Nanoscience and Nanotechnology Commons^™

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. …

Use Of Ultra High Vacuum Plasma Enhanced Chemical Vapor Deposition For Graphene Fabrication, Shannen Adcock

Graduate Theses and Dissertations

Graphene, what some are terming the "new silicon", has the possibility of revolutionizing technology through nanoscale design processes. Fabrication of graphene for device processing is limited largely by the temperatures used in conventional deposition. High temperatures are detrimental to device design where many different materials may be present. For this reason, graphene synthesis at low temperatures using plasma-enhanced chemical vapor deposition is the subject of much research. In this thesis, a tool for ultra-high vacuum plasma-enhanced chemical vapor deposition (UHV-PECVD) and accompanying subsystems, such as control systems and alarms, are designed and implemented to be used in future graphene growths. …

Broadband Purcell Effect: Radiative Decay Engineering With Metamaterials, Zubin Jacob, Igor I. Smolyaninov, Evgenii E. Narimanov

Birck and NCN Publications

We show that metamaterials with hyperbolic dispersion support a large number of electromagnetic states that can couple to quantum emitters leading to a broadband Purcell effect. The proposed approach of radiative decay engineering, useful for applications such as single photon sources, fluorescence imaging, biosensing, and single molecule detection, also opens up the possibility of using hyperbolic metamaterials to probe the spontaneous emission properties of atoms and artificial atoms such as quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4710548]

Electrochemical Preparation Of Nanostructural Pt-Ni And Pd-Ni Films For Ethanol Electro-Oxidation, Chen-Zhong Yao, Hui-Xuan Ma, Bo-Hui Wei

Journal of Electrochemistry

The Pt-Ni and Pd-Ni films were successfully prepared on Ti substrates by electrodeposition method. The porous Pt-Ni nanoflakes appeared to be uniform with the thickness of the slices about 10 ~ 20 nm. The porous Pd-Ni nanoparticles with a flower shape appeared to be uniform with the diameters of 50 ~ 60 nm. The XRD patterns also indicated that the Pd-Ni and Pt-Ni nanostructures have the poor crystallinity. The onset potentials of ethanol oxidation were negatively shifted to –0.74 V on Pt-Ni electrodes and –0.71 V on Pd-Ni electrodes, respectively. Addition of Ni could enhance catalytic activities and antitoxic properties …

Electrochemical Performances Of Carbon-Coated Na2Ti6O13 Nanotubes, Guo-Ran Li, Shuai Sun, Xue-Ping Gao

Journal of Electrochemistry

With rutile TiO₂ and NaOH as starting materials, the Na₂Ti₆O₁₃ nanotubes were prepared by a hydrothermal reaction. The carbon-coated Na₂Ti₆O₁₃ nanotubes were obtained by treating the Na₂Ti₆O₁₃ nanotubes for 4 h in glucose aqueous solutions containing 0.1 mol·L^-1 NaOH. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microcopy (TEM). The results showed that the dimensions of carbon-coated Na₂Ti₆O₁₃ nanotubes were 14 ~ 19 nm of outer diameter, 2 ~ 5 …

Characterization And Manipulation Of Nanorods Via An Applied Magnetic Field, Summer Wu '13

Student Publications & Research

A remote system capable of controlling the motion of magnetic nanorods was created. Two different systems, electromagnets and magnetic stirrers, were used to create continuously changing magnetic fields thus applying a constant torque to make nanorods rotate as “nano stirbars”. The system was tested on three different types of synthesized nanorods: multi-segmented Ni/Au, pure Ni, and pure Au nanorods. Ni and Au were chosen due to the combination of the magnetic properties of Ni and the biocompatible properties of Au. Variables such as length, shape, and geometries of the nanorods were characterized by a scanning electron microscope and an atomic …

Investigation Of Band Bending In N- And P-Type Gan, Michael Foussekis

Theses and Dissertations

This dissertation details the study of band bending in n- and p-type GaN samples with a Kelvin probe utilizing different illumination geometries, ambients (air, oxygen, vacuum 10-6 mbar), and sample temperatures (77 – 650 K). The Kelvin probe, which is mounted inside an optical cryostat, is used to measure the surface potential. Illumination of the GaN surface with band-to-band light generates electron-hole pairs, which quickly separate in the depletion region due to a strong electric field caused by the near-surface band bending. The charge that is swept to the surface reduces the band bending and generates a surface photovoltage (SPV). …

Drive-Amplitude-Modulation Atomic Force Microscopy: From Vacuum To Liquids, Miriam Jaafar, David Martinez-Martin, Mariano Cuenca, John Melcher, Arvind Raman, Julio Gomez-Herrero

Birck and NCN Publications

We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation …

Control Of Absorption With Hyperbolic Metamaterials, T.U. Tumkur, Lei Gu, J.K. Kitur, Evgenii E. Narimanov, M.A. Noginov

Birck and NCN Publications

We show that absorption of thin dye-doped polymeric films can be tuned and enhanced ( nearly threefold) by metallic and lamellar metal-dielectric hyperbolic metamaterial substrates. The effect can be controlled by a combination of the substrate's geometry and composition. As the enhancement of absorption is sustained over large range of incidence angles, the demonstrated phenomenon can lead to a variety of important applications, including solar cell technology. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4703931]

Tunable Thermal Rectification In Graphene Nanoribbons Through Defect Engineering: A Molecular Dynamics Study, Yan Wang, Siyu Chen, Xiulin Ruan

Birck and NCN Publications

Using non-equilibrium molecular dynamics, we show that asymmetrically defected graphene nanoribbons (GNR) are promising thermal rectifiers. The optimum conditions for thermal rectification (TR) include low temperature, high temperature bias, similar to 1% concentration of single-vacancy or substitutional silicon defects, and a moderate partition of the pristine and defected regions. TR ratio of similar to 80% is found in a 14-nm long and 4-nm wide GNR at a temperature of 200 K and bias of 90 K, where heat conduction is in the ballistic regime since the bulk effective phonon mean-free-path is around 775 nm. As the GNR length increases towards …

Non-Equilibrium Green's Function Calculation For Gan-Based Terahertz-Quantum Cascade Laser Structures, H. Yasuda, T. Kubis, I. Hosako, K. Hirakawa

Birck and NCN Publications

We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green's function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704389]

Tuning Entanglement And Ergodicity In Two-Dimensional Spin Systems Using Impurities And Anisotropy, Gehad Sadiek, Qing Xu, Sabre Kais

Birck and NCN Publications

We consider the entanglement in a two-dimensional XY model in an external magnetic field h. The model consists of a set of seven localized spin-1/2 particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction J. We examine the effect of single and double impurities in the system as well as the degree of anisotropy on the nearest-neighbor entanglement and ergodicity of the system. We have found that the entanglement of the system at the different degrees of anisotropy mimics that of the one-dimensional spin systems at the extremely small and large values of the parameter lambda = h/J. …

Room Temperature Deposition Of Alumina-Doped Zinc Oxide On Flexible Substrates By Direct Pulsed Laser Recrystallization, Martin Y. Zhang, Qiong Nian, Gary J. Cheng

Birck and NCN Publications

In this study, a method combining room temperature pulsed laser deposition (PLD) and direct pulsed laser recrystallization (DPLR) is introduced to deposit transparent conductive oxide (TCO) layer on low melting point flexible substrates. Alumina-doped zinc oxide (AZO), as one of the most promising TCO candidates, has now been widely used in solar cells. However, to achieve optimal, electrical, and optical properties of AZO on low melting point, flexible substrate is challenging. DPLR technique is a scalable, economic, and fast process to remove crystal defects and generate recrystallization at room temperature. It features selective processing by only heating up the TCO …

The Integration Of High-K Dielectric On Two-Dimensional Crystals By Atomic Layer Deposition, Han Liu, Kun Xu, Xujie Zhang, Peide Ye

Birck and NCN Publications

We investigate the integration of Al2O3 high-k dielectric on two-dimensional (2D) crystals of boron nitride (BN) and molybdenum disulfide (MoS2) by atomic layer deposition (ALD). We demonstrate the feasibility of direct ALD growth with trimethylaluminum and water as precursors on both 2D crystals. Through theoretical and experimental studies, we found that the initial ALD cycles play the critical role, during which physical adsorption dominates precursor adsorption at the crystal surface. We model the initial ALD growth stages at the 2D surface by analyzing Lennard-Jones potentials, which could guide future optimization of the ALD process on 2D crystals. (C) 2012 American …

Functional Magnetic Nanoparticles, James Gass

USF Tampa Graduate Theses and Dissertations

Nanoparticle system research and characterization is the focal point of this research and dissertation. In the research presented here, magnetite, cobalt, and ferrite nanoparticle systems have been explored in regard to their magnetocaloric effect (MCE) properties, as well as for use in polymer composites. Both areas of study have potential applications across a wide variety of interdisciplinary fields.

Magnetite nanoparticles have been successfully dispersed in a polymer. The surface chemistry of the magnetic nanoparticle proves critical to obtaining a homogenous and well separated high density dispersion in PMMA. Theoretical studies found in the literature have indicated that surface interface energy …

Model-Based Systems And Methods For Analyzing And Predicting Outcomes Of Vascular Interventions And Reconstructions, Yuris A. Dzenis, Alexey Kamenskiy, Iraklis I. Pipinos, Jason N. Mactaggart

Department of Mechanical and Materials Engineering: Faculty Publications

Systems and methods for analyzing and predicting treatment outcomes of medical procedures such as vascular interventions and reconstructions are disclosed. An illustrative system for analyzing and predicting therapeutic outcomes of medical procedures comprises a relational database configured for classifying and storing patient specific input data for multiple patients, a fluid-solid interaction biomechanical model configured for performing a biomechanics simulation and generating biomechanics data, and a graphical user interface.

Exploration Of The Limits To Mobility In Two-Dimensional Hole Systems In Gaas/Algaas Quantum Wells, J.D. Watson, S. Mondal, G. Gardner, Gabor A. Csathy, Michael J. Manfra

Birck and NCN Publications

We report on the growth and electrical characterization of a series of two-dimensional hole systems (2DHSs) used to study the density dependence of low temperature mobility in 20-nm GaAs/AlGaAs quantum wells. The hole density was controlled by changing the Al mole fraction and the setback of the delta-doping layer. We varied the density over a range from 1.8 x 10(10) cm(-2) to 1.9 x 10(11) cm(-2) finding a nonmonotonic dependence of mobility on density at T = 0.3 K. Surprisingly, a peak mobility of 2.3 x 10(6) cm(2)/Vs was measured at a density of 6.5 x 10(10) cm(-2), with further …

Interface Barriers At The Interfaces Of Polar Gaas(111) Faces With Al2o3, H.Y. Chou, E. O'Connor, P.K. Hurley, V.V. Afanas'ev, M. Houssa, A. Stesmans, Peide Ye, S.B. Newcomb

Birck and NCN Publications

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces. (C) 2012 American Institute of Physics. …

Basic Capillary Microfluidic Chip And Highly Sensitive Optical Detector For Point Of Care Application, Mingjin Yao

Doctoral Dissertations

A cost-effective and highly sensitive portable diagnostic device is needed to enable much more widespread monitoring of health conditions in disease prevention, detection, and control. Miniaturized and easy-to-operate devices can reduce the inherent costs and inefficiencies associated with healthcare testing in central laboratories. Hence, clinicians are beginning to use point of care (POC) testing and flexible clinical chemistry testing devices which are beneficial for the patient.

In our work, a low-cost and simple autonomous microfluidic device for biochemical detection was developed. The pumpless capillary system with capillary stop valves and trigger valves is fabricated on a silicon (Si) wafer and …