bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of Tungsten-Tellurite Glass Thin Films using Radio Frequency Magnetron Sputtering Method and Optical Property Characterization
Authors: Yoo Ki-Young , Shin Sanghoon , Kim Youngman , Moon Jong-Ha , Kim Jin Hyeok
Published: April 2011

Tungsten-tellurite glass thin films were fabricated by radio-frequency (rf) magnetron sputtering method at various processing parameters such as substrate temperatures, Ar/O2 processing gas flow ratio, processing pressure, and rf power from a 70TeO2-30WO3 target fabricated by solid–state sintering method. The effects of processing parameters on the growth rate, the surface morphologies, the crystallinity, and refractive indices of thin films were investigated using atomic force microscopy, X-ray diffractometer, scanning electron microscopy, and UV spectrometer. Amorphous glass thin films with a surface roughness of 4∼6 nm were obtained only at room temperature and crystalline phase were observed in all as-deposited thin films prepared at above the room temperature. The deposition rate strongly depends on the processing parameters. It increases as the rf power increases and the processing pressure decreases. Especially, it changes remarkably as varying the Ar/O2 gas flow ratio from 40sccm/0sccm to 0sccm/40sccm. When the films were formed in pure Ar atmosphere it shows a deposition rate of ∼0.2 μm /h, whereas ∼1.5 μm/h when the films was formed in pure O2 atmosphere.
Design and Fabrication of All-Polymer Photonic Devices
Authors: Callender Claire L. , Jiang Jia , Blanchetière Chantal , Noad Julian P. , Walker Robert B. , Mihailov Stephen J. , Ding Jianfu , Day Michael
Published: April 2011

High quality optical waveguides have been fabricated from fluorinated poly(arylene ether ketone) materials using a standard photolithographic process. Fabrication of waveguide devices on a polymer substrate is described, including a method of end-facet preparation using excimer laser micromachining. Material issues affecting waveguide birefringence and device performance are discussed.
Dye-Doped, Polymer-Nanoparticle Gain Media for Tunable Solid-State Lasers
Authors: Duarte F. J. , James R. O.
Published: April 2011

Tunable laser action, in the visible spectrum, has been established using dye-doped, polymer-silica nanoparticle gain media. The silica nanoparticles, averaging about 12 nm in diameter, appear to be uniformly dispersed in the polymethyl methacrylate (PMMA) matrix, since the optical homogeneity of the gain medium is maintained. Using rhodamine 6G dye and 30% weight-by-weight (w/w) silica nanoparticles, laser action was established in the 567–603 nm range. At the peak wavelength (λ ∼ 580 nm) laser conversion efficiency is ∼63% at a beam divergence of 1.9 mrad (∼1.3 times the diffraction limit). The new solid-state nanocomposite gain media also exhibits a reduction in |∂n/∂T| because the thermo-optic coefficient of silica is opposite in sign to that of the PMMA polymer-host component.
Enhanced Faraday rotation in garnet films and multilayers
Authors: Kahl S. , Grishin A. M.
Published: April 2011

Films were prepared by pulsed laser deposition. We investigated or measured crystallinity, morphology, film-substrate interface, cracks, roughness, composition, magnetic coercivity, refractive index and extinction coefficient, and magneto-optical Faraday rotation (FR) and ellipticity. The investigations were partly performed on selected samples, and partly on two series of films on different substrates and of different thicknesses. BIG films were successfully tested for the application of magneto-optical visualization. The effect of annealing in oxygen atmosphere was also investigated - very careful annealing can increase FR by up to 20%.

Periodical BIG-YIG multilayers with up to 25 single layers were designed and prepared with the purpose to enhance FR at a selected wavelength. A central BIG layer was introduced as defect layer into this one-dimensional magneto-optical photonic crystal (MOPC) and generated resonances in optical transmittance and FR at a chosen design wavelength. In a 17-layer structure, at the wavelength of 748 nm, FR was increased from–2.6 deg/μm to –6.3 deg/μm at a small reduction in transmittance from 69% to 58% as compared to a single-layer BIG film of equivalent thickness. In contrast to thick BIG films, the MOPCs did not crack. We were first to report preparation of all-garnet MOPCs and second to experimentally demonstrate the MOPC principle in magneto-optical garnets.
Frequency- and Temperature-Dependent Ferromagnetic Resonance of Co/CoO Core-Shell Nanoparticles
Authors: Wiedwald U. , Lindner J. , Spasova M. , Frait Z. , Hilgendorff M. , Giersig M. , Farle M.
Published: April 2011

Ferromagnetic Resonance experiments are used to investigate the magnetic properties of monodisperse Co/CoO core-shell nanoparticles with diameters of about 10nm. From frequency- dependent measurements at various frequencies of 9-80 GHz the g-value is determined to be 2.13 which suggests an fcc bulk-like environment of the Co atoms within the core of the particles. This result yields a direct measure of the ratio of orbital to spin magnetic moment νL/νS=0.065. Moreover, from temperature-dependent measurements of the resonance field the anisotropy energy is extracted and found much lower than the hcp bulk value.
Preparation of Silicon Carbide Nano-Particles Using a Pulsed Laser Deposition Method
Authors: Kawasaki H. , Suda Y. , Ohshima T. , Ueda T. , Nakashima S.
Published: April 2011

We have developed a new pulsed laser deposition technique using two Nd:YAG laser beams for the nucleation of silicon carbide (SiC) crystalline nano-particles and single crystalline SiC thin films. Transmission electron microscopy and atomic force microscopy observation suggest that several nanometer size SiC particles can be prepared by the new pulsed laser deposition (PLD) method using two Nd:YAG laser beams (1064nm and 532nm). X ray photoelectron spectroscopy measurements suggest that the silicon/carbon composition ratio of the prepared SiC thin films can be controlled by laser fluence and wavelength.
The Effects of Processing on the Morphology of Nanoparticles
Authors: Perrey Christopher R. , Deneen Julia M. , Carter C. Barry
Published: April 2011

One of the major challenges confronting the utilization of nanoparticles in industrial and social applications is that of producing the nanoscale materials. Of the methods of manufacturing nanoscale materials, processes involving plasmas have been shown to be cost-effective and versatile in the production of chemically diverse material. Using transmission electron microscopy, individual nanoparticles produced by a thermal plasma-based production method have been examined. The observations of these studies imply that the thermal history of the nanoparticles during formation is of great importance in the determination of the resulting nanoparticle morphology. Such results have the potential to enable the manufacturing of nanoparticles of a specific size and shape from plasmas.
Silicon Nanowire Growth at Relatively Low Processing Temperature
Authors: Kim Joondong , Ji Chunhai , Anderson Wayne A.
Published: April 2011

The Metal Induced Growth (MIG) of nanowires has the potential to alter the conventional lithographic techniques to provide an easier fabrication method in nanoelectronics. Our group has studied the MIG technique to synthesize poly-silicon and nano size structures. This work gave silicon nanowires of 20∼200 nm diameter, 3∼10νm length and single crystal structure. Until now, the growing of silicon nanowires has been understood by two models. One is an oxide- assisted mechanism and the other is a metal catalyst assisted mechanism. Both cases need higher growth temperatures above 900°C. We are now proposing the repeatable growth of silicon nanowires at a low processing temperature, 550∼600°C, which is the lowest silicon nanowire growth temperature without using a gas type silicon source (silane).

This novel method to grow silicon nanowires has several advantages: (1) low processing temperature; (2) straight line growth; (3) single crystal structure and (4) repeatability. This Si nanowire growing mechanism is based on NiSi formation.
Effect of Carrier Gas on the Growth Rate, Growth Density, and Structure of Carbon Nanotubes
Authors: Yap Yoke Khin , Kayastha Vijaya , Hackney Steve , Dimovski Svetlana , Gogotsi Yury
Published: April 2011

We attempt to understand the fundamental factors that determine the growth rate of carbon nanotubes. In a series of experiments on growing multiwall carbon nanotubes (MWNTs) by thermal chemical vapor deposition, we found that the addition of carrier gas and the type of carrier gas can change the growth rate, growth density, and structures of MWNTs. We explain these results based on the dissociative adsorption of C2H2 on Fe nanoparticles and the vapor-liquid-solid (VLS) growth model. Finally, high-density, vertically aligned MWNTs were grown when decomposition and segregation rates of carbon were balanced.
A Production Method for Aligned Nanowires on Arbitrary Materials
Authors: Kunz Rainer , Adelung Rainer
Published: April 2011

We present a method that allows us to produce aligned metallic nanowires on almost any material. This method recently enabled us to produce interconnected platinum nanowire networks on polymeric Nafion® or gold nanowires on Teflon AF. We will explain the principle of this method by means of a reference material, the so called layered transition metal dichalcogenides (TMDC) crystals. The method is based on producing cracks in thin films as templates, using large sticking coefficient differences and long diffusion lengths. The underlying mechanism that forms the template cracks is mechanical stress. In the case of the TMDC crystals this stress is introduced in the substrate by an electronic interaction between the metal used for the nanowires and the TMDC-crystal. The large difference in the condensation coefficient is an immanent property of layered crystals for many different adsorbates. Obtained by cleavage along a so called “Van-der-Waals-gap”, surfaces of such crystals are atomically flat over hundreds of microns. As a consequence of their layered character the surfaces have no reconstruction and almost no step edges or other defects, which is the basis for the long diffusion length. In contrast, the rare defects have a very high sticking coefficient and act as excellent nucleation centers. Therefore, after metal evaporation on such surfaces in UHV, various structures can be formed in a self organized processes. We observed, e.g., clusters in fractal or geometric arrangements or large nanowire networks on the surfaces [1]. In order to understand, why the different structures form, a systematic study of the growth parameters, (nucleation, diffusion length, evaporated metal, influence of the substrate-crystal), is necessary. Therefore, we first carried out diffusion studies on these surfaces. We could show that in extreme cases (Cu on metallic TaS2) diffusion length of more than 50νm could be observed combined with a nucleation probability of almost zero. This is evident from a growth mode showing similarities with the DLA (Diffusion Limited Aggregation) growth process. In contrast, metal diffusion (Cu) on the geometrically similar surfaces on the semiconducting (WSe2) surface shows much a shorter diffusion length and no DLA growth. We suggest a model to explain the different diffusion behavior as a key to understand the different self organized structures. Learning from the TMDC crystals, we show the application on technological more important materials.
Direct Observation of Highly Polarized Non-Linear Absorption Dipole of Single Semiconductor Quantum Rods
Authors: Rothenberg Eli , Ebenstein Yuval , Kazes Miri , Banin Uri
Published: April 2011

Polarization fluorescence microscopy was used to study the nature of the emission and nonlinear absorption dipole of single CdSe/ZnS quantum rods. Rods, with aspect ratios ranging from 2.75 to 15, showed strongly polarized emission consistent with previous one-photon studies. Non- linear excitation showed a sharp angular dependence fully consistent with the predicted two- photon absorption process. Two-photon absorption probes different transitions than linear absorption due to modified parity and angular momentum selection rules. The two-photon absorption dipole was found to be parallel to the emission polarization, and allows achieving highly orientation selective excitation of quantum rods. This is yet a further demonstration of single molecule measurements in unraveling basic principles of light-matter interaction that are otherwise masked by ensemble averaging.
Characterization of Shell Material on Colloidal CdSe/ZnS Quantum Dots
Authors: Yu Zhiheng , Guo Li , Du Hui , Krauss Todd , Silcox John
Published: April 2011

Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the distribution of ZnS shell material on colloidal core-shell CdSe/ZnS quantum dots (QDs). A sub-nm electron probe was placed at various locations on core-shell QDs to ascertain the chemical distribution of the shell material. While a definite shell of ZnS was detected surrounding the CdSe core, the integrated EELS signals from positions around the QD suggest the distribution of the shell material may not be uniform. A non-uniform shell implies a reduced quality of the QD surface passivation.
Optical Properties of Wurtzite GaN and ZnO Quantum Dots
Authors: Fonoberov Vladimir A. , Balandin Alexander A.
Published: April 2011

We have investigated exciton states in wurtzite GaN/AlN and ZnO quantum dots. A strong piezoelectric field in GaN/AlN quantum dots is found to tilt conduction and valence bands, thus pushing the electron to the top and the hole to the bottom of the GaN/AlN quantum dot. As a result, the exciton ground state energy in GaN/AlN quantum dots with heights larger than 3 nm exhibits a red shift with respect to bulk GaN energy gap. It is shown that the radiative decay time in GaN/AlN quantum dots is large and increases from 0.3 ns for quantum dots with height 1.5 nm to 1.1×103 ns for the quantum dots with height 4.5 nm. On the contrary, the electron and the hole are not separated in ZnO quantum dots. Moreover, a relatively thick “dead layer” is formed near the surface of ZnO quantum dots. As a result, the radiative decay time in ZnO quantum dots is small and decreases from 73 ps for quantum dots with diameter 1.5 nm to 29 ps for the quantum dots with diameter 6 nm.
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.
Optoelectronic detection of DNA molecules using an amorphous silicon photodetector
Authors: Fixe F. , Prazeres D.M.F. , Chu V. , Conde J.P.
Published: April 2011

This work demonstrates the use of an amorphous silicon (a-Si:H) photodetector to measure the density of covalently-bound DNA molecules tagged with a fluorescent molecule. This device is based on the photoconductivity of a-Si:H in a coplanar electrode configuration. Excitation of a fluorescently-tagged biomolecule with near UV/blue light results in the emission of visible light. The emitted light is then converted into an electrical signal in the photodetector, thus allowing the detection of the presence of the tagged DNA molecules. The design, fabrication and characterization of this integrated a-Si:H-based bio-detector is described. The detection limit of the present device is of the order of 20 pmol/cm2. A surface density of ≤ 30 pmol/cm2 for DNA covalently-bound to an active silica layer was measured with the a-Si:H-based bio-detector.
Development of Self-assembled Muscle-powered Microdevices
Authors: Xi Jianzhong , Schmidt Jacob J. , Montemagno Carlo D.
Published: April 2011

Abstrat

As microcomponents in engineered systems, biological muscles have unique advantages such as large force transduction, utilization of biochemical fuel, and self-assembly from single cells, over other inorganic actuators for biomedical engineering applications. Successful integration of muscles with inorganic fabricated structures and electronics promises the capability of precisely characterizing muscles' mechanical properties and fabricating self-assembled controllable autonomous structures powered by ubiquitous glucose. However, the use of extracted muscle tissue from animals on these devices is impractical and inefficient, as the tissues must be dissected and incorporated into each device by hand with crude interfaces between the biological tissue and inorganic materials. Integration of muscle with fabricated structures would be optimally achieved through self-assembling muscle cells on MEMS. The construction of self-assembled muscle-powered MEMS structures is complicated by the stringent requirements to spatially direct the cell growth, control the tight connection of these differentiated structures with MEMS structures, and enable the cells and the integrated hybrid freedom to move. Conventional and soft photolithography techniques have been extensively employed to pattern the growth of a variety of cell types and investigate their interaction with substrate in the micrometer level. However, all studies are only suitable for patterning static cells on an immobile surface, so a novel system of spatially patterning the contractible cells must be developed to enable the cells and the integrated hybrid devices to be free to move.

We present a novel system of self-assembling myocytes on MEMS devices. This system has shown its capability of spatially and selectively directed growth and differentiation of myocytes into single muscle bundles, attachment of these functional bundles to MEMS structures, and the controlled partial release of the resultant hybrid devices. Two groups of self-assembled muscle-MEMS devices, force-measuring cantilevers and muscle-powered microrobots have been created. Here the further detailed studies of this system are discussed, especially the concept of the self-assembly and the material interfacial problems in this system.
Impedance-based Biosensors
Authors: Huang X. , Greve D.W. , Nausieda I. , Nguyen D. , Domach M.M.
Published: April 2011

Impedance measurements on arrays of microelectrodes can provide information about the growth, motility, and physiology of cells growing on the electrodes. In this talk, we report recent results obtained for the growth of 3T3 mouse fibroblasts and HCT116 human cancer cells on gold electrodes approximately 0.4 mm2 in area. Cells produce a characteristic peak in the impedance change plotted as a function of frequency. With the aid of electrical modeling of the cell-electrode system, the details of the changes in the measured impedance can be correlated to the cell size, fractional electrode coverage, and cell-electrode gap. In particular, comparison of impedance measurements of these two cell types show clear differences in the growth rate and the ratio of the cell-electrode gap to the cell size. In addition to presenting these experimental results illustrating the utility of electrode impedance measurements, we will outline the issues encountered when electrodes are scaled to cell size and incorporated into a matrix-addressed array.
Fabrication of two-dimensional photonic structure of titanium dioxide with sub-micrometer resolution by deep x-ray lithography
Authors: Awazu Koichi , Fujimaki Makoto , Wang Xiaomin , Sai Akihide , Ohki Yoshimichi
Published: April 2011

Two dimensional photonic crystals of titanium dioxide is expected to have many advantage compared with photonic crystals of semiconductors, e.g., silicon and GaAs. For example, low optical loss in the near infrared region used for optical communication, low thermal expansion, and its refractive index which is close to that for optical fiber are attractive advantages. However, it is difficult to create micro-nano structure in titanium dioxide because micro-fabrication technique for semiconductor is not available for titanium dioxide. As the first step we calculated photonic band gap of titanium dioxide rod-slab on SiO2. Also, band gap percent against thickness of the rod-slab was examined. Finally, we confirmed the most suitable structure of 2D photonic crystals. Deep x-ray lithography technique was employed for create a very deep and precise template of PMMA. Then, liquid-phase deposition was used to faithfully deposit a tightly packed layer of titanium oxide onto the template. Finally, the template is selectively removed to obtain a photonic nano-structure. We also calculate photonic band gap on the 3D-structure of TiO2. A template for the most appropriate structure was fabricated by the method proposed by Yablonovitch. By using of the same method, it was successful to obtain 3D structure of TiO2. Refractive index of obtained TiO2 followed by heating at 700°C was determined to 2.5 which is close to that for anatase phase.
Fabricate Photonic Crystals Based on ZnS/opal System via Solvothermal Method
Authors: Cao Jieming , Chang Xin , Pan Lijia , Ji Hongmei , Liu Jinsong , Feng Jie , Zhang Fang , Wang Haiyan , Tao Jie , Xu Guoyue
Published: April 2011

We made photonic crystals composed of artificial opals infiltrated with ZnS semiconductor nanocrystals by using self-assembly and solvothermal methods. Scanning electron microscopy images show that the silica spheres exhibit a well-ordered arrangement and the ZnS nanocrystals grow homogenously inside the opal matrix and the as-synthesized ZnS nanocrystals reveal a cubic phase from X-ray diffraction pattern. Furthermore, the optical properties of the infiltrated opals with different ZnS filling ratio are also studied by transmission spectroscopy respectively. It is proposed that the position of the stop band can be easily designed by controlling the infiltration ratio of ZnS. These results demonstrate an effective and practical route to obtain high-performance photonic crystal structures.
Influence of H2 Preconditioning on the Nucleation and Growth of Self-Assembled Germanium Islands on Silicon (001)
Authors: Dilliway Gabriela D.M. , Cowern Nicholas E.B. , Xu Lu , McNally Patrick J. , Jeynes Chris , Mendoza Ernest , Ashburn Peter , Bagnall Darren M.
Published: April 2011

Understanding the effects of growth conditions on the process of self-organisation of Ge nanostructures on Si is a key requirement for their practical applications. In this study we investigate the effect of preconditioning with a high-temperature hydrogenation step on the nucleation and subsequent temporal evolution of Ge self-assembled islands on Si (001). Two sets of structures, with and without H2 preconditioning, were grown by low pressure chemical vapour deposition (LPCVD) at 650°C. Their structural and compositional evolution was characterised by Rutherford backscattering spectrometry (RBS), atomic force microscopy (AFM) and micro-Raman (νRaman) spectroscopy. In the absence of preconditioning, we observe the known evolution of self-assembled Ge nanostructures on Si (001), from small islands with a narrow size distribution, to a bimodal size distribution, through to large islands. Surface coverage and island size increase steadily as a function of deposition time. On the H2 preconditioned surface, however, both nucleation rates and surface coverage are greatly increased during the early stages of self-assembly. After the first five seconds, the density of the islands is twice that on the unconditioned surface, and the mean island size is also larger, but the subsequent evolution is much slower than in the case of the unconditioned surface. This retardation correlates with a relatively high measured stress within the islands. Our results demonstrate that standard processes used during growth, like H2 preconditioning, can yield dramatic changes in the uniformity and distribution of Ge nanostructures self-assembled on Si.
A New Synchrotron-based Technique for Measuring Stresses in Ultrathin Metallic Films
Authors: Böhm Jochen , Gruber Patric , Spolenak Ralph , Wanner Alexander , Arzt Eduard
Published: April 2011

A novel synchrotron-based X-ray diffraction technique is presented by which it is possible to characterize the evolution of stresses in polycrystalline metallic films thinner than 100 nm. The film under investigation is deposited on a flexible polyimide substrate which is subjected to a uniaxial tensile test. The evolutions of longitudinal and transverse elastic strains in the film are monitored simultaneously by means of a high-resolution area detector. The strain resolution is better than 10−4. The samples are typically subjected to 6 % total strain and subsequently unloaded. First experiments carried out on Au films in the thickness range between 20 nm and 1000 nm show the usefulness and the power of this new technique.
Utilizing On-Chip Testing and Electron Microscopy to Study Fatigue and Wear in Polysilicon Structural Films
Authors: Alsem D.H. , Stach E.A. , Muhlstein C.L. , Dugger M.T. , Ritchie R.O.
Published: April 2011

Wear and fatigue are important factors in determining the reliability of microelectromechanical systems (MEMS). While the reliability of MEMS has received extensive attention, the physical mechanisms responsible for these failure modes have yet to be conclusively determined. In our work, we use a combination of on-chip testing methodologies and electron microscopy observations to investigate these mechanisms. Our previous studies have shown that fatigue in polysilicon structural thin films is a result of a ‘reaction-layer’ process, whereby high stresses induce a room-temperature mechanical thickening of the native oxide at the root of a notched cantilever beam, which subsequently undergoes moisture-assisted cracking. Devices from a more recent fabrication run are fatigued in ambient air to show that the post-release oxide layer thicknesses that were observed in our earlier experiments were not an artifact of that particular batch of polysilicon. New in vacuo data show that these silicon films do not display fatigue behavior when the post release oxide is prevented from growing, because of the absence of oxygen. Additionally, we are using polysilicon MEMS side-wall friction test specimens to study active mechanisms in sliding wear at the microscale. In particular, we have developed in vacuo and in situ experiments in the scanning electron microscope, with the objective of eventually determining the mechanisms causing both wear development and debris generation.
Size Effect on Crack Formation in Cu/Ta and Ta/Cu/Ta Thin Film Systems
Authors: Gruber P. , Böhm J. , Wanner A. , Sauter L. , Spolenak R. , Arzt E.
Published: April 2011

Layered structures of Cu and Ta thin films on silicon are well established for many technological applications in microelectronics. Electronic circuits used for flexible displays or wearable electronics are becoming increasingly popular. For such applications, the Cu/Ta system must be transferred to flexible substrates, incorporating a design rule for several percent of total strain. We have investigated the deformation behaviour of different Cu/Ta and Ta/Cu/Ta thin film systems on a flexible polyimide substrate subjected to total strains of more than 5%. A novel synchrotron X-ray diffraction technique allowed us to characterize the evolution of mechanical stress in very thin metallic films during isothermal tensile tests. We found that samples with a Cu film thickness below 300 nm showed a sudden stress decrease at a total strain of about 2.5%. This stress drop was attributed to fracture of the entire film system, initiated by cracks in the Ta layers.
Effect of Mold Dimensions on Temperature Distribution of Sintered Body during Plasma Activated Sintering
Authors: Lee Gil-Geun
Published: April 2011

In the present study, the focus is on the analysis of the effect of the mold dimensions on the temperature distribution of a sintered body during plasma activated sintering. The temperature distribution of a cylindrical mold with various dimensions was measured using K-type thermocouples. The temperature homogeneity of the mold was studied based on the direction and dimensions of the mold. A temperature gradient existed in the radial direction of the mold during the plasma activated sintering. Also, the magnitude of the temperature gradient was increased with increasing sintering temperature. In the longitudinal direction, however, there was no temperature gradient. The temperature gradient of the mold in the radial direction decreased with increasing inner diameter of the mold and its length.
Computer Simulated 3D Virtual Reality for Dynamical Modeling and Calculations of Carbon-Based Composite Materials
Authors: Kireitseu Maksim V. , Hui David , Bochkaryova Liya , Eremeev Sergey , Nedavniy Igor
Published: April 2011

The principal goal of the present paper is to demonstrate an application of modern software engineering tools for modeling virtual reality and molecular dynamics of novel nanocomposites. The main technical components of presented system are 1) software and nanoengineering tools for modeling of virtual reality, molecular dynamic and 3D video images of novel diamonds- containing nanocomposites and 2) Problem tracking system to be used during modeling of virtual reality. For a realistic simulation of the stability behavior of the reinforced material, the nonlinear intramolecular inter-actions between neighboring atoms have to be taken into account. A comparison shows the buckling sensitivity of different geometries. In order to reduce computational costs, it is necessary to develop suited homogenization techniques, so that shell elements can be applied.
Synthesis of Zeolite as Ordered Multi-Crystal Arrays using Uniformly Aligned Polyurethane as Templates
Authors: Lee Jin Seok , Lee Yun-Jo , Tae Eunju Lee , Park Yong Soo , Yoon Kyung Byung
Published: April 2011

Two types of glass plates coated with uniformly aligned polyurethane films were produced by repeating the cycles of the alternative exposures of the glass plates to 1,4-phenylene diisocyanate (PDI) and 2-butyne-1,4-diol (BDO) and to PDI and terephthalic acid bis-(2-hydroxy ethyl) ester (TBE) for 500 times at elevated temperatures. The glass plates coated with uniformly aligned poly-(PDI-BDO)500(500 represents the number of the cycle) produced monolayers of closely packed 2D arrays of silicalite-1 crystals with the average size of 370 × 200 × 500 nm on the glass plates upon immersion of the glass plates into a dense gel consisting of tetraethylorthosilicate (TEOS), tetrapropylammonium hydroxide (TPA+OH-), and water (mole ratio = 7:1.5:330) followed by the hydrothermal reaction at 180°C for 2 h. The silicalite-1 crystals were aligned with the c-axes perpendicular to the substrate plane. Upon switching the polymer from poly-(PDI-BDO)500to poly-(PDI-TBE)500the orientations of the silicalite-1 crystals in the 2D arrays changed from c to a axes perpendicular to the substrate. This report therefore demonstrates that the uniformly aligned polyurethane films serve as the templates for the growth of closely packed multi-crystal arrays of silicalite-1 in uniform orientations and the nature of the polyurethane film affects the resulting orientations of the crystals. We propose that the supramolecularly organized organic-inorganic composites consisting of the hydrolyzed organic products and the seed crystals responsible for the above phenomena.
Mechanism-based strain gradient crystal plasticity
Authors: Han Chung-Souk , Gao Huajian , Huang Yonggang , Nix William D.
Published: April 2011

To model size dependent plastic deformation at micron and submicron length scales the theory of mechanism-based strain gradient plasticity (MSG) was developed. The MSG approach incorporates the concept of geometrically necessary dislocations into continuum plastic constitutive laws via Taylor hardening relation. This concept is extended here to develop a mechanism-based strain gradient theory for crystal plasticity (MSG-CP) based on the notions of dislocation density tensor and resolved density force corresponding to the Peach-Koehler force in dislocation theory. An effective density of geometrically necessary dislocations is defined on the basis of resolved density force for specific slip systems and is incorporated into the plastic constitutive laws via Taylor relation.
Texture and Microstructure Evolution in Silver Thin films with FACET
Authors: Rairkar Asit , Zhang Jie , Adams Jim
Published: April 2011

Metallic polycrystalline thin films are used in a plethora of applications, including especially metallic interconnects for the microelectronics industry. Despite the numerous approaches at modeling and simulating processing of these films, there have not been any simulation tools, which can accurately predict texture and microstructure evolution in these films. We have developed a novel 2D model called FACET for the simulation of polycrystalline thin film growth at realistic spatial and time scales. The basic idea is to use the results of smaller-scale atomic simulations (density functional theory, molecular dynamics, and lattice Monte Carlo) to provide input and guidance on the evolution of grain structure and texture on a micron scale. The feature scale model is based on describing grains in terms of two-dimensional faceted surfaces and grain boundaries. The model includes the major phenomena involved in film growth, including deposition, nucleation, surface diffusion (on the substrate and on the growing film), inter-facet diffusion, and grain growth and coarsening. In addition, the texture of each grain is treated individually, so that the texture evolution of the system can be simulated. Predictions of the FACET code are compared with previous experimental studies of texture and microstructure in Silver films.
Deformation Mechanisms and Ductility of Nanostructured Al Alloys
Authors: Han Bing Q. , Mohamed Farghalli A. , Lavernia Enrique J.
Published: April 2011

Low tensile ductility is one of the critical challenges facing the science and technology of nanostructured materials. As an example, despite the fact that high strength is frequently observed in bulk nanostructured Al alloys, ductility and work hardening are often observed to decrease with decreasing grain size. In the present study, the tensile ductility of bulk nanostructured aluminum alloys processed via severe plastic deformation and consolidation of mechanically milled powders is analyzed. Adding coarse grains to the nanostructured matrix is proposed as an approach to improve ductility.
On the Influence of the Misorientation of Grains, Grain Size and Boundary Volume on the Strength and Ductility of Ultrafine Grained Cu
Authors: Dalla Torre Florian H. , Lapovok Rimma , Thomson Peter F. , Sandlin James D. , Davies Chris H.J. , Pereloma Elena V.
Published: April 2011

The influence of the microstructure and the misorientation relationship of grains on mechanical properties is investigated in specimens of ultrafine-grained copper processed by equal channel angular extrusion (ECAE) route Bc for 1, 4 and 12 passes. XRD texture analyses have shown that the major texture component is developed during the first pass of ECAE, and remains approximately constant with greater number of passes. EBSD measurements indicate that the majority of grain boundaries are still of low angle (>15°), while after four and twelve passes more than 50 % of all boundaries are high angle ones. TEM analyses have shown that the microstructure evolves from microbands and elongated cells towards a more equiaxed homogenous microstructure. On the microscale observed by TEM the degree of misorientation among subgrains/cells increases and the width of boundaries decreases while the cell/subgrain size remains approximately constant as the number of passes increases. The mechanical properties show a saturation level with a maximum in the yield stress and UTS after 4 passes. The strength of the material decreases between the fourth and the twelfth passes and the uniform elongation increases. It is suggested that the increase in ductility (and decrease in strength) is associated with the decrease in width of boundaries leading to an increase in the mean free path of dislocations.
Experiment and FEM Analysis of Tensile Behavior of Bimodal Nanocrystalline Al-Mg Alloys
Authors: Lee Zonghoon , Lee Johnathan , Lavernia Enrique J. , Nutt Steven R.
Published: April 2011

The tensile behavior of bimodal nanocrystalline Al-7.5Mg alloys was investigated using experiments and two-dimensional axisymmetric elastic-plastic finite element method (FEM). Cryomilled nanocrystalline powders blended with 15% and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk bimodal nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions. The calculated stress-strain curves have acceptable agreement with experimental curves of the bimodal structures. The bimodal Al-7.5Mg alloys show reasonable ductility while retaining enhanced strength compared to conventional alloys and nanocrystalline metals.
Biological Functionalization of Carbon Nanotubes
Authors: Sirdeshmukh Ranjani , Teker Kasif , Panchapakesan Balaji
Published: April 2011

Carbon nanotubes are known for their exceptional mechanical and unique electronic properties. The size dependant properties of nanomaterials have made them attractive to develop highly sensitive sensors and detection systems. This is especially true in biological sciences, where the efficiency of detection systems reflect on the size of the detector and the sample required for detection. At approximately 1.5 to 10nm wide, and approximately 1.5 to 2μm long, the use of carbon nanotubes as sensors in biological systems would greatly increase the sensitivity of detection and diagnostics, for a reduced sample size consisting of few individual proteins and antibodies. Since all the atoms in carbon nanotubes are surface atoms, binding proteins or antibodies to the surfaces can greatly affect their surface states, and thus their electrical and optical properties. This effect can be exploited as a basis for detecting biological surface reactions in a single protein or antibody attached to carbon nanotube surfaces.

In this paper, we show the binding of fluorescently tagged antibodies in phosphate buffered saline on the surfaces of carbon nanotubes. Investigations using a confocal microscope suggest a significant interaction of the antibodies with the surfaces of the nanotubes, the intensity depending on incubation time. Since the surface area to volume ratio of CNTs is high, the use of surfactant to separate the nanotubes creates a greater surface area for antibody attachment. The interaction between CNTs and antibodies is seen to be primarily due to adsorptive surface phenomenon, between the nanotube sidewalls and antibody molecule clusters.
Nanowiring Enzymes to Carbon Nanotube Probes
Authors: Collier C.P. , Esplandiu M.J. , Bittner V.G. , Shapiro I.R.
Published: April 2011

The observation of spectroscopic signals in response to mechanically induced changes in biological macromolecules can be enabled at an unprecedented level of resolution by coupling single-molecule manipulation/sensing using carbon nanotubes with single-molecule fluorescence imaging. Proteins, DNA and other biomolecules can be attached to nanotubes to give highly specific single-molecule probes for the investigation of intermolecular dynamics, the assembly of hybrid biological and nanoscale materials and the development of molecular electronics. Recent advances in nanotube fabrication and Atomic Force Microscope (AFM) imaging with nanotube tips have demonstrated the potential of these tools to achieve high-resolution images of single molecules. In addition, proof-of-principle demonstrations of nanotube functionalization and attachment of single molecules to these probes have been successfully made.

Improved techniques for the growth and attachment of single wall carbon nanotubes as robust and well-characterized tools for AFM imaging are being developed. This work serves as a foundation toward development of single-molecule sensors and manipulators on nanotube AFM tips for a hybrid atomic force microscope that also has single-molecule fluorescence imaging capability. An individual single wall carbon nanotube (SWNT) attached to an AFM tip can function as a structural scaffold for nanoscale device fabrication on a scanning probe. Such a probe can have a novel role, to trigger specific biochemical reactions or conformational changes in a biological system with nanometer precision. The consequences of these perturbations can be read out in real time by single-molecule fluorescence and/or AFM sensing. For example, electrical wiring of single redox enzymes to carbon nanotube scanning probes will allow for observation and electrochemical control of single enzymatic reactions, by monitoring fluorescence from a redox-active cofactor or the formation of fluorescent products. Enzymes “nanowired” to carbon nanotube tips may enable extremely sensitive probing of biological stimulus-response with high spatial resolution, including product-induced signal transduction.
NanoLiterBioReactor: Monitoring of Long-Term Mammalian Cell Physiology at Nanofabricated Scale
Authors: Prokop Ales , Prokop Zdenka , Schaffer David , Kozlov Eugene , Wikswo John , Cliffel David , Baudenbacher Franz
Published: April 2011

There is a need for microminiaturized cell-culture environments, i.e., NanoLiter BioReactors (NBRs), for growing and maintaining populations of up to several hundred cultured mammalian cells in volumes three orders of magnitude smaller than those contained in standard multi-well screening plates. Reduced NBR volumes would not only shorten the time required for diffusive mixing, for achieving thermal equilibrium, and for cells to grow to confluence, but also simplify accurate cell counting, minimize required volumes of expensive analytical pharmaceuticals or toxins, and allow for thousands of culture chambers on a single instrumented chip. These devices would enable the development of a new class of miniature, automated cell- based bioanalysis arrays for monitoring the immediate environment of multiple cell lines and assessing the effects of drug or toxin exposure. The challenge, beyond that of optimizing the NBR physically, is to detect cellular response, provide appropriate control signals, and, eventually, facilitate closed-loop adjustments of the environment–e.g., to control temperature, pH, ionic concentration, etc., to maintain homeostasis, or to apply drugs or toxins followed by the adaptive administration of a selective toxin antidote. To characterize in a nonspecific manner the metabolic activity of cells, the biosensor elements of the NBR might include planar pH, dissolved oxygen, and redox potential sensors, or even an isothermal picocalorimeter (pC) to monitor thermodynamic response. Equipped with such sensors, the NBR could be used to perform short- and long-term cultivation of several mammalian cell lines in a perfused system, and to monitor their response to analytes in a massively parallel format. This approach will enable automated, parallel, and multiphasic monitoring of multiple cell lines for drug and toxicology screening. An added bonus is the possibility of studying cell populations with low cell counts whose constituents are completely detached from typical tissue environment, or populations in controlled physical and chemical gradients.
A Probabilistic Model for Degradation of the Engineered Barriers System in the Yucca Mountain Repository
Authors: Qin Z. , Shoesmith D.W.
Published: April 2011

A probabilistic model to predict the lifetimes of the engineered barrier system proposed for the Yucca Mountain repository is described. The model assumes that the titanium Grade-7 drip shield will fail by hydrogen-induced cracking and the Alloy-22 waste package by a combination of passive and crevice corrosion. The model predicts that crevice corrosion of the waste package can be completely avoided ifthe drip shield deflects seepage drips for between 2000 (realistic behaviour) and 6000 years (conservative behaviour). Sensitivity calculations on the crevice corrosion model suggest that early waste package failure is extremely unlikely providing the drip shield performs its function for a minimum of ~ 300 years.
Radionuclides Release Model for Performance Assessment Studies of Spent Nuclear Fuel in Geological Disposal
Authors: Poinssot Christophe , Lovera Patrick , Ferry Cécile
Published: April 2011

In the framework of the research conducted on the long term evolution of spent nuclear fuel in geological disposal conditions, a source term model has been developed to evaluate the instantaneous release of RN (Instant Release Fraction IRF) and the delayed release of the RN which are embedded within the matrix. This model takes into account all the scientific results currently available in the literature except the hydrogen effect. IRF was assessed by considering the evolution with time of the RN inventories located within the fuel microstructure to which no confinement properties can be allocated on the long term (rim, gap, grain boundaries). It allows to propose some reference bounding values for the IRF as a function of time of canister breaching and burnup. The matrix radiolytic dissolution was modeled by a simple kinetic model neglecting the radiolytic species recombination and the influence of aqueous ligands and radiolytic oxidants were supposed to completely react with the fuel surface. Spent fuel performance was therefore demonstrated to deeply depend on the reactive surface area.
The Effect of Cs On The Structural Properties Of Barium Titanate Hollandites
Authors: Whittle K.R. , Lumpkin G.R. , Ashbrook S.E.
Published: April 2011

Hollandite, based on Ba and Ti, has been shown to be an ideal medium by which active 135Cs and 137Cs can be immobilised. Diffraction measurements have shown that Cs modifies the symmetry of the material, from monoclinic to tetragonal. Experiments carried out here show the effects of Cs on two hollandite systems based on Ba-Al-Ti and Ba-Mg-Ti. Structural measurements are reported for neutron diffraction, and MAS NMR. The results show that Cs modifies the overall crystal symmetry while having little effect on the order/disorder of Al-Ti and Mg-Ti octahedra.
Mn Oxidation States in Bax CsyMnzTi8-zO16
Authors: Carter M.L. , Vance E.R. , Mitchell D. R. G. , Zhang Z.
Published: April 2011

Two Bax CsyMnzTi8-zO16 hollandite samples, containing excess rutile, have been prepared, targeting the Mn valence as 3+ by sintering at 1300oC in air (z = 2x +y) and as 2+ (z = x + y/2) in argon. SEM showed the sample sintered in air to contain major hollandite and minor Mn titanate and rutile. The sample sintered in argon contain major hollandite, and minor Ba titanate and rutile. X-ray absorption near edge spectroscopy (XANES), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) were used to determine the oxidation state of the Mn in the samples. Transmission manganese K-edge X-ray absorption spectra of the samples were similar but the precise ratio of oxidation states could not be calculated from these spectra.