bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppression of quasicrystallization by nonlinear viscous flow in Zr–Al–Ni–Cu–Pd glassy alloys
Authors: Saida J. , Ishihara S. , Kato H. , Inoue A. , Chen H. S.
Published: July 2002

The quasicrystallization at the initial stage under viscous flow at 673 K (20 K above the glass transition temperature) was investigated in a Zr65Al7.5Ni10Cu12.5Pd5 bulk glassy alloy. The compressive deformation at strain rates of 2×10−3 s−1 and 1×10−2 s−1 was subjected to the bulk glassy alloy for 60 s followed by the preannealing for 120 s for thermal equilibration in an Ar atmosphere. The glass undergoes Newtonian and non-Newtonian flow at the strain rates of 2×10−3 s−1 and 1×10−2 s−1, respectively. The linear viscous flow brings a significant decrease in the first exothermic peak in the differential scanning calorimetry (DSC) curve corresponding to the transformation from glassy to icosahedral phase, but is identical to that in the reference sample annealed for 180 s at 673 K without deformation. However, the number of icosahedral particles in the transmission electron microscopy image as well as the decrease of the first exothermic peak in the DSC curve in the nonlinear viscous flow is much less as compared with those in the linearly deformed and reference samples. These results indicate the suppression of the transformation from the glassy to icosahedral phase by the nonlinear viscous flow. The suppression of the transformation is suggested to be originated from the retardation of the growth by the stress-induced disordered atomic configuration in the glassy state during the nonlinear viscous flow.
Probing strained InGaN/GaN nanostructures with ultrashort acoustic phonon wave packets generated by femtosecond lasers
Authors: Yahng J. S. , Jho Y. D. , Yee K. J. , Oh E. , Woo J. C. , Kim D. S. , Sanders G. D. , Stanton C. J.
Published: July 2002

Large amplitude time-domain oscillations are detected in InxGa1−xN/GaN structures via femtosecond differential reflectivity spectroscopy. The oscillation amplitude increases with increasing indium fraction and abruptly disappears at a critical time that depends on GaN thickness. We show that spatially localized, coherent acoustic phonon wave packets are generated via the photoexcited carriers and propagate into the samples modulating the reflectivity. Our results show that a system with strong built-in strain can be a very effective source for ultrafast acoustic phonon wave packets which can be used as a powerful probe for nanoscale structures.
Brownian dynamics simulations of attractive polymers in solution
Authors: Xiao C. , Heyes D. M.
Published: July 2002

Brownian dynamics simulations have been carried out to model attractive polymers in solution. Bead–spring polymer chains with attractions between the end beads were modeled over a wide concentration range on either side of the overlap concentration, ρ*, for the corresponding random coil polymers. The polymers were treated as beads linked by finitely extensible nonlinear elastic springs and the excluded volume repulsion between unlinked beads was represented by a pair potential with a Gaussian analytic form. For the sticky end-beads the potential has an attractive tail of Gaussian form. In addition to chains with purely repulsive bead–bead nonbonded interactions, three different systems with attactive end beads were modeled. There were those with (a) head–head (H–H) attractions, (b) with both H–H and tail–tail (T–T) attractions, and (c) with head–tail (H–T) attractions. The dimensions of the chains, the bead–bead radial distribution functions, as well as the dynamic properties such as stress tensor time-correlation functions, infinity frequency elastic modulus, and specific viscosity of the solution were calculated as functions of solution density and end-bead attraction class. We show that with the three classes of attractive end-bead functionality, the model polymers all depart from random coil statistics and show evidence of enhanced association, even in the dilute regime, especially for the H–T systems, which can form necklacelike structures at low dilution and micellelike states with increasing concentration. (Not all of the polymer statistics measures show major differences though.) However, only the rheology if the H–T system is markedly different from the random coil case. The rheology of the H–T system is quite different in qualitative and quantitative behavior to the other classes studied. There is a progressive retardation and increasingly near-exponential decay in the shear stress relaxation function. The viscosity of the H–T class of polymers is typically at least an order of magnitude higher than that of the others, even at concentrations far below the overlap concentration ρ* for such polymers. The infinite frequency elastic modulus is also typically about five times larger for the H–T class across the density range when compared with the other three types modeled.
Giant magnetoresistance in laser-deposited permalloy/Ag multilayers
Authors: Faupel Jörg , Krebs Hans-Ulrich , Käufler Andrea , Luo Yuansu , Samwer Konrad , Vitta Satish
Published: July 2002

Giant magnetoresistance (GMR) of 3.5% in low fields of about 10 Oe was observed at room temperature in as-prepared laser-deposited Ni80Fe20/Ag (permalloy/Ag) multilayers. Strong columnar growth in combination with preferential sputtering of Ag from the film surface during deposition of Ni80Fe20 layer helps to directly create a discontinuous multilayer structure necessary for high GMR values. The magnetoresistance was found to increase to 5.1% after annealing for just 10 min at 275 °C. This increase is attributed to structural relaxation processes such as demixing of the intermixed interfaces, preferential diffusion of Ag to the column boundaries and reduction of structural defects. Pulsed laser deposition appears to be a suitable technique for the preparation of permalloy/Ag films with considerable GMR in a one-step process.
Electromagnetic and absorption properties of some microwave absorbers
Authors: Yusoff A. N. , Abdullah M. H. , Ahmad S. H. , Jusoh S. F. , Mansor A. A. , Hamid S. A. A.
Published: July 2002

Electromagnetic properties of a thermoplastic natural rubber (TPNR), a lithium–nickel–zinc (Li–Ni–Zn) ferrite and a TPNR–ferrite composite subjected to transverse electromagnetic (TEM) wave propagation were investigated. The incorporation of the ferrite into the matrix of the TPNR was found to reduce the dielectric loss but the magnetic loss increased. The absorption characteristics of all the samples subjected to a normal incidence of TEM wave were investigated based on a model of a single-layered plane wave absorber backed by a perfect conductor. It is evident from a computer simulation that the ferrite is a narrowband absorber, whereas the polymeric samples show broadband absorption characteristics. Minimal reflection of the microwave power or matching condition occurs when the thickness of the absorbers approximates an odd number multiple of a quarter of the propagating wavelength. This is discussed as due to cancellation of the incident and reflected waves at the surface of the absorbers. The Li–Ni–Zn ferrite exhibits another matching condition at low frequency when the magnitude of the complex relative dielectric permittivity (εr*) equals that of the complex relative magnetic permeability (μr*). The specular absorber method provides a simple theoretical graphic aid for determining the absorption characteristics and the location of the matching conditions in the frequency domain. The result for the ferrite sample was tested and confirmed directly from terminated one-port measurements.
Influence of the magnetic tip in ferromagnetic resonance force microscopy
Authors: Charbois V. , Naletov V. V. , Youssef J. Ben , Klein O.
Published: July 2002

We compare mechanically detected ferromagnetic resonance spectra for different separations h between the magnetic tip and sample surface. When the bias field generated by the tip is smaller than a few hundred gauss, the prominent changes are shifts of the entire spectrum (without line shape distortions) to higher frequency as h decreases. These results are in agreement with the Damon and Eshbach model for spin waves propagating in a potential perturbed by the additional field of the probe magnet. It is used to predict the spatial resolution limit for magnetostatic modes bounded by the stray field of the tip. The answer is ∼4 μm for yttrium iron garnet.
Height-controlled InAs quantum dots by using a thin InGaAs layer
Authors: Kim Jin Soo , Yu Phil Won , Lee Joo In , Kim Jong Su , Kim Song Gang , Leem Jae-Young , Jeon Minhyon
Published: July 2002

The structural and optical properties of height-controlled InAs quantum dots (QDs) have been investigated by transmission electron microscopy (TEM) and photoluminescence (PL). By depositing 1.4 nm In0.15Ga0.85As and a 1 monolayer (ML) InAs layer with different periods on 3 ML InAs QDs, the height of InAs QDs was systematically controlled with similar lateral size. In TEM images, the indication of dislocations due to the large strain, which can be easily seen in large QDs, is not observed even for the QD sample with the highest aspect ratio (height/width). The PL peak position is shifted toward the longer wavelength with an increase in the aspect ratio of QDs. As the aspect ratio is increased, the full width at half maximum in PL measured at 10 K is decreased from 71 to 34 meV indicating that the inhomogeneous broadening caused by the fluctuation in QD size, especially the height, is significantly reduced.
Controlled transport of latex beads through vertically aligned carbon nanofiber membranes
Authors: Zhang L. , Melechko A. V. , Merkulov V. I. , Guillorn M. A. , Simpson M. L. , Lowndes D. H. , Doktycz M. J.
Published: July 2002

Stripes of vertically aligned carbon nanofibers (VACNFs) have been used to form membranes for size selectively controlling the transport of latex beads. Fluidic structures were created in poly(dimethylsiloxane) (PDMS) and interfaced to the VACNF structures for characterization of the membrane pore size. Solutions of fluorescently labeled latex beads were introduced into the PDMS channels and characterized by fluorescence and scanning electron microscopy. Results show that the beads size selectively pass through the nanofiber barriers and the size restriction limit correlates with the interfiber spacing. The results suggest that altering VACNF array density can alter fractionation properties of the membrane. Such membranes may be useful for molecular sorting and for mimicking the properties of natural membranes.
Low-resistivity, p-type SiC layers produced by Al implantation and ion-beam-induced crystallization
Authors: Heera V. , Madhusoodanan K. N. , Mücklich A. , Panknin D. , Skorupa W.
Published: July 2002

Low-resistivity (<0.1 Ω cm), p-type SiC layers of about 500 nm width and targeted acceptor concentrations of 1.5×1020 cm−3 and 5.0×1020 cm−3 were produced by the combination of high-dose (1.0 and 3.3×1016 cm−2), multienergy (50–450 keV) Al+ ion implantation of 6H-SiC at −130 °C, ion-beam-induced crystallization with 500 keV, 5×1015 Si+ cm−2 at 500 °C and subsequent furnace annealing at 1500 °C for 10 min. The implanted SiC layers have a nanocrystalline structure consisting of randomly oriented grains of mainly 3C-SiC. The electrical properties of the doped, nanocrystalline layers were investigated by sheet resistance and Hall measurements in dependence on temperature and compared with results from single-crystalline reference samples. In comparison with the standard doping process, the hole concentration at 50 °C is enhanced by more than one order of magnitude from 9.0×1017 cm−3 to 1.6×1019 cm−3 in the case of 1.5×1020 Al cm−3 and from 6.1×1018 cm−3 to 8.0×1019 cm−3 in the case of 5.0×1020 Al cm−3, respectively. It can be speculated that the loss of active Al acceptors by precipitation is reduced in the nanocrystalline layers and, therefore, the critical concentration for the formation of an impurity band can be achieved.
Simulation of light propagation in two-dimensional photonic crystals with a point defect by a high-accuracy finite-difference time-domain method
Authors: Yamada S. , Watanabe Y. , Katayama Y. , Yan X. Y. , Cole J. B.
Published: July 2002

A high-accuracy finite-difference time-domain method based on what are called nonstandard finite differences was used to simulate optical propagation in a two-dimensional photonic crystal with a point defect. We used a photonic crystal consisting of a triangular lattice of air columns embedded in a high-refractive index medium. We found that the transmittance spectrum has four peaks in the photonic band-gap region, and that these peaks correspond to the resonant energies of light localized at the point defect. For a point defect consisting of an air hole with a radius smaller than that of the air holes of the photonic crystal, these peaks shift to higher energy. The peak shift of the resonant mode that is associated with the electric field concentrated about the center of the point defect is larger than the peak shift of the other modes.
Close to midgap trapping level in Co60 gamma irradiated silicon detectors
Authors: Pintilie I. , Fretwurst E. , Lindström G. , Stahl J.
Published: July 2002

The deep level transient spectroscopy method was applied on standard and oxygenated float-zone silicon detectors exposed to high doses of Co60–gamma irradiation. We have detected and characterized a close to midgap trapping level having an ionization energy of EC−(0.545±0.005) eV and electron/hole capture cross sections of σn=(1.7±0.2)×10−15 cm2/σp=(9±1)×10−14 cm2 respectively. This level has a strong impact on the detector performance being responsible for more than 90% of the change in the effective doping concentration. The defect is strongly oxygen related and a possible connection with the V2O complex is discussed.
Energy and temperature dependence of electron effective masses in silicon
Authors: Cavassilas Nicolas , Autran Jean-Luc , Aniel Frédéric , Fishman Guy
Published: July 2002

A k⋅p model is used to theoretically investigate the energy and lattice temperature dependence of both transverse and longitudinal “curvature” electron effective masses in silicon. The temperature dependence of the carrier concentration conduction effective masses in the range of 10–550 K is also examined. Our results highlight the energy dependence of the longitudinal effective mass, usually considered to be equal to the band-edge effective mass, which varies from 0.917 to 1.6m0 when the carrier energy ranges from the bottom of the conduction band up to 1.5 eV. This energy dependence should have a significant impact on electronic transport simulations using drift–diffusion, hydrodynamic, or Monte Carlo methods, particularly for hot-carrier phenomena in microelectronic devices.
Study on capacitance-voltage properties of Bi2Ti2O7/n-Si (100) films
Authors: Wang Shao-Wei , Lu Wei , Chen Xiao-Shuang , Dai Ning , Shen Xue-Chu , Wang Hong , Wang Min
Published: July 2002

The capacitance-voltage (C–V) behavior of the metal/Bi2Ti2O7/n-Si metal–oxide–semiconductor (MOS) structure has been studied. The analyses of C–V curves show that a high builtin voltage of 11 V on Si can be achieved by bias-temperature (BT) process. The hysteresis loops in C–V curves of the MOS structure were also observed clearly. From the dependence of C–V properties on different BT processes, it is deduced that the hysteresis loops are dominated by the mobile negative charges in the oxide.
Mixing effects of light and heavy rare earths in the Laves phase compounds Nd1−xTbxCo2
Authors: Ouyang Z. W. , Rao G. H. , Yang H. F. , Liu W. F. , Liang J. K.
Published: July 2002

The lattice constant and magnetic properties of compounds Nd1−xTbxCo2 were investigated by x-ray power diffraction and magnetic measurements. The lattice constant and Curie temperature show linear variations with the Tb concentration, while the saturation moment exhibits an anomaly at a critical concentration xc≈0.33. The compounds exhibit a field-induced metamagnetic transition from a weak ferrimagnetism to a strong ferrimagnetism in the vicinity of xc.
High-efficiency polymer light-emitting devices using organic salts: A multilayer structure to improve light-emitting electrochemical cells
Authors: Lee Tae-Woo , Lee Ho-Chul , Park O. Ok
Published: July 2002

Balanced charge injection in polymer light-emitting devices is very important for high brightness and quantum efficiency. To improve the well-known light-emitting electrochemical cells (LECs), we fabricated multilayer electroluminescent devices employing an ammonium salt-containing poly(ethylene oxide) blend as hole- or electron-injecting materials. The charge injection can be greatly promoted due to the ionic space charges near both electrodes. The current–voltage–optical output characteristics of the triple-layer device using both the hole- and the electron-injecting layers are very similar to the well-known LEC devices. We obtained high quantum efficiencies of 0.9% and 1.5% photons/electron in forward- and reverse-bias field of the triple-layer device, respectively.
Formation of epitaxial CoSi2 films on Si and on Si/Si80Ge20 (100) by reactive deposition epitaxy
Authors: Pető G. , Molnár G. , Kótai E. , Dézsi I. , Karsteen M. , Södervall U. , Willander M , Caymax M. , Loo R.
Published: July 2002

Co x Ti 1−x layers were deposited on Si (100) and on Si/Si80Ge20 (100) capped with 30- or 40-nm-thick Si at 650 °C substrate temperature at 1×10−6 Pa pressure. The Co–silicide films grown by reactive deposition epitaxy were characterized by Rutherford backscattering-channeling, x-ray difraction, by depth profile analysis of the components, and by sheet resistance measurements. The Ti content of the deposited Co layers was between 0.1 and 8 at. %. The epitaxy of the layers on Si and on Si/Si80Ge20 improved by increasing the Ti concentration. The minimum yield of the channeling and the full width at half maximum value of the rocking curve of CoSi2 decreased. The sheet resisitance of the formed layers was also minimal in these cases. The method applied is promising to form epitaxial CoSi2 layers on SixGe1−x substrates.
Hole and electron transport in strained Si: Orthorhombic versus biaxial tensile strain
Authors: Bufler F. M. , Fichtner W.
Published: July 2002

Linear, nonlinear, and ballistic transport of holes and electrons in orthorhombically strained Si is theoretically analyzed at 300 K and compared with the results in biaxially tensily strained Si. At a Ge content of 30% in the strain-defining SiGe layer a drift mobility of about 1230 cm2/(V s) is found for holes under orthorhombic strain versus 1750 cm2/(V s) for tensile strain, while the stationary velocity in the nonlinear regime as well as the velocity overshoot peak are approximately the same. In the case of electrons, there is almost no difference between orthorhombic and tensile strain.
Midinfrared IV–VI vertical-cavity surface-emitting lasers with zero-, two-, and three-dimensional systems in the active regions
Authors: Fürst J. , Pascher H. , Schwarzl T. , Böberl M. , Heiss W. , Springholz G. , Bauer G.
Published: July 2002

A comparison between IV–VI vertical-cavity surface-emitting midinfrared lasers containing active regions of different dimensionality is presented. Optically pumped laser emission is observed at wavelengths between 3.5 and 4.4 μm. The microcavities consist of high-reflectivity EuTe/PbEuTe Bragg mirrors, with active regions consisting either of a self-organized PbSe/PbEuTe quantum-dot superlattice, PbTe/PbEuTe multiquantum wells, or bulk-like PbTe. For the zero dimensional active medium, laser emission is obtained at temperatures up to 150 K. The results for the lasers with two-dimensional active region are similar to those with the three-dimensional bulk-like active region, for which lasing is observed up to 317 K. The threshold pump intensity is only 4 kW/cm2 at 195 K, and 15.6 kW/cm2 at room temperature.
Electron energy deposition in an electron-beam pumped KrF amplifier: Impact of the gas composition
Authors: Giuliani J. L. , Petrov G. M. , Dasgupta A.
Published: July 2002

Calculations for electron deposition in electron beam generated KrF laser at atmospheric pressure have been performed. The impact of the Ar/Kr/F2 gas mixture on the electron energy distribution function, electron density, and mean energy, energy per electron–ion pair, attachment, dissociation, excitation, and ionization rates have been investigated. The F2 abundance controls the low energy (≲9 eV) component of the distribution function, while both the fluorine and krypton mole fraction affect the distribution in the midenergy domain (9 to ∼25 eV). Consequently, the F2 attachment rate coefficient varies with the F2 mole fraction (xF2) such that the electron density scales as 1/xF20.7. The rate coefficient for direct dissociation of F2 is smaller than for attachment but the former contributes more to the total power dissipation (∼8% at xF2=0.01). The excitation-to-ionization ratio for Kr is not constant, as generally assumed, but increases by a factor of two with a decrease in either the Kr or F2 abundance. Combining the former and present investigations leads to a set of fitting formulas to be used in beam kinetics codes for various collision rates as a function of both the electron beam power density and the composition.
Low field magnetoresistance at the metal–insulator transition in epitaxial manganite thin films
Authors: de Andrés A. , Taboada S. , Colino J. M. , Ramı́rez R. , Garcı́a-Hernández M. , Martı́nez J. L.
Published: July 2002

We present a study of the magnetotransport behavior around Tc of epitaxial La0.7Ca0.3MnO3 thin films with controlled chemical defects introduced in order to change the electron-lattice coupling (λ). We found unexpected enhancement of the very low field (below 250 Oe) magnetoresistance around Tc and relate it to a reduction of the magnetic domain size. This process is strongly favored by the presence of chemical defects that also promote weak localization of the carriers into polaron clusters that can be overcome by relatively low magnetic fields. This behavior is characteristic of temperatures near Tc where the bandwidth is reduced and localization, due to intrinsic disorder and chemical defects, is more probable. In addition, the increase of λ raises the polaron binding energy and reduces the temperature at which percolation occurs.
Effect of the nano-oxide layer as a Mn diffusion barrier in specular spin valves
Authors: Jang S. H. , Kang T. , Kim H. J. , Kim K. Y.
Published: July 2002

In previous work an enhanced giant magnetoresistance (GMR) effect in spin valves (SVs) with a nano-oxide layer (NOL) after annealing at about 250–300 °C has been reported. We have shown that SVs with a NOL also have higher thermal stability of the MR ratio at 300 °C. From secondary-ion-mass spectroscopy and x-ray photoelectron spectroscopy depth profile analysis, the mechanism of the improved thermal stability of the SVs with a NOL is shown to be related to MnO formation within the NOL. Thus, Mn atoms from the FeMn layer are trapped, and Mn diffusion is inhibited by the NOL during annealing.
Evidence of noble metal diffusion in polymers at room temperature and its retardation by a chromium barrier
Authors: Thran A. , Strunskus T. , Zaporojtchenko V. , Faupel F.
Published: July 2002

Recent applications of organic low-k dielectrics in microelectronics have stimulated many investigations of metal diffusion in polymers. Here we report results from radiotracer measurements of110mAg diffusion in trimethylcyclohexane polycarbonate. Serial sectioning was carried out with 190 eV krypton ions in and opposite to the diffusion direction to rule out sputtering artifacts. Ag was found to be strongly immobilized by self aggregation. In contrast to earlier reports, however, trace amounts of Ag were clearly seen to diffuse into the polymer even at room temperature. A chromium film of only one tenth of a monolayer turned out to be an effective diffusion barrier.
Optical properties of gallium oxide thin films
Authors: Rebien M. , Henrion W. , Hong M. , Mannaerts J. P. , Fleischer M.
Published: July 2002

The optical functions of β-Ga2O3 thin films have been determined by ellipsometry from 0.74–5 eV. Several electron-beam evaporated and rf magnetron sputtered films of different thicknesses were investigated using a multisample technique. Refractive index values comparable to those of bulk material are found. Cauchy dispersion model fits yield a high-frequency dielectric constant ε∞ of 3.57. Above 4.7 eV a direct absorption edge is observed.
Strain-relieved Ba0.6Sr0.4TiO3 thin films for tunable microwave applications
Authors: Chang Wontae , Kirchoefer Steven W. , Pond Jeffrey M. , Horwitz James S. , Sengupta Louise
Published: July 2002

This article discusses tunable dielectric thin films, with particularly emphasis on strain-relieved and defect-reduced tunable dielectric thin films that significantly reduce dielectric loss at microwave frequencies. Ba0.6Sr0.4TiO3 (BST) thin films (∼0.3 μm thick) were deposited onto (100) MgO single crystalline substrates by pulsed laser deposition at 750 °C and 200 mTorr O2 with a nominal 600-Å-thick BST buffer layer. These films were observed to be strain relieved and show better dielectric properties by exhibiting a significantly high dielectric Q(=1/tan δ>100) while retaining a useful dielectric tuning (=[C(0)–C(23 V/μm)]/C(0)>20%, where C is the film capacitance) at 8 GHz compared to strained BST thin films. The BST buffer layer could be composed of any porous BST phase with randomly oriented grains between a nearly amorphous phase and a fully crystalline phase. A further increase in the dielectric Q was observed in strain-relieved BST thin films mixed with MgO and strain-relieved BST thin films doped with W.
Low resistivity TiSi2 on narrow p+ polycrystalline silicon lines
Authors: Herner S. B. , Vyvoda M. A.
Published: July 2002

We have achieved low resistivity TiSi2 on 0.25 μm wide polysilicon lines doped to 5×1020/cm3 with boron by use of in situ doping of polysilicon. By controlling the Si deposition such that an amorphous undoped “cap” was deposited on p+ polycrystalline Si (polysilicon) subsequently formed TiSi2 wires had a lower resistivity consistent with C54 phase formation, while maintaining direct contact between TiSi2 and p+ Si. When TiSi2 was formed directly on p+ polysilicon, it had increasing resistivity as the linewidth decreased below 0.5 μm. The mechanism for lower resistivity TiSi2 is attributed to an increased density of C49-to-C54 phase transformation sites when the silicide is formed on amorphous undoped silicon.
Transport and solidification phenomena in molten microdroplet pileup
Authors: Haferl S. , Poulikakos D.
Published: July 2002

This article presents a predominantly numerical investigation of the transient transport phenomena occurring during the pileup (deposition one upon another) of molten, picoliter-size liquid metal droplets relevant to a host of novel micromanufacturing processes. The investigated phenomena last fractions of a millisecond in severely deforming domains of typical size of a small fraction of a millimeter. The prevailing physical mechanisms of the pileup process (occurring simultaneously) are identified and quantified numerically. These are the fluid mechanics of the bulk liquid, capillarity effects at the liquid–solid interface, heat transfer, solidification, and thermal contact resistance effects at all interfaces. In terms of values of the Reynolds, Weber, and Stefan number the following ranges are covered: Re=281–453, We=2.39–5.99, and Ste=0.187–0.895. This corresponds to molten solder droplets impinging at velocities ranging between 1.12 and 1.74 m/s having an average diameter of ≈78 μm. The initial substrate temperature ranges between 25 and 150 °C. The initial droplet temperature is 210 °C. The numerical model presented is based on a Lagrangian formulation of the Navier–Stokes equations accounting for surface tension, thermal contact resistance, solidification, and a Navier slip condition at the dynamic contact line. Results of simulations are presented showing the effect of thermal contact resistance and slip at the dynamic contact line on the transients and the outcome of a pileup. Comparisons of the simulated pileup with experimental visualizations are shown, demonstrating good agreement in cases where inertia dominates over capillary effects. For decreasing Stefan number (i.e., higher substrate temperatures) an increasing importance of wetting is observed. For these cases the limitations of the employed popular boundary condition at the dynamic contact line is demonstrated and the need for experimental data (currently nonexistent in the literature) that would yield an improved condition at the contact line accounting for the temperature dependence of wetting phenomena is underpinned.
Conduction mechanism of Si single-electron transistor having a one-dimensional regular array of multiple tunnel junctions
Authors: Nakajima Anri , Ito Yuhei , Yokoyama Shin
Published: July 2002

Uniformly doped Si single-electron transistors consisting of a one-dimensional regular array of multiple tunnel junctions (MTJs) and islands have been fabricated. The Coulomb blockade effect is found to play an important role in carrier conduction in the MTJ system at low temperatures (6 K). The conduction mechanism can be interpreted well by considering soliton. The soliton extends less than three islands in our MTJs, and the energy of a single soliton is found to be 0.024 eV from an analysis of low-temperature current–voltage characteristics. For high-temperature operation, it is effective to reduce the parasitic capacitance of each island, which leads to an increase in soliton length.
Wide-range tuning of the two-dimensional confinement in V-groove quantum wires
Authors: Otterburg T. , Lelarge F. , Rudra A. , Kapon E.
Published: July 2002

We investigate how and to what extent the one-dimensional (1D) subband separation of V-groove GaAs/AlGaAs quantum wires (QWRs) can be tuned in a controlled way without compromising the wire uniformity and interface quality. Our results demonstrate that high quality V-groove QWRs with subbands separation up to ∼3kBTroom (ΔE=80 meV) can be obtained. The ratio between the subband separation and the inhomogeneous broadening of the QWRs emission line, extracted from low-temperature photoluminescence and photoluminescence excitation spectra, is as large as 7.1. Finally, we show that the 1D features in the optical spectra are maintained up to 300 K, making these QWRs suitable for room temperature device application.
Intrinsic stress development in Ti–C:H ceramic nanocomposite coatings
Authors: Shi B. , Meng W. J. , Rehn L. E. , Baldo P. M.
Published: July 2002

The development of intrinsic stresses within titanium-containing hydrocarbon (Ti–C:H) nanocomposite coatings was monitored during growth by in situ substrate curvature measurements using a multibeam optical sensing technique. Stress as a function of coating thickness was measured in a wide range of specimens, from nearly pure amorphous hydrocarbon (a-C:H) to nearly pure titanium carbide (TiC). The intrinsic stress within the nanocomposite coating was found to vary significantly in magnitude, and to depend systematically on the Ti composition. The observed stress variation as a function of the Ti composition correlates well with a previously reported percolation-type transition in the coating microstructure.
Growth kinetics of AlGaN films by plasma-assisted molecular-beam epitaxy
Authors: Iliopoulos E. , Moustakas T. D.
Published: July 2002

In this letter, we report on the kinetics of growth of aluminum gallium nitride films by rf plasma-assisted molecular-beam epitaxy on (0001) sapphire substrates at the temperature range of 750–800 °C. The determination of the incorporation probabilities of aluminum and gallium atoms was arrived at by measurements of the growth rate and composition of the films. We find that, in both the nitrogen-rich and group-III-rich growth regimes, the incorporation probability of aluminum is unity for the entire investigated temperature range. On the other hand, the incorporation probability of gallium is constant and equals 0.75 at a substrate temperature of 750 °C only in the nitrogen-rich growth regime. The temperature dependence of the incorporation probability in this regime has an activation energy of 2.88 eV which is consistent with gallium desorption from the surface. In the group-III-rich growth regime, the incorporation probability of gallium decreases monotonically with group-III fluxes due to the competition with aluminum for the available active nitrogen. In this regime, the GaN phase growth rate is determined by the capture probability of the available active nitrogen from the gallium surface adlayer.
Transmission electron microscopy evidence for phase transformation from Bi2Sr2CuO6 to Bi2Sr2Ca2Cu3O10
Authors: Chen W. M. , Li G. , Jiang S. S. , Ling H. Y. , Yao P. , Qin M. J. , Liu H. K. , Dou S. X.
Published: July 2002

The growth mechanism of the Bi-2223 phase was studied using multifilamentary Ag/Bi-2223 tapes manufactured by the powder-in-tube method. X-ray powder diffraction was performed to analyze the developments of Bi-2201, Bi-2212, and Bi-2223 phases during sintering periods at high temperatures. Transmission electron microscopy (TEM) was used to investigate the growth mechanism of the 2223 phase. TEM images indicated that 2201 and Ca2CuO3 crystals come together to form platelets of 2223. The structural phase transformation established a structural frame of the 2223 crystal. There were some vacant defects retaining in the established 2223 crystal cells at copper and oxygen sites after the phase transformation, and the Cu/O compound at high temperatures would diffuse into 2223 cells and occupy the corresponding vacancies to complete the 2223 crystal structure. The present work provides an evidence for growing the 2223 phase from the 2201 phase and Ca2CuO3 in the samples studied.
Two-dimensional array of self-assembled AlInAs quantum wires
Authors: Francoeur S. , Norman A. G. , Mascarenhas A. , Jones E. D. , Reno J. L. , Lee S. R. , Follstaedt D. M.
Published: July 2002

We present the optical and structural characterization of a two-dimensional array of self-organized AlInAs quantum wires. The structure was created by epitaxially stacking along the [001] direction thin self-assembled, [100]-oriented, superlattices separated by homogeneous layers of Al0.48In0.52As. Vertical and lateral self-alignment results in a highly regular array of wires oriented along the [010] direction. The wire cross-sectional dimensions are about 10×14.4 nm2 and their density is 1.9×1011 cm−2. The energy and the nature of the electronic transitions are significantly affected by confinement in two dimensions: (1) a blueshift of about 100 meV is observed and (2) the two lowest energy transitions are both polarized along the [010] direction. For comparison, the two lowest energy transitions of a lateral superlattice with similar characteristics have a heavy- (polarization along [010]) and a light-hole character (polarization along [100]). Large polarization ratios are measured for both transitions.
Point-defect influence on 1/f noise in HgCdTe photodiodes
Authors: Mainzer N. , Lakin E. , Zolotoyabko E.
Published: July 2002

We found experimentally a linear dependence between the 1/f noise power in the HgCdTe photodiodes and the fraction of ionized Hg vacancies in the HgCdTe layer. The number and sign of charge carriers were deduced from Hall measurements. Total point-defect concentrations were extracted by using a combination of high-resolution x-ray diffraction for precise measurements of lattice parameters and Fourier transform infrared transmission for determination the Cd content. Experimental findings support the theoretical model recently developed by Grüneis [F. Grüneis, Physica A 282, 108 (2000); 290, 512 (2001)].
Room-temperature polariton lasers based on GaN microcavities
Authors: Malpuech Guillaume , Di Carlo Aldo , Kavokin Alexey , Baumberg Jeremy J. , Zamfirescu Marian , Lugli Paolo
Published: July 2002

The critical temperature for Bose condensation of exciton polaritons in an AlGaN microcavity containing 9 GaN quantum wells is calculated to be T=460 K. We have modeled the kinetics of polaritons in such a microcavity device using the two-dimensional Boltzmann equation. Room-temperature lasing is found with a threshold as small as 100 mW. The kinetic blocking of polariton relaxation that prevents formation of the Bose-condensed phase of polaritons at low temperatures disappears at high temperatures, especially in n-doped samples. Thus, GaN microcavities are excellent candidates for realization of room-temperature polariton lasers.
Room temperature type-II interband cascade laser
Authors: Yang Rui Q. , Bradshaw J. L. , Bruno J. D. , Pham J. T. , Wortman D. E. , Tober R. L.
Published: July 2002

A mid-IR (3.3–3.5 μm) type-II interband cascade laser has been demonstrated at temperatures up to 300 K in pulsed mode and 150 K in cw mode. Threshold current densities as low as 13.2 A/cm2 and power efficiencies as large as 17% have been achieved under cw conditions at 80 K.
Midinfrared pump–probe reflection spectroscopy of the coupled phonon–plasmon mode in GaN
Authors: Nagai Masaya , Ohkawa Kazuhiro , Kuwata-Gonokami Makoto
Published: July 2002

Strong photoinduced reflectivity change in the midinfrared region in GaN is observed by femtosecond pump–probe measurements. By comparing the results of simultaneous emission and reflectivity measurements, we show that midinfrared reflectivity spectra are governed by coupled phonon-plasmon modes and spatial inhomogeneity of carrier density. Even when the plasma frequency lies in the far infrared region at low carrier density of 1018 cm−3, the strong plasmon–phonon coupling drives the position of upper phonon–plasmon mode to midinfrared region, allowing us to investigate dynamics of photogenerated free carriers in GaN-based materials by midinfrared reflectivity measurements.
Effect of Li diffusion on the domain inversion of LiNbO3 prepared by vapor transport equilibration
Authors: Chen Yunlin , Xu Jingjun , Kong Yongfa , Chen Shaolin , Zhang Guangyin , Wen Jianping
Published: July 2002

LiNbO 3 crystals with a composition close to stoichiometry were prepared by using a vapor transport equilibration (VTE) technique. The influence of the intrinsic defect density in the electric field periodic poling LiNbO3 crystal is studied. The switching field is found to decrease with the intrinsic defects. The reduction of intrinsic defects is mainly due to a change in the Li/Nb ratio in the LiNbO3 crystal, as a result of lithium diffusion during the VTE process. The switching field of ∼2 kV/mm in stoichiometric LiNbO3 is about one fourth of the previously published results obtained with near-stoichiometric crystals, and is approximately one tenth of the conventional congruent field. Periodic poling of thicker stoichiometric substrates was successfully performed by means of an electric field poling process at room temperature.
Boron suboxide: As hard as cubic boron nitride
Authors: He Duanwei , Zhao Yusheng , Daemen L. , Qian J. , Shen T. D. , Zerda T. W.
Published: July 2002

The Vickers hardness of boron suboxide single crystals was measured using a diamond indentation method. Under a loading force of 0.98 N, our test gave an average Vickers hardness of 45 GPa. The average fracture toughness was measured as 4.5 MPa m1/2. We also measured the hardness of the cubic boron nitride and sapphire single crystals for comparison. The average measured hardness for boron suboxide was found to be very close to that of cubic boron nitride under the same loading force. Our results suggest that the boron suboxide could be a new superhard material for industrial applications, surpassed in hardness only by diamond and cubic boron nitride.
Real-time optoacoustic imaging using a Schlieren transducer
Authors: Niederhauser J. J. , Frauchiger D. , Weber H. P. , Frenz M.
Published: July 2002

Optoacoustics, which combines the merits and most compelling features of light and sound, is a technique for diagnosing optical tissue properties and for performing noninvasive medical imaging. We present a detection method based on Schlieren optical imaging used to record optoacoustic waves generated with 6 ns long laser pulses. These waves result from irradiation of optically absorbing targets hidden deep inside highly scattering media. Since they are generated from one single shot, Schlieren images contain all the information necessary for the reconstruction of the absorbing structures. The detection method allows on-line imaging with a spatial resolution of about 30 μm with high contrast. The proposed real-time imaging system not only enhances the level of visible detail but it is ideally suited for monitoring dynamic tissue changes.
Local environment surrounding magnetic impurity atoms in a structural phase transition of Co-doped TiO2 nanocrystal ferromagnetic semiconductors
Authors: Soo Y. L. , Kioseoglou G. , Kim S. , Kao Y. H. , Devi P. Sujatha , Parise John , Gambino R. J. , Gouma P. I.
Published: July 2002

The local environment surrounding magnetic impurity atoms and the host crystal structure of codoped TiO2 (TiO2:Co) nanocrystal ferromagnetic semiconductors have been investigated using the x-ray absorption fine structure and powder diffraction techniques. It has been found that the magnetic Co impurity atoms substitute for the Ti sites in an anataselike local environment through a structural phase transition when the material changes from an amorphous phase to a mixture of anatase and rutile crystal structures and then to a rutile structure as a result of increasing the anneal temperature. This result reveals an interesting feature that the local structure around magnetic impurity atoms can remain practically unchanged while the material undergoes drastic structural variations and a loss of room-temperature ferromagnetism.
Random exchange-type electro-optic behavior of Pb0.865La0.09(Zr0.65Ti0.35)O3 relaxor ferroelectrics
Authors: Kim Dal-Young , Choi Jong-Jin , Kim Hyoun-Ee
Published: July 2002

Random exchange nature of Pb0.865La0.09(Zr0.65Ti0.35)O3 relaxor ferroelectrics was revealed by electro-optic study. Time decay behavior of birefringence was measured after switching off the external bias field, and showed random exchange-type behavior. Specific heat behavior was also obtained from the temperature derivatives of birefringence, and its critical exponent was α=−0.09 as predicted by the random exchange Ising model. We think the random exchange interaction is induced by nonpolar La ions and vacancies.
Capacitance–voltage studies of Al-Schottky contacts on hydrogen-terminated diamond
Authors: Garrido J. A. , Nebel C. E. , Stutzmann M. , Snidero E. , Bergonzo P.
Published: July 2002

The electrical properties of Al contacts on hydrogen-terminated diamond have been characterized. Capacitance–voltage experiments were carried out in order to obtain further insight into the origin of the Schottky contact behavior of Al. Schottky diodes with different areas and peripheries were fabricated and analyzed. We have found that the capacitance of these structures is not proportional to the area but to the length of the contact periphery, supporting the two-dimensional nature of the surface charge layer in hydrogen-terminated diamond. A model based on the negative electron affinity of hydrogen-terminated diamond and the work function of Al is used to explain the in-plane capacitance of the Al Schottky contacts.
Genetic analysis of traditional and evolved Basmati and non-Basmati rice varieties by using fluorescence-based ISSR-PCR and SSR markers
Authors: Nagaraju J. , Kathirvel M. , Kumar R. Ramesh , Siddiq E. A. , Hasnain Seyed E.
Published: July 2002

The objective of the present study was to make use of efficient molecular marker systems to reveal genetic relationships in traditional and evolved Basmati (EB) and semidwarf non-Basmati (NB) rice varieties. A subset of three rice groups was analyzed by using 19 simple sequence repeat (SSR) loci and 12 inter-SSR-PCR primers. A total of 70 SSR alleles and 481 inter-SSR-PCR markers were revealed in 24 varieties from the three groups. The lowest genetic diversity was observed among the traditional Basmati varieties, whereas the EB varieties showed the highest genetic diversity by both the marker assays. The results indicated that the subset of aromatic rice varieties analyzed in the present study is probably derived from a single land race. The traditional Basmati (TB) and semidwarf NB rice varieties used in the present study were clearly delineated by both marker assays. A number of markers, which could unambiguously distinguish the TB varieties used in the present study from the evolved and NB rice varieties, were identified. The potential use of these markers in Basmati rice-breeding programs and authentication of TB varieties used in the present study are envisaged.
Interactions of mutant and wild-type flap endonucleases with oligonucleotide substrates suggest an alternative model of DNA binding
Authors: Dervan Joe J. , Feng Min , Patel Dipak , Grasby Jane A. , Artymiuk Peter J. , Ceska Thomas A. , Sayers Jon R.
Published: July 2002

Previous structural studies on native T5 5′ nuclease, a member of the flap endonuclease family of structure-specific nucleases, demonstrated that this enzyme possesses an unusual helical arch mounted on the enzyme's active site. Based on this structure, the protein's surface charge distribution, and biochemical analyses, a model of DNA binding was proposed in which single-stranded DNA threads through the archway. We investigated the kinetic and substrate-binding characteristics of wild-type and mutant nucleases in relation to the proposed model. Five basic residues R33, K215, K241, R172, and R216, are all implicated in binding branched DNA substrates. All these residues except R172 are involved in binding to duplex DNA carrying a 5′ overhang. Replacement of either K215 or R216 with a neutral amino acid did not alter
k
cat
appreciably. However, these mutant nucleases displayed significantly increased values for
K
d
and
K
m
. A comparison of flap endonuclease binding to pseudoY substrates and duplexes with a single-stranded 5′ overhang suggests a better model for 5′ nuclease-DNA binding. We propose a major revision to the binding model consistent with these biophysical data.
Distinct recognition by two subsets of T cells of an MHC class II-peptide complex
Authors: Pu Zheng , Carrero Javier A. , Unanue Emil R.
Published: July 2002

We examine here the nature of the differential recognition by CD4+T cells of a single peptide from hen-egg white lysozyme (HEL) presented by I-Akclass II MHC molecules. Two subsets of T cells (called A and B) interact with the same peptide, each in unique ways that reflect the nature of the complex of peptide and MHC. We show that the A and B set of T cells can be distinguished by their functional interaction with the three T cell receptor (TCR) contact residues of the bound peptide. The dominant peptide of HEL selected from processing is bound in a single register where a critical TCR contact residue is situated about the middle of the core segment of the peptide: all T cells establish functional contact with it. Three sets of T cells, however, can be distinguished by their differential recognition of two TCR contacts situated at the amino and carboxyl sides of the central TCR contact residue. Type A T cells, the conventional cells that see the peptide after processing of HEL, need to recognize all three TCR contact residues. In contrast, the type B T cells recognize the peptide given exogenously, but not when processed: these T cells recognize either one of the peripheral TCR contact residues, indicating a much more flexible interaction of peptide with I-Akmolecules. We discuss the mode of generation of the various T cells and their biological relevance.