bluuebunny/crossref_metadata_2025_split huggingface dataset:
GaN and InGaN Nanowires on Si Substrates by Ga-Droplet Molecular Beam Epitaxy
Authors: Goodman Kevin , Wang Kejia , Luo Xiangning , Simon John , Kosel Tom , Jena Debdeep 
Published: April 2011

ABSTRACTMolecular beam epitaxy growth of GaN and InGaN nanowires is accomplished on Si (111) substrates using Ga-droplet nucleation. Typical diameters range from 25-80 nm and lengths can be varied by increasing the growth time; the growth rate is ∼0.25 microns/hour. The nanowires have been characterized structurally and optically. Photoluminescence spectra show band-edge emission of GaN nanowires centered at 362 nm at 290 K. Transmission electron microscopy images unveil that the nanowires are highly crystalline, and grow along the 0001 polar direction. Indium has also been successfully incorporated into GaN nanowires by modifying the growth conditions; the InGaN nanowires emit at ∼520 nm, which provides a possible route to solving strain related problems of high In-composition InGaN based efficient green emitters.
WO3-x Nanorod Arrays Based Sensors with High Sensitivity and Quick Response for Detecting Pollutants
Authors: Wang Xinpeng , Lou Jie , Wang Zhenbo , Feng Peter Xianping 
Published: April 2011

ABSTRACTTungsten oxide nanorod arrays deposited on the cylindrical substrate have been used for fabrication of a two-dimensional (2D) sensor. The sensibility and capacity towards methane and acetone at different temperatures have been examined. Experimental data have indicated that the newly designed sensor is highly sensitive to methane with low cross sensitivity towards possible mixed organic gas acetone, relying on the operating temperature. At room temperature (20°C), a quick response time and recovery time of the sensor, less than 10 ms, have been obtained.
Noise properties of a single ZnO nanowire device
Authors: Soo Han Choi , Kim Dong Wook , Jang Do Young , Ji Hyun Jin , Kim Sang Woo , Park So Jung , Moon Seung Eon , Kim Gyu Tae 
Published: April 2011

ABSTRACTThe low frequency noise of individual ZnO nanowire (NW) field effect transistors (FETs) exposed to air is systematically characterized. The measured noise power spectrum shows a classical 1/f type. The noise amplitude is independent of source-drain current and inversely proportional to gate voltage. The extracted Hooge's constant of ZnO NW is found to be 6.52×10−3. In addition, the low frequency noise of ZnO NW according to NW resistance and contact property are investigated. The noise amplitude is proportional to the square of ZnO NW resistance. If a sample shows a nonlinear current-voltage (I-V) characteristic due to a poor electrical contact, the noise power spectrum is proportional to the third power of current instead of the square of current.
Direct Growth of Single Walled Carbon Nanotubes for the Characterization of Structural and Electronic Properties
Authors: Wu Jianfeng , Walenza-Slabe Joel , Gutu Timothy , Jiao Jun 
Published: April 2011

ABSTRACTFabricating horizontally aligned single wall carbon nanotubes (CNTs) with controlled properties has been one of the significant challenges for field-effect transistor (FET) applications. This report demonstrates a novel procedure for the fabrication of horizontally aligned single walled CNTs using the focused ion beam (FIB) and chemical vapor deposition (CVD). This method allows the morphologies, internal structures, and elemental compositions of CNTs to be directly analyzed in the scanning electron microscope (SEM) and transmission electron microscope (TEM) and avoids any sample preparation procedures that might alter the structure of the CNTs. The techniques of electron beam and ion beam induced deposition (EBID and IBID) of Pt electrodes to the CNT ends were compared and both were found to produce metal contamination around the target area. The fabrication of large area electrodes to assist in testing the CNT's electronic properties, including contact resistance and I-V characteristics was investigated. Using this fabrication technique we were able to perform an I-V sweep on a CNT circuit as well as detect the metal contamination on the CNTs which occurred as a result of electrode deposition.
Large scale synthesis of vertical aligned CNT array on irregular quartz particles
Authors: Zhang Qiang , Huang Jiaqi , Zhao Mengqiang , Qian Weizhong , Wang Yao , Wei Fei 
Published: April 2011

ABSTRACTVertically aligned carbon nanotube (VACNT) arrays grown on quartz particles were produced in large amount via a floating catalysis process. Initially fast synchronous growth of VACNT arrays was observed, which is independently of the irregular shape and rough surface of the quartz particles. However, long VACNT arrays cracked and scattered anisotropically, depending on the irregular particles. The VACNTs have inner diameter of about 8.0 nm and relatively wide outer diameter distribution with a mean value of 36 nm. The outer diameter of CNTs, however, can be further decreased to 19 nm by tuning carbon source and concentration of catalyst precursor. The VACNTs have a high purity up to 97%. This work presents a simple way for controllable continuous production of VACNT array in large scale.
Entanglement and the Nonlinear Elastic Behavior of Forests of Coiled Carbon Nanotubes
Authors: Coluci Vitor R. , Fonseca Alexandre F. , Galvao Douglas S. , Daraio Chiara 
Published: April 2011

AbstractA model for the elastic response of a foamlike forest of coiled carbon nanotubes under mechanical impact is proposed according to recent experiments reported in the literature. A force vs. displacement relation is derived for different geometries of the impacting object (sphere, cube and circular cone). In the model, entanglement among neighboring coils in the superior part of the forest is explicitly taken into account and we show that it allows the full description of the strongly nonlinear elastic behavior of the forest.
Field Emission Properties of Large Area Carbon Nanotube Cathodes in DC and Pulse Modes
Authors: Liao Qingliang , Zhang Yue , Xia Liansheng , Qi Junjie , Huang Yunhua , Qin Zi , Yang Ya , Gao Zhanjun 
Published: April 2011

AbstractA large area carbon nanotube cathode was fabricated by use of a screen printing method. The emission properties of the cathode were investigated in both direct current and pulse mode experiments. In the direct current mode, the cathode has high field enhancement factor and high emission current density. In the double-pulse mode, the emission current density can approach 267 A/cm2 at an applied electric field of 15.4 V/um. Steady intense electron beams were obtained from the cathode. The results proved that the emission mechanism of CNTs at pulse electric field is plasma-induced field emission. The carbon nanotube cathode is suitable for not only field emission display applications but also high-power microwave device applications.
Molecular Dynamics Simulations of Ionic Liquids: Influence of Polarization on IL Structure and Ion Transport
Authors: Borodin Oleg 
Published: April 2011

ABSTRACTMany-body polarizable force field has been developed and validated for a wide class of ionic liquids. Classical molecular dynamics (MD) simulations have been performed on 29 ionic liquids. This presentation will focus on ability of developed force fields to predict condensed phase properties and on understanding the influence of many-body polarizable interactions on the ionic liquid structure and transport.
Ionic Liquids Interactions with Materials Surfaces Applications in Tribology and Nanotechnology
Authors: Bermúdez Maria-Dolores , Carrión Francisco-José , Iglesias Patricia , Jiménez Ana-Eva , Martínez-Nicolás Ginés , Sanes José 
Published: April 2011

ABSTRACTThe extraordinary combination of high thermal stability, low volatility and the possibility of tailoring the physical and chemical properties of ionic liquids (ILs) by modifying their molecular features such as the length and nature of the cation lateral chains and the anion size and composition, has open the field of application of these green ordered fluids.ILs have shown their ability to provide effective lubrication with very low friction coefficients and wear rates under conditions for which the currently used lubricating fluids fail. These conditions cover strategic technologies such as aerospace, microelectronics and nanotechnology applications.At the present moment, there exist no liquid lubricants for high temperature, high vacuum and cryogenic conditions. We have determined the lubricating ability of ILs under extreme temperature conditions.We have determined the conditions for the formation of tribocorrosion reaction products at metal-metal and metal-polymer interfaces. In the case of fluorine or phosphorus-containing imidazolium ionic liquids, formation of metallic fluorides and phosphates at the contact surfaces is the determining wear mechanism step.The surface interactions of imidazolium room temperature ILs have been studied in a variety of materials in sliding contact under variable conditions, both as neat lubricants and as additives of conventional basestocks.The ability of ILs molecules to interact with surfaces has also been explored in nanotechnology applications. It is well known that the use of ILs as solvents in the synthetic route, allows the control of size and shape of a variety of nanoparticles. We have developed new polymer/IL/nanoparticle nanocomposites where the size, morphology and distribution of the nanoparticles are controlled by surface interactions with IL molecules.
In-situ Investigation of the Mechanical and Electrical Properties of Nanosized Silicon Powders
Authors: Pluemel Ingo , Wiggers Hartmut 
Published: April 2011

ABSTRACTThe use of nanosized Silicon powders in nanoelectronics and photovoltaics enables new technologies and promises to reduce the production costs of devices like solar cells and printable electronics significantly. However, to understand their electrical behavior and mechanical properties, such systems must be examined carefully. In porous systems like powders, the macroscopic electrical properties result from transport mechanisms such as hopping and tunneling between particles as well as from structural properties such as the amount and shape of particle contacts. Theoretical approaches like the strongest stresses network or the brick layer model can only describe this complex relation in a simplyfied way and need to be accompanied by suitable experiments. Nanosized pure and doped Silicon powders, synthesized in a microwave supported plasma reactor, were characterized by determining in-situ the conductance, impedance, and the change of porosity while applying a uniaxial mechanical pressure ranging from 7.5 to 750MPa. The porosity change of the powder during electrical measurements was characterized by means of a laser interferometer to determine the mechanical properties of the powder more accurately. Conductance measurements as a function of the applied pressure show an exponential dependence for nanosized particles and a power law for microsized particles. Simple scaling considerations in respect of the particle size cannot explain this fundamentally different behavior. Therefore a more sophisticated model is needed. A time dependent change in conductance together with a decrease in porosity was observed while applying a constant pressure, suggesting friction limited compaction of the powder. For a constant external force, the comparison of different samples leads to a clear power law dependence between the conductance of pressed samples and their mean particle diameter. This size effect spans seven orders of magnitude of the conductance while the particle size changes by only a factor of ten, and it clearly exceeds any influence of the doping concentration and the variation of the sample mass. To separate the contributions of the particle cores, particle-particle, and particle-electrode contacts to the complex conductance and capacitance, impedance spectroscopy was performed. In agreement with the observed compaction of the powder, the spectra show a strong increase of the sample capacitance and conductance as a function of the applied pressure.
Energy Dissipation in the Mechanical-Diode Jump of a Nanoscale Contact
Authors: Martínez Juan J. , Cuberes M. Teresa 
Published: April 2011

ABSTRACTIn Ultrasonic Force Microscopy, the mechanical diode response refers to the quasistatic cantilever deflexion in the presence of surface out-of-plane ultrasonic vibration of sufficiently high amplitude. The effect has been described by introducing ultrasonic-amplitude-dependent tip-sample force-distance curves [Phys. Rev. 61 (2000) 13997]. Here, we demonstrate that the ultrasonic hysteresis phenomenon is qualitatively explained taking into account that for certain ultrasonic amplitudes, the modified tip-sample forces lead to two stable quasi-static equilibrium states, separated by an energy barrier. Experimental UFM data obtained on mica at ambient conditions are discussed in terms of ultrasonic-induced quasi-static equilibrium states, taking into account the role of the surface water layer.
Size effects on the Mechanical Behavior of Nanometric W/Cu Multilayers
Authors: Girault Baptiste , Geandier Guillaume , Eyidi Dominique , Renault Pierre-Olivier , Le Bourhis Eric , Goudeau Philippe 
Published: April 2011

AbstractThe mechanical behavior of nanostructured stratified W/Cu composites prepared by ion beam sputtering has been investigated using a method combining X-ray diffraction and tensile testing. Tests were performed on a synchrotron light source to analyze the elastic response of the tungsten phase. Three different microstructures have been analyzed: the specimen composed of the thinner tungsten layers reveals an elastic behavior different from the one expected assuming bulk elastic constants. However, Transmission Electron Microscopy (TEM) and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) measurements reveal discontinuities in the copper layers. As the strain in the related copper clusters as well grains boundary contributions are not experimentally accessible, atomistic calculation are of utmost importance. Polycrystalline materials have already been constructed through the Voronoï method and thanks to TEM observations. Atomistic simulation and calculation are underway to validation.
An Improvement of the Doerner-Nix Function for Substrate Effects in Ultrathin Films
Authors: Zhou BO , Prorok Barton C 
Published: April 2011

AbstractSubstrate effects continue to be the key issue in interrogating thin films by nanoindentation. In this study, we studies amorphous thin films of several different materials deposited onto a silicon wafer. These materials span from being considerable softer than the substrate to films significantly harder than the substrate. The thin film Young's modulusEfwas measured with a MTS Nanoindenter XP system using the continuous stiffness measurement (CSM). The so-called “flat region” was observed in the early stage of nearly every CSM modulus-displacement curve for all materials studied. The depth of this region (hcr) was found to vary with the material. Based on the experimental data, we were able to modify the Doerner & Nix model for thin film indentation on a substrate, particularly their parameter alpha (α). The modified relation was found to be adept at closely matching all experimental data collected, which spanned both soft films on hard substrates and hard films on soft substrates.
Coupled Nanoscratch and 4-Point Bending Evaluations of Adhesion in SiCN/Cu/Ta/TaN/SiO2/Si Stacked Layers
Authors: Yoneda Kouji , Shimizu Satoshi , Kojima Nobuo , Sato Chikai , Ye Jiping 
Published: April 2011

AbstractNanoscratch test used for small area measurements and four-point bending test applied for quantitative measurements were coupled to evaluate the adhesive strengths of SiCN/Cu/Ta,/TaN/SiO2/Si stacked layers. The similarities and differences of the two methods concerning adhesion, position of the delamination interface, and plastic deformation of the delaminated film were estimated. It was found that the nanoscratch test gave similar adhesion properties when the delamination interface was the same as that formed by the four-point bending test. The four-point bending test displayed clearer results compared to the nanoscratch test because energy for delamination was not used in plastic deformation and the crack could propagate further. These results suggest that coupling the nanoscratch and four-point bending tests is powerful way to estimate and understand adhesion of thin film materials.
Simulations of Nonlinear Strongly Anisotropic, Misfitting Crystals and Thin Films
Authors: Torabi Solmaz , Wise Steven , Li Shuwang , Voigt Axel , Lowengrub John , Zhou Peng 
Published: April 2011

AbstractWe present a new approach for modeling strongly anisotropic crystal and epitaxial growth using regularized, anisotropic Cahn-Hilliard-type equations as a model for the growth and coarsening of thin films. When the surface anisotropy is sufficiently strong, sharp corners form and unregularized anisotropic Cahn-Hilliard equations become ill-posed. Our models contain a high order Willmore regularization to remove the ill posedness at the corners. A key feature of our approach is the development of a new formulation in which the interface thickness is independent of crystallographic orientation. In our previous work, we have provided matched asymptotic analysis to show the convergence of our diffuse interface model to the analytical sharp interface model. In previous models there was no such convergence to sharp interface model when the Willmore energy was considered. We present 2D numerical results using an adaptive, nonlinear multigrid finite-difference method. In particular, we find excellent agreement between the computed shapes using the Cahn-Hilliard approach, with a finite but small Willmore regularization, with dynamical numerical simulations of a sharp interface model. The equilibrium shapes from our diffuse model are compared with an analytical sharp-interface theory recently developed by Spencer [1] at the corners, and there is excellent match. Away from the corners there is an excellent agreement between the diffuse model and the classical Wulff shape. Finally, in order to model the misfit and displacement strains, we add the elastic energy and corresponding forces to our diffuse model. We analyze numerically the effect of elastic stress on the corner regularization in terms of two parameters: one parameter that describes the relative strength of the elastic energy to surface energy and the second that characteristics the strength of the surface energy anisotropy. Adding elastic energy modifies the equilibrium shape and in particular affects the shape of the corners. We can predict different Qdot shapes, such as pyramids and domes, based on the strength of the elastic interactions.
Dislocation Nucleation and Growth in MOCVD GaN/AlN Films on Stepped and Step-free 4H-SiC Mesa Substrates
Authors: Twigg Mark E. , Picard Yoosuf N. , Bassim Nabil D. , Caldwell Joshua D. , Mastro Michael A. , Eddy Charles R. , Henry Richard L. , Holm Ronald T. , Neudeck Philip G. , Trunek Andrew J. , Powell J. Anthony 
Published: April 2011

AbstractUsing transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.
Nacre: A Unique Biomaterial Patterned by Liquid Crystals
Authors: Checa Antonio Gerardo , Cartwright Julyan H.E. , Escribano Bruno , Sáinz-Díaz Ignacio 
Published: April 2011

AbstractThe sequence of formation of the organic and inorganic components of nacre in bivalves and gastropods is re-studied. We reach the conclusion that interlamellar membranes are formed well in advance of the other elements. In this way, we support and refine the compartment theory for the formation of nacre. We explain the arrangement of chitin crystallites within a single interlamellar membrane and the layering of interlamellar membranes as a process of formation of a liquid crystal.
Biologically Engineered Quantum Dots for Biomedical Applications
Authors: Chornokur Ganna , Ostapenko Sergei , Emirov Yusuf , Korsunska Nadezhda , Wolcott Abraham , Zhang Jin , Phelan Catherine , Nagaram Abhilasha , Sellers Thomas 
Published: April 2011

AbstractWe report on a short-wavelength, “blue” spectral shift of the photoluminescence (PL) spectrum in CdSeTe/ZnS core/shell quantum dots (QDs) caused by bioconjugation with several monoclonal cancer related antibodies (ABs). Scanning PL spectroscopy was performed on samples dried on solid substrates at various temperatures. The influence of the AB chemical origin on the PL spectral shift was observed. The conjugation QD-AB reaction was confirmed using the agarose gel electrophoresis technique. The spectral shift is strongly increased and the process facilitated when the samples are dried above room temperature. The PL spectroscopic mapping revealed a profile of the PL spectral shift across the dried QD-AB spot. Transmission Electron Microscopy analyses of the samples were performed to reveal the shape and size of individual QDs. A mechanism of the “blue” shift is attributed to changes in the QD electronic energy levels caused by local stress field applied to the bio-conjugated QD.
A Miniaturized Cell Stretching Tool using Ionic Polymer Metal Composites Actuator
Authors: Hitsumoto Shin , Ihara Tadashi , Morishima Keisuke 
Published: April 2011

AbstractIn this paper, we proposed a novel miniaturized cell stretching tool using an Ionic Polymer-Metal Composites (IPMC) actuator. An IPMC is small, light weight and can be fabricated in any shape. And it drives flexibly like a living thing by low voltage. In this study, the PDMS chamber with PDMS membrane of 20 μEm thick for cell culturing had been fabricated on IPMC. And cultured cells were stretched by IPMC. The displacements of PDMS membrane were measured by a laser displacement sensor. And then, cells were cultured on PDMS membrane and stretched them by the motion of IPMC in an incubator. The results show that the PDMS membrane and cells were stretched by IPMC. This is the first fabrication of a cell stretching tool using IPMC. The potentiality of cell stretching tool using IPMC was demonstrated.
New Nanocomposite Biomaterials Controlling Surface and Bulk Properties using Supercritical Carbon Dioxide
Authors: Hoshi Toru , Sawagushi Takashi , Matsuno Ryosuke , Konno Tomohiro , Takai Madoka , Ishihara Kazuhiko 
Published: April 2011

AbstractThe molecular composite composed of polyethylene (PE) and poly(vinyl acetate) (PVAc) prepared using supercritical carbon dioxide (scCO2) and its surface modification for biocompatible surface demonstrated the creation of novel polymer biomaterials. In this study, this modification process was applied to the PE narrow tube (inside diameter: 300μm, outside diameter: 600μm, length: 5m). It was confirmed that PVAc was uniformly generated in PE tube by infrared imaging measurement of cross-section. After the acetyl group on the surface was hydrolyzed, phospholipid polymer was immobilized to the hydroxyl group on the surface of the tube. The phospholipid polymer immobilized surface showed a drastic reduction in protein adsorption. The surface of the minute and slender tube can be effectively modified using the feature of carbon dioxide whose surface tension is near zero. The modification technology by scCO2 is a promising for creation of variously-shaped new biomaterials.