bluuebunny/crossref_metadata_2025 huggingface dataset:
Materials Characterization of CIGS solar cells on Top of CMOS chips
Authors: Lu J. , Liu W. , Kovalgin A. Y. , Sun Y. , Schmitz J.
Published: September 2011

In the current work, we present a detailed study on the material properties of the CIGS layers, fabricated on top of the CMOS chips, and compare the results with the fabrication on standard glass substrates. Almost identical elemental composition on both glass and CMOS chips (within measurement error). From X-ray diffraction measurement, except two peaks from the Si <100> substrate, the diffraction peaks from CIGS solar cell CMOS chip and that on glass substrate coincide for all three temperatures. Helium ion microscope images of the cross-section and top view of the CIGS layers, shows that the grain size is suitable for high efficiency solar cells.
Development of a High-Durability Silver Mirror Coating System
Authors: Hashimoto Satoru , Hirano Teruyoshi O. , Okitsu Osamu , Kim Tae-Youb , Maeda Shuichi
Published: September 2011

A high-quality silver mirror coating technology capable of offering various colors for the decoration of molding items is desirable. We have developed both chemical reagents and procedures for improving the silver mirror coating layers. Treatment A with a sodium thiosulfate aqueous solution is a cleaning process for the silver layers. Treatment B with a water-based solution of silane coupling agent is a process for improving the adhesion property of mirror coating layers. Both treatments improve the durability of the silver mirror coating.
Effect of Substrate Temperature on Hardness and Transparency of SiOC(–H) Thin Films Synthesized by Atmospheric Pressure Plasma Enhanced CVD Method
Authors: Noborisaka Mayui , Nagashima So , Hayashi Hidetaka , Ueda Naoharu , Kumagai Kyoko , Shirakura Akira , Suzuki Tetsuya
Published: September 2011

Silicon-based films have gained much interest as protective coatings for transparent polymeric materials. In this study, SiOC(–H) thin films were deposited on polycarbonate (PC) or Si substrates from trimethylsilane (TrMS) gas diluted with He gas by atmospheric pressure plasma enhanced CVD (AP-PECVD) method with varying substrate temperature, and transparency and hardness of the films were investigated. The films exhibited a good optical transparency with an optical transmittance of about 90% irrespective of the substrate temperature, and the hardness increased from 0.6 to 1.3 GPa as the substrate temperature increased from 60 to 140°C. The results are discussed in terms of chemical structural changes in the films according to the substrate temperature.
Improvement of the power conversion efficiency of polymeric solar cells based on P3HT:PCBM through interfacial modification
Authors: Zheng Shizhao , Deng Xianyu , Wong King Y.
Published: September 2011

We report the study of a process which enhances the power conversion efficiency (PCE) of solar cells employing poly(3-hexythiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM). In this process, the spin-coated solution of the active material was maintained in the liquid state for a prolonged duration. It was observed that through this process, the PCE of the device was enhanced by 31% for the case of a fast-grown film. It also provided a further 19% enhancement on top of the enhancement obtained by the familiar solvent annealing process. We found that this process depends critically on the presence of a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer. It is hypothesized that the action of this enhancement process involves the interfacial interactions between P3HT and PEDOT polymers.
Pt-CdS/TiO2 nanotube catalyst for photocatalytic reduction of CO2 with water under visible light irradiation
Authors: Yuan Jian , Zhang Chuanzhao , Li Caolong , Chen Mingxia , Shangguan Wenfeng
Published: September 2011

Titanate nanotube (TNT) was prepared by alkaline hydrothermal method starting from TiO2 (P25), and then CdS-TNT was prepared for visible light harvesting by immersing TNT in Cd(CH3COO)2 and then (NH2)2CS aqueous solutions subsequently and heat treated at specialtemperature. After loading with Pt, photocatalytic reduction of gas phase CO2 with water vapor was carried out under UV-VIS and visible light irradiation. The results showed that the main reaction products were CH4, C2H4, C2H6 and H2, which were online characterized by gaschromatography when the flow rate of 5000 ppm CO2 is 0.35 ml/min. The hydrogenation process also realized under visible light illumination for Pt-CdS/TNT and producted 0.44 μmol/min CH4. The maximum yield of methane reached about 130 μmol/min when Pt-CdS/TNTwas irradiated with UV-Vis light. The time profile for production yield increased steadily with time up to about 6–7 h, then a decrease of the reaction rate occurred. It is suggested that thadsorption of intermediate products CO, O2 etc. on Pt and the oxidation of Pt might be the reasons for the photocatalytic reaction deterioration.
Specific contact resistance of ohmic contacts to n-type SiC membranes
Authors: Mohd Nasir N.F. , Holland A.S. , Reeves G.K. , Leech P.W. , Collins A. , Tanner P.
Published: September 2011

Membranes of epitaxial SiC have been used as a means of eliminating the leakage current into the Si substrate during circular transmission line model (CTLM) measurements. In the n+-3C-SiC/Si wafers, the Si substrate was etched in a patterned window with dimensions up to 10 mm × 15 mm2. An array of CTLM metal contacts was then deposited onto the upper surface of the n+-SiC membrane. The CTLM contacts on the membrane have shown an ohmic current/voltage response while electrodes located on the adjacent substrate were non-ohmic. Values of ρc were measured directly on the membranes. These results have shown a significant increase in the current flow below the metal contacts due to the presence of the Si substrate.
Statistical Analysis of Nanoimpact Testing of Hard CrAl(Si)N Coatings
Authors: Mosquera A. , Mera L. , Fox-Rabinovich G.S. , Martínez A. , Azkona I. , Endrino J. L
Published: September 2011

Statistical studies involving the fracture behavior of coatings can play an important role in the mechanical analysis of films employed in the hard coating industry. In this study, Nanoimpact tests using a cube corner indenter were carried out in various CrAl(Si)N coatings for the quantitative assessment of properties of coatings like non-catastropic failure time and catastrophic failure time. These parameters decrease in value as silicon is incorporated in coatings, showing that this addition results in a decrease in ductility. Scanning electron microscope images were taken to the analyzed coatings exhibiting the residual imprints after nanoimpact test that were correlated with the fracture behavior of CrAl(Si)N coatings.
Scattering Under Shear: Alignment of a Disordered Bicontinuous Mesophase
Authors: Seddon Annela M. , Lötze Gudrun , Plivelic Tomás , Squires Adam M.
Published: September 2011

In this work we demonstrate that the application of shear to a disordered lyoptropic liquid phase formed by a biological lipid, monoolein formed in water and butanediol results in the formation of an aligned lamellar phase. Furthermore we show that if shear is applied to this disordered phase in the presence of additional water, an highly oriented inverse bicontinous cubic phase is created. We suggest that these two phase may have applications as biological models, as templates for nanostructured materials and in improved protein crystallization techniques.
Energy Harvesting Technology Development at DARPA
Authors: Greanya Viktoria , Daniell Cynthia , Nehl Colleen
Published: September 2011

Programs in the Defense Sciences Office (DSO) at the Defense Advanced Research Projects Agency (DARPA) bridge the gap from fundamental science to applications by identifying and pursuing the most promising ideas within the science and engineering research communities and transforming these ideas into new DoD capabilities. The Department of Defense (DoD) recognizes that our dependence on fossil fuel must be reduced and is actively supporting new technical solutions to this challenge. Moreover, advancements in alternative energy generation and storage technologies will render the warfighter more efficient, capable and mobile. Energy harvesting is a central pathway to solving this critical need. This paper will highlight two DARPA DSO programs which are making significant strides in the advancement in materials to improve energy harvesting technology with a focus on rapid transition to the end user. The Nanostructured Materials for Power (NMP) program is developing high performance thermoelectric materials and devices for energy harvesting with goals of energy conversion of 30%. The Low-Cost, Lightweight Portable Photovoltaics (PoP) program is developing integrated PV technologies with high power conversion efficiency (20%) in a form factor capable of being produced at low cost on flexible substrates. The paper will review the goals of the programs, discuss their implications, and highlight some of the research strategies underway.
Electron emission from deep traps in hydrogenated amorphous silicon and silicon-germanium: Meyer-Neldel behavior and ionization entropy
Authors: Long Qi , Dinca Steluta , Schiff Eric A. , Yan Baojie , Yang Jeff , Guha Subhendu
Published: September 2011

We have measured electron drift in amorphous silicon-germanium nip photodiodes using the photocarrier time-of-flight technique. The samples show electron deep-trapping shortly after photogeneration, which is generally attributed to capture by a neutral dangling bond (D0) to form a negatively charged center (D-). An unusual feature is that electron re-emission from the trap is also clearly seen in the transients. Temperature-dependent measurements on the emission yield an activation energy of about 0.8 eV and the remarkably large value of 1015 Hz for the emission prefactor frequency. We also compiled results on electron emission from deep traps in a-Si:H, a-SiGe:H, and a-SiC:H from six previous publications. Collectively, these measurements exhibit "Meyer Neldel" behavior for electron emission over a range of activation energies from 0.2–0.8 eV and a prefactor range extending over nine decades, from 106 to 1015 Hz. The Meyer-Neldel behavior is consistent with the predictions of the multi-excitation entropy model. We extract a ionization entropy of 20kB from the measurements, which is very large compared to crystal silicon. We discuss this result in terms of a bond charge model.
Amorphous Silicon Photosensors for Detection of Intrinsic Cell Fluorophores
Authors: Joskowiak A. , Chu V. , Prazeres D.M.F. , Conde J.P.
Published: September 2011

An amorphous silicon (a-Si:H) photoconductor array with two distinct integrated amorphous silicon carbon alloy (a-SiC:H) high pass filters is used to detect two of the cell intrinsic fluorophores. The cutoff wavelength of the filters is tuned by the carbon content in the film. The fluorophores of interest – reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are indicative of the redox state of the cells. Concentrations down to 1 μM for NADH and 50 μM for FAD were detected.
A Less Damaging Patterning Regime for a Successful Integration of Ultra Low-k Materials in Modern Nanoelectronic Devices
Authors: Zimmermann Sven , Ahner Nicole , Fischer Tobias , Schaller Matthias , Schulz Stefan E. , Gessner Thomas
Published: September 2011

This paper describes a three-step process regime for the integration of porous SiCOH based ultra low-k materials in existing copper damascene technologies. During the work with these complex and sensitive materials, it became more and more clear, that a successful patterning depends not only on the etch step but also on the adjustment between the etch and the following cleaning and k-restore processes. The presented process regime starts with a reactive ion etch process for trench patterning followed by a post etch clean to remove etch residues. Finally a k-restore process was performed to repair the damaged regions in the trench sidewalls. In this work it became clear, that the etch chemistry influences not only the results of the etch process ostensibly sidewall damage but also kind and effect of the post etch clean. Each plasma composition results in the necessity of a customized post etch cleaning solution. Finally a k-restore process using Hexamethyldisilazane (HMDS) as restore chemical was demonstrated successfully. Enhanced temperatures and an additional UV-treatment are possibilities to promote the restore effect.
Array of silicon field effect transistors to detect charges propagation in neurons circuit
Authors: Delacour C. , Bugnicourt G. , Bres G. , Crozes T. , Villard C.
Published: September 2011

We present transport properties of silicon nanowires field effect transistors realized on SOI substrates and their application to probe electrical activity of biological objects. Devices are sensitive to short and weak voltage pulses (ms, mV) applied in an electrolyte solution, allowing a future efficient detection of neuronal activity. For that purpose, the organized growth of neuronal cells along chosen patterns has been obtained, leading to an accurate coupling with silicon nanowire field effect transistors. Both network architectures, neural and semiconducting, have been designed to study some aspects of the propagation and the processing of information by the nervous system.
Electric field effect in amorphous semiconductor films assembled from transition-metal-encapsulating Si clusters
Authors: Uchida N. , Miyazaki T. , Matsushita Y. , Sameshima K. , Kanayama T.
Published: September 2011

We synthesized amorphous semiconductor films composed of Mo-encapsulating Si clusters (MoSin:n∼10) on solid substrates. The MoSi10films had Si networks similar to hydrogenated amorphous Si and an optical gap of 1.5 eV. Electron spin resonance signals were not observed in the films indicating that dangling bonds of Si were terminated by Mo atoms. We fabricated thin-film-transistors using the MoSi10film as a channel material. The electric field effect of the film was clearly observed. This suggests that the density of mid-gap states in the film is low enough for the field effect to occur.
Multifunctional Fiber Solar Cell Based on TiO2 Composite Materials
Authors: Rice Adam , Kim Seong-Ku , Tanaka Zuki , Phuyal Dibya , Yang Xuan , Gu Claire , Pei Qibing , Chen Bin
Published: September 2011

The paper present a multimode optical fiber based solar lighting and photovoltaic multifunctional device. TiO2, PbS and conducting polymer poly(3-hexylthiophene) (P3HT) were coated on the optical core surface as active photovoltaic layers, with ITO and LiF/Al electrodes. The guided sunlight in the multi-moded fiber was totally internal reflected depending on the incident angle and the evanescent light mode from scattered radiation of light was absorbed by the active layer to generate the electric current. The optical-electrical behaviors such as the short circuit current, filling factor, and open circuit voltage were studied. Furthermore, optical loss and the evanescent field at the interface between the optical fiber core and ITO electrode thin layer was discussed in relation to the coupling light from the guiding medium to the devices. Comparison studies of chemical and physical thin film coating on optical fibers are discussed. In particular, we obtained in situ growth of quantum dot, composite electrolyte and plasmonic enhancement on TiO2. We have demonstrated waveguide like fiber device with photo current measurements and I-V characterizations. Furthermore, we have optimized the device transmission of visible light through total internal reflection, and PV conversion of evanescent light absorbed by solar active composite materials fabricated around optical fibers.
Improvement in the Thermoelectric Figure-of-Merit of TAGS-85 by Rare Earth Additions
Authors: Cook B. A. , Harringa J. L. , Besser M. , Venkatasubramanian R.
Published: September 2011

TAGS-85 is a well-known thermoelectric material based on germanium monotelluride that exhibits a second-order displacive transformation from a high-temperature cubic to a low-temperature rhombohedral polymorph. Recent efforts to improve the thermoelectric figure-of-merit through the addition of small amounts of the rare earth elements Ce and Yb have demonstrated a 25 percent increase in ZT at 700K in materials obtained by solidification from the melt. Preliminary analysis by x-ray diffraction of the chemically-modified alloy suggests a partial stabilization of the high-temperature cubic polymorph. 125Te NMR studies confirm the incorporation of rare earth cations into the GeTe-based lattice. Solid state synthesis has been successfully applied to the processing of rare-earth-doped TAGS-85 and has resulted in a further increase in ZT beyond the levels initially observed in melt-solidified materials. This is believed to be due to improved homogeneity in the distribution of the lanthanide.
32nm Node Highly Reliable Cu/Low-k Integration Technology with CuMn Alloy Seed
Authors: Yao Shaoning , McGahay Vincent , Angyal Matthew S. , Simon Andrew H. , Lee Tom C. , Christiansen Cathryn , Li Baozhen , Chen Fen , McLaughlin Paul S. , Ogunsola Oluwafemi O. , Grunow Stephan
Published: September 2011

This paper introduces a highly reliable Cu interconnect technology at the 32 nm node with CuMn alloy seed. A CuMn alloy liner seed process combined with a non-gouging liner has been integrated into the minimum-pitch wiring level. Stress migration fails with CuMn seed at plate-below-via structures were shut down by a non-gouging liner process. Integration with gouging liner and non-gouging liner is compared, and results of interaction with CuMn seed are discussed in this paper.
Comparison of TiN thin films grown on SiO2 by reactive dc magnetron sputtering and high power impulse magnetron sputtering
Authors: Magnus F. , Ingason A. S. , Sveinsson O. B. , Olafsson S. , Gudmundsson J. T.
Published: September 2011

Thin TiN films were grown on SiO2 by a reactive dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) at range of temperatures from 45 to 600oC and the properties compared. The HiPIMS process produces denser films at lower growth temperature than does dcMS and the surface is much smoother for films grown by the HiPIMS process. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films. The [200] crystallites have smaller size than the [111] crystallites for all growth temperatures. For the dcMS process the grain size increases with increased growth temperature for both the [111] and [200] crystallites. For the HiPIMS process the [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for growth temperature of 400 oC after which it starts to increase with growth temperature.
Microbump Impact on Reliability and Performance in Through-Silicon Via Stacks
Authors: Karmarkar Aditya P. , Xu Xiaopeng
Published: September 2011

The impact of microbump geometry, layout and underfill material properties on the device performance as well as the structural reliability is examined. Numerical simulations reveal that the magnitude of n-type carrier mobility change correlates with the increase in the underfill CTE and modulus as well as microbump pitch and height, but the decrease in the microbump radius. The crack driving force dependence on material property and geometry differs from that of mobility change. While the driving force is crack location dependent, the greater crack driving force corresponds to larger underfill CTE and bump radius, but smaller underfill modulus and microbump pitch.
Low-cost Micro- and Nano-structures in Porous Nanomaterials Realized by Direct Imprinting of Porous Substrates
Authors: Ryckman Judson D. , Liscidini Marco , Sipe J. E. , Weiss S. M.
Published: September 2011

We present a simple one-step methodology for direct structuring of porous nanomaterials on the micro- and nano-scale. Our technique, direct imprinting of porous substrates (DIPS), relies on the application of a pre-patterned and reusable stamp to directly imprint porous substrates. DIPS is performed at room temperature and pressure in less than one minute, and circumvents the conventional requirement for resist processing and etching procedures. It is shown that arbitrarily shaped patterns and structures can be transferred to porous nanomaterials with a very high (sub-100nm) feature resolution that is primarily limited by the pore dimensions of the substrate material. DIPS is demonstrated on a wide variety of porous nanomaterials including metals, semiconductors, and insulators. Furthermore, DIPS can be utilized to locally modify material properties including pore dimensions, density, dielectric function, and surface roughness. Lastly, example structures fabricated by DIPS are discussed for their relevance to important applications ranging from drug delivery and imaging, to solar energy conversion, and biosensing.
Folding Graphene with Swift Heavy Ions
Authors: Akcöltekin Sevilay , Bukowska Hanna , Akcöltekin Ender , Lebius Henning , Schleberger Marika
Published: September 2011

Swift heavy ion induced modifications on graphene were investigated by means of atomic force microscopy and Raman spectroscopy. For the experiment graphene was exfoliated onto different substrates (SrTiO3 (100), TiO2(100), Al2O3(1102) and 90 nm SiO2/Si) by the standard technique. After irradiation with heavy ions of 93 MeV kinetic energy and under glancing angles of incidence, characteristic folding structures are observed. The folding patterns on crystalline substrates are generally larger and are created with a higher efficiency than on the amorphous SiO2. This difference is attributed to the relatively large distance between graphene and SiO2 of d ≈ 1 nm.
Improved Hole Collection in Polymer Heterojunction Solar Cells with DNA/Pt-DNA Layers
Authors: Guvenc Ali Bilge , Guo Shirui , Ozkan Cengiz S. , Ozkan Mihrimah
Published: September 2011

In this study, we investigated the effects of DNA/Pt-DNA strands as hole collecting layers in polymer heterojunction solar cells based on ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al structure. We demonstrated that by introducing DNA or Pt-DNA layers between the polymer electrode (PEDOT:PSS) and the active layer (P3HT:PCBM), lead to an improvement in the hole collection efficiency and power conversion efficiency and the absorbance spectra of the devices indicate that Pt particles work as surface plasmons and increase the absorbance of the devices.
Synthesis and Characterization of Rare Earth (Tb3+ and Yb3+) Doped CdS/ZnS Core/Shell Nanocrystals for Enhanced Photovoltaic Efficiency
Authors: Das Sandip , Mandal Krishna C.
Published: September 2011

CdS host nanocrystals with 4.2-5.5 nm in diameter have been synthesized from air stable precursors via a synthetic chemical route and doped with rare earth (RE) terbium (Tb3+) and ytterbium (Yb3+) ions. RE3+-doped CdS cores were shelled by ZnS layers of different thicknesses. The resulting core/shell nanocrystals show a complete broadband absorption below 400-460 nm to the deep UV region depending on the size of the cores. RE3+-doped CdS nanocrystals showed a red shift in the emission as observed under irradiation of 302 nm UV light and was confirmed by room temperature photoluminescence (PL) measurements. The nanocrystals were further characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX) analysis. The results show that these RE3+-doped nanocrystals can be used as solar spectral matching downconversion material to enhance photovoltaic efficiency of existing solar cells.
Advanced Optical Modeling of Thin-film Silicon Solar Cells with 1-D Periodic Gratings.
Authors: Solntsev S. , Isabella O. , Caratelli D. , Kyriakou M. , Yarovyi O. , Zeman M.
Published: September 2011

Design of one-dimensional periodic gratings is investigated for enhancing the light absorption in thin-film silicon solar cells due to scattering at rough interfaces that are introduced into solar cells by the gratings. A rigorous full-wave analysis is carried out in order to determine the optical properties of amorphous and microcrystalline silicon solar cells in PIN and NIP configurations, respectively. Optimal geometrical parameters of 1-D gratings for maximizing photocurrent density in thin-film silicon solar cells are determined.
The Dye Sensitized Solar Cell Stability and Performance Study Using Different Electrolytes
Authors: Radhakrishnan Sailaja , Munukutla Lakshmi V. , Htun Aung , Kannan Arunachalanadar M.
Published: September 2011

The overarching goal of Dye Sensitized Solar Cells (DSSCs) is to improve photovoltaic performance and their long-term stability for use in practical applications because of their simple fabrication technology at a reasonable cost. The focus of this paper is to achieve cell stability and also to improve solar energy conversion efficiency experimenting with different electrolytes. The electrolyte’s role is critical to sustain the DSS cell performance over time to instill cell stability. Four different electrolytes, Iodolyte R-150, AN-50, PN-50 and MPN-100, are experimented in this work for fabricating the dye-sensitized solar cells for studying both the stability and efficiency of the DSSCs.

The electrolyte selection was made using the following key electrolyte parameters; lower viscosity for easier injection into the cell, lower vapor pressure and higher boiling point to minimize electrolyte evaporation, wide redox window to generate sufficient donating electrons to the dye, lower cost and non-toxicity. Electrolytes with higher concentration of Iodolyte were chosen for this study to widen redox potential window. These are Iodide based redox electrolytes and are made with 100 mM of tri-iodide in 3-methoxypropionitrile. The results of this investigation revealed that the cell with Iodolyte R-150 electrolyte achieved improved performance having an efficiency of 10.2% when compared to the reference cell efficiency of 8.4% with Iodolyte R-50. These cells were stabilized over a time of 4 weeks. The fill factor of the cell changed about 10% and the internal resistance decreased from 6.7 to 4.3 Ω. The results of this experiment demonstrated reduced internal resistance, and improved fill factor contributed to higher cell efficiency and stability. The results of the work presented in this paper support the argument that electrolytes with higher Iodolyte concentration can enhance the cell efficiency and stability along with scaling down of the cell size.
Mesophase ordering and structuring of porous titanium dioxide with high surface area and strong light harvesting matrix for dye-sensitized solar cell
Authors: Ho Ghim W. , Agarwala Shweta , Kevin Moe
Published: September 2011

Dye sensitized solar cells (DSSC) are attractive because they hold promise for devices that are easy to fabricate and inexpensive. In the present work, highly crystalline mesoporous TiO2 has been synthesized by evaporation induced self assembly (EISA) method using triblock copolymer Pluronic P123 as the organic template. The synthesized TiO2 is anatase in nature with a pore size of 10-15 nm. DSSC made from mesoporous TiO2 demonstrated solar conversion efficiency of ∼7%. This comes from the benefits of increased surface roughness, surface area and uniform porosity. In addition, well ordered and crystalline pores provided good sunlight absorption and low recombination path for charge carriers. To further enhance the efficiency of the DSSCs, light scattering centers were introduced in the mesoporous TiO2 film. Nanoparticles light scatterers are introduced to scatter the incoming light and hence to increase the light harvesting capability of the device. A 26 % increase in DSSC efficiency was observed with the implementation of scattering centers.
Structure and Stability of Olivine Phase FePO4
Authors: Nolis Gene M. , Chernova Natalya A. , Upreti Shailesh , Whittingham M. Stanley
Published: September 2011

LiFePO4 has shown considerable promise as a cathode material in Li-ion batteries due to its stability, low toxicity and high cyclability. However, the data on thermodynamic stability of olivine phase FePO4 (o-FePO4), the delithiated form of o-LiFePO4, remains scarce and contradictory. In this work, o-FePO4 was synthesized by chemical delithiation of o-LiFePO4 and characterized structurally and thermally. X-ray diffraction and absorption data indicate pure olivine phase, but with residual amount of Fe2+, most likely due to incomplete delithiation. Differential scanning calorimetry and thermal gravimetric analysis reveal that o-LixFePO4 decomposes exothermally above 550 °C with about 9% weight loss, the products being trigonal phase FePO4, Fe7(PO4)6, and LiPO3.
Structural and magnetic properties on F-doped LiVO2 with two-dimensional triangular lattice
Authors: Li Yang , Li Xiaoxiang , Liu Lihua , Chen Ning , García Jose , Dávila Rafael , Faica Danny , Rivera Alfred , Rodríguez Pedro , Pérez Rubén , Cao Guohui
Published: September 2011

The layered oxide LiVO2 recently has received more attention due to its interesting structural and magnetic behaviors involving the two-dimensional magnetic frustration in these systems. We synthesized a series of F-doped LiVO2 samples, and reported the F-doping effect on the structure and transition temperature Tt. The samples LiVO2-xFx (x=0, 0.1, 0.2 and 0.3) were characterized by X-ray diffraction, scanning electron microscope (SEM), differential scanning calorimetry (DSC), magnetic susceptibility and specific heat measurement. The structural analysis shows that with increasing x, the ratio of lattice parameter c/a increasing, i.e. in the a-b plane the lattice is compressed while in the c-axis direction the lattice expands. The DSC measurements show that a first-order phase transition happens at around 500 K, and the thermal hysteresis around phase transition temperature Tt increases with increasing x. Substitution of O with F ions results in a change of two dimensional characteristics and the distortion of the VO6 block in structure, which significantly influence the magnetic ordering transition temperature Tt.
Graphene Oxide as a Two-dimensional Surfactant
Authors: Koltonow Andrew R. , Kim Jaemyung , Cote Laura J. , Luo Jiayan , Huang Jiaxing
Published: September 2011

Graphene oxide (GO) is a nonstoichiometric two-dimensional material obtained from the chemical oxidation and exfoliation of graphite, which has recently attracted intense research interest as a precursor for bulk production of graphene. GO has long been believed to be hydrophilic due to its dispersibility in water. Recent work in our group, however, has found that GO is actually a two-dimensional amphiphile; the edge of the sheet-like material is hydrophilic, while the basal plane of the material contains more hydrophobic graphitic nanodomains. To prove the concept, we demonstrate GO’s surface activity at an air-water interface, as well as its utility in dispersing insoluble aromatic materials such as toluene, graphite, and carbon nanotubes in water. As a colloidal surfactant which can be converted to a conducting material, GO presents unique possibilities for aqueous solution processing of organic electronic materials.
Patterning biopolymer surfaces by enzymatic soft lithography
Authors: Guyomard-Lack A. , Moreau C. , Delorme N. , Bardeau J.-F. , Cathala B.
Published: September 2011

A novel rapid and easy-to-use method for patterning surfaces on large scale is described. Micro-patterns were created by direct contact of trypsin-functionalized poly(dimethylsiloxane) (PDMS) stamps with poly-L-lysine (PLL) layer adsorbed on silicon surface. The catalytic process does not involve ink transfer and thus lateral diffusion is avoided. As a result duplication of the stamp pattern is highly enhanced comparatively to standard microcontact printing procedure where PLL is used as ink and transferred on silicon surface. Patterning was revealed by fluorescence microscopy and atomic force microscopy (AFM). Adsorption on the patterned surfaces of cellulose nanocrystals was investigated as an example of application.
Microwave Volumetric Probe Measurements of Field localization, Zero and Negative Index within Photonic Bandgap Metamaterial Structures
Authors: Kuster Eric , Moore Ricky L. , Blalock Stephen , Cieszynski Brian , Swarner John , Habib Matthew
Published: September 2011

Electromagnetic mode localization within photonic bandgap (PBG) crystals has been evidenced by external measurement of enhanced optical emission from quantum dots or photoemissive polymers that are placed within the structure. In this paper wavelength is decreased and photonic crystal dimensions increased to allow insertion of a loop probe in the PBG to directly measure volumetric electromagnetic fields; thereby producing a volume -frequency map of field amplitude and phase within the PBG. The unit cells of the PBG are formed from arrays of Alumina strips which are supported by surrounding acrylic supports. Electromagnetic fields of single, two and three layer PBGs are predicted and these compare well with measurement.

Field localization within the PBG and transmission coefficients of the PBG, with and without electrical perturbations, are presented. Predictions assume layered unit cells formed from sections in which translational invariance along the Z-axis is assumed for zn-1 ≤ z ≤ zn for the nth section. Periodicity implies that field X dependence can be represented as a sum of Floquet modes and field solutions are found by mode matching techniques in combination with multimode cascade matrix formalism.

Transmission coefficient is measured using a focused beam, network analyzer based system and volumetric fields within the PBG are measured using a loop probe antenna inserted between Alumina strips and moved to different positions. Measurements at 1600 frequencies over the 4-18 GHz band at each of 100 positions are made. PBG fields are calibrated to probe measurements at identical positions and frequencies but absent the PBG.

Both electromagnetic model and measurement shows field localization and effective negative or zero indexes at multiple frequencies within the 4 to 18 GHz band. Volumetric field magnitudes increase by at least one order of magnitude and local field phase-frequency derivatives are negative or near zero near localization frequencies. Field localizations and transmission are sensitive to small perturbations of electrical properties or geometry. Wideband measurements of PBGs, perturbed by small cylindrical inserts placed at high field locations, allow precision measurements of an insert’s electromagnetic properties.
Data Mining-Aided Crystal Engineering for the Design of Transparent Conducting Oxides
Authors: Suh Changwon , Kim Kwiseon , Berry Joseph J. , Lee Jinsuk , Jones Wesley B.
Published: September 2011

The purpose of this paper is to accelerate the pace of material discovery processes by systematically visualizing the huge search space that conventionally needs to be explored. To this end, we demonstrate not only the use of empirical- or crystal chemistry-based physical intuition for decision-making, but also to utilize knowledge-based data mining methodologies in the context of finding p-type delafossite transparent conducting oxides (TCOs). We report on examples using high-dimensional visualizations such as radial visualization combined with machine learning algorithms such as k-nearest neighbor algorithm (k-NN) to better define and visualize the search space (i.e. structure maps) of functional materials design. The vital role of search space generated from these approaches is discussed in the context of crystal chemistry of delafossite crystal structure.
A Structural and Electrochemical Study of Li2Ti6O13
Authors: Pérez-Flores J. C. , Kuhn A. , García-Alvarado F.
Published: September 2011

The lithium titanate Li2Ti6O13 has been prepared from Na2Ti6O13 by Li ion exchange in molten LiNO3 at 325ºC. Chemical analysis and powder X-ray diffraction study of the reaction product, respectively, indicate that total Na/Li exchange takes place and the Ti-O framework of the Na2Ti6O13 parent structure is kept under those experimental conditions. The electrochemical characterization shows that Li2Ti6O13 is able to insert ca. 5 Li per formula unit under equilibrium conditions in the voltage range 1.5-1.0 V vs. Li+/Li. This corresponds to a specific discharge capacity of 250 mAh g-1. Lithium insertion occurs at an average equilibrium voltage of 1.5 V which is typical for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. After the first redox cycle a high reversible capacity is obtained (ca. 160 mAh g-1 at C/12, with a 70% capacity retention related to a phase transformation upon cycling). On the basis of these results, we are proposing Li2Ti6O13 as new lithium battery anode material to be further investigated.
ELABORATION AND CHARACTERIZATION OF La4Ni3O10 CATHODE MATERIAL (SOFC) BY SOL-GEL PROCESS
Authors: Cienfuegos Rene Fabian , Guerrero Leonardo Chávez , Carranza Sugeheidy , Jouanin Laurie , Marie Guillaume , Hinojosa Moisés
Published: September 2011

The goal in this study was to synthesize a lanthanum - nickel phase (Ruddlesden-Popper phases) La4Ni3O10. This material was prepared using a polymeric route. An easy synthesis method is presented in order to obtain an economical cathode material, which can be used in Solid Oxide Fuel Cells (SOFC). The polymeric precursors were prepared following the Castillo method. The originality of this work was to optimize the ratio HMTA/ metallic salts from 1 to 6. The obtained powders were characterized by thermal analysis; Differential Scanning Calorimetry (DSC Q10 Instrument TA), Thermogravimetric Analysis (TGA - Q50 Instrument TA-) and X-ray diffractometer (Bruker, D8 Advance diffractometer), in order to determine the crystallized phase. Experiments 5 and 6 did not present coagulation but after few days, solution 5 was transformed into a gel. Gels 2 to 5 were heated in order to obtain a solid material. These powders are characterized by thermogravimetric and thermo-differential methods. The powders obtained at 800, 900 and 1000°C were analyzed by X-ray diffraction and it was found that the temperature to get to the La4Ni3O10 phase was 1000ºC.
Band Gap Opening of Graphene after UV/Ozone and Oxygen Plasma Treatments
Authors: Aria Adrianus I. , Gani Adi W. , Gharib Morteza
Published: September 2011

Graphene grown by Chemical Vapor Deposition (CVD) on nickel subsrate is oxidized by means of oxygen plasma and UV/Ozone treatments to introduce bandgap opening in graphene. The degree of band gap opening is proportional to the degree of oxidation on the graphene. This result is analyzed and confirmed by Scanning Tunnelling Microscopy/Spectroscopy and Raman spectroscopy measurements. Compared to conventional wet-oxidation methods, oxygen plasma and UV/Ozone treatments do not require harsh chemicals to perform, allow faster oxidation rates, and enable site-specific oxidation. These features make oxygen plasma and UV/Ozone treatments ideal candidates to be implemented in high-throughput fabrication of graphene-based microelectronics.
Nonlinear Mechanical Properties of Graphene Nanoribbons
Authors: Lu Qiang , Huang Rui
Published: September 2011

Based on atomistic simulations, the nonlinear elastic properties of monolayer graphene nanoribbons under quasistatic uniaxial tension are predicted, emphasizing the effect of edge structures (armchair and zigzag, without and with hydrogen passivation). The results of atomistic simulations are interpreted using a theoretical model of thermodynamics, which enables determination of the nonlinear functions for the strain-dependent edge energy and the hydrogen adsorption energy, for both zigzag and armchair edges. Due to the edge effects, the initial Young’s modulus of graphene nanoribbons under infinitesimal strain varies with the edge chirality and the ribbon width. Furthermore, it is found that the nominal strain to fracture is considerably lower for armchair graphene nanoribbons than for zigzag ribbons. Two distinct fracture mechanisms are identified, with homogeneous nucleation for zigzag ribbons and edge-controlled heterogeneous nucleation for armchair ribbons.
A Novel Method for Sorting Single Wall Carbon Nanotubes by Length
Authors: Ohmori Shigekazu , Saito Takeshi , Shukla Bikau , Yumura Motoo , Iijima Sumio
Published: September 2011

We report a novel system for sorting single wall carbon nanotubes (SWCNTs) by length via cross-flow filtration with three membrane filters of different pore sizes, 1.0, 0.45, and 0.2 μm. SWCNTs dispersed in water with the help of polymer type detergents, such as sodium carboxymethylcellulose (CMC) and polyoxyethylene stearyl ether (Brij 700), were successfully fractionated into four samples, and the atomic force microscopy (AFM) observation of those samples confirmed that their length distribution peaks are within the expected ranges from pore sizes of used filters. However, the result of the similar filtration process using a non-polymer detergent, sodium dodecylbenzenesulfonate (SDBS), showed no pronounced correlation between the length distribution of SWCNTs and the pore size. The observed difference in the sorting phenomena caused by the detergent type suggests that the permeation property depends on the complex structure resulting from the dispersed SWCNTs and detergent molecules.
Ultrafast Switching Liquid Crystals for Electro-Optic Transmissive and Reflective Displays and Microscopic Lasers
Authors: Coles Harry J , Morris Stephen M , Castles Flynn , Hands Philip J W , Wilkinson Timothy D , Choi Su Soek
Published: September 2011

We report on novel liquid crystals with extremely large flexoelectric coefficients in a range of ultra-fast photonic modes, namely 1) the uniform lying helix, that leads to in-plain switching, birefringence phase devices with 100 μs switching times at low fields, i.e.2-5 V/μm, and analogue or grey scale capability, 2) the uniform standing helix, using planar surface alignment and in-plane fields, with sub ms response times and optical contrasts in excess of 5000:1 with a perfect optically isotropic or black “off state”, 3) the wide temperature range blue phase that leads to field controlled reflective color, 4) chiral nematic optical reflectors electric field tunable over a wide wavelength range and 5) high slope efficiency, wide wavelength range tunable narrow linewidth microscopic liquid crystal lasers.
Rewritable Photopatterning of a Bisanthracene-Functionalized Mesogenic Compound by Photodimerization and Thermal Back-Reaction of the Anthracene Moiety
Authors: Kihara Hideyuki , Motohashi Masashi , Matsumua Kazunari , Yoshida Masaru
Published: September 2011

A new method for photopatterning of a bisanthracene-functionalized mesogenic compound 1 was developed. The monomer 1 had two anthracene moieties on each molecular end, and showed crystalline and liquid-crystalline phases at room temperature and at an elevated temperature, respectively. Upon UV irradiation of 1 in the molten state, intermolecular photodimerization of the anthracene moieties was induced, and consequently resulted in the formation of a linear polymer. In contrast to the monomer 1, the obtained polymer exhibited amorphous phase at room temperature. When 1 was irradiated with UV light through a photomask in the molten state, the irradiated areas changed to amorphous phase due to photopolymerization, whereas the non-irradiated areas remained the ordered phase. This phenomenon provided visual images with a clear contrast under polarized light. In addition, the images could be erased by heating the whole sample at a temperature above ca. 200 °C, because the amorphous phase changed to the ordered phase due to a reproduction of the monomer 1 from the polymer associated with thermal back-reaction of the anthracene photodimer. Photopatterning could be performed for the erased sample again and the process was found to be fairly reversible.
PZT Thick Films for 100 MHz Ultrasonic Transducers Fabricated Using Chemical Solution Deposition Process
Authors: Kochi Naoto , Iijima Takashi , Nakajima Takashi , Okamura Soichiro
Published: September 2011

To achieve ultrasonic transducers operating above 100 MHz, square pillar shaped Pb1.1(Zr0.53Ti0.47)O3 thick film structures were fabricated using a chemical solution deposition (CSD) process. The fabricated sample showed well-saturated P-E hysteresis curve and butterfly-shaped longitudinal displacement curve. The fabricated samples generated more than 100 MHz ultrasonic waves with a pulser/receiver. Electrical impedance properties of the samples were measured with an impedance analyzer. A number of spurious resonant modes were observed in the frequency range from 40 to 300 MHz. The characteristics of the sample were investigated by finite element method (FEM). The FEM simulations were in good agreement with the experimental results. For free-standing (substrate free) 10-μm-thick PZT film models, the resonant frequency of the thickness vibration mode was estimated to be 160 MHz with the FEM simulations. These results indicate that the substrate affects the behavior of the spurious resonant modes. Therefore, a sample structure was designed using the FEM simulation. The FEM result suggests that the backside of the substrate should be removed to reduce the substrate effects. Consequently, the thickness vibration mode was observed clearly at 160 MHz. This structure is applicable to the micromachined ultrasonic transducers (MUT) operating in the thickness vibration mode above 100 MHz.
Reliability and stability of thin-film amorphous silicon MEMS on glass substrates
Authors: Sousa P. M. , Chu V. , Conde J. P.
Published: September 2011

In this work, we present a reliability and stability study of doped hydrogenated amorphous silicon (n+-a-Si:H) thin-film silicon MEMS resonators. The n+-a-Si:H structural material was deposited using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) and processed using surface micromachining at a maximum deposition temperature of 110 ºC. n+-a-Si:H resonant bridges can withstand the industry standard of 1011 cycles at high load with no structural damage. Tests performed up to 3x1011 cycles showed a negligible level of degradation in Q during the entire cycling period which in addition shows the high stability of the resonator. In measurements both in vacuum and in air a resonance frequency shift which is proportional to the number of cycles is established. This shift is between 0.1 and 0.4%/1x1011 cycles depending on the applied VDC. When following the resonance frequency in vacuum during cyclic loading, desorption of air molecules from the resonator surface is responsible for an initial higher resonance frequency shift before the linear dependence is established.
Ultrafast Laser Alignment and Processing of Carbon Nanotube Films
Authors: Murphy Ryan D. , Abere Michael J. , Zhang Huanan , Sun Haiping , Torralva Ben , Mansfield John F. , Kotov Nick , Yalisove Steven M.
Published: September 2011

Organized nanostructures are formed after irradiation of layers of randomly aligned single-wall carbon nanotube (SWNT)-polymer composites by a Ti:Sapphire 775 nm laser with a 150 fs pulse at fluences near 0.1 J/cm2. At varying peak fluences morphology is seen where the tubes are ejected from the substrate or formed into long, parallel structures of SWNT’s. These structures have been created on both glass substrates and carbon grids. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) investigation of the structures reveal that they are composed of bundled nanotubes typically 400 nm – 1 micron long. Large-area laser patterning of the film allows for structuring of the film without detrimental decreases in conductivity.