bluuebunny/crossref_metadata_2025 huggingface dataset:
Expansion rate measurements at moderate pressure of non-neutral electron plasmas in the Electron Diffusion Gauge (EDG) experiment
Authors: Morrison Kyle A. , Davidson Ronald C. , Paul Stephen F. , Belli Emily A. , Chao Edward H.
Published: July 2002

Measurements of the expansion rate of pure-electron plasmas have been performed on the Electron Diffusion Gauge (EDG) device at background helium gas pressures in the 5×10−8 Torr to 2×10−5 Torr range, where plasma expansion due to electron-neutral collisions dominates over plasma expansion due to trap asymmetries. It is found that the expansion rate, defined as the time rate of change of the particles’ mean-square radius, scales approximately linearly with pressure and inversely as the square of the magnetic field strength in this regime, in agreement with classical predictions.
Kinetic Alfvén wave instability in a dusty plasma
Authors: Salimullah M. , Islam M. K. , Banerjee A. K. , Nambu M.
Published: July 2002

On account of the presence of a dust beam parallel to the direction of the uniform magnetic field, the dust-kinetic Alfvén wave becomes unstable and grows in amplitude when the drift velocity of dust particles exceeds the parallel phase velocity of the wave. The instability growth rate depends on the temperature and density of the plasma ions/electrons, the Alfvén speed, and the dust flow velocity along the magnetic field lines.
Plasma effect on shock waves in a supersonic flow
Authors: Kuo S. P. , Bivolaru Daniel
Published: July 2002

An experimental study of the plasma effect on the structure of an attached conical shock front appearing at the front end of a cone-shaped model has been carried out in a Mach 2.5 stream. The tip and the body of the model are designed as the cathode and anode, which are separated by a conical-shaped ceramic insulator providing a 5 mm gap for gaseous discharge. The electric field intensity near the cathode is enhanced by the sharpness of the tip. The experimental results show that the diffused discharge can produce plasma distributed symmetrically around the tip in the region in front of the shock wave. It is observed that such plasma can cause shock wave moving upstream with its shock front detached from the model. The shock front is also becoming more and more diffusive and having an increasing shock angle as seen in the shadow video graphs of the flow. A physical mechanism of the observed plasma effect on this type of shock wave is also presented.
Organic metal–semiconductor field-effect phototransistors
Authors: Schön Jan Hendrik , Kloc Christian
Published: July 2002

We have prepared phototransistors based on bromine-doped pentacene. Such devices reveal light detection over a wide energy range with amplification. The illumination modifies the charge characteristics of the Schottky gate of an enhancement-mode the metal–semiconductor field-effect transistor leading to transistor amplification of the photodiode-like response. A gain of 8 is obtained for illumination at 632 nm. These phototransistors combine the excellent properties of pentacene field-effect transistors and photovoltaic devices.
Intensity noise in quantum-dot laser diodes
Authors: Wölfl F. , Ryan J. F. , Fox A. M. , Ashmore A. D. , Mowbray D. J. , Skolnick M. S. , Hopkinson M. , Hill G.
Published: July 2002

We present intensity noise studies of a self-organized InAs/GaAs quantum-dot laser. The noise power measured for the full emission spectrum was found to be smaller than that for separate longitudinal mode groups. This noise cancellation indicates that the intensity fluctuations of the mode groups were anticorrelated, with typical values of the normalized correlation coefficient of around −0.50. This surprisingly high value is not consistent with the model of the quantum-dot laser as an inhomogeneous ensemble of independent microlasers.
A novel method for increasing magnetically insulated transmission line oscillator frequency
Authors: Yang Yulin , Ding Wu
Published: July 2002

Design considerations of a high-power and high-frequency magnetically insulated transmission line oscillator (MILO) are proposed. By adding the end emission from the cathode, the insulated magnetic field is enhanced to reach the Hull cutoff criterion, therefore, the frequency can be increased. In terms of the two-dimensional fully electromagnetic particle-in-cell simulation, an output power of 1.16 GW at C band and 270 MW at X band in a MILO have been obtained.
Thermal oxide of polycrystalline silicon on steel foil as a thin-film transistor gate dielectric
Authors: Wu Ming , Wagner Sigurd
Published: July 2002

The gate dielectric of polycrystalline silicon thin-film transistors on steel foil substrates was grown by direct thermal oxidation. The silicon dioxide was formed on the polysilicon channel layer by dry oxidation for 40 min at 950 °C. Self-aligned sources and drains were ion implanted. The thin-film transistors have electron mobilities of ∼30 cm2⋅V−1 s−1 in both the linear and saturated regimes, off currents of 35 pA/μm, and on/off current ratios of ∼ 106. The thin-film transistors function even though they are processed at 950 °C separated from steel by only 0.5 μm of SiO2, and at room temperature may be under compressive strain as high as 1%. The implementation of conventional high-temperature fabrication techniques makes polycrystalline silicon on steel foil a strong contender for flexible electronic backplanes.
Uniaxial dielectric anisotropy in Ba0.5Sr0.5TiO3 films studied by evanescent-probe microscopy
Authors: Wang Y. G. , Reeves M. E. , Kim W. J. , Horwitz J. S. , Rachford F. J.
Published: July 2002

The dielectric permittivity, tunability (Δε/ε), and loss tangent of Ba1−xSrxTiO3 (BST) films grown by pulsed-laser deposition are studied by near-field microwave microscopy. Based on theoretical simulations, a method is developed to measure the uniaxial dielectric anisotropy, ε⊥/ε∥, in BST films grown at different oxygen pressures. The measured ε⊥/ε∥ decreases with the film-growth oxygen pressure, consistent with the structural anisotropy. The films prepared at 50 mT, with ε⊥≈ε∥, have the highest permittivity, tunability, and figure of merit.
Narrow electron injector for ballistic electron spectroscopy
Authors: Kast M. , Pacher C. , Strasser G. , Gornik E.
Published: July 2002

A three-terminal hot electron transistor is used to measure the normal energy distribution of ballistic electrons generated by an electron injector utilizing an improved injector design. A triple barrier resonant tunneling diode with a rectangular transmission function acts as a narrow (1 meV) energy filter. An asymmetric energy distribution with its maximum on the high-energy side with a full width at half maximum of ΔEinj=10 meV is derived.
Effect of wall shear on the propagation of a weak spark-generated shock wave in argon
Authors: White A. R. , Subramaniam V. V.
Published: July 2002

Photo-acoustic deflection (PAD) measurements are presented for a weak spark-generated shock wave propagating in argon at 40 Torr in a cylindrical tube. Measurements indicate that for a given shock strength, there is a maximum distance of travel beyond which the shock front is nonplanar, consistent with the predictions of numerical calculations reported recently [S. M. Aithal and V. V. Subramaniam, Phys. Fluids 12, 924 (2000)]. The initially planar shock wave exhibits curvature at downstream locations in the shock tube in the absence of any imposed temperature gradients. Since the PAD signal is a line-of-sight measurement, it is sensitive to the axial gradient of density at all radial locations, and shock curvature manifests itself as a split and spread PAD signal. In contrast, a planar shock registers a sharp, delta-function-like PAD signal. The curvature of weak shocks observed in the present experiments is due to viscous action alone, as the wall shear retards the near-wall portions of the front relative to its near-axis portions. The PAD signal associated with shock curvature due to wall shear alone is found to closely resemble that due to externally imposed radial temperature gradients such as in a glow discharge plasma.
Nanocrystals acting as Coulomb islands operating at room temperature created using a focused ion-beam process
Authors: Kim T. W. , Choo D. C. , Shim J. H. , Jung M. , Kang S. O. , Lee H. S. , Lee J. Y.
Published: July 2002

A Ga+ focused ion-beam (FIB) technique utilizing both lithographic and nanoparticle formation processes has been introduced to create nanocrystals acting as Coulomb islands at room temperature. High-resolution transmission electron microscopy results show that the nanocrystals acting as Coulomb islands are created in the source-drain active layer by using a Ga+ FIB. The results for the drain current and the conductance as functions of the drain voltage with an open gate voltage at room temperature show a Coulomb staircase and conductance oscillations, respectively. Nanoscale particles of Al with an amorphous phase are created in the source-drain channel by the defects due to the radiation effect of the Ga+ FIB, and collisions between Ga+ ions and Al atoms produce secondary electrons, that interact with the nanoparticles, which are acting as Coulomb islands, to form the crystal phase.
Comment on “On the correspondence between forced magnetic reconnection and Alfvén resonances” [Phys. Plasmas 7, 3808 (2000)]
Authors: Uberoi C.
Published: July 2002

In a recent paper Vekstein [Phys. Plasmas 7, 3808 (2000)] argued that the correspondence between the forced magnetic reconnection based on Alfvén resonance theory given by Uberoi and Zweibel [J. Plasma Physics 62, 345 (1999)] is not true. It is shown that the argument by Vekstein based on the asymptotic smooth decay of resonant absorption power in a resistive magnetohydrodynamic plasma for long wavelengths is not correct as in such a system there are two separate dissipative regimes determined by wavelength and resistivity for the wave decay. Solutions for long wavelength disturbances as considered by Uberoi and Zweibel have the behavior of decaying tearing normal modes for high values of the resistivity.
Analysis of the effect of external gas flow on helical instabilities of arc plasmas
Authors: Gong Ye , Lü Wenyan , Liu Jinyuan , Wang Xiaogang , Zheng Shu , Gong Jiquan
Published: July 2002

The effect of external gas flow on helical instability of arcs is studied by using an analytical method. The magnetohydrodynamic equations in an electrostatic approximation serve as the starting point of the theory. Using a linear time-dependent perturbation theory, the analytic expression that corresponds to the term of a gas flow stabilizing effect is deduced, and the growth rate of the helical instability is given. It is found that in the short wavelength perturbation case, the effect of external gas flow is large, so it is beneficial for stabilizing arcs. However, its effect is very small for intermediate and long wavelength perturbations. At the same time, numerical results show that the stabilizing effect of the flow on helical instability increases with increasing shear viscosity of external gas flow.
Low frequency noise in degenerate semiconductors
Authors: Dmitriev A. P. , Borovitskaya E. , Levinshtein M. E. , Rumyantsev S. L. , Shur M. S.
Published: July 2002

We present a model of low frequency noise for degenerate semiconductors. The model links the 1/f noise to tail states near the band edges with a capture cross section that is strongly energy dependent. It predicts that the low frequency noise is not very sensitive to a particular shape of the density of the tail states and that, in degenerate semiconductors, the level of noise should decrease with an increase in the degree of degeneracy. The model also explains the dependence of the noise level on the band-to-band illumination, in qualitative agreement with experimental data.
Effect of the azimuthal inhomogeneity of electron emission on gyrotron operation
Authors: Nusinovich G. S. , Vlasov A. N. , Botton M. , Antonsen T. M. , Cauffman S. , Felch K.
Published: July 2002

Gyrotrons are typically driven by electron beams produced by magnetron-type thermionic electron guns operating in the regime of temperature limited emission. Very often, the current density in such annular electron beams is azimuthally nonuniform. To describe the effect of this nonuniformity on gyrotron operation, the code MAGY [M. Botton et al., IEEE Trans. Plasma Sci. 26, 882 (1998)], which is widely used for modeling of slow and fast microwave sources, was properly modified. The results of numerical simulations demonstrate the effect of azimuthal inhomogeneity of the emission on the excitation of low- and high-frequency satellites of the operating mode and on the efficiency degradation. The calculations are done for parameters typical for megawatt-class, long-pulse, millimeter-wave gyrotrons, which are currently under development for electron cyclotron plasma heating and current drive experiments in controlled fusion reactors.
Dark pulse formation in a quantum-dot laser
Authors: Zimmermann J. , Cundiff S. T. , von Plessen G. , Feldmann J. , Arzberger M. , Böhm G. , Amann M.-C. , Abstreiter G.
Published: July 2002

The laser emission of an InAs/GaAs quantum-dot laser after injection of a nonresonant optical pulse is time resolved using femtosecond upconversion. The injected pulse burns a hole into the gain spectrum that leads to an ultrafast redistribution of carriers away from the lasing wavelength, thereby generating a spatial domain of reduced laser intensity. This domain propagates through the laser, is reflected at the facets, and thus repeats periodically in the output of the quantum-dot laser, forming a train of dark pulses. As a slower response to the optically induced perturbation, gigahertz-frequency relaxation oscillations are observed.
Microstructural and interband transition properties of vertically stacked InAs/GaAs self-assembled quantum dots embedded in modulation-doped heterostructures
Authors: Kim T. W. , Lee D. U. , Choo D. C. , Kim H. J. , Lee H. S. , Lee J. Y. , Kim M. D.
Published: July 2002

The transmission electron microscopy image and selected area electron diffraction pattern showed that self-assembled InAs quantum-dot (QD) arrays embedded in GaAs barriers were periodically inserted in an Al0.25Ga0.75As/GaAs heterostructure. The temperature-dependent photoluminescence spectra of the InAs/GaAs quantum dots embedded in modulation-doped heterostructures showed interband transitions from the first-excited electronic subband to the first-excited heavy-hole subband together with those from the ground subband to the ground heavy-hole band (E1–HH1) while the spectra of the InAs/GaAs QDs alone showed only the peak related to the (E1–HH1) transitions.
Carrier relaxation dynamics for As defects in GaN
Authors: Gil Bernard , Morel Aurélien , Taliercio Thierry , Lefebvre Pierre , Foxon C. T. , Harrison I. , Winser A. J. , Novikov S. V.
Published: July 2002

Long decay times in the 50–150 ns range have been measured for the characteristic blue photoluminescence that peaks at 2.6 eV in GaN:As. We interpret these long decay times according to the theoretical predictions that this blue photoluminescence is caused by the incorporation of arsenic on the gallium site. The long decay times are characteristics of the large lattice relaxation for such a deep donor with a negative-U center behavior.
Emission wavelength control by potential notch in type-II InAs/GaSb/AlSb intersubband light-emitting structures
Authors: Ohtani K. , Sakuma H. , Ohno H.
Published: July 2002

A potential notch in the well region is used to control the emission wavelength of type-II InAs/GaSb/AlSb intersubband light-emitting structures. Intersubband absorption measurements are performed to evaluate the subband structure of the active layers and are compared with theory. Type-II quantum cascade structures using these active layers are fabricated and midinfrared intersubband electroluminescence is observed. Calculation indicates that the active layer structure can emit electromagnetic waves in the THz region without employing a wide alloy well.
Si/SiGe electron resonant tunneling diodes with graded spacer wells
Authors: Paul D. J. , See P. , Bates R. , Griffin N. , Coonan B. P. , Redmond G. , Crean G. M. , Zozoulenko I. V. , Berggren K.-F. , Holländer B. , Mantl S.
Published: July 2002

Resonant tunneling diodes have been fabricated using graded Si1−xGex (x=0.3→0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the peak current density is achieved. Peak current densities of 0.08 A/cm2 with peak-to-valley current ratios of 1.67 have been achieved for a low peak voltage of 40 mV at 77 K. This represents an improvement of over an order of magnitude compared to previous work.
Growth of thin Fe/Fe2O3 films on the Cu(110) surface
Authors: Pflitsch Christian , David Rudolf , Verheij Laurens K. , Franchy René
Published: July 2002

The growth of Fe/Fe-oxide double-layers on Cu(110) was studied with thermal energy atom scattering (TEAS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). An iron film with a thickness of about 0.6 nm was evaporated at low temperature (130 K) on a smooth, well-ordered thin film of Fe2O3 prepared on Cu(110). This Fe film is disordered. Ordering of the film was observed at temperatures between 400 and 600 K. At 530 K, a structure corresponding to that of a well-ordered α-Fe(001) surface was observed with TEAS and LEED. Clear evidence was found for a mixing of the Fe and Fe2O3 layers at the interface, already beginning at the deposition temperature of 130 K. With increasing temperature, the mixing of the Fe and Fe2O3 layers became gradually more effective until, at around 600 K, it was essentially completed. Upon annealing the sample to 1000 K the structure of the film changes and a very thin (less than 2 ML) FeO film on top of the Cu(110) surface is obtained.
Chemical and thermal stability of titanium disilicide contacts on silicon
Authors: Hul’ko O. V. , Boukherroub R. , Lopinski G. P.
Published: July 2002

The suitability of titanium disilicide (TiSi2) contacts for use in electronic transport measurements on chemically modified Si(100) and Si(111) surfaces prepared in ultrahigh vacuum (UHV) or via wet chemical approaches has been examined. Rapid thermal annealing at 900 °C of patterned Ti lines was used to produce the C54 phase of TiSi2. Atomic force microscopy, UHV scanning tunneling microscopy, and resistivity measurements were used to characterize the TiSi2/Si system through different stages of the disilicide formation and subsequent high temperature annealing or wet chemical cleaning and etching. The contacts were found to maintain their integrity after annealing up to 1200 °C or 10 min etching in 40% ammonium fluoride (NH4F). Under these preparation conditions, the silicon surface in the immediate vicinity of the TiSi2 interface remains free from major defects, thus making titanium disilicide a particularly suitable material for constructing platforms for measurements of electrical transport of silicon surfaces as well as nanostructures fabricated on these surfaces.
On the response to shock of foil stress sensors in ceramics
Authors: Bourne N. K.
Published: July 2002

Measurement of the stress history at a Lagrangian position in a shocked solid has been accomplished by various means including the embedding of a thin metal piezoresistive gauge to equilibrate with the ambient conditions and register a component of the field around it. Some work has shown that such sensors may be used to show the decay of the elastic precursor amplitude recorded within a material with the distance travelled by the wave into it. Recent doubt has been placed upon the validity of such observations by pointing to an apparent increase in stress at small distances being due to an overshoot in the gauge record that results from a finite response time [J. Appl. Phys. 88, 5666 (2001)]. An analysis is presented to indicate in which regimes such effects may be important. It is compared with experiment to show the validity of the model developed. Additionally, it is used to show that some of the measured precursor decay may be a physical phenomenon in certain polycrystalline aluminas.
Local structure of implanted B in amorphous Si
Authors: Mai F. , Ittermann B. , Füllgrabe M. , Heemeier M. , Kroll F. , Marbach K. , Meier P. , Mell H. , Peters D. , Thieß H. , Ackermann H. , Stöckmann H.-J.
Published: July 2002

B 12 probe nuclei are implanted in amorphous Si and monitored by β-radiation-detected nuclear magnetic resonance (β-NMR). Independently of growth conditions and impurity content, we find the same frequency distribution in a variety of samples. This is interpreted as an intrinsic signature of the amorphous environment while preferential B–H pairing is not observed. Comparing our data with earlier B-NMR11 work, we find the local B configuration to be completely controlled by the incorporation process. In our low-dose implantation experiment, all B is fourfold coordinated and electrically active. This is in contrast to gas-phase doping or high-dose implantation where the threefold coordination prevails.
Photorefractive properties of near-stoichiometric LiNbO3 grown from congruent melts containing K2O
Authors: Chen Xiaojun , Li Bing , Xu Jingjun , Zhu Dengsong , Pan Shihong , Wu Zhongkang
Published: July 2002

The photorefractive properties of nominally pure near-stoichiometric LiNbO3 crystals grown from congruent melts containing 11 mol % K2O are studied, and some photorefractive properties which are very different from those in congruent LiNbO3 crystals are observed. Large stationary energy transfer (Γmax=25 cm−1) exists in near-stoichiometric crystals though the photovoltaic field is dominant. The light-induced scattering fanning is markedly asymmetric in the crystals, which is very different from the symmetric fanning observed in congruent ones. Our analysis shows that these differences are caused by the large photovoltaic field and the relatively small density of filled traps in as-grown near-stoichiometric LiNbO3.
Morphological transition in compressible foam
Authors: Vainchtein D. L. , Aref H.
Published: July 2002

A theory is constructed to describe the morphological transition that occurs in a compressible foam when its volume is increased. The foam is observed to separate into two bubble populations or “phases,” one consisting of a large number of small bubbles, the “liquid” phase, the other consisting of a small number of large bubbles, the “gaseous” phase. First, working along lines similar to the van der Waals theory for a fluid system, approximate forms of the equation of state of the foam are derived and explored. These describe the weakly compressible range well, but fail to capture the nature of the transition. Taking a clue from the phenomenology, a theory of the “phase-separated” regime is then formulated working with the approximation that the two phases into which the foam separates are each relatively homogeneous. The successful single-phase formulas are applied to each phase, introducing an additional “order parameter” which gives the ratio of the average size of bubbles in the two phases. Approximate expressions are written for the Helmholtz free energy and the equilibria of the foam derived from these. The theory is compared to numerical simulations using SURFACE EVOLVER with very satisfying results. The transition from a uniform to a nonuniform configuration consists of avalanches of reconnections with smooth evolution between them. Hysteresis is observed as the foam is first expanded and then compressed.
Drastic change of phase interference by small diffusion of heavy-mass electrode atoms in carbon nanotubes and phase switching device
Authors: Haruyama Junji , Takesue Izumi , Hasegawa Tetsuro
Published: July 2002

We slightly diffuse atoms of electrode materials into one end of multiwalled carbon nanotubes (MWNTs), grown using nanoporous alumina membranes. Diffusion of the light-mass materials (carbon and aluminum) lead to weak localization in Altshuler–Aronov–Spivak oscillation, consistent with past reports. In contrast, we find that diffusion of heavy-mass materials (gold and platinum) at the volume ratio of only about 5% change this weak localization to antilocalization. It is understood by a drastic change of the phase interference caused by the injection of spin-flipped electrons due to spin–orbit interaction in the diffusion region, in the entire part of the MWNTs. We also propose an electron-wave phase switching circuit using this effect.
Speed enhancement in a photorefractive multiple-quantum-well modulator by pulsed illumination
Authors: Abeeluck A. K. , Heinz P. , Garmire E.
Published: July 2002

A factor-of-four increase in the operating speed of a high-resolution low-temperature-grown photorefractive multiple-quantum-well (PRMQW) spatial light modulator is reported. This is achieved by shining a spatially uniform erasing pulse from a light-emitting diode (LED) on the device that is driven by a single-sided applied voltage. The erasing pulse is turned on briefly during the off-voltage cycle while a grating is written during the on-voltage cycle using a continuous-wave laser diode. The dependence of the change in diffraction efficiency on the frequency of the applied voltage, on the timing and duration of the LED pulse, and on the intensities of the LED and of the pump beams has been investigated. Our results are relevant to applications of PRMQW modulators where both high spatial resolution and fast operating speed are required.
Carrier screening effects in photoluminescence spectra of InGaAsP/InP multiple quantum well photovoltaic structures
Authors: Raisky O. Y. , Wang W. B. , Alfano R. R. , Reynolds C. L.
Published: July 2002

Room temperature photoluminescence of p–i–n InGaAsP/InP multiple quantum well heterostructures was investigated under different excitation intensities. Photoluminescence spectra show the effect of phase space filling in quantum wells with increasing excitation density. Bias dependence of photoluminescence clearly demonstrates field screening that occurs inside the undoped layer. Device simulation is used to explain the observed phenomena.
Simultaneous measurements of the magnetostrictive coefficient, Young’s modulus, and Poisson ratio of thin films
Authors: Jin Xuesong , Kim C. O. , Lee Y. P. , Zhou Y. , Xu Huibin
Published: July 2002

A method, which determines simultaneously the magnetostrictive coefficient, Young’s modulus, and Poisson ratio of a thin film utilizing the minimization of the total elastic energy of a cantilever film–substrate system, is suggested. An inaccuracy for the magnetostrictive coefficient, caused by assuming the elastic properties of the film as those of the corresponding bulk material, could be avoided and only a single elastic isotropic substrate is employed in the present method. The experimental data of an Fe-based amorphous thin film were analyzed by using the model. The calculated dependence of the magnetostrictive coefficient on the external magnetic field was compared with the experiment, and the discrepancy between both results were explained. The elastic properties of the film were also obtained.
Fixing solitonic y junctions in photorefractive strontium–barium–niobate
Authors: Klotz Matthew , Crosser Mike , Guo Aqiang , Henry Michael , Salamo Gregory J. , Segev Mordechai , Wood Gary L.
Published: July 2002

Two-dimensional solitonic orbital waveguides as y junctions were formed in a strontium barium niobate crystal. The waveguides are 10–20 μm in diameter and propagate unpolarized light.
Compact all-solid-state source of polarization-entangled photon pairs
Authors: Volz Jürgen , Kurtsiefer Christian , Weinfurter Harald
Published: July 2002

A compact source of polarization-entangled photon pairs at a wavelength of 856 nm is realized using a frequency-doubled laser diode as the pump source for cavity-enhanced type-II spontaneous parametric down-conversion. Our setup generates photon pairs with entanglement visibility of ⩾95% and with count rates comparable to those of standard experiments based on large-frame ion lasers.
Measurement of perfluoropolyether lubricant thickness on a magnetic disk surface
Authors: Korach C. S. , Streator J. , Danyluk S.
Published: July 2002

This letter reports on the detection of nanometer-scale perfluoropolyether (PFPE) lubricants with thickness between 2–40 nm on a magnetic disk surface using a nonvibrating Kelvin probe. Magnetic disks were partially dipped in a PFPE lubricant to create lubricated and nonlubricated regions on the disk surface. The nonvibrating Kelvin probe measures an electrical signal proportional to the surface charge gradient at the interfaces between the lubricated and nonlubricated regions, and is linearly related to the scanning velocity. The surface charge is related to the difference in surface potentials between the lubricated and nonlubricated regions. The surface potential at the nonlubricated/lubricated transition ranges from 7–30 mV. The surface potential is found to be related to the corresponding lubricant thickness through an exponential relationship.
Photoinduced optical absorption in Ca3Ga2Ge3O12:Mn garnet
Authors: Eremenko V. V. , Gnatchenko S. L. , Kachur I. S. , Piryatinskaya V. G. , Kosmyna M. B. , Nazarenko B. P. , Puzikov V. M.
Published: July 2002

Persistent photoinduced changes of optical absorption have been found in garnet Ca3Ga2Ge3O12 doped with manganese. Irradiation by a He–Ne laser of 633 nm wavelength results in a noticeable increase in the absorption coefficient of the crystal. The photoinduced changes are observed up to room temperature as distinct from concentrated manganese garnets in which the photoinduced absorption vanishes at much lower temperatures. The wide temperature range of the existence of the photoinduced effect together with a high transparency of the crystal makes it a promising material for optical recording.
Modification of the three-phonon Umklapp process in a quantum wire
Authors: Khitun A. , Wang K. L.
Published: July 2002

We have investigated the modification of the three-phonon Umklapp process in a quantum wire caused by the effect of phonon confinement. Our formalism rigorously takes into account variations in phonon group velocity as well as the presence of an energy gap between the phonon modes due to the quantization of the radial phonon wave vector. Numerical calculations of the Umklapp relaxation rate were carried out for Si wires. Based on the obtained results we predict the suppression of the acoustic phonon modes decay at low temperatures that can lead to the unusual thermal conductivity increase. We also present a simplified empiric formula for the Umklapp relaxation rate calculation in a quantum wire.
Ellipsometric study of sinusoidally modulated ZnSeTe superlattices
Authors: Lee Hosun , Lee S. , Furdyna J. K.
Published: July 2002

We report an optical study of sinusoidally modulated ZnSeTe superlattices using spectroscopic ellipsometry. The pseudodielectric function 〈ε〉=〈ε1〉+i〈ε2〉 was determined for the photon energy range 1.5–6.5 eV and critical point parameters were obtained by fitting model line shapes to numerically calculated second energy derivatives of 〈ε〉. As the degree of the compositional modulation of the superlattice increased, the energies of E1−R1 and E1+Δ1−R1 either decreased or increased depending on the superlattice period. We explain this behavior in terms of an interlayer coupling and quantum-confinement effect characteristic, respectively, for the two geometries.
Stacked Josephson junctions in view of macroscopic quantum experiments
Authors: Granata C. , Corato V. , Monaco A. , Ruggiero B. , Russo M. , Silvestrini P.
Published: July 2002

We present Nb/AlOx/Nb–Al/AlOx/Nb stacked Josephson junctions which we propose as three-terminal elements to control the quantum behavior of Josephson complex systems. A bias current can be independently injected in the “top” junction, providing a fine control of the critical current of the “bottom” junction. The reported characterization of the device refers to data in the classical limit including measurements of the switching dynamics between metastable states of the system at different temperatures and bias conditions. At low temperature, the effective dissipation of the bottom junction remains substantially unchanged when different injection currents flow in the top junction. These results are interesting to project new configurations of macroscopic quantum experiments.
Schottky barrier rectifier with high current density using vanadium as barrier metal
Authors: Kim J. S. , Choi H. H. , Son S. H. , Choi S. Y.
Published: July 2002

This letter reports on an improved forward voltage drop (VF) and reverse leakage current (IR) in Schottky barrier rectifier using vanadium (V–SBR) as the barrier metal with a low barrier height (φB) and argon implantation. The VF for a V–SBR was as low as 0.25 V compared to 0.39 V for a molybdenum (Mo)–SBR at the same forward current density (JF) of 60 A/cm2. This study was able to achieve a good result for JF in SBR. Presently, the conventional Schottky rectifier with a low φB metal is used to achieve low VF, but at the expense of a high IR. To reduce this effect, crystalline Si was altered into amorphous Si using argon implantation on the n-epitaxial layer. Finally, a SBR with a high JF and low IR could be fabricated.
Molecular dynamics simulation of the meniscus formation between two surfaces
Authors: Chen Yunfei , Weng Jian-gang , Lukes Jennifer R. , Majumdar Arunava , Tien Chang-Lin
Published: July 2002

The molecular dynamics computational method is used to simulate meniscus formation around an asperity in a rough surface represented as a sinusoidal wave. Simulation results show that the meniscus formation depends on the interaction potential between the solid wall and the liquid atoms. For completely and partially dry substrates a meniscus cannot form around an asperity. For partially and completely wetting substrates the asperity helps to adsorb the fluid atoms and form a meniscus. These simulation results confirm that if the film thickness exceeds a critical value, the capillary pressure contributes strongly to stiction.
Laser-driven high-current-density pulsed electron emission from lead zirconium titanate ferroelectric ceramic
Authors: Moorti A. , Sailaja S. , Naik P. A. , Gupta P. D. , Korobkin Yu. V. , Romanov I. V. , Rupasov A. A. , Shikhanov A. S.
Published: July 2002

Laser driven high current density pulsed electron emission is observed from a lead zirconium titanate (PZT, Zr/Ti: 53/47) ferroelectric ceramic disk using second harmonic of neodium: glass laser (wavelength ∼527 nm, pulse duration ∼3 ns, laser fluence ∼5–40 mJ/cm2) in the presence of a dc extraction field. Apart from electron current pulses of ∼100 A/cm2 [full width at half maximum (FWHM) ∼400 ns] obtained from laser irradiation of the surface towards the positive end of the polarization vector, electron current pulses of ∼30 A/cm2 (FWHM ∼1.1 μs) are also emitted from laser irradiation of the opposite surface. Dependencies of various characteristics of the electron pulse on laser fluence in the two configurations are presented.
Microstructure and field-emission characteristics of boron-doped Si nanoparticle chains
Authors: Tang Y. H. , Sun X. H. , Au F. C. K. , Liao L. S. , Peng H. Y. , Lee C. S. , Lee S. T. , Sham T. K.
Published: July 2002

One-dimensional boron-doped Si nanoparticle chains synthesized in bulk quantity using laser ablating SiO powder mixed with B2O3 powder have been investigated by transmission electron microscopy and measured by electron field emission. Transmission electron microscopy showed that the outer diameters of the nanoparticles in the chains were around 15 nm. High-resolution transmission electron microscopy showed that the nanoparticles had perfect lattices with an 11 nm crystalline core and a 2 nm amorphous oxide outerlayer while the distance of the interparticles was 4 nm. Field-emission measurement showed that the turn-on field of Si nanoparticle chains was 6 V/μm, which was much lower than that of undoped Si nanowires (9 V/μm). X-ray photoelectron spectroscopy confirmed that the Si nanoparticles had been heavily doped by boron.
Stabilization of the repetition rate of passively Q-switched diode-pumped solid-state lasers
Authors: Lai Ngoc Diep , Brunel Marc , Bretenaker Fabien , Le Floch Albert
Published: July 2002

We present a simple technique to stabilize the period of the pulses emitted by passively Q-switched lasers. By slightly modulating the pump diode power, the repetition rate of a Nd3+:YAG laser passively Q switched by Cr4+:YAG is experimentally shown to reach a time stability of 10−6 over 106 pulses. Simulations using a rate-equation model are in close agreement with the experiments.
Nanoscale investigation of hydrogen-induced degradation mechanism in Pt/(Pb, La)(Zr, Ti)O3/Pt capacitors
Authors: Yoshida Chikako , Tamura Tetsuro , Kondo Kazuaki , Takasaki Kanetake
Published: July 2002

The effects of hydrogen on Pt/(Pb, La)(Zr, Ti)O3(PLZT)/Pt capacitors have been investigated using atomic force microscopy piezoelectric measurements. The study revealed that the capacitors consist of submicron-sized ferroelectric domains, which were randomly distributed at positive or negative remanent states. After hydrogen annealing, it was observed that the local piezoelectric hysteresis loops of each domain shifted along both the voltage axis and the polarization axis. The degradation of remanent polarization can be explained by the shifted hysteresis of each domain. The degradation of saturation polarization can be understood to have been caused by the nonswitching portion within the capacitor.
Strain-induced phase-matching and tunability of acoustic gratings in fibers
Authors: Diez A. , Kakarantzas G. , Birks T. A. , Russell P. St. J.
Published: July 2002

We study the effect of strain on the properties of a one-dimensional acoustic grating: a tapered optical fiber with a periodically varying diameter. Its spectral response has a strong frequency stop band for flexural waves. Changing the tension of the fiber changes the wave velocity, and so modifies the acoustic response of the grating. The resulting tunability of the stop band over a wide frequency range is demonstrated experimentally. Furthermore, the stop band can almost disappear completely due to a strain-induced phase-matching phenomenon. Such structures are suitable as frequency-selective acoustic mirrors in acousto-optic fiber devices.
Can we make the SiC–SiO2 interface as good as the Si–SiO2 interface?
Authors: Di Ventra Massimiliano
Published: July 2002

A simple analysis based on the bulk valence and conduction densities of states was employed to estimate the interface-state densities for interfaces between the three most common SiC polytypes (3C, 4H, and 6H) and SiO2. We found that all polytypes had comparable conduction-band interface-state density with silicon dioxide as Si, being higher for the valence band. The conduction-band interface-state density should be higher for 4H-SiC than for 6H-SiC for both the C- or Si-terminated interfaces. On the contrary, the valence-band interface-state density can be either higher or lower for 4H-SiC compared to 6H-SiC according to which atom, C or Si, terminates the interface. The trends suggested by the above model are in agreement with recent mobility measurements in SiC-based field-effect transistors.
Tunable multiple-scattering system
Authors: Scales John A. , Van Wijk Kasper
Published: July 2002

To study the propagation of multiply scattered waves, it is useful to have a medium in which the scattering properties can be easily controlled. Here, we describe such a system; it involves the propagation of ultrasonic surface waves in a medium with an aligned, disordered pattern of grooves. Waves propagating parallel to the grooves see a homogeneous medium; waves propagating perpendicular to the grooves are strongly scattered. By varying the source–receiver distance and orientation with respect to the grooves, we are able to map out the transition from ballistic to diffusive propagation. In addition, by using an optical detection system we are able to measure the wave motion inside the scattering medium. We measure the angle-dependent macroscopic properties of the medium, such as the group velocity as well as the mean-free path and the diffusion constant in the strong-scattering regime.
Reduction in crystallographic tilting of lateral epitaxial overgrown GaN by removal of oxide mask
Authors: Kim Min Hong , Choi Yoonho , Yi Jaehyung , Yang Min , Jeon Jina , Khym Sungwon , Leem Shi-Jong
Published: July 2002

The lateral overgrowth of GaN was carried out by low-pressure metalorganic chemical vapor deposition. SiO2 mask was removed just before coalescence and a subsequent lateral overgrowth was carried out to complete the fabrication of a SiO2-removed lateral epitaxial overgrown (LEO) GaN layer. The crystallographic tilting of (0002) plane, that was apparent in our standard LEO GaN layers, was absent in SiO2-removed LEO layer and x-ray diffraction measurement indicated a superior crystallinity for the SiO2-removed LEO layer. These results are attributed to the elimination of the interface between oxide mask and laterally grown GaN layer. The reduced crystallographic tilting in SiO2-removed LEO GaN layer also enhanced the quality of the coalesced fronts, as determined from cathodoluminescence images.
Scanning near-field ellipsometric microscope-imaging ellipsometry with a lateral resolution in nanometer range
Authors: Karageorgiev P. , Orendi H. , Stiller B. , Brehmer L.
Published: July 2002

An apertureless optical near-field scanning microscope system has been created by combining a commercially available atomic force microscope and an ellipsometer without any prior changes in design of the respective devices. In preliminary experiments, an optical resolution of about 20 nm (λ/32) has been achieved using the combined microscope. The intensity of the measured optical signal has been found to be a periodic function of the thickness of the sample. Moreover, the period of this function is dependent upon the local optical properties of the sample material.
Impurities in dielectrics and hydrogen barriers for SrBi2Ta2O9-based ferroelectric memories
Authors: Yang B. , Oh S. H. , Chung C. H. , Noh K. H. , Kang Y. M. , Lee S. S. , Hong S. K. , Kang N. S. , Hong J. H.
Published: July 2002

We report results of systematic investigation of impurities in dielectrics and hydrogen barriers (Ti and Al2O3 films) during the integration process of SrBi2Ta2O9-based ferroelectric memories. The capacitors integrated with Ti hydrogen barriers are not electrically degraded regardless of the annealing conditions of the subdielectrics. On the contrary, electrical properties of the capacitors using Al2O3 hydrogen barriers significantly depend on the annealing temperatures for subdielectrics. It turned out that interaction of the dielectrics with plasma during sputtering of the Ti films caused fragmentation of the moisture in the dielectrics and absorption of the hydrogen in the Ti films, making annealing irrelevant. However, the alumina films blocked both hydrogen and moisture in the subdielectrics during the passivation process, resulting in dependence on the annealing temperatures.
Investigation of short-range order in nanocrystal-forming Zr60Cu20Pd10Al10 metallic glass and the mechanism of nanocrystal formation
Authors: Fan Cang , Imafuku Muneyuki , Kurokawa Hiroshi , Inoue Akihisa , Haas Volker
Published: July 2002

Rapidly solidified ribbons from the nanocrystal-forming Zr60Cu20Pd10Al10 alloy prepared at various melting liquid temperatures were used to study the influence of the liquid state upon quenched-in nuclei. With lowering quenching liquid temperatures, the small-angle x-ray scattering shows increased related periodic composition fluctuations and the radial distribution function analysis from x-ray diffraction method reveals that the coordination number of Pd around Zr increases. These results provide evidence for the stronger attractive interaction in Zr–Pd, which exhibits large negative mixing enthalpy, leads to the formation of (Zr, Pd)-rich domains of short-range order in the liquid. They remain in the amorphous phase as quenched-in nuclei and therefore contribute to nanocrystalline formation.
Analytic solution of stress distribution under a thin film edge in substrates
Authors: Wong S. P. , Peng H. J. , Zhao Shounan
Published: July 2002

We have obtained an analytic solution for the stress distribution under a thin film edge in isotropic substrates of finite thickness and of infinite extent in the other two directions. Far from the film edge on the side without the film, all stress components are zero and far from the film edge under the film, the stress distribution is in accordance with that given by the bimetallic strip theory. To demonstrate the validity of this solution, the experimental infrared photoelastic stress fringe pattern obtained by a dark-field plane polariscope in a Si substrate under an oxide film edge was successfully reproduced using this solution.
Investigation of spurious velocity overshoot using Monte Carlo data
Authors: Grasser T. , Kosina H. , Selberherr S.
Published: July 2002

For the simulation of state-of-the-art devices, hydrodynamic and energy transport models account for nonlocal effects. Although these models have been available for several decades, there are still unresolved issues. One of these issues is the occurrence of spurious peaks in the velocity profile which are inherent to both Stratton’s [Phys. Rev. 126, 2002 (1962)] and Blo/tekjær’s [IEEE Trans.Electron Devices 17, 38 (1970)] models. We investigate the origin of these peaks by introducing relaxation times, mobilities, and closure relations directly from a coupled Monte Carlo simulator. From these simulations, we conclude that the spurious peaks are a direct result of the truncation of the infinite moment series and the inaccuracies in the physical models.
Pumping picosecond optical parametric oscillators by a pulsed Nd:YAG laser mode locked using a nonlinear mirror
Authors: Mani A. A. , Dreesen L. , Hollander Ph. , Humbert C. , Caudano Y. , Thiry P. A. , Peremans A.
Published: July 2002

We report on the performances of the mode locking of a flash-lamp-pumped Nd:YAG laser using a frequency-doubling nonlinear mirror combined with a two-photon absorber. Pulse lengths from 12 to 8 ps are generated. We show that the flat shape of the pulse-train envelope generated by the oscillator is adapted for the synchronous pumping of optical parametric oscillators and we demonstrate the efficient generation of an infrared beam tunable from 3800 to 1100 cm−1 with bandwidth of 2 cm−1 in one single conversion stage in LiNbO3 or AgGaS2. The “all-solid-state” laser system enables surface sum-frequency generation spectroscopy to be performed with high sensitivity and high resolution.
In situ threshold photoemission yields correlated to surface reconstructions of InAs (001)
Authors: Zinck J. J. , Ross R. S. , Owen J. H. G. , Barvosa-Carter W. , Grosse F. , Ratsch C.
Published: July 2002

Threshold photoemission yields for As and In terminated reconstructions of InAs (001) are measured in situ and the variation of the photoyield is correlated with the surface stoichiometry. A significant excess in the measured photoelectron yield is found for the In terminated surfaces. These results are compared to a semiempirical model based on density-functional theory calculations of the surface local densities of states for the As terminated β2-(2×4) and newly predicted ζ-(4×2) reconstructions. The calculations are in good agreement with the measured trends, and provide a basis for the interpretation of threshold photoemission sensor signatures.