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Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed Coatings, Leandro Olano, Isabel Montero, María E. Dávila, JR Dennison 2017 Instituto de Ciencia de Materiales de Madrid

Dynamic Secondary Electron Emission In Dielectric/Conductor Mixed Coatings, Leandro Olano, Isabel Montero, María E. Dávila, Jr Dennison

Presentations

An unexpected behavior of the Secondary Emission Yield (SEY) on coatings composed by a mixture of conductor and dielectric microparticles was reported and modeled in [1]. As a follow up, we measured for a fixed primary energy the dynamic evolution of the SEY in similar samples and proposed a charging-roughness coupled model to simulate the experimental results. Two different coatings were selected: 1) TMM and Al microparticles (type 1), and 2) zeolites and gold nanoparticles (type 2). Pulsed and continuous tests were used to obtain the SEY as a function of the primary energy.

In both types of samples extremely ...


Stacking 2d Materials, Michael Hernandez, John C. Mann 2017 Pepperdine University

Stacking 2d Materials, Michael Hernandez, John C. Mann

Seaver College Research And Scholarly Achievement Symposium

Monolayer Transition Metal Dichalcogenides are atomically thin semi-conductors that are considered quasi 2D materials due to their extremely small thickness. It has been observed that atomically thin crystals exhibit different physical properties than their bulk counterparts due to quantum confinement effects. We are attempting discover new physical properties by developing a technique to stack two different monolayer crystals, MoS2 and MoSe2.


Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski 2017 Iowa State University

Enhancement Of The Superconducting Gap By Nesting In Cakfe4as4: A New High Temperature Superconductor, Daixiang Mou, Tai Kong, William R. Meier, Felix Lochner, Lin-Lin Wang, Qisheng Lin, Yun Wu, S. L. Bud’Ko, Ilya Eremin, Duane D. Johnson, Paul C. Canfield, Adam Kaminski

Duane D. Johnson

We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe4As4. In contrast to the related CaFe2As2 compounds, CaKFe4As4 has a high Tc of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the ...


Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson 2017 Iowa State University

Chapter 14 – Evolutionary Algorithms Applied To Electronic-Structure Informatics: Accelerated Materials Design Using Data Discovery Vs. Data Searching, Duane D. Johnson

Duane D. Johnson

We exemplify and propose extending the use of genetic programs (GPs) – a genetic algorithm (GA) that evolves computer programs via mechanisms similar to genetics and natural selection – to symbolically regress key functional relationships between materials data, especially from electronic structure. GPs can extract structure–property relations or enable simulations across multiple scales of time and/or length. Uniquely, GP-based regression permits “data discovery” – finding relevant data and/or extracting correlations (data reduction/data mining) – in contrast to searching for what you know, or you think you know (intuition). First, catalysis-related materials correlations are discussed, where simple electronic-structure-based rules are revealed ...


C2-Neb: The Nudged Elastic Band Method With Two Climbing Images, Validated On The Martensitic Transformation In Niti Shape Memory Alloy, Nikolai A. Zarkevich, Duane D. Johnson 2017 Ames Laboratory

C2-Neb: The Nudged Elastic Band Method With Two Climbing Images, Validated On The Martensitic Transformation In Niti Shape Memory Alloy, Nikolai A. Zarkevich, Duane D. Johnson

Duane D. Johnson

The nudged-elastic band (NEB) method is modified with concomitant two climbing images (C2-NEB) to find a transition state (TS) in complex energy landscapes, such as those with serpentine minimal energy path (MEP). If a single climbing image (C1-NEB) successfully finds the TS, C2-NEB finds it with higher stability and accuracy. However, C2-NEB is suitable for more complex cases, where C1-NEB misses the TS because the MEP and NEB directions near the saddle point are different. Generally, C2-NEB not only finds the TS but guarantees that the climbing images approach it from the opposite sides along the MEP, and it estimates ...


Discovery Of Dirac Node Arcs In Ptsn4, Adam Kaminski, Paul C. Canfield, Serguei Bud'ko, Daixiang Mou, Eundeok Mun, Yun Wu, Lunan Huang, Yongbin Lee, Duane D. Johnson, Linlin Wang 2017 The Ames Laboratory, Iowa State University

Discovery Of Dirac Node Arcs In Ptsn4, Adam Kaminski, Paul C. Canfield, Serguei Bud'ko, Daixiang Mou, Eundeok Mun, Yun Wu, Lunan Huang, Yongbin Lee, Duane D. Johnson, Linlin Wang

Duane D. Johnson

In topological quantum materials the conduction and valence bands are connected at points (Dirac/Weyl semimetals) or along lines (Line Node semimetals) in the momentum space. Numbers of studies demonstrated that several materials are indeed Dirac/Weyl semimetals. However, there is still no experimental confirmation of materials with line nodes, in which the Dirac nodes form closed loops in the momentum space. Here we report the discovery of a novel topological structure - Dirac node arcs - in the ultrahigh magnetoresistive material PtSn4 using laser-based angle-resolved photoemission spectroscopy (ARPES) data and density functional theory (DFT) calculations. Unlike the closed loops of line ...


Asymmetric Mass Acquisition In Labi: Topological Semimetal Candidate, Yun Wu, Tai Kong, Lin-Lin Wang, Duane D. Johnson, Daixiang Mou, Lunan Huang, Benjamin Schrunk, Sergey L. Bud'ko, Paul C. Canfield, Adam Kaminski 2017 Iowa State University

Asymmetric Mass Acquisition In Labi: Topological Semimetal Candidate, Yun Wu, Tai Kong, Lin-Lin Wang, Duane D. Johnson, Daixiang Mou, Lunan Huang, Benjamin Schrunk, Sergey L. Bud'ko, Paul C. Canfield, Adam Kaminski

Duane D. Johnson

We use our high resolution He-lamp-based, tunable laser-based angle-resolved photoemission spectroscopy measurements and density functional theory calculations to study the electronic properties of LaBi, a binary system that was proposed to be a member of a new family of topological semimetals. Both bulk and surface bands are present in the spectra. The dispersion of the surface state is highly unusual. It resembles a Dirac cone, but upon closer inspection we can clearly detect an energy gap. The bottom band follows roughly a parabolic dispersion. The dispersion of the top band remains very linear, “V” -shape like, with the tip approaching ...


Relaxation Of Radiation Effects On The Optical Transmission Of Polymers, Alexandra Hughlett, Tyler Kippen, J. R. Dennison 2017 Utah State University

Relaxation Of Radiation Effects On The Optical Transmission Of Polymers, Alexandra Hughlett, Tyler Kippen, J. R. Dennison

JR Dennison

Changes in optical transmission of polymers over time were studied to determine the factors contributing to relaxation of defect states induced by intense radiation doses. Samples of low density polyethylene (LDPE), polyether ether ketone (PEEK), polypropylene (PP), and polyimide (PI) received doses up to 500 MGy from an 8 MeV electron accelerator. These doses were intended to simulate long-term exposure of common spacecraft materials in geosynchronous orbit. Features and absorption edges in ~250 nm to 1000 nm UV to IR transmission spectra can be related to energies associated with various defects previously observed in these highly disordered materials. Recent work ...


Pulsed Electroacoustic System Development For Volume Charge Distribution Measurement In Thin Dielectric Films, Lee H. Pearson, JR Dennison, Erick W. Griffiths, Anthony C. Pearson 2017 Box Elder Innovations

Pulsed Electroacoustic System Development For Volume Charge Distribution Measurement In Thin Dielectric Films, Lee H. Pearson, Jr Dennison, Erick W. Griffiths, Anthony C. Pearson

JR Dennison

This paper discusses an effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate state-of-the-art hardware and improved signal processing and modeling to characterize embedded charge distributions in thin dielectric films. Objectives in developing this system include: (1) improved spatial resolution, while maintaining reasonable temporal resolution; (2) improved signal processing tools for increased signal/noise ratios; (3) integrated PEA modeling tools; and (4) integrated environmental controls. We emphasize system improvements required to achieve high spatial resolution for in vacuo measurements of thin dielectrics charged using electron beam injection, which are most applicable for spacecraft charging tests. PEA measurement ...


A New Physical Model For Dc Partial Discharge In Polymeric Insulators, Allen Andersen, JR Dennison 2017 Utah State University

A New Physical Model For Dc Partial Discharge In Polymeric Insulators, Allen Andersen, Jr Dennison

Presentations

The physics of DC partial discharge (DCPD) continues to pose a challenge to researchers. We present a new physically-motivated model of DCPD in amorphous polymers based on our dual-defect model of dielectric breakdown. The dual-defect model is an extension of standard static mean field theories, such as the Crine model, that describe avalanche breakdown of charge carriers trapped on uniformly distributed defect sites. It assumes the presence of both high-energy chemical defects and low-energy thermally-recoverable physical defects. We present our measurements of breakdown and DCPD for several common polymeric materials in the context of this model. Improved understanding of DCPD ...


Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials, JR Dennison 2017 Utah State Univesity

Model For Charge Injection With Electron Beams Into Highly Disordered Insulating Materials, Jr Dennison

Presentations

The Walden-Wintle model for charge injection and transport through highly disordered insulating materials has been extended to include charge injection with a charged particle beam. The original model is applicable to charge injection into a dielectric material from a pair of electrodes in a parallel-plate geometry. It provides a versatile approach to predict the time-dependent current at a rear grounded electrode and the incident surface voltage, as the injection current density evolves over time with the development of a space charge barrier near the injection electrode. The Walden-Wintle model has been applied to many standard cases including Fowler-Nordheim injection, Schottky ...


Enhancing High-Order-Harmonic Generation By Time Delays Between Two-Color, Few-Cycle Pulses, Dian Peng, Liang-Wen Pi, M. V. Frolov, Anthony F. Starace 2017 University of Nebraska - Lincoln

Enhancing High-Order-Harmonic Generation By Time Delays Between Two-Color, Few-Cycle Pulses, Dian Peng, Liang-Wen Pi, M. V. Frolov, Anthony F. Starace

Anthony F. Starace Publications

Use of time delays in high-order-harmonic generation (HHG) driven by intense two-color, few-cycle pulses is investigated in order to determine means of optimizing HHG intensities and plateau cutoff energies. Based upon numerical solutions of the time-dependent Schrõdinger equation for the H atom as well as analytical analyses, we show that introducing a time delay between the two-color, few-cycle pulses can result in an enhancement of the intensity of the HHG spectrum by an order of magnitude (or more) at the cost of a reduction in the HHG plateau cutoff energy. Results for both positive and negative time delays as well ...


Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, Amberly Evans Jensen, JR Dennison 2017 Utah State University

Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, Amberly Evans Jensen, Jr Dennison

JR Dennison

No abstract provided.


Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, JR Dennison, Amberly Evans, Justin Dekany 2017 Utah State University

Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, Jr Dennison, Amberly Evans, Justin Dekany

JR Dennison

Measurements of the charge distribution in electron-bombarded, thin-film, multilayer dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 ...


Electron Beam Induced Luminescence Of Sio2 Optical Coatings, JR Dennison, Amberly Evans, Gregory Wilson, Charles W. Bowers, Robert Meloy 2017 Utah State Univesity

Electron Beam Induced Luminescence Of Sio2 Optical Coatings, Jr Dennison, Amberly Evans, Gregory Wilson, Charles W. Bowers, Robert Meloy

JR Dennison

Optical coatings of disordered thin film SiO2/SiOx dielectric samples on reflective metal substrates exhibited cathodoluminescence under electron beam irradiation. Measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures are reported. Radiance reached a saturation plateau at high incident electron power. Well below saturation radiance scaled with deposited power, that is linearly with incident power for lower-energy non-penetrating electrons and decreasing with increasing energy for penetrating radiation. Four bands were observed in spectral measurements from 300 nm to 1000 nm. Changes in peak intensity and shifts ...


Electron Penetration Range For Every Body, Anne Starley, Lisa Montierth Phillipps, JR Dennison 2017 Utah State University

Electron Penetration Range For Every Body, Anne Starley, Lisa Montierth Phillipps, Jr Dennison

JR Dennison

The penetration range of an electron into diverse materials can be estimated using an approximation fit as a function of a single parameter, N y, which describes the effective number of valence electrons. This fit is found using the Continuous-Slow Down-Approximation (CSDA), which simplifies the process of estimating an expected penetration range of a given material by applying some of the material’s key characteristics. Using the CSDA, a simple composite analytical formula is created which estimates the range or maximum penetration depth of incident electrons. This formula generates an approximation to the range using the parameter, Nv . The range ...


Electrical Properties Study Under Electron Beam Of Annealed And Coated Boron Nitride, Kevin Guerch, Thierry Paulmier, JR Dennison, Justin Dekany, Sophie Guillemet-Fritsch, Pascal Lenormand 2017 Selected Works

Electrical Properties Study Under Electron Beam Of Annealed And Coated Boron Nitride, Kevin Guerch, Thierry Paulmier, Jr Dennison, Justin Dekany, Sophie Guillemet-Fritsch, Pascal Lenormand

JR Dennison

The charging and relaxation kinetics of pyrolytic boron nitride (BN) substrates, BN with an aluminum oxide (BN/Al2O3) coating, and thermally-annealed alumina-coated boron nitride (an–BN/Al2O3) were investigated under low power electron irradiation (5 < incident energy E0 < 20 keV and incident flux Ji = 10 nA.cm-2 at room temperature) in the CEDRE facility at ONERA (Toulouse, France). Surface potentials of each ceramics configuration were measured over time using the Kelvin probe method. The influence of coating and annealing treatments to limit charging is discussed in this paper. A thorough study of a an–BN/Al2O3 sample was carried out ...


Electric Field Dependence Of The Time To Electrostatic Breakdown In Insulating Polymers, Charles Sim, Alec Sim, JR Dennison 2017 Utah State University

Electric Field Dependence Of The Time To Electrostatic Breakdown In Insulating Polymers, Charles Sim, Alec Sim, Jr Dennison

JR Dennison

No abstract provided.


Effects Of Voltage Ramp Rates On Electrostatic Field Strength In Highly Disordered Insulating Materials, Krysta Moser, Allen Andersen, JR Dennison 2017 Utah State University

Effects Of Voltage Ramp Rates On Electrostatic Field Strength In Highly Disordered Insulating Materials, Krysta Moser, Allen Andersen, Jr Dennison

JR Dennison

At high enough electrostatic fields or after long exposure times, insulators can break down, causing large current flow through the material: this breakdown is called electrostatic discharge (ESD). ESD is a permanent, catastrophic failure of a dielectric material: what was an insulator is now essentially a conductor. Previous tests done by the USU Materials Physics Group (MPG) using our ESD custom vacuum chamber have found that, for the polymeric materials biaxially oriented polypropylene (BOPP), polyimide (PI), and low density polyethylene (LDPE), the electrostatic field strength at breakdown depends on the ramp rate of voltage applied across some materials, but possibly ...


Electrical Properties Of Annealed And Coated Boron Nitride Under Electron Beam Irradiation, Kevin Guerch, Thierry Paulmier, JR Dennison, Justin Dekany, Sophia Guillemet-Fritsch, Pascal Lenormand 2017 Utah State Univesity

Electrical Properties Of Annealed And Coated Boron Nitride Under Electron Beam Irradiation, Kevin Guerch, Thierry Paulmier, Jr Dennison, Justin Dekany, Sophia Guillemet-Fritsch, Pascal Lenormand

JR Dennison

Technical dielectric materials and ceramics are used in many different high technology industrial areas and especially for spacecraft applications. On satellites, these materials are subjected to extreme conditions due to the space plasma environment. To survive, these ceramic insulators must have exceptional electrical and thermal properties. Boron Nitride (BN) and Aluminum Oxide (Al2O3) are used in particular because they combine good electrical insulation and high thermal conductivity. However, BN and Al2O3 used in spacecraft interiors are exposed to critical radiation demands, where these insulators are irradiated by electrons with high energies and flux. Charged particles are trapped in the ceramics ...


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