bluuebunny/crossref_metadata_2025 huggingface dataset:
Etch Rate and Surface Morphology of Plasma Etched Glass Substrates
Authors: Liu Junting , Nemchuk Nikolay I. , Ast Dieter G. , Couillard J. Gregory
Published: April 2011

Micro-machined transparent components are of interest for optical MEMS and miniaturized biological systems. The glass ceramic GC6 developed by Corning is optically transparent, has a softening point in excess of 900°C, and a thermal expansion coefficient matched to silicon. These properties make it useful for the construction of devices that combine thin film silicon electronics with MEMS systems.

Both the ceramic precursor (green glass) and the glass ceramic etch at a similar rate, about 1/3 to 1/4 of that of SiO2 etched under the same conditions, indicating that chemistry rather than microstructure control the etch rate. The cleaning steps used to clean the glass precursor profoundly influence the degree of surface roughness that develops during subsequent plasma etching. In glass ceramics, the morphology of plasma etched surface is always very smooth and independent of the cleaning steps used. Assuming that the removal of spinel crystals is the rate limiting step in plasma etching glass ceramics can explain this observation.
Issues in the Flexible Integration of Sputter-Deposited PZT Thin Films with Polysilicon and Ti/Pt Electrode Layers for Use as Sensors and Actuators in Microelectromechanical Systems (MEMS)
Authors: Knollenberg C.F. , Sands T.D. , Nickles A.S. , White R.M.
Published: April 2011

Sputter-deposited piezoelectric lead zirconate titanate (PZT) thin films with Ti/Pt and polysilicon electrode layers are being investigated for use in Microelectromechanical Systems (MEMS). Existing research shows the nucleation of the perovskite phase of the PZT is linked to the lattice spacing of the underlying Pt electrode and/or seed layers, and is key in obtaining PZT layers with good piezoelectric/ferroelectric properties. Our research with piezoelectric PZT films on Ti/Pt electrode layers aims at employing these films to generate and receive acoustic waves in flexural plate wave devices (FPWs). Our experiments indicate the formation of a random polycrystalline perovskite phase is linked to the emergence of oriented <100> Pt grains within the dominant <111>-oriented crystal structure during rapid thermal annealing in an oxygen environment. Pt films annealed in nitrogen, in contrast, retained their <111> preferential orientation without the formation of Pt <100> grains. PZT films deposited on these electrodes and annealed in nitrogen were strongly oriented in the <111> direction, but exhibited lossy ferroelectric behavior and were prone to delamination. We are also investigating the feasibility of using doped polysilicon electrode layers with PZT thin films. The multiple layers used with the Pt electrode (Pt, Ti, and SiO2 adhesion layer) have significant interactions with one another, and replacing these layers with a single electrode layer should alleviate these complications. A low-temperature PZT deposition process (300°C) and short annealing cycles (30 sec.), coupled with a TiO2 barrier/seed layer should prevent interdiffusion and reactions between the polysilicon and PZT layers. Our experiments show that PZT films deposited and annealed on doped polysilicon layers develop a random polycrystalline perovskite phase, but are subject to tensile cracking. The use of polysilicon as an electrode layer should also facilitate the integration of piezoelectric PZT layers with polysilicon surface micromachined structures using SiGe sacrificial layers.
Developing a New Material for MEMS: Amorphous Diamond
Authors: Sullivan J. P. , Friedmann T. A. , de Boer M. P. , LaVan D. A. , Hohlfelder R. J. , Ashby C. I. H. , Dugger M. T. , Mitchell M. , Dunn R. G. , Magerkurth A. J.
Published: April 2011

Amorphous diamond is a new material for surface-micromachined microelectromechanical systems (MEMS) that offers promise for reducing wear and stiction of MEMS components. The material is an amorphous mixture of 4-fold and 3-fold coordinated carbon with mechanical properties close to that of crystalline diamond. A unique form of structural relaxation permits the residual stress in the material to be reduced from an as-deposited value of 8 GPa compressive down to zero stress or even to slightly tensile values. Irreversible plastic deformation, achieved by heat treating elastically strained structures, is also possible in this material. Several types of amorphous diamond MEMS devices have been fabricated, including electrostatically-actuated comb drives, micro-tensile test structures, and cantilever beams. Measurements using these structures indicate the material has an elastic modulus close to 800 GPa, fracture toughness of 8 MPa.m½, an advancing H2O contact angle of 84° to 94°, and a surface roughness of 0.1 to 0.9 nm R.M.S. on Si and SiO2, respectively.
Preparation of Mesoporous Oxides for Mems Structures
Authors: Paik Jong-Ah , Kitazawa Nobuaki , Fan Shih-Kang , Kim Chang-Jin , Wu Ming C. , Dunn Bruce
Published: April 2011

The high porosity and uniform pore size provided by mesoporous oxide films offer interesting opportunities for MEMS devices that require low density and low thermal conductivity. This paper describes recent efforts at adapting mesoporous films for MEMS fabrication. Mesoporous SiO2 and Al2O3 films were prepared using block copolymers as the structure-directing agents, leading to films which were 70% porous and < 5 nm surface roughness. A number of etchants were investigated and good etch selectivity was observed with both dry and wet systems. Micromachining methods were used to fabricate cantilevers, micro bridges and membranes.
Silicon Germanium Epitaxy: A New Material for MEMS
Authors: Borenstein J.T. , Gerrish N.D. , White R. , Currie M.T. , Fitzgerald E.A.
Published: April 2011

A wide array of materials have been investigated as candidate fabrication templates for precision microelectromechanical structures, including boron-diffused silicon, boron-doped epitaxial silicon, polysilicon, silicon-on-insulator, and wafer-thick bulk structures. Here we present the latest fabrication results for epitaxial silicon-germanium alloys, a new class of materials which possess excellent crystalline structure, are compatible with non-toxic etchants in bulk micromachining, and are capable of on-chip integration with electronics. For MEMS applications, silicon-germanium alloy layers are grown using a graded buffer approach, resulting in very high quality micromachined structures. Very low defect densities are obtained through the use of these relaxed buffers. Original etch-stop studies determined that Ge doping provided a very weak selectivity in anisotropic etchants such as KOH and EDP. However, by extending the range of Ge concentration to over 20%, we have found extremely high etch selectivities in a variety of etchants. Unlike boron-doped layers, SiGe exhibits etch stop characteristics in the non-toxic, process compatible solution TMAH. The combination of independence from boron doping concentration and etchant compatibility make SiGe a material which is ideal for integration with on-chip electronics.

In this work we present the latest fabrication data on comb-drive resonators built using SiGe epitaxial layers. Process compatibility issues related to wafer curvature, surface finish and reactive-ion-etching chemistries are addressed. An unexpected result of the fabrication process, curvature of released structures, is resolved by annealing wafers after the SiGe deposition. Changes in Young's modulus arising from the high atomic fraction of Ge in the device can be determined by simple beam analysis based on observed resonant frequencies. Overall, build precision for these devices is excellent. We conclude by addressing the remaining challenges for wide-scale implementation of silicon-germanium epitaxial MEMS.
Recrystallization of Nickel and Ni Alloy Substrates for YBCO Coated Conductors
Authors: Nast Rainer , Obst Bernhard , Goldacker Wilfried , Schauer Wolfgang
Published: April 2011

To avoid grain boundary grooving and abnormal grain growth during recrystallization of nickel and Ni alloy substrate tapes, the commonly used high recrystallization temperatures must be lowered.

The development of the cube orientation is a nucleation-growth process. So the kinetics of the cube recristallization is strongly temperature dependent, and there is a very marked effect of the stacking fault energy (SFE) of the specific alloy on the activation energy. Concurrently with measurements of the formation kinetics of the cube orientation, the recrystallization texture of Ni (+99,99 wt.%), NiCr10 wt.% and NiMn10 wt.% tapes in dependence on the deformation history, the annealing temperature and time was investigated. Profile rolling to a rectangular rod, without further high temperature annealing, leads to a worse cube texture compared to round swaged rods with an in-plane 200 peak splitting. The increase of the recrystallization temperature and time sharpens the texture due to grain growth, limited by the occurrence of secondary recrystallization when a sample specific temperature is exceeded.

In binary Ni alloys the commonly used alloying elements reduce the SFE. This favors the formation of recrystallization twins {122}<212> obstructing the oriented coating. In Mn alloyed tapes this effect is strongly pronounced. The tapes show a good cube texture, but also a high volume fraction of twins due to the low SFE. To suppress the twin formation we investigated ternary Ni based alloys with respect to possibly increased SFE and report first results.
Superconducting Thallium Oxide and Mercury Oxide Films
Authors: Bhattacharya Raghu N. , Yan S. L. , Xing Zhongwen , Xie Yiyuan , Wu Judy Z. , Feldmann Matt , Chen Jun , Xiong Qihua , Ren Z. F. , Blaugher Richard D.
Published: April 2011

Previously we reported on a two-layer electrodeposition process of thallium oxide superconductors that showed transport critical current density above 106 A/cm2 at 77 K in zero field. In this article, we report our effort to convert an electrodeposited thick film of (Tl,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox to (Hg,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox by the cation-exchange process. We are also reporting magneto-optical imaging data on Tl oxide superconductor films, which are compared with YBCO. Magneto-optical imaging provides insight into the nature of current flow in the Tl oxide superconductor, and thus, will help us to improve the critical current density in bulk high-temperature superconductor wire or tape.
Phase Relations of the Bi-2201–CuO Pseudobinary Join as a Function of Oxygen Pressure
Authors: Meen James K. , Müller Karoline , Salmeron Celia , Elthon Don
Published: April 2011

Phase relations on the join Bi-2201–CuO have been determined as a function of P(O2). Most of the major changes that occur between P(O2) of 1 and 0.01 atm occur in the most oxidizing part of the range. Stoichiometric Bi-2201 occurs only at the most oxidizing conditions and in a narrow temperature range near the solidus. In the Bi-2201–CuO system, the ternary phase that forms has higher Bi:Sr and Cu:Sr than Bi-2201. That phase, Sr14Cu24Oy, and CuO occur in the subsolidus and the invariant point at which they coexist with liquid is a ternary eutectic. The liquid is more Sr-rich than the Bi-2201–CuO join. Decrease in P(O2) produces a change in the Bi- 2201 solid solution so that stoichiometric Bi-2201 does not occur. At P(O2) ≤0.5 atm, all Bi- 2201 solid solutions have Bi:Cu<2 but Bi:Sr near unity and Sr14Cu24Oy does not form. Small amounts of a phase believed to be Bi9Sr11Cu5Ox form under these conditions and the primary phase field of that phase crosses the pseudobinary join and minimum melting is at a ternary tributary reaction point. The liquid there is more Bi-rich than the join. Further decrease in P(O2) causes a continued freezing point depression and enlargement of the CuO primary phase field so that the compositions of multiply-saturated liquids move away from the CuO apex.
Microstructural analysis of the compatibility of solution deposited buffer layers with the TFA process for YBCO
Authors: Salama K. , Sathyamurthy S. , Mironova M.
Published: April 2011

In this paper, the feasibility of applying solution deposition processes for the fabrication of coated conductors has been explored. The crystal and chemical compatibility of the buffer layers processed using metalorganic decomposition with the Y123 deposition using the trifluoroacetate process has been studied. Two buffer layer materials have been used, namely, barium zirconate and strontium titanate. The measured superconducting properties of these conductors were correlated with the microstructure observed on these samples using SEM and cross-sectional TEM. In case of barium zirconate buffer layers, though there exists a very good structural and chemical compatibility between the buffer layer and the Y123, the presence of surface defects in the buffer layer causes compositional heterogeneity and randomly oriented grains in the Y123 film. This leads to poor superconducting properties. In case of strontium titanate buffer layers, due to the excellent crystal and chemical compatibility, and the absence of surface defects, high critical current densities (of the order of 106A/cm2 at 77K and self field) were obtained. However, TEM cross section studies reveals the presence of a significant portions of a-oriented Y123 crystallites which could lead to lower critical current densities. Further studies of the TFA process is required to eliminate the occurrence of a-oriented Y123 in the microstructure. This could lead to further improvements in the properties.
Growth Mechanism of RE-Ba-Cu-O Crystal by Liquid Phase Epitaxy Process
Authors: Nomura K. , Hoshi S. , Yao X. , Nakamura Y. , Izumi T. , Shiohara Y.
Published: April 2011

Growth of YBa2Cu3Oy (YBCO) crystals both on the MgO and the YBCO substrates has been investigated in order to clarify the growth mechanism of the liquid phase epitaxy (LPE) process for the coated conductor. It was found that the slope angle of the growth grain varied with growing in the initial stage of the LPE growth. In the case of the MgO substrate, the slope angle increased with laterally growing the crystal. On the other hand, the slope angle decreased with growing the crystal in the case of the YBCO substrate. This phenomenon with the opposite tendency could be explained by considering the difference in the step-advancing rates between on the MgO and the YBCO surfaces. It was found that the deep and steep valley of the LPE grains due to the slow step-advancing rate on the MgO is the origin of the flux trapping inclusions. It is necessary that the seed films should cover the entire MgO surface without undesired orientation grains and impurity particles in order to obtain the high quality LPE layer.
Texture Formation and Superconducting Properties of YBa2Cu3Ox Thin Films Prepared by Solution Process on LaAlO3 Single Crystals
Authors: Jee Y.-A , Ma B. , Li M. , Fisher B. L. , Balachandran U.
Published: April 2011

YBa2Cu3Ox (YBCO) thin films were fabricated by the trifluoroacetate (TFA) process on LaAlO3 (LAO) single crystal in an argon atmosphere. We focused on lowering the heat treatment temperature by decreasing the oxygen partial pressure to adopt the TFA process to metallic substrates. YBCO phase formation was checked by measuring Tc with the inductive method. In-plane and out-of-plane film textures were evaluated by phi-scan and omega scan, respectively. Raman spectroscopy was used to estimate grain connectivity, in-plane texture, and second-phase formation of the films. Although Raman spectroscopy revealed some evidence of cation disorder, the film prepared at 750°C shows a sharp superconducting transition at 91 K and critical current density of 1.3 MA/cm2 at 77 K. Optimal heat treatment temperature was 750°C in the argon atmosphere, which is consistent with the thermodynamic estimate that heat treatment temperature decreases as oxygen partial pressure decreases.
Pb-doped Bi-2212: Homogeneity Area, Oxidation and Effect on jc
Authors: Veresov A. , Pulkin M. , Knotko A. , Putlayev V. , Salje E. K. H.
Published: April 2011

The most promising way to improve jc in superconductors is likely to be a creation of small precipitates in the material during decomposition of supersaturated solid solution. It was recognised recently that Pb-doping of 2212 could have beneficial effect on jc. Bi2.1−xPbxSr2CaCu2O8+d (x=0.1…0.7) was prepared at different temperatures and oxygen partial pressure (pO2=10−3 – 0.21 atm) via nitrate route. The effect of pO2 and Pb-doping on Bi-2212 phase formation was explored with XRD, SEM/EPMA and TEM/SAED. The limit of Pb solubility in Bi-2212 was found to increase with a decrease in pO2 and corresponded to a decrease in x=0.3 at pO2 = 0.21 atm (850 °C) and x=0.6 at pO2 ∼ 10−3 atm (750 °C). TEM study of the as-synthesized solid solutions revealed significant nanoscale inhomogeneity attributed to Pb-segregation. For the samples with x > 0.3 the inhomogeneity quite often looked like a well- ordered wave with the period of about 10 nm. The samples of (Bi,Pb)-2212 processed under pO2 conditions were oxidized at 600–750°C in air for 0.5–60 h in order to cause precipitation of secondary phases from the supersaturated solid solution. Thermogravimetrical study (TG) of the oxidation gave a strong evidence of two stages composing the process. It was found that jc was enhanced by a factor of 2 after annealing at 650°C (i.e. during the first stage of oxidation).
Mean Field and Monte Carlo Modeling of Multiblock Copolymers
Authors: Rasmussen K. ø. , Sewell T. D. , Lookman T. , Saxena A.
Published: April 2011

Abstract We compare for multiblock copolymers the results of mean field calculations with those from Monte Carlo simulations based on the bond uctuation method and experimental results from scattering data. The application of Leibler's [1] theory for copolymers and the results of Monte Carlo simulations indicate that the microphase separation transition occurs at largerxNas the number of blocks is increased beyond two (i.e., beyond diblock), and that the characteristic length scale of the emerging morphology decreases as the number of blocks increases. The latter is in qualitative agreement with published experimental results [2] for model multiblock poly(styrene-isoprene) systems and recent results [3] for a segmented poly(ester-urethane).
Preparation and Properties of Exfoliated Graphite/Polystyrene Composite
Authors: Xiao Peng , Sun Luyi , Xiao Min , Gong Kecheng
Published: April 2011

A composite based on exfoliated graphite (EG) and polystyrene was prepared by polymerization-filling technique. With the argument of the amount of filled EG, the molecular weight of polystyrene in the resulting composite increased and the molecular weight distribution decreased. The glass transition temperature of the polystyrene was determined by dynamic mechanical analysis (DMA) and showed the glass temperature of polystyrene increasing to 123.74°C. The thermal degradation behavior was studied using thermogravimetry (TG) and showed higher thermal stability of the composite than that of pure polystyrene and polystyrene//EG composite prepared by melt-blending. Four-probe instrument and high resistivity meter were used to measure the volume conductivity of the composites. Composites prepared by both polymerization-filling technique and melt-blending exhibit increased electrical conductivity, while composite prepared by polymerization-filling technique has a conductive percolation threshold lower than 2.5wt%.
Intercalated clay nanocomposites: Morphology, mechanics and fracture behavior
Authors: Zerda Adam S. , Lesser Alan J.
Published: April 2011

Intercalated nanocomposites of modified montmorillonite clays in a glassy epoxy were prepared by crosslinking with commercially available aliphatic diamine curing agents. These materials are shown to have improved Young's modulus but corresponding reductions in ultimate strength and strain to failure. These results are consistent with most particulate filled systems, The macroscopic compressive behavior is unchanged, although the failure mechanism in compression varies from the unmodified samples. The fracture toughness of these materials is investigated and improvements in toughness values of 200% over unmodified resis are demonstrated. The fracture surface topology is examined using SEM and tappin-mode AFM and showm to be related to the clay morphology of the system.
Controlling Diffusion of Solutes Through Ionically Crosslinked Alginate Hydrogels Designed for Tissue Engineering
Authors: Kuo Catherine K. , Ma Peter X.
Published: April 2011

Tissue engineering aims at creating new tissues as alternatives to organ transplants. Our approach is to incorporate cells into biodegradable polymer scaffolds designed to temporarily support new tissue formation. An important requirement of scaffolds is homogeneity. Homogeneity ensures structural integrity, uniform distribution of cells, and uniform porosity throughout the scaffold. Controlling pore sizes is necessary to regulate exchange of nutrients and waste products for cells. Pores too large can provide entryway to immune cells that can harm allogenic cells and developing tissue. We have fabricated three-dimensionally defined, homogeneous, ionically crosslinked alginate gels with a controlled slow-gelation system involving CaCO3 and D-glucono-δ-lactone. We varied the structural parameters and alginate types of these gels to control the diffusion of glucose, vitamin B12 and FITC-dextran (molecular weights of 180, 1355 and 9500, respectively) through the gels. Experiments were performed with gel discs placed between side-by-side donor and receptor chambers in a humidified incubator at 37°C. Samples were taken periodically and measured on a UV-Vis spectrophotometer. Generally, diffusion coefficient (D) increased with decreasing solute size. Varying structural parameters of the gels did not have a significant effect on diffusivity of vitamin B12. In contrast, for gels made with a Ca2+ to carboxyl molar ratio of 0.36, D of FITCdextran increased from (2.88 ± 0.52)×10-7 to (4.66 ± 0.48)×10-7 cm2/sec as alginate concentration decreased from 3.2% to 1.5%, respectively. D of FITC-dextran also increased from (3.17 ± 0.30)×10-7 to (4.66 ± 0.48)×10-7 cm2/sec as crosslinking density decreased for 1.5% alginate gels from a Ca2+ to carboxyl molar ratio of 0.72 to 0.36, respectively. D was highest for alginate gels with the highest guluronic acid content. Controlling diffusivity allows alginate gels with specific properties to be fabricated for tissue engineering scaffolding and other biomedical applications.
Bioactive Glass Paste in Molars of Mini-Pigs: An In Vivo Study
Authors: Efflandt Sarah E. , Lopes Manuela , Ko Ching-Chang , Perdigao Jorge , Douglas William H. , Francis Lorraine F.
Published: April 2011

Bioactive glass powder in the MgO-CaO-P2O5-SiO2 system was mixed with water to create a bioactive glass paste. The paste was then placed in 8 cavities in molars of Sinclair mini-pigs, isolated using a light-cure composite filling, and left in vivo for 4 weeks. Additionally, 4 controls were run where the bioactive glass was placed in an inert polymer substrate and then incubated at 37°C for 4 weeks. Specimens were cut longitudinally in two halves and prepared for chemical and x-ray analyses. Qualitative results showed that the paste in the molars stayed intact while there was little or no paste left in the polymer substrate after cutting. This observation suggested that the paste in the natural tissue had structural integrity which could be caused by chemical changes and/or mineralization encouraged by contact with dentinal tubule fluid. X-ray analysis did not reveal any crystallinity in the paste at 4 weeks, but chemical alterations were confirmed by electron microprobe analysis. The chemical inhomogeneity of the individual elemental maps revealed the formation of Ca-P-rich/Si-poor areas. These distinct chemical variations were not seen in chemical analyses run on the bioactive glass paste in its initial state.
Analysis of Electrostatic Effects on the Success of Retroviral-Mediated Gene Delivery
Authors: Davis Howard E. , Morgan Jeffrey R. , Yarmush Martin L.
Published: April 2011

Recombinant retroviruses are a commonly used gene delivery tool in human gene therapy clinical trials as they permanently integrate the therapeutic DNA into the genome of the target cell. Despite their widespread use, however, retroviral gene transfer efficiencies remain disappointingly low. In the years since their initial development as vectors, it has become clear that the physicochemical properties of the recombinant retrovirus, as well as the properties of the target tissue, have a major impact on the success of gene transfer. In particular, the interaction between the native negative charge present on the vector and target cell membranes results in a significant electrostatic barrier which must be overcome in order for the transduction process to begin. Using a recently developed retrovirus adsorption assay, we have demonstrated that this electrostatic interaction is the dominant interaction during the initial steps of transduction. We have also established that cationic polymers enhance adsorption, and ostensibly transduction, by neutralizing this electrostatic barrier. Interestingly, we also found that this enhanced adsorption could be demonstrated even in the absence of a cellular receptor for the virus, suggesting that the first step of transduction does not involve binding of the virus to currently identified receptors, but is either a non-specific adsorption process or involves binding to an, as of yet, uncharacterized class of receptor. Based upon our finding that virus adsorption is non-gp70 mediated, we propose a new physical model of this initial step of transduction which is diffusion-limited, receptor and envelope independent, and modulable by positively charged compounds. Our findings may have significant implications for other gene and drug delivery systems which interact directly with target tissues at the level of the cell membrane.
Small Molecule Diffusion and Solubility in Adhesives Used for Transdermal Drug Delivery: Infrared-Attenuated Total Reflectance (IR-ATR) Studies.
Authors: Cantor Adam S.
Published: April 2011

A key factor in designing a drug-in-adhesive transdermal drug delivery system is to understand the rate at which the drug and small-molecule excipients can diffuse in the adhesive matrix. The solubility of these components in the adhesive matrix is also of great importance. Results will be presented discussing the use of infrared-attenuated total reflectance (IR-ATR) spectroscopy as a method to measure both diffusion and solubility of small molecules in adhesives. In this method, the donor layer is either a doped adhesive or a free liquid that is placed in contact with a receptor layer which is an undoped adhesive in contact with an IR-ATR crystal. The IR-ATR crystal detects as a function of time any molecules that diffuse from the donor layer into and through the receptor layer.

Examples will be discussed of several different experiments that can be performed with this technique. Diffusion coefficients are presented here for testosterone and terpineol in an isooctyl acrylate based adhesive using a doped adhesive donor layer. Diffusion and solubility of liquids in several adhesives has been determined using the experiment where a free liquid is used as the donor. Solubility and diffusion coefficients determined using an oversaturated doped layer containing dispersed, as well as dissolved solute, are presented here for testosterone and for progesterone. Finally diffusion from a doped layer of one adhesive to an undoped layer of a different adhesive was performed as a partition measurement. The parameters that can be extracted from each of these experiments, as well as the limitations of each type of experiment will be discussed.
Nanoparticles and Polymeric Vesicles From New Poly-L-Lysine Based Amphiphiles
Authors: Uchegbu Ijeoma F. , Tetley Laurence , Wang Wei
Published: April 2011

Nanoparticles and polymeric vesicles for drug delivery and other industrial applications have been prepared by the probe sonication of poly-L-lysine graft copolymer amphiphiles in aqueous media. The amphiphiles, which have a poly-L-lysine backbone and varied levels of both hydrophilic methoxypolyethylene glycol (Mw ∼ 5,000) and hydrophobic palmitoyl pendant groups, were prepared from 2 different molecular weight poly-L-lysine hydrobromide samples (Mw ∼4,000 and ∼20,000 respectively). Poly-L-lysine based amphiphilic polymers (PLPs) were characterised using light scattering, 1H NMR and an assay for the level of free amino groups. Steric factors appear to limit the final level of lysine group modification that can be achieved and even an excess amount of grafting reactants still resulted in the production of polymers in which 22 – 26 mole% of the lysine terminal amino groups remain unsubstituted. Polymeric unilamellar vesicles (220 – 570nm in diameter) imaged by electron microscopy were produced by probe sonication of PLP, cholesterol. Vesicle formation was possible over a narrow spectrum of polymer architecture and was favoured by a low molecular weight and a low level of palmitoyl substitution. A vesicle formation index (F') has thus been derived for this PLP, cholesterol system = Where H = %molar level of unreacted L-lysine units, L = %molar level of substituted palmitoyl units and DP = square root of the degree of polymerisation of the polymer. Probe sonication of an aqueous dispersion of PLP samples resulted in the production of stable nanoparticles (80 -170nm in diameter) as imaged by electron microscopy. Nanoparticles were able to encapsulate the hydrophilic fluorophore fluorescein isothiocyanate (FITC)-dextran and encapsulation increased as the level of unreacted lysine terminal amino groups in PLP increased thus increasing as the level of hydrophilic domains increased. The size of both the nanoparticles and the vesicles was directly influenced by the molecular weight of PLP. PLPs of molecular weight 32,000 – 48,000 and 89,000 – 140,000 resulted in nanoparticles of 85 – 114 nm and 125 – 167 nm in diameter respectively and PLP of molecular weight 25,000 and 89,000 gave rise to polymeric vesicles of 252 nm and 570 nm in diameter respectively.
Mechanism of Carrier Photoexcitation in Semiconducting Polymers: The Role of Electron Photoemission in “Photoconductivity” Measurements
Authors: Moses Daniel , Miranda Paulo B. , Soci Cesare , Heeger Alan J.
Published: April 2011

Ultrafast photoinduced absorption by infrared-active vibrational modes (IRAV) is used to detect charged photo-excitations (polarons) in solid films of conjugated luminescent polymers. Experiments, carried out in zero applied electric field, show that polarons are generated within 100 fs with quantum efficiencies of approximately 10%. The ultrafast photoinduced IRAV Absorption, the weak pump-wavelength dependence, and the linear dependence of charge density on pump intensity indicate that both charged polarons and neutral excitons are independently generated even at the earliest times. Measurements of the excitation profile of the transient and steady-state photoconductivity of poly(phenylene vinylene) and its soluble derivatives over a wide spectral range up to hν = 6.2 eV indicate an apparent increase in the “photoconductivity” at hν > 3-4 eV that arises from external currents generated by electron photoemission (PE). After quenching the PE by addition of CO2+SF6 (90%:10%) into the sample chamber, the bulk photoconductivity is nearly independent of photon energy in all polymers studied, in a good agreement with the IRAV spectra. The single threshold for photoconductivity is spectrally close to the onset of π-π* absorption, behavior that is inconsistent with a large exciton binding energy.
Photoinduced Enhancement of Photoluminescence Intensity in PPV Films
Authors: Gobato Yara Galvão , Marletta Alexandre , Souza Jucimar M. , Pereira Ernesto , Faria Roberto M. , Guimarães Francisco E.G.
Published: April 2011

Poly(p-phenylene vinylene) (PPV) films are usually photodegraded in air. We report on the enhancement of photoluminescence (PL) intensity of PPV films induced by Ar ion laser in the presence of air. The PL spectra were measured as function of laser power, time exposure and sample thickness. The initial PL intensity increases up to 300% without significant changes in peak positions by optimizing such parameters. This effect is accompanied by a blue-shift in the absorption spectrum resulting in shortened effective conjugation length and by a formation of defects such as carbonyl groups. Mechanisms for the observed photoluminescence intensity enhancements are suggested.
Third Order Non-Linear Optical Properties of Polyphenylene Vinylene Derivatives in the Infrared Range
Authors: Dubitsky Yuri A. , Zaopo Antonio , Zappettini Andrea , Facchini Giulia , Amore Franco D , Pietralunga Silvia , Martinelli Mario
Published: April 2011

The non-linear optical properties of poly[1,4-phenylene-1-phenyl vinylene], poly[1,4-phenylene-1,2-di(4′-phenoxyphenyl) vinylene], poly[2,5-dioctyloxy-1,4-phenylene vinylene] and poly[2- methoxy -5- (2'-ethylhexyloxy)-1,4-phenylene vinylene] MEH-PPV with different molecular weights were studied by the Third Harmonic Generation (THG) technique. The dispersion of the χ3 coefficient was measured in the wide infra red range from 1.2 up to 2.1 μm. It was shown that the highest χ3 value, observed for the high molecular weight MEH-PPV (Mw 230.000), reaches the maximum of 8x10-11 esu at 1.77 μm. At the same time, the medium molecular weight MEH-PPV (Mw 95.000) demonstrated not significantly different χ3 value of 6x10-11 esu. The dispersion of the χ3 coefficient was compared to the absorption of the third harmonic beam and strong χ3 enhancement relative to the excitonic absorption was observed. However, a surprising shift of about 70 nm towards the longer wavelengths between the two peaks was always observed for all studied PPV derivatives. The results of THG measurements were compared to those obtained by conventional Zscan technique in the same range. It was shown that the THG χ3 values in infrared range were up to one order of magnitude lower than those of direct Z-scan measurements.
The Synthesis, Condensation, and Luminescence of Stilbenoid Oligomers with Alkoxysilane End Groups
Authors: Detert H. , Sugiono E.
Published: April 2011

A synthetic route to highly luminescent organic semiconductors with curable alkoxysilyl groups is described. Monodisperse oligo(phenylenevinylene)s are rigidly connected to di- and triethoxysilanes via Heck reactions or via cross-metathesis. Hydrolysis of the silicic esters yields silanols condensing to linear and cyclic oligo-OPV-siloxanes or to three-dimensional networks, thus allowing the transformation of small molecules to fluorescent materials with well-defined chromophores. Transparent films are obtained by casting of soluble cyclosiloxanes and from OPV-silanetriols, the latter can be cured to insoluble networks.
Design, Synthesis and Charaterization of Polymers Derived from Fluorene for Application in RGB Polymer Light-Emitting-Diodes
Authors: Beaupré Serge , Leclerc Mario , Lévesque Isabelle , D'Iorio Marie
Published: April 2011

In order to obtain efficient blue, green and red light-emitters as active layers in polymer light-emitting diode (PLEDs), we report herein the design, the synthesis, and the characterization of new polyesters and copolymers derived from fluorene. We will focus on a new approach to obtain a stable, high luminance blue emitter via polyesters derived from fluorene. The versatile synthetic approach allows the easy design of a whole class of new and tunable electroactive and photoactive aromatic polyesters. Poly(1,6-hexane- 9,9′,9′,9′′,9′′-hexahexyl-7,2′;7′,2′′-terfluorene-2,7′′-dicarboxylate) (PTFHHC6) and Poly(1,6-hexane-2,7-Bis(1,1′-biphenylen-4-yl-4′-dicarboxylate)-9,9-dioctylfluorene) (PE-BP-DOF-BP) exhibit strong emission in the blue range, both in solution and in the solid state. Moreover, these polyesters present some advantages over other polyfluorene derivatives. For example, their solid-state fluorescence spectrum does not show the formation of any excimer and does not vary upon thermal treatment. We will also present copolymers derived from fluorene which emit green light and a new approach to obtain red polymer light-emitting-diode will also be shown. Optical properties such as light absorption, light emission and quantum yield of fluorescence in solution as well as electrical properties such as cyclic voltammogram and conductivity in-situ are reported. Finally, some of the polymers presented have been tested in PLEDs devices and the preliminary results seem promising for the development of multicoloured displays made from the same class of polyfluorene derivatives.
Electronic Properties of Polymer-Fullerene Solar Cells
Authors: Dyakonov V. , Riedel I. , Deibel C. , Parisi J. , Brabec C. J. , Sariciftci N. S. , Hummelen J.C.
Published: April 2011

We studied the electronic transport properties of conjugated polymer/fullerene based solar cells by means of temperature and illumination intensity dependent current-voltage characteristics, admittance spectroscopy and light-induced electron spin resonance. The short-circuit current density increases with temperature at all light illumination intensities applied, i.e., from 100 mW/cm2to 0.1 mW/cm2(white light), whereas a temperature independent behavior was expected. An increase of the open-circuit voltage from 850 mV to 940 mV was observed, when cooling down the device from room temperature to 100 K. The fill factor depends strongly on temperature with a positive temperature coefficient in the whole temperature range. In contrast, the light intensity dependence of the fill factor shows a maximum of 52% at intermediate illumination intensities (3 mW/cm2) and decreases subsequently, when increasing the intensity up to 100 mW/cm2. Further studies by admittance spectroscopy revealed two frequency dependent contributions to the device capacitance. One, as we believe, originates from trapping states located at the interface between composite and metal electrode with an activation energy of EA=180 meV, and the other one is from very shallow bulk states with EA=10 meV. The origin of the latter is possibly the thermally activated conductivity. The photo-generation of charge carriers and their fate in these blends have been studied by light-induced electron spin resonance. We can clearly distinguish between photo-generated electrons and holes in the composites due to different spectroscopic splitting factors (g-factors). Additional information on the environmental axial symmetry of the holes located on the polymer chains as well as on a lower, rhombic, symmetry of the electrons located on the methanofullerene molecules has been obtained. The origin of the signals and parameters of the g-tensor have been confirmed from studies on a hole doped polymer.
Ultrafast Energy And Electron Transfer In Conjugated Oligomer-Fullerene Molecules
Authors: Hal P.A. van , Janssen R.A.J. , Lanzani G. , Cerullo G. , Zavelani-Rossi M. , Silvestri S. De
Published: April 2011

The intramolecular photoinduced energy and electron transfer within a fullereneoligothiophene-fullerene triad with nine thiophene units (C60-9T-C60) and an oligo(p-phenylene vinylene)-fullerene dyad with four phenyl groups (OPV4-C60) is investigated with femtosecond pump-probe spectroscopy with sub-10 fs and 200 fs time resolution in solvents of different polarity. Photoexcitation of the π-conjugated oligomer moiety in the triad and dyad results in an ultrafast singlet-energy transfer reaction to create the fullerene singlet-excited state with a time constant of 150-190 fs, irrespective of the polarity of the medium. In a polar solvent, intramolecular electron transfer occurs from the oligomer moiety to the C60 moiety with a time constant of 10-13 ps as a secondary reaction, subsequent to the ultrafast singlet-energy transfer. The charge-separated state has a lifetime of 50-80 ps and recombines to the ground state.
Electron Accepting Oligomers and Polymers: Chain Scission Under Quaternization Conditions
Authors: Dudis Douglas S. , Mckellar B. Robert
Published: April 2011

The methylation of polybenzobisthiazole in dimethylsulfate produces an ndopable polymer which has previously been shown to have high electrical conductivity. The reaction conditions have been shown to chemically degrade the polymer chains, decreasing the molecular weight to about 20% of the original value. A methylationdemethylation scheme has been used to clarify the degree of chain scission.
Inorganic-organic Hybrid Materials (ORMOCERs) for Multilayer Technology – Passivation and Dielectric Behavior
Authors: Houbertz R. , Fröhlich L. , Schulz J. , Popall M.
Published: April 2011

Inorganic-organic hybrid polymers (ORMOCER®s) have been synthesized by sol-gel processing. The materials can be functionalized such that their physical and chemical properties can be reproducibly tailored towards the desired application, i.e., electronics, optics (passives/actives) or passivation technology. Besides, the materials which show negative resist behavior, can be patterned by UV exposure with good resolution. The materials are well-suited for thin and thick film technology using conventional coating technology, applied in multi-layer technology. We here particularly focus on materials for passivation against environmental influences, which additionally exhibit very good dielectric properties.
Steady State Photoconductivity in Conjugated Polymers
Authors: Sitch C. D. , Halliday D. P. , Monkman A. P.
Published: April 2011

Visible and ultraviolet photoconductivity (PC) measurements have been performed on thick (7[.proportional]m) and thin (170nm) films of poly[2-methoxy, 5 ethyl (2' hexyloxy) paraphenylenevinylene] (MEH-PPV) sandwiched between indium tin oxide (ITO) and semitransparent gold (Au) electrodes. PC spectra were obtained for samples under different bias polarities and for illumination through the ITO electrode and through the Au electrode. The results obtained indicate that the absorbed photons form excitons that dissociate extrinsically at or near the electrodes to form hole polarons or intrinsically at higher photon energies in the bulk polymer.
The influence of nanostructure formation on properties for Cr implanted PET
Authors: Yuguang Wu , Tonghe Zhang , Huixing Zhang , Xiaoji Zhang , Ping Cui , Gu Zhou
Published: April 2011

Polyethylene terephthalate (PET) has been modified by Cr ion implantation with a dose range from 1×1016to 2×1017ions /cm2 using a metal vapor vacuum arc MEVVA source. The surface morphology was observed by atomic force microscopy (AFM). The Cr atom precipitation was found. The changes of the structure and composition have been observed with transmission electron microscope (TEM). The TEM photos revealed the presence of Cr nano-meter particles on the implanted PET. It is believed that the change would cause the improvement of the conductive properties and wear resistance. The electrical properties of PET have been improved after metal ion implantation. The resistivity of Cr ion implanted PET decreased obviously with an increase of ion dose. When the metal ion dose with 2×1017cm−2 was implanted into PET, the resistivity of PET could be less than 0.1 Ωm. But when Si or C ions with same dose are implanted PET, the resistivity of PET would be up to several Ωm. The result show that the resistivity of Cr ion implanted sample is obviously lower than that of Si- and C-implanted one. After Cr implantation, the surface hardness and modulus could be increased. The property of the implanted PET has modified greatly. The hardness and modulus of Cr implanted PET with dose of 2×1017/cm2 is 9.5 and 3.1 times greater than that of pristine PET. So we can see that wear resistance improved greatly. The Cr ion beam modification mechanism of PET will be discussed.
Materials Characterization and Synthesis of Conductive Aromatic-Bis(Benzothiazoles)
Authors: Alexander Max D. , Sankaran Balasubramanian , McKellar B. Robert , Dudis Douglas S.
Published: April 2011

Functionalized aromatic-bis(benzothiazoles) have been synthesized by our group and have shown promise as conductive n-dopable polymers and oligomers. When reduced (n-doped) these materials typically exhibit conductivity on the order of tens of S/cm. Here we examine the material properties of this family of derivatized, conductive aromatic-bis(benzothiazoles). A variety of synthetic approaches have been examined to produce these polymers and oligomers, and will be discussed. Material characterization has been accomplished by spectro-electrochemistry, nuclear magnetic resonance (NMR), electron spin resonance (ESR), Fourier Transform Infrared (FTIR) spectroscopy, and direct current (DC) conductivity.
Electric Field Induced Self Assembly and Template Patterning of Polymer Microstructures
Authors: Ozkan Cengiz S. , Gao Huajian
Published: April 2011

We have developed a method for fabricating polymer microstructures based on electric field induced self assembly and pattern formation. A dielectric fluid placed in between to conductive plates experiences a force in an applied electric field gradient across the plates, which can induce a diffusive surface instability and self construction of the fluid surface. This process is exploited for the fabrication of self assembled polymer microstructures as well as replicated patterns through the use of pre-patterned plates or electrodes. We have used silicon wafers and transparent ITO (Indium-Tin Oxide) coated quartz substrates to fabricate the capacitor structures. The bottom silicon plate is spin coated with a 100-200 nm thick polystyrene film. The ITO substrate was placed over the polymer surface at a distance to leave a thin air gap using spacers. For directed pattern transfer, patterned ITO substrates were used. The capacitor setup was heated above the glass transition temperature of the polymer and a voltage was applied across the plates (50-150 Volts), which induces electric fields on the order of 107–108 V/m. The capacitor structure was quenched to observe the structures using optical microscopy and atomic force microscopy. The method described can be used to fabricate a variety of structures in the micron and nanometer scales including bio-fluidic MEMS, polymer optoelectronic devices and patterned templates for nanolithography.
Conjugatged Oligomeric Coordinated Silver Phenylacetylide Derivatives With Ultrafast Optical Kerr Effect
Authors: Xu Y. H. , Teo B.K. , Wu H.M. , Guo S.L. , He Y.K. , Chen H.Y. , Qian W. , Wu S.J. , Zuo Y.H.
Published: April 2011

Silver phenylacetylide prepared by one-step process was characterized as a linear coordinated polymeric compound by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. Its prominent third-order optical nonlinearity was detected by heterodyned ultrafast optical Kerr effect (OHD-OKE) measurement. The second-order hyperpolarizability was enhanced by 2 orders of magnitude by means of incorporation of proper electron-pushing groups. The structure status was further investigated by quantum chemical calculation and molecular modeling.
Thin Film Metal Oxide Semiconductors Deposited on Polymeric Substrates
Authors: Fortunato Elvira , Nunes Patrícia , Marques António , Costa Daniel , Águas Hugo , Ferreira Isabel , Costa Maria E. V. , Martins Rodrigo
Published: April 2011

Highly textured transparent conducting ZnO:Al thin films have been prepared by r.f. magnetron sputtering. The films were deposited on polyester (Mylar type D, 100 µm thickness) and glass substrates at room temperature. Surface stylus profiling, X-ray diffraction, scanning electron microscopy, transmission electron microscope and Hall effect measurements as a function of temperature have been used to characterize the produced films. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface (columnar structure). The ZnO:Al thin films with a resistivity as low as 3.6×10−2 µcm have been obtained, as deposited.