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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Bismuth alloying properties in GaAs nanowires

First-principles calculations have been performed to investigate the structural, electronic and optical properties of bismuth alloying in GaAs nanowires. A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration and the band edge shifts when spin–orbit coupling (SOC) is considered. The insertion of Bi atom leads to hybridization of Ga/As/Bi p states which contributes a lot around Fermi level. Scissor effect is involved. The optical properties are presented, including dielectric function, optical absorption spectra and reflectivity, which are also varied with the increasing of Bi concentrations. - Graphical abstract: Top view of Bi-doped GaAs nanowires. Ga, As, and Bi atoms are denoted with grey, purple and red balls, respectively. Display Omitted - Highlights: • A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. • The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration. • The band edge shifts when spin–orbit coupling (SOC) is considered. • The insertion of Bi atom leads to hybridization of Ga/As/Bi p states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Synthesis and investigation of proton conductivity for intercalated kaolinite with 4-amidinopyridinium chloride

The proton-conducting materials have potential application in devices such as fuel cells. In this study, a mineral kaolinite-based proton conducting material, kaolinite-4-amidinopyridinium hydrochloride (K-4-APy–HCl), was synthesized by the intercalated compound kaolinite-4-amidinopyridine (K-4-APy) adsorbing volatilizing HCl. The thermogravimetric analysis (TG), powder X-ray diffraction (PXRD) and IR spectrum confirmed the HCl successfully inserting into the interlayer space of kaolinite and the 4-aminopyridine being protonated. The intercalation efficiency is estimated to be ca. 85.6%. With respect to K-4-APy, the interlayer space expends by 1.53 Å. The thermal decomposition mechanism was studied by PXRD and TG techniques. The K-4-APy–HCl shows proton conductivity with σ=3.379×10{sup −8} S cm{sup −1} at 373 K and E{sub a}=1.159 eV in the anhydrous condition, which are comparable to MOFs-based proton conducting materials. - Graphical abstract: The intercalated hybrid of mineral kaolinite with 4-amidinopyridinium hydrochloride is prepared to use as proton conducting material. - Highlights: • A new strategy is proposed for preparation of kaolinite-based proton conductor. • Intercalatied hybrid was prepared by sequentially inserting 4-amidinopyridine and adsorbing HCl. • The proton conductivity of intercalated hybrid is comparable to MOFs-based proton-conductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Solid state cathode materials for secondary magnesium-ion batteries that are compatible with magnesium metal anodes in water-free electrolyte

With high elemental abundance, large volumetric capacity, and dendrite-free metal deposition, magnesium metal anodes offer promise in beyond-lithium-ion batteries. However, the increased charge density associated with the divalent magnesium-ion (Mg{sup 2+}), relative to lithium-ion (Li{sup +}) hinders the ion-insertion and extraction processes within many materials and structures known for lithium-ion cathodes. As a result, many recent investigations incorporate known amounts of water within the electrolyte to provide temporary solvation of the Mg{sup 2+}, improving diffusion kinetics. Unfortunately with the addition of water, compatibility with magnesium metal anodes disappears due to forming an ion-insulating passivating layer. In this short review, recent advances in solid state cathode materials for rechargeable magnesium-ion batteries are highlighted, with a focus on cathode materials that do not require water contaminated electrolyte solutions for ion insertion and extraction processes. - Graphical abstract: In this short review, we present candidate materials for reversible Mg-battery cathodes that are compatible with magnesium metal in water-free electrolytes. The data suggest that soft, polarizable anions are required for reversible cycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Doping effect on the structural properties of Cu{sub 1−x}(Ni, Zn, Al and Fe){sub x}O samples (0<x<0.10): An experimental and computational study

In this work, the effect of insertion of transition metal, TM (=Ni, Zn, Al and Fe), ions in Cu{sub 1−x}TM{sub x}O samples (0<x<0.10) prepared via co-precipitation method is studied through experimental and computational methods. The analyses of X-ray diffraction (XRD) patterns using Rietveld refinement show that i) at x=0, all samples present a monoclinic crystal system with space group C2/c and ii) for increasing the TM-doping, Ni and Zn-doped samples show a small amount of spurious phases for concentrations above x=0.05. Based on these results, a defect disorder study for using atomistic computational simulations which is based on the lattice energy minimization technique is employed to predict the location of the dopant ions in the structure. In agreement with XRD data, our computational results indicate that the trivalent (Al and Fe ions) are more favorable to be incorporated into CuO matrix than the divalent (Ni and Zn ions). - Graphical Abstract: The effect of insertion of transition metal, TM (=Ni, Zn, Al and Fe), ions in Cu{sub 1−x}TM{sub x}O samples (0<x<0.10) prepared via co-precipitation method is studied through experimental and computational methods. Display Omitted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Cobalt-based metal organic framework with superior lithium anodic performance

The reversible charging of a Co-1,4-benzenedicarboxylate MOF (Co-BDC MOF) prepared via an one-pot solvothermal method was studied for use as the anode in a Li-ion cell. It was found that this MOF anode provides high reversible capacities (1090 and 611 mA h g{sup −1} at current densities of 0.2 and 1 A g{sup −1}, respectively), and an impressive rate performance. Such an outstanding Li-ion storage property has not been reported previously for the LIB anodes within the MOFs category. Ex-situ X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) studies of this material at different state of charge suggest that cobalt stays at Co{sup 2+} state during discharge/charge process, so that in this case Li{sup +} may be inserted into the organic moiety without the direct participation of cobalt ions. - Graphical abstract: Co-1,4-benzenedicarboxylate MOF, synthesized through a straightforward solvothermal method, shows outstanding lithium storage performance. - Highlights: • Co-1,4-benzenedicarboxylate MOF is synthesized by a one-pot solvothermal method. • Reversible capacity of 1090 mA h g{sup −1} is achieved at a current density of 200 mA g{sup −1}. • Reversible capacity of 611 mA h g{sup −1} is achieved at a current density of 1 A g{sup −1}. • Li-ions may be inserted into the organic moieties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Tailoring the interfacial microstructure and mechanical strength of SiC ceramic joints using joining temperature and interlayer thickness

Highlights: • Bonding temperature could be decreased from 1600 °C to 1300 °C by inserting the Ti foil between SiC and Ta-5W. • The initial thickness interlayer and the number of interlayer had a significant influence on interface bonding. • Layered reaction layers consisting of carbides and silicide formed at the SiC/Ti/Ta-5W interfaces. • The joint strength depended mainly on the reaction layer thickness, especially the thickness of silicide layer. - Abstract: Silicon carbide ceramic joints solid state diffusion bonded by spark plasma sintering with Ti/Ta-5W/Ti multi-interlayer in the temperature range from 1250 °C to 1500 °C were investigated in detail in terms of interfacial microstructure, elemental diffusion, phase constituents, shear strength, and fracture morphology. Layered reaction layers consisting of carbides (TiC, Ti{sub 3}SiC{sub 2}, (Ta,Ti,W)C), silicide ((Ta,Ti,W){sub 5}Si{sub 3}) and Ta-rich solid solution (Ta,Ti,W) formed at the SiC/Ti/Ta-5W interfaces. It was found that joining temperature could be decreased from 1600 °C to 1300 °C by inserting the Ti foil between SiC and Ta-5W. Nevertheless, an attempt to further decrease the joining temperature to 1250 °C failed even using a thin Ti foil. The initial thickness interlayer and the number of interlayer had an influence on the interfacial diffusion bonding at SiC/Ti interface. Higher joining temperature was needed to achieve a tough interface joining for a thick interlayer compared with a thin interlayer. The increase of interlayer number also required higher joining temperature. The shear strength reached 123.5 ± 25.3 MPa for the joint diffusion bonded at 1300 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Influence of composition modification on Ca{sub 0.5−x}Mg{sub x}Ti{sub 2}(PO{sub 4}){sub 3} (0.0 ≤ x ≤ 0.5) nanoparticles as electrodes for lithium batteries

Graphical abstract: - Highlights: • Cation mixing was determined in the Ca{sub 0.5−x}Mg{sub x}Ti{sub 2}(PO{sub 4}){sub 3} biphasic series. • Nanometric Ca{sub 0.15}Mg{sub 0.35}Ti{sub 2}(PO{sub 4}){sub 3} delivered 138 mAh/g at C/20 in lithium cells. • Low content of Ca{sup 2+} increases cell volume favoring Li{sup +} insertion in R-3c framework. • Diminution of R{sub SEI} and R{sub CT} for Ca{sub 0.15}Mg{sub 0.35}Ti{sub 2}(PO{sub 4}){sub 3} discharged electrodes. • Fast electrode response for x = 0.35. - Abstract: The Ca{sub 0.5−x}Mg{sub x}Ti{sub 2}(PO{sub 4}){sub 3} series (0.0 ≤ x ≤ 0.5) was prepared by a sol–gel method. X-ray diffraction patterns showed two rhombohedral phases which coexist for intermediate compositions. Despite of the absence of a solid solution mechanism for the whole stoichiometry range, an appreciable cation mixing was observed in both phases. {sup 31}P MAS NMR spectroscopy revealed that low magnesium contents are incorporated to the calcium compound inducing changes in the ordering of the alkaline earth cations in M{sub 1} sites. Derivative plots of the voltage–capacity curves revealed two reversible regions ascribed to the reduction of Ti{sup 4+} to Ti{sup 3+}, ascribable to the subsequent insertion of lithium ions into M{sub 1} and M{sub 2} vacant sites. Capacity values as high as 138 mAh/g after the first discharge were monitored for nanometric Ca{sub 0.15}Mg{sub 0.35}Ti{sub 2}(PO{sub 4}){sub 3} at C/20. Cell cycling under successive kinetic rates revealed a good capacity retention for samples with x = 0.15 and 0.25. Impedance spectra were recorded in lithium cells discharged after different number of cycles at different C rates. The increase in charge transfer resistance was shown to be an important factor determining the electrode behavior on extended cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nickel/carbon core/shell nanotubes: Lanthanum nickel alloy catalyzed synthesis, characterization and studies on their ferromagnetic and lithium-ion storage properties

Highlights: • Ni/CNTs core/shell structure was synthesized using LaNi{sub 5} alloy catalyst by CVD. • The magnetic and lithium-ion storage properties of Ni/CNTs structure were studied. • The specific Ni/CNTs structure shows strong ferromagnetic property with large coercivity value of 446.42 Oe. • Ni/CNTs structure shows enhanced electrochemical performance in terms of stable capacity and better rate capability. - Abstract: A method was developed to synthesize ferromagnetic nickel core/carbon shell nanotubes (Ni/CNTs) by chemical vapor deposition using Pauli paramagnetic lanthanum nickel (LaNi{sub 5}) alloy both as a catalyst and as a source for the Ni-core. The Ni-core was obtained through oxidative dissociation followed by hydrogen reduction during the catalytic growth of the CNTs. Transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD) analyses reveal that the Ni-core exists as a face centered cubic single crystal. The magnetic hysteresis loop of Ni/CNTs particle shows increased coercivity (446.42 Oe) than bulk Ni at room temperature. Furthermore, the Ni/CNTs core/shell particles were investigated as anode materials in lithium-ion batteries. The Ni/CNTs electrode delivered a high discharge capacity of 309 mA h g{sup −1} at 0.2 C, and a stable cycle-life, which is attributed to high structural stability of Ni/CNTs electrode during electrochemical lithium-ion insertion and de-insertion redox reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A novel iron phosphate/oxygen hybrid cathode with high power output for the aprotic lithium-oxygen battery

Highlights: • This study affords a new strategy to improve the power output of Li-O{sub 2} cell. • FePO{sub 4}@C nanorods with exposed {010} facets are prepared and applied in O{sub 2} cathode. • Hybrid cathode retains high energy output via ORR. • Hybrid cathode attains 8-fold increased power output via Li{sup +}-insertion of FePO{sub 4}. - Abstract: The aprotic lithium-oxygen (Li-O{sub 2}) battery has recently attracted the worldwide attention by virtue of its super-large energy output. However, the extremely poor power output is one of the key issues which severely restrict the commercialization of the Li-O{sub 2} technology. In this work, we demonstrate a novel and simple strategy to address the power issue of the aprotic Li-O{sub 2} battery. An iron phosphate/oxygen (FePO{sub 4}/O{sub 2}) hybrid cathode is proposed for the first time by simply introducing the {010}-oriented FePO{sub 4} nanorods into a conventional O{sub 2} cathode. The as-built hybrid cathode not only retains a high-energy output via the O{sub 2} cathodic reaction, but also achieves an 8-fold increased power output via the Li{sup +}-insertion reaction of the {010}-oriented FePO{sub 4} nanorods.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The GdF3 phosphors with enhanced multicolor luminescence via multi-channel excitation and energy migration procedure

Highlights: • Core-shell structured GdF{sub 3} phosphors were synthesized by hydrothermal method. • SiO{sub 2} coating layers prevent aggregation and sintering during thermal annealing. • The annealed CSS nanophosphors were highly dispersible. • The inserted PMA significantly enhances multicolor luminescence. • The annealed CSS phosphors exhibit enhanced multicolor luminescence properties. - Abstract: A collection of GdF{sub 3} core-shell structured (CSS) phosphors were synthesized by hydrothermal method. The as-prepared (AP) phosphors were coated with SiO{sub 2} layers to avoid aggregation and sintering during thermal annealing at 800 °C, after which the SiO{sub 2} layers were etched off and the annealed phosphors became highly dispersible. The annealed CSS phosphor aGdF{sub 3}:Eu{sup 3+}@GdF{sub 3}:Ce{sup 3+},Dy{sup 3+} shows excellent multicolor luminescence performance with the aid of dual-channel excitation and energy migration (EM) procedure of Gd{sup 3+} ions. By inserting pyromellitic acid (PMA) organic ligands into the interfaces between annealed core and AP shell layer regions, the so-called antenna effect of organic ligands of PMA forms a new excitation channel, which makes the CSS phosphor aGdF{sub 3}:Eu{sup 3+}@PMA@GdF{sub 3}:Ce{sup 3+},Dy{sup 3+} exhibit significantly enhanced multicolor luminescence via multi-channel excitation and EM process. The prepared CSS phosphors in this work are excellent candidates for applications in solid-state lighting.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of channel thickness on structure and transport properties of AlGaN/InGaN heterostructures grown by pulsed metal organic chemical vapor deposition

Highlights: • High quality AlGaN/InGaN heterostructures are grown and the effects of InGaN channel thickness on the structural and transport properties are investigated in detailed. • A high electron mobility of 1712 cm{sup 2}/Vis achieved for the heterostructures with an optimum channel thickness of 21 nm, indicating the huge potential of InGaN channel heterostructures in high frequency and high power applications. • The analyze method in this work can be generalized to both the studies of InGaN channel heterostructures with arbitrary component and all the heterostructures with inserted channel. - Abstract: High-quality AlGaN/InGaN heterostructures are grown and the effects of InGaN channel thickness on the structure and transport properties are investigated. With the increase of InGaN channel thickness from 7 nm to 28 nm, the two-dimensional electron gas density decreases continuously, while the mobility shows a trend of increasing at first, and then decreasing. The optimum thickness of 21 nm is obtained for the In{sub 0.05}Ga{sub 0.95}N channel, achieving a high electron mobility of 1712 cm{sup 2}/V, which indicates the huge potential for InGaN channel heterostructures in high-frequency and high-power applications. The variation in transport properties is studied by analyzing the structure formation, material quality, and interface characteristic in detail. The results are not only beneficial for the further study of the InGaN channel heterostructures, but also instructive for the other inserted channel system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A rationally designed polysulfide-trapping interface on the polymeric separator for high-energy Li–S batteries

A coating layer consisting of a layer of graphene oxide (GO) inserted in between two layers of multi-walled carbon nanotubes (MWCNT) forms a multifunctional polysulfide-trapping triple-interface on the polymeric separator for lithium–sulfur (Li–S) batteries. The top and bottom highly conductive MWCNT interfaces are able to physically inhibit polysulfide diffusion and effectively reutilize the trapped active material during cycling. The inserted ultrathin GO layer with negatively charged carboxyl groups, on the other hand, electrostatically repels the migrating polysulfide anions. The stacked GO sheets also extensively prolong the migration routes of the polysulfides. Additionally, the “buffer zones” interspersed within the triple-interface accommodate the migrating polysulfides. Thus, the sandwiched separators enable Li–S cells with a high-sulfur-loading (10 mg cm -2 ), high areal capacity (10.9 mA h cm -2 ), and stable cycling ability even though the coating layer is ultra-thin (~17 μm) and light-weight (~0.23 mg cm -2 ).

25 ENERGY STORAGE↗
DOE OSTI2019

NASICON-type Na 3 Fe 2 (PO 4 ) 3 as a low-cost and high-rate anode material for aqueous sodium-ion batteries

Aqueous sodium-ion batteries are attractive battery alternatives for stationary energy storage due to their inherently low cost and high safety. The development of advanced electrode materials with excellent performance and low cost is crucial for the success of aqueous Na-ion batteries. Albeit the high capacity and stable cycling of the leading anode of NaTi 2 (PO 4 ) 3 , the high price of titanium element and the low Na-insertion potential close to the hydrogen evolution reaction may plague its application. Here we introduced a NASICON-type Na 3 Fe 2 (PO 4 ) 3 as a promising anode alternative for aqueous Na-ion batteries. Synchrotron X-ray diffraction and spectroscopy confirm its phase and atomic structure. Electrochemical characterization and X-ray photoelectron spectroscopy reveal the reversible Na+ insertion in Na 3 Fe 2 (PO 4 ) 3 due to the Fe 3+ /Fe 2+ redox couple, which renders a specific capacity of ~60 mAh g -1 and excellent cycling of 1000 cycles at 10C rate. A Super high rate of 100C was also achieved for this anode with a capacity retention of 61% after 1000 cycles. In addition, the Na 3 Fe 2 (PO 4 ) 3 anode is paired with a Prussian white analogue of Na 2 Mn[Fe(CN) 6 ] into a full cell, exhibiting promising cell performance and material sustainability. Furthermore, our work underlines the importance of fabricating aqueous batteries on the basis of the Earth-abundant, cost-effective, and non-toxic elements.

25 ENERGY STORAGE↗
DOE OSTI2020

Probing local electrochemistry via mechanical cyclic voltammetry curves

Understanding the mechanical response of an electrode during electrochemical cycling and its correlation to the device electrochemical performance is crucial to improving the performance of insertion-type energy storage devices, electrochemical actuators, water purification, ion separation and neuromorphic computing applications. Here, we visualized the electro-chemo-mechanical coupling behaviors during charge storage of anhydrous and hydrated WO 3 electrodes via in situ atomic force microscopy (AFM) and developed the concept of mechanical cyclic voltammetry (mCV) curves. The relationship between electrochemical current and strain was investigated with simplified models and the results revealed that the proton insertion/deinsertion process could be described through potential-dependent electro-chemo-mechanical coupling coefficients which might indicate changes in insertion processes during electrode cycling. The mCV mapping results highlight the local heterogeneity and show that the charging processes varied across the electrode. These local variations could be further correlated to local morphology, crystal orientations or chemical compositions with proper electrode designs.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Validation and uncertainty quantification of detector response functions for a $1"×2"$ NaI collimated detector intended for inverse radioisotope source mapping applications

Detector response functions (DRFs) are often used for inverse analysis. We compute the DRF of a sodium iodide (NaI) nuclear material holdup field detector using the code named g03 developed by the Center for Engineering Applications of Radioisotopes (CEAR) at NC State University. Three measurement campaigns were performed in order to validate the DRF’s constructed by g03: on-axis detection of calibration sources, off-axis measurements of a highly enriched uranium (HEU) disk, and on-axis measurements of the HEU disk with steel plates inserted between the source and the detector to provide attenuation. Furthermore, this work quantifies the uncertainty of the Monte Carlo simulations used in and with g03, as well as the uncertainties associated with each semi-empirical model employed in the full DRF representation. Overall, for the calibration source measurements, the response computed by the DRF for the prediction of the full-energy peak region of responses was good, i.e. within two standard deviations of the experimental response. In contrast, the DRF tended to overestimate the Compton continuum by about 45–65% due to inadequate tuning of the electron range multiplier fit variable that empirically represents physics associated with electron transport that is not modeled explicitly in g03. For the HEU disk measurements, computed DRF responses tended to significantly underestimate (more than 20%) the secondary full-energy peaks (any peak of lower energy than the highest-energy peak computed) due to scattering in the detector collimator and aluminum can, which is not included in the g03 model. We ran a sufficiently large number of histories to ensure for all of the Monte Carlo simulations that the statistical uncertainties were lower than their experimental counterpart’s Poisson uncertainties. The uncertainties associated with least-squares fits to the experimental data tended to have parameter relative standard deviations lower than the peak channel relative standard deviation in most cases and good reduced chi-square values. The highest sources of uncertainty were identified as the energy calibration polynomial factor (due to limited source availability and NaI resolution) and the Ba-133 peak fit (only a very weak source was available), which were 20% and 10%, respectively.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Failure investigation and mitigation after experimental research reactor fuel plate deformation in an irradiation device

Experimental research reactor fuel testing is conducted in the Belgian Reactor 2 (BR2) of the Belgian Nuclear Research Centre (SCK CEN) in dedicated irradiation vehicles or rigs. One such vehicle allows flat full-size fuel plates to be irradiated by inserting them into slotted baskets that captures a narrow portion of the longitudinal edges of the plates. The motion of the fuel plates within the baskets is possible within the narrow slots and thus, the plate is considered to be unattached. The design intentionally omits fixing mechanisms of the fuel plates to the baskets to facilitate the inspection and repositioning of the plates between the irradiation cycles and the accommodation of thermal expansion of the plates in the lateral direction. However, loosely inserted fuel plates have weak structural boundary conditions allowing for larger out-of-plane deflections caused by hydrodynamic loads exerted by the flowing coolant, as compared to those of fixed plates. Unexpected large deformations of plates occurred in several irradiation cycles that further resulted in a loss of cladding integrity. These deformations could not be attributed to a single source. This triggered a series of thermal hydraulic, structural, and fluid-structure interaction analyses aiming at understanding the observed phenomenon. The analyses revealed that, for a certain combination of unfavorable manufacturing and assembly tolerances, fuel plate edges could escape out of the slots in the irradiation basket due to the hydrodynamic load. Subsequently, the plate could become wedged inside the basket coolant channel opening. This resulted in reduced coolant flow and accelerated temperature increase and thermal expansion of the plate while under irradiation. This unfavorable feedback loop could then lead to excessive plate surface temperatures, deformed plates and cladding failure, as was observed in the experiments. These analyses not only provided a probable cause of the fuel plate failures, but also resulted in a new and improved design of the irradiation basket to avoid these issues in the future. In conclusion, a series of recent successful irradiations confirm that the sources of failures were identified correctly, and the implemented mitigations were adequate.

BR2↗
DOE OSTI2014

Inverted, Organic WORM Device Based on PEDOT:PSS with Very Low Turn-On Voltage

An organic Write-Once-Read-Many (WORM) device based on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as the active layer was fabricated with an inverted architecture. Insertion of an ultrathin layer of poly(methylmethacrylate) (PMMA) between the bottom electrode and the PEDOT:PSS resulted in a systematic and substantial decrease in turn-on voltage, from 7.0 V to less than 1.0 V. An optimal thickness of the PMMA layer was found to yield the lowest consistent turn-on voltage of ~0.8 V, with 0.5 V being the lowest value of all fabricated devices. The switching mechanism was attributed to filamentary doping of the PEDOT:PSS. Insertion of the PMMA acted to protect the underlying ZnO from being etched by the acidic PEDOT:PSS as well as to improve its wetting properties. Moreover, devices were demonstrated on both ITO and aluminum bottom electrodes, with aluminum yielding the highest ON/OFF ratios in the study. Owing to their inverted architecture, the devices demonstrated good stability, and the retention time of the ON-state was determined to be greater than twenty months while stored in air for devices with ITO bottom electrodes. Blade-coating was demonstrated as a viable processing technique for applications requiring rapid or large-area manufacturing in addition to deposition via spin-coating.

14 SOLAR ENERGY↗
DOE OSTI2020

A data analytical approach for assessing the efficacy of Operational Technology active defenses against insider threats

In recent years, the need for Operational Technology (OT) defenses has been recognized, serving as an additional line of defense when Information Technology (IT) defenses are bypassed. This is no longer considered an uncommon possibility when dealing with advanced persistent threat (APT) actors expected to be state-sponsored and receiving insider assistance. In these extreme adversarial situations, OT defenses aim to provide another layer of defense for the system, introduced directly at the physical process level, as described by the sensors data, the system model, and control actions. Just like IT defenses, two schools of thought, i.e., passive and active defenses, have emerged to address this challenge. In active defenses, representing the focus of this paper, known signatures, synthesized based on the system's unique characteristics, are inserted into the system. In contradistinction, passive methods rely solely on observing system behavior in search of patterns of normal behavior with deviations thereof representing abnormal behavior. In their most sophisticated implementations, both passive and active defenses rely on the use of data analytics to identify the patterns and synthesize the observed and/or inserted signatures. Past research has shown that passive defenses may be bypassed by APT actors relying on data analytics and their intimate knowledge of the system to evade detection by respecting the patterns identified by the defenders. Here this manuscript explores the use of active defenses under the assumption that the attacker has privileged access to the system, including access to the system's model and sensors data. Specifically, this manuscript assesses the ability of active defenses to remain invisible to the attackers, and discusses the associated challenges that must be addressed to ensure their resiliency against APT actors.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗