Nanoscience and Nanotechnology Commons^™

The Effects Of Diameter And Chirality On The Thermal Transport In Free-Standing And Supported Carbon-Nanotubes, Bo Qiu, Yan Wang, Xiulin Ruan, Qing Zhao

Birck and NCN Publications

We use molecular dynamics simulations to explore the lattice thermal transport in free-standing and supported single-wall carbon-nanotube (SWCNT) in comparison to that in graphene nanoribbon and graphene sheet. For free-standing SWCNT, the lattice thermal conductivity increases with diameter and approaches that of graphene, partly due to the curvature. Supported SWCNT thermal conductivity is reduced by 34%-41% compared to the free-standing case, which is less than that in supported graphene. Also, it shows an evident chirality dependence by varying about 10%, which we attribute to chirality-dependent interfacial phonon scattering. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725194]

On The Best Bandstructure For Thermoelectric Performance: A Landauer Perspective, Changwook Jeong, Raseong Kim, Mark S. Lundstrom

Birck and NCN Publications

The question of what bandstructure produces the best thermoelectric device performance is revisited from a Landauer perspective. We find that a delta-function transport distribution function (TDF) results in operation at the Mahan-Sofo upper limit for the thermoelectric figure-of-merit, ZT. We show, however, the Mahan-Sofo upper limit itself depends on the bandwidth (BW) of the dispersion, and therefore, a finite BW dispersion produces a higher ZT when the lattice thermal conductivity is finite. Including a realistic model for scattering profoundly changes the results. Instead of a narrow band, we find that a broad BW is best. The prospects of increasing ZT …

Parametric Noise Squeezing And Parametric Resonance Of Microcantilevers In Air And Liquid Environments, Gyan Prakash, Arvind Raman, Jeff F. Rhoads, Ronald G. Reifenberger

Birck and NCN Publications

In this work, parametric noise squeezing and parametric resonance are realized through the use of an electronic feedback circuit to excite a microcantilever with a signal proportional to the product of the microcantilever's displacement and a harmonic signal. The cantilever's displacement is monitored using an optical lever technique. By adjusting the gain of an amplifier in the feedback circuit, regimes of parametric noise squeezing/amplification and the principal and secondary parametric resonances of fundamental and higher order eigenmodes can be easily accessed. The exceptionally symmetric amplitude response of the microcantilever in the narrow frequency bandwidth is traced to a nonlinear parametric …

Three-Dimensional Geometry Of The Human Carotid Artery, Alexey Kamenskiy, Jason N. Mactaggart, Iraklis I. Pipinos, Jai Bikhchandani, Yuris A. Dzenis

Department of Mechanical and Materials Engineering: Faculty Publications

Accurate characterization of carotid artery geometry is vital to our understanding of the pathogenesis of atherosclerosis. Three-dimensional computer reconstructions based on medical imaging are now ubiquitous; however, mean carotid artery geometry has not yet been comprehensively characterized. The goal of this work was to build and study such geometry based on data from 16 male patients with severe carotid artery disease. Results of computerized tomography angiography were used to analyze the cross-sectional images implementing a semiautomated segmentation algorithm. Extracted data were used to reconstruct the mean three-dimensional geometry and to determine average values and variability of bifurcation and planarity angles, …

Quantized Hall Effect And Shubnikov-De Haas Oscillations In Highly Doped Bi2se3: Evidence For Layered Transport Of Bulk Carriers, Helin Cao, Jifa Tian, Ireneusz Miotkowski, Tian Shen, Jiuning Hu, Shan Qiao, Yong P. Chen

Birck and NCN Publications

Bi2Se3 is an important semiconductor thermoelectric material and a prototype topological insulator. Here we report observation of Shubnikov-de Hass oscillations accompanied by quantized Hall resistances (R-xy) in highly doped n-type Bi2Se3 with bulk carrier concentrations of few 10(19) cm(-3). Measurements under tilted magnetic fields show that the magnetotransport is 2D-like, where only the c-axis component of the magnetic field controls the Landau level formation. The quantized step size in 1/R-xy is found to scale with the sample thickness, and average similar to e(2)/h per quintuple layer. We show that the observed magnetotransport features do not come from the sample surface, …

Active Response Of Polymer Materials From External Stimuli – Solvents And Light; Grafting Reactions On Perovskite Layers, Jianxia Zhang

LSU New Orleans Theses and Dissertations

The active response of a series of polymeric materials was investigated. Both solvent activated and light activated thin films and wire systems show dynamic behaviors when exposed to different stimuli.

Solvent mediated fluxional behavior of polymer thin films involved extensive, rapid curling both on infusion and evaporation of good solvents. These films can be either lab-fabricated ones or commercial ones, and the curling behavior can be as fast as seconds. Conditions including polymer materials, chosen solvents, and film geometry can affect the behavior.

Methods that allowed for the creation and retention of distorted wire structures were also developed; the asymmetric …

Amorphous Ni/Al Nanoscale Laminates As High-Energy Intermolecular Reactive Composites, Karthik Guda Vishnu, Mathew Cherukara, Hojin Kim, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics simulations to explore the potential use of amorphous metals in intermolecular reactive composites. Our simulations show that amorphous Ni/Al nanolaminates lead to an increase in temperature of up to 260 K over their crystalline counterparts; this increase corresponds to over 20% of the heat of fusion and can be explained in terms of the amorphization energy. The reactions are diffusion controlled and crystallization is observed in laminates with relatively long periods where high temperatures are experienced for sufficiently long times prior to intermixing; the effect of this process on the energetics and time involved in the …

Rehabilitation And Exercise Machine, Judith M. Burnfield, Yu Shu, Thad W. Buster, Carl Nelson

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.

Two-Temperature Nonequilibrium Molecular Dynamics Simulation Of Thermal Transport Across Metal-Nonmetal Interfaces, Yan Wang, Xiulin Ruan, Ajit K. Roy

Birck and NCN Publications

We have used a two-temperature nonequilibrium molecular dynamics method for predicting interfacial thermal resistance across metal-nonmetal interfaces. This method is an extension of the conventional nonequilibrium molecular dynamics for the dielectric-dielectric interface, where a temperature bias is imposed and the heat current is derived. We have included the electron degree of freedom for the interfacial thermal transport problem by treating the electron-phonon coupling with the two-temperature model. The method is demonstrated on two model systems, that is, silicon-copper interface and carbon-nanotube-copper interface. Temperature nonequilibrium between electrons and phonons in the metal side is quantitatively predicted, and a temperature drop across …

Reduction Of Spectral Phonon Relaxation Times From Suspended To Supported Graphene, Bo Qiu, Xiulin Ruan

Birck and NCN Publications

We have performed molecular dynamics simulations with phonon spectral analysis to predict the mode-wise phonon relaxation times (RT) of suspended and supported graphene at room temperature, and the findings are consistent with recent optical measurements. For acoustic phonons, RTs reduce from up to 50 ps to less than 5 ps when graphene is put on silicon dioxide substrate. Similarly, optical phonon RTs reduce by half when supported. Stronger interfacial bonding is found to result in more RT reduction. Our results provide a fundamental understanding at the spectral phonon property level for the observed thermal conductivity reduction in supported graphene. (C) …

High Speed Atomic Force Microscopy Techniques For The Efficient Study Of Nanotribology, James L. Bosse

Master's Theses

As mechanical devices scale down to micro/nano length scales, it is crucial to understand friction and wear at the nanoscale (nanotribology) especially at technically relevant sliding velocities. Accordingly, three novel techniques have been developed to study nanotribology, leveraging recent advances in high speed AFM. The first method utilizes high line-scanning rates coupled with sinusoidal scanning along the AFM fast scan axis, enabling rapid friction measurements as a function of velocity up to 20 mm/sec. The second method rapidly acquires friction versus force curves through disabling the feedback loop during scanning and relating the resulting lateral data with the correspondingly varying …

Nanocharacterization Of Porous Materials With Atomic Force Microscopy, Yasemin Kutes

Master's Theses

Scanning Probe Microscopy techniques have proven very useful in the investigation of porous nanostructured surfaces. Especially, Atomic Force Microscopy (AFM) has been widely used due to its compatibility with non-conducting surfaces. In particular, AFM often complements other techniques like scanning and transmission electron microscopy by providing quantitative surface information coupled with nanoscale spatial resolution. Its ability to operate in fluid is also important, as this allows researchers to mimic the physiological environment of biological materials and systems. In this work, two main types of porous materials are studied with AFM, including Phosphoric Acid Fuel Cell (PAFC) electrode catalyst layers, and …

Molecular Dynamics Study Of Diffusion Of O2 Penetrates In Uncrosslinked Polydimethysiloxane (Pdms), Crosslinked Pdms, And Pdms-Based Nanocomposites, Varun Ullal

Graduate Theses and Dissertations

Molecular dynamics simulations are used to study diffusion of O₂ molecules in pure polydimethysiloxane (PDMS), crosslinked PDMS, and PDMS-based nanocomposites. The PDMS chains and penetrates are modeled using a hybrid interatomic potential which treats the Si-O atoms along the chain backbone explicitly while coarse-graining the methyl side groups and penetrates. By tracking the diffusion of penetrates in the system and subsequently computing their mean-squared displacement, diffusion coefficients are obtained. In pure PDMS models of varying molecular weight, diffusivity of the O₂2 penetrates is found to have an inverse relationship with chain length. Simulation models with longer chains …

Properties Of Metal-Graphene Contacts, Joachim Knoch, Zhihong Chen, Joerg Appenzeller

Birck and NCN Publications

We present a study on the metal-graphene contact properties. Utilizing a dual-gate field-effect transistor device, an energetic separation between the Fermi level and the Dirac point in the contact areas can be adjusted deliberately by applying an appropriate front-gate voltage that acts only on the channel. This front-gate voltage is compensated by an opposite large-area back-gate voltage, thereby mimicking the metal induced doping effect. A back-gate voltage sweep enables identifying two distinct resistance peaks-a result of the combined impact of the graphene cones in the contact and in the channel region. Comparing our experimental data with simulations allows extracting the …

Electric Field Tuning Of Spin Splitting In A Quantum Dot Coupled To A Semimagnetic Quantum Dot, Yuli Lyanda-Geller, T.L. Reinecke, G. Bacher

Birck and NCN Publications

We develop an approach for tuning the spin splitting and g-factor of a quantum dot by coupling it to semi-magnetic quantum dot and tuning the electric field. We show that spin splittings and g-factors of the states of a non-magnetic quantum dot coupled to semi-magnetic quantum dot can be enhanced orders of magnitude. Evaluations are made for coupled CdTe/CdMnTe quantum dots. These effects are caused by electric field control of repulsion of spin sublevels in the non-magnetic dot due to tunnel coupling of quantum dots. Electric field control of spin splittings in quantum dots is of potential interest in connection …

Thermal Conductivity Of Bulk And Thin-Film Silicon: A Landauer Approach, Changwook Jeong, Supriyo Datta, Mark S. Lundstrom

Birck and NCN Publications

The question of what fraction of the total heat flow is transported by phonons with different mean-free-paths is addressed using a Landauer approach with a full dispersion description of phonons to evaluate the thermal conductivities of bulk and thin film silicon. For bulk Si, the results reproduce those of a recent molecular dynamic treatment showing that about 50% of the heat conduction is carried by phonons with a mean-free-path greater than about 1 mu m. For the in-plane thermal conductivity of thin Si films, we find that about 50% of the heat is carried by phonons with mean-free-paths shorter than …

Spectroscopy Of A Deterministic Single-Donor Device In Silicon, M. Fuechsle, J. A. Miwa, S. Mahapatra, H. Ryu, S. Lee, O. Warschkow, L. C. L. Hollenberg, G. Klimeck, M. Y. Simmons

Birck and NCN Publications

We present a single electron transistor (SET) based on an individual phosphorus dopant atom in an epitaxial silicon environment. Using scanning tunneling microscope (STM) hydrogen lithography, the single impurity is deterministically placed with a spatial accuracy of ±1 lattice site within a donor-based transport device. Low temperature transport measurements confirm the presence of the single donor and show that the donor charge state can be precisely controlled via gate voltages. We observe a charging energy that is remarkably similar to the value expected for isolated P donors in bulk silicon, which is in sharp contrast to previous experiments on single-dopant …

Physiochemical And Nanomanipulation Studies Of Carbon Nanomaterials, Siva Naga Sandeep Chalamalasetty

Graduate Theses and Dissertations

Carbon nanomaterials are, without a doubt, one of man's wonder creations. Though these nanomaterials are a very recent trend, extraordinary electromechanical properties and the light weightiness of these nanomaterials attracted the attention of researchers. Although vast research has been done since the start of the US nanotechnology initiative, much effort was in the area of synthesis and characterization of the nanomaterials. However, most of the traditional macroscopic material's theories fail at the nanoscale level, and since the material properties are dependent on size and structure at nanoscale level, the behavior of the carbon nanomaterials in different environments needs attention. High …

Experimental Study Of Novel Materials And Module For Cryogenic (4k) Superconducting Multi-Chip Modules, Ranjith John

Graduate Theses and Dissertations

The objectives of this proposal are to understand the science and technology of interfaces in the packaging of superconducting electronic (SCE) multichip modules (MCMs) at 4 K. The thermal management issue of the current SCE-MCMs was examined and the package assembly was optimized. A novel thermally conducting and electrically insulating nano-engineered polymer was developed for the thermal management of SCE-MCMs for 4 K cryogenic packaging. Finally, the nano-engineered polymer was integrated as underfill in a SCE-MCM and the thermal and electrical performance of SCE-MCM was demonstrated at 4 K.

Niobium based superconducting electronics (SCE) are the fastest known digital logic …

High Frequency Characterization Of Carbon Nanotube Networks For Device Applications, Emmanuel Decrossas

Graduate Theses and Dissertations

This work includes the microwave characterization of carbon nanotubes (CNTs) to design new CNTs-based high frequency components. A novel developed method to extract the electrical properties over a broad microwave frequency band from 10 MHz to 50 GHz of carbon nanotubes (CNTs) in a powder form is performed. The measured scattering parameters (S-parameters) with a performance network analyzer are compared to the simulated one obtained from an in-house computed mode matching technique (MMT). An optimized first order gradient method iteratively changes the unknown complex permittivity parameters to map the simulated S-parameters with the measured one until convergence criteria are satisfied. …