bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic properties of compositionally gradedBa1−xSrxTiO3 thin films
Authors: Cao Hai-Xia , Gao Yan-Hong , Jiang Qing , Li Zhen-Ya
Published: July 2004

The modified transverse Ising model considering double-peak probability distribution functions is constructed and applied to investigate the thermodynamic properties of compositionally graded Ba1−xSrxTiO3 thin films. Spatial nonuniformity in compositional concentration is exhibited to give rise to nonuniformity in polarization with corresponding spatial variation. It is found that the magnitude and the sign of the polarization gradients are dependent on the compositional gradient. We also find that the origin of polarization offset is strongly related to not only the compositional gradient but also the temperature. In addition, the compositional gradient plays an important role in the pyroelectric coefficient of the graded film versus temperature, where one or two broad and smooth pyroelectric peaks occur except for a sharp peak at the Curie temperature.
Crystal tilting of diamond heteroepitaxially grown on vicinal Ir∕SrTiO3(001)
Authors: Gsell S. , Schreck M. , Stritzker B.
Published: July 2004

In the present study SrTiO3 crystals with vicinal (001) surfaces inclined 3° and 5° towards [110] and [100], respectively, have been used to deposit iridium layers and subsequently epitaxial diamond films. The iridium grows on top of the vicinal SrTiO3(001) with a perfect cube-on-cube registry. In contrast, the diamond films on the iridium show a strong additional tilting of up to 2°. A model is proposed which explains the effect by the preferential incorporation of misfit dislocations due to the stress anisotropy on the vicinal substrate planes taking into account the lattice misfit and the islandlike growth mode of diamond. The experimental observations and their explanation suggest that the epitaxial diamond alignment on iridium takes place during lateral growth within the first few nanometers.
Crystallite coalescence during film growth based on improved contact mechanics adhesion models
Authors: Suh Allison Y. , Yu Ning , Lee Ki Myung , Polycarpou Andreas A. , Johnson H. T.
Published: July 2004

Intrinsic tensile stress, which can lead to problems in deposited thin films such as cracking, peeling, and delamination, often develops during the early stages of thin film growth. Many attempts have been made to estimate the tensile stress during crystallite coalescence, both experimentally and analytically. Most recently, using a combination of Hertzian contact mechanics and elasticity theory, Freund and Chason applied the Johnson-Kendall-Roberts (JKR) theory to account for adhesion between crystallites under specific conditions. Other existing contact mechanics models that naturally account for adhesion include the improved Derjaguin-Muller-Toporotov and Maugis-Dugdale theories. The objective of this study is to provide useful analytical and numerical techniques based on these contact mechanics theories for a wide range of conditions that accurately approximate the intrinsic tensile stress that develops during crystallite coalescence. As an analytical method, the Maugis-Dugdale model is proposed as a more general alternative to the JKR model. Parameters such as the contact radius and “net” adhesive force are computed as a function of the relative separation between two adjacent crystallites in a thin gold film. Another useful parameter known as the “jump-to-contact” separation is also calculated by the Maugis-Dugdale and JKR models. For comparison to the analytical models, a finite element method is used to simulate the crystallite coalescence problem. The numerical technique is based on a nonlinear surface interaction element developed to approximate van der Waals adhesion, and allows for full-field analysis of stress and displacement in crystallites. Two different boundary conditions are used, for which corresponding contact radius and tensile stress are computed and compared to the analytical results. As a further study, the length scale effect is also investigated by varying the radius of individual crystallites from 20nm to 300nm. It is concluded that in order to estimate the average tensile stress accurately using analytical models, the radius of individual crystallites must be large compared to the contact radius. For small length scales, the finite element approach is more appropriate.
Self-diffusion in isotopically enriched silicon carbide and its correlation with dopant diffusion
Authors: Rüschenschmidt K. , Bracht H. , Stolwijk N. A. , Laube M. , Pensl G. , Brandes G. R.
Published: July 2004

Diffusion of C13 and Si30 in silicon carbide was performed with isotopically enriched 4H-Si28C12∕natSiC heterostructures which were grown by chemical vapor phase epitaxy. After diffusion annealing at temperatures between 2000°C and 2200°C the Si30 and C13 profiles were measured by means of secondary ion mass spectrometry. We found that the Si and C diffusivity is of the same order of magnitude but several orders of magnitude lower than earlier data reported in the literature. Both Si and C tracer diffusion coefficients are in satisfactory agreement with the native point defect contribution to self-diffusion deduced from B diffusion in SiC. This reveals that the native defect which mediates B diffusion also controls self-diffusion. Assuming that B atoms within the extended tail region of B profiles are mainly dissolved on C sites, we propose that B diffuses via the kick-out mechanism involving C interstitials. Accordingly, C diffusion should proceed mainly via C interstitials. The mechanism of Si diffusion remains unsolved but Si may diffuse via both Si vacancies and interstitials, with the preference for either species depending on the doping level.
Effect of gallium nitride template layer strain on the growth of InxGa1-xN∕GaN multiple quantum well light emitting diodes
Authors: Johnson M. C. , Bourret-Courchesne E. D. , Wu J. , Liliental-Weber Z. , Zakharov D. N. , Jorgenson R. J. , Ng T. B. , McCready D. E. , Williams J. R.
Published: July 2004

GaN template layer strain effects on the growth of InGaN∕GaN light emitting diodes devices were investigated. Seven-period InGaN∕GaN multiple quantum well structures (MQW) were deposited on 5 and 15μm GaN template layers. It was found that the electroluminescence emission of the 15μm device was redshifted by approximately 132meV. Triple-axis x-ray diffraction and cross-sectional transmission electron microscopy show that the 15μm template layer device was virtually unstrained while the 5μm layer experienced tensile strain. Dynamic secondary ion mass spectrometry depth profiles show that the 15μm template layer device had an average indium concentration of 11% higher than that of the 5μm template layer device even though the MQW structures were deposited during the same growth run. It was also found that the 15μm layer device had a higher average growth rate than the 5μm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers.
High frequency magnetization rotation induced by a dc spin-polarized current in magnetic nanostructures
Authors: Xi Haiwen , Shi Yiming
Published: July 2004

While most recent studies of the spin-transfer torque effect in nanoscale magnetic structures mainly concern with spin-wave excitation and the magnetization hysteretic switching induced by spin-polarized current, we theoretically investigate the large angle magnetization precessions triggered and sustained by the spin current in great detail using the Landau-Lifshitz-Gilbert equation. The study is conducted particularly on the nanostructures comprising square magnets with an easy-plane anisotropy. A simple nanoscale magnetoelectronic device is proposed based on the structure without mechanical components to function as a motor to convert a dc current into an ac voltage of microwave frequency. The device is unique because the output amplitude and frequency can be continuously tuned by the electrical current in a wide range. Quantitative analysis of the device structure, function, and realization is provided.
Time-domain simulation of a universal quantum gate
Authors: Sullivan Dennis M. , Citrin D. S.
Published: July 2004

This paper describes the simulation of two coupled particles using the finite-difference time-domain method. We include both unrestricted spin and spatial degrees of freedom for the two particles within the Hartree-Fock approximation. Using spin as a basis, a two-qubit controlled-NOT gate as well as several single qubit gates are simulated in GaAs. We find that the double-occupancy problem can be largely circumvented.
Microstructure and electrical characterizations of yttrium oxide and yttrium silicate thin films deposited by pulsed liquid-injection plasma-enhanced metal-organic chemical vapor deposition
Authors: Durand C. , Dubourdieu C. , Vallée C. , Loup V. , Bonvalot M. , Joubert O. , Roussel H. , Renault O.
Published: July 2004

Results on yttrium oxide and yttrium silicate films elaborated by an innovative metal-organic chemical vapor deposition process combining plasma assistance and a liquid precursor supply setup are presented. Plasma assistance enables deposition at a much lower substrate temperature and the pulsed-liquid precursor source allows an accurate control of the injected reactive species. According to x-ray photoelectron spectroscopy (XPS) analyses, we show that ultrathin yttrium oxide deposition can be performed at temperature less than 380°C. Yttrium oxide films contain carbon contamination that can be reduced by increasing the deposition temperature. The plasma plays a key role in the deposition mechanisms and thus in the chemical structure of the films and of the interface. It is shown that the injection frequency, i.e., the reactive species incoming frequency, plays a significant role in the silicate and interface formation. A detailed study is presented using angle-resolved XPS. A high injection frequency limits the formation of SiO2 interfacial layer and also of the silicate and favors the growth of yttrium oxide. In addition, silicate formation also depends on the deposition temperature. Electrical results show that as-deposited film at 350°C has a low leakage current (J<10−7A∕cm2) and a high breakdown field (∼8MV∕cm).
Indentation-induced crystallization and phase transformation of amorphous germanium
Authors: Patriarche G. , Le Bourhis E. , Khayyat M. M. O. , Chaudhri M. M.
Published: July 2004

It has been known for about 15 years that when a Vickers indenter is loaded on to a crystalline semiconductor, such as silicon, a semiconductor to metallic phase transition occurs during indenter loading and on removal of the indenter the material within the residual indentation becomes amorphous. Here we report a completely opposite effect: when a Berkovich or Vickers diamond indenter is loaded onto a submicrometer thick film of amorphous germanium, it crystallizes and undergoes structural phase transitions. These observations are based on our transmission electron microscopy and Raman scattering investigations, which have been described. It has also been shown that the indentation-induced crystallization and phase transitions occur close to the indenter tip, where the plastic strains are the highest.
Band offsets at heterojunctions between SrTiO3 and BaTiO3 and Si(100)
Authors: Amy F. , Wan A. S. , Kahn A. , Walker F. J. , McKee R. A.
Published: July 2004

We use thin (∼26Å) SrTiO3 and BaTiO3 films epitaxially grown on Si(100) substrates, and ultraviolet and x-ray photoemission spectroscopy to investigate band discontinuities at the SrTiO3∕Si and BaTiO3∕Si heterojunctions. The treatment of the oxide film surface ranges from ex situ ultraviolet generated ozone to annealing in O2 or ultrahigh vacuum. Depending on surface treatment, the valence band offset varies from 2.38 to 2.64eV for SrTiO3∕Si heterostructure and from 2.35 to 2.66eV for BaTiO3∕Si. These values imply that the conduction band minimum of the oxide is below that of the semiconductor, a situation referred to as negative conduction band offset. We demonstrate that the SrTiO3∕Si and BaTiO3∕Si interfaces undergo significant chemical changes during surface cleaning of the oxide film.
Electrokinetic micropump and micromixer design based on ac faradaic polarization
Authors: Lastochkin Dmitri , Zhou Ronghui , Wang Ping , Ben Yuxing , Chang Hsueh-Chia
Published: July 2004

A microfluidic pump and mixer design based on ac faradaic polarization is proposed. Unlike ac electrokinetic devices based on capacitive charging of the electrodes, the design yields a net electro-osmotic flow for high-conductivity electrolytes at high voltages and frequencies without producing gas bubbles or generating pH gradients. The average velocity, which can be more than an order of magnitude higher than that generated by the capacitive mechanism, has an exponential dependence on the voltage and increases monotonically at low frequencies. Vortices and net flows with linear velocities in excess of 1mm∕s are generated with orthogonal microfabricated planar electrodes based on the unique flow and polarization features of this new ac charging mechanism.
Optical properties of (1-x)Pb(Mg1∕3Nb2∕3)O3-xPbTiO3 single crystals studied by spectroscopic ellipsometry
Authors: Wan Xinming , Chan H. L. W. , Choy C. L. , Zhao Xiangyong , Luo Haosu
Published: July 2004

( 1 - x ) Pb ( Mg 1 ∕ 3 Nb 2 ∕ 3 ) O 3 - x PbTiO 3  (PMN-xPT) single crystals with x=0.24, 0.30, 0.31, and 0.33 have been investigated by spectroscopic ellipsometry. The refractive indices and extinction coefficients were obtained. The modified Sellmeier equations for the refractive indices were obtained by least-squares fit. The equations can be used to calculate the refractive index with high accuracy in the low absorption wavelength range, namely, from 400 to 5800nm. The Sellmeier optical coefficients E0, λ0, S0, and Ed were calculated by fitting the single-term oscillator equation. They are related directly to the electronic energy band structure and have the physical significance. The optical band gap energies were also obtained from absorption coefficient spectra. Our results show that as the PT content increases, the refractive index of PMN-xPT single crystals increases, while the optical band gap energy decreases. Some discussions about the BO6 octahedron building block that determines the basic energy level of PMN-xPT single crystals are also presented in this article.
Structural modifications in FexCo1−x∕Cu multilayers induced by ion irradiation
Authors: Graff I. L. , Teixeira S. R. , Amaral L. , Alves M. C. Martins , Flores W. H.
Published: July 2004

The structural evolution of Fe30Co70∕Cu multilayers under ion irradiation is investigated in detail using x-ray techniques. The samples were irradiated with two different ions, 50keV of He+ and 600keV of Kr+, at room temperature. No substantial changes were observed after He+ irradiation; the He+ ions promote some disorder in the FeCo layers, an increase of the Cu(111) texture, and grain size. After Kr+ irradiation a structural phase transition from bcc to fcc occurs in the FeCo layers. A very pronounced increase of the Cu(111) texture and grain size is also observed. According to the equilibrium phase diagrams such fcc phase is not expected for the FeCo alloy at the composition of Fe30Co70. This fcc phase is imposed by the Cu fcc structure of the adjacent layers, which induce the regrowth of the FeCo layers structure from bcc to fcc during the relaxation period of the atomic collision cascades. Also, after the Kr+ irradiation a multilayer structure still persists, as showed by the x-ray reflectivity.
Effect of low-temperature baking on the radio-frequency properties of niobium superconducting cavities for particle accelerators
Authors: Ciovati Gianluigi
Published: July 2004

Radio-frequency superconducting (SRF) cavities are widely used to accelerate a charged particle beam in particle accelerators. The performance of SRF cavities made of bulk niobium has significantly improved over the last ten years and is approaching the theoretical limit for niobium. Nevertheless, RF tests of niobium cavities are still showing some “anomalous” losses that require a better understanding in order to reliably obtain better performance. These losses are characterized by a marked dependence of the surface resistance on the surface electromagnetic field and can be detected by measuring the quality factor of the resonator as a function of the peak surface field. A low-temperature (100–150°C) “in situ” bake under ultrahigh vacuum has been successfully applied as final preparation of niobium RF cavities by several laboratories over the last few years. The benefits reported consist mainly of an improvement of the cavity quality factor at low field and a recovery from “anomalous” losses (so-called “Q drop”) without field emission at higher field. A series of experiments with a CEBAF single-cell cavity have been carried out at Jefferson Lab to carefully investigate the effect of baking at progressively higher temperatures for a fixed time on all the relevant material parameters. Measurements of the cavity quality factor in the temperature range 1.37–280K and resonant frequency shift between 6–9.3K provide information about the surface resistance, energy gap, penetration depth, and mean free path. The experimental data have been analyzed with the complete BCS theory of superconductivity. The hydrogen content of small niobium samples inserted in the cavity during its surface preparation was analyzed with nuclear reaction analysis. The single-cell cavity has been tested at three different temperatures before and after baking to gain some insight on thermal conductivity and Kapitza resistance and the data are compared with different models. This paper describes the results of these experiments and comments on existing models to explain the effect of baking on the performance of niobium RF cavities.
Low work function of the (1000) Ca2N surface
Authors: Uijttewaal M. A. , Wijs G. A. de , Groot R. A. de
Published: July 2004

Polymer diodes require cathodes that do not corrode the polymer but do have low work function to minimize the electron injection barrier. First-principles calculations demonstrate that the work function of the (1000) surface of the compound Ca2N is half an eV lower than that of the elemental metal Ca (2.35 vs 2.87eV). Moreover, its reactivity is expected to be smaller. This makes Ca2N an interesting candidate to replace calcium as cathode material for polymer light emitting diode devices.
Effects of rapid thermal annealing on the optical properties of low-loss 1.3μm GaInNAs∕GaAs saturable Bragg reflectors
Authors: Sun H. D. , Macaluso R. , Calvez S. , Valentine G. J. , Burns D. , Dawson M. D. , Gundogdu K. , Hall K. C. , Boggess T. F. , Jouhti T. , Pessa M.
Published: July 2004

We report studies of the effect of rapid thermal annealing (RTA) on the optical properties of a low-loss 1.3μm saturable Bragg reflector (SBR), consisting of a GaInNAs∕GaAs single quantum well embedded in an AlAs∕GaAs Bragg reflector grown monolithically on a GaAs substrate. RTA gives rise to a blueshift of the photoluminescence (PL) peak (and therefore of the excitonic absorption peak) and an enhancement of PL intensity, while the reflectivity properties including peak reflectivity and bandwidth are not degraded. Temperature dependent photoluminescence measurements show that the RTA-induced blueshift of photoluminescence consists of two components: one originating from the increase of optical transition energies and another from the reduction of carrier localization. Time-resolved photoluminescence results at room temperature provide information about the recombination dynamics of carriers directly relevant to the application of the SBR in laser mode locking.
Nonlinear optical phase shift in InAs quantum dots measured by a unique two-color pump∕probe ellipsometric polarization analysis
Authors: Nakamura H. , Kanamoto K. , Nakamura Y. , Ohkouchi S. , Ishikawa H. , Asakawa K.
Published: July 2004

The nonlinear optical phase shift in self-assembled InAs quantum dots (QDs) under resonant excitation in a ground-state transition was measured by a unique two-color pump∕probe ellipsometric polarization analysis. This ellipsometric analysis makes use of the large optical birefringence of SK-QD [(SK) — Stranski-Krastanov] originating from the asymmetric structure. A phase shift of 0.5π rad was obtained at an input pump pulse energy density of 30pJ∕μm2, a detuning of 11meV, and a time delay of 20ps in a 1mm long waveguide having QDs with a peak wavelength of 1290nm, a volume density of 4×1015cm−3, and inhomogeneous broadening of 35meV. Analysis revealed that the phase shift is mainly attributed to the absorption saturation for TE-polarized light, though other mechanisms also could contribute at higher pumping. The calculation, based on the two-level approximation, revealed that the minimum energy density for π shift is 240fJ∕μm2, calculated under ideal conditions.
Up-conversion in Er3+:Y2O3 Nanocrystals Pumped at 808nm
Authors: Xiao Siguo , Yang Xiaoliang , Liu Zhengwei , Yan X. H.
Published: July 2004

Er 3 + ion-doped Y2O3 nanocrystals were prepared by coprecipitation synthesis technique. Visible emissions at 650, 540, and 523nm have been observed under excitation at 808nm. Comparing with the stokes emission characteristics of the nanocrystals pumped at 488nm, the up-conversion mechanisms excited at 808nm have been investigated in detail. Excitation power dependent behaviors of the up-converted emission intensities indicate that a two-photon excited state absorption process is responsible for the S3∕24(H11∕22)→I15∕24 transition while a no-resonant energy transfer I9∕24+I11∕24→I9∕24+I13∕24 principally performs the red up-conversion of the F9∕24→I15∕24 transition.
Electron transport in the downstream region of planar unbalanced magnetron discharge
Authors: Seo Sang-Hun , Chang Hong-Young
Published: July 2004

In this study, we will investigate the electron transport in the downstream region of a planar and unbalanced (type II) magnetron discharge. The effects of the anode sheath boundary and diverging magnetic field on the electron kinetics such as the electron loss mechanism at plasma-sheath boundary and the electron distribution function will be examined through the probe measurements. The spatially resolved probe measurements reveal the existence of an electron drift from the cathode fall region to the downstream region. It is found that this drift is caused by the axial gradient of magnetic field (the magnetic mirror force) and then derives an electron current to the grounded substrate on which the potential of the sheath is very low; so the current balance between the cathode and anode currents is kept. The experimental results show that the electron transport in the downstream region is not governed by the classical diffusion (mobility and diffusion dominated) but is dominated by the modified diffusion including the electron drift caused by the magnetic mirror force. Additionally, the mechanism and the experimental evidence on the presence of a non-Maxwellian electron energy distribution function (in particular, bi-Maxwellian distribution) in magnetron discharge will be presented showing that the non-Maxwellian electron energy distribution function is due to the combined effects of the electron drift toward the substrate and the sheath boundary condition.
Effect of growth temperature and postmetallization annealing on the interface and dielectric quality of atomic layer deposited HfO2 on p and n silicon
Authors: Dueñas S. , Castán H. , García H. , Barbolla J. , Kukli K. , Aarik J.
Published: July 2004

The effect of growth temperature and postmetallization annealing on the electrical characteristics of atomic layer deposited HfO2 films has been studied. Trap distributions at the interface have been obtained by means of deep level transient spectroscopy, whereas conductance transient technique provided the energy and geometrical profiles of electrically active defects at the insulator bulk. Differences in the interface quality have been observed between films on n- and p-type substrates. The most suitable growth temperatures seem to be 300°C for p-type and 500°C for n-type substrates. In all cases, postmetallization annealing in forming gas causes displacements of defects from the insulator bulk to the interface.
Comment on “Thickness dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer” [J. Appl. Phys. 94, 2529 (2003)]
Authors: Geshev J. , Pereira L. G. , Schmidt J. E.
Published: July 2004

Hu, Jin, and Ma have proposed a theoretical investigation on the influence of the antiferromagnetic layer thickness on the magnetic properties of ferromagnetic∕antiferromagnetic bilayers [J. Appl. Phys. 94, 2529 (2003)], considering both the bilinear and biquadratic exchange couplings, and have claimed that from their formulas for the hysteresis loop displacement and coercivity many interesting conclusions can be extracted. Unfortunately, the mathematical procedure used to find the equilibrium of the system is based on inadequate stability conditions and has led to nonphysical results. More importantly, the simple phenomenological model, employed by the authors, is intrinsically not capable to give the antiferromagnetic layer thickness dependence of the magnetic properties of such exchange-coupled bilayers.
Response to “Comment on ‘Thickness and angular dependencies of exchange bias in ferromagnetic/antiferromagnetic bilayers’ [J. Appl. Phys. 92, 1009 (2002)] and ‘Thickness dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer’ [J. Appl. Phys. 94, 2529 (2003)]”
Authors: Hu Jing-guo , Jin Guo-jun , Ma Yu-qiang
Published: July 2004

The approach of using the generalized Meiklejohn-Bean model to derive the antiferromagnetic thickness dependence of exchange bias and coercivity in ferromagnetic/antiferromagnetic bilayers is justified. The mathematical procedure to obtain the analytical expressions through finding the critical fields is illuminated.
Photoluminescence studies of implantation damage centers in Si30
Authors: Hayama S. , Davies G. , Itoh K. M.
Published: July 2004

We report photoluminescence (PL) studies of implant-damage centers in Si30. The X and W zero-phonon lines (ZPLs) shift by +1.55(5) and +1.27(5)meV, respectively, between Sinat and Si30. Using a simple empirical approach, we calculate the shifts to within ∼20%. Local vibrational modes are identified at the X center and confirmed at the W center, supporting the assignment of these centers to self-interstitial clusters. All the strong PL lines produced by ion implantation in the sample have isotope shifts characteristic of ZPLs; they all correspond to independent defect centers, the majority of which have undetermined structures.
Effects of low attenuation in a nanomechanical electron shuttle
Authors: Scheible Dominik V. , Weiss Christoph , Blick Robert H.
Published: July 2004

We have measured the spectral current characteristics of a nanomechanical electron shuttle in a tuning-fork configuration. This particular design enhances the quality factor Q of the nanoelectromechanical system. Comparing the experimental results to a precedingly studied low-Q device, we find a substantially different current behavior, indicating an increase of Q: the current flips direction around the frequency of mechanical resonance. We support our conclusion with a model calculation via a master equation. The device is nanomachined in silicon and shows response up to 0.5GHz at room temperature.
Direction-tunable cholesteric phase gratings
Authors: Yao I-An , Liaw Chien-Huang , Chen Shu-Hsia , Wu Jin-Jei
Published: July 2004

In suitable conditions, the homeotropic aligned cholesteric liquid crystal (ChLC) cell can be in fingerprint texture when abruptly switching off the applied electric field. The stripe orientation depends not only on the thickness-to-pitch (d∕P0) ratio, but also on the applied driving voltage. In this paper, the ChLC phase grating with the field-controllable grating orientation is realized and the operational mechanism of this device is presented.
Stable violet cathodoluminescence of α-quartz after Ge+ implantation at elevated temperature
Authors: Sahoo P. K. , Dhar S. , Gasiorek S. , Lieb K. P.
Published: July 2004

Doping single-crystalline α-quartz with 120keV Ge+-ion implantation under the conditions of dynamic solid phase epitaxial regrowth has been studied as function of ion fluence and substrate temperature. In particular, the light emitting properties possibly suitable for optoelectronic devices have been investigated by measuring cathodoluminescence spectra for implantation temperatures from 300 to 1223K and for analyzing temperatures from 10−300K. Rutherford backscattering channeling analysis showed that the Ge implantation produced amorphous layers varying in depth with temperature. At a fluence of 7×1014Ge-ions∕cm2 and an implantation temperature of 1073K, Ge implantation is accompanied by a strong increase in the luminescence intensity of a violet band, which we associate with Ge-related defects or Ge clusters. This violet band is very stable and has a long lifetime of 6μs. All the other bands observed are connected to known oxygen defect centers in the SiO2 network.
Cobalt nanoparticles deposited and embedded in AlN: Magnetic, magneto-optical, and morphological properties
Authors: Huttel Y. , Gómez H. , Clavero C. , Cebollada A. , Armelles G. , Navarro E. , Ciria M. , Benito L. , Arnaudas J. I. , Kellock A. J.
Published: July 2004

We present a structural, morphological, magnetic, and magneto-optical study of cobalt nanoparticles deposited on 50Å AlN∕c-sapphire substrates and embedded in an AlN matrix. The dependence of the properties of Co nanoclusters deposited on AlN with growth temperature and amount of deposited Co are studied and discussed. Also we directly compare the properties of as grown and AlN embedded Co nanoclusters and show that the AlN matrix has a strong impact on their magnetic and magneto-optical properties.
State of the metal core in nanosecond exploding wires and related phenomena
Authors: Sarkisov G. S. , Sasorov P. V. , Struve K. W. , McDaniel D. H.
Published: July 2004

Experiments show that an expanding metal wire core that results from a nanosecond electrical explosion in vacuum consists primarily of three different states: solid, microdrop, and gas-plasma. The state of the wire core depends both on the amount of energy deposited before the voltage breakdown and on the heating conditions. For small amounts of deposited energy (on the order of solid-stage enthalpy), the wire core remains in a solid state or is partially disintegrated. For a high level of deposited energy (more than vaporization energy) the wire core is in a gas-plasma state. For an intermediate level of deposited energy (more than melting but less than vaporization), the wire disintegrates into hot liquid microdrops or clusters of submicron size. For a wire core in the cluster state, interferometry demonstrates weak (or even absent) phaseshift. Light emission shows a "firework effect"—the long late-time radiation related to the emission by the expanding cylinder of hot microparticles. For the wire core in a gas-plasma state, interferometry demonstrates a large phaseshift and a fast reduction in light emission due to adiabatic cooling of the expanding wire core. The simulation of this firework effect agrees well with experimental data, assuming submicron size and a temperature approaching boiling for the expanded microparticles cylinder.
Contact-free photovoltage measurements of photoabsorbers using a Kelvin probe
Authors: Rühle Sven , Cahen David
Published: July 2004

A contact-free method to measure the photovoltage that can be generated by an absorber, upon illumination, is presented. The measurement is based on Kelvin’s well-known capacitor method which measures the contact potential difference that builds up between two sufficiently conducting materials of different work function that are electrically connected. We show that the photovoltage of an absorber, which is introduced into the Kelvin capacitor, can be measured accurately, even though it is not in electrical contact to any of the capacitor plates. Comparative measurements of the surface photovoltage of an n-type Si semiconductor surface in grounded and nongrounded mode as well as the interface photovoltage of mesoporous TiO2, deposited onto a conducting substrate, are presented to demonstrate the feasibility of the concept. This approach enables to measure the photovoltage of complete solar cells and also its single components (absorber, absorber + buffer layer, absorber + buffer layer + electron and∕or hole conductor), a matter that is of particular importance for a better understanding of photovoltaic devices such as extreme thin absorber cells, dye sensitized solar cells, or organic (so-called plastic) solar cells.
Effect of constituent phases of reactively sputtered AgOx film on recording and readout mechanisms of super-resolution near-field structure disk
Authors: Her Yung-Chiun , Lan Yuh-Chang , Hsu Wei-Chih , Tsai Song-Yeu
Published: July 2004

We have studied the dependence of the constituent phases of reactively sputtered AgOx mask layer on the recording and readout mechanisms of super-resolution near-field disk. At low oxygen flow ratios, the AgOx mask layer was found to be composed of an appreciable amount of Ag particles with sizes of tens of nanometers and Ag2O phase. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with O2 was formed in the AgOx mask layer. The hollow Ag cylinder would serve as an aperture and could effectively reduce the laser spot size during readout, leading to the super-resolution effect only. At high oxygen flow ratios, the AgOx mask layer was found to be mostly composed of Ag2O and/or AgO phases. After recording by a high power laser pulse, a hollow Ag cylinder that had its center filled with nanosized Ag particles was formed in the AgOx mask layer. The nanosized Ag precipitates would serve as light-scattering centers and could yield strong near-field interaction with the subwavelength marks, resulting in both the super-resolution and near-field effects during readout.
Effect of fluorine incorporation on silicon dioxide prepared by high density plasma chemical vapor deposition with SiH4∕O2∕NF3 chemistry
Authors: Kim Jae-Hong , Chung Chai-O , Sheen Dongsun , Sohn Yong-Sun , Sohn Hyun-Chul , Kim Jin-Woong , Park Sung-Wook
Published: July 2004

The effect of fluorine incorporation on properties of silicon dioxide thin films has been studied as a function of NF3∕O2 gas flow ratio. Fluorine was incorporated into silicon dioxide films during high density plasma chemical vapor deposition with the SiH4∕O2∕NF3∕He gas mixture used to improve the gap-filling ability for shallow trench isolation of devices. Refractive index measured by ellipsometry decreased with increasing NF3∕O2 flow ratios for both as-deposited and annealed films. X-ray reflectivity measurements showed that both fluorine incorporation and thermal annealing reduced the film density. The analysis of infrared absorption spectra showed the relaxation of the Si-O-Si bond with increasing NF3∕O2 flow ratios and thermal annealing. The secondary ion mass spectroscopy and x-ray photoelectron spectroscopy studies confirmed the behavior of fluorine diffusion and the binding energy for each species in the films, respectively. These results showed that through fluorine incorporation and thermal annealing, the network structures of silicon dioxide could be modified from low order rings to high order rings accompanied by the enlargement of nanovoids.
Optical emission from silicon-based SiO2 islands fabricated by anodic alumina templates
Authors: Huang G. S. , Wu X. L. , Mei Y. F. , Chen P. , Chu Paul K.
Published: July 2004

We have investigated the photoluminescence spectra of silicon-based nanoscale SiO2 islands obtained by anodization of silicon-based aluminum membranes in a 0.3m sulfuric acid solution under a constant voltage of 25V. Two ultraviolet emission bands were observed at 290 and 370nm. After annealing the samples in 900°C in O2, the 290nm band vanishes, but the 370nm band still exists. We suggest that the 290nm band originates from optical transition in the E′ centers in the SiO2 islands according to its annealing behavior. The 370nm band is considered to be from Al-related luminescence centers, [AlO4]0, because a decrease of intensity of the 370nm band is in agreement with that of amount of the Al ion impurities located in the SiO2 islands. This work shows a clear understanding of the light-emitting mechanism of silicon-based SiO2 island array. The obtained result can be expected to have important applications in modem optoelectronics.
Ultralow-threshold cryogenic vertical-cavity surface-emitting laser with AlAsoxide–GaAs distributed Bragg reflectors
Authors: Haisler V. A. , Toropov A. I. , Bakarov A. K. , Bajutova O. R. , Derebezov I. A. , Kalagin A. K. , Kachanova M. M. , Kuzmin N. B. , Medvedev A. S. , Suranov A. S.
Published: July 2004

Data are presented on vertical-cavity surface-emitting lasers designed for cryogenic operation. Low-loss cavity design and high quality factor of the cavity provide the superior lasing characteristics at T=80K. Ultralow lasing threshold current of 15μA with external differential quantum efficiency 26% is achieved for a 5μm aperture device, and a 31% efficiency is achieved for a 8μm aperture device with a 30μA threshold and 47A∕cm2 threshold current density.
1-octadecene monolayers on Si(111) hydrogen-terminated surfaces: Effect of substrate doping
Authors: Miramond Corinne , Vuillaume Dominique
Published: July 2004

We have studied the electronic properties, in relation to structural properties, of monolayers of 1-octadecene attached on a hydrogen-terminated (111) silicon surface. The molecules are attached using the free-radical reaction between CC and SiH activated by an ultraviolet illumination. We have compared the structural and electrical properties of monolayers formed on silicon substrates of different types (n type and p type) and different doping concentrations, from low-doped (∼1014cm−3) to highly doped (∼1019cm−3). We show that the monolayers on n-, p-, and p+-silicon are densely packed and that they act as very good insulating films at a nanometer thickness with leakage currents as low as ∼10−7Acm−2 and high-quality capacitance-voltage characteristics. The monolayers formed on n+-type silicon are more disordered and therefore exhibit larger leakage current densities (>10−4Acm−2) when embedded in a silicon∕monolayer∕metal junction. The inferior structural and electronic properties obtained with n+-type silicon pinpoint the important role of surface potential and of the position of the surface Fermi level during the chemisorption of the organic monolayers.
Influence of sulfur and phosphorus placement, and sulfur particle size, on elemental sulfur oxidation and the growth response of maize (Zea mays)
Authors: Lefroy Rod D. B. , Sholeh  , Blair Graeme
Published: August 2004

The oxidation rate of elemental sulfur (S) can be manipulated by a number of
controllable factors to match formation of sulfate to plant demand. Two of
these factors are particle size and the presence of adequate nutrients for the
oxidising bacteria. A factorial experiment was conducted in a glasshouse
consisting of 3 combinations of S and phosphorus (P) placements × 2 S
particle sizes [ 35S-labelled 50–150 µm
(fine sulfur, Sf) and 150–250 µm (coarse
sulfur, Sc)] × 2 harvesting times of maize
(Zea mays) (28 and 56 days). In the 3 fertiliser
placement treatments, all of the S was evenly mixed with the soil in the front
compartment of a split-root box. The treatments differed in the placement of
the P fertiliser: (i) all of the P was applied in the
front compartment with the S (SPF);
(ii) the P was applied evenly throughout the soil in
both compartments (SPFB); and
(iii) all of the P was applied in the back compartment
(SPB). A high P- and S-sorbing basaltic soil
(Haplohumult) from Walcha, New South Wales, was used in the split-root boxes.
Plant dry weight and fertiliser S uptake were increased when P was mixed with
elemental S. Elemental S oxidation after 28 days was higher when mixed with P
than when separated from P, and higher with Sf than with
Sc. Root proliferation occurred in direct response to
the placement of P. There were significant linear relationships between the
amount of applied P in the front compartment and root length and root surface
area of the front compartment roots.
This study shows that the increase in S uptake by the plant from elemental S
when it was mixed with P was due to the combined effect of P on elemental S
oxidation and on root proliferation.
The partition of nutrients in ewes maintained in a moderate compared with a lean body condition in late pregnancy
Authors: McNeill D. M. , Kelly R. W. , Williams I. H.
Published: August 2004

The effect of ewe fatness on fetal weight at term was tested without the
confounding effects of placental weight and feed intake. We hypothesised that
fetal weights should be similar in fat or lean ewes with placentas of a
similar size, and tested the hypothesis by manipulating nutrition so that, at
mating, Merino ewes carrying a single fetus were in a medium (score
2·9, liveweight 46·6 kg) or lean (score 2·0, liveweight
40·6 kg) condition. They were maintained at this fatness difference
until slaughter at Day 146 of pregnancy when fetal, placental, and maternal
tissues were weighed and analysed for composition. Subgroups
(n = 8 per fatness group) slaughtered at Day 110,
a stage when most placental hypertrophy is complete but the majority of fetal
hypertrophy is yet to occur, confirmed that the treatments differed in ewe
fatness (3·82 v. 9·19 kg empty-body fat,
s.e.m. = 0·960; P < 0·001) but
not placental weight (487 v. 538 g, s.e.m. =
41·5, P > 0·05). By Day 146, fatness
differences (4·77 v. 9·56 kg empty-body
fat, s.e.m. = 0·960, P < 0·001)
and placental similarities (434 v. 502 g, s.e.m.
= 38·3, P > 0·05) were
maintained, and both groups produced fetuses of similar size (4408
v. 4382 g, s.e.m. = 204·6,
P > 0·05). However, the fetuses in the lean
ewes had 20% less fat/kg fat-free body weight (24
v. 30 g/kg, s.e.m. = 1·3,
P < 0·01). Fetal weight was correlated with
placental weight (r = 0·70;
P < 0·01) but not with ewe fatness. Fetal
fatness, however, was correlated with ewe fatness (r
= 0·69; P < 0·01). Ewe fatness
per se did not influence fetal size but did influence the deposition of fat in
the fetus, possibly via a greater ability of fatter ewes to partition more
glucose toward their fetus.
Dry matter accumulation and partitioning, and seed yield in indeterminate Andean lupin (Lupinus mutabilis Sweet)
Authors: Hardy A. , Huyghe C. , Papineau J.
Published: August 2004

Despite the high oil and protein content of the seeds, the agronomic potential
of Lupinus mutabilis Sweet, a South American lupin
species, is limited because of its low seed yield and its uncertain maturity.
Dry matter accumulation and partitioning, and seed yield, of 2 genotypes
(early-maturing LM34 and late-maturing LM268) were studied in 2 seasons at 2
densities at Lusignan, France. Total dry matter at harvest was, on average,
680 g/m2. The mainstem and first-order branches
mainly contributed to total plant biomass but pods were only produced on the
mainstem. On average, across the different crops, the maximum leaf area index
(LAI) was 2· 8. The duration of LAI above 2·5 was short and not
correlated with the total dry matter production. The partitioning of the dry
matter varied according to the genotype. LM34 showed enhanced pod growth, its
harvest index (HI) was 0·32, and seed yield averaged 1·28
t/ha. LM268 showed enhanced vegetative growth, both HI and seed yield were
lower (0·16 and 1·13 t/ha, respectively), and whole plant
maturity was never reached. For both genotypes during the pod filling, no
remobilisation of assimilates occurred from stems to pods.
Further studies on the incidence of virus infection in white clover pastures
Authors: McKirdy S. J. , Jones R. A. C.
Published: August 2004

Leaf samples of white clover were collected from 19 irrigated white clover
(Trifolium repens) pastures in the south-west of Western
Australia and tested for virus infection by enzyme-linked immunosorbent assay.
Clover yellow vein virus (CYVV) was found in 16 pastures at infection levels
of up to 23% and white clover mosaic virus (WCMV) in 10 at levels up to
83%. None of the white clover pastures with a high incidence of WCMV
had been resown with white clover within the last 10 years, whereas those
resown within the last 5 years had little or no infection. As previously
reported in tests on different white clover pastures in the same irrigation
area, widespread infection with alfalfa mosaic virus (AMV) and occasional
infection with subterranean clover red leaf virus (SCRLV) was also found. Two
or more viruses were found within 16 of the pastures with at least 3 having
all 4 viruses. AMV and WCMV were detected in flatweed
(Hypochaeris glabra) and AMV was detected in clustered
dock (Rumex conglomeratus), both commonly occurring
weeds in the pastures. In tests on the perennial ryegrass
(Lolium perenne) component of 18 white clover pastures,
infection with barley yellow dwarf virus was found in 14 at levels up to
5%. In addition, 11 of the pastures contained a virus which reacted
with potyvirus-specific monoclonal antibodies, presumably ryegrass mosaic
virus (RyMV), which was detected at levels up to 34%.
Live aphids were trapped at 8 different times during 1995 in one pasture that
was infected with WCMV, CYVV, AMV, and SCRLV. Blue-green aphid
(Acyrthosiphon kondoi) and oat aphid
(Rhopalosiphum padi) were the only species caught, both
reaching peak populations in midwinter, but only the latter was found in
summer. No virus transmission was detected when the aphids caught were fed
individually on subterranean clover (T. subterraneum)
indicator plants.
It is concluded that WCMV poses a threat to the productivity of white clover
within irrigated pastures, especially when present in mixed infection with
AMV. CYVV is also commonly found but normally not at high enough incidences to
pose a serious threat. RyMV may pose a threat to the productivity of the
perennial ryegrass component within white clover-based pastures.
An evaluation of sulfur efficiency parameters in soybean and wheat cropping systems in relation to fertiliser sulfur on a Typic Haplustert
Authors: Ganeshamurthy A. N.
Published: August 2004

Sulfur (S) efficiency parameters were evaluated in soybean-wheat cropping
systems in relation to rates of applied S in field experiments on Typic
Haplusterts. The parameters evaluated were grain yield per kg fertiliser S
applied, S harvest index (SHI), S utilisation from soil (SUS), and fertiliser
(SUF) and S efficiency ratios measured as grain yield per kg S uptake by the
shoot or grain yield per kg S uptake by the grain. In addition, grain and
straw yields, S uptake by both crops, and fertiliser S requirements for
optimum production of the 2 crops were also studied. Both soybean and wheat
crops responded significantly to S when applied at 0-40 kg/ha on
S-deficient soils. The calculated optimum rates of application of fertiliser S
to achieve 90% of the maximum yield were 19-38 kg S/ha for soybean
and 28-33 kg S/ha for wheat over the 2-year period. The efficiency of crop
production as measured by grain or seed yield per kg S applied was greater at
lower rates of S application; however, when fertiliser S was applied at a
higher rate than 40 kg S/ha, the efficiency declined. Wheat produced more
grain yield per kg S applied than soybean. The SHI indicated more efficient
translocation of S to soybean seeds than wheat grain. The SUF was greater in
wheat, whereas SUS was similar in both soybean and wheat.