bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of Nanocarbon-Supported Titanium Dioxide
Authors: Worsley Marcus A , Kuntz Joshua D. , Cervantes Octavio , Han T Yong-Jin , Pauzauskie Peter , Satcher Joe H , Baumann Theodore F
Published: August 2010

In this report, we describe recent efforts in fabricating new nanocarbon-supported titanium dioxide structures that exhibit high surface area and improved electrical conductivity. Nanocarbons consisting of single-walled carbon nanotubes and carbon aerogel nanoparticles were used to support titanium dioxide particles and produce monoliths with densities as low as 80 mg/cm 3. The electrical conductivity of the nanocarbon-supported titanium dioxide was dictated by the conductivity of the nanocarbon support while the pore structure was dominated by the titanium dioxide aerogel particles. The conductivity of the monoliths presented here was 72 S/m and the surface area was 203 m2/g.
Trends of Nanoclusters' Growth by Physical Vapor Deposition Studied by Atomistic Simulation
Authors: Bhuiyan Abuhanif , Dew Steven K. , Stepanova Maria
Published: August 2010

Efficient methodologies for synthesis of nanocrystals (NC) are a crucial component for creation of nanostructured electronic components. Physical vapor deposition (PVD) is one of the most flexible techniques to fabricate self-assembled arrangements of nanoclusters. Controllable fabrication of such assemblies can improve reliability of nanocapacitors, enhance performance of magnetic memories, and has many applications in opto-electronics devices, etc. However, size, shape and density of nanocrystals are highly sensitive to the process conditions such as duration of deposition, temperature, substrate material, etc. To efficiently synthesize nanocrystalline arrays by PVD, the process control factors should be understood in greater detail. In this work, we present a kinetic Monte Carlo (KMC) model and report simulations that explicitly represent the PVD synthesis of nanocrystals on substrates. Here we study how varying the most important process parameters affects the morphologies of self-assembled metallic islands on substrates. We compare our results with experimentally observed surface morphologies generated by PVD and demonstrate that KMC models like this are an efficient tool for computer-aided design of PVD processes for synthesis of nanocrystals.
Combined AFM-SEM for mechanical testing of fibrous biological materials
Authors: Hang Fei , Lu Dun , Barber Asa H
Published: August 2010

A technique combining both atomic force microscopy (AFM) and scanning electron microscopy (SEM) is used to evaluate the mechanical properties of individual collagen fibrils from the fractured surface of antler. SEM is used to locate individual mineralized collagen fibrils and allow visualization of the attachment of these fibrils to the end of an AFM probe. Tensile testing of individual collagen fibril to failure was performed using the AFM with resultant stress-strain curves obtained. Tensile strengths of up to 0.18GPa are found for some individual collagen fibrils, indicating the presence of mineral in improving mechanical performance. Consideration of the SEM operating parameters indicates that the amount of time the sample is within the SEM vacuum can affect the resultant mechanical behavior of individual fibrils.
The Role of the Organic Component in the Mechanical Behavior of Biomineralized Composites
Authors: Mayer George , Zhou Jason
Published: August 2010

The roles of minor organic layers in influencing the mechanical response of such biomineralized composites as mollusk shells and sponge spicules have been investigated. The mechanisms whereby such minor constituents govern energy dissipation in rigid biomineralized structures are discussed, and a rationale for new modes of toughening that may relate more generally to families of ceramic- or glass/organic composites is offered. New results of simple torsional tests conducted on spicule fibers of a hexactinellid sponge, Euplectella aspergillum (Euplectella a.), compared with those done on melt-drawn glass fibers, showed an enhanced ability to resist failure in torsion, whereas the glass fibers did not. This behavior was attributed to the presence of a very thin adhesive viscoelastic phase between the siliceous layers of the spicule fibers, combined with the architectural and surface features of the spicule fiber.
Epitaxial Growth of Highly Crystallized InSb films on Si Substrate by MBE and Their Devices Properties
Authors: Kunimi Yoshihisa , Fujita Hiromi , Sakurai Ayano , Akiyama Shinichiro , Miyahara Masatoshi , Shibata Yoshihiko
Published: August 2010

High crystallized thin InSb epitaxial growth directly on Si substrate was investigated by molecular-beam epitaxy (MBE). Experimental results indicated that suppressing the desorption of hydrogen atoms which terminated the dangling bonds of Si wafer surface and incorporation of As around the interface between film and Si substrate were the most important to obtained high crystallized InSb film. It could be achieved by the irradiation of As4 cluster beam onto the Si wafer just before film growth. Obtained thin InSb film showed mirror like surface, and its thickness was 0.7 μm. Its electron mobility was 47,600 cm2/V-s, and FWHM of HR-XRD rocking curve was about 300 arcsec. This InSb film on Si wafer was applied to Hall element, and it passed ordinary reliability tests.
Mechanical Sintering Techniques for Printed Electrodes with Various Work-function on a Plastic Substrate
Authors: Yoshida Manabu , Suemori Kouji , Uemura Sei , Hoshino Satoshi , Takada Noriyuki , Kodzasa Takehito , Kamata Toshihide
Published: August 2010

A print technique of an electrode on a plastic substrate is one of the most important techniques for developing a printed large area device. Especially, preparation of a metal electrode with low work function by printing is very important to develop printed active devices such as diode and transistors. Work function values of electrodes strongly affect device properties (1,2), because the work function difference between a semiconductor and an electrode is related to charge injection from the electrode to the semiconductor. Recently, many solution-processable n-type semiconductors have been developed (3), because these are required to fabricate printable EL devices, printable CMOS devices, and so on. Low-work function metals are necessary to inject electrons to n-type semiconductor. In spite of this fact, very few printable low-work function metal inks have been developed, because low-work function metals are easily oxidized during print process owing to high temperature annealing treatment and their conductivities are lost.

In this study, we have examined to develop a new annealing technique on a printed electrode to reduce the process temperature during metal printing. We have newly developed a mechanical sintering technique in which mechanical forces is applied on a printed metal pattern. Control of the direction balance of applied mechanical force was effective to reduce resistivity of the printed metal without any destruction of plastic substrate. Furthermore, distribution control of metal particle in the metal ink was also effective to reduce resistivity. By using this technique, we have succeeded in the preparation of an aluminum, zinc, copper and tin electrode on a plastic substrate. On the other hand, we have tried to prepare a metal alloy ink to control the work function of printed electrode. Metal alloy ink was composed of two kinds of metal particles. Work function of the electrode was controlled by changing composition of these metal contents in an alloy ink. By applying our developed mechanical sintering technique on the printed alloy pattern, printed electrode with various work functions from 3.5eV to 5eV could be prepared on a plastic substrate. These printed alloys were effective to improve the performance of printed diode and transistors.
Manipulation of Room Temperature Ferromagnetic behavior of GaMnN Epilayers
Authors: Nepal Neeraj , Luen M. Oliver , Frajtag Pavel , Zavada John , Bedair Salah M. , El-Masry Nadia
Published: August 2010

We report on metal organic chemical vapor deposition growth of GaMnN/p-GaN/n-GaN multilayer structures and manipulation of room temperature (RT) ferromagnetism (FM) in a GaMnN layer. The GaMnN layer was grown on top of a n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. Ms was almost doubled after annealing demonstrating that the FM observed in GaMnN film is carrier-mediated. To control the hole concentration of the p-GaN layer by depletion, GaMnN/p-GaN/n-GaN multilayer structures of different p-GaN thickness (Xp) were grown on sapphire substrates. We have demonstrated that the FM depends on the Xp and the applied bias to the GaN p-n junction. The FM of these multilayer is independent on the top GaMnN layer thickness (tGaMnN) for tGaMnN >200 nm and decreases for tGaMnN < 200 nm. Thus the room temperature FM of GaMnN i-p-n structure can also be controlled by changing Xp and tGaMnN in the GaMnN i-p-n structures.
Pulsed Laser Deposition as a Novel Growth Technique of Multiferroic LuFe2O4 Thin Films
Authors: Rejman Jason , Dhakal Tara , Mukherjee Pritish , Srikanth Hariharan , Witanachchi Sarath
Published: August 2010

Growth of polycrystalline Lutetium Iron Oxide via pulsed laser deposition in thin film form is reported for the first time herein, and the multiferroic LuFe2O4 phase is stabilized. Fluence and pressure dependent phase growth is demonstrated, along with crystalline structure in vacuum (˜10-5 torr) conditions. Thermodynamic considerations at the laser-target interaction were investigated, as well as at the plume-substrate interface, which reveal that the necessary Gibbs free energy is available in the optimized growth environment to allow formation of the LuFe2O4 polycrystalline phase. The resulting growth rate is found to be related to the Gibbs free energy and concentration of nucleation sites on the substrate. Characterization of the multiferroic aspect of LuFe2O4 entailed direct measurement of the ferroelectricity in the thin film, as well as magnetic behavior, both at various temperatures. In particular, the ferroelectric polarization vs. voltage data yield values of 0.61 μC/cm2 at 300 K to 3.29 μC/cm2 at 183 K; moreover, these data are in agreement with those reported in the literature. Magnetization vs. applied field data shows the magnetization at 300 K to be 180 emu/cm3 and increasing to 200 emu/cm3 at 10 K.
Structural Characterization of Cu2+Functional Centers In ‘Lead-Free’ KNN Piezoelectrics
Authors: Erünal Ebru , Eichel Rüdiger-A. , Acker Jerome , Kungl Hans , Hoffmann Michael J.
Published: August 2010

The alkali niobate ferroelectrics ((K0.5Na0.5)NbO3, KNN) are promising candidates as alternatives for PZT (Pb(ZrxTi(1-x))O3) ceramics in piezoelectric technologies. In order to obtain dense compounds with desirable properties, CuO has been used as sintering aid. In this work, the defect chemistry of Cu2+doped KNN was investigated by means of electron paramagnetic resonance (EPR). Copper is found to be incorporated as acceptor-type centers on B-site in the perovskite structure and, due to charge compensation, two kinds of mutually compensating defect dipoles are formed.
Comparative Study of the Magnetocaloric Properties in Ni-Mn-X (X = Ga, In, Sn) by Magnetization and Specific Heat Measurements
Authors: Khovaylo V V , Skokov K P , Avilova E V , Novosad Val , Miki H , Kainuma Ryosuke , Wang G , Palacios E , Bartolomé J , Burriel R
Published: August 2010

Some compositions of Ni-Mn-X (X = Ga, In, Sn) ferromagnetic shape memory alloys exhibit a first order magnetostructural phase transition. Magnetic entropy change ΔSm in the vicinity of this transition has been studied by magnetization and heat capacity measurements. Comparison of these results point to a large difference in magnitudes of ΔSm obtained from magnetization and heat capacity data. It is suggested that this discrepancy originates from overestimation of \Delta S_m determined from the magnetization measurements and underestimation of ΔSm obtained from the heat capacity measurements.
Thermal Annealing Influence on Magnetic and Structural Properties of Cu56Ga28Mn16 Microwires
Authors: Prida Víctor , Vega Victor , Sanchez Llamazares Jose , Sanchez Maria L , Santos Jesus D , Hernando Blanca , Escoda Lluisa , Suñol Joan J , Garcia Carlos , Ross Caroline
Published: August 2010

We report on the crystalline structure, morphology and thermomagnetic properties of glass-coated magnetic microwires with Cu56Ga28Mn16 composition, as well as the thermal annealing influence on its magneto-structural properties. As-cast CuMnGa microwires exhibit a majority cubic B2 phase, and upon annealing at temperatures up to 573 K a new hexagonal phase appears coexisting with the cubic B2 major phase. Thermal annealing treatments also shift the Curie temperature about 150 K with respect to the one for the as-cast microwire. Furthermore, the signature of a structural phase transition is observed for the microwire annealed at 523 K
Study of the Adhesion and Biocompatibility of Nanocrystalline Diamond (NCD) Films on 3C-SiC Substrates
Authors: Gomez Humberto , Frewin Christopher L. , Kumar Ashok , Saddow Stephen , Locke Christopher
Published: August 2010

The unique material characteristics of silicon carbide (SiC) and nanocrystalline diamond (NCD) present solutions to many problems in conventional MEMS applications and especially for biologically compatible devices. Both materials have a wide bandgap along with excellent optical, thermal and mechanical properties. Initial experiments were performed for NCD films grown on 3C-SiC using a microwave plasma chemical vapor deposition (MPCVD) reactor. It was observed from the atomic force microscopy (AFM) analysis that the NCD films on 3C-SiC possess a more uniform grain structure, with sizes ranging from approximately 5 – 10 nm, whereas on the Si surface, the NCD has large, non-unioform inclusions of grains ≈1 μm in size. The in vitro biocompatibility performance of NCD/3C-SiC was measured utilizing 2 immortalized neural cell lines: H4 human neuroglioma (ATCC #HTB-148) and PC12 rat pheochromocytoma (ATCC #CRL-1721). MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to measure viability of the cells for 96 hours and live/ fixed cell. AFM was performed to determine the general cell morphology. The H4 cell line shows a good biocompatibility level with hydrogen treated NCD as compared with the cell treated polystyrene control well, while the PC12 cells show decreased viability on the NCD surfaces.
Synthesis of Few-Layer and Multi-Layer Graphene and Fabrication of Top-Gated Field Effect Transistors without Using Transferring Processes
Authors: Kondo Daiyu , Yagi Katsunori , Harada Naoki , Sato Motonobu , Nihei Mizuhisa , Sato Shintaro , Yokoyama Naoki
Published: August 2010

We have fabricated top-gated field effect transistors (FETs) using graphene synthesized by chemical vapor deposition directly on a SiO2/Si substrate without using any transferring processes. Graphene was synthesized on an Fe catalyst film on the substrate at 650°C. The catalyst film was then etched after both ends of the graphene were fixed by source and drain electrodes, leaving the graphene channel connecting the two electrodes. Top-gated FETs were then made by covering graphene channels with HfO2 and depositing top electrodes. The drain current was successfully modulated by the gate voltage and exhibited the bipolar behavior that is characteristic of graphene. Also, it has been shown that graphene channels can sustain an electric current with a density of 107–108 /cm2. Our newly developed fabrication process paves a way to fabricate graphene transistors all over large substrates including Si and glass.
Incoherent Transport in Nanowire - The Effect of Electron-phonon Interaction
Authors: Nishizawa Hideyuki , Itoh Satoshi
Published: August 2010

The incoherent transport model based on electron-phonon interaction was introduced for calculating the current-voltage characteristics of the nanowire conductor. The current-voltage characteristics of silicon nanowire calculated based on this model was discussed. The charge transport was described by the rate equation containing the coherent (tunneling) and incoherent (energy dissipation) rates, and the incoherent rate was calculated from the Hamiltonian in which the electron-phonon interaction was incorporated. The coherent transition corresponds to the electronic transition between electrode states and channel states without any energy dissipation. On the other hand, the incoherent transition corresponds to the electronic transition between electrode states and channel states where the energy difference of those two states means a thermal dissipation. Therefore, in order to carry out the calculation by the rate equation, the density of states (DOSs) of the carriers in electrode and the channel and the DOS of the phonon in the channel are needed. The current-voltage characteristics were calculated by using the DOS of n-type semiconductor for the electrode and by using intrinsic semiconductor DOS for the channel. In addition, the calculation was performed by using the DOS of the silicon nanowire phonon.
Adamantane Derivative as Host Material for Efficient Deep-Blue Phosphorescent Organic Light Emitting Diodes
Authors: Fukagawa Hirohiko , Yokoyama Norimasa , Irisa Shiro , Tokito Shizuo
Published: August 2010

We report on a high efficiency deep-blue phosphorescent organic light-emitting diode (POLED) based on new electron-transporting host material. The new electron-transporting host material is an adamantane derivative with high triplet energy and high electron mobility. The deep blue POLED that we have developed utilizes a deep-blue phosphorescent guest material, iridium(III)bis(4’,6’,-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate, and exhibits a power efficiency of about 10.2 lm/W at luminance of 100 cd/m2 and maximum external quantum efficiency (EQE) of about 13 %. The power efficiency of our POLED is much higher than that of POLED using p–bis(triphenylsilyly)benzene (UGH2). The maximum EQE of our POLED was also slightly more than that of POLED using UGH2. The obtained difference in power efficiency originates from the new host material having higher electron mobility than that of UGH2.
Behaviour of Nanocrystalline Silicon Carbide Under Low Energy Heavy Ion Irradiation
Authors: Gosset Dominique , Luneville Laurence , Baldinozzi Gianguido , Simeone David , Audren Auregane , Leconte Yann
Published: August 2010

Silicon carbide is one of the most studied materials for core components of the next generation of nuclear plants (Gen IV). In order to overcome its brittle properties, materials with nanometric grain size are considered. In spite of the growing interest for nano-structured materials, only few experiments deal with their behaviour under irradiation. To assess and predict their evolution under working conditions, it is important to characterize their microstructure and structure. To this purpose, we have studied microcrystalline and nanocrystalline samples before and after irradiation at room temperature with 4 MeV Au ions. In fact, it is well established that such irradiation conditions lead to amorphisation of the material, which can be restored after annealing at high temperature. We have performed isochronal annealings of both materials to point out the characteristics of the healing process and eventual differences related to the initial microstructure of the samples. To this purpose Grazing Incidence X-Ray Diffraction has been performed to determine the microstructure and structure parameters. We observe the amorphisation of both samples at similar doses but different annealing kinetics are observed. The amorphous nanocrystalline sample recovers its initial crystalline state at higher temperature than the microcrystalline one. This effect is clearly related to the initial microstructures of the materials. Therefore, the grain size appears as a key parameter for the structural stability and mechanical properties of this ceramic material under irradiation.
Materials Development by a Surface Modification for the Sulfuric Acid Decomposer in Iodine-Sulfur(IS)cycle for Nuclear Hydrogen Production System
Authors: Park Jae-Won , Kim Hyung-Jin , Kim Yong-Wan
Published: August 2010

Efforts have been made to develop long term sustainable materials for use above 900°C in the SO3/SO2 environments utilized in Nuclear Hydrogen Production Systems. In this study, the surface of Hastelloy X was serially modified by evaporative SiC coating, ion beam mixing (IBM), additional coatings, and final ion beam hammering (IBH). Subsequent heating above 900°C results in no peeling-off of the SiC coating layer in spite of the huge difference in their coefficients of thermal expansion (CTE). It was also found that ion beam hammering (irradiation) suppresses the vacuum sublimation of the low density (∼40% of bulk) ceramic film (bulk materials begin to sublime at ∼ 750°C in a vacuum of 1.5×10−5 torr). The sublimation rate is ≤ 30% of the bulk rate after an annealing at 950 for 2 hrs but is decreased to ≤10% of the bulk rate after irradiation with 70 keV ions to a total dose of 1×1017 N ions/cm2. Further irradiation (up to 4×1017 N ions/cm2) does not further decrease the rate. Both an immersion test in 98% sulfuric acid and the potentiodynamic polarization test suggest that the surface modified Hastelloy X has a greatly prolonged life time in the corrosive sulfuric acid atmosphere, suggesting the serial surface modification process is applicable to the thermo-chemical system for the nuclear hydrogen production.
Mechanical Properties of Nanostructured Hard Coating of ZrO2
Authors: Sabirianov Renat F. , Namavar Fereydoon , Zeng Xiao Cheng , Bai Jaeil , Mei Wai-Ning
Published: August 2010

Nano-crystalline films of pure cubic ZrO2 have been produced by ion beam assisted deposition (IBAD) processes which combine physical vapor deposition with the concurrent ion beam bombardment in a high vacuum environment and exhibit superior properties and strong adhesion to the substrate. Oxygen and argon gases are used as source materials to generate energetic ions to produce these coatings with differential nanoscale (7 to 70 nm grain size) characteristics that affect the wettability, roughness, mechanical and optical properties of the coating. The nanostructurally stabilized chemically pure cubic phase has been shown to possess hardness as high as 16 GPa and a bulk modulus of 235 GPa. We examine the mechanical properties and the phase stability in zirconia nanoparticles using first principle electronic structure method. The elastic constants of the bulk systems were calculated for monoclinic, tetragonal and cubic phases. We find that calculated bulk modulus of cubic phase (237GPa) agrees well with the measured values, while that of monoclinic (189GPa) or tetragonal (155GPa) are considerably lower. We observe considerable relaxation of lattice in the monoclinic phase near the surface. This effect combined with surface tension and possibly vacancies in nanostructures are sources of stability of cubic zirconia at nanoscale.
Residual Stress Reduction in Sputter Deposited Thin Films by Density Modulation
Authors: Alagoz Arif Sinan , Kamminga Jan-Dirk , Grachev Sergey Yu , Lu Toh-Ming , Karabacak Tansel
Published: August 2010

Control of residual stress in thin films is critical in obtaining high mechanical quality coatings without cracking, buckling, or delamination. In this work, we present a simple and effective method of residual stress reduction in sputter deposited thin films by stacking low and high material density layers of the same material. This multilayer density modulated film is formed by successively changing working gas pressure between high and low values, which results in columnar nanostructured and dense continuous layers, respectively. In order to investigate the evolution of residual stress in density modulated thin films, we deposited ruthenium (Ru) films using a DC magnetron sputtering system at alternating argon (Ar) pressures of 20 and 2 mTorr. Wafer’s radius of curvature was measured to calculate the intrinsic thin film stress of multilayer Ru coatings as a function of total film thickness by changing the number of high density and low density layers. By engineering the film density, we were able to reduce film stress more than one order of magnitude compared to the conventional dense films produced at low working gas pressures. Due to their low stress and enhanced mechanical stability, we were able to grow these density modulated films to much higher thicknesses without suffering from buckling. Morphology and crystal structure of the thin films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A previously proposed model for stress reduction by means of relatively rough and compliant sublayers was used to explain the unusually low stress in the specimens investigated.
Implications for Ultrafast Reflection Electron Diffraction from Temporal and Spatial Evolution of Transient Electric Fields
Authors: Park Hyuk , Zuo J.M.
Published: August 2010

Understanding interaction of ultrafast pulsed laser with matter is critical for probing ultrafast processes in materials science, understanding the physics of laser ablation and the laser induced non-equilibrium carrier dynamics in metals and semiconductors, including plasmonics. When an intense laser pulse of femtoseconds (fs) in duration hits the surface of a targeted matter, it excites a hot electron gas. Part of the hot electrons is emitted from the surface in a way similar to thermionic emission. Electrons can also be emitted through multiphoton photoemission (MPPE) or thermally assisted MPPE. The emitted electrons travel at speeds that create transient electric fields (TEFs). To detect TEFs and study the dynamics of emitted electrons, we have developed a time resolved electron beam imaging technique that allows us to measure TEFs above a sample surface at picoseconds time resolution. We have also developed a model of the TEFs based on the propagation of emitted electrons and the percentage of electrons escaping from the surface. We examine the significance of TEFs for ultrafast reflection electron diffraction by examining anomalous effects in ultrafast reflection high energy electron diffraction (RHEED) of silicon surfaces.
Additive Manufacturing Technologies for the 3D Fabrication of Biocompatible and Biodegradable Photopolymers
Authors: Heller Christian , Schwentenwein Martin , Varga Franz , Stampfl Jürgen , Liska Robert
Published: August 2010

High molecular weight vinyl esters and carbonates based on oligo(ethylene glycol), oligomeric fatty acids and poly(hexamethylene carbonate), as alternatives for potentially cytotoxic acrylate based monomers have been structured by Additive Manufacturing Technologies (AMTs) like Microstereolithography (μ-SLA), Digital Light Processing (DLP) and Two-Photon Induced Photopolymerization (TPIP). With these techniques feature resolutions down to 10 μm (μ-SLA and DLP) or even 200 nm (TPIP) can be obtained.
This new class of monomers exhibits LC50 values for cytotoxicity up to two orders of magnitude lower than acrylate references. Beside a high reactivity of the resin, the shrinkage and the mechanical properties of the final part material are another essential parameter. Low molecular weight monomers are very reactive and lead to densely cross-linked materials which suffer from high shrinkage and strains within the cured material. Therefore, mixtures of high molecular weight vinyl esters/carbonates with low molecular weight crosslinkers have been evaluated regarding their photoreactivity and mechanical properties.
Production Nozzle-Less Electrospinning Nanofiber Technology
Authors: Petrik Stanislav , Maly Miroslav
Published: August 2010

The theoretical background and technical capabilities of the free liquid surface (nozzle-less) electrospinnig process is described. The process is the basis of both laboratory and industrial production machines known as NanospiderTM and developed by Elmarco s.r.o. Technical capabilities of the machines (productivity, nanofiber layer metrics, and quality) are described in detail.
Comparison with competing/complementary technologies is given, e.g. nozzle electrospinning, nano-meltblown, and islets-in-the sea. Application fields for nanofiber materials produced by various methods are discussed. Consistency of the technology performance and production capabilities are demonstrated using an example of polyamide nanofiber air filter media.
Controllable Chemical Modification of Polyaniline Nanofibres
Authors: Lahiff Emer , Lynam Carol , Gilmartin Niamh , Wallace Gordon G , O’Kennedy Richard , Diamond Dermot
Published: August 2010

A method for simply and controllably modifying the surface of polyaniline nanofibres is described. The technique can be used to attach substituents bearing both acid and amine functional groups, making the materials suitable for further modification. Acid/amine functionalisation is achieved by a simple reflux reaction and therefore is a quick and easily scalable process. The modified nanofibres maintain their ability to switch between different states displaying distinctly different properties, thus making them suitable for adaptive sensing applications. As an example, we demonstrate how biomolecules can be attached to these functionalised nanofibres, to produce conducting polymer-based biosensors.
Poly(3,4-alkylenedioxythiophene) Nanostructures
Authors: Sarac A.Sezai
Published: August 2010

Electropolymerization of unsubstituted and substituted propylene - dioxythiophenes (i.e., ProDOT & ProDOT-Bz) on ( ˜7 μm diameter) single carbon fiber microelectrodes (SCFMEs) in different electrolytes resulted the network of nanopore structures.
Surface morphology of coatings were investigated by Scanning Electron Microscopy (SEM), the attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used for the characterization . Electrochemical impedance spectroscopic investigation of these nanostructures has been indicated the capacitive behavior of electrode system. Data were used to simulate at applied potential and explained by equivalent circuit modeling.
Synthesis and Cytotoxicity of Luminescent InP Quantum Dots
Authors: Wang Yuxuan , Quek Chai Hoon , Leong Kam W. , Fang Jiye
Published: August 2010

As a potential biological imaging probe with a long-wavelength of emission, InP quantum dots were prepared via a high-temperature organic solution approach, and successfully transferred into an aqueous system through a ligand-exchange process using various functional surfactants. Photoluminescence and X-ray characterizations confirmed the desired properties of the InP quantum dots. The cytotoxicity of the water-soluble InP quantum dots against phaeochromocytoma PC12 cells as evaluated by the MTS cell viability assay was low relative to a positive control, poly(ethyleneimine). This study suggests a bright potential for this new type of InP quantum dots in bioimaging applications.
Critical Concentrations of Atmospheric Contaminants in a-Si:H and μc-Si:H Solar Cells
Authors: Merdzhanova Tsvetelina , Woerdenweber Jan , Kilper Thilo , Stiebig Helmut , Beyer Wolfhard , Gordijn Aad
Published: August 2010

We report on a direct comparison of the effect of the atmospheric contaminants on a-Si:H and μc-Si:H p-i-n solar cells deposited by plasma-enhanced chemical vapor deposition (PECVD) at 13.56 MHz. Nitrogen and oxygen were inserted by two types of controllable contamination sources: (i) directly into the plasma through a leak at the deposition chamber wall or (ii) into the process gas supply line. Similar critical concentrations in the range of 4-6×1018 cm-3 for nitrogen and 1.2-5×1019 cm-3 for oxygen were observed for both a-Si:H and μc-Si:H cells for the chamber wall leak. Above these critical concentrations the solar cell efficiency decreases for a-Si:H solar cells due to losses in the fill factor under red light illumination (FFred). For μc-Si:H cells the losses in FFred and in short-circuit current density deteriorate the device performance. Only for a-Si:H the critical oxygen concentration is found to depend on the contamination source. Conductivity measurements suggest that at the critical oxygen concentration the Fermi level is located about 0.05 eV above midgap for both a-Si:H and μc-Si:H.
A New Approach to Light Scattering from Nanotextured Interfaces For Silicon Thin-film Solar Cells
Authors: Battaglia Corsin , Escarre Jordi , Söderström Karin , Haug Franz-Josef , Dominé Didier , Feltrin Andrea , Ballif Christophe
Published: August 2010

We investigate the influence of refractive index contrast on the light scattering properties of nanotextured interfaces, which serve as front contact for p-i-n thin-film silicon solar cells. We here focus on ZnO surfaces with randomly oriented pyramidal features, known for their excellent light trapping performance. Transparent replicas, with a different refractive index, but practically identical morphology compared to their ZnO masters, were fabricated via nanoimprinting. Within the theoretical framework we recently proposed, we show how the angular and spectral dependence of light scattered by nanostructures with identical morphology but different refractive index may be related to each other allowing direct comparison of their light trapping potential within the device.
Influence of Hydrogen on the Germanium Incorporation in a-Si1-xGex:H for Thin-film Solar Cell Application
Authors: Wang Chien-Ming , Huang Yen-Tang , Kuo-Hsi Yen , Hsu Hung-Jung , Hsu Cheng-Hang , Zan Hsiao-Wen , Tsai Chuang-Chuang
Published: August 2010

In this work, we examined the Ge incorporation and the accompanied defect formation during PECVD deposition of hydrogenated amorphous silicon-germanium alloys (a-Si1-xGex:H). In particular, we studied the effect of hydrogen on film growth, defect formation, Ge and Si incorporation efficiencies, and the H-bonding configuration. Our results indicate that hydrogen has a strong effect on improving the a-Si1-xGex:H film quality and the Ge incorporation in a-Si1-xGex:H. With adequate hydrogen dilution, the a-Si1-xGex:H thin-film quality significantly improved. However, excessive hydrogen dilution degraded the film properties. A number of analytical tools were employed, including FTIR, XPS, UV-Visible spectroscopy, photoconductivity, etc. The a-Si1-xGex:H material having 24% Ge content and a bangap of 1.61ev produced the solar cell with a conversion efficiency of 7.07%.
Ultrafast Deposition of Crystalline Si Films Using a High Density Microwave Plasma
Authors: Jia Haijun , Kondo Michio
Published: August 2010

A multi-pressure microwave plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed firstly. Electron density, electron temperature and discharge gas temperature of the plasmas generated in ambient air are studied using optical emission spectroscopy (OES) method. By using the high density microwave plasma source, depositions of crystalline silicon films from SiH4+He mixture at reduced pressure conditions are investigated systematically. After optimizing the film deposition conditions, highly crystallized Si films are deposited at a rate higher than 700 nm/s. We also find that the deposited films are fully crystallized and crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.
FDTD Simulation of Light Propagation Inside a-Si:H Structures
Authors: Fantoni Alessandro , Pinho Pedro
Published: August 2010

We have developed a computer program based on the Finite Difference Time Domain (FDTD) algorithm able to simulate the propagation of electromagnetic waves with wavelengths in the range of the visible spectrum within a-Si:H p-i-n structures. Understanding of light transmission, reflection and propagation inside semiconductor structures is crucial for development of photovoltaic devices. Permitting 1D analysis of light propagation over time evolution, our software produces results in well agreement with experimental values of the absorption coefficient. It shows the light absorption process together with light reflection effects at the incident surface as well as at the semiconductor interfaces. While the effects of surface reflections are easily taken into account by the algorithm, light absorption represents a more critical point, because of its non-linear dependence from conductivity. Doping density, density of states and photoconductivity calculation are therefore crucial parameters for a correct description of the light absorption-transmission phenomena through a light propagation model.

The results presented in this paper demonstrate that is possible to describe the effect of the light-semiconductor interaction through the application of the FDTD model to a a-Si:H solar cell. A more general application of the model to 2D geometries will permit the analysis of the influence of surface and interface roughness on the device photovoltaic efficiency.
Self-catalyzed Tritium Incorporation in Amorphous and Crystalline
Authors: Liu Baojun , Kherani Nazir , Chen Kevin P , Kosteski Tome , Leong Keith , Zuktynski Stefan
Published: August 2010

Tritiated amorphous and crystalline silicon is prepared by exposing silicon samples to tritium gas (T2) at various pressures and temperatures. Total tritium content and tritium concentration depth profiles in the tritiated samples are obtained using thermal effusion and Secondary Ion Mass Spectroscopy (SIMS) measurements. The results indicate that tritium incorporation is a function of the material microstructure rather than the tritium exposure condition. The highest tritium concentration attained in the amorphous silicon is about 20 at.% on average with a penetration depth of about 50 nm. In contrast, the tritium occluded in the c-Si is about 4 at.% with a penetration depth of about 10 nm. The tritium concentration observed in a-Si:H and c-Si is higher than reported results from post-hydrogenation experiments. The beta irradiation appears to catalyze the tritiation process and enhance the tritium dissolution in silicon material.
Light-triggered Silicon-carbon Pi'npin Devices for Optical Communications: Theoretical and Electrical Approaches
Authors: Vieira Manuela , Vieira M. A. , Costa João , Louro Paula , Fernandes Miguel , Fantoni Alessandro
Published: August 2010

In this paper a light-activated multiplexer/demultiplexer silicon-carbon device is analysed. An electrical model for the device operation is presented and used to compare output signals with experimental data. An algorithm that takes into accounts the voltage and the optical bias controlled sensitivities is developed. The device is a double pi'n/pin a-SiC:H heterostructure with two optical gate connections for light triggering in different spectral regions. Multiple monochromatic pulsed communication channels were transmitted together, each one with a specific bit sequence. The combined optical signal was analyzed by reading out, under different applied voltages and optical bias, the generated photocurrent across the device. Experimental and simulated results show that the output multiplexed signal has a strong nonlinear dependence on the light absorption profile, i.e. on the incident light wavelength, bit rate and intensity under unbalanced light generation of carriers. By switching between positive and negative voltages the input channels can be recovered or removed from the output signal.
Evolution of Stacking Faults Defects During Epitaxial Growths: Role of Surface Kinetics
Authors: Camarda Massimo , La Magna Antonino , Canino Andrea , La Via Francesco
Published: August 2010

Three dimensional kinetic Monte Carlo simulations on super-lattices are applied to study the evolution of stacking faults during epitaxial growths. We show that, in the case of misoriented close packed substrates, these defects can either extend throughout the entire epilayer (i.e. extended from the substrate up to the surface) or close in dislocation loops, in dependence of the deposition conditions. We explain this behavior in terms of a surface kinetic competition between these defects and the surrounding crystal: if the local growth rate of the defect is larger compared with that of the perfect crystal the defect will expands, otherwise it will closes. This mechanisms allows to explain several experimental results on homo and hetero epitaxies.
Recent Developments in SiC Homoepitaxy Using Dichlorosilane for High Power Devices
Authors: Chowdhury Iftekhar , Chandrasekhar MVS , Klein Paul B , Caldwell Joshua D , Sudarshan Tangali
Published: August 2010

Thick and high quality 4H-SiC epilayers have been grown in a vertical hot-wall chemical vapor deposition system at a high growth rate on (0001) 80off-axis substrates. We discuss the use of dichlorosilane as the Si-precursor for 4H-SiC epitaxial growth as it provides the most direct decomposition route into SiCl2, which is the predominant growth species in chlorinated chemistries. The RMS roughness of the films ranged from 0.5-2.0 nm with very few morphological defects (carrots, triangular defects, etc.) being introduced, while enabling growth rates of 30-100 μm/hr, 5-15 times higher than most conventional growths. A specular surface morphology was attained by limiting the hydrogen etch rate until the system was equilibrated at the desired growth temperature. Site-competition epitaxy was observed over a wide range of C/Si ratios, with doping concentrations as low as 2x1014cm-3being recorded. X-ray rocking curves indicated that the epilayers were of high crystallinity, with linewidths as narrow as 7.8 arcsec being observed, while microwave photoconductive decay (μPCD) measurements indicated that these films had high injection (ambipolar) carrier lifetimes in the range of 2 μs. These films also appeared to be free of polytype inclusions.
Single-crystal Silicon Carbide: A Biocompatible and Hemocompatible Semiconductor for Advanced Biomedical Applications
Authors: Saddow Stephen E. , Coletti Camilla , Frewin Christopher , Schettini Norelli Castro , Oliveros Alexandra , Jaroszeski Mark
Published: August 2010

Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluatedin vitroby directly culturing three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays and fluorescent microscopy. For the neural cells studied AFM was also used to quantify the filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was also used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible materialin vitrothat is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property.
Interconnect Technologies for Heterogeneous 3D Integration : CMOS and MEMS
Authors: Yang Hyung Suk , Bakir Muhannad
Published: August 2010

Microelectromechanical Systems (MEMS) market is a rapidly growing market with a wide range of devices. Most of these devices require an interaction with an electronic circuit, and with the increasing number of high performance MEMS devices that are being introduced, a demand for integrating CMOS and MEMS using high-density and low-parasitic interconnects have also been on the rise.

Unfortunately, conventional methods of integrating CMOS with MEMS cannot provide the high density and low-parasitic interconnections required by modern high performance MEMS devices, and at the same time provide the flexibility required to accommodate new devices that are made using new materials and highly innovative fabrication processes.

Heterogeneous 3D integration of MEMS and CMOS has the potential to provide both the performance and the integration flexibility; however there are two interconnect challenges that need to be addressed. This paper outlines the details of these interconnect challenges and introduces two interconnect technologies, Mechanically Flexible Interconnects (MFI) and Through-Silicon Via (TSV), developed specifically to address these challenges.
Fluxless Bonding Using Vacuum Ultraviolet and Formic Acid for 3D Interconnects
Authors: Sakuma Katsuyuki , Unami Naoko , Shoji shuichi , Mizuno Jun
Published: August 2010

We have developed a novel surface treatment process using vacuum ultraviolet (VUV) light with a wavelength of 172 nm and formic acid vapor. A previous study showed that the VUV process can help remove the organic contaminants on the bonding surfaces and improve the shear strength. This new work focuses on studying the effects of VUV/O3and formic acid treatments. The formic acid (HCOOH) vapor removes the metal oxides from the surfaces before the bonding process. Evaporated Cu/Sn and immersion Au were used for the bonding micro-bumps and bonding pads in our evaluations. Different cleaning conditions with VUV/O3, formic acid vapor, or both were compared and evaluated. X-ray Photoelectron Spectroscopy (XPS) was used to study the surface elemental composition of the micro-bumps and pad surfaces before and after the cleaning process. The photoelectron spectra of C1s, Sn3d, and Au4f were obtained with XPS. The XPS results showed the atomic carbon concentrations were significantly decreased by the VUV/O3treatment process, while the Sn and Au concentrations were increased by the VUV/O3and formic acid treatment because of the removal of the organic contaminants and metal oxides from the surfaces. The bonding strength of the Cu/Sn bumps was evaluated using a shear test tool. The results shows that the combination of VUV/O3and formic acid treatment obtains the highest average shear strength among the treatments tested, with a shear strength almost 2.5 times stronger than the untreated samples.
A Three Dimensional Self-folding Package (SFP) for Electronics
Authors: Gracias David , Cho Jeong-Hyun , Hu Steve
Published: August 2010

We describe the concept of a 3D self-folding package (SFP) for sensors and electronic devices. The strategy is based on a self-assembly strategy wherein 2D panels interconnected with hinges spontaneously fold-up when they are released from the substrate; self-folding can be triggered by temperature or selected chemicals. The strategy enables packaging of devices in porous polyhedral geometries that can either be untethered or substrate-bound. Self-folding can enable packaging of devices in small 3D form factors and may enable efficient cooling due to porosity. The utilization of this self-folding platform to enable 3D packaging of cantilever sensors and magnetic field sensitive strain gauges is summarized.