bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymeric waveguide wavelength filters using electron-beam direct writing
Authors: Wong W. H. , Pun E. Y. B.
Published: July 2002

Polymeric waveguide wavelength filters based on a low-loss negative tone epoxy Novolak resin polymer have been fabricated using electron-beam direct writing. Both the waveguides and the gratings were exposed simultaneously, which effectively eliminate the alignment errors that can be generated during fabrication. A first-order Bragg grating around 1550 nm wavelength was used, and a transmission peak of −27 dB was obtained with a 5 mm long grating length, corresponding to >99% reflection. The 3 dB transmission bandwidth was found to be ∼0.8 nm and the 10 dB bandwidth was ∼1.0 nm. Dependence of the Bragg wavelength on electron-beam dosage and waveguide width was also investigated.
Multilevel Redfield description of the dissipative dynamics at conical intersections
Authors: Kühl Axel , Domcke Wolfgang
Published: July 2002

Redfield theory is applied to investigate the photoinduced dynamics at a conical intersection (the so-called system) which is weakly coupled to a thermal environment (the so-called bath). The dynamics of the system is described by a two-state three-mode model Hamiltonian, chosen to represent the S1(nπ*)–S2(ππ*) conical intersection in pyrazine. Dissipative effects are introduced through a bilinear coupling of the system vibrational modes with a harmonic bath, which represents the remaining vibrational degrees of freedom of the molecule and/or interactions with a condensed-phase environment. The Redfield equations for the reduced density matrix are solved numerically without further approximations. From the reduced density matrix the time evolutions of electronic-state populations and vibrational coherences are obtained, as well as time-dependent probability densities of individual vibrational modes. The results provide a visualization of the essential features of the ultrafast (time scale of 10 fs) internal-conversion process at the conical intersection and the ensuing vibrational cooling process on the lower adiabatic potential-energy surface. The effect of vibrational damping on the linear optical absorption spectrum is also investigated.
Enhanced dopant activation and elimination of end-of-range defects in BF2+-implanted silicon-on-insulator by high-density current
Authors: Lin H. H. , Cheng S. L. , Chen L. J. , Chen Chih , Tu K. N.
Published: July 2002

Enhanced dopant activation and elimination of end-of-range (EOR) defects in BF2+-implanted silicon-on-insulator (SOI) have been achieved by high-density current stressing. With the high-density current stressing, the implantation amorphous silicon underwent recrystallization, enhanced dopant activation and elimination of the (EOR) defects. The current stressing method allows the complete removal of EOR defects that has not been possible with conventional thermal annealing in the processing of high-performance SOI devices.
Oxygen-plasma effects of a La0.7Ca0.3MnO3−δ single crystal
Authors: Kim H. S. , Lee C. H. , Lee Cheol Eui , Kim K. M. , Noh S. J. , Hong C. S. , Hur N. H. , Shim S. Y. , Ri H.-C.
Published: July 2002

A La0.7Ca0.3MnO3−δ single crystal was oxygen-plasma treated at 200 °C. Our electrical and magnetic measurements indicate that the oxygen-plasma treatment can be an effective low temperature method of oxygen stoichiometry modification of colossal magnetoresistance manganites. The oxygen plasma is also shown to introduce structural defects, whose effects are prominent near the Curie temperature (Tc), giving rise to anomalies in the resistivity and magnetic behaviors.
Effects of arsenic concentration profile in gate oxide on electric properties of metal–oxide–silicon devices
Authors: Chang-Liao Kuei-Shu , Chuang Ching-Sang
Published: July 2002

The effects of arsenic concentration profiles in gate oxides on the electrical properties of metal–oxide–silicon (MOS) capacitors were investigated. It is found that arsenic in the bulk of gate oxide degrades the electric property of MOS devices, which could be due to the electron traps introduced by arsenic. Interestingly, the electric properties of MOS devices can be improved by an increase in the arsenic concentration at the SiO2/Si interface. This improvement may be attributed to the interfacial strain relaxation and/or the replacement of nonbridging bonds. The arsenic concentration profile in gate oxide plays a crucial role for the electric properties of MOS devices.
Carrier relaxation dynamics in an ultrafast all-optical modulator using an intersubband transition
Authors: Asano T. , Yoshizawa S. , Noda S.
Published: July 2002

An improvement of an all-optical modulation scheme that utilizes an intersubband transition is proposed and investigated in connection with intersubband carrier relaxation dynamics. N-doped GaAs/AlGaAs quantum wells are pumped by an ultrashort (∼120 fs) intersubband-resonant pulse and probed by an interband-resonant white-light continuum. Ultrafast modulation speed of ∼0.4 ps is demonstrated, which is faster than that of the previous scheme by as much as a factor of 10. It is found that a large part of the carriers, which are excited from the first conduction subband to the second conduction subband, transfer to unknown trapping states at a relaxation time that is comparable to that of the pump–pulse duration. The existence of the carrier relaxation path via L valley subbands is strongly suggested as the cause.
Electrical characteristics of a TaOxNy/ZrSixOy stack gate dielectric for metal–oxide–semiconductor device applications
Authors: Jung Hyungsuk , Yang Hyundoek , Im Kiju , Hwang Hyunsang
Published: July 2002

In this letter, we describe a process for the preparation of high-quality tantalum oxynitride (TaOxNy) with zirconium silicate (ZrSixOy) as an interfacial layer for use in gate dielectric applications. Compared with conventional chemical oxide and nitride as interfacial layers, TaOxNy metal–oxide–semiconductor capacitors using ZrSixOy as an interfacial layer exhibit lower leakage current levels at the same oxide thickness and a lower interface state density. We were able to confirm the TaOxNy/ZrSixOy stack structure by Auger electron spectroscopy and transmission electron microscopy analyses. Zirconium silicate is a promising interfacial layer for future high-k gate dielectric applications.
High-quality MgB2 films on boron crystals with onset Tc of 41.7 K
Authors: Hur N. , Sharma P. A. , Guha S. , Cieplak Marta Z. , Werder D. J. , Horibe Y. , Chen C. H. , Cheong S.-W.
Published: July 2002

The simple binary compound, MgB2, has created enormous excitement, due to its remarkably high Tc (39 K), its exotic electronic and phononic structure, as well as its potential technological application. However, contrary to the initial expectation, worldwide efforts to enhance the Tc of this material by means of chemical doping and applying hydrostatic pressure have failed. Investigations of other diborides or related materials have also resulted in finding of lower Tc’s. In this letter we report a slight, but significant enhancement of Tc in MgB2 films grown on boron crystals, which may stem from tensile-type strain. This finding opens up a new possibility for further optimizing Tc in MgB2 and perhaps in related materials.
Microdischarge array-assisted ignition of a high-pressure discharge: Application to arc lamps
Authors: Eden J. G. , Wagner C. J. , Gao J. , Ostrom N. P. , Park S.-J.
Published: July 2002

An array of cylindrical microdischarges has been demonstrated to significantly improve the ignition characteristics of a high-pressure arc discharge by preionizing the anode–cathode gap. Situated behind the cathode, the microdischarge array serves to reduce both the statistical and formative time delays by providing seed electrons in the critical early phases of the startup of a cold lamp. Experiments conducted in Ar and Ne/2% Xe mixtures at pressures ranging from 35 to 600 Torr with spacings between the tungsten electrodes of 1–3.5 cm show that a three element array of 400-μm-diam cylindrical microdischarges lowers the dc ignition voltage for the lamp by at least a factor of 2 when the Ar pressure is between 50 and 75 Torr. The required voltage is constant over a broad range in Ar pressure (35 to ∼90 Torr) and similar results are observed with 200-μm-diam microdischarges and for lamp ignition in Ne/2% Xe gas mixtures.
High-performance photorefractive polymer composite with 2-dicyanomethylen-3-cyano-2,5-dihydrofuran chromophore
Authors: Wright Daniel , Gubler Ulrich , Roh Yeonsuk , Moerner W. E. , He Meng , Twieg Robert J.
Published: July 2002

A nonlinear optical chromophore for photorefractive applications containing a 2-dicyanomethylen- 3-cyano-2,5-dihydrofuran acceptor group is presented. When doped into a plasticized composite of poly(n-vinylcarbazole), large gain coefficients (Γ) are observed with photorefractive speed similar to the best composites reported in the literature while maintaining low sample absorption (∼15 cm−1).
Flux dependence of oxygen-beam-induced ripple growth on silicon
Authors: Liu Z. X. , Alkemade P. F. A.
Published: July 2002

The influence of flux on the growth of ripples on Si(111) under bombardment of oblique, 1 keV O2+ beams was investigated. We found that a low flux leads to a significantly higher ripple growth rate per ion than a high flux. This effect is attributed to a reduction in the viscous flow of the amorphized material. At low fluxes, the viscous flow is reduced because there is more thermal annealing of the radiation damage. Current models of surface roughening remain valid if the flux dependence of the viscous flow is taken into account.
Time domain measurement of spin-dependent recombination
Authors: Boehme Christoph , Lips Klaus
Published: July 2002

A defect characterization method is presented, the time domain measurement of spin-dependent recombination (TSR). Recombination between paramagnetic states is changed rapidly by electron spin resonant excitation through strong nanosecond microwave pulses. After the pulse, a slow relaxation of the recombination rate towards its steady state takes place. By measuring the current transient after the resonant pulse, information about dissociation and recombination probabilities of spin pairs is directly obtained for a distinct recombination path. Dangling bond recombination in microcrystalline silicon was used as model process for the demonstration of TSR.
Multilayer-array growth of SiGeC alloys on Si(001)
Authors: LeThanh Vinh , Calmes C. , Zheng Y. , Bouchier D.
Published: July 2002

The growth of SiGeC alloys on Si(001) in an ultrahigh vacuum chemical-vapor deposition system was investigated by means of in situ reflection high-energy electron diffraction, transmission electron microscopy, and high resolution x-ray diffraction. It is shown that when the total amount of deposited carbon exceeds a value of about 1.5%, the grown layers contain a high density of stacking faults and/or microtwins. However, such defects are found to be formed only after the deposition of a certain thickness, whose value depends on the deposited carbon amount. By realizing SiGeC/Si multilayer arrays, we show that defect-free SiGeC films with a substitutional carbon content up to 3.3% can be achieved.
Nanobelts of the dielectric material Ge3N4
Authors: Gao Y. H. , Bando Y. , Sato T.
Published: July 2002

Ge 3 N 4 nanobelts 30–300 nm in width were synthesized by thermal reduction of a mixed Ge+SiO2 powder in NH3 atmosphere. These nanobelts were studied by high-resolution transmission electron microscope equipped with an x-ray energy dispersive spectrometer. In these synthesized nanobelts, the existence of α and β phases of Ge3N4 was identified. The α phase exhibiting slight difference from an ideal α-Ge3N4 phase was also found in the present Ge3N4 material. The mechanism of formation of the Ge3N4 nanobelts is discussed.
Effect of lattice mismatch on surface morphology of InAs quantum dots on (100) In1−xAlxAs/InP
Authors: Koo B. H. , Hanada T. , Makino H. , Yao T.
Published: July 2002

We present the results of the formation of the InAs quantum dots (QDs) on the (100) In1−xAlxAs(InAlAs)/InP substrate by using relaxed InAlAs buffer layers with different compositions. Variations of surface morphology of InAs QDs as a function of InAs–InAlAs lattice mismatch have been evaluated by atomic force microscopy. When the lattice mismatch increases from 2.4% to 4.2%, the size of QDs decreases, and the density of QDs increases. Each of these dependences can be fitted to a power function of the misfit unless the Al diffusion, roughness of the buffer layer, and/or the ripening of small dots modify the size and density.
Formation of sprays from liquid jets by a superimposed sequence of nonaxial disturbances
Authors: Zimmels Y. , Sadik S.
Published: July 2002

A fundamental physical mechanism whereby sprays are formed is formulated. A model of nonaxial sequence of superimposed disturbances, propagating one on top of the other, is used to describe the evolution of liquid jets into sprays. It is postulated that every consecutive superimposed disturbance travels tangent to the surface that supports its propagation. Model outputs show highly nonlinear profiles of the jet surface. Fourier analysis, of the derived superimposed disturbance functions, is performed in conjunction with the basic building blocks of the classical instability theory. Starting from the first superimposed disturbance, the sum of these linear building blocks results in nonlinear intricate profiles of the jet. These profiles are shown to be the source of drops from which a spray is made.
Coupled technique to produce two-dimensional superlattices of nanoparticles
Authors: Renard C. , Ricolleau C. , Fort E. , Besson S. , Gacoin T. , Boilot J.-P.
Published: July 2002

We present an original technique to produce high-quality monodisperse two-dimensional (2D) superlattices of nanoparticles. This technique is based on the diffusion of metal atoms deposited by pulsed-laser ablation technique into the first layer of a 3D-structured mesoporous silica film obtained by a sol-gel method. This hybrid technique is very promising since it can potentially produce a wide variety of 2D superlattices by changing the host mesoporous film parameters (particle size and shape, 2D structure symmetry) or the type of deposited materials. In this letter, we show experimental results obtained with 2D square and hexagonal silver superstructures.
Low field Overhauser images of the formation process of a hydrogel
Authors: Barros Wilson , de Souza Ricardo E. , Engelsberg M. , Golman Klaes , Ardenkjær-Larsen J. H.
Published: July 2002

The gelation of sodium alginate by calcium ions is studied by proton-electron double resonance imaging in a magnetic field of only 16 mT using a newly developed free radical. The high sensitivity of the Overhauser enhancement to small variations in water mobility permits the detection of minute changes in gel composition. Spatial inhomogeneity and temporal evolution of this, and possibly other processes involving diffusion and chemical reaction, could be accurately monitored by this technique.
Nanoscale cube-on-cube growth of SrS on MgO substrate by solid-source molecular-beam epitaxy
Authors: Feng J. , Teo K. L. , Chong T. C. , Wu Y. H. , Liu Z. Y. , Luo P. , Chong J. F.
Published: July 2002

We report the growth of epitaxial SrS on (001)MgO substrates by solid-source molecular-beam epitaxy. During the deposition, the film structure and orientation were characterized by reflection high-energy electron diffraction. It was shown that the film epitaxial planes conserved the substrate surface symmetry—cubic. X-ray diffraction results establish the epitaxial relationship as cube-on-cube (001)SrS ‖(001)MgO with [100]SrS ‖[100]MgO for growth temperature between 400 and 600 °C. Scanning electron microscopy and atomic force microscopy analyses were used to study the films’ surface morphology. Depending on the growth temperature, different sizes of SrS islands can be achieved. The growth of SrS on MgO is thought to occur in step-flow growth mode.
In situ electrical-field-induced growth and properties of Bi3TiNbO9 ferroelectric thin films
Authors: Yang B. , Zhang X. J. , Zhang S. T. , Chen X. Y. , Wu Z. C. , Chen Y. F. , Zhu Y. Y. , Liu Z. G. , Ming N. B.
Published: July 2002

With Bi3TiNbO9 (BTN) ferroelectric samples, in situ electrical-field-induced growth of ferroelectric thin films was demonstrated to control the films’ microstructure and manipulate their ferroelectric properties. BTN films on Ti/SiO2/Si substrates were grown at a relatively low temperature (650 °C) with a biased electrical field during pulsed-laser deposition. The (001) orientation of the films, which makes no contribution to their polarization, was effectively reduced by the in situ electrical field of strength of 70 V/cm. This results in a large increase of remnant polarization from 1.1 to 6.2 μC/cm2, and reduction of the coercive field from 70 to 50 kV/cm, comparing the films grown freely under the same condition. Furthermore, the films showed an excellent fatigue-free property of up to 1010 switching cycles.
Cross-correlation measurement of ultrashort soft x-ray pulse emitted from femtosecond laser-produced plasma using optical field-induced ionization
Authors: Oguri Katsuya , Nakano Hidetoshi , Nishikawa Tadashi , Uesugi Naoshi
Published: July 2002

We propose a cross-correlation technique for measuring ultrashort soft x-ray pulse shapes using the rapid increase in Kr+ ion density caused by optical field-induced ionization, which operates as an ultrafast x-ray absorption switch. Using this technique, we measured the shape of a soft x-ray pulse near 15.6 nm emitted from W plasma produced by a 100 fs laser pulse, and found the duration to be about 4 ps assuming a Gaussian pulse. This result was in good agreement with the duration measured with an x-ray streak camera thus confirming the feasibility of our technique. The temporal resolution of this technique has the potential to overcome the limitation of the ionizing pulse duration.
Do ballistic channels contribute to the magnetoresistance in magnetic tunnel junctions?
Authors: Price E. P. , Smith David J. , Dynes R. C. , Berkowitz A. E.
Published: July 2002

The barrier quality and conduction mechanisms in ferromagnet–insulator–ferromagnet (FIF) junctions are studied by fabricating adjacent ferromagnet–insulator–superconductor (FIS) junctions, using the same barrier and top electrode in both junctions. Transport measurements on the FIS junctions provide information about the transport processes in the FIF junctions. The FIS junctions have a large zero-bias conductance (ZBC) that varies with barrier thickness, in part due to ballistic channels in parallel with the tunnel barrier. As the ZBC increases, the magnetoresistance (MR) in the FIF junctions decreases, implying that these ballistic channels are not magnetoresistive and that their presence reduces the total MR in the FIF junctions.
Quantum description of the resistor–capacitor circuit and Brownian motion
Authors: Richardson W. H.
Published: July 2002

An equation for the reduced density matrix which describes a capacitor, that is coupled to a resistor, is derived using the total Hamiltonian, and without resorting to any artificial model. A Master equation is also obtained for the dissipative medium. The theory erases the notion of the reservoir. It is shown that the dynamical interaction with the medium is not completely determined by the resistance (or the corresponding fluctuation–dissipation relation). Unexpectedly, through the charge density–density correlation, the longitudinal dielectric function is shown to play a critical role.
Polarity determination by atomic location by channeling-enhanced microanalysis
Authors: Jiang N. , Eustis T. J. , Cai J. , Ponce F. A. , Spence J. C. H. , Silcox J.
Published: July 2002

In this letter, an alternative approach to determine the polarity of GaN thin films based on the atomic location by channeling-enhanced microanalysis technique is described. Theoretical calculations provide a straightforward criterion for polarity determination that is a major advantage of this method. At the Bragg position, the thickness-averaged incident electron intensity, and hence, electron induced characteristic x-ray yield, is higher on the N plane than on the Ga if the g vector of the diffraction beam is parallel to the Ga–N bond direction, and vice versa. Experimental results support the theoretical predictions. The possible errors in the experiments are also discussed.
Simple model for patterned bidirectional anchoring of nematic liquid crystal and its bistability
Authors: Yoneya Makoto , Kim Jong-Hyun , Yokoyama Hiroshi
Published: July 2002

An effective anchoring model for the patterned surface with bidirectional rubbing by atomic force microscope was proposed. The model was a simple additive function of two bidirectional anchoring contributions of the patterned surface, with consideration of higher-order terms of the anchoring function. The bistable switching behavior of the nematic liquid crystal cells with the patterned surface was investigated analytically and numerically using this anchoring model.
Quantitative comparison of trimethylindium sources and assessment of their suitability for low threshold 980 nm InGaAs/GaAs lasers grown by chemical beam epitaxy
Authors: Maclean J. O. , Martin T. , Houlton M. R. , Calcott P. D. J. , Ayling S. G. , Hilton K. P. , Rushworth S. A. , Smith L. M.
Published: July 2002

Metalorganic compounds used as precursors for epitaxial growth by metalorganic vapor phase epitaxy (MOVPE) and chemical beam epitaxy (CBE), may be contaminated with oxygen-containing impurities. These impurities are a particular problem in the precursor purification process when they, or their adducts, are of similar volatility to the precursor. We report that improvements in precursor purity, in this case trimethylindium (TMIn), may be quantitatively assessed through growth at low temperatures by CBE and subsequent two-stage testing. Indium-containing III–V semiconductor test structures were characterized first using secondary ion mass spectrometry (SIMS) and second by photoluminescence (PL) lifetime measurements which sensitively probe the presence of nonradiative centers. A factor of 4 improvement in PL lifetime was found for Epipure™ TMIn as compared with conventional adduct-purified TMIn. The Epipure™ grade of TMIn was used for 980 nm lasers. State-of-the-art threshold currents (162 A cm−2) and low internal optical cavity losses (3.9 cm−1) were obtained using CBE growth at the very low temperature of 540 °C.
Rapid thermal low-pressure metal organic chemical vapor deposition of Fe-doped InP layers
Authors: Kreinin O. , Bahir G.
Published: July 2002

High quality Fe-doped InP layers have been grown by means of rapid thermal low-pressure metal organic chemical vapor deposition. Trimethylindium, tertiarybutylphosphine, and ferrocene were used as indium, phosphorus, and iron sources, respectively. The best growth conditions are: V–III ratio of 100 temperature of 650 °C, pressure of 4 Torr and growth rate of 2 μm/h. Featureless films were grown with a flat iron concentration of 2×1018 cm−3 as a function of depth, with an average specific resistivity of 108 Ω cm and a narrow x-ray half-maximum peak of 15 arcs.
Irreversibility field and superconducting screening currents in EuBa2Cu3O7 films
Authors: Senapati K. , Sahoo Leena K. , Pandey N. K. , Budhani R. C.
Published: July 2002

Measurements of the critical current density (Jc) and irreversibility field [Birr(T)] of epitaxial, c-axis-oriented EuBa2Cu3O7 (Eu-123) films are reported. The transition temperature (Tc), Jc, and Birr(T) of these pulsed-laser-deposited films depend critically on the growth temperature (TD), growth rate (Gr), and the oxygen partial pressure (pO2) during growth. As compared to YBa2Cu3O7, Eu-based films require lower Gr, higher pO2, and higher TD. These differences are attributed to the lower adatom mobility of Eu and its propensity for a 2+ oxidation state. The lattice mismatch between (100) LaAlO3 and the ab-plane of Eu-123 leads to an elongated c axis and some randomly oriented islands whose growth is truncated by epitaxial lateral overgrowth as the film thickness increases.
Crystal orientation dependence of the piezoelectric d33 coefficient in tetragonal BaTiO3 as a function of temperature
Authors: Damjanovic Dragan , Brem Franziska , Setter Nava
Published: July 2002

Using the Landau–Ginzburg–Devonshire approach, the longitudinal piezoelectric coefficient in an arbitrary direction, d33*(θ), was calculated as a function of temperature in tetragonal BaTiO3 crystals. The direction along which d33*(θ) is maximum is a function of piezoelectric dij coefficients referred to the crystallographic coordinate system. Below a critical ratio of the shear and longitudinal coefficients, d15/d33, the maximum d33*(θ) lies along the [001] axis. As the low-temperature orthorhombic phase is approached on cooling, the d15 increases, reflecting softening of the lattice along the axis of the incipient orthorhombic distortion, and the direction of maximum d33*(θ) deviates significantly from the [001] axis. Our results suggest that the enhanced d33*(θ) coefficient along a direction other than the polar axis recently reported in some ferroelectrics is at least in part controlled by these intrinsic lattice effects.
Discrete rocket effect and its implication for micron grain acceleration
Authors: Wang Zhehui
Published: July 2002

The rocket equation breaks down for micron grains because the number of particles per grain is small compared with that within macroscopic objects. Therefore, the discrete rocket effect replaces the classical continuous rocket effect for micron grains. The discrete rocket effect is due to the fact that ejected mass from a micron grain can be comparable to the total mass for these intermediate size objects. Electron beam and laser ablation are possible means to accelerate micron grains to 106 m/s and higher velocity.
Scattering of the charge carriers by ordered arrays of defect pairs in ternary chalcopyrite semiconductors
Authors: Rincón C. , Wasim S. M. , Marı́n G.
Published: July 2002

The electrical properties of CuIn3Se5, CuGa3Te5, and CuIn3Te5 that contain arrays of donor–acceptor defect pairs (DADPs) in the lattice structure are studied. An expression for the scattering of the charge carriers with the DADPs, calculated from simple first principles, is proposed. This, when combined with other well-established mechanisms, explains the temperature dependence of the relatively low carrier mobility in these compounds in the activation regime very well.
Submicron YBa2Cu3Ox ramp Josephson junctions
Authors: Komissinski Philippe V. , Högberg Björn , Tzalenchuk Alexander Ya. , Ivanov Zdravko
Published: July 2002

Submicron YBa2Cu3Ox/PrBa2Cu2.6Ga0.4Ox/YBa2Cu3Ox ramp-type Josephson junctions were fabricated and tested. The submicron bridges in the top electrode were patterned by e-beam lithography and Ar ion milling through an amorphous carbon (a-C) mask. Junctions with width ranging from 0.2 to 8 μm and oriented along different crystal directions of YBa2Cu3Ox have been produced. Current–voltage characteristics show a behavior consistent with the resistively shunted junction model with small excess current. Junction critical current densities of about 10 kA/cm2 and characteristic voltages up to 6 mV were measured at 4.2 K for the submicron junctions. Junctions along different crystal orientations showed different characteristics suggesting an influence from the d-wave order parameter.
Tuning the electrical properties of zirconium oxide thin films
Authors: Cho Byeong-Ok , Wang Jianjun , Sha Lin , Chang Jane P.
Published: July 2002

ZrO 2 films obtained using plasma-enhanced chemical-vapor deposition exhibit various electrical properties tuned by the flow rate ratio of O2 to precursor-carrying Ar (O2/Ar), which controls the hydrocarbon incorporation in the films and the interfacial layer formation. As-deposited ZrO2 films obtained in oxygen-rich plasmas (O2/Ar⩾1) showed good electrical properties, including an overall dielectric constant of 16, a flatband voltage shift of −24 mV, an interfacial trap density of ∼1011 cm−2 eV−1, and a leakage current density of 3.3×10−6 A/cm2 at an equivalent oxide thickness of 25 Å, suitable for metal–oxide–semiconductor device applications.
Fast analog electro-optic effect in an achiral smectic C liquid crystal in a transverse electrode configuration
Authors: Yu Chang-Jae , Kim Jin-Yun , Lee Sin-Doo
Published: July 2002

We demonstrated a fast analog electro-optic effect in an achiral smectic C (ASC) liquid crystal in a transverse electrode configuration. In this configuration, wide viewing characteristics are also achieved. The analog gray scales in the ASC mode are obtained in a dielectrically driving scheme as those in the nematic mode. The rising and falling times, 3.2 and 13.8 ms, are suitable for video-rate display applications.
Spatially resolved cathodoluminescence of laterally overgrown GaN pyramids on (111) silicon substrate: Strong correlation between structural and optical properties
Authors: Cho Yong-Hoon , Kim H. M. , Kang T. W. , Song J. J. , Yang W.
Published: July 2002

Spatially resolved optical emission properties of laterally overgrown GaN hexagonal pyramids on (111) Si substrates are investigated by cathodoluminescence (CL) spectroscopy and mapping techniques. The results are compared with structural properties obtained by scanning and transmission electron microscopic techniques. To clarify the origin of the band edge and yellow-band emissions from the GaN pyramids, wavelength-resolved CL properties of normal and cleaved GaN pyramids are investigated in top and/or cross-sectional view configurations. The cross-sectional view CL images for cleaved GaN pyramid samples show significant differences between the overgrown areas on top of the mask and the coherently grown regions over the windows. Precise reverse (identical) contrast between the band-edge (yellow-band) emission intensity and threading dislocation density is observed by comparing the cross-sectional view CL and transmission electron microscopic images. It is demonstrated that a strong correlation exists between structural defects and optical properties in laterally overgrown GaN hexagonal pyramids.
Magnetic properties of Zn2+ substituted ultrafine Co-ferrite grown by a sol-gel method
Authors: Lee Seung Wha , Ryu Yeon Guk , Yang Kea Joon , Jung Kwang-Deog , An Sung Yong , Kim Chul Sung
Published: July 2002

Ultrafine Co1−xZnxFe2O4 (0⩽x⩽1.0) particles are fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with x-ray diffraction, vibrating samples magnetometer and Mössbauer spectroscopy. The lattice parameter (a0) increases linearly with increasing Zn concentration (x) and follows Vegard’s law approximately. Co0.9Zn0.1Fe2O4 powders that were annealed at and above 673 K have only a single phase spinel structure and behave ferrimagnetically. Powders annealed at 523 K and 573 K have a typical spinel structure and are simultaneously paramagnetic and ferrimagnetic in nature. The magnetic behavior of Co0.9Zn0.1Fe2O4 powders annealed at and above 573 K shows that an increase of the annealing temperature yields a decrease of the coercivity and an increase of the saturation magnetization. The maximum coercivity and the saturation magnetization of Co0.9Zn0.1Fe2O4 ferrite powders are 1328 Oe and 81.1 emu/g, respectively. Mössbauer spectra of Co–Zn ferrite have been taken at various temperatures from 20 to 800 K. The isomer shifts indicate that the iron ions were ferric at the tetrahedral [A] and the octahedral [B]. The Néel temperature of Co0.9Zn0.1Fe2O4 was determined to be TN=790 K and It is found that Debye temperature for the A and B sites of the sample annealed at 1123 K is found to be ΘA=756±5 K and ΘB=199±5 K, respectively. The Néel temperature dramatically decreased with increasing x from about TN=870 K for x=0.0 to TN=35 K for x=1.0.
Deposition of organic electrodes based on wet process for organic devices
Authors: Saito Kazuhiro , Kobayashi Shunsuke
Published: July 2002

Patterned organic electrodes of charge-transfer complexes were deposited based on a printing method and solution chemistry without a vacuum and high temperature. The deposited organic electrodes showed large work functions, and they were examined as upper electrodes of organic photovoltaic cells. It is found that the charge-transfer complexes can be used as wiring material instead of metals without secondary treatment. In comparison with the cells using the conventional metals, a few different properties were observed for those with organic electrodes. The differences are assignable to the difference between the organic–organic and the organic–inorganic contacts.
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double-barrier junction arrays for programmable voltage standards
Authors: Yamamori H. , Ishizaki M. , Itoh M. , Shoji A.
Published: July 2002

A series array of NbN/TiNx/NbN/TiNx/NbN double-barrier junctions was fabricated on Si wafers, and their current–voltage (I–V) characteristics were measured with and without microwave power in order to investigate their performance for programmable voltage standards. By adjusting the thickness of the TiNx barrier, nearly identical critical currents were obtained for 128 lower and 128 upper junctions in an array. When applying 8 GHz microwave power to an array, a large constant-voltage step (∼3 mA) appeared on the I–V curve. The zero-voltage critical current and the height of the first (n=1) constant-voltage step showed microwave-power dependences coincident with theoretical prediction.
From integrable nets to integrable lattices
Authors: Mañas Manuel
Published: July 2002

Inspired by the results of Jonas, Einsenhart, Demoulin, and Bianchi on the permutability property of classical geometrical transformations of conjugate nets and its reductions—of pseudo-orthogonal, pseudo-symmetric, and pseudo-Egorov types—dressing transformations of the N-component KP hierarchy (described within the Grassmannian) are used to generate quadrilateral lattices and its corresponding reductions. As a byproduct we get the corresponding discrete dressing transformations; in particular, we characterize the vectorial fundamental discrete transformations preserving the symmetric lattice.
Kinetics of surface relief gratings tailored by laser-induced photochemical deposition
Authors: Hugonnot Emmanuel , Delville Jean-Pierre
Published: July 2002

We theoretically describe and experimentally explore the real-time formation of gratings induced by photochemical deposition in liquids. Considering the diffusion and the surface adsorption on the deposit of photochemically produced molecules, we show that the pattern induced (1) is not necessarily an exact replica of the light intensity distribution and (2) can become thick. By implementing experiments with chromate solutions photoactivated by two interfering continuous wave Ar+ laser waves, we validate the model by analyzing the temporal behavior of the first three harmonics of the induced grating.
Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films
Authors: Kim Keunjoo , Chung Sang Jo
Published: July 2002

The thermal quenching of an infrared deep level of 1.2–1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF=0.1–0.15 eV above the valence band at a hole carrier concentration of 2.0–2.5×1017/cm3.
Trap-limited migration of vacancy-type defects in 7.5 keV H−-implanted Si
Authors: Deenapanray Prakash N. K.
Published: July 2002

We have investigated the generation and migration of defects in crystalline Si following their introduction at room temperature by low-energy hydrogen ions in a region confined to the near-surface region. The fluence dependence of free carrier compensation and creation of electrically active defects in the n-type samples was monitored by capacitance–voltage and deep level transient spectroscopy measurements, respectively. The defects were responsible for free carrier compensation to depths exceeding ∼1 μm beyond the top ∼0.25 μm region of samples where they were generated. We describe a close relationship between generation of the VO–H complex and the VP pair on the free carrier compensation.
Scanning probe microscopy of well-defined periodically poled ferroelectric domain structure
Authors: Shvebelman M. , Urenski P. , Shikler R. , Rosenman G. , Rosenwaks Y. , Molotskii M.
Published: July 2002

We analyze and determine the factors governing the contrast in contact mode atomic force microscopy of domain-structured ferroelectric crystals. The analysis is applied to measurements conducted on KTiOPO4 crystals with artificially created well-defined domain structure. It is found that the amplitude contrast is due to difference in the work functions of the antiparallel domains.
Neutron irradiation effects on visible-blind Au/GaN Schottky barrier detectors grown on Si(111)
Authors: Wang Ching-Wu
Published: July 2002

Neutron irradiation effects on the Au/sputtered–GaN Schottky barrier photodetectors grown on Si(111) were investigated. Evidence showed that the optimal fluence (1×1013 n/cm2) of neutron irradiation could not only promote the crystallinity of GaN films, but also effectively repress the occurrence of nitrogen–vacancy-related Et1 traps. We suggested that these two reasons are the main contributing factors to the superior rectifying current–voltage characteristics as well as the enhanced spectral response of Au/sputtered–GaN Schottky detectors.
Current transport in InP/In0.5(Al0.6Ga0.4)0.5P self-assembled quantum dot heterostructures using ballistic electron emission microscopy/spectroscopy
Authors: Reddy C. V. , Narayanamurti V. , Ryou J. H. , Dupuis R. D.
Published: July 2002

Ballistic electron emission microscopy/spectroscopy (BEEM/S) has been employed to image, inject, and investigate the current transport through self-assembled InP quantum dots embedded in InAlGaP barriers. The spectroscopy performed on the dot and off the dot revealed that the charge confinement within the dots is more effective than the leakage through the quasibound states. Evidence for the charge accumulation in the quantum dots is presented with the help of BEEM imaging as a function of the tip bias.
Broadband tuning and dual-spectral/temporal outputs from a nonresonantly injection-seeded diode laser
Authors: Birkin D. J. L. , Rafailov E. U. , Sibbett W.
Published: July 2002

We demonstrate spectral narrowing and continuous broadband tuning of the picosecond pulse outputs from a nonresonantly injection-seeded, gain-switched diode laser that can be operated in dual spectral/temporal regimes. A single spectral output was continuously tunable over a range of 85 nm and in a dual-wavelength operation the outputs had spectral separations were adjustable from 3.5 to 53 nm.
Extremely low critical cooling rate measured on dispersed Pd43Ni10Cu27P20
Authors: Schroers Jan , Johnson William L.
Published: July 2002

Crystallization of dispersed Pd43Ni10Cu27P20 melts is studied during constant cooling and heating. Investigations are carried out on samples that are dispersed into several hundred particles which are fluxed in B2O3. The size of the particles is chosen in such a way that crystallization of individual particles can be observed. Constant cooling experiments with rates between 0.3 and 0.0016 K/s are performed. In order to determine the fraction of particles that crystallize upon cooling, the crystallization during subsequent heating at 0.3 K/s is utilized. 10%–15% of the particles do not crystallize during cooling with a rate as low as 0.005 K/s. This is the lowest rate that avoids crystallization ever measured for a metallic system. This extremely low critical cooling rate suggests that a fraction of the particles do not contain the impurities that act as nuclei in bulk samples. Therefore, in these particles, nuclei first have to form and crystallization does not take place, as it was found for bulk Pd43Ni10Cu27P20, by the growth on pre-existing nuclei formed by impurities.
Influence of metalorganic chemical vapor deposition growth conditions on In-rich nanoislands formation in InGaN/GaN structures
Authors: Musikhin Yu. G. , Gerthsen D. , Bedarev D. A. , Bert N. A. , Lundin W. V. , Tsatsul’nikov A. F. , Sakharov A. V. , Usikov A. S. , Alferov Zh. I. , Krestnikov I. L. , Ledentsov N. N. , Hoffmann A. , Bimberg D.
Published: July 2002

The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4–5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects.
Concurrent evaluation of strain in heteroepitaxial thin films with continuous lattice mismatch spread
Authors: Ohtani M. , Fukumura T. , Kawasaki M. , Omote K. , Kikuchi T. , Harada J. , Koinuma H.
Published: July 2002

We have developed a way to map out concurrently the in-plane lattice constant of a heteroepitaxial thin film with a spatial resolution of 0.1 mm by using concurrent x-ray diffractometer equipped with a convergent x-ray source and two-dimensional detector. Spatial distribution of heteroepitaxial strain is analyzed for a (BaxSr1−x)TiO3 composition-spread thin film grown on a SrTiO3 substrate. As x increases, elastic deformation caused by compressive stress due to the lattice mismatch forces the lattice of the film to be coherent with that of the substrate until a critical point of x=0.6, above which the film lattice relaxes. By just taking three snap shots of x-ray diffraction image at a symmetric and two asymmetric diffraction configurations, such useful information inherent in heteroepitaxy can be revealed.
Tunable reflectance Mg–Ni–H films
Authors: Isidorsson J. , Giebels I. A. M. E. , Griessen R. , Di Vece M.
Published: July 2002

Mg 2 NiH x switchable mirrors, which switch from shiny metallic Mg2Ni to transparent Mg2NiH4, are shown to exhibit also dramatic reversible changes in reflectance at remarkably low hydrogen concentrations. Already for x≅0.3 a 232 nm thick Mg2NiHx film has an absorptance of ∼90% over the whole visible optical spectrum. The transition from highly reflective to black occurs in the concentration interval 0.1<x<0.3. The volume changes involved are one order of magnitude smaller than in the transition from reflecting to transparent. This is expected to enhance the lifetime of future devices based on these materials.
Tetragonal distortion of c domains in fatigued Pb(Zr,Ti)O3 thin films determined by x-ray diffraction measurements with highly brilliant synchrotron radiation
Authors: Kimura Shigeru , Izumi Koichi , Tatsumi Toru
Published: July 2002

We performed x-ray diffraction measurements by using highly brilliant synchrotron radiation on only a small region of 250-nm-thick Pb(Zr0.33Ti0.67)O3 polycrystalline films with gold top electrodes after applying various numbers of switching cycles of the electric field. The films were deposited on Pt/SiO2/Si substrates by low-temperature metalorganic chemical vapor deposition. The plane spacing and integrated intensity of 004 and 400 diffraction patterns were plotted against the number of switching cycles. We found a good correlation between the increase in 004-plane spacing and the decrease in remanent polarization. This correlation indicates that tetragonal distortion of c domains is closely related to the fatigue phenomenon.
Improved chemical stability of Ti-doped MgB2 in water
Authors: Zhao Y. , Cheng C. H. , Machi T. , Koshizuka N. , Murakami M.
Published: July 2002

We investigated the degradation of critical current density (Jc) and irreversibility field (Hirr) of pure and Ti-doped MgB2 bulks by exposing the samples to water for a total of 10, 48, 100, and 124 h. We found that both Jc and Hirr of the samples were degraded by exposure to water, in various degrees depending on the doping level. In the same exposure duration, the Ti-doped samples exhibited a less sensitivity to water, which was confirmed by the less degradation of Jc and Hirr. Our results demonstrate that Ti doping is not only effective in improving the superconducting properties of MgB2 but also in enhancing its chemical stability against water.
Dual-frequency quantum-cascade terahertz emitter
Authors: Menon V. M. , Goodhue W. D. , Karakashian A. S. , Naweed A. , Plant J. , Ram-Mohan L. R. , Gatesman A. , Badami V. , Waldman J.
Published: July 2002

We report the realization of a GaAs/AlGaAs quantum-cascade terahertz emitter capable of emitting at two entirely different frequencies from the same structure. This is realized through judicious wavefunction engineering of the relevant electronic states. Emission is observed at 6.32 meV (1.5 THz) and 12.18 meV (2.9 THz) with full width at half maximum of 0.72 meV and 0.58 meV, respectively, at T=10 K. The structure consisted of 40 periods of the quantum-cascade module. Emission occurred between two sets of distinct energy levels that came into the desired configuration at different biases due to the quantum-confined Stark effect. Higher-energy AlAs-like phonons were utilized for the depopulation mechanism.
First-principles study of transition-metal aluminates as high-k gate dielectrics
Authors: Haverty Michael , Kawamoto Atsushi , Cho Kyeongjae , Dutton Robert
Published: July 2002

The semiconductor industry is searching for a high-k gate dielectric replacement for silica. We study the electronic properties of Nb, Zr, Y, and Sc aluminates using density functional theory to screen aluminates for further study. The transition metals substituted favorably at the octahedral Al sites in the κ-alumina model system. Zirconium and niobium substitution for Al introduced localized d-electron states 0.6 and 1.1 eV below the conduction band. Yttrium and scandium introduced states 0.1 and 1.4 eV above the delocalized s and p states of the conduction band causing little change in the κ-alumina band gap and are promising replacement candidates that maintain the large alumina band offset.