bluuebunny/crossref_metadata_2025 huggingface dataset:
GaAs on Si heterostructures obtained by He and/or H implantation and direct wafer bonding
Authors: Radu I. , Szafraniak I. , Scholz R. , Alexe M. , Gösele U.
Published: December 2003

Transfer of GaAs layers onto Si by helium and/or hydrogen implantation and wafer bonding was investigated. The optimum conditions for achieving blistering/splitting only after postimplantation annealing were experimentally obtained. It was found that specific implantation conditions induce large area exfoliation instead of blistering after annealing of unbonded GaAs. This effect is related to a narrow size and/or a depth distribution of the platelets in as-implanted GaAs and their evolution with annealing. The influence of substrate orientation in blistering/splitting of GaAs was also investigated. Thin GaAs layers were transferred onto silicon by a combination of He and/or H implantation, wafer bonding and low temperature annealing.
Origin and microscopic mechanism for suppression of leakage currents in Schottky contacts to GaN grown by molecular-beam epitaxy
Authors: Miller E. J. , Schaadt D. M. , Yu E. T. , Sun X. L. , Brillson L. J. , Waltereit P. , Speck J. S.
Published: December 2003

Dislocation-related conduction paths in n-type GaN grown by molecular-beam epitaxy and a mechanism for local suppression of current flow along these paths are analyzed using conductive atomic force microscopy, scanning Auger spectroscopy, and macroscopic current–voltage measurements. Application of an electric field at the GaN surface in an ambient atmospheric environment is shown to lead to local formation of gallium oxide in the immediate vicinity of the conduction paths, resulting in the strong suppression of subsequent current flow. Current–voltage measurements for Schottky diodes in which local conduction paths have been suppressed in this manner exhibit reverse-bias leakage currents reduced by two to four orders of magnitude compared to those in Schottky diodes not subjected to any surface modification process. These results demonstrate that the dislocation-related current leakage paths are the dominant source of leakage current in Schottky contacts to n-type GaN grown by molecular-beam epitaxy, and elucidate the nature of a microscopic process for their suppression.
Prediction of boron transient enhanced diffusion through the atom-by-atom modeling of extended defects
Authors: Lampin E. , Cristiano F. , Lamrani Y. , Claverie A. , Colombeau B. , Cowern N. E. B.
Published: December 2003

The modeling of the atom-by-atom growth of extended defects is coupled to the diffusion equations of boron by transferring the free interstitial supersaturation calculated with a defect model into a process simulator. Two methods to achieve this coupling (equilibrium method and fully coupled method, respectively) are presented and tested against a variety of experimental conditions. They are first applied to a transient enhanced diffusion experiment carried out on a structure containing several B delta-doped layers, in which the amount of diffusion of the different layers is accurately predicted. The fully coupled method is then used to simulate the diffusion of ultrashallow B-implanted profiles. This work definitely demonstrates the relevance of accurate physical defect models for the successful design of ultrashallow junctions in future generations of integrated circuits.
Effect of process parameters on the structural characteristics of laterally grown, laser-annealed polycrystalline silicon films
Authors: Voutsas A. T. , Limanov A. , Im J. S.
Published: December 2003

In this work, we have conducted a systematic study aiming at assessing the effects of process parameters on the microstructural characteristics of laterally grown polycrystalline silicon (poly-Si) films. Poly-Si films were formed by the sequential lateral solidification (SLS) method. The Si film thickness was found to affect significantly the quality of the poly-Si microstructure, manifested by a decreased crystal-growth defect density and increased subboundary spacing in thicker films. A weak (100) texture was observed in the lateral growth direction, except for very thin films (<30 nm) where (110) texture was observed. No specific texture was identified in the normal and transverse directions. Lateral crystallization proceeds by seeded, lateral epitaxial growth at an advancing pitch. We investigated the quality of lateral growth as a function of the advancing, substrate pitch. We found that an optimum pitch range exists, bound on the low end by the detailed shape of the beam-edge profile and on the high end by the quality of crystal formed under deep, interfacial undercooling. In that sense, only a fraction of the laser beamlet can be effectively used for lateral growth and the process should be tuned towards maximizing this fraction. Thin film transistor data were used to further refine the considerations driving the selection of optimum process parameters for SLS lateral crystallization providing the least sensitivity to process-induced variations.
Thermally assisted tunneling and the Poole–Frenkel effect in homogenous a-Si
Authors: Furlan Joz̆e , Gorup Z̆arko , Levstek Andrej , Amon Slavko
Published: December 2003

Basic ideas for carrier capture and emission are applied to a homogenous a-Si exposed to high electric fields. By adding anisotropic Poole–Frenkel and tunneling transitions to the isotropic pure thermal transitions of free carriers between band states and traps, an analytical model for capture-emission rate of carriers in a-Si is developed. A stream of lateral electron flow in the conduction band incident to the potential barrier is obtained by integrating the contributions of all electrons within a thin electron sheet above the conduction band edge striking the potential barrier. Some of the incident electrons either tunnel through the barrier to the capturing funnel or cross the barrier apex as the Poole–Frenkel contribution to the captured electron flux. The opposite process of electron release from traps is described as an enhanced thermal emission of electrons crossing the barrier or tunneling through it to the conduction band. Equivalent expressions can be obtained for holes communicating between traps and the valence band. The effect of a high electric field is much more intense on carrier emission than on carrier capture. The balance between capture and emission rates in steady-state conditions is maintained at increased free carrier concentrations, resulting in strongly enhanced conductivity.
Electroluminescence from Tm-doped GaN deposited by radio-frequency planar magnetron sputtering
Authors: Kim Joo Han , Davidson M. R. , Holloway Paul. H.
Published: December 2003

Room-temperature blue and near-infrared (NIR) electroluminescence ac (EL) has been demonstrated from Tm-doped GaN thin films prepared by rf planar magnetron sputter deposition. Blue and NIR EL emission peaks at ∼475 and ∼800 nm, respectively, were observed from the Tm3+ 4f intrashell transitions from the G41 and F43 excited states to the H63 ground state, respectively. The threshold voltage for the 475 nm blue emission was consistently 11 to 19 V higher than that for the 800 nm NIR emission. The EL intensity ratio of the 475 to 800 nm emission (I475/I800) was increased ∼900% with a 67% increase in the applied ac voltage from 120 to 200 V. These results indicate that the excitation process of EL from GaN:Tm ACTFEL devices is dominated by impact excitation of the Tm3+ luminescent centers by direct interaction between hot electrons and the ground state 4f electrons.
Raman study of the A1(LO) phonon in relaxed and pseudomorphic InGaN epilayers
Authors: Correia M. R. , Pereira S. , Pereira E. , Frandon J. , Alves E.
Published: December 2003

The behavior of the A1(LO) phonon mode of relaxed and pseudomorphic InxGa1−xN epilayers, at the surface, is investigated by Raman spectroscopy. This study involves relaxed and pseudomorphic samples, with a compositional range of 0.12⩽x<0.30 and 0.04<x⩽0.20, respectively. Raman measurements were performed under excitation at 3.71 eV. Due to the low depth penetration of the incident light (40 nm), the major contribution to Raman scattering comes from the surface, where strain and composition have been independently determined. For relaxed samples, a linear dependence of the A1(LO) phonon frequency is obtained, as theoretically expected for an one-mode behavior alloy: Ω0(x)=(736±1)-(149±2)x. In the case of pseudomorphic samples, the phonon frequency is almost composition independent up to x=0.11, probably due to the opposite effects of strain and alloying.
Electron thermometry and refrigeration with doped silicon and superconducting electrodes
Authors: Buonomo B. , Leoni R. , Castellano M. G. , Mattioli F. , Torrioli G. , Di Gaspare L. , Evangelisti F.
Published: December 2003

We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junctions made by a thin film of heavily doped silicon in contact with superconducting electrodes through Schottky barriers. Doped silicon films were chemical vapor deposited on silicon-on-insulator substrates and laterally dry etched in mesas. Aluminum or, alternatively, niobium contacts were deposited on the mesas. Below the superconducting critical temperature Tc, an energy gap opens in the superconductor and the current–voltage characteristics become nonlinear and strongly sensitive to temperature changes. We have also characterized the heavily doped silicon in terms of the electron–phonon thermal decoupling by cooling the electron gas by means of aluminum–silicon–aluminum structures. With Nb electrodes, we have observed an anomaly of the electrical differential conductance at zero voltage and a larger electron dissipation, as a result of a less opaque barrier.
Polarized Raman-scattering study of Ge and Sn-filled CoSb3
Authors: Nolas G. S. , Kendziora C. A. , Takizawa Hirotsugu
Published: December 2003

Raman-scattering spectra of Ge-filled and Sn-filled CoSb3 were studied as a function of polarization. Polarized Raman-scattering spectra of CoSb3 were used to help distinguish the symmetry of each vibrational mode observed in the filled skutterudite specimens. Seven out of the eight Raman-active Sb vibrational modes of CoSb3 and the Ge-filled skutterudites were identified for each specimen. We also compare our experimental assignments with theoretical calculations for CoSb3. The Sn atoms “rattle” inside the voids of the crystal structure and interact strongly with the lattice vibrations to shift and broaden the Sb-vibrational modes as compared to the spectra of CoSb3. The smaller and lighter Ge atoms however do not have such an effect on the lattice vibrations, indicating that the interaction of Ge with the lattice is relatively weak in comparison.
Enhancement of giant magnetoimpedance effect of electroplated NiFe/Cu composite wires by dc Joule annealing
Authors: Li X. P. , Zhao Z. J. , Chua C. , Seet H. L. , Lu L.
Published: December 2003

The influence of dc Joule annealing of electroplated Ni80Fe20/Cu composite wires on their giant magnetoimpedance (GMI) effect is presented in this article. Successive thermal treatments by dc Joule annealing with the current density ranging from 2.4 to 9.6×108 A/m2 were applied to the composite wires for a fixed annealing time of 1 min to release the residual stresses in the plated NiFe layer. The results showed that the magnetoimpedance (MI) effect of the composite wires can be greatly enhanced by dc Joule annealing. For electroplated 1.5 μm of the Ni80Fe20 layer on a copper wire of 20 μm diameter, the optimum annealing current density was found to be 7.2×108 A/m2 and from such annealing the MI ratio was increased from 637% to 1110%, a 74% increment. The optimum ac driving frequency for the GMI effect of the annealed wires under the influence of the annealing conditions in relation to the skin effect and permeability variation in the wires was investigated and discussed. The optimum procedure of dc Joule annealing and the cooling rate against the MI ratio of the annealed wire were also investigated. The results showed that stepped annealing is better than single step annealing and the lower the cooling rate the higher the MI ratio.
Patterned arrays of porous InP from photolithography and electrochemical etching
Authors: Su G. , Guo Q. , Palmer R. E.
Published: December 2003

Patterned arrays of porous InP have been produced using electrochemical etching method at room temperature in combination with photolithography. n-type InP wafers with (001) orientation were used as the anode, and gold was used as the cathode. The porous structure was produced in either aqueous HCl or a mixture of HCl and HNO3 with a voltage bias ranging from 2 to 10 V. Alternating stripes of porous and nonporous InP have been fabricated on an InP substrate by etching a masked sample. Surface morphology measurements and cross sectional analysis of the porous layer have been conducted using atomic force microscopy and scanning electron microscopy. Photoluminescence from the porous surface shows a significant suppression of the interband transition. An energy barrier at the porous/bulk InP interface, identified from conductance measurements, is proposed to arise from the effect of surface states.
Influence of low energy–high flux nitrogen implantation on the oxidation behavior of AISI 304L austenitic stainless steel
Authors: Pedraza F. , Grosseau-Poussard J. L. , Abrasonis G. , Rivière J. P. , Dinhut J. F.
Published: December 2003

Low energy–high flux (1.2 keV, 1 mA/cm2) nitriding of an austenitic AISI 304L stainless steel has been carried out by implanting a dose of 3.5×1019 ions cm−2 at 400 °C for 1 h. An important increase in surface hardness has been found to occur as a result of the formation of the so-called expanded austenite γN phase. Transmission electron microscopy studies have also shown the existence of hexagonal Cr2N precipitates at the nitrided layer/matrix interfacial region. The oxidation behavior has been then studied in the temperature range between 400 and 550 °C for 24 h under synthetic air. It is shown that nitridation slightly modifies the oxidation kinetics as a result of the progressive transformation of the γN phase towards CrN precipitation and α-FeNi matrix formation. More chromium enriched scales are, anyhow, developed on the nitrided steel than in the untreated one. These results are discussed on the basis of the chromium diffusion in the nitrided layer and its preferential chemical bonding with nitrogen atoms.
Statistical study of subthreshold characteristics in polycrystalline silicon thin-film transistors
Authors: Kitahara Yoshiyuki , Takagi Shigeyuki , Sano Nobuyuki
Published: December 2003

We investigate the influence of grain size variations on device properties of polycrystalline silicon thin-film transistors (poly-Si TFTs) by drift–diffusion device simulations. Employing our grain boundary model which represents the intrinsic variations of grain size [Jpn. J. Appl. Phys., 42, L634 (2003)], the subthreshold characteristics are simulated for the various configurations of grains in the channel region so that the statistical fluctuation of device characteristics is investigated. It is shown that the variations in subthreshold characteristics are caused mainly by the number of grains included in the channel because the grain boundaries act as highly resistive regions. However, as the channel length shrinks, the grain boundary located close to the drain critically determines the channel resistance of poly-Si TFTs and the device characteristics could differ even if the number of grains included in the channel region is the same.
Remote Coulomb scattering in metal–oxide–semiconductor field effect transistors: Screening by electrons in the gate
Authors: Gámiz F. , Fischetti M. V.
Published: December 2003

The effect of screening of remote Coulomb scattering (RCS) by free electrons in the polycrystalline silicon (polysilicon) gate of a metal–oxide–semiconductor transistor has been analyzed. We have completed a previous model of RCS by adding the effects of the screening by electrons in the gate assuming a Thomas–Fermi dielectric function to take into account the response of the gate. A Monte Carlo simulator has been included in this model, in addition to phonon scattering, surface-roughness scattering, and Coulomb scattering due to substrate impurities. Using this Monte Carlo simulator, we have evaluated mobility curves for different values of the oxide thickness. Although the RCS effect is certainly weakened by the screening, it is still quite important for very thin oxide layers (Tox⩽1 nm), and therefore should be taken into account.
Time-of-flight secondary ion mass spectroscopy for surface analysis of insulators using a cluster ion beam
Authors: Hirata K. , Saitoh Y. , Chiba A. , Narumi K. , Kobayashi Y. , Arakawa K.
Published: December 2003

An effect of the impact of cluster ions into insulating materials on charged secondary emission [K. Hirata, Y. Saitoh, K. Narumi, and Y. Kobayashi, Appl. Phys. Lett. 81, 3669 (2002)] was applied to secondary ion mass spectroscopy. Positive secondary ion time-of-flight (TOF) measurements of polycarbonate films using 0.5 MeV/atom C1+ monoatomic and 0.5 MeV/atom C8+ cluster ions as primary ions were performed as a function of atomic dose without charge compensation. The use of C8+ instead of C1+ eliminated dose-dependent peak shifts and overall spectrum compression due to charging observed with C1+ bombardment. Furthermore, the C8+ bombardment was found to provide better spectrum resolution than the C1+ bombardment. The superior stability of the TOF spectra against charging makes mass spectrometry with cluster ion ionization a promising tool for the chemical analysis of insulating materials.
Atomic-to-mesoscopic scale structural transition in metal–carbon diamondlike composites probed by second-harmonic generation
Authors: Murzina T. V. , Kapra R. V. , Aktsipetrov O. A. , Dorfman V. F.
Published: December 2003

Structural features of diamondlike metal-doped carbon films are studied by means of optical second-harmonic generation (SHG). A high interfacial sensitivity of the SHG probe and its significant enhancement in metal nanoparticles allows one to distinguish between clusterlike and amorphous atomic scale structure of carbon-metal composites. These films appear to retain a stable amorphous atomic-scale structure in a wide range of metal concentration above the percolation threshold. Atomic-to-mesoscopic scale structural transition in diamondlike metaldoped carbon films is observed, which takes place under the thermal annealing.
Surface-layer band gap widening in Cu(In,Ga)Se2 thin films
Authors: Romero M. J. , Jones K. M. , AbuShama J. , Yan Y. , Al-Jassim M. M. , Noufi R.
Published: December 2003

Transmission electron microscopy observations, cathodoluminescence spectroscopy and spectrum imaging are combined to investigate the emission spectrum in Cu(In,Ga)Se2 (CIGS) thin films with improved spatial resolution. We report direct evidence for a surface layer of wider band gap, which forms spontaneously in CIGS films. The existence of such a surface layer is critical for attaining high efficiency in solar cells based on these chalcopyrite semiconductor compounds.
Field-emission studies on thin films of zinc oxide nanowires
Authors: Jo S. H. , Lao J. Y. , Ren Z. F. , Farrer R. A. , Baldacchini T. , Fourkas J. T.
Published: December 2003

Studies on field emission (FE) from thin films of zinc oxide (ZnO) nanowires found that both the turn-on voltage and emission current density depend on the areal density of nanowires. The density of ZnO nanowires is controlled by the gold (Au) nanoparticle density deposited on the silicon substrates. The growth of ZnO nanowires was achieved by the thermal evaporation/condensation method. It is shown that the same screening effect observed on carbon nanotube field emitters also affects the FE from thin films of ZnO nanowires. Thin films with the lowest areal density of ZnO nanowires showed much better FE characteristics, comparable to that of carbon nanotubes. More importantly, the FE characteristics of ZnO nanowire thin film were further improved with annealing in hydrogen.
Field-effect transistor on pentacene single crystal
Authors: Butko V. Y. , Chi X. , Lang D. V. , Ramirez A. P.
Published: December 2003

We report on the fabrication and characterization of field-effect transistors (FETs) on single-crystal pentacene. These FETs exhibit hole conductivity with room-temperature effective mobility (μeff) up to 0.30 cm2/V s and on/off ratios up to 5×106. A negative gate voltage of −50 V significantly decreases the activation energy (Ea) down to 0.143 eV near room temperature. Using this value of Ea and a simple model, we find the number of free carriers is only ∼0.4% of the total number of injected carriers. Along with μeff∼0.3 cm2/V s, this places the intrinsic mobility in the range of tens of cm2/V s.
Artificial flux pinning centers in large, single-grain (RE)-Ba-Cu-O superconductors
Authors: Hari Babu N. , Reddy E. S. , Cardwell D. A. , Campbell A. M. , Tarrant C. D. , Schneider K. R.
Published: December 2003

Second-phase, nanoscale inclusions of composition Y2Ba4CuMOy (M=U, Nb, Ta, W, Mo, and Re), which form artificial pinning centers, have been introduced into large, single-grain [rare-earth (RE)]-Ba-Cu-O superconductors. A significant improvement in critical current density is observed in these samples, due presumably to various combinations of normal conducting, paramagnetic, and geometrical properties of the Y2Ba4CuMOy particles in the superconducting (RE)Ba2Cu3O7−δ (RE-123) phase matrix. These Y2Ba4CuMOy phase particles are chemically stable in the Ba-Cu-O liquid during peritectic solidification, unlike Y2BaCuO5 (Y-211) phase particles in Y-Ba-Cu-O, which opens a processing window for the fabrication of nanostructured large, single-grain (RE)-Ba-Cu-O superconductors with enhanced flux pinning for high-field engineering applications.
Enhancement of collimated low-energy broad-beam ion source with four-grid accelerator system
Authors: Wåhlin E. K. , Watanabe M. , Shimonek J. , Burtner D. , Siegfried D.
Published: December 2003

An application of a four-grid ion acceleration system for generating highly collimated low-energy (<1.5 keV) ion beams is presented. The four-grid system offers significantly reduced beam divergence angles for practical low-energy source designs compared to current two- and three-grid systems. Ion beam divergence of the entire beam envelope has been reduced to less than 2° at 250 and 750 eV. Results are also compared with a conventional three-grid system.
Intrinsic electronic transport properties of organic field-effect transitors based on single crystalline tetramethyltetraselenafulvalene
Authors: Nam M.-S. , Ardavan A. , Cava R. J. , Chaikin P. M.
Published: December 2003

We report the fabrication of field-effect transistors on single crystals of the highly anisotropic organic semiconductor tetramethyltetraselenafulvalene. We find maximum mobilities of 0.2 cm2/V s at room temperature. We observe an exponential decrease of mobility with decreasing temperature with an activation energy 160±30 meV, independent of sample quality or fabrication method.
Plasma frequency measurements for absolute plasma density by means of wave cutoff method
Authors: Kim Jung-Hyung , Seong Dae-Jin , Lim Jong-Yeon , Chung Kwang-Hwa
Published: December 2003

A method for precise measurements of absolute electron density in the plasma using plasma frequency is developed. A microwave perturbation of a frequency is introduced to plasma from a network analyzer and transmits in the plasma. The transmitting wave at a distance from a radiating antenna is monitored using a spectrum analyzer to scan the perturbing frequency. The transmitting wave rapidly decays by a cutoff at the plasma frequency, which gives the absolute electron density. The transmitting waves of some frequency including plasma frequency are characterized. The measured plasma frequency by this method is coincident with that obtained by the plasma oscillation method.
Low-temperature hydrophobic silicon wafer bonding
Authors: Tong Q.-Y. , Gan Q. , Hudson G. , Fountain G. , Enquist P. , Scholz R. , Gösele U.
Published: December 2003

By introducing a nanometer-scale H trapping defective silicon layer on bonding surfaces, the bonding surface energy of bonded oxide-free, HF dipped, hydrophobic silicon wafers can reach a silicon fracture surface energy of 2500 mJ/m2 at 300 to 400 °C compared with 700 °C conventionally achieved. Adding boron atoms on bonding surfaces can reduce the surface hydrogen release temperature but would not increase the bonding energy unless a defective layer is also formed. This indicates that, in order to achieve high bonding energy, the released hydrogen must be removed from the bonding interface. Many prebonding treatments are available for low-temperature hydrophobic wafer bonding including the formation of an amorphous silicon layer by As+ implantation, by B2H6 or Ar plasma treatment, or by sputter deposition, followed by an HF dip and room temperature bonding in air. The interface amorphous layer may be recrystallized by annealing at elevated temperatures, e.g., at 450 °C for As+-implanted samples.
Argon excimer emission from high-pressure microdischarges in metal capillaries
Authors: Sankaran R. Mohan , Giapis Konstantinos P. , Moselhy Mohamed , Schoenbach Karl H.
Published: December 2003

We report on argon excimer emission from high-pressure microdischarges formed inside metal capillaries with or without gas flow. Excimer emission intensity from a single tube increases linearly with gas pressure between 400 and 1000 Torr. Higher discharge current also results in initial intensity gains until gas heating causes saturation or intensity drop. Argon flow through the discharge intensifies emission perhaps by gas cooling. Emission intensity was found to be additive in prealigned dual microdischarges, suggesting that an array of microdischarges could produce a high-intensity excimer source.
Fragmentation of Fe2O3 nanoparticles driven by a phase transition in a flame and their magnetic properties
Authors: Yang Sangsun , Yi Ji-Hyun , Son Soonil , Jang Jungho , Altman Igor S. , Pikhitsa Peter V. , Choi Mansoo
Published: December 2003

The size and crystalline phase changes of Fe2O3 nanoparticles formed in a H2/O2 flame have been investigated. At flame temperatures below 1350 °C, the mean particle size increased monotonously with the distance from the burner edge; but in high-temperature flames above 1650 °C, it suddenly decreased from 20 to ∼3 nm with the distance from the burner edge. The results of X-ray diffraction and high-resolution transmission electron microscopy showed that this sudden reduction of the size of nanoparticles was accompanied by a partial phase transformation from the metastable γ-Fe2O3 into α-Fe2O3. We suggest the structural instability due to γ- to α-phase transformation as a mechanism for a rapid fragmentation of 20 nm particles into 3 nm ones.
Spontaneous InAs quantum dot nucleation at strained InP/GaInAs interfaces
Authors: Borgstrom M. , Samuelson L. , Seifert W. , Mikkelsen A. , Ouattara L. , Lundgren E.
Published: December 2003

We present a cross-sectional scanning-tunneling microscopy investigation of twofold stacked InAs quantum dots in InP, between layers of GaInAs. The dots are vertically aligned, and images with atomic resolution show that the dots consist of pure InAs. Despite the intended twofold stacking of dots, three dots were often found in the stacks. The third dot formed immediately on top of the final InP layer, at the InP/GaInAs interface. Atomically resolved images of these spontaneously formed dots indicate that they also consist of pure InAs. The effect is discussed in terms of phase segregation of GaInAs and arsenic–phosphorus exchange reactions.
Reduction of the hydrophobic attraction between charged solutes in water
Authors: Dzubiella J. , Hansen J.-P.
Published: December 2003

We examine the effective force between two nanometer scale solutes in water by Molecular Dynamics simulations. Macroscopic considerations predict a strong reduction of the hydrophobic attraction between solutes when the latter are charged. This is confirmed by the simulations which point to a surprising constancy of the effective force between oppositely charged solutes at contact, while like charged solutes lead to significantly different behavior between positive and negative pairs. The latter exhibit the phenomenon of “like-charge attraction” previously observed in some colloidal dispersions.
Formation mechanism of crater defects on HgCdTe/CdZnTe (211) B epilayers grown by molecular beam epitaxy
Authors: Chang Y. , Badano G. , Zhao J. , Grein C. H. , Sivananthan S. , Aoki T. , Smith David J.
Published: December 2003

Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been investigated. A semiempirical model coupled with observations by transmission electron microscopy was used to analyze the defect formation mechanism. We find that Te2 dissociation plays an important role. The defect density can be controlled by adjusting growth conditions such as the substrate growth temperature, Hg flux, growth rate and composition. Tight control over the pretreatment procedures before molecular beam epitaxy growth is also necessary.
Responses of freshwater biota to rising salinity levels and implications for saline water management: a review
Authors: James Kimberley R. , Cant Belinda , Ryan Tom
Published: December 2003

All of the plants and animals that make up freshwater aquatic communities are affected by salinity. Many taxa possess morphological, physiological and life-history characteristics that provide some capacity for tolerance, acclimatisation or avoidance. These characteristics impart a level of resilience to freshwater communities.To maintain biodiversity in aquatic systems it is important to manage the rate, timing, pattern, frequency and duration of increases in salinity in terms of lethal and sublethal effects, sensitive life stages, the capacity of freshwater biota to acclimatise to salinity and long-term impacts on community structure.We have limited understanding of the impacts of saline water management on species interactions, food-web structures and how elevated salinity levels affect the integrity of communities. Little is known about the effect of salinity on complex ecosystem processes involving microbes and microalgae, or the salinity thresholds that prevent semi-aquatic and terrestrial species from using aquatic resources. Compounding effects of salinity and other stressors are also poorly understood.Our current understanding needs to be reinterpreted in a form that is accessible and useful for water managers. Because of their complexity, many of the remaining knowledge gaps can only be addressed through a multidisciplinary approach carried out in an adaptive management framework, utilising decision-making and ecological risk assessment tools.
Salinisation and prospects for biodiversity in rivers and wetlands of south-west Western Australia
Authors: Halse S. A. , Ruprecht J. K. , Pinder A. M.
Published: December 2003

Saline water was common in south-west Western Australian aquatic systems prior to land-clearing because most streams and wetlands were ephemeral and evapo-concentrated as they dried, and there were high concentrations of stored salt in groundwater and soil profiles. Nevertheless, a 1998 review of salinity trends in rivers of south-west Western Australia showed that 20-fold increases in salinity concentrations had occurred since clearing in the medium-rainfall zone (300–700 mm). More recent data confirm these trends and show that elevated salinities have already caused substantial changes to the biological communities of aquatic ecosystems. Further substantial changes will occur, despite the flora and fauna of the south-west being comparatively well adapted to the presence of salinity in the landscape. Up to one-third of wetland and river invertebrate species, large numbers of plants and a substantial proportion of the waterbird fauna will disappear from the wheatbelt, a region that has high biodiversity value and endemism. Increased salinities are not the only threat associated with salinisation: increased water volumes, longer periods of inundation and more widespread acidity are also likely to be detrimental to the biota.
Natural diversity of Santalum spicatum host species in south-coast river systems and their incorporation into profitable and biodiverse revegetation
Authors: Woodall G. S. , Robinson C. J
Published: December 2003

The commercially valuable root hemiparasite Santalum spicatum (R.Br.) A.DC. (sandalwood) once grew throughout the medium- to low-rainfall areas of the south-western agricultural region of Australia; however, this resource has been exhausted by over-exploitation and clearing for agriculture. There has been growing interest from the farming community and other investors in the development of a plantation Santalum spicatum industry in southern Western Australia. This study investigated the distribution of remnant S. spicatum within the Pallinup River catchment and assessed the risk of S. spicatum population decline due to salinity. The natural range of host species at different sites (river catchments) across the south coast was also investigated. Remnant populations of S.�spicatum within and adjacent to the Pallinup River catchment were small (1–70 trees) and highly fragmented. The risk of further population decline due to salinity was concluded to be small because remnant trees were generally growing in well drained, sandy soils that were elevated above (median 9 m) their immediate drainage line. Across the seven river catchments surveyed, S. spicatum occurred in a range of vegetation associations and parasitised numerous species (68) from a wide range of genera and families. The suite of species exploited varied within and between catchments. Thirty species, including most monocots and Myrtaceae, were not successfully parasitised. Remnant S. spicatum always occurred on well drained soil types that supported open-woodland or mallee–heath communities. Sandalwood plantations, supported by numerous individuals of a range of host species (10–40 species), were shown to be productive in terms of sandalwood growth. The scale of the developing sandalwood plantation industry is likely to be small and unlikely to cover large areas of catchments. Thus, this industry alone is unlikely to address the salinity crisis through broadscale recharge management. However, additional to on-site recharge reduction, biodiverse host plantations may improve the prospects for biodiversity and rivers in salinising landscapes through the protection and enhancement of natural biodiversity, creation of new habitat, conservation of plant species and by providing a commercial incentive to protect biodiversity.
Environmental flows, river salinity and biodiversity conservation: managing trade-offs in the Murray - Darling basin
Authors: Goss Kevin F.
Published: December 2003

The Murray–Darling basin's river system suffers from over-allocation of water resources to consumptive use and salinity threats to water quality. This paper draws attention to the current state of knowledge and the need for further investigations into the biological effect of river salinity on aquatic biota and ecosystems, the threats of dryland salinity to terrestrial biodiversity, and managing environmental flows and salinity control to limit the trade-offs in water-resource security and river salinity.There is growing evidence that river salt concentrations lower than the normally adopted threshold have sublethal effects on species and ecosystems, over a longer time period. Further knowledge is required.There is no agreed process for incorporating terrestrial biodiversity values at risk into a strategic response for dryland-salinity management. This is a public policy issue to be addressed.Recent studies have quantified the trade-off in surface water flow and river salinity from refforestation and revegetation of upland catchments to control salinity. The potential losses or benefits to environmental values have not been quantified.Such improved knowledge is important to the Murray–Darling basin and relevant to other river basins and catchments in Australia.
A cladistic and biogeographic analysis of Chinese Neopsylla Wagner (Siphonaptera : Ctenophthalmidae)
Authors: Lu Liang , Wu Houyong
Published: November 2003

A cladistic analysis of 29 Chinese species of Neopsylla Wagner, 1903 is carried out based on morphology. Rothschildiana Smit, 1952 and Tamiophila Jordan, 1938, two close relatives of Neopsylla, are also included in the analysis. The results support four species-groups among the Neopsylla: the anoma-group, the stevensi-group, the specialis-group and the setosa-group, and an independent species, N. angustimanubra Wu, Wu�& Liu, 1966. Species of Rothschildiana are included in the stevensi-group and Tamiophila grandis is a member of the setosa-group. Therefore Neopsylla is a paraphyletic group and Rothschildiana and Tamiophila are junior synonyms. The four species-groups show different distributions and host preferences. Rattus is the primary host of the anoma- and stevensi-groups, although some species of the anoma-group have shifted to Myospalax. The specialis-group predominantly infects Apodemus. The setosa-group shifted host preference from the Murinae to genera of Cricetinae and Sciurinae. The reasons for the changes in host and distributions of the species-groups are discussed in relation to the zoogeographic history of China.
Phylogenetic revision of the endemic New Zealand carabid genus OregusPutzeys (Coleoptera : Carabidae : Broscini)
Authors: Pawson S. M. , Emberson R. M. , Armstrong K. F. , Paterson A. M.
Published: November 2003

This study explores the taxonomy and phylogeny of the New Zealand endemic carabid beetle genus Oregus. The genus was previously known from two species, Oregus aereus, which is widespread throughout the South Island, and Oregus inaequalis, which is highly restricted in its distribution (only found on the outskirts of Dunedin City) and prioritised as a category B threatened species by the Department of Conservation. Both morphology and mitochondrial DNA sequences were used for phylogenetic analysis. Twenty-six DNA sequences of partial cytochrome oxidase subunit 1 and NADH dehydrogenase subunit 1 were analysed. Analyses indicated four species – the existing O. aereus and O. inaequalis and two new morphologically cryptic species from the upper South Island, O. crypticus and O. septentrionalis. Oregus crypticus and O. septentrionalis form a basal clade and O. aereus is the most derived species. Oregus aereus remains the most widespread species, but the northern limit of its geographical range is now Porters Pass (approximately 150 km south of its historically assigned range). Male genitalic characters proved to be the most useful morphological characters. Oregus crypticus and O. septentrionalis are easily separated from O. aereus and O. inaequalis by external morphology. Differentiation between the two northern species was only possible by dissection of male genitalia or DNA sequencing. Oregus inaequalis remains highly restricted in its distribution (morphological analysis did not identify any new populations) and its species status is confirmed. Redescriptions are given for O. aereus and O. inaequalis and new descriptions and type designations are presented for O. crypticus and O. septentrionalis.
Subsurface drip irrigation in raised bed tomato production. I. Nitrogen and phosphate losses under current commercial practice
Authors: Stork P. R. , Jerie P. H. , Callinan A. P. L.
Published: November 2003

The leaching of inorganic nitrogen and phosphate was studied at field sites that utilised subsurface drip irrigation (SDI) for commercial production of processing tomatoes. Irrigation expended for the establishment of crops, at emergence, accounted for 34% of the seasonal total in a Rochester clay (site 1) and 25% in a Binabbin clay (site 2). In the period after emergence and up to crop harvests, irrigation and rainfall amounted to 88% and 105% of calculated crop evapotranspiration for site 1 and site 2, respectively. Drainage between the commencement of irrigation and crop harvests amounted to 66 mm below 2 m at site 1 and 60 mm below 0.9 m at site 2. Total irrigation caused a 2- and 5-fold depletion of soil chloride at site 1 (within 2 m) and site 2 (within 0.9 m), respectively. The drainage and chloride depletion showed that irrigation regimes at these sites were conducive to the leaching of fertiliser inputs. It was calculated that ~32 kg NO–3-N + NH+4-N/ha and 7 kg HPO2–4-P/ha was leached below 2 m during irrigation at site 1. At site 2, ~75 kg NO–3-N + NH+4-N/ha was leached below 0.9 m during irrigation.Post harvest amounts of inorganic nitrogen and phosphate at site 1 and site 2 indicated that fertiliser applications exceeded total crop uptake of both compounds. Post harvest quantities of inorganic nitrogen and phosphate at several other commercial locations (sites 3, 4, 5, 6) showed that excessive fertiliser use was not restricted to site 1 and site 2. At site 1, between an early autumn harvest and early spring, when vegetable beds were fallow, the leaching losses of post harvest amounts of both compounds below 2 m were 137 kg NO–3-N + NH+4-N/ha and 11 kg HPO2–4-P/ha. The irrigation and fertiliser management practices at all sites were similar to those reported for studies of SDI production of other vegetable and grain crops. Altogether, these results indicated that the effects of SDI combined with excessive fertiliser inputs in current commercial practice may cause the leaching of significant amounts of nitrogen and phosphate to groundwater depths.
Alteration of groundwater and sediment geochemistry in a sulfidic backswamp due to Melaleuca quinquenervia encroachment
Authors: Johnston S. G. , Slavich P. G. , Hirst P.
Published: November 2003

Extensive encroachment of the native tree species Melaleuca quinquenervia (Cav.) Blake has occurred on a coastal floodplain sulfidic backswamp in eastern Australia. Almost 50% of the open swamp area c. 1870 is now monospecific M. quinquenervia forest. Encroachment has been associated with shortened hydroperiods and land management changes following drainage for agriculture. Large differences to shallow groundwater and sediment geochemistry were observed beneath both individual M. quinquenervia trees and encroaching forests compared to open swamp. Groundwater beneath M. quinquenervia had enhanced titratable acidity and acidic metal cations, increased concentrations of other ionic species (Cl–, SO42–), altered ionic ratios, and increased dissolved organic carbon. Soil beneath M. quinquenervia displayed enhanced accumulation of acidity and soluble ions, with concentration profiles suggesting vertical redistribution towards the surface. Deepening of the sulfide oxidation front in the soil beneath encroached M. quinquenervia suggests that enhanced sulfide oxidation may be occurring. Changes in soil pH, redox potential, and Fe mineral precipitation/dissolution were also evident. These changes appear to be the result of interactions between M. quinquenervia physiology and the unique groundwater and sediment geochemistry of the surrounding sulfidic/sulfuric horizons. Mechanisms to explain the observed changes are discussed along with potential management implications.
The use of remote sensing data to extract information from agricultural land with emphasis on soil salinity
Authors: Howari F. M.
Published: November 2003

The rapid growth of information technologies has provided exciting new sources of data, interpretation tools, and modelling techniques to soil research and education communities at all levels. This paper presents some examples of the capability of remote sensing data such as Landsat ETM+, airborne visible/infrared imaging spectrometer (AVIRIS), colour infrared aerial photos (CIR), and high-resolution field spectroradiometer (GER 3700) to extract surface information about soil salinity. The study used image processing techniques such as supervised classification, spectral extraction, and matching techniques to investigate types and occurrences of salts in the Rio Grande Valley on the United States–Mexico border. Soil salinity groups were established using soil physico-chemical properties and image elements (absorption-reflectivity profiles, band combinations, grey tones of the investigated images, and textures of soil and vegetation covers as they appear in images). The lack of vegetation or scattered vegetation on salt-affected soil (SAS) surfaces makes it possible to detect salt in several locations of the investigated area. The presented remote sensing datasets reveal the presence of gypsum and halite as the dominant salt crusts in the Rio Grande Valley. This information can help agricultural scientists and engineers to produce large-scale maps of salt-affected lands, which will help improve salinity management in watersheds and ecosystems.
A review of current space-based fire monitoring in Australia and the GOFC/GOLD program for international coordination
Authors: Justice Christopher O. , Smith Richard , Gill A. Malcolm , Csiszar Ivan
Published: November 2003

Satellite remote sensing of fires provides a unique view of our planet and quantitative information that can inform resource management and policy. Operational and experimental satellite sensing systems have the capability to provide regional and global monitoring of fires. These systems provide different types of fire information for estimation of fire danger, detecting active fires, estimating burned area, quantifying emissions products, estimating fire damage and monitoring post-fire ecosystem recovery. Efforts to extract and provide such information fall largely in the research domain and are in various stages of development. The pressing demand for reliable and up-to-date information, on fire occurrence, extent and emissions, warrants the transition of the mature research methods and experimental sensors into the operational domain. Providing consistent, timely and easily useable fire information of known accuracy for improved resource management is a challenge facing the research and operational communities. As part of the Integrated Global Observing Systems initiative, an international program called Global Observations of Forest Cover/Global Observations of Land Dynamics (GOFC/GOLD) is coordinating a concerted effort to meet this challenge. This paper describes the goals of this international program and provides a case study of the development and current status of satellite-based fire monitoring in Australia. We identify the major obstacles to a broader adoption of the technology by the fire community, the current needs and the relevance of the broader international program to national satellite-based fire monitoring activities.
Application of NDVI for predicting fuel curing at landscape scales in northern Australia: can remotely sensed data help schedule fire management operations?
Authors: Allan Grant , Johnson Andrea , Cridland Shane , Fitzgerald Nikki
Published: November 2003

The success of early dry season burning programs in tropical savannas of northern Australia could be improved with timely information on curing state of fuel loads. Variable characteristics of each wet season, the onset of the dry season, and variations of fuel loads within major landscape types affect the annual cycle of curing. Significant relationships were derived between ground-based visual estimates of curing, and estimates of relative greenness derived from NDVI images from NOAA AVHRR and SPOT Vegetation satellite sensors. There were distinct differences between soil types (red v. black) and seasons (1999 v. 2000). The next stage is to test if relationships are robust enough to be used operationally to schedule aerial control burning operations in remote, inaccessible and sparsely unpopulated areas.