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Birck and NCN Publications

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Full-Text Articles in Nanoscience and Nanotechnology

Right Sizes Of Nano- And Microstructures For High-Performance And Rigid Bulk Thermoelectrics, Hongchao Wang, Je-Hyeong Bahk, Chanyoung Kang, Junphil Hwang, Kangmin Kim, Jungwon Kim, Peter Burke, John E. Bowers, Arthur C. Gossard, Ali Shakouri, Woochul Kim Jul 2014

Right Sizes Of Nano- And Microstructures For High-Performance And Rigid Bulk Thermoelectrics, Hongchao Wang, Je-Hyeong Bahk, Chanyoung Kang, Junphil Hwang, Kangmin Kim, Jungwon Kim, Peter Burke, John E. Bowers, Arthur C. Gossard, Ali Shakouri, Woochul Kim

Birck and NCN Publications

In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to similar to 2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the ...


Thermal Interfacial Transport In The Presence Of Ballistic Heat Modes, Bjorn Vermeersch, Amr M.S. Mohammed, Gilles Pernot, Yee Rui Koh, Ali Shakouri Jul 2014

Thermal Interfacial Transport In The Presence Of Ballistic Heat Modes, Bjorn Vermeersch, Amr M.S. Mohammed, Gilles Pernot, Yee Rui Koh, Ali Shakouri

Birck and NCN Publications

Thermal interface (Kapitza) resistance expresses how hard it is for heat to flow across material junctions inside multilayer structures. This quantity plays a crucial role in the thermal performance of nanoscale devices but is still poorly understood. Here we show that conventional Fourier-based metrology overestimates metal/semiconductor resistances by up to threefold due to misinterpretation of ballistic heat flow modes. We achieve improved identification and a different physical insight with a truncated Levy formalism. This approach properly distinguishes interfacial dynamics from nearby quasiballistic heat flow suppression in the semiconductor. Unlike conventionally extracted values, interface resistances obtained with our new approach ...


Superradiant Decay Of Cyclotron Resonance Of Two-Dimensional Electron Gases, Qi Zhang, Takashi Arikawa, Eiji Kato, John L. Reno, Wei Pan, John D. Watson, Michael J. Manfra, Michael A. Zudov, Mikhail Tokman, Maria Erukhimova, Alexey Belyanin, Junichiro Kono Jul 2014

Superradiant Decay Of Cyclotron Resonance Of Two-Dimensional Electron Gases, Qi Zhang, Takashi Arikawa, Eiji Kato, John L. Reno, Wei Pan, John D. Watson, Michael J. Manfra, Michael A. Zudov, Mikhail Tokman, Maria Erukhimova, Alexey Belyanin, Junichiro Kono

Birck and NCN Publications

We report on the observation of collective radiative decay, or superradiance, of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay rate of coherent CR oscillations increases linearly with the electron density in a wide range, which is a hallmark of superradiant damping. Our fully quantum mechanical theory provides a universal formula for the decay rate, which reproduces our experimental data without any adjustable parameter. These results firmly establish the many-body nature of CR decoherence in this system, despite the fact that the CR frequency is immune to electron-electron interactions due ...


High Temperature Thermoreflectance Imaging And Transient Harman Characterization Of Thermoelectric Energy Conversion Devices, T. Favaloro, Amirkoushyar Ziabari, Je-Hyeong Bahk, P. Burke, H. Lu, J. Bowers, A. Gossard, Z. Bian, Ali Shakouri Jul 2014

High Temperature Thermoreflectance Imaging And Transient Harman Characterization Of Thermoelectric Energy Conversion Devices, T. Favaloro, Amirkoushyar Ziabari, Je-Hyeong Bahk, P. Burke, H. Lu, J. Bowers, A. Gossard, Z. Bian, Ali Shakouri

Birck and NCN Publications

Advances in thin film growth technology have enabled the selective engineering of material properties to improve the thermoelectric figure of merit and thus the efficiency of energy conversion devices. Precise characterization at the operational temperature of novel thermoelectric materials is crucial to evaluate their performance and optimize their behavior. However, measurements on thin film devices are subject to complications from the growth substrate, non-ideal contacts, and other thermal and electrical parasitic effects. In this manuscript, we determine the cross-plane thermoelectric material properties in a single measurement of a 25 mu m InGaAs thin film with embedded ErAs (0.2%) nanoparticles ...


Veselago Lens By Photonic Hyper-Crystals, Zun Huang, Evgenii Narimanov Jul 2014

Veselago Lens By Photonic Hyper-Crystals, Zun Huang, Evgenii Narimanov

Birck and NCN Publications

Based on the recent concept of the photonic hyper-crystal-an artificial optical medium that combines the properties of hyperbolic materials and photonic crystals, we present the imaging system functioning as a Veselago lens. This planar lens shows a nearly constant negative refractive index with substantially reduced image aberrations, and can find potential applications in photolithography and hot-spots detection of silicon-based integrated circuits. (C) 2014 AIP Publishing LLC.


Tunable Landau-Zener Transitions In A Spin-Orbit-Coupled Bose-Einstein Condensate, Abraham J. Olson, Su-Ju Wang, Robert J. Niffenegger, Chuan-Hsun Li, Chris H. Greene, Yong P. Chen Jul 2014

Tunable Landau-Zener Transitions In A Spin-Orbit-Coupled Bose-Einstein Condensate, Abraham J. Olson, Su-Ju Wang, Robert J. Niffenegger, Chuan-Hsun Li, Chris H. Greene, Yong P. Chen

Birck and NCN Publications

The Landau-Zener (LZ) transition is one of the most fundamental phenomena in quantum dynamics. It describes nonadiabatic transitions between quantum states near an avoided crossing that can occur in diverse physical systems. Here we report experimental measurements and tuning of LZ transitions between the dressed eigenlevels of a Bose-Einstein condensate (BEC) that is synthetically spin-orbit (SO) coupled. We measure the transition probability as the BEC is accelerated through the SO avoided crossing and study its dependence on the coupling between the diabatic (bare) states, eigenlevel slope, and eigenstate velocity-the three parameters of the LZ model that are independently controlled in ...


Self-Assembled Tunable Photonic Hyper-Crystals, Vera N. Smolyaninova, Bradley Yost, David Lhneman, Evgenii Narimanov, Igor I. Smolyaninov Jul 2014

Self-Assembled Tunable Photonic Hyper-Crystals, Vera N. Smolyaninova, Bradley Yost, David Lhneman, Evgenii Narimanov, Igor I. Smolyaninov

Birck and NCN Publications

We demonstrate a novel artificial optical material, the "photonic hyper-crystal'', which combines the most interesting features of hyperbolic metamaterials and photonic crystals. Similar to hyperbolic metamaterials, photonic hyper-crystals exhibit broadband divergence in their photonic density of states due to the lack of usual diffraction limit on the photon wave vector. On the other hand, similar to photonic crystals, hyperbolic dispersion law of extraordinary photons is modulated by forbidden gaps near the boundaries of photonic Brillouin zones. Three dimensional self-assembly of photonic hyper-crystals has been achieved by application of external magnetic field to a cobalt nanoparticle-based ferrofluid. Unique spectral properties of ...


Impact Of Short-Range Scattering On The Metallic Transport Of Strongly Correlated Two-Dimensional Holes In Gaas Quantum Wells, Nicholas J. Goble, John D. Watson, Michael J. Manfra, Xuan P.A. Gao Jul 2014

Impact Of Short-Range Scattering On The Metallic Transport Of Strongly Correlated Two-Dimensional Holes In Gaas Quantum Wells, Nicholas J. Goble, John D. Watson, Michael J. Manfra, Xuan P.A. Gao

Birck and NCN Publications

Understanding the nonmonotonic behavior in the temperature dependent resistance R(T) of strongly correlated two-dimensional (2D) carriers in clean semiconductors has been a central issue in the studies of 2D metallic states and metal-insulator transitions. We have studied the transport of high mobility 2D holes in 20-nm-wide GaAs quantum wells with varying short-range disorder strength by changing the Al fraction x in the AlxGa1-xAs barrier. Via varying the short-range interface roughness and alloy scattering, it is observed that increasing x suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short-range vs ...


Impact Of Short-Range Scattering On The Metallic Transport Of Strongly Correlated Two-Dimensional Holes In Gaas Quantum Wells, Nicholas J. Goble, J. D. Watson, Michael J. Manfra, Xuan P.A. Gao Jul 2014

Impact Of Short-Range Scattering On The Metallic Transport Of Strongly Correlated Two-Dimensional Holes In Gaas Quantum Wells, Nicholas J. Goble, J. D. Watson, Michael J. Manfra, Xuan P.A. Gao

Birck and NCN Publications

Understanding the nonmonotonic behavior in the temperature dependent resistance R(T) of strongly correlated two-dimensional (2D) carriers in clean semiconductors has been a central issue in the studies of 2D metallic states and metal-insulator transitions. We have studied the transport of high mobility 2D holes in 20-nm-wide GaAs quantum wells with varying short-range disorder strength by changing the Al fraction x in the AlxGa1-xAs barrier. Via varying the short-range interface roughness and alloy scattering, it is observed that increasing x suppresses both the strength and characteristic temperature scale of the 2D metallicity, pointing to the distinct role of short-range vs ...


Photonic-Band-Gap Engineering For Volume Plasmon Polaritons In Multiscale Multilayer Hyperbolic Metamaterials, Sergei V. Zhukovsky, Alexey A. Orlov, Viktoriia E. Babicheva, Andrei V. Lavrinenko, J. E. Sipe Jul 2014

Photonic-Band-Gap Engineering For Volume Plasmon Polaritons In Multiscale Multilayer Hyperbolic Metamaterials, Sergei V. Zhukovsky, Alexey A. Orlov, Viktoriia E. Babicheva, Andrei V. Lavrinenko, J. E. Sipe

Birck and NCN Publications

We study theoretically the propagation of large-wave-vector waves (volume plasmon polaritons) in multilayer hyperbolic metamaterials with two levels of structuring. We show that when the parameters of a subwavelength metal-dielectric multilayer (substructure) are modulated (superstructured) on a larger, wavelength scale, the propagation of volume plasmon polaritons in the resulting multiscale hyperbolic metamaterials is subject to photonic-band-gap phenomena. A great degree of control over such plasmons can be exerted by varying the superstructure geometry. When this geometry is periodic, stop bands due to Bragg reflection form within the volume plasmonic band. When a cavity layer is introduced in an otherwise periodic ...


Quantifying The Local Density Of Optical States Of Nanorods By Fluorescence Lifetime Imaging, Jingjing Liu, Xunpeng Jiang, Satoshi Ishii, V. M. Shalaev, Joseph Irudayaraj Jun 2014

Quantifying The Local Density Of Optical States Of Nanorods By Fluorescence Lifetime Imaging, Jingjing Liu, Xunpeng Jiang, Satoshi Ishii, V. M. Shalaev, Joseph Irudayaraj

Birck and NCN Publications

In this paper, we demonstrate a facile far-field approach to quantify the near-field local density of optical states (LDOS) of a nanorod using CdTe quantum dot (QD) emitters tethered to the surface of the nanorods as beacons for optical readouts. The radiative decay rate was extracted to quantify the LDOS; our analysis indicates that the LDOS of the nanorod enhances both the radiative and nonradiative decay of QDs, particularly the radiative decay of QDs at the end of a nanorod is enhanced by 1.17 times greater than that at the waist, while the nonradiative decay was enhanced uniformly over ...


Role Of Strain On Electronic And Mechanical Response Of Semiconducting Transition-Metal Dichalcogenide Monolayers: An Ab-Initio Study, David M. Guzman, Alejandro Strachan Jun 2014

Role Of Strain On Electronic And Mechanical Response Of Semiconducting Transition-Metal Dichalcogenide Monolayers: An Ab-Initio Study, David M. Guzman, Alejandro Strachan

Birck and NCN Publications

We characterize the electronic structure and elasticity of monolayer transition-metal dichalcogenides MX2 (M = Mo, W, Sn, Hf and X = S, Se, Te) based on 2H and 1T structures using fully relativistic first principles calculations based on density functional theory. We focus on the role of strain on the band structure and band alignment across the series of materials. We find that strain has a significant effect on the band gap; a biaxial strain of 1% decreases the band gap in the 2H structures, by as a much as 0.2 eV in MoS2 and WS2, while increasing it for the ...


Computational Study Of Heterojunction Graphene Nanoribbon Tunneling Transistors With P-D Orbital Tight-Binding Method, Sung Geun Kim, Mathieu Luisier, Timothy B. Boykin, Gerhard Klimeck Jun 2014

Computational Study Of Heterojunction Graphene Nanoribbon Tunneling Transistors With P-D Orbital Tight-Binding Method, Sung Geun Kim, Mathieu Luisier, Timothy B. Boykin, Gerhard Klimeck

Birck and NCN Publications

The graphene nanoribbon (GNR) tunneling field effect transistor (TFET) has been a promising candidate for a future low power logic device due to its sub-60 mV/dec subthreshold characteristic and its superior gate control on the channel electrons due to its one-dimensional nature. Even though many theoretical studies have been carried out, it is not clear that GNR TFETs would outperform conventional silicon metal oxide semiconductor field effect transistors (MOSFETs). With rigorous atomistic simulations using the p/d orbital tight-binding model, this study focuses on the optimization of GNR TFETs by tuning the doping density and the size of GNRs ...


Ultraviolet Laser Crystallized Zno:Al Films On Sapphire With High Hall Mobility For Simultaneous Enhancement Of Conductivity And Transparency, Qiong Nian, Martin Y. Zhang, Bradley D. Schwartz, Gary J. Cheng May 2014

Ultraviolet Laser Crystallized Zno:Al Films On Sapphire With High Hall Mobility For Simultaneous Enhancement Of Conductivity And Transparency, Qiong Nian, Martin Y. Zhang, Bradley D. Schwartz, Gary J. Cheng

Birck and NCN Publications

One of the most challenging issues in transparent conductive oxides (TCOs) is to improve their conductivity without compromising transparency. High conductivity in TCO films often comes from a high carrier concentration, which is detrimental to transparency due to free carrier absorption. Here we show that UV laser crystallization (UVLC) of aluminum-doped ZnO (AZO) films prepared by pulsed laser deposition on sapphire results in much higher Hall mobility, allowing relaxation of the constraints of the conductivity/transparency trade-off. X-ray diffraction patterns and morphological characterizations show grain growth and crystallinity enhancement during UVLC, resulting in less film internal imperfections. Optoelectronic measurements show ...


Time-Dependent Density Functional Theory Of Coupled Electronic Lattice Motion In Quasi-Two-Dimensional Crystals, Vladimir U. Nazarov, Fhhad Alharbi, Timothy Fisher, Sabre Kais May 2014

Time-Dependent Density Functional Theory Of Coupled Electronic Lattice Motion In Quasi-Two-Dimensional Crystals, Vladimir U. Nazarov, Fhhad Alharbi, Timothy Fisher, Sabre Kais

Birck and NCN Publications

Electron-holes, phonons, and plasmons come in close proximity to each other in the low-energy range of the excitation spectrum of two-dimensional (2D) crystals, breaking the validity of the weakly interacting-quasiparticles picture. By including the lattice oscillations into the scheme of time-dependent density-functional theory, we open a pathway to the ab initio treatment of the coupled low-energy excitations in 2D crystals. With the use of graphene as an important test system, we find the strong coupling of the elementary excitations, giving rise to new hybrid collective modes. The total (including both the electronic and ionic response) dielectric function epsilon(tot)(omega ...


Quantum And Classical Magnetoresistance In Ambipolar Topological Insulator Transistors With Gate-Tunable Bulk And Surface Conduction, Jifa Tian, Cuizu Chang, Helin Cao, Ke He, Xucun Ma, Qikun Xue, Yong P. Chen May 2014

Quantum And Classical Magnetoresistance In Ambipolar Topological Insulator Transistors With Gate-Tunable Bulk And Surface Conduction, Jifa Tian, Cuizu Chang, Helin Cao, Ke He, Xucun Ma, Qikun Xue, Yong P. Chen

Birck and NCN Publications

Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)(2)Te-3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching ...


In-Situ Tem Observation Of The Response Of Ultrafine- And Nanocrystalline-Grained Tungsten To Extreme Irradiation Environments, Osman El-Atwani, J. A. Hinks, G. Greaves, Sean Gonderman, T. Qiu, M. Efe, Jean P. Allain May 2014

In-Situ Tem Observation Of The Response Of Ultrafine- And Nanocrystalline-Grained Tungsten To Extreme Irradiation Environments, Osman El-Atwani, J. A. Hinks, G. Greaves, Sean Gonderman, T. Qiu, M. Efe, Jean P. Allain

Birck and NCN Publications

The accumulation of defects, and in particular He bubbles, can have significant implications for the performance of materials exposed to the plasma in magnetic-confinement nuclear fusion reactors. Some of the most promising candidates for deployment into such environments are nanocrystalline materials as the engineering of grain boundary density offers the possibility of tailoring their radiation resistance properties. In order to investigate the microstructural evolution of ultrafine- and nanocrystalline-grained tungsten under conditions similar to those in a reactor, a transmission electron microscopy study with in situ 2 keV He+ ion irradiation at 950 degrees C has been completed. A dynamic and ...


Full Control Of Quadruple Quantum Dot Circuit Charge States In The Single Electron Regime, M. R. Delbecq, T. Nakajima, T. Otsuka, S. Amaha, J. D. Watson, Michael J. Manfra, S. Tarucha May 2014

Full Control Of Quadruple Quantum Dot Circuit Charge States In The Single Electron Regime, M. R. Delbecq, T. Nakajima, T. Otsuka, S. Amaha, J. D. Watson, Michael J. Manfra, S. Tarucha

Birck and NCN Publications

We report the realization of an array of four tunnel coupled quantum dots in the single electron regime, which is the first required step toward a scalable solid state spin qubit architecture. We achieve an efficient tunability of the system but also find out that the conditions to realize spin blockade readout are not as straightforwardly obtained as for double and triple quantum dot circuits. We use a simple capacitive model of the series quadruple quantum dots circuit to investigate its complex charge state diagrams and are able to find the most suitable configurations for future Pauli spin blockade measurements ...


Electron Spin Magnetism Of Zigzag Graphene Nanoribbon Edge States, Kun Xu, Peide D. Ye Apr 2014

Electron Spin Magnetism Of Zigzag Graphene Nanoribbon Edge States, Kun Xu, Peide D. Ye

Birck and NCN Publications

The electron spin states of zigzag graphene nanoribbon (ZGNR) edge play a pivotal role in the applications of graphene nanoribbons. However, the exact arrangements of the electron spins remain unclear to date. In this report, the electronic spin states of the ZGNR edge have been elucidated through a combination of quantum chemical investigation and previous electron spin resonance experiment observations. An alternating alpha and beta spin configuration of the unpaired electrons along the ZGNR edge is established in ambient condition without any external magnetic field, and the origin of the spin magnetism of the ZGNR edge is revealed. It paves ...


Observation Of Coulomb Repulsion Between Cu Intercalants In Cuxbi2se3, Chris Mann, Damien West, Ireneusz Miotkowski, Yong P. Chen, Shengbai Zhang, Chih-Kang Shih Apr 2014

Observation Of Coulomb Repulsion Between Cu Intercalants In Cuxbi2se3, Chris Mann, Damien West, Ireneusz Miotkowski, Yong P. Chen, Shengbai Zhang, Chih-Kang Shih

Birck and NCN Publications

Using scanning tunneling microscopy and ab initio simulations, we have identified several configurations for Cu dopants in CuxBi2Se3, with Cu intercalants being the most abundant. Through statistical analysis, we show strong short-range repulsive interactions between Cu intercalants. At intermediate range (>5 nm), the pair distribution function shows oscillatory structure along the < 10 (1) over bar > directions, which appear to be influenced by different diffusion barriers along the < 10 (1) over bar > and < 2 (1) over bar(1) over bar > directions.


Droplet Evaporation On Heated Hydrophobic And Superhydrophobic Surfaces, Susmita Dash, Suresh V. Garimella Apr 2014

Droplet Evaporation On Heated Hydrophobic And Superhydrophobic Surfaces, Susmita Dash, Suresh V. Garimella

Birck and NCN Publications

The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (similar to 160 degrees) and demonstrate low roll-off angle (similar to 1 degrees), while the hydrophobic substrate supports corresponding values of 120 degrees and similar to 10 degrees. The substrates are heated to different constant temperatures in the range of 40-60 degrees C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact ...


Variable-Cell Method For Stress-Controlled Jamming Of Athermal, Frictionless Grains, Kyle C. Smith, Ishan Srivastava, Timothy Fisher, Meheboob Alam Apr 2014

Variable-Cell Method For Stress-Controlled Jamming Of Athermal, Frictionless Grains, Kyle C. Smith, Ishan Srivastava, Timothy Fisher, Meheboob Alam

Birck and NCN Publications

A method is introduced to simulate jamming of polyhedral grains under controlled stress that incorporates global degrees of freedom through the metric tensor of a periodic cell containing grains. Jamming under hydrostatic (isotropic) stress and athermal conditions leads to a precise definition of the ideal jamming point at zero shear stress. The structures of tetrahedra jammed hydrostatically exhibit less translational order and lower jamming-point density than previously described maximally random jammed hard tetrahedra. Under the same conditions, cubes jam with negligible nematic order. Grains with octahedral symmetry having s > 0.5 (where s interpolates from octahedra [s = 0] to cubes ...


Tunable Hyperbolic Metamaterials Utilizing Phase Change Heterostructures, Harish N.S. Krishnamoorthy, You Zhou, Shriram Ramanathan, Evgenii Narimanov, Vinod M. Menon Mar 2014

Tunable Hyperbolic Metamaterials Utilizing Phase Change Heterostructures, Harish N.S. Krishnamoorthy, You Zhou, Shriram Ramanathan, Evgenii Narimanov, Vinod M. Menon

Birck and NCN Publications

We present a metal-free tunable anisotropic metamaterial where the iso-frequency surface is tuned from elliptical to hyperbolic dispersion by exploiting the metal-insulator phase transition in the correlated material vanadium dioxide (VO2). Using VO2-TiO2 heterostructures, we demonstrate the transition in the effective dielectric constant parallel to the layers to undergo a sign change from positive to negative as the VO2 undergoes the phase transition. The possibility to tune the iso-frequency surface in real time using external perturbations such as temperature, voltage, or optical pulses creates new avenues for controlling light-matter interaction. (C) 2014 AIP Publishing LLC.


Laser Sintering Of Separated And Uniformly Distributed Multiwall Carbon Nanotubes Integrated Iron Nanocomposites, Dong Lin, Chunghorng Richard Liu, Gary J. Cheng Mar 2014

Laser Sintering Of Separated And Uniformly Distributed Multiwall Carbon Nanotubes Integrated Iron Nanocomposites, Dong Lin, Chunghorng Richard Liu, Gary J. Cheng

Birck and NCN Publications

Uniform distribution of carbon nanotubes (CNTs) in metal matrix during additive manufacturing of nanocomposites is always a challenge since the CNTs tend to aggregate in the molten pool. In this study, Multiwall carbon nanotubes (MWNTs) were separated and distributed uniformly into iron matrix by laser sintering process. MWNTs and iron powders were mixed together by magnetic stir, coated on steel 4140 surface, followed by laser sintering. Due to the fast heating and cooling rate, the CNTs are evenly distributed in the metal matrix. The temperature field was calculated by multiphysics simulation considering size effects, including size dependent melting temperature, thermal ...


Nu=5/2 Fractional Quantum Hall State In The Presence Of Alloy Disorder, Nianpei Deng, Geoff C. Gardner, Sumit Mondal, Ethan Kleinbaum, Michael J. Manfra, Gabor Csathy Mar 2014

Nu=5/2 Fractional Quantum Hall State In The Presence Of Alloy Disorder, Nianpei Deng, Geoff C. Gardner, Sumit Mondal, Ethan Kleinbaum, Michael J. Manfra, Gabor Csathy

Birck and NCN Publications

We report quantitative measurements of the impact of alloy disorder on the. nu = 5/2 fractional quantum Hall state. Alloy disorder is controlled by the aluminum content x in the AlxGa1-xAs channel of a quantum well. We find that the nu = 5/2 state is suppressed with alloy scattering. To our surprise, in samples with alloy disorder the nu = 5/2 state appears at significantly reduced mobilities when compared to samples in which alloy disorder is not the dominant scattering mechanism. Our results highlight the distinct roles of the different types of disorder present in these samples, such as the ...


Electrical And Thermal Conductivities Of Reduced Graphene Oxide/Polystyrene Composites, Wonjung Park, Jiuning Hu, Luis A. Jauregui, Xiulin Ruan, Yong P. Chen Mar 2014

Electrical And Thermal Conductivities Of Reduced Graphene Oxide/Polystyrene Composites, Wonjung Park, Jiuning Hu, Luis A. Jauregui, Xiulin Ruan, Yong P. Chen

Birck and NCN Publications

The author reports an experimental study of electrical and thermal transport in reduced graphene oxide (RGO)/polystyrene (PS) composites. The electrical conductivity (sigma) of RGO/PS composites with different RGO concentrations at room temperature shows a percolation behavior with the percolation threshold of similar to 0.25 vol. %. Their temperature-dependent electrical conductivity follows Efros-Shklovskii variable range hopping conduction in the temperature range of 30-300K. The thermal conductivity (kappa) of composites is enhanced by similar to 90% as the concentration is increased from 0 to 10 vol. %. The thermal conductivity of composites approximately linearly increases with increasing temperature from 150 to ...


Gas Mixing System For Imaging Of Nanomaterials Under Dynamic Environments By Environmental Transmission Electron Microscopy, M. Cem Akatay, Yury Zvinevich, Philipp Baumann, Fabio H. Ribeiro, Eric A. Stach Mar 2014

Gas Mixing System For Imaging Of Nanomaterials Under Dynamic Environments By Environmental Transmission Electron Microscopy, M. Cem Akatay, Yury Zvinevich, Philipp Baumann, Fabio H. Ribeiro, Eric A. Stach

Birck and NCN Publications

A gas mixing manifold system that is capable of delivering a stable pressure stream of a desired composition of gases into an environmental transmission electron microscope has been developed. The system is designed to provide a stable imaging environment upon changes of either the composition of the gas mixture or upon switching from one gas to another. The design of the system is described and the response of the pressure inside the microscope, the sample temperature, and sample drift in response to flow and composition changes of the system are reported. (C) 2014 AIP Publishing LLC.


Use Of Graphene As Protection Film In Biological Environments, Weixia Zhang, Sudarat Lee, Kelly L. Mcnear, Ting Fung Chung, Seunghyun Lee, Kyunghoon Lee, Scott A. Crist, Timothy L. Ratliff, Zhaohui Zhong, Yong P. Chen, Chen Yang Feb 2014

Use Of Graphene As Protection Film In Biological Environments, Weixia Zhang, Sudarat Lee, Kelly L. Mcnear, Ting Fung Chung, Seunghyun Lee, Kyunghoon Lee, Scott A. Crist, Timothy L. Ratliff, Zhaohui Zhong, Yong P. Chen, Chen Yang

Birck and NCN Publications

Corrosion of metal in biomedical devices could cause serious health problems to patients. Currently ceramics coating materials used in metal implants can reduce corrosion to some extent with limitations. Here we proposed graphene as a biocompatible protective film for metal potentially for biomedical application. We confirmed graphene effectively inhibits Cu surface from corrosion in different biological aqueous environments. Results from cell viability tests suggested that graphene greatly eliminates the toxicity of Cu by inhibiting corrosion and reducing the concentration of Cu2+ ions produced. We demonstrated that additional thiol derivatives assembled on graphene coated Cu surface can prominently enhance durability of ...


Sub-Diffraction Laser Synthesis Of Silicon Nanowires, James I. Mitchell, Nan Zhou, Woongsik Nam, Luis M. Traverso, Xianfan Xu Jan 2014

Sub-Diffraction Laser Synthesis Of Silicon Nanowires, James I. Mitchell, Nan Zhou, Woongsik Nam, Luis M. Traverso, Xianfan Xu

Birck and NCN Publications

We demonstrate synthesis of silicon nanowires of tens of nanometers via laser induced chemical vapor deposition. These nanowires with diameters as small as 60 nm are produced by the interference between incident laser radiation and surface scattered radiation within a diffraction limited spot, which causes spatially confined, periodic heating needed for high resolution chemical vapor deposition. By controlling the intensity and polarization direction of the incident radiation, multiple parallel nanowires can be simultaneously synthesized. The nanowires are produced on a dielectric substrate with controlled diameter, length, orientation, and the possibility of in-situ doping, and therefore are ready for device fabrication ...


Integrating Non-Planar Metamaterials With Magnetic Absorbing Materials To Yield Ultra-Broadband Microwave Hybrid Absorbers, Wei Li, Tianlong Wu, Wei Wang, Jianguo Guan, Pengcheng Zhai Jan 2014

Integrating Non-Planar Metamaterials With Magnetic Absorbing Materials To Yield Ultra-Broadband Microwave Hybrid Absorbers, Wei Li, Tianlong Wu, Wei Wang, Jianguo Guan, Pengcheng Zhai

Birck and NCN Publications

Broadening the bandwidth of electromagnetic wave absorbers has greatly challenged material scientists. Here, we propose a two-layer hybrid absorber consisting of a non-planar metamaterial (MM) and a magnetic microwave absorbing material (MAM). The non-planar MM using magnetic MAMs instead of dielectric substrates shows good low frequency absorption and low reflection across a broad spectrum. Benefiting from this and the high frequency strong absorption of the MAM layer, the lightweight hybrid absorber exhibits 90% absorptivity over the whole 2-18 GHz range. Our result reveals a promising and flexible method to greatly extend or control the absorption bandwidth of absorbers. (C) 2014 ...