bluuebunny/crossref_metadata_2025 huggingface dataset:
Many-body optical gain of (101̄0) wurtzite GaN/AlGaN quantum-well lasers
Authors: Park Seoung-Hwan
Published: July 2002

Optical properties of (101̄0)-oriented wurtzite (WZ) GaN/AlGaN quantum well (QW) lasers are investigated by the non-Markovian gain model with many-body effects. These results are compared with those of (0001)-oriented WZ GaN/AlGaN QW with spontaneous and piezoelectric polarization taken into account. The energy pattern of the (101̄0) orientation shows two-fold symmetry while the energy pattern of the (0001) orientation is completely isotropic. It is found that the many-body effects are more dominant in the (0001)-oriented QW compared to the (101̄0)-oriented QW. This is because the average hole effective mass of the (0001)-oriented QW is larger than that of the (101̄0)-oriented QW. Thus, the flatband model shows that the optical gain of the (101̄0)-oriented QW is smaller than that of the (0001)-oriented QW. However, with the inclusion of the internal fields, it is observed that the optical gain of the (0001)-oriented QW is significantly smaller than that of the (101̄0)-oriented QW.
Structural and magnetoresistance characteristics of CoFe/Ag/NiFe/Ag composite discontinuous multilayers
Authors: Lee Kwan-Hoon , Lee Seong-Rae , Kim Young Keun
Published: July 2002

The structural, magnetic, and giant magnetoresistance (GMR) behaviors of new types of composite multilayers were investigated. The main objective of this study was to accomplish high MR sensitivity while maintaining magnetic softness. The MR sensitivity of CoFe/Ag/NiFe/Ag multilayers was higher compared to CoFe/Ag multilayers mainly due to the switching field difference between NiFe and CoFe. The x-ray diffraction analysis and temperature dependence of Δρ provided evidence of the structural evolution in the CoFe/Ag/NiFe/Ag upon annealing. The temperature dependence of Δρ in CoFe/Ag/NiFe/Ag multilayers annealed for 1 min compared with as-deposited multilayers were reduced because the interface structure was sharpened and structural defects were reduced.
Angular distribution of x-ray emission from a copper target irradiated with a femtosecond laser
Authors: Hironaka Yoichiro , Nakamura Kazutaka G. , Kondo Ken-ichi
Published: July 2002

Angular distribution of hard x rays that are generated by focusing a femtosecond (41 fs) laser with a power density of 1.3×1017 W/cm2 onto a copper target was studied. The total x rays over an energy range of 4–20 keV, which were mainly assigned to bremsstrahlung, showed forward emission particularly at s-polarized incidence and the characteristic x rays (Cu Kα emission) were almost isotropic.
Super sequential lateral growth of Nd:YAG laser crystallized hydrogenated amorphous silicon
Authors: Tang Y. F. , Silva S. R. P. , Rose M. J.
Published: July 2002

Lateral growth crystallization of hydrogenated amorphous silicon with single and multiple pulse excitation using a Nd:YAG laser at a wavelength of 532 nm and a 3 ns pulse width at a repetition of 10 Hz is shown. With single pulse crystallization, large grain sizes of the order of 1 μm were obtained with an energy density >400 mJ/cm2, and these have been studied using transmission electron microscopy (TEM) and atomic force microscopy. We show that, by using extremely short (3 ns) multiple pulse excitation of significantly lower powers (<150 mJ/cm2), than that used to crystallize amorphous silicon with single pulse excitation, a uniform growth of crystalline grains is observed. TEM gives evidence for lateral grain growth with multiple pulse crystallization at low energies. We suggest that a “super sequential lateral growth” mechanism is occurring.
Temperature and pressure dependence of Mg local modes in GaN
Authors: Kaczmarczyk G. , Kaschner A. , Hoffmann A. , Thomsen C.
Published: July 2002

The temperature and pressure dependence of the zone-center phonons and of the local vibrational modes of magnesium in the hexagonal modification of GaN was studied within a valence-force model. The contribution caused by thermal expansion was calculated and compared with the experiment. We find that the frequency shift of the local vibrational modes arises to a much larger extent from anharmonic decay into lower energy phonons than the shift of the GaN host modes.
Minimization of noise-induced bit error rate in a high Tc superconducting dc/single flux quantum converter
Authors: Ortlepp Thomas , Toepfer Hannes , Uhlmann Hermann F.
Published: July 2002

The thermally induced bit error rate of a rapid single flux quantum logic circuit is theoretically examined using the Fokker–Planck equation. The error rate versus design parameters of a high Tc dc/single flux quantum converter is derived. In comparison with other design methodologies, a vanishingly small error rate at optimal parameters can be achieved.
Electron mobility enhancement in strained SiGe vertical n-type metal–oxide–semiconductor field-effect transistors
Authors: Chen Xiangdong , Liu Kou-Chen , Jayanarayanan Sankaran Kartik , Banerjee Sanjay
Published: July 2002

We have fabricated strained SiGe vertical n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) by Ge ion implantation and solid phase epitaxy. No Si cap is needed in this process because Ge is implanted after gate oxide growth. The vertical MOSFETs are fabricated with a channel length below 0.2 μm without sophisticated lithography and the whole process is compatible with a regular complementary metal–oxide–semiconductor process. The drive current for these devices has been observed to be enhanced by 50% compared with Si control devices on the same wafer. Electron mobility enhancement in the out-of-plane direction for the strained SiGe layer was demonstrated in this study.
Neutron transmutation of 10B isotope-doped diamond
Authors: Jagannadham K. , Verghese K. , Butler J. E.
Published: July 2002

Diamond samples grown by microwave plasma chemical vapor deposition and doped with 10B have been irradiated under thermal neutron flux of 1013 cm−2 s−1 for 76 h to examine transmutation of 10B to 7Li and the attendant lattice damage to diamond. To prevent graphitization and formation of diamond-like carbon, continuous cooling in water is provided during irradiation. Characterization of the diamond samples using Raman spectroscopy, photoluminescence spectroscopy, and secondary ion mass spectrometry showed that diamond remained crystalline without a major damage. Formation of vacancies due to neutron irradiation is inferred from photoluminescence spectroscopy.
X-ray scattering from misfit dislocations in heteroepitaxial films: The case of Nb(110) on Al2O3
Authors: Barabash R. I. , Donner W. , Dosch H.
Published: July 2002

We apply the Krivoglaz theory of x-ray scattering to thin epitaxial films containing misfit dislocations and reanalyze the seemingly puzzling x-ray scattering phenomena observed in several heteroepitaxial films. We show that the two-line shape scattering distribution and its dependence upon film thickness and momentum transfer can be understood in natural way and on a quantitative level. Extended diffuse x-ray scattering maps have been obtained from Nb(110)/Al2O3(112̄0) which are discussed within the framework of this theory disclose a particular dislocation network at the Nb–Al2O3 interface.
Helix unwinding of doped cholesteric liquid crystals
Authors: Yip W. C. , Kwok H. S.
Published: July 2002

By introducing benzoyl–benzene into a cholesteric liquid crystal, the helix unwinding voltage was reduced. This reduction was roughly proportional to the concentration of the dopant and was present for driving frequencies across the audio spectrum. It is believed that this voltage reduction is primarily due to a perturbation of the intermolecular coupling in the liquid crystal mixture. It was found that so long as the long-range order was not destroyed, the helix unwinding voltage could be reduced by as much as 24% at 60 Hz.
Network structure in poly(vinylidene fluoride–trifluoroethylene) electrostrictive films
Authors: Buckley G. S. , Roland C. M.
Published: July 2002

Recent studies of electron-irradiated copolymers of vinylidene fluoride and trifluoroethylene have demonstrated the potential for achieving a large electrostrictive response in these materials. Since the principal effect of the radiation is network formation, alternative methods of achieving improved electromechanical properties are available. In this letter, we use a two-solvent swelling technique to quantify the polymer-solvent interaction parameter for the copolymer networks. This enables determination of their crosslink densities, along with a measure of the degree of degradation accompanying radiolysis. Copolymer networks were then prepared chemically using organic peroxide. These networks were found to be similar to the radiation-crosslinked materials, both in the extent of degradation and with respect to the Curie temperature and crystalline melting behavior. The latter are crucial to the development of better electrostrictive properties.
Hanle effect measurements of spin lifetimes in InAs self-assembled quantum dots
Authors: Epstein R. J. , Fuchs D. T. , Schoenfeld W. V. , Petroff P. M. , Awschalom D. D.
Published: July 2002

Transverse spin lifetimes of spin-polarized photogenerated carriers in InAs self-assembled quantum dots are extracted from the depolarization of their photoluminescence in a magnetic field perpendicular to the spin (the Hanle effect). Hanle measurements on a series of samples reveal that the dot dimensions influence the spin lifetime and its dependence on temperature. The spin lifetime as a function of excitation intensity is qualitatively distinct for carrier spins created in the GaAs host as compared to in the InAs wetting layer.
From simple to complex oscillatory behavior in metabolic and genetic control networks
Authors: Goldbeter Albert , Gonze Didier , Houart Gérald , Leloup Jean-Christophe , Halloy José , Dupont Geneviève
Published: July 2002

We present an overview of mechanisms responsible for simple or complex oscillatory behavior in metabolic and genetic control networks. Besides simple periodic behavior corresponding to the evolution toward a limit cycle we consider complex modes of oscillatory behavior such as complex periodic oscillations of the bursting type and chaos. Multiple attractors are also discussed, e.g., the coexistence between a stable steady state and a stable limit cycle (hard excitation), or the coexistence between two simultaneously stable limit cycles (birhythmicity). We discuss mechanisms responsible for the transition from simple to complex oscillatory behavior by means of a number of models serving as selected examples. The models were originally proposed to account for simple periodic oscillations observed experimentally at the cellular level in a variety of biological systems. In a second stage, these models were modified to allow for complex oscillatory phenomena such as bursting, birhythmicity, or chaos. We consider successively (1) models based on enzyme regulation, proposed for glycolytic oscillations and for the control of successive phases of the cell cycle, respectively; (2) a model for intracellular Ca2+ oscillations based on transport regulation; (3) a model for oscillations of cyclic AMP based on receptor desensitization in Dictyostelium cells; and (4) a model based on genetic regulation for circadian rhythms in Drosophila. Two main classes of mechanism leading from simple to complex oscillatory behavior are identified, namely (i) the interplay between two endogenous oscillatory mechanisms, which can take multiple forms, overt or more subtle, depending on whether the two oscillators each involve their own regulatory feedback loop or share a common feedback loop while differing by some related process, and (ii) self-modulation of the oscillator through feedback from the system’s output on one of the parameters controlling oscillatory behavior. However, the latter mechanism may also be viewed as involving the interplay between two feedback processes, each of which might be capable of producing oscillations. Although our discussion primarily focuses on the case of autonomous oscillatory behavior, we also consider the case of nonautonomous complex oscillations in a model for circadian oscillations subjected to periodic forcing by a light-dark cycle and show that the occurrence of entrainment versus chaos in these conditions markedly depends on the wave form of periodic forcing.
Voltage induced photoluminescence quenching in porous silicon revisited
Authors: Reshotko M. R. , Balberg I.
Published: July 2002

We have reexamined the features of the voltage induced quenching of the photoluminescence in solid state structures in which the active material is porous silicon. By comparing the increase of the quenching due to the increase of temperature or bias with the corresponding increase in the electrical transport and phototransport, we conclude that this effect is not a field-enhanced carrier-separation effect, as suggested previously. Rather, this is a thermal effect, which is very pronounced, due to the inefficient cooling in the open, coral-like structure of luminescent porous silicon.
Effects of Mg doping on photoelectrical properties of hydrogenated GaN films grown at 380 °C
Authors: Yagi Shigeru , Suzuki Seiji
Published: July 2002

The effects of Mg doping on hydrogenated GaN films grown at 380 °C are investigated in terms of the photoelectrical properties of simple sandwich-type cells. The photocurrent increases with Mg until it reaches maximum and the dark current decreases monotonically with Mg doping. The photovoltaic current of the cells using transparent conductive glass substrates exhibits excellent linearity with an optical power. The peak responsivity at a 0 V bias is 0.02 A/W at 340 nm, which corresponds to an internal quantum efficiency of approximately 0.3. This simple cell functions as a visible-blind ultraviolet detector and also a transparent solar cell.
A fast, primary Coulomb blockade thermometer
Authors: Bergsten Tobias , Claeson Tord , Delsing Per
Published: July 2002

We have measured the third derivative of the current–voltage characteristics, d3I/dV3, in a two-dimensional array of small tunnel junctions using a lock-in amplifier. We show that this derivative is zero at a voltage which scales linearly with the temperature and depends only on the temperature and natural constants, thus providing a primary thermometer. We demonstrate a measurement method which extracts the zero crossing voltage directly using a feedback circuit. This method requires only one voltage measurement, which makes it substantially faster than the original Coulomb blockade thermometry method.
The effect of strain field seeding on the epitaxial growth of Ge islands on Si(001)
Authors: Dunbar A. , Halsall M. , Dawson P. , Bangert U. , Miura M. , Shiraki Y.
Published: July 2002

The effect of strain, due to a buried, nominally 6 ML Ge quantum dot layer, upon the growth of subsequent Ge layers grown by gas source molecular beam epitaxy has been investigated. A series of samples were grown at 700 °C with a nominally 6 ML Ge layer followed by a 30 nm Si spacer and then a second, thinner Ge layer. In each sample, the thickness of the second Ge layer was varied (2, 3, and 4 ML). Atomic force microscopy shows that in the second Ge layer islands form at thicknesses below the established critical thickness for this material system. This is confirmed by transmission electron microscopy images which also show the quantum dots in the second layers are stacked above those in the first layer, the island growth in the thin Ge layer being seeded by the strain field from the buried Ge islands. Photoluminescence results show a luminescence feature attributed to the strain-controlled quantum dots in the thin Ge layer. This band has properties similar to the frequently observed Ge dot luminescence but is observed at higher energies, depending upon the nominal thickness of the second Ge layer.
Role of the buildup oscillations on the speed of resonant tunneling diodes
Authors: Romo Roberto , Villavicencio Jorge
Published: July 2002

The fastest tunneling response in double barrier resonant structures is investigated by considering explicit analytic solutions of the time-dependent Schrödinger equation. For cutoff initial plane waves, we find that the earliest tunneling events consist of the emission of a series of propagating pulses of the probability density governed by the buildup oscillations in the quantum well. We show that the fastest tunneling response comes from the contribution of incident carriers at energies different from resonance, and that its relevant time scale is given by τr=πℏ/|E−ε|, where ε is the resonance energy and E is the incidence energy.
Ferroelectric lead barium zirconate thin film of high fatigue resistance
Authors: Tseng J. H. , Wu T. B.
Published: July 2002

Highly (100)-textured lead barium zirconate (PBZ) thin films of ∼0.1 μm and with a composition of (Pb0.742+Ba0.262+)(Pb0.154+ Zr0.854+)O3 were grown on LaNiO3/Pt/Ti electrode-coated Si by rf magnetron sputtering at 500 °C. The Pt/PBZ/LaNiO3 capacitor shows a hysteresis loop with remanent polarization, Pr, of 12 μC/cm2 and coercive field of 185 kV/cm at an applied voltage of 10 V, along with a dielectric constant of 270. More importantly, it has a high fatigue resistance against polarization switching up to 1011 cycles.
High-resolution imaging of surface acoustic wave scattering
Authors: Hesjedal T. , Behme G.
Published: July 2002

We examine the scattering of surface acoustic waves (SAWs) by single dots, periodic and locally damped two-dimensional dot lattices. Employing the scanning acoustic force microscope, SAW fields are imaged with nanometer resolution. We study the influence of a roughly wavelength-sized single dot on SAW diffraction. In order to distinguish between forward- and backscattered components, we insonify the dot with the pump and probe beam under 0° and 90°. We furthermore analyze the SAW diffraction by a regular dot array. The wave field appears to be localized around the dots. Adding surface distortions, the regular SAW localization pattern brakes down in the vicinity of the distortion.
Influence of electric field on the photoluminescence of a liquid crystalline monosubstituted polyacetylene
Authors: Huang Yuan Ming , Ge Weikun , Lam Jacky W. Y. , Tang Ben Zhong
Published: July 2002

It has been shown recently that strong photoluminescence (PL) can occur in monosubstituted polyacetylenes (PAs). In this letter, we investigate the PL of tetrahydrofuran solutions of a highly luminescent liquid crystalline PA, poly(11-{[4′-heptoxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PBU), under the influence of direct current electric fields. The applied electric fields can dramatically tune the PL structures of a moderately concentrated PBU solution (∼11.3 mM) at and above an electric field threshold of about 3×105 V/m. Combined with the director simulations, our results indicate that the electrically induced molecular reorientation and intermolecular interaction are responsible for the observed spectral changes.
Large improvement of pumping rate in the He–CuCl–NiBr2 laser system
Authors: Saito H. , Shiraiwa Y. , Ishikawa T. , Uno K. , Fujii K.
Published: July 2002

A Ni atom is employed as the energy donor to a Cu upper laser level. After the energy transfer is done by collision between Ni and Cu atoms, the population of the Cu upper laser level is enhanced via a cascading decay resulting in a four-level excitation loop. The peak value of the lasing pulse was increased by a rate of 400%, whereas the pulse width was not changed. The near-infrared spectra, λ=809.3 and 793.3 nm, emitted via this cascading decay method, were also observed and the intensity properties agreed with that of the lasing lines.
Surfactant-assisted synthesis of semiconductor nanotubes and nanowires
Authors: Rao C. N. R. , Govindaraj A. , Deepak F. Leonard , Gunari N. A. , Nath Manashi
Published: July 2002

Nanotubes and nanowires of CdSe and CdS have been obtained from solutions containing a surfactant such as Triton 100-X. They have been characterized by x-ray diffraction, electron microscopy, and optical spectroscopy.
Transparent organic light-emitting diodes using metal acethylacetonate complexes as an electron injective buffer layer
Authors: Yamamori Asuka , Hayashi Sachiko , Koyama Toshiki , Taniguchi Yoshio
Published: July 2002

We studied transparent organic light-emitting diodes, which had a transparent top electrode deposited by sputtering, for possible application to a transparent light-emitting display. In the fabrication of a transparent electrode on an organic layer, steps must be taken to reduce the damage incurred by the organic layer during the sputter deposition process. We report the results of our study where we found that we could reduce the damage to the organic layer by suppressing the temperature rise of substrate resulting from the intermittent plasma irradiation. We also found that a thin film of metal acethylacetonate complexes [Mt(acac)2] is useful as a buffer layer to prevent an underlying emission layer from incurring damage in the sputter process. In previous reports, a thin film of copper phthalocyanine (CuPc) was used as an electron injective buffer layer. However, the absorption of the CuPc Q bands at λ=620 and 665 nm decreased the total optical transmission of the device. Transmittance in the visible region of our device reached ∼90%, because Mt(acac)2 has no absorption properties that reduce the transmittance of visible light. The device using Ni(acac)2 as a buffer layer showed better electron injection properties and luminance of 1500 cd/m2 than the one using CuPc.
Numerical evidence that the perturbation expansion for a non-Hermitian PT-symmetric Hamiltonian is Stieltjes
Authors: Bender Carl M. , Weniger Ernst Joachim
Published: July 2002

Recently, several studies of non-Hermitian Hamiltonians having PT symmetry have been conducted. Most striking about these complex Hamiltonians is how closely their properties resemble those of conventional Hermitian Hamiltonians. This paper presents further evidence of the similarity of these Hamiltonians to Hermitian Hamiltonians by examining the summation of the divergent weak-coupling perturbation series for the ground-state energy of the PT-symmetric Hamiltonian H=p2+14x2+iλx3 recently studied by Bender and Dunne. For this purpose the first 193 (nonzero) coefficients of the Rayleigh–Schrödinger perturbation series in powers of λ2 for the ground-state energy were calculated. Padé-summation and Padé-prediction techniques recently described by Weniger are applied to this perturbation series. The qualitative features of the results obtained in this way are indistinguishable from those obtained in the case of the perturbation series for the quartic anharmonic oscillator, which is known to be a Stieltjes series.
Direct measurement of the attenuation of capillary waves by laser interferometry: Noncontact determination of viscosity
Authors: Behroozi F. , Lambert B. , Buhrow B.
Published: July 2002

The determination of viscosity from the damping of capillary waves has been of great interest, as it affords the possibility of measuring viscosity without contact with the fluid. Here we describe a noncontact method for precision measurement of the amplitude of capillary waves on fluids. The technique utilizes a miniature laser interferometer to map the wave profile with a resolution of about 10 nm. We use this technique to obtain the dispersion and attenuation of capillary waves on water as a test case. Furthermore, the attenuation data is used to obtain the viscosity of water as a function of temperature.
Multiple scattering of thermal waves by a coated subsurface cylindrical inclusion
Authors: Terrón J. M. , Sánchez-Lavega A. , Salazar A.
Published: July 2002

In this article we present a theoretical and experimental study of the multiple scattering of a plane thermal wave between a two-layer subsurface cylinder and the material surface. The thermal wave is generated at the surface of an opaque material by a modulated extended laser beam. First we study the multiple scattering of the thermal wave produced by a single conducting cylinder with arbitrary thermal properties. Then, we present a model of the multiple scattering of the wave produced by the two-layer cylinder and the surface. We calculate the surface temperature for two extreme cases of layering: (i) a coating air layer and (ii) a highly conducting coating. Measurements performed with an infrared radiometry photothermal technique on a calibrated set of samples are presented. They validate our models for the homogeneous layered cylindrical conductors. It is demonstrated that the most direct application of this study is the quantitative analysis of the thermal contact resistance (or the characteristics of a coating layer) in a fiber reinforced composite.
Effect of indium content on the normal-incident photoresponse of InGaAs/GaAs quantum-well infrared photodetectors
Authors: Hernando J. , Sánchez-Rojas J. L. , Guzmán A. , Muñoz E. , Tijero J. M. G. , González D. , Aragón G. , Garcı́a R.
Published: July 2002

Longwavelength InGaAs/GaAs quantum-well infrared photodetectors with indium contents ranging from 25% to 40% have been grown and characterized. Material quality has been assessed by photoluminescence and transmission electron microscopy. Intersubband photocurrent, excited by polarized (TE or TM) infrared light, has been analyzed in order to determine the responsivity for normal-incident radiation. It is found that the TE to TM responsivity ratio is lower than 10% in all the samples studied. By changing the indium content from 25% to 40%, the increase in the TE to TM photoresponse ratio is as low as 3%. Our results are opposite to previous reports of experimental observation of significant TE-polarized light absorption. However, the low efficiency for normal-incident radiation agrees with various theoretical predictions.
First principles study of the initial stages of SiC growth on Si(001)
Authors: Cicero Giancarlo , Catellani Alessandra
Published: July 2002

The initial stages of SiC growth on Si(001) are studied via ab initio molecular dynamics simulations at finite temperature. Several C coverages are considered, at various adsorption sites. At low T, C is adsorbed at the surface, with Si–C bond lengths close to that of bulk SiC. When increasing temperature, C adatoms are incorporated in the substrate subsurface layers, giving rise to the carbonization process. On the contrary, C dimers do not penetrate the substrate and remain stable even at the highest temperatures considered: our results point at radicals with single C atoms as efficient precursors for SiC growth.
Shear-mode scanning capacitance microscope
Authors: Naitou Yuichi , Ookubo Norio
Published: July 2002

Scanning capacitance microscope (SCM) is developed using an all-metallic probe, whose distance from the sample is controlled by detecting the shear-force drag on the laterally oscillating probe. The oscillatory motion of the probe is electromechanically excited and detected. Using this SCM, a set of images of topography, dC/dV, and dC/dX is simultaneously obtained, where C and V are, respectively, capacitance and applied voltage between the probe and the sample, and X is the coordinate along probe tip oscillation. The SCM developed shows sensitivity for dC/dV higher than the conventional SCM. The dC/dX image clearly indicates the built-in depletion region due to the p–n junction.
Recording of x-ray holograms on a position-sensitive detector
Authors: Kopecky Milos , Busetto Edoardo , Lausi Andrea , Miculin Marino , Savoia Adolfo
Published: July 2002

An unconventional x-ray fluorescence holography experiment was carried out by using an area detector in combination with an absorption filter. The high angular resolution and the very precise detection of intensities allowed the reconstruction of images of distant, as well as light, atoms. The simultaneous recording of the full hologram opens the possibility of one-shot imaging at atomic resolution. The hologram of a CoO single crystal was recorded on the imaging plate and the images of atoms located up to more than 7 Å far from the emitter were obtained.
Time-resolved optical microscopy of a laser-based forward transfer process
Authors: Young D. , Auyeung R. C. Y. , Piqué A. , Chrisey D. B. , Dlott Dana D.
Published: July 2002

Matrix-assisted pulsed laser evaporation direct write was investigated by ultrahigh speed optical microscopy. A composite barium–zirconium titanate/α-terpineol layer was irradiated by 355 nm laser pulses with a 150 ns pulse width, and it was observed that material removal does not begin until after the end of the pulse (t>200 ns) and continues for 1 μs after the irradiation. The desorption plume consists of micron-size particles moving with a velocity of ∼0.2 km/s. The slow response is attributed to the combination of particle absorbers and highly viscous fluid. The ability to form continuous, pinhole-free coatings is due to slow coalescence of the particles.
In situ observation of stress relaxation in CdTe/ZnTe heterostructures by reflectance-difference spectroscopy
Authors: Balderas-Navarro R. E. , Hingerl K. , Bonanni A. , Sitter H. , Stifter D.
Published: July 2002

The first stages of epitaxial growth of CdTe on ZnTe and ZnTe on CdTe are monitored with reflectance difference spectroscopy. Spectroscopic reflectance difference data show strong optical anisotropy responses at the critical points of the bulk dielectric function at the E0, E1, and E1+Δ1 interband transitions of ZnTe, respectively, CdTe, which indicate that anisotropic in-plane strain occurs during epitaxial growth. Applying a model it is possible to determine the in-plane strain due to the disbalance of 60° dislocations along [11̄0] and [110]. Kinetic reflectance difference data taken at the E1 transition of the respective material exhibit with an accuracy of one monolayer the onset of the formation of misfit dislocations for these material systems.
Ferroelectricity and ferromagnetism in (Pb, La)(Ca, Ti)O3–La0.67Sr0.33MnOx multilayers
Authors: Gao Jianxia , Zhu Xiangrong , Liu Weili , Zhang Zhibin , Cao Jianqing , Lin Chenglu , Zhu Dezhang , Liu E.
Published: July 2002

Multilayer ferroelectric and ferromagnetic thin films were fabricated with the following composition and structure: La0.67Sr0.33MnOx/(Pb, La)(Ca, Ti)O3 (LSMO/PLCT) and (Pb, La)(Ca, Ti)O3/La0.67Sr0.33MnOx (PLCT/LSMO), with an intention of creating a device of new concept. The films were fabricated using metalorganic deposition. The LSMO/PLCT structured films exhibit the ferroelectric properties while the PLCT/LSMO structured films exhibit the ferromagnetic properties. Compared with the PLCT/Pt structure, the capacitance-frequency and tan δ-frequency properties of the LSMO/PLCT structure are degraded. The magnetoresistance of the PLCT/LSMO structure was measured and the results show that the metal-insulator transition temperature is lower than that of the LSMO/SiO2/Si structure. Furthermore, the magnetoresistance at 77 K and at the transition temperature for the PLCT/LSMO structure is higher than that of the LSMO/SiO2/Si structure. These effects can be explained by the piezoelectricity of the PLCT film deposited on the LSMO layer. In addition, these effects demonstrate that the ferromagnetic properties can be controlled by the ferroelectric properties of the multilayer films.
Shielding of pulsed magnetic fields with already sintered 1 μm sized powder-pressed Bi-based superconducting rings
Authors: Matsuzawa Hidenori , Mikami Koji , Ibi Akira
Published: July 2002

To confirm a ferrite-core model for the superconducting rings (supertrons) to focus and guide electron current beams, we examined a bismuth-based ring into the configuration of which already sintered 1 μm sized 2223-phase powders were cold-isostatic pressed. No additional sintering was performed on the ring. Although the four-probe dc electric resistance of the ring increased with decreasing temperatures down to 77 K, the ring effectively shielded the self-magnetic field of single pulsed nanosecond-order electron currents (∼340 keV, ∼1 kA, ∼10 ns), below the Tc. These results certainly support the model, and provide a clue useful in applications of bulk superconductors.
Correlation of power handling capability and intermodulation distortion in YBa2Cu3O7−δ thin films
Authors: Lahl P. , Wördenweber R. , Hein M.
Published: July 2002

The nonlinearity of the microwave properties of coplanar thin-film YBa2Cu3O7−δ resonators are examined by measurements of the degradation of the quality factor QL and the increase of the two-tone third-order intermodulation distortion signal with increasing microwave power. A linear correlation between the data of the characteristic microwave powers, which are obtained for the degradation of QL and the intermodulation signal, is experimentally observed and explained in terms of a theoretical model based solely on well-known expressions for the nonlinear surface resistance. Due to these experimental observations and the theoretical model, we conclude, that the degradation of the resonator Q factor and the generation of intermodulation distortion are determined by the same physical mechanism and that thermal effects can most likely be excluded.
Method for the measurement of anisotropy and rotational hysteresis using linear dichroism
Authors: Antel W. J. , Coulthard I. , Freeland J. W. , Stampfl A. P. J. , Schwickert M. M.
Published: July 2002

A technique combining x-ray magnetic linear dichroism absorption spectroscopy and rotational hysteresis loops is demonstrated. This technique, x-ray magnetic linear loops (XMLL), is used to extract magnetocrystalline anisotropy information. Results from two systems, a polycrystalline Fe film, and an epitaxial Fe film which exhibit different magnetic anisotropies, are shown. The measured XMLL is described using a simple single-domain anisotropy model.
Nonlinear current–voltage relations in polycrystalline perovskite manganites ceramics
Authors: Philip John , Kutty T. R. N.
Published: July 2002

Highly nonlinear current–voltage (J∝Eα) relations with voltage-limiting characteristics are observed for Mg-doped lanthanum calcium manganite polycrystalline ceramics with nonlinearity coefficient, α=2–9 at low-electric-field strengths of 2–5 V/mm, below magnetic transition temperatures. The current density increases with external magnetic field, so that magnetically tunable low-voltage varistors are realized. The α increases on annealing at 1375 K in atmospheres of lower pO2, and becomes more pronounced with decreasing grain size, indicating that nonlinear behavior is related to the outdiffusion of oxygen through the grain-boundary-layer regions. The increasing deficiency in Mn3+/Mn4+ pairs reduces the hole-hopping probability leading to insulating barriers in the grain-boundary-layer regions. The barrier height is lowered by the external electric field, facilitating the charge-carrier movement between the grains. Since the conduction is due to spin-polarized tunneling, the external magnetic field increases the current.
Ion-irradiation-induced mixing, interface broadening and period dilation in Pt/C multilayers
Authors: Ghose S. K. , Goswami D. K. , Rout B. , Dev B. N. , Kuri G. , Materlik G.
Published: July 2002

Pt/C multilayers of nanometric dimension have been irradiated with 2-MeV-Au ions to a fluence of 1×1014 ions/cm2 and analyzed by x-ray reflectivity and x-ray standing wave measurements. The multilayer period has expanded by ∼9%, the expansion of the Pt layers being larger than that of the C layers. Ion-induced displacement of atoms across the interfaces led to an increased interface roughness and an increase of 2 at. % Pt in C layers. Monte Carlo simulations for ion-induced atomic displacement have been used to explain the observed effects.
Binding energy of vacancy clusters generated by high-energy ion implantation and annealing of silicon
Authors: Venezia V. C. , Pelaz L. , Gossmann H.-J. L. , Haynes T. E. , Rafferty C. S.
Published: July 2002

We have measured the evolution of the excess-vacancy region created by a 2 MeV, 1016/cm2 Si implant in the silicon surface layer of silicon-on-insulator substrates. Free vacancy supersaturations were measured with Sb dopant diffusion markers during postimplant annealing at 700, 800, and 900 °C, while vacancy clusters were detected by Au labeling. We demonstrate that a large free vacancy supersaturation exists for short times, during the very early stages of annealing between the surface and the buried oxide (1 μm below). Afterwards, the free vacancy concentration returns to equilibrium in the presence of vacancy clusters. These vacancy clusters form at low temperatures and are stable to high temperatures, i.e., they have a low formation energy and high binding energy.
Optical constants of ice Ih crystal at terahertz frequencies
Authors: Zhang Chun , Lee Kwang-Su , Zhang X.-C. , Wei Xing , Shen Y. R.
Published: July 2002

Terahertz time-domain spectroscopy was used to measure the refractive indices of Ih crystalline ice in the frequency range of 0.25–1.0 THz. With increasing frequency, the real part, n′, of the refractive index increases from 1.787 to 1.793 at 243 K, and the imaginary part, n″, increases from 0.005 to 0.020. The temperature dependence of n′ is less than 0.01%/K and that of n″ is ∼1%/K. Our results connect smoothly to the data of Matsuoka and co-workers [T. Matsuoka, S. Fujita, and S. Mae, J. Appl. Phys. 80, 5884 (1996)] in the microwave range and the data in the far IR range, and can be well described by the existing theoretical models.
Low-temperature selective deposition of silicon on silicon nitride by time-modulated disilane flow and formation of silicon narrow wires
Authors: Yokoyama Shin , Ohba Kenji , Kawamura Kensaku , Kidera Toshiro , Nakajima Anri
Published: July 2002

The low-temperature (410 °C) selective deposition of Si on silicon nitride has been achieved by means of the time-modulated flow of disilane while a very small amount of Si is deposited on SiO2. Very narrow (21 nm width and 28 nm thick) Si wires have been fabricated using the selective deposition. The resistivity of the Si wires fabricated by the selective deposition is much smaller (∼1/5) than that fabricated by the conventional reactive ion etching followed by annealing. This technique will be applicable to the formation of a polycrystalline silicon gate with small resistivity for the high-performance ultrasmall metal–oxide–semiconductor transistors and quantum effect devices.
Electron-stimulated surface stress relaxation of Si
Authors: Narushima Tetsuya , Itakura Akiko N. , Kawabe Takaya , Kitajima Masahiro
Published: July 2002

We have observed the nonthermal relaxation of surface stress in Si induced by electron irradiation at room temperature. An atomically thin disordered layer was introduced by Ar ion bombardment. The surface stress change during ion bombardment and the following electron irradiation of Si(100) was measured by means of an optical microcantilever technique. We have found that the compressive stress in the Si surface due to disorder induced by ion bombardment was completely relaxed by electron irradiation at low energy. The criterion for complete relaxation is found not to be total energy deposition, but the number of irradiated electrons.
Scaling behavior of higher harmonic responses in textured (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tapes
Authors: Zhang Y. J. , Ong C. K.
Published: July 2002

A silver-sheathed (Bi,Pb)2Sr2Ca2Cu3Oy tape was studied in terms of harmonic responses χn=χn′−iχn″ (n=3, 5, 7) to reveal the angular dependence of its physical properties. In the screening method higher harmonic responses are directly related to the nonlinear voltage–current [E(J)] relation of the sample. Therefore, the effect of the silver sheath on the harmonic measurements can be neglected. We performed measurements of the harmonic responses as a function of applied magnetic field or angle between the magnetic field and the tape plane at various temperatures. The measured data could be scaled onto a single curve by using the three-dimensional scaling relation. The derived anisotropic parameter γ ranged from 5.1 to 5.6 at the measured temperature region. Such a small γ value was attributed to the misalignment of the grains in the tape.
Absorption bleaching of squarylium dye J aggregates via a two-photon excitation process
Authors: Furuki Makoto , Tian Minquan , Sato Yasuhiro , Pu Lyong Sun , Tatsuura Satoshi , Abe Shuji
Published: July 2002

Squarylium dye J aggregates exhibit ultrafast nonlinear optical response of absorption saturation at the resonant wavelength of 770 nm. We studied the two-photon excitation process of J aggregates. By fluorescence measurement, we found the two-photon absorption band at 1.3 μm, which was different from that of the dye solution at 1.2 μm. Absorption saturation at 770 nm via a two-photon excitation process was observed by two-photon resonant excitation at 1.3 μm and also by off-resonant excitation at 1.55 μm, suggesting the possibility of J aggregates for optical switching materials working at the wavelength used in optical communications.
Conduction mechanisms for off-state leakage current of Schottky barrier thin-film transistors
Authors: Yeh Kuan-Lin , Lin Horng-Chih , Huang Rou-Gu , Tsai Ren-Wei , Huang Tiao-Yuan
Published: July 2002

Conduction mechanisms for the off-state leakage in Schottky barrier thin-film transistor were explored. It was found that the field-emission process dominates the leakage conduction of the device with the conventional structure as the field strength in the drain junction becomes high, and results in the strong gate-induced drain leakage (GIDL) like phenomenon. In contrast, for the device with a field-induced-drain structure, the high-field region is pulled away from the silicided drain. As a result, the field-emission conduction is eliminated, so the GIDL-like leakage current is effectively suppressed.
Plasma wave instability in gated collisionless two-dimensional electron gas
Authors: Dmitriev A. P. , Kachorovskii V. Yu. , Shur M. S.
Published: July 2002

We present the solution of the Boltzmann equation for relatively low density gated two-dimensional electron gas where electron–electron collisions are not significant. This solution describes the plasma waves with the same dispersion law as for a high electron sheet density. In both cases, the plasma waves become instable in a short channel field effect transistor with asymmetric boundary conditions at small channel currents (provided that the scattering by phonons and impurity is sufficiently small). Our analysis also shows that for realistic values of the device parameters, the Landau damping is small.
Quantum beats of free and bound excitons in GaN
Authors: Kyhm K. , Taylor R. A. , Ryan J. F. , Aoki T. , Kuwata-Gonokami M. , Beaumont B. , Gibart P.
Published: July 2002

We present spectrally resolved and time-integrated four-wave mixing measurements at coherent dynamics of bound excitons in a high-quality GaN epilayer. Coherent excitation, with co-circular polarized light, of the neutral donor-bound excitons (D 0X) and A excitons (XA) results in quantum beats, corresponding to the energy splitting between D 0X and XA. The temperature-dependent dephasing rate is used to deduce the strength of the D 0X-acoustic–phonon interaction via the homogeneous linewidth.
Conductive phosphate and fluorophosphate glasses with fullerene doping
Authors: Zeng Heping , Lin Fucheng , Mao Sen , Xu Zhizhan
Published: July 2002

The appropriate amount of fullerene doping in phosphate and fluorophosphate optical glasses modifies the structures of glass matrices by bonding the nearby -[PO4]- tetrahedra with nonbridging oxygen anions, and consequently building up observable conductivity at room temperature. Non-Arrhenius ionic conductivity is observed, which is interpreted as a result of the temperature dependence of the activation energies of the mobile cations. The variation of microphotoluminescence induced by the electric field presents us with an indirect way to characterize the random activation, percolation migration, and retrap of metal cations near fullerene-related amorphous islands.
Simple and accurate expressions for distributed mutual inductance and resistance of semiconducting interconnects
Authors: Ymeri Hasan , Nauwelaers Bart , Maex Karen
Published: July 2002

An analytic model is presented (based on the induced current density distribution inside a silicon substrate) to calculate the frequency-dependent distributed mutual inductance and the associated distributed series mutual resistance of silicon semiconducting integrated circuit (IC) interconnects. The validity of the proposed model was checked by a comparison with a quasi-static transmission electron microscopy spectral domain approach and an equivalent-circuit modeling procedure. It is found that the silicon semiconducting substrate skin effect must be considered for accurate prediction of the high-frequency characteristics of IC interconnects.
Γ–L–X
mixed symmetry of nitrogen-induced states in GaAs1−xNx probed by resonant Raman scattering
Authors: Seong M. J. , Mascarenhas A. , Geisz J. F.
Published: July 2002

A resonant Raman scattering study near the nitrogen-induced E+ state in GaAs1−xNx at 80 K with special emphasis on all the zone-boundary phonons is used to investigate the full symmetry of the E+ state. We have observed that various phonons at the L- and X-zone boundaries not only emerge as strong and sharp Raman features for excitations near the E+ transition but also exhibit the same intensity resonance enhancement as observed for the zone center phonons, longitudinal-optical (Γ) and transverse-optical (Γ). Our data provide strong evidence of significant L and X components in the wave function of the nitrogen-induced E+ state in GaAs1−xNx.
Metal/III–V diodes engineered by means of Si interlayers: Interface reactions versus local interface dipoles
Authors: Bonanni B. , Orani D. , Lazzarino M. , Rubini S. , Franciosi A.
Published: July 2002

We present studies of Al/n-GaAs(001) and Al/p-GaAs(001) diodes in which the Schottky barrier height was varied by fabricating Si bilayers at the interface under either Ga or Al flux. Comparison of the effect of each interlayer on the n- and p-type barrier height allowed us to rule out any major role of interface reactions and test the predictions of the local interface-dipole model of Schottky barrier tuning.
Vibrational and photoemission study of the interface between phenyl diamine and indium tin oxide
Authors: He P. , Wang S. D. , Wong W. K. , Lee C. S. , Lee S. T.
Published: July 2002

High-resolution electron-energy-loss spectroscopy (HREELS) and ultraviolet photoemission (UPS) measurements of the interface of phenyl diamine (NPB) and indium tin oxide (ITO) were performed. The HREELS spectrum of the oxygen-plasma-treated ITO was characterized by dipolar-active-phonon modes at 71 and 134 meV. Upon deposition of NPB on ITO, the HREELS loss peaks of ITO gradually diminished, while the NPB-derived loss peaks appeared. The negligible energy shifts of the NPB peaks with NPB thickness suggested a rather weak interaction between NPB and ITO. The remarkable intensity change of the loss band at 71–65 meV gave evidence for a strong vibrational coupling between the ITO phonon mode at 71 meV and the NPB-derived vibrational mode at 65 meV. Annealing of the NPB/ITO interface with 20 Å of NPB resulted in the decoupling of the two vibrational modes, presumably due to crystallization of the NPB overlayer. UPS measurements showed a sharp decrease in work function at the initial NPB deposition, which is attributable to a dipole layer formed at the interface.