Nanoscience and Nanotechnology Commons^™

Electrocatalytic Determination Of 15 Kinds Of Phenolic Compounds By Novel Gold Nanoparticles-Modified Glassy Carbon Electrode, Yan-Ping Cui, Wei-Xing Wang, Chang-Zhu Yang, Wen-Hong Pu

Journal of Electrochemistry

A gold nanoparticles modified glassy carbon electrode (Au/GCE) was used to detect 15 kinds of phenolic compounds. In the cyclic voltammetry measurements, the peak currents of phenolic compounds at Au/GCE were all increased as compared with GCE and planar gold electrodes, and the oxidation potentials were determined by the activity of analytes. Besides, electrocatalysis of salicylic acid was studied at Au/GCE. The results showed that, there was a good linear relationship between the oxidation current and the concentration of salicylic acid, and the current sensitivity was 1.8 fold higher than that obtained on GCE. Trace phenolic compounds determination could be …

Electronic Structure Of Realistically Extended Atomistically Resolved Disordered Si:P Delta-Doped Layers, Sunhee Lee, Hoon Ryu, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck

Birck and NCN Publications

The emergence of scanning tunneling microscope (STM) lithography and low temperature molecular beam epitaxy (MBE) opens the possibility of creating scalable donor based quantum computing architectures. In particular, atomically precise Si:P monolayer structures (delta-doped layers) serve as crucial contact regions and in-plane gates in single impurity devices. In this paper we study highly confined delta-doped layers to explain the disorder in the P dopant placements in realistically extended systems. The band structure is computed using the tight-binding formalism and charge-potential self-consistency. The exchange-correlation corrected impurity potential pulls down subbands below the silicon valley minima to create impurity bands. Our methodology …

Effects Of Carbon Nanotube-Tethered Nanosphere Density On Amperometric Biosensing: Simulation And Experiment, Jonathan Caussen, James Hengenius, Monique Wickner, Timothy Fisher, David Umulis, Marshall Porterfield

Birck and NCN Publications

Nascent nanofabrication approaches are being applied to reduce electrode feature dimensions from the microscale to the nanoscale, creating biosensors that are capable of working more efficiently at the biomolecular level. The development of nanoscale biosensors has been driven largely by experimental empiricism to date. Consequently, the precise positioning of nanoscale electrode elements is typically neglected, and its impact on biosensor performance is subsequently overlooked. Herein, we present a bottom-up nanoelectrode array fabrication approach that utilizes low-density and horizontally oriented single-walled carbon nanotubes (SWCNTs) as a template for the growth and precise positioning of Pt nanospheres. We further develop a computational …

Spectral Phonon Conduction And Dominant Scattering Pathways In Graphene, Dhruv Singh, Jayathi Murthy, Timothy Fisher

Birck and NCN Publications

In this paper, we examine the lattice thermal conductivity and dominant phonon scattering mechanisms of graphene. The interatomic interactions are modeled using the Tersoff interatomic potential and perturbation theory is applied to calculate the transition probabilities for three-phonon scattering. The matrix elements of the perturbing Hamiltonian are calculated using the anharmonic interatomic force constants obtained from the interatomic potential as well. The linearized Boltzmann transport equation is applied to compute the thermal conductivity of graphene for a wide range of parameters giving spectral and polarization-resolved information. The complete spectral detail of selection rules, important phonon scattering pathways, and phonon relaxation …

Enhanced Valence Force Field Model For The Lattice Properties Of Gallium Arsenide, Sebastian Steiger, Mehdi Salmani-Jelodar, Denis Areshkin, Abhijeet Paul, Tillmann Kubis, Michael Povolotskyi, Hong-Hyun Park, Gerhard Klimeck

Birck and NCN Publications

An enhanced valence force field model for zinc-blende crystals is developed to provide a unified description of the isothermal static and dynamical lattice properties of gallium arsenide. The expression for the lattice energy includes a second-nearest-neighbor coplanar interaction term, the Coulomb interaction between partially charged ions, and anharmonicity corrections. General relations are derived between the microscopic force constants and the macroscopic elastic constants in zinc-blende crystals. Applying the model to gallium arsenide, parameter sets are presented that yield quantitative agreement with experimental results for the phonon dispersion, elastic constants, sound velocities, and Gru ̈neisen mode parameters.

Effects Of (Nh(4))(2)S Passivation On The Off-State Performance Of 3-Dimensional Ingaas Metal-Oxide-Semiconductor Field-Effect Transistors, J J Gu, A T. Neal, P D. Ye

Birck and NCN Publications

Planar and 3-dimensional (3D) buried-channel InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) have been experimentally demonstrated at deep-submicron gate lengths. The effect of (NH(4))(2)S passivation with different concentrations (20%, 10%, or 5%) on the off-state performance of these devices has been systematically studied. 10% (Na(4))(2)S treatment is found to yield the optimized high-k/InP harrier layer interface property, resulting in a minimum subthreshold swing (SS) lower than 100 mV/dec. Moreover, the 3D device structure greatly improves the off-state performance and facilitates enhancement-mode operation. A scaling metrics study has been carried out for 10% (NH(4))(2)S treated 3D devices with gate lengths down to 100 …

Technical Note: Friction Factor Diagrams For Pipe Flow, Jim Mcgovern

Articles

This technical note describes diagrams of friction factor for pipe flow that have been prepared using, mainly, the equations that Lewis Moody used to prepare his famous diagram in 1944. The preparation of the new diagrams was prompted by the need for vector graphics versions that could be used for teaching purposes and that could be distributed freely to students and others under a Creative Commons Attribution-Share-Alike license. Using a structure very similar to that of Moody's diagram, variants with the Darcy friction factor and the Fanning friction factor have been prepared. In addition, variants have been prepared that include …

Introducing Porous Silicon As A Sacrificial Material To Obtain Cavities In Substrate Of Soi Wafers And A Getter Material For Mems Devices, Wajihuddin Mohammad

Doctoral Dissertations

Microelectromechanical system (MEMS) resonators have been a subject of research for more than four decades. The reason is the huge potential they possess for frequency applications. The use of a MEMS resonator as the timing element has an experimental history and huge progress has been made in this direction. Vacuum encapsulated MEMS resonators are required for high precision frequency control. Hence, a device with a high quality factor and durability is needed. In this effort, a new process for producing a cavity in the substrate of Silicon on insulator (SOI) MEMS devices and augmenting it with a getter using porous …

Graphene Formation On Step-Free 4h-Sic(0001), M. L. Bolen, R. Colby, E A. Stach, Michael A. Capano

Birck and NCN Publications

Step-free SiC was thermally decomposed in vacuum to better understand graphene formation in the absence of step fronts. Atomic force microscopy revealed graphene nucleating at surface pits that preferentially form along SiC{1 $(1) over bar $ 00} planes. The density of these pits is 1 x 10(8)cm(-2), which is three orders of magnitude greater than the measured density of SiC threading dislocations. Additionally, Raman spectroscopy demonstrated that graphene on step-free regions have a redshifted 2D peak position and a smaller peak width than does graphene grown on stepped regions. This difference is attributed to film thickness, which is confirmed by …

The Significance Of In Situ Conditions In The Characterization Of Gasb Nanopatterned Surfaces Via Ion Beam Sputtering, Osman El-Atwani, Jean Paul, Alex Cimaroli, Anastassiya Suslova, Sami Ortoleva

Birck and NCN Publications

A systematic study is conducted in order to elucidate the underlying mechanism(s) for nanopatterning with low-energy irradiation of GaSb (100) under normal incidence. Ion energies between 50 and 1000 eV of Ar+ and ion fluences of up to 10(18) cm(-2) were employed. Characterization of the shallow (e.g., 1 to 6 nm) amorphous phase region induced by irradiation and the subsurface crystalline phase region is accomplished with low-energy ion scattering spectroscopy and x-ray photoelectron spectroscopy, respectively. In situ studies are conducted due to the strong chemical affinity for oxygen of GaSb. The studies conclude that at energies below 200 eV, the …

Laser Direct Write Of Silicon Nanowires, James Mitchell, Se Jun Park, C Adam Watson, Pornsak Srisungsitthisunti, Chookiat Tansarawiput, Minghao Qi, Eric Stach, Chen Yang, Xianfan Xu

Birck and NCN Publications

Using laser direct writing in combination with chemical vapor deposition to produce nanometer scale electronics holds several advantages over current large scale photolithography methods. These include single step electrical interconnect deposition, mask-less patterning, and parallel processing. When taken together they make quick production of individualized electronic circuits possible. This work demonstrates the ability of combining laser direct write and chemical vapor deposition to produce silicon wires a few hundred nanometers wide. Optimized parameters will be discussed, with a particular emphasis paid to the laser-material interactions. The feasibility for electronic applications will be shown by examining the deposition formation on a …

Role Of Ammonia In The Activiation Of Methanol Dehydrogenase/Cytochrome C(L) Enzyme, Ancy Kunjumon

Doctoral Dissertations

Recent advancement in enzyme catalysis has opened ways to design efficient biocatalysts, bio-sensors and bio-fuel cells. An in-depth knowledge about the mechanism of the reaction taking place within the enzymes is of great importance to achieve these goals. In this dissertation, various computation methods are applied to investigate the mechanism behind enzyme catalysis in the presence of compounds called activators.

Methanol dehydrogenase (MDH) is a well-known bio-catalyst that can oxidize excess of methanol from the environment to formaldehyde. The enzyme works well within the bacterial environment, but under in vitro, it loses activity. Ammonia is used as an activator …

Passive Micromixers And Organic Electrochemical Transistors For Biosensor Applications, Senaka Krishna Kanakamedala

Doctoral Dissertations

Fluid handling at the microscale has greatly affected different fields such as biomedical, pharmaceutical, biochemical engineering and environmental monitoring due to its reduced reagent consumption, portability, high throughput, lower hardware cost and shorter analysis time compared to large devices. The challenges associated with mixing of fluids in microscale enabled us in designing, simulating, fabricating and characterizing various micromixers on silicon and flexible polyester substrates. The mixing efficiency was evaluated by injecting the fluids through the two inlets and collecting the sample at outlet. The images collected from the microscope were analyzed, and the absorbance of the color product at the …

Thickness-Shear And Thickness-Twist Vibrations Of An At-Cut Quartz Mesa Resonator, Huijing He, Jinxi Liu, Jiashi Yang

Department of Mechanical and Materials Engineering: Faculty Publications

We study thickness-shear and thickness-twist vibrations of an AT-cut quartz plate mesa resonator with stepped thickness. The equations of anisotropic elasticity are used with the omission of the small elastic constant c56. An analytical solution is obtained using Fourier series from which the resonant frequencies, mode shapes, and energy trapping are calculated and examined. The solution shows that a mesa resonator exhibits strong energy trapping of thickness-shear and thickness-twist modes, and that the trapping is sensitive to some of the structural parameters of the resonator.

In Vivo Three-Dimensional Blood Velocity Profile Shapes In The Human Common, Internal, And External Carotid Arteries, Alexey Kamenskiy, Yuris A. Dzenis, Jason N. Mactaggart, Anastasia Desyatova, Iraklis I. Pipinos

Department of Mechanical and Materials Engineering: Faculty Publications

Objective: True understanding of carotid bifurcation pathophysiology requires a detailed knowledge of the hemodynamic conditions within the arteries. Data on carotid artery hemodynamics are usually based on simplified, computer-based, or in vitro experimental models, most of which assume that the velocity profiles are axially symmetric away from the carotid bulb. Modeling accuracy and, more importantly, our understanding of the pathophysiology of carotid bifurcation disease could be considerably improved by more precise knowledge of the in vivo flow properties within the human carotid artery. The purpose of this work was to determine the three-dimensional pulsatile velocity profiles of human carotid arteries. …

Ridge Aperture Antenna Array As A High Efficiency Coupler For Photovoltaic Applications, Edward C. Kinzel, Pornsak Srisungsitthisunti, Xianfan Xu

Birck and NCN Publications

Weak absorption of light near the absorption band edge of a photovoltaic material is one limiting factor on the efficiency of photovoltaics. This is particularly true for silicon thin-film solar cells because of the short optical path lengths and limited options for texturing the front and back surfaces. Directing light laterally is one way to increase the optical path length and absorption. We investigate the use of a periodic array of apertures originated from bowtie aperture antennas to couple incident light into guided modes supported within a thin silicon film. We show the presence of the aperture array can increase …

Isostaticity Of Constraints In Amorphous Jammed Systems Of Soft Frictionless Platonic Solids, Kyle C. Smith, Timothy Fisher, Meheboob Alam

Birck and NCN Publications

The average number of constraints per particle < C(total)> in mechanically stable amorphous systems of Platonic solids approaches the isostatic limit at the jamming point (< C(total)> -> 12), though average number of contacts are hypostatic. By introducing angular alignment metrics to classify the degree of constraint imposed by each contact, constraints are shown to arise as a direct result of local orientational order reflected in edge-face and face-face alignment angle distributions. With approximately one face-face contact per particle at jamming, chainlike face-face clusters form with finite extent-a signature of amorphous jammed systems.

Experimental And Atomistic Theoretical Study Of Degree Of Polarization From Multilayer Inas/Gaas Quantum Dot Stacks, Muhammad Usman, Tomoya Inoue, Yukihiro Harda, Gerhard Klimeck, Takashi Kita

Birck and NCN Publications

Recent experimental measurements, without any theoretical guidance, showed that isotropic po- larization response can be achieved by increasing the number of QD layers in a QD stack. Here we analyse the polarization response of multi-layer quantum dot stacks containing up to nine quan- tum dot layers by linearly polarized PL measurements and by carrying out a systematic set of multi-million atom simulations. The atomistic modeling and simulations allow us to include cor- rect symmetry properties in the calculations of the optical spectra: a factor critical to explain the experimental evidence. The values of the degree of polarization (DOP) calculated from …

Lifetime Enhanced Transport In Silicon Due To Spin And Valley Blockade, Gabriel Lansbergen, Rajib Rahman, J. Verdujin, Giuseppe Tettamanzi, Nadine Collaert, Serge Biesemans, Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge

Birck and NCN Publications

We report the observation of Lifetime Enhanced Transport (LET) based on perpendicular valleys in silicon by transport spectroscopy measurements of a two-electron system in a silicon transistor. The LET is manifested as a peculiar current step in the stability diagram due to a forbidden transition between an excited state and any of the lower energy states due perpendicular valley (and spin) configurations, offering an additional current path. By employing a detailed temperature dependence study in combination with a rate equation model, we estimate the lifetime of this particular state to exceed 48 ns. The two-electron spin-valley configurations of all relevant …

Quantitative Analysis Of The Disorder Broadening And The Intrinsic Gap For The V=5/2 Fractional Quantum Hall State, N. Samkharadze, J. D. Watson, G. Gardner, Michael J. Manfra, L. N. Pfeiffer, K. W. West, G. A. Csathy

Birck and NCN Publications

We report a reliable method to estimate the disorder broadening parameter from the scaling of the gaps of the even and major odd denominator fractional quantum Hall states of the second Landau level. We apply this technique to several samples of vastly different densities and grown in different molecular beam epitaxy chambers. Excellent agreement is found between the estimated intrinsic and numerically obtained energy gaps for the v = 5/2 fractional quantum Hall state. Furthermore, we quantify the dependence of the intrinsic gap at v = 5/2 on Landau-level mixing.

Nonlinear Thermal Transport And Negative Differential Thermal Conductance In Graphene Nanoribbons, Jiuning Hu, Yan Wang, Ajit Vallabhaneni, Xiulin Ruan, Yong P. Chen

Birck and NCN Publications

We employ classical molecular dynamics to study the nonlinear thermal transport in graphene nanoribbons (GNRs). For GNRs under large temperature biases beyond linear response regime, we have observed the onset of negative differential thermal conductance (NDTC). NDTC is tunable by varying the manner of applying the temperature biases. NDTC is reduced and eventually disappears when the length of the GNR increases. We have also observed NDTC in triangular GNRs, where NDTC exists only when the heat current is from the narrower to the wider end. These effects may be useful in nanoscale thermal managements and thermal signal processing utilizing GNRs. …

Strain Engineering Via Amorphization And Recrystallization In Si/Ge Heterostructures, Yumi Park, Winnie Tan, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics with the reactive potential ReaxFF to study strain relaxation during the amorphization and recrystallization of silicon-germanium epitaxial nanolaminates. Starting with a coherent heterostructure with (010) Si/Ge interfaces and 3D periodic boundary conditions, we use local heating and quenching to amorphize half of the simulation cell with crystal-amorphous interfaces normal to [001]. We find strain relaxation along [001] as the crystalline Ge section expands into the amorphous material and crystalline Si contracts from it. The amount of strain relaxation correlates with the atomic transport from the amorphized Ge to Si section and increases as the periodic width …

Amorphous Interface Layer In Thin Graphite Films Grown On The Carbon Face Of Sic, R. Colby, M. L. Bolen, Michael A. Capano, E. A. Stach

Birck and NCN Publications

Cross-sectional transmission electron microscopy (TEM) is used to characterize an amorphous layer observed at the interface in graphite and graphene films grown via thermal decomposition of C-face 4H-SiC. The amorphous layer does not cover the entire interface, but uniform contiguous regions span microns of cross-sectional interface. Scanning transmission electron microscopy (STEM) images and electron energy loss spectroscopy (EELS) demonstrate that the amorphous layer is a carbon-rich composition of Si/C. The amorphous layer is clearly observed in samples grown at 1600 degrees C for a range of growth pressures in argon, but not at 1500 degrees C, suggesting a temperature-dependent formation …

Design Of A Gainp/Gaas Tandem Solar Cell For Maximum Daily, Monthly, And Yearly Energy Output, Alexander W. Haas, John R. Wilcox, Jeffery L. Gray, Richard J. Schwartz

Birck and NCN Publications

Solar concentrator cells are typically designed for maximum efficiency under the AM1.5d standard spectrum. While this methodology does allow for a direct comparison of cells produced by various laboratories, it does not guarantee maximum daily, monthly, or yearly energy production, as the relative distribution of spectral energy changes throughout the day and year. It has been suggested that achieving this goal requires designing under a nonstandard spectrum. In this work, a GaInP/GaAs tandem solar cell is designed for maximum energy production by optimizing for a set of geographically-dependent solar spectra using detailed numerical models. The optimization procedure focuses on finding …

Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan

Birck and NCN Publications

We investigate the initial surface reaction pathways in the atomic layer deposition (ALD) of Al2O3 on GaAs (111)A and (111)B substrates using precursors trimethylaluminum (TMA) and water to ascertain the effect of surface orientation on device performance. We find that the condition of the respective substrates prior to deposition of TMA and water has a major impact on the surface reactions that follow and on the resulting interface structure. The simulations explain the atomistic mechanism of the interfacial self-cleaning effect in ALD that preferentially removes As oxides. The electronic structure of the resulting atomic configurations indicates states throughout the bandgap …

Synthesis And Characterization Of Highly Textured Pt–Bi Thin Films, Xingzhong Li, Parashu Kharel, Shah R. Valloppilly, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi2 phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi2 phase with a small amount of β-PtBi2 and α-PtBi2 phases. Both the PtBi and γ-PtBi2 phases are highly textured in these two kinds of film: the c-axis of …

Ferromagnetic Resonance On Ni Nanowire Arrays, Mircea Chipara, Ralph Skomski, Roger D. Kirby, David J. Sellmyer

Physics & Astronomy Faculty Publications

Ferromagnetic resonance investigations on Ni nanowires are reported. The angular dependence of the resonance line position is analyzed within a thermodynamic approach that includes shape anisotropy (ellipsoids of revolution), magnetocrystalline anisotropies (cubic and uniaxial), and dipole–dipole interactions. The results are supported by hysteresis loops, obtained on the same sample.

Rehabilitation And Exercise Machine, Judith M. Burnfield, Yu Shu, Adam P. Taylor, 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.

Study On The Fluorescent Carbon Nanodots With Electrochemical Methods, Bao-Ping Qi, Yan-Min Long, Lei Bao, Cui Liu, Zhi-Ling Zhang, Dai-Wen Pang

Journal of Electrochemistry

Carbon nanodots are a new class of fluorescent nanoparticles with a carbon-based core, which possess wavelength-tunable luminescence, high photostability, resistance to photobleaching, water-solubility, and ease of bioconjugation. Owing to their attractive merits, carbon nanodots like other carbon nanomaterials such as fullerene, carbon nanotubes and graphene, have attracted much attention. In addition, carbon nanodots can be inexpensively produced by electrochemical methods with simple post-processing under mild conditions. Electrochemical approaches have unique advantages in the analysis of surface structures and luminescence mechanism of materials. In this review, recent advances in electrochemical methods used for the synthesis and luminescence mechanism of fluorescent carbon …

Development Of Dehydrogenase-Based Bioanode Using Poly(Phenosafranin)-Functionalized Swcnt Nanocomposites And Its Application To Ethanol Biosensor, S. Saleh Farhana, Okajima Takeyoshi, Lanqun Mao, Takeo Ohsaka

Journal of Electrochemistry

A New type of dehydrogenase-based amperometric ethanol biosensor was constructed using alcohol dehydrogenase (ADH) which was immobilized on the edge-plane pyrolytic graphite (EPPG) electrode modified with poly(phenosafranin)-functionalized single-walled carbon nanotube (PPS-SWCNT). The PPS-SWCNT modified EPPG electrode was prepared by electropolymerization of phenosafranin on the EPPG electrode which was previously coated with SWCNT. The performance of the ADH/PPS-SWCNT/EPPG electrode was evaluated using cyclic voltammetry and amperometry in the presence of ethanol. The fabricated ethanol biosensor provided a reasonable sensitivity of 2.0 μA cm–2 mM–1 and a low detection limit (36 μM) for the electrocatalytic oxidation of ethanol with a linear concentration …