bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 1. Spirit
Authors: Johnson Jeffrey R. , Grundy William M. , Lemmon Mark T. , Bell James F. , Johnson Miles J. , Deen Robert G. , Arvidson Raymond E. , Farrand William H. , Guinness Edward A. , Hayes Alexander G. , Herkenhoff Ken E. , Seelos Frank , Soderblom Jason , Squyres Steve
Published: February 2006

Multispectral observations of rocks and soils were acquired under varying illumination and viewing geometries in visible/near‐infrared wavelengths by the Panoramic Camera (Pancam) on the Spirit Mars Exploration Rover to provide constraints on the physical and mineralogical nature of geologic materials in Gusev Crater. Data sets were acquired at six sites located near the landing site, in the surrounding plains, and in the West Spur and Husband Hill regions of the Columbia Hills. From these ∼600 images, over 10,000 regions of interest were selected of rocks and soils over a wide range of phase angles (0–130°). Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of estimates of local facet orientations in the sky models. Single‐term and two‐term phase functions derived from Hapke scattering models exhibit a dominantly broad backscattering trend for soils and “Red” rocks inferred to be covered with variable amounts of dust and other coatings, consistent with the results from the Viking Lander and Imager for Mars Pathfinder cameras. Darker “Gray” rock surfaces (inferred to be relatively less dust covered) display more narrow, forward scattering behaviors, consistent with particles exhibiting little internal scattering. Gray and Red rocks are macroscopically rougher than most soil units, although a “dust‐cleaning” event observed near the Paso Robles site caused an increase in soil surface roughness in addition to a substantial decrease in surface single scattering albedo. Gray rocks near the rim of Bonneville Crater exhibit the largest macroscopic roughness () among all units, as well as the greatest backscattering among Gray rocks. Photometric properties of coated Red rocks vary in the West Spur region, possibly as a result of weathering differences related to elevation‐dependent aeolian regimes.
Global change: The nitrogen cycle and rivers
Authors: Schlesinger William H. , Reckhow Kenneth H. , Bernhardt Emily S.
Published: February 2006

The hydrologic sciences must play a major role in improving our understanding of the transport and fate of the vast amount of reactive nitrogen that is being added to the environment by human activities. Detailed understanding of the function of different landscape units will help predict watershed losses of nitrogen. A better understanding of the processes that control denitrification in surface and groundwaters is essential to ascertain total gaseous N loss and the percentage that is nitrous oxide, a greenhouse gas that is accumulating in Earth's atmosphere.
The PITSLRE/CDK11p58 protein kinase promotes centrosome maturation and bipolar spindle formation
Authors: Petretti Clotilde , Savoian Matthew , Montembault Emilie , Glover David M , Prigent Claude , Giet Régis
Published: February 2006

The CDK11 (cyclin‐dependent kinase 11) gene has an internal ribosome entry site (IRES), allowing the expression of two protein kinases. The longer 110‐kDa isoform is expressed at constant levels during the cell cycle and the shorter 58‐kDa isoform is expressed only during G2 and M phases. By means of RNA interference (RNAi), we show that the CDK11 gene is required for mitotic spindle formation. CDK11 RNAi leads to mitotic checkpoint activation. Mitotic cells are arrested with short or monopolar spindles. γ‐Tubulin as well as Plk1 and Aurora A protein kinase levels are greatly reduced at centrosomes, resulting in microtubule nucleation defects. We show that the mitotic CDK11p58 isoform, but not the CDK11p110 isoform, associates with mitotic centrosomes and rescues the phenotypes resulting from CDK11 RNAi. This work demonstrates for the first time the role of CDK11p58 in centrosome maturation and bipolar spindle morphogenesis.
Influence of a superconducting transition on the macroscopic characteristics of the plasticity of metals and alloys: Fundamental and applied aspects (Review)
Authors: Pustovalov V. V. , Fomenko V. S.
Published: February 2006

The results of observations and investigations of a new phenomenon—changes in the macroscopic characteristics of plastic the deformation of metals and alloys at a superconducting transition—are systematized. In these works it is shown for the first time that the electronic drag of dislocations accompanying low-temperature deformation is effective. The main experimental features of the phenomenon—the dependences of the characteristics of the change in plasticity at a superconducting transition on the stress, deformation, temperature, deformation rate, and concentration of the alloying element in the superconductor—and results indicating a correlation between the characteristics of the effect and the superconducting properties are presented. Experiments clarifying the mechanisms of the phenomenon are analyzed. A brief exposition of the theoretical investigations of the electronic drag of dislocations in metals in the normal and superconducting states and the influence of a superconducting transition on the plasticity is given. The theoretical results are compared with the experimental results. Examples of the application of the effect as a new method for investigating the physical mechanisms of low-temperature plastic deformation are presented. The applied aspects of the phenomenon are discussed separately.
Internal structure and dynamics of sheet cavitation
Authors: Coutier-Delgosha Olivier , Devillers Jean-François , Pichon Thierry , Vabre Alexandre , Woo Romuald , Legoupil Samuel
Published: February 2006

The internal structure and the dynamics of two-dimensional (2D) sheet cavitation on the suction side of a 2D foil section were investigated experimentally. Experiments were conducted in a cavitation tunnel and situations ranging from steady sheet cavitation to unsteady cloud cavitation were obtained by varying the foil incidence and the cavitation number. Using a novel endoscopic technique, coupled with x-ray attenuation measurements, the two-phase morphology and the void fraction within the sheet cavitation were investigated. Supplemental information on the instantaneous shape of the sheet cavity and its instability frequency were also obtained by visualization and pressure measurements, respectively. The investigations focused on (a) the void fraction distribution and (b) the frequency of the cavity oscillations. It was found that the void ratio can reach as much as 50% depending on the conditions of operation, and the Strouhal numbers are around 0.25 in the case of partial cavity instability and 0.12 in the case of transitional sheet cavitation. Finally, the visualization of the vapor structures within the sheet cavity for various stations along the chord gives a qualitative understanding of the process of vapor production and condensation.
Temperature dependence of mobility and carrier density in InN films
Authors: Thakur J. S. , Naik R. , Naik V. M. , Haddad D. , Auner G. W. , Lu H. , Schaff W. J.
Published: February 2006

We investigate the temperature dependence of Hall mobility μ and carrier density Ne for thin InN films grown by molecular-beam epitaxy and plasma source molecular-beam epitaxy over three orders-of-magnitude difference in their carrier density: for the low-density film Ne=5.8×1017∕cm3 and for the high-density film Ne=3.2×1020∕cm3. In both the films, for temperature up to 300 K, a large temperature-independent concentration of carriers is observed. For higher temperatures, however, carrier density increases with temperature. The characteristic behavior of the mobility for the low-density film is different from that of the high-density film, particularly for temperatures less than 300 K. The low-density film shows a peak behavior in the mobility around 250 K in contrast to the temperature-independent mobility observed for the high-density film for T<300K. We investigate theoretically the concentrations of donor, acceptor, and threading dislocations for both the films and also discussed various electron-scattering mechanisms which contribute to the mobility in these films.
Revealing ionic motion molecular solids
Authors: Thurzo I. , Zahn D. R. T.
Published: February 2006

Thin films of mixed valence semiconductor copper-tetracyano-quinodimethane (Cu-TCNQ) and small molecule tris(8-hydroxyquinolinato)aluminum (Alq3) were investigated by current-voltage (I-V) and admittance (C-V,G-V) techniques in single-layer configuration with different combinations of electrodes. The predicted hysteresis of I-V curves and nearly constant loss (NCL) could be observed for both materials. When cycling devices between negative and positive biases, slowly decaying ionic transient currents interfere with steady-state currents and point to unidirectional motions of the ionic species with subsequent redox reaction at one of the electrodes. Plotting the frequency f dependence of the equivalent parallel capacitance at zero bias as log10C(0) versus log10(f), the dielectric behavior of Cu-TCNQ and Alq3 complies with the effective-medium model for NCL in ionic conductors [J. R. Macdonald J. Appl. Phys. 94, 558 (2003)]. It also holds for a similar plot of the equivalent parallel zero-bias conductance G(0). The nature of the revealed mobile ions is discussed with emphasis on their sources.
Targeted manipulation of grain boundaries and triple junctions on thin films using lasers: A Potts model simulation
Authors: Lusk Mark T. , Upmanyu Moneesh , Vincent Tyrone
Published: February 2006

A two-dimensional Potts model is used to simulate the motion of a laser spot on a polycrystalline thin film. The model is used to demonstrate the feasibility of reshaping individual grain boundaries by either dragging grain boundaries or by repositioning triple junctions.
Nanoscale Weibull statistics
Authors: Pugno N. M. , Ruoff R. S.
Published: February 2006

In this paper a modification of the classical Weibull statistics is developed for nanoscale applications. It is called nanoscale Weibull statistics. A comparison between nanoscale and classical Weibull statistics applied to experimental results on fracture strength of carbon nanotubes clearly shows the effectiveness of the proposed modification. A Weibull’s modulus of ∼3 is deduced for nanotubes. The approach can treat (also) a small number of structural defects, as required for nearly defect-free structures (e.g., nanotubes) as well as a quantized crack propagation (e.g., as a consequence of the discrete nature of matter), allowing to remove the paradoxes caused by the presence of stress intensifications.
Lift-up process in a heated-cylinder wake flow
Authors: Ren Maosheng , Rindt Camilo , van Steenhoven Anton
Published: February 2006

A three-dimensional flow transition behind a heated cylinder is analyzed at low Reynolds numbers: Re=O(100). Both visualizations and numerical simulations show that the transition manifests itself in the form of mushroom-type structures in the far wake and Λ-shaped structures in the near wake. The legs of the Λ-shaped structures coincide with streamwise vorticity regions. An intermediate stage is observed between the Λ-shaped structures and the escaping mushroom-type structures. This intermediate step is characterized by a lift-up process, which takes place in the center region between the legs and head of the Λ-shaped structures. As a result, hot fluid is being pulled out of the upper vortex core. Due to this lift-up process, mushroom-type structures are generated in the form of escaping vortex rings in the far wake.
Nondestructive photolithography of conducting polymer structures
Authors: Chan J. R. , Huang X. Q. , Song A. M.
Published: February 2006

We have demonstrated a nondestructive method using ultraviolet (UV) photolithography to fabricate micrometer-sized conducting polymer structures. By coating a polymer film on patterned photoresist and then performing liftoff, UV exposure to the conducting polymer film was prevented throughout the lithography processes. We created features down to 1μm with high yield. Such complementary metal-oxide-semiconductor-compatible microfabrication can be applied generally to various organic films, and may allow the speed of organic electronics to be improved. Organic thin-film transistors (OTFTs) were fabricated using poly(3-hexylthiophene) as the active material, and typical OTFT characteristics were obtained.
Enhanced ferromagnetic damping in Permalloy∕Cu bilayers
Authors: Gerrits Th. , Schneider M. L. , Silva T. J.
Published: February 2006

We have investigated the enhancement of ferromagnetic damping for thin Permalloy (Ni80Fe20) films grown with Cu capping layers of variable thickness (5–1000 nm). The measurements were performed with a pulsed inductive microwave magnetometer in the frequency range between 2.3 and 2.7 GHz. The damping was enhanced if the Cu layers were thicker than the spin-diffusion length of ls≈250nm. For example, the damping was enhanced by 30% for a Permalloy (3nm)∕Cu (1000 nm) bilayer relative to the damping for Permalloy with a 5-nm-thick Cu capping layer. Existing theory for spin pumping from the Permalloy layer into the Cu layer was used to model the additional contribution to damping for these bilayer systems. Additional experiments on Permalloy (5nm)∕Cu(xnm)∕Ta (5 nm) provided indirect evidence for spin accumulation inside the Cu layer.
Microwave heating of conductive powder materials
Authors: Rybakov K. I. , Semenov V. E. , Egorov S. V. , Eremeev A. G. , Plotnikov I. V. , Bykov Yu. V.
Published: February 2006

In recent years, a considerable interest has been drawn to microwave heating of powder metals and other electrically conductive materials. In this paper a consistent formulation describing the absorption of microwaves in electrically conductive materials under different microwave heating conditions is developed. A special case when conductive powder particles are surrounded by insulating oxide layers is investigated in detail using the effective-medium approximation. The conditions giving rise to skin effect governed, volumetric, and localized microwave heating are analyzed. Experimental observations of different microwave heating regimes in silicon, iron, and copper powder compacts are in general agreement with the theoretical model.
Hugoniot and strength behavior of silicon carbide
Authors: Vogler T. J. , Reinhart W. D. , Chhabildas L. C. , Dandekar D. P.
Published: February 2006

The shock behavior of two varieties of the ceramic silicon carbide was investigated through a series of time-resolved plate impact experiments reaching stresses of over 140 GPa. The Hugoniot data obtained are consistent for the two varieties tested as well as with most data from the literature. Through the use of reshock and release configurations, reloading and unloading responses for the material were found. Analysis of these responses provides a measure of the ceramic’s strength behavior as quantified by the shear stress and the strength in the Hugoniot state. While previous strength measurements were limited to stresses of 20–25 GPa, measurements were made to 105 GPa in the current study. The initial unloading response is found to be elastic to stresses as high as 105 GPa, the level at which a solid-to-solid phase transformation is observed. While the unloading response lies significantly below the Hugoniot, the reloading response essentially follows it. This differs significantly from previous results for B4C and Al2O3. The strength of the material increases by about 50% at stresses of 50–75 GPa before falling off somewhat as the phase transformation is approached. Thus, the strength behavior of SiC in planar impact experiments could be characterized as metal-like in character. The previously reported phase transformation at ∼105GPa was readily detected by the reshock technique, but it initially eluded detection with traditional shock experiments. This illustrates the utility of the reshock technique for identifying phase transformations. The transformation in SiC was found to occur at about 104 GPa with an associated volume change of about 9%.
Theoretical accuracy of using Boltzmann and ionized impurity approximations in the analyses of recombination current at interface traps in metal-oxide-silicon structures
Authors: Chen Zuhui , Jie Bin B. , Sah Chih-Tang
Published: February 2006

In order to provide high computation speed, the Boltzmann distribution and fully ionized impurity (BI) approximations have been used to analyze experimental recombination current data to extract interface properties of metal-oxide-semiconductor (MOS) structures. The accuracy of the BI approximation is theoretically estimated in this paper by computing its deviation from the exact Fermi distribution and de-ionizable-impurity theory. Five device and material parameters of the MOS transistor structures are varied: substrate dopant-impurity concentration, gate oxide thickness, forward source and drain junction bias, interface-trap energy level, and transistor temperature. The results show that the BI approximation gives less than 5% deviation over the practical ranges of the five parameters.
Liquid-gas separation in colloidal electrolytes
Authors: Caballero José B. , Puertas Antonio M. , Fernández-Barbero Antonio , Javier de las Nieves F. , Romero-Enrique J. M. , Rull L. F.
Published: February 2006

The liquid-gas transition of an electroneutral mixture of oppositely charged colloids, studied by Monte Carlo simulations, is found in the low-temperature–low-density region. The critical temperature shows a nonmonotonous behavior as a function of the interaction range, κ−1, with a maximum at κσ≈10, implying an island of coexistence in the κ-ρ plane. The system is arranged in such a way that each particle is surrounded by shells of particles with alternating charge. In contrast with the electrolyte primitive model, both neutral and charged clusters are obtained in the vapor phase.
Simultaneous in situ monitoring of surface and gas species and surface properties by modulation excitation polarization-modulation infrared reflection-absorption spectroscopy: CO oxidation over Pt film
Authors: Urakawa Atsushi , Bürgi Thomas , Schläpfer Hans-Peter , Baiker Alfons
Published: February 2006

A method for in situ monitoring of surface and gas species utilizing separately the difference and sum reflectivity of two polarizations, normal and parallel to the surface, measured by polarization-modulation infrared reflection-absorption spectroscopy is presented. Surface and gas-phase spectra were separately but simultaneously obtained from the reflectivities. The technique is combined with modulation excitation spectroscopy to further enhance the sensitivity, and a small-volume cell was designed for this purpose. CO oxidation over a 40nm Pt film on aluminum was investigated under moderate pressure (atmospheric pressure, 5% CO, and 5%–40% O2) at 373–433K. The surface species involved in the oxidation process and the gas-phase species, both reactant (CO) and product (CO2), could be simultaneously monitored and analyzed quantitatively. In addition, the reflectivity change of the sample during the reaction was assigned to a near-surface bulk property change, that is, surface reconstruction to the oxide phase. Under an O2-rich atmosphere, two reactive phases, denoted as low- and high-activity phases, were identified. A large amount of atop CO was observed during the low-activity phase, while the adsorbed CO completely disappeared during the high-activity phase. The presence of an infrared-inactive CO2 precursor formed by the reaction between surface oxide and gaseous CO during the high-activity phase was inferred. The desorption of the CO2 precursor is facilitated under a CO-rich atmosphere, most likely, by surface reconstruction to metallic Pt and a competitive adsorption of CO on the surface.
Voltammetric study of Bphen electron-transport layer in contact with LiF∕Al cathode in organic light-emitting diodes
Authors: Kondakov D. Y.
Published: February 2006

We report that the similarities of I-V characteristics of organic light-emitting diodes (OLEDs) incorporating Bphen (4,7-diphenyl-1,10-phenanthroline) electron-transport layer, with or without lithium doping, do not stem from the analogous compositions of the respective electron-transport layers. Voltammetric studies of OLED devices of the following general structure: anode ∣ NPB (N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine) ∣ TBADN (9,10-bis(2-naphthyl)-2-t-butylanthracene) ∣ Bphen ∣ LiF ∣ Al, indicate that the bulk of the Bphen electron-transport layer has insulating rather than semiconducting properties. A previously unknown feature is also detected by voltammetry: the presence of a macroscopic dipole comprised of a negative interfacial charge at the NPB ∣ TBADN interface and a positive charge in the Bphen layer and∕or at the TBADN ∣ Bphen interface, which could result from the diffusion of lithium ions. We also find that, in contrast to the bulk of the Bphen layer, its thin sublayer has, in fact, semiconducting properties, which also could be reasonably explained by the diffusion of lithium ions along with the migration of a countercharge, e.g., electron hopping between Bphen molecules.
Rapid thermal annealing of hot wire chemical-vapor-deposited a-Si:H films: The effect of the film hydrogen content on the crystallization kinetics, surface morphology, and grain growth
Authors: Mahan A. H. , Roy B. , Reedy R. C. , Readey D. W. , Ginley D. S.
Published: February 2006

The ability to crystallize thin amorphous Si layers into large grain Si can lead to significant improvements in Si solar cells and thin-film transistors. Here we report on the effect of the hydrogen content in as-grown films on the crystallization kinetics, surface morphology, and grain growth for hot wire chemical-vapor-deposited a-Si:H films crystallized by rapid thermal annealing (RTA). At RTA temperatures >750°C for high-hydrogen-content films, we observe the explosive evolution of hydrogen, with a resultant destruction of the film. Little or no damage is observed for films containing low hydrogen content. At a lower RTA temperature (600°C), the films remain intact with similar morphologies. At this same lower RTA temperature, both the incubation time and crystallization time decrease, and the grain size as measured by x-ray diffraction increases with decreasing hydrogen film content. Measurements of the crystallization time versus H evolution time indicate that the vast majority of the hydrogen must evolve from both films before crystallization commences. To examine the relationship between hydrogen evolution and crystallization, a two-step annealing process was utilized. For the high hydrogen content films, the final grain size increases if a large portion of the hydrogen is driven out at temperatures well below the crystallization temperature.
Emission characteristics of near-stoichiometric Er∕Yb-codoped LiNbO3 crystals
Authors: Zhang De-Long , Pun E. Y. B.
Published: February 2006

Polarized visible, near-infrared, and 980-nm up-conversion emission characteristics in near-stoichiometric Z-cut Er(0.6mol%)∕Yb(0.3mol%)-codoped LiNbO3 crystals, prepared by vapor-transport-equilibration (VTE) technique, were investigated and discussed in comparison with corresponding as-grown crystal, thermally calcined ErNbO4 powder, as well as Z-cut only Er(2.0mol%)-doped LiNbO3 crystal that was subjected to the same VTE procedure as one of the Er∕Yb-codoped crystals. The VTE-induced crystalline phase transformation is discussed in combination with optical absorption results reported previously. The percentage of Er3+ ions present in the crystals as the ErNbO4 phase is evaluated based upon the optical absorption and the emission data at 1.5μm. An empirical expression for evaluating the Li composition in a near-stoichiometric Er(/Yb)-doped LiNbO3 crystal from the narrowing percentage of the σ- or α-polarized 1530nm emission peak is established based upon the emission spectra of singly Er-doped VTE LiNbO3 crystals. From the measured absorption band areas and the Judd-Ofelt theory, the influence of the VTE treatment on the Er3+ spectroscopic property was studied. The experimentally observed VTE effect on the emission intensity is conducted with the theoretical results of the transition probability. Both the theoretical and experimental results reveal that the VTE treatment results in the lengthening of the 1.5μm lifetime as much as 15%. A mechanism that the VTE treatment induces the crystalline phase transformation and the reduction of both OH− and intrinsic defect contents is proposed to explain the VTE effect on the lifetime.
In situ measurements of cobalt thin-film surface roughening upon annealing
Authors: Espinosa Jorge , Shi Hongtao , Lederman D.
Published: February 2006

Atomic force and scanning tunneling microscopies were employed to investigate the surface roughness of 5.0- and 8.0-nm-thick Co films as a function of annealing temperature. Films were epitaxially grown on (110) Al2O3 at 315°C via molecular-beam epitaxy. The as-grown films had a surface roughness average of approximately 0.7nm. Images were acquired in situ at temperatures ranging from room temperature to 600°C. For the 5.0nm films, surface roughening abruptly starts at a critical temperature T0=459°C and increases depending on the final annealing temperature and annealing time. After waiting long periods of time, so that the film is in quasiequilibrium, the roughness increases with increasing temperature T with a power-law dependence (T∕T0−1)0.5. This sudden roughening process is irreversible and possibly related to the hcp-fcc martensitic phase transition in cobalt, which occurs at 415°C in bulk, or due to bulk defect diffusion. The autocorrelation function of the images above T0 shows that the in-plane island size during roughening is larger in a direction perpendicular to the sapphire terraces. The 8.0-nm-thick film sample revealed the formation of irregularly shaped pits with a lateral size of ∼350nm at temperatures greater than ∼550°C.
Transient and steady-state amplitudes of resonant three-dimensional sloshing in a square base tank with a finite fluid depth
Authors: Faltinsen O. M. , Rognebakke O. F. , Timokha A. N.
Published: February 2006

An adaptive asymptotic nonlinear modal system is used for systematic quantification of three-dimensional steady-state resonant sloshing in a square base tank with a finite fill depth. The depth/breadth ratios are ⩾0.4. The tank is laterally excited with frequency close to the lowest natural frequency. The main emphasis is on the “swirling” wave regime and its special features, e.g., stability, feedback of higher modes, and regular and irregular switch of the apparent direction of rotation. Theoretical results are validated for both steady-state solutions and “beating” that does not die out in experimental investigations. Frequency domains with no stable steady-state waves and occurrence of “chaotic” waves are discussed.
Biglobal linear stability analysis of the flow induced by wall injection
Authors: Chedevergne F. , Casalis G. , Féraille Th.
Published: February 2006

The hydrodynamic stability of the flow in a solid rocket motor is revisited using a general linear stability approach. A harmonic perturbation is introduced into the linearized Navier-Stokes equations leading to an eigenvalue problem posed as a system of partial differential equations with respect to the spatial coordinates. The system is discretized by a spectral collocation method applied to each spatial coordinate and the eigenvalues are determined using Arnoldi’s procedure. A special emphasis is placed on the boundary conditions. The main result is the discrete nature of the eigenvalue set. According to the present theory and the obtained results, only some discrete frequencies may exist in the motor (as eigenmodes). These frequencies only depend on the Reynolds number based on the injection velocity and the radius of the pipe flow. They are compared to measurements that have been performed at ONERA in one case with a cold-gas setup and in another case with a reduced scale live motor. Due to the agreement obtained with both experiments, the biglobal stability approach seems to offer new insight into the unresolved thrust oscillations problem.
Ultraviolet emission intensity, visible luminance, and electrical characteristics of small arrays of Al∕Al2O3 microcavity plasma devices operating in Ar∕N2 or Ne at high-power loadings
Authors: Park S.-J. , Kim K.-S. , Eden J. G.
Published: February 2006

Small arrays (3×3→10×10) of microcavity plasma devices, having a two-stage structure comprising multilayer stacks of nanostructured Al2O3 grown on Al foil with cylindrical microcavities 100–300μm in diameter, produce intense ultraviolet (UV) and visible emission when operated in Ar∕3% N2 gas mixtures or Ne and excited by a sinusoidal ac voltage wave form. Near-UV (300–400nm) intensities emitted into a solid angle of ∼10−2sr above 30 mW per cm2 of radiating area are measured for Ar∕N2 gas mixture pressures of 400–800Torr, an excitation frequency of 15kHz, and an average current ⩾20mA (rms). Two or more conjoined cylindrical microcavities of differing diameters allow for the confinement of the plasma to progressively smaller volumes as the power deposited is increased (thereby decreasing the Debye length and the spatial extent of the cathode fall region) and provides a convenient tool with which the luminosity of an array can be modulated. The transition of a microplasma from confinement in a 200-μm-diam cavity into an adjacent 100-μm-diam microcavity is accompanied by an order-of-magnitude increase in the luminance of Ne plasmas in a 3×3 array as the rms current is increased by ∼1mA.
Detailed balance method for ideal single-stage fluorescent collectors
Authors: Markvart T.
Published: February 2006

It is shown that fluorescent collectors where radiation is confined with the use of selective reflectors can be modeled as converters of blackbody radiation. By decreasing the temperature and frequency of the radiation, the effective étendue of the emitted beam can be reduced substantially in the conversion process without violating the second law of thermodynamics. This type of collector can, in principle, achieve surprisingly high efficiencies: the output from a silicon solar cell operating with an ideal collector can exceed 90% of the output from a directly illuminated solar cell.
Influence of the injection current sweep rate on the polarization switching of vertical-cavity surface-emitting lasers
Authors: Masoller C. , Torre M. S. , Mandel Paul
Published: February 2006

We study the polarization switching of vertical-cavity surface-emitting lasers based on simulations of the spin-flip model. We show that the switching point depends on the ramp signal used to scan the injected current. Fast current ramps enlarge the hysteresis region since the switching point moves to high pump values for increasing injection and to low pump values for decreasing injection. The delay of the bifurcation follows a power law with the slope of the current ramp.
Contamination of silicon dioxide films by aqueous zirconium and hafnium species
Authors: Lowalekar V. , Raghavan S. , Pandit V. , Parks H. G. , Jeon J.
Published: February 2006

Zirconium and hafnium oxides and silicates have emerged as potential replacements for SiO2 as gate dielectric material. Patterning of these materials by wet etching in fabrication areas originally designed for SiO2 gates may give rise to contamination of SiO2 by aqueous zirconium and hafnium species. This paper summarizes the work carried out to characterize the adsorption behavior of aqueous zirconium and hafnium species onto thermally grown silicon dioxide. Electrokinetic and adsorption measurements were carried out to understand the extent and nature of interaction. The adsorption of both Zr and Hf species showed a maximum at pH 5.5. Significant reduction in the adsorption of both Zr and Hf occurred upon addition of fluoride ions to the solution. Using appropriate speciation diagrams, an adsorption model has been developed to explain the experimental data.
Imaging carious human dental tissue with optical coherence tomography
Authors: Freitas A. Z. , Zezell D. M. , Vieira N. D. , Ribeiro A. C. , Gomes A. S. L.
Published: February 2006

Optical coherence tomography is an imaging technology that produces high-resolution cross-sectional images of turbid media and internal microstructures including inside living tissue. In this work, three-dimensional images of a dental microstructure, that can be used to make both qualitative and quantitative assessments of oral tissue health, were obtained. It was possible to detect subclinical caries in third molar human teeth, showing that the lesion is located below the surface at 10μm with a maximum depth lesion of 50μm. A three-dimensional image was constructed confirming that it is possible to observe different planes inside the sample. It is important to notice that the optical changes induced by the carious disease in dental tissue can be readily detected by the optical coherence tomography method, before structural changes become apparent.
Efficient computation of the first passage time distribution of the generalized master equation by steady-state relaxation
Authors: Shalloway David , Faradjian Anton K.
Published: February 2006

The generalized master equation or the equivalent continuous time random walk equations can be used to compute the macroscopic first passage time distribution (FPTD) of a complex stochastic system from short-term microscopic simulation data. The computation of the mean first passage time and additional low-order FPTD moments can be simplified by directly relating the FPTD moment generating function to the moments of the local FPTD matrix. This relationship can be physically interpreted in terms of steady-state relaxation, an extension of steady-state flow. Moreover, it is amenable to a statistical error analysis that can be used to significantly increase computational efficiency. The efficiency improvement can be extended to the FPTD itself by modelling it using a gamma distribution or rational function approximation to its Laplace transform.
Wavelength dependence of combined local and carrier transport optical nonlinearities in a hetero n-i-p-i structure
Authors: Kost Alan R. , Jupina Michael H. , Hasenberg Thomas C. , Garmire Elsa M.
Published: February 2006

The combination of carrier transport-type optical nonlinearity and absorption saturation is examined for a hetero n-i-p-i sample at wavelengths between 966 and 985 nm and for intensities up to 1000W∕cm2. Transmission changes are found to depend on the interplay between the shift, narrowing, and increasing peak height of an excitonic absorption resonance. Transmission changes previously attributed to absorption saturation are found to be due to carrier transport nonlinearity. Absorption saturation contributed to transmission change for intensities greater than 100W∕cm2, a larger value than previously reported; however saturation intensity still appears to have been reduced by charge separation and a correspondingly slower electron-hole relaxation rate.
A study of HfO2 film interfaces with Si and SiO2
Authors: Lopez C. M. , Irene E. A.
Published: February 2006

The interfaces studied were formed by the thermal oxidation of sputter-deposited Hf metal onto Si(100)- and SiO2-covered Si(100) wafers and were analyzed in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5–4.5 photon energy range and with mass spectrometry of recoiled ions (MSRI). SE yielded optical properties and MSRI yielded film and interface composition. Reactivity between HfO2 and both substrates was found to be similar based upon the optical properties of the interface layer. Equivalent oxide thicknesses and interface trap levels were determined and significant reduction in interface traps was noticed for samples with a 2 nm SiO2 film on Si. In addition, hillock formation was seen to occur upon oxidation of Hf metal on the Si substrates and depended on the starting thickness of the metal layer and was not seen for the SiO2-covered substrates.
Modified charge-transfer emission in perylene tetracarboxylic dianhydride-aluminum quinoline layer structures
Authors: Wagner H. P. , DeSilva A. , Gangilenka V. R. , Kampen T. U.
Published: February 2006

Light emission from thin films of low molecular weight organic semiconductors is dominated by excitons. Here, we study the nature of exciton emission in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) films, in PTCDA∕aluminum-tris-hydroxyquinoline (Alq3) multilayers, and in PTCDA∕Alq3 codeposited films by photoluminescence spectroscopy at temperatures between 10 and 80 K. The films are grown by organic molecular beam deposition on Si(001) substrates covered with a natural oxide. In PTCDA∕Alq3 structures, we observe a redshift and an enhancement of the charge-transfer exciton emission (CT2) between stacked PTCDA molecules. The modification of the CT2 emission is attributed to compressive strain fields generated by tilted or distorted crystallites within the PTCDA layers. The internal strain increases the CT2 exciton trapping probability and its binding energy. The interpretation of the modified CT2 emission is supported by x-ray diffraction measurements and Fourier transform infrared spectroscopy revealing an enhancement of out-of-plane disorder of PTCDA molecules in PTCDA∕Alq3 multilayers and codeposited structures.
Nonlinear anisotropic description for the thermomechanical response of shocked single crystals: Inelastic deformation
Authors: Winey J. M. , Gupta Y. M.
Published: February 2006

A nonlinear anisotropic continuum framework for describing the thermoelastic-plastic response of single crystals shocked along arbitrary orientations has been developed. Our modeling approach incorporates nonlinear elasticity, crystal plasticity, and thermodynamic consistency within an incremental tensor formulation. Crystal plasticity was incorporated by considering dislocation motion along specified slip planes. The theoretical developments presented here are sufficiently general to also accommodate other types of inelastic deformation mechanisms. As representative applications of the theoretical developments, numerical simulations of shock wave propagation in lithium fluoride (LiF) and copper single crystals are presented and compared to wave profile data for several crystal orientations. Simulations of shock wave propagation along low-symmetry directions, where data are not available, are also presented to examine the propagation of quasilongitudinal and quasishear waves in crystals undergoing elastic-plastic deformation. Temperature calculations for the shocked single crystals are discussed.
Strain and its effect on optical properties of Al-N codoped ZnO films
Authors: He H. P. , Zhuge F. , Ye Z. Z. , Zhu L. P. , Wang F. Z. , Zhao B. H. , Huang J. Y.
Published: February 2006

The dependence of lattice strain in Al-N codoped p-type ZnO films on Al content and growth temperature was investigated. With increasing Al content, the compressive strain in the film first increases and then decreases. We suggest that the strain decrease is due to the occupation of more substitutional sites by Al at relatively high Al content, which partially compensates the compressive strain. Reversion of conduction type at high Al content and high temperature was also observed. By studying the strain and electrical properties of the codoped films, we conclude that ZnO film should be grown at intermediate temperatures and with low Al content to achieve both good p-type conduction and reasonable crystal quality. The compressive strain results in increase of the optical band gap, and a linear relationship between them was obtained.
Effect of phosphorus dopant on photoluminescence and field-emission characteristics of Mg0.1Zn0.9O nanowires
Authors: Lee Chia Ying , Tseng Tseung Yuen , Li Seu Yi , Lin Pang
Published: February 2006

The photoluminescence and field-emission properties of Mg0.1Zn0.9O nanowires (MZO NWs) hydrothermally grown on the p-type silicon (100) substrates with and without phosphorus dopant were investigated in this study. Parts of MZO NWs were treated with PH3 plasma to form phosphorus-doped MZO NWs (PMZO NWs). The MZO and PMZO are wurtzite single crystals, and the surface morphologies of MZO NWs are identical to those of PMZO NWs with an average diameter of 50 nm and a length of 500 nm. The direct band gaps and emitted ultraviolet photoluminescences of the MZO and PMZO NWs are 3.41 eV and 403.8 nm and 3.56 eV and 385.4 nm, respectively. The MZO NWs grown on Si substrates have an emission threshold electric field of 1.8V∕μm (current density of 1.0mA∕cm2) and a field enhancement factor, β, of 3048 while the PMZO NWs show enhanced properties with a threshold electric field of 1.5V∕μm and a β value of 3054. These field-emission properties are also enhanced by illumination, which reveals that the emission behavior is affected by the surface charge state. Therefore, it is suggested that the band structure of MZO NWs has been modulated by phosphorus incorporation.
Critical thickness and lattice relaxation of Mg-rich strained Mg0.37Zn0.63O (0001) layers towards multi-quantum-wells
Authors: Matsui Hiroaki , Tabata Hitoshi , Hasuike Noriyuki , Harima Hiroshi
Published: February 2006

The heteroepitaxy of Mg-rich Mg0.37Zn0.63O layers on ZnO (0001) substrates was carried out using laser molecular-beam epitaxy. Mg0.37Zn0.63O layers changed from a two-dimensional (2D) to three-dimensional growth mode at a layer thickness (tc) between 38 and 100 nm through lattice-strain relaxation. For tc>100nm, hexagonal nanodots with a density in the order of 109cm−2 formed naturally by the Stranski-Krastanov mode. The individual nanodots possessed pyramidal hillocks with lateral sizes raging from 100 to 200 nm, and phase separation to Mg-rich and Mg-poor regions in the Mg0.37Zn0.63O alloys was found from the results of atomic force microscopy and microphotoluminescence spectroscopy. A suitable layer thickness of Mg0.37Zn0.63O concerning quantum barriers was speculated as being 38 nm from a theoretical calculation based on the Matthew and Blakeslee model [J. Cryst. Growth 27, 118 (1974)]. For tc≦38nm, the top surface of the Mg0.37Zn0.63O layer was very flat due to the curtailment of 2D growth. This contributed to the coherent growth of Mg-rich Mg0.37Zn0.63O∕ZnO multi-quantum-well structure (MQWS) with high crystallinity, as characterized from structural analyses using high-resolution x-ray diffraction. The two-dimensional properties of the MQWS were confirmed from the anisotropic optical property and electrical conductivity with 2D electron transport at low temperatures.
Correlation between structure and properties in multiferroic La0.7Ca0.3MnO3∕BaTiO3 superlattices
Authors: Singh M. P. , Prellier W. , Mechin L. , Simon Ch. , Raveau B.
Published: February 2006

Superlattices composed of ferromagnetics, namely La0.7Ca0.3MnO3 (LCMO), and ferroelectrics, namely, BaTiO3 (BTO), were grown on SrTiO3 at 720 °C by a pulsed laser deposition process. While the out-of-plane lattice parameters of the superlattices, as extracted from the x-ray diffraction studies, were found to be dependent on the BTO layer thickness, the in-plane lattice parameter is almost constant. The evolution of the strains, their nature, and their distribution in the samples were examined by the conventional sin2ψ method. The effects of structural variation on the physical properties, as well as the possible role of the strain on inducing the multiferroism in the superlattices, have also been discussed.
Electrical and optical properties of PbTe p-n junction infrared sensors
Authors: Barros A. S. , Abramof E. , Rappl P. H. O.
Published: February 2006

Lead telluride mesa diodes were fabricated from a series of p-n junctions grown on (111) BaF2 substrates, in which the hole concentration p was kept constant at 1017cm−3 and the electron concentration n varied between 1017 and 1019cm−3. Capacitance-voltage analysis showed that for n>1018cm−3 the PbTe p-n junction is one sided and abrupt. The parameters (incremental resistance, series and parallel resistances, and ideality factor) obtained from the current-voltage (I-V) characteristics and the detectivity D* exhibited a large fluctuation among the photodiodes. In spite of these fluctuations, it was possible to correlate the noise and D* values to the parameters obtained from the I-V analysis. These results allow predicting the PbTe detector’s figures of merit from the data obtained from the I-V curves. The best PbTe photodiodes fabricated here showed D* values close to 1011cmHz1∕2W−1, comparable to InSb and HgCdTe commercial detectors and to PbTe sensors fabricated on Si substrates.
Nanogap capacitors: Sensitivity to sample permittivity changes
Authors: Ionescu-Zanetti C. , Nevill J. T. , Di Carlo D. , Jeong K. H. , Lee L. P.
Published: February 2006

Sensors based on nanogap capacitance changes are being developed for genomic and proteomic applications because they offer label-free detection on platforms amenable to high throughput configurations. We compare impedance spectroscopy measurements with a rigorously characterized model that predicts the impedance spectrum of these devices based on geometry. Sensitivity to permittivity changes is also predicted by the model and compared to the measured values in the frequency range from 1Hz to 3MHz. The lowest detection limit for the magnitude of the impedance (∣Z∣) is in the region of 100–0.2MHz, and was measured to be a 1.7% change in permittivity across different devices.
Cooperative effects of a combined substitution on the magnetic properties of Nd2−xYxFe17−ySiy intermetallic compounds (⩽x⩽1.5,⩽y⩽3.0)
Authors: Liu X. F. , Lv J. Y. , Han S. B. , Hao Y. M. , Hu Z. B. , Chen D. F. , Xue Y. J. , Li J. H.
Published: February 2006

The effects of a combined substitution of Nd by Y and Fe by Si in Nd2−xYxFe17−ySiy compounds (0⩽x⩽1.5,0⩽y⩽3.0) on structural and magnetic properties have been investigated by means of x-ray diffraction, neutron diffraction, and magnetic measurements. The investigated samples crystallize in Th2Zn17-type structure with only small amounts of alpha-Fe. The unit cell volume decreases with increasing Y content or Si content. Neutron diffraction analysis indicates that substitution of Y for Nd induces a decrease of Si occupancy in 18h sites and increases in 9d sites and 18f sites. With the substitution of Y for Nd, the average site bond lengths in 6c, 9d, 18f, and 18h sites all decrease, but the distances of all Fe-Fe pairs do not change negatively. The TC of Nd2−xYxFe17−ySiy increases significantly with increasing Si substitution (y⩽3.0), but it changes slightly with increasing Y substitution. Similar to the case of Si substitution, the Ms also first increases and then decreases with increasing Y substitution. The highest TC of 535K and the highest Ms of 121.1emu∕g were observed in Nd1.5Y0.5Fe14.0Si3.0 and Nd1.5Y0.5Fe15.0Si2.0, respectively, which indicates that the combined substitution of Nd by Y and Fe by Si can have a strongly cooperative effect on the improvements of magnetic properties.