bluuebunny/crossref_metadata_2025 huggingface dataset:
Semi-Coherent Yttria Inclusions Occurring Spontaneously in YBa2Cu3O6+× Films Grown by Dc Magnetron Sputtering
Authors: Selinder T. I. , Han Z. , Helmersson U. , Magnusson J. , Norling P. , Svedlindh P.
Published: March 2011

Semi-coherent Y2O3 (yttria) inclusions have been observed in high quality, c-axis oriented YBa2Cu3O6+×,(YBCO) Alms. The inclusions were studied by transmission electron microscopy (TEM), and were found to be embedded in the YBCO matrix without disturbing its structure seriously. Their number density is estimated to higher than 2 × 1016 cm−3 in epitaxial YBCO films, having transport critical current densities in excess of 1 × 106 A cm−2 at 77 K. Magnetization measurements indicate a possible correlation between a high density of yttria inclusions and high pinning strength. The effects of the inclusions on film growth and microstructure is discussed.
Critical Scaling of LöW Frequency Ac Resistivity in Superconducting Y-Ba-Cu-O Single Crystals
Authors: Reed D. S. , Yeh N. -C. , Jiang W. , Kriplanp U. , Holtzberg F.
Published: March 2011

AC transport measurements show that the vortex dynamics in a twinned superconducting Y-Ba-Cu-O single crystal are consistant with a second order vortex-solid melting transition. Indentification of the universal functions and consistent measurements of the critical exponents v = 0.7 and z= 3.0 found in magnetic fields from IkOe to 90kOe as well as DC transport measurements offer strong evidence for this transition.
Fabrication of YBa2Cu37/Ag Sputtered Multilayers
Authors: Colino J. , Vicent J. L.
Published: March 2011

Thin films of YBa2Cu3O7/Ag multilayered structures have been grown by dc magnetron sputtering on MgO(lOO) substrates. The samples have been characterized by X-ray diffraction, scanning tunneling microscopy and resistivity measurements. Multilayers with YBCO layer thickness above 40nm show superconducting transitions and zero resistances higher than 70K. These layers show c-axis growth perpendicular to the substrate and the silver layers have preferential (111) orientation normal to the substrate too. Finally STM images reveal screw dislocation spirals at the YBCO layer surface even when the superconducting layer is grown on silver (111) underlayers.
YBa2 Cu(3-x)CoxOy- A Substrate Material for YBCO Superconductors
Authors: Vienna J. D. , Balachandran U. , Cermignani W. , Poeppel R. B. , Taylor J. A.
Published: March 2011

The physical properties of the ceramic YBa2Cu(3-x)CoxOy have been investigated in order to evaluate its usefulness as a substrate material for YBCO superconductors. YBa2Cu(3-x)CoxOy has been found to be thermally and chemically compatible with 123 and displays adequate electrical properties for a substrate material. A material with the nominal composition of YBa2Cu2.2CO0.8O7 was investigated, extensively. The mechanical properties of this material were found to be poor, e.g., tensile strength was only 60 MPa. A semiconductor-like behavior was observed with a room-temperature resistivity of 70 mμ.cm and a resistivity equal to 4 × 106 mn.cm at 77K. [ Key words: YBa2Cu3Oy, cobalt substitution, substrate, electrical properties, thermal properties, processing]
Rheed Intensity Oscillation During Layer-by-Layer Growth of Bi-Sr-Ca-Cu-O Thin Films
Authors: Yoshikawa K. , Sasaki N.
Published: March 2011

Using in-situ reflection high-energy electron diffraction (RHEED), we studied the growth of Bi-Sr-Ca-Cu-O (BSCCO) thin films prepared by reactive evaporation using layer-by-layer deposition. Bi2Sr2CaCu2Ox(2212) tends to be grown three-dimensionally if it is grown directly on (100) SrTiO3, in contrast to Bi2Sr2CuOx(2201) which is easily grown two-dimensionally on SrTiO3. Two-dimensional 2212 growth can be realized, if a buffer layer of 2201 is deposited on (100) SrTiO3 and growth interruption is utilized after SrO layer deposition. A buffer layer of only two 2201 unit cells improved the surface crystallinity of the substrate for the epitaxial growth of 2212. Growth interruption for two minutes after the 2nd SrO layer in the half unit cell is necessary to keep two-dimensional layered growth. The resulting Tc (zero) is 76 K and Jc (at 4.2 K) is 1.5 × 106 (A/cm2) with these epitaxial films.
Preparation of YBa2Cu4O8 Thin Films by MOCVD
Authors: Sakai H. , Hayashi H. , Uehara K. , Kubota N. , Sugimoto T. , Shiohara Y. , Tanaka S.
Published: March 2011

Preparation processing to obtain 124 single phase films has been studied by MOCVD. The YBCO thin films which were fabricated on MgO(100) and SrTiO3(100) substrates, respectively, were obtained under both conditions of Ts(temperature of susceptor)=800°C and Po2(oxygen partial pressure)=17.5torr. It was found that the oriented peaks of 124 c-axis and of 123 a-axis were more prominent than others at the composition ratio(Y/Ba/Cu=l.0/2.7/4.7), using the MgO(100) substrates. The 123 a-axis oriented grain was observed by using SEM and TEM. We have obtained thin films which were dominant in the 124 phase on the SrTiO3(100) substrates. The film surface morphology on the SrTiO3(100) substrate was smoother than that on the MgO(100) substrate. The origin of a-axis oriented grain growth was explained by the surface step(about 10 À) on MgO(100).
Growth of Sr1−xNdxCuOy Thin Films by Rf-Magnetron Sputtering and Pulsed-Laser Deposition
Authors: Sugii Nobuyuki , Ichikawa Michiharu , Kubo Koichi , Sakurai Takeshi , Yamamoto Kiyoshi , Yamauchi H.
Published: March 2011

Sr1−xNdxCuOy thin films are grown on SrTiO3 substrates by rf-magnetron sputtering and pulsed-laser deposition. The sputter-deposited film with x=0 has an “infinite-layer” structure whose lattice constants are: α=0.390 nm and c=0.347 nm. When x is larger than 0.1, the films contain a phase of the Sr14CuO24O41 structure. The laser-deposited films of Sr1−xNdxCuOy with x≤.075 were single phase of the “infinite-layer” structure. The lattice parameter c decreased and the lattice parameter αincreased, as the Nd content, x, increased. The films with α=0.10 and 0.125 exhibited superconducting onset temperatures around 26 K. Weak Meissner signals were observed for these films at temperatures below 30 K.
Characterization of DyBa2Cu3O7+δ thin Films Prepared by Ozone-Assisted Co-Evaporation Technique
Authors: Hsieh T. J. , Smilgys R. V. , Chiang C. K. , Robey S. W. , Arsenault R. J. , Salamanca-Riba L.
Published: March 2011

Superconducting thin films of DyBa2Cu3O7-δ_ are deposited on MgO(100) substrates by an ozone-assisted coevaporation technique. At a relatively low substrate temperature (610°C) and with a fixed ozone flux we prepare highly c-axis oriented films with very good superconducting properties. The critical temperatures of the films are commonly above 85 K with critical currents above 10 5 A/cm2. We report on composition, microstructure, electrical resistivity and critical current of two good films.
CO-Sputtered Composite films Of YBa2Cu3O7−xand LaAIO3
Authors: Allen L. H. , Cukauskas E. J. , Sherrill G. K. , Holm R. T.
Published: March 2011

We have grown thin film composites of and YBa2Cu3O7−x and LaAlO3 by co-sputtering. A film with composition of 10% LaAIO3 by volume had a transition temperature of 58K and critical current density of 1.2 × 106 A/cm2 at 4K. We measured the temperature dependence of the critical current and obtained a good fit with Ginzburg-Landau theory for thin films. A perpendicular magnetic field was applied, and the critical current and pinning force measured. At 70 kOe, the critical current was suppressed only a factor of 4 from its zero-field value. The measured pinning force was 2 × 109 dyn/cm3 at 70 kOe and is comparable to that of YBa2Cu3O7−x films.
Substrate Influence in YBaCuO Melt-Texturing Growth
Authors: Pellerin N. , Gervais M. , Odier P.
Published: March 2011

Melt-texturing of YBaCuO is generally processed on substrates. Due to its high chemical activity, the non-stoichiometric liquid, mainly due to the barium element, generally reacts with the substrate which is therefore subjected to play a role in the crystallization of YBaCuO and in the development of the texture. The particular case of Y2O3, which is a reacting but non-polluting substrate, is treated in details. The comparison of textured YBaCuO in similar conditions but on different substrates: Al2O3, Y2O3 and MgO gives some insight in the texturing process.
Electric Field Effect in High-Tc Superconductors, Evaluation of Field-Induced Superconductivity and Device Applications
Authors: Mannhart J. , Kleinsasser A.
Published: March 2011

In the past two years, it has been demonstrated that applied electric fields can be used to modulate significantly the normal state resistivity, the critical temperature and the critical current density of high-Tc films. Whereas earlier publications focussed on experimental aspects of high-Tc field effects, this contribution will discuss the conditions that are required to induce superconductivity on the surface of insulators. In addition, evaluations for performance limits of potential high-Tc field effect devices will be presented.
Temperature Dependent C-V Characteristics of YBCO/YSZ/Si MIS Capacitors
Authors: Qiao Jianmin , Ajimine Eric M. , Patel Paresh P. , Segovia Marco A. , Yang Cary Y. , Fork David K. , Ponce Fernando A. , Tramontana Joseph C.
Published: March 2011

Metal-insulator-semiconductor capacitors are fabricated from a YBa2Cu3O7-δ (YBCOVYttria-Stabilized Zirconia(YSZ)/Si structure. Current-voltage(I-V) measurements reveal that thicker YBCO films(≤150Å) tend to result in more stable capacitors. Results of capacitance-voltage(C-V) measurements during bias-temperature cycling suggest the presence of a thermally activated process in the YSZ and/or YSZ/Si interface. This process is probably related to trapping/detrapping mechanisms in the SiOx, layer formed between YSZ and Si. It is shown that the distribution of mobile ions in YSZ can be “set” with biases at room temperature and then “frozen” by lowering the temperature, giving rise to adjustable threshold voltages at 80K.
RHEED-Controlled Unit-Cell by Unit-Cell Layer-Growth of High-Tc Cuprate Films with Laser-Ablation Technique
Authors: Frey T. , Chi C. C. , Tsuei C. C. , Shaw T. , Trafas G.
Published: March 2011

Thin films of PrBa2Cu3O7 and in-situ superconducting YBa2Cu3O7 were grown on (100)-oriented SrTiO3 substrates by laser ablation under molecular beam epitaxial condition. The unit-cell by unit-cell growth of these high-Tc cuprate materials has been indicated by RHEED-oscillations and further confirmed by cross-sectional TEM (X-TEM) and small angle X-ray. Superconductivity with Tc (R = 0) at 35 K was observed for samples with one unit-cell YBa2Cu3O7 layers sandwiched between PrBa2Cu3O7 layers. TC varies with the number of YBa2Cu3O7 unit-cell layers. An eight unit-cell thick YBa2Cu3O7 film is superconducting at 86 K. Substrate temperature is found to be the most crucial parameter in determining the growth mode and superconducting properties.
Degradation and Recovery of Transport Properties of Strained HTS Conductors
Authors: Patel S. , Ye J. , Haugan T. , Chen S. , Li S. S. , Wong F. , Shaw D. T. , Tsuei C. C.
Published: March 2011

Mechanical bending of HTS tapes can result in the deterioration and destruction of their transport properties. Depending on the magnitude and type of strain (tensile or compressive), the films can be permanently damaged by fracture and recoverable only by post heat treatment, or simply elastically strained with recoverable transport properties upon release of the strain. Here we present results of strain effects on BSCCO (2212) /Ag tape transport properties and post heat treatment recovery of those properties.
Dependence of Critical Current Density on Granular Arrangement in Ceramic Superconductors
Authors: Wang Jui H. , Ren Zhifeng
Published: March 2011

The critical current density Jc of bulk ceramic superconductors is often several orders of magnitude lower than that of a single crystal or oriented fílm of the same material due to the weak links residing at the boundaries between single crystals within the ceramic sample. Assuming that the rate of electron transport within each single crystal is much faster than the average rate of electron transport between adjacent single crystals, a working hypothesis of Jc enhancement by granular reorientation is formulated which includes the“brickwall”model and melt-texturing as special cases with long-range granular alignment which usually leads to rigid and brittle bulk samples. Simple geometric considerations show that only short-range local granular alignment is necessary for high Jc. For mis reason, it should be possible to make flexible superconducting wires and tapes for commercial applications at or above 77K.
The Synthesis of“1223”TL-CA-BA-CU-Oxide Superconducting Films Via the Reaction of Silver-Containing Spray Deposited Oxide Precursors with Thallium Oxide Vapor in a Two-Zone Reactor
Authors: DeLuca J. A. , Karas P. L. , Tkaczyk J. E. , Briant C. L. , Garbauskas M. F. , Bednarczyk P. J.
Published: March 2011

Superconducting films of“1223”Tlx Ca2Ba2Cu3Oy (0.65<×<l.00) have been prepared on polycrystalline yttria stabilized zirconia substrates via the reaction of thallium oxide vapor with spray-deposited Ca-Ba-Cu-oxide films containing silver. The silver addition permits the formation at 860C of oriented, interconnected polycrystalline superconducting films with Tc(0) values of 104–107K. Samples have been prepared routinely with 77K zero-field dc transport critical current densities >10,000A/cm2 with values as high as 105,000A/cm2 having been measured. The range in Jc values measured is believed to be related, at least in part, to inhomogeneities in the films. The excellent in-field characteristics of the“1223”thick films are reflected in the behavior of the“105,000A/cm” sample for which J >10,000A/cm was measured at 60K in a 2 Tesla field applied parallel to the crystallographic c-axis
Critical Current Density of the AG-Clad BI-Based Superconductors
Authors: Dou S. X. , Guo Y. C. , Liu H. K.
Published: March 2011

A high-Tc phase formation-decomposition-recovery process(PFDR) through the use of a short period of melting has been developed for fabrication of Ag-clad Bi-Pb-Sr-Ca-Cu-O (BPSCCO) wires. The weak links and flux pinning have been significantly improved and an extended plateau regime in the Jc-H curve has been observed. The PFDR processed tapes exhibit 3 to 10-fold increase in the Jc at 77 K and 1 Tesla over the normally processed tapes. A Jc of 40000 A/cm2 at 77 K and 0 T and 9000 A/cm2 at 77 K and 1 T have been achieved. The Jc correlates well with the degree of grain alignment which can be measured through the Jc dependence on the orientation of the applied field. The improved Jc - H characteristics is attributed to the desirable microstructures consisting of well aligned (Bi,Pb)2Sr2Ca2Cu3O10+y (2223) grains, fraction of (Bi,Pb)2Sr2CaCu2O8+y(2212) and high density of dislocations produced through PFDR process. The superconducting Ag/Bi-Pb-Sr-Ca-Cu-O wires can be made flexible. The Jc remains unchanged when wires of superconductor thickness 25 μm are bent to a strain rate of 1.5%
Relative Reactivity Trends OP High Temperature Superconductor Phases
Authors: Riley David R. , Zhou Ji-Ping , Manthiram A. , McDevitt John T.
Published: March 2011

Many of the high temperature superconductor phases degrade rapidly when in the presence of water, acids, carbon dioxide or carbon monoxide. In order to foster more rapid developments in the area of high-Tc research, it will be necessary to acquire a more complete understanding of the surface chemistry of these superconducting materials. In this paper, the relative reactivity of the common cuprate phases toward water is reported. X-ray powder diffraction and scanning electron microscopy measurements are utilized here to establish the reactivity trends.
Controlling the Microstructure of the 2223 Phase Grains for the Fabrication of Silver Clad (Bi,Pb)2Sr2Ca2Cu3Ox Tapes Through the Growth Kinetics of the Superconducting Phases
Authors: Lo Wai , Glowacki B. A.
Published: March 2011

Our study concentrated on the relationship between the proportions of the phases in the precursors used to synthesise the Bi-2223 phase and the ultimate microstructures of the 2223 phase materials, although the overall cation stoichiometry fixed. It was found that the final 2223 phase grains were larger, although the bulk density tended to be lower with the grains loosely packed together, when the major phase in the precursor was 2212 phase. This was proved to be partly caused by the fast growth rate of the 2212 phase grains which were eventually converted into the 2223 phase. When 2223 phase was present in the precursor, the bulk density became higher and 2223 phase grains became closely packed together, although the average grain size became smaller. This was explained by the existence of a liquid phase at higher temperatures during the formation of the 2223 phase and the sintering of the 2223 phase grains.
Applications of Parallel Josephson Junction Arrays for the Detection of Magnetic Flux
Authors: Miller J. H. , Gunaratne G. H. , Zou Z. , Huang J. , Golding T. D.
Published: March 2011

We have carried out finite-inductance calculations of the critical current vs, flux(Ic-φ) and voltage vs, flux (V-φ) characteristics of superconducting interferometers with many Josephson junctions (JJ's) in parallel. At least two features of our calculations suggest that interferometers with many junctions, which we call Superconducting QUantum Interference Gratings, or SQUIG's, might be advantageous for the detection of magnetic flux. First, the voltage noise can potentially be reduced significantly as compared to a dc SQUID with the same overall voltage-to-flux transfer coefficient - a feature which might reduce 1/f noise and enhance the magnetic flux sensitivity of both low and high Tc superconducting (HTS) devices. In addition, nonuniformity of the junction critical currents appears to have little adverse effect on the predicted diffraction-grating like enhancement and narrowing of the peaks in the Ic-φcharacteristic, suggesting that flux uniformity, rather that critical current uniformity, is of primary importance.
Some Observations on the Measurement of Transport Critical Current Density in Bulk Ceramic Superconductive Wire
Authors: Samajdar S. , Samanta Shyam K.
Published: March 2011

The transition temperature and the critical current density of a bulk YBa2Cu3O7−x-Ag microcomposite superconductive wire, prepared by powder processing followed by warm extrusion, have been measured employing the standard AC four probe technique. Measurements were performed, at 15K and zero applied field, with varying distance between the voltage contacts, while the current contacts remained a constant distance apart. It is observed that the resistance-temperature behavior remained identical in all the cases. Interestingly, the critical current density, determined from the experimentally recorded current-voltage characteristic by applying a constant electric field criterion, is seen to increase significantly, smoothly and steadily with increasing voltage tap length. However, the critical current density remains virtually unchanged if a constant voltages criterion is applied for its determination. This paradoxical dependence of critical current density, a material property, on measurement length has been explained with the help of a simple theoretical treatment, taking into account the nature of current-voltage chracteristics as well as the phenomenon of current transfer through the metallic to the superconducting ceramic phase. It is suggested that the constant electric field criterion may not be an appropriate one to use in the evaluation of critical current density of metal-ceramic superconductive composites.
Weakening of Flux-Pinning Strength for High Tc Superconductors in an Alternating Magnetic Field
Authors: Chen Q. Y.
Published: March 2011

The flux-pinning forces in high temperature superconductors were found to be weakened in an ac field as the applied field strength or the frequency increases. In the weakly pinned regime, flux dynamics could be described widi the concept of magnetic diffusion. Flux-motion-induced finite resistivity could lead to significant skin-effect which was reflected in the ac screening effectiveness. The frequency dependence of the relative local field within a superconducting hollow cylinder were used to deduce the flux-motion resistivity (ρ). For superconducting YB2Cu3O7−x compounds at 77K it was found that ρ≈ 1μΩ-cm. The corresponding magnetic diffusion coefficient was ≈224 cm2/s. At 750 Hz the skin depth is around 1.54 mm as compared with the 2-mra sample wall thickness.
Superconductivity of Dc Reactive Magnetron Sputtered Epitaxial TiN/NbN Superlattices
Authors: Shinn M. , Hong B. -S. , Barnett S. A.
Published: March 2011

Epitaxial B1-structure TiN/NbN superlattices have been grown by reactive magnetron sputtering On MgO(001). X-ray diffraction and transmission electron microscopy (TEM) diffraction spectra exhibited up to nine orders of superlattice reflections, indicating that the superlattice interfaces were relatively sharp. TEM images also showed well-defined layers. The superlattice wavelength (∧) dependence of the superconducting transition temperature (Tc), critical Current density (Jc), and electrical resistivity (ρ) have been investigated. Tc values increased from 12 K to 17 K with increasing ∧. Jc in a magnetic field perpendicular to the film surface ranged from 104 to 106 A/cm2, increasing with increasing wavelength and decreasing with increasing applied magnetic field. Jc in a field parallel to the film surface was > 10 times higher, ≈ 107 A/cm2. The resistivity exhibited different ∧ dependencies in three different A ranges.
Transformation of a vortex lattice and an inclusion in superconductors
Authors: Tokuono Shinya , Tanaka Shoji , Fukuyama Hidetoshi
Published: March 2011

Interaction between vortices and inhomogeneity in superconductors is studied. As a typical example, we investigated the case of a single vortex and some vortices near an inclusion of the cylindrical shape and derived the interaction potential for the vortices as a function of the distance by use of the solution of London equation.
Long Time Power Law Magnetic Relaxation in Detwinned YBa2Cu3O7-δ Single Crystals
Authors: Zhang Lu , Liu J. Z. , Lan M. D. , Klavins P. , Shelton R. N.
Published: March 2011

The time-dependent magnetic relaxation was measured in a full field penetrated YBa2Cu3O7-δ detwinned crystal for long times up to 5×105 sec. The relaxation data exhibit a power-law time dependence over a wide range of temperatures and magnetic fields indicative of flux creep with logarithmic dependence of the effective creep activation barrier U(J). A theoretical model is employed to analyze the data and to determine the activation energy.
Studies of Crystalunity for Sputter Deposited Bi-Based Oxide Films
Authors: Mizuno Koichi , Ichikawa Yo , Setsune Kentaro
Published: March 2011

Crystalline quality of Bi-based oxide films has been evaluated by means of X-ray diffraction (XRD) and ion-channeling on the Rutherford backscattering (RBS). The films were sputter deposited 2201-phase Bi2Sr2Cu1O8-δ (BSCO) and 2212-phase Bi2Sr2Ca1Cu2O8-δ (BSCCO). They were prepared on MgO(100) and SrTiO3(100) substrates at the low temperature of 650°C during the deposition. The best quality, however thin films had poor crystallinity compared to single crystals, was obtained with the 2201-phase BSCO film that was deposited on a SrTiO3(100) substrate. The full width at half maximum (FWHM) value of the rocking curve on XRD for the film was estimated as 1560 (arc sec).
Smart Ferroelectric Films and Fibers; Applications in Micromechanics
Authors: Brooks Keith G. , Udayakumar K. R. , Chen Jiayu , Selvaraj Ulagaraj , Cross L. Eric
Published: March 2011

Smart electroceramics, in the form of ferroelectric thin films show great potential for applications in the field of microelectromechanical systems. Ferroelectric thin films will become a key player due to their optical, mechanical, electrical and thermal sensing with actuating capabilities. Recent results on electromechanical transduction in piezoelectric (e.g. PZT), electrostrictive (e.g. PLZT), and antiferroelectricferroelectric phase switching (e.g. PLZSnT) thin films and their potential applications in smart micromechanical systems are discussed. The possibility of three dimensional structures exists in the emerging technology of ferroelectric fibers. Some exciting applications for these films and fibers include microvalves, ultrasonic micromotors, microrobotic actuators and micropumps.
A Silicon-Based Shape Memory Alloy Microvalve
Authors: Ray Curtis A. , Sloan Charles L. , Johnson A. David , Busch John D. , Petty Bruce R.
Published: March 2011

A new actuator for silicon micro-valves has been developed and tested. A thin film shape memory alloy provides for large deflections with high speed, low power, and small size. The actuator is batch fabricated with planar processes.
Metallization at Microindentations
Authors: Gilman John J.
Published: March 2011

It is shown that quite generally there is a correlation between insulator-metal transition pressures and indentation hardness numbers for covalent crystals. They are numerically equal for the Group IV elements. Three elements plus five III–V compounds acquire the β-Sn structure upon metallizing. Bondbending, rather than bond-shortening, appears to lead to their transformations. A simple version of the theory of covalent bonds gives the critical transformation bond-angle correctly.
Charactervation of Adhesion in Thin-Film Materials by the Blister Test
Authors: Chu Y Z. , Jeong H. S. , White R. C. , Durning C. J.
Published: March 2011

In this work a blister test is applied to study the adhesion of thin films to substrates. In the blister test one injects a fluid at constant rate at the interface between the substrate and an overlayer to create a “blister”. The fluid pressure is measured as function of time. An analysis gives a reliable way of calculating the adhesion energy Ga. from the time-dependent pressure data. The method was applied to a variety of systems including polymer/polymer, polymer/silicon and polymer/metal interfaces. The results show that the test is very sensitive and is able to determine small adhesion energies inaccessible in conventional peel tests. This work demonstrates that the blister test provides a means of relating the mechanical strength of an interface to its microscopic dynamic and structural features.
A Novel Process for Fabricating Force Sensors for Atomic Force Microscopy
Authors: Farooqui M. M. , Evans A. G. R.
Published: March 2011

The new technique of scanned force microscopy which enables imaging surface features with sub nanometre resolution has been made possible by the development of highly sensitive, hysteresis free force sensing cantilevers and the availability extremely sharp probing tips. Such cantilevers with integral tips can be micromachined using IC compatible technology, and several processes have been described in literature for their fabrication. These are based on different etching schemes, and require two or more masking stages. A novel process using a single mask is described here for the fabrication of single crystal silicon cantilevers with integral sensing tips. The cantilever thickness can be tailored to provide a range of force constants and resonant frequencies, and the tip profile can be varied from pyramidal to highly cusped. As only a single mask is used in the fabrication, there are no mask alignment errors and precise location of the tip is thereby achieved. This eliminates any twist in the cantilever during scanning which could give rise to distorted imaging. The complete fabrication process and the mask design is described together with SEM photographs of the first batch of devices, which have been evaluated by retrofitting to a commercial atomic force microscope.
LPCVD Silicon Dioxide Sacrificial Layer Etching for Surface Micromachining
Authors: Monk David J. , Soane David S. , Howe Roger T.
Published: March 2011

The key step in producing a movable microstructure is the controllable sacrificial layer etching process. For the current study, a 1 μm silicon-rich silicon nitride structural layer was deposited on a 2 μm phosphosilicate glass (PSG) sacrificial layer that had been deposited on a single-crystal silicon wafer. Silicon nitride, unlike the more common polycrystalline silicon (poly-Si) structural material, is transparent and, therefore, allows the observation of an etch front in the underlying PSG sacrificial layer. The PSG is an amorphous silicon dioxide, with phosphorus added as a controlled impurity, that can be selectively etched in hydrofluoric acid. Several experiments have been performed with four HF concentrations using these test structures. Diffusion limited etching is observed at long etching times for each concentration. Additional experimental work has been done to determine appropriate kinetic expressions for the PSG/HF reactions.

The sacrificial layer etching process has been modeled as a chemical reaction/diffusion system. Constants for the kinetic expression have been found from independent experimental work. This Deal-Grove type model assumes isothermal conditions, constant density solution, onedimensional etching, and the equality of the diffusion and reaction fluxes. The model calculates the HF surface concentration and the length of PSG underetched as a function of time. It fits the data well but requires the use of an unphysical diffusion coefficient. An extension of the Deal-Grove model to nonfirst order kinetics allows for a reasonable estimate of the reactant/product mixture diffusivity in water to be used when fitting the model to experimental data.
Non-Linear Constitutive Properties of Piezoelectric Ceramics
Authors: Cao H. C. , Evans A. G.
Published: March 2011

Experiments have been conducted to study the nonlinear constitutive properties of ferroelectric ceramics for large strain operation applications, where the mechanical behavior of the material dictates the overall electromechanical response of the devices. For this purpose, polarization and strain are measured continuously on a compression cuboid. Severe non-linear and hysteretic behavior is observed in these materials. An empirical formulation has been proposed to model the constitutive laws applicable to this non-linear deformation. Physical mechanism is provided, that is attributed to this constitutive law.
Characterization of Pulsed Laser Deposited Zinc Oxide
Authors: Ianno N. J. , McConville L. , Shaikh N.
Published: March 2011

The pulsed laser deposition of zinc oxide films (ZnO) has been studied as a function of laser wavelength, and substrate temperature. The deposited films were characterized by x-ray diffractometry, Auger electron spectroscopy, and scanning electron microscopy. Highly textured (002) ZnO films have been deposited at substrate temperatures of 300 C with laser wavelengths of 532 nm and 248 nm. However, the energy fluence of 248 nm radiation controls the degree of texturing, allowing highly textured films to be deposited at room temperature.

Smart structures based on embedded, textured ZnO coated fibers, and wires exhibit excellent piezoelectric response to external stress.
Impact, Friction, and Wear Testing of Microsamples of Polycrystalline Silicon
Authors: Lee Abraham P. , Pisano Albert P. , Lim Martin G.
Published: March 2011

This paper gives an overview of the recent developments in impact, friction, and wear testing of polycrystalline silicon (polysilicon) based micro electromechanical structures. Impact-friction actuated micromechanisms form a new type of actuators. In this type of actuators, lateral resonant structures are retracted by electrostatic comb drives and are propelled forward toward the actuated micromechanism by elastic forces generated by folded beam flexures at frequencies ranging from 10 kHz to 20 kHz. This sequence generates normal impact and tangential friction contact between the two microstructures, raising wear concerns. Two sorts of impact test structures are introduced in this paper, One with a resonant micro impact bumper (MIB) striking a stationary impact wall anchored ofn the substrate. Another is a testing of two MIBs driven to impact each other. Two types of impact actuators are also described, an impact actuated micro angular oscillator (MAO) and a polysilicon micro vibromotor. The vibromotor is a rotor driven by oblique impact on the rim by a converter pointer tip attached to a lateral resonator. Some initial results of impact wear testing as well as static and dynamic friction done by researchers in the field are also described in the paper. Finally, many areas where material scientists can contribute to this field are suggested.
Guest-Host Composite Films Containing Oligomeric Ladder Subunits for χ(3) NLO Applications
Authors: Sapochak Linda , Strohkendl Friedrich , McLean Malcolm R. , Dalton Larry R. , Spangler Charles W. , Nickel Eric G.
Published: March 2011

Several ladder polymer systems, such as POL and PTL, have displayed large third-order optical nonlinearities. However, these polymers are insoluble in common organic solvents, and as such are not amenable to studies of substituent effects on the nonlinear optical properties. During the past year we have developed synthetic and processing methodology to produce optical quality guest-host composites in polycarbonate, poly(methyl vinyl ether) and most recently polystyrene. In this paper we describe the synthesis of selected guest ladder 5-ring oligomers, and describe the preliminary NLO characterization as thin film composites.
Preparation and Optical Properties of a Reverse-Mode Polymer Dispersed Liquid Crystal Film
Authors: Gotoh Tomohisa , Murai Hideya , Hasegawa Etsuo , Mizoguchi Katsuhiro
Published: March 2011

Two new types of reverse-mode polymer-dispersed liquid crystal films have been developed and successfully produced. The first was produced by UV-curing of a mixture of dual frequency addressable liquid crystal (DFALC) and UV-curable polymers under an applied voltage at a frequency lower than the crossover frequency (fc) of the DFALC. This first type is referred to as a dual frequency type. The second type was produced by injecting a liquid crystal having negative dielectric anisotropy into a specially prepared porous polymer film from which liquid crystal having positive dielectric anisotropy had previously been extracted. The type thus produced through such “negative-for-positive” substitution is referred to as a substitution type. While the dual frequency type can not be driven at a low frequency, substitution type can, which gives it a distinct advantage. Other electro-optic characteristics of the two types of films, including alignment properties of the liquid crystal molecules, are also discussed.
Linear and Non-Linear Optical Properties of (2-Cyano-5-Methoxy-1,4-Phenylenevinylene) and Paraphenylenevinylene Copolymers
Authors: Kim Jang-Joo , Hwang Do-Hoon , Kang Shin-Woong , Shim Hong-Ku
Published: March 2011

Poly(CMPV-co-PV) have been synthesized via water soluble sulfonium salt precursor route and their linear and non-linear optical properties were characterized. The electro-optic response was stable up to 100°C when the materials were poled during the elimination. The thermal stability and mechanical strength of PPV and its derivatives, and easy processibility from the precursor polymers suggest a new approach for the molecular design of the 2nd order non-linear optical polymers.
Monoclonal Antibodies as New Macromolecular Hosts for Porphyrins
Authors: Harada Akira , Okamoto Kazutake , Fukushima Hiroyuki , Shiotsuki Keizou , Kamachi Mikiharu
Published: March 2011

Monoclonal antibodies against meso-tetrakis(4-carboxyphenyl porphine)(TCPP) were prepared by immunizing Balb/c mice with TCPP bound keyhole limpet hemocyanin covalently and fusing the spleen cells with myeloma cells by using poly(ethylene glycol). The antibodies bind TCPP strongly with the dissociation constants of 10−6−2.5 × 10−7 M. One of the antibodies causes a large shift of the Soret band of TCPP to a longer wavelength and large induced Cotton effects(ICD) on TCPP. Quantitative analyses of the binding of TCPP to the antibody by ICD show that not only one-to-one binding but two-to one(binding site: TCPP) binding occurs in excess of the antibody over TCPP.
Encapsulation and Reactivity of Proteins in Optically Transparent Porous Silicate Glasses Prepared by the Sol-Gel Method
Authors: Yamanaka Stacey A. , Ellerby Lisa M. , Lan Ester H. , Nishida Clinton R. , Nishida Fumito , Dunn Bruce , Valentine Joan Selverstone , Zink Jeffrey I.
Published: March 2011

Copper-zinc superoxide dismutase (CuZnSOD), myoglobin, hemoglobin and glucose oxidase are encapsulated in stable, optically transparent, porous, silica glass matrices synthesized under mild conditions using novel sol-gel synthetic techniques. The biomolecules retain their characteristic reactivities and spectroscopic properties. The porous glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within the pores. The chemical reactions of the immobilized proteins are monitored by means of changes in their visible absorption spectra. Four encapsulated proteins are studied: CuZnSOD reacts with CN−; metmyoglobin is reduced to its deoxy form and then reacts with O2to make the oxy form and CO to make the carbonyl form; methemoglobin is reduced to its deoxy form and reacted with CO to make the carbonyl form; and glucose oxidase is reacted with glucose to make gluconic acid.
Oxygen Configurations and their Effect on Charge Transfer in YBa2Cu3OZ
Authors: Mccormack Ryan , Ceder Gerbrand , Fontaine Didier De
Published: March 2011

The relationship between oxygen structure, charge transfer (hole count), and oxygen content in the YBa2Cu3Oz superconductor is studied by combining Monte-Carlo simulation with existing electronic structure calculations. The present model proposes an expansion of the hole count in terms of oxygen configuration variables for states of an arbitrary degree of order. Calculations of hole count as a function of oxygen content suggest that oxygen ordering is, at least in part, responsible for the observed plateau structure of Tc vs. oxygen content z.
Fracture Modelling of Granular Materials
Authors: Schlangen E. , Van Mier J.G.M.
Published: March 2011

A lattice type model is used for simulating fracture processes in concrete and sandstone. Two type of lattices were adopted: a regular triangular lattice and a random lattice. With both lattices the fracture process in four point shear specimens can be simulated. The results are in good agreement with experimental observations. With the regular lattice, where disorder is implemented via a generated grain structure, the typical failure mechanism for granular materials, crack face bridging, is retrieved. With the random lattice, these details cannot be simulated, but the macroscopic crack pattern is obtained correctly with an enormous decrease in the number of elements.
Effects of Hydrogen on the Fracture Properties of Σ9 and Σ11 Tilt Boundaries in Nickel
Authors: Angelo J.E. , Gerberich W.W. , Moody N.R. , Foiles S.M.
Published: March 2011

In this study, the Embedded Atom Method is combined with Monte Carlo and molecular dynamics simulations to study the fracture properties of Σ9 and Σ11 tilt boundaries in nickel. The Monte Carlo simulations are used to simulate the exposure of the bicrystal to a hydrogen environment at 300° C. These simulations establish the equilibrium distribution of hydrogen at the boundaries as a function of far-field concentration. The effect of the hydrogen on the fracture process is then studied with molecular dynamics. It will be shown that the fracture stress of the Σ9 boundary is affected over a wider range of far-field concentrations than the Σ11 boundary, although the Σ11 boundary shows that catastrophic failure occurs when the sample is charged beyond a certain far-field concentration.
Creation of Dislocations in a Shall Copper Single Crystal
Authors: Doyama Masao
Published: March 2011

Edge dislocations were created on a surface of a small copper single crystal. Very sharp yield stress was observed when a partial dislocation was created. Edge dislocations in copper were split into Heidenreich–Shockley partial dislocations connected with the stacking fault.
Dynamics of Cu Surfaces at High Temperatures
Authors: Stoltze Per
Published: March 2011

The structure and dynamics of Cu(100), Cu(110) and Cu(111) have been studied by Molecular Dynamics simulations using the potential derived from effective medium theory. The formation energy for adatoms is lower for Cu(llO) than for Cu(lO0) or Cu(lll). The relatively high concentration of defects on Cu(11O) makes this surface premelt near the bulk melting point. The surface diffusivity is high for all three surfaces at elevated temperatures, the diffusion mechanism at the disordered surfaces appears to be quite complicated.
Monte Carlo Simulations of Solute-Atom Segregation at [001] Symmetrical Twist Boundaries in the Ni-Pi System
Authors: Udler D. , Seidman D. N.
Published: March 2011

Atomistic Monte Carlo simulations utilizing many-body embedded atom method (EAM) potentials have been carried out for a series of symmetrical [001] twist boundaries in Pt-3 at.% Ni and Ni-3 at.% Pt alloy bicrystals at 850 K throughout the misorientation range 0° to 45°. The results demonstrate enhancement of the solute-atom concentration at twist boundaries for both alloys; the interfacial Gibbsian excess is a factor of two greater on the Ni-rich side of the phase diagram. The spatial distributions of solute atoms in the vicinity of the interfaces are found to be markedly different on the two sides of the Ni-Pt phase diagram. For low-angle boundaries on the Pt-rich side solute atoms tend to segregate in hourglass-like regions along the cores of the primary grain boundary screw dislocations, while in the case of Ni-3 at.% Pt they occupy bipyramidal regions centered on the cells of the dislocation grid. The former behavior explains the oscillatory solute-atom concentration profiles nomnal to the plane of an intetface.
Combining Molecular Dynamics and Monte Carlo Simulations to Model Chemical Vapor Deposition: Application to Diamond
Authors: Brenner D.W. , Robertson D.H. , Carty R.J. , Srivastava D. , Garrison B.J.
Published: March 2011

Gas-surface reactions of the type that contribute to growth during the chemical vapor deposition (CVD) of diamond films are generally completed in picoseconds, well within timescales accessible by molecular dynamics (MD) simulations. For low-pressure deposition, however, the time between collisions for a surface site can be microseconds, which makes direct modeling of CVD crystal growth impossible using standard MD methods. To effectively bridge this discrepancy in timescales, the gas-surface reactions can be modeled using MD trajectories, and then this data can be used to define probabilities in a Monte Carlo algorithm where each step represents a gas-surface collision. We illustrate this approach using the reaction of atomic hydrogen with a diamond (111) surface as an example, where we use abstraction and sticking probabilities generated using classical trajectories in a simple Monte Carlo algorithm to determine the number of open sites as a function of temperature. We also include models for the thermal desorption of hydrogen that predict that growth temperatures are not restricted by the thermal loss of chemisorbed hydrogen.
Monte Carlo Simulations on SIMD Computer Architectures
Authors: Burmester C. P. , Wille L. T. , Gronsky R.
Published: March 2011

Algorithmic considerations regarding the implementation of various materials science applications of the Monte Carlo technique to single instruction multiple data (SIMD) computer architectures are presented. In particular, implementation of the Ising model with nearest, next nearest. and long range screened Coulomb interactions on the SIMD architecture MasPar MP-1 (DEC mpp-12000) series of massively parallel computers is demonstrated. Methods of code development which optimize processor array use and minimize inter-processor communication are presented including lattice partitioning and the use of processor array spanning tree structures for data reduction. Both geometric and algorithmic parallel approaches are utilized. Benchmarks in terms of Monte Carlo updates per second for the MasPar architecture are presented and compared to values reported in the literature from comparable studies on other architectures.
Finite-Temperature Properties From a Single Zero-Temperature Energy Minimization
Authors: Rickman J. M. , Najafabadi R. , Srolovitz D. J.
Published: March 2011

A method for calculating the thermodynamic properties of both perfect crystals and defects from a single zero-temperature energy minimization is described. The validity of the method is demonstrated by determining the free energy and the lattice parameter of a perfect Au crystal, as modelled by an embedded-atom method (EAM) potential. In addition, we determine the temperature dependence of the vacancy formation energy and the excess free energy of a (100) free surface.
Molecular Origins of the Unique Conformational Properties of the Polysilanes: A Molecular Dynamics Study of Poly(Di-N-Hexylsilane)
Authors: Welsh William J. , Tersigni Samuel H. , Lin Wangkan
Published: March 2011

The conformational dynamics of a model compound for poly(di-n-hexylsilane) (PDHS) has been explored using the new molecular dynamics program MM3-MD. MM3-MD trajectories at variable temperatures reveal two abrupt conformational transitions, one near -182°C and another near -175°C, associated with two energy barriers on the potential-energy surface. The first transition near -182°C allows shifts in the backbone torsion angle from that defined by the global energy minimum designated off-trans to that corresponding to a statistical collection of torsion angles within the range trans ±30°. The second transition near -175°C allows the backbone torsion angle to explore the remainder of its torsional space. The sidechain dynamics follows a similar pattern. We suggest that the abrupt transition calculated here at -182°C for “gas.phase” PDHS corresponds to that observed for PDHS at -28°C in solution and at 42°C in the solid state.
Scanning Simulation Procedures for Calculation of the Entropy, the Pressure, and the Chemical Potential of Many-Chain Systems
Authors: Meirovitch Hagai
Published: March 2011

Using two simulation techniques, the scanning and the hypothetical scanning methods we study a system of many chains with excluded volume contained in a “box” on a square lattice. With these methods the value of the sampling probability P of a configuration is known and therefore the entropy S can be calculated (S ∼ In P) without the need to resort to thermodynamic integration. Thus, the pressure and the chemical potential can be obtained with high accuracy directly from the entropy using standard thermodynamic relations. Our simulation results are compared to the approximate theories of Flory, Huggins, Miller and Guggenheim and to the recent improved theories of Freed and coworkers.
Formation of Buried Ternary Silicide Layers in Silicon by Ion Beam Synthesis (IBS)
Authors: Panknin D. , Wieser E. , Skorupa W. , Querner G. , Vöhse H. , Albrecht J.
Published: March 2011

A buried (Fe1−xCox) Si2 (x < 0.2) layer was formed by two step high dose implantation of Fe and Co into {100}-Si with as well as without intermediate annealing between the implantations. The suicide layer remains semiconducting if the temperature of the post implantation annealing is lower than 850°C. The depth distribution of Fe and Co, the phase composition as well as the microstructure of the layer system was investigated.