bluuebunny/crossref_metadata_2025_split huggingface dataset:
Meso-Scale Pressure Transducers Utilizing Low Temperature Co-Fired Ceramic Tapes
Authors: Lynch H. , Park J. , Espinoza-Valejos P. A. , Santiago-Aviles J. J. , Sola-Laguna L. 
Published: April 2011

AbstractPressure transducers with promising characteristics at high pressure and temperatures have been developed using low temperature co-fired ceramic (LTCC) tape technology. All parts for the transducer were machined from DuPont 951 series LTCC tapes utilizing either a numerically controlled milling machine, or an isotropic etching technique involving the removal of the glassy binder of a partially sintered LTCC tape. Device dimensions are in the meso (intermediate) scale range, with the smallest device size of 8mm in diameter, and the cavity of 2 mm. Utilizing the anisotropy induced during the casting process a chemical exfoliation technique was developed. This technique allowed us to separate the original tape in three layers, the middle one being highly elastic, isotropic and homogeneous. The middle layer can be chemically thinned to achieve membrane like behavior, with thickness of the order of 50 µm. The pressure is measured as a function of the membrane deformation where two piezo-resistors are screen printed. Two piezo-resistors were used to achieve temperature compensation. Using shrinkage matched paste, nominal thick film technology was used in the screen printing of the piezoresistors. The rest of the transducer was fabricated using several layers of LTCC tapes, which were laminated and fired. Devices of different sizes were fabricated and compared. Devices were characterized by comparing its dynamic response with a micro-fabricated silicon pressure transducer.
Fabrication of Mems Devices by Powder-Filling into DXRL-Formed Molds
Authors: Garino Terry J. , Christenson Todd , Venturini Eugene 
Published: April 2011

AbstractWe have developed a variety of processes for fabricating components for micro devices based on deep x-ray lithography (DXRL). Although the techniques are applicable to many materials, we have demonstrated them using hard (Nd2Fe14B) and soft (Ni-Zn ferrite) magnetic materials because of the importance of these materials in magnetic micro-actuators and other devices and because of the difficulty fabricating them by other means. The simplest technique involves pressing a mixture of magnetic powder and a binder into a DXRL-formed mold. In the second technique, powder is pressed into the mold and then sintered to densify. The other two processes involve pressing at high temperature either powder or a dense bulk material into a ceramic mold that was previously made using a DXRL mold. These techniques allow arbitrary 2-dimensional shapes to be made 10 to 1000 μm thick with in-plane dimensions as small as 50μm and dimensional tolerances in the micron range. Bonded isotropic Nd2Fe14B micro-magnets made by these processes had an energy product of 7 MGOe.
Micrometer-scale machining of metals and polymers enabled by focused ion beam sputtering
Authors: Adams D. P. , Benavides G. L. , vasile M. J. 
Published: April 2011

AbstractThis work combines focused ion beam sputtering and ultra-precision machining for microfabrication of metal alloys and polymers. Specifically, micro-end mills are made by Ga ion beam sputtering of a cylindrical tool shank. Using an ion energy of 20keV, the focused beam defines the tool cutting edges that have submicrometer radii of curvature. We demonstrate 25μm diameter micromilling tools having 2, 4 and 5 cutting edges. These tools fabricate fine channels, 26–28 microns wide, in 6061 aluminum, brass, and polymethyl methacrylate. Micro-tools are structurally robust and operate for more than 5 hours without fracture.
Dependence Of Silicon Fracture Strength And Surface Morphology On Deep Reactive Ion Etching Parameters
Authors: Chen Kuo-Shen , Ayon Arturo A. , Lohner Kevin A. , Kepets Mark A. , Melconian Terran K. , Spearing S. Mark 
Published: April 2011

AbstractThe development of a high power-density micro-gas turbine engine is currently underway at MIT. The initial goal is to produce the components by deep reactive ion etching (DRIE) single crystal silicon. The capability of the silicon structures to withstand the very high stress levels within the engine limits the performance of the device. This capability is determined by the material strength and by the achievable fillet radii at the root of turbine blades and other etched features rotating at high speeds. These factors are strongly dependent on the DRIE parameters. Etching conditions that yield large fillet radii and good surface quality are desirable from a mechanical standpoint. In order to identify optimal DRIE conditions, a mechanical testing program has been implemented. The designed experiment involves a matrix of 55 silicon wafers with radiused hub flexure specimens etched under different DRIE conditions. The resulting fracture strengths were determined through mechanical testing, while SEM analysis was used to characterize the corresponding fillet radii. The test results will provide the basis for process optimization of micro-turbomachinery fabrication and play an important role in the overall engine redesign.
Recent Developments in Experimental and Theoretical Studies of The Mechanical Behavior of Polycrystalline Silicon for Microelectromechanical Systems
Authors: Ballarini R. 
Published: April 2011

AbstractA review of recent developments in experimental and theoretical studies of the mechanicalbehavior of polycrystalline silicon structures whose dimensions are comparable to those of typicalmicro electromechanical systems devices is presented. It is concluded that although great strides have been made towards understanding this behavior, there is a need to develop robust standardized experimental techniques, and in turn, material data bases that are required to verify and calibrate predictive models for calculating device reliability.
Stress-Caused Deflections of Asymmetrical Coated Single-Crystal Silicon Elements
Authors: Kuechler M. , Griesbach K. , Bertz A. , Gessner T. , Faust W. , Dudek R. 
Published: April 2011

AbstractLong and narrow beams of single crystal silicon were made by surrounding them with trenches of different width followed by dry release etch. The beams were coated nonconformally during fabrication. Depending on the asymmetry of the films coated onto the beam sidewalls they tend to bend laterally. This deflection has been analyzed experimentally and by FEM-Simulations.
Mechanical and Thermophysical Properties of Silicon Nitride Thin Films at High Temperatures Using In-Situ Mems Temperature Sensors
Authors: Nieva Patricia , Tada Haruna , Zavracky Paul , Adams George , Miaoulis Ioannis , Wong Peter 
Published: April 2011

AbstractThe optimization of microelectronic devices and Microelectromechanical Systems (MEMS) technology depends on the knowledge of the mechanical and thermophysical properties of the thin film materials used to fabricate them. The thickness, stoichiometry, structure and thermal history can affect the properties of thin films causing their mechanical and thermophysical properties to diverge from bulk values. Moreover, it is known that the mechanical and thermophysical properties of thin films vary considerably at different temperatures. Bulk properties of semiconductors have been characterized over a wide range of temperatures; however there is limited information on thin film properties of silicon-based compounds such as silicon nitride, specially at high temperatures. In our work, MEMS devices designed to record the localized maximum temperature during high temperature thermal processes, which we call Breaking T-MEMS, will be presented as a way to determine some of the mechanical properties (Young's modulus and fracture strength) and thermophysical properties (coefficient of thermal expansion) of silicon-rich nitride thin films at high temperatures.The Breaking T-MEMS device consists of a thin film bridge suspended over a substrate. During testing, the devices are thermally loaded in tension by heating the sample. The low coefficient of thermal expansion of the film relative to that of the substrate causes the thin film bridge to break at a specific temperature. Through a combination of indirect experimental measurements, analytical expressions, numerical and statistical analysis, and if the experiments are conducted using at least two different substrates of known temperaturedependent coefficients of thermal expansion, some of the material properties of the film can be calculated from the breaking temperatures of various devices. The two candidate materials for the substrate are silicon and aluminum oxide (sapphire).
Cation Size and Disorder Effects in Conducting Perovskite Oxides
Authors: Attifield J. Paul , Kharlanov Andrei L. , McAllister Judith A. , Rodriguez-Martinez Lide M. 
Published: April 2011

AbstractThe electronic and magnetic properties of ATO3 and related perovskites (A is a mixture of lanthanide Ln3+ and alkaline earth M2+ cations; T is a transition metal) are very sensitive to the A site composition. The importance of doping effects controlled by the Ln3+/M2+ ratio is well-known, but the other lattice effects controlled by the sizes of these cations are less well understood. A simple approach making use of the mean (first moment) and the variance (second moment) in the A cation distribution has been applied to the metal-insulator transition temperature in colossal magnetoresistance AMnO3 perovskites and to the critical temperature in A2CuO4 and LnBa2Cu3O7-δ superconductors. Series of compositions prepared with a constant doping level and mean A cation radius show a linear decrease of the transition temperature Tt with the A cation size variance σ2. The rate of decrease -dTt/dσ2 is found to lie in the range 1,000-30,000 KÅ-2. The orthorhombic-tetra onal structural transition in the A2CuO4 materials is found to show a linear increase with σ2. A pair of quadratic relationships for the mean size and size variance effects are proposed to be the result of changing strain energies that give rise to these effects.
Preparation and Characterization of Sodium and Iron-Containing Diopside Crystal by Several Methods from Solution
Authors: Iwata Noriyuki , Yokoyama Masashi , Ishinabe Akiko , Tsuchiya Tatsunori , Tsunakawa Sukenari , Lee Geun-Hyoung 
Published: April 2011

AbstractDiopside (CaMgSi2O6) crystals were synthesized mainly by several methods from solution. Sol-gel methods and coprecipitation procedures were carried out using the metal chlorides, nitrates and TEOS as the starting materials. The diopsides obtained from the solutions, in which MgCl2 was used as one of the the starting reagents, showed the single phase diopside XRD patterns and fairly high mechnical strength. Sodium carbonate and iron nitrate were added to the starting solutions in order to examine the morphological effects of these extra elements. Resulted XRD patterns showed the small 2 θ shifts from the pure diopside patterns. The distribution maps of each elements were obtained by EPMA.To confirm the bioactivity of these compounds, the end products pellets were immersed in the SBF. The apatite layer formations were inspected by XRD and SEM.
Non Trivial Processes for Obtaining Bi-Based High Tc Superconductors
Authors: Cloots R. , Ausloos M. 
Published: April 2011

AbstractDysprosium doped Bi-based 2212 ceramics were synthesized by a melt-texturing growth process in a 1.2T magnetic field, applied perpendicularly to the main axis of a cylindrically shaped sample. The materials were characterized by X-ray diffraction, optical and scanning electron microscopy and energy dispersive X-ray analyses. The texturing process was optimized with respect to the sample electrical resistivity and AC magnetic susceptibility.
Thin Film Synthesis of Copper-Based Perovskites Having Two-Dimensional Cation Order: (La0.8Ba0.2CuO2.6±x) (AECuO2)n Superlattices
Authors: Salvador P.A. , Doan T-D. , Mercey B. , Raveau B. 
Published: April 2011

AbstractUsing a multi-target pulsed laser deposition (PLD) process we synthesized superlattices in the (La0.8Ba0.2CuO2.6±x)m(AECuO2)n system, where AE = Ca or Sr, and m and n were varied. Owing to the sequential deposition process, two-dimensional order is obtained on the perovskite A-sites in the superlattice structures, as evidenced by X-ray diffraction for the materials where AE = Sr. However, when AE = Ca, the films were unstable. Structural units of CaCuO2 could be incorporated into the superlattices by containing them between layers of SrCuO2: (SrCuO2)l(CaCuO2)m(SrCuO2)l(La0.8Ba0.2CuO2.6±x)n. The stability and structural characteristics of particular stacking sequences are discussed with respect to their chemical preferences and are compared to bulk materials of similar stoichiometries, i.e., the (La,AE)CuO3-x system. The latter materials do not exhibit two-dimensional cation-order. Resistance measurements of as-synthesized and post-annealed materials are also discussed.
Phase Segregation in Manganese Perovskites
Authors: Radaelli P.G. , Argyriou D.N. , Cox D.E. , Capogna L. , Casalta H. , Andersen K. , Cheong S-W. , Mitchell J.F. , Marezio M. 
Published: April 2011

AbstractThe structural, magnetic and transport phase diagrams of the manganese perovskites (general formula: A1-xA'xMnO3) are characterised by a variety of exotic phenomena, including high-temperature polaronic behaviour, charge, orbital and magnetic ordering and colossal magnetoresistance (CMR). These properties can be “tuned” by changing the doping level x, the electronic bandwidth (through the average A-site ionic radius, <rA>), and the A-site disorder, and are believed to be a manifestation of the underlying competition between electron-lattice coupling and double exchange. Usually, at low temperatures, one of these two interactions is dominant, resulting in a homogeneous ground state, which is either a metallic ferromagnet or a charge-ordered insulator. We have recently found, however, that, for special points in the phase diagram (x ~ 0.3,,<rA> ~ 1.18 Å), the competition can be preserved down to low temperatures, resulting in an inhomogeneous ground state at the microscopic level. This unusual state is characterised by the coexistence of charge-ordered and metallic domains, which are intertwined over a variety of length-scales, and appear to show spin-glass-like dynamics. Upon application of an external field (magnetic field, pressure or even x-rays), the domains grow to macroscopic sizes, resulting in phase segregation. We speculate that the evolution of the local magnetic and crystal structures during this phase segregation process may parallel those occurring, at much higher temperatures, for compounds displaying CMR behaviour at the paramagnetic-toferromagnetic transition. Very recently, it has been suggested that the charge-ordered state, which is stable for higher values of the Mn oxidation state (x ≥ 0.5), may also be associated with modulated mesoscopic phase segregation, in the form of “stripes”. This hypothesis will be discussed in the light of recent x-ray synchrotron and neutron diffraction data on the crystallographic and magnetic modulation in La0.33Ca0.67MnO3
Epitaxial Growth of Rare-Earth Gallates on Single-Crystal Oxide Substrates
Authors: Morrell Jonathan S. , Xue Ziling B. , Specht Eliot D. , Beach David B. 
Published: April 2011

AbstractEpitaxial films of lanthanum gallate, praseodymium gallate, and neodymium gallate were prepared on [100] strontium titanate and [100] lanthanum aluminate single crystal substrates using solution techniques. The solutions employed were mixed-metal methoxyethoxides in 2-methoxyethanol. Films were prepared by spin-coating with a partially hydrolyzed solution, followed by firing at 850 °C for 20 minutes in air. Theta/2-theta scans revealed only [h00] reflections and omega scans (rocking curves) indicated good out-of-plane orientation. Pole figures and phi scans revealed good in-plane orientation and a [100] || [100] epitaxial relationship between the film and the substrate.
Hydrogen-Bonding and Phase Transitions in Proton-Conducting Solid Acids
Authors: Haile Sossina M. 
Published: April 2011

AbstractFrom an investigation of the structures and electrical properties of compounds in the CsHSO4 - CsH2PO4 system, a simple model is presented for predicting whether or not a solid acid will undergo a structural transition to a disordered, superprotonic phase. Such a transition was measured in ß-Cs3(HSO4)2(H2-x(SxP1-x)O4), α-Cs3(HSO4)2(H2PO4) and Cs2(HSO4)(H2PO4), but not CsH2PO4. It is proposed that entropy drives any solid acid to a high-temperature structure in which the oxygen atoms participate equally in forming hydrogen bonds. If the H:XO4 ratio is not precisely 2:1, such chemical equivalence of oxygen atoms can only be achieved if the structure transforms to a state in which proton occupancies at hydrogen bonds are less than one and/or oxygen site occupancies are less than one. This disorder simultaneously leads to fast proton transport in the high-temperature phase, and thus superprotonic conductivity.
Crystal Chemistry of Y2(ZrySn1-y)2O7Pyrochlore Solid Solutions and its Relation to Fast-Ion Conduction
Authors: Ku Esther M. , Yeo Evangeline M.E. , Wuensch Bernhardt J. 
Published: April 2011

AbstractPyrochlore oxides, A2B2O7, are of interest as fuel cell materials and sensors because, with suitable doping, they may be fast-ion conducting or p- or n-type electronic conductors. An earlier analysis of Y2(ZryTi1-y)2O7solid solutions showed that substitution of the larger Zr ion for Ti induced progressive disorder in both the cation and anion arrays causing a 103increase in oxygen ion conductivity. In contrast, Y2(SnyTi1-y)2O7solid solutions remained essentially fully ordered over their entire range of composition even though the range of average radii of the cation species in the B site overlapped to a considerable degree with those of the (ZryTi1-y) materials. The present work used Rietveld analysis of both neutron and x-ray powder profiles to examine Y2(ZrySn1-y)2O7compositions along the third leg of the pseudo-ternary system: solid solutions between the stannate, with strong tendency to remain ordered, and the zirconate which has predilection toward complete disorder. Progressive disorder in the oxygen ion array was again observed with increasing y. Mixing between cation sites was found to progress at a rate independent of anion disordering. The behavior was very similar to Y2(ZryTi1-y)2O7, suggesting that the differing behavior of the three systems is due to the ability of Zr to readily enter the eight-coordinated A site.
Effect of Co3+Ion on Metal-Insulator Transition in (La0.1Ca0.9)(Mn1-xCox)O3
Authors: Taguchi Hideki 
Published: April 2011

AbstractOrthorhombic perovskite-type (La0.1Ca0.9)(Mn1-xCox)O3was synthesized in the range 0.00 ≤x≤ 0.08. The Rietveld analysis indicates that the (Mn, Co)-O(1 and 2) distances are independent of the composition (x). Measurements of the electrical resistivity (ρ) and the Seebeck coefficient (α) indicate that (La0.1Ca0.9)(Mn1-xCox)O3is an n-type semiconductor at the low temperature. At the high temperature, (La0.1Ca0.9)(Mn1-xCox)O3exhibits a metal-insulator transition in the range 0.0 ≤x≤ 0.04. The metal-insulator transition temperature (Tt) increases with increasing the Co3+ion content, whiledρ/dTin the metallic region decreases with increasing the Co3+ion content. The variation of Eaand T+is explained by the difference in the electronegativity between Mn and Co atoms. The variation ofdρ/dTin the metallic region is explained by the increase in the collective o bond.
Reactivity and Stability of Superionics MSnF4 at High Temperature in Various Media
Authors: Dénès Georges , Madamba M. Cecilia , Muntasar Abdualhafeed 
Published: April 2011

AbstractSuperionic MSnF4 are the highest performance fluoride ion conductors, with PbSnF4 being the best. Prototypes of devices using PbSnF4 have been constructed and tested. Since the fluoride ion mobility is thermally activated, some devices might be used more efficiently above ambient temperature. Therefore, it is of prime importance that the stability of these materials be tested under potential conditions of use, since thermal degradation and phase transitions are likely to alter the conducting properties. Tetragonal SrSnF4, α-PbSnF4 and BaSnF4, and orthorhombic o-PbSnF4, are stable at ambient conditions, even in air. However, all undergo significant deterioration when heated in air: the color changes from white to yellowish, and tin hydrolysis and oxidation takes place. They are much more stable under inert conditions (nitrogen or argon). However, PbSnF4 undergoes several phase transitions at high temperatures: o to α starting at ca. 100°C, α to β (reversible, but the reverse reaction is very sluggish) starting at 250°C, β to γ (reversible) at 390°C. β-PbSnF4 can be quenched to ambient temperature and is metastable for long times, however, eventually it starts changing to stable α-PbSnF4 and this change is uncontrollable and is faster above ambient temperature. Microcrystalline μγ-PbSnF4, obtained by ball milling any other phase of PbSnF4, gives rapidly a-PbSnF4 at 200°C. In addition, for all MSnF4, hydrolysis of the Sn-F bonds to Sn-O occurs with traces of moisture.
Reactivity of SnF2 with Fluorite Type MF2 Versus M: Synthesis of High Performance Fluoride Ion Conductors
Authors: Dénès Georges , Madamba M. Cecilia , Muntasar Abdualhafeed 
Published: April 2011

AbstractThe fluorite type MF2 materials react at high temperature with tin(II) fluoride SnF2 in the 1: 1 stoichiometry to give high performance fluoride ion conductors MSnF4. However, the reaction takes place only for the largest M cations (M = Sr, Pb and Ba). For the others (M = Cd and Ca), no reaction takes place. Furthermore, when the reaction occurs, it is observed that the reactivity of SnF2 with MF2 is highly dependent on M. The reaction with PbF2 is the easiest; it is complete at 250°C, whereas 500°C is required with SrF2 and BaF2. In addition, with SrF2, an incomplete reaction is observed very often. Moreover, PbF2 and SnF2 fully react at other stoichiometries to give other materials, whereas SrF2 and BaF2 do not, and with CdF2 and CaF2 not even MSnF4 is formed. A structural analysis based on bond angles and using the size of the M2+ cations is used in an attempt to explain the lack of reactivity for the smallest M2+ cations and the poor reactivity of SrF2. However, the relative cationic sizes cannot explain all the trends, inclusing the exceptionally high reactivity of PbF2 (lower reaction temperature, much richer source of materials). An explanation based on the electronic structure of tin(II) and lead(II) has been developped in order to account for the results.
Synthesis, Structure and Magnetic Properties of the Group IV Ternary Nitrides, AMN2 (A = Alkaline Earth Metal, M = Transition Metal)
Authors: Gregory Duncan H. , Barker Marten G. , Siddons Daniel J. , Edwards Peter P. , Slaski Marcin 
Published: April 2011

AbstractThe ternary transition metal nitrides of general formulation AMN2 (A = alkaline earth metal, M = transition metal) have been systematically studied. These compounds have been synthesised by high temperature solid state reaction from their component binary nitrides in sealed systems. The structures of these materials have been determined by powder X-ray diffraction (PXD) and two layered structure-types (α-NaFeO2-type and KCoO2-type) have been observed, thus far. Intriguingly, magnetic measurements performed on nitride samples indicate they may not be diamagnetic (d = 0, S = 0) as their nominal stoichiometry suggests.