bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solution-Based Synthesis of Magnesium Oxide Nanorods
Authors: Wei Q. , Lieber C.M. 
Published: April 2011

ABSTRACTA solution-based synthesis route was developed to produce large quantities of MgO nanorods. Hydrated basic magnesium chloride, which has needle-like crystal structure, was used as a precursor. A subsequent two-step transformation process with magnesium hydroxide as an intermediate product was used to preserve the morphology of the precursor to yield magnesium oxide nanorods. Scanning electron microscopy, powder X-ray diffraction and energy dispersive X-ray spectroscopy show that the products are very pure (>95%) crystalline MgO nanorods with diameters from 40 nm to 200 nm and lengths 10 microns or longer. High-resolution transmission electron microscopy and electron diffraction further reveal that these MgO nanorods are single crystals and that the rod axis is along the <110> crystal direction. A model for the structural transformation from hydrated basic magnesium chloride to magnesium oxide has been developed and compared to our experimental results. This solution-based process can be easily scaled-up, and is a low-cost source of pure magnesium oxide nanorods needed in many industrial applications, for example, as reinforcing agents in matrix composites and as flux-pinning centers in high-TC superconductors.
Preparation of Aerogel and Xerogel Nanocomposite Materials
Authors: Casula M.F. , Corrias A. , Paschina G. 
Published: April 2011

ABSTRACTSol-gel method was used to prepare nickel oxide-silica and iron oxide-silica nanocomposites materials in form of aerogels and xerogels. The samples were characterized by thermal analysis, X-ray diffraction, N2 physisorption and transmission electron microscopy techniques. The variation of the supercritical solvent extraction conditions gives rise to differences in the morphological characteristics of the aerogels. These differences influence the size of the nickel oxide nanoparticles in nickel containing aerogels. On the other hand they do not affect the structure and size of the iron oxide nanoparticles in iron containing aerogels. The differences between the xerogel and aerogel nanocomposites are discussed.
Superparamagnetic Ferrites Realization and Physical Obstacles
Authors: Vollath D. , Pellegrin E. , Szabó D. V. 
Published: April 2011

ABSTRACTIn superparamagnetic materials, the change of the direction of the magnetization is not associated with the movement of Bloch walls, but with thermal fluctuation of the magnetization vector. Therefore, the resonance frequency of the Bloch walls is no longer limiting the maximum frequency for applications. The limit found in superparamagnetic materials is given by the frequency of electron spin resonance. This behavior was verified for spinelle type ferrites made of ceramic or polymer coated oxide nanoparticles produced by the microwave plasma process. By selecting the composition of the spinelle type ferrites the energy of magnetic anisotropy controlling the susceptibility and the maximum frequency for applications can be adjusted. Superparamagnetic materials have their frequency limit beyond 2 GHz. Coating of the particles reduces dipole – dipole interaction destroying superparamagnetism. Even when the susceptibility is in the order of magnitude of today's commercial ferrites, the saturation magnetization is found to be smaller than the theoretically expected value. This phenomenon is partly clarified by soft X-ray magnetic circular dichroism (SXMCD) measurements, showing a significant orbital magnetic moment anti arallel to the direction of the spin moment. Additionally, it was found that the amount of Fe2+ ions is possibly larger than expected by thermodynamic data of bulk materials.
Ultrasonic Force Microscopic Characterization of Nanosized Copper Particles
Authors: Schumaker E. J. , Shen L. , Ruddell M. J. , Sathish S. , Murray P. T. 
Published: April 2011

ABSTRACTAn Ultrasonic Force Microscope capable of imaging elastic modulus variations with nanometer resolution has been developed by modifying a Scanning Probe Microscope. Images of ultrasonic properties have been simultaneously obtained with the topography images. The technique has been utilized to characterize nanoscale copper droplets and grains deposited on a quartz substrate by ionized cluster beam deposition. Images of the same region obtained with atomic force microscope, lateral force microscope, and ultrasonic force microscope are compared. The origin of image contrast in ultrasonic force microscopy and its utilization for quantitative elastic property measurement of nanometer particles are discussed.
Dielectric Characterization of Thin Films Consisting of Tin Doped Indium Oxide Nanoparticles
Authors: Hultåker A. , Niklasson G. A. 
Published: April 2011

ABSTRACTIn recent years there has been a growing interest in cheap and easy production techniques for transparent conducting thin films. One way of making these uses a nanoparticle dispersion. We prepared thin films of tin doped indium oxide by spin-coating of a solution of nanoparticles. The sintering behavior of these ceramic particles was studied by dielectric spectroscopy and by grazing incidence X-ray diffraction. The grain growth was found to start at 1000°C and to be prominent at 1250°C. However, the electrical conductivity reached a maximum below these temperatures.
Z-Contrast Stem Imaging and Eels of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces
Authors: Kadavanich A.V. , Kippeny T. , Erwin M. , Rosenthal S. J. , Pennycook S. J. 
Published: April 2011

ABSTRACTWe have applied Atomic Number Contrast Scanning Transmission Electron Microscopy (Z-Contrast STEM) and STEMIEELS (Electron Energy Loss Spectroscopy) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. Z-Contrast images are direct projections of the atomic structure. Hence they can be interpreted without the need for sophisticated image simulation and the image intensity is a direct measure of the thickness of a nanocrystal. Our thickness measurements are in agreement with the predicted faceted shape of these nanocrystals.Our unique 1.3Å resolution STEM has successfully resolved the sublattice structure of these CdSe nanocrystals. In [010] projection (the polar axis in the image plane) we can distinguish Se atom columns from Cd columns.EELS measurements on individual nanocrystals indicate a significant amount (equivalent to 0.5-1 surface monolayers) of oxygen on the nanocrystals, despite processing in an inert atmosphere. Spatially resolved measurements at 7Å resolution suggest a surface oxide layer.
Nanoporous Alumina Films Prepared from Colloidal Solution
Authors: Petrovsky Vladimir , Anderson Harlan U. , Petrovsky Tatiana 
Published: April 2011

ABSTRACTAlumina layers were deposited by spin coating and dip coating on different substrates (Pt, Si, Al2O3) from the water suspension of nanosize boehmite particles. It was shown, that addition of the butoxyethanol in the suspension improves wetting and the quality of the film. No separation from the substrate or cracking of the film took place up to 1000°C on all types of the substrates for the film thickness up to 10μm. Because of the minimal shrinkage, the coating can be used to smooth rough substrates as well as provide interfacial layers for either single layer or multilayer structures.
Optical Properties of Nanocrystalline Silicon Films with Different Deposition Temperatures
Authors: Ali A. M. , Inokuma T. , Kurata Y. , Hasegawa S. 
Published: April 2011

AbsrtactNanocrystalline silicon (nc-Si) films were deposited on fused quartz and single (100) crystal Si substrates by plasma-enhanced chemical vapor deposition from a SiH4-H2 mixture at various deposition temperatures, Tδ. The effects of plasma-assisted hydrogenation at 300°C on the optical and structural properties were examined for the nc-Si films. The film deposited at Tδ = 730°C exhibits photoluminescence (PL) in its as-deposited state, but the intensity of PL decreases after hydrogenation. We find that a correlation between the PL intensity and infrared absorption bands at around 850 and 1000 cm−1.
Synthesis and Characterization of Resorcinarene-Encapsulated Nanoparticles
Authors: Wei Alexander , Stavens Kevin B. , Pusztay Stephen V. , Andres Ronald P. 
Published: April 2011

ABSTRACTA new strategy for stabilizing inorganic nanoparticles in nonpolar solutions is described. Resorcinarenes 1-3 were synthesized and evaluated as surfactants because of their large concave headgroups with multiple contact sites. Au nanoparticles ranging from 3-20 nm in diameter were generated in the vapor phase and dispersed into dilute hydrocarbon solutions of 1-3, where they were stabilized for up to several months. Chemisorption is most likely mediated by multiple Au-O interactions, as indicated by several control experiments and by surface-enhanced Raman spectroscopy. The resorcinarenes were readily displaced by dodecanethiol, which resulted in the precipitation of particles >5 nm as determined by absorption spectroscopy and transmission electron microscopy. This suggests that the mobility of the resorcinarene tailgroups are important for maintaining the larger nanoparticles in a dispersed state. Resorcinarene surfactants with stronger chemisorptive properties are currently being explored.
Synthesis, Characterization, and Utilization of Single Crystalline Nanoparticles of Silver
Authors: Yin Yadong , Zhong Ziyi , Gates Byron , Xia Younan 
Published: April 2011

ABSTRACTThis paper describes a procedure based on the Tollens' process for preparing crystalline nanoparticles of silver with well-controlled, uniform sizes. The starting reagents are similar to those commonly used for electroless deposition of silver and are commercially available from the Peacock Laboratories (Philadelphia, PA). Only under appropriate conditions, mixing of these reagents was able to generate stable dispersions of silver colloids, rather than thin films of silver coated on surfaces of objects immersed in the solution (including the inner surface of the container). We have demonstrated the capability and feasibility of this method by forming stable dispersions of highly monodispersed, single crystalline colloids of silver with dimensions in the range of 20-50 nm.
Identification of Shape Transitions in Coherent Ge/Si Islands Using Transmission Electron Microscopy
Authors: Liu Chuan-Pu , Henstrom William L. , Cahill David G. , Gibson J. Murray 
Published: April 2011

AbstractAs a consequence of strain relaxation, Ge coherent islands on Si(001) substrates evolve to different shapes as islands grow. By measuring the size and the strain simultaneously in a large population of individual islands using two simple and robust plan-view transmission electron microscopy-based techniques, we can identify island shapes easily because island shape is a function of strain. We briefly introduce the mechanisms of these two techniques. We then show that there is a metastable shape of Ge islands involved in the shape transition between pyramids and domes. The strain relaxation changes discontinuously as islands grow from pyramids to the metastable form and then finally to domes indicating that the shape transition between pyramids and domes is first order. We also show that the shape of this metastable island is a truncated dome and the faceted planes are {103}.
Surfactant Effects on Ordering in GaInP Grown by Omvpe
Authors: Stringfellow G. B. , Fetzer C. M. , Lee R. T. , Jun S. W. , Shurtleff J. K. 
Published: April 2011

AbstractCuPt ordering in III/V semiconductor alloys is significant because of the dependence of bandgap energy on degree of order. This paper presents the effects of surfactants isoelectronic with P on ordering in GaInP grown by organometallic vapor phase epitaxy. Each of the three surfactants studied, As, Sb, and Bi, is found to result in disordering for layers grown using conditions that would otherwise produce highly ordered materials. The amount of surfactant required in the vapor phase (as the organometallic precursors TMAs, TESb, and TMBi) increases as the volatility of the group V element increases. Thus, the amount of TEAs required to produce disordered GaInP is approximately two orders of magnitude greater than for TMBi.For Sb, the disordering is shown to be caused by a replacement of [110 ] P dimers on the nominally (001) surface by Sb dimers with the same orientation. For Bi, a marked change in the step structure coincides with the loss of order. For singular (001) substrates, island formation is suppressed by Bi.
Spatially Resolved Photoluminescence in Spontaneously-ordered GaInP2
Authors: Smith S. , Mascarenhas A. , Olson J. M. , Kazmerski L. L. 
Published: April 2011

AbstractThe low-temperature (5K) photoluminescence (PL) of partially-ordered GaInP2 is spatially resolved using high-resolution (from ˜ 0.2μm-0.7μm) scanning optical microscopy, revealing the spatial variation in band gap energy and the spatial origin of the ordering-induced low-energy emission and the associated ‘quantum-dot-like’ narrow spikes which appear when examining areas smaller, or of comparable size, than a single ordered domain. The large number of spectra taken within a micronsized area allow a detailed look at the statistical variation in band-gap energy and lineshape. A systematic study of a series of samples where the order parameter varies from η ˜ 0 to 0.45 shows that for the most highly-ordered samples, the statisitical distribution of excitonic energy and linewidth show evidence of exciton localization, which is also clearly seen by examining the spatial maps of the excitornic energy and linewidth extracted from the measured spectra.
Electronic and Optical Properties of Orientational Superlattices in Gainp Alloys
Authors: Zhang Yong , Fluegel B. , Ahrenkiel S. P. , Friedman D. J. , Geisz J. F. , Olson J. M. , Mascarenhas A. 
Published: April 2011

AbstractWe demonstrate the formation, and the electronic and optical properties of a novel type of semiconductor superlattice in spontaneously ordered GaInP alloys. The most frequently observed ordered structure in MOCVD grown GaInP has CuPt symmetry where the ordering directions occur in the two [111]B directions, corresponding to two distinct ordered variants. A new type of superlattice, termed an orientational superlattice, emerges as the ordered domains are stacked in a sequence whereby the ordering direction switches alternatively from the [111] direction in one domain to the [111] direction in the next domain. The novelty of this type of superlattice lies in that there is neither a band-gap nor an effective mass discontinuity along the superlattice axis. When the GaInP epilayer is grown on an exact (001) or [111]A tilt GaAs substrate, the two ordered variants are equally favorable. Thus, ordered domain twins appear in ordered GaInP epilayers. We present a comparitive study between the single-variant ordered structure and the double-variant ordered superlattice structure, using TEM and time-resolved differential absorption. We show that for a same order parameter, the band-gap of an orientational superlattice is higher than that of a single-variant ordered structure, and the in-plane optical anisotropy between the [110] and [110]B directions is greatly enhanced due to the superlattice effect. The experimental results are explained in terms of the band structure of the orientational superlattice.
Finite Carrier Confinement and Biexcitonic Complexes in Self-Assembled Inas Quantum Dots
Authors: Jaeger A. , Mankad T. , Schoenfeld W. V. , Lundstrom T. , Petroff P. M. 
Published: April 2011

AbstractThe luminescence properties of a single lnAs self-assembled quantum dot (QD) are studied by confocal scanning optical microscopy at low temperature. The observation of single QDs has been accomplished by epitaxial growth of QDs samples with low QD density (less than one QD per μm2) required by the diffraction limited spatial resolution of the microscope. In thick QDs with large confinement energies biexciton binding energies of up to 5.0 meV are found, while in thin and more weakly confined QDs the electron wavefunction penetrates into the surrounding barriers causing reduced biexciton binding energies of less than 2.0 meV. This result can be understood in terms of theoretical calculations of biexcitonic complexes in QDs with finite potential barriers.
Quenching Effects in Scanning Tunneling Microscopy Studies of Epitaxial Growth
Authors: Bell G. R. 
Published: April 2011

AbstractThe experimental aspects of rapid-quench scanning tunneling microscopy are discussed. In particular, the effects of sample quenching are investigated in atomic-scale studies of the molecular beam epitaxial growth of GaAs. Implications for the study of the heteroepitaxial system InAs-GaAs are discussed.
Tem Investigation of Self-Organized Pbse Quantum Dots as a Function of Spacer Layer Thickness and Growth Temperature
Authors: Kang H. H. , Salamanca-Riba L. , Pinczolits M. , Springholz G. , Holy V. , Bauer G. 
Published: April 2011

AbstractThe study of the morphology, lateral and vertical correlation of self-organized PbSe quantum dots in Pb1−xEux Te is presented. The samples consist of quantum dot superlattices of n periods of (PbSe/Pb1−xEux Te) grown on PbTe/(111) BaF2 by the S-K mode using MBE. The Pb1−xEux Te spacer thickness was varied from 34.3nm to 312nm and the growth temperature was varied between 335°C and 380°C. Our TEM results show very good lateral and vertical correlation of the dots. The dots form an array with either a/b/c/a/b/c/... or a/a/a/... vertical stacking sequence along the [111] growth direction. The stacking sequence is accurately controlled by the thickness of the Pb1−xEux Te spacer layer thickness and the growth temperature. The best a/b/c/... spatial correlation was obtained for temperatures around 380°C and spacer thickness of ˜40nm. The dots are highly strained and form triangular pyramids with (111) bases and (100) facets as observed by AFM. The shape of the dots also varied with the Pb1−xEux Te spacer thickness. An analysis of the spatial correlation of the dots' size and shape with respect to spacer thickness and growth temperature is presented.
Gate Technology Issues for Silicon Mos Nanotransistors
Authors: Tennant D. M , Timp G. L. , Ocola L. E. , Green M. , Sorsch T. , Komblit A. , Klemens F. , Kleiman R. , Muller D. A. , Kim Y. , Timp W. 
Published: April 2011

AbstractThis article reviews technology issues in scaling conventional planar transistors to a physical gate length of 30nm that are expected to produce an effective channel length of 10 nm. Gate fabrication features direct write e-beam lithography to form a ring structure capable of exploring the practical limits of gate processing while requiring only a single level of lithography. Other processing elements include ultra-thin gate dielectric formation (∼ 0.6nm); highly selective transformer coupled plasma (TCP) etching; and low energy ion implantation. DC electrical results obtained for high performance n-MOS and p-MOS type nanotransistors made using this process are discussed as are simulations of sub-threshold currents for n-MOS transistors with physical gate lengths down to 26nm
Spm Based Lithography for Nanometer Scale Electrodes Fabrication
Authors: Notargiacomo A. , Giovine E. , Cianci E. , Foglietti V. , Evangelisti F. 
Published: April 2011

AbstractScanning probe assisted nanolithography is a very attractive technique in terms of low-cost, patterning resolution and positioning accuracy. Our approach makes use of a commercial atomic force microscope and silicon probes to build simple nanostructures, such as metal electrode pairs, for application in novel quantum devices.Sub-100 nm patterning was successfully performed using three different techniques: direct material removal, scanning probe assisted mask patterning and local oxidation.
The Mechanism of Mixed-Mode Phase Transformations
Authors: Pond R. C. , Shang P. , Cheng T. T. , Aindow M. 
Published: April 2011

ABSTRACTThe topological theory of interfacial defects and the associated flux analysis are reviewed. It is shown that the shears and diffusive fluxes associated with the motion of disconnections can be determined directly from their crystallographic characteristics, and that the effects of changes in chemical composition, interfacial misfit and ordering can be incorporated into the analysis. The special conditions are identified for which there is conservation of atomic sites during the motion of disconnections. It is shown that, under these circumstances, disconnection motion may result in mixed-mode displacive-diffusive transformations whereby diffusion is required for the transformation to proceed but the interfaces exhibit crystallographic characteristics which one would normally associate with a martensitic transformation. It is shown that the growth of γ lamellae in TiAl-based alloys is an example of such a mixed-mode transformation.
Biaxial Zero Creep Measurements of Interface Energies in Ni/Ag Multilayers
Authors: Lewis A. C. , Mann A. B. , Josell D. , Tapson J. , Weihs T. P. 
Published: April 2011

ABSTRACTBiaxial zero creep experiments were performed on Ni/Ag multilayer films on sapphire substrates. The equilibrium curvature was measured using a scanning laser and position sensitive photodetector. The experiments were designed to measure the free energy of Ni/Ag interfaces and to investigate their effect on the structural stability of multilayered materials. For the Ni/Ag multilayers studied, significant plastic straining occurs at temperatures above 400°C, enabling the growth stresses and thermal stresses in the multilayers to decay to zero. After a long time at elevated temperatures, the equilibrium curvature is reached for the film/substrate couple. This curvature is determined by the number and the energy of the Ni/Ag interfaces. Using this equilibrium technique, a free energy of 0.44 ± 0.03 N/m was measured for Ni/Ag interfaces at an equilibrium temperature of 550°C.
The Critical Stress for Transmission of a Dislocation Across an Interface: Results From Peierls and Embedded Atom Models
Authors: Anderson P. M. , Rao S. , Cheng Y. , Hazzledine P. M. 
Published: April 2011

ABSTRACTA continuum Peierls model of a screw dislocation being pushed through an interface and an atomistic EAM study of dislocation transmission across a [0 0 1] Al-Ni interface suggest that core spreading into the interface and misfit dislocations in the interface are both potent effects that can significantly increase barrier strength of interfaces.
Thermodynamics and Kinetics of Interfacial Decohesion
Authors: Mishin Y. , McMahon C. J. , Bassani J. L. , Sofronis P. 
Published: April 2011

ABSTRACTThermodynamic and kinetic aspects of interfacial decohesion are analyzed for a uniform separation along an interface subjected to a uniform tensile stress normal to the interface. During the separation process, an embrittling impurity can penetrate into the interface and reduce its cohesive strength. Rice(1976) and Hirth and Rice (1980) analyzed this process in great detail, and in particular considered two limiting cases: slow separation (constant chemical potential of the impurity) and fast separation (constant impurity concentration). Our work extends their analysis to intermediate, time-dependent situations, which correspond to the problem at hand. A phenomenological model is introduced to describe the free energy of the interfacial “solid solution”, stress-separation curves as functions of the impurity concentration, and kinetics of separation. The observed separation kinetics, as well as the work of decohesion, cohesive strength and other interfacial properties, depend on the interrelation between the strain rate and the impurity diffusion rate. An equation of stress-driven diffusion along the interface is derived, and the origin of the stress effect on diffusion is analyzed.