bluuebunny/crossref_metadata_2025_split huggingface dataset:
A first-principles study of the martensitic instabilities in magnetic shape memory alloys
Authors: Entel Peter , Gruner Markus Ernst , Hucht Alfred 
Published: April 2011

AbstractAmong the magnetic shape memory Heusler alloys, Ni-Mn-Ga near stoichiometry displays the largest shape change in the martensitic 5M or 7M structure with a strain of the order of 10% in an external magnetic field of less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites with the modulated structures usually appearing at c/a < 1 while the low-temperature nonmodulated tetragonal structures have c/a > 1. Typically, the martensitic phase changes are accompanied by a shift of a peak in the electronic density arising from the non-bonding Ni states, a reconstruction of the associated Fermi surface, and, in some cases, by pronounced phonon anomalies. These appear in the cubic high-temperature austenitic and premartensitic phases but also in the modulated phases. In addition, the modulated phases have highly mobile twins which can be rearranged under the action of an external magnetic field due to the high magnetic anisotropy, which builds up in martensite and which is at the origin of the magnetic shape memory effect. First-principles calculations confirm the overall scenario.
Determination of symmetry reduced structures by a soft-phonon analysis in Ni2MnGa
Authors: Hickel Tilmann , Uijttewaal Matthe A. , Grabowski Blazej , Neugebauer Jörg 
Published: April 2011

AbstractThe shape memory effect of Ni2MnGa is closely related to the fact that the material undergoes a martensitic phase transition, which results in symmetry reductions and deformations when cooling down. However, there are still substantial uncertainties about the phase diagram in the martensitic phase. Particularly challenging is the determination of those phases, which are characterized by shuffling structures. We have applied density functional theory to this problem, which allows an accurate determination of the potential energy surface as a function of the lattice constants. Based on these results we compute ab initio phonon spectra and discuss in detail how they can be used to extract detailed information about the type of shuffling structures and to systematically and efficiently identify stable atomic configurations.
Cast and Rolling Textures of NiMnGa Alloys
Authors: Chulist Robert , Poetschke Martin , Boehm Andrea , Brokmeier Heinz-Guenter , Garbe Ulf , Lippmann Thomas , Oertel Carl-Georg , Skrotzki Werner 
Published: April 2011

AbstractThe texture of two polycrystalline NiMnGa magnetic shape memory alloys fabricated by directional solidification and hot rolling has been measured with high-energy synchrotron radiation and neutron diffraction. At room temperature the alloys used are composed of a modulated (7M) and non-modulated (NM) martensitic structure. The texture of the directionally solidified alloy for all phases is a pronounced fibre texture with <100> preferentially aligned along the growth direction. In the directionally solidified case a variant selection took place with [001] dominating. The texture of the hot rolled alloy shows a weak recrystallization texture with {111} and <112> aligned parallel to the rolling plane and rolling direction, respectively. The texture results are discussed with respect to material, processing and phase transformations including variant selection.
A Review of Tension Test Methods for Thin Films
Authors: Sharpe William N. 
Published: April 2011

AbstractTest methods for mechanical property measurement of the thin films used in MEMS have been developed and refined over the last decade. This brief review considers only tensile testing since that is the preferred method for measuring Young's modulus, strength, etc. for macroscale structural materials. There are basically two kinds of tensile specimens – framed specimens whose support strips are cut after mounting and semidetached specimens fastened to the substrate at one end. The loading and force measurement systems are similar and use commercial transducers. Strain is measured either by overall grip displacement or by digital imaging in most cases. Initial works are described and followed by descriptions of some recent applications. The paper concludes with a suggested test method that could be amenable to standardization.
Passive devices for determining fracture strength of MEMS structural materials
Authors: Kahn H , Ballarini R , Heuer A H 
Published: April 2011

AbstractIn microelectromechanical systems (MEMS) device design and fabrication there exists a need for quick determination of fracture strength. This report describes several passive devices that use the residual stresses contained within structural MEMS materials to determine fracture strength. Stress concentrations of varying degrees are generated at micromachined notch roots, and the critical stress required for failure indicates the fracture strength. A variety of devices have been fabricated from materials, such as polysilicon, silicon nitride, and aluminum, with widely varying residual stresses, including both tensile and compressive.
Fabrication and Characterization of Normal and Shear Stresses Sensitive Tactile Sensors by Using Inclined Micro-cantilevers Covered with Elastomer
Authors: Sohgawa Masayuki , Huang Yu-Ming , Noda Minoru , Kanashima Takeshi , Yamashita Kaoru , Okuyama Masanori , Ikeda Masaaki , Noma Haruo 
Published: April 2011

AbstractThe tactile sensors for human support robots which can detect both normal stress and shear stress and have human-friendly surface have been proposed. Micro-cantilevers adequately inclined by Cr deflection control layer were fabricated by the surface micromachining on SOI wafer. The cantilevers were covered with the PDMS elastomer for human-friendly surface. When the stress is added to the surface of elastomer, the deformation of cantilevers along with elastomer is detected as piezoresistive layer in the cantilevers. The piezoresistive response of the cantilever is analyzed by FEM calculation. The response of the fabricated tactile sensor to normal stress and shear stress was measured by output from this resistance. The tactile sensor with PDMS elastomer can detect both normal stress and shear stress. On the other hand, it hardly has sensitivity to shear stress of orthogonal direction to the cantilever. It means that the tactile sensor can distinguish the direction of shear stress. The sensitivity of tactile sensor vary widely with cantilever pattern and relation between direction of cantilever and crystallite orientation of Si. It is suggested that the sensitivity of tactile sensor can be improved by using FEM estimation and selective ion implantation.
Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substrates
Authors: Ishiyama Chiemi , Shibata Akinobu , Sone Masato , Higo Yakichi 
Published: April 2011

AbstractAdhesive bend testing for micro-sized photoresist components has been performed to clarify the effects of supercritical CO2 (ScCO2) treatment. Multiple microsized cylindrical specimens were fabricated on a silicon substrate using epoxy-type photoresist. The specimens were ScCO2 treated at a temperature of 323K at a pressure of 15MPa for 30 min, and then, decompressed to atmospheric pressure at two different rates. Double refraction appeared in the SU-8 specimens near by the interface between the SU-8 specimens and a substrate after ScCO2 treatment. Adhesive bend strength of ScCO2 treated specimen with slow decompression process is approximately 60% higher than that of non- ScCO2 treated specimens, however, the strength of the microsized photoresist was slightly degraded by ScCO2 treatment with quick decompression process. All the results suggest that ScCO2 treatment improves the adhesive strength between microsized photoresist components and a silicon substrate by control of the decompression process.
Science and Technology of Piezoelectric/Diamond Hybrid Heterostructures for High Performance MEMS/NEMS Devices
Authors: Auciello Orlando , Sumant Anirudha , Hiller Jon , Kabius Bernd , Srinivasa Sudarsan 
Published: April 2011

AbstractMost current micro/nanoelectromechanical systems (MEMS/NEMS) are based on silicon. However, silicon exhibits relatively poor mechanical/tribological properties, compromising applications to some devices. Diamond films with superior mechanical/tribological properties provide an excellent alternative platform material. Ultrananocrystalline diamond (UNCD®) in film form with 2-5 nm grains exhibits excellent mechanical and tribological properties for high-performance MEMS/NEMS devices. Concurrently, piezoelectric Pb(ZrxTi1-x)O3 (PZT) films provide high sensitivity/low electrical noise for sensing/high-force actuation at relatively low voltages. Therefore, integration of PZT and UNCD films provides a high-performance platform for advanced MEMS/NEMS devices. This paper describes the bases of such integration and demonstration of low voltage piezoactuated hybrid PZT/UNCD cantilevers.
Novel Fabrication Process for the Integration of MEMS Devices with Thick Amorphous Soft Magnetic Field Concentrators
Authors: Brugger Simon , Pfleging Wilhelm , Paul Oliver 
Published: April 2011

AbstractThis paper reports a novel fabrication process enabling the integration of mechanical MEMS devices with thick amorphous soft magnetic field concentrators. The integration process combines silicon on insulator technology for the MEMS device fabrication and epoxy-resin-based attachment of 18-µm-thick amorphous soft magnetic ribbons followed by a wet chemical structuring process. The fabrication process is reported on the basis of a field-concentrator-based resonant magnetic sensor combining an electrostatically driven micromechanical resonator and a planar magnetic field concentrator with two narrow gaps. For realization of the concentrator gaps, the integration process is extended by micro-patterning of the soft magnetic ribbons via UV-laser ablation using an excimer laser system. The characterization of the fabricated resonant magnetic sensor using a stroboscopic video microscope for in-plane motion measurement shows a high sensitivity of 390 kHz/T at a magnetic flux density of 158 µT.
Patterning of Hard Coatings for Incorporation of Solid Lubricant Microreservoirs
Authors: Guleryuz Canan G , Krzanowski James 
Published: April 2011

ABSTRACTHard coatings containing microscopic reservoirs for solid lubricant storage have the potential to advance the development of dry, self-lubricating coatings. In the present study we have investigated several methods for fabricating hard coatings that incorporate microscopic reservoirs. These methods all involve the use of placeholders on the substrate surface that are later removed after deposition of the hard coating. One method uses a solution containing ceramic beads, while the second method uses conventional photolithography methods. Coatings using both of these methods were fabricated using TiN as the hard coating. The effectiveness of the microreservoirs for solid lubricant storage was examined by conducting pin-on-disk test using various solid lubricants, including graphite and indium. The performance of coatings with random arrangements of microreservoirs was scattered while samples with the ordered arrangements of microreservoirs all performed well. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs, the significant improvements in tribological performance can be realized.
Fiber Reinforced Multiphase Polymer Composites by In situ Fiber Alignment
Authors: Viratyaporn Wantinee , Twu Nancy , Lehman Richard 
Published: April 2011

ABSTRACTA novel approach has been explored for the efficient dispersion and uniaxial alignment of fibers in dual phase polymer matrices based on the streaming flow that occurs when two immiscible polymer blends are melt processed under high shear conditions. Such conditions improve the alignment and distribution of fibers in the matrix, a feature of particular importance when fine nanofibers are used. This self-alignment mechanism seeks to produce optimum properties from relatively small volume fractions of fiber. Recent efforts have focused on a model system containing micron-size glass fibers in immiscible polymer blends. This paper presents selected mechanical properties measured for the model system and the flow/orientation paradigm that produces the observed morphologies.
Nano-Surface Modification on Titanium Implants for Drug Delivery
Authors: Yao Chang , Webster Thomas J 
Published: April 2011

ABSTRACTThe surface layer of titanium implants, i.e. titanium dioxide, is responsible for the inertness of titanium-based implants within the human body. However, their cytocompatibility properties and long-term efficacy are limited without further surface engineering since the average functional lifetime of an orthopedic implant is only 10 to 15 years. In this study, an electrochemical method known as anodization was used to create titania nanotubular structures on titanium implant surfaces. These nanotubes were about 60 nm wide (inner diameter) and 200 nm deep. In vitro studies found that anodized surfaces consisting of titania nanotube arrays were favored by bone-forming cells (osteoblasts) compared to unanodized surfaces. These titania nano-tubular structures were utilized here as novel drug release delivery systems. It is proposed that the system designed here can have multi-functional drug release to inhibit infection and wound inflammation while increasing new bone formation. For this purpose, antibiotic drugs (penicillin and streptomycin) were loaded into these nanotubular structures by physical adsorption. To mediate interactions between drug molecules and nanotube walls, anodized titanium nanotubes were modified by silanization to possess amine or methyl groups on their surface instead of −OH groups. Results showed increased hydrophobicity of chemically modified titania nanotubes (methyl > amine > hydroxyl terminated surface). These drug loaded substrates were soaked in phosphate buffered solution in a simulated body environment to determine drug release behavior. Buffer solutions were collected and replaced every day. The eluted drug amounts were measured spectroscopically. Results showed more antibiotic penicillin and streptomycin released from chemically modified nanotubes compared to unanodized titanium substrates; specifically, titania anodized nanotubes functionalized with −OH groups did quite well. In this manner, this study advances titanium currently used in orthopedics to possess drug release behavior which can improve orthopedic implant efficacy.
Selective Growth of Al Nanowhiskers on the Patterned Substrate by Glancing Angle Deposition at High Temperature
Authors: Suzuki Motofumi , Kita Ryo , Hamachi Kenji , Nagai Koji , Nakajima Kaoru , Kimura Kenji 
Published: April 2011

ABSTRACTWe demonstrated high temperature glancing deposition (HT-GLAD) of Al on the heated substrate with trench patterns. When Al was deposited under the condition, where the Al vapor is incident at very glancing on the sidewall but on the surface, Al nano-whiskers grew only on the sidewall of the trenches since HT-GLAD condition is achieved only for the sidewall. On the other, Al was deposited at glancing angle both on the surface and the sidewalls, nano-whiskers grow both on the surface and the sidewalls of the trenches. The selective growth of the nano-whisker is successfully achieved by controlling the geometrical deposition conditions. Remarkably, moreover, the nano-whiskers grow not only on the illuminated sidewalls but also on the shadow sidewall. In addition, few nano-whiskers grow on the shadow region of the bottom of the trenches. In order to understand the peculiar growth of Al nano-whiskers, novel transport processes of Al atoms other than the surface diffusion have to be clarified. The reevaporation or reflective scattering on the sidewalls of the trenches is likely to play an important role in the growth of nano-whiskers.
Fabrication and Characterization of Spectroscopically Encoded Core-shell Nanoparticle-polymer Nanocomposite
Authors: Dai Sheng , Farah Abdiaziz A. , Alvarez-Puebla Ramon A , Bravo-Vasquez Juan P , Fenniri Hicham 
Published: April 2011

ABSTRACTMetal nanoparticles are of great importance in the fabrication of new nanocomposite materials. One area of increasing interest is the application of metal nanoparticles (NP) as substrates for surface enhanced Raman scattering (SERS). In this regard, self-assembled monolayers (SAMs) of sulfur containing organic compounds are ideal target for SERS studies due to the strong affinity of sulfur for noble metals. Two types of molecules were synthesized for this study, an organic-soluble and a water-soluble styrene derivative. Self-assembling behaviors of these monomers on gold or silver nanostructured surfaces at room temperature were studied by UV-Vis spectroscopy, dynamic light scattering (DLS), SERS spectroscopy, and scanning electron microscopy (SEM). It was found that the interaction between sulfur compounds and metal NPs is strongly dependent on the NP size and the monomer environment. The hydrophilic NP surface switches to hydrophobic upon binding of sulfur-containing monomers, which leads to the formation of aggregates in aqueous solution for both water-soluble and oil-soluble monomers. The self-assembling behavior of these monomers on the metallic surface was compared with that of the corresponding homopolymers. Due to macromolecular and steric effects, the binding interaction between homopolymer and metal NP is weaker than that between NP and monomers. Surface polymerization of these monomers on metallic surfaces was observed as supported by SERS. Core-shell nanoparticles could also be obtained through seeded emulsion polymerization, but a decrease in SERS activity was observed.
Raman Characterization of Silicon Nanoclusters Embedded in Fused Silica
Authors: Barba David , Clavel Milene , Martin Francois , Ross Guy 
Published: April 2011

ABSTRACTSilicon nanocrystals (Si-nc) and amorphous silicon (a–Si) aggregates either produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Under certain experimental conditions, relevant information regarding both the dimension and the size distribution of Si-nc can be extracted from the energy shifts and the spectral distortion of the phonon excitation observed near 520 cm−1. Results are presented for different sample annealing times and ion fluences. These data agree with the direct observation by TEM of non-uniformly depth-distributed silicon nanocrystals. Moreover, measurements recorded for different Raman probing depths give evidence of chemical composition changes within the fused silica matrix. The depth evolution of the phonon peak associated with the Raman signature of a-Si near 470 cm−1 shows the presence of amorphous silicon, whose concentration is higher in the region where the large Si-nc are located.
Radiological Control of Gold Octahedral and Prism Nanoparticles
Authors: Nenoff Tina M. , Jones Jason C. , Provencio Paula P. , Berry Donald T. 
Published: April 2011

ABSTRACTWe report on a fundamental morphology growth of gold-based nanoparticles by solution radiolysis. Radiolysis of pure gold-polymer solutions of different dose rates and aging time is examined. A detailed description will be presented of the experimentation, testing and analysis. In particular, we will present data on the formation of gold nano-octahedra and -prism particles. The γ-irradiations were carried out with a 60Co source of 1.345 × 105 Ci (Sandia National Laboratories Gamma Irradiation Facility (GIF). Nanoparticle characterization techniques included are UV-vis and TEM. Similar to what has been seen in earlier silver nanoparticle studies, dose rate dictates the size of nanoparticles formed. At high dose rate, all reducing species are produced and scavenged within a short time, and then coalesce into separate nanoparticles. At low dose rate, the coalescence process is faster than the production rate of the reducing radicals. The reduction of radicals occurs mainly on clusters already formed. The differences in the morphologies result from a combination of dose rate, aging and lack of radical scavengers (e.g. isopropyl alcohol), resulting in either gold nano-spheres, octahedral or prism nanoparticles. The progressive evolution with dose rate of the UV-visible absorption spectra of radiation-induced metal clusters is discussed.
Electronic and Magnetic Characterization of in vivo Produced vs. in vitro Reconstituted Horse Spleen Ferritin
Authors: Papaefthymiou Georgia C. , Viescas Arthur J. , Devlin Eamonn , Simopoulos Athanassios 
Published: April 2011

ABSTRACTMagnetic nanophases nucleated within horse spleen apoferritin nanotemplates underin vivophysiological conditions andin vitroreconstitution were characterized by Mössbauer spectroscopy in lyophilized form. Mössbauer spectra recorded at 80 K indicate that for thein vivoproduced ferritin the presence of phosphates within the ferritin biomineral core results in larger quadrupole splittings, both at interior and surface sites, 0.62 mm/s and 1.06 mm/s, respectively, as compared to 0.56 mm/s and 0.75 mm/s for the reconstituted ferritin. Data collected at lower temperatures give blocking temperatures of 55 and 40 K forin vitroandin vivosamples. At 4.2 K, both samples give similar saturation hyperfine field values for the interior (495 kOe) and surface (450 kOe) iron sites. The temperature dependence of the reduced hyperfine magnetic fields at the interior iron sites is consistent with the collective magnetic excitations model, due to the particle's magnetization precession about the anisotropy axis. In contrast, a marked decrease in the reduced hyperfine field at surface sites with increasing temperature indicates a more complex spin excitation energy landscape at the surface.
Reaction Dynamics for Gold Nanoparticles Synthesis in Solution Plasma
Authors: Hieda Junko , Saito Nagahiro , Takai Osamu 
Published: April 2011

ABSTRACTWe describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl4]− concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl4]− vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl4]− was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles ∼150 nm in size were formed after discharge for 1 min. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 min. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution.