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Nebraska Center for Materials and Nanoscience: Faculty Publications
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- Electron diffraction (4)
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- Precession technique (1)
- Pt–Bi (1)
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- Rietveld method (1)
Articles 1 - 30 of 94
Full-Text Articles in Engineering
Large-Scale Solution Synthesis Of Narrow Graphene Nanoribbons, Timothy H. Vo, Mikhail Shekhirev, Donna A. Kunkel, Martha D. Morton, Eric Berglund, Lingmei Kong, Peter M. Wilson, Peter A. Dowben, Axel Enders, Alexander Sinitskii
Large-Scale Solution Synthesis Of Narrow Graphene Nanoribbons, Timothy H. Vo, Mikhail Shekhirev, Donna A. Kunkel, Martha D. Morton, Eric Berglund, Lingmei Kong, Peter M. Wilson, Peter A. Dowben, Axel Enders, Alexander Sinitskii
Nebraska Center for Materials and Nanoscience: Faculty Publications
According to theoretical studies, narrow graphene nanoribbons with atomically precise armchair edges and widths of(1.1 eV), which makes them potentially promising for logic applications. Different top–down fabrication approaches typically yield ribbons with width >10nm and have limited control over their edge structure. Here we demonstrate a novel bottom–up approach that yields gram quantities of high-aspect-ratio graphene nanoribbons, which are only ~1 nm wide and have atomically smooth armchair edges. These ribbons are shown to have a large electronic bandgap of ~1.3 eV, which is significantly higher than any value reported so far in experimental studies of graphene nanoribbons prepared by …
Synthesis And Characterization Of Highly Textured Pt–Bi Thin Films, Xingzhong Li, Parashu Kharel, Shah R. Valloppilly, David J. Sellmyer
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 …
Pced2.0—A Computer Program For The Simulation Of Polycrystalline Electron Diffraction Pattern, Xingzhong Li
Pced2.0—A Computer Program For The Simulation Of Polycrystalline Electron Diffraction Pattern, Xingzhong Li
Nebraska Center for Materials and Nanoscience: Faculty Publications
A computer program for the simulation of polycrystalline electron diffraction patterns is described. PCED2.0, an upgraded version of the previous JECP/PCED, can be used as a teaching aid and research tool for phase identification, microstructure texture analysis, and phase fraction determination. In addition to kinematical theory for diffraction intensity calculation of polycrystalline samples, Blackman two-beam dynamical correction is included. March model is used for out-of-plane and in-plane texture simulation. A pseudo-Voigt function is used for the peak profile fitting of diffraction rings. User-friendly interface is improved in the handling of experimental diffraction data and the flexibility of indexing. Application of …
Monoclinic Optical Constants, Birefringence, And Dichroism Of Slanted Titanium Nanocolumns Determined By Generalized Ellipsometry, Daniel Schmidt, Benjamin Booso, Tino Hofmann, Eva Schubert, Andrew Sarangan, Mathias Schubert
Monoclinic Optical Constants, Birefringence, And Dichroism Of Slanted Titanium Nanocolumns Determined By Generalized Ellipsometry, Daniel Schmidt, Benjamin Booso, Tino Hofmann, Eva Schubert, Andrew Sarangan, Mathias Schubert
Nebraska Center for Materials and Nanoscience: Faculty Publications
Generalized spectroscopic ellipsometry determines the principal monoclinic optical constants of thin films consisting of slanted titanium nanocolumns deposited by glancing angle deposition under 85° incidence and tilted from the surface normal by 47°. Form birefringence measured for wavelengths from 500 to 1000 nm renders the Ti nanocolumns monoclinic absorbing crystals with c-axis along the nanocolumns, b-axis parallel to the film interface, and 67.5° monoclinic angle between the a- and c-axes. The columnar thin film reveals anomalous optical dispersion, extreme birefringence, strong dichroism, and differs completely from bulk titanium. Characteristic bulk interband transitions are absent in the spectral range investigated.
Rapidly Solidified Sm–Co–V Nanocomposite Permanent Magnets, R. S. K. Valiveti, A. Ingmire, Jeffrey E. Shield
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 …
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
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 …
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
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.
Optical, Structural, And Magnetic Properties Of Cobalt Nanostructure Thin Films, D. Schmidt, A. C. Kjerstad, Tino Hofmann, Ralph Skomski, Eva Schubert, Mathias Schubert
Optical, Structural, And Magnetic Properties Of Cobalt Nanostructure Thin Films, D. Schmidt, A. C. Kjerstad, Tino Hofmann, Ralph Skomski, Eva Schubert, Mathias Schubert
Nebraska Center for Materials and Nanoscience: Faculty Publications
We report on optical, structural, and magnetic properties of two substantially different cobalt nanostructure thin films deposited at an oblique angle of incidence of 85° away from the substrate normal. Comparison is made between an achiral columnar thin film grown without substrate rotation and a chiral nanocoil sculptured thin film by glancing angle deposition with substrate rotation. Generalized spectroscopic ellipsometry is employed to determine geometrical structure properties and the anisotropic optical constants of the films in the spectral range from 400 to 1000 nm. The magnetic properties are analyzed with a superconducting quantum interference device magnetometer. Both nanostructure thin films …
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
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 …
Annealing Effects On The Optical Properties Of Semiconducting Boron Carbide, R. B. Billa, Tino Hofmann, Mathias Schubert, Brian W. Robertson
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.
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
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.
Structural Nanocomposites, Yuris A. Dzenis
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 …
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
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.
The Quest For Stronger, Tougher Materials: A Letter And A Response, Robert O. Ritchie, Yuris A. Dzenis
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 …
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
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.
Magnetism Of Laalo3/Srtio3 Superlattices, Karolina Janicka, Julian P. Velev, Evgeny Y. Tsymbal
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 …
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
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 …
Enhanced Blocking Temperature And Isothermal Control Of Hysteresis Loop Shifts In Co/Nio/[Co/Pt] Heterostructures With Orthogonal Easy Axes, A. Baruth, Shireen Adenwalla
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 …
Geometrical Interpretation And Simulation Of Holz Patterns, Xingzhong Li
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 …
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
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 …
Role Of Covalent Fe-As Bonding In The Magnetic Moment Formation And Exchange Mechanisms In Iron-Pnictide Superconductors, Kirill D. Belashchenko, Vladimir P. Antropov
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 …
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
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 …
Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Lmehrdad Negahban, Z. Li
Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Lmehrdad Negahban, Z. Li
Nebraska Center for Materials and Nanoscience: Faculty Publications
The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 µm) atop, respectively. It was found that both static …
Size Effect In Polymer Nanofibers Under Tension, Xiangfa Wu, Yuris A. Dzenis
Size Effect In Polymer Nanofibers Under Tension, Xiangfa Wu, Yuris A. Dzenis
Nebraska Center for Materials and Nanoscience: Faculty Publications
This article studies the size effect on the elastic behavior of solid and hollow polymer nanofibers (e.g., electrospun nanofibers) subjected to uniaxial tension. A one-dimensional nonlinear elastic tension model is proposed that takes into account the coupling effect of fiber elastic deformation and surface tension. The fiber axial force-displacement and stress-strain relations are obtained in explicit forms. It is shown that, at nanoscale, fiber radius has appreciable effect on the elastic response of polymer nanofibers. With consideration of the fiber radial effect, it is shown that the actual contribution of surface energy of the solid polymer fibers to the axial …
Novel Method For Mechanical Characterization Of Polymeric Nanofibers, Mohammad Naraghi, Loannis Chasiotis, Harold Kahn, Yongkui Wen, Yuris A. Dzenis
Novel Method For Mechanical Characterization Of Polymeric Nanofibers, Mohammad Naraghi, Loannis Chasiotis, Harold Kahn, Yongkui Wen, Yuris A. Dzenis
Nebraska Center for Materials and Nanoscience: Faculty Publications
A novel method to perform nanoscale mechanical characterization of highly deformable nanofibers has been developed. A microelectromechanical system (MEMS) test platform with an on-chip leaf-spring load cell that was tuned with the aid of a focused ion beam was built for fiber gripping and force measurement and it was actuated with an external piezoelectric transducer. Submicron scale tensile tests were performed in ambient conditions under an optical microscope. Engineering stresses and strains were obtained directly from images of the MEMS platform, by extracting the relative rigid body displacements of the device components by digital image correlation. The accuracy in determining …
Measurement Of Poisson’S Ratio With Contact-Resonance Atomic Force Microscopy, D.C. Hurley, Joseph A. Turner
Measurement Of Poisson’S Ratio With Contact-Resonance Atomic Force Microscopy, D.C. Hurley, Joseph A. Turner
Nebraska Center for Materials and Nanoscience: Faculty Publications
We describe contact-resonance atomic force microscopy (AFM) methods to quantitatively measure Poisson’s ratio ν or shear modulus G at the same time as Young’s modulus E. In contact-resonance AFM, the frequencies of the cantilever’s resonant vibrations are measured while the tip is in contact with the sample. Simultaneous measurement of flexural and torsional vibrational modes enables E and ν to be determined separately. Analysis methods are presented to relate the contact-resonance frequencies to the tip-sample contact stiffness, which in turn determines the sample’s nanoscale elastic properties. Experimental results are presented for a glass specimen with fused silica used as …
Effects Of Magnetostatic Coupling On Stripe Domain Structures In Magnetic Multilayers With Perpendicular Anisotropy, K. Janicka, John D. Burton, Evgeny Y. Tsymbal
Effects Of Magnetostatic Coupling On Stripe Domain Structures In Magnetic Multilayers With Perpendicular Anisotropy, K. Janicka, John D. Burton, Evgeny Y. Tsymbal
Nebraska Center for Materials and Nanoscience: Faculty Publications
We investigate the effects of magnetostatic interlayer coupling on the formation of magnetic domains in exchange-coupled ferromagnetic films exhibiting perpendicular magnetic anisotropy. Using simple models for the stripe domain structures we investigate how the magnetostatic interlayer interaction affects the domain size. For antiferromagnetically exchange-coupled multilayers, we show that there is a domain overlap due to the magnetostatic interaction which exists only above a critical thickness and below a critical separation between the ferromagnetic films where it is scaled inversely proportional to the antiferromagnetic exchange coupling constant. We show that the magnetostatic coupling is responsible for the periodic “tiger tail” domain …
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
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 cE1(TO) , cE1(LO) , and cE2 are determined. A distinct correlation between anisotropic strain and the A1(TO) and E1(LO) …
Interface Proximity Effects In Current-Perpendicular-To-Plane Magnetoresistance, R.J. Baxter, David G. Pettifor, Evgeny Y. Tsymbal
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 ARF/N* and γF/N, to be dependent on the layer thickness separating the two interfaces. This leads to a decrease in the measurable quantity SR=√(ARAP)(ARAP-ARP) with the Cu layer thickness and, therefore, …
Elasticity Of Planar Fiber Networks, X.-F. Wu, Yuris A. Dzenis
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) …