bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical Measurement of the Vanadium Acceptor Level in 4H- and 6H-SiC
Authors: Mitchel William C , Mitchell William D. , Smith H. E. , Zvanut M. E. , Lee Wonwoo 
Published: April 2011

AbstractTemperature dependent Hall effect, Fourier transform infrared absorption, and electron paramagnetic resonance (EPR) studies have been performed on both 6H and 4H vanadium doped semi-insulating SiC samples grown by the physical vapor transport technique. Nitrogen and boron concentrations have been measured in some samples by secondary ion mass spectrometry (SIMS). Unlike undoped s.i. SiC, where several different thermal ionization energies have been observed, the ionization energies for all of the vanadium doped s.i. samples studied here were found to cluster around only two values for the two polytypes, EC – 0.85 eV and EC – 1.54 eV for 6H and EC – 1.11 eV and EC – 1.57 eV for 4H. SIMS measurements indicate that the nitrogen concentration exceeds the boron concentration in samples with the shallower of two values while the opposite is true for the deeper level samples. EPR detected both V3+ and V4+ in shallower level samples while only V4+ was detected in the deeper level samples. These results indicate that the vanadium acceptor level, V3+/4+, is located at EC – 0.85 eV in 6H-SiC and EC – 1.11 eV in 4H-SiC. However, some EPR results do show a small, unexpected asymmetry in the angular dependence of the V4+ signal, most noticeably in the 4H samples. This suggests that at least some of the vanadium related levels might be complexed with another defect or be under higher local strain than expected.
Process Control During Liquid Phase Rerowth of 3C-SiC on Si Substrates
Authors: Smith Mark , Voelskow Matthias , McMahon Richard A. , Muecklich Andreas , Anwand Wolfgang , Skorupa Wolgang 
Published: April 2011

AbstractFlash lamp annealing in the millisecond regime of heteroepitaxial silicon carbide on silicon structures involves melting the Si below the SiC layer, but the deep facetted nature of the solid-liquid interface leads to unacceptable surface roughness. This paper describes a method of controlling melting by implanting a high dose of carbon or germanium at a controlled depth below the Si/SiC interface, which significantly alters the melting characteristics of the silicon. Results confirm the effectiveness of these approaches for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques. A thermal model has also been developed to describe this process and results indicate that the theoretical work is consistent with the experimental evidence. The model is a valuable tool for predicting onset of melting, maximum temperatures and process windows for liquid phase epitaxy.
Creating catalytically active nanoparticles via block copolymer templates for carbon nanotube and silicon nanowire growth
Authors: Lu Jennifer , Chamberlin Danielle 
Published: April 2011

AbstractUsing solution micelles formed by a block copolymer template, a variety of highly ordered catalytically active transition metal nanoparticles, ranging from single metallic nanoparticles of Fe, Co, Ni and Au to bimetallic nanoparticles such as Ni/Fe with uniform size and periodicity, have been created. These nanoparticles are excellent catalyst systems for the synthesis of carbon nanotubes and silicon nanowires. High quality, small diameter carbon nanotubes and silicon nanowires with narrow size distribution have been successfully produced. Since this block copolymer is fully compatible with conventional top-down photolithography, spatially selective growth of carbon nanotubes and silicon nanowires on a surface or carbon nanotubes suspended across trenches have been achieved using standard semiconductor processing techniques. The ability of the block copolymer template to generate catalyst with adjustable size and composition on a variety of surfaces not only enhance the manufacturability of these 1D nanobuilding blocks but also facilitates studying the growth mechanism.
Formation of Epitaxial Ge Nanorings on Si by Self-assembled SiO2 Particles and Touchdown of Ge Through a Thin Layer of SiO2
Authors: Li Qiming , Krauss Joshua L. , Hersee Stephen , Han Sang M. 
Published: April 2011

AbstractWe demonstrate that hexagonally packed single-crystalline Ge rings can be grown around the contact region between self-assembled SiO2 spheres and 1.2-nm-thick chemical SiO2 on Si. When the oxide-covered Si substrate is pulled from a colloidal suspension of SiO2 spheres, the SiO2 spheres self-assemble into a hexagonally packed monolayer on the substrate. These SiO2 spheres provide a surface diffusion path to guide the Ge adspecies to reach the substrate. We have previously determined that the Ge adspecies readily desorb from the bulk SiO2 surface with a desorption activation energy of 42±3 kJ/mol. This low desorption activation energy gives rise to a low surface diffusion barrier, which in turn leads to a high diffusion length on the order of several micrometers, exceeding the dimension of the SiO2 spheres. With a flux of Ge impinging at 45° from the surface normal, the Ge beam cannot directly impinge on the underlying substrate through the openings between SiO2 spheres. The Ge adspecies diffuse around the SiO2 spheres and "touchdown"[Li et al., APL, 85(11), 1928 (2004)] through the chemical SiO2, forming epitaxial ring structures. The touchdown process anchors nanoscale Ge seed pads to the underlying Si substrate. The ring formation uniquely takes advantage of the SiO2 sphere self-assembly; the weak interaction between Ge adspecies and SiO2; and the touchdown where Ge densely nucleates on Si surface through the 1.2-nm-thick chemical oxide.
SiC Based Neutron Flux Monitors for Very High Temperature Nuclear Reactors
Authors: Windl Wolfgang , Khorsandi Behrooz , Luo Weiqi , Blue Thomas E. 
Published: April 2011

ABSTRACTThe Gas Turbine-Modular Helium Reactor (GT-MHR) and the Very-High-Temperature Reactor (VHTR) are next-generation high-temperature reactor types that are being designed to operate under normal conditions with primary coolant outlet temperatures in the range of 850 °C and 1000 °C, respectively. A new type of silicon carbide based diode neutron detector is currently under development in order to monitor the neutron flux in this environment. An important problem, in this context, is the long-time reliability of the diodes under continuous irradiation at high temperatures. In this paper, we discuss a computational methodology to study the accumulation of radiation damage in the detectors as a function of temperature and its influence on the electrical properties.
Nanostructural Evolution of Au on Silica Surfaces Exposed to Low Energy Ions
Authors: Abidzina Volha , Tereshko I. , Elkin I. , Zimmerman R.L. , Budak S. , Zheng B. , Muntele C. , Ila D. 
Published: April 2011

ABSTRACTWe studied the effects of the low energy ions to induce nucleation of nanoscale crystals on and near surface of silica nano-layer containing low concentrations of Au. Suprasil substrates were coated with thin layer of gold followed by low-energy ion irradiation in a glow discharge plasma. The formation of nanoscale crystals due to low energy ion irradiation were then studied using RBS and optical absorption spectrometry.
Study of the Effects of Various Nanopowders in the Properties of GPC
Authors: Minamisawa Renato Amaral , Chhay Bopha , Muntele Iulia , holland Lawrence , Zimmerman Robert Lee , Muntele Claudiu , Daryush Ila 
Published: April 2011

ABSTRACTWe have introduced various nanopowders in the precursor of glassy polymeric carbon (GPC) and studied its electrical, thermal, and mechanical properties as well as its chemical structure. In general the GPC ware produced at AAMU is used for making crucibles, heat exchangers, and for prosthetic devices because of its biocompatibility. GPC ware at AAMU is synthesized from a phenolic resin solution from Georgia Pacific in a pyrolyser system at temperatures between 100 °C all the way to 2800 °C. The heat treatment includes several stages: gelling, curing, postcuring, precarbonization and carbonization. The fabrication of GPC is complicated because of the high production rate of gaseous products in critical temperature ranges where out-diffusion is relatively slow. Special care should be taken in temperature programming to avoid kilning faults and misshapen or porous GPC end results. In this work we have introduced SiC, CNT or Al2O3 to the precursor and studied the properties of the final product treated at 1000oC pyrolysis temperature.
Controlling Cell Growth by Nanoparticles
Authors: Zankovych Sergiy , Bossert Joerg , Thiele Ines , Jandt Klaus D. , Berzina-Cimdina Liga 
Published: April 2011

ABSTRACTWe report preliminary results of using nanoparticles to control cell attachment and growth. We present the way to create titanium surfaces with different roughness in a rage between 2 nm and 117 nm by using nanoparticles as a superficial layer and varying the evaporation parameters. We examined cell proliferation on titanium substrates with increased surface roughness compared to smooth titanium surface. We used nanoparticles to create a micrometer-sized lateral layout onto substrates preliminary structured by microcontact printing. We demonstrate controlled cell growth on substrates laterally structured with nanoparticles.
Microstructured Bioactive Interfaces using Piezoelectric Ink Jet Technology
Authors: Doraiswamy Anand , Dinu Cerasela Z. , Sumerel Jan , Chrisey Douglas B. , Narayan Roger J. 
Published: April 2011

ABSTRACTWe have demonstrated microscale patterning of biotin and streptaividin proteins using an athermal rapid prototyping process based on piezoelectric inkjet technology. A MEMS-based piezoelectric actuator was used to dispense picoliter quantities of fluid through micron-sized nozzles. Atomic force microscopy and Fourier infrared spectroscopy studies were performed on CAD/CAM deposited proteins that were prepared using several firing voltages. Our results indicate that piezoelectric inkjet deposition is a powerful non-contact, non-destructive process for developing high-throughput biological microarrays for use in biosensing, cell culturing, and tissue engineering.
Modeling Block Copolymer Interactions with Biomimetic Membranes
Authors: Adiga Shashishekar P. , Zapol Peter , Firestone Millicent A. 
Published: April 2011

ABSTRACTAssociation of amphiphilic triblock copolymers with lipid membranes results in versatile novel materials with enormous potential in many areas of bionanotechnology. The molecular architecture and concentration of block copolymers along with environmental variables such as temperature and pH provide means to tune these structures for desired applications and also allow for designing signal-responsive materials. Understanding interaction between block copolymers and lipid bilayers is crucial for applications in nanomedicine. Monte Carlo simulations are used to explore the effect of molecular architecture on the mode of insertion of triblock copolymers into lipid bilayers. The results are compared with small angle X-ray scattering data.
Silicon Photonic Devices and Polarisation Independence
Authors: Reed Graham T. , Mashanovich Goran Z. , Timotijevic Branislav D , Gardes Frederic Y. , Headley William R. , Wright Nicholas 
Published: April 2011

ABSTRACTSilicon Photonics is experiencing a dramatic increase in interest due to emerging application areas and several high profile successes in device and technology development. For both performance and cost reasons, there is a worldwide trend towards miniaturising silicon photonic waveguides. The shrinking of the device dimensions provides advantages in terms of cost and packing density, modulation bandwidth, improved performance in resonant structures, and an increase in optical power density within the devices. However, the size reduction comes at some costs in increased difficulty in maintaining single mode operation of the waveguides whilst controlling the polarisation properties of the device.For some applications, it is essential that optical modulators and filters, as well as other components, operate in the single mode regime. It is also desirable that these components are polarisation insensitive. Design of the waveguide, which is the basic element of these devices, is therefore crucial. Due to the compatibility with single mode fibre dimensions as well as the possibility of control of polarisation, rib waveguides represent promising candidates for integration in SOI. The main limitation for rib waveguides is that the bend radius cannot always be sufficiently small to minimise the device footprint. Strip waveguides, on the other hand, are often considered as a good choice in this respect, as they allow very small bend radii resulting in a compact footprint. However, polarisation dependence of these waveguides can be significant. Therefore, both waveguide configurations are investigated in this paper, together with the implications for optical modulators.Following from this discussion, we also consider optical modulators that operate in the depletion mode with the intrinsic bandwidth of several tens of gigahertz. We have previously reported a modulator based on a small rib waveguide with the height of < 500nm for high speed operation. However, in this paper we consider slightly larger designs to accommodate polarisation independence. Finally we discuss the characteristics of ring and racetrack resonators based on both rib and strip waveguides and methods of improving free spectral range whilst considering polarization effects. Both theoretical and experimental results are presented. The maximum free spectral range that we have demonstrated experimentally is ∼43nm.
Photoluminescent Silicon Nanocrystals with Mixed Surface Functionalization for Biophotonics
Authors: Erogbogbo Folarin , Swihart Mark T. 
Published: April 2011

ABSTRACTOrange-emitting photoluminescent silicon nanocrystals have been grafted with pairs of compounds to produce a mixed monolayer on their surface. Vinyl acetic acid (VA) is used to enhance dispersibility in water by providing carboxyl termination, while alkyl groups are used to improve the stability of the photoluminescence (PL). The grafting of these molecules to the surface is enabled by an etching procedure that leaves a hydrogen terminated surface on the silicon nanocrystals. Multiple molecules can be grafted in series by taking advantage of the residual hydrogen present after initial grafting with a first compound. Multiple molecules can also be grafted in parallel by allowing them to compete for surface reactive sites and varying their concentration in solution to control the composition of the mixed surface layer. Both series and parallel grafting result in particles that have a mixture of two distinct molecules on their surface, and thereby allow control of the particle dispersibility in different solvents and the density of reactive groups for subsequent functionalization steps. Optimizing the surface composition may allow production of particles that can be reacted with proteins via carbodiimide linking chemistries while maintaining their PL and their dispersibility in water and buffer solutions. Here we focus on the parallel grafting approach.
Understanding of the Synthesis and Structure of Si Nanocrystals in an Oxide Matrix from First Principles Based Atomistic Modeling
Authors: Lee Sangheon , Yu Decai , Hwang Gyeong S. 
Published: April 2011

ABSTRACTKinetic Monte Carlo simulations were performed to examine mechanisms underlying the formation of Si nanoparticles in Si-rich SiO2. We have determined two important features of the embedded Si nanoparticle growth: “coalescence-like” and “pseudo Ostwald ripening”. The former is mainly responsible for fast Si particle growth at the early stage of annealing where the particles are close to each other, while the latter becomes important when the density of particles is low such that they are separated by large distances. The pseudo ripening process takes place several orders of magnitude slower than the “coalescence-like” growth. The predominance of “coalescence-like” behavior in the growth of Si nanoparticles results in a big variation in the particle size in terms of the Si:O ratio. Overall the predicted growth behavior based on our Monte Carlo simulations agrees well with experiments.
Spectroscopic Characterization of Alkyl-Passivated Si Nanoparticles Synthesized by a Solution Route
Authors: Tanaka Akinori , Kamikake Tadafumi , Imamura Masaki , Murase Yoshiaki , Yasuda Hidehiro 
Published: April 2011

ABSTRACTWe have synthesized the alkyl-passivated Si nanoparticles by a solution route, and have carried out the various spectroscopic studies in order to investigate their intrinsic optical properties, electronic structures, and surface chemistry. Photoluminescence (PL) spectra of the n-butyl-passivated Si nanoparticles with mean diameter less than 2 nm exhibit the strong ultraviolet-blue emission. Moreover, it is found that their valence-band maximum energies directly estimated from the synchrotron-radiation valence-band photoemission spectra correspond to the resonance features in the PL excitation spectra. Therefore, it is concluded that the PL from the present n-butyl-passivated Si nanoparticles originates from the electron-hole pair recombination between the modified valence-band and conduction-band due to the quantum size effect. From the synchrotron-radiation Si 2p core-level photoemission spectra, their interfacial electronic structures of these Si nanoparticles have also been characterized. From these results, we discuss the detailed electronic and chemical properties of alkyl-passivated Si nanoparticles.
Morphology and Optical Properties of ZnO Nanorods Grown by Catalyst-assisted Vapor Transport on Various Substrates
Authors: Avrutin Vitaliy , Ozgur Umit , Izyumskaya Natalia , Chevtchenko Serguei , Leach Jacob , Moore James C. , Baski Alison A. , Everitt Henry O. , Tsen Kong-Thon , Ruterana Pierre , Morkoc Hadis 
Published: April 2011

ABSTRACTZnO nanorods were grown by catalyst-assisted vapor phase transport on Si(001), GaN(0001)/c-Al2O3, and bulk ZnO(0001) substrates. Morphology studies showed that ZnO nanorods grew mostly perpendicularly to the GaN substrate surface, whereas a more random directional distribution was found for nanorods on Si. Optical properties of fabricated nanorods were studied by steady-state photoluminescence and time-resolved photoluminescence. Stimulated emission was observed from ZnO nanorods on GaN substrates. Raman spectroscopy revealed biaxial strain in the nanorod samples grown on Si. Conductive atomic force microscopy was applied to study I-V spectra of individual nanorods.
Fabrication and Modeling of Gated Field-Emission Devices Using Carbon Nanotubes on Si Substrates
Authors: Javad - Koohsorkhi  , Shams - Mohajerzadeh  , Yaser - Abdi  , Pouya - Hashemi  
Published: April 2011

ABSTRACTWe report fabrication and modeling of self-defined gated filed-emission devices based on encapsulated vertically aligned carbon nanotubes grown on Si substrates with a PECVD method. The electrical characteristics of such devices have been theoretically modeled using an expanded Fowler-Nordheim tunneling effect. Devices fabricated here, resemble vacuum tubes where CNTs act as cathode. They show a saturation behavior for large distances between anode and cathode electrodes, making them suitable for transistor applications. The physical properties of the CNTs were investigated using SEM, evidencing the evolution of vertical CNTs with a tip-growth mechanism. The triode structure proposed in this paper uses CNT as the field-emission electrode (cathode), the surrounding Cr as the gate and a second Si substrate as the anode electrode. The emission current from the nanotube tips is significantly controlled by applying a negative voltage between CNT and the gate. The effect of the anode-cathode and gate-cathode voltages on the emission current has been experimentally observed and theoretically modeled using an expanded F-N effect.
p- and n-Type Charge Transport in Field-Effect Transistors of Pristine Poly(p-Phenylenevinylene)
Authors: Kayashima Hiroshi , Yasuda Takeshi , Fujita Katsuhiko , Tsutsui Tetsuo 
Published: April 2011

ABSTRACTPoly(p-phenylenevinylene) (PPV) thin films were prepared by using drop casting under high gravity condition and p- and n-type PPV based field effect transistors (FET) have been fabricated. PPV FETs with gold source-drain electrodes showed the p-channel FET conduction. The FET characteristics of PPV were improved by annealing and the field-effect hole mobility was 8.8×10−4cm2V−1s−1. On the other hand, PPV FET with calcium source-drain electrodes showed the n-channel FET conduction and the field-effect electron mobility was 1.0×10−6cm2V−1s−1.
Enhanced Efficiency and Stability in P3HT:PCBM Bulk Heterojunction Solar Cell by using TiO2 Hole Blocking Layer
Authors: Yoshikawa Osamu , Hayakawa Akinobu , Fujieda Takuya , Uehara Kaku , Yoshikawa Susumu 
Published: April 2011

ABSTRACTInsertion of TiO2 layer between Al negative electrode and active layer of bulk-heterojunction gave a high solar conversion efficiency and high stability. The TiO2 layer was prepared by spin-coating titanium(IV)isopropoxide (Ti(OC3H7)4) on active layer of blended P3HT:PCBM. The parallel resistance (Rp) is increased by inserting TiO2 layer leading to an increase in Voc. The TiO2 layer works as a hole blocking layer and prevents the physical and chemical damages by the direct contact between P3HT:PCBM active layer and Al electrode resulting in improvement of the parallel resistance and rectification. The efficiency of P3HT:PCBM bulk heterojunction cell with TiO2 hole blocking layer attained 4.05% with a Isc 9.72 mA/cm2, Voc 0.60 V, and FF 0.70 by using optimized TiO2 film thickness and ratio of P3HT:PCBM condition.
Using Atomic Steps to Control Pentacene Crystal Orientation Texture
Authors: Ignatescu Valerian , Hsu Jing-Chih M. , Mayer Alex C. , Blakely Jack M. , Malliaras George G. 
Published: April 2011

ABSTRACTWe have studied the effect of substrate atomic steps on the azimuthal alignment of vapor-deposited pentacene crystals. Si(111) substrates with a low miscut angle were annealed at high temperature in ultra-high vacuum before the pentacene deposition; this produced surfaces with atomically flat terraces and arrays of parallel atomic steps. AFM analysis shows that pentacene deposited on these heated samples, at a low deposition rate, results in significant alignment of the pentacene crystals along the atomic steps.
Enhanced [111] Preferred Orientation of Ag Thin Film on Amorphous SiO2 by Cu Addition
Authors: Zoo Yeongseok , Han Hauk , Alford Terry L. 
Published: April 2011

ABSTRACTSmall amounts of copper were added to enhance the adhesion and minimize agglomeration of Ag thin films on SiO2 substrates. Comparison of texture profiles between Ag and Ag(Cu) thin films showed that Cu additions enhanced (111) texture in Ag thin films. For the case of Ag film, (111) texture was enhanced mainly by recrystallization of amorphous regions during annealing. In addition to the recrystallization, (111) texture enhancement in Ag(Cu) film attributes to the dissociation of grains with other crystallographic orientations.