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Full-Text Articles in Nanoscience and Nanotechnology

Local Heating With Lithographically Fabricated Plasmonic Titanium Nitride Nanoparticles, Urcan Guler, Justus Ndukaife, Gururaj Naik, Agbai Nnanna, Alexander Kildishev, V. Shalaev, Alexandra Boltasseva Jul 2015

Local Heating With Lithographically Fabricated Plasmonic Titanium Nitride Nanoparticles, Urcan Guler, Justus Ndukaife, Gururaj Naik, Agbai Nnanna, Alexander Kildishev, V. Shalaev, Alexandra Boltasseva

U. Guler

Titanium nitride is considered a promising alternative plasmonic material and is known to exhibit localized surface plasmon resonances within the near-infrared biological transparency window. Here, local heating efficiencies of disk-shaped nanoparticles made of titanium nitride and gold are compared in the visible and near-infrared regions numerically and experimentally with samples fabricated using e-beam lithography. Results show that plasmonic titanium nitride nanodisks are efficient local heat sources and outperform gold nanodisks in the biological transparency window, dispensing the need for complex particle geometries.


High Density, Vertically-Aligned Carbon Nanotube Membranes, Miao Yu, H. Funke, J. Falconer, R. Noble Jun 2015

High Density, Vertically-Aligned Carbon Nanotube Membranes, Miao Yu, H. Funke, J. Falconer, R. Noble

Miao Yu

No abstract provided.


Analytical Models For Atomic Friction, Yalin Dong, Ajay Vadakkepatt, Ashlie Martini Apr 2015

Analytical Models For Atomic Friction, Yalin Dong, Ajay Vadakkepatt, Ashlie Martini

Dr. Yalin Dong

In this methods article, we describe application of Prandtl–Tomlinson models and their extensions to interpret dry atomic-scale friction. The goal is to provide a practical overview of how to use these models to study frictional phenomena. We begin with the fundamental equations and build on them step-by-step—from the simple quasistatic one-spring, one-mass model for predicting transitions between friction regimes to the two-dimensional and multi-atom models for describing the effect of contact area. The intention is to bridge the gap between theoretical analysis, numerical implementation, and predicted physical phenomena. In the process, we provide an introductory manual with example ...


Atomic Roughness Enhanced Friction On Hydrogenated Graphene, Yalin Dong, Xiawa Wu, Ashlie Martini Apr 2015

Atomic Roughness Enhanced Friction On Hydrogenated Graphene, Yalin Dong, Xiawa Wu, Ashlie Martini

Dr. Yalin Dong

Atomic friction on hydrogenated graphene is investigated using molecular dynamics simulations. Hydrogenation is found to increase friction significantly, and the atomic-level information provided by the simulations reveals that atomic roughness induced by hydrogenation is the primary cause of the friction enhancement. Other proposed mechanisms, specifically adhesion and rigidity, are excluded based on the simulation results and analyses performed using the Prandtl–Tomlinson model. In addition, it is found that friction does not monotonically increase with hydrogen coverage on the graphene surface; instead, a maximum friction is observed at a hydrogen coverage between 5 and 10%.


Micro-Rve Modeling Of Mechanistic Response In Porous Intermetallics Subject To Weak And Moderate Impact Loading, A Nair, B Mason, L Groven, S Son, A Strachan, A Cuitino Mar 2015

Micro-Rve Modeling Of Mechanistic Response In Porous Intermetallics Subject To Weak And Moderate Impact Loading, A Nair, B Mason, L Groven, S Son, A Strachan, A Cuitino

Steven F. Son

In this article we propose macroscopic (continuum) simulation schemes to predict response of porous heterogeneous material systems subjected to weak and moderate impact velocities. The proposed simulation model includes (1) an equation of state for porous solids that describes the evolution of porosity in the material as a function of shock pressure and, (2) a macroscopic rate dependent plasticity model for the porous composite that accounts for the deviatoric strength of the material at weak to moderate shock strengths. In addition, the numerical scheme employs cold-mixture theory to predict shock response of porous intermetallics. The material model is validated using ...


Refractory Plasmonics With Titanium Nitride: Broadband Metamaterial Absorber, W Li, U. Guler, N. Kinsey, G. Naik, A. Boltasseva, J. Guan, V Shalaev, A. Kildishev Oct 2014

Refractory Plasmonics With Titanium Nitride: Broadband Metamaterial Absorber, W Li, U. Guler, N. Kinsey, G. Naik, A. Boltasseva, J. Guan, V Shalaev, A. Kildishev

U. Guler

A high-temperature stable broadband plasmonic absorber is designed, fabricated, and optically characterized. A broadband absorber with an average high absorption of 95% and a total thickness of 240 nm is fabricated, using a refractory plasmonic material, titanium nitride. This absorber integrates both the plasmonic resonances and the dielectric-like loss. It opens a path for the interesting applications such as solar thermophotovoltaics and optical circuits.


Multiscale Contact Mechanics Model For Rf-Mems Switches With Quantified Uncertainties, Hojin Kim, Nurul Shaik, Xin Xu, Arvind Raman, Alejandro Strachan Sep 2014

Multiscale Contact Mechanics Model For Rf-Mems Switches With Quantified Uncertainties, Hojin Kim, Nurul Shaik, Xin Xu, Arvind Raman, Alejandro Strachan

Xin Xu

We introduce a multiscale model for contact mechanics between rough surfaces and apply it to characterize the force-displacement relationship for a metal-dielectric contact relevant for radio frequency micro-electromechanicl system (MEMS) switches. We propose a mesoscale model to describe the history-dependent force-displacement relationships in terms of the surface roughness, the long-range attractive interaction between the two surfaces, and the repulsive interaction between contacting asperities (including elastic and plastic deformation). The inputs to this model are the experimentally determined surface topography and the Hamaker constant as well as the mechanical response of individual asperities obtained from density functional theory calculations and large-scale ...


Atomic Force Microscopy Characterization Of Cellulose Nanocrystals, Roya Lahiji, Xin Xu, R. Reifenberger, Arvind Raman, Alan Rudie, Robert Moon Sep 2014

Atomic Force Microscopy Characterization Of Cellulose Nanocrystals, Roya Lahiji, Xin Xu, R. Reifenberger, Arvind Raman, Alan Rudie, Robert Moon

Xin Xu

Cellulose nanocrystals (CNCs) are gaining interest as a "green" nanomaterial with superior mechanical and chemical properties for high-performance nanocomposite materials; however, there is a lack of accurate material property characterization of individual CNCs. Here, a detailed Study of the topography, elastic and adhesive properties of individual wood-derived CNCs is performed using atomic force microscopy (AFM). AFM experiments involving high-resolution dynamic mode imaging and jump-mode measurements were performed on individual CNCs under ambient conditions with 30% relative humidity (RH) and under a N-2 atmosphere with 0.1% RH. A procedure was also developed to calculate the CNC transverse elastic modulus (E-T ...


Large Scale, Highly Dense Nanoholes On Metal Surfaces By Underwater Laser Assisted Hydrogen Etching Near Nanocrystalline Boundary, Dong Lin, Martin Yi Zhang, Chang Ye, Zhikun Liu, Richard Liu, Gary Cheng Aug 2014

Large Scale, Highly Dense Nanoholes On Metal Surfaces By Underwater Laser Assisted Hydrogen Etching Near Nanocrystalline Boundary, Dong Lin, Martin Yi Zhang, Chang Ye, Zhikun Liu, Richard Liu, Gary Cheng

dong lin

A new method to generate large scale and highly dense nanoholes is presented in this paper. By the pulsed laser irradiation under water, the hydrogen etching is introduced to form high density nanoholes on the surfaces of AISI 4140 steel and Ti. In order to achieve higher nanohole density, laser shock peening (LSP) followed by recrystallization is used for grain refinement. It is found that the nanohole density does not increase until recrystallization of the substructures after laser shock peening. The mechanism of nanohole generation is studied in detail. This method can be also applied to generate nanoholes on other ...


Laser Assisted Embedding Of Nanoparticles Into Metallic Materials, Dong Lin, Sergey Suslov, Chang Ye, Yiliang Liao, C. Richard Liu, Gary Cheng Aug 2014

Laser Assisted Embedding Of Nanoparticles Into Metallic Materials, Dong Lin, Sergey Suslov, Chang Ye, Yiliang Liao, C. Richard Liu, Gary Cheng

dong lin

This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transparent and opaque nanoparticles are chosen to demonstrate the process of laser assisted nanoparticle embedding. Dip coating method is used to coat transparent or opaque nanoparticle on the surface of metallic material. Nanoparticles are embedded into substrate by laser irradiation. In this study, the mechanism and process of nanoparticle embedding are investigated. It is found both transparent and opaque nanoparticles embedding are with high densities and good uniformities. (C) 2011 Elsevier B. V. All rights reserved.


Magnetic Field Assisted Growth Of Highly Dense Alpha-Fe2o3 Single Crystal Nanosheets And Their Application In Water Treatment, Dong Lin, Biwei Deng, Stephen Sassman, Yaowu Hu, Sergey Suslov, Gary Cheng Aug 2014

Magnetic Field Assisted Growth Of Highly Dense Alpha-Fe2o3 Single Crystal Nanosheets And Their Application In Water Treatment, Dong Lin, Biwei Deng, Stephen Sassman, Yaowu Hu, Sergey Suslov, Gary Cheng

dong lin

Highly dense 2D nanostructures are desirable in photocatalysis, water treatment and energy storage, due to their high surface to volume areas. This paper describes a novel approach combining thermal stress and magnetic force to generate highly dense alpha-Fe2O3 nanosheets on the surface of various iron substrates, including plates and powders. This technique involves the thermal oxidation of iron substrates on a hot plate with a magnetic field. The Lorentz force acting on the ions induced by the magnetic field facilitates the lateral growth of nanosheets. This effect results in a highly porous nanostructure consisting of dense 2D nanosheets with extremely ...


Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough Apr 2014

Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough

B. Scott Day

The study of biomolecular motors represents a rapidly and progressing field of nanobiotechnology. Here, we present a simple method for patterning myosin II on a microstructured surface. Our findings indicate that UV/ozone treatment can be used to alter the hydrophobicity of trimethyl-chloro-silane (TMCS) coated glass surfaces, to alter protein binding, and effectively produce localized motor activity. Taken together, these data suggest that photoreactive patterning may be useful for the selective localization of functional myosin II motor tracks.


Modeling, Analysis, And Experimental Validation Of A Bifurcation-Based Microsensor, Vijay Kumar, Yushi Yang, J. William Boley, Geroge Chiu, Jeff Rhoads Apr 2014

Modeling, Analysis, And Experimental Validation Of A Bifurcation-Based Microsensor, Vijay Kumar, Yushi Yang, J. William Boley, Geroge Chiu, Jeff Rhoads

Geroge T.-C. Chiu

The potential to detect very small amounts of added mass has driven research in chemical and biological sensors based on resonant micro-and nanoelectromechanical systems over the past two decades. While traditional resonant mass sensors utilize chemomechanically induced shifts in linear natural frequency for mass detection, alternate sensing approaches which exploit near-resonant nonlinear behaviors have garnered interest from the research community due to their potential to yield improved sensor metrics and to simplify final device implementations. This paper investigates the development of an amplitude-based mass sensing approach which utilizes the dynamic transitions that occur near a cyclic-fold/saddle-node bifurcation in the ...


Direction-Tunable Nanotwins In Copper Nanowires By Laser-Assisted Electrochemical Deposition, Zhikun Liu, Yuefeng Wang, Yiliang Liao, Gary Cheng Oct 2013

Direction-Tunable Nanotwins In Copper Nanowires By Laser-Assisted Electrochemical Deposition, Zhikun Liu, Yuefeng Wang, Yiliang Liao, Gary Cheng

Yuefeng Wang

Nanotwins can improve mechanical strength and maintain high electrical conductivity in metallic nanowires. We demonstrated a method of pulsed-laser-assisted electrodeposition, which could form dense nanotwins with tunable directions in copper nanowires of uniform sizes. Transmission electron microscopy characterization showed with a growth potential of -0.2 V, nanotwins tend to align along the longitudinal direction of the nanowires, whereas at a larger potential of -0.8 V, nanotwins of {111}/< 112 > type perpendicular to the longitudinal direction of the wire were formed. The two types of nanotwins were investigated by comparing the microstructures under different electrochemical conditions and laser irradiation energies ...


A Taper To Reduce The Straight-To-Bend Transition Loss In Compact Silicon Waveguides, Hao Shen, Li Fan, Jian Wang, Justin Wirth, Minghao Qi Oct 2013

A Taper To Reduce The Straight-To-Bend Transition Loss In Compact Silicon Waveguides, Hao Shen, Li Fan, Jian Wang, Justin Wirth, Minghao Qi

Jian Wang

Strong confinement of light in silicon waveguides allows for sharp bends and, as a result, high-density integration. However, the mode transition loss between the straight and bent portions of a silicon waveguide begins to affect the device performance when the bending radius becomes small. In this letter, we show that a transition region with a step taper between the straight and bent portions of the waveguide can effectively reduce this transition loss. This is demonstrated by measuring the intrinsic round-trip losses of micro-racetrack resonators, where ultralow loss can be precisely characterized according to the quality (Q)-factor change. The results ...


Direct Fabrication Of Silicon Photonic Devices On A Flexible Platform And Its Application For Strain Sensing, Li Fan, Leo Varghese, Yi Xuan, Jian Wang, Ben Niu, Minghao Qi Oct 2013

Direct Fabrication Of Silicon Photonic Devices On A Flexible Platform And Its Application For Strain Sensing, Li Fan, Leo Varghese, Yi Xuan, Jian Wang, Ben Niu, Minghao Qi

Jian Wang

We demonstrate a process to fabricate silicon photonic devices directly on a plastic film which is both flexible and transparent. This process allows the integration of complex structures on plastic films without the need of transferring from another substrate. Waveguides, grating couplers, and microring resonators are fabricated and optically characterized. An optical strain sensor is shown as an application using 5 mu m-radius microring resonators on the flexible substrate. When strain is applied, resonance wavelength shifts of the microring resonators are observed. Contributions of different effects are analyzed and evaluated. Finally, we measure the influence of residual strain and confirm ...


An All-Silicon Passive Optical Diode, Li Fan, Jian Wang, Leo Varghese, Hao Shen, Ben Niu, Yi Xuan, Andrew Weiner, Minghao Qi Oct 2013

An All-Silicon Passive Optical Diode, Li Fan, Jian Wang, Leo Varghese, Hao Shen, Ben Niu, Yi Xuan, Andrew Weiner, Minghao Qi

Jian Wang

A passive optical diode effect would be useful for on-chip optical information processing but has been difficult to achieve. Using a method based on optical nonlinearity, we demonstrate a forward-backward transmission ratio of up to 28 decibels within telecommunication wavelengths. Our device, which uses two silicon rings 5 micrometers in radius, is passive yet maintains optical nonreciprocity for a broad range of input power levels, and it performs equally well even if the backward input power is higher than the forward input. The silicon optical diode is ultracompact and is compatible with current complementary metal-oxide semiconductor processing.


Observation Of Correlation Between Route To Formation, Coherence, Noise, And Communication Performance Of Kerr Combs, Pei-Hsun Wang, Fahmida Ferdous, Houxun Miao, Jian Wang, Daniel Leaird, Kartik Srinivasan, Lei Chen, Vladimir Aksyuk, Andrew Weiner Oct 2013

Observation Of Correlation Between Route To Formation, Coherence, Noise, And Communication Performance Of Kerr Combs, Pei-Hsun Wang, Fahmida Ferdous, Houxun Miao, Jian Wang, Daniel Leaird, Kartik Srinivasan, Lei Chen, Vladimir Aksyuk, Andrew Weiner

Jian Wang

Microresonator optical frequency combs based on cascaded four-wave mixing are potentially attractive as a multi-wavelength source for on-chip optical communications. In this paper we compare time domain coherence, radio-frequency (RF) intensity noise, and individual line optical communications performance for combs generated from two different silicon nitride microresonators. The comb generated by one microresonator forms directly with lines spaced by a single free spectral range (FSR) and exhibits high coherence, low noise, and excellent 10 Gbit/s optical communications results. The comb generated by the second microresonator forms initially with multiple FSR line spacing, with additional lines later filling to reach ...


Spectral Line-By-Line Pulse Shaping Of On-Chip Microresonator Frequency Combs, Fahmida Ferdous, Houxun Miao, Daniel Leaird, Kartik Srinivasan, Jian Wang, Lei Chen, Leo Tom Varghese, Andrew Weiner Oct 2013

Spectral Line-By-Line Pulse Shaping Of On-Chip Microresonator Frequency Combs, Fahmida Ferdous, Houxun Miao, Daniel Leaird, Kartik Srinivasan, Jian Wang, Lei Chen, Leo Tom Varghese, Andrew Weiner

Jian Wang

Recently, on-chip comb generation methods based on nonlinear optical modulation in ultrahigh-quality-factor monolithic microresonators have been demonstrated, where two pump photons are transformed into sideband photons in a four-wave-mixing process mediated by Kerr nonlinearity. Here, we investigate line-by-line pulse shaping of such combs generated in silicon nitride ring resonators. We observe two distinct paths to comb formation that exhibit strikingly different time-domain behaviours. For combs formed as a cascade of sidebands spaced by a single free spectral range that spread from the pump, we are able to compress stably to nearly bandwidth-limited pulses. This indicates high coherence across the spectra ...


Tuning The Magnetostructural Phase Transition In Ferh Nanocomposites, Radhika Barua, Xiujuan Jiang, Felix Jiménez-Villacorta, J. Shield, D. Heiman, L. Lewis Aug 2013

Tuning The Magnetostructural Phase Transition In Ferh Nanocomposites, Radhika Barua, Xiujuan Jiang, Felix Jiménez-Villacorta, J. Shield, D. Heiman, L. Lewis

Donald Heiman

Effects of nanostructuring on the magnetostructural response of the near-equiatomic FeRh phase were investigated in nanocomposite materials synthesized by rapid solidification and subsequent annealing of an alloy of nominal atomic composition (FeRh)5Cu95. Transmission electron microscopy studies confirm attainment of a phase-separated system of nanoscaled (∼10–15 nm diameter) precipitates, consistent with FeRh embedded in a Cu matrix. These nanoprecipitates are crystallographically aligned with the coarse-grained Cu matrix and possess an L10-type (CuAu 1) structure, in contrast to the B2 (CsCl)-type structure of bulk FeRh. It is proposed that the face-centered cubic crystal structure of ...


Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough May 2013

Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough

Kevin M Rice

The study of biomolecular motors represents a rapidly and progressing field of nanobiotechnology. Here, we present a simple method for patterning myosin II on a microstructured surface. Our findings indicate that UV/ozone treatment can be used to alter the hydrophobicity of trimethyl-chloro-silane (TMCS) coated glass surfaces, to alter protein binding, and effectively produce localized motor activity. Taken together, these data suggest that photoreactive patterning may be useful for the selective localization of functional myosin II motor tracks.


Multi-Scale Models For Sulfonated Cross-Linked Poly (1, 3-Cyclohexadiene) Polymer, Qifei Wang, David Keffer, Suxiang Deng, Jimmy Mays May 2013

Multi-Scale Models For Sulfonated Cross-Linked Poly (1, 3-Cyclohexadiene) Polymer, Qifei Wang, David Keffer, Suxiang Deng, Jimmy Mays

Jimmy W. Mays

Atomistic and coarse-grained (CG) models of cross-linked sulfonated Poly (1, 3-cyclohexadiene) (xsPCHD) were developed and implemented in Molecular Dynamics (MD) simulations of PCHD chains with different architectures. In the atomistic model, PCHD chains are cross linked by a sulfur–sulfur bond. Sulfonic acid groups are evenly distributed along the chain. The architecture is specifically aimed for application as a proton exchange membrane used in fuel cells. An atomistic force field for this architecture was tested and applied in the atomistic MD simulation of xsPCHD for the first time. The atomistic simulations generate the density and cross-linker separation distribution. To further ...


Cause And Prevention Of Moisture-Induced Degradation Of Resistance Random Access Memory Nanodevices, Albert Chen Jan 2013

Cause And Prevention Of Moisture-Induced Degradation Of Resistance Random Access Memory Nanodevices, Albert Chen

Albert B Chen

Dielectric thin films in nanodevices may absorb moisture, leading to physical changes and property/performance degradation, such as altered data storage and readout in resistance random access memory. Here we demonstrate using a nanometallic memory that such degradation proceeds via nanoporosity, which facilitates water wetting in otherwise nonwetting dielectrics. Electric degradation only occurs when the device is in the charge-storage state, which provides a nanoscale dielectrophoretic force directing H2O to internal field centers (sites of trapped charge) to enable bond rupture and charged hydroxyl formation. While these processes are dramatically enhanced by an external DC or AC field and electron-donating ...


Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough Jan 2013

Assembly And Function Of Myosin Ii On Ultraviolet/Ozone Patterned Trimethylchlorosilane Substrates, Hideyo Takatsuki, Madhukar Kolli, Kevin Rice, B. Day, Shinichi Asano, Mashiur Rahman, Yue Zhang, Ryoki Ishikawa, Kazuhiro Kohama, Eric Blough

Eric Blough

The study of biomolecular motors represents a rapidly and progressing field of nanobiotechnology. Here, we present a simple method for patterning myosin II on a microstructured surface. Our findings indicate that UV/ozone treatment can be used to alter the hydrophobicity of trimethyl-chloro-silane (TMCS) coated glass surfaces, to alter protein binding, and effectively produce localized motor activity. Taken together, these data suggest that photoreactive patterning may be useful for the selective localization of functional myosin II motor tracks.


Demonstration And Modeling Of Multi-Bit Resistance Random Access Memory, Albert Chen Dec 2012

Demonstration And Modeling Of Multi-Bit Resistance Random Access Memory, Albert Chen

Albert B Chen

Although intermediates resistance states are common in resistance random access memory (RRAM), two-way switching among them has not been demonstrated. Using a nanometallic bipolar RRAM, we have illustrated a general scheme for writing/rewriting multi-bit memory using voltage pulses. Stability conditions for accessing intermediate states have also been determined in terms of a state distribution function and the weight of serial load resistance. A multi-bit memory is shown to realize considerable space saving at a modest decrease of switching speed.


Super-Resolution Imaging Using A Three-Dimensional Metamaterials Nanolens, B. Casse, W. Lu, Y. Huang, E. Gultepe, L. Menon, S. Sridhar Oct 2012

Super-Resolution Imaging Using A Three-Dimensional Metamaterials Nanolens, B. Casse, W. Lu, Y. Huang, E. Gultepe, L. Menon, S. Sridhar

Srinivas Sridhar

Super-resolution imaging beyond Abbe's diffraction limit can be achieved by utilizing an optical medium or "metamaterial" that can either amplify or transport the decaying near-field evanescent waves that carry subwavelength features of objects. Earlier approaches at optical frequencies mostly utilized the amplification of evanescent waves in thin metallic films or metal-dielectric multilayers, but were restricted to very small thicknesses (⪡λ, wavelength) and accordingly short object-image distances, due to losses in the material. Here, we present an experimental demonstration of super-resolution imaging by a low-loss three-dimensional metamaterial nanolens consisting of aligned gold nanowires embedded in a porous alumina matrix. This ...


Large Coercivity In Nanostructured Rare-Earth-Free MnₓGa Films, Don Heiman, Tom Nummy, Steve Bennett, Tom Cardinal Oct 2012

Large Coercivity In Nanostructured Rare-Earth-Free MnₓGa Films, Don Heiman, Tom Nummy, Steve Bennett, Tom Cardinal

Donald Heiman

The magnetic hysteresis of MnₓGa films exhibit remarkably large coercive fields as high as μₒHC=2.5 T when fabricated with nanoscale particles of a suitable size and orientation. This coercivity is an order of magnitude larger than in well-ordered epitaxial film counterparts and bulk materials. The enhanced coercivity is attributed to the combination of large magnetocrystalline anisotropy and ~50-100 nm size nanoparticles. The large coercivity is also replicated in the electrical properties through the anomalous Hall effect. The magnitude of the coercivity approaches that found in rare-earth magnets, making them attractive for rare-earth-free magnet applications.


Magnetic Properties Of Gamnas Nanodot Arrays Fabricated Using Porous Alumina Templates, S. Bennett, L. Menon, D. Heiman Oct 2012

Magnetic Properties Of Gamnas Nanodot Arrays Fabricated Using Porous Alumina Templates, S. Bennett, L. Menon, D. Heiman

Donald Heiman

Ordered arrays of GaMnAs magnetic semiconductor nanodots have been fabricated using anodic porous alumina templates as etch masks. The magnetic behavior is studied for prepared arrays with 40 nm dot diameter, 15 nm dot thickness, and 80 nm periodicity. The disklike nanodots exhibit an easy axis for fields applied in the radial direction and a hard axis in the smaller direction. In the radial direction superparamagnetism is observed with a blocking temperature of 30 K. The fabrication technique is convenient for preparing nanodot arrays of compound semiconductors that cannot be formed by self-assembly techniques.


Multimodal Grain Size Distribution And High Hardness In Fine Grained Tungsten Fabricated By Spark Plasma Sintering, Osman El-Atwani, D.V. Quach, Mert Efe, Patrick Cantwell, Bryan Heim, Bradley Schultz, Eric Stach, Joanna Groza, Jean Allain Jun 2012

Multimodal Grain Size Distribution And High Hardness In Fine Grained Tungsten Fabricated By Spark Plasma Sintering, Osman El-Atwani, D.V. Quach, Mert Efe, Patrick Cantwell, Bryan Heim, Bradley Schultz, Eric Stach, Joanna Groza, Jean Allain

Osman El-Atwani

Preparation of fine grained, hard and ductile pure tungsten for future fusion reactor applications was tested using the bottom-up approach via powder consolidation by spark plasma sintering (SPS) at different temperature (1300-1800 degrees C) and pressure (90-266 MPa) conditions. Pure tungsten powders with an average particle size of about 1 mu m were sintered to high density (about 94%) with almost no grain growth at a temperature below 1400 degrees C and an applied pressure up to 266 MPa. These samples had a multi-modal grain size distribution (resembling the size distribution of the initial powder) and a very high Vickers ...


Molecular Dynamic Simulations Of The Effect On The Hydration Of Nafion In The Presence Of A Platinum Nanoparticle, Myvizhi Esai Selvan, Qianping He, Elisa Calvo-Muñoz, David Keffer Apr 2012

Molecular Dynamic Simulations Of The Effect On The Hydration Of Nafion In The Presence Of A Platinum Nanoparticle, Myvizhi Esai Selvan, Qianping He, Elisa Calvo-Muñoz, David Keffer

David Keffer

Platinum catalysts play a critical role in fuel cell technology. Current optimization efforts focus on reducing the amount of Pt in the system and optimizing the utilization of that which remains. The effect of the presence of Pt nanoparticles on the local structure and morphology of the polymer electrolyte membrane, water, and hydronium ions has been studied at molecular level in this work. Classical molecular dynamics simulation has been used to examine a system containing a 4 nm fcc cubic ({100} face) platinum nanoparticle at the center surrounded by Nafion polymer, water molecules, and hydronium ions at λ = 3, 6 ...