bluuebunny/crossref_metadata_2025 huggingface dataset:
Al-Oxynitride Buffer Layer Facilities for PrOX/SiC Interfaces
Authors: Henkel Karsten , Sohal Rakesh , Schwiertz Carola , Burkov Yevgen , Torche Mohamed , Schmeißer Dieter
Published: April 2011

We investigate the dielectric properties of Praseodymium based oxides and silicates by preparing MIS structures consisting of a metal layer (M), PrOX (praseodymium oxide) as a high-k insulating layer (I), and silicon (Si) or silicon carbide (SiC) as semiconductor substrates (S).

The use of a buffer layer between PrOX and SiC is necessary as we found destructive interactions like silicate and graphite formation between these materials. Based on a higher permittivity value than SiO2 and a good lattice matching in conjunction with nearly the same thermal expansion coefficient to SiC, we focus on aluminum oxynitride (AlON) as a suitable buffer layer for this high-k/wide-bandgap system. We report on results achieved by Synchrotron Radiation Photoemission Spectroscopy (SRPES) and by electrical measurements.

In our spectroscopic investigations we found a stable AlON/3C-SiC interface as well as no elemental carbon and silicate contributions in the core levels after thin PrOX deposition and annealing up to 900°C.

In electrical characterizations of PrOX/AlON stacks on silicon we already found a strong improvement in the leakage current down to values of 10-7 A/cm2 at an CET of 4nm. We observed an interface state density in the range of 5x1011-1x1012/eVcm2 and 1-5x1012/eVcm2 on Si and SiC, respectively.
Investigation of Local Coordination and Electronic Structure of Dielectric Thin Films from Theoretical Energy-Loss Spectra
Authors: Singh Manish K. , Rosado Javier , Katamreddy Rajesh , Deshpande Anand , Takoudis Christos G.
Published: April 2011

Quantum mechanical simulations were performed to calculate the valence electron energy-loss spectra (VEELS) for hafnium oxide, hafnium silicate, silicon oxide and silicon systems using the full potential Linearized Augmented Plane Wave (LAPW) formalism within the Density Functional Theory (DFT) framework. The needed energy-loss function (ELF) was derived from the calculation of the complex dielectric tensor within the random phase approximation (RPA). The calculated spectra were compared with experimental scanning transmission electron microscopy (STEM)/EELS of atomic layer deposited (ALD) HfO2 on Si(100) to evaluate their use as a “fingerprint” method that can be used to distinguish among various polymorphs of HfO2 thin films and relate the fine structure to the electronic structure and local bonding environment. Calculated low-loss spectra are found to be in satisfactory agreement with experimental data. Also, the combination of such theoretical calculations and experimental data could be of key importance in our understanding of fundamental issues of these systems. Compared to energy-loss near edge structure (ELNES) or core energy-loss spectra, the ELF calculated for low-loss spectra is computationally less expensive and can prove useful for prompt analysis.
X-Ray Reflectometry Determination of Structural Information from Atomic Layer Deposition Nanometer-scale Hafnium Oxide Thin Films
Authors: Windover Donald , Gil D. L. , Cline J. P. , Henins A , Armstrong N. , Hung P. Y. , Song S. C. , Jammy R. , Diebold A.
Published: April 2011

This work demonstrates the application of a Markov Chain Monte Carlo (MCMC) approach to modeling X-ray reflectometry (XRR) data taken from a sub 10 nm Hafnium oxide film. We present here a comparison of two structural models for a 6 nm HfxOy atomic layer deposition (ALD) film on Si. Using the MCMC method and two distinct structural models, we show evidence of a thin interface between the HfxOy and Si layers with a density much higher than native SiO2. Results from genetic algorithm XRR analysis and thickness measurements using cross-sectional transmission electron microscopy are included for comparison. We also demonstrate that our interpretation of HfxOy thickness differs between the two structural models (i.e., total film thicknesses may be partially additive within each model).
Ir/Au Ohmic Contacts on Bulk, Single-Crystal n-Type ZnO
Authors: Wright J.S. , Khanna R. , Stafford L. , Gila B.P. , Norton D.P. , Pearton S.J. , Ren F. , Kravchenko I.I.
Published: April 2011

Purpose: Need for reliable, thermally stable Ohmic metallizations for ZnO. Because of difficulties with current common contact metals, there exists a heavy desire for metals with high melting temperatures and low reactivities.
Reactive Co-Evaporation of YBCO for 2G HTS Tapes
Authors: Storer Jonathan , Hänisch Jens , Sheehan Chris , Matias Vladimir
Published: April 2011

We present a new reel-to-reel method for growth of high temperature super-conducting (HTS) films by reactive co-evaporation on flexible metal tapes. We have demonstrated proof of principle for this method with a small laboratory-scale setup using 8 cm long tape pieces. YBa2Cu3O7-δ is deposited on ion-beam assisted deposition textured MgO layers on top of flexible polycrystalline metal tapes. Critical current densities at 75.5 K of over 2 MA/cm2 have been achieved in HTS films with over 2 μm in thickness, yielding a self field critical current of 450 A/cm-width. A 4.5 μm thick film had a self field critical current of 590 A/cm. We discuss some practical possibilities for manufacturing of superconducting wire using this process and present new areas of research that are still needed.
Fabrication of Piezoelectric Polyvinylidene Fluoride (PVDF) Microstructures by Soft Lithography for Tissue Engineering and Cell Biology Applications
Authors: Gallego Daniel , Ferrell Nicholas J. , Hansford Derek J.
Published: April 2011

A method for the fabrication of piezoelectric polyvinylidene fluoride (PVDF) microstructures is described. Embossed and individual features with highly defined geometries at the microscale were obtained using soft lithography-based techniques. Various structure geometries were obtained, including pillars (three different aspect ratios), parallel lines, and criss-crossed lines. SEM characterization revealed uniform patterns with dimensions ranging from 2 μm ñ 15 μm. Human osteosarcoma (HOS) cell cultures were used to evaluate the cytocompatibility of the microstructures. SEM and fluorescence microscopy showed adequate cell adhesion, proliferation, and strong interaction with tips and corners of the microdiscontinuities. Microfabricated piezoelectric PVDF structures could find applications in the fabrication of mechanically active tissue engineering scaffolds, and the development of dynamic sensors at the cellular and subcellular levels.
Fabrication of Molecular Micro-NanoStructures by Surface-Tension-Driven Technique
Authors: Viola Ilenia , Sala Fabio Della , Piacenza Manuel , Favaretto Laura , Gazzano Massimo , Barbarella Giovanna , Cingolani Roberto , Gigli Giuseppe
Published: April 2011

We present the fabrication of a pixels structure by a well-defined pattern replication of a micrometer template driven by a surface free-energy lithographic technique, realized by molecular aggregation in dewetting conditions and by confining the liquid solution with geometric boundaries. The organization in the solid-state of the selected thiophene-based molecular materials allows to realize a bicoloured, green and red-emitting pixels structure, by exploiting the molecular structural arrangement, induced during a dewetting process, and the great conformational flexibility of DTT7Me.
Photoresist Free Negative and Positive Photolithographic Deposition of Zirconium Oxide Films from Photosensitive Metal Organic Compounds
Authors: Zhang Xin , Hill Ross H.
Published: April 2011

Photoresist free photolithographic deposition of zirconium oxide from photosensitive zirconium complexes has been achieved using photochemical metal organic deposition. In this contribution, the deposition of patterned zirconium oxide is used as an example to demonstrate both negative and positive photolithographic deposition. In the prototypical deposition of zirconium oxide by photochemical metal organic deposition, a solution containing zirconium (IV) di-n-butoxide bis(2, 4-pentanedionate) was used to spin coat a silicon substrate, resulting in an amorphous film. The film was then exposed to UV light leading to the formation of zirconium oxide and other volatile products. The resultant zirconium oxide film was investigated by X-ray diffraction and Auger Electron Spectroscopy. Irradiating the precursor film through a photo mask led to a latent image which yielded either a negative or a positive pattern dependent upon developer. Subject to further photochemical or thermal treatment, a zirconium oxide pattern can be obtained. Similar results were obtained using a series of zirconium (IV) complexes. Both positive and negative patterns of zirconium oxide with 2 micron feature sizes were obtained.
Device Model for Light-Emitting Field-Effect Transistors with Organic Semiconductor Channel
Authors: Ruden P. Paul , Smith Darryl L.
Published: April 2011

We present a device model for light-emitting, ambipolar, organic field-effect transistors based on the gradual channel approximation. The model results are in very good agreement with recent experimental data. Trapping of injected carriers in localized states in the channel region is shown to be an important mechanism that can strongly affect the transfer characteristics and the light emission of these devices.
Role of Charge Interaction in the Behavior of Organic Thin Film Transistors
Authors: Erlen Christoph , Brunetti Francesca , Fiebig Matthias , Scarpa Giuseppe , Nickel Bert , Di Carlo Aldo , Lugli Paolo
Published: April 2011

Strong hysteresis in the I-V characteristics of organic thin film transistors are a severe obstacle for the implementation of large circuits. It therefore is a key success factor for the optimization and widespread application of organic electronics to understand the underlying principles. We report the fabrication of two types of pentacene transistors with either polyvinyl alcohol (PVA) or SiO2 as gate dielectric. These devices respond to transient measurement sweeps with a fundamentally different I-V hysteresis. A self-contained model is presented, which associates this behavior with the influence of traps at the SiO2/pentacene interface and polarization in the PVA layer. Simulations employing the commercial drift-diffusion tool SENTAURUSTM are performed to verify our models.
Study of Oxetane Toughened Cationic UV Curable Marine Fouling Release Coating
Authors: Chen Zhigang , Wagner Rachel , Patel Sandeep , Kim Jongsoo , Stafslien Shane , Daniels Justin , Wal Lyndsi Vander , Siripirom Chavanin , Chisholm Bret
Published: April 2011

To develop a cationic UV curable, tough fouling-release coating for marine vessels, a difunctional oxetane monomer was used to copolymerize with the epoxy-siloxane oligomer at loading levels from 10% to 40% wt.. The resulting coatings showed enhanced solvent resistance, impact resistance and modulus, while remained hydrophobic before and after immersion in artificial sea water. In marine microorganism bioassay, these oxetane toughened coatings showed no leachate toxicity and the coating surfaces were non-toxic to biofilm growth. The fouling removal performance for these coatings was found to be microorganism dependent. Live barnacle reattachment assay showed that the toughened coatings had a removal force comparable to the reference silicone coatings Dow Corning T2 and 3140.
Electrical Transport Behavior in Phenolic Resin-based Composites Doped with Multi-walled Carbon Nanotubes
Authors: Minamisawa Renato Amaral , Chhay Bopha , ILA Daryush
Published: April 2011

The reported electromagnetic properties of carbon nanotubes (CNT) make them a promising material for nanoelectronic applications [1,2]. Addition of CNT has recently been shown to enhance mechanical properties of phenolic-resin polymers [3]. We are attempting to control the electrical transport behavior of phenolic-based polymers doped with CNT as a function of the different nanopowder concentration added to the polymer. In that regard, we developed a technique to obtain a material with homogenous dispersion of nanopowders, an important factor that influences the transport behavior. The chemical structure characterization was also evaluated using optical techniques.
Glassy Polymeric Carbon Resistivity as a Function of Carbon Nanotubes
Authors: ILA Daryush , Minamisawa Renato , Budak Satilmis , Zheng Bangke , Ila Daryush
Published: April 2011

Glassy Polymeric Carbon (GPC) is a material widely used because of its high temperature properties, inertness and biocompatibility [1]. GPC samples were prepared from a phenolic resin, cured in a careful process at 100 ºC and pyrolyzed to 1000 ºC. In this work, we have introduced 3wt%, 10wt%, and 20 wt% of Carbon Nano Tubes (CNT) in the precursor resin to study the evolution of the electrical conductivities of the nanocomposite as a function of the CNT concentration.
Nanostructuring of Hybrid Silicas: New Approach to Bridged Silsesquioxanes with Purine-Pyrimidine Base Pairs as Bridging Units
Authors: Man Michel Wong Chi , Arrachart Guilhem , Carcel Carole , Moreau Joël J.E. , Bonhomme Christian , Babonneau Florence , Creff Gaëlle , Bantignies Jean-Louis , Dieudonne Philippe , Alonso Bruno
Published: April 2011

A new route to synthesize hybrid silica-based network with bridging organic units via molecular recognition is described. The hydrolysis of two monosilylated complementary base pairs, one bearing an adenine fragment and the other a thymine fragment leads to the formation of a powdered sample that has been characterized by Scanning Electron Microscopy (SEM), Powder X-ray Diffraction (PXRD) FTIR and solid state NMR (1H, 13C and 29Si). This last technique proved to be extremely powerful to directly demonstrate the occurrence of heteroassembly of the nucleobase-based silylated fragments, through the use of two-dimensional 1H double-quanta MAS-NMR that could probe spatial proximities between the thymine NH groups and the adenine NH2 groups.
Phase Separation in Alkoxy-Derived Silica System Containing Polyacrylamide
Authors: Kawamoto Kousuke , Nakanishi Kazuki , Hanada Teiichi
Published: April 2011

By inducing phase separation parallel to the sol-gel transition of alkoxy-derived silica systems, gels having both macroporous and mesoporous structures can be obtained. Using poly(acrylamide) (PAAm) as a phase-separation inducer, macro/mesoporous silica gels were synthesized. After solvent exchange by water, the size distribution of mesopores of wet gels was evaluated by thermoporometry using a differential scanning calorimetry (DSC). Alternatively, gels were evaporation-dried after solvent exchange by ethanol or water/ethanol, followed by heat-treatment to completely remove volatile and organic components. Characterization of the dried or heat-treated samples was carried out using a scanning electron microscope (SEM) and by nitrogen adsorption measurements. Experimental results showed that the interaction between PAAm and silica is not so strong as the case of polymers having poly(oxyethylene) chains. The contribution of the secondary phase separation within the crosslinking silica-rich phase was suggested to be responsible for the mesopore formation in the PAAm-silica system.
Material Characterisation of a Novel Permeation Barrier for Flexible Organic Displays
Authors: Gartside Jonathan , Mandlik Prashant , Wagner Sigurd , Zhou Teddy , Silvernail Jeff , Hack Mike
Published: April 2011

Encapsulation for flexible organic light emitting diodes (OLEDs) is an area of active research. Multilayer barriers, with alternating organic and inorganic layers, currently offer the best resistance to oxygen and water ingression. However, the complexity of the multilayer structure makes the deposition costly and time-consuming. Here we report an effective single-compound barrier layer deposited by single-chamber plasma enhanced chemical vapour deposition (PE-CVD) from hexamethyl disiloxane (HMDSO) and oxygen source gases. The barrier layer has displayed excellent permeation resistance, with coated OLED devices surviving over 1000 hours in accelerated shelf-life tests (65°C and 85% relative humidity) in near perfect condition. Material characterisation detailed in this paper indicates that the material is an inorganic-polymer hybrid, combining the permeation resistance of an oxide with the flexibility of a polymer. The surface characteristics, chemical composition and mechanical properties of the novel barrier material are investigated with variation in PE-CVD deposition conditions.
Polymer-Silica Nanocomposite Aerogels with Enhanced Mechanical Properties Using Chemical Vapor Deposition (CVD) of Cyanoacrylates
Authors: Boday Dylan J. , Loy Douglas A. , DeFriend Kimberley A. , Wilson Kennard V. , Coder David
Published: April 2011

Aerogels were structurally modified using chemical vapor deposition (CVD) of cyanoacrylate monomers to afford polycyanoacrylate-aerogel nanocomposites. Silica aerogels are low density, high surface area materials whose applications are limited by their fragility. Cyanoacrylate CVD allowed us to deposit a film of organic polymer throughout fragile porous monoliths within hours. Our experiments have shown that polymerization of the cyanoacrylate monomers was initiated by the adsorbed water on the surface of the silica permitting the nanocomposites structures to be formed with little or no sample preparation. We found that the strength of the polycyanoacrylate-aerogel nanocomposites increased thirty two-fold over the untreated aerogels with only a three-fold increase in density and an eight-fold decrease in surface area. Along with the improvement in mechanical properties, the aerogels became less hydrophilic than un-modified aerogels. Polycyanoacrylate-coated aerogels were placed directly into water and did not suffer catastrophic fragmentation as observed with un-modified silica aerogels.
Synthesis and Orientation of Poly(Dialkylstannane)s
Authors: Choffat Fabien , Fornera Sara , Smith Paul , Caseri Walter
Published: April 2011

Polystannanes, i.e. organometallic polymers of the chemical formula (SnR2)n, are relatively little explored, although they belong to the rare examples of polymers which are characterized by a backbone of metal atoms which are linked by covalent bonds. We developed a new synthetic route which yields pure linear poly(dibutylstannane) [Sn(Bu)2]n by polymerization of dibutylstannane (dibutyltin dihydride) with the catalyst [RhCl(PPh3)3]. Here, we report that the conversion and the reaction rate of dibutylstannane depends crucially on the temperature and [RhCl(PPh3)3] is also suited for the polymerization of dioctylstannane and didodecylstannane. The polymers thus obtained were characterized by 1H, 13C and 119Sn NMR spectroscopy: Orientation of all polystannanes was achieved by tensile drawing. The orientation was examined by UV-vis spectroscopy with polarized light and X-ray diffraction. Remarkably, the orientation of the backbone depended on the length of the alkyl groups.
Fabrication of Fluorescent Cellular Probes: Hybrid Dendrimer/Gold Nanoclusters
Authors: Zhong Chang , Bao Yuping , Vu Dung M. , Dyer R. Brian , Martinez Jennifer S.
Published: April 2011

Fluorescent metal nanoclusters, which consist of collections of small numbers of noble metal atoms, are of great interest in photochemistry and photophysics due to their strong size-dependent emission. Historically their generation was confined to gaseous and solid phases; however, recently a unique organic/inorganic hybrid materials approach was developed that utilizes dendrimers as templates to protect nanoclusters from solution based fluorescence quenching. These hybrid dendrimer/gold nanoclusters are water-soluble and highly fluorescent. Yet there are several intrinsic deficiencies in their synthetic method: first, NaBH4, a toxic chemical, was used as reducing agent in the reaction; and second, the reaction yield was low due to the concurrent formation of large, non-emissive, gold particles. Here we report a particle-free method to produce dendrimer-encapsulated gold nanoclusters in high-yield. Proof of concept is demonstrated using OH-terminated poly(amidoamine) dendrimer and Au(PX3)3Cl (X = Ph, Me), but the approach can also be extended to the combination of other dendrimers and organic noble metal salts. Our approach yields fluorescent clusters with homogeneous size distribution. These clusters can be transferred to aqueous solution and used directly for biological applications.
Bio-Inspired Mineralization from Aqueous Solutions of Zinc Nitrate Directed by Building Blocks of DNA
Authors: Jost Micha , Gerstel Peter , Bill Joachim , Aldinger Fritz
Published: April 2011

In this paper, the suitability of DNA- and RNA-bases, nucleosides and nucleotides, and DNA itself as structure-directing agents for the mineralization of ZnO-based materials is discussed. Those bioorganic molecules are able to trigger the morphology of mineralization products ranging from smooth, homogenous thin films to sponge-like, sheet-like and fibrous products. Besides the investigation of morphological features by scanning electron microscopy, the structural characterization of these materials by X-ray diffraction, vibrational spectroscopy, photoluminescence spectroscopy and photoelectron spectroscopy is discussed.
A method to Generate Biomimetic Superhydrophobic Engineering Surfaces
Authors: Zhang Yilei , Sundararajan Sriram
Published: April 2011

A versatile hybrid processing method that combines electrostatic deposition of microparticles and subsequent anisotropic plasma etching is described that can generate superhydrophobic engineering surfaces with tunable bimodal roughness and a thin hydrophobic fluorocarbon film. These surfaces exhibit contact angles with water of more than 160°.
Electrochemical Release of Immobilized IgG Protein
Authors: Mahmud Tanveer , Wlodarski Wojtek , Mitchell Arnan , Gras Sally , Trinchi Adrian , Kalantar-zadeh Kourosh
Published: April 2011

In this paper, we present the electrochemically programmed release of immobilized IgG protein molecules that have been attached to gold coated surfaces via a thiol-gold linkage. Fluorescence microscopy has been used to image the release of fluorescently tagged IgGs in phosphate buffered saline. In this technique, the reductive desorption of self-assembled monolayers is employed for the release of proteins, which are immobilized on the surface either by non-covalent or covalent interactions. The voltage applied for the release of proteins is in a range of -1.5V to -60V.
High Sensitivity Photonic Crystal Biosensor Incorporating Nanorod Structures for Enhanced Surface Area
Authors: Zhang Wei , Ganesh Nikhil , Block Ian D. , Cunningham Brian T.
Published: April 2011

We report efforts at enhancement of the surface area of a photonic crystal biosensor through incorporation of a porous titanium dioxide film into the device. The film possessing the structure of nanorods is deposited by the glancing angle deposition technique. Results for detection of polymer films, large proteins and small molecules indicate up to a four-fold enhancement of detected adsorbed mass density for high surface area sensors, compared with sensors without the high surface area coating.
ITO-Based Cathode for Application in Semitransparent Organic Photovoltaic Cells
Authors: Ng Ging-Meng , Kietzke Elizabeth Lekha , Kietzke Thomas , Tan Li-Wei , Liew Pooi-Kwan , Zhu Furong
Published: April 2011

A high performance semitransparent cathode is one of the major impediments to the high performance semitransparent and tandem organic photovoltaic (OPV) cells. In this work, we discuss the possible designs of semitransparent cathode to improve the performance of semitransparent OPV cells. The optical properties of the poly(3-hexylthiophene) (P3HT): 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)-based OPV cells were studied by the optical admittance analysis. The performance of the OPV cells made with an opaque Ca(10nm)/Ag(100nm) cathode and a semitransparent Ca(10nm)/Ag(10nm)/ITO cathode are discussed. The interfacial properties at the cathode/organic interface were analyzed using the time-of-flight secondary ion mass spectroscopy (TOF-SIMS). The TOF-SIMS depth profile revealed that calcium oxide formed at the Ca/organic interface in semitransparent OPV cells, which was induced by the ITO sputtering process. It shows that the presence of calcium oxide at the organic/cathode interface could be the main reason resulting in a poor fill factor of a semitransparent OPV cell (∼23%) as compared to that of a reference cell (∼43%).
Electrical and Photoelectrical Properties of Nanostructured ZnO Thin Films for Photovoltaic Applications
Authors: Antohe Stefan , Tazlaoanu Cezar , Socol Gabriel , Magherusan Larisa , Enculescu Ionut , Bazavan Dan , Mihailescu Ion , Antohe Stefan
Published: April 2011

Structural, electrical and optical characterizations of nanostructured ZnO thin films used as photosensitized electrodes in photovoltaic cells applications are reported. Nanostructured ZnO thin films were deposited on optical glass substrates by pulsed-laser deposition (PLD), their structure and morphology being optimized for photovoltaic applications. Structural analysis of the samples by X-ray diffraction revealed that the films consist of a hexagonal-close-packed wurtzite type phase ZnO, (001) preferentially oriented in the growth direction. The ZnO films are highly transparent in visible region of solar spectrum, and exhibit electrical resistivities in the range 10-4 - 10-2Ω.m
Photonic Crystal Structures of Biologic Origin: Butterfly Wing Scales
Authors: Biró L´szló Péter , Bálint Zsolt , Kertész Krisztián , Vértesy Zofia , Márk Géza István , Tapasztó Levente , Vigneron Jean-Pol , Lousse Virginie , Biro Laszlo Peter
Published: April 2011

Photonic crystal type nanoarchitectures (built of chitin and air) occurring in the scales of two male butterflies, with dorsal blue and ventral green coloration were investigated by optical microscopy, SEM and TEM. Reflectance data were collected by normal incidence measurements and by integrated reflectance measurements, too. Reflectance peaks with close positions in the blue range of the spectrum were found both for the single crystalline scales and for the most disordered photonic band gap material. Polycrystalline structures with grain size on the micron scale produce matt reflectors, while moderately ordered “pepper-pot” type structures can yield surfaces with shiny aspect. It was found that the cover scales on each sides of the wing are primarily responsible for the observed colors. The character of the observed colors (shiny, or matt) correlates with the habitat of the investigated butterflies.
Chemical Tension in VLS Nanostructure Growth Process: From Nanohillocks to Nanowires
Authors: Li Na , Tan Teh Y. , Gösele Ulrich
Published: April 2011

ABSTRACT

We formulate a global equilibrium model to describe the growth of 1-d nanostructures in the VLS process by including also the chemical tension in addition to the physical tensions. The chemical tension derives from the Gibbs free energy release due to the growth of a crystal layer. The system global equilibrium is attained via the balance of the static physical tensions and the dynamic chemical tension, which allows the system to reach the minimum Gibbs free energy state. The model predicts, and provides conditions for the growth of nanowires of all sizes exceeding a lower thermodynamic limit. The model also predicts the conditions distinguishing the growth of nanaohillocks from nanowires.
Enhanced Tunneling through sub 30 Angstroms Thick Gallium Nitride Cap Layers on Silicon Carbide for Low Contact Resistance
Authors: Praharaj Choudhury Jayant
Published: April 2011

We present numerical calculations of tunneling through ultra thin wurtzite Gallium Nitride cap layers on p-doped wurtzite silicon carbide . We demonstrate the predominance of tunneling of the split-off holes to the total carrier flux, with the contribution of the heavy and the light holes damped by the large potential barrier. We calculate the contributions of spontaneous and piezoelectric polarizations to the tunneling profile seen by the holes. Two orders of magnitude enhancement is seen in the transmission probabilities for a 10 angstroms thick Gallium Nitride cap layer for holes very close to the valence band edge, compared to a barrier without any gallium nitride cap. The contact resistances are also calculated for the Gallium Nitride tunneling caps and more than two orders of magnitude lowering is seen with the ultra-thin caps. Larger cap widths induce hole accumulation layers, but the advantages of hole accumulation are offset by the higher effective tunneling width. Our calculations are relevant to nanostructures and nanodevices involving heterojunctions between gallium nitride and silicon carbide and provide the basis for low contact resistances with as-deposited metals. While our calculations focus on the regime of very high barriers to the metal of the order of 1.5 - 2 electron volts, where the method of ultra-thin caps is most useful, similar conclusions also hold for lower barrier heights.
Permittivity in Molecular Nanofilms
Authors: Vucenovic Sinisa , Ilic Dusan , Setrajcic Jovan , Sajfert Vjekoslav , Mirjanic Dragoljub
Published: April 2011

A microscopic theory of dielectrical properties of thin molecular films, i.e. quasi 2D systems bounded by two surfaces parallel to XY planes was formulated. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green's functions. It has been shown that two types of excitations can occur: bulk and surface exciton states. Analysis of the optical properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. Conditions for the appearance of localized exciton states have been especially analyzed.
Electron Energy Spectra of Single and Multiple AlGaN/GaN Quantum Dots with Spontaneous and Piezoelectric Polarization Effects
Authors: Praharaj Choudhury Jayant
Published: April 2011

We present numerical calculations of electron spectra of single and multiple coupled quantum dots based on Aluminium Gallium Nitride / Gallium Nitride heterostructures. The effect of spontaneous and piezoelectric polarization on the confinement potential seen by the electrons is taken into account through bound interface sheet charges. We also calculated the spectra without polarization effects for reference. For some quantum dot dimensions, the energy eigenvalues shift by several hundred meVs due to the polarization charges. We calculate the spectra for the two cases of box-shaped and cylindrical quantum dots. The latter case is an approximation to quantum dots with hexagonal-facet shapes recently reported in the literature. The quantum dots in our calculations are surrounded by vacuum in the lateral direction, but the same qualitative conclusions will hold if the dots are embedded in some material, as long as the barrier heights are large. For GaN vertical confinement of less than 30 angstroms, most of the bound states are associated with the lowest eigenvalue of the vertical confinement potential. This is also true for higher vertical confinement dimensions because the triangular potential seen by the electrons is the same for the lowest energy eigenstates. The electric field in the vertical direction is a strong function of the aluminium concentration in the AlGaN layer. As the AlGaN layer composition is varied from very high Al concentration to medium Al concentration, the spectra shift by several hundred meVs, referred to the onset of the continuous spectra. The transition frequencies between bound states and between bound and the lowest continuum states lie in the low to the high infra-red range, and can be varied over a wide range by both the dimensions and the barrier aluminium concentration. For the case of 4 coupled quantum dots formed by repeated AlGaN/GaN heterojunctions, we find that the polarization-induced electric fields lead to excessive band-bending and as a consequence there are fewer bound states compared to the spectrum calculated without polarization effects.
MOCVD Behaviors of Two-Sized InGaAs Ordered Nano-Bar Arrays Grown Selectively on a GaAs Substrate
Authors: Wang Benzhong , Chua Soo-Jin
Published: April 2011

Nanosphere lithography was used to form a nano-scaled SiO2 template on a GaAs substrate. Especially, a simple method for fabricating nanopatterns with multi feature sizes within one step has been invented. These nanopatterns, as a template, can be used to grow selectively ordered nanostructures arrays such as quantum dots, quantum bars with different feature sizes in one step. Two sized In0.25Ga0.75As nano-bar arrays have been successfully grown on a GaAs substrate by MOCVD.
Growth and Characterization of InAs Quantum Dot Enhanced Photovoltaic Devices
Authors: Hubbard Seth Martin , Raffaelle Ryne , Robinson Ross , Bailey Christopher , Wilt David , Wolford David , Maurer William , Bailey Sheila
Published: April 2011

The growth of InAs quantum dots (QDs) by organometallic vapor phase epitaxy (OMVPE) for use in GaAs based photovoltaics devices was investigated. Growth of InAs quantum dots was optimized according to their morphology and photoluminescence using growth temperature and V/III ratio. The optimized InAs QDs had sizes near 7×40 nm with a dot density of 5(±0.5)×1010 cm-2. These optimized QDs were incorporated into GaAs based p-i-n solar cell structures. Cells with single and multiple (5x) layers of QDs were embedded in the i-region of the GaAs p-i-n cell structure. An array of 1 cm2 solar cells was fabricated on these wafers, IV curves collected under 1 sun AM0 conditions, and the spectral response measured from 300-1100 nm. The quantum efficiency for each QD cell clearly shows sub-bandgap conversion, indicating a contribution due to the QDs. Unfortunately, the overarching result of the addition of quantum dots to the baseline p-i-n GaAs cells was a decrease in efficiency. However, the addition of thin GaP strain compensating layers between the QD layers, was found to reduce this efficiency degradation and significantly enhance the subgap conversion in comparison to the un-compensated quantum dot cells.
Surfactant-SWNT Assembly and Static Dielectrics of SWNTs
Authors: Wang Dan , Lu Wei , Zhang Ru , Li Zi-Chen , Chen Liwei
Published: April 2011

In this invited presentation, we report (1) the assembly of polymer surfactants at the single-walled carbon nanotube (SWNT) and water interface, which not only results in the dispersion of SWNTs in aqueous environments but also provides opportunities for controlled assembly of ternary complexes and the introduction of external stimuli-responsive SWNT dispersions; (2) the first experimental measurement of dc polarization of individual carbon nanotubes using modified scanning force microscopy techniques. The transverse dielectric constant of carbon nanotube is about 10, and this method could be used to distinguish metallic from semiconducting nanotubes.
Synthesis of Controllably Grown Carbon Nanotubes Interconnects
Authors: Lee Seon Woo , Katz David , Kornblit Avi , Lopez Daniel , Grebel Haim
Published: April 2011

Intra-connects (bridges spanning across in plane electrodes), which were made of carbon nanotube (CNT), were fabricated by CO Plasma Enhanced Chemical Vapor Deposition (PECVD), ethanol CVD and pyrolitic CO CVD. CO PECVD has been used with CO/H2 mixture at relatively low temperatures. Its yield was relatively low though and the quality of CNT intra-connect was not to par. Ethanol CVD resulted in many more multi-wall carbon nanotube (MWCNT) than single-wall carbon nanotube (SWCNT) intra-connects. CO CVD was the most effective and simplest way to grow CNT interconnects among the three methods, yielding well-aligned and straight SWCNT bridges.
Application of the G'/D Raman Ratio for Purity Assessment of Multi-Walled Carbon Nanotubes
Authors: DiLeo Roberta , Landi Brian , Raffaelle Ryne
Published: April 2011

Carbonaceous purity assessment methods are being sought after for all types of carbon nanotubes as a means to standardize the material metrology. Our most recent work has evaluated chemical vapor synthesized multi-walled carbon nanotubes (MWNTs). This effort included a protocol for assessment involving qualitative information from scanning electron microscopy (SEM) images and quantitative information from thermogravimetric analysis (TGA) and Raman spectroscopy. Presently, the analysis using Raman spectroscopy on a constructed sample set has been extended to a second excitation energy (HeNe laser at 1.96 eV) and the similar trends in the relative Raman peak ratios have been measured. In contrast to the G-band, the D and G' peaks demonstrate a Raman shift that is excitation energy-dependent, consistent with the double resonance theory. However, the Raman ratio of IG'/ID is independent of excitation energy and is observed to be the most sensitive to MWNT carbonaceous purity. Application of this approach to MWNT arrays grown on SiO2 is compared to conventional bulk powders synthesized under similar conditions. The MWNT arrays show a high degree of vertical alignment based upon SEM and a measured carbonaceous purity using the IG'/ID ratio of 75% w/w.
Doping of Al-catalyzed Vapor-liquid-solid Grown Si Nnanowires
Authors: Whang Sung Jin , Lee Sung Joo , Yang Wei Feng , Zhu Hai Chen , Gu Han Lu , Cho Byung Jin , Liew Yun Fook
Published: April 2011

We successfully synthesized high quality single crystal Si nanowires using Al catalyst via vapor-liquid-solid (VLS) mechanism, having diameters ranging from 10 to 200 nm with 10∽20 §­ of length. Characterization of physical and chemical properties of Al-catalyzed Si nanowires using transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) analysis showed that single crystal Si nanowires can be grown with Al-catalyst at 540 ¡C and selective etching of Al existing at the tip of nanowire can provide metal-free Si nanowires that are compatible with conventional Si-based IC process. By using plasma doping method, it was confirmed that the doping level can be controlled and the boron was successfully introduced on Si substrate with 3×1022/cm3 of peak doping concentration.
1-D and 2-D forms of Copper Sulfide: Electrochemical Deposition and Morphological Analysis
Authors: Singh Krishna Veer , Martinez-Morales Alfredo A. , Ozkan Mihrimah
Published: April 2011

Copper sulfide is a material with immense potential for applications in photovoltaics. Particularly, copper sulfide 1-D nanostructures (i.e. nanowires, nanorods) with well-defined morphologies may enable new types of applications or may enhance the performance of existing photoelectric devices with quantum confinement effects. In this work, we report the synthesis of copper sulfide nanorods by simple, yet very effective template assisted electrochemical deposition. Before synthesizing 1-D copper sulfide nanorods, a detailed study was conducted on electrodeposited 2-D copper sulfide films to ascertain the right parameters for electrodeposition including; electrolyte composition, temperature, deposition potential and membrane type. Excellent structural properties of these resultant nanorods make them desirable for applications in the future nano-opto-electronic devices.
Scaffolding Carbon Nanotubes into Single-Molecule Circuitry
Authors: Collins Philip G. , Coroneus John G. , Weiss Gregory A. , Collins Philip G.
Published: April 2011

While nanowires and nanotubes have been shown to be electrically sensitive to various chemicals, not enough is known about the underlying mechanisms to control or tailor this sensitivity. By limiting the chemically sensitive region of a nanostructure to a single binding site, single molecule precision can be obtained in order to study the chemoresistive response. We have developed techniques using single-walled-carbon-nanotube (SWCNT) circuits that enable single-site experimentation and illuminate the dynamics of chemical interactions. Discrete changes in the circuit conductance reveal chemical processes happening in real-time and allow SWCNT sidewalls to be deterministically broken, reformed, and conjugated to target species.
Development of Polymeric Micro/Nanostructures For Gene Delivery
Authors: Alyounes Dania , Yengo Christopher , Doran Tim , Lu Qi , Gonsalves Kenneth
Published: April 2011

Pluronic® polymers were screened for binding affinity to oligoribonucleotides (ORN) using fluorescence techniques. F127 (Mw 12600 g/mole) proved to have the strongest binding affinity. Urethane linkages were introduced into F127 and two other Pluronics, F38 (Mw 4700 g/mole) and F77 (Mw 6600 g/mole) to prepare polymers that were multiples of their respective initial molecular weights. A series of these polyurethane Pluronics were screened for binding affinity. Fluorescence studies showed a relationship between the molecular weight of the PO units and the binding affinity in the structures of the newly synthesized polyPluronics, especially in the case of F77. Light scattering confirmed the binding affinity between the ORN and F77 polymers. Particle size analysis showed an exponential increase until the critical micelle concentration. Other analogs of these polymers also studied for their binding affinity were poly(ester amines) and PINC.
Cell Response and Tissue Scaffold Triggers Investigated by Scanning Probe Recognition Microscopy
Authors: Chen Qian , Fan Y. , Kumar S. , Baczewski A. D. , Udpa L. , Ayres V. M. , Ahmed I. , Meiners S. , Rice A. F.
Published: April 2011

Tissue scaffolds have recently demonstrated widespread application in injury healing due to their biomimetic properties and their structural resemblance to the extracellular matrix in cell re-growth. The investigation of cell response to biomimetic triggers provided by tissue scaffolds will greatly extend the impact of this field.

In this paper, the response of 3T3 NIH fibroblasts to 2D planar surfaces versus their response to nanofiber mat surfaces, which have 3D effects, are investigated. A difference in cell shape from triangular cell body with prominent vertices to triangular cell body with blunted vertices and increased cell-cell adhesions at such vertices was observed using fluorescent microscopy, optical microscopy and atomic force microscopy. A new and powerful atomic force microscopy technique developed by our group, Scanning Probe Recognition Microscopy, is introduced and implemented to directly recognize and auto-focus on fibroblast vertex regions.
Cluster Ion Beam Process for Nanofabrication
Authors: Yamada Isao , Toyoda Noriaki
Published: April 2011

This paper reviews gas cluster ion beam (GCIB) technology, including the generation of cluster beams, fundamental characteristics of cluster ion to solid surface interactions, emerging industrial applications, and identification of some of the significant events which occurred as the technology has evolved into what it is today. More than 20 years have passed since the author (I.Y) first began to explore feasibility of processing by gas cluster ion beams at the Ion Beam Engineering Experimental Laboratory of Kyoto University. Processes employing ions of gaseous material clusters comprised of a few hundred to many thousand atoms are now being developed into a new field of ion beam technology. Cluster-surface collisions produce important non-linear effects which are being applied to shallow junction formation, to etching and smoothing of semiconductors, metals, and dielectrics, to assisted formation of thin films with nano-scale accuracy, and to other surface modification applications.
Ion-Beam Assist Nano-Texturing of Films
Authors: Matias Vladimir , Sheehan Chris , Findikoglu Alp T.
Published: April 2011

We present an ion-beam based fabrication method for growth of single-crystal-like films that does not utilize epitaxy on single crystal substrates. We use ion-beam assisted texturing to obtain biaxial crystalline alignment in a film. This ion-beam assisted deposition (IBAD) texturing can be done on arbitrary, but smooth substrates, including flexible polycrystalline metal tapes. With IBAD texturing of MgO and subsequent homoepitaxial growth we have demonstrated an in-plane mosaic spread FWHM as low as 2° and out-of-plane alignment of 1°. The deposition system we use includes reel-to-reel tape transport for a linear transport of substrate materials through the deposition zones. This allows for high-throughput experimentation via a linear combinatorial experimental design.
Resolution Performance of Programmable Proximity Aperture MeV Ion Beam Lithography System
Authors: Gorelick Sergey , Sajavaara Timo , Laitinen Mikko , Puttaraksa Nitipon , Whitlow Harry J.
Published: April 2011

An ion beam lithography system for light and heavy ions has been developed at the University of Jyväskylä's Accelerator Laboratory. The system employs a programmable proximity aperture to define the beam. The proximity aperture is made up of four Ta blades with precise straight edges that cut the beam in the horizontal and vertical directions. The blade positions and dimensions are controlled by a pair of high-precision linear-motion positioners. The sample is mounted on a X-Y-Z stage capable of moving with 100 nm precision steps under computer control. The resolution performance of the system is primarily governed by the proximity aperture. Pattern edge sharpness is set by the beam divergence, aperture blade straightness, and secondary and scattered particles from the aperture blade edges. Ray tracing simulations using the object oriented toolkit GEANT4 were performed to investigate the beam spatial resolution on the sample defined by the proximity aperture. The results indicate that the edge-scattering does not significantly affect the pattern edge sharpness.
Modification of Surface Morphology of UHMWPE for Biomedical Implants
Authors: Oztarhan Ahmet , Sokullu Urkac Emel , Kaya Nusret , Yenigul Mesut , Tihminlioglu Funda , Ezdesir Ayhan , Zimmerman Robert , Budak Satilmis , Muntele C , Chhay Bopha , Ila Daryush , Oks Efim , Nikolaev Alexey , Tek Zekai , Eltem Rengin
Published: April 2011

UHMWPE samples were implanted with metal and metal-gas hybrid ions (Ag, Ag+N, C+H, C+H+Ar, Ti+O ) by using improved MEVVA Ion implantation technique [1,2]. with an extraction voltage of 30 kV and fluence of 1017 ions/cm2 in an attempt to change their surface morphologies in order to understand the effect of ion implantation on the surface properties of UHMWPEs. Characterizations of the implanted samples with RBS , ATR - FTIR, spectra were compared with the un-implanted ones. Implanted and unimplanted samples were also thermally characterized by TGA and DSC. It was generally observed that C-H bond concentration seemed to be decreasing with ion implantation and the results indicated that the chain structure of UHMWPE were changed and crosslink density and polymer crystallinity were increased compared to unimplanted ones resulting in increased hardness. It was also observed that nano size cracks (approx.10nm) were significantly disappeared after Ag implantation, which also has an improved antibacterial effect. Contact angle measurements showed that wettability of samples increased with ion implantation. Results showed that metal and metal+gas hybrid ion implantation could be an effective way to improve the surface properties of UHMWPE to be used in hip and knee prosthesis.
Core-Satellite Metallic Nanoclusters in Silica Obtained by Multiple Ion Beam Processing
Authors: Mattei Giovanni , Bello Valentina , Mazzoldi Paolo , Pellegrini Giovanni , Maurizio Chiara , Battaglin Giancarlo
Published: April 2011

Ion irradiation has been used to transform spherical bimetallic AuAg nanocluster embedded in silica in a more complex structure made of a central cluster surrounded by a halo of smaller satellite nanoclusters, whose composition, size and distance from the central cluster can be tailored by controlling the irradiation parameters. This peculiar topology produces a red-shift of the surface plasma resonance of the composite through the electromagnetic coupling between the central cluster and the satellites. A calculation of the local field properties of the investigated systems within the fully-interacting generalized Mie theory showed that the satellite topology produces large local field enhancements around the central cluster.