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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Polymerized small molecular acceptor based all-polymer solar cells with an efficiency of 16.16% via tuning polymer blend morphology by molecular design

All-polymer solar cells (all-PSCs) based on polymerized small molecular acceptors (PSMAs) have made significant progress recently. Here, we synthesize two A-DA’D-A small molecule acceptor based PSMAs of PS-Se with benzo[c][1,2,5]thiadiazole A’-core and PN-Se with benzotriazole A’-core, for the studies of the effect of molecular structure on the photovoltaic performance of the PSMAs. The two PSMAs possess broad absorption with PN-Se showing more red-shifted absorption than PS-Se and suitable electronic energy levels for the application as polymer acceptors in the all-PSCs with PBDB-T as polymer donor. Cryogenic transmission electron microscopy visualizes the aggregation behavior of the PBDB-T donor and the PSMA in their solutions. In addition, a bicontinuous-interpenetrating network in the PBDB-T:PN-Se blend film with aggregation size of 10~20 nm is clearly observed by the photoinduced force microscopy. The desirable morphology of the PBDB-T:PN-Se active layer leads its all-PSC showing higher power conversion efficiency of 16.16%.

14 SOLAR ENERGY↗
DOE OSTI2021

Reversible electrochemical conversion from selenium to cuprous selenide

Using elemental selenium as an electrode, the redox-active Cu 2+ /Cu + ion is reversibly hosted via the sequential conversion reactions of Se → CuSe → Cu 3 Se 2 → Cu 2 Se. Here, the four-electron redox process from Se to Cu 2 Se produces a high initial specific capacity of 1233 mA h g –1 based on the mass of selenium alone or 472 mA h g –1 based on the mass of Cu 2 Se, the fully discharged product.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Self-regulated growth of candidate topological superconducting parkerite by molecular beam epitaxy

Ternary chalcogenides, such as parkerites and shandites, are a broad class of materials exhibiting a rich diversity of transport and magnetic behavior and an array of topological phases, including Weyl and Dirac nodes. However, they remain largely unexplored as high-quality epitaxial thin films. Here, we report the self-regulated growth of thin films of the strong spin–orbit coupled superconductor Pd 3 Bi 2 Se 2 on SrTiO 3 by molecular beam epitaxy. Films are found to grow in a self-regulated fashion, where, in excess Se, the temperature and relative flux ratio of Pd to Bi control the formation of Pd 3 Bi 2 Se 2 due to the combined volatility of Bi, Se, and Bi–Se bonded phases. The resulting films are shown to be of high structural quality, and the stoichiometry is independent of the Pd:Bi and Se flux ratio and exhibits a superconducting transition temperature of 800 mK and a critical field of 17.7 ± 0.5 mT, as probed by transport and magnetometry. Understanding and navigating the growth of the chemically and structurally diverse classes of ternary chalcogenides open a vast space for discovering new phenomena and enabling new applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantitative assessment of selenium diffusion and passivation in CdSeTe solar cells probed by spatially resolved cathodoluminescence

The introduction of selenium in CdSeTe/CdTe solar cells has led to improved device performances attributed to the passivation of bulk defects. In this work, high-resolution cathodoluminescence experiments are performed on a series of CdSeTe/CdTe thin films with different Se concentrations to quantify the mechanisms and the passivation role of Se. We demonstrate a universal dependence between the Se concentration and the radiative efficiency and a ten-fold enhancement of the luminescence between CdTe and CdSe 0.4 Te 0.6 . Raw luminescence maps are converted into maps of the Se concentration, revealing its graded profile within the stack. We demonstrate the diffusion of Se along CdTe grain boundaries induced by the cadmium chloride annealing treatment and determine the diffusion coefficients, which are more than eight times higher at grain boundaries than in grain interiors. These results provide microscopic insights into the distribution of Se and its impact on the passivation of CdSeTe/CdTe solar cells.

14 SOLAR ENERGY↗
DOE OSTI2026

Characterization of lateral amorphous selenium photodetectors for low-photon and VUV detection at cryogenic temperatures

The performance of amorphous selenium (a-Se) as a cryogenic photodetector material is evaluated through a series of experiments using laterally structured devices operated in a custom optical test stand. These studies investigate the response of a-Se detectors to low-photon fluxes at high electric fields near avalanche conditions, the linearity of the photoconductive response over a wide dynamic range and the direct detection of narrowband 130 nm vacuum ultraviolet (VUV) illumination. At 87 K, matched-filter analysis shows reliable single-shot detection with efficiencies ≥80% and area under the curve (AUC) ≥ 0.85 using as few as ∼ 6800 incident 401 nm photons, corresponding to ∼ 3400 photons within field-active regions after accounting for geometric constraints. Measurements are performed at cryogenic temperatures using calibrated photon fluxes derived from a silicon photomultiplier reference and a characterized optical filter stack. Additional experiments using a tellurium-doped a-Se (a-SeTe) device explore the material's behavior under identical test conditions and demonstrate that avalanche is achievable in a-SeTe at cryogenic temperatures. The results demonstrate reproducible low-noise operation, VUV sensitivity and field-dependent gain behavior in a lateral a-Se architecture, representing the first reported observation of avalanche multiplication in laterally structured a-Se and a-SeTe devices at cryogenic temperatures. These findings support the potential integration of laterally structured a-Se devices into next-generation pixelated liquid-argon time projection chambers (TPCs) requiring scalable, high-field-compatible photon detection systems.

Amorphous selenium↗
DOE OSTI2020

Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe 2 Te 3

Since the discovery of pressure-induced superconductivity in the two-leg ladder system BaFe 2 X 3 (X=S, Se), with the 3d iron electronic density n=6, quasi-one-dimensional iron-based ladders have attracted considerable attention. In this work, we use density-functional theory to predict that the novel n=6 iron ladder BaFe 2 Se 3 could be stable with a similar crystal structure as BaFe 2 Se 3 . Furthermore, our results also indicate that BaFe2Te3 will display a complex 2×2 block-type magnetic order. Due to the magnetic striction effects of this block order, BaFe2Te3 should be a magnetic noncollinear ferrielectric system with a net polarization 0.31μC/cm2. In summary, the similar electronic density and magnetic ground state of Te- and Se-based ladders indicates both should display similar properties. In particular, the physical and structural similarity with BaFe 2 Se 3 suggests that BaFe 2 Se 3 could become superconducting under high pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Characterization of Lateral Amorphous Selenium Photodetectors for Low-Photon and VUV Detection at Cryogenic Temperatures

The performance of amorphous selenium (a-Se) as a cryogenic photodetector material is evaluated through a series of experiments using laterally structured devices operated in a custom optical test stand. These studies investigate the response of a-Se detectors to low-photon fluxes at high electric fields near avalanche conditions, the linearity of the photoconductive response over a wide dynamic range and the direct detection of narrowband 130 nm vacuum ultraviolet (VUV) illumination. At 87 K, matched-filter analysis shows reliable single-shot detection with efficiencies greater than or equal to 80 percent and area under the curve (AUC) greater than or equal to 0.85 using as few as approximately 6800 incident 401 nm photons, corresponding to approximately 3400 photons within field-active regions after accounting for geometric constraints. Measurements are performed at cryogenic temperatures using calibrated photon fluxes derived from a silicon photomultiplier reference and a characterized optical filter stack. Additional experiments using a tellurium-doped a-Se (a-SeTe) device explore the material's behavior under identical test conditions and demonstrate that avalanche is achievable in a-SeTe at cryogenic temperatures. The results demonstrate reproducible low-noise operation, VUV sensitivity and field-dependent gain behavior in a lateral a-Se architecture, representing the first reported observation of avalanche multiplication in laterally structured a-Se and a-SeTe devices at cryogenic temperatures. These findings support the potential integration of laterally structured a-Se devices into next-generation pixelated liquid-argon time projection chambers (TPCs) requiring scalable, high-field-compatible photon detection systems.

FOS: Physical sciences↗
NASA NTRS1993

Faulty behavior of asynchronous storage elements

It is often assumed that the faults in storage elements (SE's) can be modeled as output/input stuck-at-faults of the element. They are implicitly considered equivalent to the stuck-at faults in the combinational logic surrounding the SE cells. A more accurate higher level fault model for elementary SE's used in asynchronous circuits is presented. This model offers better representation of the physical failures. It is shown that the stuck-at model may be adequate if only modest fault coverage is desired. The enhanced model includes some common fault behaviors of SE's that are not covered by the stuck-at model. These include data-feed-through behaviors that cause the SE to be combinational. Fault models for complex SE cells can be obtained without a significant loss of information about the structure of the circuit.

Al-Assadi, Waleed K.↗
NASA NTRS2000

Comments on "The Sensitivity Study of Radiative-Convective Equilibrium in the Tropics with a Convective Resolving Model"

In general, there are two broad scientific objectives when using cloud resolving models (CRMs or cloud ensemble models-CEMs) to study tropical convection. The first one is to use them as a physics resolving models to understand the dynamic and microphysical processes associated with the tropical water and energy cycles and their role in the climate system. The second approach is to use the CRMs to improve the representation of moist processes and their interaction with radiation in large-scale models. In order to improve the credibility of the CRMs and achieve the above goals, CRMs using identical initial conditions and large-scale influences need to produce very similar results. Two CRMs produced different statistical equilibrium (SE) states even though both used the same initial thermodynamic and wind conditions. Sensitivity tests to identify the major physical processes that determine the SE states for the different CRM simulations were performed. Their results indicated that atmospheric horizontal wind is treated quite differently in these two CRMs. The model that had stronger surface winds and consequently larger latent and sensible heat fluxes from the ocean produced a warmer and more humid modeled thermodynamic SE state. In addition, the domain mean thermodynamic state is more unstable for those experiments that produced a warmer and more humid SE state. Their simulated wet (warm and humid) SE states are thermally more stable in the lower troposphere (from the surface to 4-5 km in altitude). The large-scale horizontal advective effects on temperature and water vapor mixing ratio are needed when using CRMs to perform long-term integrations to study convective feedback under specified large-scale environments. In addition, it is suggested that the dry and cold SE state simulated was caused by enhanced precipitation but not enough surface evaporation. We find some problems with the interpretation of these three phenomena.

Tao, W.-K.↗
NASA NTRS2006

Numerical Skip-Entry Guidance

This paper assesses a preliminary guidance and targeting strategy for accomplishing Skip-Entry (SE) flight during a lunar return-capsule entry flight. One of the primary benefits of flying a SE trajectory is to provide the crew with continuous Continental United States (CONUS) landing site access throughout the lunar month. Without a SE capability, the capsule must land either in water or at one of several distributed land sites in the Southern Hemisphere for a significant portion of a lunar month using a landing and recovery scenario similar to that employed during the Apollo program. With a SE trajectory, the capsule can land either in water at a site in proximity to CONUS or at one of several distributed landing sites within CONUS, thereby simplifying the operational requirements for crew retrieval and vehicle recovery, and possibly enabling a high degree of vehicle reusability. Note that a SE capability does not require that the vehicle land on land. A SE capability enables a longer-range flight than a direct-entry flight, which permits the vehicle to land at a much greater distance from the Entry Interface (EI) point. This does not exclude using this approach to push the landing point to a water location in proximity of CONUS and utilizing water or airborne recovery forces.

Tigges, Michael↗
NASA NTRS2014

A Systems Engineering Approach to Quality Assurance for Aerospace Testing

On the surface, it appears that AS9100 has little to say about how to apply a Quality Management System (QMS) to major aerospace test programs (or even smaller ones). It also appears that there is little in the quality engineering Body of Knowledge (BOK) that applies to testing, unless it is nondestructive examination (NDE), or some type of lab or bench testing associated with the manufacturing process. However, if one examines: a) how the systems engineering (SE) processes are implemented throughout a test program; and b) how these SE processes can be mapped to the requirements of AS9100, a number of areas for involvement of the quality professional are revealed. What often happens is that quality assurance during a test program is limited to inspections of the test article; what could be considered a manufacturing al fresco approach. This limits the quality professional and is a disservice to the programs and projects, since there are a number of ways that quality can enhance critical processes, and support efforts to improve risk reduction, efficiency and effectiveness. The Systems Engineering (SE) discipline is widely used in aerospace to ensure the progress from Stakeholder Expectations (the President, Congress, the taxpayers) to a successful, delivered product or service. Although this is well known, what is not well known is that these same SE processes are implemented in varying complexity, to prepare for and implement test projects that support research, development, verification and validation, qualification, and acceptance test projects. Although the test organization's terminology may vary from the SE terminology, and from one test service provider to another, the basic process is followed by successful, reliable testing organizations. For this analysis, NASA Procedural Requirements (NPR) 7123.1, NASA Systems Engineering Processes and Requirements is used to illustrate the SE processes that are used for major aerospace testing. Many of these processes are also implemented for smaller test projects, and this set of processes will also look familiar to those who have participated in launch site activation and flight demonstrations.

Shepherd, Christena C.↗
NASA NTRS2015

Establishing a Disruptive New Capability for NASA to Fly UAV's into Hazardous Conditions

A 2015 NASA Aeronautics Mission "Seedling" Proposal is described for a Severe-Environment UAV (SE-UAV) that can perform in-situ measurements in hazardous atmospheric conditions like lightning, volcanic ash and radiation. Specifically, this paper describes the design of a proof-of-concept vehicle and measurement system that can survive lightning attachment during flight operations into thunderstorms. Elements from three NASA centers draw together for the SE-UAV concept. 1) The NASA KSC Genesis UAV was developed in collaboration with the DARPA Nimbus program to measure electric field and X-rays present within thunderstorms. 2) A novel NASA LaRC fiber-optic sensor uses Faraday-effect polarization rotation to measure total lightning electric current on an air vehicle fuselage. 3) NASA AFRC's state-of-the-art Fiber Optics and Systems Integration Laboratory is envisioned to transition the Faraday system to a compact, light-weight, all-fiber design. The SE-UAV will provide in-flight lightning electric-current return stroke and recoil leader data, and serve as a platform for development of emerging sensors and new missions into hazardous environments. NASA's Aeronautics and Science Missions are interested in a capability to perform in-situ volcanic plume measurements and long-endurance UAV operations in various weather conditions. (Figure 1 shows an artist concept of a SE-UAV flying near a volcano.) This paper concludes with an overview of the NASA Aeronautics Strategic Vision, Programs, and how a SE-UAV is envisioned to impact them. The SE-UAV concept leverages high-value legacy research products into a new capability for NASA to fly a pathfinder UAV into hazardous conditions, and is presented in the SPIE DSS venue to explore teaming, collaboration and advocacy opportunities outside NASA.

Ely, Jay↗
NASA NTRS1993

Characterization of Si (sub X)Ge (sub 1-x)/Si Heterostructures for Device Applications Using Spectroscopic Ellipsometry

Spectroscopic ellipsometry (SE) characterization of several complex Si (sub X)Ge (sub 1-x)/Si heterostructures prepared for device fabrication, including structures for heterojunction bipolar transistors (HBT), p-type and n-type heterostructure modulation doped field effect transistors, has been performed. We have shown that SE can simultaneously determine all active layer thicknesses, Si (sub X)Ge (sub 1-x) compositions, and the oxide overlayer thickness, with only a general knowledge of the structure topology needed a priori. The characterization of HBT material included the SE analysis of a Si (sub X)Ge (sub 1-x) layer deeply buried (600 nanometers) under the silicon emitter and cap layers. In the SE analysis of n-type heterostructures, we examined for the first time a silicon layer under tensile strain. We found that an excellent fit can be obtained using optical constants of unstrained silicon to represent the strained silicon conduction layer. We also used SE to measure lateral sample homogeneity, providing quantitative identification of the inhomogeneous layer. Surface overlayers resulting from prior sample processing were also detected and measured quantitatively. These results should allow SE to be used extensively as a non-destructive means of characterizing Si (sub X)Ge (sub 1-x)/Si heterostructures prior to device fabrication and testing.

Sieg, R. M.↗
DOE OSTI2025

Estrategias de agua caliente para edificios comerciales: Una guia breve

Las calderas comerciales utilizan gas combustible o petroleo, y a veces electricidad, para producir agua caliente o vapor que se distribuye en un edificio para calefaccion de espacios y/o agua caliente sanitaria. Las calderas se encuentran en edificios de todos los tamanos, desde viviendas residenciales hasta grandes complejos comerciales y, en general, las calderas se vuelven menos eficientes y confiables con el tiempo. La vida util media de una caldera de gas es de 24 a 35 anos1 y, aunque la caldera continue funcionando, se debe planificar su reemplazo alrededor de los 15 a 20 anos de antiguedad o cuando aumentan las necesidades de mantenimiento. La lista de opciones de equipo para reemplazar calderas a gas esta creciendo, especialmente en lo que respecta a bombas de calor. Es fundamental evaluar las opciones para identificar la mejor solucion antes de su instalacion, antes de que sea necesario un reemplazo urgente. En muchos edificios existentes, el equipo se reemplaza con poca planificacion, lo que puede resultar en una operacion ineficiente, mayores costos y mantener al edificio en un ciclo de 25 anos de alto consumo energetico y emisiones. Al planificar un nuevo sistema de agua caliente, se deben considerar las emisiones de carbono, el consumo de energia, los costos y los cambios en las demandas del edificio para lograr un sistema optimo. Un enfoque colaborativo, integral e innovador puede resultar en un sistema mas limpio, energeticamente eficiente y rentable que cumpla con las necesidades de su instalacion y favorezca la disminucion de emisiones en el lugar. Este documento informativo asiste a propietarios y administradores de edificios en la planificacion del reemplazo de calderas, comprendiendo las opciones y encontrando las soluciones mas adecuadas para su situacion.

caldera↗
DOE OSTI2020

Materials Data on Sm3CrSe6 by Materials Project

Sm3CrSe6 crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. there are three inequivalent Sm3+ sites. In the first Sm3+ site, Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.96–3.35 Å. In the second Sm3+ site, Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.97–3.11 Å. In the third Sm3+ site, Sm3+ is bonded to seven Se2- atoms to form distorted SmSe7 pentagonal bipyramids that share a cornercorner with one CrSe6 octahedra, edges with two equivalent CrSe6 octahedra, and edges with two equivalent SmSe7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 32°. There are a spread of Sm–Se bond distances ranging from 2.91–3.03 Å. There are two inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six Se2- atoms to form CrSe6 octahedra that share corners with two equivalent SmSe7 pentagonal bipyramids and edges with two equivalent CrSe6 octahedra. There are two shorter (2.50 Å) and four longer (2.63 Å) Cr–Se bond lengths. In the second Cr3+ site, Cr3+ is bonded to six Se2- atoms to form CrSe6 octahedra that share edges with two equivalent CrSe6 octahedra and edges with four equivalent SmSe7 pentagonal bipyramids. There are two shorter (2.56 Å) and four longer (2.61 Å) Cr–Se bond lengths. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Sm3+ atoms to form distorted SeSm5 trigonal bipyramids that share corners with four equivalent SeSm4Cr trigonal bipyramids, corners with two equivalent SeSm3Cr trigonal pyramids, edges with three SeSm5 trigonal bipyramids, and a faceface with one SeSm3Cr trigonal pyramid. In the second Se2- site, Se2- is bonded to four Sm3+ and one Cr3+ atom to form distorted SeSm4Cr trigonal bipyramids that share corners with five SeSm5 trigonal bipyramids, corners with two equivalent SeSm3Cr trigonal pyramids, and edges with three SeSm5 trigonal bipyramids. In the third Se2- site, Se2- is bonded in a 5-coordinate geometry to three Sm3+ and two equivalent Cr3+ atoms. In the fourth Se2- site, Se2- is bonded in a 5-coordinate geometry to three Sm3+ and two equivalent Cr3+ atoms. In the fifth Se2- site, Se2- is bonded in a 5-coordinate geometry to five Sm3+ atoms. In the sixth Se2- site, Se2- is bonded to three Sm3+ and one Cr3+ atom to form distorted SeSm3Cr trigonal pyramids that share corners with four SeSm5 trigonal bipyramids, corners with three equivalent SeSm3Cr trigonal pyramids, and a faceface with one SeSm5 trigonal bipyramid.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ti5Se4 by Materials Project

Ti5Se4 is Titanium telluride structured and crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a square co-planar geometry to four equivalent Se atoms. All Ti–Se bond lengths are 2.71 Å. In the second Ti site, Ti is bonded to five equivalent Se atoms to form a mixture of distorted edge and corner-sharing TiSe5 square pyramids. There are a spread of Ti–Se bond distances ranging from 2.60–2.63 Å. Se is bonded in a 6-coordinate geometry to six Ti atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co(PdSe)2 by Materials Project

Pd2CoSe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Co is bonded to four equivalent Pd and four equivalent Se atoms to form distorted face-sharing CoPd4Se4 tetrahedra. All Co–Pd bond lengths are 2.86 Å. All Co–Se bond lengths are 2.34 Å. Pd is bonded in a 4-coordinate geometry to two equivalent Co, three equivalent Pd, and five equivalent Se atoms. There are one shorter (2.83 Å) and two longer (2.93 Å) Pd–Pd bond lengths. There are a spread of Pd–Se bond distances ranging from 2.52–2.88 Å. Se is bonded in a 7-coordinate geometry to two equivalent Co and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe(PdSe)2 by Materials Project

Pd2FeSe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Fe is bonded in a 4-coordinate geometry to four equivalent Pd and four equivalent Se atoms. All Fe–Pd bond lengths are 2.86 Å. All Fe–Se bond lengths are 2.33 Å. Pd is bonded in a 2-coordinate geometry to two equivalent Fe, three equivalent Pd, and five equivalent Se atoms. There are one shorter (2.78 Å) and two longer (2.92 Å) Pd–Pd bond lengths. There are a spread of Pd–Se bond distances ranging from 2.51–2.93 Å. Se is bonded in a 4-coordinate geometry to two equivalent Fe and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗