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2008

University of Nebraska - Lincoln

Articles 1 - 13 of 13

Full-Text Articles in Nanoscience and Nanotechnology

Structural Nanocomposites, Yuris A. Dzenis Nov 2008

Structural Nanocomposites, Yuris A. Dzenis

Nebraska Center for Materials and Nanoscience: Faculty Publications

Materials scientists predict that composites made with nanoscale reinforcing materials such as nanotubes, platelets, and nanofibers will have exceptional mechanical properties. However, the results obtained so far are disappointing, particularly when compared to advanced composites reinforced with high-performance continuous fibers (1–4). The reasons include inadequate dispersion and alignment of the nanoreinforcement, low nanoreinforcement volume fraction, and poor bonding and load transfer at interfaces. Intensive work is under way, but the prospect of bulk structural supernanocomposites appears more remote now than it did just a few years ago. However, recent work shows that some applications in reinforcement of small structures may …

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Surface Magnetoelectric Effect In Ferromagnetic Metal Films, Chun-Gang Duan, Julian P. Velev, Renat F. Sabirianov, Ziqiang Zhu, Junhao Chu, Sitaram Jaswal, Evgeny Y. Tsymbal Sep 2008

Surface Magnetoelectric Effect In Ferromagnetic Metal Films, Chun-Gang Duan, Julian P. Velev, Renat F. Sabirianov, Ziqiang Zhu, Junhao Chu, Sitaram Jaswal, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

A surface magnetoelectric effect is revealed by density-functional calculations that are applied to ferromagnetic Fe(001), Ni(001), and Co(0001) films in the presence of an external electric field. The effect originates from spin-dependent screening of the electric field which leads to notable changes in the surface magnetization and the surface magnetocrystalline anisotropy. These results are of considerable interest in the area of electrically controlled magnetism and magnetoelectric phenomena.

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The Quest For Stronger, Tougher Materials: A Letter And A Response, Robert O. Ritchie, Yuris A. Dzenis Apr 2008

The Quest For Stronger, Tougher Materials: A Letter And A Response, Robert O. Ritchie, Yuris A. Dzenis

Nebraska Center for Materials and Nanoscience: Faculty Publications

Dr. Ritchie writes: "The perspective “Structural Nanocomposites” (Y. Dzenis, 25 January, p. 419) describes a quest for improved structural materials and indicates that composites with nanoscale reinforcements would have “exceptional mechanical properties.” Is this true?

Why would reinforcements that are small in size or volume offer any particular benefit over larger-scale reinforcements? As the Perspective correctly asserts, if the composite material is to be used for a small-volume structure, clearly the reinforcements must also be small. In addition, small-volume reinforcements are stronger, as has been known since the early days of research on whiskers (1). In this regard, reinforcement by …

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Interfaces, Volume 10, Issue 1 - Spring 2008 Apr 2008

Interfaces, Volume 10, Issue 1 - Spring 2008

INTERFACES: Newsletter of the Nebraska Center for Materials and Nanoscience

CONTENTS
From the Director
Facility Focus: Nano-Fabrication Facility
Recent Achievements of Center Researchers
Magnetic Nanoclusters Put in Order – Insights with Scanning Tunneling Microscopy
NCMN Welcomes Eva Franke Schubert
Research Spotlight: Barry Cheung
UNL Hosts 54th Annual Midwest Solid State Conference
Published Books
Engineers Part of $9 Million Project Studying Cell Context of Genes

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Tailoring Magnetic Anisotropy At The Ferromagnetic/Ferroelectric Interface, Chun-Gang Duan, Julian P. Velev, Renat F. Sabirianov, Wai-Ning Mei, Sitaram Jaswal, Evgeny Y. Tsymbal Mar 2008

Tailoring Magnetic Anisotropy At The Ferromagnetic/Ferroelectric Interface, Chun-Gang Duan, Julian P. Velev, Renat F. Sabirianov, Wai-Ning Mei, Sitaram Jaswal, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

It is predicted that magnetic anisotropy of a thin magnetic film may be affected by the polarization of a ferroelectric material. Using a Fe/BaTiO3 bilayer as a representative model and performing first-principles calculations, we demonstrate that a reversal of the electric polarization of BaTiO3 produces a sizable change in magnetic anisotropy energy of Fe films. Tailoring the magnetic anisotropy of a nanomagnet by an adjacent ferroelectric material may yield entirely new device concepts, such as electric-field controlled magnetic data storage.

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Magnetism Of Laalo3/Srtio3 Superlattices, Karolina Janicka, Julian P. Velev, Evgeny Y. Tsymbal Jan 2008

Magnetism Of Laalo3/Srtio3 Superlattices, Karolina Janicka, Julian P. Velev, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

First-principles electronic structure calculations are performed to elucidate magnetic properties of LaAlO3 /SrTiO3 heterostructures. We find that TiO2-terminated interfaces are n-type conducting which is consistent with experimental observations. In a (LaAlO3 ) 3 / (SrTiO3)3 superlattice, this interface is magnetic with a magnetic moment on the Ti3+ atom of 0.2 μB, as revealed by the spin-polarized calculations within the local density approximation (LDA). For thicker SrTiO3 layers the magnetic moment decreases and eventually disappears because the electron gas spreads over more than one unit cell, making the …

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Effects Of Ferroelectricity And Magnetism On Electron And Spin Transport In Fe/Batio3 /Fe Multiferroic Tunnel Junctions, Julian P. Velev, Chun-Gang Duan, Kirill D. Belashchenko, Sitaram Jaswal, Evgeny Y. Tsymbal Jan 2008

Effects Of Ferroelectricity And Magnetism On Electron And Spin Transport In Fe/Batio3 /Fe Multiferroic Tunnel Junctions, Julian P. Velev, Chun-Gang Duan, Kirill D. Belashchenko, Sitaram Jaswal, Evgeny Y. Tsymbal

Nebraska Center for Materials and Nanoscience: Faculty Publications

First principles electronic structure and transport calculations are used to demonstrate the impact of the electric polarization on electron and spin transport in Fe/BaTiO3/Fe multiferroic tunnel junctions (MFTJs). We find that the polarization of BaTiO3 reduces the tunneling conductance, as compared to a nonpolarized barrier, due to the change in the electronic structure driven by ferroelectric displacements, similar to that found previously for Pt/BaTiO3/Pt. For the MFTJ, however, this effect has different magnitudes for majority- and minority-spin channels and for parallel and antiparallel orientations of the magnetization of the electrodes. As a result, we find …

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Enhanced Blocking Temperature And Isothermal Control Of Hysteresis Loop Shifts In Co/Nio/[Co/Pt] Heterostructures With Orthogonal Easy Axes, A. Baruth, Shireen Adenwalla Jan 2008

Enhanced Blocking Temperature And Isothermal Control Of Hysteresis Loop Shifts In Co/Nio/[Co/Pt] Heterostructures With Orthogonal Easy Axes, A. Baruth, Shireen Adenwalla

Nebraska Center for Materials and Nanoscience: Faculty Publications

Heterostructures of Co 4 nm/NiO 1.1 nm/[Co 0.4 nm/Pt 0.6 nm] with mutually orthogonal easy axes allow for isothermal tuning of the hysteresis loop shifts along the applied field axis at room temperature, as well as displaying a greatly enhanced blocking temperature. The loop shifts can be varied up to 35 Oe through the application of moderate dc magnetic fields of 3 kOe. The presence of the [Co/Pt] multilayer with perpendicular anisotropy is responsible for a significant enhancement of the blocking temperature. For this thickness of NiO, the blocking temperature is expected to be well below 50 K, in contrast …

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Geometrical Interpretation And Simulation Of Holz Patterns, Xingzhong Li Jan 2008

Geometrical Interpretation And Simulation Of Holz Patterns, Xingzhong Li

Nebraska Center for Materials and Nanoscience: Faculty Publications

Higher-order Laue zone (HOLZ) pattern is very useful in measurement of crystalline lattice parameters, strain and composition variation in a small area of sample. Bloch dynamical theory on convergent-beam electron diffraction (CBED), including the formation of HOLZ lines, has been well developed and documented in Ref. and references therein. Although CBED patterns and included HOLZ lines are best modeled using a dynamical formulation, models based on a geometrical interpretation for the HOLZ-line positions have remained in widespread use because of their simplicity. Moreover, the geometrical interpretation is helpful to understand the formation of HOLZ lines for beginners. The geometrical interpretation …

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Polaron And Phonon Properties In Proton Intercalated Amorphous Tungsten Oxide Thin Films, M. Saenger, T. Hoing, Brian W. Robertson, R. Billa, Tino Hofmann, Eva Schubert, Mathias Schubert Jan 2008

Polaron And Phonon Properties In Proton Intercalated Amorphous Tungsten Oxide Thin Films, M. Saenger, T. Hoing, Brian W. Robertson, R. Billa, Tino Hofmann, Eva Schubert, Mathias Schubert

Nebraska Center for Materials and Nanoscience: Faculty Publications

We report on the evolution of the polaron and phonon mode properties in amorphous tungsten oxide thin films measured by spectroscopic ellipsometry in the infrared to ultraviolet spectral regions as a function of the intercalated proton density. A parametric physical model dielectric function is presented, which excellently describes the ellipsometry data over a large intercalated charge-density range. Upon increased amounts of intercalated charge we observe a strong increase in the polaron absorption in the visible spectral range, a decrease in the infrared W–O bond polarity, and an increase in the W=O bond polarity. Our findings support the oxygen-extraction model as …

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Role Of Covalent Fe-As Bonding In The Magnetic Moment Formation And Exchange Mechanisms In Iron-Pnictide Superconductors, Kirill D. Belashchenko, Vladimir P. Antropov Jan 2008

Role Of Covalent Fe-As Bonding In The Magnetic Moment Formation And Exchange Mechanisms In Iron-Pnictide Superconductors, Kirill D. Belashchenko, Vladimir P. Antropov

Nebraska Center for Materials and Nanoscience: Faculty Publications

The electronic origin of the huge magnetostructural effect in layered Fe-As compounds is elucidated using LiFeAs as a prototype. The crucial feature of these materials is the strong covalent bonding between Fe and As, which tends to suppress the exchange splitting. The bonding-antibonding splitting is very sensitive to the distance between Fe and As nuclei. We argue that the fragile interplay between bonding and magnetism is universal for this family of compounds. The exchange interaction is analyzed in real space, along with its correlation with covalency and doping. The range of interaction and itinerancy increase as the Fe-As distance is …

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A Low-Temperature Specific Heat Study Of Giant Dielectric Constant Materials, C. P. Sun, Jianjun Liu, J.-Y. Lin, Chun-Gang Duan, Wao-Ning Mei, H. D. Yang Jan 2008

A Low-Temperature Specific Heat Study Of Giant Dielectric Constant Materials, C. P. Sun, Jianjun Liu, J.-Y. Lin, Chun-Gang Duan, Wao-Ning Mei, H. D. Yang

Nebraska Center for Materials and Nanoscience: Faculty Publications

A low-temperature specific heat study has been performed on the insulating giant dielectric constant material CaCu3Ti4O12 and two related compounds, Bi2/3Cu3Ti4O12 and La0.5Na0.5Cu3Ti4O12, from 0.6 to 10 K. From analyzing the specific heat data in a very low-temperature range, 0.6–1.5 K, and moderately low-temperature range, 1.5–5 K, in addition to the expected Debye terms, we observed significant contributions originating from the linear and Einstein terms, which we attributed as the manifestation of low-lying elementary excitations due to lattice …

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Control Of The Nanoscale Crystallinity And Phase Separation In Polymer Solar Cells, Chih-Wei Chu, Hoichang Yang, Wei-Jen Hou, Jinsong Huang, Gang Li, Yang Yang Jan 2008

Control Of The Nanoscale Crystallinity And Phase Separation In Polymer Solar Cells, Chih-Wei Chu, Hoichang Yang, Wei-Jen Hou, Jinsong Huang, Gang Li, Yang Yang

Department of Mechanical and Materials Engineering: Faculty Publications

Grazing-incidence x-ray diffraction and atomic force microscopy were performed on bulk heterojunction regioregular poly(3-hexylthiophene) (RR-P3HT) [6,6]-phenyl-C71-butyric acid methyl esters spin-cast films with different film processing conditions to correlate the crystalline nanostructure of P3HT with the corresponding solar cell performance. The increase in long wavelength absorption for solvent annealed films is related to highly conjugated crystal structure of RR-P3HT phase-separated in the active layer. Upon thermal annealing, the solvent annealed 50-nm-thick device shows high solar cell performance with fill factor up to 73% and power conversion efficiency of 3.80%.

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