current density at threshold corresponds to a characteristic temperature T0≊300 K, close to that expected from theory, whereas T0 of the threshold current is around 60 K. We conclude from our analysis that the large temperature dependence of long wavelength lasers is due to Auger recombination.
Noncontact photothermal infrared radiometric deep-level transient spectroscopy of GaAs wafers
Authors: Mandelis A. , Budiman R. A. , Vargas M. , Wolff D.
Published: July 2002

A novel infrared photothermal radiometric deep-level transient spectroscopy (PTR-DLTS) has been developed for semiconductor noncontact characterization and applied to GaAs wafer diagnostics. The technique is based on rate-window detection combined with wafer temperature ramping. Unlike other deep-level methodologies, PTR-DLTS should be easily implemented remotely for on-line or off-line impurity/electronic defect diagnostics and enjoys high spectral peak separation and spatial resolution limited only by the pump laser beam focus (≥1 μm). The impurity level in a Cr-compensated semi-insulating GaAs wafer has been detected at ∼375 K using the 514 nm line of an Ar+ laser. A Te-doped GaAs sample exhibited behavior consistent with photoinjected carrier lifetime enhancement due to surface state (trap) thermal filling at elevated temperatures.
Nonradiative capture of hot photoelectrons by multiphonon emission in highly excited CdS crystals
Authors: Žukauskas A. , Juršėnas S.
Published: July 2002

Luminescence kinetics of nonthermalized electron-hole plasma in highly excited CdS crystals with different concentration of native defects has been studied at T=298 K. The shape of the kinetics indicated an enhancement of the plasma nonradiative recombination with increased carrier effective temperature. The experimental results are in good agreement with a model of thermal activation of nonradiative capture by multiphonon emission in centers with the barrier energy of W=110 meV.
Thermal expansion measurement of pure aluminum using a very low thermal expansion heating stage for x-ray diffraction experiments
Authors: Langelaan G. , Saimoto S.
Published: July 2002

Precise lattice parameter measurements for residual stress analysis requires good specimen alignment in the beam path. If these measurements are to be performed at elevated temperatures, then the effects of thermal expansion must be accounted for in the alignment and calibration procedure. During a recent study, residual strains in a metal matrix composite were measured in situ during dynamic temperature cycling. These experiments required a stage capable of rapid heating and cooling as well as a very low thermal expansion to minimize the specimen displacement during the cycling. A low expansion stage, heated with a programmable infrared heater, was developed in which the front (irradiated) surface is the reference plane. The thermal expansion of the stage was measured using a diffraction technique to determine false lattice parameter shifts due to specimen displacement and was found to be less than the measurement limit of the apparatus. With small specimens, the temperature control became difficult and fluctuations of ±1.5 °C were observed. The temperature dependence of the lattice parameter for pure Al was measured between 30 and 386 °C. Very good agreement was obtained with previously published data. Thus a new rapid technique which allows complete measurement of the lattice thermal expansion in less than 2 h has been demonstrated. This technique can also be applied to measurement of the temperature dependence of residual stresses in complex materials such as metallizations for microelectronics and for metal matrix composites.
Strain and temperature effects on erbium-doped fiber for decay-time based sensing
Authors: Arnaud A. , Forsyth D. I. , Sun T. , Zhang Z. Y. , Grattan K. T. V.
Published: July 2002

An experimental investigation into the strain and temperature sensitivity of the fluorescence decay time in commercial erbium-doped optical fiber has been carried out. Results show that a strain effect on the performance of temperature-based sensors using such fiber is larger than that for neodymium-doped fiber, but a little smaller than is seen in similar ytterbium-doped material. For the materials studied, the relative change in lifetime ranges from about 5×10−7 (for Yb) to 14×10−7 (for Nd) με−1 and the associated error in the temperature measurement ranges from 1.8×10−3 (for Nd) to 6.1×10−3 Kμε−1 for the Yb sample used. The application to simultaneous strain and temperature monitoring is discussed.
Current transport in as-grown and annealed intermediate temperature molecular beam epitaxy grown GaAs
Authors: Nabet B. , Youtz A. , Castro F. , Cooke P. , Paolella A.
Published: July 2002

Molecular beam epitaxy (MBE) GaAs grown in the intermediate temperature range of about 400 °C may provide combination of low lifetime, high resistivity, and high mobility. We compare current conduction in unannealed and annealed material grown at 400 °C by fabricating photodetectors on substrates grown between temperature ranges of 250–500 °C. The unannealed version of the device grown at 400 °C shows substantial difference of conduction properties in dark and under light. It is shown that while at low biases the unannealed material may be semi-insulating, at high biases more current is conducted than in annealed material. We attribute this to the effect of intergap states on current conduction and suggest that defect state assisted tunneling is the dominant current transport mechanism in these ranges. Quenching of response by light suggests that occupancy of traps can eliminate their role in current conduction.
Properties of deep photoluminescence bands in SiGe/Si quantum structures grown by molecular beam epitaxy
Authors: Buyanova I. A. , Chen W. M. , Henry A. , Ni W.-X. , Hansson G. V. , Monemar B.
Published: July 2002

The appearance of broad photoluminescence (PL) bands in the energy range 0.70–0.96 eV in SiGe/Si heterostructures is shown to be related to the ion bombardment during the molecular beam epitaxy. From the optically detected cyclotron resonance, polarization, and postgrowth treatments, the PL is shown to be composed of at least two components. No evidence of lattice distortion is found for the main PL band, while the low energy tail is believed to arise from lattice distorted regions. Both PL centers are demonstrated to originate from the SiGe quantum wells by PL excitation measurements.
Giant Hall effect in percolating ferromagnetic granular metal-insulator films
Authors: Pakhomov A. B. , Yan X. , Zhao B.
Published: July 2002

We studied both the resistivity and the Hall resistivity of cosputtered granular Ni–SiO2 films with the metal volume fraction x in the range of 0.5–1.0. Near the metal-insulator transition, or x of about 0.53–0.61, the saturated value of the Hall resistivity was up to 2×10−4 Ω cm. This value is almost 4 orders of magnitude greater than that of pure nickel. Both the resistivity and the Hall resistivity varied weakly with temperature, throughout the range of 5–300 K. We suggest that the percolating ferromagnetic granular metal films can be an alternative candidate material for high sensitivity Hall sensors.
Infrared investigation of deuterated Si(111) surface formed in hot heavy water
Authors: Watanabe Satoru
Published: July 2002

A deuterated Si(111) surface has been fabricated by wetting in deionized hot heavy water without oxidizing the surface. The surface had a single dominant absorption feature with a narrow width in the infrared spectrum. The surface was mainly composed of monodeuterides whose Si–D bonds are normal to the surface, and partially of other deuteride structures. The surface structure was quite similar to H/Si(111) formed in hot water.
Butterfly bistability in an InGaAs/InP multiple-quantum well waveguide with distributed feedback
Authors: Coriasso C. , Campi D. , Cacciatore C. , Faustini L. , Leo G. , Buscaglia F. , Rigo C. , Stano A.
Published: July 2002

We report the experimental observation of butterfly bistability in an InGaAs/InP multiple-quantum well waveguide with a distributed feedback grating, under cw operation and at sub-milliwatt input power. Plasma effects on the excitonic optical properties in multiple-quantum well structures are the basis of the observed bistability. Insight provided by a simple coupled-mode description of the device and by many-body theory of the field-matter interaction is used both for device design and for interpretation of the results. In particular, the unconventional shape of the hysteresis is due to increased optical absorption at high injected optical power.
Hypersound generation by resonant-tunneling structure
Authors: Kozub V. I. , Rudin A. M.
Published: July 2002

The possibility of hypersound generation by means of a double-barrier resonant-tunneling structure is suggested. The intensity of the generated sound is estimated. Prospects for phonon spectroscopy and acoustoelectronics based on the resonant-tunneling devices are suggested.
Positive giant magnetoresistance in antiferromagnetic RE2Ni3Si5 (RE=Tb, Sm, Nd)
Authors: Mazumdar Chandan , Nigam A. K. , Nagarajan R. , Godart C. , Gupta L. C. , Padalia B. D. , Chandra G. , Vijayaraghavan R.
Published: July 2002

Positive giant magnetoresistance (GMR), Δρ/ρ, is reported here in polycrystalline antiferromagnetic materials RE2Ni3Si5 (RE=Tb, Sm, Nd); Δρ/ρ, at 4.4 K and in a field of 45 kOe, is 85%, 75%, and 58%, respectively. Positive GMR of such large magnitude has not been reported earlier in magnetically ordered polycrystalline compounds. The observed GMR is not correlated to the RE-moments. It is, however, associated with the magnetic ordering of the lattice as its magnitude is significantly reduced in the paramagnetic state. Surprisingly, MR in Y2Ni3Si5, a non-magnetic rare earth analogue, is also relatively large (16% at 4.4 K; 45 kOe) and is even slightly higher than that of antiferromagnetically ordered Gd2Ni3Si5 (12% at 4.4 K; 45 kOe). The layered structure of the materials is suggested to be responsible for the observed GMR.
Characterization of stacked gate oxides by electron holography
Authors: Rau W.-D. , Baumann F. H. , Rentschler J. A. , Roy P. K. , Ourmazd A.
Published: July 2002

We have used off-axis electron holography at a resolution of 3 Å to investigate amorphous bilayer gate oxides consisting of thermal and chemically deposited SiO2. The values of the mean inner potential were measured to be: thermal oxide: (10.51±0.35)V (undensified); (10.65±0.32)V (‘‘densified’’); deposited oxide: (11.19±0.38)V (undensified); (10.58±0.69)V (densified). Exploiting the chemical etch rate differences between different oxides, we have delineated stacked gate oxides consisting of closely similar layers. Our results establish that measurement of thickness differences produced by etching can be used to reveal the densification state of the oxide.
Unambiguous photoreflectance determination of electric fields using phase suppression
Authors: Tyan S. L. , Wang Y. C. , Hwang J. S. , Shen H.
Published: July 2002

Photoreflectance measurements have been performed on a δ-doped GaAs homojunction. Two Franz–Keldysh oscillation features originating from two different regions (a buffer layer and a top layer) of the structure superimpose with each other in the photoreflectance spectrum. By properly selecting the reference phase, one of the features can be suppressed, thus enabling us to determine the electric fields from the two regions unambiguously. The electric field in the top layer is 3.5±0.2×105 V/cm, which is in good agreement with theoretical calculation. The electric field in the buffer layer is 1.2±0.1×104 V/cm.
Observation of Si in SiC composite fibers: A micro-Raman investigation
Authors: Kim Jeongyong , Tlali Spirit , Jackson Howard E. , Webb James E. , Singh Raj N.
Published: July 2002

The chemical composition and microstructure of SiC composite fibers were studied by spatially resolved Raman spectroscopy. The spectra display a strong peak in the outer SiC layer identified as a Si signature and thus provide direct evidence of the presence of excess Si in the fiber composites. The Si crystallite size as well as the stress in the Si were estimated. Excess silicon has been previously suggested as the cause of the unusual creep and the anomalous thermal expansion behavior of these composites at high temperatures.
Fabrication of highly oriented Si:SiO2 nanoparticles using low energy oxygen ion implantation during Si molecular beam epitaxy
Authors: Ishikawa Yukari , Shibata N. , Fukatsu S.
Published: July 2002

A novel technique is developed for fabricating highly oriented Si nanoparticles (SNP) embedded in SiO2 using multiple low energy oxygen ion implantation during Si molecular beam epitaxy. The SNPs are of nearly isotropic but faceted morphologies with almost perfect crystallinity as revealed by transmission electron microscopy. The preferred axis of SNP cores is found to be aligned to [100] due to epitaxy on a Si(100) substrate, reflecting the highly oriented character of SNPs. Visible luminescence from SNPs with dimensions approaching the quantum confinement regime is observed at room temperature.
Variation of the confinement potential of a quasi-one-dimensional electron gas by lateral p-n junctions
Authors: Evans R. J. , Burke T. M. , Burroughes J. H. , Grimshaw M. P. , Ritchie D. A. , Pepper M.
Published: July 2002

We present the first study of a new system where the confinement potential of a high mobility quasi-one-dimensional electron gas on the (100) GaAs surface is varied using two, two-dimensional hole gases produced on the adjacent (311)A surfaces. The structure consists of two lateral two-dimensional p-n junctions, placed back-to-back to form a p-n-p structure. The confinement potential of the narrow n-type channel can thus be modulated by applying a bias to the adjacent p-type regions. Magnetoresistance measurements of the narrow channel show magnetic depopulation of the one-dimensional subbands [K.-F. Berggren, T. J. Thornton, D. J. Newson, and M. Pepper, Phys. Rev. Lett. 57, 1769 (1986)], following the model of Berggren et al. [Phys. Rev. B 37, 10118 (1988)] widths and one-dimensional carrier concentrations are extracted to fully characterize the dependence of the channel on the applied ‘‘hole-gate’’ voltage.
Strain and phonon shifts in GaAs1−xPx alloys
Authors: Armelles G. , Sanjuán M. J. , González L. , González Y.
Published: July 2002

We have studied the influence of an in-plane (001) strain on the energy position of the long wavelength optical modes of GaAs1−xPx alloys. These alloys have a two mode behavior. We have observed that the strain-induced shift of the Raman peaks corresponding to the GaAs-like vibration is greater than that of the GaP-like vibration. This result shows that the two modes are not affected in the same way by the strain.
Generation of terahertz acoustic-phonon signals by heated electrons in AlxGa1−xAs/GaAs-based quantum wires
Authors: Xu W.
Published: July 2002

A detailed theoretical study that explores the possibility to apply AlxGa1−xAs/GaAs-based quantum wire systems to terahertz (THz) ultrasonic generator is presented. The THz ultrasound can be generated through generating the acoustic phonons by heated electrons in these structures. Taking into account the generation of acoustic phonons via deformation potential and piezoelectric coupling, the frequency and angular distribution of the acoustic-phonon emission can be obtained. The theoretical results indicate that: (i) AlxGa1−xAs/GaAs-based quantum wires are suitable for generating THz acoustic-phonon signals; (ii) both longitudinal and transverse phonon modes contribute to the detected phonon signals; and (iii) the THz acoustic phonons can be generated from both intra- and intersubband scattering processes.
Electron-emission-enhanced diamond nucleation on Si by hot filament chemical vapor deposition
Authors: Chen Qijin , Lin Zhangda
Published: July 2002

Diamond nucleation on mirror-polished Si was enhanced by electron emission using hot filament chemical vapor deposition. The nucleation density was 108 cm−2. The mechanism of diamond nucleation is carefully discussed. It is surmised that it is electron emission that is responsible for the enhancement of the diamond nucleation in our experiments.
Enhancing discharge uniformity in a multi-kilowatt radio frequency excited CO2 slab laser array
Authors: Strohschein J. D. , Bilida W. D. , Seguin H. J. J. , Capjack C. E.
Published: July 2002

A computational model is reported which is able to accurately predict discharge uniformity in large-area electrodes for transverse rf-excited CO2 lasers. The model has been employed in the development of a multi-kW radial slab array. Shunt inductors are resonated directly with the discharge impedance, thereby achieving excellent discharge uniformity while eliminating the need for frequency stabilized power sources. Experimental results suggest the model will generally be of major assistance in optimizing large-area electrodes designs, and specifically in scaling slab laser systems to multi-kW levels.
Photoconductive sampling with an integrated source follower/amplifier
Authors: Hwang Jiunn-Ren , Cheng Heng-Ju , Whitaker John F. , Rudd James V.
Published: July 2002

A hybrid, optoelectronic sampling circuit based on a photoconductive switch and a junction-field-effect-transistor (JFET) source follower/amplifier has been demonstrated to have picosecond response, high-sensitivity, absolute-voltage capability, and a very high impedance. The distributed capacitance of the electrical measurement system is reduced to the gate input capacitance of the JFET, and the conventional photoconductive current measurement is transferred into an absolute voltage measurement. Gating measurements with an improvement of 150 times in output voltage over unamplified photoconductive gates have been made using only 10 μW of average optical power. The effective on-state resistance of the photogate has also been increased by more than 150 times, indicating that a photoconductive probe with very low invasiveness may be produced.
Photopumped laser operation of a planar disorder- and native-oxide-defined AlAs–GaAs photonic lattice
Authors: Ries M. J. , Chen E. I. , Holonyak N.
Published: July 2002

Data are presented demonstrating photopumped laser operation of a planar photonic lattice (∼1 μm thick) that is comprised of 9 μm disks with 2 μm separation arranged in a two-dimensional hexagonal close-packed pattern. The active region of each disk is an AlAs (70 Å)–GaAs (30 Å) superlattice (100 periods). The disks are defined by impurity-induced layer disordering, followed by wet oxidation (N2+H2O vapor, 400  °C), which surrounds each disk with a low-refractive-index AlGaAs native oxide. The photonic lattice exhibits laser operation within wide (Δλ∼17 Å) spectral bands that are spaced according to the disk modes, and that propagate light anisotropically in the plane of the lattice. In addition to the extended lattice, groups of seven disks are studied and are seen to display similar behavior.
The influence of TiSi2 and CoSi2 growth on Si native point defects: The role of the diffusing species
Authors: Herner S. B. , Jones K. S. , Gossmann H.-J. , Tung R. T. , Poate J. M. , Luftman H. S.
Published: July 2002

Boron- and Sb-doped superlattice samples have been used to investigate intrinsic point defects in Si after formation of TiSi2 and CoSi2 films from codeposited metal and Si. The as-deposited films had the compositions Ti, TiSi0.8, TiSi2.2, and CoSi0.8. After annealing in argon for 1 h at 850 °C, the films formed TiSi2 and CoSi2, respectively. All samples showed the same slight interstitial undersaturation and vacancy supersaturation. Since TiSi2 and all its precursor phases form completely by Si diffusion and the CoSi+Si→CoSi2 transformation occurs by Co diffusion, this indicates that the diffusing species during film growth is not the determining factor in the point defect perturbance in the Si substrate.
Optical properties of InGaAs linear graded buffer layers on GaAs grown by metalorganic chemical vapor deposition
Authors: Lee B. , Baek J. H. , Lee J. H. , Choi S. W. , Jung S. D. , Han W. S. , Lee E. H.
Published: July 2002

We report optical characteristics of linear graded InxGa1−xAs (XIn=0–0.58) buffer layers grown on GaAs by low-pressure metalorganic chemical vapor deposition. Two types of wirelike surface structures were observed from the layers grown at two different temperatures. Low-temperature photoluminescence (PL) and double-crystal x-ray diffractometric measurements indicate that the PL energy and the relaxation of the graded layers were strongly dependent on the top surface structure. InGaAs cap layers were grown on top of the graded buffer layers with a variation of indium composition. A strong PL signal was observed from the top region of the graded layer grown with a lattice-matched cap layer. It suggests that the top region of the grade, similar to a graded well structure, is compressively strained but is of high structural quality without dislocations.
2×106 cm2/V s electron mobility by metalorganic chemical vapor deposition with tertiarybutylarsine
Authors: Chui H. C. , Hammons B. E. , Harff N. E. , Simmons J. A. , Sherwin M. E.
Published: July 2002

We demonstrate the metalorganic chemical vapor deposition (MOCVD) growth of two-dimensional electron gases (2DEGs) with electron mobilities up to 2.0×106 cm2/V s at 0.3 K. These are the highest mobilities to date for MOCVD materials, and were achieved using a safer replacement precursor for arsine, tertiarybutylarsine (TBA). For structures grown using arsine, we obtained a maximum mobility of 1.0×106 cm2/V s, which although comparable to the best by MOCVD to date, is half that obtained using TBA. Our studies on thick GaAs and AlGaAs layers indicate that the use of TBA in place of arsine reduces both the carbon and donor impurity concentrations. Thus, TBA is not only a safe alternative to arsine, but also produces significantly purer films.
First order gain and index coupled distributed feedback lasers in ZnSe-based structures with finely tunable emission wavelengths
Authors: Eisert D. , Bacher G. , Mais N. , Reithmaier J. P. , Forchel A. , Jobst B. , Hommel D. , Landwehr G.
Published: July 2002

First order gain and index coupled distributed feedback (DFB) gratings were realized in ZnSe-based laser structures using direct implantation with a focused ion beam for gain-modulated structures and conventional electron beam lithography for index modulation. With both technologies, gratings with periods below 90 nm could be achieved, permitting DFB emission in the blue spectral range. Fine tuning of the emission wavelength in steps of 0.14 nm is demonstrated by sampled DFB gratings based on a periodic modulation of the resonator period.
Enhancement of terahertz acoustic-phonon generation by the magnetic field applied parallel to a two-dimensional semiconductor system
Authors: Xu W. , Zhang C.
Published: July 2002

In this letter, we present a theoretical study on terahertz (THz) acoustic-phonon emission in AlxGa1−xAs parabolic quantum-well structures in parallel magnetic fields. Our theoretical results show that (i) the generation of acoustic-phonon signals can be enhanced significantly by the in-plane magnetic fields; (ii) the strongest acoustic-phonon emission can be observed around a magnetic field where an electronic subband becomes depopulated; (iii) the generated acoustic-phonon frequency depends weakly on the magnetic fields; and (iv) the presence of an in-plane magnetic field slightly varies the acoustic-phonon emission angle from that at zero magnetic field.
The nucleation of highly oriented diamond on silicon via an alternating current substrate bias
Authors: Wolter S. D. , Borst T. H. , Vescan A. , Kohn E.
Published: July 2002

A new bias-enhanced nucleation method of forming highly oriented diamond on Si(100) is reported using an alternating current bias source. The percentage of aligned particles via alternating current bias-enhanced nucleation (ac BEN) was greater than 50%. This is compared to less than 10% highly oriented particles when using a conventional negative dc substrate bias. Based on previous work in this area, the peak negative voltage portion of the ac wave form is believed to be responsible for enhancing diamond nucleation. The positive and moderate negative voltage portion of the ac wave form appears to aid the process of forming the highly oriented diamond.
Temperature dependence of reflectance and transmittance at 514.5 nm of CdS films formed by laser ablation
Authors: Ullrich B. , Ezumi H. , Keitoku S. , Kobayashi T.
Published: July 2002

The temperature dependence of reflectance and transmittance of a thin (2 μm) CdS film prepared by laser ablation was investigated. The measurements were performed with the 514.5 nm line of an argon laser in the range 180–350 K. It occurred that due to locally enhanced absorption at the film/substrate interface, the transmitted light was considerably weaker than would be theoretically expected for a homogeneous layer. The reflectance, however, followed the theory based on Urbach’s rule. The interfacial enhancement of the absorption was confirmed by luminescence investigations.
Electrical properties of paraelectric (Pb,La)(Nb,Ti)O3 thin films for dynamic random access memory devices
Authors: Lee Su Jae , Cho Chae Ryong , Kang Min Soo , Jang Min Su , Kang Kwang Yong
Published: July 2002

Paraelectric (Pb,La)(Nb,Ti)O3 (PLNT) thin films were deposited by the sol-gel method on (111)Pt/Ti/SiO2/Si substrates at temperatures as low as 600 °C for the use of ULSI (ultralarge scale integration) DRAM (dynamic random access memory) capacitors. Films exhibited a regular polycrystalline cubic perovskite phase and showed the presence of paraelectricity in terms of hysteresis of capacitance–voltage (C–V) and polarization–electric field (P–E) characteristics in metal–insulator–metal (MIM) capacitors. The dielectric constants of the films are 611 for a 200 nm thick film and 619 for a 300 nm thick film in a frequency of 100 kHz. The charge storage density obtained from the polarization measurement for a 200 nm thick film was about 50 fC/μm2, while a leakage current density of 70 nA/cm2 was observed at an applied field of 100 kV/cm. These values qualify the PLNT thin films for an alternate storage node dielectric in DRAM capacitors.
Microhollow cathode discharges
Authors: Schoenbach K. H. , Verhappen R. , Tessnow T. , Peterkin F. E. , Byszewski W. W.
Published: July 2002

The current–voltage characteristics of hollow cathode discharges and their predischarges in argon under dc and pulsed conditions were found to have a positive slope at pressures up to approximately 50 Torr, and currents up to 20 mA, at a hole diameter of 0.7 mm. In this range of pressure and current, parallel operation of hollow cathode discharges, without ballast, was demonstrated. Scaling to higher pressure is possible by reducing the hole diameter. Pulsed experiments with an array of cathode rings of 75 μm diameter allowed us to obtain parallel operation of more than 50 discharges at a pressure of 350 Torr in air.
Fabrication and characterization of ion-exchanged waveguides in potassium titanyl arsenate
Authors: Risk W. P. , Loiacono G. M.
Published: July 2002

Optical waveguides can be fabricated in the nonlinear material potassium titanyl arsenate (KTiOAsO4) using ion exchange in a mixed RbNO3/Ba(NO3)2 melt. The guiding properties of such waveguides were measured and the variation of these properties with changes in processing conditions was investigated.
Photoemission from K–Te photocathodes
Authors: Bisero D. , van Oerle B. M. , Ernst G. J. , Verschuur J. W. J. , Witteman W. J.
Published: July 2002

In this letter the photoemissive properties of K–Te films produced under ultrahigh vacuum conditions are reported. K–Te photocathodes were fabricated by vapor deposition of Te and K onto a Mo substrate into the preparation chamber of the Free Electron Laser of the University of Twente. The highest quantum efficiency obtained at 259 nm was 11.1%, measured just after evaporation; this value decreased in a few minutes to a stable quantum efficiency of 8.3%. The reported results show that K–Te can be considered a promising material for the use as a photocathode in photoinjectors.
Densification of amorphous silicon prepared by hydrogen-ion-beam-assisted evaporation
Authors: Rinnert H. , Vergnat M. , Marchal G. , Burneau A.
Published: July 2002

Hydrogenated amorphous silicon films were deposited by ion-beam-assisted evaporation onto substrates maintained at 120 °C. The influence of the substrate bias was studied. By combined infrared spectrometry and thermal desorption spectrometry experiments, it is inferred that the bombardment of the growing a-Si:H film by energetic hydrogen ions produces a densification of the material without modification of the Si:H bonding.
Photoexcited carrier dynamics in InAlGaAs/InP quantum well laser structures
Authors: Marcinkevičius S. , Hillmer H. , Lösch R. , Olin U.
Published: July 2002

Experimental investigations of carrier transport and capture into quantum wells are performed for InAlGaAs/InP laser structures. Time-resolved photoluminescence measurements are made by upconversion technique. The characteristic times for the ambipolar carrier transport in the confinement region and the electron capture into the quantum wells are about 2–5 and 1 ps, respectively. The obtained results show a good potential for high-speed InAlGaAs/InP quantum well lasers operating in the 1.5 μm spectral region.
Polymeric light-emitting diodes from molecularly thin poly(3-hexylthiophene) Langmuir–Blodgett films
Authors: Pal A. J. , Östergård T. , Paloheimo J. , Stubb H.
Published: July 2002

Light-emitting diodes based on molecularly thin films of a conjugated polymer have been fabricated. A few Langmuir–Blodgett layers of poly(3-hexylthiophene) have been used as the active emitting material of the devices. Even the thinnest devices with only 3 monolayers, each having a thickness of ≊3 nm, yield the same luminance as thicker ones. The emission results from excitons in the polymer chains, and has a spectrum similar to that of photoluminescence, with a maximum at about 2.0 eV.
Dictation of the shape of mesoscale semiconductor nanoparticle assemblies by plasmid DNA
Authors: Coffer Jeffrey L. , Bigham Shelli R. , Li Xin , Pinizzotto Russell F. , Rho Young Gyu , Pirtle Robert M. , Pirtle Irma L.
Published: July 2002

We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455-basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self-assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates.