Condensed Matter Physics Commons^™

Finite-Size Scaling Of Flexoelectricity In Langmuir-Blodgett Polymer Thin Films, Shashi Poddar, Keith Foreman, Shireen Adenwalla, Stephen Ducharme

Stephen Ducharme Publications

The flexoelectric effect, which is a linear coupling between a strain gradient and electrical polarization, is a fundamental electromechanical property of all materials with potential for use in nanoscale devices, where strain gradients can be quite large. We report a study of the dependence of the flexoelectric response on thickness in ultrathin films of polar and non-polar polymers. The measurements of the flexoelectric response in non-polar polyethylene and the polar relaxor polymer polyvinylidene-co-trifluoroethylene-co-chlorofluoroethylene were made using a bent cantilever method and corrected for the contribution from the electrode oxide. The results show that the value of …

Ferroelectric Characterization And Growth Optimization Of Thermally Evaporated Vinylidene Fluoride Thin Films, Keith Foreman, N. Hong, C. Labedz, C. Shearer, Stephen Ducharme, Shireen Adenwalla

Shireen Adenwalla Papers

Organic thin films have numerous advantages over inorganics in device processing and price. The large polarization of the organic ferroelectric oligomer vinylidene fluoride (VDF) could prove useful for both device applications and the investigation of fundamental physical phenomena. A VDF oligomer thin film vacuum deposition process, such as thermal evaporation, preserves film and interface cleanliness, but is challenging, with successful deposition occurring only within a narrow parameter space. We report on the optimal deposition parameters for VDF oligomer thin films, refining the parameter space for successful deposition, resulting in a high yield of robust ferroelectric films. In particular, we investigate …

Electron Diffraction Study Of Cobalt-Rich Hf-Co, Xingzhong Li, Yunlong Jin, Jeffrey E. Shield, Ralph Skomski, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Intermetallic compounds having compositions from HfCo₄ to HfCo₈ were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr₂Co₁₁ phase in structure, has been observed in the samples with the composition ranges from HfCo₆ to HfCo₈. The phase, referred to as either Hf₂Co₁₁ or HfCo₇ phase in the literature, is actually one common phase, having a broad composition range and referred to as μ-phase in the present paper. In addition to the μ-phase, we …

The Space Survivability Test Chamber, Alex Souvall, Benjamin Russon, Brian Wood, Gregory Wilson, Jr Dennison

Posters

No abstract provided.

The First Calibration Of Sbf Using Multi-Conjugate Adaptive Optics, Zachary Gibson, Joseph B. Jenson, John P. Blakeslee, Mischa Schirmer

Presentations

We measured Surface Brightness FluctuaIons (SBF) in three galaxies, ESO137-G006, NGC 3309, and NGC 5128, using the GeMS MulI-Conjugate AdapIve OpIcs (MCAO) system on the Gemini South telescope. ESO137-G006 is located in the Norma Cluster, NGC 3309 is located in the Hydra Cluster, while NGC 5128, also known as Centaurus A, is a nearby galaxy with numerous other distance measurements, including Cepheids. These galaxies were observed as a path finder to establish the SBF technique using the MCAO system. The J and Ks-band images taken with MCAO were astrometrically corrected and combined using the THELI so_ware.1 This method allowed us …

Predictive Formula For Electron Penetration Depth Of Diverse Materials Over Large Energy Ranges, Anne C. Starley, Gregory Wilson, Lisa D. Montierth, Jr Dennison

Conference Proceedings

An empirical model that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous Slow Down Approximation (CSDA) for energy deposition in a material to develop a composite analytical formula which estimated the range from10 MeV with an uncertainty of200 materials which have tabulated range and inelastic mean free path data in the NIST ESTAR and …

Voltage Ramp-Rate Dependence Of Dc Breakdown In Polymeric Insulators: Physical Models Versus Data, Allen Andersen, Krysta Moser, Jr Dennison

Conference Proceedings

The standard handbook values for dielectric breakdown strength of necessity come from accelerated test methods. In some cases, the breakdown voltage may vary significantly with voltage ramp rates; therefore, a theoretical model for the ramp-rate dependence of breakdown is needed to extrapolate from realistic tests to long-duration material service lifetimes. Series of step-up to breakdown tests were performed for ramp rates from 0.5 to 500 V/s for biaxially-oriented polypropylene (BOPP), low density polyethylene (LDPE), and polyimide (PI) films. The data were fit with standard empirical methods, as well as two physics-based defect-driven models. Empirical models can be fit to a …

Space Environment Effects Of Ionizing Radiation On Seed Germination And Growth, Alexander Souvall, Jr Dennison, Takayuki Sakai, Yuta Takahashi, Midori Morikawa, Shusuke Okita, Akihiro Nagata, Toshihiro Kameda, Shaunda Wenger

Presentations

No abstract provided.

Thermal Effects On Spin Currents In Non-Local Metallic Spin Valves, Alex Hojem

Electronic Theses and Dissertations

The study of non-local spin valves (NLSVs) has recently proven to be a fertile area for both applied and fundamental research in nanomagnetism due to the unique ability to separate charge currents and spin currents. NLSVs may also prove essential for a new class of high-density hard disk read heads due to their favorable scalability. Recent studies have shown thermal effects created by high current densities play a significant role in the response of NLSVs. These thermal effects also provide the opportunity to create a pure spin current from thermal gradients via a mechanism call the spin dependent Seebeck effect …

An Improved Tight-Binding Model For Phosphorene, Kursti Delello

Honors Undergraduate Theses

The intent of this thesis is to improve upon previously proposed tight-binding models for one dimensional black phosphorus, or phosphorene. Previous models offer only a qualitative analysis of the band structure of phosphorene, and fail to fully realize critical elements in the electronic band structure necessary for transport calculations. In this work we propose an improved tight-binding model for phosphorene by including up to eight nearest-neighbor interactions. The efficacy of the model is verified by comparison with DFT-HSE06 calculations, and the anisotropy of the effective masses in the armchair and zigzag directions is considered.

Electronic Structure And Stability Of The Ch3Nh3Pbbr3 (001) Surface, Xin Huang, Tula R. Paudel, Peter A. Dowben, Shuai Dong, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The energetics and the electronic structure of methylammonium lead bromine (CH₃NH₃PbBr₃) perovskite (001) surfaces are studied based on density functional theory. By examining the surface grand potential, we predict that the CH₃NH₃Br-terminated (001) surface is energetically more favorable than the PbBr₂-terminated (001) surface, under thermodynamic equilibrium conditions of bulk CH₃NH₃PbBr₃. The electronic structure of each of these two different surface terminations retains some of the characteristics of the bulk, while new surface states are found near band edges which may affect the …

Band Structure And Spin Texture Of Bi2Se3 3D Ferromagnetic Metal Interface, Jia Zhang, Julian P. Velev, Xiaoqian Dang, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The spin-helical surface states in a three-dimensional topological insulator (TI), such as Bi₂Se₃, are predicted to have superior efficiency in converting charge current into spin polarization. This property is said to be responsible for the giant spin-orbit torques observed in ferromagnetic metal/TI structures. In this work, using first-principles and model tight-binding calculations, we investigate the interface between the topological insulator Bi₂Se₃ and 3d-transition ferromagnetic metals Ni and Co. We find that the difference in the work functions of the topological insulator and the ferromagnetic metals shift the topological surface states down about 0.5 …

Enhanced Tunneling Electroresistance In Ferroelectric Tunnel Junctions Due To The Reversible Metallization Of The Barrier, Xiaohui Liu, J. D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Realizing a large tunneling electroresistance (TER) effect is crucial for device application of ferroelectric tunnel junctions (FTJs). FTJs are typically composed of a thin ferroelectric layer sandwiched by two metallic electrodes, where TER generally results from the dependence of the effective tunneling barrier height on the ferroelectric polarization. Since the resistance depends exponentially not only on barrier height but also on barrier width, TER is expected to be greatly enhanced when one of the electrodes is a semiconductor where the depletion region near the interface can be controlled via ferroelectric polarization. To explore this possibility, we perform studies of SrRuO …

How Geometric Distortions Scatter Electronic Excitations In Conjugated Macromolecules: Towards Photoinduced Relaxation And Energy Transfer, Tian Shi

Wayne State University Dissertations

The exciton scattering (ES) approach has been developed to study electronic excitations in large branched conjugated molecules. It attributes excited states to standing waves in the quasi-one-dimensional system by assuming a quasi-particle picture of optical excitations. Tight binding models extend capability of the ES approach to investigate the exciton-phonon coupling.

The topological counting method plays a substantial role in constructing tight binding models. It depicts the ES equations as a topological intersection problem. Then, by applying the index theorem, we can get the total number of excited states, which is equal to the number of repeat units plus topological charges …

Electronic Transport In Two-Dimensional Systems In The Quantum Hall Regime, Vinicio Tarquini

Wayne State University Dissertations

The integer and the fractional quantum Hall effects are essential to the exploration of quantum matters characterized by topological phases. A quantum Hall system hosts one-dimensional (1D) chiral edge channels that manifest zero magnetoresistance, dissipationless due to the broken time reversal symmetry, and quantized Hall resistance v h e^2 with v being the topological invariant (or Chern number). The 1-1 correspondence between the conducting gapless edge channels to the gapped incompressible bulk states is a defining character of a topological insulator (TI). Understanding this correspondence in real systems, especially the origin of its robustness (in terms of the limit of …

Phase Separation In Lufeo3 Films, Shi Cao, Xiaozhe Zhang, Kishan Sinha, Wenbin Wang, Jian Wang, Peter A. Dowben, Xiaoshan Xu

Peter Dowben Publications

The structural transition at about 1000°C, from the hexagonal to the orthorhombic phase of LuFeO₃, has been investigated in thin films of LuFeO₃. Separation of the two structural phases of LuFeO₃ occurs on a length scale of micrometer, as visualized in real space using X-ray photoemission electron microscopy. The results are consistent with X-ray diffraction and atomic force microscopy obtained from LuFeO₃ thin films undergoing the irreversible structural transition from the hexagonal to the orthorhombic phase of LuFeO₃, at elevated temperatures. The sharp phase boundaries between the structural phases are observed to …

Influence Of Steric Hindrance On The Molecular Packing And The Anchoring Of Quinonoid Zwitterions On Gold Surfaces, Minghui Yuan, Iori Tababe, Jean-Marie Bernard- Schaaf, Qin-Yin Shi, Vicki Schlegel, Rachel Schurhammer, Peter A. Dowben, Bernard Doudin, Lucie Routaboul, Pierre Braunstein

Peter Dowben Publications

Driven by the huge potential of engineering the molecular band offset with highly dipolar molecules for improving charge injection into organic electrics, the anchoring of various N-alkyl substituted quinonoid zwitterions of formula C₆H₂ (···NHR)₂ (···O)₂ (R = iPr, Cy, CH₂CH(Et)CH₂CH₂CH₂CH₃,. . .) on gold surfaces is studied. The N–Au interactions result in an orthogonal arrangement of the zwitterions cores with respect to the surface, and stabilize adsorbed compact rows of molecules. IR spectroscopy is used as a straightforward diagnostic tool to validate the presence of …

Fabrication Of Diisopropylammonium Bromide Aligned Microcrystals With In-Plane Uniaxial Polarization, Shashi Poddar, Haidong Lu, Jingfeng Song, Om Goit, Shah Valloppilly, Alexei Gruverman, Stephen Ducharme

Stephen Ducharme Publications

Textured arrays of ferroelectric microcrystals of diisopropylammonium bromide were grown from solution at room temperature onto silicon substrates and studied by means of x-ray diffraction, atomic force microscopy, electron microscopy, and piezoresponse force microscopy. The needle-shaped crystals had dimensions of approximately 50 μm × 5 μm in the plane and were approximately 200 nm thick, where the dimensions and arrangement were influenced by growth conditions. The observations suggest an Ostwald ripening mechanism of the microcrystal growth. The crystals had the structure of the ferroelectric phase, where the polarization axis was in-plane and parallel to the long axis of …

The Effect Of Impurities On The Superconductivity Of Bscco-2212, John Vastola

Honors Undergraduate Theses

BSCCO-2212 is a high-temperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with s-wave or d-wave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with d-wave behavior. We present some calculations using the many-body theory approach to superconductivity that suggest that such order parameters would lead to a suppression of the critical temperature in the presence of impurities. Because some experiments have suggested the critical temperature of BSCCO-2212 is relatively independent of the concentration of impurities, this lends …

Multiferroicity In Iron Vanadate, Magnetite And Polyvinylidene Fluoride Nanocomposite Films, Ehab Hamdy Abdelmonaim Abdelhamid

Wayne State University Dissertations

With the increasing demand on cheaper and better performance multifunctional materials for different applications, it is becoming more crucial to have a better understanding of the physics needed to tailor more devices and materials to fit better in every day’s technological needs. Materials which show more than one ferroic order simultaneously –namely, multiferroics– are of particular importance for their potential applications as multiple state memory elements, transducers and electrically tunable microwave devices.

In this work, we studied FeVO4 single crystals as an example on low symmetry multiferroics. We focused on the anisotropy in those crystals in an attempt to nail …