bluuebunny/crossref_metadata_2025 huggingface dataset:
Irradiation Effects of Methanol Cluster Ion Beams on Solid Surfaces
Authors: Takaoka Gikan , Kawashita Masakazu , Okada Takeshi
Published: April 2011

In order to investigate the interactions of methanol cluster ion beams with solid surfaces, Si substrates and SiO2 films were irradiated at different acceleration voltages. The sputtered depth increased with increase of the acceleration voltage. When the acceleration voltage was 9 kV, the sputtered depths of Si and SiO2 at a dose of 1×1016ions/cm2 were 1497.1 nm and 147.8 nm, respectively. The selectivity between Si and SiO2 surfaces arose from the volatility of the reaction products. Furthermore, the sputtering yield for the Si surface was approximately seven hundreds times larger than that by Ar monomer ion beams. This suggested that chemical sputtering was predominant for the methanol cluster ion irradiation. In addition, the etching and cleaning process by the methanol cluster ion irradiation was performed on the Si surfaces contaminated with a small amount of metal particles such as Au and Al. Thus, methanol cluster ion beams have unique characteristics such as surface etching and cleaning with high sputtering yield and smooth surface.
In Vitro Apatite Formation on Polymer Substrates Irradiated by the Simultaneous Use of Oxygen Cluster and Monomer Ion Beams
Authors: Kawashita Masakazu , Araki Rei , Takaoka Gikan H
Published: April 2011

Polyethylene (PE) and silicone rubber substrates were irradiated at an acceleration voltage of 7kV and a dose of 1×1015 ions/cm2 by the simultaneous use of oxygen cluster and monomer ion beams, and then soaked in CaCl2 solution. Apatite-forming ability of the substrates was examined using a metastable calcium phosphate solution that had 1.5 times the ion concentrations of a normal simulated body fluid (1.5SBF). After the irradiation, the hydrophilic functional groups such as COOH and silicon oxide cluster (SiOx) were formed at the PE and silicone rubber surfaces, respectively. The hydrophilicity of the substrates was remarkably improved by the irradiation. The irradiated PE and silicone rubber substrates formed apatite in 1.5SBF, whereas unirradiated ones did not form it. These results suggest that the functional groups such as COOH groups and Si-OH groups induced apatite nucleation in 1.5SBF.
High Resolution XRD Studies of Ion Beam Irradiated InGaAs/InP Multi Quantum Wells
Authors: Dhamodaran S. , Sathish N , Pathak Anand P , Turos Andrzej , Avasthi Devesh K , Arora Brij M
Published: April 2011

Multi quantum wells of InGaAs/InP grown by metal organic chemical vapor deposition have been irradiated using swift heavy ions. Irradiation has been performed using 150MeV Ag and 200MeV Au ions. Both as-grown and irradiated samples were subjected to rapid thermal annealing at 500 and 7000C for 60s. As-grown, irradiated and annealed samples were subjected to high resolution x-ray diffraction studies. Both symmetric and asymmetric scans were analyzed. The as-grown and Ag ion irradiated samples show sharp and highly ordered satellite peaks whereas, the Au ion irradiated samples show broad and low intense peaks. The higher order satellite peaks of the annealed samples vanished with increase of annealing temperature from 500 to 7000C, indicating mixing induced interfacial disorder. Annealing of irradiated samples show higher mixing and disorder and no higher order satellite peaks were observed. Negligible strain was observed after high temperature annealing of as grown samples. Strain values calculated from the X-ray studies indicate that the irradiated samples have higher strain which has been reduced upon annealing. This indicates that the annealing induced mixing occurs maintaining the lattice parameter close to that of the substrate. The effect of electronic energy loss for interface mixing has been discussed in detail. The role of incident ion fluence in combination with the electronic energy loss will also be discussed in detail. The results have been compared with the literature and discussed in detail.
Focused Ion Beam Fabrication of Individual Carbon Nanotube Devices
Authors: Chow Lee , Chai Guangyu
Published: April 2011

Focused ion beam (FIB) techniques have found many applications in nanoscience and nanotechnology applications in recent years. However, not much work has been done using FIB to fabricate carbon nanotube devices. This is mainly due to the fact that carbon nanotubes are very fragile and energetic ion beam from FIB can easily damage the carbon nanotubes. Here we report the fabrication of carbon nanotube (CNT) devices, including electron field emitters, atomic force microscope tips, and nano-pores for biomedical applications. This is made possible by a unique, coaxial configuration consisting of a CNT embedded in a graphitic carbon coating, which was developed by us for FIB processing of carbon nanotubes. The CNT-based atomic force microscope tip has been demonstrated. The electron field emission from the tip and the side wall of CNT will be discussed. We will also report the fabrication of a multiwall carbon nanotube nanopore for future applications.
A Piezoresistive Cantilever Force Sensor for Direct AFM Force Calibration
Authors: Pratt Jon R. , Kramar John A. , Shaw Gordon A. , Smith Douglas T. , Moreland John M.
Published: April 2011

We describe the design, fabrication, and calibration testing of a new piezoresistive cantilever force sensor suitable for the force calibration of atomic force microscopes in a range between tens of nanonewtons to hundreds of micronewtons. The sensor is calibrated using the NIST Electrostatic Force Balance (EFB) and functions either as a force reference or stiffness artifact that is traceable to the International System of Units. The cantilever has evenly spaced fiducial marks along its length. We report stiffnesses that vary quadratically with location, from a high of 12.1 N/m at the first fiducial to a low of 0.394 N/m at the last; with force sensitivities that vary linearly, ranging from 18.1 Ù/mN to 106 Ù/mN. We also test the device to transfer the unit of force to an atomic force microscope, finding that force and stiffness based approaches yield independent estimates of the contact force consistent within 2 % of each other.
Molecular Dynamics Simulation of Thermal Conductivity of Diamondoid Crystals
Authors: Hu Ming , Shenogin Sergei , Keblinski Pawel , Majumdar Arun
Published: April 2011

Hydrocarbon molecules with diamond structure, called diamondoids have gain considerable interest as promising nanoscale building blocks. Very large mismatch between strong, covalent intramolecular bonding and weak intermolecular bonding suggests interesting phonon related properties for diamondoid crystal. We use molecular dynamics (MD) simulations to examine thermal transport of diamondoid crystals. In particular, thermal conductivity of small molecule adamantine and larger molecule pentamantane crystal is studied by equilibrium and non-equilibrium MD. The thermal conductivity of both materials is low, but comparable with that characterizing fullerene crystal.
Nanoscale Thermal Property of Amorphous SiC: A Molecular Dynamics Study
Authors: Wang Weiqiang , Kalia Rajiv K. , Nakano Aiichiro , Vashishta Priya
Published: April 2011

Thermal properties of amorphous silicon carbide (a-SiC) at nanometric scales are studied by molecular dynamics (MD) simulations based on an empirical interatomic potential. A scalable parallel MD algorithm is used for studying systems as long as 30nm. To validate the potential, phonon density of states and specific heat of a-SiC are first calculated. Size effects are studied, and errors are estimated for the temperature profile for different system sizes. Simulation time required to achieve steady temperature profiles is also determined. Finally the thermal conductivities of a-SiC at various temperatures are calculated. The results show that thermal conductivities of a-SiC at nanometric scale also agree with Slack's minimum thermal conductivity model.
Dynamic Pathway Models for Ion Transport in Nanostructured Heterolayers
Authors: Adams Stefan , Tan Esther S
Published: April 2011

The influence of local structure variations on the charge transport properties are still not well understood at an atomic level. In this work the experimentally observed drastic conductivity enhancement in epitactic stacks of BaF2:CaF2 heterolayers compared to any of the two fluoride ion conducting phases is reproduced by molecular dynamics simulations and analyzed in detail with particular emphasis on the variation of properties with the distance to the two-phase boundary. Ion mobility varies with the distance to the interface but remains significantly enhanced throughout the modeled layers when compared to bulk materials.

The bond valence method is utilized to study correlations between the conductivity enhancement and the microstructure. A time-averaged violation of local electroneutrality postulated in the mesoscopic multiphase model is verified by the bond valence analysis of the molecular dynamics simulation trajectories. The variation of the ion mobility can be related to the extension of clusters of unoccupied accessible pathway regions.
Solid Oxide Fuel Cell with Nanostructured Fuel Electrode
Authors: Ansar Syed Asif , Ilhan Zeynep
Published: April 2011

Nanostructured YSZ+NiO anodes (fuel electrode) for solid oxide fuel cell (SOFC) were developed by plasma spraying. Influence of processing parameters was correlated with deposit microstructure and properties. During particle in-flight with in the plasma jet, the high temperatures of plasma resulted in an increase in average crystallite size; the nanostructure was, however, conserved. Anodes with well distributed finely porous nanostructure exhibiting high gas permeability, suitable high temperature electronic conductivity, enhanced triple phase boundaries and catalytic activity were produced by controlling plasma enthalpy and velocity. Properties of nanostructured anodes were compared with conventional ones. At room temperature the permeability of nanostructured anodes was an order of magnitude higher than their conventional counter parts whereas in-plane conductivity at 800°C in reducing atmosphere of former was 4% higher than that of the latter. Electrochemical performance of optimized nanostructured anode was compared with conventional NiO+YSZ anodes by testing full cells at 800°C. 9.5 mol% YSZ electrolyte and LSM cathode were deposited onto these anodes for electrochemical testing in static and dynamic conditions. Impedance spectroscopy measurements were performed to collect data on polarization resistance and catalytic behavior of anode layers. Gas and temperature variation on both cells was performed and data was compared. It was established that enlarged reaction zone provided by high specific surface area of nanostructured anodes and finely porous microstructure led to lower activation and concentration polarizations and enhanced cell performance by more than 30% compared to conventional cells. During redox (oxidation and reduction of nickel in anode electrode) cycling the cell composed of nanostructured anode exhibited lower degradation.
Electron Diffuse Scattering Characterization of Perovskite Thin Films
Authors: Pacaud Jerome , Pailloux Frederic
Published: April 2011

For perfect crystal, diffuse scattering is mostly inelastic due to phonons, plasmons and other processes. Thermal diffuse scattering or phonon scattering can lead to large effects in the electron diffraction pattern especially near second order phase transition where phonon softening occurs. Additionally, elastic diffuse scattering comes from structural deviations from a periodic lattice. These structural deviations can be defects, partial ordering of otherwise disordered structure or structural fluctuations. By studying diffuse scattering we can obtain information about the crystal imperfections and dynamics which can not be obtained from other characterization methods.
Ultra-fast High Resolution Microscopy: Options for Pump-probe Methods
Authors: Howie Archie
Published: April 2011

Recent applications of scanned probe microscopy are defined often going hand in hand with improved spectroscopy. These methods can provide information about dynamic response extending down towards the femotsecond time scale for resettable, repeatable phenomena and may thus help to fill the gap in the microscopist's coverage of material behavior. Although the use of photon pulses is best developed, ultra-short electron pulses are now available. Various options are therefore to hand in either transmission electron microscopy or scanning transmission electron microscopy operation for combining the spatial resolution of electrons with the spectral selectivity and precision of photons. With purely photon pump-probe operation, good spatial resolution can perhaps be obtained using the tip field-enhancement effect in scanning probe microscopy (SPM) and has also recently been impressively demonstrated in two-photon photo-electron microscopy (PEEM) operation.
Magnetic Chiral Dichroism Studies using Energy Filtered Images
Authors: Snoeck Etienne , Warot-Fonrose Benedicte , Gatel Christophe , Houdellier Florent
Published: April 2011

We present the quantitative measurement of inelastic intensity distributions in diffraction patterns with the aim of studying magnetic materials. The original idea of using inelastic signal in a transmission electron microscope to measure magnetic information has been proposed recently by Schattschneider et al [1] and various experimental set-ups can be imagined [2,3]. We focus on a new experimental configuration which we use to acquire and collect a map of the signal with a high signal-to-noise ratio. We will also present the numerical treatments that need to be performed to get spatially accurate information and energy resolution. We will illustrate our method studying iron single crystal and discuss the effects of the drift and non-isochromaticity corrections.
A Simple and Effective Route to Annihilate Defects in Nanocrystalline SnO2 Thin Films Prepared by Pulsed Laser Deposition
Authors: Chen Zhiwen , Wu C. M. L. , Shek C. H. , Lai J. K. L. , Jiao Z. , Wu M. H.
Published: April 2011

The microstructural defects of nanocrystalline SnO2 thin films prepared by pulsed laser deposition have been investigated using transmission electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. Defects inside nanocrystalline SnO2 thin films could be significantly reduced by annealing the SnO2 thin films at 300 °C for 2 h. High-resolution transmission electron microscopy showed that stacking faults and twins were annihilated upon annealing. In particular, the edges of the SnO2 nanoparticles demonstrated perfect lattices free of defects after annealing. Raman spectra also confirmed that annealing the specimen was almost defect-free. By using thermal annealing, defect-free nanocrystalline SnO2 thin films can be prepared in a simple and practical way, which holds promise for applications as transparent electrodes and solid-state gas sensors.
Automated Electron Nanocrystallography
Authors: Spence John , McKeown Joseph , He Haifeng , Wu Jinsong
Published: April 2011

We review methods to solve nanocrystals and obtain a 3D charge-density map at the electron microscope. Experimental tests are demonstrated for kinematic CBED and precession techniques.
In-Situ Neutron Diffraction Study of Gas Tungsten Arc Welding of a 1018 Plain Carbon Steel
Authors: Gharghouri Michael , Watson Michael J , Dye David , Rogge Ronald B
Published: April 2011

In-situ neutron diffraction measurements of a dynamic Gas Tungsten Arc Welding (GTAW) process have been performed using a unique instrument that establishes steady-state conditions by translating and rotating a cylindrical specimen past a stationary weld torch. The fixed neutron sampling volume is at a constant location with respect to the torch as new material is brought into the fusion zone. We present maps of lattice spacing and integrated intensity as a function of location about the weld torch, which provide insight into the temperature and phase distributions around the weld.
In-situ GISAXS on Nanocomposite Films of CdS Nanoparticles and Polymers
Authors: Di Luccio Tiziana , Carbone Dina , Laera Anna Maria , Peeper Katrin , Mauser Christian , Da Como Enrico
Published: April 2011

We investigated the growth of CdS nanoparticles in polymer films by means of ex-situ and in-situ x-ray scattering experiments using synchrotron radiation. The CdS nanoparticles were synthesized by thermal decomposition of a Cd thiolate precursor dispersed in a cyclic olefin copolymer. The films were deposited by spin coating. Grazing incidence diffraction (GID) reveals the Bragg reflections of the CdS nanoparticles. In-situ diffraction and grazing incidence small angle scattering (GISAXS) experiments were recorded during the thermal treatment of the precursor/polymer films from room temperature up to 250°C. The diffraction curves show that the initial precursor structure is soon lost at 100°C. Correspondingly, the GISAXS data show a peak at a momentum transfer value q ∼ 0.2Å−1 that shifts towards smaller values with the temperature. Under UV excitation the films show photoluminescence in the range 400 – 700 nm.
Investigation on different organic semiconductor/organic dielectric interfaces in pentacene-based thin-film transistors
Authors: Orgiu Emanuele , Taki Mohammad , Fraboni Beatrice , Locci Simone , Bonfiglio Annalisa
Published: April 2011

Organic Thin-Film Transistors (OTFTs) in top-contact configuration and Metal-Insulator-Semiconductor (MIS) structures with different organic dielectrics as the gate insulator have been fabricated using the same organic semiconductor layer, pentacene, in order to investigate the changes in the electrical behavior by varying the interface properties. A gold bottom gate electrode was sputtered on a glass substrate whereas gold source and drain were thermally evaporated onto the pentacene layer. Several organic dielectrics have been tested as insulating layers, namely were poly(vinyl alcohol) (PVA), polyvinyl alcohol with ammonium dichromate (PVAad) as a cross-linking agent, poly (4-vinyl phenol) (PVP), poly(dimethylsiloxane) (PDMS) and poly(methylsilsesquioxane) (pMSSQ). The interesting differences found out by varying the interface confirm that the chemical-physical interaction between semiconductor and dielectric is crucial for the conduction mechanisms of the charge carriers. In particular we observed that the electron traps can influence not only the electron transport, therefore allowing a more or less marked ambipolar behavior, but also affect the hole transport.
Modification on the Unoccupied Electronic Structure of Organic Semiconductor by Alkali Metal
Authors: Ding Huanjun , Park Kiwan , Gao Yongli
Published: April 2011

We have investigated the evolution of both the occupied and unoccupied states for alkali metal (Cs and Na) doped Copper-Phthalocyanine (CuPc) with photoemission and inverse photoemission spectroscopy. As the doping ratio increases, the lowest unoccupied molecular orbital (LUMO) of CuPc shifts downward, reaching the Fermi level. After the saturation, the LUMO intensity decreases monotonically, while a gap state grows in the valence spectra, which gives direct evidence for the origin of the doping-induced gap state in CuPc molecules.
Large Area Processing and Patterning with Ink Jet Technology
Authors: Grove Michael , Hayes Donal , Shah Virang
Published: April 2011

Patterning materials over large areas on flexible plastic or metal substrates, and on rigid ones, where multiple layers of different materials are being applied in order to create active devices brings with it the real challenge of accurate materials placement [1]. The additive process of printing expensive functional materials reduces costs associated with the losses of subtractive processing, but focuses the technological necessity on the precision of materials alignments on the target substrates. During the past decade, both materials and their print processing have developed to a near commercial level for optical and electronic devices. Industrial success will be assured when their production enjoys the economies of scale that large area processing can bring. Ink jet technology has developed in the last twenty-five years to a level of sophistication that is now adequate for the challenges of processing large area substrates for optical and electronic devices. Some equipment and processing will be covered in this paper.
Electrical and Optical Properties of High Mobility W-doped In2O3 Thin Films
Authors: Gupta Ram , Ghosh K. , Mishra S. R. , Kahol P. K.
Published: April 2011

Transparent conducting oxides (TCO) have been widely used for opto-electronic devices such as light emitting diodes, photo-detectors, touch panels, flat panel displays, and solar cells. Low resistivity, high mobility, and good transparency are the prime requirements for these devices. There is an increasing interest in TCO with high mobility to decrease their electrical resistivity without a significant decrease in the optical transparency. Highly conducting and transparent tungsten doped indium oxide thin films were deposited on quartz substrate by ablating the sintered In2O3 target containing WO3 with a KrF excimer laser (λ = 248 nm and pulsed duration of 20 ns). The effect of growth temperature and oxygen pressure on structural, optical, and electrical properties has been studied. The transparency of the films largely depends on the growth temperature. The electrical properties are found to depend strongly on the growth temperature as well as on oxygen pressure. The temperature dependence resistivity measurement shows the transition from semiconductor to metallic behavior as the growth temperature increases from room temperature to 500 °C. The high mobility (up to 358 cm2V−1s−1), low resistivity (1.1 × 10−4 Ω.cm), and relatively high transmittance of ∼90 % have been observed on the optimized film grown at 500 °C and under oxygen pressure at 1 × 10−6 bar.
III-V Semiconductor Vertical and Tilted Nanowires on Silicon Using Chemical Beam Epitaxy
Authors: Radhakrishnan Gokul , Freundlich Alex , Charlson Joe , Fuhrmann Bodo
Published: April 2011

Nowadays nanostructures play a vital part in the rapidly expanding areas of photovoltaics. The ability of nanowires to transfer photo-generated carriers rapidly across a solar cell has lead our interest in growth of nanowires . Currently Vapor Liquid Solid (VLS) epitaxy is the most common method used to grow epitaxial vertical nanowires. A metal particle such as gold is used to form a liquid alloy eutectic with the material of a substrate or with material supplied in the vapor phase. In growing semiconductor wires using metal droplets, it has been shown that the wires grow in the (111) direction and have clean facets . Furthermore these wires generally present an undesirable larger pyramidal base at the bottom and there is also evidence of surface migration of the metal catalyst. Thus far, most of the effort in the development of vertical III-V semiconductor nanowires has been limited to homo-polar combinations (e.g. InAs on InP). The ability to fabricate III-V nanowires on silicon could however pave the way toward the monolithic integration of III-V nanostructured solar cells with Si. Here we demonstrate the growth of GaAs and InP nanowires on silicon (111) using gold as the metal seed particle. An ordered array of gold nano dots is integrated on the surface of a silicon substrate using self-assembled polystyrene nanospheres as the Au evaporation template. The size of the gold dots range from 40 nm to 150 nm and the pitch is about 500 nm. The growth of the wires is done by chemical beam epitaxy under a vapour phase environment. Scanning electron microscopy and photoluminescence are used to characterize these nanowires. Wire exhibit high crystallinity and there is an absence of the pyramidal base at the bottom of the nanowire using this technique. Furthermore the study also shows evidence of pregrowth motion of some of the gold particles causing coalescence of nanowires and leading to the development of nanopods and tilted (off-normal) nanowires. Finally in the light of their optical properties the relevance of these wires to photovoltaic applications is discussed.
Fabrication of Copper Indium Diselenide Nanowires
Authors: Phok Sovannary , Rajaputra Suresh , Singh Vijay
Published: April 2011

Nanostructured semiconductors have received a great deal of attention due to their unusual physical properties. The possibility of controlling these properties by varying the particle size, shape and surface properties is of great interest for nanoscale device applications in microelectronics, non-linear optics and optoelectronics in particular. Copper Indium diselenide (CIS), a p-type semiconductor with a band gap of about 1.04 eV has shown promise as an absorber for photovoltaic cells. Polycrystalline CIS film has been fabricated by various physical and chemical techniques over the past couple of decades. However, the preparation of nanostructured CIS is still challenging due to the fact that CIS tends to agglomerate resulting in large grains. Furthermore, an annealing step is also required to improve the film properties, which results in increased grain size. Here we report a simple, low cost solution to this problem through electrochemical deposition of CIS into the confined nanopores of an anodic aluminum oxide (AAO) template. The nanoporous aluminum oxide template, a few microns thick was prepared by either a one step or a two anodization in oxalic acidic media. CIS was deposited into the nanoporous AAO template by pulsed cathodic electro-deposition from an aqueous mixture. The electrodeposited nanowires had diameter ranging up to 40 nm and length ranging from 600 nm to 5 μm depending on the length of the template. The hybrid nanostructured CIS/AAO was annealed in vacuum at 230ºC for several hours to achieve stoichiometric CuInSe2 phase. The embedded CIS nanowires were characterized by X-ray diffraction and scanning electron microscopy. The optical bandgap was deduced from UV-Vis absorption spectroscopy measurements.
Application of Cylinder Forming Block Copolymers as Templates for Formation of Bit Patterned and Graded Media
Authors: Warke Vishal , Bakker Martin Gerard , Hong Kunlun , Mays Jimmy , Britt Phillip
Published: April 2011

Bit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The formation of metal nanopillars with 20-30 nm repeat spacing and precisely controlled magnetic properties presents a significant challenge to current fabrication methods. We have been developing cylinder forming block copolymer phases as a method to generate the desired patterns coupled with the processing steps necessary to transfer the pattern into magnetic material. This involves spin coating of the polymer on an appropriate orienting layer, annealing to allow the pattern to form by self-organization of the block copolymer, solvent processing to remove the minority domain, electrodeposition to form a hard mask, followed by ion-milling to transfer the pattern to the magnetic material. We have demonstrated each step in this process and report on the quality of the pattern achieved.
Ferromagnetic Ge1-xMx (M = Mn, Co, and Fe) Nanowires
Authors: Cho Yong Jae , Kim chang hyun , Park jeunghee
Published: April 2011

We synthesized Ge and Ge1-xMx (M = Mn, Co, and Fe, x ≤ 0.2) nanowires using thermal vapour transport method. All nanowires consisted of single-crystalline Ge nanocrystals grown uniformly with the [111] direction. High-resolution X-ray diffraction pattern shows no cluster formation for all Ge1-xMx nanowires. The Mn and Fe doping decreases the lattice constant, but not Co doping. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurement revealed that the Mn2+ and Fe2+ ions preferentially occupy the tetrahedral sites, substituting for Ge. We suggest that the Mn or Fe ions produce dopant-acceptor hybridization with host defects in p-type Ge, but not Co ions. The magnetic moment of Mn2+ ions reaches a maximum for x = ∼ 0.1, which is much larger than that of the Fe2+ ions. The magnetization measurement also confirms the room-temperature ferromagnetism of Mn-doped Ge nanowires, which is maximized at x = ∼ 0.1. We conclude that the Mn ions are most efficiently doped into the Ge nanowires to form a ferromagnetic semiconductor.
Synthesis and Characterization of PMMA Coated Magnetite Nanocomposites by Emulsion Polymerization
Authors: Zhang Ming , O'Connor Charles J
Published: April 2011

In this paper, we report the synthesis and characterization of the PMMA-coated magnetite nanocomposite obtained from the emulsion polymerization method. In this approach, the magnetite particles were prepared separately with oleic acid as the capping ligands in nonaqueous solution and disperse in non-polar solvent. The micells structure consisting water, oil phase and surfactant will contain the oleic acid stabilized magnetite particles inside and the polymerization process will only occur on the surface of the emulsion system. This method allows the individual magnetic particles encapsulated in the polymer matrix. The resulting nanocomposites were characterized by TGA, XRD and SQUID
Cell Specific Targeting of Multifunctional γ-Fe2O3 Nanoparticles Through Surface Binding of dsDNA
Authors: Tremel Wolfgang , Shukoor Mohammed Ibrahim , Natalio Filipe , Tahir Muhammad Nawaz , Müller Werner E. G. , Schröder Heinz Christoph
Published: April 2011

The immobilization of polyinosinic-polycytidylic acid [poly(IC)] on ã-Fe2O3 maghemite nanoparticles via the phosphor-amidate route using a multifunctional polymer is reported. The dsRNA coupled nanoparticles were used to visualize the Toll-like (TLR3) receptors at the cell surface. The presence of TLR3 was demonstrated independently in the Caki-1 cell line by RT-PCR and immunostaining techniques
Study of Chromium Impurities in SrTiO3 by Photo-Electron Paramagnetic Resonance Spectroscopy
Authors: Dashdorj Jamiyanaa , Zvanut Mary Ellen
Published: April 2011

Chromium impurities in SrTiO3 grown by Verneuil and Float-zone methods were investigated using photo-electron paramagnetic resonance spectroscopy. The samples are the substrates typically used for deposition of multifunctional and ferromagnetic films. A maximum optical cross section for Cr3+ of 2.6×10−18 cm2 is obtained from the time-dependent data, and steady state measurements suggest the presence of a defect level 2 eV from one of the band edges. The cross section is similar to that obtained from optical absorption studies of Cr3+ in semiconductors. The results produced here should be useful for those trying to interpret photoluminescence or similar optical characterization data.
Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTiO3 Films During Pulsed Laser Deposition
Authors: Ferguson John David , Woll Arthur R. , Arikan Gokhan , Dale Darren S. , Amassian Aram , Tate Mark W. , Brock Joel D.
Published: April 2011

Homoepitaxial SrTiO3 thin films were grown on SrTiO3 (001) using Pulsed Laser Deposition (PLD). The deposition process was monitored in-situ, via both x-ray reflectivity and surface diffuse x-ray scattering measurements in the G3 experimental station at the Cornell High Energy Synchrotron Source (CHESS). Using a CCD detector in 1D, or streak-camera, mode with approximately 0.3-second time resolution, data were collected during growths performed at two substrate temperatures: 695°C and 1000°C. While the specular reflectivity oscillations for the two growths are very similar, the diffuse scattering clearly shows a distinct change in the peak position. Using Atomic Force Microscopy (AFM), we illustrate how the peak position for the diffuse lobes of scattered intensity is directly related to the distribution of single unit cell high islands on the growing surface. Thus, the peak shift of the diffuse scattering indicates an order of magnitude change in the island density.
Effect of Growth Conditions on Structural and Electrical Properties of Pb(ZrxTi1−x)O3 layers grown by peroxide MBE
Authors: Izyumskaya Natalia , Avrutin V. , Gu X. , Xiao B. , Chevtchenko S. , Zhou Lin , Smith David J. , Yoon J.-G. , Morkoc H.
Published: April 2011

Pb(ZrxTi1−x)O3 (PZT) films were grown by molecular beam epitaxy using hydrogen peroxide as a source of reactive oxygen. Phase composition as well as structural and electrical properties of the films were studied by x-ray diffractometry, scanning and transmission electron microscopy, conductive atomic force microscopy, and electrical (I-V and polarization-field) measurements. The hydrogen peroxide pressure was found to control the phase composition of the films. Excess peroxide leads to PbO inclusions in PZT layers, whereas deficiency results in the TiO2 or the ZrO2 phase. The second-phase inclusions can be responsible for high leakage current in the films. Precise control over the peroxide pressure is imperative for single-phase PZT films with good ferroelectric properties.
Self-consistent Calculation of the Photocurrent in Polycrystalline Polarized Pb(ZrTi)O3 Films
Authors: Delimova Lyuba A. , Yuferev V. S. , Petrov A. A. , Afanasjev V. P. , Grekhov I. V.
Published: April 2011

A polycrystalline Pb(ZrTi)O3 (PZT) film with Pb excess is considered as a heterophase medium that consists of PZT grains and semiconductor PbO phase. The latter is segregated on PZT grain boundaries during the PZT formation and forms conducting channels between the electrodes. In such medium, uncompensated polarization charge of PZT grains generates an electric field both inside PZT grains and PbO phase. This electric field affects on ferroelectric polarization itself and stimulates carrier transport through the PbO channels. A theory is developed, where the reciprocal effect of the electric field on the polarization is taken into account. The polarization is found due to this effect to be increased up to ∼30% near the interfaces, which differs from reduction of the polarization near the interfaces in homogeneous PZT films. Using the theory, the electric field, electrostatic potential and carriers transport in PbO channels are calculated. A comparison is made with the results calculated for the approach of the polarization constancy.
Radiation of X-rays Using Uniaxially Polarized LiNbO3 Single Crystal
Authors: Fukao Shinji , Nakanishi Yoshikazu , Mizoguchi Tadahiro , Ito Yoshiaki , Nakamura Toru , Yoshikado Shinzo
Published: April 2011

It is well known that by changing the temperature for the polarized hemimorphy single crystal, such as LiNbO3 or BaTiO3, the electric field with high intensity is generated and then atmospheric gas atoms or molecules around the crystal are ionized. Using these phenomena, X-rays could be radiated by the bremsstrahlung radiation of electrons in low pressure [1,2]. However, this method has some disadvantages. For example, it is difficult to maintain the intensity of X-rays for a long term. The gas pressure range, where the intensity of X-rays is high, is narrow. The purpose of this study is to increase the intensity of X-rays in a high vacuum. In a low vacuum, positive charges generated by the ionization of gas molecules near the crystal weaken the electric field strength. Consequently, the intensity of X-rays also becomes weak. On the other hand, in a high vacuum, the number of electrons decreases. Thus, thermally emitted electrons are supplied to the X-rays radiation system in high vacuum to increase and stabilize the intensity of X-rays.

The -z plane of the congruent LiNbO3 single crystal polarized in the z-axis direction of a 5 mm thickness and a 10 mm diameter was opposed to the Cu target of a 10 μm thickness placed at a distance of 21 mm from the –z plane in the gas pressure of 10-2-10-4 Pa. The temperature of crystal was changed between from -5 to 75 °C using Peltiert device. The temperature history of the crystal consists of a repetition of a series of the increasing and decreasing processes with the same period. Filament of thorium-added-tungsten as a thermal electrons source was placed at a distance of approximately 20 mm from the crystal side edge. DC current flowing in the filament was adjusted from 0 to 4 A.

In the increasing process of the temperature, the characteristic X-ray of Nb was radiated. This result indicates that the sign of net charge on -z plane of the crystal is positive. Because thermally emitted electrons are supplied to the positively charged –z plane, the electric field strength generated by the crystal is very low. Thus, the intensity of characteristic X-ray of Nb is low. On the other hand, in the decreasing process of the temperature, the characteristic X-ray of Cu was radiated. At the pressure of approximately 10-2 Pa and the filament current of 2.5 A, the intensity of X-rays showed the local maximum. If electrons are supplied more, synthetic electric field strength is weakened by the electric field made by the electron. The intensity of X-rays using thermal electron source was ten or more times higher at the maximum than that without the source and was almost comparable as the case of a low vacuum or more than it. Using thermal electron source, the intensity of X-rays increased with decreasing the pressure down to approximately 10-2 Pa and became constant at lower pressure.
Shape-Controlled Solution-Synthesis of Single Crystalline ZnTe 1D Nanocrystals
Authors: Fang Jiye , Kumbhar Amar , Sun Kai , Fang Jiye
Published: April 2011

Precursor-reduction method is employed to synthesize nanostructures of ZnTe. The shape of zinc blende ZnTe nanocrystals could be influenced by reaction temperature, concentration of the precursors as well as the use of stabilizing agent. By controlling the synthetic conditions, three types of nanoscaled ZnTe, quasi-spherical ZnTe nanocrystals, ZnTe nanobelts and ZnTe nanorods have been observed. Their crystalline structures are also discussed.
Electrochemical Fabrication of Zn1−xMgxO Films from an Aqueous Solution Containing Magnesium Nitrate and Zinc Sulfate
Authors: Ishizaki Hiroki , Maeda Hideaki
Published: April 2011

Zn1−xMgxO films with wurtzite structure were electrochemically grown on the conductive glass substrates from a 0.1mol/L magnesium nitrate aqueous solution containing 0.001mol/L zinc Sulfate kept at 323K. With a decrease in the cathodic potential, Mg/(Zn+Mg) atomic ratios of Zn1−xMgxO films decreased and the lattice parameter for c axes decreased. The band gap energy of Zn1−xMgxO films increased with an increase of Mg/(Zn+Mg) atomic ratio. Thus, Mg/(Mg+Zn) atomic ratio and the bandgap energy of these Zn1−xMgxO films will be controlled by the cathodic potential.
Electron carrier concentration dependent magnetization in ZnO:Co and ZnO:Mn thin films
Authors: Yang Zheng , Biasini Maurizio , Mandalapu Leelaprasanna J , Zuo Zheng , Beyermann Ward P , Liu Jianlin
Published: April 2011

Co and Mn ions were implanted into n-type ZnO thin films with different electron carrier concentrations. X-ray diffraction measurements show that the ZnO:Co and ZnO:Mn thin films are of high crystallinity. From magnetization measurements, ferromagnetism was observed in both n-type ZnO:Co and n-type ZnO:Mn thin films with Curie temperatures well-above room temperature. Furthermore, the electron carrier concentration dependence of the saturated magnetization was measured in both types of thin films, and our results support an electron-mediated mechanism for ferromagnetism in ZnO:Co, as predicted by theory. However, our measurements seem to contradict theory for ZnO:Mn, which only predicts long-range ferromagnetism for p-type mediated material.
Mechanisms in the Formation of High Quality Schottky Contacts to n-type ZnO
Authors: Allen Martin Ward , von Wenckstern Holger , Grundmann Marius , Hatfield Stuart , Jefferson Paul , King Philip , Veal Timothy , McConville Chris , Durbin Steven
Published: April 2011

Pt, Ir, Ni, Pd, and silver oxide Schottky contacts were fabricated on the Zn-polar surface of hydrothermally grown bulk ZnO. A relationship was observed between the barrier height of the contact and the free energy of formation of the “metal” oxide. This is consistent with the dominating influence of oxygen vacancies (VO) which tend to pin the ZnO Fermi level close to the VO (+2,0) defect level at approximately EC - 0.7 eV, where EC is the conduction band minimum. Valence band x-ray photoemission spectroscopy and the current - voltage characteristics of planar Schottky diodes, measured on similar Zn-polar surfaces, showed the existence of a vacuum activated surface accumulation layer. This is possibly a consequence of the observed OH termination of the Zn-polar surface. The surface accumulation layer is compensated in atmospheric conditions by the presence of acceptor-like adsorbates, such as O2 and H2O. The formation of high quality Schottky contacts to ZnO should therefore involve the reduction of near surface oxygen vacancies and the removal of H or OH from the surface.
A Study of High Quality Al-doped ZnO Thin Films Grown at Low Temperature by Pulsed Laser Deposition
Authors: Gupta Ram , Ghosh K. , Mishra S. R. , Kahol P. K.
Published: April 2011

Highly conducting and transparent Al-doped ZnO (AZO) thin films, which are oriented along c-axis and have wurtzite structure, were grown on quartz substrate at low temperature by pulsed laser deposition. The techniques of x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), optical transmission spectroscopy (OTS), electrical resistivity, and Hall Effect were used to study the effect of growth temperature and oxygen pressure on the structural, electrical transport, and optical properties of these films. The optical transparency in all the films is high and does not change much with oxygen pressure and growth temperature. However, electrical parameters such as resistivity, carrier concentration, and mobility strongly depend on both oxygen pressure and growth temperature. The temperature dependence resistivity measurement indicates semiconducting behavior of all the films. A detailed study indicates that the films which are highly conducting and transparent correspond to an optimum temperature of 200 °C and an oxygen pressure of 5 × 10−7 bar. Higher transmittance of the AZO films compared with pure ZnO and ITO and comparable mobility make us to suggest that Al-doped ZnO is an excellent material for optoelectronic applications.
Top-gate ZnO-based TFTs by RF Sputtering
Authors: Khan Shahrukh , jamshidi-Roudbari Abbas , Hatalis Miltiadis
Published: April 2011

This work emphasizes room temperature deposition and fabrication of top-gated staggered structure ZnO-TFTs and integration of ZnO-TFT based simple logic circuits. We synthesized ZnO thin films by RF sputtering in an Ar/Oxygen ambience with no intentional heating of the substrates. The electrical, optical and structural properties of the ZnO thin films can be well-controlled by altering process parameters such as RF power density and relative Oxygen partial pressure. Typical deposition was carried out at a chamber pressure of 15 mTorr, Ar/Oxygen flow rates of 15 sccm/1 sccm and RF power density of 3W/cm2. The resistivity of the as-deposited films was between 104-106 Ù-cm with high optical transparency (>80%) in the visible spectrum and minimal surface roughness as detected by high-resolution AFM imaging. Gated van der Pauw and Kelvin-bridge structures were lithographically patterned to asses ZnO channel resistance. In the completed devices, a dual-stack (Ta2O5/SiO2) dielectric layer was effective in suppressing gate-leakage current below 10 pA and enabled depletion-mode ZnO-TFT operation exhibiting hard saturation. A Ti/Au metallization scheme was adopted to provide good ohmic contact to ZnO. TFTs retained well-behaved transfer characteristics down to a channel length of 4 ìm with on/off drain current ratio exceeding 105, threshold voltage between -15 V to -5 V and inverse sub-threshold slope of around 1.75 V/decade.
Gas phase synthesis of zinc oxide nanocrystals and their surface modification using small and large acidic ligands
Authors: Chowdhury Sankhanilay Roy , Ali Moazzam , Sudfeld Daniela , Winterer Markus
Published: April 2011

Zinc oxide nanocrystals are synthesized using the chemical vapor synthesis (CVS) technique. Diethylzinc is used as zinc precursor. Synthesized zinc oxide nanocrystals are characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption, transmission electron microscopy (TEM) and dynamic laser scattering. As-synthesized zinc oxide has a primary particle size of about 10 nm and an isoelectric point at pH 9.5. The surface of zinc oxide nanocrystals can be modified using short chain organic acids like formic acid and glycine as well as using low molecular weight polyacrylic acid (PAA). The isoelectric point shifts towards acidic pH when glycine is used as surface modifier whereas it shifts towards basic pH with formic acid. The use of PAA eliminates the isoelectric point with very high value of zeta potential over the range of pH studied in these experiments.
Polymer Composites for Radiation Detection: Diiodobenzene and light emitting polymer molecular solutions for gamma detection
Authors: Pei Qibing , Zhao Yongsheng , Zhong Haizheng
Published: April 2011

Conjugated polymers are largely intact by gamma exposure but can be energized in the presence of high-Z compounds. The resulting alteration of the polymer's high optical density and photoluminescence efficiency can be exploited for the detection of gamma radiation with high sensitivity. Diiodobenzene and conjugated polymers mix on the molecular level in solid thin films. Composite films of various thicknesses were conveniently cast from solution and exposed to gamma radiation. The responses of the films to gamma dosage were observed with dramatic changes in ultraviolet-visible absorption and photoluminescence.
Topographical Evolution of Nanocrystalline Diamond and Its Effect on Osteoblast Interactions
Authors: Yang Lei , Sheldon Brian W , Webster Thomas J
Published: April 2011

The potential of nanocrystalline diamond films (NDFs) for biological applications has been addressed by a variety of recent researchers. In the present work, we consider the topographical evolution of NDFs fabricated by microwave plasma assisted chemical-vapor-deposition (MPCVD) and its influence on osteoblast (bone forming cells) functions. One group of NDFs formed in this study were grown with 0.67% methane, 5%∼20% hydrogen and argon. The other group of NDFs composed of nano diamond and amorphous carbon was created with indirect exposure to plasma with 0.67% methane, 20% hydrogen and argon. Scanning electron microscope (SEM) images revealed that the nano diamond grains in the first group of NDFs evolved from round shapes into faceted and successively cubic shapes as hydrogen increased, whereas the second group of NDFs consisted of nano platelet grains. Atomic force microscopy (AFM) analysis confirmed this evolution as well as the variation of surface roughness. Cell results demonstrated that osteoblast adhesion and proliferation on NDFs varied dramatically depending on the different topographical features of the films. Specifically, results showed that NDFs with grain size less than 100 nm could be coated on the stem of a hip implant to promote cell adhesion. In contrast, NDFs with grain size greater than 200 nm or NDF with nano platelet grains may be optimal for the inside of acetabular articulation where cell adhesion is not preferred but wear-resistance is important. Further observation by contact angle measurement suggested that the differences in cellular adhesion and proliferation were related to the wettability associated to the topographical features of NDFs surfaces.