Nanoscience and Nanotechnology Commons^™

Study On The Electrogeneration And Properties Of Superoxide Ion In Aprotic Media By Using Carbon Nanotubes Powder Microelectrode, Ying-Liang Wei, Chen Shao, Hui Feng

Journal of Electrochemistry

Multi-wall carbon nanotubes are filled in the cavity at the tip of a microelectrode to form a carbon nanotubes powder microelectrode(CNTs-PME).The CNTs-PME is used to study the electrochemical reduction of oxygen in aprotic media.It is a nearly reversible redox process of the O2/O·-2 couple at the CNTs-PME in the dimethyl sulfoxide(DMSO)solution.The heterogeneous electron transfer rate constant(ks)can be measured by steady-state voltammogram and the result is 9.8 10-3cm /s.As a weak oxidant,the reaction of O·-2 with epinephrine was studied by cyclic voltammetry.Additionally,the reaction of O·-2 with benzoic acid was also discussed in detail.

Anisotropic Strain And Phonon Deformation Potentials In Gan, V. Darakchieva, T. Paskova, Mathias Schubert, H. Arwin, P.P. Paskov, B. Monemar, D. Hommel, M. Heuken, J. Off, F. Scholz, B.A. Haskell, P.T. Fini, J.S. Speck, S. Nakamura

Nebraska Center for Materials and Nanoscience: Faculty Publications

We report optical phonon frequency studies in anisotropically strained c-plane- and a-plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E₁(TO), E₁(LO), and E₂ phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c_E1(TO) , c_E1(LO) , and c_E2 are determined. A distinct correlation between anisotropic strain and the A₁(TO) and E₁(LO) …

Atomic Force Microscope Imaging Of Dna And Multi Walled Carbon Nanotubes, Jacob Hohnbaum

Mechanical Engineering Undergraduate Honors Theses

The Micro and Nano System Laboratory at the University of Arkansas currently is equipped with an Atomic Force Microscope (AFM). This device can be used to measure objects with resolution on the nanometer scale, but there are a number of technical difficulties in performing scans of carbon nanotubes and DNA. The goal of this research is to successfully perform scans on both carbon nanotubes and DNA and to also establish laboratory processing protocols to re-perform such scans in the future. Previous works performed by other researchers in the laboratory provided basic protocols with which to begin the present research. These …

Growth By Molecular Beam Epitaxy Of Self-Assembled Inas Quantum Dots On Inalas And Ingaas Lattice-Matched To Inp, Paul J. Simmonds, H W. Li, H E. Beere, P See, A J. Shields, D A. Ritchie

Paul J. Simmonds

The authors report the results of a detailed study of the effect of growth conditions, for molecular beam epitaxy, on the structural and optical properties of self-assembled InAs quantum dots (QDs) on In_0.524Al_0.476As. InAs QDs both buried in, and on top of, In_0.524Al_0.476As were analyzed using photoluminescence (PL) and atomic force microscopy. InAs QD morphology and peak PL emission wavelength both scale linearly with deposition thickness in monolayers (MLs). InAs deposition thickness can be used to tune QD PL wavelength by 170 nm/ML, over a range of almost 700 nm. Increasing growth …

1/F Noise In Carbon Nanotube Devices - On The Impact Of Contacts And Device Geometry, Joerg Appenzeller, Yu-Ming Lin, Joachim Knoch, Zhihong Chen, Phaedon Avouris

Other Nanotechnology Publications

We report on the 1/f noise in various ballistic carbon nanotube devices. A common means to characterize the quality of a transistor in terms of noise is to evaluate the ratio of the noise amplitude A and the sample resistance R. By contacting semiconducting tubes with different metal electrodes we are able to show that a small A/R value by itself is no indication of a suitable metal/tube combination for logic applications. We discuss how current in a nanotube transistor is determined by the injection of carriers at the electrode/nanotube interface, while at the same time excess noise is related …

Interface Proximity Effects In Current-Perpendicular-To-Plane Magnetoresistance, R.J. Baxter, David G. Pettifor, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

Using a tight-binding model that takes into account a realistic electronic band structure and includes defect scattering we investigate spin-dependent transport in Co/Cu/Co trilayers when current flows perpendicular to the plane. We show that resistance of the Co/Cu interface depends on the proximity of another interface, which makes the parameters characterizing the spin-dependent interface resistance AR_F/N^* and γ_F/N, to be dependent on the layer thickness separating the two interfaces. This leads to a decrease in the measurable quantity SR=√(AR_AP)(AR_AP-AR_P) with the Cu layer thickness and, therefore, …

Elasticity Of Planar Fiber Networks, X.-F. Wu, Yuris A. Dzenis

Nebraska Center for Materials and Nanoscience: Faculty Publications

A micromechanics model is proposed for the elasticity of planar fiber networks (FNs). The FN is created by random deposition of linearly elastic straight rods within a region. The rods are bonded rigidly at contacts. Under external in-plane loading, the FN deformation consists of fiber bending, elongation, and contraction. An effective constitutive relation for fiber network is developed by averaging the strain energy dissipated by all possible fiber deformations in all directions. Numerical calculations are performed to analyze the effects of fiber aspect ratio and fiber concentration on the effective stiffness of the planar random FN. Finite element analysis (FEA) …

Guided Self-Assembly Of Diblock Copolymer Thin Films On Chemically Patterned Substrates, Xiang-Fa Wu, Yuris A. Dzenis

Nebraska Center for Materials and Nanoscience: Faculty Publications

We study the guided self-assembly of symmetric/asymmetric diblock copolymer (BCP) films on heterogeneous substrates with chemically patterned surface by using a coarse-grained phase-separation model. During the procedure, the free energy employed for the BCP films was modeled by the Ginzburg-Landau free energy with nonlocal interaction, and the flat, chemically patterned surface was considered as a heterogeneous surface with short-range interaction with the BCP molecules. The resulting Cahn-Hilliard equation was solved by means of an efficient semi-implicit Fourier-spectral algorithm. Effects of pattern scale, surface chemical potential, and BCP asymmetry on the self-assembly process were explored in detail and compared with those …

Interfaces, Volume 9, Issue 1 - Spring 2007

INTERFACES: Newsletter of the Nebraska Center for Materials and Nanoscience

CONTENTS
From the Director
Facility Focus: Crystallography
Recent Achievements of Center Researchers
Catalysts For Carbon Monoxide Conversion
NCMN Welcomes Li Tan
Research Spotlight: Christian Binek
LNK Chemsolutions Receives Funding

Effect Of Ferroelectricity On Electron Transport In Pt/Batio3/Pt Tunnel Junctions, Julian P. Velev, Chun-Gang Duan, Kirill D. Belashchenko, Sitaram Jaswal, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

Based on first-principles calculations, we demonstrate the impact of the electric polarization on electron transport in ferroelectric tunnel junctions (FTJs). Using a Pt/BaTiO₃ /Pt FTJ as a model system, we show that the polarization of the BaTiO₃ barrier leads to a substantial drop in the tunneling conductance due to changes in the electronic structure driven by ferroelectric displacements. We find a sizable change in the transmission probability across the Pt/BaTiO₃ interface with polarization reversal, a signature of the electroresistance effect. These results reveal exciting prospects that FTJs offer as resistive switches in nanoscale electronic devices.

Calculations Of Spin-Disorder Resistivity From First Principles, Aleksander L. Wysocki, Kirill D. Belashchenko, Julian P. Velev, Mark Van Schilfgaarde

Nebraska Center for Materials and Nanoscience: Faculty Publications

Spin-disorder resistivity of Fe and Ni is studied using the noncollinear density functional theory. The Landauer conductance is averaged over random disorder configurations and fitted to Ohm’s law. The distribution function is approximated by the mean-field theory. The dependence of spin-disorder resistivity on magnetization in Fe is found to be in excellent agreement with the results for the isotropic s-d model. In the fully disordered state, spin-disorder resistivity for Fe is close to experiment, while for fcc Ni it exceeds the experimental value by a factor of 2.3. This result indicates strong magnetic short-range order in Ni at …

Determination Of Young’S Modulus Of Individual Electrospun Nanofibers, Philip A. Yuya, Yongkui Wen, Joseph A. Turner, Yuris A. Dzenis, Zheng Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

The authors report a technique for measuring Young’s modulus of a single electrospun nanofiber using the vibrations of two microcantilevers coupled with the nanofiber. The modulus is calculated from the resonant frequency shift resulting from the nanofiber. Polyacrylonitrile nanofibers (200 nm diameter) were collected during electrospinning and wrapped on two similar microcantilevers causing a shift in first resonance from 10.0 to 19.4 kHz. Finite element analysis was used to analyze the frequency shift using images from a scanning electron microscope giving a modulus of the as-spun polyacrylonitrile nanofiber of 26.8 GPa.

Accessibility Of Home Blood Pressure Monitors For Blind And Visually Impaired People, Mark M. Uslan, Darren M. Burton, Thomas E. Wilson, Steven Taylor, Bruce S. Chertow, Jack E. Terry

Physics Faculty Research

Background: The prevalence of hypertension comorbid with diabetes is a significant health care issue. Use of the home blood pressure monitor (HBPM) for aiding in the control of hypertension is noteworthy because of benefits that accrue from following a home measurement regimen. To be usable by blind and visually impaired patients, HBPMs must have speech output to convey all screen information, an easily readable visual display, identifiable controls that are easy to use, and an accessible user manual.

Methods: Data on the physical aspects and the features and functions of nine Food and Drug Administration-approved HBPMs (eight of which were …

Improved Carrier Injection In Ultrathin-Body Soi Schottky-Barrier Mosfets, M Zhang, Joachim Knoch, Joerg Appenzeller, S Mantl

Other Nanotechnology Publications

The impact of the gate oxide and the silicon-on-insulator (SOI) body thickness on the electrical performance of SOI Schottky-barrier (SB) MOSFETs with fully nickel silicided source and drain contacts is experimentally investigated. The subthreshold swing S is extracted from the experimental data and serves as a measure for the carrier injection through the Sills. It is shown that decreasing the gate oxide and body thickness allows to strongly increase the carrier injection and hence, a significantly improved ON-state of SB-MOSFETs can be obtained.

Comparison Of The Electrochemical Reactivity Of Electrodes Modified By Carbon Nanotubes With Different Sizes, Guo-Feng Yang, Neng-Qin Jia, Zhi-Yong Wang

Journal of Electrochemistry

The electrochemical activity of multi-walled carbon nanotubes(MWNTs) with different sizes,including four different MWNTs with the same length and different diameter,two different MWNTs with the same diameter and different length has been assessed and compared.The various MWNTs modified electrodes were prepared by immobilizing the suitable amount of MWNTs onto a glassy carbon electrode,and their voltammetric responses to ferricyanide,uric acid and dopamine were examined.The corresponding cyclic voltammetric data was showed that the electrochemical and electrocatalytic activities are depended on the nanotube length.The electrochemical reactivity of short MWNT(S-MWNT) is better than that of long MWNT(L-MWNT),which may be mainly attributed to the existence of …

Studies On The Ion Conductive Performance Of Composite Polymer Electrolyte Containing Nano-Scale Sio_2, Lin Ye, Yu-Mei Zhao, Xiao-Wen Zhang, Zeng-Guo Feng, Ying Bai, Feng Wu

Journal of Electrochemistry

Nano-silicon oxide was doped into a novel comblike polyether,poly(3-(methoxy(triethylenoxy))methyl-3'-methyloxetane) to prepare a series of composite polymer electrolyte.The ion conductivity measurement revealed that the composite polymer electrolyte added with 5% weight fraction of SiO2 has the highest ion conductivity of 7.8×10-5 S/cm at 30℃ and 4.5×10-4 S/cm at 80℃,which is increased 30%~60% as compared to the polymer electrolyte without adding any SiO2.DSC results implied that the nano-silicon oxide inserts into the macromolecule chains to increase the free volume and decrease the glass transition temperature to enhance the ion conductivity.In addition,it seems that the crystallization occurred due to the hydrogen bonds between …

Preparation And Lithium Storage Performance Of Nano-Structural Sno_2/Carbon Nanotubes Composite Electrodes, Hong-Bing Wei, Ling Huang, Xiao-Bin Wu, Fu-Sheng Ke, Jin-Shu Cai, Xiao-Yong Fan, Fang-Zu Yang, Shi-Gang Sun

Journal of Electrochemistry

The Nano-structural SnO2/Carbon Nanotubes Composites were prepared in a solution of SnCl2,ethylene glycol(EG),purified MWCNTs and sodium dodecyl sulfate(SDS) at 160 ℃.The phase structure and surface morphology of the composites were measured by XRD HRTEM and SEM.The results indicate that there are high dispersions and high loadings of SnO2 nanoparticles on MWCNTs.Electrochemical lithium storage performance was studied preliminarily on the obtained samples.MWCNTs modified with SnO2 nanoparicles were shown to have a higher electrochemical reversible capacity than that of MWCNTs during the charge and discharge process.MWCNTs can accommodate the larger structure strain of the active materials produced during Li-ion insertion and extraction,which …

Effect Of Oxygen Vacancies On Spin-Dependent Tunneling In Fe/Mgo/Fe, Julian P. Velev, Kirill D. Belashchenko, Sitaram S. Jaswal, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

First-principles calculations based on density functional theory are used to elucidate the effect of O vacancies, forming F centers, on spin-dependent tunneling in Fe/MgO/Fe(001) magnetic tunnel junctions. O vacancies produce occupied localized s states and unoccupied resonant p states, which is consistent with available experimental data. The authors find that O vacancies affect the conductance by nonresonant scattering of tunneling electrons causing a substantial reduction of tunneling magnetoresistance (TMR). Improving the quality of the MgO barrier to reduce O vacancy concentration would improve TMR in these and similar junctions.

Granular Layers On Vibrating Plates: Effective Bending Stiffness And Particle-Size Effects, Wonmo Kang, Joseph A. Turner, Florin Bobaru, Liyong Yang, Kitti Rattanidit

Nebraska Center for Materials and Nanoscience: Faculty Publications

Acoustic methods of land mine detection rely on the vibrations of the top plate of the mine in response to sound. For granular soil (e.g., sand), the particle size is expected to influence the mine response. This hypothesis is studied experimentally using a plate loaded with dry sand of various sizes from hundreds of microns to a few millimeters. For low values of sand mass, the plate resonance decreases with added mass and eventually reaches a minimum without particle size dependence. After the minimum, a frequency increase is observed with additional mass that includes a particle-size effect. Analytical nondissipative continuum …

Hyperthermic Effects Of Gold Nanorods On Tumor Cells, Terry B. Huff, Ling Tong, Matthew N. Hansen, Ji-Xin Cheng, Alexander Wei

Other Nanotechnology Publications

Plasmon-resonant gold nanorods, which have large absorption cross sections at near-infrared frequencies, are excellent candidates as multifunctional agents for image-guided therapies based on localized hyperthermia. The controlled modification of the surface chemistry of the nanorods is of critical importance, as issues of cell-specific targeting and nonspecific uptake must be addressed prior to clinical evaluation. Nanorods coated with cetyltrimethylammonium bromide (a cationic surfactant used in nanorod synthesis) are internalized within hours into KB cells by a nonspecific uptake pathway, whereas the careful removal of cetyltrimethylammonium bromide from nanorods functionalized with folate results in their accumulation on the cell surface over the …

Tunneling Anisotropic Magnetoresistance Driven By Resonant Surface States: First-Principles Calculations On An Fe(001) Surface, Athanasios N. Chantis, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Mark Van Schilfgaarde

Nebraska Center for Materials and Nanoscience: Faculty Publications

Fully relativistic first-principles calculations of the Fe(001) surface demonstrate that resonant surface (interface) states may produce sizable tunneling anisotropic magnetoresistance in magnetic tunnel junctions with a single magnetic electrode. The effect is driven by the spin-orbit coupling. It shifts the resonant surface band via the Rashba effect when the magnetization direction changes. We find that spin-flip scattering at the interface is controlled not only by the strength of the spin-orbit coupling, but depends strongly on the intrinsic width of the resonant surface states.

A Simple Sol-Gel Processing For The Development Of High-Temperature Stable Photoactive Anatase Titania, Suresh Pillai, Declan Mccormack, John Colreavy

Articles

No abstract provided.

Microwave Absorption Of Patterned Arrays Of Nanosized Magnetic Stripes With Different Aspect Ratios, Leszek M. Malkinski, Minghui Yu, Andriy Y. Voyk, Donald J. Scherer Ii, Leonard Spinu, Weillie Zhou, Scott Whittenburg, Zachary Davis, Jin-Seung Jung

Physics Faculty Publications

Arrays consisting of nanosized stripes of Permalloy with different length-to-width ratios have been fabricated using electron beam nanolithography, magnetron sputtering, and lift-off process. These stripes have a thickness of 100 nm, a width of 300 nm, and different lengths ranging from 300 nm to 100 μm. The stripes are separated by a distance of 1 μm. Magnetization hysteresis loops were measured using a superconducting quantum interference device susceptometer. Microwave absorption at 9.8 GHz was determined by means of ferromagnetic resonance technique. The dependence of the resonant field on the angle between the nanostructure and the in-plane dc magnetic …

Origin Of Photomultiplication In C60 Based Devices, Jinsong Huang, Yang Yang

Department of Mechanical and Materials Engineering: Faculty Publications

In this manuscript, the origin of the photomultiplication effect was studied in C₆₀ based devices by evaluating the wavelength dependent external and internal quantum efficiencies under various biases. The effect of materials with disordered structures on the photomultiplication effect was determined by intentionally integrating both ordered and disordered material structures into one organic solar cell device with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/pentacene/C₆₀ fullerene/bathocuproine (BCP)/Al. Our results show that both the disordered structure of C₆₀ and the charge trapping effect at the C₆₀ /PEDOT:PSS interface contribute to the photomultiplication effect. By studying the C60-only …

The Effect Of Nanoparticle Shape On Polymer-Nanocomposite Rheology And Tensile Strength, Scott Knauert, Jack Douglas, Francis Starr

Francis Starr

No abstract provided.

Assessing The Possibility Of Corrosion Occurrence In Metallic Stacks Caused By Hydrochloric Acid, João F. Gomes

João F Gomes

This article presents a simple method to estimate the possibility of corrosion in metallic stacks and surfaces due to hydrochloric acid deposition from stack gases, based on the HCl content in gases and also the flue gas temperature

New Technologies For Effective Forest Fire Fighting, João Gomes

João F Gomes

Efficient fire extinction with water could be greatly improved by using superabsorbent polymers, added to the water used for fire fighting, or sprayed over surfaces of combustible materials in order to protect them from fire. Specially developed superabsorbent polymers such as acrylamide/2-acrylamide-2-methyl-propane-sulphonate (AA/AMPS) seem to be particularly efficient for this purpose. In terms of water absorption, the experimental tests performed, showed that the optimal composition of this polymer is 30:70 AMPS versus AA, using 0.5% of bis-acrylamide (BA) as crosslinking agent.

Deriving An Indoor Environmental Index For Portuguese Office Buildings, João F. Gomes

João F Gomes

The EC issued a Directive in 2002 aiming to reduce the energy consumption of buildings, which was adopted by the EU member states and came into force in 2006. Portugal adopted it by issuing law decrees in 2006 which considered not only the energy saving aspects but also additional specific measures aiming to protect indoor air quality (IAQ). This new legislation is now being enforced and it will be necessary to define compliance acceptance levels for the prescribed indoor air limits. The use of comfort or environmental indexes could be of considerable help in order to ameliorate the evaluation of …

The Importance Of Considering Building Downwash When Assessing The Need To Heighten Stacks Of Existing Small And Medium Sized Industries, João F. Gomes

João F Gomes

No abstract provided.

Measurements Of Indoor Air Pollutant Levels In A University Office Building, João F. Gomes

João F Gomes

This work consisted of a series of determinations performed in typical rooms of a building belonging to the Technical University of Lisbon, which is located in a central urban area of Lisbon. The main objective was to evaluate the Indoor Air Quality (IAQ) of the rooms so that further corrective measures could be taken if unsatisfactory IAQ levels were to be found. Correlations were derived, between indoor and outdoor pollutant concentrations, in order to assess the existence of contaminations coming from outside. Also, correlations were derived between total volatile organic compounds (VOC) concentrations and specific individual organic species measured in …