Condensed Matter Physics Commons^™

Reconfigurable Ferromagnetic Liquid Droplets, Xubo Liu, Noah Kent, Alejandro Ceballos, Robert Streubel, Yufeng Jiang, Yu Chai, Paul Y. Kim, Joe Forth, Frances Hellman, Shaowei Shi, Dong Wang, Brett A. Helms, Paul D. Ashby, Peter Fischer, Thomas P. Russell

Robert Streubel Papers

Solid ferromagnetic materials are rigid in shape and cannot be reconfigured. Ferrofluids, although reconfigurable, are paramagnetic at room temperature and lose their magnetization when the applied magnetic field is removed. Here, we show a reversible paramagnetic-to-ferromagnetic transformation of ferrofluid droplets by the jamming of a monolayer of magnetic nanoparticles assembled at the water-oil interface. These ferromagnetic liquid droplets exhibit a finite coercivity and remanent magnetization. They can be easily reconfigured into different shapes while preserving themagnetic properties of solid ferromagnets with classic north-south dipole interactions. Their translational and rotational motions can be actuated remotely and precisely by an external magnetic …

A Room-Temperature Ferroelectric Semimetal, Pankaj Sharma, Fei-Xiang Xiang, Ding-Fu Shao, Dawei Zhang, Evgeny Y. Tsymbal, Alex R. Hamilton, Jan Seidel

Evgeny Tsymbal Publications

Coexistence of reversible polar distortions and metallicity leading to a ferroelectric metal, first suggested by Anderson and Blount in 1965, has so far remained elusive. Electrically switchable intrinsic electric polarization, together with the direct observation of ferroelectric domains, has not yet been realized in a bulk crystalline metal, although incomplete screening by mobile conduction charges should, in principle, be possible. Here, we provide evidence that native metallicity and ferroelectricity coexist in bulk crystalline van der Waals WTe2 by means of electrical transport, nanoscale piezoresponse measurements, and first-principles calculations. We show that, despite being a Weyl semimetal, WTe2 has switchable spontaneous …

Usu Materials Physics Group Nasa Missions, Jr Dennison

Posters

No abstract provided.

Dielectric Function Tensor (1.5 Ev To 9.0 Ev), Anisotropy, And Band To Band Transitions Of Monoclinic Β-(AlXGa1–X)2O3 (X ≤ 0.21) Films, Matthew Hilfiker, Ufuk Kilic, Alyssa Mock, Vanya Darakchieva, Sean Knight, Rafal Korlacki, Akhil Mauze, Yuewei Zhang, James Speck, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

A set of monoclinic β-(Al_xGa_1–x)₂O₃ films coherently grown by plasma-assisted molecular beam epitaxy onto (010)-oriented β-Ga₂O₃ substrates for compositions x ≤ 0.21 is investigated by generalized spectroscopic ellipsometry at room temperature in the spectral range of 1.5 eV–9.0 eV. We present the composition dependence of the excitonic and band to band transition energy parameters using a previously described eigendielectric summation approach for β-Ga₂O₃ from the study by Mock et al. All energies shift to a shorter wavelength with the increasing Al content in …

Voltage Controlled Magnetism In Cr2o3 Based All-Thin-Film Systems, Junlei Wang, Will Echtenkamp, Ather Mahmood, Christian Binek

Christian Binek Publications

Voltage-control of exchange biases through active selection of distinct domain states of the magnetoelectric and antiferromagnetic pinning layer is demonstrated for Cr2O3/CoPd heterostructures. Progress and obstacles towards an isothermal switching of exchange bias are discussed. An alternative approach avoiding exchange bias for voltage-controlled memory exploits boundary magnetization at the surface of Cr2O3 as voltage-controlled state variable. We demonstrate readout and switching of boundary magnetization in ultra-thin Cr2O3/Pt Hall bar devices where reversal of boundary magnetization is achieved via magnetoelectric annealing with simultaneously applied ±0.5 V and 400 mT electric and magnetic fields.

New Heusler Compounds In Ni-Mn-In And Ni-Mn-Sn Alloys, Xingzhong Li, W.-Y. Zhang, Shah R. Valloppilly, David J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Rapidly quenched ternary Ni-Mn-T (T = In, Sn) alloys exhibit features associated with magnetic skyrmions, so that XRD, TEM, EDS, SAED and HREM investigations were carried out for structural characterization on the two alloy systems. In this paper, we report a new type of Mn-rich Heusler compound with a cubic unit cell, a = 0.9150 nm in Ni-Mn-In and a = 0.9051 nm in Ni-Mn-Sn, which coexist with a Ni-rich full-Heusler compound with defects, a = 0.6094 nm in Ni-Mn-In and a = 0.6034 nm in Ni-Mn-Sn. A further analysis of the experimental results reveals a close structural relationship between …

Magnetization Dynamics In Coupled Thin Film Systems, Daniel J. Adams

LSU New Orleans Theses and Dissertations

A study is presented detailing experimental investigations of magnetization dynamics in nanostructured systems which are coupled magnetically. This work seeks to characterize the anisotropy of such systems through experimental techniques which probe microwave resonant absorption in the materials.

A custom-built experimental setup, designed and assembled in our labs, is explained in detail. This setup allows for angular-dependent ferromagnetic resonance (FMR) measurements in the sample plane through vector network analyzer spectroscopy and is adaptable to two different types of coplanar waveguides. This technique has proven effective for characterization of multiple types of magnetic systems, including multilayered structures as detailed here, with …

Space-Charge Limited Conduction In Epitaxial Chromia Films Grown On Elemental And Oxide-Based Metallic Substrates, C.-P. Kwan, Mike Street, Ather Mahmood, Will Echtenkamp, M. Randle, K. He, J. Nathawat, N. Arabchigavkani, B. Barut, S. Yin, R. Dixit, Uttam Singisetti, Christian Binek, J. P. Bird

Christian Binek Publications

We study temperature dependent (200 – 400 K) dielectric current leakage in high-quality, epitaxial chromia films, synthesized on various conductive substrates (Pd, Pt and V2O3). We find that trap-assisted space-charge limited conduction is the dominant source of electrical leakage in the films, and that the density and distribution of charge traps within them is strongly dependent upon the choice of the underlying substrate. Pd-based chromia is found to exhibit leakage consistent with the presence of deep, discrete traps, a characteristic that is related to the known properties of twinning defects in the material. The Pt- and V2O3-based films, in contrast, …

Nonlinear Optical Studies Of Bulk And Thin Film Complex Materials, Joel E. Taylor

LSU Doctoral Dissertations

Nonlinear optical studies of bulk and thin film materials provide a vast playground for physical and dynamical characterization. In this thesis, we have implemented experimental methods to probe novel phase transitions in single crystals using rotational anisotropic second harmonic generation (RASHG) and carrier dynamics in thin films with time-resolved pump-probe reflectivity. Furthermore, a novel low temperature ultra-high vacuum system coupled to nonlinear optics has been developed to extend lab capabilities. Doping (Bi_1-xSb_x)₂Se₃ with antimony, the surface electronic reconstruction near x=80% was identified with RASHG by deviations in the six-fold and three-fold polarization anisotropic …

Nuclear Magnetic Resonance Characterization Of Dynamics In Novel Electrochemical Materials, Christopher T. Mallia

Theses and Dissertations

As our daily use of electronics and electronic technology grows, so does the societal need for sustainable, renewable and portable electrical power. To this end, materials of interest in the electrochemical world are needed to advance the frontier of battery science and energy storage technologies so that a safer, more efficient and reliable electrical future can be realized. This work focuses on characterization of materials primarily of interest for use as electrolytes in rechargeable Lithium-Ion Batteries (LIBs). Despite their extraordinary power, LIB application in certain fields, such as in electric vehicles, has been limited due to performance and safety concerns. …

Toward Devices For Exploring Pt-Symmetry In Electronic Transport Of Graphene, Michael Carovillano

Senior Honors Papers / Undergraduate Theses

Parity-time symmetry, or PT -symmetry is the principle that in quantum mechanics a non- Hermitian Hamiltonian is capable of returning real eigenstates and real spectra.Recent research has demonstrated real world observation of PT -symmetry in electronics and optics. We aim to expand the regime of observed PT -symmetry through measurement of the electronic transport of graphene devices. Drawing from analogous experiments, we plan to use balanced ohmic resistance acting as both loss and relative gain to induce the required unbroken PT -symmetry regime. This paper analyzes techniques used in fabrication of such devices as well as the basis of the …

Electron Yield Measurements Of Multilayer Conductive Materials, Gregory Wilson, Matthew Robertson, Jordan Lee, Jr Dennison

Conference Proceedings

As energetic electrons interact with the surface of materials, they impart energy throughout the material. If the energy exchange is near the surface, secondary electrons within the material can be excited and emitted. It is also possible for the incident primary electron to undergo a quasi-elastic collision within the material, wherein the electron is backscattered and emitted from the surface. As the backscattered electron is leaving the material, it can continue to impart energy to the material, potentially exciting more secondary electrons as it approaches the surface on the way back out.

This process of imparting energy and charge to …

Strategies For Determining Electron Yield Material Parameters For Spacecraft Charge Modeling, Phil Lundgreen, Jr Dennison

Conference Proceedings

Modeling of space plasma environment-induced anomalies requires knowledge of:

• Environment and impinging fluxes during spacecraft orbits, which are mission specific and can be incorporated through environmental models and databases.
• Satellite geometry and orientation in the space environment, accomplished through such charging codes as NASCAP-2K, SPENVIS, or MUSCAT.
• Materials used in spacecraft construction, from the specific spacecraft design.
• Relevant materials properties characterizing the interaction of the materials with the environment and how these properties may change with exposure to the space environment.

A reliable, comprehensive database of spacecraft materials and the characterization of those materials is being created in the form …

Suppresion Of Electron Yield With Carbon Nanotube Forests: A Case Study, Brian Wood, Jordan Lee, Gregory Wilson, T.-C. Shen, Jr Dennison

Conference Proceedings

Electron emission of carbon nanotube (CNT) forests grown on silicon substrates was measured to investigate possible electron yield suppression due to the composition and morphology of CNT forests. CNT forests are vertically-oriented tubular formations of graphitic carbon grown on a substrate; these have been widely investigated for their extreme properties in optical, electrical, and mechanical aspects of physics and material sciences. CNT coatings are good candidates for yield reduction, in analogy with the near-ideal blackbody optical properties of CNT forests. Carbon with its low atomic number has an inherent low yield due to its low density of bulk electrons. Furthermore, …

Influence Of Vibrationally-Induced Structural Changes On Carbon Nanotube Forests Suppression Of Electron Yield, Jordan Lee, Brian Wood, Gregory Wilson, T.-C. Shen, Jr Dennison

Conference Proceedings

Carbon nanotube (CNT) forest coatings have been found to lower electron yield from material surfaces. The suppressed yields have been attributed to both the lower inherent yields of low-atomic number carbon and the enhanced electron recapture resulting from the morphology of the carbon layer. To explore the relative contributions of these two causes of yield suppression, tests have been made on CNT forest-coated conducting substrate samples subjected to vibrationally-induced changes of the coating structure. The extent of vibrationally-induced structural changes—due, for example, to shear-force conditions during space-vehicle transit—are of interest, as CNT have been a frequent topic of scientific curiosity …

Exploring The Electrical Properties Of Twisted Bilayer Graphene, William Shannon

Senior Theses

Two-dimensional materials exhibit properties unlike anything else seen in conventional substances. Electrons in these materials are confined to move only in the plane. In order to explore the effects of these materials, we have built apparatus and refined procedures with which to create two-dimensional structures. Two-dimensional devices have been made using exfoliated graphene and placed on gold contacts. Their topography has been observed using Atomic Force Microscopy (AFM) confirming samples with monolayer, bilayer, and twisted bilayer structure. Relative work functions of each have been measured using Kelvin Probe Force Microscopy (KPFM) showing that twisted bilayer graphene has a surface potential …

Lithium Molybdate-Sulfur Battery., Ruchira Ravinath Dharmasena

Electronic Theses and Dissertations

Rechargeable energy storage systems play a vital role in today’s automobile industry with the emergence of electric vehicles (EVs). In order to meet the targets set by the department of energy (DOE), there is an immediate need of new battery chemistries with higher energy density than the current Li- ion technology. Lithium–sulfur (Li–S) batteries have attracted enormous attention in the energy-storage, due to their high specific energy density of 2600 Wh kg^-1 and operational voltage of 2.0 V. Despite the promising electrochemical characteristics, Li-S batteries suffer from serious technical challenges such as dissolution of polysulfides Li₂S_{x …}

2d Materials Based Heterostructures : A Lithography Free Method., Adel Alruqi

Electronic Theses and Dissertations

Many properties of Two-dimensional (2D) materials are vastly different from those of their 3D counterparts. A large family of 2D materials ranging from gapless graphene to metallic NbSe2 (also superconducting), semiconducting MoS2, and insulating hexagonal boron nitride (h-BN) possessing a broad range of exciting new properties have emerged in recent years. Moreover, 2D materials provide the perfect platform to create laterally and vertically stacked heterostructures with intriguing properties. The physics of 2D materials based heterostructures is extremely interesting and novel 2D-heterostructured devices including tunneling diodes, tunneling transistors, photovoltaic cells, and light-emitting diodes have started to emerge. In this work, we …

Super Rapid Crystal Growth And Quench Of Monoclinic Bi-Ii* During Dynamic Compression, Zachary Allen Fussell

UNLV Theses, Dissertations, Professional Papers, and Capstones

We show that monoclinic Bi-II* forms during a dynamic compression regime with crystal growth rates from melt of ≈ 70 m/s. This extreme quench rate implies crystallization by non-diffusive processes and indicates that the liquid had a high degree of pre-ordering. Using ambient condition single crystal structure analysis we show for the first time that the monoclinic distorted phase of Bi (Bi-II) exists at ambient pressure, albeit bound to formation under dynamic compression. We review the pressure, temperature, and time conditions for formation and growth of this structure.

High-Pressure High-Temperature Exploration Of Phase Boundaries Using Raman Spectroscopy, Jasmine Kashmir Hinton

UNLV Theses, Dissertations, Professional Papers, and Capstones

Metastability of states can provide interesting properties that may not be readily accessible in a material’s ground state. Many materials show high levels of polymorphism, indicating a rich energy landscape and a potential for metastable states. Melt crystallization techniques provide a potential route to these states. We use a resistively heated diamond anvil cell (DAC) with fine control of a system’s pressure and temperature to explore these systems. Raman spectroscopy is used to track subtle structural changes across phase boundaries. Organic systems, such as glycine and aspirin, were our initial interest due to their high polymorphism and reported low melting …