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Articles 2671 - 2700 of 3535

Full-Text Articles in Nanoscience and Nanotechnology

The Design And Manufacture Of A Microfluidic Reactor For Synthesis Of Cadmium Selenide Quantum Dots Using Silicon And Glass Substrates, Peter Gonsalves Jun 2011

The Design And Manufacture Of A Microfluidic Reactor For Synthesis Of Cadmium Selenide Quantum Dots Using Silicon And Glass Substrates, Peter Gonsalves

Materials Engineering

A microfluidic reactor for synthesizing cadmium selenide (CdSe) quantum dots (QDs) was synthesized out of silicon and Pyrex glass. Microfabrication techniques were used to etch the channels into the silicon wafer. Holes were wet-drilled into Pyrex glass using a diamond-tip drill bit. The Pyrex wafer was aligned to the etched silicon wafer and both were anodically bonded to complete the microfluidic reactor. Conditions for anodic bonding were created by exposing the stacked substrates to 300V at ~350oC under 5.46N of force.  Bulk CdSe solution was mixed at room temperature and treated as a single injection. The syringe containing …

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Comparison Of Photothermal And Piezoacoustic Excitation Methods For Frequency And Phase Modulation Atomic Force Microscopy In Liquid Environments, A. Labuda, K. Kobayashi, Daniel Kiracofe, K. Suzuki, P. H. Gruetter, H. Yamada Jun 2011

Comparison Of Photothermal And Piezoacoustic Excitation Methods For Frequency And Phase Modulation Atomic Force Microscopy In Liquid Environments, A. Labuda, K. Kobayashi, Daniel Kiracofe, K. Suzuki, P. H. Gruetter, H. Yamada

Birck and NCN Publications

In attempting to perform frequency modulation atomic force microscopy (FM-AFM) in liquids, a non-flat phase transfer function in the self-excitation system prevents proper tracking of the cantilever natural frequency. This results in frequency-and-phase modulation atomic force microscopy (FPM-AFM) which lies in between phase modulation atomic force microscopy (PM-AFM) and FM-AFM. We derive the theory necessary to recover the conservative force and damping in such a situation, where standard FM-AFM theory no longer applies. Although our recovery procedure applies to all cantilever excitation methods in principle, its practical implementation may be difficult, or even impossible, if the cantilever is driven piezoacoustically. …

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Formation Of Silicon Nanodots Via Ion Beam Sputtering Of Ultrathin Gold Thin Film Coatings On Si, Osman El-Atwani, Sami Ortoleva, Alex Cimaroli, Jean Paul Allain May 2011

Formation Of Silicon Nanodots Via Ion Beam Sputtering Of Ultrathin Gold Thin Film Coatings On Si, Osman El-Atwani, Sami Ortoleva, Alex Cimaroli, Jean Paul Allain

Birck and NCN Publications

Ion beam sputtering of ultrathin film Au coatings used as a physical catalyst for self-organization of Si nanostructures has been achieved by tuning the incident particle energy. This approach holds promise as a scalable nanomanufacturing parallel processing alternative to candidate nanolithography techniques. Structures of 11- to 14-nm Si nanodots are formed with normal incidence low-energy Ar ions of 200 eV and fluences above 2 x 10(17) cm(-2). In situ surface characterization during ion irradiation elucidates early stage ion mixing migration mechanism for nanodot self-organization. In particular, the evolution from gold film islands to the formation of ion-induced metastable gold silicide …

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Improving Near-Field Confinement Of A Bowtie Aperture Using Surface Plasmon Polaritons, Pornsak Srisungsitthisunti, Okan Ersoy, Xianfan Xu May 2011

Improving Near-Field Confinement Of A Bowtie Aperture Using Surface Plasmon Polaritons, Pornsak Srisungsitthisunti, Okan Ersoy, Xianfan Xu

Birck and NCN Publications

Bowtie aperture is known to produce subdiffraction-limited optical spot with high intensity. In this work, we investigate integrating a bowtie aperture with circular grooves to reduce the divergence of the near-field produced by the bowtie aperture. Numerical results indicate that surface waves reflected from circular grooves improve the field confinement of a bowtie aperture along the polarization axis. These circular grooves with period near half the wavelength of surface plasmon polaritons reduce the spot size by as much as 40% at distances between 20 and 100 nm from the surface and create a more symmetrical optical spot. (C) 2011 American …

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Synthesis And Catalytic Property Of Flaked Spindle-Like Cuo Nanocrystals, Jian-Feng Fan, Li-Qing Li, Yu-Feng Huang, Lou-Zhen Fan May 2011

Synthesis And Catalytic Property Of Flaked Spindle-Like Cuo Nanocrystals, Jian-Feng Fan, Li-Qing Li, Yu-Feng Huang, Lou-Zhen Fan

Journal of Electrochemistry

A simple and efficient electrochemical route was developed for the synthesis of flaked spindle-like CuO nanocrystals using aqueous electrolyte and Cu sacrificial anode (graphite as the cathode) in an undivided cell at a constant potential mode under room temperature. The morphologies, structure and component of CuO nanocrystals obtained were characterized by SEM, XRD, respectively. Flaked spindle-like CuO nanocrystals were successfully used to modify a GC electrode to detect H2O2 with cyclic voltammetry (CV) and amperometric (AC).The results showed that products were pure monoclinic CuO nanocrystals. The linear range for the determination of hydrogen peroxide is from 1.0 …

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Influence Of Tert-Butylpyridine On The Band Energetics Of Nanostructured Tio2 Electrodes And The Photoelectrochemical Properties Of Dye-Seneitized Electrodes, Shu-Ming Yang, Ji-Chao Wang, Hui-Zhi Kou, Hong-Bin Xue, Hong-Jun Wang, Yu-Ling Guo May 2011

Influence Of Tert-Butylpyridine On The Band Energetics Of Nanostructured Tio2 Electrodes And The Photoelectrochemical Properties Of Dye-Seneitized Electrodes, Shu-Ming Yang, Ji-Chao Wang, Hui-Zhi Kou, Hong-Bin Xue, Hong-Jun Wang, Yu-Ling Guo

Journal of Electrochemistry

The flat band edges (Efb) of nanostructured TiO2 electrodes in electrolyte solutions with tert-butylpyridine (TBP) of different concentrations have been determined with spectroelectrochemical technique. TBP played a role in band energetics of nanostructured TiO2 electrodes. The Efb values of -2.25, -2.46 and -2.62 V were determined in three 0.2 mol•L-1 tetrabutylammonium perchlorate (TBAP) acetonitrile electrolytes which contain 0, 0.2 and 0.4 mol•L-1 TBP respectively. The addition of Li+ ions shifted Efb positively. The Efb values of -1.12, -1.22 and -1.30 V were determined in three 0.2 mol•L-1 LiClO4 acetonitrile electrolytes which contain 0, 0.2 …

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Dft Study Of Co2 Reduction To Hydrocarbons On Cu Surfaces, Li-Hui Ou, Sheng-Li Chen May 2011

Dft Study Of Co2 Reduction To Hydrocarbons On Cu Surfaces, Li-Hui Ou, Sheng-Li Chen

Journal of Electrochemistry

CO2 reduction on Cu(111) single crystal surfaces was studied using DFT calculations on the reaction energies and the minimum energy paths. The results indicated that the possible reaction paths for CO2 reduction on Cu(111) surface are CO2(g) + H* → COOH* → (CO +OH)*, (CO + H)* → CHO*, CHO + H → CH2O* → (CH2+O)*, CH2* + 2H* → CH4 or 2CH2* → C2H4. On Cu(111) surface, the reaction rate is controlled by steps of CH2O* → (CH2 …

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The Flip-Flop Behavior Of Acetonitrile At Au Electrode Surface Investigated By Sum Frequency Generation Vibrational Spectroscopy, Zhi Huang, Xin Tang, Gang-Hua Deng, En-Cai Zhou, Hong-Fei Wang, Yuan Guo May 2011

The Flip-Flop Behavior Of Acetonitrile At Au Electrode Surface Investigated By Sum Frequency Generation Vibrational Spectroscopy, Zhi Huang, Xin Tang, Gang-Hua Deng, En-Cai Zhou, Hong-Fei Wang, Yuan Guo

Journal of Electrochemistry

The electrochemical interface between liquid acetonitrile and polycrystal gold electrode is investigated by in situ infrared visible sum frequency generation spectroscopy (SFG-VS). The structure of acetonitrile adsorbed at polycrystal gold electrode surface is studied as a function of electrode potential. The SFG spectra of CH3 group indicate acetonitrile orients in response to the electrode potential. The SFG signal of CH3 group turns lower as the electrode potential changes from -700mV to 300mV, and vanishes around the 300mV(pzc), then becomes a negative signal above 500mV, which indicates that the orientation is predominately with the CH3 group toward the …

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Chaos-Assisted Emission From Asymmetric Resonant Cavity Microlasers, Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Satoshi Sunada, Evgenii Narimanov May 2011

Chaos-Assisted Emission From Asymmetric Resonant Cavity Microlasers, Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Satoshi Sunada, Evgenii Narimanov

Birck and NCN Publications

We study emission from quasi-one-dimensional modes of an asymmetric resonant cavity that are associated with a stable periodic ray orbit confined inside the cavity by total internal reflection. It is numerically demonstrated that such modes exhibit directional emission, which is explained by chaos-assisted emission induced by dynamical tunneling. Fabricating semiconductor microlasers with an asymmetric resonant cavity, we experimentally demonstrate the selective excitation of the quasi-one-dimensional modes by employing the device structure to preferentially inject currents to these modes and observe directional emission in good accordance with the theoretical prediction based on chaos-assisted emission.

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Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge May 2011

Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge

Birck and NCN Publications

An important challenge in silicon quantum electronics in the few electron regime is the poten- tially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the “valley-orbit” (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a …

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Fabrication And Realistic Modeling Of Three-Dimensional Metal-Dielectric Composites, Mark D. Thoreson, Jieran R. Fang, Alexander V. Kildishev, Ludmila J. Prokopeva, Piotr Nyga, Uday K. Chettiar, Vladimir M. Shalaev, Vladimir P. Drachev May 2011

Fabrication And Realistic Modeling Of Three-Dimensional Metal-Dielectric Composites, Mark D. Thoreson, Jieran R. Fang, Alexander V. Kildishev, Ludmila J. Prokopeva, Piotr Nyga, Uday K. Chettiar, Vladimir M. Shalaev, Vladimir P. Drachev

Birck and NCN Publications

Historically, the methods used to describe the electromagnetic response of random, three-dimensional (3D), metal-dielectric composites (MDCs) have been limited to approximations such as effective-medium theories that employ easily-obtained, macroscopic parameters. Full-wave numerical simulations such as finite-difference time domain (FDTD) calculations are difficult for random MDCs due to the fact that the nanoscale geometry of a random composite is generally difficult to ascertain after fabrication. We have developed a fabrication method for creating semicontinuous metal films with arbitrary thicknesses and a modeling technique for such films using realistic geometries. We extended our two-dimensional simulation method to obtain realistic geometries of 3D …

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Particle-Hole Asymmetry Of Fractional Quantum Hall States In The Second Landau Level Of A Two-Dimensional Hole System, A. Kumar, N. Samkharadze, Gabor A. Csathy, Michael J. Manfra, L. N. Pfeiffer, K. W. West May 2011

Particle-Hole Asymmetry Of Fractional Quantum Hall States In The Second Landau Level Of A Two-Dimensional Hole System, A. Kumar, N. Samkharadze, Gabor A. Csathy, Michael J. Manfra, L. N. Pfeiffer, K. W. West

Birck and NCN Publications

We report the unambiguous observation of a fractional quantum Hall state in the Landau level of a two-dimensional-hole sample at the filling factor v = 8/3. We identified this state by a quantized Hall resistance and an activated temperature dependence of the longitudinal resistance and found an energy gap of 40 mK. Notably, the particle-hole conjugate state at filling factor v = 7/3 in our sample did not develop down to 6.9 mK. This observation is contrary to that in electron samples, in which the 7/3 state is typically more stable than the 8/3 state. We present evidence that the …

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Self-Assembling Organic Semiconductors With Tunable Electronic Properties Based On Novel Asymmetric Phenazine And Bisphenazine, Kyoungmi Jang May 2011

Self-Assembling Organic Semiconductors With Tunable Electronic Properties Based On Novel Asymmetric Phenazine And Bisphenazine, Kyoungmi Jang

UNLV Theses, Dissertations, Professional Papers, and Capstones

Current demands in the area of organic semiconductors focus on both electronic and self-assembling properties. Particularly, one-dimensionally grown nanostructures of small organic semiconductors have drawn much attention for nanodevice fabrication. Self-assembly through various intermolecular interactions has been widely used to produce one-dimensionally grown nanostructures which can be induced by various methods such as rapid solution dispersion, a phase transfer method, vapor annealing, crystallization, and organogelation in conjunction with proper molecular design. Controlling the morphology of the nanostructures plays an important role in achieving desirable properties in optoelectronic device applications. While significant advancements have been made in developing molecular architectures for …

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Optical And Raman Characterization Of Ald Alumina Coated Multiwall Carbon Nanotubes And Nanoporous Gold Film, Naod Belai May 2011

Optical And Raman Characterization Of Ald Alumina Coated Multiwall Carbon Nanotubes And Nanoporous Gold Film, Naod Belai

UNLV Theses, Dissertations, Professional Papers, and Capstones

Due to their large surface to volume ratio nanostructures are inherently unstable. To insure long term stability of nano-devices, they have to be rendered inert to their environment. In this study, nanoporous gold films(NPGF) and multiwall carbon nanotubes were coated with ALD alumina of varying thicknesses. Subsequently, the plasmonic property of the former and electronic property of the latter was monitored by Transmittance and Raman Spectroscopy respectively. Transmittance spectra revealed that NPGF passivated by ALD-alumina maintains its plasmonic properties, i.e. its LSPR supporting properties remained intact. Raman spectra of ALD alumina passivated MWNTs show no coating induced changes in its …

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Analysis Of A Monolithic Crystal Plate Acoustic Wave Filter, Huijing He May 2011

Analysis Of A Monolithic Crystal Plate Acoustic Wave Filter, Huijing He

Department of Mechanical and Materials Engineering: Faculty Publications

We study thickness–shear and thickness–twist vibrations of a finite, monolithic, AT-cut quartz plate crystal filter with two pairs of electrodes. The equations of anisotropic elasticity are used with the omission of the small elastic constant c56 . An analytical solution is obtained using Fourier series from which the res-onant frequencies, mode shapes, and the vibration confinement due to the electrode inertia are calculated and examined.

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New Interfacial Nanochemistry On Sensory Bioscaffold-Membranes Of Nanobelts, Feng Chen May 2011

New Interfacial Nanochemistry On Sensory Bioscaffold-Membranes Of Nanobelts, Feng Chen

Graduate Theses and Dissertations

Nanostructured bioscaffolds and biosensors are evolving as popular and powerful tools in life science and biotechnology, due to the possible control of their surface and structural properties at the nm-scale. Being seldom discussed in literature and long-underexploited in materials and biomedical sciences, development of nanofiber-based sensory bioscaffolds has great promises and grand challenges in finding an ideal platform for low-cost quantifications of biological and chemical species in real-time, label-free, and ultrasensitive fashion. In this study, titanate nanobelts were first of all synthesized, from hydrothermal reactions of a NaOH (or KOH solution) with TiO2 powder, to possess underexploited structure and surface …

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Atomistic Approach To Alloy Scattering In Si(1-X)Ge(X), Saumitra R. Mehrotra, Abhijeet Paul, Gerhard Klimeck Apr 2011

Atomistic Approach To Alloy Scattering In Si(1-X)Ge(X), Saumitra R. Mehrotra, Abhijeet Paul, Gerhard Klimeck

Birck and NCN Publications

SiGe alloy scattering is of significant importance with the introduction of strained layers and SiGe channels into complementary metal-oxide semiconductor technology. However, alloy scattering has till now been treated in an empirical fashion with a fitting parameter. We present a theoretical model within the atomistic tight-binding representation for treating alloy scattering in SiGe. This approach puts the scattering model on a solid atomistic footing with physical insights. The approach is shown to inherently capture the bulk alloy scattering potential parameters for both n-type and p-type
carriers and matches experimental mobility data.

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Transverse Permeability Of Fibrous Porous Media, Ali Tamayol, Majid Bahrami Apr 2011

Transverse Permeability Of Fibrous Porous Media, Ali Tamayol, Majid Bahrami

Department of Mechanical and Materials Engineering: Faculty Publications

In this study, the transverse permeability of fibrous porous media is studied both experimentally and theoretically. A scale analysis technique is employed for determining the transverse permeability of various fibrous matrices including square, staggered, and hexagonal arrangements of unidirectionally aligned fibers, as well as simple two-directional mats and simple cubic structures. In the present approach, the permeability is related to the porosity, fiber diameter, and tortuosity of the medium. In addition, the pressure drop in several samples of tube banks of different arrangements and metal foams are measured in the creeping flow regime. The pressure-drop results are then used to …

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Improved Rehabilitation And Exercise Machine / Machine De Reeducation Et D'Exercice Amelioree, Judith M. Burnfield, Adam Taylor, Thad W. Buster, Carla A. Nelson, Yu Shu Apr 2011

Improved Rehabilitation And Exercise Machine / Machine De Reeducation Et D'Exercice Amelioree, Judith M. Burnfield, Adam Taylor, Thad W. Buster, Carla A. Nelson, Yu Shu

Department of Mechanical and Materials Engineering: Faculty Publications

An improved rehabilitation and exercise machine is provided which allows a person with physical limitations, disabilities or chronic conditions to use the machine in order to rehabilitate their muscles, improve joint flexibility, and enhance cardiovascular fitness. An embodiment of the device includes a framework, a first and second crank arm, a first and second handle bar, a first and second foot pedal, a motor and pulley assembly, a first and second coupler link, and a motor controller with speed knob,

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Investigation Of Structural And Magnetic Properties Of Iron Clusters Encapsulated In Carbon, Andrew Mohrland, Eunja Kim, Phillipe Weck, Pang Tao, Kenneth Czerwinski Apr 2011

Investigation Of Structural And Magnetic Properties Of Iron Clusters Encapsulated In Carbon, Andrew Mohrland, Eunja Kim, Phillipe Weck, Pang Tao, Kenneth Czerwinski

Festival of Communities: UG Symposium (Posters)

Our goal is to investigate and predict the properties of iron-carbon nanostructures by performing numerical calculations using the density-functional theory. We are interested in which nanostructures are most stable, and in how they are likely to form. We have a particular interest in the magnetic properties of carbon "buckyballs" containing iron particles. These structures have potential for biomedical application, including use in anti-cancer treatment. Lone iron clusters have potential for use as a catalyst designed to reduce vehicle emissions.

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Computational Study Of Carbon Nanotubes Under Strain, Jeremy Feliciano, William Wolfs Apr 2011

Computational Study Of Carbon Nanotubes Under Strain, Jeremy Feliciano, William Wolfs

Festival of Communities: UG Symposium (Posters)

We perform computational studies of carbon nanotubes (CNTs) using molecular dynamics simulations to examine the behavior of single-walled (SW) and multiwalled (MW) CNTs under large compressive and bending strains. We study the effects of defects, heating and chirality on their properties. Research on CNTs holds great promise for developing new advanced materials in applications ranging from high-strength composites to next-generation electronics.

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First-Principles Analysis Of Zrn/Scn Metal/Semiconductor Superlattices For Thermoelectric Energy Conversion, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare Apr 2011

First-Principles Analysis Of Zrn/Scn Metal/Semiconductor Superlattices For Thermoelectric Energy Conversion, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare

Birck and NCN Publications

We present a first-principles density functional theory-based analysis of the electronic structure, vibrational spectra, and transport properties of ZrN/ScN metal/semiconductor superlattices aiming to understand its potential and suitability for thermoelectric applications. We demonstrate (a) the presence of Schottky barriers of 0.34 eV at the metal/semiconductor interface and (b) a large asymmetry in the electronic densities of states and flattening of electronic bands along the cross-plane directions near the Fermi energy of these superlattices, desirable for high Seebeck coefficient. The vibrational spectra of these superlattices show softening of transverse acoustic phonon modes along the growth direction and localization of ScN phonons …

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Decomposition Of Unitary Matrices For Finding Quantum Circuits: Application To Molecular Hamiltonians, Anmer Daskin, Sabre Kais Apr 2011

Decomposition Of Unitary Matrices For Finding Quantum Circuits: Application To Molecular Hamiltonians, Anmer Daskin, Sabre Kais

Birck and NCN Publications

Constructing appropriate unitary matrix operators for new quantum algorithms and finding the minimum cost gate sequences for the implementation of these unitary operators is of fundamental importance in the field of quantum information and quantum computation. Evolution of quantum circuits faces two major challenges: complex and huge search space and the high costs of simulating quantum circuits on classical computers. Here, we use the group leaders optimization algorithm to decompose a given unitary matrix into a proper-minimum cost quantum gate sequence. We test the method on the known decompositions of Toffoli gate, the amplification step of the Grover search algorithm, …

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Bifurcation-Based Mass Sensing Using Piezoelectrically-Actuated Microcantilevers, Vijay Kumar, J. William Boley, Yushi Yang, Hendrik Ekowaluyo, Jacob K. Miller, George T.C. Chiu, Jeff F. Rhoads Apr 2011

Bifurcation-Based Mass Sensing Using Piezoelectrically-Actuated Microcantilevers, Vijay Kumar, J. William Boley, Yushi Yang, Hendrik Ekowaluyo, Jacob K. Miller, George T.C. Chiu, Jeff F. Rhoads

Birck and NCN Publications

In conventional implementations, resonant chemical and biological sensors exploit chemomechanically-induced frequency shifts, which occur in linear systems, for analyte detection. In this letter, an alternative sensing approach, based upon dynamic transitions across saddle-node bifurcations is investigated. This technique not only has the potential to render improved sensor metrics but also to eliminate frequency tracking components from final device implementations. The present work details proof-of-concept experiments on bifurcation-based sensing, which were conducted using selectively functionalized, piezoelectrically-actuated microcantilevers. Preliminary results reveal the proposed sensing technique to be a viable alternative to existing resonant sensing methods. (C) 2011 American Institute of Physics. [doi:10.1063/1.3574920]

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Single Molecule In Vivo Analysis Of Toll-Like Receptor 9 And Cpg Dna Interaction, Jiji Chen, Suman Nag, Pierre-Alexandre Vidi, Joseph Irudayaraj Apr 2011

Single Molecule In Vivo Analysis Of Toll-Like Receptor 9 And Cpg Dna Interaction, Jiji Chen, Suman Nag, Pierre-Alexandre Vidi, Joseph Irudayaraj

Birck and NCN Publications

Toll-like receptor 9 (TLR9) activates the innate immune system in response to oligonucleotides rich in CpG whereas DNA lacking CpG could inhibit its activation. However, the mechanism of how TLR9 interacts with nucleic acid and becomes activated in live cells is not well understood. Here, we report on the successful implementation of single molecule tools, constituting fluorescence correlation/cross-correlation spectroscopy (FCS and FCCS) and photon count histogram (PCH) with fluorescence lifetime imaging (FLIM) to study the interaction of TLR9-GFP with Cy5 labeled oligonucleotide containing CpG or lacking CpG in live HEK 293 cells. Our findings show that i) TLR9 predominantly forms …

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Full Dispersion Versus Debye Model Evaluation Of Lattice Thermal Conductivity With A Landauer Approach, Changwook Jeong, Supriyo Datta, Mark S. Lundstrom Apr 2011

Full Dispersion Versus Debye Model Evaluation Of Lattice Thermal Conductivity With A Landauer Approach, Changwook Jeong, Supriyo Datta, Mark S. Lundstrom

Birck and NCN Publications

Using a full dispersion description of phonons, the thermal conductivities of bulk Si and Bi(2)Te(3) are evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation. A procedure to extract a well-defined average phonon mean-free-path from the measured thermal conductivity and given phonon-dispersion is presented. The extracted mean-free-path has strong physical significance and differs greatly from simple estimates. The use of simplified dispersion models for phonons is discussed, and it is shown that two different Debye temperatures must be used to treat the specific heat and thermal conductivity (analogous to the two different …

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Electronic Structure, Vibrational Spectrum, And Thermal Properties Of Yttrium Nitride: A First-Principles Study, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare Apr 2011

Electronic Structure, Vibrational Spectrum, And Thermal Properties Of Yttrium Nitride: A First-Principles Study, Bivas Saha, Timothy D. Sands, Umesh V. Waghmare

Birck and NCN Publications

Yttrium nitride (YN) is a promising semiconductor for use in metal/semiconductor superlattices for thermoelectric applications. We determine its electronic structure, vibrational spectrum, and thermal properties using first-principles density functional theory (DFT) based simulations with a generalized gradient approximation (GGA) of the exchange correlation energy. We employ GGA+U and GW approximations in our calculations to (a) improve the accuracy of the calculation of bandgaps and (b) determine specific features of its electronic structure relevant to transport properties, such as transverse (m(t)*) and longitudinal (m(1)*) conduction band effective mass. To evaluate consequences of forming alloys of YN with other materials to its …

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A Modeling And Simulation Framework For Electrokinetic Nanoparticle Treatment, James Phillips Apr 2011

A Modeling And Simulation Framework For Electrokinetic Nanoparticle Treatment, James Phillips

Doctoral Dissertations

The focus of this research is to model and provide a simulation framework for the packing of differently sized spheres within a hard boundary. The novel contributions of this dissertation are the cylinders of influence (COI) method and sectoring method implementations. The impetus for this research stems from modeling electrokinetic nanoparticle (EN) treatment, which packs concrete pores with differently sized nanoparticles. We show an improved speed of the simulation compared to previously published results of EN treatment simulation while obtaining similar porosity reduction results. We mainly focused on readily, commercially available particle sizes of 2 nm and 20 nm particles, …

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An Atomistic Study Of Thermal Conductance Across A Metal-Graphene Nanoribbon Interface, Zhen Huang, Timothy S. Fisher, Jayathi Y. Murthy Apr 2011

An Atomistic Study Of Thermal Conductance Across A Metal-Graphene Nanoribbon Interface, Zhen Huang, Timothy S. Fisher, Jayathi Y. Murthy

Birck and NCN Publications

This paper presents an atomistic Green's function study of phonon transport through a heterogeneous interface between bulk TiC substrates and graphene nanoribbons (GNRs). The force constants that govern the lattice dynamical equations are obtained from first-principles density functional theory (DFT) calculations and then optimized for the Green's function formulation. Phonon vibrational properties of TiC and GNRs are investigated by lattice dynamics calculations with optimized force constants that correlate well to direct DFT results. Thermal conductances of TiC-GNR-TiC systems are studied together with TiC-GNR structures. The conductances of TiC-GNR interfaces are normalized by ribbon width and are found to converge. The …

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Calculation Of Single Chain Cellulose Elasticity Using Fully Atomistic Modeling, Xiawa Wu, Robert Moon, Ashlie Martini Apr 2011

Calculation Of Single Chain Cellulose Elasticity Using Fully Atomistic Modeling, Xiawa Wu, Robert Moon, Ashlie Martini

Birck and NCN Publications

Cellulose nanocrystals, a potential base material for green nanocomposites, are ordered bundles of cellulose chains. The properties of these chains have been studied for many years using atomic-scale modeling. However, model predictions are difficult to interpret because of the significant dependence of predicted properties on model details. The goal of this study is to begin to understand these dependencies. We focus on the investigation on model cellulose chains with different lengths and having both periodic and nonperiodic boundary conditions, and predict elasticity in the axial (chain) direction with three commonly used calculation methods. We find that chain length, boundary conditions, …

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