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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Detector Materials Scoping Study: Research and Development Recommendations

Radiation detection materials have a unique role in many nuclear security missions. The variety of different applications requires the use of different materials whose characteristics are determined by the specific application requirements. While baseline capabilities have been established to use radiation detection in these applications, the potential to greatly advance those capabilities still exists through the development of superior radiation detection materials and/or the development of new materials that enable new technologies to be implemented more effectively. In 2024 the Defense Nuclear Nonproliferation Research and Development (DNN R&D) Near Field Detection Portfolio charged a detector materials scoping study, composed of a group of radiation-detection materials subject matter experts, to produce a community-wide consensus view of the current state of radiation materials research and to set recommendations for expanded investment over a ten-year time frame. This scoping study sought to understand and document the landscape of how radiation detection materials are used, what characteristics drive the selection of various materials, and what developments are needed to drive the state of the art. To respond to this charge, the scoping study created three working groups, each focusing on a different topical area in radiation detection materials research - Semiconductor Materials, Inorganic Scintillators and Organic Scintillators - with the task to identify the current state of the art in materials research and to provide mission-relevant research and development recommendations. Each working group was chaired by two members of the project team with widely recognized expertise in the field. Solicitations were sent out to experts at the DOE national laboratories, industry, academia and federal government agencies to participate in these working groups. The working groups met at regular intervals throughout 2024 and early 2025, each delivering a technical roadmap designed to enable the pursuit of R&D more intensely on high-impact materials challenges and detector solutions that are deemed as the greatest strategic value to DNN R&D and its stakeholders. The roadmap is also intended to help communicate recommended programmatic priorities within DNN R&D and across the nonproliferation and research communities.

36 MATERIALS SCIENCE↗
NASA NTRS1993

High Speed Solid State Circuit Breaker

The U.S. Army Research Laboratory, Fort Monmouth, NJ, has developed and is installing two 3.3 MW high speed solid state circuit breakers at the Army's Pulse Power Center. These circuit breakers will interrupt 4160V three phase power mains in no more than 300 microseconds, two orders of magnitude faster than conventional mechanical contact type circuit breakers. These circuit breakers utilize Gate Turnoff Thyristors (GTO's) and are currently utility type devices using air cooling in an air conditioned enclosure. Future refinements include liquid cooling, either water or two phase organic coolant, and more advanced semiconductors. Each of these refinements promises a more compact, more reliable unit.

Podlesak, Thomas F.↗
NASA NTRS1992

Water Purification Systems

A water purification/recycling system developed by Photo-Catalytics, Inc. (PCI) for NASA is commercially available. The system cleanses and recycles water, using a "photo-catalysis" process in which light or radiant energy sparks a chemical reaction. Chemically stable semiconductor powders are added to organically polluted water. The powder absorbs ultraviolet light, and pollutants are oxidized and converted to carbon dioxide. Potential markets for the system include research and pharmaceutical manufacturing applications, as well as microchip manufacture and wastewater cleansing.

Source record↗
DOE OSTI2020

Bright magnetic dipole radiation from two-dimensional lead-halide perovskites

Light-matter interactions in semiconductors are uniformly treated within the electric dipole approximation; multipolar interactions are considered “forbidden.” We experimentally demonstrate that this approximation inadequately describes light emission in two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs), solution processable semiconductors with promising optoelectronic properties. By exploiting the highly oriented crystal structure, we use energy-momentum spectroscopies to demonstrate that an exciton-like sideband in 2D HOIPs exhibits a multipolar radiation pattern with highly directed emission. Electromagnetic and quantum-mechanical analyses indicate that this emission originates from an out-of-plane magnetic dipole transition arising from the 2D character of electronic states. Symmetry arguments and temperature-dependent measurements suggest a dynamic symmetry-breaking mechanism that is active over a broad temperature range. These results challenge the paradigm of electric dipole–dominated light-matter interactions in optoelectronic materials, provide new perspectives on the origins of unexpected sideband emission in HOIPs, and tease the possibility of metamaterial-like scattering phenomena at the quantum-mechanical level.

42 ENGINEERING↗
DOE OSTI2020

Tunable exciton binding energy in 2D hybrid layered perovskites through donor–acceptor interactions within the organic layer

The strength of electrostatic interactions within semiconductors strongly affects their performance in optoelectronic devices. An important target is the tuning of a material’s exciton binding energy—the energy binding an electron–hole pair through the electrostatic Coulomb force—independent of its electronic band gap. Here, we report on the doping of a family of two-dimensional hybrid perovskites, in which inorganic lead halide sheets alternate with naphthalene-based organic layers, with tetrachloro-1,2-benzoquinone (TCBQ). For four out of seven n = 1 perovskites, the incorporation of the electron-accepting TCBQ dopant into the organic sublattice containing the electron-donating naphthalene species enabled the tuning of the materials’ 1s exciton binding energy. The naphthalene–TCBQ electron donor–acceptor interactions increased the electrostatic screening of the exciton, in turn lowering its binding energy relative to the undoped perovskite—by almost 50% in one system. Structural and optical characterization showed that the inorganic lattice is not significantly perturbed even though the layer-to-layer spacing increases upon molecular dopant incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Material Needs and Measurement Challenges for Advanced Semiconductor Packaging: Understanding the Soft Side of Science

This Perspective builds upon insights from the National Institute of Standards and Technology (NIST)-organized workshop, “Materials and Metrology Needs for Advanced Semiconductor Packaging Strategies,” held at the 35th annual Electronics Packaging Symposium in Binghamton, NY, on September 5, 2024. It outlines critical challenges and opportunities related to polymer-based “soft” materials in advanced semiconductor packaging, with emphasis on polymer science, measurement science (metrology), and the strategic development of Research-Grade Test Materials (RGTMs). These efforts, led by the NIST CHIPS team, aim to advance the fundamental understanding of structure-property-processing relationships, promote standardized guidelines and innovative methods for material characterization, and accelerate the development, qualification, and adoption of next-generation packaging materials. The Perspective also distills key insights from the panel discussion with industry experts, emphasizing the need for close collaboration among materials scientists, process engineers, and metrology experts to enable a holistic strategy, further highlighting the importance of cross-sector partnerships among industry, academia, and government to address pressing challenges in packaging materials and processes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Impact of Chiral Symmetry Breaking on Spin-Texture and Lone Pair Expression in Chiral Crystals of Hybrid Antimony and Bismuth Halides

Chiral organic building blocks can be incorporated into hybrid organic-inorganic metal-halide crystalline semiconductors so as to control and impact the interconversion between light, charge, and spin. Here, we report a series of hybrid antimony and bismuth halide materials of the general formula MBA 4 B 2 X 10 (B = Sb 3+ , Bi 3+ ; X = Br - , I - ) and study how chiral symmetry breaking imposed by the templating organic chiral methylbenzylammonium (MBA) cations induces symmetry breaking within the inorganic sublattice and leads to a unique spin-texture. The chiral MBA cations introduce two structural modifications to the metal-halide sublattice that consists of isolated edge-sharing dimers of B 2 X 10 octahedra: (1) the dimers have a chiral spatial arrangement with respect to one another and (2) there is an asymmetric distortion of the two subunits within the individual dimers with a higher distortion caused by strong stereochemical activity of the Sb 5s 2 lone pair electrons. The structural distortions and chiral arrangement result in circular dichroism (CD) at the band edge of the inorganic framework with dissymmetry factors in the range of 10 -4 . Chiral spin-splitting of the inorganic states, caused by breaking of the inversion symmetry and large spin-orbit coupling, is studied via density functional theory (DFT), and a multiband effective mass theory was developed that links the DFT-derived spin-splitting of helical character (i.e., spin expectation value not perpendicular to the crystal momentum) to the observed CD. Furthermore, we also find broad red photoluminescence from the MBA 4 Sb 2 Br 10 compounds, which we attribute to self-trapped excitonic emission driven by the large distortion due to the lone pair expression.

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

Processable High Electron Mobility {pi}-Copolymers via Mesoscale Backbone Conformational Ordering

The synthesis and experimental/theoretical characterization of a new series of electron-transporting copolymers based on the naphthalene bis(4,8-diamino-1,5-dicarboxyl)amide (NBA) building block are reported. Comonomers are designed to test the emergent effects of manipulating backbone torsional characteristics, and density functional theory (DFT) analysis reveals the key role of backbone conformation in optimizing electronic delocalization and transport. The NBA copolymer conformational and electronic properties are characterized using a broad array of molecular/macromolecular, thermal, optical, electrochemical, and charge transport techniques. All NBA copolymers exhibit strongly aggregated morphologies with significant nanoscale order. Copolymer charge transport properties are investigated in thin-film transistors and exhibit excellent electron mobilities ranging from 0.4 to 4.5 cm(2) V-1 s(-1). Importantly, the electron transport efficiency correlates with the film mesoscale order, which emerges from comonomer-dependent backbone planarity and extension. These results illuminate the key NBA building block structure-morphology-bulk property design relationships essential for processable, electronics-applicable high-performance polymeric semiconductors.

n‐↗
DOE OSTI2023

Interfacial Connections between Organic Perovskite/n + Silicon/Catalyst that Allow Integration of Solar Cell and Catalyst for Hydrogen Evolution from Water

Abstract The rapidly increasing solar conversion efficiency (PCE) of hybrid organic–inorganic perovskite (HOIP) thin‐film semiconductors has triggered interest in their use for direct solar‐driven water splitting to produce hydrogen. However, application of these low‐cost, electronic‐structure‐tunable HOIP tandem photoabsorbers has been hindered by the instability of the photovoltaic‐catalyst‐electrolyte (PV+E) interfaces. Here, photolytic water splitting is demonstrated using an integrated configuration consisting of an HOIP/n + silicon single junction photoabsorber and a platinum (Pt) thin film catalyst. An extended electrochemical (EC) lifetime in alkaline media is achieved using titanium nitride on both sides of the Si support to eliminate formation of insulating silicon oxide, and as an effective diffusion barrier to allow high‐temperature annealing of the catalyst/TiO 2 ‐protected‐n + silicon interface necessary to retard electrolytic corrosion. Halide composition is examined in the (FA 1‐x Cs x )PbI 3 system with a bandgap suitable for tandem operation. A fill factor of 72.5% is achieved using a Spiro‐OMeTAD‐hole‐transport‐layer (HTL)‐based HOIP/n + Si solar cell, and a high photocurrent density of −15.9 mA cm −2 (at 0 V vs reversible hydrogen electrode) is attained for the HOIP/n + Si/Pt photocathode in 1 m NaOH under simulated 1‐sun illumination. While this thin‐film design creates stable interfaces, the intrinsic photo‐ and electro‐degradation of the HOIP photoabsorber remains the main obstacle for future HOIP/Si tandem PEC devices.

08 HYDROGEN↗
DOE OSTI2023

Mechanistic origins of excitonic properties in 2D perovskites: Implications for exciton engineering

As the field of 2D halide perovskites (HPs) matures, state-of-the-art techniques to measure important properties, such as the band gap (E g ) and exciton binding energy (E b ), continue to produce inconsistent values. Here, we tackle this long-standing problem by obtaining direct measurements of E g and E b for 31 unique HP structures. The E b values are lower than in previous literature reports and lower than expected from standard theory that assumes excitons are screened by optical-frequency dielectric constants. These low E b values are shown to be a consequence of unique screening effects, such as superlattice screening and phonon screening. Here, we find a strikingly strong correlation between E b and E g and provide design principles to a priori tune E g and E b to their optimal values. As such, this work offers a blueprint for E g -E b engineering of low-dimensional semiconductors as an even more useful replacement for simply band-gap engineering.

14 SOLAR ENERGY↗
DOE OSTI2021

Observation of Single-Electron Transport and Charging on Individual Point Defects in Atomically Thin WSe 2

Defects significantly impact the properties of 2D semiconductors, providing in-gap quantum states that can serve as a natural platform for single-electron operations, localization sites for excitons to serve as single-photon sources, and potentially quantum spin memories. To date, however, a microscopic observation of such a single-electron transport (SET) behavior has been rarely reported on single defects of 2D semiconductors. In this study, we report a SET and charge-state transition on individual point-defect states buried in the bilayer WSe 2 using scanning tunneling microscopy. SET characteristics of their states is evidenced by both the Coulomb staircase and the saturation behavior of the transport current, consistent with the SET model. Furthermore, we demonstrate that, through the local field of a scanning tunneling microscope tip, it is possible to successively charge the defects by single electrons, suggested by both the ring structures and charging peaks in dI/dV measurements. Our results provide new insights into the quantum nature of these defect-bound states, as well as the possibility of using their single-electron behavior and response for applications in quantum information and local-field sensing.

2D semiconductor↗
DOE OSTI2020

Wannier–Koopmans method calculations for transition metal oxide band gaps

The widely used density functional theory (DFT) has a major drawback of underestimating the band gaps of materials. Wannier–Koopmans method (WKM) was recently developed for band gap calculations with accuracy on a par with more complicated methods. WKM has been tested for main group covalent semiconductors, alkali halides, 2D materials, and organic crystals. Here we apply the WKM to another interesting type of material system: the transition metal (TM) oxides. TM oxides can be classified as either with d 0 or d 10 closed shell occupancy or partially occupied open shell configuration, and the latter is known to be strongly correlated Mott insulators. We found that, while WKM provides adequate band gaps for the d0 and d10 TM oxides, it fails to provide correct band gaps for the group with partially occupied d states. This issue is also found in other mean-field approaches like the GW calculations. We believe that the problem comes from a strong interaction between the occupied and unoccupied d-state Wannier functions in a partially occupied d-state system. We also found that, for pseudopotential calculations including deep core levels, it is necessary to remove the electron densities of these deep core levels in the Hartree and exchange–correlation energy functional when calculating the WKM correction parameters for the d-state Wannier functions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of a redox-mediating ligand shell on photocatalysis by CdS quantum dots

Semiconductor quantum dots (QDs) are efficient organic photoredox catalysts due to their high extinction coefficients and easily tunable band edge potentials. Despite the majority of the surface being covered by ligands, our understanding of the effect of the ligand shell on organic photocatalysis is limited to steric effects. We hypothesize that we can increase the activity of QD photocatalysts by designing a ligand shell with targeted electronic properties, namely, redox-mediating ligands. Herein, we functionalize our QDs with hole-mediating ferrocene (Fc) derivative ligands and perform a reaction where the slow step is hole transfer from QD to substrate. Surprisingly, we find that a hole-shuttling Fc inhibits catalysis, but confers much greater stability to the catalyst by preventing a build-up of destructive holes. We also find that dynamically bound Fc ligands can promote catalysis by surface exchange and creation of a more permeable ligand shell. Finally, we find that trapping the electron on a ligand dramatically increases the rate of reaction. Furthermore, these results have major implications for understanding the rate-limiting processes for charge transfer from QDs and the role of the ligand shell in modulating it.

Chemistry↗
DOE OSTI2024

Observation of negative surface and interface energies of quantum dots

Surface energy is a fundamental property of materials and is particularly important in describing nanomaterials where atoms or molecules at the surface constitute a large fraction of the material. Traditionally, surface energy is considered to be a positive quantity, where atoms or molecules at the surface are less thermodynamically stable than their counterparts in the interior of the material because they have fewer bonds or interactions at the surface. Using calorimetric methods, we show that the surface energy is negative in some prototypical colloidal semiconductor nanocrystals, or quantum dots with organic ligand coatings. This implies that the surface atoms are more thermodynamically stable than those on the interior due to the strong bonds between these atoms and surfactant molecules, or ligands, that coat their surface. In addition, we extend this work to core/shell indium phosphide/zinc sulfide nanocrystals and show that the interfacial energy between these materials is highly thermodynamically favorable in spite of their large lattice mismatch. This work challenges many of the assumptions that have guided thinking about colloidal nanomaterial thermodynamics, investigates the fundamental stability of many technologically relevant colloidal nanomaterials, and paves the way for future experimental and theoretical work on nanocrystal thermodynamics.

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

Nanoscale dynamics during self-organized ion beam patterning of Si. II. Kr + bombardment

Understanding the self-organized ion beam nanopatterning of elemental semiconductors, particularly silicon, is of intrinsic scientific and technological interest. This is the second component of a two-part coherent x-ray scattering and x-ray photon correlation spectroscopy (XPCS) investigation of the kinetics and fluctuation dynamics of nanoscale ripple development on silicon during 1 keV Ar + (part I) and Kr + bombardment at 65° polar angle. Here it is found that the ion-enhanced viscous flow relaxation is essentially equal for Kr + -induced patterning as previously found for Ar + patterning despite the difference in ion masses. However, the magnitude of the surface curvature-dependent roughening rate in the early-stage kinetics is larger for Kr + than for Ar + , consistent with expectations that the heavier ion gives an increased mass redistributive contribution to the initial surface instability. As with the Ar + case, fluctuation dynamics in the late stage show a peak in correlation times at the length scale corresponding to the dominant structural feature on the surface—the ripples. Finally, it is shown that speckle motion during the surface evolution can be analyzed to determine spatial inhomogeneities in erosion rate and ripple velocity. This allows the direction and speed of ripple motion to be measured in a real time experiment. In the present case, ripple motion is found to be into the projected direction of the ion source, in contrast to expectations from an existing sputter erosion driven model with parameters derived from binary collision approximation simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Chiral-induced spin selectivity enables a room-temperature spin light-emitting diode

In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2019

Radiolysis of Macromolecular Organic Material in Mars-Relevant Mineral Matrices

The fate of organic material on Mars after deposition is crucial to interpreting the source of these molecules. Previous work has addressed how various organic compounds at millimeter depths in sediments respond to ultraviolet radiation. In contrast, this study addressed how high‐energy particle radiation (200‐MeV protons, simulating the effect of galactic cosmic rays and solar wind at depths of <4–5 cm) influences organic macromolecules in sediments. Specifically, we report the generation of organic‐acid radiolysis products after exposure to radiation doses equivalent to geological time scales (1–7 Myr). We found that formate and oxalate were produced from a variety of organic starting materials and mineral matrices. Unlike ultraviolet‐driven reactions that can invoke Fenton chemistry to produce organic acids, our work suggests that irradiation of semiconductor surfaces, such as TiO2 or possible clay minerals found on Mars, forms oxygen and hydroxyl radical species, which can break down macromolecules into organic acids. We also investigated the metastability of benzoate in multiple mineral matrices. Benzoate was added to samples prior to irradiation and persisted up to 500 kGys of exposure. Our findings suggest that organic acids are likely a major component of organic material buried at depth on Mars.

Fox, A. C.↗