bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoconductivity and Photoluminescence of Amorphous Carbon Nitride a-CNx Films Prepared by the Layer-by-Layer Method
Authors: Katsuno T. , Nitta S. , Habuchi H. , Iwasaki T. , Itoh T. , Nonomura S. 
Published: April 2011

ABSTRACTAmorphous carbon nitride films a-CNx, which made in our laboratory, show high photosensitivity Ps that is a ratio of photoconductivity σp and dark-electrical conductivity σd Maximum Ps of a-CNx is about 5×106 which is about 50 times larger than that of hydrogenated amorphous silicon a-Si:H.We have succeeded to observe photoconductivity spectra where photoconductivity starts nearly at 2 eV and saturates at 3 eV. Then σp increase again at 3.7 eV up to 6.2 eV. The dependence of σp on excitation energy and intensity is observed. Photoluminescence spectrum is also obtained which have a spectrum from infrared of 0.8 eV up to ultraviolet of 3.5 eV. Using these data together with photothermal deflection spectra, we have presented a refined model of the electronic density of states for LLa-CNx.
Mechanical and Chemical Properties of CBxNy and CSixNy Thin Films Grown by N*-Plasma Assisted Pulsed Laser Deposition
Authors: Thärigen T. , Riede V. , Lippold G. , Hartmann E. , Hesse R. , Streubel P. , Lorenz D. , Grau P. , Lorenz M. 
Published: April 2011

ABSTRACTCarbon silicon nitride (CSixNy), and carbon boron nitride (CBxNy) thin films have been grown by pulsed laser deposition (PLD) of various carbon (silicon/boron) (nitride) targets using an additional nitrogen RF plasma source on [100] oriented silicon substrates without additional heating. The CSixNy and CBxNy thin films were amorphous and showed nano hardness up to 23 GPa compared to 14 GPa for silicon and maximum nitrogen content of 30 at%. The maximum nanohardness was achieved for 10% Si and 10% B content in the films. The lower hardness of this films compared to the nanohardness of 30-50 GPa of DLC films indicates a lower amount of covalent carbon-nitrogen bonding in the films. However, in contrast to DLC films, the CSixNy and CBxNy films can be grown to thickness above 3 μm due to lower internal compressive stress. XPS of CSixNy and CBxNy film surfaces shows clear correlation of binding energy and intensity of N ls, C ls, and Si 2p peaks to composition of the PLD-targets and to nitrogen flow through plasma source, indicating soft changes of binding structure due to variation of PLD parameters. The results demonstrate the capability of the plasma assisted PLD process to deposit hard amorphous CSixNy, and CBxNy thin films with adjustable properties.
Atomic Transformations and Quantum Transport in Carbon Nanotubes
Authors: Bernholc J. , Nardelli M. Buongiorno , Fattebert J.-L. , Orlikowski D. , Roland C. , Rosef F. , Zhao Q. 
Published: April 2011

ABSTRACTHigh strain conditions can lead to a variety of atomic transformations in nanotubes, which usually occur via successive bond rotations. The energetic barrier for the rotation is dramatically lowered by strain, and ab initio results for its strain dependence are presented. While very high strain rates must lead to tube breakage, (n,m) nanotubes with n, m < 14 can display plastic flow under suitable conditions. This occurs through the formation of a 5-7-7-5 defect, which then splits into two 5-7 pairs. The index of the tube changes between the 5-7 pairs, potentially leading to metal-semiconductor junctions. The high strain conditions can be imposed on the tube via, e.g., AFM tip manipulations, and we show that such procedures can lead to intratube device formation.The defects and the index changes occurring during the mechanical transformations also affect the electrical properties of nanotubes. We have computed the quantum conductances of strained defective and deformed tubes using the tight binding method. The results show that the defect density and the contacts play key roles in reducing the conductance at the Fermi energy. We also explored the role of bending in changing the electrical properties and found that mechanical deformations affect differently the transport properties of achiral and chiral nanotubes. Our results are in good agreement with recent experimental data.
Novel Silica-Sol Mediated Synthesis of Nanoporous Carbons
Authors: Hyeon Taeghwan , Han Sangjin , Sohn Kwonnam 
Published: April 2011

ABSTRACTNew preparative methods for the synthesis of nanoporous carbons using silica particles as templates will be presented. Gellation of resorcinol and formaldehyde in the presence of silica sol particles generated RF gel-silica nanocomposite. Carbonization followed by HF etching of silica templates generated nanoporous carbons with pore size ranging 10 ∼ 100 nm. When silica particles stabilized with surfactant were used as templates, uniform ∼ 10 nm pore-sized carbons have been formed. These nanoporous carbons exhibited excellent adsorption capacity for dyes.
Smart Polymer Composite Thermistor
Authors: Strümpler Ralf , Glatz-Reichenbach Joachim 
Published: April 2011

AbstractAn industrially important class of passively smart materials is electrically nonlinear polymer composites. The transition of conducting composites from low to high resistivity can be utilized for current limitation. Due to Joule losses the material is heated by a fault or short-circuit current. With increasing temperature the polymer matrix expands and the current paths over the conducting filler particles are interrupted. Within milliseconds, the material responds to the fault current by an increase in resistivity up to eight orders of magnitude. Due to the strong nonlinear resistivity - temperature relation, a narrow hot-zone is formed even for long samples. The length of the hot-zone limits the maximum switching voltage. By adding a second filler material of varistor- type, however, the maximum voltage can be considerably increased. When a hot spot is formed in one of the current paths over the conducting particles, a small voltage increase allows already a commutation of the current to neighboring varistor particles. Consequently, the current can still flow to a certain degree and allows to heat also the rest of the material around its path. This leads finally to a very broad hot area, which can resist much higher voltages. By the development of a smart material with two strong non-linearities, a dramatic improvement has been achieved for the application of thermistor composites in current limitation.
Fast Proton Conductors from Inorganic-Organic Composites: I. Amorphous Phosphate-Nafion and Silicophosphate-PMA/PWA Hybrids
Authors: Park Yong-Il , Kim Jae-Dong , Nagai Masayuki 
Published: April 2011

AbstractA drastic increase of electrical conductivity was observed in the composite of amorphous phosphate and ion-exchange resins (Nafion) as phosphorus concentration increased. Incorporation of amorphous phosphate into Nafion caused a large increase of conductivity to about 4×10−1S/cm at 23°C. However, the fabricated composite showed very low chemical stability.A high proton conductivity was also observed in a new inorganic-organic hybrids through incorporating PMA(molibdo-phosphoric acid)/PWA(tungsto-phosphoric acid) as a proton source in amorphous silicophosphate gel structure. Obtained gels were homogeneous and chemically stable. Resulting proton conductivity is very high (up to 5.5×10−3S/cm) compared to those of silicophosphate gels.
Fast Proton Conductors from Inorganic-Organic Composites: II. Amorphous Phosphate-PTFE and ZrP-PTFE Composites
Authors: Park Yong-Il , Kim Jae-Dong , Nagai Masayuki 
Published: April 2011

AbstractA high proton-conductivity was observed in the composite of amorphous phosphate and polytetafluoroethylene (PTFE). Incorporation of amorphous phosphate into PTFE emulsion caused a large increase of conductivity to about 4×10−2S/cm at 23°C. However, the conductivity decreased with increasing heat-treatment temperature, and the fabricated composite showed very low chemical stability.As a chemically stable composite, PTFE-based composite was also synthesized from α- or γ-zirconium phosphate crystalline powders dispersed in partially polymerized PTFE particles. By addition of zirconium phosphate powders, the proton conductivity jumped up to 2.2×10−3S/cm from 10−13S/cm of PTFE.
Dynamics of Pyroelectricity of a Copolymer of Vinylidene Fluoride with Trifluoroethylene
Authors: Takahashi Y. , Taniwaki J. , Furukawa T. 
Published: April 2011

AbstractThe pyroelectric response of a copolymer of vinylidene fluoride with trifluoroethylene was measured as a function of time by applying a laser pulse to give an abrupt increase in temperature. The response curve shows several processes: the thickness extensional mode TEM, the length extensional mode LEM and the heat transfer to the environment. By fitting a theoretical curve for the TEM mode, the pyroelectric primary and secondary effects are separated. The primary effect is found to be small at room temperature. Additional gradual response shows that there exists a surface layer which has smaller polarization than in the bulk.The temperature dependence of the pyroelectric response curve shows that the primary effect increases with temperature. It dominates the response at just below the ferroelectric-paraelectric transition temperature.
Some Aspects of Plastic Flow in Silicon Nitride
Authors: Rouxel T. , Rabier J. , Testu S. , Milhet X. 
Published: April 2011

AbstractThe different scales of plastic flow in silicon nitride were investigated either by indentation experiments and compression under hydrostatic pressure in the 20-850°C temperature range, and by stress relaxation and creep above 1350°C. [0001], 1/3<11-20> and 1/3<11-23> dislocations were evidenced by Transmission Electron Microscopy (TEM) in the low temperature range. Cross-slip events in {10-10} prismatic planes were observed at temperature as low as 20°C by Atomic Force Microscopy (AFM) on micro-hardness indents. By increasing the temperature, the deviation plane becomes {11-20} prismatic planes. The easiest slip system is by far the [0001]{10-10} system. Above 1350°C, the creep strain could be fitted by the sum of a transient component, εt=ε∞[1-exp-(t/τc)bc], where τc reflects the duration of the transient creep stage, and bc is between 0 and 1, and a stationary component, εs=εst =Aσnt, where σ is the stress and n is the stress exponent. The increase of ε∞ with temperature is interpreted on the basis of the formation of liquid intergranulary phases above 1400°C by progressive melting of some of the grains. A creep exponent of 1.8 was determined. A single value could hardly be given to the activation energy since an S-shape curve was observed in the In εs versus l/T plot, as for most glasses over large temperature ranges. The stress relaxation kinetics was found to follow the Kohlrausch-Williams-Watt expression: σ/σo=exp [-(t/τr)br], where br ranges between 0 (solid state) and I (liquid state) and τr is a characteristic relaxation time constant. As in the case of glasses, τr decreases rapidly whereas br increases from about 0.2 to 0.7 as the temperature increases from 1400 to 1650°C. But again, it is very difficult to get a single value for the activation energy from the In τr versus 1/T plot.
Newtonian Flow in Bulk Amorphous Alloys
Authors: Wadsworth J. , Nieh T.G. 
Published: April 2011

AbstractBulk amorphous alloys have many unique properties, e.g., superior strength and hardness, excellent corrosion resistance, reduced sliding friction and improved wear resistance, and easy formability in a viscous state. These properties, and particularly easy formability, are expected to lead to applications in the fields of near-net-shape fabrication of structural components. Whereas large tensile ductility has generally been observed in the supercooled liquid region in metallic glasses, the exact deformation mechanism, and in particular whether such alloys deform by Newtonian viscous flow, remains a controversial issue. In this paper, existing data are analyzed and an interpretation for the apparent controversy is offered. In addition, new results obtained from an amorphous alloy (composition: Zr–10Al–5Ti–17.9Cu–14.6Ni, in at. %) are presented. Structural evolution during plastic deformation is particularly characterized. It is suggested that the appearance of non-Newtonian behavior is a result of the concurrent crystallization of the amorphous structure during deformation.
High-Resolution EBSD Analysis of Severely Deformed Submicron Grained Aluminum Alloys
Authors: Prangnell P. B. , Bowen J. R. , Gholinia A. , Markushev M. V. 
Published: April 2011

AbstractThere is currently much interest in the use of severe plastic deformation techniques for the production of submicron grained Al-alloys. Because of their small grain sizes, previous investigations have relied on the TEM to study the grain structures after processing. However, the TEM is not that well suited to obtaining statistically significant data on the misorientations of the boundaries present in the deformed state. Recent improvements in the resolution of SEMEBSD systems means that this powerful technique can now be used to quantitatively analyse severely deformed structures more reliably than was previously possible. Results using this method have shown that the deformation structure is very sensitive to the strain path, material, and processing conditions. With a constant strain path fibrous grain structures tend to be formed and homogeneous submicron grain structures can only be produced at very high plastic strains, of greater than ten. Materials deformed with cyclic strain paths are more isotropic, but generally have bimodal grain structures and contain a lower density of high angle boundaries and only bands of submicron grains.
Cavitation in a Uniaxially deformed Superplastic Al-Mg Alloy
Authors: Bae D. H. , Ghosh A. K. 
Published: April 2011

AbstractCavitation caused by superplastic straining of a fine-grained Al-Mg-Mn-Cu alloy under uniaxial tension has been systematically evaluated. Tensile tests were conducted in the strain-rate range of 10−4s−1 to 10−2s−1 and in the temperature range of 450°C to 550°C. Measurements of the number and size of cavities were made by image analysis through optical microscopy on tested specimens. With increasing imposed strain, the cavity population density increases. Cavity growth has been found to be primarily due to the plastic deformation of the matrix. These results are characterized by the total volume fraction of cavities which is found to increase exponentially with strain. However, the dependencies of cavity volume fraction on strain-rate and temperature are not straightforward and the notion of just a few large cavities controlling the total cavity volume is not always true. Attempts to explain these complex dependencies have been carried out based on the concepts of debonding between the matrix and non-deformable particles, the continuous nucleation of new cavities, and plasticity-based cavity growth for large cavities.
Superplasticity and Joining of Zirconia-Based Ceramics
Authors: Gutierrez-Mora F. , Dominguez-Rodriguez A. , Jimenez-Melendo M. , Chaim R. , Ravi G. B. , Routbort J. L. 
Published: April 2011

AbstractSteady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1250 and 1350°C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1200°C
Temperature Dependence of High Field Characteristics in PMN-PT-BT Ceramics Containing Chemical Additives
Authors: Cho Yong S. , Yoon Chang H. , Pilgrim Steven M. , Bridger Keith 
Published: April 2011

AbstractA chemical additive method was used to modify the composition and resultant properties of a commercially available 0.96(0.9lPb(Mg1/3Nb2/3)O3 - 0.09PbTiO3) - 0.04 BaTiO3 (PMN-PT-BT) ceramic. Without an additional ball-mixing process, several combinations of minor additives such as Fe, Ba, Sr, Zn and Ti were incorporated by the chemical method. Weak- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200°C for 4 hrs. All properties were found to depend on the chemical additives and temperature. Especially, the temperature dependence of high-field characteristics revealed different behavior from that reported for conventionally-prepared samples. For example, the samples containing 0.5 wt% SrO, 0.5 wt% ZnO, and 0.5wt% TiO2 did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements. Overall, the coating process has been successfully used to modify, and in some cases, enhance the high-field characteristics of PMN-based ceramics for electromechanical uses.
The Effect of Hafnium and Thermal Cycling on the Transformation Temperatures of NiTi-Based Shape Memory Alloys
Authors: Thoma Paul E. , Boehm John J. 
Published: April 2011

AbstractThe effect of thermal cycling on the austenite to martensite (A→M) and martensite to austenite (M→A) transformation temperatures (TTs) of Ni49.8Ti50.2 and Ni49.8Ti40.2Hf10 shape memory alloys is investigated. Test specimens are from arc melted buttons homogenized at 900°C for 100 hours. Results show that the A→M and M→A TTs for the alloys decrease with increasing number of thermal cycles through the phase transformations. The A→M TT of the NiTiHf alloy stabilizes more quickly than the A→M TT of the NiTi alloy when cycled. However, the M→A TT of the binary NiTi alloy stabilizes more quickly than the M→A TT of the NiTiHf alloy when cycled.
Development of High Frequency Terfenol-D Transducer Material
Authors: Lindgen E. A. , Poret J. C. , Whalen J. J. , Rosen M. , Wun-Fogle M. , Restorff J. B. , Clark A.E. 
Published: April 2011

AbstractThe objective of this research and development program is to develop production methods to obtain thin strips of oriented crystalline Terfenol-D and to develop multi-layered driver rods for transducers that will operate over a broad spectrum into the MHz frequency range. To reach this goal, special methods must be used to minimize the amount of mechanical processing, such as machining, as the material is both brittle and expensive. A modified rapid solidification method has been developed to process Terfenol-D to obtain the desired geometric configuration of long thin strips. Currently, sections that are 500 mm long, 2 mm wide and 0.1 mm thick can be produced. In addition, this method enables the crystallographic orientation of the strips of Terfenol-D to be controlled to obtain the preferred orientation that will maximize the magnetostrictive displacement of the material. Magnetostrictive measurements have shown that the samples prepared by this approach have a 62 percent improved magnetostrictive performance when compared to non-oriented Terfenol-D. The ribbons have been consolidated into transducer driver rods. The magnetostrictive performance of the driver rods has been measured to be 60 percent of the as prepared ribbons. The reduction in performance is attributed primarily to the geometric placement of the ribbons inside the driver rods.
Investigation of the Deposition and Integration of Hard Coatings for Moving MEMS Applications
Authors: Adams P.M. , Robertson R.E. , Cole R.C. , Hinkley D. , Radhakrishnan G. 
Published: April 2011

AbstractMicroelectromechanical systems (MEMS) have been identified as a key technology for small-scale satellites, integrated sensors, and intelligent control systems. Using methods developed for highly integrated electronics, mechanical components are co-fabricated on planar wafers and subsequently etched free for mechanical movements in three dimensions. A major design limitation for these systems is their inability to withstand prolonged sliding surface contact. The fundamental problem is that the surface properties of silicon and poly-silicon, two of the most widely used materials for MEMS, are highly unsuitable for moving MEMS devices, resulting in high wear during operation. This work explores the feasibility and benefits of depositing thin, wear-resistant, low-friction coatings on silicon or poly-silicon. To achieve this goal, three-dimensional test silicon microstructures have been fabricated. Wear-resistant titanium carbide (TiC) coatings are deposited on these test structures using a novel non-line-of-sight pulsed laser deposition (PLD) process. In parallel, this paper addresses the integration of the TiC coating directly into the MEMS fabrication processes and its compatibility with standard silicon processing.
MEMS Material Microstructure and Elastic Property Modeling
Authors: Last Howard R. , Hemker Kevin J. , Witt Ronald 
Published: April 2011

AbstractResults from initial efforts to develop a quantitative understanding of the material microstructure – elastic properties relationship for electroplated LIGA nickel will be presented. Microsample tensile testing and microstructural characterization results including grain size and grain orientation measurements obtained using orientation imaging microscopy (OIM) are discussed. The use of these data in the development of a finite element modeling approach to represent the mechanical response of “meso-scale” LIGA nickel MEMS material will be highlighted.
Two- and Three-Dimensional Ultrananocrystalline Diamond (UNCD) Structures for a High Resolution Diamond-Based MEMS Technology
Authors: Auciello O. , Krauss A.R. , Gruen D.M. , Meyer E.M. , Busmann H.G. , Tucek J. , Sumant A. , Jayatissa A. , Moldovan N. , Mancini D. C. , Gardos M. N. 
Published: April 2011

AbstractSilicon is currently the most commonly used material for the fabrication of microelectromechanical systems (MEMS). However, silicon-based MEMS will not be suitable for long-endurance devices involving components rotating at high speed, where friction and wear need to be minimized, components such as 2-D cantilevers that may be subjected to very large flexural displacements, where stiction is a problem, or components that will be exposed to corrosive environments. The mechanical, thermal, chemical, and tribological properties of diamond make it an ideal material for the fabrication of long-endurance MEMS components. Cost-effective fabrication of these components could in principle be achieved by coating Si with diamond films and using conventional lithographic patterning methods in conjunction with e. g. sacrificial Ti or SiO2 layers. However, diamond coatings grown by conventional chemical vapor deposition (CVD) methods exhibit a coarse-grained structure that prevents high-resolution patterning, or a fine-grained microstructure with a significant amount of intergranular non-diamond carbon. We demonstrate here the fabrication of 2-D and 3-D phase-pure ultrananocrystalline diamond (UNCD) MEMS components by coating Si with UNCD films, coupled with lithographic patterning methods involving sacrificial release layers. UNCD films are grown by microwave plasma CVD using C60-Ar or CH4-Ar gas mixtures, which result in films that have 3-5 nm grain size, are 10-20 times smoother than conventionally grown diamond films, are extremely resistant to corrosive environments, and are predicted to have a brittle fracture strength similar to that of single crystal diamond.
Stereochemical Structure for Sodium in Native and Thermal Silica Layers
Authors: Flank A.-M. , Tenegal F. , Lagarde P. , Mazzara C. , Jupille J. 
Published: April 2011

AbstractSodium-covered silica films formed on silicon substrates have been examined by X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS) in ultra-high vacuumconditions at 300K. The results show that sodium diffuses into the silica layer on a reversible manner and that it modifies the silica network in order to create its own site. Sodium atoms are surrounded by oxygen atoms at an average distance of 2.3 Å and by a second shell which is assigned to silicon atoms located at 3.8 Å. At high Na concentrations, sodium atoms are also present in the close environment of one sodium atom.