bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the Morphology of Faceted Particles by Transmission Electron Microscopy
Authors: Turner Shirley , Bright David S. 
Published: April 2011

ABSTRACTFaceting in a polyhedral rutile particle was modeled from transmission electron microscopy images. A double-tilt, rotate transmission electron microscope (TEM) sample holder was used to manipulate the particle. Using this holder, it was possible to align the c axis of the particle along one of the axes of the sample holder. This alignment allowed images to be obtained of the particle in several orientations around its c axis. Comparison of dimensions and angles obtained to those obtained for hypothetical models of the particle gives information about its likely prismatic and pyramidal faceting. This approach to facet modeling is useful for more complete determination of the faceting in individual euhedral particles using transmission electron microscopy.
Nickel Nanocomposite Thin Films
Authors: Zhou Honghui , Kvit A. , Kumar D. , Narayan J. 
Published: April 2011

ABSTRACTNickel was deposited on epitaxial TiN matrix layer grown on Si (100) substrate by pulsed laser deposition process (PLD). Transmission electron microscopy (TEM) study shows that nanoparticles formed are single crystals with two kinds of epitaxial relationship with respect to matrix TiN. One is cube on cube, where (200) Ni // (200) TiN // (200) Si and (022) Ni // (022) TiN // (022) Si. The particles grown in this orientation have a trapezoidal morphology in [011] projection. The other involves a 90 ° rotation with respect to [011] direction of TiN matrix (zone axis), where (022) Ni // (200) TiN // (200) Si and (200) Ni // (022) TiN // (022) Si. The particles grown in this rotated orientation have a triangular morphology in [011] projection and a smaller lattice constant compared with that of pure nickel. The possible mechanism of forming these two epitaxial orientations is discussed. Superconducting quantum interference device (SQUID) magnetometer was used for magnetic measurements. In order to investigate the effect of texturing on magnetic properties of nanoparticles, results were compared with those obtained from Ni nanoparticles grown on amorphous Al2O3 matrix layer in previous research. It was found that both blocking temperature and coercivity of Ni nanoparticles grown on epitaxial TiN matrix are significantly higher than that of Ni grown on amorphous Al2O3. The higher value of coercivity is possibly associated with the stronger tendency of crystallographically oriented particles to retain their magnetic moments in the presence of reversing magnetic field.
Substrate Dependence in the Growth of Three-Dimensional Gold Nanoparticle Superlattices
Authors: Sato S. , Yamamoto N. , Yao H. , Kimura K. 
Published: April 2011

ABSTRACTThree-dimensional superlattices consisting of gold nanoparticles were grown at air/suspension or suspension/solid interfaces. The growth of superlattices was found to be strongly dependent on substrate materials: Micrometer-sized superlattices were grown at air/suspension interfaces and upon silver substrates, whereas no growth was observed on silicon, silicon oxide, or amorphous carbon substrates. To explain the observed substrate dependence, Lifshitz theory was used to calculate the Hamaker constants between gold nanoparticle assemblies and substrates through the suspension. Van der Waals interactions estimated from this calculation fully explain the experimental results.
The Effect of Interfacial Viscosity on the Kinetics of Formation of Silver Nanoparticles Using Water-in-Oil Microemulsions as Nanoreactors
Authors: Shah D.O. , Bagwe R.P. , Parmar B.S. 
Published: April 2011

AbstractSilver nanoparticles were prepared by the method of mixing of two microemulsions having similar chemical composition but different reactants in their respective aqueous core. One microemulsion contains silver nitrate in the aqueous core and other contains sodium borohydride. The silver nanoparticles formed were characterized using UV-Visible absorption spectra and TEM micrographs. Effect of chain length of solvent and addition of Arlacel-20 to the AOT/Heptane, AOT/Decane and AOT/Dodecane microemulsion on particle size and absorption spectra of silver nanoparticles was studied. TEM photographs showed agglomerated and bigger particles in case of pure AOT/dodecane whereas addition of Arlacel-20 showed dispersed and smaller particles. Reaction kinetics was observed for silver nanoparticles using UV-visible spectrophotometer. Silver nanoparticles prepared using pure AOT surfactant showed plasmon band (416 nm) immediately after preparation whereas no absorption band of silver nanoparticles was observed for mixed surfactant microemulsion of AOT and Arlacel 20 for few hours indicating the reaction kinetics is slowed down upon addition of Arlacel-20. Growth rate of silver nanoparticles was plotted by monitoring absorption coefficient ratio (ε416/ε475) as a function of time. AOT/heptane system showed slower growth rate as compared to AOT/decane and AOT/dodecane and also larger particle size. Presence of Arlacel-20 significantly decreases the growth rate in all three alkanes and this observation can be explained using the concept of rigidity of surfactant film at the oil/water interface. It is proposed that higher the interfacial viscosity, slower is the coalescence rate of nanodroplets in the microemulsion system, and hence slower the growth rate of particles and smaller is the final particle size.
Size and Composition Effects in the Structure and Properties of Polymer-Protected Bimetallic Particles
Authors: Casanove Marie-José , Lecante Pierre , Fromen Marie-Claire , Respaud Marc , Zitoun David , Pan Cheng , Philippot Karine , Amiens Catherine , Chaudret Bruno , Dassenoy Fabrice 
Published: April 2011

AbstractWe investigate the structural evolution of PtRu and CoRh ultra fine bimetallic particles as a function of their composition in the whole range of stoichiometry. Isolated particles embedded in an organic matrix are synthesized using chemical techniques in mild conditions. Their size, dispersion and structure are analyzed by HRTEM, WAXS and EXAFS techniques. The magnetic behavior of cobalt-based alloys is investigated by SQUID magnetometry. In the PtRu alloys, we demonstrate the role of composition in the structural transition from the face-centered cubic to the hexagonal close packed structure in nanoparticles and detail the mechanism of the transition. We point out the effect of size reduction and core-shell atomic distribution in the structure and the enhanced magnetization in CoRh bimetallic particles.
Ab Initio Molecular Dynamics and Elastic Properties of TiC and TiN Nanoparticles
Authors: Postnikov A. V. , Entel P. 
Published: April 2011

AbstractThe results of first-principles simulations of relaxed ground-state structure and vibrational modes are presented for titanium carbide and titanium nitride clusters of nearly stoichiometric composition and compared to frozen phonon and molecular dynamics calculations for crystalline TiC and TiN. The calculations have been done with the SIESTA method, using norm-conserving pseudopotentials and the basis of strictly localized numerical pseudoatomic orbitals. The dominant vibration mode corresponding to the zone-center TO phonon (14 THz) persists and gets hardened (21 THz) in the small Ti4C4 cluster. The increase of the cluster size to Ti14C13 leads to an enhancement of vibrational density of states in the intermediate range of frequencies, including the phonon band gap of pure crystalline TiC (near 15 THz). Similar trends can be noted for the Ti-N system, with the vibration spectrum slightly scaled upwards but otherwise very close to that of TiC. The clusters studied are yet too small to perform a reliable analysis of acoustic modes.
Controlled and Selective Aggregation of Submicrometer Cu-Crystallites on FIB Sensitized p-Si
Authors: Spiegel Adrian , Schmuki Patrik 
Published: April 2011

AbstractElectrochemical deposition of metals and alloys onto metallic substrates plays an important role in many modern technologies. Usually, a photolithographic patterning process is used to produce the desired feature on the substrate surface. An alternative method to patterned metal deposition on semiconductors is presented here: it is based on changing the electrochemical properties of the semiconductor by controlled surface defect creation. A focused ion beam (FIB) was used to introduce defects into p-Si, followed by a selective electrochemical reaction to produce metal structures in the sub-micrometer range.In this work we study the selective deposition behavior of Cu on FIB sensitized surface locations and show that crystallite growth follows a three- dimensional growth law. Crystallites grow very rapidly in a first phase and reach a size of roughly 200nm after 5s. Factors determining nucleation, growth, and coalescence of metal clusters are identified and investigated.
Microstructure of Physical Vapour Deposited Ti-Si-N Coatings
Authors: Kauffmann Florian , Dehm Gerhard , Arzt Eduard , Schier Veit , Henke Sascha , Schattke Alaexander , Beck Thomas 
Published: April 2011

AbstractThe influence of Si on the microstrucure of Ti-Si-N coatings was studied, since it controls the mechanical properties of the coatings. At low Si-contents columnar {111}-textured TiN grains form. Increasin the Si-content to >4at% causes a transition to equiaxed {200}-textured TiN grains. The equiaxed TiN grains reveal grain diameters of ∼6 nm for coatings containing 11 at% Si.
Formation of Ferromagnetic FePt Nanoparticles by Ion Implantation
Authors: White C. W. , Withrow S. P. , Budai J. D. , Boatner L. A. , Sorge K. D. , Thompson J. R. , Beaty K. S. , Meldrum A. 
Published: April 2011

AbstractOriented ferromagnetic FePt nanoparticles with the face-centered tetragonal L10 structure were produced in Al2O3 single crystal hosts by ion implantation and annealing. Both the orientation and particle-size of the FePt particles depend strongly on the implantation conditions. The magnetic coercivities are extremely high, reaching values in excess of 20 kOe for Pt concentrations of ∼45% in the FePt alloy. Ferromagnetic FePt nanoparticles were also produced in amorphous SiO2 by ion implantation and annealing.
Characterizations of Nanostructured Films as Responsive Electrode Materials
Authors: Kariuki Nancy , Luo Jin , Moussa Laura , Israel Lisa B. , Zhong Chuan-Jian , Hepel Maria 
Published: April 2011

AbstractNanostructured thin films were assembled as metal-responsive electrode materials from monolayer-capped gold nanoparticles (2 nm) and carboxylic acid functionalized alkyl thiol linkers via an exchange-crosslinking-precipitation reaction pathway. The network assemblies have open frameworks in which void space forms channels or chambers with the nanometer sized cores defining its size and the shell structures defining its chemical specificity. Such nanostructures were investigated as responsive materials for the detection of metal ion fluxes. Cyclic voltammetry, in-situ electrochemical quartz-crystal nanobalance, and surface infrared reflection spectroscopy techniques were used to characterize the interfacial redox reactivity and mass fluxes at the nanostructured electrode materials. The system showed remarkable reversible mass loading arising from incorporation of ionic species into the film. The diagnostic stretching bands of the carboxylic and carboxylate groups at the shell allowed the identification and assessment of the interfacial carboxylate-metal ion reactivity.
Microstructure and Magnetic Properties of Fe(C) and Fe(O) Nanoparticles
Authors: Sun Xiang-Cheng , Nava N. , Reyes-Gasga J. 
Published: April 2011

AbstractTwo types of iron (Fe) nanoparticles, carbon-coated Fe nanoparticles (Fe(C)) and pure α-Fe nanoparticles that coated with oxide layers (Fe(O)), have been successfully synthesized using modified graphite arc-discharge method. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM) and electron diffraction (SAED) analysis have been used to characterize these distinct structural morphologies. It is indicated that those two Fe nanoparticles have an average grain size of 15-20nm. The presence of carbon encapsulated α-Fe, γ-Fe and Fe3C phases are clearly identified by X-ray diffraction and SAED patterns in those Fe(C) particles. However, the evidence of pure α-Fe nanocrystal coated with oxide layer is also revealed by HR-TEM images and SAED patterns in these Fe(O) particles.Mössbauer spectra and hyperfine magnetic fields at room temperature for the assemblies of Fe(C) and Fe(O) nanoparticles further confirm their distinct nanophases that detected by XRD analysis and HRTEM observation. Specially, the assemblies of Fe(O) nanoparticles exhibit ferromagnetic properties at room temperature due to the stronger interparticle interaction and bigger magnetocrystalline anisotropy effects among these Fe(O) nanoparticles. Moreover, modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles, which is attributed to the nanocrystalline nature of the carbon-coated nanoparticles.
Carbon-Nanofibre-Filled Thermoplastic Composites
Authors: Sandler Jan , Shaffer MiloS.P. , Lam Yeng-Ming , Windle Alan H. , Werner Philipp , Altstädt Volker , Nastalczyk Jacek , Broza Georg , Schulte Karl , Keun Christian-André 
Published: April 2011

AbstractMacroscopic poly(ether ether ketone) (PEEK) and polypropylene (PP) nanocomposites containing vapour-grown carbon nanofibres (CNF) were produced using standard polymer processing. Tensile tests revealed a linear increase in composite stiffness with nanofibre content. A detailed DSC study verified that under standard processing conditions the degree of crystallinity and the crystalline structure of these semicrystalline thermoplastics were not affected by the nanofibres. Nevertheless, we provide evidence that the nanoscale filler can alter the polymer morphology under certain conditions, an effect which needs to be considered when evaluating nanocomposite properties. Given the absence of morphological changes in the standard nanocomposites we were able to calculate the intrinsic nanofibre modulus using short fibre theory; both distinctively different matrix systems show a similar effective nanofibre modulus.
Fabrication and Characterization of Carbon Nanotube Field Emitters
Authors: Jiao Jun , Dong Lifeng , Tuggle David W. , Mosher Catherine L. , Foxley Sean , Tawdekar Jaswant 
Published: April 2011

AbstractWe report an effective procedure for fabricating carbon nanotube emitters by directly synthesizing carbon nanotubes on an electrochemically sharpened tungsten tip. The nanotubes adhere very well to the tip of tungsten without any painting materials. Thermal cleaning of the tungsten tip under applied electric field reduced the number of nanotubes formed on the tip resulting in a single nanotube emitter. Electron field emission properties were investigated by employing a field emission microscope with a base pressure ~ 1 × 10-9 Torr. The emission images with respect to the applied field and time were obtained. Different emission images consisting of one to four lobes at different applied fields were observed. The characteristic of the emission current vs. applied voltage was analyzed. Applied potentials up to 3000 V were tested. The estimated field on the emitter was on the order of several tens of volts per nanometer. Our investigation suggests that at lower fields, the I-V characteristic of the nanotube emitter follows Fowler-Nordheim (F-N) emission behavior. At higher applied field, current saturation was observed.
Pneumatic Actuator Response from Carbon Nanotube Sheets
Authors: Spinks Geoffrey M. , Wallace Gordon G. , Fifield Leonard S. , Dalton Larry R. , Mazzoldi Alberto , Rossi Danilo De , Khayrullin Ilyas I. , Baughman Ray H. 
Published: April 2011

AbstractReversible actuation strains in excess of 2% in the sheet direction and over 300% in the thickness direction have been produced by single wall carbon nanotube mats when electrochemically charged to +1.5V (vs. SCE) in aqueous sodium chloride solution. The observed strains represent a ten-fold increase over that previously reported for carbon nanotube actuators, and is considerably larger than that achievable with polymer ferroelectric actuators. The enhanced actuator strains result from a new mechanism of electrochemically induced “pnuematic actuation” where high pressure gas forms within the porous structure of the nanotube mat causing partial delamination and swelling. An erasable “memory” effect was also observed for pneumatic actuation driven by hydrogen gas evolution/storage in the nanotube electrodes.
Focused Electron Beam Induced Deposition of High Resolution Magnetic Scanning Probe Tips
Authors: Utke I. , Cicoira F. , Jaenchen G. , Hoffmann P. , Scandella L. , Dwir B. , Kapon E. , Laub D. , Buffat Ph. , Xanthopoulos N. , Mathieu H.J. 
Published: April 2011

AbstractApexes of commercial pyramidal silicon scanning microscopy tips were magnetically functionalized by means of local focused electron beam induced deposition. High aspect ratio supertips and local tip coatings with varying apex diameters can be produced by varying exposure time, beam current, and scan mode. The carbonyl precursor Co2(CO)8 was used as source of magnetic metal. Tip performance was tested with magnetic force microscopy (tapping / lift-retrace mode) and magnetically actuated cantilever atomic force microscopy. The deposit contains 34±2 at.% Co, dispersed as 2-5 nm metal nanocrystals in a carbonaceous matrix. Specific surface reactions and Boudouard reactions are proposed to explain the resulting deposit composition measured by Auger spectroscopy. The electrical resistivity is 104 higher than bulk Co resistivity.
Atomistic Study of Mechanical Properties of Carbon Nanotubes
Authors: Narita T. , Shintani K. 
Published: April 2011

AbstractThe mechanical properties of single-walled carbon nanotubes are investigated by means of molecular dynamics simulations. The Tersoff-Brenner potential is used for the calculation of the interatomic forces. Two kinds of simulation cells are considered; one adopts the periodic boundary condition along the tube axis and the other corresponds to tube clusters. The atoms at the ends of a simulation cell are translated along its axis, and the Young's modulus and Poisson's ratio are estimated. How these mechanical properties of carbon nanotubes depend on their chiralities is discussed.
Effect of Solvent Quality on the Friction Forces Between Polymer Brushes
Authors: Forster Aaron M. , Kilbey S. Michael 
Published: April 2011

ABSTRACTWe have used the surface forces apparatus to measure the structural and frictional force profiles between opposing, solvated brush layers as a function of temperature. Two different polyvinylpyridine-polystyrene [PVP-PS] diblock copolymers were used to make PS brushes. The molecular weights (in thousands) of these PVP-PS materials were [114/103]k, [30/70]k, respectively. Structural and frictional force profiles in toluene and cyclohexane were measured, and the cyclohexane experiments were conducted at temperatures ranging from the theta-point to 50 C. In toluene the PS brushes needed to be compressed to ∼1/5th of their equilibrium height before frictional forces were measured, but this onset of frictional forces was detected at a much lower level of compression in near-theta cyclohexane. In cyclohexane the structural force profiles were basically insensitive to the temperature change, but the frictional forces depended strongly on the solvent temperature. When the cyclohexane temperature was raised, the onset of frictional forces decreased toward the good-solvent onset. We also discuss the dependence of frictional force on shearing parameters.
Photonic Crystals at Near-Infrared and Optical Wavelengths
Authors: Moroz Alexander 
Published: April 2011

ABSTRACTAs demonstrated for the example of a diamond and zinc blende structure of dielectric spheres, small inclusions of a low absorbing metal with the volume fraction can have a fm dramatic effect on a complete photonic band gap (CPBG) between the 2nd-3rd bands. For example, in the case of silica coated silver spheres, the CPBG opens for 1:1% and fm exceeds 5% for 2:5%. Consequently, any dielectric material can be used to fabricate fm a photonic crystal with a sizeable and robust CPBG in three dimensions. Absorption in the CPBG of 5% remains very small ( 2:6% for 750 nm). The structure enjoys almost perfect scaling, enabling one to scale the CPBG from microwaves down to ultraviolet wavelengths.
A Theoretical Study of Structural Disorder and Photoluminescence Linewidth in InGaAs/GaAs Self Assembled Quantum Dots
Authors: Lin Yih-Yin , Jiang Hongtao , Singh Jasprit 
Published: April 2011

ABSTRACTThe past few years have seen considerable efforts in growth and device application of self-assembled quantum dots. However, the photoluminescence (PL) linewidth, which represents structural fluctuations in dot sizes, is still in the range of 30-50 meV. This large linewidth has deleterious effects on devices such as lasers based on self-assembled dots. In this paper we will examine the configuration-energy diagram of self-assembled dots. Our formalism is based on: (1) an atomistic Monte Carlo method which allows us to find the minimum energy configuration and strain tensors as well as intermediate configurations of dots; (2) an 8-band k p method to calculate the electronic spectra. We present results on the strain energy per unit cell for various distributions of InAs/GaAs quantum dots and relate them to published experimental results. In particular we examine uncovered InAs/GaAs dots and show that in the uncovered state a well-defined minimum exists in the configuration energy plot. The minimum corresponds to the size that agrees well with experiments.
InAs Quantum Dots in AlAs/GaAs Short Period Superlattices: Structure, Optical Characteristics and Laser Diodes
Authors: Tokranov Vadim , Yakimov M. , Katsnelson A. , Dovidenko K. , Todt R. , Oktyabrsky S. 
Published: April 2011

ABSTRACTThe influence of two monolayer - thick AlAs under- and overlayers on the formation and properties of self-assembled InAs quantum dots (QDs) has been studied using transmission electron microscopy (TEM) and photoluminescence (PL). Single sheets of InAs QDs were grown inside a 2ML/8ML AlAs/GaAs short-period superlattice with various combinations of under- and overlayers. It was found that 2.4ML InAs QDs with GaAs underlayer and 2ML AlAs overlayer exhibited the lowest QD surface density of 4.2x1010 cm-2 and the largest QD lateral size of about 19 nm as compared to the other combinations of cladding layers. This InAs QD ensemble has also shown the highest room temperature PL intensity with a peak at 1210 nm and the narrowest linewidth, 34 meV. Fabricated edge-emitting lasers using triple layers of InAs QDs with AlAs overlayer demonstrated 120 A/cm2 threshold current density and 1230 nm emission wavelength at room temperature. Excited state QD lasers have shown high thermal stability of threshold current up to 130°C.
Fabrication and Properties of Self-Assembled Nanosized Magnetic Particles
Authors: Salazar-Alvarez G. , Mikhailova M. , Toprak M. , Zhang Y. , Muhammed M. 
Published: April 2011

ABSTRACTThe 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).