bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Molecularly Imprinted TiO2 Nanoparticle for Photoreduction of Viologen
Authors: Sagawa Takashi , Kudo Mayu , Steinke Joachim H. G. , Morii Takashi
Published: April 2011

When small organic molecules (e.g. amino acids, nucleotides, and so on) are incorporated in metal oxide particles formed from metal alkoxide in the sol-gel process, the organic moieties can be removed readily by solvent washing or by degradative oxidation. Under proper conditions, nano-sized cavities corresponding to the shape of the individual organic moiety are produced within the metal oxide network as molecularly imprinted material such as surface molecularly imprinted TiO2. We tried to fabricate nano-sized particle of TiO2 to increase the effective contact area for the reactants, and further additional function for molecular recognition was intended to introduce through the surface modification of the molecular imprinting method in order to enhance the photoreduction of viologen. In this context, we prepared viologen imprinted TiO2 as an active and stable photocatalyst for photoreduction of viologen as a well-defined and readily identifiable and reversible electron carrier with appropriate redox potential for photoactivated TiO2. The basic concept of molecularly imprinting in this system is as follows. Oxidized viologen is generally twisted and dication molecule. While, reduced viologen is planar and monocation radical. Once TiO2 has such recognition site on its surface, it would be distinguishable through shape or charge recognition or both factors and facilitate the inclusion or exclusion of the target molecule result the enhancement of the reduction. After the preparation of the template, sol-gel imprinting was performed. Measuring its dynamic light scattering monitored changes of the particle sizes and the diameter was stabilized ca 120 nm after 1 week stirring. X-ray diffraction pattern of the TiO2 powder after the dryness without calcination indicates the dominant peak for anatase. Removal of the template was almost 36% after the alkaline rinsing by measuring its UV vis spectra of the washings. A buffered solution of Tris including viologen was irradiated through a xenon lamp under stirring in a quartz cuvett in Ar with or without the TiO2 with cut-off filter at room temperature. The formation of viologen monocation radical whose color is blue was easily recognized only in the reaction with TiO2. The formation of viologen monocation radicals from three types of (methyl, hexyl, and pentacarboxyl) viologens with time in the presence of the imprinted TiO2 and blank one was monitored spectrophotometrically. Blank means that it was fabricated similar way to the imprinted one without the template. Among these results, aliphatic C6 side chains of bipyridinium and terminal carboxyl groups were not effective to enhance. On the other hand, the less bulkiness methyl viologen resulted the highest yield. The most important result is that higher conversion was observed in every case of imprinted TiO2 compared with blank one. Therefore, the key point for recognition is not peripheral part, but bipyridinium part of the viologen.
Time Induced Changes in Phase Transition Behavior and Stability of Zn4Sb3
Authors: Pedersen Birgitte Lodberg , Birkedal Henrik , Nishibori Eiji , Sakata Makoto , Iversen Bo Brummerstedt
Published: April 2011

The stability of high performance thermoelectric Zn4Sb3 has been studied, by using synchrotron powder diffraction to establish differences in phase transition temperatures of two samples. High resolution multi temperature diffraction data has been collected, with a time interval of 13 months, and the phase transition temperature was determined based on the results of Rietveld refinements. The refinements show a difference in transition temperature from data collected the first time till data collected the second time. Furthermore the samples showed impurity peaks after being exposed to air for 13 months, indicating that the sample decomposes over time.
Time Resolved Magneto-Optical Imaging in High Frequency AC Currents of YBa2Cu3O7-&[delta]Thin Films
Authors: Lucarelli Andrea , Frey Alexander , Yang Ran , Luepke Gunter , Haugan Timothy J , Levin George A , Barnes Paul N
Published: April 2011

We present a time-resolved magneto-optical (MO) imaging study of high-temperature superconductor (HTS) in high-frequency alternating current (AC) regime. The evolution of the magnetic flux density distribution in YBa2Cu3O7-d (YBCO) thin film samples is studied in small steps of the phase of the applied AC current. The flux distribution at 10 K exhibits instabilities including flux jumps and flux creep. A quantitative analysis of the data allows us to obtain the current density evolution. The current profile changes considerably with the phase differently from the prediction of the critical state model. These observations can be explained by the higher self-field at the sample edge and the effects of flux creep.
Preparation and Characterization Silver and Copper Layers on Polyimide Prepared by Electroless Copper Plating
Authors: Ji Eun Sun , Kim Young Hwan , Kang Young Soo
Published: April 2011

Ag particles were generated on Ag+-doped polyimide film by ion exchanging, followed by copper deposition using metallic silver particles as seeds. The Cu layers were coated on the surface of polyimide films by electroless plating method. The surface image and morphology of Cu layers on the polyimide films were characterized with scanning electron microscopy (SEM), and atomic force microscopy (AFM). The chemical composition on the PI film was investigated energy dispersive X-ray (EDX) spectrometer.
A General Approach to Patterning Micron-Scale Particles
Authors: Sieb Nathanael , Gates Byron D.
Published: April 2011

Multiple techniques have been developed to assemble micro- or nanostructured materials into well-defined patterns. These techniques are, however, often dependent on the size, shape, composition and/or surface chemistry of the structures being patterned. We have developed a general approach to pattern materials with a wide range of physical and chemical characteristics. We are able to assemble these materials into isolated or interconnected patterns covering areas up to ∼1 mm2.
Nanocomposite Conductive Elastomer: Microfabrication Processes and Applications in Soft-Matter MEMS Sensors
Authors: Liu Chang
Published: April 2011

3D micro-molded PDMS (polydimethylsiloxane) elastomer is widely used in MEMS. However, traditional PDMS is non-conductive and as a result is used in mostly structural applications. It is difficult to embed elastomeric, “stretchy” conductors and transduction elements in molded PDMS matrix. We report general methods for monolithic fabrication of multi-layer PDMS structures with embedded conductive and non-conductive elastomer elements. Conductive PDMS parts, made of carbon-nanotube-filled composite PDMS, can form internal elastomer wires, electrodes, heaters, and sensors. The process uses a series of PDMS patterning, micromolding, and bonding techniques. In this work we demonstrate elastomer strain gauges, capacitive pressure sensors, as well as microfluidic channels with integrated heaters and sensors.
Interactions, Dynamics and Self-assembly of Magnetic Holes
Authors: de lang Kristiansen Kai , Svåsand Eldrid , Helgesen Geir , Skjeltorp Arne T.
Published: April 2011

Nonmagnetic microspheres dispersed in a ferrofluid are denoted magnetic holes. When the spheres are confined to a monolayer between two plane, parallel plates and subjected to AC magnetic fields, they show a variety of dynamical behaviors and assemblages. The magnetic interactions between the particles and their dynamical behavior are influenced by the boundaries and the degree of confinement. We have derived analytical results for the pair-wise competing interactions, and these compare favorably with experimental results.

It is also possible to characterize the self-assembly and dynamics of the spheres by the theory of braids. It involves classifying different ways of tracing curves in space. The essentially two-dimensional motion of a sphere can be represented as a curve in a three-dimensional space-time diagram, and so several spheres in motion produce a set of braided curves. The dynamical modes can then be described in terms of braid-words. We also present a few other examples on how this system can be used to study dynamical processes.
Electronic Transport Measurements in Tin Oxide Microfibers Created From a Polymer Solution
Authors: Taku Maria , Rodd Chris , Santiago Jorge
Published: April 2011

Tin oxide microfibers were created through electrospinning using a precursor solution consisting of poly(ethylene oxide) (PEO) and chloroform (CHCl3) which was then mixed with its tin precursor, dimethyldineodecanoatin (C22H44O4Sn). Since the conductivity of SnO2 is affected by any chemisorbed oxygen molecules on its surface, this semiconductor has high potential for use as a gas sensor for both oxidizing and reducing gases. Due to the fact that a greater surface area will produce gas sensors with improved sensitivity, work is underway to reduce the fibers size into the nanoscale range. Thus, this study explores various electronic transport characteristics—such as the conductivity and magnetoresistance—of the tin oxide microfibers. Additionally, the composition and phase of the fibers were characterized through XRD and Raman spectroscopy.
Taking Advantage of Supramolecular Structure in Melt and Solution Electrospinning
Authors: Hunley Matthew T. , McKee Matthew G. , Gupta Pankaj , Wilkes Garth L. , Long Timothy E.
Published: April 2011

Electrospinning, a polymer processing technique to create nanofibrous membranes, has been used to fabricate fibrous membranes from solution and melt phases showing supramolecular order. Wormlike micellar phases of low molar mass amphiphiles, including the phospholipid mixture asolectin, were electrospun under normal conditions to form micron-sized fibers. From the melt, well defined phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine was electrospun into a similar fibrous membrane. Additionally, thermoreversible physical crosslinks were used to prepare fibers from low molecular weight, star-shaped poly(D,L-lactide) under melt electrospinning conditions.
Micropatterned Polythiophene Nanofibers via Electrostatic Spinning and Photolithography
Authors: Asemota Chris Ik , Kumar Arvind , Sotzing Gregory A
Published: April 2011

Herein we report the patterning of large conducting polymer nanofiber mats of the polyterthiophene precursor, into regular micron scale arrays of smaller mats each of which has the potential of being independently addressed. These fiber grids, micro mats of conducting polymer fibers, were prepared by the combined techniques of electrospinning, soft photolithography, and solid state electrochemical crosslinking. The micro size mats are shown to retain their electrochromic behavior, subject to expected degradation in air as reported in the literature. Our contribution to the investigation of conducting polymers in display technology is oriented towards processibility and preparation of regular conducting polymer structures.
Characterization of Fibers Electrospun from Organometallic Tin Precursors in a Polymer Binder
Authors: Rodd Christopher , Santiago-Avilés Jorge J.
Published: April 2011

Electrospinning has been thought of as an effective, low cost technique for producing nanofibers for use in gas sensor applications with nanofibers of tin oxide showing particular promise in this area. Critical to the success of tin oxide in these applications are nanowires with a rutile phase structure and well defined current-voltage characteristics which requires controlled fiber diameters. This paper reports on the characterization of the pre and post sintered fibers deposited via electrospinning of two different tin precursor chemicals, dimethyl dineodecanoate tin and dimethyl dichloro tin, both spun within a polyethylene oxide / chloroform binder system. Both tin precursor systems were evaluated at different concentration levels to investigate morphological changes due to concentration. Mats of fibers were spun on silicon wafers and sintered at 600°C for 2 hours. Morphology was characterized by optical microscope while chemical composition was determined via Raman spectrometry. Fibers of dimethyl dineodecanoate tin were found be ∼30μm in diameter and to have considerable component separation upon deposition. After sintering, SnO2 islands were found but there was no fiber appearance. Fibers of dimethyl dichloro tin were found to be ∼10μm in diameter and lacked the component separation seen in the other tin precursor system with some SnO2 domains found directly inline with initial fiber deposition. Comparison of results from both systems shows that the interaction of the polymer and tin precursor is of paramount importance for development of micro- or nanosized ceramic wires deposited by electrospinning.
Effect of Molecular Structure of Scavengers on Copper Diffusion Deterrence in Low k Film
Authors: Nomura Yutaka , Ryuzaki Daisuke , Koyanagi Mitsumasa
Published: April 2011

Low k material with high deterrence ability of copper diffusion has been proposed to reduce the effective electrical resistance of copper wirings. Providing organic low k material with deterrence ability was attempted by adding a chemical agent that chemically combines with copper. The insulation lifetime of the low k film with benzotriazole (BTA) as the copper scavenger was about two orders of magnitude higher than that of BTA-free low k film, at the practical electric field strength of 0.1 MV/cm. The copper diffusion deterrence ability was clearly dependent on the ability of the copper scavenger.
Multiple Relaxations in Poly (p-hydroxybenzoic acid-CO-ethylene terephthalate) Liquid Crystal Polymer: TSD Current Investigations
Authors: Quamara Jitendra Kumar , Yarramaneni Sridharbabu , Goyal Geetika
Published: April 2011

The PET/x.PHB samples were polarized at different temperatures (30-250°C) under various biasing fields ranging from 40 to 200 kV/ cm. The TSD currents were obtained at a heating rate of 2 °C/min in the temperature range (15-250)°C. The TSD current spectra in general comprise of three maxima namely β, α and δ in ascending order of temperature. However number of peaks actually appearing in these spectra, their location, height and sharpness are governed by polarization/depolarization parameters as well as the value of ‘x’ in a particular sample. The β peak appearing around (110-140°C) has been recognized as a dipolar relaxation process and is due to PET rich phase. The α- peak (160-180°C) recognized as space charge process is due to PHB rich phase and cold crystallization of PET rich phase. The δ peak (190-210°C) is a melting process due to the movement of large segments leading to Smectic-E like phase. In addition PET/x.PHB also exhibit a weak low temperature dipolar relaxation process β′ peak around (30-40)°C. In the vicinity of α-relaxation a rigid amorphous phase dipolar relaxation process γ relaxation is also observed.
Microstructure-Based Simulation of the Dielectric Properties of Polymer-Ceramic Composites for Capacitor Applications
Authors: Calame Jeffrey P.
Published: April 2011

Research on the microstructure-based modeling of composite dielectrics for capacitor applications is described. Methods for predicting the composite dielectric permittivity and internal electric field distributions within the microstructure using finite difference quasi-electrostatic modeling are described, along with methods of generating realistic model spaces of particulate microstructures. An existing algorithm for generating random, monosized spheres-in-a-dielectric matrix model spaces is modified to allow the treatment of bimodal composites in which small particles are deliberately segregated into the spaces between large particles. Such composites can have substantially higher total volumetric filling fractions of particles, leading to higher composite permittivity. The variations in permittivity with the filling fractions of bimodal inclusions are studied with the new model, with cases covering three different types of polymer matrix material. The effect of the small particle additions on the electric field statistics within the polymer matrix is also explored.
Hydrophobic Dielectrics of Fluoropolymer / BaTiO3 Nanocomposites for Low-Voltage and Charge Storing Electrowetting Devices
Authors: Kilaru Murali K. , Lin Gui , Mark James E , Heikenfeld Jason C
Published: April 2011

A hydrophobic fluoropolymer:BaTiO3 nanocomposite is presented for achieving lower-voltage electrowetting operation. The composite fluoropolymer film exhibits as much as a 10X increase in measured dielectric constant. Increased surface roughness with BaTiO3 content increased the sessile drop contact angle from θ∼104° to 121° with compositions ranging from 0 to 97 vol. % of BaTiO3 in the fluoropolymer. A larger change in electrowetted contact angle is observed for the 50 vol. % of BaTiO3 nanocomposite (delta theta∼60°) compared to a standard fluoropolymer film of 1 um thickness (delta theta∼30°). Furthermore, required operating voltage for electrowetting decreases by ∼30V for films with high BaTiO3 content. Strong charge storage in the nanocomposite was observed via a new bistable electrowetting effect. For samples with strong charge storage, the droplet remains wetted (>2 minutes) even after removing the applied voltage. Rapid (< 1s) droplet de-wetting could be achieved by briefly applying a reverse polarity voltage to remove the stored charge in the nanocomposite.
A Novel Method To Prepare Cysteine Capped Cadmium Selenide Nanoparticles
Authors: Oluwafemi Oluwatobi Samuel , Revaprasadu Neerish
Published: April 2011

Water dispersable and potentially biocompatible L-cysteine-capped CdSe nanoparticles with a narrow size distribution and blue fluoresence have been synthesized by a facile method without using any additional stabilizer. FTIR study shows that CdSe nanoparticles are capped through mercapto-group of the amino acid cysteine whilst its free amino and carboxylate groups make it amenable to bio-conjugation establishing the possibility of using these as fluorescent biomarkers.
Investigation of Cantilever Resonance Applied to Potentiometric Sensing
Authors: Koley Goutam , Lakshmanan Lakshminarayanan
Published: April 2011

We demonstrate a highly sensitive potentiometric gas sensor based on a resonating Si microcantilever. Using a scanning probe microscope based set up in non-contact mode, the microcantilever was made to oscillate at its resonance frequency with periodically changing amplitude, using simultaneous mechanical and electrical excitation sources. The variation of the oscillation amplitude was found to be extremely sensitive to changes in surface potential, and served as a linear indicator for surface work function changes caused by molecular adsorption. The microcantilever sensor was found to be able to detect changes in surface potential down to 50 microvolt, which is basically limited by the system noise. When applied to sensing hydrogen using platinum coated cantilevers, it was observed that the microcantilever sensor can detect 1000 ppm hydrogen with an estimated lower limit of the detection time of 70 ms, at a cantilever-ground electrode distance of ∼10 micron. Several parameters, such as ac signal amplitude, cantilever – reference electrode distance, quality factor, area, and spring constant of the cantilever, can be adjusted to significantly enhance the sensitivity, possibly by orders of magnitude. Excitation of the cantilever at subharmonic resonance frequencies was also performed to study possible parametric resonance effects. In this system it was possible to observe sub-harmonic resonance of order more than 50 (i.e. lower than one-fiftieth the resonance frequency).
Detection of Bacillus Anthracis Spores Using Magnetostrictive Microcantilever-based Biosensor
Authors: Fu Liling , Li Suiqiong , Zhang Kewei , Cheng Z.-Y.
Published: April 2011

Recently, the magnetostrictive microcantilever (MSMC) as a high performance biosensor platform was introduced. The MSMC is a wireless acoustic wave (AW) sensor and exhibits a high Q value. More importantly, the MSMC works well in liquid. In this paper, the detection of Bacillus anthracis spores using MSMCs with filamentous phage as the bioprobe is reported. The phased-coated MSMC biosensors were exposed to cultures containing target spores with increasing concentrations ranging from 5 × 104 to 5 × 108 spores/mL. By monitoring the shift in the resonance frequency of the MSMCs, the spores were detected in a real-time manner and a detection limit of 105 spores/mL was obtained for the MSMCs used in this research. Higher sensitivity is expected for the MSMCs with smaller size.
Post-processing of Commercial CMOS Chips for the Fabrication of DNA Bio-FET Sensor Arrays
Authors: Jiang Weihong , Landheer D. , Lopinski G. , Rankin A. , Tarr N. G. , Deen M. J.
Published: April 2011

A BioFET array can be fabricated by post-processing of a standard CMOS chip if temperatures are kept below 450 ° and radiation or ion-bombardment damage is minimized. The processing starts with encapsulation by deposition of a low stress, electrolyte-impermeable silicon nitride layer by PECVD at 375 °C. Anisotropic reactive ion etching with an inductively coupled plasma using C4F8 and Ar was used to remove the silicon nitride and oxide layers above the poly-silicon gates. The poly-silicon was then etched off using a selective wet etch. The effect of the processing was characterized by making current-voltage and capacitance-voltage measurements with MOS capacitor structures at each stage of processing and results showed that trapped charges or interface states could be annealed out at low temperatures. Scanning electron microscopy was used to examine the cross-section of the gate areas after the etching. The results of current-voltage measurements with a Ag/AgCl reference electrode on devices in electrolyte solutions were compared to the results of charge-sheet model calculations including the effect of amphoteric charging sites on the oxide and the potential drops in the electrolyte. Measurements showing the threshold shifts subsequently produced by DNA probe attachment and hybridization will also be presented.
Increased Stem Cell Adhesion on Carbon Nanotubes Grown from Anodized Titanium
Authors: Ercan Batur , Webster Thomas
Published: April 2011

Stem cells are the source of all differentiated cells in the body. However, the stimuli that control stem cell differentiation into other cell types is still not well understood. In order to investigate this, novel carbon nanotubes (CNT's) were synthesized on anodized titanium substrates by chemical vapor deposition. Human mesenchymal stem cell (HMCS) adhesion was investigated on this nano-structured surface. The results showed significant evidence for the enhancement of HMSC adhesion on carbon nanotubes with respect to the template they were synthesized on, specifically, anodized titanium. Such evidence provides promise for the use of carbon nanotubes grown from anodized titanium to serve as novel stem cell differentiation devices.
Hydrothermal Synthesis of Nanorods/Nanoparticles TiO2 for Photocatalytic Activity and Dye-sensitized Solar Cell Applications
Authors: Pavasupree Sorapong , Ngamsinlapasathian Supachai , Suzuki Yoshikazu , Yoshikawa Susumu
Published: April 2011

Nanorods/nanoparticles TiO2 with mesoporous structure were synthesized by hydrothermal method at 150 °C for 20 h. The samples characterized by XRD, SEM, TEM, SAED, HRTEM, and BET surface area. The nanorods had diameter about 10-20 nm and the lengths of 100-200 nm, the nanoparticles had diameter about 5-10 nm. The prepared material had average pore diameter about 7-12 nm. The BET surface area and pore volume of the sample are about 203 m2/g and 0.655 cm3/g, respectively. The nanorods/nanoparticles TiO2 with mesoporous structure showed higher photocatalytic activity (I3− concentration) than the nanorods TiO2, nanofibers TiO2, mesoporous TiO2, and commercial TiO2 (ST-01, P-25, JRC-01, and JRC-03). The solar energy conversion efficiency (η) of the cell using nanorods/nanoparticles TiO2 with mesoporous structure was about 7.12 % with Jsc of 13.97 mA/cm2, Voc of 0.73 V and ff of 0.70; while η of the cell using P-25 reached 5.82 % with Jsc of 12.74 mA/cm2, Voc of 0.704 V and ff of 0.649.
Process Characterization of Ultra-fine Tin Oxide Fibers Synthesis
Authors: Wang Yu , Ramos Idalia , Santiago-Avilés Jorge J.
Published: April 2011

Tin oxide (SnO2) with rutile structure is a wide-band gap semiconductor that has been used extensively in optoelectronic devices and sensors. A fibrous shape is especially favorable for the sensor applications. The authors synthesized micro-/nano- SnO2 fibers from a precursor solution of poly (ethylene oxide) (PEO), chloroform (CHCl3) and dimethyldineodecanoate tin (C22H44O4Sn) using electrospinning and metallorganics decomposition techniques. This paper uses Fourier-transform infrared spectroscopy, thermogravimetric and differential thermal analysis, and x-ray diffraction to reveal a series of chemical and physical changes from the starting chemicals to the final product of ultra-fine SnO2 fibers: the solvent CHCl3 evaporates during the electrospinning; the organic groups in PEO and C22H44O4Sn decompose with Sn-C bond in C22H44O4Sn replaced by Sn-O between 220 and 300°C, and transform into rutile structure between 300 and 380°C; the incipient rutile lattice develops into a relatively complete degree after sintering at higher temperatures up to 600°C.
Effect of anodization conditions on the synthesis of TiO2 nanopores
Authors: Chatterjee Subhasish , Ginzberg Miriam , Gersten Bonnie
Published: April 2011

Nanoporous structures play a promising role in the development of nanomechanical, nanoelectrical and biosensing devices. In addition, nanopores can be utilized as chemical and gas sensors. TiO2 is a semiconductor material, which can have a wide range of applications in nanopore-based sensors. In this study, TiO2 nanopores were prepared by electrochemical anodization. Titanium was used as the anode, while platinum was used as the cathode in an electrochemical cell filled with a hydrofluoric acid electrolyte solution. During the preparation process, titanium was converted to its oxide form. Nanostructures were synthesized under varying physical conditions, including HF concentrations of 0.5-10% and anodization times of 5-30 minutes. The resulting nanopore structures were characterized by scanning electron microscopy (SEM). With a progressive increase in HF concentration (from 0.5% to 10%), the diameter of the nanopores decreased, from approximately 100 nm in diameter to 50 nm. The nanopores showed a transformation from tube-like structures to pore networks with increased HF concentration or anodization time. The results show that the dimensions and morphology of the nanopores can be controlled by alteration of the anodization conditions.
Fabrication and Luminescence Properties of Monoclinic Gallium Oxide (β-Ga2O3) Nanostructures
Authors: Khan Aurangzeb , Jadwisienczak Wojciech M. , Lozykowski Henryk J. , Kordesch Martin E.
Published: April 2011

β-Ga2O3 nanostructures including nanowires, nanorods, nano and micro-pillars, nanosheets and nanobelts were successfully fabricated by simple and efficient thermal evaporation and condensation technique under argon flow.. The structures have been investigated by the electron microscope, XRD and EDX techniques and shown that nanostructures are predominatly β-Ga2O3 without other crystallographic phases. Cathodouminescence of as-grown nanostructures was investigated in the 10-300 K temperature range and exhibit luminescence band centered at 485 nm at 300 K due to donor-acceptor pair recombination. A new luminescence band centered at 387 nm developes at temperature below 150 K due to self-trapped exciton recombination.
Fabrication of Porous Nanostructured Thin Films For Microfluidic and Microarray Applications
Authors: Bezuidenhout Louis Wentzel , Brett Michael J.
Published: April 2011

The functionality of microfluidic and microassay devices could be enhanced through further development of porous engineered microstructures. New structural elements fabricated with porous nanostructured thin films deposited by the glancing angle deposition (GLAD) technique have been developed for these devices, and are reviewed here. With the GLAD technique, engineered structures such as vertical posts, slanted posts, helices, and square spirals can be directly grown inside microfluidic channels. A high surface area channel (517cm2/cm2) was made by depositing a silicon oxide porous film in glass microchannels (up to 4.5μm deep and 50μm wide). Similar channels were also fabricated by patterning channels in a photoresist-coated porous film. Self-sealed microchambers and channels were made by growing a SiO2 porous film on 14μm high silicon mesas (2.5×2.5μm, 7×7μm, and 25×25μm) and lines (2.5 to 50μm wide). Devices with channels containing periodic arrays of Si pillars with controllable porosity and architecture were fabricated with only one lithography and deposition cycle. The entire device was made by depositing a single GLAD porous film with areas of different porosity defining the channels. The channels, 200μm wide and 10.5μm deep, contained helical pillars with pore sizes ranging from 100nm-2μm, while a more dense nanofibrous helical film made up the remainder of the device. Fluid flow activated by negative pressure was demonstrated in this device, using both a dye solution and a 50nm microsphere solution. Material selection is not limited to silicon or silicon oxide, but may include a wide range of semiconductors, insulators and metals. A GLAD film was used to separate a test dye solution, demonstrating its potential for use in thin layer chromatography. The reported elements are suitable for a range of applications, including – but not limited to – chromatography, nano-assays and capillary electrophoresis.
Electrostatically Directed Assembly of Silver Nanoparticles for Application to Metal Enhanced Fluorescence Biosensing
Authors: Tsai De-Hao , Guo Shy-Hauh , Phaneuf Ray J , Zachariah Michael R.
Published: April 2011

In this paper we demonstrate a gas-phase process to fabricate Ag nanoparticles-based bio-sensing devices. Ag nanoparticles, prepared from the gas phase through spray pyrolysis, are size-selected via electrostatic classification. These size-selected nanoparticles are then successfully attracted and aligned onto an electrostatic-patterned biased P-N junction substrate to form high- resolution nanoparticle patterns. Particles in the size range of 30-100 nm were evaluated. Our approach provides a promising tool for precise assembly of nanoparticles for future device applications.
A Novel Gas-phase Hydrogen Peroxide Sensor Basing on a Combined Physical/chemical Transduction Mechanism
Authors: Naether Niko , Emmerich Ruediger , Berger Joerg , Friedrich Peter , Henkel Hartmut , Schneider Andreas , Schoening Michael J.
Published: April 2011

In this work, different set-ups as well as different transducer materials have been investigated in order to develop a hydrogen peroxide (H2O2) sensor for the gas phase. The sensor is based on a combined physical/chemical transduction mechanism and should be able to detect high H2O2 concentrations up to 10 Vol.%. Different sensor arrangements are presented that are based on a “three sensor” cell and a diffusion cell. As transducer materials manganese oxide and copper alloys have been investigated. For the reference part of the sensor set-up, Teflon and enamel have been tested as passivating material.
Simulations of Sub-wavelength Metallo-dielectric Photonic Crystals for Gas Sensing
Authors: Biswas Rana , Puscasu Irina , Pralle Martin , McNeal Martin , Greenwald Anton , Daly James , Johnson Edward , Neginhal Srinivas , Ding Changgeng
Published: April 2011

We have simulated metallo-dielectric photonic crystals that are sharp thermal emitters at infrared wavelengths, and are being employed in gas sensors. The simulations were performed with a rigorous scattering matrix approach where Maxwell's equations are solved in Fourier space. These metallo-dielectric photonic crystals consist of a sub-wavelength hole array in a metal layer coupled to a two-dimensional photonic crystal of the same periodicity. The sub-wavelength hole array has an enhanced transmission mode that couples to a guided mode of the photonic crystal. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum feature found for a range of lattice spacing. The structure thermally emits in a narrow band of wavelengths controlled by the lattice spacing that can be tuned over the infrared region. The underlying physics of this emissive device is modeled with rigorous scattering matrix simulations.
Multispectral Photonic Crystal Photo Sensor
Authors: Sun Xiaochen , Hu Juejun , Hong Ching-yin , Viens Jeff , Das Rupa , Agarwal Anuradha M. M. , Kimerling Lionel C.
Published: April 2011

A novel photo sensor pixel using a one-dimensional (1D) photonic crystal structure incorporating photoconductive layers has been realized. The fabricated device exploits mode discrimination to provide simultaneous multispectral photo sensing capability. Resonant cavity enhancement (RCE) design allows the use of very thin photoconductive layer to achieve dramatically suppressed shot noise, as well as high quantum efficiency. Low cost amorphous silicon is used to be photoconductive material and the simply fabrication process is completely CMOS-compatible. Detectivities as high as 2.6×1010 cmHz1/2W−1 and 2.0×1010 cmHz1/2W−1 at the two pre-selected wavelengths, 632nm and 728nm, were achieved, respectively.
Effect of Aggregation on the Rheological Properties of Carbon Nanotube Dispersions
Authors: Rahatekar Sameer Sharad , Gilman Jeffrey W , Koziol K K , Butler Simon , Elliott James A , Shaffer Milo , Mackley Malcolm , Windle Alan H
Published: April 2011

In this pape effect of nanotube aggrates on the rheological properties of multiwall carbonanntube abd epoxy suspension in epoxy resin.The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected network between aggregates of nanotubes, and not by nanotube alignment.
Synthesis and control of micro to noanscale porous structures of diamond like carbon films
Authors: Feng Peter , Yang Ben , Zhang H. X. , Wang X. P. , Upia Noel , Morella G. , Weinerd B.R.
Published: April 2011

Diamond like carbon (DLC) films are synthesized on various substrates using a pulsed KrF excimer laser ablation deposition technique. Variations of laser power density, substrate temperature, angle and distance between the substrate and target yield different sizes of porous surfaces of DLC films. Microscope is used to examine the surfaces. Raman scattering is used to characterize the samples, and the typical G and D bands have been identified. Intensities and profiles of the G and D bands closely depend on laser power density. The relationship between the deposition rate and the power density is also studied.
Electrical Characterization of GaN Based Ultraviolet and Blue Light Emitting Diodes
Authors: Tegueu Alphonse-Marie Kamto , Akpa Okechukwu , Guha Arindra , Das Kalyankumar
Published: April 2011

Gallium nitride based ultraviolet (UV) and blue AlGaN/GaN/AlGaN double heterojunction structure light emitting diodes (LEDs) were electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements as a function of frequency. An analysis of logarithmic plots of the forward I-V characteristics indicated that current in these diodes was proportional to Vx, as opposed to eqV/nkT, where x was observed to be either 1 or 2 at low biases increasing to as high as 40 at higher biases. The dependence of diode forward current on Vx is likely to be due to space charge limited current in the presence of a high concentration of deep level states in the bandgap. The concentration of deep states and their position in the band gap were extracted from these logarithmic plots. For both the blue and the UV LEDs, several closely spaced levels were obtained, located most likely in the range between EV and EV + 0.5 eV with concentrations of the order of 1016/cm3 to 1017/cm3. Capacitance-voltage measurements as a function of frequency (200 Hz - 1 MHz) at room temperature yielded a density of approximately 1 × 1015 cm−3 located at 0.46 eV above the valence band-edge for both the UV and blue LED. Even though the location of these deep states from the I-V and C-V measurements are within the same range, the two orders magnitude difference in the concentration of deep states is not well understood at this point.
Selective Area Growth of GaN Nano Islands by Metal Organic Chemical Vapor Deposition: Experiments and Computer Simulations
Authors: Chandolu Anilkumar , Kipshidze Gela D , Nikishin Sergey A , Tian Lu , Daoying Song , Holtz Mark , Lobanova Anya
Published: April 2011

We report the properties of GaN islands selectively grown by MOCVD on (0001) GaN/sapphire templates and on bare (0001) sapphire substrates. The approach allows us to grow GaN crystals with control over size and density through optical (micro-scale) and e-beam (nano-scale) lithography, and control over shape through MOCVD growth parameters. We have obtained complete pyramidal and prismatic hexagonal GaN islands. The growth characteristics are found to be very different from what we obtain for epitaxial layers, an effect which is attributed to micro/nanoloading and surface diffusion of source materials on the hard mask. From the dependence of growth rate of the pyramids with pitch we evaluate Ga surface diffusion length of ∼ 10 μm over SiO2 mask. We present a growth model based on diffusion and discuss the results of modeling with experimental data. Using micro-Raman spectroscopy the stress in pyramidal and prismatic islands was evaluated to be 20 MPa and 85 MPa, respectively. This implies that the selectively grown islands are relatively more relaxed compared to similar thickness of uniform layers. Micro catholdoluminescence (CL) shows a narrow line width and a better quality of GaN nano islands grown on e-beam lithography patterned templates. The GaN islands, of varying shapes, were overgrown with InGaN multiple quantum wells, which showed a few times stronger micro-CL emission than from GaN.
Position-Controlled InN Nano-dot Growth on Patterned Substrates by ECR-MBE
Authors: Yamaguchi Taihei , Araki Tsutomu , Naoi Hiroyuki , Nanishi Yasushi
Published: April 2011

We report on the growth of self-aligned InN nano-dots on nano-patterned GaN templates by electron cyclotron resonance plasma-excited molecular beam epitaxy (ECR-MBE). In the fabrication of the nano-dots, InN was grown on GaN templates with reticular patterns of holes, which were prepared by the focused ion beam (FIB) technique. The InN nano-dots were formed selectively at the holes, resulting in the reticular array of InN nano-dos. The size of InN dots was controlled by varying the hole-pitch and the growth temperature. Furthermore, the shape of InN dots improved by thermal annealing after the growth. We have succeeded in controlling the position and size of InN nano-dots on nano-patterned substrates. Typically, InN nano-dots with a diameter of 50 nm and a height of 10 nm were fabricated in 410°C growth.
Electroluminescence from Single 3D GaN Nanowire Grown by Self-Catalytic Molecular Beam Epitaxy
Authors: Kendrick Chito E. , Tilley R. , Kobayashi M. , Reeves R. J. , Durbin S. M.
Published: April 2011

3-D branching GaN nanowires have been grown using the intermediate and Ga-rich growth regimes of plasma assisted molecular beam epitaxy. Evidence that the growth is due to an auto-catalytic VLS process is obtained through SEM images showing droplet termination heads, the composition of which is essentially pure Ga. TEM analysis revealed a defect free crystal structure, even in the trunk to branch junction. Cathodoluminescence from the trunk of the branching nanowires produced a strong luminescence feature at 3.44 eV, while a slight decrease in energy to 3.1 eV was observed at the interface between the nanowire and epilayer or kink site. No yellow luminescence was detected, further suggesting a defect free growth. Preliminary I-V measurements give mixed results, suggesting intrinsic n-type nanowires.
Properties of InN layers grown by High Pressure CVD
Authors: Alevli Mustafa , Durkaya Goksel , Kirste Ronny , Weesekara Aruna , Perera Unil , Fenwick William , Woods Vincent , Ferguson Ian T. , Hoffmann Axel , Dietz Nikolaus
Published: April 2011

Indium nitride (InN) and indium-rich group III-nitride alloys are promising materials for advanced optoelectronic device applications. Indium-rich alloys, e.g. (Ga1-y-xAlyInx)N will enable the fabrication of high-efficient light emitting diodes tunable in the whole visible spectral region, as well as advanced high speed optoelectronics for optical communication operating. The present limitation in this area is the growth of high quality InN and indium-rich group III-nitride alloys as documented in many controversial reports on the true physical properties of InN. The difficulties arise from the low dissociation temperature of InN that requires an extraordinarily high nitrogen overpressure to stabilize the material up to optimum growth temperatures. We developed a novel “high-pressure chemical vapor deposition” (HPCVD) system, capable to control and analyze the vast different partial pressures of the constituents. Our results show that the chosen HPCVD pathway leads to high-quality single crystalline InN, demonstrating that HPCVD is a viable tool for the growth of indium rich group III nitride alloys. The structural analysis of InN deposited on GaN-sapphire substrate by XRD show single phase InN(0002) peaks with full width half maximum (FWHM) around 400 arcsec. Infrared reflectance spectroscopy is used to analyze the plasmon frequencies, high frequency dielectric constants, the free carrier concentrations and carrier mobilities in these layers. For nominal undoped InN layers, free carrier concentrations in the mid 1019 cm−3 and mobilities around 600 cm−2-V-1-s-1 are observed. Further improvements are expected as the growth parameters are optimized. The explored growth parameters are close to of those employed for GaN growth conditions, which is a major step towards the fabrication of indium rich (Ga1−y−xAlyInx)N alloys and heterostructures.
Photoluminescence, Capacitance-Voltage, and Variable Field Hall Effect Measurements of Mg-Doped InN
Authors: Swartz Craig Hartley , Durbin Steven M. , Reeves Roger J. , Prince Katherine , Kennedy John V. , Chandril Sandeep , Myers Thomas H. , Carder Damian
Published: April 2011

Variable magnetic field Hall effect, photoluminescence (PL) and capacitance-voltage (CV) analysis have been used to study InN layers grown by plasma assisted molecular beam epitaxy. All three techniques reveal evidence of a buried p-type layer beneath a surface electron accumulation layer in heavily Mg-doped samples. The use of lattice-matched Yttria-stablized Zirconia substrates also provides evidence of a p-type layer.
Photoluminescence from Gd-implanted AlN and GaN Epilayers
Authors: Zavada John M , Nepal Neeraj , Lin J. , Kim K. H. , Jiang H. X. , Hite J. , Thaler G. T. , Frazier R. M. , Abernathy C. R. , Pearton S. J.
Published: April 2011

GaN and AlN thin films were implanted with gadolinium (Gd)atoms and characterized using deep ultra-violet (UV) photoluminescence(PL). The Gd-implanted samples were annealed at temperatures up to 1178K in a flowing N2 gas to facilitate recovery of implantation-related damage. Using the output at 195 nm from a quadrupled Ti:sapphire laser, narrow PL emission was observed at 318 nm from the Gd- implanted AlN thin films. This emission is characteristic of the lowest energy 4f transition of the trivalent Gd ion. A boarder emission band, also centered at 318 nm, was observed under excitation at 266 nm. No PL emission was observed from the Gd-implanted GaN thin films at either the bandedge or due to a 4f transition. The dependence of the UV emission on AlN sample temperature was systematically studied. The peak PL emission intensity decreased by less that a factor of 3 over the temperature range of 10 K to 300 K. Decay transients of the UV emission were measured indicating that the lifetime of this emission is very fast.
Structural Defects in Laterally Overgrown GaN Layers Grown on Non-polar Substrates
Authors: Liliental-Weber Zuzanna , Ni X. , Morkoc H.
Published: April 2011

Transmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (1120) GaN grown on (1102) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.
AlGaN/GaN-sensors for Monitoring of Enzyme Activity by pH-Measurements
Authors: Kittler Gabriel , Spitznas Armin , Luebbers Benedikt , Lebedev Vadim , Wegener Dennis , Gebinoga Michael , Weise Frank , Schober Andreas , Ambacher Oliver
Published: April 2011

GaN based pH-sensors were used to measure the reaction and the kinetics of a lipase assay producing caprylic acid. Sensor structures consist of an AlGaN/GaN-heterostructure grown by plasma-induced molecular beam epitaxy with a thin GaN cap layer. The carrier concentration of the two-dimensional electron gas is manipulated by changing the surface potential due to changes in pH value.
Magnetic and Optical Properties of Eu-doped GaN
Authors: Hite Jennifer , Thaler G T , Park J H , Steckl A J , Abernathy C R , Zavada J M , Pearton Stephen
Published: April 2011

GaN films were doped with Eu to a concentration of ∼0.12 at. % during growth at 800°C by molecular beam epitaxy, with the Eu cell temperature held constant at 470°C. All samples were post-annealed at 675°C. The films exhibited strong photoluminescence (PL) in the red (622 nm) whose absolute intensity was a function of the Ga flux during growth, which ranged from 3-5.4×10−7 Torr. The maximum PL intensity was obtained at a Ga flux of 3.6×10−7 Torr. The samples showed room temperature ferromagnetism with saturation magnetization of ∼0.1-0.45 emu/cm3, consistent with past reports where the Eu was found to be predominantly occupying substitutional Ga sites. There was an inverse correlation between the PL intensity and the saturation magnetization in the films. X-ray diffraction showed the presence of EuGa phases under all of our growth conditions but these cannot account for the observed magnetic properties.