bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Chemistry for Surface Engineering in Mems
Authors: Zhu X.-Y. , Jun Y. , Boiadjiev V. , Major R. , Kim H. I. , Houston J. E.
Published: April 2011

It is well recognized that controlling surface forces is one of the key issues in the design, fabrication, and operation of microelectromechanical systems (MEMS). In this report we present a novel strategy for the efficient assembly of organic monolayers onto silicon surfaces to control surface energy. This is achieved by the reaction between an alcohol functional group and a chlorinated Si surface. The resulting molecular monolayers are thermally and chemically stable. Surface adhesion energy on silicon is reduced by a factor of 40 by the monolayer coating and friction coefficient of the coated surface is only 0.013. The coatings are successfully demonstrated in adhesion reduction in a model MEMS structure: cantilever beam array (CBA). Polycrystalline beams with length up to 1.5 mm can be released.
Structural and Micromechanical Assessment of Electrochemically Grown Metal Layers for Si Magnetic Microactuators
Authors: Martinez Susanna , Yaakoubi Nourdin , Serre Christophe , Pérez-Rodríguez Alejandro , Morante Joan Ramon , Díez-Pérez Ismael , Gorostiza Pau , Esteve Jaume
Published: April 2011

The electrochemical deposition of Cu metal layers for Si based microactuator devices is investigated as a function of the substrate structure. For the direct deposition of Cu onto Si, a two step process involving pre-deposition of an intermediate layer under alkaline conditions has been developed. This has allowed the optimization of the process in terms of film adherence and thickness. On the other hand, for processes involving the use of dielectric sacrificial layers, the electrochemical growth of the Cu film requires a metallic seed layer. In this case, the growth of Cu onto Au coated surfaces has been investigated, and the process has been applied to the development of test microactuator structures based on the integration of Cu coils onto Si micromachined devices. The fabrication of these devices demonstrates the full compatibility of Electrochemical processes with Si standard micromachining technologies.
Temperature and Doping Dependency of Piezoresistivity in p-type Silicon
Authors: Lund Eivind , Finstad Terje G.
Published: April 2011

We have performed new measurements of the temperature and doping dependency of the piezoresistive effect in p-type silicon. Piezoresistivity is one of the most common sensing principles of micro-electro-mechanical-systems (MEMS). Our measurements are performed in a specially designed setup based on the well-known 4 point bending technique. The samples are beams of full wafer thickness. To minimize leakage currents and to obtain uniform doping profiles, we have used SIMOX (Separation by IMplantation of OXygen) substrates with resistors defined in an epitaxial layer. Spreading resistance measurements show that the doping profiles are uniform with depth, while measurements of leakage current versus temperature indicate low leakage current. In this paper we present results for the doping concentration range from 1×1017 – 1×1020 cm−3 and the temperature range from –30 to 150 degrees Celsius. The results show a doping dependency of piezoresistivity well described by the current models. The measurements of the temperature dependency of the coefficients of piezoresistivity are compared to a linear model with a negative temperature coefficient whose absolute value decreases with increasing doping.
Optical Manipulation of Inorganic and Organic Objects in Soft Microfluidic Devices
Authors: Ozkan Cengiz S. , Ata Erhan , Ozkan Mihrimah , Esener Sadik C.
Published: April 2011

We describe a technique for trapping and manipulation of inorganic and organic objects in microfluidic channels, based on photonic momentum transfer using an optical tweezers arrangement. Microfluidic devices have been fabricated by polydimethylsiloxane (PDMS) elastomer molding of patterns lithographically defined on a thick negative photoresist. Polystyrene microspheres dispersed in water were transferred into the fluidic channels using a syringe pump. Microspheres and live biological cells are trapped and redirected by optical manipulation within the fluidic channels. Optical trapping and patterning will have applications in creation of active cellular arrays for cell biology research, tissue engineering, cell sorting and drug discovery.
Simple and Low Cost Patterning Process for Sputtered Pb(Zr,Ti)O3 Thin Films and Electrodes for Membrane-Based Microsystems Applications
Authors: Millon Cyril , Malhaire Christophe , Defaÿ Emmanuel , Barbier Daniel
Published: April 2011

Micromachined silicon membranes actuated by a piezoelectric thin film are of great interest for microfluidic or ultrasonic applications. In this paper, we present a simple and low cost patterning process for sputtered Ti and Pt electrodes and Pb(Zr,Ti)O3 thin films using lift-off and a wet HCl etching methods respectively. We have showed by finite element analysis the incentive to pattern electrodes in order to get higher actuation performances. Moreover, in order to reduce the stress on the diaphragm, the PZT film has been also patterned. We propose an optimized flow chart taking into account the different material properties in the multi-layer stack constituting the actuator and the need of a PZT crystallization annealing. To show the influence of the actuator layout, finite element models of a 20μm thick, 3 × 3 mm2 silicon membrane with variable electrode design, actuated by a 1μm PZT (10 V bias) thin film have been developed. We found a maximum deflection for a 1.7 mm side length square electrode located at the membrane center. Sputtering was achieved on a non-heated silicon substrate, in pure Argon, using a stoichiometric PZT target. The metallic electrodes have been structured by standard lift- off technique. Different concentrations of HCl [4 % - 35 %] with temperature up to 90°C have been tested for PZT patterning. Well defined PZT microstructures were better achieved by wet etching of unannealed PZT film on SiO2 or Pt (HCl 35%, room temperature). The etching rate was 40 nm.s−1. The presence of the perovskyte phase in the PZT films after a 700°C, 30 s RTA in air, has been checked by X-ray measurements. Finally, the silicon membranes have been realized by anisotropic chemical etching in an aqueous KOH (40 %, 60°C) solution. Membrane deflection under low bias have been successfully tested.
Measurement of Electrical Charge During Nanoindentation of Ferroelectric Thin Films
Authors: Algueró M. , Bushby A.J. , Reece M.J.
Published: April 2011

Electrical charge transients have been measured during the nanoindentation of lanthanum modified lead titanate ferroelectric thin films. Using the spherical indenter as the top electrode, the films were locally poled. The films were then reindented at the exact same positions. The origin of the charge released is discussed in terms of piezoelectricity and depolarisation. The depolarisation must have been produced by a stress induced ferroelastic domain reorientation. Current intensity transients recorded during indentation showed a distinct maximum. This maximum corresponded to a force at which the depolarisation rate was a maximum. This provides the basis to define a coercive indentation force, and then a coercive indentation stress.
Finite Element Analysis of the Precracked Line Scratch Test
Authors: Volinsky A.A. , Mercado L. , Sarihan V. , Gerberich W.W.
Published: April 2011

In MEMS packages and silicon devices, the adhesion of interconnects to the substrate is a critical reliability issue. A Precracked Line Scratch Test (PLST) is among one of the available tests to measure the thin line adhesion. In the test, an initial crack is introduced at the interface between the thin line and the substrate. The line is then loaded from the precracked end. The load is recorded continuously while the crack propagates before and after the line buckles. This precracked line scratch test has been applied earlier to tungsten thin lines on silicon wafers [1]. A macroscopic version of the test was also performed to evaluate the analytical model [2]. In the macroscopic tests, polycarbonate lines were bonded to steel substrates with cyanoacrylate.

In this paper, finite element analysis is performed for the Precracked Line Scratch Test before line buckling. The energy release rates and phase angles are calculated based on the corresponding load and crack length. The results are then compared to the closed-form solution. Macroscopic experimental model along with the finite element solution has provided a way to derive the interface fracture toughness as a function of the crack length based on the load and crack length history. With the analysis in place, the precracked line scratch test can be used conveniently to study the adhesion of interconnects to passivation layers, MEMS devices and packages on different scales.
High Temperature, High-Pressure Fluid Connections for Power Micro-Systems
Authors: Harrison Todd S. , London Adam P. , Spearing S. Mark
Published: April 2011

High power density micro-systems offer the potential to revolutionize technologies for portable electrical power generation, propulsion and flow control. Devices are being designed and fabricated which include micro-gas turbine engines, micro-rocket engines, micro-motor- compressors, micro-pumps and micro-hydraulic transducers. Common to all of this family of devices is the need to create packages that service the devices, and interface them with the macro-scale environment. Fluid interconnections are a particularly demanding packaging element for this class of devices. In order to achieve high power densities, these devices are required to operate at high pressures and, in some cases, high temperatures. This paper describes the design, analysis, fabrication and testing of high-pressure, high temperature fluid connections for the micro-engine and micro-rocket applications. A glass bonding technology has been developed to allow the creation of multiple fluidic connections consisting of Ni/Fe alloy tubes to silicon devices. Key strategies to achieve high strength connections are: to minimize the mismatch in coefficients of thermal expansion between the components, to eliminate voids from the glass and to promote adequate wetting of the glass to both the tubes and the silicon. Mechanical test results are presented which correlate the strength and statistical reliability of such bonds to the processing conditions, choice of glass and surface preparation prior to bonding. Successful examples of packaged micro-engine and micro-rocket devices are presented.
The Characterization of TiNi Shape-Memory Actuated Microvalves
Authors: Lai B.-K. , Hahm G. , You L. , Shih C.-L. , Kahn H. , Phillips S. M. , Heuer A. H.
Published: April 2011

Co-sputtering has been used to fabricate equiatomic thin films of TiNi, a shape memory alloy, which form the basis of microactuators with many applications in MEMS. The stress evolution of TiNi films will be described. The performance of the TiNi actuators has been characterized, with regards to actuation force, recoverable strain, time response, and fatigue resistance. The performance of microvalves using these actuators will also be presented.
Microbridge Testing of Silicon Oxide/Silicon Nitride Bilayer Films
Authors: Qian C.-F. , Su Y.-J. , Zhao M.-H. , Zhang T.-Y.
Published: April 2011

The present work further develops the microbridge testing method to characterize mechanical properties of bilayer thin films. A closed-form formula for deflection versus load under small deflection is derived with consideration of the substrate deformation and residual stress in each layer. The analysis shows that the solution for bending a bilayer beam is equivalent to that for bending a single-layer beam with an equivalent bending stiffness, an equivalent residual force and a residual moment. One can estimate the Young's modulus and residual stress in a layer if the corresponding values in the other layer are known. The analytic results are confirmed by finite element calculations. The microbridge tests are conducted on low-temperature-silicon oxide (LTO)/silicon nitride bilayer films as well as on silicon nitride single-layer films. All microbridge specimens are prepared by the microfabricating technique. The tests on the single-layer films provide the material properties of the silicon nitride films. Then, applying the proposed method for bilayer films under small deflection yields the Young's modulus of 37 GPa and the residual stress of -148 MPa for LTO films.
Dissipation and anisotropy in ultrathin YBa2Cu3O7/PrBa2Cu3O7 superlattices
Authors: Villegas J.E. , Gonzalez E.M. , Vicent J.L , Sefrioui Z. , Varela M. , Santamaría J.
Published: April 2011

Ultrathin superlattices of 123 superconducting cuprates have been fabricated by high oxygen pressure sputtering technique. The superlattices show high quality, with negligible step disorder, roughness and interdiffusion. The insulating PrBa2Cu3O7 (PBCO) layer thickness has been kept constant at 5 unit cells (u.c.) and the superconducting YBa2Cu3O7 (YBCO) layer thickness has been changed from 8 u.c. to 1 u.c. In these uncoupled multilayers the critical temperature (Tc0) changes from 44 (1 u.c. YBCO) to 80 K (8 u.c. YBCO). In the vortex liquid regime, at constant temperature, the angular dependence of the magnetoresistance scales down with the applied magnetic field values in all the temperature range. This behavior allows us to study the anisotropy and dimensionality behavior of the mixed state in ultrathin superlattices. A dimensional crossover 3D-2D is found in the anisotropy with the 1 u.c. YBCO superlattices following a pure 2D behavior.
Micron-Thick Sr-Based (Hg,Pb)-1223 Films with jc(77K) of above 106 A/cm2
Authors: Klimonsky S.O. , Samoilenkov S.V. , Gorbenko O.Yu. , Kiryakov N.P. , Emelianov D.A. , Liashenko A.V. , Lee S.R. , Kaul A.R. , Andrianov D.G.
Published: April 2011

For the first time the (001)-oriented Sr-based (Hg,Pb)-1223 films have been synthesized using the two-step procedure. Hg-free precursor films with the thickness of 1 μm have been deposited by MOCVD or PLD and then the films were annealed in sealed quartz ampoules together with synthesised (Hg,Pb)-1223 ceramics or a pressed precursor mixture of the same cation composition. No post-annealing in oxygen was used for these films. The phase composition of the PLD-films depended crucially on the deposition temperature of the precursor films. The best MOCVD films contained predominantly (Hg,Pb)-1223 and small amounts of non-superconducting phases according to XRD. The Tc=118 K and jc(77K,0.01T) = 2.5×106 A/cm2were measured for the MOCVD-samples.
Metal Organic Deposition of REBa2Cu3O7-y Films from Metal Trifluoroacetate Precursors
Authors: Honjo Tetsuji , Fuji Hiroshi , Huang Daxiang , Nakamura Yuichi , Izumi Teruo , Shiohara Yuh
Published: April 2011

Metal organic deposition (MOD) process using metal trifluoroacetate (TFA) precursors was applied to the Nd1+XBa2−XCu3Oy (Nd123) and the Tc dependence on experimental conditions such as the oxygen partial pressure (PO2) and the substrate temperature (Ts) for annealing was investigated. Thin films grown on SrTiO3 substrates at Ts = 800°C under PO2 = 300 ppm showed a Tc value of 89 K. However, from the results of TEM-EDS measurements, the substitution values of x in the Nd123 films increased from the substrate toward the surface in the film. These experimental results could be thermodynamically explained by the following model. The basic idea of the model is that the Ba potential in the precursor decreases by coarsening of BaF2 particles during the annealing for the Nd123 crystal growth. This model predicts that the small substitution value can be obtained with a higher growth rate of the Nd123 phase under low PO2.
Magnetic Field Dependence of Critical Current Density of TFA-MOD Processed YBCO Coated Conductors
Authors: Yamada Yutaka , Kim SeokBeom , Araki Takeshi , Yuasa Toyotaka , Takahashi Yasuo , Kurosaki Haruhiko , Shiohara Yuh , Hirabayashi Izumi , Iijima Yasuhiro , Takeda Kaoru
Published: April 2011

YBCO films on LaAlO3and IBAD (YSZ/Hastelloy) substrate were made by TFA-MOD (metalorganic deposition using trifluoroacetate) process. Improved coating solution resulted in high Jc at 77.3K and 0T of 7 MA/cm2 and 1.7 MA/cm2 for LaAlO3 and IBAD substrates, respectively. The magnetic field dependence of Jc at 77.3K also showed superior property: 105 A/cm2 at 4T (B//c-axis) for the LaAlO3substrate and at 3T (B//c-axis)) for IBAD substrate. Furthermore, the difference in Jc between single crystal LaAlO3and IBAD was small up to 3T. The present results imply that TFA-MOD process is promising for the practical YBCO coated conductor process.
Effect of YBCO film characteristics on RF properties of MSL resonators with these films
Authors: Yamanaka Kazunori , Akasegawa Akihiko , Nakanishi Teru
Published: April 2011

The effect of YBCO film characteristics on the RF properties of microstrip-line (MSL) resonators using two surface resistance Rs value types of films was investigated in terms of weak links. The films were characterized in both cystallinity and microstructure. The RF properties of the resonators were measured at frequencies of about 2 GHz. It was understood that the film samples with higher Rs at 70 K, which exhibited strong c-axis orientation, both the 90 and 45- degree angle grains in plane of the films, Y211 segregation, and porous structures show large influence on RF magnetic field dependence of normalized resonant frequency-shift Δfc/fc, compared with the lower Rs type. On the other hand, the films with lower Rs at 70 K had much stronger c-axis orientation, the 90-degree angle grains, and dense structures. Consequently, it was considered that the lower Rs type films possessed fewer weak-links compared with the higher Rs type films, suggesting that the misorientation in the higher Rs films result in weak-links.
Magneto-optical study of grain boundaries, interfaces and grain boundary networks in YBaCuO
Authors: Jooss Ch. , Kautschor L.-O. , Delamare M.P. , Bringmann B. , Guth K. , Born V. , Sievers S. , Walter H. , Dzick J. , Holzmann J. , Freyhardt H. C. , de Boer B. , Holzapfel B. , Sandiumenge F.
Published: April 2011

Using quantitative magneto-optics and an inversion scheme of Biot-Savart's law the local current carrying capability of various types of grain boundaries (GB's) and interfaces in YBaCuO thin films and bulk material was investigated. In all GB's and interfaces a spatial variation of the local critical current density jc was observed which, however, has different reasons, such as microstructural inhomogeneities, magnetic field dependence of jc and size effects in extended GB's and networks of low angle grain boundaries (LAGB's).
Jc Enhancement in Melt Textured YBCO with Different 211 Content by Fast Neutron Irradiation
Authors: Köhler Anke , Plain Jérôme , Seeböck Wolfgang , Puig Teresa , Carrillo Anna E. , Weber Harald W. , Obradors Xavier
Published: April 2011

Melt textured YBCO samples with and without 211 inclusions were irradiated by fast neutrons. The enhancement of the critical current density was studied as a function of the 211 content by means of SQUID magnetometry at temperatures from 5 to 77 K and magnetic fields from 0 to 8 T. The highest enhancement factor, found at 77 K and 1.5 T for a 211-free sample, is 27. The enhancement is less effective for samples with 211 inclusions. However, the critical current densities after irradiation show a similar temperature and field dependence in all samples. The role of the initial microstructure on the radiation effects is discussed.
Inter-chain Interaction of Metallic 1D-chain in PrBa2Cu4O8
Authors: Horii Shigeru , Takagi H. , Ikuta H. , Mizutani U. , Yamada Y. , Hirabayashi I. , Shimoyama J. , Kishio K.
Published: April 2011

The a- and b-axis resistivities and the a-axis magnetoresistivities applying magnetic field (B) along all three crystallographic axes in non-superconductive PrBa2Cu4O8 single crystals have been measured using four-probe method. Resistivitiy along the b-axis (parallel to double-chains) showed a highly conductive behavior, of which the origin is attributed to the double-chains because of a large anisotropic conduction between a- and b-axis directions. However, a metallic behavior along the a-axis was also observed in temperature region below 130 K, which could be understood in terms of presence of finite and coherent inter-chain interaction along the a-axis direction. This conclusion is derived from good agreement with values of mean-free path length in the double chain, lchain estimated from both the ρb-T curve and the a-axis MR applying B//c using quasi-one-dimensional (quasi-1D) band model.
High-Temperature Superconducting Tapes Deposited by the Non-Vacuum, Low-Cost Combustion Chemical Vapor Deposition Technique
Authors: White Marvis K. , Campbell Ian H. , King Adam C. , Krebs Steve L. , Mattox Dave S. , Polley Todd A. , Shoup Shara S. , Xue Yibin
Published: April 2011

The enormous technological potential of high-temperature superconductors (HTS) was realized immediately following their discovery in 1986, yet these materials largely remain laboratory curiosities as scientists struggle to scale from coupons to long lengths of practical coated conductor. Although both vacuum and non-vacuum processes are being investigated for commercial production, low-throughput vacuum techniques were the first to succeed in producing the buffer and superconducting layers necessary for superconducting tape with high critical currents. However, vacuum processes are not only expensive but impractical when addressing the needs for rapid production of kilometer lengths of wire. The innovative Combustion Chemical Vapor Deposition (CCVD) method used with the Rolling Assisted Biaxially Textured Substrates (RABiTS™) technology has shown significant promise in fabricating the multi-layer structures necessary for successful HTS tape while overcoming many of the shortcomings of traditional vacuum techniques. The key advantage of the CCVD technology is its ability to deposit high quality thin films in the open atmosphere using inexpensive precursor chemicals in solution. As a result, continuous, production-line manufacturing is possible with significantly reduced capital requirements and operating costs when compared to competing vacuum-based technologies. The current status of development for production of long lengths of high-temperature superconductors using CCVD will be discussed.
Some Organic-Inorganic Composites, Illustrative Simulations on Elastomer Reinforcement, and an Overview of Symposium Contributions
Authors: Mark J. E.
Published: April 2011

This review first describes organic-inorganic composites which have been prepared using techniques similar to those employed in the new sol-gel approach to ceramics. Organometallics such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyamides) that typically contain hydroxyl groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming novel organic-inorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic-type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer-modified ceramic. Under some conditions,bicontinuous systems are obtained.

The second part addresses one of the major unsolved problems in the area of rubberlike elasticity, specifically a molecular understanding of the mechanisms by which the mechanical properties of elastomers are improved by the incorporation of particulate fillers such as carbon black or silica. Theoretical work on the reinforcement thus obtained is illustrated by some Monte Carlo calculations on one aspect of the problem, namely excluded volume effects of the filler particles on the network chain configurations. The resulting end-to-end distributions are then used in standard molecular models to generate stress-strain isotherms, which document the nature of the reinforcement obtained.

The final part provides an overview of the specific papers presented at this symposium, and attempts to place them into the broad general context of “Filled and Nanocomposite Polymer Materials”.
Nanostructures from POSS-Grafted Block Copolymer Precursors
Authors: Chun Seung B. , Mather Patrick T.
Published: April 2011

A new method to prepare novel nanocomposites has been studied in which a polyhedral oligomeric silsesquioxane (POSS) monomer is grafted to a polyisoprene-block-polystyrene copolymer to yield an inorganic-organic hybrid copolymer (POSS-g-PI-block-PS). PS-block-PI copolymers (SI) were synthesized via anionic polymerization in tetrahydrofuran (THF) as solvent. The polyisoprene block of the SI diblock copolymers in this study featured a very high vinyl group fraction (65 mole % of 3,4- addition and 35 mole % of 1,2-addition) available to react with hydride-substituted POSS (isobutyldimethyl silane-POSS) to form a grafted block copolymer. Due to the immiscibility between POSS-grafted PI block and PS block, the grafted block copolymer developed a microdomain structure. The volume fraction of PS block in the grafted block copolymer was varied in the range of 0.45 to 0.37 in order to yield cylindrical PS microdomains in the matrix of POSS-grafted PI. After exposure to an oxygen plasma, it is expected that preferential erosion of the grafted block copolymer will occur for the organic potion (PS microdomains) thus leaving a well-defined nanoporous surface structure for nonlithographic functionalization of coated substrates.
“Green” nano-composite materials - new possibilities for bioplastics1
Authors: Fischer Sabine , de Vlieger Jan , Kock Theo , Batenburg Lawrence , Fischer Hartmut
Published: April 2011

Research in the area of biological renewable materials has shown that the main building blocks of life – carbohydrates, fats, proteins, and their derivatives - could substitute products from traditional nonrenewable sources. However its realization will need significant and continuous improvement of those materials. Problems of applications of bioplastics arise not only from the (price) competition with the highly developed synthetic polymers but also from their, up to now not sufficient property levels. Possibilities to decrease the hydrophilicity and to increase the values of mechanical properties so far are: i) application of hydrophobic coating(s); ii) blending with different, biodegradable synthetic polymers (polyesters) and iii) new ways of reactive extrusion of natural. A new possibility in this direction is seen in the creation of composite materials of thermoplastic organic biopolymer and nanoscopic inorganic particles incorporated on a molecular scale.

This paper will show the results of the first experiments to get nano-scale starch/clay composites. The starch will be fully gelatinized and the modified clay can be dispersed homogeneously on a truly nanoscale. Therefore all requirements of a significant increase in mechanics and a decrease in permeability of this composite material are present.
Influence of Filler Particles and Filler Clusters on Phase Separation in Binary Polymer Blends
Authors: Jiang Y. , Saxena A. , Lookman T. , Douglas J. F.
Published: April 2011

Motivated by recent experiments on filled polymer thin films, we study the effect of the presence of filler particles on phase separating mixtures. Using a generalized Cahn-Hillard-cook model, we show that the preferential wetting of one phase on the filler surface generates transient composition waves in the phase separating blends. The interference of the composition waves from different particles can stabilize the transient patterns, leading to desirable control of the morphology.
The Synthesis of Liquid Crystalline Polymer on Gold Nanoparticles
Authors: Fu Qinghong , Seery Thomas A. P.
Published: April 2011

Gold nanoparticles with thiol stabilizing layers were prepared with various fractions of end-functional thiols. Alcohol end-groups were further elaborated to norbornyl moieties so that a ruthenium alkylidene initiator could be tethered to the nanoparticle surfaces. In two different nanoparticle formulations the functional thiols possessed hydrocarbon chains that held the metal centers either near to or far from the surface of the thiol stabilizing layer. The tethered organometallic complexes were used to initiate polymerization from the nanoparticle surfaces. Liquid crystalline polymer was grown from nanoparticles where the metal center was tethered far from the surface but polymerization could not be initiated when the metal centers were held close to the surface. We hypothesize that steric hindrance is controlled by the length of the tethering thiol. Polarized optical microscopy showed that the polymer coated gold nanoparticles could still form a nematic mesophase at elevated temperature although the orientation of mesogens is restricted by crowding at the nanoparticle surface. Samples of unbound polymer were also prepared and exhibited similar transition behavior.
X-ray diffraction study of crystallite size-distribution and strain in carbon blacks
Authors: Ungár T. , Gubicza J. , Ribárik G. , Zerda T. W.
Published: April 2011

The crystallite size and size-distribution in carbon blacks in the presence of strain are determined by recently developed procedure of X-ray diffraction peak profile analysis. The Fourier coefficients of the measured physical profiles are fitted by Fourier coefficients of well established ab initio functions of size and strain peak profiles. Strain anisotropy is accounted for by expressing the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modelled by ellipsoids incorporated into the size profile function. To make the fitting procedure faster, the Fourier transform of the size profile is given as an analitical function. The method is applied to carbon blacks treated at different preassures and temperatures. The microstructure is characterised in terms of crystallite size distribution, dislocation density, and crystallite shape anisotropy.
Carbon Coated Silica For Elastomer Reinforcement
Authors: Kohls D. , Beaucage G. , Pratsinis S.E. , Kammler H. , Skillas G.
Published: April 2011

Carbon coated silica made by flame synthesis was investigated for reinforcement of styrene-butadiene (SBR) rubber. These composite silica/carbon fillers were examined through small angle x-ray scattering (SAXS), TEM, and AFM showing that these fillers have a rough fractal surface and have fractal aggregate structures. The carbon coated silica fillers were compounded with elastomers and their effect on reinforcement was measured using dynamic mechanical analysis and tensile testing. These fillers were also compared to commercial fumed silica, carbon black, and carbon black/silica composite fillers.
Bioactivity Responses of Different Uhmwpe Particles from In-Vivo and In-Vitro Tests
Authors: Park YoungSoo , Yang ShangYou , Wooley Paul H. , Merritt Katharine , Hsu Stephen , McNallan Michael J.
Published: April 2011

This paper describes the results of bioactivity responses to different ultra high molecular weight polyethylene (UHMWPE) particles. Particles were produced by a wear tester using two different textures of steel counters, one with cross-hatched and the other with uni-hatched grooves. These two textured surfaces produced two distinct populations of wear particles. One is larger and more elongated (fibril shapes) than the other. The mean sizes and aspect ratios of the particles are in the ranges of 5 μm to 25 μm and about 1.5 to 3, respectively. These two distinct UHMWPE particles were examined through in-vitro and in-vivo tests. Macrophages RAW 264.7 and the murine air-pouch model of inflammation were employed to characterize the effect of the particle size and shape. Preliminary in-vivo tests results showed that more elongated and larger particles enhanced bio-reactions.
Crystal Morphology Control by Melt Phase Separation in Biodegradable Polymer Blends
Authors: Akpalu Y. A. , Meredith J. C. , Amis E. J.
Published: April 2011

The effect of lower critical solution temperature (LCST) phase separation on the crystallization of poly(ε-caprolactone) PCL in PCL/poly(D,L-lactide) (PDLA) blends is studied by simultaneous small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS). Phase separation is induced by controlled temperature jumps into the LCST (two-phase) region, which is above the melting temperature (60 °C) of PCL and the glass transition temperature (50 °C) of PDLA. We have followed the nanoscale structural changes (< 100 nm) during subsequent crystallization at 45 °C of critical (0.36 PCL) and off-critical (0.50 PCL) blend compositions in both one-phase and two-phase melts. The spherulite morphology (1-100 μm) is examined with optical microscopy. When crystallization follows LCST phase separation, the shape, size and distribution of the spherulites depends on the extent of melt phase separation. In our x-ray measurements, the WAXS crystallinity of PCL is less than 40 % for the temperature range of interest. We perform a correlation function and intensity model analysis of our SAXS data to obtain morphological variables that characterize the intraspherulitic morphology. These morphological variables are relatively constant during crystallization and are also independent of melt phase separation. On the other hand, the ultimate crystallinity and the crystallization rate depend on the extent of melt phase separation.
Adhesion of Pressure Sensitive Adhesives with Applications in Transdermal Drug Delivery
Authors: Taub Marc B. , Dauskardt Reinhold H.
Published: April 2011

The development and implementation of successful transdermal devices for drug delivery requires an understanding of the adhesion occurring between the device and the soft dermal layer. This study utilizes a mechanics approach to quantify the adhesive properties of representative pressure sensitive adhesives (PSAs) used as the adhesive layer in these systems. Debonding of PSAs is accompanied by cavitation in the PSA and the formation of an extensive cohesive zone behind the debond tip. The presence of such large-scale bridging provides significant energy dissipation and increased resistance to delamination. The strain energy release rate (G) during debonding of a cantilever-beam sample, containing at its midline a thin layer of PSA, was utilized to quantify the adhesion of the PSA. The analysis accounts for both the work of adhesion as well as the viscoelastic constitutive behavior of the soft adhesive layer. Effects of strain rate, physiological environment, and permeation-enhancement additions are considered. The resistance of human stratum corneum to debonding between corneocyte layers is also presented, as knowledge of this parameter is essential for developing techniques to test the fracture resistance of the PSA-stratum corneum interface present in the clinical use of these transdermal devices.
Effect of Interface and Crystallinity on the Ferroelectric Properties of Poly(Vinylidene Fluoride-Trifluoroethylene) Copolymer Thin Films
Authors: Xia Feng , Xu H.S. , Razavi Babak , Zhang Q. M.
Published: April 2011

Ferroelectric polymer thin films are attractive for a wide range of applications such as MEMS, IR sensors, and memory devices. We present the results of a recent investigation on the thickness dependence of the ferroelectric properties of poly(vinylidene fluoridetrifluoroethylene) copolymer spin cast films on electroded Si substrate. We show that as the film thickness is reduced, there exist two thickness regions. For films at thickness above 100 nm, the thickness dependence of the ferroelectric properties can be attributed to the interface effect. However, for thinner films, there is a large change in the ferroelectric properties such as the polarization level, the coercive field, and polarization switching speed, which is related to the large drop of the crystallinity in the ultrathin film region (below 100 nm). The results from Xray, dielectric measurement, and AFM all indicate that there is a threshold thickness at about 100 nm below which the crystallinity in the film reduces abruptly.
Statistical Method to Optimize the Efficiency of Multi-Layer Polymer LEDs
Authors: Cecchi Michele , Braun David , Smith Heather , Vanasupa Linda
Published: April 2011

Research and development of displays and image sensors based on semiconducting polymers require design of new polymer materials and evaluation of film properties. Optimizing device performance using a one-factor-at-a-time (OFAT) requires screening the effect of several process parameters, running numerous samples, and may consume more scarce new material than desired. This paper investigates the effects of Indium-tin oxide (ITO), alkoxy-poly(pphenylene vinylene) (OC1C10-PPV) and poly(3,4-ethylene dioxythiophene) (PEDOT) layer preparation on polymer LED brightness and power efficiency by performing and analyzing a two-cubed full-factorial design experiment with 3 replicated center points. Full-factorial design evaluates all main factors and all interactions. Design of experiments (DOE) showed that correct selection of ITO anneal temperature can significantly improve brightness. Atomic Force Microscopy (AFM) measurements affirm that the increased brightness correlates with a reduction in ITO average surface roughness.
Stabilization of Optical Molecules Using Dendritic Boxes against Singlet Oxygen in Photobleaching
Authors: Otomo Sonoko , Otomo Akira , Mashiko Shinro
Published: April 2011

The stabilizing effect of dendritic boxes (DBoxes) as a means to protect against photo- degradation of encapsulated dye molecules was experimentally investigated. We focused on photoinduced oxidation and studied the ability of DBoxes to protect dyes inside them from reactive singlet oxygen. Rubrene was captured in a DBox, and then the box was closed at the surface by other stable molecules. A singlet oxygen generator was added to a Rubrene solution to exaggerate photo-oxidation in the complicated total-photodegradation process, and then the solution was exposed to a laser beam to generate singlet oxygen. Bleaching of the encapsulated Rubrene in a DBox was 50 times slower than that of Rubrene alone. We also compared the dependence of surface molecules of a DBox with other kinds of molecules that have different efficiencies of quenching singlet oxygen. Further improved stability was observed by attaching singlet-oxygen-quencher molecules on the DBox surface.
Lateral and Vertical Phase Separation Control of Thin-film Structures for Photovoltaics
Authors: Arias A. C. , MacKenzie J. D. , Corcoran N. , Friend R. H.
Published: April 2011

Investigations on microscopic and photovoltaic properties of polyfluorene blends are presented here. The length scale of lateral phase separation is manipulated by control of solvent evaporation conditions. Photoluminescence efficiency measurements show that charge transfer is more effective in blends phase separated on the nanometer scale. Vertically segregated structures are obtained by a combination of solution viscosity and spin coating conditions. The external quantum efficiency of photovoltaic devices fabricated with vertically segregated blend is found to be 4 times higher than that of devices made with laterally segregated blends.
High Performance Organic Field-Effect Transistors and Integrated Inverters
Authors: Ullmann A. , Ficker J. , Fix W. , Rost H. , Clemens W. , Mcculloch I. , Giles M.
Published: April 2011

Integrated plastic circuits (IPCs) will become an integral component of future low cost electronics. For low cost processes IPCs have to be made of all-polymer Transistors. We present our recent results on fabrication of Organic Field-Effect Transistors (OFETs) and integrated inverters. Top-gate transistors were fabricated using polymer semiconductors and insulators. The source-drain structures were defined by standard lithography of Au on a flexible plastic film, and on top of these electrodes, poly(3-alkylthiophene) (P3AT) as semiconductor, and poly(4-hydroxystyrene) (PHS) as insulator were homogeneously deposited by spin-coating. The gate electrodes consist of metal contacts. With this simple set-up, the transistors exhibit excellent electric performance with a high source-drain current at source - drain and gate voltages below 30V. The characteristics show very good saturation behaviour for low biases and are comparable to results published for precursor pentacene. With this setup we obtain a mobility of 0.2cm2/Vs for P3AT. Furthermore, we discuss organic integrated inverters exhibiting logic capability. All devices show shelf-lives of several months without encapsulation.
Image Sensor Arrays with Organic Photoconductors
Authors: Street R. A. , Graham J. , Popovic Z. , Hor A. , Mulato M. , Lau R. , Ho J.
Published: April 2011

Two-dimensional image sensor arrays incorporating an organic light sensor are reported, with potential application to digital cameras and x-ray imaging. The 512×512 element array has pixel size of 100 micron, and operates with active matrix addressing using amorphous silicon thin film transistors. The array design allows the use of a continuous layer of the organic sensor material without the need for pixel-level patterning. The sensor is a bilayer comprising a thin generator layer and a thicker hole transport layer. Generator materials benzimidazole perylene (BZP) and hydroxy gallium phthalocyanine (HOGaPc) have been studied, with a tetraphenyldiamine (TPD) transport layer. Both sensors give excellent imaging properties with low leakage current, good charge collection and high spatial resolution.
Luminescent Polymer Fibers for Light Amplification and Lasing
Authors: Kobayashi Takeyuki , Blau Werner J. , Tillmann Hartwig , Härhold Hans-Heinrich
Published: April 2011

We report on the fabrication of step index polymer optical fibers that use a novel conjugated polymer and fluorescent stilbenoid compounds for lasing and amplification applications in the blue-green regions. The green-emitting polymer, Thianthrene-MEH-PPV, and the blue-emitting compounds, 1,2-bis(4-diphenylaminophenyl)-ethylene and 1,4-bis(4-diphenylamino-styryl)-benzene, are designed for the blue-green region of the spectrum and have very high quantum yields and large Stokes shifts. Significant spectral narrowing and superlinear increase of output intensity are observed under photoexcitation at 355 nm, which are indicative of the occurrence of amplified spontaneous emission. By gain spectroscopy, a high gain coefficient of 36 cm−1 at 494 nm has been obtained for the 1,4-bis(4-diphenylamino-styryl)-benzene-doped fiber when it is transversely photoexcited at 12 mJ/cm2.
A Unified Model for the Space Charge Limited Currents in Organic Materials Combining Field Dependent Mobility and Poole-Frenkel Detrapping
Authors: Jain S. C. , Geens W. , Kumar V. , Kapoor A. , Mehra A. , Aernouts T. , Poortmans J. , Mertens R. , Willander M.
Published: April 2011

We have calculated J-V characteristics of an organic conducting sample (containing traps) including the Poole-Frenkel Effect (PFE). Both shallow and exponentially distributed traps are considered. We show that our approach is equivalent to combining the effect of trapping and using the field dependent mobility in one unified model. For shallow single level or shallow Gaussian traps, inclusion of PFE or using the (well-known) field dependent mobility gives the same dependence of current on voltage at a given temperature. However the value of zero field mobility µ0 comes out to be different. We have fabricated and measured the J-V curves of the ITO/MEH-OPV5/Al diodes. An extremely fast rise with voltage V is observed at small voltages, which can be interpreted either by the Schottky contact limited Shockley like current or by bulk space charge limited current with PFE. The correct mechanism can be determined by making J-V measurements at different temperatures.
Synthesis and Characterization of Low Content of Structural Defects of Aryl-Substituted Electroluminescent Poly(p-phenylenevinylene)s
Authors: Chen Zhi-Kuan , Lee Nancy Hoi Sim , Huang Wei
Published: April 2011

We report the synthesis and characterization of a novel series of aryl-substituted PPVs, which have shown excellent processability, good thermal stability, high photoluminescence quantum efficiency and low content of structural defects. The substituents of the polymers were designed with different degree of hindrance effect on the main chain. 1H NMR measurement indicates that the defect structure in the polymer main chain can be effectively depressed by introducing bulk and hindrance substituents.
Molecular Assemblies, Patterning, and Deposition of Conjugated Polymers: Ultrathin Films Prepared using the Layer-by-Layer and Precursor Polymer Electrodeposition Approach
Authors: Advincula Rigoberto , Park Mi-kyoung , Xia Chuanjun
Published: April 2011

In this paper we present a combined protocol for ultrathin film formation and assembly of Φ- conjugated polymer materials using the layer-by-layer (LbL) technique and a precursor polymer approach to electrodeposition. While much work has been done on investigating the chemistry (synthesis) and properties (physics) of these materials, little focus has been given on the multilayer and ordering issues associated with ultrathin film formation especially using novel “wet-processing” approaches. This work details our molecular assembly approaches on conjugated polymer systems for polyfluorene and polythiophene derivatives. This was demonstrated in the following systems: a) ionene precursor polyfluorene polymers deposited as ultrathin films using the LbL technique from an aqueous solution and b) electrodeposition of polysiloxane modified precursor polymers. Important strategies are outlined for combining the two techniques as a novel method for preparing ultrathin films and patterning.
Ionic Self Assembly and Low Conversion Temperature (P-Phenylene Vinylene)
Authors: Marletta A. , Castro F. A. , Borges C. A. M. , Faria R. M. , Guimarães F. E. G.
Published: April 2011

We developed an alternative approach to produce self-assembled (SA) thin films of poly(p-phenylene vinylene) (PPV) by controlled substitution of the chloride counterion of the precursor poly(xylylidene tetrahydrothiophenium chloride) (PTHT) by a long chain dodecylbenzenesulfonate (DBS) anion. The main advantage of this novel procedure is that thermal conversion through the elimination of DBS may be performed at considerably lower temperatures (80-100 °C) in few minutes. In addition it provides PPV films with better optical properties and low incorporation of structural defects, like carbonyl groups. An important feature of these SA-PPV films is the well resolved vibronic structures in the photoluminescence and absorption spectra. We observe a dramatic improvement in quantum efficiency of PPV when the conversion temperature is decreased from 230 to 80 °C. This effect may be explained by the decrease of extrinsic defect incorporations (carbonyl groups) detected by infrared (IR) measurements. This improvement in the optical properties at low temperatures may help us to understand basic phenomena, such as the nature of excitons in PPVs.
Electrical, Optical, and Structural Properties of Fluorine-Doped CdO
Authors: Barnes Teresa M. , Li Xiaonan , Dehart Clay , Moutinho Helio , Asher Sally , Yan Yanfa , Gessert Timothy A.
Published: April 2011

We have investigated the effects of fluorine doping and deposition temperature on CdO grown by metal-organic chemical vapor deposition (MOCVD). Fluorine doping increases the carrier concentration of the films by about one order of magnitude at a deposition temperature of 300°C. The increased carrier concentration increases the optical bandgap from 2.4 eV to 2.85 eV. On the other hand, the higher deposition temperatures enabled by fluorine doping improve the crystal structure of the films. Therefore a higher mobility has been reached. The polycrystalline thin film CdO deposited at 450°C has the Hall mobility of 262 cm2/V-s and a carrier concentration of 3.8×1019/cm3.