bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed laser deposition and characterization of LiMn2O4thin Films for applications in Li Ion rechargeable battery systems
Authors: Singh D. , Houriet R. , Vacassy R. , Hofinann H. , Craciun V. , Singh R.K
Published: April 2011

Most studies focused on fundamental aspects of cathode materials in lithium ion battery employ porous electrodes, which are made of polymer bonded transition metal oxide powders mixed with conductors such as carbon. However, the powder morphology and the presence of carbon and polymeric binders affect the physical, chemical and electrochemical behaviors significantly. Therefore, transition metal oxide based materials in thin film form, which are dense and contain no additives, are emerging as promising alternatives to study fundamental properties in lithium ion batteries. Pulsed laser ablation (PLD) was used to deposit highly textured thin and thick porous films of LiMn2O4. Effect of various parameters such as substrates and deposition conditions were studied on the microstructure of these films. Microstructure studies of these films were carried out using x-ray diffraction and scanning electron microscopy. The electrochemical measurements were carried out in a glove box using cyclic voltammetery, electrochemical cycling and AC Impedance spectroscopy in a half-cell configuration with lithium metal as an anode and reference electrode and LiMn2O4film as a cathode. Results indicate differences in film morphology greatly effect electrochemical kinetics of Li intercalation and de-intercalation. Thin films show good electrochemical characteristics such as high rate capability, good coulombic efficiency and rechargeability till 400 cycles.
Self-Assembly of Meso- and Nanoparticles into 3d Ordered Arrays and its Applications
Authors: Gates Byron , Xia Younan
Published: April 2011

This presentation describes a simple and practical method for self-assembling meso- and nanoparticles into three-dimensionally ordered lattices (opals) over large areas, and the use of these lattices as templates in fabricating highly ordered porous structures such as inverse opals. This method has been applied to a variety of colloidal particles, including silica colloids and polymer beads with diameters in the range of˜50 nm to ˜50 μm. Templating against the 3D opaline lattices provides an effective route to inorganic-organic composite materials and inverse opals having 3D periodic structures.
Formation And Hydrolytic Stabilty Of Oxygen Bridged Heterometal Bonds (Si-O-Ti, Si-O-Zr, Si-O-Ta) In Sol - Gel Materials
Authors: Nacken M. , Hoebbel D. , Schmidt H.
Published: April 2011

Glycidoxypropyltrimethoxysilane (GPTS) and metal alkoxides are frequently used in preparation of heterometal hybrid polymers and find application e. g. as contact lens materials and hard coatings on polymers. Such materials require a high homogeneity of the structural unit at the molecular level, which is supported by the formation of oxygen bridged heterometal bonds and their hydrolytic stability. By means of 29Si and 17O NMR the formation of heterometal bonds like Si-O-Ti, Si-O-Zr, Si-O-Ta was evidenced in GPTS-hydrolysates with Ti(OEt)4, Ti(OEt)3AcAc, Zr(OBun)4, Zr(OBun)3AcAc, Ta(OEt)5 or Ta(OEt)4AcAc (AcAc = acetylacetone ligand) as additives. Signals of heterometal bonds can be detected in 17O NMR spectra in the range of 170 to 350 ppm and are characterized in 29Si NMIR spectra by defined chemical shifts to low (Si-O-Ta) and high magnetic fields (Si-O-Ti, Si-O-Zr) in comparison with signals of Si-O-Si bonds. The use of AcAc modified metal alkoxides leads to well resolved 29Si NMR spectra, which make the distinction between homo- and heterocondensed species easier. The addition of water to the sols (2 H2O / alkoxy group) leads to a degradation of heterometal bonds in favour of more homocondensed species, which reduces the homogeneity of such hybrid materials at the molecular level.
In Situ Intercalation/Polymerization of Melanin into Vanadium Pentoxide
Authors: Oliveira H. P. , Zanta C. L. P. S. , Galina A. C. , Graeff C. F. O.
Published: April 2011

In this work, intercalated material was prepared consisting of a regular interchange of organic/inorganic layers. The products were obtained by reacting 3,4-dihidroxi-fenilalanina (DL-DOPA) in a solution with V2O5.nH2O gel, which suffered an oxidative polymerization/intercalation process, forming a film with a dark blue metallic color. The films were characterized using UV\Vis transmission spectroscopy, FTLR, ESR, X-ray diffraction, dc conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved but the inter-planar space increase from 1.18 nm to 1.38 nm. The FTIR and ESR spectra confirms that the V2O5 structure is preserved, however the presence of melanin induces the reduction of Vv ions to Viv. The increase in the inter-planar spacing is observed to increase the stability and reproducibility of the electrochemical insertion/de-insertion of Li+. This increase in stability is also observed in the electrochromic properties of the film, which are fully reproducible even after more than 60 oxidation-reduction cycles. The melanin affects also the activation energy of the dc conductivity which changes from 0.35 eV to 0.20 eV.
Surface Modification Of Polymers With Grafting And Coating Of Silane Hybrids And Their Bioactivity
Authors: Kubo Masaaki , Takashima Seisuke , Tsuru Kanji , Hayakawa Satoshi , Osaka Akiyoshi , Ohtsuki Chikara
Published: April 2011

Hydrated silica rich Si-OH and Si-0- groups serve in a body environment as sites for nucleation of apatite, and are known as an essential chemical species for bioactive materials. Organic polymers having surface modified with the hydrated silica will show bioactivity: bone tissues grow toward the apatite layer and bond to materials. Thus MOPS-M (3-methacryloxypropyltrimethoxysilane) was grafted under emulsion polymerization procedure to high density polyethylene (HDPE), poly (vinyl chloride) (PVC) and polyamide (PA) substrates to examine in vitro deposition of apatite (bioactivity) after soaking in a simulated body fluid (Kokubo solution). Bioactivity was confirmed for the grafted PVC and PA substrates and discussed in terms of contact angle and relative amount of grafted silane molecules.
Electronic Properties Of The Model Organometallic Polymer [M-C=C(N)]n (M = Cu(I), Ag(I), Au(I))
Authors: Su Z. M. , Wang R. S. , Che C. M.
Published: April 2011

The organometallic complexes of transition metal M = Cu(I), Ag(I), Au(I) with d10 electronic configuration have interesting optical, electronic and magnetic properties. It is possible to prepare the high functional organometallic polymer materials by coordinating π-conjugated organic molecules with d10 metals. According to the experimental structures, the model polymers [M-C-C(N)]n are built up and quantum chemistry methods are used to calculate their properties. It is indicated from theoretical analysis that the organometallic polymers would have comparable conductivity when interactions exist between metals and π electrons of different chains.
Sol-Gel Nir-Reflective Multilayer Coatings On Glass Through Uvpolymerizable Ceramic Nanoparticles
Authors: Mennig M. , Oliveira P. W. , Schmidt H.
Published: April 2011

A new preparation route for an dielectric NIR-reflexion filter on glass is described. Coating sols are synthesized from SiO2 and TiO2 nanoparticles with photopolymerizable surface ligands. A 5-layer stack consisting of 2 SiO2 and 3 TiO2 layers was deposited on float glass by angledependent dip-coating (ADDC) with a fixed angle of 4° to the vertical and subsequent UV-curing. Finally, the whole stack was densified at 450 °C without cracking or discolouring. UV-vis-NIR transmittance and reflectance spectra show a steep increase of reflectance at 750 nm. In the range between 800 nm and 1200 nm, the reflectance is > 80 %. The visible transmittance is about 72 % due to single reflexion peaks. The bandwidth of the NIR reflection filter prepared by ADDC is about 200 nm larger and its maximum reflectance is only 5 % smaller compared to vertical dip-coating. The interference layer stack shows excellent stability in Taber Abraser, rubber, saline and UV tests, indicating a high potential for practical application.
Inorganic Quantum Dot - Organic Dendrimer Nanocomposite Materials
Authors: Sooklal K. , Huang J. , Murphy C. J. , Hanus L. , Ploehn H. J.
Published: April 2011

Semiconductor quantum dots are of great current interest for their optical properties. We have developed a method for preparing CdS quantum dots in commercially available PAMAM Starburst dendrimers. The resulting CdS-dendrimer nanocomposites are exceptionally stable and emit brightly in the blue. The size of the dendrimer (its “generation”) has a surprisingly small effect on the optical properties of the resulting nanocomposites. The dot-dendrimer nanocomposites can be captured in a silica sol-gel matrix to yield a stable, bright blue-emitting glass.
Electronic Structure and Magnetic Properties of Nd5Fe17
Authors: Sabiryanov R. F. , Jaswal S. S.
Published: April 2011

The Nd5Fel compound has attracted some attention lately as a possible permanent-magnet material. This compound has a very complicated crystal structure (264 atoms per unit cell with 14 and 7 different Fe and Nd sites respectively!) Using linear-muffin-tin-orbital method, self-consistent spin-polarized studies of NdFe1 - have been carried out to determine the electronic structure, magnetic moments, and the Curie temperature. The results show strong effect of the local environment on the magnetic properties of individual Fe sites. The calculated moments are compared with the magnetization data. The Curie temperature estimated for the iron sublattice using the mean-field approximation is in a reasonable agreement with the experimental result.
Hard Magnetic Nanoparticles and Nanocomposites
Authors: Giri Anit , Chowdary Krishna , Majetich Sara A.
Published: April 2011

Many high performance permanent magnets are nanostructured materials. The magnetic properties of nanoparticles are discussed in terms of characteristic length scales, including the maximum monodomain size and the exchange length. Experimental results for ball milled SmCo5 nanoparticles are presented, showing deviations from idealized behavior. Because of the short exchange length, this can be understood in terms of independent nucleation of reverse domains in grains within larger particles. With a much longer exchange length, FeCo alloy nanoparticles show reduced coercivity in a high density compact, in accordance with the random anisotropy model. The SmCo5 and FeCo nanoparticles were mixed and compacted in an attempt to make an exchange spring nanocomposite. However, significant exchange between the hard and soft phases was not observed because the sample density was too low. Processing considerations for improved co-compaction of these nanoparticles are discussed.
The Kinetics of Formation Of Nanocrystalline γ-Ni-Fe During Mechano-Chemical Synthesis
Authors: Knorr P. , Kim B.S. , Lee J.S.
Published: April 2011

An experimental study of the kinetics of the three partial processes involved in the mechano-chemical synthesis of nanocrystalline (nc) Ni-Fe is presented. These processes are the reduction of nc NiO, the reduction of nc Fe2O3, and the alloying of Ni and Fe to a γ-Ni-Fe solid solution. Fr the reaction rates of the reduction of nc NiO and nc Fe2O3 activation enthalpies of 82 kJ mol−1 and 47 kJ mol− were obtained. The progress of the overall synthesis was found to follow the sequence ‘NiO red. → Fe2O3 red. → γ-Ni-Fe form.’.
Surface Coating of Hddr Processed and Mechanically Alloyed Powder Based on RE-TM
Authors: Kobe S. , Novak S. , Mcguiness P.J. , Mandrino D , Jenko M.
Published: April 2011

Chemical surface modification can be used as a method for corrosion protection of sensitive powders based on intermetallic alloys between rare earth and transition metals. Surface coating is used for preventing fine powders, based on Nd-Fe-B, or Sm2Fe17−xTaxN3−δ prepared by HDDR processing and mechanically alloying, from hydrolysis. Powders coated by chemisorbed organic substance, after exposing to a humid atmosphere, do not show any chemical or physical change.

Different coating agents were used and the sufficient amount of various materials was optimised with the emphasis on minimising their quantity. Simple experiment shows that the surfactant is successfully chemisorbed on the powder surface and that the coated powders are hydrophobic indefinitely. Magnetic properties were measured on samples after they were exposed to the same corrosion tests. Measurements on coated and bonded samples were compared with the measurements of non-coated and bonded samples. By using Auger electron spectroscopy the thickness of the coating was controlled. In order to distinguish the nature of the bonding between the powder surface and the surface-active substance FT-IR spectroscopy in absorbency and diffuse reflection modes was used. The protection of the fine particles is based on the formation of a covalent bond between the hydroxyl groups at the particle surface and the surface-active substance. The monomolecular layer of organic substance does not damage the magnetic properties of the powder, but successfully protect the powder against humidity.
Synthesis and Characterization of Antiferromagnetic Kmnf3Nanoparticles
Authors: Sangregorio C. , Carpenter E. E. , O'connor C. J.
Published: April 2011

The magnetic properties of nanosized antiferromagnetic particles of KMnF3are presented. The particles were synthesized using the microemulsion technique, i.e. by using the aqueous core of reverse micelles as constrained microreactors for the precipitation of the particles. The structural characterization of the samples, accomplished by TEM and XRD, reveal that the samples consist of cubic-shaped, crystalline KMnF3nanoparticles of uniform size. Control over the average size of the particles was achieved by changing the reaction time. Four different samples of average size in the range 13-35 nm were prepared. DC magnetic susceptibility measurements revealed superparamagnetic behavior of the particles. Hysteresis loops measured after field cooling the samples through TNwere shifted. The shift is ascribed to the exchange coupling between the antiferromagnetic core of the particles and the uncompensated spin shell surrounding it.
Microstructural and Magnetic Studies of Hddr Magnets from High Boron NdFeB(Zr) Alloys
Authors: Brown DN , Williams AJ , Gutfleisch O , Strangwood M , Harris IR
Published: April 2011

Some boron-rich (with respect to the Nd 2Fe,4B composition) NdFeB alloys (with and without small additions of zirconium) have been investigated in an attempt to understand the influence of zirconium in the subsequent magnetic properties of HDDR hot pressed magnets. It was found that zirconium additions had a marked influence on the as-cast microstructures with a general refinement of the grain size and evidence of a zirconium-rich phase (probably ZrB2) at the grain boundaries. The magnetic property measurements of fully dense, isotropic HDDR hot pressed magnets indicated that those containing zirconium maintained their coercivity to significantly higher hot pressing temperatures and this was attributed to the pinning of grain boundaries by the zirconium rich phase.
Influence of The Alloy Composition on The Magnetic Properties of Nanocrystalline Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo)
Authors: Kopcewicz M. , Grabias A. , Idzikowski B.
Published: April 2011

Formation of the nanocrystalline bcc Fe phase due to thermal treatment of the amorphous Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) precursors is studied by the Mössbauer and differential scanning calorimetry techniques. The dependence of the formation of the bcc Fe phase on the alloy composition is discussed. In order to determine the optimal soft magnetic properties of these nanocrystalline alloys the rf-Mössbauer technique is used in which rf collapse effect induced by a radio-frequency (rf) magnetic field is employed. It was found that anisotropy fields in the nanocrystalline phase were smaller in Nb- and Mo-containing alloys as compared to the alloys which contain Ti or Ta. Variations of the anisotropy field vs. alloy composition and annealing temperature are discussed in detail.
Quantitative Crystallization and Nano-Grain Size Distribution Studies of a Fecunbsib Nanocrystalline Alloy
Authors: Leu M.S. , Chin T.S.
Published: April 2011

Superior soft magnetic properties of nanocrystalline two-phase FeCuNbSiB alloy can only be attainable from a suitably nano-crystallized structure in the amorphous matrix. In this study a thermal-cycling-annealing process was adopted to anneal the amorphous specimens. The crystallization fraction of Fe73.5Cu1Nb3Si13 5B9 ribbons after different annealing was quantitatively measured by a DTA method through the integrated crystallization enthalpy from annealed samples versus that of as-cast amorphous specimen. The crystallization fraction was estimated to be 70 % as the specimen was annealed for 550°C×7.63 ks, the optimal annealing condition. Using this method, the crystallization quantity of the crystallized FeCuNbSiB amorphous alloy was accurately estimated and controlled during nano-crystallization processes.

Abstact:

The nanostructure of the annealed flake were investigated by high resolution TEM. The population of grain size is dominant in the range of 3-9 and 3-11 nm, corresponding to isothermal annealing at 520 and 550 °C, respectively, for 910 s. The average grain size associated with the above two annealing conditions is estimated to be 7 and 8.5 nm, respectively. The portion of nanocrystals with grain size smaller than 10 nm is about 80 % for the annealing at 520°C×910 s and 72 % for the annealing at 550°C×910 s, respectively. However, there is only one α-Fe(Si) phase evidenced in the TEM diffraction patterns.
Rf-Mössbauer Study of the Compositional Dependence of Short Range Order in Amorphous Fe-M-B-Cu Alloys
Authors: Kopcewicz M. , Grabias A. , Idzikowski B.
Published: April 2011

The radio-frequency collapse of the magnetic hyperfine structure in the Mössbauer spectra is employed to study directly the short range order in amorphous Fe-M-B-Cu (M: Zr, Ti, Ta, Nb, Mo) alloys via the electric quadrupole hyperfine interaction. The shape of the quadrupole splitting distributions obtained from the rf collapsed spectra strongly suggests the existence of two short range orders with a high and low local content of iron. The decrease of boron content in FeZrB alloys leads to a more symmetric local structure experienced by Fe atoms.
Effects of Quenching Environment on the Structure of Melt- Spun Nd2Fe14B
Authors: Kramer M. J. , Tang Yali , Dennis K.W. , Mccallum R. W.
Published: April 2011

Melt-spun Nd2Fe14B (2–14–1) ribbons were produced under active vacuum and different partial pressures of inert gases of Ar and He. Microstructure and thermal analyses were performed to understand the microstructural evolution and glass formability (GF) of the ribbons. He atmosphere enhances the quenchability of the ribbons over Ar and vacuum. Ribbons made under 250 Torr He have more uniform microstructure and smoother surfaces than those under 760 Torr He. The higher quenchability induced by He, which increases the interfacial heat transfer coefficient between the melt and rotating wheel during melt spinning, is due to its higher thermal conductivity compared to Ar. The lower pressure stabilizes the turbulence between the melt-pool and Cu wheel, enhancing the heat transfer resulting in a more uniform quench. As a result, a more uniform ribbon microstructure can be obtained at relatively low wheel speeds.
Magnetic And Structural Properties Of Laser-Ablated Planar And Cylindrical Co Thin Films
Authors: Madurga V. , Vergara J. , Ortega R. J. , Landazabal I. P. De , Favieres C.
Published: April 2011

Planar and cylindrical Co thin films have been obtained by pulsed laser ablation. X-ray diffractograms have shown no crystalline structure for the as-deposited samples, while the 450 °C annealed samples exhibit Co fcc crystalline peaks. The Scanning Tunnelling Microscopy has revealed a small increase of the surface roughness for the annealed films. The Hall effect has been used to determine the value of the spontaneous magnetization, Ms, at room temperature; Ms, = 14 kgauss for the as-deposited sample and Ms, = 17.6 kgauss for the 450 °C annealed sample. From transverse magnetooptic Kerr effect, it has been found that the as-deposited samples exhibit magnetic bistability, with a coercive field, Hc, = 6 0e. The annealed samples also show a bistable behavior until the annealing temperature is 450 °C. Besides, it has been observed an increase of Hc up to = 50 Oe, when the annealing temperature increases. The vibrating sample magnetometry has confirmed these results, showing that the magnetization participating in the magnetooptic effect for these low fields is the total spontaneous magnetization of these samples. Moreover, the cylindrical films exhibit magnetoelastic behavior when they are subjected to angular deformation. It has been found that the saturation magnetostriction constant is negative.
In-Situ TEM Deformation Studies of Dislocation Generation and Motion in High-Purity MO Single Crystals
Authors: Jouiad M. , Lagow B. W. , Robertson I. M. , Lassila D. H.
Published: April 2011

The generation and motion of dislocations in high-purity single crystals of Mo have been observed in real time by deforming electron-transparent samples in-situ in a transmission electron microscope. At 300 K and at low levels of stress, a novel dislocation source was observed that generated a long, straight screw dislocation. The source was a dislocation tangle that existed in the annealed material. An edge dislocation emerged from the tangle, trailing behind it the screw dislocation. These screw dislocations were immobile at this stress level. At higher stresses, the same dislocation tangle generated many dislocations, but now by a pole mechanism. The nature of these tangles and the source operation mechanisms will be described.
The Energetics of Dislocation-Obstacle Interactions by 3-D Quasicontinuum Simulations
Authors: Hardikar Kedar , Phillips R.
Published: April 2011

The goal of this work is to study the interaction of dislocations with local obstacles to glide such as point defects, precipitates and other dislocations. The quasicontinuum method is used as the basis of this study. It is demonstrated that two types of boundary effects are of concern in the calculation of hardening parameters using finite sized simulation cells. A recently developed technique to incorporate periodic boundary conditions in the quasicontinuum method is used to eliminate surface effects which were present in earlier implementations and to simulate a dislocation of infinite extent interacting with an array of obstacles. The second type of boundary effect is due to the boundary conditions on the lateral boundaries. A method based on finite element calculations is proposed for quantifying the effect of lateral boundaries in these simulations. Preliminary results for the validation of the method are presented as well as a simulation of the interaction between a conventional edge dislocation in Al with an array of clusters of Ni atoms.
Atomic-Scale Modeling of the Annihilation of Jogged Screw Dislocation Dipoles
Authors: Vegge T. , Pedersen O. B. , Leffers T. , Jacobsen K. W.
Published: April 2011

Using atomistic simulations we investigate the annihilation of screw dislocation dipoles in Cu. In particular we determine the influence of jogs on the annihilation barrier for screw dislocation dipoles. The simulations involve energy minimizations, molecular dynamics, and the Nudged Elastic Band method. We find that jogs on screw dislocations substantially reduce the annihilation barrier, hence leading to an increase in the minimum stable dipole height.
Damage and Crack Propagation at a Microstructural Scale
Authors: Bouchaud Elisabeth , Paun Florin , Ducourthial Elodie
Published: April 2011

A quantitative analysis of the morphology of damage cavities in metallic materials is performed. At larger length scales, the self-affine correlation length of fracture surfaces is shown to be correlated to the grain size. These observations suggest a new scenario for the origin of scaling laws observed on fracture surfaces. It is argued that they reflect strong correlations in damage created prior to fracture during crack propagation.
A Partitioned-Problem Approach to Microstructural Modelling of a Glass-Ceramic
Authors: Fischer-Cripps A.C.
Published: April 2011

The indentation response of a mica-containing glass-ceramic that exhibits yield in an indentation test is interpreted in terms of events occurring on the microstructural scale. This work is unique in that it links the macroscopic and microstructural properties of the specimen material in the indentation process.
Long Distance Fracture Surface Roughness on a Dendritic Aluminum Alloy
Authors: Aldaco J. , Garza F.J. , Hinojosa M.
Published: April 2011

The long distance roughness of the fracture surface of a dendritic aluminum alloy is studied over a wide range of length scales. Self-affinity analysis was performed over samples broken in Charpy impact tests. Simultaneous use of Atomic Force Microscopy, SEM and stylus profilometry allowed us to cover a wide spectrum of length scales, spanning over seven decades, from a few nanometers up to one centimeter. The roughness exponent and correlation length were obtained using the variable bandwidth method. For the roughness exponent, a value of 0.8 was obtained, corresponding to the reported universal exponent. Correlation length was found to correspond well to the characteristic length of the largest heterogeneities in the complex microstructure. Our results provide information that can help to improve our understanding of the role of microstructural parameters on crack propagation mechanisms.
Effect of Precipitate Morphology on the Gradient-Dependent Behaviour of Two-Phase Single Crystals
Authors: Busso E. P. , Meissonnier F. T. , O'Dowd N. P.
Published: April 2011

In this work a recently proposed gradient and rate-dependent crystallographic formulation is used to investigate the macroscopic behaviour of a precipitated single crystal. It relies on strain gradient concepts to account for the additional strengthening mechanism caused by presence of interfacial and geometrically necessary dislocations (GNDs). The total slip resistance is assumed to be due to a mixed population of mobile and sessile forest obstacles arising from both statistically stored dislocations (SSDs) and GNDs. The non-local crystallographic theory is implemented numerically into the finite element method. It requires the calculation of the slip rate gradients at the element level to determine the evolutionary behaviour of the GND densities, and a fully implicit numerical algorithm within a large strain kinematics framework and non-isothermal conditions. The effects of the relevant microstructural features (precipitate size, morphology and volume fraction) and deformation gradient-related length scales on the macroscopic behaviour is investigated and compared with experimental results.
Glass Formation and Nanostructure Development in Al-Based Alloys
Authors: Wu R. I. , Wilde G. , Perepezko J. H.
Published: April 2011

Al-Sm and Al-Y-Fe alloys with a high number density of nanocrystalline fcc-Al homogeneously dispersed within the amorphous matrix have been synthesized by devitrifying the precursor metallic glasses produced by rapid solidification. The kinetics of metallic glass formation and the development of the nanostructure during devitrification are discussed in terms of the rate limiting mechanism. The glass transition temperature of the two metallic glasses has been successfully assessed with the application of the modulated-temperature differential scanning calorimetry (DDSC). In addition, the formation of quenched-in nuclei was investigated by a comparison study on the cold-rolled and melt-spun Al92Sm8 amorphous samples. Furthermore, the enhancement of the particle density of the fcc-Al nanocrystals in the amorphous matrix after devitrification has been demonstrated by the incorporation of nanosize Pb particles.
Nanocrystalline Alloys of II-VI Semiconductors from Molecular Multi-Layer Templates
Authors: Cristofolini L. , Facci P. , Fontana M.P.
Published: April 2011

We present the synthesis and characterization of nanocrystalline II-VI semiconductors of mixed composition (CdSe/ZnSe, CdS) grown in fatty acid Langmuir-Schaefer multi-layer templates. The controlled production of i) homogeneous nanocrystalline CdxZn1−xSe alloys and ii) heterogeneous mixtures of different pure composition II-VI semiconductors such as CdSe and ZnSe provides, in addition to the size control, the parameter of the chemical composition for the fine tuning of the electronic properties. The samples are characterized bty optical and quasi-resonance micro-Raman spectroscopy.
Synthesis of Nanostructured WC Films by Supersonic Impaction of Nanoparticle Aerosols
Authors: Nichols W.T. , Malyavanatham G. , Beam M.P. , Henneke D.E. , Brock J.R. , Becker M.F. , Keto J.W.
Published: April 2011

Tungsten carbide (WC) coatings were prepared using supersonic impaction of nanoparticles produced by pulsed laser ablation of microparticle aerosols. The influence of experimental parameters such as, carrier gas type and impaction velocity on the structure, composition and physical properties of the resultant particles and films were studied. It was found that stoichiometric, crystalline films could be grown. These films pass both the adhesive lift off and scratch tests. TEM investigations indicate that the laser ablation forms individual particles with mean size of 7 ± 3 nm. At the highest aersol pressures small aggregates were also observed, and adjustment of the gas pressure in the laser interaction cell was found to control the degree of aggregation. Upon impaction, the separate particles form dense, self sintering nanocrystalline films, with helium forming the most dense as determined from SEM images.
Formation of Nanocrystalline SiC Powder from Chlorine-Containing Polycarbosilane Precursors
Authors: Mitchell Brian S. , Zhang Haoyue , Ade Martin , Kurtenbach Dirk , Müller Eberhard
Published: April 2011

Nanocrystalline β-SiC particulates with a grain size range of 5-20 nm were prepared by heating a pre-pyrolyzed, chlorine-containing polysilane/polycarbosilane (PS/PCS) to 1600°C. The transformation from the pre-pyrolyzed PS/PCS to nanocrystalline SiC was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), mass-spectrometry and infrared spectroscopy. The results indicated that the nanocrystalline P-SiC was formed by the crystallization of the PS/PCS random network, and crosslinking of Si-Si, Si-Cl, and Si-CH2-Si bonds. The TEM observation showed that SiC particulates consist of equiaxed, randomly oriented, ultrafine grains.
Structure and Composition of Bismuth Nanowire Arrays
Authors: Sander M. S. , Lin Y-M. , Dresselhaus M. S. , Gronsky R.
Published: April 2011

Arrays of nanowires have attracted considerable recent attention due to their unique electronic and optical properties. While much effort has been directed at fabricating arrays and measuring their properties, much less has been done to characterize these materials. Understanding the structure and composition of the constituents in these arrays is crucial in order to control their properties. In this work, arrays with wire diameters from 35-90nm were fabricated by pressure injecting liquid bismuth into porous alumina templates. Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) were used to characterize the arrays.
Synthesis of Single Crystal Bismuth-Telluride and Lead-Telluride Nanowires for New Thermoelectric Materials
Authors: Wei Q. , Lieber C.M.
Published: April 2011

Dimensionality can play an important role in determining the properties of materials. In the case of thermoelectric materials, it has been proposed that one-dimensional quantum wires, or nanowires, and two-dimensional superlattices could exhibit substantially higher efficiencies compared to the corresponding bulk, three-dimensional solids. To explore such predictions we have initiated a program directed towards the controlled growth of nanowires, and herein, we report the synthesis of single crystal Bi2Te3 and PbTe nanowires by a pulsed laser ablation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that Bi2Te3 wires 80 nm to 200 nm in diameter and lengths exceeding 10 microns, and PbTe wires 25 nm to 60 nm in diameter and lengths to 2 microns can be readily produced by the laser ablation method. High-resolution TEM and electron diffraction show that Bi2Te3 nanowires are single crystals with wire axes along the <110> crystal direction. TEM and electron diffraction measurements also show that the PbTe nanowires are single crystals with a <100> growth axis. The transport properties of these new nanowire materials will be discussed.
Oriented Si nanowires grown via an SLS mechanism
Authors: Xing Y. J. , Xi Z. H. , Hang Q. L. , Yan H. F. , Feng S. Q. , Xu J. , Zhang H.Z. , Yu D. P.
Published: April 2011

Highly oriented silicon nanowires were grown on Si (111) substrate via a solid-liquid-solid (SLS) mechanism. Unlike the well known vapor-liquid-solid (VLS) mechanism of whisker growth, no gaseous or liquid Si source was supplied during growth. Ni was used as the liquid forming agent and mixture of H2 and Ar was introduced in the experiment. Oriented silicon nanowires grew at 950°C and the ambient pressure kept at about 200 Torr. The oriented silicon nanowires have a length around I il m and uniform diameter about 25nm. Selected area electron diffraction showed that silicon nanowires are completely amorphous. The approach used here is simple and controllable, and may be useful in large-scale synthesis of various nanowires.
Synthesis of Cubic and Rhombohedral Phased Nanocrystalline SnO2 Doped In2O3 [ITO] Powders with Coprecipitation Method
Authors: Kim Bong-Chull , Kim Jeong-Joo , Chang Se-Hong
Published: April 2011

Nanocrystalline ITO powders have been prepared by a hydroxide coprecipitation method. Through the variation of aging time after precipitation, we have characterized the size, morphology and the structure of the precipitates. It was found that the precipitates are in the state of InOOH at first. Further aging up to 48 h changed it to In(OH)3 structure. After calcinations of the precipitates, rhombohedral nanocrystalline ITO powder with spherical shape was produced from InOOH structured precipitates, while cubic nanocrystalline ITO powder was produced from In(OH)3. Fraction of the rhombohedral ITO powder decreased as the aging time increased. The particle size of the cubic ITO increased with aging time but that of rhombohedral ITO (∼15 nm) was almost invariant.
Solution-Based Synthesis of Magnesium Oxide Nanorods
Authors: Wei Q. , Lieber C.M.
Published: April 2011

A 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

Sol-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

In 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

An 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

In 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

We 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

Alumina 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

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Nanocrystalline 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

A 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

This 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

As 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

CuPt 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.