bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct calculation of liquid–vapor phase equilibria from transition matrix Monte Carlo simulation
Authors: Errington Jeffrey R.
Published: May 2003

An approach for directly determining the liquid–vapor phase equilibrium of a model system at any temperature along the coexistence line is described. The method relies on transition matrix Monte Carlo ideas developed by Fitzgerald, Picard, and Silver [Europhys. Lett. 46, 282 (1999)]. During a Monte Carlo simulation attempted transitions between states along the Markov chain are monitored as opposed to tracking the number of times the chain visits a given state as is done in conventional simulations. Data collection is highly efficient and very precise results are obtained. The method is implemented in both the grand canonical and isothermal–isobaric ensemble. The main result from a simulation conducted at a given temperature is a density probability distribution for a range of densities that includes both liquid and vapor states. Vapor pressures and coexisting densities are calculated in a straightforward manner from the probability distribution. The approach is demonstrated with the Lennard-Jones fluid. Coexistence properties are directly calculated at temperatures spanning from the triple point to the critical point.
Hugoniot measurements for polyimide with laser and explosives
Authors: Ozaki N. , Tanaka K. A. , Sasatani Y. , Fujita K. , Takamatsu K. , Nakano M. , Yoshida M. , Okada K. , Takahashi E. , Owadano Y. , Takenaka H. , Kondo K.
Published: May 2003

Equation-of-state measurements for a polyimide are presented. High-power KrF laser and chemical explosive-driven experiments provided Hugoniot data on the polyimide up to about 65 GPa. Conventional reflected-light measurements in the explosive experiments and velocity interferometry measurements in the laser experiments were performed. From both laser and explosive results the change of Hugoniot was indicated at near 30 GPa.
Laser cleaning of alumina particles on glass and silica substrates: Experiment and quasistatic model
Authors: Pleasants S. , Kane D. M.
Published: May 2003

Silica and microscope slides that had been pretreated with a variety of wet chemical, ultrasonic and laser irradiation surface preparation methods were contaminated with alumina particles of around 3 μm. The samples were prepared and processed without delay so as to avoid capillary condensation in a high humidity environment and thus ensuring that the process is dry laser cleaning. They were then irradiated with a pulse of 248 nm radiation from a KrF excimer laser, over a range of fluences. The laser cleaning results show that, in this case, the surface preparation method appears to have little effect on the laser cleaning efficiency. They also demonstrate that the threshold fluence for particle removal of silica is approximately eight times higher than that for microscope slides, when so prepared. In contrast, application of Arnold et al.’s thermal expansion model of laser cleaning in the quasistatic limit to this material system predicts that the threshold fluence for silica will be about 15 times greater than that for glass. One possible explanation for this discrepancy may be that the particle’s absorptivity (0.16) is inaccurate. A value of 0.35 gives good agreement between theory and experiment.
Effects of heat treatment on absorption bands in OH-free and OH-containing fused quartz
Authors: Kuzuu Nobu , Horikoshi Hideharu , Nishimura Tsutomu , Kokubo Yosuke
Published: May 2003

Effects of heat treatment on absorption bands in fused quartz produced by melting natural quartz powder containing 2×1017 cm−3 (sample I) and 1.3×1019 cm−3 of OH (sample II) were studied. Both samples have an absorption peak at ≈5.2 eV. Fluorescent spectra and the results of Gaussian peak decomposition suggest that this absorption is associated with the B2β band with a peak at 5.15 eV and full width at half maximum of 0.42 eV. The 5.15 eV band and an absorption component at 7.5 eV in sample II were annealed out at 1423 K, whereas almost no change was observed in the absorption spectra of sample I. The decrement of the 5.15 and 7.5 eV bands was proportional to the decrement of the OH content. The annealing mechanism in sample II can be explained using a previously proposed model for OH-containing fused quartz wherein the B2β band is the twofold-oxygen-coordinated silicon (=Si:) coordinated with two ≡Si-OH structures. Sample I must have a =Si: structure, but it may not be annealed out because it does not have sufficient OH to form the twofold-coordinated ≡Si-OH on =Si:. The origin of the other absorption bands was also discussed.
Influence of temperature on vertical Bloch lines in the domain walls of three kinds of hard domains
Authors: Nie X. F. , Guo G. X. , Ma L. M. , Sun H. Y. , Tang G. D. , Han Z. Y. , Li Zh. Q.
Published: May 2003

The temperature stability of vertical Bloch lines in the domain walls of three kinds of hard domains in uncompressed states is investigated experimentally. It is found that there exist three critical temperature ranges in which vertical Bloch lines are unstable for each kind of hard domain, i.e., [T01,(T0)OHB] for ordinary hard bubbles (OHBs), [T01,(T0)ID] for the first kind of dumbbells (IDs), and [T01,(T0)IID] for the second kind of dumbbells (IIDs). Here T01 is the initial critical temperatures in which vertical Bloch lines, in the walls of ordinary hard bubbles, the first kind of dumbbells and the second kind of dumbbells, are annihilated, while (T0)OHB, (T0)ID, and (T0)IID are the final critical temperatures at which vertical Bloch lines in their corresponding hard domains annihilate completely.
Midinfrared emission properties of Pr3+-doped chalcogenide glasses at cryogenic temperature
Authors: Han Yong Seop , Heo Jong
Published: May 2003

Low-temperature midinfrared emission properties of Pr3+-doped Ge30Ga2As6S62 and Ge28Ga5As12Se55 glasses (at. %) were investigated. Emissions centered at 3400 and 4700 nm were clearly observed from sulfide and selenide glasses, respectively, when the specimens were cooled to 20 K. The measured lifetime of the G41 level in sulfide glass increased from 320 μs at room temperature to 400 μs at 20 K. The intensity and quantum efficiency of the emission from the Pr3+:(3F3, 3F4) level in selenide glass also increased as the temperature decreased to 120 K. The enhancement resulted from a decrease in nonradiative multiphonon relaxation at low temperatures. The temperature dependence of the multiphonon relaxation rates indicated that the asymmetrical stretching vibration of GeS4 tetrahedra (375 cm−1) is primarily responsible for the multiphonon relaxation process in sulfide glass.
Calculation of the Xe129 chemical shift in Xe@C60
Authors: Sears Devin N. , Jameson Cynthia J.
Published: May 2003

We report, for the first time, a reasonably good calculation of Xe shielding in a fullerene. We find the Xe129 intermolecular shielding value [σ(129Xe@C60)−σ(Xe atom)]=−181.58 ppm (B3LYP), in very good agreement with the value observed for Xe@C60129 dissolved in liquid benzene.
Transmission electron microscopy investigation of the high temperature BiScO3−PbTiO3 piezoelectric ceramic system
Authors: Randall C. A. , Eitel R. E. , Shrout T. R. , Woodward D. I. , Reaney I. M.
Published: May 2003

Recently, a perovskite solid-solution ((1−x)BiScO3−(x)PbTiO3) with superior electromechanical properties than PbZrO3−PbTiO3 (PZT) ceramics has been discovered. The system has a morphotropic phase boundary (MPB) between ferroelectric rhombohedral (R) and tetragonal (T) symmetries similar to PZT but the underlying domain structures and some aspects of the crystal chemistry remain to be elucidated. Therefore, transmission electron microscopy has been used to study changes in domain structure and symmetry as a function of x. Domain structures in the R and T phases have been found which closely resemble those in PZT. In addition, 12{hkl} superlattice reflections were observed, particularly in the 〈110〉 zone axis diffraction patterns from grains of the R phase (e.g., x=0.5), which were consistent with rotations of the octahedra in antiphase and the space group R3c. These reflections were absent in the R phase close to the MPB (x=0.64) and in the T phase (x=0.75). From these results, the low temperature phase diagram for BiScO3−PbTiO3 has been modified.
Photoluminescence and damage recovery studies in Fe-implanted ZnO single crystals
Authors: Monteiro T. , Boemare C. , Soares M. J. , Rita E. , Alves E.
Published: May 2003

We report Fe3+-related emission in ion-implanted ZnO single crystals. Iron ions were implanted at room temperature with 100 keV and a fluence of 1×1016 Fe+/cm2, and were submitted to annealing treatments in vacuum and in air. After implantation, the damage raises the minimum yield (χmin) from 2% to 50%. Annealing in an oxidizing atmosphere leads to a reduction of the implantation damage, which is fully recovered after annealing at 1050 °C with a χmin∼3% in the implanted region. With extrinsic excitation, red Fe-related emission is observed at low temperatures. The intensity is dependent on the annealing conditions. For samples annealed in air, the luminescence can be detected up to 120 K. When a comparison is made between unimplanted and post-implanted annealed samples, noticeable changes on near-band-edge and deep-level photoluminescence spectra are observed. A thermally populated structured green emission could be observed in the sample annealed in air, as shown by the temperature-dependent photoluminescence excitation studies.
Role of electron inertia in nonlinear electron magnetohydrodynamics
Authors: Ravi G. , Mattoo S. K. , Awasthi L. M. , Anitha V. P.
Published: May 2003

This paper reports experimental investigations of nonlinear electron magnetohydrodynamic (EMHD) structures of the size of skin depth. It is shown that the difficulty of exciting EMHD structures with k⊥de∼1 is not related to any specifics of antenna–plasma coupling mechanisms but to a general attenuation scaling with antenna size. Formation of null-point or mirror geometry with contribution from antenna current leads to nonlinear effects in case of EMHD structures with k⊥de≪1. However, there is weakening of nonlinearity in case of k⊥de∼1. Observations indicate that reconnection rates in EMHD may not be independent of the plasma skin depth, in contrast to theoretical predictions. It is pointed out that electron inertia takes the role of magnetic field in the region where adiabatic constants of motion do not remain constant.
Effects of a nonresonant m=0, n=1 perturbation driven by coupling to the m=2, n=1 mode in an elongated tokamak
Authors: Lazzaro Enzo , Zanca Paolo
Published: May 2003

In a tokamak the coupling of resonant tearing modes with the plasma shape effects like toroidicity, elongation, and triangularity produces sidebands harmonics. In particular an m=0, n=1 nonresonant sideband can be driven by a m=2, n=1 tearing mode in an elliptic cross section tokamak. It is shown that this is an important effect. The m=0 mode is expected to produce a neoclassical toroidal viscous force which could explain the dramatic braking of the bulk plasma toroidal velocity observed during the onset of locked modes driven by resonant helical error fields or by spontaneous magnetohydrodynamic activity.
Dielectric properties of Bi2O3–ZnO–Ta2O5 pyrochlore and zirconolite structure ceramics
Authors: Ang Chen , Yu Zhi , Youn H. J. , Randall C. A. , Bhalla A. S. , Cross L. E. , Lanagan M.
Published: May 2003

This letter reports the dielectric properties of the cubic pyrochlore (Bi3/4Zn1/4)2(Zn1/4Ta3/4)2O7, monoclinic zirconolite Bi2(Zn1/3Ta2/3)2O7, and their composites in the temperature range of 10–400 K from 102 to ∼1010 Hz. Composites with a near zero temperature coefficient of capacitance (TCC) consisting of the cubic pyrochlore and monoclinic zirconolite phases have been obtained. The observed microwave dielectric properties (ε=∼60, Q=∼325, and TCC=∼30 ppm/K at ∼5.1 GHz) as well as their low sintering temperatures (950–1100 °C) show that the compounds are promising materials for recently developed microwave devices, which demand that dielectric ceramics can be cofired with silver electrodes.
Particle-in-cell simulations of ponderomotive particle acceleration in a plasma
Authors: Startsev E. A. , McKinstrie C. J.
Published: May 2003

In previous publications [C. J. McKinstrie and E. A. Startsev, Phys. Rev. E 54, R1070 (1996); 56, 2130 (1997)] the ponderomotive acceleration of electrons by an idealized (one-dimensional) circularly polarized laser pulse in a plasma was studied analytically. Acceleration gradients of order 100 GeV/m were predicted. To verify the predictions of the theoretical model, a two-dimensional relativistic particle-in-cell code was developed. Simulations of the interaction of a preaccelerated electron bunch with a realistic (two-dimensional) laser pulse in a plasma are presented and analyzed. The simulation results validate the theoretical model and show that significant ponderomotive acceleration is possible.
Intrinsic and extrinsic properties of epitaxial Nd2Fe14B films
Authors: Hannemann Ullrich , Fähler Sebastian , Neu Volker , Holzapfel Bernhard , Schultz Ludwig
Published: May 2003

Epitaxial Nd2Fe14B films with the c axis (easy magnetization axis) perpendicular to the film plane were prepared on a Ta(110) buffer on single crystalline Al2O3(0001) substrates using pulsed laser deposition. Due to the epitaxial film growth an almost perfect alignment of all magnetic moments perpendicular to the film plane is achieved. Coercivities up to 2 T are obtained for Nd-rich films where the Nd2Fe14B grains are magnetically decoupled. An analysis of the coercivity mechanism shows that the switching mechanism is nucleation dominated and the high coercivity is achieved by avoiding nucleation within the grains. Intrinsic properties like the spin reorientation temperature of 135 K and spin reorientation angle of 30° at 4.2 K of these films are in very good agreement to single crystal data.
High-performance photorefractive organic glass with near-infrared sensitivity
Authors: Ostroverkhova Oksana , Moerner W. E. , He Meng , Twieg Robert J.
Published: May 2003

A high-performance organic glass mixture comprised of two dicyanomethylenedihydrofuran derivatives is presented. A pronounced two-beam coupling effect was observed at a wavelength of 830 nm in an unsensitized composition. Sensitization with (2,4,7-trinitro-9fluorenylidene)malononitrile (TNFM) led to a significant increase in the two-beam coupling gain coefficient, reaching a net value of ∼370 cm−1 at an electric field of 45 V/μm at 1% TNFM, and resulted in an improvement in photorefractive speed.
Speed and shape of dust acoustic solitary waves
Authors: Maitra Sarit , Roychoudhury Rajkumar
Published: May 2003

Parametric conditions for the existence of dust acoustic solitary waves are investigated without dust charge variation, as well as with dust charge variation. The Sagdeev potential equation is derived in terms of the dust velocity ud0 in both cases. It is found that there exists, in both cases, a critical value of ud0(≠0), the value of ud at which (ud′)2=0, beyond which the soliton solution ceases to exist. This is demonstrated clearly in the plots given for ud against the traveling wave coordinate ξ=x−Vt.
Optical filtering by leaky guided modes in macroporous silicon
Authors: Avrutsky Ivan , Kochergin Vladimir
Published: May 2003

We propose an optical filtering mechanism in a porous material based on wavelength-dependent losses for leaky modes in pore waveguides. The spectral transmission characteristics of such filters can be controlled by applying thin-film coatings to the pore walls. Such filters will find application in the deep UV spectral range where traditional approaches to filter design fail due to lack of suitable materials.
Shape effect on magnetization reversal in chains of interacting ferromagnetic elements
Authors: Novosad V. , Grimsditch M. , Darrouzet J. , Pearson J. , Bader S. D. , Metlushko V. , Guslienko K. , Otani Y. , Shima H. , Fukamichi K.
Published: May 2003

The magnetization reversal in the chains of submicron square- and disk-shaped Permalloy dots with lateral size of 800 nm, thickness of 50 nm and variable inter dot distance was investigated by using the magneto-optical Kerr effect technique, magnetic force microscopy and micromagnetic modeling. We have found that the particle shape strongly affects the characteristic switching fields of well-separated dots, and has almost no influence on strength of inter dot interaction in chains of magnetostatically coupled elements.
A high-extraction-efficiency nanopatterned organic light-emitting diode
Authors: Lee Yong-Jae , Kim Se-Heon , Huh Joon , Kim Guk-Hyun , Lee Yong-Hee , Cho Sang-Hwan , Kim Yoon-Chang , Do Young Rag
Published: May 2003

To improve light extraction from organic light-emitting diodes (OLEDs), we introduced a photonic crystal pattern into the glass substrate of an OLED. The periodic modulation converts the guided waves in the high-refractive-index indium-tin-oxide/organic layers into external leaky waves. We used the finite-difference time-domain method to optimize the structural parameters of the photonic crystal pattern and to analyze the microcavity effect by the metallic cathode of the OLED. With the use of an optimized photonic crystal pattern, an increase of over 80% in the extraction efficiency of the OLED is expected theoretically. An increase in the extraction efficiency of over 50% was achieved experimentally, without detriment to the crucial electrical properties of the OLED.
Interface structure and chemistry in ZnSe/Ga1−xMnxAs/ZnSe heterostructures
Authors: Lian G. D. , Dickey E. C. , Chun S. H. , Ku K. C. , Samarth N.
Published: May 2003

The structure and chemical composition of ZnSe/Ga1−xMnxAs/ZnSe multilayers grown on (100) GaAs substrates are investigated by high-resolution transmission electron microscopy imaging and spectroscopy techniques. While all layers grow epitaxially and the Ga1−xMnxAs layer is free of planar defects, a high density of stacking faults is observed in the ZnSe layer over Ga1−xMnxAs. The composition of the ferromagnetic layer is measured to be Ga0.93Mn0.07As, and the Mn valence was determined to be 2+. Compositional profiles across the interfaces quantified by electron energy-loss spectroscopy show that the ZnSe/Ga1−xMnxAs interfaces are wider than the ZnSe/GaAs–substrate interface, which is mainly attributed to interfacial roughness.
Electrically color-tunable defect mode lasing in one-dimensional photonic-band-gap system containing liquid crystal
Authors: Ozaki Ryotaro , Matsui Tatsunosuke , Ozaki Masanori , Yoshino Katsumi
Published: May 2003

Electrical tuning of the wavelength of the defect-mode lasing in a one-dimensional periodic structure has been demonstrated using a dye-doped nematic liquid crystal as a defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying an electric field, which is due to the refractive index change in the defect layer caused by the field-induced realignment of the liquid crystal molecules.
Carrier storage and capture dynamics in quantum-dot heterostructures
Authors: Smith J. M. , Dalgarno P. A. , Urbaszek B. , McGhee E. J. , Buller G. S. , Nott G. J. , Warburton R. J. , Garcia J. M. , Schoenfeld W. , Petroff P. M.
Published: May 2003

Photoluminescence and time-resolved photoluminescence measurements of charge tunable quantum-dot heterostructures reveal that by appropriate biasing of the device, about 90% of photogenerated holes can be stored at an interface near to the nanostructures and subsequently transferred into the nanostructures in a controlled fashion. The capture dynamics are sensitive to the form of the valence band potential in the layer that caps the Stranski–Krastanow dots. The dependence of the capture rate on applied electric field suggests that the valence band confinement potential is “soft” in the capping layer, with a spatial extent of around 14 nm.
Mass spectrometry sampling method for characterizing high-density plasma etching mechanisms
Authors: Eddy C. R. , Leonhardt D. , Shamamian V. A. , Butler J. E. , Thoms B. D.
Published: May 2003

Mass spectrometry sampling using a “through-the-platen” technique is described with respect to its utility in characterizing high-density plasma etching processes for semiconductors. A custom substrate platen/sampling aperture is described and its effectiveness in characterizing plasma/surface reactions is demonstrated. The technique is applied to the characterization of GaAs etching in a Cl2/Ar high-density plasma chemistry.
Direction-dependent band nonparabolicity effects on high-field transient electron transport in GaN
Authors: Wraback M. , Shen H. , Rudin S. , Bellotti E. , Goano M. , Carrano J. C. , Collins C. J. , Campbell J. C. , Dupuis R. D.
Published: May 2003

Time-resolved electroabsorption measurements on an AlGaN/GaN heterojunction p–i–n diode provide evidence of electron velocity overshoot at fields as low as ∼130 kV/cm for transport in the c-direction of wurtzite GaN. Theoretical Monte Carlo calculations employing a full band structure indicate that at fields below ∼300 kV/cm, this velocity overshoot is associated primarily with band nonparabolicity in the Γ valley related to a negative electron effective mass rather than intervalley transfer. Similar calculations of transport in the basal plane indicate that in this case, both a higher threshold field for velocity overshoot and a lower steady-state velocity at a given field are expected.
Vertical-cavity surface-emitting laser operating with photonic crystal seven-point defect structure
Authors: Yokouchi Noriyuki , Danner Aaron J. , Choquette Kent D.
Published: May 2003

A vertical-cavity surface-emitting laser with a two-dimensional photonic crystal (PC) structure has been investigated for single lateral mode operation. The PC confined mode can be controlled by the lattice constant, the hole diameter, the etching depth, and the defect structure. A seven-point defect structure is proposed to enhance the confinement effect, which is diluted by finite hole depth of the PC structure. We obtained a pure PC confined mode under room-temperature cw conditions with a PC lattice constant of 2 μm, hole diameters of 1.0 and 1.4 μm, and depths of 1.85 and 1.92 μm, respectively.
Deep level defect in Si-implanted GaN n+-p junction
Authors: Chen X. D. , Huang Y. , Fung S. , Beling C. D. , Ling C. C. , Sheu J. K. , Lee M. L. , Chi G. C. , Chang S. J.
Published: May 2003

A deep level transient spectroscopy (DLTS) study has been performed on a GaN n+-p junction fabricated by implanting Si into a Mg-doped p-type GaN epilayer. A high concentration of a deep level defect has been revealed within the interfacial region of the junctions by the unusual appearance of a minority peak in the majority carrier DLTS spectra. The deep level defect appears to be an electron trap at EC-0.59 eV in the p-side region of the junction and has tentatively been attributed to the VN–Mg complex. The high concentration of this electrically active deep level defect in the depletion layer of the Si-implanted GaN n+-p junction diodes suggests the need for further investigations.
Electron spin relaxation under drift in GaAs
Authors: Barry E. A. , Kiselev A. A. , Kim K. W.
Published: May 2003

Based on a Monte Carlo method, we investigate the influence of transport conditions on the electron spin relaxation in GaAs. The decay of initial electron spin polarization is calculated as a function of distance under the presence of moderate drift fields and/or nonzero injection energies. For relatively low fields (a couple of kV/cm), a substantial amount of spin polarization is preserved for several microns at 300 K. However, it is also found that the spin relaxation rate increases rapidly with the drift field, scaling as the square of the electron wave vector in the direction of the field. When the electrons are injected with a high energy, a pronounced decrease is observed in the spin relaxation length due to an initial increase in the spin precession frequency. Hence, high-field or high-energy transport conditions may not be desirable for spin-based devices.
Optical detection of electron paramagnetic resonance in CdMnTe single quantum wells
Authors: Sadowski M. L. , Byszewski M. , Potemski M. , Sachrajda A. , Karczewski G.
Published: May 2003

The electron paramagnetic resonance of Mn2+ ions localized in a CdTe quantum well is measured by an all-optical method. The photoluminescence transitions of a two-dimensional electron gas are used to monitor changes in the Mn spin polarization. The local character of this probe and the detection technique permit us to achieve a very high sensitivity for the number of spins detected (better than 108 spins). Two simultaneous effects are observed at resonance: A blueshift of the whole photoluminescence spectrum, and a dramatic transfer of photoluminescence intensity from neutral to negatively charged excitons.
Hydrogen-induced improvements in optical quality of GaNAs alloys
Authors: Buyanova I. A. , Izadifard M. , Chen W. M. , Polimeni A. , Capizzi M. , Xin H. P. , Tu C. W.
Published: May 2003

Strong suppression of potential fluctuations in the band edges of GaNAs alloys due to postgrowth hydrogen treatment, which is accompanied by a reopening of the alloy band gap, is revealed from temperature-dependent photoluminescence (PL) and PL excitation measurements. The effect likely indicates preferential trapping of hydrogen near the lattice sites with the highest nitrogen content. A remarkable improvement in the radiative efficiency of the alloys at room temperature is also demonstrated and is ascribed to efficient hydrogen passivation of competing nonradiative centers.
InAs nanowires and whiskers grown by reaction of indium with GaAs
Authors: He Maoqi , Fahmi M. M. E. , Mohammad S. Noor , Jacobs Randolph N. , Salamanca-Riba Lourdes , Felt Frederick , Jah Muzar , Sharma Ashok , Lakins Darryl
Published: May 2003

Free-standing InAs nanowires and whiskers were grown employing reaction of indium (In) liquid and vapor with GaAs substrate. The arsenic (As) atoms resulting from this reaction were transported by a flow of N2 or NH3 to the growth location where they reacted with In to produce InAs nanowires and whiskers. Scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy of the products indicate that the diameter of the nanowires and whiskers ranges from 15 nm to 2 μm depending on the growth temperature, the composition is InAs, and the structure is zinc-blende crystal with [110] or [100] growth direction. The As source and growth mechanism were discussed. The method for synthesis involved no any template, catalyst, toxic As source, nor even lattice matched substrate.
Interface defects responsible for negative-bias temperature instability in plasma-nitrided SiON/Si(100) systems
Authors: Fujieda Shinji , Miura Yoshinao , Saitoh Motofumi , Hasegawa Eiji , Koyama Shin , Ando Koichi
Published: May 2003

Interface defects generated by negative-bias temperature stress (NBTS) in an ultrathin plasma- nitrided SiON/Si(100) system were characterized by using D2 annealing, conductance-frequency measurements, and electron-spin resonance measurements. D2 annealing was shown to lower negative-bias temperature instability (NBTI) than H2 annealing. Interfacial Si dangling bonds (Pb1 and Pb0 centers), whose density is comparable to an increase in interface trap density, were detected in a NBTS-stressed sample. The NBTI of the plasma-nitrided SiON/Si system was thus shown to occur through Pb depassivation. Furthermore, the nitridation was shown to increase the Pb1/Pb0 density ratio and modify the Pb1 structure. Such a predominance and structural modification of Pb1 centers are presumed to increase NBTI by enhancing the Pb–H dissociation. Although we suggest that NBTS may also induce non-Pb defects, nitrogen dangling bonds do not seem to be included in them.
Nanostructuring of silicon by electron-beam lithography of self-assembled hydroxybiphenyl monolayers
Authors: Küller A. , Eck W. , Stadler V. , Geyer W. , Gölzhäuser A.
Published: May 2003

We report the fabrication of silicon nanostructures using aromatic hydroxybiphenyl self-assembled monolayers as ultrathin (1.1 nm) negative tone electron-beam resist. The formation of the monolayer and the electron-induced crosslinking have been characterized by x-ray photoelectron spectroscopy. Nanometer size patterns were defined by electron-beam lithography in the molecular layer and transferred into silicon by wet chemical etching with potassium hydroxide. We demonstrate the fabrication of silicon line gratings with a resolution of ∼20 nm and of isolated silicon lines with linewidths down to ∼10 nm.
Photonic band gap in (Pb,La)(Zr,Ti)O3 inverse opals
Authors: Li Bo , Zhou Ji , Hao Lifeng , Hu Wei , Zong Ruilong , Cai Minmin , Fu Min , Gui Zhilun , Li Longtu , Li Qi
Published: May 2003

(Pb,La)(Zr,Ti)O 3 (PLZT) inverse opal photonic crystals were synthesized by a process of self-assembly in combination with a sol-gel technique. In this process, PLZT precursors were infiltrated into the interstices of the opal template assembled by monodisperse submicron polystyrene spheres, and then gelled in a humid environment. Polystyrene template was removed by calcining the specimen at a final temperature of 700 °C accompanied with the crystallization of perovskite phase in PLZT inverse opal network. Scanning electron microscope images show that the inverse opals possess a fcc structure with a lattice constant of 250 nm. A wide photonic band gap in the visible range is observed from transmission spectra of the sample. Such PLZT inverse opals as photonic crystals should be of importance in device applications.
Cubic local order around Al and intermixing in short-period AlN/TiN multilayers studied by Al K-edge extended x-ray absorption fine structure spectroscopy and x-ray diffraction
Authors: Ersen O. , Tuilier M.-H. , Thomas O. , Gergaud P. , Lagarde P.
Published: May 2003

Al K-edge extended x-ray absorption fine structure (EXAFS) experiments are performed on short-period TiN (50 nm)/AlN (Λ=1, 2, 3, 5, and 15 nm) multilayers prepared by dc magnetron sputtering on MgO(100). It is shown that the local order around Al is hexagonal down to Λ=3 nm and becomes clearly cubic B1 rocksalt-type below this thickness. This phase transition is correlated with x-ray diffraction results, which reveal increased compressive stresses in TiN layers for Λ=3 nm. In addition, EXAFS provides direct evidence of substitution of Ti for Al within AlN layers, as well as an estimation of Ti content as a function of layer thickness.
Anticompetition of laser modes
Authors: Lin Ching-Fuh , Huang Chi-Chia , Chu Fei-Hung , Su Yi-Shin
Published: May 2003

Anticompetition of laser modes is observed. In this behavior, the increase of intensity in one lasing mode could enhance the intensity of another mode, which is opposite to the usual competition behavior and so-called anticompetition. In our experiments using the semiconductor laser with very broadband gain medium, anticompetition exists when the laser modes have their wavelengths widely separated. Anticompetition can be observed for spectral separation of 138 nm and is even more prominent for spectral separation up to 167 nm. Theoretical analysis shows that anticompetition is due to the physics similar to optical pumping.
Stacked low-growth-rate InAs quantum dots studied at the atomic level by cross-sectional scanning tunneling microscopy
Authors: Bruls D. M. , Koenraad P. M. , Salemink H. W. M. , Wolter J. H. , Hopkinson M. , Skolnick M. S.
Published: May 2003

Structures containing stacked self-assembled InAs quantum dots within a GaAs matrix are studied by cross-sectional scanning tunneling microscopy. The dots consist of an InGaAs alloy with an increasing indium concentration in the growth direction. From comparison of the lattice constant profiles of stacked and unstacked dots, it is evident that the strain in the GaAs matrix around the dots is strongly affected by the stacking process. The results show an increasing deformation of the dots in the stack and a reduced growth rate of the GaAs spacer layers, resulting in the formation of terraces on the growth surface on which new dots form. If the total structure, containing the dot layers and the spacer layers, exceeds 30 nm, the local GaAs growth rate remains constant from this point on. The InAs dot growth rate remains constant throughout the entire stack.
Designer infrared filters using stacked metal lattices
Authors: Smith Howard A. , Rebbert M. , Sternberg O.
Published: May 2003

We have designed and fabricated infrared filters for use at wavelengths ≳15 microns. Unlike conventional dielectric filters used at the short wavelengths, ours are made from stacked metal grids, spaced at a very small fraction of the performance wavelengths. The individual lattice layers are gold, the spacers are polyimide, and they are assembled using integrated circuit processing techniques; they resemble some metallic photonic band-gap structures. We simulate the filter performance accurately, including the coupling of the propagating, near-field electromagnetic modes, using computer aided design codes. We find no anomalous absorption. The geometrical parameters of the grids are easily altered in practice, allowing for the production of tuned filters with predictable useful transmission characteristics. Although developed for astronomical instrumentation, the filters are broadly applicable in systems across infrared and terahertz bands.
Doping-induced strain in N-doped 4H–SiC crystals
Authors: Jacobson H. , Birch J. , Hallin C. , Henry A. , Yakimova R. , Tuomi T. , Janzén E. , Lindefelt U.
Published: May 2003

Stress in epitaxial layers due to crystal lattice mismatch directly influences the growth, structure, and basic electrophysical parameters of epitaxial films and also to a large extent the degradation processes in semiconductor devices. In this letter, we present a theoretical model for calculating the induced lattice compression due to N doping and the critical thickness concerning formation of misfit dislocations in homoepitaxial 4H–SiC layers with different N-doping levels. For example: The model predicts that substrates with a N concentration of 3×1019 cm−3 induce misfit dislocations when the epilayer thickness reaches ∼10 μm. Also, the N-doping concentration in the 1×1018–1×1019 cm−3 range yields a strain that not will cause misfit dislocactions at the substrate and epilayer interface until an epilayer thickness of 200–300 μm is reached. Supporting evidence of the induced lattice compression due to N doping have been done by synchrotron white-beam x-ray topography on samples with different N-doping levels and are compared with the predicted results from the model.
8-W high-efficiency continuous-wave semiconductor disk laser at 1000 nm
Authors: Lutgen S. , Albrecht T. , Brick P. , Reill W. , Luft J. , Späth W.
Published: May 2003

We demonstrate more than 8-W continuous-wave output power with good beam quality (M2<1.8) from an optically pumped semiconductor disk laser. The combination of low threshold density of 470 W/cm2 and high differential efficiency of 60% results in an optical-to-optical conversion efficiency of 46% for this high output level. Good epitaxial quality and low thermal resistance allow the scaling of output power with pump spot area.
Nitride microlens arrays for blue and ultraviolet wavelength applications
Authors: Oder T. N. , Shakya J. , Lin J. Y. , Jiang H. X.
Published: May 2003

Nitride microlens arrays with sizes as small as 10 μm in diameter have been fabricated on GaN and AlN epilayers using the method of photoresist reflow and inductively coupled plasma dry etching. The focal lengths of the microlenses varied from 7–30 μm as determined by theoretical fitting as well as by the near-field scanning optical microscopy measurement. Scanning electron and atomic force microscopies were used to obtain the surface profile of the microlenses which were found to match very well with hemispherical fitting and a surface roughness value around 1 nm was obtained. Nitride microlens arrays would be naturally chosen for green/blue to deep ultraviolet wavelength applications. In addition, nitride microlenses offer the possibility of integrating nitride-based microsize photonic devices as well as of coupling light into, out of, and between arrays of III-nitride emitters for other applications, such as spatially resolved fluorescence spectroscopy studies of biological and medical systems and optical links, thereby further expanding the applications of III nitrides.
Structural defects and the diagnosis of amyloidogenic propensity
Authors: Fernández Ariel , Kardos József , Scott L. Ridgway , Goto Yuji , Berry R. Stephen
Published: May 2003

Disease-related amyloidogenic propensity has been unexpectedly found in proteins driven to adopt a monomeric uncomplexed state at high concentrations under near-physiological conditions. This situation occasionally arises in new health treatments, such as kidney dialysis. Assuming that under such conditions a partial retention of native structure takes place, this work identifies a structural characteristic indicating amyloidogenic propensity: a high density of backbone hydrogen bonds exposed to water attack in monomeric structure. On this basis, we propose a diagnostic tool based on the identification of hydrogen bonds with a paucity of intramolecular dehydration or “wrapping.” We use this predictor to identify potentially pathogenic mutations that foster amyloidogenic propensity in human prions. Such mutations either enhance the intramolecular dehydration of β-sheet hydrogen bonds, thus stabilizing the nucleus for rearrangement into the scrapie fold, or contribute to the destabilization of the cellular form by introducing additional underwrapped hydrogen bonds. Our predictions are consistent with known disease-related mutations and lead to a cogent explanation of the pathogenic nature of specific mutations affecting the cellular prion protein structural wrapping. On the other hand, a different wrapping of a very similar fold, mouse doppel, induces a dramatically different level of amyloidogenic propensity, suggesting that the packing within the fold, and not the fold itself, contains the signal for aggregation.
Tracing the origin and history of the HIV-2 epidemic
Authors: Lemey Philippe , Pybus Oliver G. , Wang Bin , Saksena Nitin K. , Salemi Marco , Vandamme Anne-Mieke
Published: May 2003

In this study we date the introduction of HIV-2 into the human population and estimate the epidemic history of HIV-2 subtype A in Guinea-Bissau, the putative geographic origin of HIV-2. The evolutionary history of the simian immunodeficiency virus
sooty mangabey
/HIV-2 lineage was reconstructed by using available database sequences with known sampling dates, and a timescale for this history was calculated by using maximum likelihood methods. The date of the most recent common ancestor of HIV-2 subtype A strains was estimated to be 1940 ± 16 and that of B strains was estimated to be 1945 ± 14. In addition we used coalescent theory to estimate the past population dynamics of HIV-2 subtype A in a rural population of Guinea-Bissau. Parametric and nonparametric estimates of the effective number of infections through time were obtained for an equal sample of
gag, pol
, and
env
sequences. Our estimates of the epidemic history of HIV-2 subtype A in Guinea-Bissau show a transition from constant size to rapid exponential growth around 1955–1970. Our analysis provides evidence for a zoonotic transfer of HIV-2 during the first half of the 20th century and an epidemic initiation in Guinea-Bissau that coincides with the independence war (1963–1974), suggesting that war-related changes in sociocultural patterns had a major impact on the HIV-2 epidemic.
Adrenergic regulation of clock gene expression in mouse liver
Authors: Terazono Hideyuki , Mutoh Tatsushi , Yamaguchi Shun , Kobayashi Masaki , Akiyama Masashi , Udo Rhyuta , Ohdo Shigehiro , Okamura Hitoshi , Shibata Shigenobu
Published: May 2003

A main oscillator in the suprachiasmatic nucleus (SCN) conveys circadian information to the peripheral clock systems for the regulation of fundamental physiological functions. Although polysynaptic autonomic neural pathways between the SCN and the liver were observed in rats, whether activation of the sympathetic nervous system entrains clock gene expression in the liver has yet to be understood. To assess sympathetic innervation from the SCN to liver tissue, we investigated whether injection of adrenaline/noradrenaline (epinephrine/norepinephrine) or sympathetic nerve stimulation could induce
mPer
gene expression in mouse liver. Acute administration of adrenaline or noradrenaline increased
mPer1
but not
mPer2
expression in the liver of mice
in vivo
and in hepatic slices
in vitro
. Electrical stimulation of the sympathetic nerves or adrenaline injection caused an elevation of bioluminescence in the liver area of transgenic mice carrying
mPer1
promoter-luciferase. Under a light–dark cycle, destruction of the SCN flattened the daily rhythms of not only
mPer1, mPer2
, and
mBmal1
genes but also noradrenaline content in the liver. Daily injection of adrenaline, administered at a fixed time for 6 days, recovered oscillations of
mPer2
and
mBmal1
gene expression in the liver of mice with SCN lesion on day 7. Sympathetic nerve denervation by 6-hydroxydopamine flattened the daily rhythm of
mPer1
and
mPer2
gene expression. Thus, on the basis of the present results, activation of the sympathetic nerves through noradrenaline and/or adrenaline release was a factor controlling the peripheral clock.
TRAP230/ARC240 and TRAP240/ARC250 Mediator subunits are functionally conserved through evolution
Authors: Samuelsen Camilla O. , Baraznenok Vera , Khorosjutina Olga , Spåhr Henrik , Kieselbach Thomas , Holmberg Steen , Gustafsson Claes M.
Published: May 2003

In
Saccharomyces cerevisiae
Mediator, a subgroup of proteins (Srb8, Srb9, Srb10, and Srb11) form a module, which is involved in negative regulation of transcription. Homologues of Srb10 and Srb11 are found in some mammalian Mediator preparations, whereas no clear homologues have been reported for Srb8 and Srb9. Here, we identify a TRAP240/ARC250 homologue in
Schizosaccharomyces pombe
and demonstrate that this protein, spTrap240, is stably associated with a larger form of Mediator, which also contains conserved homologues of Srb8, Srb10, and Srb11. We find that spTrap240 and
Sch. pombe
Srb8 (spSrb8) regulate the same distinct subset of genes and have indistinguishable phenotypic characteristics. Importantly, Mediator containing the spSrb8/spTrap240/spSrb10/spSrb11 subunits is isolated only in free form, devoid of RNA polymerase II. In contrast, Mediator lacking this module associates with the polymerase. Our findings provide experimental evidence for recent suggestions that TRAP230/ARC240 and TRAP240/ARC250 may indeed be the Srb8 and Srb9 homologues of mammalian Mediator. Apparently Srb8/TRAP230/ARC240, Srb9/TRAP240/ARC250, Srb10, and Srb11 constitute a conserved Mediator submodule, which is involved in negative regulation of transcription in all eukaryotes.
Spontaneous regression of advanced cancer: Identification of a unique genetically determined, age-dependent trait in mice
Authors: Cui Zheng , Willingham Mark C. , Hicks Amy M. , Alexander-Miller Martha A. , Howard Timothy D. , Hawkins Gregory A. , Miller Mark S. , Weir Holly M. , Du Wei , DeLong Cynthia J.
Published: May 2003

We have established and studied a colony of mice with a unique trait of host resistance to both ascites and solid cancers induced by transplantable cells. One dramatic manifestation of this trait is age-dependent spontaneous regression of advanced cancers. This powerful resistance segregates as a single-locus dominant trait, is independent of tumor burden, and is effective against cell lines from multiple types of cancer. During spontaneous regression or immediately after exposure, cancer cells provoke a massive infiltration of host leukocytes, which form aggregates and rosettes with tumor cells. The cytolytic destruction of cancer cells by innate leukocytes is rapid and specific without apparent damage to normal cells. The mice are healthy and cancer-free and have a normal life span. These observations suggest a previously unrecognized mechanism of immune surveillance, which may have potential for therapy or prevention of cancer.
Epidermal growth factor receptor signaling intensity determines intracellular protein interactions, ubiquitination, and internalization
Authors: Schmidt Mirko H. H. , Furnari Frank B. , Cavenee Webster K. , Bögler Oliver
Published: May 2003

Ligand activation of the epidermal growth factor receptor (EGFR) causes the binding of Cbls, which leads to EGFR polyubiquitination and internalization through endophilin complexes that contain the adaptor protein SH3-domain encoding, expressed in tumorigenic astrocytes/Cbl-interacting protein of 85 kDa/regulator of ubiquitous kinase (SETA/CIN85/Ruk). In cells grown at high density, high levels of SETA interfered in the recruitment of Casitas B-lineage (Cbl) proteins to the EGFR and reduced its polyubiquitination, suggesting that SETA has a regulatory function in the formation of the EGFR–Cbl–endophilin complex and in EGFR down-regulation. In a situation where there is EGFR signaling but no internalization or down-regulation, as is the case with the EGFR with exons 2–7 deleted (ΔEGFR) oncogene, these proteins were absent altogether. By using mAb 806, which recognizes an EGFR-activation state and preferentially immunoprecipitates ΔEGFR, we show that ΔEGFR did not interact with Cbls, SETA, or endophilin A1, providing a mechanistic explanation for its lack of internalization. As would be expected by the absence of Cbl proteins in the ΔEGFR complex, the mutant receptor was also not polyubiquitinated. The intracellular C terminus and tyrosine autophosphorylation pattern of ΔEGFR are similar to wild-type EGFR, but it signals at a lower intensity as determined by levels of EGFR phosphotyrosine. To test the implication that the lack of interaction with the Cbl–SETA–endophilin complex is because of differences in signal intensity, EGFR-expressing cells were treated with tyrphostin AG1478 EGFR inhibitor. Attenuation of wild-type EGFR signal to levels similar to that found in ΔEGFR resulted in the dissociation of SETA and Cbl proteins and a concomitant attenuation of receptor internalization.
Evidence for a genetic discontinuity between Neandertals and 24,000-year-old anatomically modern Europeans
Authors: Caramelli David , Lalueza-Fox Carles , Vernesi Cristiano , Lari Martina , Casoli Antonella , Mallegni Francesco , Chiarelli Brunetto , Dupanloup Isabelle , Bertranpetit Jaume , Barbujani Guido , Bertorelle Giorgio
Published: May 2003

During the late Pleistocene, early anatomically modern humans coexisted in Europe with the anatomically archaic Neandertals for some thousand years. Under the recent variants of the multiregional model of human evolution, modern and archaic forms were different but related populations within a single evolving species, and both have contributed to the gene pool of current humans. Conversely, the Out-of-Africa model considers the transition between Neandertals and anatomically modern humans as the result of a demographic replacement, and hence it predicts a genetic discontinuity between them. Following the most stringent current standards for validation of ancient DNA sequences, we typed the mtDNA hypervariable region I of two anatomically modern
Homo sapiens sapiens
individuals of the Cro-Magnon type dated at about 23 and 25 thousand years ago. Here we show that the mtDNAs of these individuals fall well within the range of variation of today's humans, but differ sharply from the available sequences of the chronologically closer Neandertals. This discontinuity is difficult to reconcile with the hypothesis that both Neandertals and early anatomically modern humans contributed to the current European gene pool.