bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Structure-Activity Relationships (QSARs) for Materials Science
Authors: Rajan Krishna , Suh Changwon , Rajagopalan Arun , Li Xiang
Published: April 2011

The field of combinatorial synthesis and “artificial intelligence” in materials science is still in its infancy. In order to develop and accelerated strategy in the discovery of new materials and processes, requires the need to integrate both the experimental aspects of combinatorial synthesis with the computational aspects of information based design of materials. In biology and organic chemistry, this has been accomplished by developing descriptors which help to specify “quantitative structure- activity relationships” at the molecular level. If materials science is to adopt these strategies as well, a similar framework of “QSARs” is required. In this paper, we outline some approaches that can lay the foundations for QSARs in materials science.
Continuum Limit of a Step Flow Model of Epitaxial Growth
Authors: Kohn R.V. , Lo T.S. , Yip N.K.
Published: April 2011

We examine a class of step ow models of epitaxial growth obtained from a Burton-Cabrera-Frank (BCF) type approach in one space dimension. Our goal is to derive a consistent contin uummodel for the evolutionof the film surface. Away from peaks and valleys, the surface height solves a Hamilton-Jacobi equation (HJE). The peaks are free boundaries for this HJE. Their evolution must be specified by boundary conditions reecting the micro- scopic physics of nucleation. We inv estigate this boundary condition by numerical simulation of the step ow dynamics using a simple nucleation law. Our results rev ealthe presence of special structures in the profile near a peak; we discuss the relationship between these structures and the contin uumequation. We further address the importance of evaporation for matching the local behavior near the peak to the solution of the contin uum equation.
Coarse-Grained Molecular Dynamics: Dissipation due to Internal Modes
Authors: Rudd Robert E.
Published: April 2011

We describe progress on the issue of pathological elastic wave reflection in atomistic and multiscale simulation. First we briefly r eview Coarse-Grained Molecular Dynamics (CGMD). Originally CGMD was formulated as a Hamiltonian system in which energy is conserved. This formulation is useful for many applications, but recently CGMD has been extended to include generalized Langevin forces. Here we describe how Langevin dynamics arise naturally in CGMD, and we examine the implication for elastic wave scattering.
Convection Effects in Three-Dimensional Dendritic Growth
Authors: Lu Yili , Beckermann C. , Karma A.
Published: April 2011

A phase-field model is developed to simulate free dendritic growth coupled with fluid flow for a pure material in three dimensions. The preliminary results presented here illustrate the strong influence of convection on the three-dimensional (3D) dendrite growth morphology. The knowledge of the flow and temperature fields in the melt from the simulations allows for a detailed understanding of the convection effects on dendritic growth.
Computational Investigation of Selective MOVPE of AlxGa1-xAs in Presence of Hcl
Authors: Nemirovskaya Maria , Cavallotti Carlo , Jensen Klavs
Published: April 2011

The deposition of AlGaAs in the presence of HCl was investigated at the macroscopic and mesoscopic scales. Fluid dynamics simulations were first performed in order to study the dependence of the deposition rate on the operating conditions. Unknown gas phase and surface kinetic parameters were estimated by quantum chemistry and transition state computations. The fluxes of all species to the surface were thus computed and provided the input to a kinetic Monte Carlo model used to investigate the morphology evolution of the film.
Microcrystalline Keratin: From Feathers To Composite Products
Authors: Schmidt Walter F.
Published: April 2011

Molecular order and morphological order are two characteristics of feather fiber that make it unique. The fiber is highly microcrystalline and is very durable, i.e., resistant to both mechanical and thermal stress. Feather structure at the microscopic level is a complicated mixture of straight and branched fibers held together by a central fiber to form specific macroscopic structures. The proper design of processes to incorporate feathers into composite products 1) preserves the fiber's molecular properties and 2) alters its micro-/macroscopic morphology to conform to existing composite process requirements.
Electrospinning of Polycarbonates and their Surface Characterization using the SEM and TEM
Authors: Krishnappa Ravi V.N , Sung Changmo , Schreuder-Gibson Heidi
Published: April 2011

Unlike conventional spin methods, electrospinning is capable of yielding fibers with sub-micron range diameters and high specific surface areas. The use of such electrospun materials in applications, whose functionality depends on the area available, such as separation processes, will be useful. In this study a Bisphenol-A polycarbonate was dissolved in two solvents: Chloroform and a 1:1 mixture of Tetrahydrofuran (THF) and Dimethylformamide (DMF) and resulting polycarbonate solutions were then electrospun to produce polycarbonate fiber-mats. The morphological features of the electrospun polycarbonate fibers have been studied as a function of the solvent used and also as a function of the processing voltage. The studies were conducted using the SEM, TEM and Scion image analysis program. The results indicate bold differences in the fiber morphology and bead density trends with the solvent used. Electrospun polycarbonate fibers exhibit a “Raisin like” puckered structure. Such a structure will enhance the functional efficiency of an electrospun material when used in an area-based application. In addition, studies on crazing of bulk polycarbonate and the surface features of electrospun polycarbonate fibers have been conducted. Results indicate a relation between crazing and the topological features of electrospun polycarbonates.
Microstructure and Mechanical Properties of Silicon Nitride Reinforced Aluminum Matrix Composites Fabricated by Pressure Infiltration
Authors: Peng L.M. , Noda K. , Kawamoto H.
Published: April 2011

The present study aimed to investigate the microstructure and mechanical properties of aluminum matrix composites reinforced with high volume fraction of Si3N4 fabricated by the pressure casting technique, with variations in the composition of matrix alloy and microstructure of preforms. Characterization was carried out by a combination of metallography, flexural and load-controlled fatigue tests to study the flexural strength, fracture toughness and fatigue behavior in the composites. The findings indicated that increasing matrix strength resulted in an increase in flexural strength and fatigue resistance of composites. The fracture toughness of composites increased with the volume fraction of infiltrated tough Al phase. The CIP pressure exerted a significant effect on mechanical properties of composites. The improvement in mechanical properties of composites is associated with the load transfer effect from matrix to the stiffer reinforcement.
High Toughness Ceramic Laminates by Design of Residual Stresses
Authors: Orlovskaya Nina A. , Kuebler Jakob , Subotin Vladimir I. , Lugovy Mykola
Published: April 2011

Multilayered ceramic composites are very promising materials for different engineering applications. Laminates with strong interfaces can provide high apparent fracture toughness and damage tolerance along with the high strength and reliability. The control over the mechanical behavior of laminates can be obtained through design of residual stresses in separate layers. Here we report a development of tough silicon nitride based layered ceramics with controlled compressive and tensile stresses in separate layers. We design laminates in a way to achieve high compressive residual stresses in thin (100-150 micron) Si3N4 layers and low tensile residual stresses in thick (600-700 micron) Si3N4-TiN layers. The residual stresses are controlled by the amount of TiN in layers with residual tensile stresses and the layers thickness. The fracture toughness of pure Si3N4(5wt%Y2O3+2wt%Al2O3) ceramics was measured to be of 5 MPa m1/2, while the apparent fracture toughness of Si3N4/Si3N4-TiN laminates was in the range of 7-8 MPa m1/2 depending on the composition and thickness of the layers.
Analysis of the Atomic-Scale Defect Chemistry at Interfaces in Fluorite Structured Oxides by Electron Energy Loss Spectroscopy
Authors: Ito Y. , Lei Y , Browning N.D. , Mazanec T.J.
Published: April 2011

Gd3+ doped Ce oxides are a major candidate for use as the electrolyte in solid oxide fuel cells operating at ∼500 °C. Here, the effect of the atomic structure on the local electronic properties, i.e. oxygen coordination and cation valence, at grain boundaries in the fluorite structured Gd0.2Ce0.8O2-x ceramic electrolyte is investigated by a combination of atomic resolution Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). In particular, EELS analyses from grain boundaries reveals a complex interaction between segregation of the dopant (Gd3+), oxygen vacancies and the valence state of Ce. These results are similar to observations from fluorite-structured Yttria-Stabilized Zirconium (YSZ) bicrystal grain boundaries.
Exploring The Consequences of Negative Triple Junction Energy
Authors: Gupta Gaurav K. , King Alexander H.
Published: April 2011

We have investigated the consequences of negative triple junction energy in grain growth. Two and three-dimensional models for total system energy, incorporating varying triple junction energy are developed. These models show that there is a decrease in overall system energy with grain size corresponding to the driving force for grain growth. Although the free energy available to drive grain growth is reduced under some conditions, it is never removed for any reasonable values of the triple junction energy.
Thermal Characterization of Nanowire Array in a-Al2O3 Matrix
Authors: Borca-Tasciuc Diana-Andra , Chen Gang , Lin Yu-Ming , Rabin Oded , Dresselhaus Mildred S. , Borshchevsky Alexander , Fleurial Jean-Pierre , Ryan Margaret A.
Published: April 2011

Thermal properties characterization of Bi nanowires is critical in order to validate the predicted enhancement of their thermoelectric figure-of-merit. In this paper we report the effective thermal diffusivity of Bi nanowires array embedded in a-Al2O3 (alumina) template. The composite material consists of 85% alumina and approximately 15% Bi nanowires with a diameter of 40 nm and an average length of 40 [.proportional]m. Measurements are performed along the nanowire axis. A thermal wave is produced at the front side of the sample and it is monitored at the backside through a fast thermoelectric effect. A one-dimensional heat conduction model is used to extract the thermal diffusivity.
Polymerization in Inverse Microemulsion: An Effective Tool to Produce Biodegradable and non Biodegradable Nanoparticles
Authors: Lebon F. , Grandfils C. , Jérôme R. , Barakat I. , Sartore L.
Published: April 2011

Potential of polymerization in inverse microemulsions has been illustrated by the preparation of crosslinked nanoparticles with functional groups on the surface. Nonbiodegradable polyacrylamide nanoparticles have been prepared, with the purpose to use these stable monodisperse lattices as enzymatic reactors and in diagnostic applications. Their size is in the 50 to 90 nm range and they contain a model enzyme (alkaline phosphatase) immobilized. In another example, monodisperse biodegradable nanoparticles of polyamidoamines with a size from 90 to 130 nm have been prepared. They are envisioned for intravenous administration because of a low content of non-metabolized material and absence of toxicity.
Self-Energy corrections to DFT-LDA Gaps of Realistic Carbon Nanotubes
Authors: Satta Guido , Cappellini Giancarlo , Casula Francesco
Published: April 2011

Since their discovery carbon nanotubes have attracted much interest for their peculiar electronic properties which go from metalic to semiconducting behaviour, depending both on diameter and chirality. The exact vaue of their band gap is obviously a crucial point to be addressed because it enters in the nanotube application as microelectronic devices. By making use of an efficient GW scheme, previousy tested on bulk systems, as well as of a model screening function, we obtained for the first time excitation energies and band-gap vaues for carbon nanotubes. Results for (6,0) and (7,0) will be presented and discussed.
Formation of Gold Nanowires on MgO Surfaces
Authors: Ueda Akira , Mu Richard R. , Saunders Vanessa , Livingston Thurston , Wu Marvin H. , Arantes Vera L. , Henderson Don O.
Published: April 2011

Gold nanowires were fabricated on the stepped MgO (100) surfaces. The stepped MgO (100) surfaces were produced by polishing (100) surfaces at an inclined angle ∼1° toward a [110] direction. An atomic force microscope image indicates that gold nanowires have grown at the steps on MgO (100) surface with a height of ∼ 2 nm and a width of ∼60 nm.
Characterization of the order-annealing response of nanostructured iron-palladium based ferromagnetic thin-films
Authors: Xu Huiping , Wise Adam T. , Klemmer Timothy J. , Wiezorek Jörg M. K.
Published: April 2011

A combination of XRD and TEM techniques have been used to characterize the response of room temperature magnetron sputtered Fe-Pd thin films on Si-susbtrates to post-deposition order-annealing at temperatures between 400-500°C. Deposition produced the disordered Fe-Pd phase with (111)-twinned grains approximately 18nm in size. Ordering occurred for annealing at 450°C and 500°C after 1.8ks, accompanied by grain growth (40-70nm). The ordered FePd grains contained (111)-twins rather than {101}-twins typical of bulk ordered FePd. The metallic overlayers and underlayers selected here produced detrimental dissolution (Pt into Fe-Pd phases) and precipitation reactions between Pd and the Si substrate.
In-situ Analysis of the Chemical Vapor Synthesis of Nanocrystalline Silicon Carbide by Aerosol Mass Spectrometry
Authors: Lee In-Kyum , Winterer Markus , Hahn Horst , Janzen Christian , Lindackers Dirk , Roth Paul
Published: April 2011

An Aerosol Mass Spectrometer (AMS) is a combination of a Quadrupol- (QMS) and a Particle Mass Spectrometer (PMS) and enables the in-situ analysis of gas phase processes for the generation of nanoparticles. Size distributions of ultrafine silicon carbide particles in the range of 104atomic mass units (amu) to 107amu are measured in the PMS. Simultaneously, molecular species up to 300 amu can be detected in the QMS. Aerosols containing nanocrystalline silicon carbide are produced from tetramethylsilane (TMS) by thermal decomposition. In situ process analysis with the AMS as a function of process parameters was performed to elucidate the formation and growth mechanism of SiC nanoparticles.
Temperature Dependence of Electroresistivity, Negative and Positive Magnetoresistivity of Graphite/Diamond Nanocomposites and Onion-Like Carbon
Authors: Romanenko Anatoliy I. , Anikeeva Olga B. , Okotrub Alexander V. , Kuznetsov Vladimir L. , Butenko Yuriy V. , Chuvilin Andrew L. , Dong C. , Ni Y.
Published: April 2011

Here we present the result of measurements of electrical resistivity and magnetoresistivity of graphite/diamond nanocomposites (GDNC) and onion-like carbon (OLC) prepared by vacuum annealing of nanodiamond (ND) at various fixed temperatures. GDNC contain particles with a diamond core covered by closed curved graphitic shells. The electrical resistivity of annealed ND is characteristic of systems with localized electrons and can be described in terms of variable hopping-length hopping conductivity (VHLHC). The magnetoresistivity of OLC is negative in the range of field 0<B<2 T, and is positive at B>2 T. The conduction carrier concentration for OLC samples was estimated in the framework of the theory of negative magnetoresistance in semiconductors in the hopping conduction region. The free path length for conducting electrons at liquid helium temperature was estimated from the data on positive magnetoresistivity. The localization length of current carriers was also estimated. The determined parameters are in agreement with proposed structure model of OLC constructed using HRTEM data.
Crystalline-Amorphous Interface: Molecular Dynamics Simulation of Thermal Conductivity
Authors: Alfthan Sebastian von , Kuronen Antti , Kaski Kimmo
Published: April 2011

Effect of a crystalline-amorphous interface on heat conduction has been studied using atom-istic simulations of a silicon system. System with amorphous silicon was created using the bond-switching Monte Carlo simulation method and heat conduction near room temperature was studied by molecular dynamics simulations of this system.
Fe/SiO2 Nanocomposite Soft Magnetic Materials
Authors: Hui S. , Zhang Y. D. , Xiao T. D. , Wu Mingzhong , Ge Shihui , Hines W. A. , Budnick J. I. , Yacaman M. J. , Troiani H. E.
Published: April 2011

In an effort to explore new highly resistive soft magnetic materials, Fe/SiO2 nanocomposite materials have been synthesized using a wet chemical reaction approach in which the precursor complex was annealed at various temperatures. The crystallographic structure, nanostructure, morphology, and magnetic properties of the synthetic Fe/SiO2 particles were studied by x-ray diffraction, transmission electron microscopy, and magnetic measurements. The experimental results show that for this approach, the [.alpha]-Fe particles are coated with amorphous silica. The progress of the reaction, the purity of Fe/SiO2 in the synthetic powder, and the Fe particle size are highly dependent on the annealing temperature. By adjusting the annealing temperature, the particle size can be controlled from approximately 20 nm to 70 nm. For the synthetic nanopowder obtained by H2 reduction at 400 °C, there exists a superparamagnetic behavior below room temperature; while for the nanopowders obtained by reduction at higher temperatures, the ferromagnetic behavior is dominant. Based on these studies, optimum synthesis conditions for Fe/SiO2 nanocomposites is determined.
Synthesis of Nanosized Lithium Manganate For Lithium-ion Secondary Batteries
Authors: Wang Hsien-Cheng , Lin Yueh , Wen Ming-Chang , Lu Chung-Hsin
Published: April 2011

Nanosized lithium manganate powders are successfully synthesized via a newly developed reverse-microemulsion (RμE) process. Monophasic LiMn2O4 powders are obtained after calcining the precursor powders at 700°C. The particle size of the spinel compound significantly depends on the concentration of the aqueous phase. Increasing the water-to-oil volume ratio results in an increase in the particle size. While the aqueous phase is equal to 0.5 M, the size of the obtained LiMn2O4 powder is around 60-70 nm. It is found that the specific capacity of nanosized LiMn2O4 particles is greater than that of submicron particles. The large surface area of ultrafine particles is considered to facilitate the intercalation and deintercalation of lithium ions during the cycling test.
Preparation of Copper Aluminium Oxide by Spray Pyrolysis
Authors: Rim Ji Youn , Song Shin Ae , Park Seung Bin
Published: April 2011

Copper aluminium oxide(CuAlO2) particles, a promissing p-type TCO(transparent conducting oxide), were prepared by spray pyrolysis. Delafossite phase of CuAlO2 was obtained when copper nitrate, copper acetate and copper sulfate, divalent copper precursors, were used as copper precursor and aluminium nitrate as aluminium precursors. However, when copper chloride (CuCl, a monovalent copper precursor) was used, the delafossite phase was not obtained regardless of the type of aluminium precursor. The O2-doped CuAlO2 was obtained by using oxygen as carrier gas.
Nanocomposite Coatings - Applications and Properties
Authors: Cayton Roger H. , Brotzman R. W.
Published: April 2011

Nanocomposite coatings were made by incorporating nano-sized and micron-sized alumina into aqueous and non-aqueous polymer systems. At approximately 50wt% nano-sized alumina a synergistic effect was observed in coating hardness with no degradation in optical properties.
Structure and Nanocrystallites of Ni and NiO Three Dimensional Ordered Macromeshes
Authors: Zhou W.L. , Xu L. , Zakhidov A.A. , Baughman R.H. , Wiley J.B.
Published: April 2011

Three dimensional Ni and NiO inverse opal macromeshes were characterized by scanning electron microscope (SEM) and transmission electron microscope (SEM). The octahedral cubes of the macroporous Ni were found mostly grown as single crystals with staking faults and microtwins. There was no preferential growth of these cubes as determined by selected area diffraction pattern (SADP). Some NiO nanocrystals with size of about 5 nm were formed on the surface of inverse Ni opal membrane during etching away of silica spheres. The oxidation of Ni mesh turned it into NiO macromesh with grain size of about 20 nm at 550°C. The nanocrystalline NiO mesh is suitable for further fabrication of three dimensional nanobeads. By annealing the meshes at 650°C, the NiO nanograins grew to a size of over 50 nm. This three dimensional ordered macroporous structure with higher temperature treatment is considered as stable and important for further application.
Microwave Plasma CVD of Silicon Nanocrystalline and Amorphous Silicon as a Function of Deposition Conditions
Authors: Jeung J-H , Lee Hak-Gue , Teng Lihong , Anderson W.A.
Published: April 2011

Using ECR-CVD (electron cyclotron resonance-chemical vapor deposition), we can make amorphous-silicon (a-Si) and nanocrystalline (nc-Si) thin films. We are looking forward to improve the photo/dark conductivity ratio (σp/σd) by measuring the photo and dark current-voltage (I-V). In the ECR deposition, there are several factors which we can control and adjust for improved results, such as the amounts of silane and argon, the vacuum, and the temperature of the substrate. These become the critical factors for ECR deposition in order to make better films. Input gases consist of Ar, 2%SiH4 in He and H2. In the process, SiH4 is decomposed into SiHx. A residual gas analyzer (RGA) gives composition in the plasma. Because Ar possibly etches the substrate and Si is to be deposited, the best RGA signal is obtained with low Ar content. This work serves to correlate process conditions, RGA signals and electrical data. The best RGA signal occurs for 5 mTorr Ar, 60 mTorr SiH4:He, and power of 600 W. Best value of dark conductivity (σd) was 1.53 × 10-9 S/cm and1.58 × 10-5 S/cm for photo conductivity (σp and low value of σd indicate material with fewer defects. Adding extra H2 improves the photo-conductivity (σp). Applications of these films are heterojunction solar cells and thin film transistors. The heterojunction solar cell had a structure of metal grid/ 500°A of aSi:H/p-Si wafer/Ohmic contact. These cells gave an open circuit voltage (Voc) = 0.51 (V) and short circuit current density (Jsc) = 5.5 mA/cm2 under 50mW/cm2 tungsten halogen lamp. Thin film transistors using nc-Si, with gate length/width (L/W) =450/65 gave field effect mobility of 18 cm2/V-s, and Ion/Ioff of 1.25×105.
Using Ion Beams to Modify Nanocrystalline Composites: Co Nanoparticles in Sapphire
Authors: Meldrum A. , Beaty K.S. , Lam M. , White C.W. , Zuhr R.A. , Boatner L.A.
Published: April 2011

Ion implantation and thermal processing were used to create a layer of Co nanoclusters embedded in the near-surface region of single-crystal sapphire. The Co nanoparticles ranged in size from 2-20 nm and were crystallographically aligned with the host sapphire. Specimens were irradiated with Xe and Pt ions, and the microstructural evolution of the nanoclusters was investigated by transmission electron microscopy. With increasing Pt or Xe ion dose, the Co nanoparticles lost their initially excellent faceting, although they remained crystalline. The host Al2O3 became amorphous and the resulting microstructure consisted of a buried amorphous layer containing the still-crystalline Co nanoparticles. EDS mapping and electron diffraction were used to determine the distribution of the implanted species, and the magnetic properties of the composite were measured with a SQUID magnetometer. The results show that ion beams can be applied to modify and control the properties of ferromagnetic nanocomposites, and, combined with lithographic techniques, will find applications in exercising fine-scale spatial control over the properties of magnetic materials.
Preparation of Line Patterned Mesoporous DAM-1 Thin Films via Pulsed Laser Deposition
Authors: Coutinho Decio , Balkus Kenneth J.
Published: April 2011

Patterned mesoporous DAM-1 thin films were prepared on flexible transparent film utilizing the pulsed laser deposition and a line patterning technique. The patterned lines are transferred to the transparent film using a laser printer or copy machine. Laser ablation of DAM-1 onto the patterned substrate followed by a hydrothermal treatment resulted in a densely packed mesoporous film. Upon removal of the patterned lines (i.e. the underlying toner) by ultrasonic treatment in toluene, patterned DAM-1 films were produced.
Formation of Ni/SiO2 and Ag/SiO2 Nanosphere Composites
Authors: Prokes S. M. , Carlos W. E. , Seals Lenward , Lewis Stephen , Gole James L.
Published: April 2011

SiO2 nanospheres have been produced via a high temperature evaporation process and they have been Ni or Ag plated using electroless plating solutions. These samples were examined by Atomic Force Microscopy (AFM) and Magnetic Resonance (MR). The initial SiO2 nanospheres were about 30 nm in diameter, and the Ni plating layer resulted in a 25nm thick metallic Ni coverage, while the Ag coverage was estimated to be in the 150 nm range. In the case of the Ni/SiO2 nanosphere composites, the MR signals show the presence of Ni+2 and Ni+3 paramagnetic centers, seen below 40K, and ferromagnetic metallic Ni, which is seen above 40K. The dried Ni plating solution (with no SiO2) shows only the presence of paramagnetic Ni+3. These results suggest that an interfacial reaction at the surface of the SiO2 nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a ferromagnetic Ni/SiO2 nanosphere composite. In the case of the Ag/SiO2 nanosphere composites, no MR signal is seen from the non-magnetic Ag, but strong paramagnetic behavior has been noted for Co+2, which originates from the plating solution.
Fabrication of Two- and Three-Dimensional Structures of Nanoparticles Using Lb Method and DNA Hybridization
Authors: Takahagi Takayuki , Huang Shujuan , Tsutsui Gen , Sakaue Hiroyuki , Shingubara Shoso
Published: April 2011

In this paper we describe fabrication methods for two types of nanostructures, two- and three-dimensional arrays of gold nanoparticles. Large-scale and high-ordered monolayers of alkanethiol-encapsulated gold particles were fabricated by using Langmuir-Blodgett (LB) method. Three-dimensional nanoparticle arrays composed of gold nanoparticles of two different sizes, which were encapsulated by complementary thiol-capped DNA oligonucleotides, were fabricated by using DNA hybridization. DNA hybridization occurred upon mixing these particles, which resulted in the assembly of three-dimensional nanostructure of gold particles. Scanning electron microscopy observations and UV spectroscopy measurement were performed to confirm the construction of the nanostructures.
Nano-Particulate of Aluminum Nitride Prepared by Pulsed Wire Discharge
Authors: Kinemuchi Yoshiaki , Sangurai Channarong , Suzuki Tsuneo , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: April 2011

Nanoparticulates of aluminum nitride (AlN) have been synthesized by novel dry process, namely pulsed wire discharge where aluminum wire is exploded by an intense pulsed current (10-20 kA at the peak, half cycle of 10 μs) in NH3/N2 gas. The average size of the nanoparticulates was found to be 28 nm. Furthermore, narrow particle distribution of the particulates was observed, where geometric standard deviation was 1.29. Increasing charging energy enhances the nitridation of aluminum. The maximum content of AlN in synthesized particulates was ∼95 %. The sintered body with 80 % of density has been obtained by sintering at 1, 600°C for one hour.
A Facile Wet Synthesis of Nanoparticles of Litharge, the Tetragonal Form of PbO
Authors: Wilkinson Tommy J. , Perry Dale L. , Spiller Erik , Berdahl Paul , Derenzo Stephen E. , Weber Marvin J.
Published: April 2011

The red, tetragonal form of lead oxide, α-PbO, litharge, has been synthesized in the nanoparticle range using a rapid, one-step reaction sequence using water as the reaction medium. The product was characterized by powder x-ray diffraction and scanning electron microscopy. With time at room temperature, the original material slowly changed in color intensity, indicating its alteration to β-PbO, massicot. Grinding the aged material converted it back to the original litharge form. The role of impurities in the experimental synthesis of the material and microstructural variations in the final product are discussed, along with the PbO-phase compositions of commercial products.
Fabrication and Properties of Self-Assembled Nanosized Magnetic Particles
Authors: Salazar-Alvarez G. , Mikhailova M. , Toprak M. , Zhang Y. , Muhammed M.
Published: April 2011

The synthesis and characterisation of gold-coated cobalt nanoparticles, as well as their chemically- and magnetically-induced self-organisation have been studied. Metallic core-shell nanoparticles were prepared using two different experimental techniques: bulk reductive precipitation, with average particles size ∼15 nm, and microemulsion confining method, with average particle size of ∼6 nm. The self-assembly of prepared nanoparticles on flat substrates was achieved by derivatising the substrate and particle surfaces with bifunctional organic molecules that attaches to both particles and substrates.

Examination of the self-assembled systems was carried out by a number of characterisation techniques including transmission electron microscopy (TEM), UV-visible spectrophotometry (UV-VIS), and atomic force microscopy (AFM).
XPS and Magnetization Measurements Study of CrMn Nanoparticles
Authors: Abdul-Razzaq Wathiq , Lee Unchul
Published: April 2011

Cr1-xMnx (x < 6.3 %) alloy in the bulk form is an interesting complex system that behaves in many but not all respects like a spin-glass system. In this study, 14 nm-size CrMn nanoparticles with 5% Mn, were synthesized by ball milling of Cr and Mn particles in Ar atmosphere. After 50 hours of milling, the x-ray diffraction pattern indicated alloying of the two metals Cr and Mn. However XPS data indicated the formation of MnO2 and Cr2O3oxides on the surface of the chromium core in the nanoparticle. These oxides on the surface, like the Cr core, are antiferromagnets. Magnetization (M) measurement at 200 G as a function of temperature (T), after zero-field-cooling, showed that M increased as T increased from 5 K all the way to 330 K, beyond the Neel temperatures of the Cr and the oxides. Even though the magnetization value is in the range of a typical antiferromagnet at all temperatures from 5 to 330 K, the shape of M versus T curve is neither that of an antiferromagnet nor of a spin-glass. It appears that the behavior of the magnetization curve is due to the frustration of the spins by weak fields associated with spin-density-wave and by the existence of the oxides. This frustration should be different from the frustration of the spins due to the ferromagnetic-antiferromagnetic competition in spin-glass systems.
Preparation and Magnetic Properties of Fe Nanoparticles by Chemical Vapor Condensation Process
Authors: Choi C. J. , Kim B. K. , Dong X. L.
Published: April 2011

Nano-sized Fe particles were synthesized by Chemical Vapor Condensation (CVC) Process using the precursor of iron carbonyl (Fe(CO)5) as the source. We investigated the microstructures, magnetic properties of the Fe nanoparticles and their oxidation behavior during annealing systematically by means of HRTEM, DTA-TG, Mössbauer spectroscopy. The prepared particle was nearly spherical shape and core-shell type structure. The magnetic states of Fe nanoparticles changed from superparamagnetism to ferromagnetism with the particle size and microstructure. Oxidation heat treatment leads to the successive appearance of oxide phases.
Thermoelectric Study of Hydrogen Storage in Carbon Nanotubes
Authors: Sumanasekera G. U. , Adu C. K. W. , Pradhan B. K. , Chen G. , Romero H. E. , Eklund P. C.
Published: April 2011

In situ resistivity and thermoelectric power (S) have been used to study the nature of the adsorption of hydrogen in bundles of single-walled carbon nanotubes for H2 pressure P <1 atm and temperatures 77 K<T<500 K. Isothermal plots of S vs. Δρ/ρ0 are found to exhibit linear behavior as a function of gas coverage, consistent with a physisorption process. Studies of S, ρ at T = 500 K as a function of pressure exhibit a plateau at a pressure P~40 Torr, the same pressure where the H % measurements suggest the highest binding energy sites are being saturated. The effects of H2 exposure at 500 K on the thermoelectric transport properties are fully reversible.
Nanoengineering of Carbon Nanotubes and the Status of its Applications
Authors: Nakayama Yoshikazu , Akita Seiji
Published: April 2011

We have developed a well-controlled method for manipulating carbon nanotubes. The first crucial process involved is to prepare a nanotube array, named nanotube cartridge. We have found the ac electrophoresis of nanotubes by which nanotubes are aligned at the knife-edge. The nanotubes used were multiwalled and prepared by an arc discharge with a relatively high gas temperature. The second important process is to transfer a nanotube from the nanotube cartridge onto a substrate in a scanning electron microscope. Using this method, we have developed nanotube tips and nanotube tweezers that operate in a scanning probe microscope. The nanotube probes have been applied for observation of biological samples and industrial samples to clarify their advantages. The nanotube tweezers have demonstrated their motion in scanning-electron-microscope and operated to carry nanomaterials in a scanning probe microscope.
AFM-Based Surface Potential Measurements on Carbon Nanotubes
Authors: Schujman Sandra B. , Vajtai Robert , Shusterman Yuriy , Biswas Sujit , Dewhirst Brian , Schowalter Leo J. , Wei Bin Q. , Ajayan Pulickel M.
Published: April 2011

In order to build electrical devices based on carbon nanotubes, it is crucial to understand the effects of the substrate, electrical contacts, defects and junctions on the transport properties of both multi-wall and single-wall carbon nanotubes (MWNT and SWNT). In the present study two different dispositions are analyzed. In one of them, isolated MWNT were deposited onto an insulating oxide layer over a conducting substrate and platinum electrical contacts were prepared via a focused ion beam (FIB) deposition method. An ohmic contact to the substrate allowed us to polarize it at a different potential than the nanotubes themselves. In the second one, a vertical array of MWNT was grown on a template of alumina in which one of the ends was coated with gold, to provide an electric contact. To investigate transport properties, we used an atomic force microscope (AFM) to determine the electric surface potential of MWNT. The technique employed, scanning surface potential microscopy (SSPM), applied a dc-voltage to the tip that equilibrates the local electrostatic potential on the sample so as to eliminate forces on the AFM tip caused by electric repulsion or attraction between tip and sample. There is no alteration of the sample potential caused by the tip. Surface potential measurements on the first system show that the electric transport on the MWNT has a diffusive character. The application of a (4.5V) bias between nanotube and substrate causes the resistance of the nanotube to drop by a factor of four. We can also resolve the voltage drop on the nanotube and at the contacts. The measurements in the second system (vertical arrangement) show that the nanotubes are uncapped and we can observe a contrast that varies with the application of different voltages to the back contact.
MRS 2001 (Boston): Design and Quantification of a Nanoscale Field Effect Transistor: Distributed Response Analysis for Investigating Conductive Behaviour.
Authors: Panhuis Marc in het , Coleman Jonathan N. , Popelier Paul. A. , Foley Brian , Munn Robert W. , Blau Werner J.
Published: April 2011

A new design for a field effect transistor able to push back the physical limits of Moore's Law is described. An ab initio computational approach is presented that can be further developed to characterize the ON/OFF states of such a device. Distributed response analysis (M. in het Panhuis, P.L.A. Popelier, R.W. Munn, J.G. Ágyán (2001), J. Chem. Phys. 114, 7951-7961) is employed to investigate conductive behavior. The method demonstrates that in analogy to conduction an electron can move across a possible conjugated molecular switching element (para-nitroaniline) in an electric field.
Reproducible Synthesis of C60@SWNT in 90% Yields
Authors: Smith Brian W. , Russo Richard M. , Chikkannanavar S.B. , Stercel Ferenc , Luzzi David E.
Published: April 2011

In previous works, we have shown our discovery of C60@SWNT and first described the general mechanism of filling, which involves the vapor phase transport of C60 molecules to openings in the SWNTs' walls. Here, we discuss the high-yield synthesis of C60@SWNT by refinements to our method. Yields are measured by a calibrated weight uptake technique, a methodology that is not subject to many of the potential pitfalls inherent to other techniques that have been applied. At certain processing conditions, yields exceeding 90% were obtained and corroborated by transmission electron microscopy. From our data, we determine the parameters most important for creating endohedral SWNT supramolecular assemblies by the vapor phase method. Our results pave the way for successful single-tube measurements and for high-yield filling with non-fullerenes.
Effects of Fe film Thickness and Ammonia on the Growth Behavior of Carbon Nanotubes grown by thermal Chemical Vapor Deposition
Authors: Sohn Jung Inn , Choi Chel-Jong , Seong Tae-Yeon , Lee Seonghoon
Published: April 2011

The growth behaviour of carbon nanotubes on the Fe-deposited Si (001) substrates by thermal chemical vapor deposition (CVD) has been investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The Fe films are deposited for 20 s–20 min by pulse-laser deposition. SEM results show that the growth characteristics of carbon nanotubes strongly depend on the Fe film deposition time. TEM and SEM results show that the pretreatment annealing at 800 °C causes the continuous Fe films to be broken up into nanoparticles 8–50 nm across and discontinuous islands 100 nm– 1.1 μm in size. It is shown that the Fe nanoparticles are essentially required for the formation of aligned carbon nanotubes. SEM results show that the growth behaviors of carbon nanotubes are strongly dependent on the pretreatment atmospheres. In addition, for the Ar gas-pretreated sample, a carbonaceous layer is formed near the surface region. TEM results show direct evidence that a base growth mode is responsible for the growth of carbon nanotubes in the present work. Based on the microscopy results, the pretreatment condition dependence of the growth behaviors of carbon nanotubes is discussed.
Plasma Enhanced Chemical Vapour Deposited Carbon Nanotubes for Field Emission Applications
Authors: Teo K. B. K. , Pirio G. , Lee S.B. , Chhowalla M. , Legagneux P. , Nedellec Y. , Hasko D.G. , Ahmed H. , Pribat D. , Amaratunga G.A.J. , Milne W.I.
Published: April 2011

Plasma Enhanced Chemical Vapour Deposition is an extremely versatile technique for directly growing multiwalled carbon nanotubes onto various substrates. We will demonstrate the deposition of vertically aligned nanotube arrays, sparsely or densely populated nanotube forests, and precisely patterned arrays of nanotubes. The high-aspect ratio nanotubes (~50 nm in diameter and 5 microns long) produced are metallic in nature and direct contact electrical measurements reveal that each nanotube has a current carrying capacity of 107-108 A/cm2, making them excellent candidates as field emission sources. We examined the field emission characteristics of dense nanotube forests as well as sparse nanotube forests and found that the sparse forests had significantly lower turn-on fields and higher emission currents. This is due to a reduction in the field enhancement of the nanotubes due to electric field shielding from adjacent nanotubes in the dense nanotube arrays. We thus fabricated a uniform array of single nanotubes to attempt to overcome these issues and will present the field emission characteristics of this.
Effects of Ion Irradiation on Supported Carbon Nanotubes and Nanotube-Substrate Interfaces
Authors: Krasheninnikov A. V. , Nordlund K. , Keinonen J.
Published: April 2011

We employ molecular dynamics to study the effects of ion irradiation on carbon nanotubes lying on different substrates. We show that defect production depends on the type of the substrate and that the damage is higher for metallic heavy-atom substrates than for light-atom substrates, since in the former case sputtered metal atoms and backscattered recoils produce extra damage in the nanotube. We further study the behavior of defects and demonstrate that although ions may severely damage nanotubes in a local region, the nanotube carbon network can heal such a strong localized damage due to defect migration and dangling bond saturation. Finally, we predict the pinning of nanotubes to substrates by forming nanotube-substrate bonds which appear near irradiation-induced defects.
Magnetic Anisotropy of Cerium Endohedral Metallofullerene
Authors: Inakuma Masayasu , Enoki Toshiaki , Kato Haruhito , Shinohara Hisanori
Published: April 2011

The magnetic properties of Ce@C82 have been studied. The magnetic anisotropy of Ce@C82 was analyzed taking account of the crystal field of the interior C82 cage acting on Ce3+ ion. Results showed that the reduction of the susceptibility at low temperature was caused due to the antiferromagnetic coupling between Ce3+ ion and C82 cage. The magnetization measurement at several temperatures also supported the antiferromagnetic interaction at low temperature. The magnetic susceptibility larger than the calculated one was measured at higher temperatures due to the magnetic interaction between the metallofullerenes and between the particles in the crystal. The magnetization of some frozen Ce@C82 solutions was found to depend on the applied field magnitude. The dependence suggested that the magnetic anisotropy of Ce ion induced a torque to restrict the rotational motion of Ce@C82 by the field.
Thermodynamic Analysis of Carbon Nucleation on a Metal Surface
Authors: Kuznetsov Vladimir L. , Usoltseva Anna N. , Chuvilin Andrew L. , Obraztsova Elena D. , Bonard Jean-Marc
Published: April 2011

A thermodynamic analysis of the carbon nucleation on the metal surface was performed. From the consideration of the catalytic mechanisms of carbon deposit formation on the metal surface we concluded that majority of these mechanisms include some common steps. The most important of them is the step of nucleation of carbon deposit on the metal surface. The master equation for the dependence of critical radius of the nucleus on reaction parameters was obtained. This equation demonstrates that a variation of the reaction parameters, such as the temperature, the nature of metal catalyst and the degree of supersaturation of the metal-carbon solution, can lead to the formation of different carbon deposits, such as filamentous carbon, multi-wall nanotubes (MWNT) or single-wall nanotubes (SWNT). The analysis performed allows us to conclude that for selective production of SWNT the nucleation must proceed at high temperature on the surface of liquid metal particles (Fe, Co, Ni). For solid metal particles (Mo) a high degree of supersaturation with carbon is also required.
Large-Area Deposition of Carbon Nanotubes for Field Emission Displays
Authors: Park Young-Jun , Han In-Taek , Kim Ha-Jin , Woo Yun-Sung , Lee Nae-Sung , Jin Yong-Wan , Jung Jae-Eun , Park Chong-Yun , Kim Jong-Min
Published: April 2011

A direct synthesis of carbon nanotubes (CNTs) on substrates by chemical vapor deposition (CVD) is one of highly probable routes to reach their application to field emission displays. Several stringent requirements are prerequisite for this purpose, including low temperature growth below 600°C to engage glass substrates and large area deposition for practical use. This study carried out synthesis of CNTs by thermal CVD on glass substrates at temperatures as low as 500~550°C. CNTs were grown by thermal decomposition of CO and H2 gases at an atmospheric pressure for different thickness of Invar (an Fe-Ni-Co alloy ) catalytic layers. The growth of CNTs was strongly correlated with preparation of catalytic layers. The diameters and heights of as-grown CNTs increased as the catalytic layers became thicker from 2nm to 30nm. Measurements of the field emission properties of CNTs showed that the threshold electric fields were lowered with increasing thickness of catalytic layers. A uniform electron emission was observed over a large area of 150 × 150mm2, with high emission currents and high brightness.
Binary Phase of Layered Nanotubes
Authors: Whitby R.L.D. , Hsu W.K. , Boothroyd C.B. , Fearon P.K. , Kroto H.W. , Walton D.R.M.
Published: April 2011

A binary phase of layered nanotubes, where MWCNs (Multi-walled carbon nanotubes) are coated by WS2, are generated by pyrolysing WO3-coated MWCNs in an H2S/N2 atmosphere at 900 °C. TGA and TEM show that WS2 acts as an antioxidant with respect to the MWCN core.
Utilizing Old Egyptian Wisdom for Stabilization of Individual Carbon Nanotubes in Aqueous Dispersions
Authors: Bandyopadhyaya Rajdip , Nativ-Roth Einat , Regev Oren , Rozen Rachel Yerushalmi
Published: April 2011

The tendency of single wall carbon nanotubes to organize into crystalline ropes and the aggregation of the ropes into tangled networks act as an obstacle for most applications, and diminishes the special properties of the individual tubes. We describe a procedure for dispersing as-produced nanotube powder in aqueous solutions of Gum Arabic. Dispersion results in spontaneous exfoliation of nanotubes ropes into individual tubes, as demonstrated via x-ray scattering and electron microscopy.
Self-Assembling and Ordering of Ge/Si Quantum Dots on Flat and Nanostructured Surfaces
Authors: Motta N. , Sgarlata A. , Balzarotti A. , Rosei F.
Published: April 2011

We have studied by Scanning Tunneling Microscopy (STM) the effect of step bunching on Ge/Si(111) epitaxy. We have verified that self-organization of Ge islands is greatly influenced by “step bunching” which arises from the flash-annealing procedure used to reconstruct the Si surface. Two different growth regimes arise: initially islands nucleate and evolve only at steps, up to complete ripening; subsequently the same evolution is observed on flat areas of the sample. The average distance between islands and steps is nearly constant, originating a single row of equally spaced islands, followed by other rows of islands in between. The exploitation of this phenomenon, which is governed by the surface diffusion length of Ge on Si (estimated from our data) and by the terrace width, constitutes one possible path to achieve self-organization of quantum dots.