bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Shot Peening on Fatigue Properties of Zr-based Amorphous Matrix Composites
Authors: Jeon Changwoo , Kim Choongnyun Paul , Lee Sunghak 
Published: September 2011

AbstractEffects of shot peening on fatigue properties of Zr-based amorphous matrix composite containing ductile crystalline particles were investigated, and fatigue processes were analyzed and compared with those of an as-cast composite. The microstructural analysis results of the shot-peened composite surface indicated that the deformation and surface flexion were observed as the shot-peening time or pressure increased. The compressive residual stress formed on the shot-peened surface was about the half of the ultimate tensile strength, and was not varied much with shot-peening time or pressure. The fatigue limit and fatigue ratio of the shot-peened composite were considerably higher than those of the as-cast composite. This was because the compressive residual stress formed by the shot peening induced the initiation of fatigue cracks at the specimen interior, instead of the specimen surface, thereby leading to the enhanced fatigue limit and fatigue life.
Broadband Coverage Optical Sensor with Liquid Crystalline Materials and Pyroelectrics
Authors: Zhang Jingwen W. , Sun Xiudong , Zhao Hua 
Published: September 2011

ABSTRACTBy utilizing a thin layer of supertwisted liquid crystal and potassium sodium strontium barium noibate crystal material with excellent pyroelectric effect, a broadband coverage optical sensing concept was proposed. Coating the pyroelectric substrate with a carbon layer of excellent absorption in the frequency range of interest, the intensity of an incident mid- or far-IR radiation can be converted to a corresponding intensity variation of a reflected near-IR beam via optical modulation of the liquid crystal film. As the result, the spatial intensity distribution of an incident mid- or far-IR radiation can thus be perceived directly by a low-cost semiconductor sensor/ sensor array. With flexible design of wave collecting arrangement, the broadband coverage sensor is suitable for viewing IR-giving objects with a large field-of-view.
Excitation-Induced Low Temperature Epitaxial Growth of Ge on Si(100)
Authors: Er Ali Oguz , Elsayed-Ali Hani 
Published: September 2011

ABSTRACTThe effect of laser-induced electronic excitations on the self-assembly of Ge quantum dots (QD) on Si(100)-(2x1) grown by pulsed laser deposition is studied. The experiment was conducted in ultrahigh vacuum. A Q-switched Nd:YAG laser (wavelength λ = 1064 nm, 10 Hz repetition rate) was split into two beams; one used to ablate a Ge target while the other to electronically excite the substrate. In situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) were used to study the morphology of the grown QDs. The dependence of the QD morphology on substrate temperature and ablation and excitation laser energy density was studied. Electronic excitation is shown to affect the surface morphology. For Ge coverage of 22 monolayer, it was observed that the excitation laser reduces the epitaxial growth temperature to 250 °C, a temperature at which no epitaxy is possible without excitation. Applying the excitation laser to the substrate during the growth changes the QD morphology and island density and improves the size uniformity of QDs at 390 °C. Surface diffusion measurement calculated from RHEED recovery curves show that the excitation-laser increases the surface diffusion of the Ge atoms. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is involved.
Stability and Dynamics of Boron Nitride Nanoscrolls
Authors: Perim Eric , Galvao Douglas S. 
Published: September 2011

ABSTRACTWe report here molecular dynamics results for boron nitride nanoscroll structures (BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping layers. The energy balance between losses and gains (due to elastic deformations and van der Waals interactions, respectively) when the structure is rolled up leads to the existence of a critical value of the internal scroll diameter where stable or metastable structures can be formed. The mechanisms of scroll formation and stability as a function of their chirality were also investigated.
Gold in Flux-less Bonding: Noble or not Noble
Authors: Balucani Marco , Nenzi Paolo , Palma Fabrizio , Bandarenka Hanna , Dolgyi Leonid , Shapel Aliksandr 
Published: September 2011

ABSTRACTThis work highlights the solder joints reliability issues emerged during the development of a novel compliant contacting technology. The peculiar process in this technology is a mechanical lifting procedure in which a pulling force is exerted onto 63Sn-37Pb (eutectic) solder joints (realized by a flux-less thermo compression process), releasing metal traces from the substrate, to form free standing vertical structures. Since joints mechanical characteristics are critical for the successful fabrication of contacts, different bonding conditions (inert or forming atmosphere, temperature rates) and surface finishing (electroplated gold and preformed solder) have been tested. SEM and EDX analyses have been performed on failing joints to investigate failure causes and classify defect typologies. A constantly higher failure rate (percent number of failing joints) has been observed on gold finished surfaces. Analyses proved that such unusual rate was due to contamination of gold surface left by additives in the plating bath and to the embrittlement caused by gold diffusion into molten solder. Plating additives contamination reduces the wettability of gold surfaces. Concentration values of 3 wt.% for gold, considered safe for surface mount applications, caused embrittlement in solder bumps of 20-40 μm diameters.
Investigation of Nanofibrillar Influence on Cell-Cell Interactions of Astrocytes by Epi-fluorescence and Atomic Force Microscopies
Authors: Tiryaki Volkan M. , Ayres Virginia M. , Khan Adeel A. , Flowers Dexter A. , Ahmed Ijaz , Delgado-Rivera Roberto , Meiners Sally 
Published: September 2011

ABSTRACTLong distance intercellular communication between astrocytes on nanofibrillar and planar surfaces was investigated by epi-fluorescence microscopy and atomic force microscopy. We found that astrocytes on nanofibrillar surfaces and astrocytes on planar surfaces diverged in apparent cell-cell contact structures. Astrocytes on nanofibrillar surfaces exhibited a “single cellular process” response, while astrocytes on planar surfaces exhibited a filopodial network response. The possibility that astrocytes can sense their geometrical environment and form different cell-to-cell contacts on nanofibrillar versus planar surfaces, with activation of different signaling pathways, is discussed.
Development and Fundamental Characteristics of a Prototype Magnetocaloric Heat Pump
Authors: Kawanami Tsuyoshi , Hirano Shigeki 
Published: September 2011

ABSTRACTThe primary objective of this study is to discuss the optimum operating conditions of magnetocaloric heat pumps according to the fundamental heat transfer characteristics of an active magnetic regenerator (AMR) bed. The AMR cycle has four sequential processes: magnetization, heat exchange fluid flow, demagnetization, and heat exchange fluid blow. The fundamental heat transfer characteristics of each process of the AMR cycle is investigated minutely. Moreover, the cooling power and the overall system performance are evaluated when the system is running continuously.In addition to the aforementioned investigation, we have developed a prototype rotational magnetocaloric heat pump having a compact component arrangement and an uncomplicated control system. A performance evaluation has been conducted to obtain the optimum conditions for practical operation. The operation parameters such as the heat transfer fluid flow rate, rotational frequency, and initial temperature of the heat transfer fluid are examined, and the variations of the maximum temperature span between the inlet and outlet for the heat transfer fluid are discussed. As a result, the values of the optimum rotational frequency and flow rate are obtained to obtain the maximum temperature span between the inlet and outlet of the present magnetocaloric heat pump.
Discovery of γ-B28, a Novel Boron Allotrope with Partially Ionic Bonding
Authors: Oganov Artem R. 
Published: September 2011

ABSTRACTγ-B28is a recently discovered high-pressure phase of boron, with the structure consisting f icosahedral B12clusters and B2pairs in a NaCl-type arrangement: (B2)δ+(B12)δ-, and displaying a significant charge transfer δ~0.48. Boron is the only light element, for which the phase diagram has become clear only a few years ago, with the discovery of γ-B28, and this phase diagram is discussed here among other recent findings. γ-B28was first experimentally obtained as a pure boron allotrope in early 2004 by J.H. Chen and V.L. Solozhenko (although a similar diffraction pattern was published in a 1965 by R.H. Wentorf, in a paper that until recently was believed to be wrong) and its unique structure was discovered by A.R. Oganov in 2006 with the use of theab initioevolutionary algorithm USPEX (Oganov & Glass, 2006) and later confirmed by other studies. This allotrope, thermodynamically stable at high pressures, is shown to be also quenchable and dynamically stable upon decompression to 1 atm, and we show its phonon dispersion curves. Present discussion includes also the relative stability of other boron allotropes as a function of pressure. We also discuss more recent publications on the putative isosymmetric phase transition in γ-B28and the nature of chemical bonding in it. We demonstrate that a qualitative difference in the evolution of the band gap of γ-B28and the related α-B12structure, which is due to the partial ionicity of γ-B28.
Nanostructured Telluride Films on Macroporous Silicon for High Efficiency Thermoelectric Devices
Authors: Robinson Hans D. , Sneh Ofer , Kochergin Vladimir 
Published: September 2011

ABSTRACTWe propose using macroporous silicon as an ultra-high aspect ratio scaffolding for epitaxially grown thermoelectric materials, so that thin films can be shaped into materials thick enough for practical devices. The self-limiting nature of atomic layer deposition (ALD) makes it an ideal growth technique for this substrate, as uniform thickness can be obtained at all points inside the macroporous structure, and we demonstrate successful deposition of antimony telluride on pore walls using ALD. Extension of this work to telluride superlattices should enable fabrication of thermoelectric devices with figures of merit (ZT) in excess of 2. Characterization of the thermoelectric and other properties of ALD grown telluride on silicon is ongoing.
Effects of temperature dependent chemical potential on the Seebeck coefficient of TiS2 thermoelectric material
Authors: Takeuchi Tsunehiro , Yamamoto Akio , Ogawa Koto 
Published: September 2011

ABSTRACTThe relation between chemical potential and Seebeck coefficient was investigated by using high-resolution angle resolved photoemission spectroscopy. The temperature dependence of chemical potential was experimentally determined for the n-type TiS2 thermoelectric material and compared with the measured Seebeck coefficient. We found that the temperature dependence of chemical potential of TiS2 is significantly large, and its effect on Seebeck coefficient is not negligible. This fact strongly indicates that the temperature dependence of chemical potential has to be properly understood to construct the guiding principle for developing new, practical thermoelectric materials.
Excited Multiplets of Eu in GaN
Authors: Hourahine Ben 
Published: September 2011

ABSTRACTA method to calculate the multiplet states of lanthanide impurities in solids is presented. This approach is based on a semi-empirical density functional method which includes corrections to account for the correlation and spin-orbit coupling of the 4f electrons. Specific multiplet states of the rare earth are produced by constraining the system. This approach is then used to investigate some of the properties of substitutional europium impurities in gallium nitride, reproducing the relative energy of two multiplets, and discussing a potential excitation mechanism for these centers.
Pt/TiO2 Growth Templates for Enhanced PZT films and MEMS Devices
Authors: Potrepka Daniel M. , Fox Glen R. , Sanchez Luz M. , Polcawich Ronald G. 
Published: September 2011

ABSTRACTThe crystallographic texture of lead zirconate titanate (PZT) thin films strongly influences the piezoelectric properties used in MEMS applications. For PZT films poled to saturation, the piezoelectric response is sequentially greater for random, {111}, and {001} texture. Textured growth can be achieved by relying on crystal growth habit and can also be initiated by the use of a seed layer that provides a heteroepitaxial template. Template choice and the process used to form it determine the structural quality and ultimately influence performance and reliability of MEMS PZT devices such as switches, filters, and actuators. This study focuses on how {111}-textured PZT is generated by a combination of crystal habit and templating mechanisms that occur in the PZT/bottom-electrode stack. The sequence begins with {0001}-textured Ti deposited on thermally grown SiO2 on a Si wafer. The Ti is converted to {100}-textured TiO2 (rutile) through thermal oxidation. Then {111}-textured Pt can be grown to act as a template for {111}-textured PZT. The Ti and Pt are deposited by DC magnetron sputtering. The TiO2 and Pt film textures and structure were optimized by variation of sputtering deposition times, temperatures and power levels, and post-deposition anneal conditions. The relationship between Ti, TiO2, and Pt texture and their impact on PZT growth will be presented.
Giant Piezoresistive Variation of Metal Particles Dispersed in PDMS Matrix
Authors: Stassi Stefano , Canavese Giancarlo , Lombardi Mariangela , Guerriero Andrea , Fabrizio Pirri Candido 
Published: September 2011

ABSTRACTAn Investigation of the piezoresistive response of a metal-polymer composite based on nickel conductive filler in a polydimethylsiloxane (PDMS) insulating matrix for tactile sensor application is presented in this paper. Lacking a mechanical deformation, the prepared composites show no electric conductivity, even though the metal particle content is well above the expected percolation threshold. In contrast, when subjected to uniaxial compression, the electric resistance is strongly reduced. A variation of up to nine orders of magnitude was registered. The thickness of the insulating layer between particles decreases when the sample composite is compressed. Therefore, the electric conduction which is related to a tunneling phenomena, increases exponentially. This behavior is further enhanced by the presence of very sharp nanometric spikes on the particles surface which act as field enhancement factors. In the presented work, the piezoresistive behavior of the composite, the stability in time of the resistance value and the response to several cycles of compression and decompression are evaluated on samples with different physical parameters like nickel content, PDMS copolymer/curing agent ratio and thickness.
The Impact of Hands-on Experience in Undergraduate Nanotechnology Education
Authors: Oxenham Joseph A. , Teker Kasif 
Published: September 2011

ABSTRACTNanotechnology, a field interested in materials with features smaller than 100 nanometers and possessing novel properties, is a field that is unquestionably in a period of rapid growth. As the limits of existing technologies are pressed, the need arises for faster, better, and stronger materials and devices. Manipulation of matter on the nanoscale is quickly becoming the next frontier of materials and technology. Due to the scale of the phenomena and the exploratory nature of nanoscience and nanotechnology, a high degree of knowledge in many diverse fields is required. This requires a centralized presentation to students in order to best teach them the required knowledge.In the past, knowledge has mostly been transferred hand-to-hand on an active level. However, in modern education, the classroom and lectures take a more active role. With this rise, the position and focus of hands-on work has diminished [1], while at the same time undergraduates remain isolated from research being conducted at universities [2]. With the broad nature of nanoscience and nanotechnology, it is becoming more important to maximize students’ learning ability in order to train future researchers and workforce. This paper explores the impact of a hands-on research experience in undergraduate nanotechnology education. This experience is presented to show the importance of student involvement on hands-on projects for their learning process.
High Yield Polymer MEMS Process for CMOS/MEMS Integration
Authors: Ray Prasenjit , Seena V. , Apte Prakash R. , Rao Ramgopal 
Published: September 2011

ABSTRACTMEMS community is increasingly using SU-8 as a structural material because it is self-patternable, compliant and needs a low thermal budget. While the exposed layers act as the structural layers, the unexposed SU-8 layers can act as the sacrificial layers, thus making it similar to a surface micromachining process. A sequence of exposed and unexposed SU-8 layers should lead to the development of a SU-8 based MEMS chip integrated with a pre-processed CMOS wafer. A process consisting of optical lithography to obtain SU-8 structures on a CMOS wafer is described in this paper.
Anti-Tumor Chloroquine-Gold Nanocomposites and their Binding Interaction with Bovine Serum Albumin: Biophysical and Biochemical Aspects of Protein Binding
Authors: Joshi Prachi , Chakraborti Soumyananda , Ramirez-Vick Jaime E. , Ansari Z. A. , Shanker Virendra , Chakrabarti Pinak , Singh Surinder P. 
Published: September 2011

ABSTRACTWe have conjugated chloroquine onto nano-sized, thiol-stabilized gold nanoparticles by using 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) / N-hydroxysulfosuccinimide (NHS) chemistry. The formation of gold nanoparticles was confirmed using optical spectra for characteristic surface plasmon band; the average size of gold nanoparticles was found to be 5-7 nm from electron microscopy measurements. The anti-tumor activity of prepared nanocomposite, vis-à-vis chloroquine itself, had been demonstrated using MCF-7 breast cancer cell line. To determine the binding affinity of gold-chloroquine nanocomposites to transport proteins present in blood serum, we studied the binding interaction of gold-chloroquine to bovine serum albumin (BSA), the most abundant plasma protein. The binding was studied by using isothermal titration calorimetry and fluorescence spectroscopy and was analyzed in terms of binding constant, entropy and enthalpy change. The gold-chloroquine nanocomposites were found to interact efficiently with BSA and fluorescence quenching experiments involving Trp212 suggests that the nanocomposites bind at site I of BSA.
Assembly Strategies for Fully Aligned and Dispersed Morphology Controlled Carbon Nanotube Reinforced Composites Grown in Net-Shape
Authors: Farmer Benjamin L. , Beard Mark A. , Ghita Oana , Allen Robert , Evans Ken E. 
Published: September 2011

ABSTRACTLong carbon fibre polymer composites represent the state-of-the-art materials technology for high performance weight driven structures, such as airframes. Although a significant amount of optimisation remains to be done to fully exploit the benefits of long fibre composites, these materials are relatively speaking still very crude, when compared to what nature has achieved with wood or bone for example. Nanomaterials, and specifically carbon nanotubes (CNTs), have teased with their spectacular mechanical and physical properties in isolation. These headline properties have prompted much work into the manufacturing of composite materials using CNTs as reinforcements, but thus far, successful exploitation of these impressive properties has been modest. A gap remains before these materials represent a real competition to long carbon fibre composites, even though fairly modest applications such as CNTs as fillers for matrix toughening and imparting electrical functionality are showing some promise. In this paper a critique is made of various reinforcement approaches through the lens of ’nano-augmented, ’nano-engineered’ and ’nano-enabled’ categories as defined by Airbus. These approaches are compared to an analysis of nature’s ’baseline’. A new ’nano-enabled’ strategy for the growth of fully aligned and dispersed bulk CNT composite materials and structures, allowing for simultaneous multi-scalar morphological and topological optimisation, is described. This new strategy, analogous to nature’s approach, consists of the vapour phase growth of aligned forests of carbon nanotubes coupled to the environment of Additive Layer Manufacturing (ALM). Early feasibility results are presented and currently identified challenges to successful scale-up are discussed.
Formation of Micro and Nanostructured Nickel/Silica and Nickel/Metal Composites by Electrodeposition of Mesoporous Silica onto Nickel Foam
Authors: Cordes Nikolaus L. , Bakker Martin G. 
Published: September 2011

ABSTRACTExtremely high surface area porous electrodes are of interest as current collectors for advanced batteries and as the basis for supercapacitors. For moderate to large scale storage applications a three-dimensional material is needed with porosity at multiple length scales. We are developing a combined bottom up/top down approach to creating such materials by using electrodeposition of mesoporous silica on nickel foam, a commercially available porous conductor widely used as the current collector in various batteries. Electrodeposition produces a conformal coating on the nickel foam. By controlling the electrodeposition time the morphology of the mesoporous silica can be varied from a thin film up to 500 nm thick to a loosely bound agglomeration of mesoporous silica particles capable of completely filling the 0.3-0.5 mm voids of the nickel foam. The internal diameter of the mesopores in the silica can be controlled in the range 2.5-4.8 nm by changing the chain length of the templating surfactant used. Gas adsorption shows surface areas of 400-1600 m2/g of silica deposited, consistent with the assumed structure of the material.
Magnetic refrigeration with GdN by Active Magnetic Refrigerator cycle
Authors: Hirayama Yusuke , Okada Hiroyuki , Nakagawa Takashi , Yamamoto Takao. A. , Kusunose Takafumi , Takenori Numazawa , Mastumoto Koichi , Irie Toshio , Nakamura Eiji 
Published: September 2011

ABSTRACTA magnetic refrigeration test was performed using a test device filled with spherical GdN material synthesized by the hot isostatic pressing (HIP) method. Refrigeration with an active magnetic regenerator cycle was tested in the temperature range between 48 and 66 K, with the field changing from 1.2 to 3.7 T and 2.0 to 4.0 T at upper and lower sides of the regenerator bed filled with the GdN spheres, respectively. Temperature spans about of 2 K were obtained at both sides, and the total temperature span in each cycle attained about 5 K. The specific heat of the material was measured to calculate the magnetic entropy change ΔS and the adiabatic temperature change ΔT induced by the magnetic field change ΔH. It was suggested that for a given ΔH, larger ΔS and ΔT can be exploited when demagnetized to lower H, especially, to zero field.