Nanoscience and Nanotechnology Commons^™

A Reactive Molecular Dynamics Simulation Of The Silica-Water Interface, Joseph C. Fogarty, Hasan Metin Aktulga, Ananth Y. Grama, Adri C. T. Van Duin, Sagar A. Pandit

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We report our study of a silica-water interface using reactive molecular dynamics. This first-of-its-kind simulation achieves length and time scales required to investigate the detailed chemistry of the system. Our molecular dynamics approach is based on the ReaxFF force field of van Duin [J. Phys. Chem. A 107, 3803 (2003)]. The specific ReaxFF implementation (SERIALREAX) and force fields are first validated on structural properties of pure silica and water systems. Chemical reactions between reactive water and dangling bonds on a freshly cut silica surface are analyzed by studying changing chemical composition at the interface. In our simulations, reactions involving silanol …

Experimental Observation Of The Trapped Rainbow, Vera N. Smolyaninova, Igor Smolyaninov, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

We report on the experimental demonstration of the broadband "trapped rainbow" in the visible frequency range using an adiabatically tapered optical nano waveguide. Being a distinct case of the slow light phenomenon, the trapped rainbow effect could be applied to optical computing and signal processing, such as spectroscopy on a chip, and to providing enhanced light-matter interactions. (C) 2010 American Institute of Physics.

Higher-Order Eigenmodes Of Qplus Sensors For High Resolution Dynamic Atomic Force Microscopy, Ryan C. Tung, Thorsten Wutscher, David Martinez-Martin, R. Reifenberger, Franz Giessibl, Arvind Raman

Birck and NCN Publications

The time response of tuning-fork based sensors can be improved by operating them at higher eigenmodes because a measurement takes at least one oscillation cycle in dynamic force microscopy and the oscillation period of the second eigenmode is only about one sixth of the fundamental mode. Here we study the higher-order eigenmodes of quartz qPlus sensors [Bettac et al., Nanotechnology 20, 264009 (2009); Giessibl and Reichling, Nanotechnology 16, S118 (2005); Giessibl, Appl. Phys. Lett. 76, 1470 (2000); and Giessibl, Appl. Phys. Lett. 73, 3956 (1998)], their equivalent stiffness, and piezoelectric sensitivity, while paying special attention to the influence of the …

An Experimental Investigation On Viscoelastic Behavior In Tunable, Hao-Han Hsu, Dimitrios Peroulis

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Abstract—In this paper, the viscoelastic behavior of a tunable RF-MEMS resonator and its impacts are studied by means of direct RF measurements for the first time. This tunable resonator consists of one λ/2 coplanar waveguide (CPW) resonator and two nanocrystalline-Ni RF-MEMS varactors. S-parameters of this tunable resonator have been measured for 80 hours under a bi-state bias condition of 0 and 40 V. It is demonstrated that the resonant frequency is shifted by 90 MHz and the varactor deformed by 0.12 μm over the 80 hour period. The gap of the loaded varactor is extracted from the measured S-parameters using …

Nanoscale Metal-Metal Contact Physics From Molecular Dynamics: The Strongest Contact Size, Hojin Kim, Alejandro Strachan

Birck and NCN Publications

Using molecular dynamics we find that the tensile strength of the contacts between two clean platinum surfaces with nanoscale asperities is strongly size dependent with a maximum strength for contact lengths of approximately 5 nm. This is the first time a strongest size is observed in single crystals. The strengthening with decreasing size down to 5 nm results from a decrease in the initial density of mobile dislocations available for plastic deformation and the subsequent weakening originates from a reduction in the constraint to mechanical deformation inside the contact by the bulk.

Production Of Multiwall Carbon Nanotuse For Alcohol Sensor Application., Ebtehal Saleh Alshaqaq

Student Works (2010-2019)

Multiwall carbon nanotube/polyethylene oxide (PEO), multiwall carbon nanoube/polyvinyl alcohol(PVA) and multiwall carbon nanotube/ polyvinyl alcohol(PVA)/zinc oxide(ZnO) have been tested as chemical sensors and detailed study on the effect of different gas concentration and material properties on gas sensitivity is presented. Initial composites were prepared by a simple solution casting and characterized by x-ray diffraction for ZnO, Fourier transform infra-red spectroscopy (FTIR) and scanning electron microscopy (SEM) to demonstrate crystallite size of ZnO, the morphology and surface area respectively. On the other hand, MWCNT/PEO , MWCNT/PVA , MWCNT/PVA/ZnO were prepared with different loading MWCNT and ZnO. The chemical sensing properties of …

Extraordinary Transmission From High-Gain Nanoaperture Antennas, Edward C. Kinzel, Pornsak Srisungsitthisunti, Yan Li, Arvind Raman, Xianfan Xu

Birck and NCN Publications

This letter describes a bowtie nanoaperture antenna for coupling light to a subdiffraction limited near-field spot (<λ/8). The gain of the antenna is increased using a concentric grating structure to coherently diffract normally incident light toward the aperture. We experimentally demonstrate that the addition of the grating structure enhances the far-field transmission through the aperture by 6.9 times while the intensity at the near-field is increased more than 15 times. The nanoantenna is useful for applications including nanolithography and data storage.

Simulation Of Nanowire Tunneling Transistors: From The Wentzel-Kramers-Brillouin Approximation To Full-Band Phonon-Assisted Tunneling, Mathieu Luisier, Gerhard Klimeck

Birck and NCN Publications

Nanowire band-to-band tunneling field-effect transistors 􏰀TFETs􏰁 are simulated using the Wentzel– Kramers–Brillouin 􏰀WKB􏰁 approximation and an atomistic, full-band quantum transport solver including direct and phonon-assisted tunneling 􏰀PAT􏰁. It is found that the WKB approximation properly works if one single imaginary path connecting the valence band 􏰀VB􏰁 and the conduction band 􏰀CB􏰁 dominates the tunneling process as in direct band gap semiconductors. However, PAT is essential in Si and Ge nanowire TFETs where multiple, tightly-coupled, imaginary paths exist between the VB and the CB. © 2010 American Institute of Physics. 􏰂doi:10.1063/1.3386521􏰃

Chaos-Assisted Directional Light Emission From Microcavity Lasers, Susumu Shinohara, Takahisa Harayama, Takehiro Fukushima, Martina Hentschel, Takahiko Sasaki, Evgenii Narimanov

Birck and NCN Publications

We study the effect of dynamical tunneling on emission from ray-chaotic microcavities by introducing a suitably designed deformed disk cavity. We focus on its high quality factor modes strongly localized along a stable periodic ray orbit confined by total internal reflection. It is shown that dominant emission originates from the tunneling from the periodic ray orbit to chaotic ones; the latter eventually escape from the cavity refractively, resulting in directional emission that is unexpected from the geometry of the periodic orbit, but fully explained by unstable manifolds of chaotic ray dynamics. Experimentally performing selective excitation of those modes, we succeeded …

Analysis Of Conjugated Polymer Nanotubules Formed By Template Wetting Nanofabrication, Steven D. Bearden Jr.

Doctoral Dissertations

Semiconducting and optoelectric conjugated polymers have potential in micro and nano-electronic applications. Their widely tunable physical conformations and orientations make these polymers ideal material for engineering small scale devices. The polymers have been incorporated into several electronic devices including light-emitting diodes, solar cells, and field-effect transistors. Widespread adoption of these materials will not be a reality until the issues of poor device performance, short lifespans, and device degradation are resolved.

Nanostructures have been demonstrated to have improvements in molecular ordering and electronic transport. In the work presented here, tubular nanostructures of conjugated polymers fabricated by the template wetting nanofabrication process …

Computational Study Of An Ingan/Gan Nanocolumn Light-Emitting Diode, Christoph Boecklin, Ratko G. Veprek, Sebastian Steiger, Bernd Witzigmann

Birck and NCN Publications

A comprehensive three-dimensional analysis of the operation of an In0.4Ga0.6N/GaN nanocolumn light-emitting diode is presented. Focus is put on the investigation of the nature and location of the emitting states. Calculations of strain and polarization-induced internal fields show that the strong lateral dependence of the potential gives rise to states confined to the periphery and to the center of the nanocolumn. However, lateral confinement of states near the column center is weak such that a quantum-well-like treatment of the remaining bound states seems appropriate where coherence is lost in the lateral directions. Within this picture, a coupled and self-consistent three-dimensional …

Uncertainty Quantification Models For Micro-Scale Squeeze-Film Damping, Xiaohui Guo, Jia Li, Dongbin Xiu, Alina Alexeenko

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Two squeeze-film gas damping models are proposed to quantify uncertainties associated with the gap size and the ambient pressure. Modeling of gas damping has become a subject of increased interest in recent years due to its importance in micro-electro-mechanical systems (MEMS). In addition to the need for gas damping models for design of MEMS with movable micro-structures, knowledge of parameter dependence in gas damping contributes to the understanding of device-level reliability. In this work, two damping models quantifying the uncertainty in parameters are generated based on rarefied flow simulations. One is a generalized polynomial chaos (gPC) model, which is a …

Fabrication Of Conductive Interconnects By Ag Migration In Cu-Ag Core-Shell Nanoparticles, Suk Jun Kim, E A. Stach, Carol A. Handwerker

Birck and NCN Publications

Fabrication of conductive nanoparticle films is observed in Cu-Ag core-shell nanoparticles by fast diffusion of Ag at 220 degrees C from particle surfaces, leading to the formation of sintered necks of Ag at the initial particle-particle contacts. Transmission electron microscopy showed that the necks were pure Ag and that particle surfaces away from the contacts were nearly Ag-free. The extent of neck formation is controllable by the choice of initial Ag thickness. Analysis of the thermodynamics of the Ag-Cu system and the relative diffusivities of Ag and Cu provide criteria for fabrication of other core-shell two-phase systems by the same …

Optical Limiting Study Of Double Wall Carbon Nanotube-Fullerene Hybrids, Kang-Shyang Liao, Jun Wang, Daniel Fruchtl, Nigel Alley, Enrico Andreoli, Eoghan Dillon, Andrew Barron, Hansoo Kim, Hugh Byrne, Werner Blau, Seamus Curran

Articles

In order to merge complementary temporal and spatial nonlinear optical characteristics of Fullerene and carbon nanotubes, synthesis of double wall carbon nanotube-Fullerene hybrid was performed by covalently linking DWNT and C60 by amination reaction with polyethylenimine. DWNT-Fullerene hybrids were characterized by thermogravimetric analysis, UV-vis spectroscopy and transmission electron microscopy. Optical limiting performance of DWNT-Fullerene hybrids is superior to those of Fullerenes and SWNTs at the same level (~ 80%) of transmission. Whereas nonlinear scattering is an evident mechanism, reverse saturable absorption from Fullerene moieties has significant contribution. Charge transfer between the DWNT and Fullerene moieties may play an important role …

Morphological Evolution Of Single-Crystal Ultrathin Solid Films, Mikhail Khenner

Mathematics Faculty Publications

An introduction to mathematical modeling of ultrathin solid films and the role of such modeling in nanotechnologies: Educational presentation for senior physics majors

Morphological Evolution Of Single-Crystal Ultrathin Solid Films, Mikhail Khenner

Mathematics Faculty Publications

An introduction to mathematical modeling of ultrathin solid films and the role of such modeling in nanotechnologies: Educational/Research presentation for senior physics majors

Artificial Intelligence: Soon To Be The World’S Greatest Intelligence, Or Just A Wild Dream?, Edward R. Kollett

Academic Symposium of Undergraduate Scholarship

The purpose of the paper was to examine the field of artificial intelligence. In particular, the paper focused on what has been accomplished towards the goal of making a machine that can think like a human, and the hardships that researchers in the field has faced. It also touched upon the potential outcomes of success. Why is this paper important? As computers become more powerful, the common conception is that they are becoming more intelligent. As computers become more integrated with society and more connected with each other, people again believe they are becoming smarter. Therefore, it is important that …

Strain-Induced, Off-Diagonal, Same-Atom Parameters In Empirical Tight-Binding Theory Suitable For [110] Uniaxial Strain Applied To A Silicon Parametrization, Timothy B. Boykin, Mathieu Luisier, Mehdi Salmani-Jelodar, Gerhard Klimeck

Birck and NCN Publications

State-of-the-art transistors achieve their improved performance through strain engineering. The somewhat unusual uniaxial [110] strain is of particular importance as it provides a significant mobility increase for electrons. Empirical tight binding has shown tremendous benefits in modeling realistically large structures including standard strain conditions, but often fails to predict the correct uniaxial [110] strain behavior because most treatments neglect the same-atom different-orbital matrix elements induced by this strain. Two separate mechanisms are responsible for these conditions: Loumlwdin orbital changes and displacement of nearest-neighbor potentials. We present a model which separately includes both mechanisms via parameters whose range of validity can …

Electronic Transport In Chemical Vapor Deposited Graphene Synthesized On Cu: Quantum Hall Effect And Weak Localization, Helin Cao, Qingkai Yu, Luis A. Jauregui, J Tian, W Wu, Z Liu, Ramaneh Jalilian, D K. Benjamin, Z Jiang, J Bao, S S. Pei, Yong P. Chen

Birck and NCN Publications

We report on electronic properties of graphene synthesized by chemical vapor deposition (CVD) on copper then transferred to SiO2/Si. Wafer-scale (up to 4 in.) graphene films have been synthesized, consisting dominantly of monolayer graphene as indicated by spectroscopic Raman mapping. Low temperature transport measurements are performed on microdevices fabricated from such CVD graphene, displaying ambipolar field effect (with on/off ratio similar to 5 and carrier mobilities up to similar to 3000 cm(2)/V s) and "half-integer" quantum Hall effect, a hall-mark of intrinsic electronic properties of monolayer graphene. We also observe weak localization and extract information about phase coherence and scattering …

Note: Thermal Analog To Atomic Force Microscopy Force-Displacement Measurements For Nanoscale Interfacial Contact Resistance, Brian D. Iverson, John Blendell, Suresh Garimella

Birck and NCN Publications

Thermal diffusion measurements on polymethylmethacrylate-coated Si substrates using heated atomic force microscopy tips were performed to determine the contact resistance between an organic thin film and Si. The measurement methodology presented demonstrates how the thermal contrast signal obtained during a force-displacement ramp is used to quantify the resistance to heat transfer through an internal interface. The results also delineate the interrogation thickness beyond which thermal diffusion in the organic thin film is not affected appreciably by the underlying substrate.

A Continuum Plasticity Model That Accounts For Hardening And Size Effects In Thin Films, Abigail Hunter, Hariharanath Kavuri, Marisol Koslowski

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We conducted three-dimensional finite element simulations of the mechanical response of passivated single crystal copper thin films with a continuum crystal plasticity model. The model introduces the formation of high density dislocation layers close to the substrate and passivation interfaces obtained from dislocation dynamics simulations. These dislocation structures are responsible for an increase in strain hardening as the film thickness decreases. The model predicts an increase in strain hardening as the film thickness decreases in agreement with experimental observation in films with thickness in the range 0.2 to 2μm.

Pced2.0—A Computer Program For The Simulation Of Polycrystalline Electron Diffraction Pattern, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

A computer program for the simulation of polycrystalline electron diffraction patterns is described. PCED2.0, an upgraded version of the previous JECP/PCED, can be used as a teaching aid and research tool for phase identification, microstructure texture analysis, and phase fraction determination. In addition to kinematical theory for diffraction intensity calculation of polycrystalline samples, Blackman two-beam dynamical correction is included. March model is used for out-of-plane and in-plane texture simulation. A pseudo-Voigt function is used for the peak profile fitting of diffraction rings. User-friendly interface is improved in the handling of experimental diffraction data and the flexibility of indexing. Application of …

On Momentum Conservation And Thermionic Emission Cooling, Raseong Kim, Changwook Jeong, Mark S. Lundstrom

Birck and NCN Publications

The possibility of increasing the performance of thermionic cooling devices by relaxing lateral momentum conservation is examined. Upper limits for the ballistic emission current are established. It is then shown that for most cases, nonconserved lateral momentum model produces a current that exceeds this upper limit. For the case of heterojunctions with a much heavier effective mass in the barrier and with a low barrier height, however, relaxing lateral momentum may increase the current. These results can be simply understood from the general principle that the current is limited by the location, well or barrier, with the smallest number of …

Communications: Entanglement Switch For Dipole Arrays, Qi Wei, Sabre Kais, Yong P. Chen

Birck and NCN Publications

We propose a new entanglement switch of qubits consisting of electric dipoles oriented along or against an external electric field and coupled by the electric dipole-dipole interaction. The pairwise entanglement can be tuned and controlled by the ratio of the Rabi frequency and the dipole-dipole coupling strength. Tuning the entanglement can be achieved for one, two, and three-dimensional arrangements of the qubits. The feasibility of building such an entanglement switch is also discussed.

Microscopic And Spectroscopic Studies Of Thermally Enhanced Electrospun Pmma Micro- And Nanofibers, Sean Pelfrey, Travis Cantu, Michael R. Papantonakis, Duane L. Simonson, R. Andrew Mcgill, Javier Macossay-Torres

School of Integrative Biological & Chemical Sciences (Formerly Dept. of Chemistry)

Carbon nanofibers (CNFs) have been incorporated into poly(methyl methacrylate) (PMMA) through electrospinning. The resulting micro- and nanofibers have been characterized by Scanning Electron Microscopy (SEM), which confirmed fiber formation and demonstrated a core-sheath structure of the PMMA fibers. Thermogravimetric Analysis (TGA) was used to obtain the thermal properties of the materials, indicating an enhancement in the thermal properties of the composite fibers. In addition, Fourier Transform Infrared Spectroscopy (FTIR) was utilized to investigate the interactions of PMMA micro- and nanofibers with CNFs, demonstrating the preferred sites of intermolecular interactions between the polymer matrix and the filler.

Automated Nanocrystal Orientation And Phase Mapping In The Transmission Electron Microscope On The Basis Of Precession Electron Diffraction, Edgar F. Rauch, Joaquin Portillo, Stavros Nicolopoulos, Daniel Bultreys, Sergei Rouvimov, Peter Moeck

Physics Faculty Publications and Presentations

An automated technique for the mapping of nanocrystal phases and orientations in a transmission electron microscope is described. It is primarily based on the projected reciprocal lattice geometry that is extracted from electron diffraction spot patterns. Precession electron diffraction patterns are especially useful for this purpose. The required hardware allows for a scanning-precession movement of the primary electron beam on the crystalline sample and can be interfaced to any older or newer mid-voltage transmission electron microscope (TEM). Experimentally obtained crystal phase and orientation maps are shown for a variety of samples. Comprehensive commercial and open-access crystallographic databases may be used …

Preparation And Electrochemical Behavior Of Li4Ti5O12 Nanosheets As Anode Material For Lithium Ion Battery, Yi-Fei Wang, Yu-Feng Tang, Zheng Qiu, Li Yang

Journal of Electrochemistry

Spinel lithium titanate(Li₄Ti₅O₁₂) nanosheets with a size range of 200 ～400 nm were synthesized by hydrothermal process from the amorphous hydrous titanium oxide precursors.The as-prepared products were characterized by X-ray powder diffraction(XRD),scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The electrochemical behaviors of Li₄Ti₅O₁₂ electrode in conventional organic electrolyte and ionic liquid electrolyte were investigated by using cyclic voltammetry,galvanostatic charge-discharge and AC impedance techniques.The experimental results indicate that the as-prepared nanostructured Li₄Ti₅O₁₂,evaluated as anode material,exhibited good reversibility and cycle performance.It is expected to be a …

Electrocatalytic Reduction Of L-Cystine At Pb/Nanotio2 Film Electrode, Dao-Bao Chu, Feng Wang, Ying Xiao, Xue-Jiao Zhang

Journal of Electrochemistry

The nanoporous Ti-based TiO₂ films electrodes modified with Pb particles(Pb/nanoTiO₂) were prepared by using anodization and potentiostatic electro-deposition.The optimum deposition conditions were determined by comparing with various deposition potentials and time.The SEM analyses indicated that the TiO₂ films were homogeneous nanoporous structure,and the Pb particles well dispersed on the TiO₂ films.The L-cystine electrocatalytic activity reduction on the Pb/nanoTiO₂ film electrodes was investigated by cyclic voltammetry and Chronoamperometric curves.The results showed that this type of the electrode posseses high acticity and stability.

Electronic Structure, Phonons, And Thermal Properties Of Scn, Zrn, And Hfn: A First-Principles Study, Bivas Saha, Jagaran Acharya, Timothy D. Sands, Umesh Waghmare

Birck and NCN Publications

With a motivation to understand microscopic aspects of ScN, ZrN, and HfN relevant to the thermoelectric properties of nitride metal/semiconductor superlattices, we determine their electronic structure, vibrational spectra and thermal properties using first-principles calculations based on density functional theory with a generalized gradient approximation of the exchange correlation energy. We find a large energy gap in the phonon dispersions of metallic ZrN and HfN, but a gapless phonon spectrum for ScN spanning the same energy range, this suggests that a reduced thermal conductivity, suitable for thermoelectric applications, should arise in superlattices made with ScN and ZrN or ScN and HfN. …

On Eigenmodes, Stiffness, And Sensitivity Of Atomic Force Microscope Cantilevers In Air Versus Liquids, Daniel Kiracofe, Arvind Raman

Birck and NCN Publications

The effect of hydrodynamic loading on the eigenmode shapes, modal stiffnesses, and optical lever sensitivities of atomic force microscope (AFM) microcantilevers is investigated by measuring the vibrations of such microcantilevers in air and water using a scanning laser Doppler vibrometer. It is found that for rectangular tipless microcantilevers, the measured fundamental and higher eigenmodes and their equivalent stiffnesses are nearly identical in air and in water. However, for microcantilevers with a tip mass or for picket shaped cantilevers, there is a marked difference in the second (and higher) eigenmode shapes between air and water that leads to a large decrease …