Open Access. Powered by Scholars. Published by Universities.®

Condensed Matter Physics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Engineering

2020

Institution
Keyword
Publication
Publication Type

Articles 1 - 30 of 30

Full-Text Articles in Condensed Matter Physics

Ultrafast Spin-Currents And Charge Conversion At 3d-5d Interfaces Probed By Time-Domain Terahertz Spectroscopy, T. H. Dang, J. Hawecker, E. Rongione, G. Baez Flores, D. Q. To, J. C. Rojas-Sanchez, H. Nong, J. Mangeney, J. Tignon, F. Godel, S. Collin, P. Seneor, M. Bibes, A. Fert, M. Anane, J. M. George, L. Vila, M. Cosset-Cheneau, D. Dolfi, R. Lebrun, P. Bortolotti, Kirill Belashchenko, S. Dhillon, H. Jaffrès Dec 2020

Ultrafast Spin-Currents And Charge Conversion At 3d-5d Interfaces Probed By Time-Domain Terahertz Spectroscopy, T. H. Dang, J. Hawecker, E. Rongione, G. Baez Flores, D. Q. To, J. C. Rojas-Sanchez, H. Nong, J. Mangeney, J. Tignon, F. Godel, S. Collin, P. Seneor, M. Bibes, A. Fert, M. Anane, J. M. George, L. Vila, M. Cosset-Cheneau, D. Dolfi, R. Lebrun, P. Bortolotti, Kirill Belashchenko, S. Dhillon, H. Jaffrès

Kirill Belashchenko Publications

Spintronic structures are extensively investigated for their spin-orbit torque properties, required for magnetic commutation functionalities. Current progress in these materials is dependent on the interface engineering for the optimization of spin transmission. Here, we advance the analysis of ultrafast spin-charge conversion phenomena at ferromagnetic-Transition metal interfaces due to their inverse spin-Hall effect properties. In particular, the intrinsic inverse spin-Hall effect of Pt-based systems and extrinsic inverse spin-Hall effect of Au:W and Au:Ta in NiFe/Au:(W,Ta) bilayers are investigated. The spin-charge conversion is probed by complementary techniques-ultrafast THz time-domain spectroscopy in the dynamic regime for THz pulse emission and ferromagnetic resonance spin-pumping …

Go to article

Static And Dynamical Properties Of Multiferroics, Sayed Omid Sayedaghaee Dec 2020

Static And Dynamical Properties Of Multiferroics, Sayed Omid Sayedaghaee

Graduate Theses and Dissertations

Since the silicon industrial revolution in the 1950s, a lot of effort was dedicated to the research and development activities focused on material and solid-state sciences. As a result, several cutting-edge technologies are emerging including the applications of functional materials in the design and enhancement of novel devices such as sensors, highly capable data storage media, actuators, transducers, and several other types of electronic tools. In the last two decades, a class of functional materials known as multiferroics has captured significant attention because of providing a huge potential for new designs due to possessing multiple ferroic order parameters at the …

Go to article

Proximity-Induced Magnetization In Graphene: Towards Efficient Spin Gating, Mihovil Bosnar, Ivor Lončarić, P. Lazić, Kirill Belashchenko, Igor Žutić Nov 2020

Proximity-Induced Magnetization In Graphene: Towards Efficient Spin Gating, Mihovil Bosnar, Ivor Lončarić, P. Lazić, Kirill Belashchenko, Igor Žutić

Kirill Belashchenko Publications

Gate-tunable spin-dependent properties could be induced in graphene at room temperature through the magnetic proximity effect by placing it in contact with a metallic ferromagnet. Because strong chemical bonding with the metallic substrate makes gating ineffective, an intervening passivation layer is needed. Previously considered passivation layers result in a large shift of the Dirac point away from the Fermi level, so that unrealistically large gate fields are required to tune the spin polarization in graphene (Gr). We show that a monolayer of Au or Pt used as the passivation layer between Co and graphene brings the Dirac point closer to …

Go to article

Adsorption And Reconfiguration Of Amphiphiles At Silica-Water Interfaces: Role Of Electrostatic Interactions, Van Der Waals Forces And Hydrogen Bonds, Yao Wu Nov 2020

Adsorption And Reconfiguration Of Amphiphiles At Silica-Water Interfaces: Role Of Electrostatic Interactions, Van Der Waals Forces And Hydrogen Bonds, Yao Wu

LSU Doctoral Dissertations

The ability to explore and predict metastable structures of hybrid self-assemblies is of central importance for the next generation of advanced materials with novel properties. As compared to their thermodynamically stable forms, the kinetically stabilized materials show improved functionality potentially over their stable counterparts. The self-assembly processes usually originate from weak intermolecular interactions, involving a dynamic competition between attractive and repulsive interactions. These weak forces, including van der Waals (vdW), electrostatic interaction and the hydrogen bonding (H-bonding), can be tuned by external stimuli, e.g., confinement, temperature and ionization, and consequently driving hybrid materials into different configurations. It is challenging to …

Go to article

Detection Of Uncompensated Magnetization At The Interface Of An Epitaxial Antiferromagnetic Insulator, Pavel N. Lapa, Min Han Lee, Igor V. Roshchin, Kirill Belashchenko, Ivan K. Schuller Nov 2020

Detection Of Uncompensated Magnetization At The Interface Of An Epitaxial Antiferromagnetic Insulator, Pavel N. Lapa, Min Han Lee, Igor V. Roshchin, Kirill Belashchenko, Ivan K. Schuller

Kirill Belashchenko Publications

We have probed directly the temperature and magnetic field dependence of pinned uncompensated magnetization at the interface of antiferromagnetic FeF2 with Cu, using FeF2-Cu-Co spin valves. Electrons polarized by the Co layer are scattered by the pinned uncompensated moments at the FeF2-Cu interface giving rise to giant magnetoresistance. We determined the direction and magnitude of the pinned uncompensated magnetization at different magnetic fields and temperatures using the angular dependencies of resistance. The strong FeF2 anisotropy pins the uncompensated magnetization along the easy axis independent of the cooling field orientation. Most interestingly, magnetic fields as …

Go to article

Organic-Inorganic Halide Perovskite Nanocrystals And Solar Cells, Rui Guo Nov 2020

Organic-Inorganic Halide Perovskite Nanocrystals And Solar Cells, Rui Guo

FIU Electronic Theses and Dissertations

A great challenge facing humanity in the 21st century is finding inexhaustible and inexpensive energy sources to power the planet. Renewable energies are the best solutions because of their abundance, diversity, and pollution-free emission. Solar energy is the cleanest and most abundant renewable energy source available. In the continuing quest for efficient and low-cost solar cells, perovskite solar cells (PSCs) have emerged as a potential replacement for silicon solar cells. Since 2009, the record efficiencies of PSCs have been skyrocketing from 3.8 % to 25.2 % and are now approaching the theoretical limit. Along with the three-dimensional perovskites used …

Go to article

Strain And Stress Relationships For Optical Phonon Modes In Monoclinic Crystals With Β-Ga2O3 As An Example, Rafal Korlacki, Megan Stokey, Alyssa Lynn Mock, Sean Knight, Alexis Papamichail, Vanya Darakchieva, Mathias Schubert Nov 2020

Strain And Stress Relationships For Optical Phonon Modes In Monoclinic Crystals With Β-Ga2O3 As An Example, Rafal Korlacki, Megan Stokey, Alyssa Lynn Mock, Sean Knight, Alexis Papamichail, Vanya Darakchieva, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

Strain-stress relationships for physical properties are of interest for heteroepitaxial material systems, where strain and stress are inherent due to thermal expansion and lattice mismatch. We report linear perturbation theory strain and stress relationships for optical phonon modes in monoclinic crystals for strain and stress situations which maintain the monoclinic symmetry of the crystal. By using symmetry group analysis and phonon frequencies obtained under various deformation scenarios from density-functional perturbation theory calculations on β-Ga2O3, we obtain four strain and four stress potential parameters for each phonon mode. We demonstrate that these parameters are sufficient to …

Go to article

Reinvestigation Of The Intrinsic Magnetic Properties Of (Fe1-Xcox)2b Alloys And Crystallization Behavior Of Ribbons, Tej Nath Lamichhane, Olena Palasyuk, Vladimir P. Antropov, Ivan A. Zhuravlev, Kirill Belashchenko, Ikenna C. Nlebedim, Kevin W. Dennis, Anton Jesche, Matthew J. Kramer, Sergey L. Bud'ko, R. William Mccallum, Paul C. Canfield, Valentin Taufour Nov 2020

Reinvestigation Of The Intrinsic Magnetic Properties Of (Fe1-Xcox)2b Alloys And Crystallization Behavior Of Ribbons, Tej Nath Lamichhane, Olena Palasyuk, Vladimir P. Antropov, Ivan A. Zhuravlev, Kirill Belashchenko, Ikenna C. Nlebedim, Kevin W. Dennis, Anton Jesche, Matthew J. Kramer, Sergey L. Bud'ko, R. William Mccallum, Paul C. Canfield, Valentin Taufour

Kirill Belashchenko Publications

New determination of the magnetic anisotropy from single crystals of (Fe1-xCox)2B alloys are presented. The anomalous temperature dependence of the anisotropy constant is discussed using the standard Callen-Callen theory, which is shown to be insufficient to explain the experimental results. A more material specific study using first-principles calculations with disordered moments approach gives a much more consistent interpretation of the experimental data. Since the intrinsic properties of the alloys with x=0.3-0.35 are promising for permanent magnets applications, initial investigation of the extrinsic properties are described, in particular the crystallization of melt spun ribbons with Cu, Al, …

Go to article

Electronic And Local Structures Of Pt-Based Bimetallic Alloy And Core-Shell Systems, Jiatang Chen Aug 2020

Electronic And Local Structures Of Pt-Based Bimetallic Alloy And Core-Shell Systems, Jiatang Chen

Electronic Thesis and Dissertation Repository

This thesis investigates the electronic structure of Pt for catalysis applications. The importance of the Pt 5d band is discussed in terms of the bonding capability of Pt. The oxygen reduction reaction in proton exchange membrane fuel cells is chosen as the catalytic reaction model to illustrate the effect of Pt 5d states on Pt-O interaction. Pt-based bimetallic systems are introduced as a solution for the high price and limited resources of Pt. Despite lower usage of Pt, the tuning capability to optimize the Pt 5d band in bimetallic catalysts is supposed to provide superior catalytic activity. Advanced synchrotron X-ray …

Go to article

Brillouin Zone Center Phonon Modes In Znga2O4, Megan Stokey, Rafal Korlacki, Sean Knight, Matthew J. Hilfiker, Zbigniew Galazka, Klaus Irmscher, Vanya Darakchieva, Mathias Schubert Aug 2020

Brillouin Zone Center Phonon Modes In Znga2O4, Megan Stokey, Rafal Korlacki, Sean Knight, Matthew J. Hilfiker, Zbigniew Galazka, Klaus Irmscher, Vanya Darakchieva, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

Infrared-active lattice mode properties of melt-grown high-quality single bulk crystals of ZnGa2O4 are investigated by combined spectroscopic ellipsometry and density functional theory computation analysis. The normal spinel structure crystals are measured by spectroscopic ellipsometry at room temperature in the range of 100 cm–1–1200 cm–1. The complex-valued dielectric function is determined from a wavenumber-by-wavenumber approach, which is then analyzed by the four-parameter semi-quantum model dielectric function approach augmented by impurity mode contributions. We determine four infrared-active transverse and longitudinal optical mode pairs, five localized impurity mode pairs, and the high frequency dielectric constant. All …

Go to article

Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight Aug 2020

Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

In this dissertation, optical Hall effect (OHE) measurements are used to determine the free charge carrier properties of important two-dimensional materials and monoclinic oxides. Two-dimensional material systems have proven useful in high-frequency electronic devices due to their unique properties, such as high mobility, which arise from their two-dimensional nature. Monoclinic oxides exhibit many desirable characteristics, for example low-crystal symmetry which could lead to anisotropic carrier properties. Here, single-crystal monoclinic gallium oxide, an AlInN/GaN-based high-electron-mobility transistor (HEMT) structure, and epitaxial graphene are studied as examples. To characterize these material systems, the OHE measurement technique is employed. The OHE is a physical …

Go to article

Kinetics Of The Crystal-Melt Phase Transformation In Semicrystalline Polymers, Kiran Subramaniam Iyer Jul 2020

Kinetics Of The Crystal-Melt Phase Transformation In Semicrystalline Polymers, Kiran Subramaniam Iyer

Doctoral Dissertations

The assembly of long-chain polymers into an ordered state is a process that has puzzled polymer scientists for several decades. A process that is largely controlled by the strength of intermolecular attractions in small molecular systems, this crystallization in the case of polymers is controlled by a competition between the aforementioned force of attraction between monomers and the formidable conformational entropy of polymer chains. Any factor that affects this conformational entropy, whether that is an equilibrium thermodynamic factor or a kinetic factor, has the ability to control polymer crystallization. In this thesis, we focus on understanding the underlying kinetic processes …

Go to article

Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey Jun 2020

Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey

Publications and Research

La(Fe,Si)13–based compounds are considered to be very promising magnetocaloric materials for magnetic refrigeration applications. Many studies have focused on this material family but only in bulk form. In this paper we report on the fabrication of thick films of La(Fe,Si)13, both with and without post-hydriding. These films exhibit magnetic and structural properties comparable to bulk materials. We also observe that the ferromagnetic phase transition has a negative thermal hysteresis, a phenomenon not previously found in this material but which may have its origins in the availability of a strain energy reservoir, as in the cases of …

Go to article

Modeling Single Microtubules As A Colloidal System To Measure The Harmonic Interactions Between Tubulin Dimers In Bovine Brain Derived Versus Cancer Cell Derived Microtubules, Arooj Aslam May 2020

Modeling Single Microtubules As A Colloidal System To Measure The Harmonic Interactions Between Tubulin Dimers In Bovine Brain Derived Versus Cancer Cell Derived Microtubules, Arooj Aslam

Dissertations

The local properties of tubulin dimers dictate the properties of the larger microtubule assembly. In order to elucidate this connection, tubulin-tubulin interactions are be modeled as harmonic interactions to map the stiffness matrix along the length of the microtubule. The strength of the interactions are measured by imaging and tracking the movement of segments along the microtubule over time, and then performing a fourier transform to extract the natural vibrational frequencies. Using this method the first ever reported experimental phonon spectrum of the microtubule is reported. This method can also be applied to other biological materials, and opens new doors …

Go to article

First-Principles Studies Of Anion Engineering In Functional Ceramics, Steven Timothy Hartman May 2020

First-Principles Studies Of Anion Engineering In Functional Ceramics, Steven Timothy Hartman

McKelvey School of Engineering Theses & Dissertations

Ceramic materials display a wide variety of valuable properties, such as ferroelectricity, superconductivity, and magnetic ordering, due to the partially covalent bonds which connect the cations and anions. While many breakthroughs have been made by mixing multiple cations on a sublattice, the equivalent mixed-anion ceramics have not received nearly as much attention, despite the key role the anion plays in the materials’ properties. There is great potential for functional ceramics design using anion engineering, which aims to tune the materials properties by adding and removing different types of anions in existing classes of ceramic materials. In this dissertation, I present …

Go to article

Applied-Force Oscillations In Avalanche Dynamics, Louis W. Mcfaul, Gregory Sparks, Jordan Sickle, Jonathan T. Uhl, Wendelin J. Wright, Robert Maass, Karin A. Dahmen May 2020

Applied-Force Oscillations In Avalanche Dynamics, Louis W. Mcfaul, Gregory Sparks, Jordan Sickle, Jonathan T. Uhl, Wendelin J. Wright, Robert Maass, Karin A. Dahmen

Faculty Journal Articles

Until now most studies of discrete plasticity have focused on systems that are assumed to be driven by a monotonically increasing force; in many real systems, however, the driving force includes damped oscillations or oscillations induced by the propagation of discrete events or “slip avalanches.” In both cases, these oscillations may obscure the true dynamics. Here we effectively consider both cases by investigating the effects of damped oscillations in the external driving force on avalanche dynamics. We compare model simulations of slip avalanches under mean-field dynamics with observations in slip-avalanche experiments on slowly compressed micrometer-sized Au specimens using open-loop force …

Go to article

Mid-Ir Optical Refrigeration And Radiation Balanced Lasers, Saeid Rostami Apr 2020

Mid-Ir Optical Refrigeration And Radiation Balanced Lasers, Saeid Rostami

Optical Science and Engineering ETDs

This dissertation reports recent advances in mid-infrared (mid-IR) optical refrigeration and Radiation Balanced Lasers (RBLs). The first demonstration of optical refrigeration in Ho:YLF and Tm:YLF crystals as promising mid-IR laser cooling candidates is reported. Room temperature laser cooling efficiency of Tm- and Ho-doped crystals at different excitation polarization is measured and their external quantum efficiency and background absorption are extracted. Complete characterization of laser cooling samples is obtained via performing detailed low-temperature spectroscopic analysis, and their minimum achievable temperature as well as conditions to achieve laser cooling efficiency enhancement in mid-IR are investigated. By developing a Thulium-doped fiber amplifier, seeded …

Go to article

Growth And Characterization Of 2d Layered Materials, Algene Fryer Ii Apr 2020

Growth And Characterization Of 2d Layered Materials, Algene Fryer Ii

USF Tampa Graduate Theses and Dissertations

2D layered materials are becoming an important area of research due to their exceptional electrical and optical properties. Specifically, 2D layered monochalcogenides are known for their high carrier motilities, whereas layered metal halides have been shown to have noteworthy photoresponsivity. Despite the assortment of 2D layered materials, the search for reliable and scalable synthesis methods is still a challenge in this family of materials. Often a certain growth technique will compromise a desirable trait needed for further fabrication, such as the quality of the crystal or its coverage on a substrate. In this study, two growth techniques that incorporate changeable …

Go to article

Questaal: A Package Of Electronic Structure Methods Based On The Linear Muffin-Tin Orbital Technique, Dimitar Pashov, Swagata Acharya, Walter R.L. Lambrecht, Jerome Jackson, Kirill Belashchenko, Athanasios Chantis, Francois Jamet, Mark Van Schilfgaarde Apr 2020

Questaal: A Package Of Electronic Structure Methods Based On The Linear Muffin-Tin Orbital Technique, Dimitar Pashov, Swagata Acharya, Walter R.L. Lambrecht, Jerome Jackson, Kirill Belashchenko, Athanasios Chantis, Francois Jamet, Mark Van Schilfgaarde

Kirill Belashchenko Publications

This paper summarises the theory and functionality behind Questaal, an open-source suite of codes for calculating the electronic structure and related properties of materials from first principles. The formalism of the linearised muffin-tin orbital (LMTO) method is revisited in detail and developed further by the introduction of short-ranged tight-binding basis functions for full-potential calculations. The LMTO method is presented in both Green's function and wave function formulations for bulk and layered systems. The suite's full-potential LMTO code uses a sophisticated basis and augmentation method that allows an efficient and precise solution to the band problem at different levels of theory, …

Go to article

Infrared-Active Phonon Modes In Single-Crystal Thorium Dioxide And Uranium Dioxide, Sean Knight, Rafal Korlacki, Christina Dugan, James C. Petrosky, Alyssa Lynn Mock, Peter A. Dowben, J. Matthew Mann, Martin M. Kimani, Mathias Schubert Mar 2020

Infrared-Active Phonon Modes In Single-Crystal Thorium Dioxide And Uranium Dioxide, Sean Knight, Rafal Korlacki, Christina Dugan, James C. Petrosky, Alyssa Lynn Mock, Peter A. Dowben, J. Matthew Mann, Martin M. Kimani, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

The infrared-active phonon modes, in single-crystal samples of thorium dioxide (ThO2) and uranium dioxide (UO2), were investigated using spectroscopic ellipsometry and compared with density functional theory. Both ThO2 and UO2 are found to have one infrared-active phonon mode pair [consisting of one transverse optic (TO) and one associated longitudinal optic (LO) mode], which is responsible for the dominant features in the ellipsometric data. At room temperature, our results for the mode pair’s resonant frequencies and broadening parameters are comparable with previous reflectance spectroscopy characterizations and density functional theory predictions. For ThO2, our …

Go to article

Effects Of Intrinsic Defects And Alloying With Fe On The Half-Metallicity Of Co2Mnsi, G. G. Baez Flores, Ivan A. Zhuravlev, Kirill Belashchenko Feb 2020

Effects Of Intrinsic Defects And Alloying With Fe On The Half-Metallicity Of Co2Mnsi, G. G. Baez Flores, Ivan A. Zhuravlev, Kirill Belashchenko

Kirill Belashchenko Publications

The electronic structure and half-metallic gap of Co2MnSi in the presence of crystallographic defects, partial Fe substitution for Mn, and thermal spin fluctuations are studied using the coherent potential approximation and the disordered local moment method. In the presence of 5% Co or Mn vacancies the Fermi level shifts down to the minority-spin valence-band maximum. In contrast to NiMnSb, both types of Mn antisite defects in Co2MnSi are strongly exchange coupled to the host magnetization, and thermal spin fluctuations do not strongly affect the half-metallic gap. Partial substitution of Mn by Fe results in considerable changes in the Bloch spectral …

Go to article

Defect-Free Plastic Deformation Through Dimensionality Reduction And Self-Annihilation Of Topological Defects In Crystalline Solids, Yipeng Gao, Yongfeng Zhang, Larry K. Aagesen, Jianguo Yu, Min Long, Yunzhi Wang Feb 2020

Defect-Free Plastic Deformation Through Dimensionality Reduction And Self-Annihilation Of Topological Defects In Crystalline Solids, Yipeng Gao, Yongfeng Zhang, Larry K. Aagesen, Jianguo Yu, Min Long, Yunzhi Wang

Computer Science Faculty Publications and Presentations

As a signature of symmetry-breaking processes, the generation and annihilation of topological defects (domain walls, strings, etc.) are of great interest in condensed matter physics and cosmology. Here we propose a distinctive self-organization process through phase transitions, in which all the generated topological defects are dimensionality reduced and self-annihilated. In crystalline solids, such a unique mechanism allows a perfect single crystal after plastic deformation, which originates from the coupling of different types of broken symmetries.

Go to article

Ii-Vi Type-Ii Quantum Dot Superlattices For Novel Applications, Vasilios Deligiannakis Feb 2020

Ii-Vi Type-Ii Quantum Dot Superlattices For Novel Applications, Vasilios Deligiannakis

Dissertations, Theses, and Capstone Projects

In this thesis, we discuss the growth procedure and the characterization results obtained for epitaxially grown submonolayer type-II quantum dot superlattices made of II-VI semiconductors. We have investigated the spin dynamics of ZnSe layers with embedded type-II ZnTe quantum dots and the use of (Zn)CdTe/ZnCdSe QDs for intermediate band solar cell (IBSC). Samples with a higher quantum dot density exhibit longer electron spin lifetimes, up to ~1 ns at low temperatures. Tellurium isoelectronic centers, which form in the ZnSe spacer regions as a result of the growth conditions, were also probed. A new growth sequence for type-II (Zn)CdTe/ZnCdSe (QDs) was …

Go to article

Development Of Software Tools And Experimental In Situ Electron Spin Resonance For Characterizing The Magnetic And Electrocatalytic Properties Of Transition Metal Chalcogenide Crystals, Jose Armando Delgado Jan 2020

Development Of Software Tools And Experimental In Situ Electron Spin Resonance For Characterizing The Magnetic And Electrocatalytic Properties Of Transition Metal Chalcogenide Crystals, Jose Armando Delgado

Open Access Theses & Dissertations

Studying the magnetic properties and crystal defects of transition metal chalcogenide crystals is of paramount importance for utilizing them for next generation spintronics devices and hydrogen evolution reaction catalysts. Hydrothermally grown transition metal chalcogenide nanocrystals (MoS2, Ru2S3, Rh2S3, Co2S8) were chosen as catalysts for the hydrogen evolution reaction due to their low dimensionality and previous utilization as catalysts for hydrodesulfurization. The relationship between crystal defect sites and catalytic activity must be discerned to maximize the efficiency of hydrogen production during the hydrogen evolution reaction. ESR spectroscopy was utilized as a spin sensitive technique to study the defects and local changes …

Go to article

Magnetism In Γ-Fesi2 Nanostructures: A First Principles Study, Sahil Dhoka Jan 2020

Magnetism In Γ-Fesi2 Nanostructures: A First Principles Study, Sahil Dhoka

Dissertations, Master's Theses and Master's Reports

First-principles calculations are performed on γ-FeSi2 nanostructures grown on Si (111) and (001) substrate. An attempt to explain the origin of emergent magnetic properties of the metastable gamma phase of iron di-silicide (γ-FeSi2) is made, which show ferromagnetic behavior on nanoscale, unlike its possible bulk form. Many papers try to explain this magnetism from factors like bulk, epitaxial strain, interface, surface, edges, and corners but doesn’t provide an analytical study for these explanations. Density functional theory is used to analyze the magnetic effects of these factors. The results for the epitaxial structures show no magnetic behavior for …

Go to article

The Synthesis Of Pb2sr2sm1-Xcaxcu3o8 And Characterization Of Its Structural And Superconducting Properties., Deblina Das Jan 2020

The Synthesis Of Pb2sr2sm1-Xcaxcu3o8 And Characterization Of Its Structural And Superconducting Properties., Deblina Das

Graduate Research Theses & Dissertations

Superconducting lead-based cuprate materials of the 2213 structural type, Pb2Sr2MCu3O8 (M=Sm1-xCax, Y1-xCax, Er1-xCax and Yb1-xCax), were synthesized and characterized using x-ray powder diffraction and the Rietveld structural refinements method. Pb2Sr2Sm1-xCaxCu3O8 single crystals were grown by an optimized flux method using various combinations of PbO/PbF2 solvents. Samples with different Sm/Ca ratios were investigated for their superconducting properties. Magnetic measurements reveal the presence of a transition at 120K. Preliminary x-ray diffuse scattering experiment at the Advanced Photon Source of Argonne National Laboratory demonstrates the high quality of one of our crystals and the presence of rod-like diffuse scattering connecting the Bragg peaks …

Go to article

Electric Field Control Of Fixed Magnetic Skyrmions For Energy Efficient Nanomagnetic Memory, Dhritiman Bhattacharya Jan 2020

Electric Field Control Of Fixed Magnetic Skyrmions For Energy Efficient Nanomagnetic Memory, Dhritiman Bhattacharya

Theses and Dissertations

To meet the ever-growing demand of faster and smaller computers, increasing number of transistors are needed in the same chip area. Unfortunately, Silicon based transistors have almost reached their miniaturization limits mainly due to excessive heat generation. Nanomagnetic devices are one of the most promising alternatives of CMOS. In nanomagnetic devices, electron spin, instead of charge, is the information carrier. Hence, these devices are non-volatile: information can be stored in these devices without needing any external power which could enable computing architectures beyond traditional von-Neumann computing. Additionally, these devices are also expected to be more energy efficient than CMOS devices …

Go to article

A Theoretical And Experimental Study Of Charge Transport In Organic Thermoelectric Materials And Charge Transfer States In Organic Photovoltaics, Ashkan Abtahi Jan 2020

A Theoretical And Experimental Study Of Charge Transport In Organic Thermoelectric Materials And Charge Transfer States In Organic Photovoltaics, Ashkan Abtahi

Theses and Dissertations--Physics and Astronomy

Applications of organic electronics have increased significantly over the past two decades. Organic semiconductors (OSC) can be used in mechanically flexible devices with potentially lower cost of fabrication than their inorganic counterparts, yet in many cases organic semiconductor-based devices suffer from lower performance and stability. Investigating the doping mechanism, charge transport, and charge transfer in such materials will allow us to address the parameters that limit performance and potentially resolve them. In this dissertation, organic materials are used in three different device structures to investigate charge transport and charge transfer. Chemically doped π-conjugated polymers are promising materials to be used …

Go to article

Synthesis Of Graphene Using Plasma Etching And Atmospheric Pressure Annealing: Process And Sensor Development, Andrew Robert Graves Jan 2020

Synthesis Of Graphene Using Plasma Etching And Atmospheric Pressure Annealing: Process And Sensor Development, Andrew Robert Graves

Graduate Theses, Dissertations, and Problem Reports

Having been theorized in 1947, it was not until 2004 that graphene was first isolated. In the years since its isolation, graphene has been the subject of intense, world-wide study due to its incredibly diverse array of useful properties. Even though many billions of dollars have been spent on its development, graphene has yet to break out of the laboratory and penetrate mainstream industrial applications markets. This is because graphene faces a ‘grand challenge.’ Simply put, there is currently no method of manufacturing high-quality graphene on the industrial scale. This grand challenge looms particularly large for electronic applications where the …

Go to article

Superconducting Phase Transition In Inhomogeneous Chains Of Superconducting Islands, Eduard Ilin, Irina Burkova, Xiangyu Song, Michael Pak, Dmitri S. Golubev, Alexey Bezryadin Jan 2020

Superconducting Phase Transition In Inhomogeneous Chains Of Superconducting Islands, Eduard Ilin, Irina Burkova, Xiangyu Song, Michael Pak, Dmitri S. Golubev, Alexey Bezryadin

Faculty Publications

We study one-dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical …

Go to article