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Articles 3031 - 3060 of 3535

Full-Text Articles in Nanoscience and Nanotechnology

Materializing A Binary Hyperlens Design, Alexander V. Kildishev, Uday K. Chettiar, Zubin Jacob, V. M. Shalaev, Evgenii Narimanov Feb 2009

Materializing A Binary Hyperlens Design, Alexander V. Kildishev, Uday K. Chettiar, Zubin Jacob, V. M. Shalaev, Evgenii Narimanov

Birck and NCN Publications

We present a design of cylindrical hyperlens made of a layered binary material. The design approach uses an improved effective medium theory to take account of radius-dependent effects due to curvature of material interfaces resulting in nonperiodically distributed thicknesses of the lens layers. The performance of this lens is compared versus the designs with periodically thick layers, which we showed in earlier papers. Detailed quantitative results analyzed for the lenses with the same number and starting order of layers prove better functioning of the lens designed with this approach.

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Imaging Gold Nanorods By Plasmon-Resonance-Enhanced Four Wave Mixing, Yookyung Jung, Hongtao Chen, Ling Tong, Ji-Xin Cheng Feb 2009

Imaging Gold Nanorods By Plasmon-Resonance-Enhanced Four Wave Mixing, Yookyung Jung, Hongtao Chen, Ling Tong, Ji-Xin Cheng

Other Nanotechnology Publications

The current work investigates the four-wave mixing (FWM) signal from gold nanorods (NRs) using two synchronized lasers and its potential applications in bioimaging. Using the lightning rod model, we show that the strongest FWM occurs when the pump laser wavelength is tuned to be resonant with the longitudinal plasmon resonance wavelength of NR. The calculation is experimentally demonstrated by comparing the intensities of FWM from NRs with different plasmon resonance wavelengths. The FWM signal is further found to be enhanced by aggregation of NRs and is strongly dependent on pulse width. The FWM intensity from NRs is similar to 39 …

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Influence Of Dimensionality On Thermoelectric Device Performance, Raseong Kim, Supriyo Datta, Mark S. Lundstrom Feb 2009

Influence Of Dimensionality On Thermoelectric Device Performance, Raseong Kim, Supriyo Datta, Mark S. Lundstrom

Birck and NCN Publications

The role of dimensionality on the electronic performance of thermoelectric devices is clarified using the Landauer formalism, which shows that the thermoelectric coefficients are related to the transmission, T(E), and how the conducting channels, M(E), are distributed in energy. The Landauer formalism applies from the ballistic to diffusive limits and provides a clear way to compare performance in different dimensions. It also provides a physical interpretation of the "transport distribution," a quantity that arises in the Boltzmann transport equation approach. Quantitative comparison of thermoelectric coefficients in one, two, and three dimensions shows that the channels are utilized more effectively in …

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Valley Degeneracies In (111) Silicon Quantum Wells, Neerav Kharche, Seongmin Kim, Timothy B. Boykin, Gerhard Klimeck Jan 2009

Valley Degeneracies In (111) Silicon Quantum Wells, Neerav Kharche, Seongmin Kim, Timothy B. Boykin, Gerhard Klimeck

Birck and NCN Publications

(111) silicon quantum wells have been studied extensively, yet no convincing explanation exists for the experimentally observed breaking of sixfold valley degeneracy into two- and fourfold degeneracies. Here, systematic sp(3)d(5)s(*) tight-binding and effective mass calculations are presented to show that a typical miscut modulates the energy levels, which leads to breaking of sixfold valley degeneracy into two lower and four raised valleys. An effective mass based valley-projection model is used to determine the directions of valley minima in tight-binding calculations of large supercells. Tight-binding calculations are in better agreement with experiments compared to effective mass calculations.

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Nanometrology Device Standards For Scanning Probe Mmicroscopes And Processes For Their Fabrication And Use, Peter Moeck Jan 2009

Nanometrology Device Standards For Scanning Probe Mmicroscopes And Processes For Their Fabrication And Use, Peter Moeck

Physics Faculty Publications and Presentations

Nanometrology device standards and methods for fabricating and using such devices in conjunction With scanning probe microscopes are described. The fabrication methods comprise: (1) epitaxial growth that produces nanometer sized islands of knoWn morphology, structural, morphological and chemical stability in typical nanometrology environments, and large height-to-width nano-island aspect ratios, and (2) marking suitable crystallographic directions on the device for alignment With a scanning direction.

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Characterization Of A Viscoelastic Response From Thin Metal Films Deposited On Silicon For Microsystem Applications, Steven L. Meredith Jan 2009

Characterization Of A Viscoelastic Response From Thin Metal Films Deposited On Silicon For Microsystem Applications, Steven L. Meredith

Master's Theses

Understanding the mechanisms that control the mechanical behavior of microscale actuators is necessary to design an actuator that responds to an applied actuation force with the desired behavior. Micro actuators which employ a diaphragm supported by torsional hinges which deform during actuation are used in many applications where device stability and reliability are critical. The material response to the stress developed within the hinge during actuation controls how the actuator will respond to the actuating force. A fully recoverable non-linear viscoelastic response has been observed in electrostatically driven micro actuators employing torsional hinges of silicon covered with thin metal films. …

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Annealing Effects On The Optical Properties Of Semiconducting Boron Carbide, R. B. Billa, Tino Hofmann, Mathias Schubert, Brian W. Robertson Jan 2009

Annealing Effects On The Optical Properties Of Semiconducting Boron Carbide, R. B. Billa, Tino Hofmann, Mathias Schubert, Brian W. Robertson

Nebraska Center for Materials and Nanoscience: Faculty Publications

Infrared vibrations of as-deposited and annealed semiconducting boron carbide thin films were investigated by midinfrared spectroscopic ellipsometry. The strong boron-hydrogen resonance at ~2560 cm−1 in as-deposited films reveals considerable hydrogen incorporation during plasma-enhanced chemical vapor deposition. Extended annealing at 600 °C caused significant reduction in film thickness, substantial reduction of boron-hydrogen bond resonance absorption, and development of distinct blue-shifted boron-carbon and icosahedral vibration mode resonances. Our findings suggest that annealing results in substantial loss of hydrogen and in development of icosahedral structure, accompanied by strain relaxation and densification.

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Thermocapillary Effects In Driven Dewetting And Self-Assembly Of Pulsed Laser-Irradiated Metallic Films, Agegnehu Atena, Mikhail Khenner Jan 2009

Thermocapillary Effects In Driven Dewetting And Self-Assembly Of Pulsed Laser-Irradiated Metallic Films, Agegnehu Atena, Mikhail Khenner

Mathematics Faculty Publications

In this paper the lubrication-type dynamical model is developed of a molten, pulsed laser-irradiated metallic film. The heat transfer problem that incorporates the absorbed heat from a single beam or interfering beams is solved analytically. Using this temperature field, we derive the 3D long-wave evolution PDE for the film height. To get insights into dynamics of dewetting, we study the 2D version of the evolution equation by means of a linear stability analysis and by numerical simulations. The stabilizing and destabilizing effects of various system parameters, such as the peak laser beam intensity, the film optical thickness, the Biot and …

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Thermocapillary Effects In Driven Dewetting And Self-Assembly Of Pulsed Laser-Irradiated Metallic Films, Agegnehu Atena, Mikhail Khenner Jan 2009

Thermocapillary Effects In Driven Dewetting And Self-Assembly Of Pulsed Laser-Irradiated Metallic Films, Agegnehu Atena, Mikhail Khenner

Mathematics Faculty Publications

In this paper the lubrication-type dynamical model is developed of a molten, pulsed laser-irradiated metallic film. The heat transfer problem that incorporates the absorbed heat from a single beam or interfering beams is solved analytically. Using this temperature field, we derive the 3D long-wave evolution PDE for the film height. To get insights into dynamics of dewetting, we study the 2D version of the evolution equation by means of a linear stability analysis and by numerical simulations. The stabilizing and destabilizing effects of various system parameters, such as the peak laser beam intensity, the film optical thickness, the Biot and …

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One-Pot Synthesis Of Anionic (Nitrogen) And Cationic (Sulfur) Codoped High-Temperature Stable, Visible Light Active, Anatase Photocatalysts, Suresh Pillai, Declan Mccormack, Steven Hinder, Pradeepan Periyat Jan 2009

One-Pot Synthesis Of Anionic (Nitrogen) And Cationic (Sulfur) Codoped High-Temperature Stable, Visible Light Active, Anatase Photocatalysts, Suresh Pillai, Declan Mccormack, Steven Hinder, Pradeepan Periyat

Articles

No abstract provided.

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Electrical Properties Of Zno–Batio3–Zno Heterostructures With Asymmetric Interface Charge Distribution, V. M. Voora, Tino Hofmann, M. Brandt, M. Lorenz, N. Ashkenov, M. Grundmann, Mathias Schubert Jan 2009

Electrical Properties Of Zno–Batio3–Zno Heterostructures With Asymmetric Interface Charge Distribution, V. M. Voora, Tino Hofmann, M. Brandt, M. Lorenz, N. Ashkenov, M. Grundmann, Mathias Schubert

Nebraska Center for Materials and Nanoscience: Faculty Publications

We report on capacitance-voltage, current-voltage, Sawyer–Tower, and transient current switching measurements for a ZnO–BaTiO3–ZnO heterostructure deposited on (001) silicon by using pulsed laser deposition. The triple-layer structure reveals asymmetric capacitance- and current-voltage hysteresis and cycling-voltage dependent Sawyer–Tower polarization drift. We explain our findings by coupling of the ferroelectric (BaTiO3) and piezoelectric (ZnO) interface charges and parallel polarization orientation of the ZnO layers causing asymmetric space charge region formation under positive and negative bias. The transient current characteristics suggest use of this structure as nonvolatile memory device.

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Spin-Orbit Splittings In Si/Sige Quantum Wells: From Ideal Si Membranes To Realistic Hterostructures, M. Prada, G. Klimeck, R. Joynt Jan 2009

Spin-Orbit Splittings In Si/Sige Quantum Wells: From Ideal Si Membranes To Realistic Hterostructures, M. Prada, G. Klimeck, R. Joynt

Birck and NCN Publications

We present a calculation of the wavevector-dependent subband level splitting from spin-orbit coupling in Si/SiGe quantum wells. We first use the effective-mass approach, where the splittings are parameterized by separating contributions from the Rashba and Dresselhaus terms. We then determine the inversion asymmetry parameters by fitting tight-binding numerical results obtained using the quantitative nanoelectronic modeling tool, NEMO-3D. We describe the relevant coefficients as a function of applied electric field and well width in our numerical simulations. Symmetry arguments can also predict the behavior, and an extensive analysis is also presented in this work. Using vast computational resources, we treat alloy …

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Nano-Switch For Study Of Gold Contact Behavior, Adam Fruehling, Shijun Xiao, Minghao Qi, Kaushik Roy, Dimitrios Peroulis Jan 2009

Nano-Switch For Study Of Gold Contact Behavior, Adam Fruehling, Shijun Xiao, Minghao Qi, Kaushik Roy, Dimitrios Peroulis

Birck and NCN Publications

In this paper we present the fabrication and characterization of a new NEMS DC switch as a vehicle to characterize Au-to-Au contacts at nano-scale. The switch consists of a 1050-nm long, 200-nm wide and 50-nm thick cantilever gold beam. The measured on-state resistance values range from 83 Omega to 640 Omega and the actuation voltages from 4 V to 22 V. All measurements are conducted at a current of 1 mu A and the obtained values are in good qualitative agreement with traditional elastic-plastic contact models. The calculated switching time is 55 ns. Characterization of contacts at nano-scale will be …

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Stabilizing Nanostructured Materials By Coherent Nanotwins And Their Grain Boundary Triple Junction Drag, C Saldana, T G. Murthy, M R. Shankar, E A. Stach, S Chandrasekar Jan 2009

Stabilizing Nanostructured Materials By Coherent Nanotwins And Their Grain Boundary Triple Junction Drag, C Saldana, T G. Murthy, M R. Shankar, E A. Stach, S Chandrasekar

Birck and NCN Publications

The role of nanotwin lamellae in enhancing thermal stability of nanostructured materials is examined. Nanostructured copper with varying densities of twins was generated by controlling the deformation strain rate during severe plastic deformation at cryogenic temperatures. While the nanostructured materials produced under cryogenic conditions are characteristically unstable even at room temperatures, their stability is markedly improved when a dense dispersion of nanotwins is introduced. Observations of the role of nanotwins in pinning grain and subgrain structures suggest an interfacial engineering approach to enhancing the stability of nanostructured alloys.

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Identification Of Multiple Oscillation States Of Carbon Nanotube Tipped Cantilevers Interacting With Surfaces In Dynamic Atomic Force Microscopy, Mark Strus, Arvind Raman Jan 2009

Identification Of Multiple Oscillation States Of Carbon Nanotube Tipped Cantilevers Interacting With Surfaces In Dynamic Atomic Force Microscopy, Mark Strus, Arvind Raman

Birck and NCN Publications

Carbon nanotubes (CNTs) have gained increased interest in dynamic atomic force microscopy (dAFM) as sharp, flexible, conducting, nonreactive tips for high-resolution imaging, oxidation lithography, and electrostatic force microscopy. By means of theory and experiments we lay out a map of several distinct tapping mode AFM oscillation states for CNT tipped AFM cantilevers: namely, noncontact attractive regime oscillation, intermittent contact with CNT slipping or pinning, or permanent contact with the CNT in point or line contact with the surface while the cantilever oscillates with large amplitude. Each state represents fundamentally different origins of CNT-surface interactions, CNT tip-substrate dissipation, and phase contrast …

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Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg Jan 2009

Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg

Birck and NCN Publications

Adiabatic shuttling of single impurity bound electrons to gate-induced surface states in semiconductors has attracted much attention in recent times, mostly in the context of solid-state quantum computer architecture. A recent transport spectroscopy experiment for the first time was able to probe the Stark shifted spectrum of a single donor in silicon buried close to a gate. Here, we present the full theoretical model involving large-scale quantum mechanical simulations that was used to compute the Stark shifted donor states in order to interpret the experimental data. Use of atomistic tight-binding technique on a domain of over a million atoms helped …

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Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck Jan 2009

Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck

Birck and NCN Publications

An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors (FETs) in the presence of electron-phonon scattering. The Non-equilibrium Green's Function (NEGF) formalism is solved in a nearest-neighbor sp(3)d(5)s* tight-binding basis. The scattering self-energies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of …

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A Stochastic Collocation Approach To Bayesian Inference In Inverse Problems, Youssef Marzouk, Dongbin Xiu Jan 2009

A Stochastic Collocation Approach To Bayesian Inference In Inverse Problems, Youssef Marzouk, Dongbin Xiu

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

We present an efficient numerical strategy for the Bayesian solution of inverse problems. Stochastic collocation methods, based on generalized polynomial chaos (gPC), are used to construct a polynomial approximation of the forward solution over the support of the prior distribution. This approximation then defines a surrogate posterior probability density that can be evaluated repeatedly at minimal computational cost. The ability to simulate a large number of samples from the posterior distribution results in very accurate estimates of the inverse solution and its associated uncertainty. Combined with high accuracy of the gPC-based forward solver, the new algorithm can provide great efficiency …

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Coarse Grain Modeling Of Spall Failure In Molecular Crystals: Role Of Intra-Molecular Degrees Of Freedom, Karen Lynch, Alexander Thompson, Alejandro Strachan Jan 2009

Coarse Grain Modeling Of Spall Failure In Molecular Crystals: Role Of Intra-Molecular Degrees Of Freedom, Karen Lynch, Alexander Thompson, Alejandro Strachan

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

We use a recently developed thermodynamically accurate mesodynamical method (Strachan and Holian 2005 Phys. Rev. Lett. 94 014301) where groups of atoms are represented by mesoparticles to characterize the shock compression and dynamical failure (spall) of a model molecular crystal. We characterize how the temperature rise caused by the shockwave depends on the specific heat of the degrees of freedom (DoFs) internal to the mesoparticles (Cint) and the strength of the coupling between the internal DoFs and the mesoparticles. We find that the temperature of the shocked material decreases with increasing Cint and decreasing coupling and quantify these effects. Our …

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A Generalized Polynomial Chaos Based Ensemble Kalman Filter, Jia Li, Dongbin Xiu Jan 2009

A Generalized Polynomial Chaos Based Ensemble Kalman Filter, Jia Li, Dongbin Xiu

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

As one of the most adopted sequential data assimilation methods in many areas, especially those involving complex nonlinear dynamics, the ensemble Kalman filter (EnKF) has been under extensive investigation regarding its properties and efficiency. Compared to other variants of the Kalman filter (KF), EnKF is straightforward to implement, as it employs random ensembles to represent solution states. This, however, introduces sampling errors that affect the accuracy of EnKF in a negative manner. Though sampling errors can be easily reduced by using a large number of samples, in practice this is undesirable as each ensemble member is a solution of the …

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Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck Jan 2009

Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck

Birck and NCN Publications

Recent improvements to existing HPC codes NEMO 3-D and OMEN, combined with access to peta-scale computing resources, have enabled realistic device engineering simulations that were previously infeasible. NEMO 3-D can now simulate 1 billion atom systems, and, using 3D spatial decomposition, scale to 32768 cores. Simulation time for the band structure of an experimental P doped Si quantum computing device fell from 40 minutes to I minute. OMEN can perform fully quantum mechanical transport calculations for real-word UTB FETs on 147,456 cores in roughly 5 minutes. Both of these tools power simulation engines on the nanoHUB, giving the community access …

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Parallel Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Joseph C. Fogarty, Sagar A. Pandit, Ananth Y. Grama Jan 2009

Parallel Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Joseph C. Fogarty, Sagar A. Pandit, Ananth Y. Grama

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

No abstract provided.

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Gold Nanorods As Contrast Agents For Biological Imaging: Optical Properties, Surface Conjugation And Photothermal Effects, Ling Tong, Qingshan Wei, Alexander Wei, Ji-Xin Cheng Jan 2009

Gold Nanorods As Contrast Agents For Biological Imaging: Optical Properties, Surface Conjugation And Photothermal Effects, Ling Tong, Qingshan Wei, Alexander Wei, Ji-Xin Cheng

Other Nanotechnology Publications

Gold nanorods (NRs) have plasmon-resonant absorption and scattering in the near-infrared (NIR) region, making them attractive probes for in vitro and in vivo imaging. In the cellular environment, NRs can provide scattering contrast for darkfield microscopy, or emit a strong two-photon luminescence due to plasmon-enhanced two-photon absorption. NRs have also been employed in biomedical imaging modalities such as optical coherence tomography or photoacoustic tomography. Careful control over surface chemistry enhances the capacity of NRs as biological imaging agents by enabling cell-specific targeting, and by increasing their dispersion stability and circulation lifetimes. NRs can also efficiently convert optical energy into heat, …

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Influence Of Magnesium Nitrate On The Corrosion Performance Of Sol-Gel Coated Aa2024-T3 Aluminium Alloy, Rajath Varma, Brendan Duffy, John Cassidy Jan 2009

Influence Of Magnesium Nitrate On The Corrosion Performance Of Sol-Gel Coated Aa2024-T3 Aluminium Alloy, Rajath Varma, Brendan Duffy, John Cassidy

Articles

Traditional anti-corrosion technology has relied heavily on using reducible metal species, predominantly hexavalent chromium (Cr(VI)), for protecting reactive metal alloys such as aluminium which is extensively used in the aerospace sector. However, the impending changes in the use of Cr(VI) in Europe and the United States have forced aerospace manufacturers to examine alternative materials for protecting aluminium. One of the most promising alternatives being investigated are organosilane based sol-gels containing anticorrosion additives. In this work the anti-corrosion properties of magnesium (II) nitrate (Mg(NO3)2) as a inhibitor was investigated at different concentrations (0.1% - 1.0 wt %) in a methyltriethoxysilane (MTEOS) …

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Rapidly Solidified Sm–Co–V Nanocomposite Permanent Magnets, R. S. K. Valiveti, A. Ingmire, Jeffrey E. Shield Jan 2009

Rapidly Solidified Sm–Co–V Nanocomposite Permanent Magnets, R. S. K. Valiveti, A. Ingmire, Jeffrey E. Shield

Nebraska Center for Materials and Nanoscience: Faculty Publications

Alloys around the Sm–Co eutectic composition provide an opportunity to form two-phase nanocomposite permanent magnets consisting of nanoscale Co fibers embedded in Sm2Co17.While ternary alloying elements may refine the scale of the structure, they may also disrupt the eutectic growth and lead to the formation of primary Co. Thus, microstructural selection maps were constructed for conventionally solidified Sm–Co–V alloys. It was found that V additions enlarged the primary Sm2Co17-forming region and, at (Sm0.09Co0.91)97 V3, resulted in a eutectic structure. Upon rapid solidification, this alloy was …

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Free Electron Behavior In Inn: On The Role Of Dislocations And Surface Electron Accumulation, V. Darakchieva, Tino Hofmann, Mathias Schubert, B. E. Sernelius, B. Monemar, P. O. A. Persson, F. Giuliani, E. Alves, H. Lu, W. J. Schaff Jan 2009

Free Electron Behavior In Inn: On The Role Of Dislocations And Surface Electron Accumulation, V. Darakchieva, Tino Hofmann, Mathias Schubert, B. E. Sernelius, B. Monemar, P. O. A. Persson, F. Giuliani, E. Alves, H. Lu, W. J. Schaff

Nebraska Center for Materials and Nanoscience: Faculty Publications

The free electron behavior in InN is studied on the basis of decoupled bulk and surface accumulation electron densities in InN films measured by contactless optical Hall effect. It is shown that the variation in the bulk electron density with film thickness does not follow the models of free electrons generated by dislocation-associated nitrogen vacancies. This finding, further supported by transmission electron microscopy results, indicates the existence of a different thickness-dependent doping mechanism. Furthermore, we observe a noticeable dependence of the surface electron density on the bulk density, which can be exploited for tuning the surface charge in future InN …

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Hole Diffusion Profile In A P-P+ Silicon Homojunction Determined By Terahertz And Midinfrared Spectroscopic Ellipsometry, Tino Hofmann, C. M. Herzinger, T. E. Tiwald, John A. Woollam, Mathias Schubert Jan 2009

Hole Diffusion Profile In A P-P+ Silicon Homojunction Determined By Terahertz And Midinfrared Spectroscopic Ellipsometry, Tino Hofmann, C. M. Herzinger, T. E. Tiwald, John A. Woollam, Mathias Schubert

Nebraska Center for Materials and Nanoscience: Faculty Publications

The noncontact and nondestructive optical determination of spatial distributions of free-charge-carriers in low-doped semiconductor homo- and heterojunctions addresses fundamental physical properties of device related structures. For low-density free-charge-carriers, particularly for hole densities with their intrinsically lower mobility parameters than electron densities, optical characterization is a challenge. The carrier density plasma frequencies are located at long wavelength equivalents within the terahertz spectral region.

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Resistive Hysteresis And Interface Charge Coupling In Batio3-Zno Heterostructures, V. M. Voora, Tino Hofmann, M. Brandt, M. Lorenz, M. Grundmann, N. Ashkenov, Mathias Schubert Jan 2009

Resistive Hysteresis And Interface Charge Coupling In Batio3-Zno Heterostructures, V. M. Voora, Tino Hofmann, M. Brandt, M. Lorenz, M. Grundmann, N. Ashkenov, Mathias Schubert

Nebraska Center for Materials and Nanoscience: Faculty Publications

We report on temperature, time, and voltage dependent resistive hysteresis measurements of BaTiO3-ZnO heterostructures grown on (001) Si substrates by pulsed laser deposition. We observe a diodelike behavior and cycling-voltage dependent hysteresis formation under forward bias. We explain these effects with depletion layer formation between the ZnO and BaTiO3 layers, an additional barrier due to the spontaneous polarization of ZnO and the ferroelectric nature of BaTiO3. The disappearance of the resistive hysteresis above the ferroelectric-paraelectric phase transition temperature of BaTiO3 conformed that the hysteresis is related to the ferroelectricity of BaTiO3. Time …

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Computational Model For Predicting Nonlinear Viscoelastic Damage Evolution In Materials Subjected To Dynamic Loading, Flavio V. Souza, Yong-Rak Kim, George A. Gazonas, David H. Allen Jan 2009

Computational Model For Predicting Nonlinear Viscoelastic Damage Evolution In Materials Subjected To Dynamic Loading, Flavio V. Souza, Yong-Rak Kim, George A. Gazonas, David H. Allen

Department of Mechanical and Materials Engineering: Faculty Publications

Many inelastic solids accumulate numerous cracks before failure due to impact loading, thus rendering any exact solution of the IBVP untenable. It is therefore useful to construct computational models that can accurately predict the evolution of damage during actual impact/dynamic events in order to develop design tools for assessing performance characteristics. This paper presents a computational model for predicting the evolution of cracking in structures subjected to dynamic loading. Fracture is modeled via a nonlinear viscoelastic cohesive zone model. Two example problems are shown: one for model validation through comparison with a one-dimensional analytical solution for dynamic viscoelastic debonding, and …

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Precession Electron Diffraction And Its Advantages For Structural Fingerprinting In The Transmission Electron Microscope, Peter Moeck, Sergei Rouvimov Jan 2009

Precession Electron Diffraction And Its Advantages For Structural Fingerprinting In The Transmission Electron Microscope, Peter Moeck, Sergei Rouvimov

Physics Faculty Publications and Presentations

The foundations of precession electron diffraction in a transmission electron microscope are outlined. A brief illustration of the fact that laboratory-based powder X-ray diffraction fingerprinting is not feasible for nanocrystals is given. A procedure for structural fingerprinting of nanocrystals on the basis of structural data that can be extracted from precession electron diffraction spot patterns is proposed.

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