bluuebunny/crossref_metadata_2025 huggingface dataset:
Strengthening Nanoscience Education through Multidisciplinary Collaborations
Authors: Cosby Ronald M
Published: April 2011

Recent collaborations with science and engineering faculty in major research universities have dramatically increased and strengthened research and educational opportunities in nanoscience and nanotechnology at Ball State University. The three-year Center for Computational Nanoscience (CCN) project involved eleven co-principal investigators from three disciplines (physics, chemistry, electrical engineering) and five universities, including Ball State University, University of Notre Dame, Ohio University, Purdue University, and Valparaiso University. Funded by the Indiana 21st Century Research and Technology Fund, this $1.5 million project focused on theoretical and computational investigations of the electrical and optical properties of quantum dots and included partial support for software development for the Purdue NanoHub, a web-based software repository. The effects of this collaborative project (and previous contacts) on nanoscience education and research at the undergraduate and master's levels in the Department of Physics & Astronomy at Ball State University have been extensive and are described in this paper. University and community impacts include an enhanced awareness of nanoscience and nanotechnology.
Excellent Room-Temperature Ferroelectricity in Mn-substituted BiFeO3 Thin Films Formed by Chemical Solution DepositionΨ
Authors: Singh Sushil Kumar , Ishiwara Hiroshi
Published: April 2011

Mn-substituted BiFeO3 (BFO) thin films were formed by chemical solutions deposition on Pt/Ti/SiO2/Si(100) structures. Effects of the Mn-substitution on the structure and ferroelectricity of BFO films were examined. We found that the lattice structure of the film is sensitive to the Mn-substitution and the secondary phase is appears in 50% Mn-substituted BFO films. The leakage current were increased with the Mn-substitution. However, the 5% Mn-substituted BFO film shows low leakage current than undoped BFO films in a high electric field than 0.5 MV/cm. Due to the low leakage current in Mn-doped 3, 5 and 7% BFO films, the saturated P-E hysteresis loops with remanent polarization around 100 μC/cm2 were obtained at RT.
Oxidation of Structured Silicon Thin Films for Inverse Silicon Square Spiral Photonic Crystal Fabrication
Authors: Summers Mark Alan , Brett Michael J
Published: April 2011

Photonic Band Gap (PBG) crystals are artificially engineered structures of periodically alternating dielectric materials that enable manipulation of light in unique ways. As proposed by O. Toader and S. John, large bandwidth PBG crystals based on the diamond lattice can be constructed by fabricating a two-dimensional periodic array of silicon square spirals. Furthermore, an improved photonic crystal can be constructed by fabricating the inverse of this structure, such that void square spirals are situated in a silicon backfill. This structure yields a theoretical maximum PBG of 24%, while the direct silicon square spiral structure yields a theoretical maximum of 16%. [1]

The direct silicon square spiral structure has previously been successfully fabricated using the glancing angle deposition (GLAD) process [2]. The GLAD fabrication process uses advanced substrate motion and oblique incidence deposition to engineer precise nanostructures such as helices, chevrons, or polygonal spirals. These nanostructures are grown with lateral and longitudinal periodicity using a pre-patterned substrate consisting of a tetragonal array of relief structures.

Upon successful fabrication of the direct silicon square spiral structure, it was proposed that fabrication of the inverse structure could be completed using a backfill process with a silica template [2]. A periodic array of silica square spirals would be fabricated using the GLAD technique. The template would then be filled with amorphous silicon using low-pressure chemical vapour deposition (LPCVD). To reveal the inverse silicon structure, the silica template would be removed by means of chemical etching with an isotropic chemical etchant. Creation of a suitable template for the inversion of silicon square spirals is an important step in the realization of the inverse silicon square spiral PBG crystal. However, we have seen empirically that silica square spiral films grown directly via the GLAD technique are structurally inferior to silicon films. We present an intermediate step for the fabrication of a suitable template, whereby a silicon structure is fabricated with appropriate geometries and subsequently oxidized. The procedure has been optimized to ensure a thorough oxidization of the silicon posts, while minimally distorting the structure of the square spiral template.
Adhesion Property of ITO Film on Polymer Treated by Linear Ion Source
Authors: Hsiao Shih Hsiu , Tanaka Yoshikazu , Ide-Ektessabi Ari
Published: April 2011

Indium oxide doped with tin oxide, ITO, has been extensively used as the transparent conductive electrode in display industry, and also been utilized on polymeric substrate for flexible display. The polymeric material used in flexible display has its flexibility and lightweight compared to glass-based substrate. However, it does not completely meet with the requirements in mechanical properties. The ion irradiations modify the polymeric surface that can be expected to improve its adhesion property. In this study, linear ion source was developed to treat the polymeric surface, and then ITO thin film was deposited by sputter deposition commonly utilized in display industry. Atomic Force Microscope was used to analyze the physical transformation of surface structure after the various argon and oxygen ion irradiated. Finally, the scratch testing showed the adhesive strength improved between ITO thin film and polymeric substrate when surface modified by optimum ion irradiation. Moreover, linear ion source provides the good uniformity of surface treatment and is very suitable for production-scale process.
Fabrication of Organic Thin Film Transistor Based on the Ink-Jet Printed Electrodes of Nano Silver Particles
Authors: Kim Dongjo , Jeong Sunho , Lee Sul , Park Bong-Kyun , Moon Jooho
Published: April 2011

In this work, we here developed a conductive ink which contains silver nano-particles from which the electrodes for organic thin film transistor were directly patterned by ink-jet printing. Nano-sized silver particles having ∼ 20nm diameter was used for the direct metal printing. Silver conductive ink was printed on the heavily doped n-type silicon wafer with 200-nm thick thermal SiO2 layer as a substrate. To achieve a high line resolution and smooth conductive path, the printing conditions such as the inter-drop distance, stage moving velocity and temperature of the pre-heated substrates were optimized. After the heat-treatment at temperatures of about 100 ∼ 300 ° for 30 min, the printed silver patterns exhibit metal-like appearance and the conductivity. To fabricate a coplanar type TFTs, an active material of semiconducting polymer, which was dissolved in a proper solvent, was deposited between the ink-jet printed silver electrodes by solution process. The output and transfer characterization was measured in air. The OTFT with the ink-jetted source/drain electrodes show a mobility of 1.3 × 10−3 cm2 V−1 s−1 in the saturation regime and on/off current ratio over 103 and a threshold voltage of about −13 V.
Polymer-Clay Hybrid Dielectric Layer for Flexible Organic Thin Film Transistors
Authors: Uemura Sei , Suemori Koji , Yoshida Manabu , Hoshino Satoshi , Kodzasa Takehito , Kamata Toshihide
Published: April 2011

A polymer field-effect transistor (FET) was fabricated with poly(3-hexylthophene) as an active layer and poly(methyl-methacrylate) gate dielectric modified with poly(vinyl alcohol). The influences of air atmosphere on the FET property were investigated. Under the air atmosphere, FET properties such as modulation of drain current by gate bias, leakage current and threshold voltage shift were strongly influenced by humidity. An influence was investigated by temperature dependence of FET properties. It cleared the relationship between the FET property and intrinsic mobile ion in the gate dielectric. The influence of humidity on the FET property can be prevented by insertion of a clay mineral layer, which clogs motion of ion transport in gate dielectric layer.
Connecting Curable Siloxanes to Luminescent Organic Semiconductors - Monomers for Functional Hybrid Materials
Authors: Detert Heiner , Sugiono Erli
Published: April 2011

Luminescent stilbenoid chromophores with two alkoxysilane end groups are prepared via hydrosilylation or condensation / reduction of substituted 5-ring OPVs with hydro- and aminopropylsilanes. Chromophore and curable units are connected via flexible spacers. To obtain compounds with a rigid connection between silane and π-system, iodo- or bromo-OPVs were coupled to alkoxysilanes carrying vinyl- or p-vinylphenyl moieties under Heck conditions. This approach allowed a combined connection of the chromophore to the silane moiety with an extension of the π-system. Hydrolysis of the alkoxysilanes yields silanols condensing to curable three-dimensional networks, thus allowing the transformation of small molecules to transparent and fluorescent films with well-defined chromophores.
Bias Dependent TMR in Fe/MgO/Fe(100) Tunnel Junctions
Authors: Rungger Ivan , Rocha Alexandre Reily , Mryasov Oleg , Heinonen Olle , Sanvito Stefano
Published: April 2011

We calculate from first principles the I-V characteristics of Fe/MgO/Fe(100) tunnel junctions. In particular we compare the zero-bias transmission with self-consistent calculations at finite bias. In the case the magnetizations of the two Fe layers are parallel to each other, at small bias there is a significant contribution to the transmission coming from the minority spin channel. This is due to a sharp resonance in the transmission coefficient close to the Fermi level, originating from a surface state. As a bias exceeding 25 mV is applied, the surface states get out of resonance and the current through the minority spin channel saturates, so that the current flows mainly through the majority channel. The same effect is not present for the antiparallel alignment of the magnetization with the net result of large TMR at low bias, which then saturates for a bias larger than 25 mV.
Ferroelectric-Specific Peptides as Building Blocks for Bio-Inorganic Devices
Authors: Reiss Brian Dennis , Ocola Leonidas , Auciello Orlando , Firestone Millicent A.
Published: April 2011

The integration of biomolecules with inorganic materials to create functional composites represents a critical step in the development of next-generation biosensors, micro/nanofluidic devices, and biochips that require a combination of abiotic (inorganics) and biotic (proteins, DNA, antibodies) components. Toward this end, we have previously applied combinatorial phage display techniques to identify a constrained heptapeptide sequence (CISLLHSTC) that selectively binds to a perovskite ferroelectric (MOCVD-deposited lead zirconium titanate, PZT). In this work, we examine the binding of this heptapeptide sequence, prepared by solid phase peptide synthesis to sol-gel PZT. In particular, the surface roughness has been examined and the long-term stability of the PZT films in biological buffered aqueous solutions by atomic force microscopy, X-ray diffraction and P-E hysteresis loop. In addition, the selectivity of the peptide binding to PZT has been determined by immunofluorescence microscopy and the nature of peptide binding to the PZT surface is probed by X-ray photoemission spectroscopy.
The Design and Control of Catalytic Motors: Manipulating Colloids and Fluids with Self-Generated Forces
Authors: Kline Timothy R. , Iwata Jodi , Lammert Paul , Velegol Darrell , Mallouk Thomas , Sen Ayusman
Published: April 2011

Microfabrication was employed to pattern silver (Ag) on a gold (Au) surface. The two metals served as bimetallic heterogeneous catalysts for the heterogeneous decomposition of H2O2. Silver was the cathode, carrying out H2O2 reduction (to water) and gold the anode carrying out H2O2 oxidation (to oxygen). Both protons and electrons are created at the anode (as a part of the reaction) and migrate to the cathode (migration of ions is a current) where they are consumed. Thereby establishing an electric field (migration of ions obeys Ohm's law), which passively pumps fluids through electroosmosis. Electrophoresis also present as either an additive component to the electroosmotic flow or results in pattern formation (occurs at point where electroosmosis is equal and opposite to that of electrophoresis). Herein, the electrokinetic model is further tested and validated as chemical methods to tune the tracer behavior (convection to pattern formation), design of asymmetric patterns through microfabrication and attempts to indirectly measure the electric field were successful.
Influence of CNT on the Crystallization Behavior of P(VDF-CTFE) Copolymers
Authors: Shan Xiaobing , Li Suiqiong , Yang Xin , Cheng Zhongyang
Published: April 2011

P(VDF-CTFE) based nanocomposites were prepared by mixing the polymer with carbon nanotube (CNT) or C60 using solution cast method. The volume fraction of the CNT or C60 was from 0.1 % to 1.0%. The influence of CNT and C60 on the crystallization behavior of P(VDF-CTFE) was determined using XRD and DSC as well as the P-E loop. It is found that the CNT or C60 enhances the β-phase and the crystallinity. The crystallinity process in the composites was studied using DSC.
Dielectric characteristics of Poly(chloro-p-Xylene) thin films for high energy density pulsed power capacitors
Authors: Tewari Pratyush , Furman Eugene , Lanagan Michael T.
Published: April 2011

Poly(chloro-p- Xylene) or Parylene –C thin films are particularly attractive for dielectric as well as biomedical applications. In the current work the dielectric properties of Parylene-C thin films are investigated to form laminar composites with oxide thin films for high energy density pulsed power capacitors. Parylene-C thin films were synthesized by pyrolytic vapor decomposition polymerization of dichloro-di(p-Xylene) monomer. Annealing of films at 225°C has shown to enhance crystallinity of film. Conduction in Parylene-C thin films appears to be bulk-controlled with the hopping charges contributing to leakage current. The barrier height of 0.89eV and hopping distance of 2 - 2.5nm are physically plausible and similar to previously reported values in polymer literature.
Fabrication and Characterization of a Poly (3-Hexylthiophene) Thin Film Micro-sensor for Hypergolic Vapor Detection
Authors: Shu Huihua , Wan Jiehui , Shu John , Yang Hong , Chin Bryan A.
Published: April 2011

A passive chemiresistor micro-sensor was investigated for the detection of hydrazine compounds. Hydrazine compounds are a highly toxic and carcinogenic species exhibiting toxic effects in humans at very low levels of exposure. Therefore, a sensor capable of detecting ppb levels of hydrazine compounds is required to insure the safety of personnel. The present study describes the fabrication, testing, and characterization of a low-cost, ultrasensitive Poly (3-Hexylthiophene) (P3HT) thin film-based micro-sensor for the detection of hydrazine compounds. Standard microelectronic manufacturing techniques were used to form a micro-sensor composed of a silicon substrate, interdigitated gold electrodes, and P3HT sensing film. Responses of the micro-sensor to hydrazine compounds at different temperatures and concentration levels are reported. When exposed to 25 ppm hydrazine in nitrogen, the sensor's resistance was measured to change from a few ohms to over 10 Megaohms. The thermal stability of the P3HT micro-sensor and the method to improve thermal stability are also explored. Thermally annealing the P3HT micro-sensor was found to improve thermal stability at high temperatures. Moreover, the sensor exhibits good specificity to hydrazine and does not respond to the presence of NO2 and/or N2O.
Photonic-Fluidic Integrated Microstructures for Sensor and Photonic Device Applications
Authors: Callender Claire L. , Dumais Patrick , Ledderhof Christopher J. , Noad Julian P.
Published: April 2011

The design, fabrication and characterization of liquid-filled microchannels embedded in silica layers and integrated with optical waveguides for applications in on-chip sensors and novel photonic devices are presented. These integrated microstructures are formed using plasma-enhanced chemical vapor deposition (PECVD), photolithography and reactive ion etching (RIE). Surface accessible fluid introduction ports have been developed, and microfluidic circuits including bends, T-junctions and splitters are demonstrated. Coupling of light from integrated solid silica waveguides via directional coupling or direct end-fire coupling into fluid filled channels has been achieved on-chip, and optical losses assessed experimentally and theoretically. Optimization of the microstructures for sensor applications and for novel photonic devices based on nonlinear and other optical properties of fluids in integrated liquid waveguide segments is discussed.
Plasmonic and Diffractive Coupling in 2D Arrays of Nanoparticles produced by Electron Beam Lithography
Authors: McLellan Erin , Gunnarsson Linda , Rindzevicius Tomas , Kall Mikael , Zou Shengli , Spears Kenneth , Schatz George , Van Duyne Richard
Published: April 2011

Nanofabrication is one of the driving forces leading to developments in a variety of fields including microelectronics, medicine, and sensors. Precise control over nanoscale architecture is an essential aspect in relating new size-dependent material properties. Both direct write methods and natural lithography's offer a unique opportunity to fabricate “user-defined” writing of nanostructures in a wide range of materials. Electron Beam Lithography (EBL) and Nanosphere Lithography (NSL) provide the opportunity to fabricate precise nanostructures on a wide variety of substrates with a large range of materials. Using electrodynamics calculations, Schatz and coworkers have discovered one and two dimensional array structures that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicularly to the array axis. In order to investigate these interactions, precise control of nanoparticle orientation, size, shape and spacing is necessary. If the overall structures have excessive defects then the effect may not be seen. For the two dimensional arrays, to have the best control over array fabrication and to look at these interactions experimentally, EBL was used to construct both hexagonal arrays of circular cylinders and the Kagome lattice. The interparticle spacing in each of these structures was varied systematically. Dark field microscopy was used to look at overall sample homogeneity and collect the single particle plasmon resonance spectrum. Additionally, both dark-field and extinction spectroscopies were used to look at the bulk spectral properties of each array type and each spacing. In investigating of the two dimensional arrays, the Kagome structure was also compared to samples produced by traditional NSL to study the optical interaction of defects, domains, and overall sample uniformity on the shape and location of the plasmon resonance. This work illustrates a deeper understanding in the nature of the optical coupling in nanostructures and this knowledge can be utilized in the future to fabricate designer (tailor made) substrates for plasmonic and surface-enhanced raman applications.
Biocompatible Ceramics for Implants Based on Calcium Phosphates
Authors: Safronova Tatiana , Putlayev Valery I. , Veresov Alexander G. , Kuznetsov Anton V. , Shekhirev Mikhail A. , Agahi Kamila A.
Published: April 2011

Hydroxyapatite (HAp), tricalcium phosphate (TCP) and calcium pyrophosphate (CPP) are known to be among calcium phosphates used in clinical medicine due to their biocompatibility. HAp and other complex calcium phosphate salts are the end-products of the biological mineralization process. Calcium pyrophosphate Ca2P2O7 (β-CPP) is one of the intermediate products involved in this process. The biological response with respect to new bone formation is quite similar for CPP and HAp. Sintered CPP has better biological responses, and, thus, a great potential as a biodegradable bone substitute. The rate of biodegradation depends on: (i) material texture (porosity type and level), (ii) quality of biodegradation phase (phase composition, grain size, properties of grain boundaries). Several sources for CPP phase in ceramics can be assumed. CPP phase may come from frit (CaO-P2O5, Ca/P=0.2-0.75) used as a sintering additive. Ceramics can be fabricated from powder of CPP with Na4P2O7 as sintering additive, via interaction between H3PO4 or (NH4)2HPO4 and porous HAp at high temperature after soaking it in the former solutions. The aim of the present work was focused on fabrication of multiphase ceramics with enhanced resorptivity due to presence of CPP phase and investigation of processes leading to formation of the multiphase ceramics based on HAp and CPP originated from CaHPO4. Ceramic materials have been made from mixtures of powders of stoihiometric HAp (Ca/P=1.67) and monetite (CaHPO4, Ca/P=1). Powders of HAp and monetite were synthesized by means of wet chemical precipitation from aqueous solutions of Ca(NO3)2*4H2O and (NH4)2HPO4 at 60 °C and pH=9 for HAp and pH=4-5 for monetite. Component ratio HAp:monetite was varied from 0:100 to 100:0 % with a step of 20%. Powders of raw materials and the mixtures were tested by means of XRD, TG, DTG, SEM, dilatometry. Linear shrinkage, density and microstructure of samples of ceramic materials sintered at 900, 1000, 1100°C with isothermal holding during 6 hours were tested. Complicated consequence of phase transformations took place during heating the the mixtures from 20 to 1200 C. The CPP (Ca/P=1, converted from CaHPO4 at 400-500°C ) reacts with HAp (Ca/P=1.67) causing additional weight loss in the region of 600-1050°C due to solid state reaction leading to TCP (Ca/P=1.55) formation. Linear shrinkage of HAp at 1100°C after 6 hours was found to be about 21%; for Ca2P2O7 formed from monetite, and for the mixtures - less than 11%. Resulted ceramics with the phase composition of HAp, CPP and TCP, i.e. with a different content of degradable phase and different ratio of CPP/TCP, can be treated as a biocompatible bioactive material with a tunable rate and limit of biodegradation.
Rapid Detection of Bacillus anthracis in a Microchip-based Real-time PCR Biosensor
Authors: Cady Nathaniel Charles , Stelick Scott J. , Batt Carl
Published: April 2011

A miniaturized, fully-automated, PCR-based detection system has been developed for the rapid detection of the pathogenic bacteriumBacillus anthracis. Monolithic silicon DNA purification / real-time PCR chips were fabricated and tested for their ability to purify and detect DNA from bacterial cells. Using silica-coated microstructures and chemical-based lysis, nucleic acids could be isolated, washed and eluted for subsequent real-time PCR. These microstructures were integrated into a detection microchip containing two distinct regions, one for DNA purification and one for real-time PCR. Using an automated detection platform with integrated microprocessor, pumps, valves, thermocycler and fluorescence detector, target bacterial DNA was detected by real-time PCR amplification using SYBR Green fluorescent dye. As few as 40B. anthraciscells could be detected using this system with an average time for detection of 60 min. Detection was augmented by on-chip melting curve analysis capable of differentiating between positive and false-positive results.
High Temperature MOVPE Growth of AlxGa1−xN (0.2-1) Layers on Sapphire and SiC Substrates for the Fabrication Deep UV Optical Devices
Authors: Krishnan Balakrishnan , Imura Masataka , Iida Kazuyoshi , Nagamatsu Kentaro , Sugimura Hiroki , Nagai Tetsuya , Sumii Takafumi , Mori Fumiaki , Bandoh Akira , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu
Published: April 2011

Single crystalline AlN epitaxial layers have been grown on and (0001) sapphire and 6H-SiC substrates by MOVPE technique at high temperatures in the range of 1340-1500°C. The structural qualities of the high temperature grown AlN layers were found to be good as evidenced by X-ray diffraction analyses results. By transmission electron microscopic analysis, dislocation densities of the layers were found to be 6.2 × 107 cm−2 or lower and the formation of dislocation loops was confirmed. High temperature bridge layers of AlN and AlxGa1−xN layers were grown on linear-groove patterned sapphire based AlN templates and 6H-SiC substrates. AlxGa1−xN bridge layers exhibited different growth behaviours depending on the direction of groove patterns on the sub-strates.
Blue-green-red LEDs based on InGaN Quantum Dots by Plasma-assisted MBE using GaN QDs for Dislocation Filtering
Authors: Xu Tao , Nikiforov Alexey Yu , France Ryan , Thomidis Christos , Williams Adrian , Moustakas Theodore D. , Zhou Lin , Smith David J
Published: April 2011

In this paper, we report the development of blue-green-red LEDs based on InGaN quantum dots (QDs) and quantum wells in the active region, and GaN QDs in the nucleation layer for dislocation filtering, by plasma assisted molecular beam epitaxy. Self-assembled InGaN QDs and GaN QDs were grown in the Stranski-Krastanov mode. For the GaN QDs grown at 770 °C, the height distribution of the dots shows a bimodal distribution, which can be attributed to the interaction of the GaN QDs with the threading dislocations. TEM and XRD studies indicate that GaN QDs in the nucleation region help threading dislocations to deviate and annihilate. The average dot height, diameter and density of the InGaN QDs were estimated to be 3 nm, 30 nm and 7×1010 cm−2, respectively. The cathodoluminescence emission peak of the InGaN/GaN multiple layer quantum dots (MQDs) was found to red shift 330 meV with respect to the emission peak of the uncapped single layer of InGaN QDs due to Quantum Confined Stark effect. Blue LEDs based on InGaN/GaN multiple quantum wells (MQWs) as well as green and red LEDs based on InGaN MQDs emitting at 440 nm, 560 nm and 640 nm with FWHM of 30 nm, 87 nm and 97 nm, respectively, were grown and fabricated. The electroluminescence peak positions of both the green and red InGaN MQD LEDs are shown to be more blue-shifted with increasing injection current than that of the blue InGaN/GaN MQW LEDs.
Recombination dynamics in ultraviolet light-emitting diodes with Si-doped AlxGa1−xN/AlyGa1−yN multiple quantum well active regions
Authors: Chen Kaixuan , Xi Y. A. , Mont F. W. , Kim J. K. , Schubert E. F. , Li X. , Liu W. , Smart J. A.
Published: April 2011

Ultraviolet light-emitting diodes (UV LEDs) with AlxGa1−xN/AlyGa1−yN multiple quantum well (MQW) active regions, doped in the barriers with different Si doping level, show a sharp near band-edge emission (UV luminescence). Besides the near band-edge emission, some samples also show parasitic emissions with a broad peak centered at about 520 nm (green luminescence). The EL intensities of the UV emission line and the green emission line are studied. The UV luminescence peak intensity increases superlinearly with the injection current, following a power law with an exponent of about 2.0. In contrast, the green luminescence peak intensity increases linearly with the injection current, with an exponent of about 1.0. A theoretical model is proposed to explain the relationship between the peak intensities and the injection current. The results obtained from the model are in excellent agreement with the experimental results. The model provides a method to evaluate the dominant recombination process by measuring the exponent of the power-law dependence.
Investigation of the Optical Properties of epitaxial-lateral-overgrown GaN on R- and M- plane Sapphire
Authors: Guhne Tobias , Bougrioua Zahia , Albrecht Martin , Vennéguès Phillippe , Leroux Mathieu , Laügt Marguerite , Ndiaye Sosse , Teisseire Monique , Nguyen Luan , Gibart Pierre
Published: April 2011

Optical properties of GaN templates grown by the Epitaxial Lateral Overgrowth (ELO) technique along the nonpolar (1120) and the semipolar (1122) directions on R- and M-sapphire were investigated. Spatially resolved Cathodoluminescence (CL) was carried out in order to identify defect related transitions, to resolve their localization and to study the efficiency of ELO concerning defect filtration. The wing region of semipolar GaN is shown to be almost defect free with a luminescence spectrum dominated by the GaN emission at 3,472 eV. It is shown that the defect related emissions are localized in the seed, but different defects occur as well in the wing, especially in A-plane (nonpolar) GaN.
n-Type Doping of Diamond
Authors: Koizumi Satoshi
Published: April 2011

n-Type doping of diamond is one of the most important issues for electronic application of diamond. Phosphorus is the best candidate as an n-type dopant at this moment. We have succeeded to grow high quality phosphorus doped diamond thin films on {111} diamond substrates. Although the ionization energy of phosphorus donor is large (0.57 eV), the n-type conductivity is clearly observed by Hall measurements. The Hall mobility is as high as 660 cm2/V-sec at room temperature. In this paper, current status of n-type diamond research are mentioned mainly focused on the growth of high mobility n-type diamond and its electrical properties. The Hall measurements performed in a wide temperature range gives detailed information about the n-type conductivity nature of phosphorus doped diamond.
Single Crystal CVD Diamond growth and characterizations
Authors: Tranchant Nicolas Olivier , Tromson Dominique , Remes Zdenek , Rocha Licinio , Nesladek Milos , Bergonzo Philippe
Published: April 2011

Due to its radiation harness, single crystal CVD diamond is a remarkable material for the construction of detectors used in hadron physics and for medical therapy. In this work, single crystal CVD diamond plates were grown in a microwave plasma reactor, using home design substrate holder and a relatively high pressure. Optical Emission Spectroscopy was employed during the MW-PECVD growth to characterize excited species present in the plasma and to detect the presence of residual gases such as nitrogen which is unsuitable for detector's applications.

The samples were characterized using various methods such as Raman spectroscopy, photoluminescence (PL), photocurrent spectroscopy, Raman mapping, birefringence microscopy, optical microscopy and also AFM. The best sample, exhibits a FWHM for the 1332 cm−1 Raman peak about 1.6 cm−1. Room temperature PL spectra showed no N–related luminescence, confirming the high quality of the grown single crystal diamond.
Electrical Characterization of Proton Irradiated n-Type ZnO
Authors: Auret F Danie , Hayes Michael , Nel Jackie , Meyer Walter , Janse van Rensburg Pieter Johan , Wesch Werner , Wendler E
Published: April 2011

Ru Schottky barrier diodes (SBD's) were fabricated on the Zn face of n-type ZnO. These diodes were irradiated with 1.8 MeV at fluences ranging from 1 ´ 1013 cm-2 to 2.4 ´ 1014 cm-2. Capacitance and current (I) deep level transient spectroscopy (DLTS) was used to characterise the irradiation induced defects. Capacitance DLTS showed that proton irradiation introduced a level, Ep1, at 0.52 eV below the conduction band at an introduction rate of 13±1 cm-1. A defect with a very similar DLTS signature was also present in low concentrations in unirradiated ZnO. I-DLTS revealed that this proton irradiation introduced a defect with an energy level at (0.036± 0.004) eV below the conduction band. This defect is clearly distinguishable from a defect with a level at (0.033± 0.004) eV below the conduction band that was present in the unirradiated sample. It is speculated that these shallow level defects are related to zinc interstitials or complexes involving them.
Visible-Light Sensitivity in N-Doped ZnO Films Prepared by Reactive Magnetron Sputtering
Authors: Nakano Yoshitaka , Morikawa Takeshi , Ohwaki Takeshi
Published: April 2011

We report on visible-light sensitivity in N-doped ZnO (ZnO:N) films that were deposited on ITO/quartz substrates by reactive magnetron sputtering. Colored ZnO:N samples showed enhanced polycrystallization and a significant decrease in optical band gap from 3.1 to 2.3 eV with increasing N doping concentration, as determined by x-ray diffraction and optical absorption measurements. Deep-level optical spectroscopy measurements revealed three characteristic deep levels located at ∼0.98, ∼1.20, and ∼2.21 eV below the conduction band. In particular, the pronounced 2.21 eV band is newly introduced by the N doping and behaves as part of the valence band, resulting in the band-gap narrowing of ZnO. Therefore, this deep level is probably one origin of visible-light sensitivity in ZnO:N.
Elaboration and Characterization of ZnO Transition Metal (Co, Mn, Ni, Fe) Doped Aerogel Nanoparticles
Authors: El Mir Lassaad , Ben Mahmoud Aroussi , von Bardeleben H.Jurgen , Cantin Jean-Louis
Published: April 2011

Nanocrystalline transition metal (TM=Co, Mn, Ni, Fe) doped zinc oxide powders have been elaborated by a new protocol based on slow hydrolyse of zinc acetate dissolved in methanol and supercritical drying in ethyl alcohol. The powders have a narrow size distribution with an average value of ∼ 25nm. Electron microscopy characterization showed that the size of the ZnO:TM particles did not change significantly for the different dopants. High doping levels of up to [TM] =0.25 have been investigated. X-ray diffraction studies showed the formation of the ZnO wurtzite phase for all dopants but secondary phases are equally detected. High temperature ferromagnetism was observed for Ni and Co doped powders whereas Mn doped powders showed only antiferromagnetic interactions. EPR spectroscopy indicates that the magnetism is related to the presence of extrinsic phases.
Structural, Optical and Magnetic Properties of Co and Fe Doped ZnO Thin Films Grown by Radio Frequency Magnetron Sputtering
Authors: Angelats Luis Manuel , Tomar Maharaj S , Singhal Rahul , Perez Oscar P , Jimenez Hector J , Martinez Ricardo
Published: April 2011

Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O targets were used to grow thin films by rf magnetron sputtering. XRD patterns of the films showed a strong preferred orientation along c-axis. Zn0.90Co0.10O film showed a transmittance above 75% in the visible range, while the transmittance of the Zn0.85[Co0.50Fe0.50]0.15O film was about 45%; with three absorption peaks attributed to d-d transitions of tetrahedrally coordinated Co2+. The band gap values for Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films were 2.95 and 2.70 eV respectively, which are slightly less than ZnO bulk. The Zn0.90Co0.10O film showed a relatively large positive magnetoresistance (MR) at the high magnetic field in the temperature range from 7 to 50 K, which reached 11.9% a 7K for the magnetoresistance. The lowest MR was found at 100 K. From M-H curve measured at room temperature shown a probable antiferromagnetic behavior, although was possible to observe little coercive field of 30 Oe and 40 Oe for Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films, respectively.
Forces that Drive the Self-assembly of Metallic Dots on Semiconductor Substrates
Authors: Salac David , Lu Wei
Published: April 2011

The scaling and ordering of metallic nanoclusters on semiconductor substrates has been explored computationally. Numerical techniques were implemented to calculate the total electrostatic and van der Waals energies for systems containing multiple disks. Observations show that interactions in charge clouds beneath the metallic disks led to an electrostatic repulsive force. Attraction was observed due to the van der Waals energy. An energy barrier exists for disk coalescence. This work suggests the potential of double layer charges in the development of large-scale nanodot systems that require precise control over both dot location and size.
InAs and InP Quantum Dot Molecules and their Potentials for Photovoltaic Applications
Authors: Jevasuwan Wipakorn , Thainoi Supachok , Kanjanachuchai Songphol , Ratanathammaphan Somchai , Panyakeow Somsak
Published: April 2011

Self-assembled InAs and InP quantum dot molecules (QDMs) are grown on GaAs substrates using different molecular beam epitaxial (MBE) growth techniques. The structural and optical properties of the two types of QDMs are then compared and reported. Multi-stack high-density (1012 cm-2) InAs QDMs are grown and when inserted into GaAlAs/GaAs heterostructure results in high-efficiency solar cells. As an alternative to InAs, InP QDMs are grown by droplet epitaxy of In and annealing under P2 pressure. While the number of quantum dots per QDM in the case of InP is in the range of 10 to 12 dots, those in the case of InAs can be smaller or much larger depending on exact growth parameters prior to QD growth. Photoluminescence (PL) measurements show that while InAs QDMs provide room-temperature optical output that peaks at 1.1 eV, InP QDMs have no PL output, possibly due to crystal defects created by low-temperature processing associated with droplet epitaxy. Discussion on the practicality of our QDMs as material for intermediate band solar cells is also provided.
Laser-Induced Formation of Periodic Structures in Plasma Deposited Polymer Films Containing Au, Ag, and Cu Nanoparticles
Authors: Loeschner Katrin , Kiesow Andreas , Heilmann Andreas
Published: April 2011

Thin polymer films containing metal nanoparticles were irradiated with linearly polarized femtosecond laser pulses. The resulting laser-induced periodic modification of the nanoparticle assemblies was studied by using scanning and transmission electron microscopy. The structure period Lambda is correlated with the applied laser wavelength lambda by Lambda = 0.7 lambda. The effect was observed for gold, silver and copper nanoparticles. Optical spectra of the laser-irradiated films show a clear dichroism.
Highly Charged Ion Modified Magnetic Tunnel Junctions
Authors: Grube Holger , Pomeroy J. M. , Perrella A. C. , Gillaspy J. D.
Published: April 2011

We have used highly charged ions (HCIs) such as Xe44+ to modify ultrathin aluminum oxide barriers in magnetic tunnel junctions (MTJs) in order to controllably adjust their electrical properties independently of oxide thickness. We have reduced the resistance area (RA) product of our MTJ devices by up to three orders of magnitude down to our present measurement uncertainty limit of 30 Ω·μm2 by varying the HCI dose. Preliminary experiments indicate that HCI modified Co/Al2O3/Co MTJs have a reduced magnetoresistance (MR) of ≈ 1% at room temperature as compared to ≈ 10% for undosed devices. The goal of this effort is to fabricate a magnetic field sensor in current-perpendicular-to-plane (CPP) geometry with an RA optimized for hard drive read heads. This is an improvement over presently demonstrated CPP architectures based on giant magnetoresistance or tunnel junctions, whose RAs are either to low or too high.
Fabrication of Piezoelectric PZT Film Actuators on Thin Metal Plates Prepared by a Hydrothermal Method
Authors: Aoki Tuyoshi , Umemiya Shigeyoshi , Hida Masaharu , Satoh Keisuke , Kondo Masao , Kurihara Kazuaki
Published: April 2011

Hydrothermal lead zirconate titanate (Pb(Zr,Ti)O3: PZT) films with a thick of about 10 μm on both a Ti foil and a Ti layer sputtered stainless steel (SS) foil were obtained. Both PZT films showed same morphology and crystalinity. After repeating the hydrothermal process, the films were formed to cantilever shape. A tip displacement measurement of the cantilevers was carried out in order to estimate transverse piezoelectric constant (d31). The obtained d31 value of the PZT films on Ti sputtered SS foils is -29 pm/V, which is larger than that on Ti foil (-24 pm/V). Amorphous layer consist of Pb and Ti was observed at the interfaces between the both PZT film and the Ti metals. The thickness of the layer for PZT film on Ti foil (350 nm) is thicker than that for PZT film on SS foil (200 nm). The relative permittivity of the layer is estimated to be small compared with that of PZT. Accordingly, the effective electric field for PZT layer is decreased. The deference of d31 values between the obtained PZT films is thought to be attributed to the thickness of amorphous layer.
Fabrication of Piezoelectric ZnO and PZT Films for FPW Device
Authors: Yoon Sang Hoon , Kim Dong-Joo
Published: April 2011

Piezoelectric ZnO and PZT films for acoustic wave device have been investigated. The films used for acoustic wave devices require textured structure, high piezoelectric coefficients, and high electromechanical coupling coefficients, because the piezoelectric films launch and receive the acoustic wave. We fabricated ZnO films by RF magnetron sputtering, and PZT films by chemical solution deposition (CSD). Results showed that uniform, dense and highly textured films were obtained under optimal process parameters. The film texture was controlled by modifying process parameters, such as gas kinds, gas ratio, and substrate type for sputtered ZnO films, and the presence of chelating agent, temperature of heat treatment, and substrate type for solution derived PZT films. Flexural plate wave (FPW) device has been successfully integrated onto 4-inch silicon wafers with optimized piezoelectric films.
Theoretical Investigation of the Band Alignment at the LaAlO3/SrTiO3 Interface
Authors: Lee Jaekwang , Demkov Alexander A.
Published: April 2011

Epitaxially grown oxide superlattices are attracting considerable attention due to their unusual properties and possible applications ranging from sensors to electronic devices [1]. We report a first-principles study of interfaces in the epitaxial LaAlO3/SrTiO3 system within density functional theory. We consider the electronic structure of the n-type interface, and compute the band alignment
Effect of Interfaces on the Properties of Polycrystalline Thin-Film PZT Ferroelectric Capacitors
Authors: Delimova Lyuba A. , Grekhov Igor , Mashovets Dmitri , Titkov Ilya , Afanasjev Valentin , Afanasjev Petr , Kramar Galina , Petrov Anatolii
Published: April 2011

A photocurrent directed opposite to ferroelectric (FE) polarization is observed in short-circuit thin-film polycrystalline Pt/PZT/Ir structures. The direction and magnitude of photocurrent are defined by the sign and magnitude of the FE polarization. A model based on a photovoltaic effect with characteristics determined by polarization of PZT grains is proposed. The model considers the field interaction of FE polarization charge with the charge carriers in intergranular PbO channel. Thin-film FE capacitor is considered as a photosensitive heterogeneous medium, where the conduction of PbO channels along PZT grain boundaries is controlled by FE polarization.
Effect of Zn Addition on the Interfacial Reactions between Cu and Lead-Free Solders
Authors: Yang Su-Chun , Ho Cheng-En , Chang Chien-Wei , Kao C. Robert
Published: April 2011

Recently, it was reported that adding Zn to solder was an effective way for reducing the formation of both Cu3Sn and Cu6Sn5 and inhibiting Kirkendall voids formation. The objective of this study is to investigate this Zn effect in detail. Three Sn-xZn solders (x = 0.5, 0.7, and 2 wt. %) were reacted with Cu substrates at 250°J for 2-10 mins. A slight variation in the Zn concentration changed the reaction product formed at the interface. When the Zn concentration was low (x = 0.5 wt. %), the reaction product was Cu6Sn5. At high Zn concentration (x = 2 wt. %), the reaction product became Cu5Zn8. When Zn concentration was in-between (x = 0.7 wt. %), Cu6Sn5 and CuZn co-existed. The above findings are explained using the Cu–Sn–Zn phase diagram. The implication is that the type of compound forms at the interface can be controlled by adjusting the Zn concentration of the Sn-based solders.
Thermal Management in High-Density, Stacked-Die, Multi-chip Modules
Authors: Marinis Thomas , Pryputniewicz Dariusz , Kondoleon Caroline , Haley Jason
Published: April 2011

Very high density multi-chip modules are being manufactured by tiling an alumina substrate with IC chips and passive components, laminating a film of Kapton over them, laser drilling vias to their I/O pads, and interconnecting them with photo patterned, copper metallization. Additional layers of components and interconnects are added on top of the base layer, as needed, to allow greater integration of large circuits. Current products are typically two layers of chips and seven layers of interconnect. As higher power applications have emerged and the power density of IC chips has increased, thermal management has become a significant factor impacting module design. We have been conducting a thermal modeling effort to map the design space for this technology. Our principal objective is to define and evaluate low thermal impedance (heat removal) configurations for a given chip set. A second objective is to determine what gains in module performance might be realized by improvements in material properties or changes in the relative thicknesses of dielectric and metal layers.
Milling and Additive Effects on Hydrogen Desorption Reactions of Li-N-H and Li-Mg-N-H Hydrogen Storage Systems
Authors: Matsumoto Mitsuru , Kojima Yoshitsugu , Towata Shin-ichi , Nakamori Yuko , Orimo Shin-ichi
Published: April 2011

Hydrogen desorption reactions of the mixtures of (i) lithium amide and lithium hydride (LiNH2/LiH), and (ii) magnesium amide and lithium hydride (Mg(NH2)2/4LiH) were studied. Titanium compounds and nano-particles including fullerene (C60), were doped to those hydrogen storage mixtures respectively. The hydrogen desorption reactions were monitored by means of temperature programmed desorption (TPD) technique under an Ar atmosphere. The reaction of LiNH2/LiH was accelerated by adding either 1 mol% of Ti species or 0.2 mol% of fullerene (C60), while those additives did not show significant acceleration effects on the reaction of Mg(NH2)2/4LiH. Kinetic studies revealed the enhanced hydrogen desorption reaction rate constant for TiCl3 doped LiNH2/LiH, k = 3.1 × 10−4 s−1 at 493 K, and the prolonged ball-milling further improved reaction rate, k = 1.1 × 10−3 s−1 at the same temperature. For the dehydrogenation reaction of TiCl3 doped LiNH2/LiH, the activation energies estimated by Kissinger plot (95 kJ mol−1) and Arrhenius plot (110 kJ mol−1) were in reasonable agreement each other. The LiNH2/LiH mixture without additive exhibited slower hydrogen desorption process and the kinetic traces deviated from single exponential behavior. The results indicated the Ti(III) additives change the hydrogen desorption reaction mechanism of LiNH2/LiH.
Characterization of (La0.9Sr0.1)0.95Cr0.85Mg0.1Ni0.05O3 Perovskite Ceramics for a Perovskite Related Membrane Reactor
Authors: Rosten Rachel , Swanson Matthew , Kuebler Jakob , Kapat Jayanta , Orlovskaya Nina
Published: April 2011

In this research we investigated the sintering behavior of (La0.9Sr0.1)0.95Cr0.85Mg0.1Ni0.05O3 perovskite which is a potential candidate material for enhancing the oxidation reactions in oxygen separation and syngas production. It was found that solid state sintering occurs as a single step event and it was possible to produce gas tight ceramics after using cold isostatic pressing followed by sintering at 1700°C in air. Grain size, porosity, and lattice parameter measurements of the presureless sintered ceramics were performed as a function of sintering temperature. A small amount of secondary phases was also detected by XRD and EDS analysis.
Thermoelectric Power Devices Based on InN Thin Films
Authors: Matsumoto Takayuki , Yamaguchi Shigeo , Yamamoto Atsushi
Published: April 2011

We have studied the temperature dependence of thermoelectric properties of amorphous InN thin films prepared by reactive radio-frequency sputtering. We fabricated 60-pair and 120-pair InN-chromel films, which were deposited on polyimide films. For the 120-pair device, the maximum open output voltage and the maximum output power were 210 mV and 65 nW, respectively, at temperature difference of 168 K.