bluuebunny/crossref_metadata_2025 huggingface dataset:
Ordered Micro-Particle Structures in a Liquid Crystal: Formation and Physical Properties
Authors: Zhang Ke , Glushchenko Anatoliy , West John L.
Published: April 2011

Ordered colloids are of great scientific and practical interests. Liquid crystals offer enhanced ways of producing and stabilizing these complex structures. We therefore studied the rheological and electro-rheological properties of the structured colloids as a means of probing this stabilization. We found that the mechanical properties of the colloids and stability of their 3D structures can be controlled by the particles size and distribution. In addition, when an electric field is applied, we observed an increase in the apparent viscosity with saturation at high electric fields. This effect depends on the shear rate and temperature. The results are also compared with the published data for the viscosity measurements of pure liquid crystals and isotropic colloids. While we are only beginning to understand the details of these complex colloids we expect they will find a wide variety of applications.
Integrated Optics/Electronics Using Electro-Optic Polymers
Authors: Dalton Larry R.
Published: April 2011

Organic electro-optic materials afford the realization of devices with terahertz bandwidths, providing bandwidths are not limited by resistive losses in metal electrodes. Recent realization of electro-optic coefficients (at telecommunication wavelengths) on the order of 200 pm/V permits construction of devices with operating voltage requirements of 1 volt or less. In like manner, substantial progress has been made in both understanding and improving thermal and photostability suggesting that organic electro-optic materials can meet Telacordia standards. However, one of the most intriguing advances afforded by organic materials is their processability including the ability to be integrated with diverse materials. This communication discusses both the systematic improvement, by theoretically-inspired rational design, of relevant material properties and the development of a variety of new processing methodologies, including soft lithography methods, for the fabrication of stripline, cascaded prism, and ring microresonator devices. The fabrication of flexible devices is also discussed.
Partial Pressure Differential and Rapid Thermal Annealing for Integrated Yttrium Iron Garnet (Yig)
Authors: Sung Sang-Yeob , Qi Xiaoyaun , Mondal Samir K. , Stadler Bethanie J. H
Published: April 2011

In this work, magneto-optical garnets were grown monolithically by low-temperature reactive RF sputtering, followed by an ultra-short (< 15sec) anneal. It was found that in addition to low thermal budgets due to timing, the temperature required (< 750°C) for garnet crystallization was also reduced compared to standard tube furnace annealing (> 1000°C). MgO and fused quartz were used as substrates because they will be useful for future buffer layers and optical claddings. Y-Fe-O films were made with systematically varied compositions and the chemical, structural, and optical properties of the resulting films were analyzed. A solid solution single phase field for YIG was found that spanned a wide range of compositions (30.1 ∼ 49.0 atomic % of Fe). The resulting YIG quality was measured by vibrating sample magnetometry (VSM), X-ray diffraction (XRD), and measurements of Faraday rotation (FR). Although the XRD results showed that the films had isotropic crystallinity, the VSM indicated that shape anisotropy dominated the magnetic properties. Out of plane FR measurements yielded up to 0.2°/μm at 632nm rotations. This rotation will be higher in plane. All of these tests demonstrated that the YIG was comparable to YIG grown by standard annealing and also by in-situ crystallization.
Reliable InGaAsP/GaAs 40W lasers grown in solid source MBE with phosphorus-cracker
Authors: Kuang G. K. , Hernandez I. , McElhinney M. , Zeng L. , Caliva B. , Walker R.
Published: April 2011

Laser structures with InGaAsP quantum well were grown on GaAs substrates in a solid source MBE system. Threshold current density Jth as low as 290A/cm2 and slope efficiency as high as 0.68W/A per facet were obtained for uncoated laser chips at 25°C. After 857 hours burn-in at 47A (corresponding to around 47W) at room temperature, power degradation rate was measured to be less than 3×10−6/h.
The Influence of Processing Parameters on Photoluminescent Properties of Ba2ZnS3:Mn Phosphors by Double-Crucible Method
Authors: Lin Yu-Feng , Chang Yen-Hwei , Tsai Bin-Siang
Published: April 2011

Red light emitting of Mn2+doped Ba2ZnS3phosphor powders have been synthesized by double-crucible method at different thermal treatments. XRD results indicate that the raw materials are completely sulfurized above 950°C, and the Ba2ZnS3: Mn2+powders don't change its orthorhombic crystal structure with increasing doping concentration from 0 to 0.8 mol%. The photoluminescence of Ba2ZnS3: Mn2+powders fulfilled the most efficient emission at the excitation wavelength λex=358 nm and showed the red emission light with peak wavelength λem=627nm at the doping concentration of Mn2+ion between 0.2 and 0.8 mol%. The high-luminance red emission results from the4T1(4G)—6A1(6S) transition in the Mn2+ion. Ba2ZnS3: Mn2+phosphors synthesized by double-crucible method have broad emission spectra (550nm∼750nm) with FWHM (full width at half maximum broadband) about 66nm. In our research, the Ba2ZnS3doped with 0.4 mol% Mn2+has the highest luminescent intensity as thermal treatment at 950°C for 16 hours and the CIE coordinate is x=0.66, y=0.33.
Nanochemistry of Ceria Abrasive Particles
Authors: Gilliss Shelley R. , Bentley James , Barry C.
Published: April 2011

Surfaces of ceria (CeO2) particles have been studied by electron energy-loss spectroscopy in a field-emission gun scanning transmission electron microscope. All the ceria particles analyzed contained Ce3+ at the surface. Rare-earth impurities such as La were enriched at the surface and were observed for particles ranging from tens to hundreds of nanometers in size. The oxidation state of the cerium ion is measured from the Ce M5/M4white-line intensity ratio.
An Optimized Synthetic Route for the Preparation of Water-Soluble Nanomagnetic Conducting Polyaniline with High Processability
Authors: Koul Sarswati , Nathan Arokia
Published: April 2011

The synthesis of water soluble nanomagnetic conducting polyaniline with an average particle size of 8nm ±1nm is presented. The particle growth morphology during reaction kinetics was controlled by using polyelectrolyte mediated dual oxidant-dopant system. The synthesis was carried out in a single reactor and the entire synthetic approach follows the principles of green chemistry. Dual oxidant-dopant system offers a solvent less chemical route for the synthesis of nanomagnetic polyaniline with maximum yield production.
Transport Properties of Magnetic Nanowires with Multiple Constrictions Formed by FIB
Authors: Liu Tie , Wu Yihong
Published: April 2011

Ni nanowires were fabricated by electrochemical deposition in the pores of alumina filtration membranes, with the diameter around 200nm. To study the magnetic and electrical properties of Ni nanowires, individual nanowire was selected and connected with metal electrodes. Single and multiple constrictions were formed on the nanowires by focused ion beam (FIB). The wires were further thinned using oxygen plasma oxidation. Magnetoresistance curves were studied and compared before and after FIB trimming and oxidization.
Metallic and Semiconducting Nanowires from Single Wall Carbon Nanotubes
Authors: Sivakumar Kousik , Lu Shaoxin , Panchapakesan Balaji
Published: April 2011

The focus of today's research has largely shifted from macro scale to micro scale and further to nano scale. The reason being the desire to realize quantum size effects in devices that has long eluded scientists around the world alike. With the discovery of nanoparticles, nanowires, and nanotubes, the ability to realize these effects practically into devices has increased manifold. Integration of carbon nanotubes with different types of functional materials may become mandatory in the future for electronics and sensing applications and in this sense, nucleation, growth and evolution of the structure of metallic and semiconducting materials on carbon nanotubes may be necessary. Further, it also provides opportunities to do fundamental research on understanding the structure-property relationships of these nanowires using carbon nanotubes. In this paper, we present a technique to form metallic and semiconducting nanowires using carbon nanotubes themselves as templates. Nanowires of silver and platinum have been fabricated by the electric field assisted deposition of nano particles of these metals on single walled carbon nanotubes. SEM and TEM investigations have shown the dimensions of the nanowires to be dependent only on the size of the nanoparticles, 10 - 100 nm in our case. The silver nanowires exhibited linear current – voltage characteristics whereas the platinum nanowires exhibited non-linear characteristics beyond a certain bias. This technique provides a high degree of selectivity by manipulating the charges on the surface of the nanotubes, which enables the deposition of metals only on the nanotubes and not anywhere else. The versatility of this technique allows for the fabrication of different types of metallic and semiconducting nanowires at the same dimensions as carbon nanotubes.
Site Selective Electrodeposition of Metals and Conductive Polymer Nano-Structures on Isolated Carbon Nanopipes Using Electric Fields
Authors: Bradley Jean-Claude , Babu Sundar , Ndungu Patrick
Published: April 2011

We report the successful application of bipolar electrochemistry for depositing metals and conducting polymer nano-structures on isolated template-grown carbon nanopipes (CVD-CNP). Metals such as tin, cobalt and nickel were reduced electrochemically at the tips of isolated CVD- CNP from their chloride or nitrate salts. Polypyrrole dendrites could also be grown on both ends of selected CVD-CNP. The potential applications of thus encapsulated CVD-CNP in nano- fluidics and other areas will be discussed.
Functionalized Polymeric Nanoparticles
Authors: Sussman Eric , Clark Michael , Shastri V. Prasad
Published: April 2011

Surface-functionalized polymeric nanoparticles (NP) are a versatile medium for drug delivery and imaging. The surface functionality is typically exploited to introduce molecules such as polymers and biomolecules to improve cellular localization, DNA binding and circulation. NP bearing surface functionality are typically prepared from polymers possessing functionalizable backbones or by layer-by-layer assembly of polyelectrolytes onto unmodified particles. We have developed a process to produce functionalized polymeric NP in a single step using non-functionalized polymers. This is achieved by the entrapment of polymeric functional moieties from an aqueous phase in a rapidly solidifying polymer core. NP were characterized using light scattering, scanning electron microscopy, zeta potential (ζ) measurement, fluorescent microscopy, and X-ray photoelectron spectroscopy (XPS). Stable NP ranging in diameter from 70 to 400nm with narrow polydispersity (PDI) can be produced by this process. The presence of functional moieties on the NP surface was verified by isoelectric point measurement and XPS. We foresee a number of uses for these functionalized nanoparticles, including drug delivery and modification of hard and soft material surfaces (both synthetic and biological) for tissue engineering.
Magnetic Properties and Fabrication of Monodisperse FePd Nanoparticles
Authors: Hou Yanglong , Kondoh Hiroshi , Ohta Toshiaki
Published: April 2011

The combination of 1-adamantanecarboxylic acid and tri-alkylphosphine was applied to produce monodisperse FePd nanoparticles by the polyol reduction of palladium acetylacetonate and thermally decomposition of iron pentacarbonyl. Images of high resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) data indicate a highly monodisperse and crystalline nature of the FePd nanoparticles. Magnetic studies performed by Quantum Design SQUID magnetometer show that FePd (16nm) nanoparticles are superparamagnetic at room temperature.
Magnetic nanowires and Y-Junctions
Authors: Kim Na Hyoung , Stadler Bethanie
Published: April 2011

Self-assembled nanopore templates were fabricated by anodizing aluminum in several electrolytes under specially selected conditions. The size of the nanopores was controlled, and many sizes were fabricated. Y-junction nanopore templates were also fabricated using a two-step anodization. Magnetic nanowires and Y-junction nanowires were then fabricated by electrochemical deposition of magnetic material into the nanopore templates and Y-junction nanopore templates. The magnetic properties of nanowires were investigated by VSM and compared.
Synthesis of Superparamagnetic Magnesium Ferrite Nanoparticles by Microwave-Hydrothermal Method
Authors: Verma Seema , Potdar Hari S. , Date Sadgopal K. , Joy Pattayil A.
Published: April 2011

Superparamagnetic magnesium ferrite, MgFe2O4, nanoparticles were synthesized under mild microwave hydrothermal (MH) conditions. Transmission electron microscopic studies showed that the average particle size of the ferrite obtained is ∼3 nm, with a narrow size distribution. Temperature dependent AC magnetic susceptibility measurements at 2 Oe showed characteristic feature of superparamagnetism with blocking temperature, TB, at 47 K. TB decreases with increasing DC magnetic field as evidenced by zero-field-cooled susceptibility studies at 50 and 500 Oe (TB = 38 and 27 K respectively). As a typical superparamagnetic behavior, the zero-field- cooled and the field-cooled magnetizations diverge below TB. Magnetic hysteresis behavior is observed below TB, with a high coercivity of 185 Oe at 12 K, and magnetic hysteresis behavior disappears when measured above TB. The results indicate that MH method is highly suitable for the synthesis of superparamagnetic ferrite nanoparticles of uniform size distribution.
Growth and Characterization of ZnO Nano-Rods on Si Substrate by Pulsed Laser Ablation
Authors: Gupta Vinay , Bhattacharya P. , Yuzyuk Yu. I. , Katiyar R.S.
Published: April 2011

Zinc oxide (ZnO) nanorods were fabricated directly on silicon substrate with diameters in the range of 70-350 nm and up to 15 νm long using pulsed-laser deposition at a relatively low processing temperature (450°C) without any catalytic template. The influences of substrate temperatures and the oxygen pressures on the formation of ZnO nanorods were investigated. The Raman scattering studies and scanning electron microscopy results indicated that the ZnO nanorods were well aligned along c-axis and isolated from each other. The additional Raman modes at ∼ 477 cm−1 and 574 cm−1 were observed in the c-axis oriented ZnO nanorods which attributed to the activation of the upper and lower surface phonon modes respectively.
On the Role of Grain-Boundary Films in Optimizing the Mechanical Properties of Silicon Carbide Ceramics
Authors: Ritchie R. O. , Zhang X.-F. , De Jonghe L. C.
Published: April 2011

Through control of the grain-boundary structure, principally in the nature of the nanoscale intergranular films, a silicon carbide with a fracture toughness as high as 9.1 MPa.m1/2 has been developed by hot pressing β-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features. Elongated SiC grains with 1 nm-wide amorphous intergranular films were believed to be responsible for the in situ toughening of this material, specifically by mechanisms of crack deflection and grain bridging. Two methods were found to be effective in modifying microstructure and optimizing mechanical performance. First, prescribed post-annealing treatments at temperatures between 1100 and 1500°C were seen to cause full crystallization of the amorphous intergranular films and to introduce uniformly dispersed nanoprecipitates within SiC matrix grains; in addition, lattice diffusion of aluminum at elevated temperatures was seen to alter grain-boundary composition. Second, adjusting the nominal content of sintering additives was also observed to change the grain morphology, the grain-boundary structure, and the phase composition of the ABC-SiC. In this regard, the roles of individual additives in developing boundary microstructures were identified; this was demonstrated to be critical in optimizing the mechanical properties, including fracture toughness and fatigue resistance at ambient and elevated temperatures, flexural strength, wear resistance, and creep resistance.
Ion Channel Sensor on a Silicon Support
Authors: Goryll Michael , Wilk Seth , Laws Gerard M. , Goodnick Stephen M. , Thornton Trevor J. , Saraniti Marco , Tang John M. , Eisenberg Robert S.
Published: April 2011

We are building a biosensor based on ion channels inserted into lipid bilayers that are suspended across an aperture in silicon. The process flow only involves conventional optical lithography and deep Si reactive ion etching to create micromachined apertures in a silicon wafer. In order to provide surface properties for lipid bilayer attachment that are similar to those of the fluorocarbon films that are currently used, we coated the silicon surface with a fluoropolymer using plasma-assisted chemical vapor deposition. When compared with the surface treatment methods using self-assembled monolayers of fluorocarbon chemicals, this novel approach towards modifying the wettability of a silicon dioxide surface provides an easy and fast method for subsequent lipid bilayer formation. Current-Voltage measurements on OmpF ion channels incorporated into these membranes show the voltage dependent gating action expected from a working porin ion channel.
A study of the growth curves of C. xerosis and E. coli Bacteria in Mediums Containing Cobalt Ferrite Nanoparticles
Authors: Flores Marjorie , Colón Nanell , Rivera Omayra , Villalba Nicole , Baez Yahira , Quispitupa David , Avalos Javier , Perales Oscar
Published: April 2011

Previous publications demonstrated the sensibility of the bacteria, when these were reproduced in mediums that contain nanoparticles of luminescent silicon. The mentioned effect takes place in the development of a bacteriological sensor. The present investigation is centered on the study of the growth curves of E. coli and C. xerosis, but now in the presence of nanosize particles of Cobalt Ferrite (CoFe2O4) which were produced by the co-precipitation method in a watery phase. These nanoparticles present ferromagnetism characteristics (coercivity at room temperature among 600-5000 Oe for a size around 15-40nm). The experiment results evidence that the adaptation period of the bacteria, in contact with a stable suspension of nanoparticles of Ferrite, shows a growth curve of above the one obtained in absence of the nanoparticles (standard curve). The probable interaction of the electric polarity that these possess should be involved with the observed phenomena.
Optimization of mechanical properties of thin free-standing metal films for RF-MEMS
Authors: Toonder Jaap M.J. den , Dijken Auke R. van
Published: April 2011

The mechanical properties of the thin film materials used in RF-MEMS are crucial for the reliability and proper functioning of the devices. In this paper we study a large number of aluminum alloys as possible RF-MEMS thin film materials. The yield strength and creep properties are measured using nano-indentation. The results show that the mechanical properties of thin aluminum films can be improved substantially by alloying elements. Of the alloys studied in this paper, AlCuMgMn in particular seems quite promising as a thin film material for RF MEMS, having both high yield strength and little creep. Using X-ray diffraction and electron microscopy, the observed effects are partly explained.
Microstructural Design and Evaluation of Porcelain/Mullite/Alumina Layered Structure for Dental Application
Authors: Jang Hyung-Jun , Park Dong-Ho , Jung Yeon-Gil , Lee Hee-soo
Published: April 2011

Porcelain (veneer layer)/alumina (core layer) is a typical dental crown structure. Due to its high incidence of failure, a new porcelain/mullite (buffer layer)/alumina trilayer structure is designed, fabricated, and evaluated. Alumina green bodies were prepared by gel-casting process, and then calcined at 900 and 1100°C to infiltrate mullite precursor slurry of silica-rich (Al2O3·2SiO2) composition into the bodies. Porosity in the bodies is not dependent on calcination temperature, resulting in a similar infiltration depth. Porcelain was coated on the alumina sintered at 1600°C with and without mullite buffer layer. There are no delamination or cracks observed after firing the layered materials. Rod type microstructure and continuous composition are indicated at the interface in the case of the layered structure with mullite buffer layer. To investigate the cracking resistance behavior for this new structure, Vickers indentation and Hertzian contact fatigue tests were conducted. Cracks do not penetrate the interface with mullite buffer layer into the porcelain, showing a reversal case for the layered structure without mullite buffer layer. The layered structure with mullite buffer layer shows higher critical load for fracture than that without mullite buffer layer. Fracture mode of the layered structures in cyclic fatigue shows a top layer (porcelain) fracture at relatively low load (P = 250 N) and higher cycles (n = 106), and a bottom layer (alumina) fracture at higher load (P = 300 N) and relatively low cycles (n = 105).
Low Coherence Interferometric Metrology for Ultra-thin MEMs Structures
Authors: Walecki Wojciech , Wei Frank , Van Phuc , Lai Kevin , Lee Tim , Souchkov Vitali , Lau SH , Koo Ann
Published: April 2011

We present application of low coherence interferometry to characterization of ultra-thin MEMs structures such as membranes in micro-machined devices.
From an Integrated Biochip Detection System to a Defensive Weapon Against the SARS-CoV Virus: OBMorph
Authors: Lee Chih-Kung , Lin Chi-Wan , Lin Shiming , Lee Adam Shih-Yuan , Wu Jiun-Yan , Lee Shu-Sheng , Hsiao Wen-Hsin , Chen Shih-Jui , Wang An-Bang
Published: April 2011

In this paper, an integrated multifunctional biochip detection system, which we call “OBMorph“, are presented. This unique system integrates several optoelectronic-based biological diagnostic tools such as an ellipsometer, a laser Doppler vibrometer/interferometer, a SPR (surface plasmon resonance) analyzer, an interference microscope, a photon tunneling microscope, an optical coherence tomography unit and a confocal scanning microscope. This OBMorph system, useful as a powerful optical metrology diagnostic tool, can be used at the beginning of sensor chip fabrication, on to signal detecting and monitoring, and to the final biological analysis. The principles and experimental results of this multifunctional biochip detection OBMorph system are presented.

In addition, an innovative SARS (Severe Acute Respiratory Syndrome) virus denaturing chemical compound that was derived using the OBMorph system to study biolinker fabrication in biochips, are discussed. Several testing strategies are presented herein which proves the effectiveness of the new chemical compound, biochip technology in denaturing the SARS virus. Analysis under an atomic force microscope confirms the actual breaking down of the virus treated by the chemical compound. The fundamentals of how the chemical compound denatures the virus and renders it toxicity useless, is based on principles of nanotechnology and bio-mechanics. Results from preliminary studies show that this denaturing principle can be also effective against other deadly viruses and even bacteria. Some design strategies and innovative working mechanisms derived from study of this chemical compound which can denature the SARS-CoV, are also discussed.
Ab-initio Structural Properties and Stress-Deformation Analysis by Rheological Modeling of Diamonds-containing Nanocarbon nanotubes
Authors: Kireitseu Maksim V. , Bochkaryova Liya
Published: April 2011

In our laboratory, we developed a simple method for measuring the mechanical properties of single nanotubes and modeling its mechanical properties by rheological analysis. The technique involves depositing nanotubes from a suspension in a suitable liquid onto well- polished alumina ultrafiltration membranes with a pore size of about 200 nm. Rheological models of the composite systems have been proposed and confirmed by in-situ experiments at AFM indentation.
Controlling the Sensing Volume of Metal Nanosphere Molecular Sensors
Authors: Miller Molly M. , Lazarides Anne A.
Published: April 2011

Noble metal nanoparticles and nanoshells support surface plasmons at optical frequencies. These resonances, known as localized surface plasmons (LSPs), are sensitive to the dielectric properties of the environment and, in particular, to the refractive index of the material close to the surface of the particle. This sensitivity can be exploited in molecular detection systems that use nanoparticles functionalized with receptors to (a) bind target molecules and (b) optically transduce the resulting change in the dielectric environment. Optimization of an optical nanoparticle sensor involves tailoring the particle to the target so as to maximize the sensitivity of spectroscopic features to the dielectric variation associated with binding of target molecules to the particle surface.
Namomechanical Imaging and Nanoscale Elastic Modulus Measurements of SnO2 Nanobelts
Authors: Zheng Y. , Geer R. E.
Published: April 2011

The relative surface contact stiffness of SnO2 nanobelts has been investigated via ultrasonic force microscopy (UFM). The nanobelt crystal structure, as determined via transmission electron microscopy, was indexed to the tetragonal rutile structure (with lattice constants identical to those of bulk SnO2) as reported previously. The atomic Sn:O composition of the nanobelts studied was at or near 1:2. Topographic imaging studies revealed the nanobelt surface to be atomically flat with the exception of surface nanodots, assumed to be local SnO2 crystallites. Preliminary reduced modulus measurements were carried out via differential UFM on both the flat and nanodot regions of the nanobelt. Using the underlying Si substrate as a calibration standard the SnO2 modulus was estimated at 157±12 GPa, significantly lower than corresponding bulk values for any of the observed crystal orientations. We speculate this discrepancy is due in part to a combination of the aspherical probe tip and unknown adhesive properties of nanobelt. An intrinsic reduction of the SnO2 nanobelt modulus cannot be ruled out.
Evaluation of Interface Strength between a Copper Submicron Dot and Silicondioxide Substrate
Authors: Hirakata Hiroyuki , Kitamura Takayuki , Yamamoto Yoshitake
Published: April 2011

An experimental evaluation method of interface strength between ductile submicron-dots and a hard substrate is developed. The validity is examined with copper (Cu) cylindrical dots of submicron scale on a silicondioxide (SiO2) substrate. A hard-layer of tungsten (W) is employed to restrain the deformation and concentrate the stress near the free-edge of Cu/SiO2. A diamond tip is dragged horizontally along the SiO2 surface and the load is applied to the side edge of the W layer at a constant displacement rate using a modified atomic force microscope. Both the lateral and the vertical loads and displacements are continuously monitored during the test. After the tip hits the W layer, the lateral load, Fl, increases almost proportionally with the lateral displacement, σl. The Cu dot with the W layer then is clearly separated from the SiO2 along the interface. The restraint by the W layer works well so that there are little damages in both the delaminated W/Cu dot and the substrate. The delamination lateral load, FlC, is successfully evaluated.
Synthesis and Study of Nanostructures Via Microwave Heating
Authors: Kharissova Oxana V. , Zavala Eder , Ortíz Ubaldo , Hernández-Piñero Jorge L. , Soloviev Stanislav
Published: April 2011

This work is devoted to microwave heating of graphite, sucrose, calcined sucrose, and a mixture of graphite with sucrose to produce carbon nanotubes (CNT's). The samples were submitted to microwave radiation (power 800W, frequency 2.45 GHz) in air and high vacuum (10−5Torr) for 30 – 60 min. The oven temperature was approximately 1200°C. After vaporization the condensed material was collected on various fused silica targets (different morphologies were used). The samples were found to contain a significant proportion of nanotubes, nanoparticles and fibers (1-2.8 micrometers), which appeared to be highly graphitized and helical structured. After deposition, the morphology of carbon nanotubes was studied with SEM, TEM and AFM techniques. It was observed that multi-walled nanotubes (MWNT's) were produced by this method. The morphology of fused silicon based substrates (SiO2, SiC) was studied as an important factor for the growth of carbon nanotubes. Many aspects as the size and shape of the obtained nanotubes on different substrates (porous and non-porous fused silicon substrates) were achieved, as well as the concentration of them across the substrate and other properties.
Effect of Substrate Bias on Structure and Properties of W incorporated Diamond-like Carbon Films
Authors: Wang Ai-Ying , Lee Kwang-Ryeol
Published: April 2011

W incorporated diamond-like carbon (W-DLC) films were deposited on silicon (100) wafers by a hybrid deposition method combining ion beam deposition of carbon with DC magnetron sputtering of tungsten. During the films deposition, a wide range of negative bias voltage from 0 to -600 V was applied. W concentration in the film could be controlled by varying the Ar/C6H6 ratio in the supplying gas. In the present experimental condition, WC1−x nano-sized particles were not observed in the amorphous carbon matrix. Regardless of the W concentration in the film, it was found that the G-peak position of the Raman spectra had a lowest value at a bias voltage of - 200 V, which represents the highest sp3 bond fraction in the film. The highest residual stress, hardness and Young's modulus were also observed when the bias voltage was -200 V. This result shows that the mechanical properties of W-DLC films were mainly dependent on the atomic bond structure of carbon. On the other hand, the electrical resistivity significantly decreased by the W incorporation.
Characterization of Carbon Nanotubes/Cu Nanocomposites Processed by Using Nano-sized Cu Powders
Authors: Kim Kyung Tae , Lee Kyong Ho , Cha Seung Il , Mo Chan-Bin , Hong Soon Hyung
Published: April 2011

Carbon nanotubes (CNTs) have attracted remarkable attention as reinforcement for composites owing to their outstanding properties1-3. CNT/Cu nanocomposites were fabricated by mixing the nano-sized Cu powders with multi-wall carbon nanotubes and followed by the spark plasma sintering process. The CNT/Cu nanocomposite fabricated from nano-sized Cu powders shows more homogeneous distribution of CNTs in matrix compared to that fabricated from macro-sized Cu powders. The hardness of CNT/Cu nanocomposite fabricated from nano-sized Cu powders increases with increasing the volume fraction of CNTs, while the hardness of that fabricated from macro-sized Cu powders decreases with the addition of CNTs.
A Molecular Dynamics Simulation Framework for an Al+Fe2O3 Reactive Metal Powder Mixture
Authors: Tomar Vikas , Zhou Min
Published: April 2011

This work focuses on the development of a classical molecular dynamics (MD) framework that can be used to analyze the quasi-static strength, elastic-constants, and dynamic strength of nanostructured Fe2O3+Al reactive metal powder (NRMP) mixtures. An interatomic potential is developed for the Fe2O3+Al NRMP system, accounting for the behavior of Al, Fe, Fe-Al intermetallics, Fe2O3, and Al2O3. This potential can be regarded as a generalization and combination of several existing potentials for the individual components in the system. The potential incorporates electronegativity equalization to account for pressure-induced phase transformation. In addition, the parameter set of the potential is capable of predicting the elastic properties of components over a range of 0 - 900 K.
Unconfined Twist: a Simple Method to Prepare Ultrafine Grained Metallic Materials
Authors: Zhao Yonghao , Liao Xiaozhou , Zhu Yuntian T.
Published: April 2011

A new simple method – unconfined twist was employed to prepare ultrafine grained (UFG) Fe wire. A coarse grained (CG) Fe wire with a diameter of 0.85 mm was fixed at one end, and twisted at the other end. After maximum twist before fracture, in the cross-sectional plane, concentrically deformed layers with a width of several micrometers formed surrounding the center axis of the wire. The near-surface deformed layers consist of lamella grains with a width in submicrometer range. In the longitudinal plane, deformed bands (with a width of several micrometers) formed uniformly, which were composed of lamella crystallites (with a width in submicrometer range). The tensile yield strength and ultimate strength of the twisted Fe wire are increased by about 150 % and 100 % compared with the values of its CG counterpart.
The Role Of Vorticity In The Formation Of Tribomaterial During Sliding
Authors: Subramanian Karthikeyan , Wu Jian-Hui , Rigney David A.
Published: April 2011

The formation of tribomaterial during sliding is well documented for a wide range of materials. Transfer, adhesion, mechanical mixing and formation of nanocrystals are commonly reported, but the mechanisms involved have not been well understood. Recently, molecular dynamics (MD) simulations have been performed to obtain new information on the response of materials to sliding interactions. The results help to explain experimental observations on simple metals such as copper, bulk metallic glasses and multi-component nanocomposite coatings. When the sliding speed is sufficiently high, the strain rate allows vorticity to develop. It is suggested that the resulting eddies are largely responsible for frictional energy dissipation and mechanical mixing in both crystalline and amorphous materials and for the shear mixing of soft embedded particles in nanocomposite coatings. Similarities of flow behavior with that of fluids are noted.
Grain Size Distribution Effect on Mechanical Behavior of Nanocrystalline Materials
Authors: Sergueeva A.V. , Mara N.A. , Mukherjee A.K.
Published: April 2011

Grain size distribution effect on the mechanical behavior of NiTi and Vitroperm alloys were investigated. Yielding at significantly lower stresses than found in equiaxed counterparts, along with well defined strain hardening was observed in these nanocrystalline materials with large grains embedded in the matrix during tensile deformation at temperatures of 0.4Tm. At higher temperature the effect of grain size distribution on yield stress was not revealed while plasticity was increased in 50% in NiTi alloy with bimodal grain size structure.
Theoretical Investigations of Polymer Based Solar Cells
Authors: Echols Robert S. , France Chris E.
Published: April 2011

We investigate the behavior of a polymer blend (M3EH-PPV:CN-ether-PPV) bulk heterojunction solar cell using a numeric model that self-consistently solves Poisson's equation and the charge continuity equation while incorporating electric field dependent mobilities. We obtain good quantitative agreement with present experimental data for J-V curves and photocurrent action spectra. To reproduce experimental photocurrent action spectra, our model predicts 36% exciton dissociation efficiencies in the bulk of the polymer. We also study the limiting conditions of polymer solar cell development by simulating an ideal solar cell using an AM1.5 global spectrum and assuming all absorbed photons hitting a M3EH-PPV:CN-ether-PPV polymer blend (band gap ∼2.0 eV) based solar cell at normal incidence contribute to current. If such a solar cell has 100 nm length, open circuit voltage=0.6 V and 50% fill factor, then the maximum theoretical power conversion efficiency is ηp=5.6%. A similar analysis for a M3EH-PPV:PCBM bulk heterojunction cell yields, ηp=3.5%. These results further highlight the need to develop smaller band gap materials and help explain why the best polymer based solar cells have power conversion efficiencies that remain stuck at about 3%. Our model is used to investigate the important increase in power conversion efficiencies we can expect as lower band gap polymers become available.
The fabrication of self-assembling peptides into nanofiber scaffolds through molecular self-assembly
Authors: Zhao Xiaojun , Dai Jessica , Zhang Shuguang
Published: April 2011

We designed and fabricated a class of self-assembling peptides into nanofiber scaffolds. KLDL-12 has been shown to be a permissible nanofiber scaffold for chondrocytes in cartilage 3-D cell cultures. However, the biochemical, structural, and biophysical properties of KLDL-12 remain unclear. We show that KLDL-12 peptides form stable β-sheet structures at different pH values and that KLDL-12 and RIDI-12 self-assemble into nanofibers. The nanofiber length, though, is sensitive to pH changes. These results not only suggest the importance of electrostatic attraction or repulsion affecting the fiber lengths but also provide us with useful information for rational design and fabrication of peptide scaffolds.
Effect of Metal Substrate Nanometer Topography on Osteoblast Metabolic Activities
Authors: Ward Brian C. , Webster Thomas J.
Published: April 2011

Surgeons and bioengineers have continuously been challenged by implant failure. Many of these engineers and surgeons trace implant failure to poor osseointegration (the bonding of an orthopedic implant to juxtaposed bone) and to the inability of implants to match the physical properties of surrounding bone. Researchers have recently shown that nanostructured materials (or materials with fundamental length scales less than 100 nm) enhance cell functions pertinent to effectively regenerating the tissue of numerous organs. Specifically, in a recent study, researchers demonstrated that metal surfaces utilizing low-micron to nanophase topography fostered increased adhesion of osteoblasts, the cells that create the matrix of bone. In this study, Ti, Ti6Al4V, and CoCrMo alloys were investigated, and these alloys were identical to current orthopedic implant alloys except for surface topography. The objective of this in vitro research was to determine whether these same nanophase metal surfaces not only foster osteoblast adhesion but also increase osteoblast metabolic activities leading to bone regeneration. Light microscopy and Energy Dispersion Spectroscopy (EDS) were used to verify the presence of calcium and phosphorous deposition by osteoblasts cultured on the metal substrates. Results indicated that both calcium and phosphorous are being deposited on several of the metal substrates. More importantly, compared to conventional metals, results provided the first evidence that more calcium and phosphorous was deposited by osteoblasts cultured on respective nanophase metals (Ti, Ti6Al4V, and CoCrMo). Nanophase CoCrMo had the most calcium and phosphorous minerals deposited by osteoblasts compared to any other metal substrate. Thus, the results of this study continue to provide evidence for the use of nanophase metals for the design of the next generation of more successful orthopedic implants.
Calcium Oxalate Monohydrate Precipitation at Phospholipid Monolayer Phase Boundaries
Authors: Benítez Isa O. , Talham Daniel R.
Published: April 2011

The precipitation of calcium oxalate monohydrate (COM) was observed at biphasic phospholipid Langmuir monolayers with the aid of Brewster angle microscopy. COM appears preferentially at phase boundaries of a monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in a state of liquid expanded/liquid condensed coexistance. However, when the phase boundary is created by two different phospholipids that are phase segregated, such as DPPC and 1,2-dimiristoyl-sn-glycero-3-phosphocholine (DMPC), crystal formation occurs away from the interface. It is suggested that COM growth at phase boundaries is preferred only when there is molecular exchange between the phases.
Intrafibrillar demineralization study of single human dentin collagen fibrils by AFM
Authors: Balooch M. , Balooch G. , Habelitz S. , Marshall S. J. , Marshall G. W.
Published: April 2011

In situ atomic force microscopy (AFM) was used to investigate the kinetics of demineralization of human dentin collagen fibrils. Individual dentin collagen fibrils containing intrafibrillar mineral were isolated, transferred onto a glass slide and exposed to water for a day prior to demineralization studies. The fibrils then were exposed to trypsin for removal of non-collagenous proteins and subsequently demineralized in 10 vol % citric acid. Topographic images showed a gradual increase in gap-overlap depth of the fibril. The gap-overlap depth varied linearly with the square root of time before saturation at 7 nm in approximately sixty minutes, suggesting a diffusion process for demineralization of intrafibrillar mineral. Micro Raman studies of partially demineralized dentin revealed the existence of a phosphate peak at wave number close to 960 cm-1. The peak gradually disappeared in 60 minutes as the samples were exposed to 10% citric acid, supporting the notion that AFM topography may be correlated to the degree of intrafibrillar mineralization.
Effect of the free energies of formation of the core and shell and of the density of the casein phosphate centres on the thermodynamic stability of calcium phosphate nanoclusters
Authors: Holt Carl
Published: April 2011

Calcium phosphate is sparingly soluble at neutral pH but the milk of nearly all species contains many times the concentrations of calcium and phosphate that this solubility allows. The explanation for this apparent paradox is that milk calcium is mainly present in the form of thermodynamically stable nanoclusters formed from casein phosphoproteins and amorphous calcium phosphate. A simplified model system comprising the main milk salts and a hydrophilic N-terminal phosphopeptide from β-casein, at or about neutral pH, forms complexes called calcium phosphate nanoclusters. It is shown that two constants, KS and y, together with the empirical chemical formula of the nanoclusters allow the concentrations of all the important chemical species in this model system to be calculated. The method has been extended successfully to the more complex problem of calculating all the important chemical species in milk. It is suggested, on the basis of a simple analysis of the thermodynamics of the formation of nanoclusters, that their size and stability is determined principally by three factors. These are the relatively low free energy of formation of the amorphous core material, the particular pattern of phosphorylation of seryl residues in the caseins that gives a large chelate effect during the sequestration of the calcium phosphate and the unfolded conformation of the caseins that allows a high density of phosphate centres on the core surface.
Conductivity Behavior of Salt Deposits on the Surface of Engineered Barrier Materials for the Potential High-Level Nuclear Waste Repository at Yucca Mountain, Nevada
Authors: Yang Lietai , Juckett Miriam R. , Pabalan Roberto T.
Published: April 2011

The electrical conductance or conductivity of three salt mixtures, Na-K-Cl-NO3, Ca-K-Cl and Ca-Na-Cl, were measured at 25, 50 and 70°C [77, 122, and 158 °F] as a function of relative humidity (RH). Mutual deliquescence and efflorescence RH (MDRH and MERH) values were determined based on the conductivity measurements. It was found that the conductivity of the three salt mixtures started to increase at RH values that are approximately 40 % of their MDRH and increased by 1to 2 orders of magnitude just before reaching the MDRH. At the MDRH, a significant increase in conductivity was observed. The MDRH and MERH for the Ca-K-Cl and Ca-Na-Cl mixtures were found to be approximately 15 % in the temperature range of 50 to 70 °C [122 to 158 °F]. The MDRH and MERH for the Na-K-Cl-NO3system were found to be approximately 54 % at 50 °C [122 °F] and decreased significantly with an increase in temperature.
Can Spent Nuclear Fuel Decay Heat Prevent Radionuclide Release?
Authors: Jerden James L. , Goldberg Margaret M. , Cunnane James C. , Bauer Theodore H. , Wigeland Roald A. , Nietert Russell E.
Published: April 2011

Heat generated by radioactive decay of spent fuel represents a potentially important barrier to water accumulation on commercial spent nuclear fuel in breached waste packages. In the absence of water, fuel degradation and radionuclide release will be negligible. Thermal models for the proposed Yucca Mountain Repository suggest that, after a period of approximately 1000-4000 years (depending on loadingand ventilation conditions), the repository drift walls may decline to sub-boiling temperatures, thus allowing humidity in the drift to increase. The question thus arises, is the thermal gradient between the fuel and the drift sufficient to prevent water accumulation in a humid drift environment throughout the regulatory period? The answer depends on the balance between processes that oppose water condensation ontothe fuel (decay heat) and those that promote condensation such as the deliquescence of hygroscopic phaseswithin the fuel.

Our experimental results indicate that deliquescence could lead to the condensation of water onto spent fuel despite the thermal “self-drying”effect if the following criteria are met: (1) the fission product salt CsI is present in the fuel or in the fuel-cladding gap, (2) the relative humidity in the driftexceeds 80% while temperatures in the waste package are around 90oC. Previous work suggests that these criteria may be met for some fuel pins within the proposed Yucca Mountain Repository. However,experiments that account for the role of U(VI) alteration phases suggest that deliquescence may be a self-limiting process in the sense that deliquescent components (e.g. Cs, Ba, Sr) may be incorporatedinto nondeliquescent U(VI) phases that form from the corrosion of spent fuel.
Performance Assessments of Geologic Repositories for High-Level Nuclear Waste: Are TheyNecessaryorSufficient?
Authors: Ewing Rodney C.
Published: April 2011

Performance assessments of geologic repositories for high-level nuclear waste will be used to determine regulatory compliance. The determination, that with a “reasonable expectation” regulatory limits are met, is based on the presumption that all of the relevant physical, chemical and biological processes have been modeled with enough accuracy to insure that a confident judgment of safety may be made. For the geologic disposal of high-level nuclear waste, this generally means that models must be capable of calculating radiation exposures to a specified population at distances of tens of kilometers for periods of tens to hundreds of thousands of years. A total system performance assessment will consist of a series of cascading models that are meantin tototo capture repository performance. There are numerous sources of uncertainty in these models: scenario uncertainty, conceptual model uncertainty and data uncertainty. These uncertainties will propagate through the analysis, and the uncertainty in the total system analysis must necessarily increase with time. For the highly-coupled, non-linear systems that are characteristic of many of the physical and chemical processes, one may anticipate emergent properties that cannot, in fact, be predicted. For all of these reasons, a performance assessment is not in and of itself a sufficient basis for determining the safety of a repository, but it remains a necessary part of the effort to develop a substantive understanding of a repository site.