bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Laser Ablation on Growth of ZnO/ZnS/ZnO Multilayer Structured Nanorods by Chemical Vapor Deposition
Authors: Hirate Takashi , Koisikawa Hiroaki , Yugi Makoto , Kumada Takuya , Matsuzawa Yuki , Satoh Tomomasa
Published: February 2009

ZnO is an attractive II-VI compound semiconductor material for various optoelectronic devices. Recently, growth of various nanostructures of ZnO such as nanorod, nanobelt, nanowall, etc. has been reported, and ZnO has been considered as a promising material for nanodevices. We have studied on fabrication of aligned ZnO nanorods by a low-pressure thermal chemical vapor deposition (CVD) method cooperated with laser ablation of Mn pellet. In this paper, we report on fabrication of ZnO/ZnS/ZnO multilayer structured nanorods and particularly on effects of laser ablation on the morphology of the nanorods intending to develop a new electroluminescent device including ZnO nanorods. The fabrication method of ZnO/ZnS/ZnO multilayer structured nanorods is almost same method used in our previous study. Metal Zn vapor and O2 gas or H2S are used as precursors to synthesize ZnO or ZnS, and N2 is used as carrier gas. A Mn pellet is placed near a Si(111) substrate in a deposition chamber and ablated by a pulsed Nd:YAG laser beam (wavelength =1.064 mm, pulse width = 8 ns, repetition frequency = 10 shots/sec). The pressure is 13.3 Pa and the temperature is 550 C. When ZnO is grown, O2 of 0.88 SCCM mass flow rate is used as a precursor. When ZnS is grown, on the other hand, H2S of 2.0 SCCM mass flow rate is used as a precursor. The growth time is 15 min for each layer. Firstly, ZnO nanorods are grown. Laser ablation of Mn is executed for initial 3 min and only CVD is performed for remaining 12 min. The vertically aligned ZnO nanorods with 100 nm diameter and 1500 nm height are grown. Secondly, ZnS nanorod is grown on the top surface of the first ZnO nanorods. In this process, the morphology is not so dependent on execution of laser ablation of Mn for initial 3 min in this growth process. Finally, ZnO layer is again grown on ZnS/ZnO nanorods described above. When the laser ablation of Mn for initial 3 min is not executed, many fine ZnO whiskers with long length are grown with random directions on the top surface and on the side surfaces of ZnS/ZnO nanorods. When the laser ablation of Mn for initial 3 min is executed, on the other side, a thick whisker is grown on top surface of ZnS/ZnO nanorods. The shape is not nanorod. The diameter is abruptly decreased and the tip is very sharp. The growth of ZnO whisker on the side surface of ZnS/ZnO nanorods is not almost observed. It is found that the laser ablation of Mn for initial 3 min in the third ZnO growth strongly influences the morphology of the third ZnO layer. We estimate that the Mn species that are ablated from a Mn pellet and reaches the surface of ZnS/ZnO nanorods change any quality of the surface of ZnS/ZnO nanorods. We are now studying of finding the growth conditions of the third ZnO layer with morphology of nanorod on ZnS/ZnO nanorods that is considered to be suitable for electroluminescent devices.
Electrofluidic Positioning of Biofunctionalized Nanowires
Authors: Morrow Thomas J. , Kim Jaekyun , Li Mingwei , Mayer Theresa S. , Keating Christine D.
Published: February 2009

We functionalized nanowires with three different probe peptide nucleic acid (PNA) sequences, and assembled the three populations onto a lithographically patterned chip. Electrofluidic assembly enabled positioning each set of nanowires to span a different pair of guiding electrodes. Fluorescence imaging was used to probe whether the PNA on the individual nanowires remained able to selectively bind complementary DNA targets following assembly and integration of the positioned nanowires onto the chip surface.
Photodetector Using Surface-Plasmon Antenna for Optical Interconnect
Authors: Ohashi Keishi , Fujikata Junichi
Published: February 2009

We used a surface-plasmon antenna to obtain small photodetectors for LSI on-chip optical interconnection by using near-field light generated by the antenna. Such near-field devices are not constrained by the diffraction limit and they offer an approach to integrated nanoscale photonic devices. A small semiconductor structure is located near the antenna to absorb the near-field light. This structure can be made as small as the Schottky depletion layer, so the separation between electrodes can be reduced to almost the size of the near-field region. We have demonstrated a “Si nano-photodiode” or plasmon photodiode that uses the near-field localized in a subwavelength region, which is usually relatively large in size because of the long absorption length for Si (˜10 μm at a wavelength of ˜800 nm). The Si nano-photodiode has a fast impulse response with a full-width at half-maximum of ˜20 ps even when the bias voltage is small (˜1 V or less). We demonstrated an on-chip optical interconnect chip to operate circuitry in an LSI chip by using waveguide-coupled Si nano-photodiodes.
Photoluminescence from Ge/Si Nanocrystals Embedded in Silicon Oxide Matrix Annealed in Hydrogen Gas
Authors: Uekusa Shin-ichiro , Kosaka Naoki
Published: February 2009

Photoluminescence (PL) spectra from Si nanocrystals embedded in silicon oxide matrix (Si-SiO2) thin films, Ge embedded in silicon oxide matrix (Ge-SiO2) thin films and both Ge and Si embedded in silicon oxide matrix (Ge/Si-SiO2) thin films prepared by RF magnetron sputtering were investigated. All as-deposited thin films were annealed for 1h in the temperature range from 500°C to 1100°C in Ar or H2 atmosphere. The PL spectra of Si-SiO2 thin films exhibited red luminescence at an annealing temperature of 1100°C and the PL intensity of the sample annealed in H2 gas increased by a factor of approximately 6.3 in comparison with sample annealed in Ar gas. Subsequently, The PL intensity of main peak centered at about 400 nm (V-band) of Ge-SiO2 thin films annealed in H2 gas exhibited strong comparison with the sample annealed in Ar gas. Finally, the PL spectra of Ge/Si-SiO2 thin films exhibited strong peak centered at approximately 500-530 nm (G-band) besides V-band and others in the temperature range from 700°C to 1000°C. The PL intensity of G-band of the samples annealed in H2 gas exhibited weak comparison with Ar gas.
Ab initio Computationally Generated Nanoporous Carbon and its Comparison to Experiment
Authors: Romero Cristina , Valladares Ariel A. , Valladares R. M. , Valladares Alexander , Calles Alipio G.
Published: February 2009

Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. Here we present an application of our recently developed ab initio method [1] for the generation of group IV porous materials. The method consists in constructing a crystalline diamond supercell with 216 atoms of carbon and a density of 3.546 g/cm3, then lengthening the supercell edge to obtain a density of 1.38 g/cm3, yielding a porosity of 61.1 % in order to be able to compare with experimental results reported in the literature [2]. We then subject the resulting supercell to an ab initio molecular dynamics process at 1000 K during 295 steps. The radial distribution functions obtained are compared to experiment to discern coincidences and discrepancies.
Opto-Electronic Properties of Ge and Si Related Nanostructures on Ultrathin Si Oxide Covered Si Surfaces
Authors: Ichikawa Masakazu , Nakamura Yoshiaki , Shklyaev Alexander , Fujinoki Norohito
Published: February 2009

We present a method to form semiconductor nanodots on Si substrates by using ultrathin Si oxide technology and the results on their opto-electronic properties. We can form ultra-small semiconductor nanodots with the size of ˜5nm and ultra-high density of ˜1012 cm−2 on Si surfaces covered with ultrathin SiO2 films of ˜0.3nm thickness. We focus on the Ge and GeSn nanodots on Si substrates and those embedded in Si films. These structures exhibit quantum confinement effects and intense luminescence in the energy region of about 0.8 eV.
Design, Fabrication and Characterization of Si3N4 Photonic Crystal Nanocavities for Diamond-based Quantum Information Processing Applications
Authors: Khan Mughees , McCutcheon Murray W. , Babinec Thomas , Deotare Parag , Lončar Marko
Published: February 2009

In order to improve the efficiency of quantum emitters, in particular nitrogen-vacancy (NV) color centers in diamond nanocrystals (NCs), it is important to enhance their photon production rate as well as the collection efficiency of the emitted photons. This can be achieved by embedding the emitters within optical cavities. Here we describe the design and fabrication of 1-D photonic crystal nanocavities in an air-bridge silicon nitride (SiNx) structure. In spite of the low index of silicon nitride (n˜2), we were able to design optical nanocavities with Quality factors as high as Q˜1 × 106. These nanocavities were designed to operate near 637 nm in order to strongly enhance the zero-phonon line (ZPL) emission of an NV center in a diamond NC while suppressing the in-plane emission into the phonon side-band. Simulation results show that a NV center placed near the top of the cavity would experience a reduction of radiative lifetime from ˜15ns to ˜2ps (Purcell factor ˜7000), thus significantly improving the photon production rate. Experimental results show a cavity resonance at ˜630nm, with a linewidth corresponding to Q˜1250, limited by the spectrometer resolution. The presented work is an important step towards the realization of diamond-based single photon devices, including switches.
Si Single-Electron SOI-MOSFETs: Interplay with Individual Dopants and Photons
Authors: Tabe Michiharu , Burhanudin Zainal Arif , Nuryadi Ratno , Moraru Daniel , Ligowski Maciej , Jablonski Ryszard , Mizuno Takeshi
Published: February 2009

We have demonstrated that Si single-electron or single-hole SOI-MOSFETs with the multi-dots channel have attractive new functions such as photon detection and single-electron transfer. Multi-dots formed by selective-oxidation-induced patterning of the thin SOI layer have been used in the experiments of photon detection, while, most recently, we have utilized smaller dots consisting of individual dopant potentials in single electron transfer devices. Furthermore, in order to directly observe spatial landscape of single charges in the channel region, we have developed Low Temperature-Kelvin Probe Force Microscopy and succeeded in detecting single-dopant potential in the channel region. In this paper, photon detection by these devices will be primarily described.
In-situ electrical probing of zones of nanoindentation-induced phases of silicon
Authors: Ruffell Simon , Bradby Jodie , Williams Jim , Major Ryan , Warren Oden
Published: February 2009

Phase transformed zones of silicon have been formed by nanoindentation both at the micro- and nanoscale and electrically probed using an in-situ measurement system. Zones composed of the high pressure crystalline phases (Si-III/Si-XII) have higher conductivity than those of amorphous silicon (a-Si). At the microscale probing laterally across the surface shows that the conductivity varies within the zones composed of the high pressure phases. The sensitivity to the different conductivities of the two phases allows mapping within the zones. Finally, at the nanoscale the conductivity of the high pressure phase zones can be correlated with the position of the pop-out associated with the formation of the phases. The zones have higher conductivity when the pop-out occurs earlier on unloading and we suggest that this is due to the reduction in trace volumes of a-Si formed during the early portion of the unloading cycle.
In situ XPS investigation about the growth of the first atomic layer of Ta(N) films deposited by thermal TBTDET ALD
Authors: Strehle Steffen , Schmidt Daniela , Gutsch Sebastian , Knaut Martin , Albert Matthias , Bartha Johann W.
Published: February 2009

Ta based films are important building blocks for modern microelectronic applications. To meet the requirements of miniaturization, atomic layer deposition appears to be an alternative technology in comparison to PVD and CVD. In the present paper investigations of a thermal TBTDET ALD process will be presented with emphasis to the first ALD reaction cycles on native silicon oxide and HF etched silicon surfaces. The investigations show that the substrate chemistry is a crucial parameter for the film growth and appears to be a key to control the ALD deposition. The investigations were done by XPS without any vacuum break between the deposition and the surface analysis.
Topochemical Modification of Layered Perovskites
Authors: Choi Jong-Lak , Josepha Elisha , Zhang Xiao , Wiley John
Published: February 2009

Topochemical reaction strategies based on two-step intercalation methods are studied. Reactions involving reductive followed by oxidative intercalation are quite effective in making new compounds; the synthesis and characterization of (A2Cl)LaNb2O7 (A = Rb, Cs) are presented. An alternative synthetic route, oxidative followed by reductive intercalation, is also discussed.
Swelling of Layered Potassium Ruthenate into Nanosheet Crystallites
Authors: Fukuda Katsutoshi , Kato Hisato , Sugimoto Wataru , Takasu Yoshio
Published: February 2009

The swelling and exfoliation behaviors of layered potassium ruthenate and the resultant unilamellar crystallites of RuO2.10.2− with nanosheet morphology were studied. The reaction of layered H0.2RuO2.1·0.9H2O with tetrabutylammonium hydroxide (TBA+OH−) was found to be extremely sensitive to the interlayer water content. The use of highly hydrous layered protonic ruthenate was essential for obtaining direct exfoliation. The swelling behavior was also affected by the ratio of TBA+ to ion-exchangeable H+ in the layered compound. At low ratios of TBA+/H+≤1, the layered precursor scarcely exfoliated and mostly deposited as an intercalation compound. In the intermediate TBA+/H+ range, an auburn colloidal suspension containing exfoliated nanosheets was formed, while much larger ratios were less favorable for the exfoliation.
Spin, Orbital and Lattice Coupling in the Double Perovskite Ba2154SmMoO6
Authors: Mclaughlin Abbie
Published: February 2009

An unexpectedly high antiferromagnetic transition temperature (TN = 130 K) has been observed in the double perovskite Ba2154SmMoO6 as a result of a strong interplay between spin, orbital and lattice degrees of freedom. A variable temperature neutron diffraction study of Ba2154SmMoO6 demonstrates that the orbital order below TN is as a result of a Jahn-Teller distortion of the MoO6 octahedra.
Synthesis and Structures of Novel Lanthanide Benzenedicarboxylates
Authors: Gil-Mateo Paola , Wang Xiqu , Jacobson Allan
Published: February 2009

Three novel lanthanum benzenedicarboxylates La2(BDC)3(H2O)4 (1), La4(BDC)3(OH)6 (2) and La3(BDC)2(OH)5 (3) (BDC = 1,4-benzenedicarboxylate) were synthesized by hydrothermal reactions and their structures determined from single crystal X-ray diffraction. All three compounds are 3D framework structures consisting of layers of LaOn polyhedra cross-linked by BDC ligands along the layer stacking direction. In 1 the layers contain separated [LaO6(H2O)2] polyhedra that are bridged by the carboxylate groups of the BDC anions. Compounds 2 and 3 both have highly condensed lanthanum oxide-hydroxide polyhedra. In 2 the layers are wavy and consist of [LaO5(OH)4] and [LaO4(OH)5] polyhedra that share common corners, edges, and faces. In 3, the layers are similar but comprise [LaO3(OH)5] and [LaO4(OH)5] polyhedra.
Synthesis of porous biomorphic Cu/CeO2/Al2O3by using cotton as templates
Authors: Chiu Ka Lok , Kwong Fung Luen , Jia Juncai , Li Jia , Ng Hang Leung
Published: February 2009

Methanol has high volumetric energy density and is relatively easy to handle, thus methanol fuel cells have potential applications in automobiles and portable devices. There are two types of methanol fuel cells. The direct type cell oxidizes methanol for power generation while the indirect type first converts methanol to hydrogen and uses it as fuel. Indirect methanol fuel cell has several advantages. It has a higher efficiency compared to the direct type, and does not need hydrogen supply and storage as in the hydrogen fuel cell. However, its size is larger and it is heavier as reforming methanol and removing CO are required. Meanwhile, the catalyst with mechanical support such as ceramic foam or honeycomb accounts for a significant part of its total weight. Thus, its applications are limited, especially in portable devices. As a remedy, we have developed a high surface area/weight ratio, low cost and self-supported catalyst for the indirect methanol fuel cell by using porous biomorphic Cu/CeO2/Al2O3. This ternary system is produced via a chemical method by using cotton as templates. Cu/CeO2is a catalyst for reforming methanol and for oxidation of CO, and the Al2O3is to prevent segregation of the Cu and CeO2fine particles.

To prepare this biomorphic Cu/CeO2/Al2O3, a 0.5 M Boehmite solution was prepared with C9H21O3Al via the Yoldas process. It was then mixed with 0.5 M Cu(NO3)2and 0.5 M Ce(NO3)3solutions. The weight percentage ratio of Cu:Ce:Al was 3:2:5 in the mixture. Cotton balls were soaked in the mixture, and they were air dried before sintered in air at temperatures ranged from 400°C to 800°C. The sintered samples were further reduced with diluted hydrogen at 250°C for 2 hours. The final products were characterized via SEM, TEM, XRD, BET, DTA and TGA.

We found that the products maintained the original macroscopic shape and size of the cotton ball and no obvious shrinkage was observed. The SEM images showed that the original internal fibrous networks in the raw cotton was retained in the biomorphic product, however, the fibers became hollow. The XRD result confirmed that the Cu/CeO2/Al2O3compound was produced when the sintering temperatures between 500°C and 700°C. The sizes of the Cu and CeO2particles in the products were in nanometer scale. When the sintering temperature was higher than 700°C, CuAl2O4was produced. When temperature was below 500°C, Cu2O was produced. From the DTA and TGA results, the pyrolysis of soaked cotton occurred between 190°C and 380°C. The sample weight decreased to about 16% of its original at 380°C, and kept almost constant at higher temperatures. The BET area of our products was about 100m2per gram, which was comparable to those of similar products synthesized by other methods. Our products are self supported and mechanical support was not required. It is expected that the weight of catalysts can be greatly reduced and the energy utilization of the indirect methanol fuel cell can be improved.
Fabrication and Characterization of Electrically Functional Lanthanum Hexaboride Thin Films on Ultrasmooth Sapphire Substrates
Authors: Kato Yushi , Ono Yusaburo , Akita Yasuyuki , Hosaka Makoto , Shiraishi Naoki , Tsuchimine Nobuo , Kobayashi Susumu , Yoshimoto Mamoru
Published: February 2009

The crystal growth of lanthanum hexaboride (LaB6) thin films was examined by applying the laser molecular beam epitaxy (laser MBE) process. C-axis (100) highly-oriented LaB6 thin films could be fabricated on ultrasmooth sapphire (α-Al2O3 single crystal) (0001) substrates with atomic steps of 0.2 nm in height and atomically flat terraces. The obtained film exhibited a smooth surface with root mean square roughness of 0.15 nm. The lattice parameter of the LaB6 thin film was close to the bulk value reported previously. In the case of deposition on commercial mirror-polished sapphire substrates, the grown film was amorphous. The resistivity of the prepared crystalline LaB6 thin films was as low as 2.2 × 10−4 Ω cm and almost constant in the temperature range of 10–300 K.
Inducing Grain Alignment in Metals, Compounds and Multicomponent Thin Films
Authors: Harper James M.E.
Published: February 2009

Several methods to induce grain alignment in polycrystalline thin films are discussed, in which directional effects can dominate over the normal evolution of fiber texture during thin film growth. Early experiments with ion beam assisted deposition showed the importance of channeling directions in selecting grain orientations with low sputtering yield or low ion damage energy density. Examples of this approach include the formation of biaxial fiber textures in Nb, Al and AlN. Grain orientations may also be selected by the release of stored energy during abnormal grain growth initiated by solute precipitation (Cu-Co) or phase transformation (TiSi2). Other energy sources such as mechanical deformation, crystallization or compound formation may also contribute to producing desired grain alignments. In multicomponent thin films, combinations of these mechanisms provide opportunities for more specific control of grain orientations.
Investigation of Early Nucleation Events in Magnesium Oxide During Ion Beam Assisted Deposition
Authors: Groves James , Hammond Robert , DePaula Raymond F. , Clemens Bruce M.
Published: February 2009

Ion beam assisted deposition (IBAD) is used to biaxially texture magnesium oxide (MgO), which is useful as a template for the heteroepitaxial growth of various thin film devices and most notably as a template layer for high temperature superconductors. Improvements in the quality of IBAD MgO films have been largely empirical and there is uncertainty as to the exact mechanism by which this biaxial texture is developed. Using a specially built quartz crystal microbalance (QCM) as both a substrate and monitor in conjunction with reflected high-energy electron diffraction (RHEED) acting on the same surface, we have probed the initial stages of IBAD MgO growth in-situ. We have correlated corresponding RHEED images with real-time mass accumulation QCM data during the film growth. During IBAD growth, the mass accumulation exhibits a sharp change in slope corresponding to a sudden decrease in growth rate. Corresponding RHEED images show an abrupt onset of crystallographic texture at this point. A simple model incorporating differential etch rates of the MgO film and silicon nitride substrate can be used to fit the data but is inconsistent with the behavior during ion etching with no growth. It is, therefore, postulated that a more complex mechanism is responsible for the observed behavior.
Ion-beam assisted pulsed laser deposition of textured transition-metal nitride films
Authors: Hühne Ruben , Kidszun Martin , Güth Konrad , Thoss Franziska , Rellinghaus Bernd , Schultz Ludwig , Holzapfel Bernhard
Published: February 2009

Ion-beam assisted deposition (IBAD) offers the possibility to prepare thin textured films on amorphous or non-textured substrates. It was shown within the last decade that the ion beam influences the nucleation in material with a rocksalt structure leading to a strong cube texture already within the first 10 nanometres. Among these materials, transition metal nitrides exhibit interesting physical properties as superconductivity, metallic behaviour or superior hardness. Therefore, a reactive IBAD process was applied for the preparation of highly textured transition metal nitride layers using pulsed laser deposition of pure metals in combination with a nitrogen-containing ion beam. The results on the in-plane textured growth of TiN are promising for the development of conducting buffer layer architectures for YBCO coated conductors based on the IBAD approach. Furthermore, this approach was used to prepare other highly textured transition metal nitride thin films like NbN and ZrN.
Low-Temperature Selective Growth of Heteroepitaxial α-Al2O3 Thin Films on a NiO Layer by the Electron-Beam Assisted PLD Process
Authors: Hosaka Makoto , Akita Yasuyuki , Sugimoto Yuki , Kato Yushi , Ono Yusaburo , Matsuda Akifumi , Koyama Koji , Yoshimoto Mamoru
Published: February 2009

Selective heteroepitaxial growth of α-Al2O3 thin films on a NiO layer was investigated using an electron-beam assisted pulsed laser deposition process. The epitaxial NiO layer was grown on an ultrasmooth sapphire (α-Al2O3 single crystal) (0001) substrate. The α-Al2O3 thin film could be grown epitaxially only in the electron-beam irradiated region of the epitaxial NiO layer at 300°C, while the amorphous Al2O3 film was grown in the non-irradiated region. The homoepitaxial growth of α-Al2O3 thin films could not be attained on the sapphire (0001) substrate at 300°C. This indicates that the electron-beam irradiation enhances heteroepitaxial growth of the α-Al2O3 thin films on the NiO layer at 300°C. When we annealed the epitaxial Al2O3/NiO bilayer film at 350°C in a hydrogen atmosphere, we could reduce only the NiO layer to an epitaxial Ni metal layer, allowing the fabrication of epitaxial Al2O3/Ni (insulator/metal structure) films. The fabricated Al2O3/Ni bilayer films exhibited a very smooth surface.
Carbon Nanotube-Induced Changes of Crystal Growth In Polymer Films
Authors: Georgiev Georgi Yordanov , Cabrera Yaniel , Wielgus Lauren , Iftikhar Zarnab , Mattera Michael , Gati Peter , Potter Austin , Cebe Peggy
Published: February 2009

Isotactic Polypropylene (iPP) nanocomposites with low concentrations of multiwall carbon nanotubes (CNTs) 0-1% were studied, using differential scanning calorimetry and Avrami analysis. The nanocomposites were isothermally crystallized at 135°C, in order to measure the effect of nanotubes on the kinetics of crystallization. In our study there is a great effect of the CNTs on the iPP crystallization kinetics. The Avrami analysis shows increase in the crystallization rate constant and constancy the Avrami exponent with increase of the CNTs concentration. The full width at half maximum (FWHM) of the heat flow exotherm and the peak time for crystallization (tp) change dramatically. For iPP, the carbon nanotubes serve as nucleation agents to speed up the crystallization process.
Artificial Grain Alignment of Organic Crystalline Thin Films
Authors: Shimada Toshihiro
Published: February 2009

It is important to obtain single crystalline organic thin films for electronics and optics applications. Due to the mismatching in the crystal symmetry, it is difficult to align the crystalline grains of organic molecular films even on single crystalline surfaces. We have developed several techniques for the artificial grain alignment in organic epitaxial growth. (1) Use of nanoscale-textured surfaces prepared by step bunching of vicinally-cut single crystalline surfaces, in which the height of the steps is critically important. (2) Application of external electric field. (3) Optical excitation of the molecules which can be applied to the polar semiconducting molecules. These techniques might be applicable to other materials including ionic materials and ferroelectrics.
Liquid-Liquid Phase Transition in Undercooled Silicon: Structural, Electronic and Dynamical Aspects
Authors: Jakse Noel , Pasturel Alain
Published: February 2009

We have proposed a new mixed approach by combining efficiently classical and first-principles molecular dynamics to study undercooling of liquid silicon, regardless of a specific empirical interaction model. Our results show an enhancement of the local tetrahedral ordering in the deep undercooled region associated to the appearance of propagating shear waves and give a strong support to the existence of a transition between a high density liquid to a low density liquid near 1050 K. An analysis of the structural, dynamics and electronic properties is proposed to elucidate these features.
Improved bond valence models for ion transport pathways in glasses
Authors: Adams Stefan N.
Published: February 2009

Structure property function relationships provide valuable guidelines for a systematic development of functional materials. It is demonstrated how an augmented bond valence (BV) approach helps to establish such relationships in solid electrolytes. In principle it permits to identify mobile species, transport pathways and provides estimates for ion mobilities. In this work we discuss ion conduction pathways in glassy Lithium metasilicate as an illustrative example. The required representative local structure model is derived from Molecular Dynamics simulations, which provides the opportunity to compare the bond-valence-based predictions from a static structure model with a comprehensive analysis of a complete simulation trajectory. It is shown that understanding the bond valence mismatch as an effective Morse-type interaction opens up a way for systematically analyzing ion transport pathways and for a generally applicable method with improved reliability to predict ion transport characteristics in solid electrolytes from the structure model.
Major dimensions in food‐web structure properties
Authors: Vermaat Jan E. , Dunne Jennifer A. , Gilbert Alison J.
Published: February 2009

The covariance among a range of 20 network structural properties of food webs plus net primary productivity was assessed for 14 published food webs using principal components analysis. Three primary components explained 84% of the variability in the data sets, suggesting substantial covariance among the properties employed in the literature. The first dimension explained 48% of the variance and could be ascribed to connectance, covarying significantly with the proportion of intermediate species and characteristic path length. The second dimension explained 19% and was related to trophic species richness. The third axis explained 17% and was related to ecosystem net primary productivity. A distinct opposite clustering of connectance, the proportion of intermediate species, and mean trophic level vs. the proportion of top and basal species and path length suggests a dichotomy in food‐web structure. Food webs appear either clustered and highly interconnected or elongated with fewer links.
Quantifying a dynamic risk landscape: heterogeneous predator activity and implications for prey persistence
Authors: Schauber Eric M. , Connors Matthew J. , Goodwin Brett J. , Jones Clive G. , Ostfeld Richard S.
Published: February 2009

Spatial heterogeneity in predation risk can ameliorate impacts on prey populations, particularly for prey of generalists. Spatially heterogeneous risk implies the existence of refugia, and the spatial scale of those refugia and their persistence over time affect whether prey can avoid predation by aggregating therein. Our objective was to quantify the magnitude, spatial scale, and temporal persistence of heterogeneity in risk of predation by white‐footed mice (Peromyscus leucopus), an abundant generalist predator of gypsy moths (Lymantria dispar) and songbirds. We used track plates to measure white‐footed mouse activity at >170 trees in each of three forest plots in upstate New York during summers of 2003–2005. We quantified the mean and coefficient of variation of track activity among trees by fitting the beta‐binomial distribution to data from each plot and study period. We measured temporal persistence by disattenuated autocorrelation, and spatial scale by fitting exponential variograms. Mice were much less abundant in 2005 than the other two years, leading to lower overall track activity but higher coefficient of variation among trees. Mouse track activity at individual trees was positively autocorrelated between monthly study periods in 2003 and 2004, and even between the two years, whereas temporal autocorrelation in 2005 was much weaker. Track activity showed positive spatial autocorrelation over lag distances from ∼30 to >1000 m. These findings indicate that mouse activity, and hence risk to their prey, varies substantially in space at spatial and temporal scales that appear responsive to mouse population dynamics. The spatial scale and temporal persistence of that variation imply that prey may benefit from returning to, or failing to disperse from, refugia.
Marketing time predicts naturalization of horticultural plants
Authors: Pemberton Robert W. , Liu Hong
Published: February 2009

Horticulture is an important source of naturalized plants, but our knowledge about naturalization frequencies and potential patterns of naturalization in horticultural plants is limited. We analyzed a unique set of data derived from the detailed sales catalogs (1887–1930) of the most important early Florida, USA, plant nursery (Royal Palm Nursery) to detect naturalization patterns of these horticultural plants in the state. Of the 1903 nonnative species sold by the nursery, 15% naturalized. The probability of plants becoming naturalized increases significantly with the number of years the plants were marketed. Plants that became invasive and naturalized were sold for an average of 19.6 and 14.8 years, respectively, compared to 6.8 years for non‐naturalized plants, and the naturalization of plants sold for 30 years or more is 70%. Unexpectedly, plants that were sold earlier were less likely to naturalize than those sold later. The nursery's inexperience, which caused them to grow and market many plants unsuited to Florida during their early period, may account for this pattern. Plants with pantropical distributions and those native to both Africa and Asia were more likely to naturalize (42%), than were plants native to other smaller regions, suggesting that plants with large native ranges were more likely to naturalize. Naturalization percentages also differed according to plant life form, with the most naturalization occurring in aquatic herbs (36.8%) and vines (30.8%). Plants belonging to the families Araceae, Apocynaceae, Convolvulaceae, Moraceae, Oleaceae, and Verbenaceae had higher than expected naturalization. Information theoretic model selection indicated that the number of years a plant was sold, alone or together with the first year a plant was sold, was the strongest predictor of naturalization. Because continued importation and marketing of nonnative horticultural plants will lead to additional plant naturalization and invasion, a comprehensive approach to address this problem, including research to identify and select noninvasive forms and types of horticultural plants is urgently needed.
Long‐term disease dynamics in lakes: causes and consequences of chytrid infections in Daphnia populations
Authors: Johnson Pieter T. J. , Ives Anthony R. , Lathrop Richard C. , Carpenter Stephen R.
Published: February 2009

Understanding the drivers and consequences of disease epidemics is an important frontier in ecology. However, long‐term data on hosts, their parasites, and the corresponding environmental conditions necessary to explore these interactions are often unavailable. We examined the dynamics of Daphnia pulicaria, a keystone zooplankter in lake ecosystems, to explore the long‐term causes and consequences of infection by a chytridiomycete parasitoid (Polycaryum laeve). After quantifying host–pathogen dynamics from vouchered samples collected over 15 years, we used autoregressive models to evaluate (1) hypothesized drivers of infection, including host density, water temperature, dissolved oxygen, host‐food availability, and lake mixing; and (2) the effects of epidemics on host populations. Infection was present in most years but varied widely in prevalence, from <1% to 34%, with seasonal peaks in early spring and late fall. Within years, lake stratification strongly inhibited P. laeve transmission, such that epidemics occurred primarily during periods of water mixing. Development of the thermocline likely reduced transmission by spatially separating susceptible hosts from infectious zoospores. Among years, ice duration and cumulative snowfall correlated negatively with infection prevalence, likely because of reductions in spring phytoplankton and D. pulicaria density in years with extended winters. Epidemics also influenced dynamics of the host population. Infected D. pulicaria rarely (<1%) contained eggs, and P. laeve prevalence was positively correlated with sexual reproduction in D. pulicaria. Analyses of D. pulicaria density‐dependent population dynamics predicted that, in the absence of P. laeve infection, host abundance would be 11–50% higher than what was observed. By underscoring the importance of complex physical processes in controlling host–parasite interactions and of epidemic disease in influencing host populations, our results highlight the value of long‐term data for understanding wildlife disease dynamics.
Latitudinal variation in herbivore pressure in Atlantic Coast salt marshes
Authors: Pennings Steven C. , Ho Chuan-Kai , Salgado Cristiano S. , Więski Kazimierz , Davé Nilam , Kunza Amy E. , Wason Elizabeth L.
Published: February 2009

Despite long‐standing interest in latitudinal variation in ecological patterns and processes, there is to date weak and conflicting evidence that herbivore pressure varies with latitude. We used three approaches to examine latitudinal variation in herbivore pressure in Atlantic Coast salt marshes, focusing on five abundant plant taxa: the grass Spartina alterniflora, the congeneric rushes Juncus gerardii and J. roemerianus, the forb Solidago sempervirens, and the shrubs Iva frutescens and Baccharis halimifolia. Herbivore counts indicated that chewing and gall‐making herbivores were typically ≥10 times more abundant at low‐latitude sites than at high‐latitude sites, but sucking herbivores did not show a clear pattern. For two herbivore taxa (snails and tettigoniid grasshoppers), correctly interpreting latitudinal patterns required an understanding of the feeding ecology of the species, because the species common at high latitudes did not feed heavily on plant leaves whereas the related species common at low latitudes did. Damage to plants from chewing herbivores was 2–10 times greater at low‐latitude sites than at high‐latitude sites. Damage to transplanted “phytometer” plants was 100 times greater for plants transplanted to low‐ than to high‐latitude sites, and two to three times greater for plants originating from high‐ vs. low‐latitude sites. Taken together, these results provide compelling evidence that pressure from chewing and gall‐making herbivores is greater at low vs. high latitudes in Atlantic Coast salt marshes. Sucking herbivores do not show this pattern and deserve greater study. Selective pressure due to greater herbivore damage at low latitudes is likely to partially explain documented patterns of low plant palatability to chewing herbivores and greater plant defenses at low latitudes, but other factors may also play a role in mediating these geographic patterns.
Long‐term effects of plant diversity and composition on soil nematode communities in model grasslands
Authors: Viketoft Maria , Bengtsson Janne , Sohlenius Björn , Berg Matty P. , Petchey Owen , Palmborg Cecilia , Huss-Danell Kerstin
Published: February 2009

An important component of plant–soil feedbacks is how plant species identity and diversity influence soil organism communities. We examine the effects of grassland plant species growing alone and together up to a richness of 12 species on nematode diversity and feeding group composition, eight years after the establishment of experimental grassland plots at the BIODEPTH site in northern Sweden. This is a substantially longer time than most other experimental studies of plant effects on soil fauna. We address the hypotheses that (1a) higher species or functional diversity of plants increases nematode diversity, as well as influences nematode community composition. Alternatively, (1b) individual plant species traits are most important for nematode diversity and community composition. (2) Plant effects on soil organisms will decrease with increasing number of trophic links between plants and soil fauna.

Plant species identity was often more important than plant diversity for nematode community composition, supporting hypothesis 1b. There was a weak positive relation between plant and nematode richness, which could be attributed to the presence of the legume Trifolium pratense, but also to some other plant species, suggesting a selection or sampling effect. Several plant species in different functional groups affected nematode community composition. For example, we found that legumes increased bacterial‐feeding nematodes, most notably r‐selected Rhabditida, while fungal‐feeding nematodes were enhanced by forbs. Other bacterial feeders and obligate root feeders were positively related to grasses. Plant effects were usually stronger on plant‐, bacterial‐ and fungal‐feeding nematodes than on omnivores/predators, which supports hypothesis 2.

Our study suggests that plant identity has stronger effects than plant diversity on nematode community composition, but when comparing our results with similar previous studies the effects of particular plant species appear to vary. We also found that more productive plant species affected bacterial‐feeding nematodes more than fungal feeders. Moreover, we observed stronger effects the fewer the number of trophic links there were between a nematode feeding group and plants. Although we found clear effects of plants on soil nematodes, these were probably not large enough to result in strong and persistent plant–soil‐organism–plant feedback loops.
Stage‐structured matrix models for organisms with non‐geometric development times
Authors: Birt Andrew , Feldman Richard M. , Cairns David M. , Coulson Robert N. , Tchakerian Maria , Xi Weimin , Guldin James M.
Published: February 2009

Matrix models have been used to model population growth of organisms for many decades. They are popular because of both their conceptual simplicity and their computational efficiency. For some types of organisms they are relatively accurate in predicting population growth; however, for others the matrix approach does not adequately model growth rate. One of the reasons for the lack of accuracy is that most matrix‐based models implicitly assume a specific degree of variability in development times for the organism. Because the variability is implicit, the implied variances are often not verified with experimental data. In this paper, we shall present extensions to the stage‐classified matrix models so that organisms with arbitrary means and standard deviations of development times can be modeled.
Nesting lizards (Bassiana duperreyi) compensate partly, but not completely, for climate change
Authors: Telemeco Rory S. , Elphick Melanie J. , Shine Richard
Published: February 2009

Species in which ambient temperatures directly determine offspring sex may be at particular risk as global climates change. Whether or not climate change affects sex ratio depends upon the effectiveness of buffering mechanisms that link ambient regimes to actual nest temperatures. For example, females may simply lay nests earlier in the season, or in more shaded areas, such that incubation thermal regimes are unchanged despite massive ambient fluctuation. Based on eight years of monitoring nests over a 10‐year period in the field at an alpine site in southeastern Australia, we show that, even though lizards (Bassiana duperreyi, Scincidae) have adjusted both nest depth and seasonal timing of oviposition in response to rising ambient temperatures, they have been unable to compensate entirely for climate change. That inability stems from the fact that the seasonal progression of soil temperatures, and thus, the degree to which thermal regimes at the time of laying predict subsequent conditions during incubation, also has shifted with climate change. As a result, mean incubation temperatures in natural nests now have crossed the thermal threshold at which incubation temperature directly affects offspring sex in this population.
The Other Pathway to the Boardroom: Interpersonal Influence Behavior as a Substitute for Elite Credentials and Majority Status in Obtaining Board Appointments
Authors: Westphal James D. , Stern Ithai
Published: February 2009

Using survey data on interpersonal influence behavior from a large sample of managers and chief executive officers (CEOs) at Forbes 500 companies, we examine how ingratiatory behavior directed at individuals who control access to board positions can provide an alternative pathway to the boardroom for managers who lack the social and educational credentials associated with the power elite. Findings show that top managers who engage in ingratiatory behavior toward their CEO, with ingratiation comprising flattery, opinion conformity, and favor-rendering, will be more likely to receive board appointments at other firms where their CEO serves as director and at boards to which the CEO is indirectly connected in the board interlock network. Further results suggest that interpersonal influence behavior substitutes to some degree for the advantages of an elite background or demographic majority status. Our findings help explain why norms of director deference to CEOs have persisted despite increased diversity in the corporate elite and have implications for research on corporate governance, social networks in the corporate elite, and for the sociological question of whether demographic minorities and individuals who lack privileged backgrounds have equal access to positions of leadership in large U.S. companies. Our study ultimately suggests that such individuals face a rather subtle and perhaps unexpected form of social discrimination, in that they must engage in a higher level of interpersonal influence behavior in order to have the same chance of obtaining a board appointment.
A model for the intrinsic kinetic parameters of the direct reduction of MoS2 with hydrogen
Authors: Mehdi Afsahi Mohammad , Sohrabi Morteza , Ale Ebrahim Habib
Published: February 2009

This study was carried out in order to obtain intrinsic kinetic parameters for the reaction between molybdenum disulfide and hydrogen. The experiments were performed using thermogravimetry within the temperature range of 1073 – 1223 K and at atmospheric pressure. The reaction was conducted by applying thin pellets and the data obtained were analyzed using a nucleation and growth kinetic model. The reaction was first order with respect to the gas phase reactant. The activation energy for the reduction process was determined to be 135.4 kJ mol− 1.
Thermodynamic consideration and experimental study on the preparation of heat-treated hollow nickel fibres
Authors: Li Fan , Sichen Du
Published: February 2009

In the present work, heat-treated hollow nickel fibres were prepared by thermal decomposition from nickel viscose composite. The thermodynamic properties of viscose fibre, namely standard enthalpy of formation, heat capacity, absolute entropy, and standard Gibbs free energy of formation were estimated by bond enthalpy. Thermodynamic analysis showed that viscose fibres could decompose at any reachable temperature, when the kinetic conditions were favourable. The results of thermogravimetric analysis experiments indicated that viscose filling could be removed by heat treatment in air. The thermogravimetric analysis results along with X-ray diffraction, scanning electron microscopy and X-ray energy dispersive spectrum analysis showed that hollow nickel fibre could be prepared by direct thermal decomposition in air flow at low temperatures, e. g. 573 K. Decomposition of the viscose filling could also be carried out at higher temperatures. However, serious oxidation of nickel would also take place during the decomposition. To remove nickel oxide, reduction by hydrogen gas could be applied.
Are data correctly fitted by the sin2 ψ and similar methods?
Authors: Ortner Balder
Published: February 2009

The sin2 ψ method is a frequently used, very successful method for data evaluation in X-ray or neutron stress measurements, but besides all its merits it also has a number of disadvantages and shortcomings. One of the shortcomings is the fact that in the general case of an in-plane stress measurement the method is not a correct least-squares fit. This results in an unnecessary loss of accuracy of the calculated stress tensor. The same must be said about some other methods which are similar to the sin2 ψ method, inasmuch as they also rely on a linear dependence of measured data on sin2 ψ or some other function of ψ. This is proved by analyzing the mathematical basis of these methods.