bluuebunny/crossref_metadata_2025 huggingface dataset:
Compact flashlamp-based fluorescence imager for use under ambient-light conditions
Authors: Lanni Frederick , Pane David A. , Weinstein Shmuel J. , Waggoner Alan S.
Published: March 2007

A low-power, lightweight, multiwavelength fluorescence imager based on the use of a compact xenon flashlamp, bandpass filters, gated charge-coupled device camera, and digital image processing was developed for use on an autonomous rover vehicle. The imager discriminates against ambient light by use of microsecond excitation pulses along with synchronized camera operation to limit the time period in which ambient-light photocounts are accumulated, and digital image subtraction to remove background counts. In a 10 cm square field of view, weak fluorescence, equivalent to 0.05pmol fluorescein∕mm2, can be quantified against a white-light background equivalent to shaded sunlight. For application in autonomous search for organisms in extreme environments such as in situ desert rock or soil, the instrument was equipped with a set of fluorescence excitation filters (380, 450, 545, and 600nm) and emission filters (460, 510, 620, and 740nm) suitable for detection of chlorophyll, applied stains for protein, DNA, lipid and carbohydrate, and autofluorescence. True-color images were obtained through red-green-blue imaging filters (630, 535, and 470nm) used with white-light flashes. Automated focusing on ground features was based on the R-band image and was carried out prior to fluorescence image acquisition.
Noncollinear magnetism in Permalloy
Authors: Eisenbach Markus , Stocks G. Malcolm , Nicholson Don M.
Published: March 2007

Permalloy is an important material in a wide variety of magnetic systems, most notably in giant-magnetoresistive read heads. However, despite this great interest, its properties are not fully understood. For an in depth analysis of important physical properties as, e.g., electric transport or magnetic anisotropy, a detailed understanding of the distribution of magnetic moments on an atomic level is necessary. Using our first principles locally self-consistent multiple scattering method, we calculate the magnetic ground state structure for a large supercell model of Permalloy. Our code allows us to solve both the usual nonrelativistic Schrödinger equation as well as the fully relativistic Dirac equation and to find the magnitude and direction of the magnetic moments at each atomic site. While the nonrelativistic calculation yields a collinear ground state in accordance with previous calculations, we find the ground state for the fully relativistic calculation to be slightly noncollinear. We also investigate the influence of variations in the iron concentration on the distribution of magnetic moments.
Intermediate nonlinear regime of a line-tied g mode
Authors: Zhu P. , Hegna C. C. , Sovinec C. R. , Bhattacharjee A. , Germaschewski K.
Published: March 2007

A sequence of nonlinear regimes is identified for the nonlinear development of a line-tied g mode. The dynamics of the intermediate nonlinear regime is described. This regime is operable when the mode’s convection amplitude is comparable to the mode width in the direction of the density gradient. The governing equations are derived. Comparisons between these equations and direct magnetohydrodynamic simulations show agreement.
Antiferromagnetic interlayer coupling through a thin MgO layer in γ-Fe2O3∕MgO∕Fe(001) multilayers
Authors: Yanagihara H. , Toyoda Yuta , Kita Eiji
Published: March 2007

We investigated the magnetization process of epitaxial MgO(001)∕γ-Fe2O3∕MgO∕Fe(001) multilayers. When the thickness of a MgO spacer layer was less than 1.0nm, an antiferromagnetic interlayer exchange coupling (IEC) between Fe(001) and γ-Fe2O3(001) layers appeared. Unlike the oscillatory IEC in metallic systems, the sign of the observed IEC is only antiferromagnetic. The strongest coupling constant was found to be around −1.8erg∕cm2 at the MgO thickness of 0.5nm. This antiferromagnetic coupling via the insulating MgO layer is possibly understood within the framework of spin polarized tunneling models.
Anomalous neutron Compton scattering cross sections in ammonium hexachlorometallates
Authors: Krzystyniak M. , Chatzidimitriou-Dreismann C. A. , Lerch M. , Lalowicz Z. T. , Szymocha A.
Published: March 2007

The authors have performed neutron Compton scattering measurements on ammonium hexachloropalladate (NH4)2PdCl6 and ammonium hexachlorotellurate (NH4)2TeCl6. Both substances belong to the family of ammonium metallates. The aim of the experiment was to investigate the possible role of electronic environment of a proton on the anomaly of the neutron scattering intensity. The quantity of interest that was subject to experimental test was the reduction factor of the neutron scattering intensities. In both samples, the reduction factor was found to be smaller than unity, thus indicating the anomalous neutron Compton scattering from protons. Interestingly, the anomaly decreases with decreasing scattering angle and disappears at the lowest scattering angle (longest scattering time). The dependence of the amount of the anomaly on the scattering angle (scattering time) is the same in both substances (within experimental error). Also, the measured widths of proton momentum distributions are equal in both metallates. This is consistent with the fact that the attosecond proton dynamics of ammonium cations is fairly well decoupled from the dynamics of the sublattice of the octahedral anions PdCl62− and TeCl62−, respectively. The hypothesis is put forward that proton-electron decoherence processes are responsible for the considered effect. Decoherence processes may have to do rather with the direct electronic environment of ammonium protons and not with the electronic structure of the metal-chlorine bond.
Pulsed inductive measurement of ultrafast magnetization dynamics in interlayer exchange coupled NiFe∕Ru∕NiFe films
Authors: Martin T. , Belmeguenai M. , Maier M. , Perzlmaier K. , Bayreuther G.
Published: March 2007

Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR), as well as quasistatic methods such as a magneto-optic Kerr effect magnetometer and a vibrating sample magnetometer, have been used for complementary studies of interlayer exchange coupled Si∕Ta∕NiFe(30nm)∕Ru(t)∕NiFe(30nm)∕Ta films of variable Ru thickness t. The coupling constants were determined from the measured magnetization curves by fitting them to simulated ones. The dynamics measurements revealed two spin wave modes, which could be identified as optical and acoustical ones. The optical mode changes significantly with the coupling, whereas the slight change of the acoustical mode is due to different relative orientations of the layer magnetizations. Numerical simulations helped to identify optical and acoustical modes. The intensity of these two modes changes with the bias field and coupling. Using VNA-FMR the optical mode could be observed up to higher bias fields than with the PIMM at small excitation angles. While varying the pulse field up to 150Oe using the PIMM, the intensity ratio of optical and acoustical modes changed and additional modes occurred.
Latent heat of the fcc Ising antiferromagnet
Authors: Beath A. D. , Ryan D. H.
Published: March 2007

To obtain critical parameters of the fcc Ising antiferromagnet from Monte Carlo data, a numerical estimate of the latent heat Δ is required. The precision of current estimates is about 3%, and ultimately limits the precision achieved for the disordered state at the Néel temperature TN. Here we make several different estimates of the latent heat, using finite size scaling of Monte Carlo data, and show that a superior method yields a 25-fold improvement [Δ=0.4559(6)] in comparison with our older result [Δ=0.455(15)].
All-ion accelerators: An injector-free synchrotron
Authors: Takayama Ken , Arakida Yoshio , Iwashita Taiki , Shimosaki Yoshito , Dixit Tanuja , Torikai Kota
Published: March 2007

A medium-energy synchrotron capable of accelerating all-ion species is proposed. The accelerator employs a strong focusing lattice for ion-beam guiding and induction acceleration for acceleration and longitudinal capture, which is driven by a switching power supply. All ions, including cluster ions in their possible and arbitrary charge state, are accelerated in a single accelerator. Since the switching power supply employing solid-state switching elements is energized by a trigger signal, which is generated from a bunch monitor signal produced by a circulating ion bunch, the induction acceleration always synchronizes with the bunch circulation. This feature enables the realization of an almost injector-free synchrotron.
Equiaxed Nd–Fe–B fine powder with high performance prepared by mechanical alloying
Authors: Han Jingzhi , Liu Shunquan , Zhang Xiaodong , Du Honglin , Wang Changsheng , Yang Yingchang , Yue Ming , Liu Xubo
Published: March 2007

Equiaxed Nd11.9Fe76.9Co4.8B5.9Zr0.5 fine powders with high performance are fabricated by mechanical alloying method in this work. The mechanically alloyed Nd–Fe–B powders have a Br of 8.7kGs, an Hci of 10283Oe, and a (BH)max of 15.03MGOe. Moreover, it is notable that the Mr∕Ms ratio of these powders reaches 0.73. According to x-ray diffraction and high-resolution transmission electron microscopy studies, the powders consist of two phases, the Nd2Fe14B and α-Fe phase, and an average grain size of both phases is about 30nm. These results show that the remanence enhancement of the powders may be from the exchange coupling among Nd2Fe14B grains as well as between Nd2Fe14B and Fe grains. Scanning electron microscopy studies show that the mechanically alloyed powders are equiaxed, and the powders’ size distribution is very broad. Further investigation using a laser scattering particle size distribution analyzer shows that the size distribution of the powders is bimodal, and the mean size is merely about 16μm. Finally, thermal stability of the above powders is measured, and the initial irreversible flux loss of the above powders is about 5% at 120°C at a permeance of 2. Based on the above results, it is inferred that the equiaxed Nd–Fe–B fine powders made by the mechanical alloying process are suitable for preparing injection-molded magnets.
The magnetocaloric effect in soft magnetic amorphous alloys
Authors: Franco V. , Blázquez J. S. , Millán M. , Borrego J. M. , Conde C. F. , Conde A.
Published: March 2007

The influence of different compositional modifications on the magnetic entropy change and refrigerant capacity of Finemet, Nanoperm, HiTperm, and bulk amorphous alloys is presented. For all the studied alloys, the field dependence of the magnetic entropy change exhibits a quadratic dependence in the paramagnetic regime, a linear dependence in the ferromagnetic temperature range, and a potential law with a field exponent ∼0.75 at the Curie temperature. This exponent can be explained using the critical exponents of the Curie transition. It is shown that for alloys of similar compositional series, the magnetic entropy change follows a master curve behavior.
Stark effect on quantum well states in Au∕Fe(100)
Authors: Ogawa S. , Heike S. , Takahashi H. , Hashizume T.
Published: March 2007

The quantum well (QW) states in Au∕Fe(100) and their energy dependence on tip-sample distance are observed using scanning tunneling spectroscopy. When the tip-sample distance is decreased by 0.2nm, the QW states shift by as large as 40meV, which is approximately 20 times larger than the Stark shift observed in the surface state in noble metals. The observed shifts may be caused by the phase shift of the QW wave functions in the Au film as well as at the vacuum∕Au interface.
Application of the accelerated molecular dynamics simulations to the folding of a small protein
Authors: Yang Lijiang , Grubb Michael Patrick , Gao Yi Qin
Published: March 2007

In this paper, we further explore the applicability of the accelerated molecular dynamics simulation method using a bias potential. The method is applied to both simple model systems and real multidimensional systems. The method is also compared to replica exchange simulations in folding a small protein, Trp cage, using an all atom potential for the protein and an implicit model for the solvent. We show that the bias potential method allows quick searches of folding pathways. We also show that the choice of the bias potential has significant influence on the efficiency of the bias potential method.
Liquid-vapor and liquid-liquid interfaces in Ising fluids: An integral equation approach
Authors: Omelyan I. P. , Folk R. , Mryglod I. M. , Fenz W.
Published: March 2007

The microscopic structure and thermodynamic properties of liquid-vapor and liquid-liquid interfaces in Ising fluids are studied using an integral equation approach. The calculations are performed in the absence and presence of an external magnetic field by solving the corresponding set of Lovett-Mou-Buff-Wertheim integrodifferential equations for the one-particle density distribution functions. The two-particle inhomogeneous direct correlation functions are consistently constructed by nonlinear interpolation between the bulk ones. The bulk correlation functions of the coexisting phases are obtained from the Ornstein-Zernike equations with a modified soft mean spherical approximation for the closure relation. As a result, the density and magnetization profiles at liquid-vapor and liquid-liquid interfaces as well as the surface tension and adsorption coefficients are evaluated in a wide temperature range including subcritical regions. The influence of an external magnetic field on the liquid-vapor interfaces is also considered.
Transmission line impedance of carbon nanotube thin films for chemical sensing
Authors: Esen G. , Fuhrer M. S. , Ishigami M. , Williams E. D.
Published: March 2007

The authors measure the resistance and frequency-dependent gate capacitance of carbon nanotube (CNT) thin films in ambient, vacuum, and under low pressure (10−6Torr) analyte environments. They model the CNT film as a RC transmission line and show that changes in the measured capacitance as a function of gate bias and analyte pressure are consistent with changes in the transmission line impedance due to changes in the CNT film resistivity alone; the electrostatic gate capacitance of the CNT film does not depend on gate voltage or chemical analyte adsorption. However, the CNT film resistance is enormously sensitive to low pressure analyte exposure.
Molecular dynamics methodology to investigate steady-state heterogeneous crystal growth
Authors: Vatamanu J. , Kusalik P. G.
Published: March 2007

In this paper a new molecular dynamics simulation methodology to investigate steady-state heterogeneous crystal growth from a supercooled liquid is presented. The method is tested on pure component systems such as Lennard-Jonesium and water/ice, as well as multicomponent systems such as methane hydrate crystals. The setup uses periodicity in all three directions and two interfaces; at one interface, crystallization occurs, while at the other, melting is enforced by locally heating the crystal only near that interface. Steady-state conditions are achieved when the crystal is melted at the same rate as the growth occurs. A self-adaptive scheme that automatically modifies the rate of melting to match the rate of growth, crucial for establishing steady-state conditions, is described. In contrast with the recently developed method of Razul et al. [Mol. Phys. 103, 1929 (2005)], where the rates of growth (melting) were constant and the temperatures determined, the present approach fixes the supercooling temperature at the growing interface and identifies the corresponding steady-state crystal growth rate that corresponds to the thermodynamic force provided. The static properties of the interface (e.g., the interfacial widths) and the kinetics of the crystal growth are found to reproduce well previous findings. The importance of establishing steady-state conditions in such investigations is also briefly discussed.
Doorway mechanism for dissociative electron attachment to fructose
Authors: Sommerfeld Thomas
Published: March 2007

Recently, the three sugars ribose, deoxyribose, and fructose have been shown to undergo dissociative electron attachment at threshold, that is, to fragment upon capture of a zero-energy electron. Here the electron acceptor properties of three fructose isomers are investigated in view of a doorway mechanism. Two key ingredients for a doorway mechanism, a weakly bound state able to support a vibrational Feshbach resonance, and a valence anion more stable than neutral fructose are characterized. Moreover, possible structures for the observed fragment anion (fructose-H2O)− are suggested.
Modeling and simulation of axisymmetric coating growth on nanofibers
Authors: Moore K. , Clemons C. B. , Kreider K. L. , Young G. W.
Published: March 2007

This work is a modeling and simulation extension of an integrated experimental/modeling investigation of a procedure to coat nanofibers and core-clad nanostructures with thin film materials using plasma enhanced physical vapor deposition. In the experimental effort, electrospun polymer nanofibers are coated with metallic materials under different operating conditions to observe changes in the coating morphology. The modeling effort focuses on linking simple models at the reactor level, nanofiber level, and atomic level to form a comprehensive model. The comprehensive model leads to the definition of an evolution equation for the coating free surface. This equation was previously derived and solved under a single-valued assumption in a polar geometry to determine the coating morphology as a function of operating conditions. The present work considers the axisymmetric geometry and solves the evolution equation without the single-valued assumption and under less restrictive assumptions on the concentration field than the previous work.
(
p
,
q
)
deformations and (p,q)-vector coherent states of the Jaynes-Cummings model in the rotating wave approximation
Authors: Ben Geloun Joseph , Govaerts Jan , Hounkonnou M. Norbert
Published: March 2007

Classes of (p,q) deformations of the Jaynes-Cummings model in the rotating wave approximation are considered. Diagonalization of the Hamiltonian is performed exactly, leading to useful spectral decompositions of a series of relevant operators. The latter include ladder operators acting between adjacent energy eigenstates within two separate infinite discrete towers, except for a singleton state. These ladder operators allow for the construction of (p,q)-deformed vector coherent states. Using (p,q) arithmetics, explicit and exact solutions to the associated moment problem are displayed, providing new classes of coherent states for such models. Finally, in the limit of decoupled spin sectors, our analysis translates into (p,q) deformations of the supersymmetric harmonic oscillator, such that the two supersymmetric sectors get intertwined through the action of the ladder operators as well as in the associated coherent states.
Gas acoustic and ion acoustic waves in partially ionized plasmas with magnetized electrons
Authors: Vranjes J. , Pandey B. P. , Poedts S.
Published: March 2007

The properties of gas acoustic and ion acoustic modes are investigated in a collisional, weakly ionized plasma in the presence of unmagnetized ions and magnetized electrons. In such a plasma, an ion acoustic mode, driven by an electron flow along the magnetic field lines, can propagate almost at any angle with respect to the ambient field lines as long as the electrons are capable of participating in the perturbations by moving only along the field lines. Several effects, including the electron-ion collisions, the perturbations of the neutral gas, and the electromagnetic perturbations, are studied in the present work. The electron-ion collisions are shown to modify the previously obtained angle-dependent instability threshold for the driving electron flow. The inclusion of the neutral dynamics implies an additional neutral sound mode, which couples to the current driven ion acoustic mode, and these two modes can interchange their identities in certain parameter regimes. The electromagnetic effects, which in the present model imply a bending of the magnetic field lines, result in a further destabilization of an already unstable ion acoustic wave. The applicability of these results to the solar and/or space and laboratory plasmas is discussed.
Saturation of a tearing mode in zero-β full magnetohydrodynamics
Authors: Arcis N. , Escande D. F. , Ottaviani M.
Published: March 2007

Within the cylindrical approximation, the nonlinear saturation of a tearing mode island in the full magnetohydrodynamics (MHD) model with no pressure and a uniform resistivity profile is described using a recent perturbation method based on the technique of matched asymptotic expansion, where the perturbation parameter is the island width ws. The matching condition provides the saturation equation for ws that is given to the adequate order and does not depend on the normalization length. This enables to prove that the errors due to reduced MHD (RMHD) are negligible in the calculation of tearing mode saturation in the tokamak. It also provides a way to benchmark MHD numerical simulations of magnetic self-reversal for the reversed-field pinch where RMHD does not apply.
Anticipating synchronization of chaotic Lur’e systems
Authors: Huijberts Henri , Nijmeijer Henk , Oguchi Toshiki
Published: March 2007

In this paper we consider the anticipating synchronization of chaotic time-delayed Lur’e-type systems in a master-slave setting. We introduce three scenarios for anticipating synchronization, and give sufficient conditions for the existence of anticipating synchronizing slave systems in terms of linear matrix inequalities. The results obtained are illustrated on a time-delayed Rössler system and a time-delayed Chua oscillator.
Mechanisms of friction in diamondlike nanocomposite coatings
Authors: Scharf T. W. , Ohlhausen J. A. , Tallant D. R. , Prasad S. V.
Published: March 2007

Diamondlike nanocomposite (DLN) coatings (C:H:Si:O) processed from siloxane precursors by plasma enhanced chemical vapor deposition are well known for their low friction and wear behaviors. In the current study, we have investigated the fundamental mechanisms of friction and interfacial shear strength in DLN coatings and the roles of contact stress and environment on their tribological behavior. Friction and wear measurements were performed from 0.25to0.6GPa contact pressures in three environments: dry (<1% RH) nitrogen, dry (<1% RH) air, and humid (50% RH) air, with precise control of dew point and oxygen content. At 0.3GPa contact stress, the coefficient of friction (COF) in dry nitrogen was extremely low, ∼0.02, whereas in humid air it increased to ∼0.2, with minimal amount of wear in both environments. The coatings also exhibited non-Amontonian friction behavior, with COF decreasing with an increase in Hertzian contact stress. The main mechanism responsible for low friction and wear under varying contact stresses and environments is governed by the interfacial sliding between the DLN coating and the friction-induced transfer film adhered to the ball counterface. This interfacial shear strength, computed from COF-inverse Hertzian contact stress plots, was found to be 9MPa in dry nitrogen and 78MPa in humid air. Time-of-flight secondary ion mass spectroscopy analysis of the interfaces (wear tracks and transfer films) was used to explain the tribochemical effects in both environments. The transfer films generated in humid air were found to be enriched with SiO2 containing fragments, whereas those formed in dry nitrogen had hydrogenated and long range ordered carbons with practically no SiO2 fragments, ultimately resulting in much lower interfacial shear strength and COF.
Duality and exact correlations for a model of heat conduction
Authors: Giardinà Cristian , Kurchan Jorge , Redig Frank
Published: March 2007

We study a model of heat conduction with stochastic diffusion of energy. We obtain a dual particle process which describes the evolution of all the correlation functions. An exact expression for the covariance of the energy exhibits long-range correlations in the presence of a current. We discuss the formal connection of this model with the simple symmetric exclusion process.
Design of acoustic wave biochemical sensors using micro-electro-mechanical systems
Authors: Valentine Jane E. , Przybycien Todd M. , Hauan Steinar
Published: March 2007

Acoustic wave biochemical sensors work by detecting the frequency shifts resulting from the binding of target molecules to a functionalized resonator. Resonator types currently in use or under development include macroscopic quartz crystal microbalances (QCMs) as well as a number of different integrated Micro-electro-mechanical Systems (MEMS) structures. Due to an increased resonator surface area to mass ratio, we believe that membrane-based MEMS systems are particularly promising with regard to sensitivity. Prototypes have been developed [S. Hauan et al., U.S. Patent Application (filed 6 Nov. 2003)] and preliminary calculations [M. J. Bartkovsky et al., paper 385e presented at the AIChE Annual Meeting, Nov. 2003; J. E. Valentine et al., paper 197h presented at the AICHE Annual Meeting, Nov. 2003] indicate significant improvements over other methods, both macroscopic and MEMS based. In this article we describe our work on a MEMS-based acoustic wave biochemical sensor using a membrane resonator. We demonstrate the effects of spatial distributions of mass on the membrane on sensitivity and show how to use this spatial sensitivity to detect multiple targets simultaneously. To do so we derive a function approximating the membrane response surface to spatial mass loadings under the applicable range of conditions. We verify the agreement using finite element methods, and present our initial sensitivity calculations demonstrating the advantages of variable mass loadings.
Effects of island coalescence on the compensation mechanisms in chlorine doped polycrystalline CdTe
Authors: Consonni V. , Feuillet G. , Bleuse J. , Donatini F.
Published: March 2007

Combined structural, chemical, and spectroscopic analyses have been carried out on chlorine (Cl) doped polycrystalline CdTe before, upon, and after coalescence of the initial isolated islands in order to investigate the effects of the formation of grain boundaries on Cl incorporation and on the related compensation mechanisms. From 4 K cathodoluminescence measurements, coalescence is found to be associated with a change in the Cl related compensation mechanisms in particular with the appearance of shallow acceptor complexes noted β. Simultaneously, the donor acceptor pair transitions involving A centers shift toward higher energies, indicating a decrease of the donor to acceptor separation. These observations are tentatively assigned to the segregation of Cl atoms in the vicinity of grain boundaries, upon coalescence, as directly shown by time-of-flight secondary ion mass spectroscopy imaging. Furthermore, long after coalescence, on thick polycrystalline CdTe, the density of β acceptor complexes is even larger due to twinning deformation processes suggesting further segregation phenomena within grains.
A stochastic subgrid model with application to turbulent flow and scalar mixing
Authors: Marstorp Linus , Brethouwer Geert , Johansson Arne V.
Published: March 2007

A new computationally cheap stochastic Smagorinsky model which allows for backscatter of subgrid scale energy is proposed. The new model is applied in the large eddy simulation of decaying isotropic turbulence, rotating homogeneous shear flow and turbulent channel flow at Reτ=360. The results of the simulations are compared to direct numerical simulation data. The inclusion of stochastic backscatter has no significant influence on the development of the kinetic energy in homogeneous flows, but it improves the prediction of the fluctuation magnitudes as well as the anisotropy of the fluctuations in turbulent channel flow compared to the standard Smagorinsky model with wall damping of CS. Moreover, the stochastic model improves the description of the energy transfer by reducing its length scale and increasing its variance. Some improvements were also found in isotropic turbulence where the stochastic contribution improved the shape of the enstrophy spectrum at the smallest resolved scales and reduced the time scale of the smallest resolved scales in better agreement with earlier observations.
Improved near-infrared transparency in sputtered In2O3-based transparent conductive oxide thin films by Zr-doping
Authors: Koida T. , Kondo M.
Published: March 2007

Transparent conductive Zr-doped In2O3 (In2−2xZr2xO3) films were deposited on glasses by sputtering method. High mobility of over 80 cm2∕V s was achieved under a carrier density of 1.3−2.9×1020 cm−3 at Zr concentrations (x) of 0.014–0.022, and the film at x=0.022 showed the lowest resistivity of 2.6×10−4 Ω cm. Reflecting the high mobility and the low carrier density, the transparency extended from the visible to the near-infrared (NIR) wavelength region with reduced magnitude of the free-carrier absorption. The results indicate that Zr-doped In2O3 films have a performance advantage for applications that require high conductivity and transparency in NIR wavelength region.
Thermal stability of Er2O3 thin films grown epitaxially on Si substrates
Authors: Chen Sheng , Zhu Yanyan , Wu Rong , Wu Yueqin , Fan Yongliang , Jiang Zuimin
Published: March 2007

The thermal stability of Er2O3 thin films grown epitaxially on Si substrates has been investigated in this paper by x-ray diffraction and high resolution transmission electron microscopy. The Er2O3∕Si(001) films are found to react with Si to form silicates at the temperature of 450°C in N2 ambience, whereas O2 ambience can prevent the silicate formation even at the temperature of 600°C. However, at a high temperature of 900°C in either N2 or O2 ambience, Er2O3 films react with Si, and both silicate and SiO2 are formed in the films. In addition, the Er2O3 films grown on Si(111) substrates show poorer thermal stability than those grown on Si(001) substrates; Er silicide is formed at the interface in the films annealed at 450°C in O2 ambience, which is attributed to that the reaction product hexagonal ErSi2 is formed more easily on Si(111) than on Si(001) due to structure similarity as well as small lattice mismatch.
Purity assessment of multiwalled carbon nanotubes by Raman spectroscopy
Authors: DiLeo Roberta A. , Landi Brian J. , Raffaelle Ryne P.
Published: March 2007

Carbonaceous purity assessment for chemical vapor deposition multiwalled carbon nanotubes (MWNTs) using Raman spectroscopy was investigated. Raman spectroscopy was performed on a reference sample set containing predetermined ratios of MWNTs and representative synthesis by-products. Changes in the characteristic Raman peak ratios (i.e., ID∕IG, IG′∕IG, and IG′∕ID) as a function of MWNT content were measured. Calibration curves were generated from the reference samples and used to evaluate MWNTs synthesized under different conditions with varying purity. The efficacy of using Raman spectroscopy in conjunction with thermogravimetric analysis for quantitative MWNT purity assessment is discussed.
Compositional modulation and surface stability in InGaP films: Understanding and controlling surface properties
Authors: Bortoleto J. R. R. , Gutiérrez H. R. , Cotta M. A. , Bettini J.
Published: March 2007

We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties—as well as surface morphologies—present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures.
Quantum probabilities for time-extended alternatives
Authors: Anastopoulos Charis , Savvidou Ntina
Published: March 2007

We study the probability assignment for the outcomes of time-extended measurements. We construct the class operator that incorporates the information about a generic time-smeared quantity. These class operators are employed for the construction of positive-operator-valued measures for the time-averaged quantities. The scheme highlights the distinction between velocity and momentum in quantum theory. Propositions about velocity and momentum are represented by different class operators, hence they define different probability measures. We provide some examples, we study the classical limit, and we construct probabilities for generalized time-extended phase space variables.
Nanoparticle decoration of ferroelectric domain patterns in LiNbO3 crystal
Authors: Ke C. , Wang X. , Hu X. P. , Zhu S. N. , Qi M.
Published: March 2007

A scatheless visualization has demonstrated that the engineered and spontaneous domains of lithium niobate (LiNbO3) crystal can be delineated by means of the nanoparticle decoration. These nanoparticles were monodispersed in nonpolar solvent and negatively charged under the existence of aerosol-OT (AOT or sodium di-2-ethylhexylsulfosuccinate). This method was based on the process of electrostatic interaction, in which the LiNbO3 crystal wafers were heated in the presence of decorating colloid solvent. The charged nanoparticles deposited preferentially on the surfaces of those domains with the opposite charges. The delineated patterns corresponded with the polarization property of domain structures and consequently provided a domain contrast image with resolution down to micron scale. This decoration technique is effective, easily operated, nondestructive for sample, noninvasive for human body, and especially, is more suitable for the domain mapping of oxide ferroelectric crystals. In addition, the initial exploration of the model of such decoration process is also presented in this article.
Investigation of the dielectric response in
PbNb
2
O
6
ferroelectric ceramics
Authors: Leyet Y. , Guerrero F. , de Los S. Guerra J. , Venet M. , Eiras J. A.
Published: March 2007

High Curie temperature ferroelectrics are promising materials to construct transducers for high-temperature piezoelectric applications. Among them, the lead niobate system is one that displays such characteristic. In this work, the dielectric behavior of lead niobate ferroelectric ceramics was analyzed in the frequency range of 20 Hz−2 GHz. Ceramic samples with nominal formula PbNb2O6 (PN) were prepared by the solid-state reaction method. The phase transition was investigated with the Santos-Eiras’ phenomenological model. The values of the parameter, which determine the phase transition character (ξ), are close to 1, indicating a conventional ferroelectric phase transition. The PN materials showed two different dispersion processes: (1) a typical high-frequency dispersion process, which may be associated with the polar region boundaries dynamics, as observed in ferroelectric materials in the microwave frequency region, and (2) that associated with the charge carrier conduction, observed in the lowest frequencies and high-temperature region. An additional dispersion process, in the intermediate frequency range (around 2 MHz), was identified, which may be related to the overlapping between both the normal dipolar process (characteristic of the dipolar materials) and the strong low-frequency conductive process.
Crystalline ZnO with an enhanced surface area obtained by nanocasting
Authors: Waitz T. , Tiemann M. , Klar P. J. , Sann J. , Stehr J. , Meyer B. K.
Published: March 2007

The authors report the synthesis of nanoporous ZnO, which exhibits a periodically ordered, uniform pore system with crystalline pore walls. The crystalline structure is investigated by x-ray diffraction, transmission electron microscopy, and selected area electron diffraction. The large specific surface area and the uniformity of the pore system are confirmed by nitrogen physisorption. Raman spectroscopy along with low-temperature photoluminescence measurements confirms the high degree of crystallinity and gives insight into defects participating in the radiative recombination processes.
Ultrafast time-domain spectroscopy based on high-speed asynchronous optical sampling
Authors: Bartels A. , Cerna R. , Kistner C. , Thoma A. , Hudert F. , Janke C. , Dekorsy T.
Published: March 2007

High-speed asynchronous optical sampling (ASOPS) is a novel technique for ultrafast time-domain spectroscopy (TDS). It employs two mode-locked femtosecond oscillators operating at a fixed repetition frequency difference as sources of pump and probe pulses. We present a system where the 1 GHz pulse repetition frequencies of two Ti:sapphire oscillators are linked at an offset of ΔfR=10 kHz. As a result, their relative time delay is repetitively ramped from zero to 1 ns within a scan time of 100 μs. Mechanical delay scanners common to conventional TDS systems are eliminated, thus systematic errors due to beam pointing instabilities and spot size variations are avoided when long time delays are scanned. Owing to the multikilohertz scan-rate, high-speed ASOPS permits data acquisition speeds impossible with conventional schemes. Within only 1 s of data acquisition time, a signal resolution of 6×10−7 is achieved for optical pump-probe spectroscopy over a time-delay window of 1 ns. When applied to terahertz TDS, the same acquisition time yields high-resolution terahertz spectra with 37 dB signal-to-noise ratio under nitrogen purging of the spectrometer. Spectra with 57 dB are obtained within 2 min. A new approach to perform the offset lock between the two femtosecond oscillators in a master-slave configuration using a frequency shifter at the third harmonic of the pulse repetition frequency is employed. This approach permits an unprecedented time-delay resolution of better than 160 fs. High-speed ASOPS provides the functionality of an all-optical oscilloscope with a bandwidth in excess of 3000 GHz and with 1 GHz frequency resolution.
Particle positioning techniques for dusty plasma experiments
Authors: Ivanov Yuriy , Melzer André
Published: March 2007

Video microscopy is a widely applied diagnostic to investigate the structure and the dynamics of particles in dusty plasmas. Reliable algorithms are required to accurately recover particle positions from the camera images. Here, four different particle positioning techniques have been tested on artificial and experimental data of dusty plasma situations. Two methods that rely on pixel-intensity thresholds were found to be strongly affected by pixel-locking errors and by noise. Two other methods—one applying spatial bandpass filters and the other fitting polynomials to the intensity pattern—yield subpixel resolution under various conditions. These two methods have been shown to be ideally suited to recover particle positions even from small-scale fluctuations that are used to derive the normal mode spectra of finite dust clusters.
Modeling and simulation of the plasma absorption probe
Authors: Lapke M. , Mussenbrock T. , Brinkmann R. P. , Scharwitz C. , Böke M. , Winter J.
Published: March 2007

The plasma absorption probe (PAP) was invented as an economical and robust diagnostic device to determine the electron density distribution in technical plasmas. It consists of a small antenna enclosed by a dielectric tube which is immersed in the plasma. A network analyzer feeds a rf signal to the antenna and displays the frequency dependence of the power absorption. From the absorption spectrum the value of the electron density is calculated. The original evaluation formula was based on the dispersion relation of plasma surface waves propagating along an infinite dielectric cylinder. In this letter the authors present the analysis of a less idealized configuration. The calculated spectra are in good qualitative agreement with their experimental counterparts, but differ considerably from those predicted by the surface wave ansatz. An evaluation scheme which takes our findings into account will improve the performance of the PAP technique further.
Infrared lasing in InN nanobelts
Authors: Hu Ming-Shien , Hsu Geng-Ming , Chen Kuei-Hsien , Yu Chia-Ju , Hsu Hsu-Cheng , Chen Li-Chyong , Hwang Jih-Shang , Hong Lu-Sheng , Chen Yang-Fang
Published: March 2007

Infrared lasing from single-crystalline InN nanobelts grown by metal organic chemical vapor deposition was demonstrated. Transmission electron microscopy studies revealed that the InN nanobelts of rectangular cross section grew along [110] direction and were enclosed by ±(001) and ±(11¯0) planes. The infrared lasing action was observed at 20K in the InN nanobelts grown on an amorphous silicon nitride coated silicon substrate by continuous wave laser pumping.
Polymer monolayers with a small viscoelastic linear regime: Equilibrium and rheology of poly(octadecyl acrylate) and poly(vinyl stearate)
Authors: Hilles Hani , Maestro Armando , Monroy Francisco , Ortega Francisco , Rubio Ramón G. , Velarde Manuel G.
Published: March 2007

The equilibrium properties of monolayers of two polymers: poly(octadecyl acrylate) and poly(vinyl stearate) on water have been measured. The surface pressure (Π) versus surface concentration (Γ) curves indicate that the water-air interface is a poor solvent for both polymers. The thermal expansivity shows a sharp change near room temperature. This behavior is typical of a glass transition; this is the first time that such a plot is observed for Langmuir films. The Π vs Γ curves measured by the continuous compression method show strong anisotropy effects. They also show that the monolayer is brought into nonequilibrium states depending on the compression rate. Within the linear regime, the relaxation experiments were bimodal. The longest relaxation time strongly increases as T is decreased, which might be compatible with the high increase of viscosity in the glass transition. The oscillatory barrier experiments showed that the maximum strain of the linear regime is smaller than 3% for both monolayers. The Fourier-transform analysis of the oscillatory experiments beyond the linear regime points out the contribution of different harmonics in the response function. Oscillations in the nonlinear regime show hysteresis cycles. The results obtained indicate that some of the previously published data for these polymer monolayers correspond to nonequilibrium states.
Two-photon absorption in quantum dots based on a nonconjugated conductive polymer
Authors: Titus Jitto , Thakur M.
Published: March 2007

Two-photon absorption has been measured in a nano-optical material (quantum dots) based on the nonconjugated conductive polymer, iodine-doped poly(β-pinene). The measurement has been made using open-aperture z scan at 730–860nm with 150fs pulses. Exceptionally large two-photon absorption coefficient has been observed with a peak of magnitude ∼2.6cm∕MW that appeared at ∼1.53eV which is close to half of the optical gap corresponding to the charge-transfer transition involving the isolated double bond. Saturation of absorption was observed at lower intensities and shorter wavelengths. The results have been attributed to the quantum dots (subnanometer size) formed upon doping.
Wafer-level microelectromechanical system structural material test by electrical signal before pull-in
Authors: Hu Yuh-Chung , Huang Po-Yuan
Published: March 2007

The letter develops a wafer-level testing method to examine Young’s modulus and residual stress of structural material of capacitive microdevice by measuring the pre-pull-in capacitance variation of the microtest beam made of the material to be tested. The required instrument is only a precision LCR meter. The extracted Young’s moduli and residual stresses of demonstrated samples agree very well with the experimental measurement. The present method is expected to be applicable to the wafer-level testing in microdevice manufacture and compatible with the wafer-level testing in integrated circuit industry, since the test and pickup signals are both electrical.
Precise replication of antireflective nanostructures from biotemplates
Authors: Gao Hongjun , Liu Zhongfan , Zhang Jin , Zhang Guoming , Xie Guoyong
Published: March 2007

The authors report herein a new type of nanonipple structures on the cicada’s eye and the direct structural replication of the complex micro- and nanostructures for potential functional emulation. A two-step direct molding process is developed to replicate these natural micro- and nanostructures using epoxy resin with high fidelity, which demonstrates a general way of fabricating functional nanostructures by direct replication of natural biotemplates via a suitable physicochemical process. Measurements of spectral reflectance showed that this kind of replicated nanostructure has remarkable antireflective property, suggestive of its potential applications to optical devices.
Electrical characteristics and interface structure of HfAlO∕SiON∕Si(001) stacks
Authors: Edon V. , Li Z. , Hugon M.-C. , Agius B. , Krug C. , Baumvol I. J. R. , Durand O. , Eypert C.
Published: March 2007

The electrical characteristics of RuO2∕HfAlO∕SiON∕Si(001) capacitors prepared by thermal nitridation of the Si substrate previously to HfAlO ultrathin film deposition were determined. A dielectric constant of 19 and a gate current density of 67mA∕cm2 for an equivalent oxide thickness of 1.1nm have been determined, whereas non-nitrided capacitors gave substantially lower dielectric constant and higher gate current density. The structure and integrity of the stacks after thermal annealing were accessed by means of spectroscopic ellipsometry and x-ray reflectometry, indicating that thermal N incorporation into the gate dielectric stacks forms an effective diffusion barrier, leading to a smoother, SiO2-like interface. The HfAlO films grown on nitrided substrates were seen also to have lower porosity, percentage of voids, and density of oxygen vacancies.
Defect distribution in a-plane GaN on Al2O3
Authors: Tuomisto F. , Paskova T. , Kröger R. , Figge S. , Hommel D. , Monemar B. , Kersting R.
Published: March 2007

The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11−20] a direction on (1−102) r-plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation.
Effect of ionization rates on dynamic recovery processes during electron-beam irradiation of 6H-SiC
Authors: Bae In-Tae , Weber William J. , Ishimaru Manabu , Hirotsu Yoshihiko
Published: March 2007

The authors have investigated the effects of 200 and 300keV electron-beam irradiations on amorphization in 6H-SiC at 100 and 295K. Amorphization is induced by the accumulation of defects produced by direct atomic displacements. Dynamic recovery of these defects during irradiation, due to temperature increases and ionization effects, results in increases in the amorphization dose. By comparing with previous data for 2MeV electrons and 1.5MeV Xe ions, the results demonstrate that ionization-enhanced recovery in 6H-SiC dramatically increases above an ionization rate threshold.
Modified efficient cluster packing model for calculating alloy compositions with high glass forming ability
Authors: Wang A. P. , Wang J. Q. , Ma E.
Published: March 2007

The efficient cluster packing model for bulk metallic glasses (BMGs) has been modified and extended to allow quantitative predictions of alloy compositions with high glass forming ability. The compositions calculated using this simple method compare favorably with the vast majority of the BMGs discovered in recent years. In addition, a Hf-based BMG has been obtained at the predicted composition.