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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Metasurface-enhanced photochemical activity in visible light absorbing semiconductors

Heterogeneous photocatalysis is an important research problem relevant to a variety of sustainable energy technologies. However, obtaining high photocatalytic efficiency from visible light absorbing semiconductors is challenging due to a combination of weak absorption, transport losses, and low activity. Aspects of this problem have been addressed by multilayer approaches, which provide a general scheme for engineering surface reactivity and stability independent of electronic considerations. However, an analogous broad framework for optimizing light–matter interactions has not yet been demonstrated. Here, we establish a photonic approach using semiconductor metasurfaces that is highly effective in enhancing the photocatalytic activity of GaAs, a high-performance semiconductor with a near-infrared bandgap. Our engineered pillar arrays with heights of ∼150 nm exhibit Mie resonances near 700 nm that result in near-unity absorption and exhibit a field profile that maximizes charge carrier generation near the solid–liquid interface, enabling short transport distances. Our hybrid metasurface photoanodes facilitate oxygen evolution and exhibit enhanced incident photon-to-current efficiencies that are ∼22× larger than a corresponding thin film for resonant excitation and 3× larger for white light illumination. Key to these improvements is the preferential generation of photogenerated carriers near the semiconductor interface that results from the field enhancement profile of magnetic dipolar-type modes.

Chemistry↗
DOE OSTI2025

Conin

SAND2025-07645O Conin is a Python library that supports constrained analysis of probabilistic graphical models (PGMs). It enables constrained inference and learning for hidden Markov models, Bayesian networks, dynamic Bayesian networks, and Markov networks. Conin interfaces with the pgmpy library to specify general probabilistic graphical models with a variety of optimization solvers to support learning and inference. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Hart, William [Sandia National Lab. (SNL-CA), Live↗
DOE OSTI2022

Preliminary Reversible Solid Oxide System Specification

This report presents the preliminary documentation of a 10 MWe DC reversible solid oxide cell (rSOC) system designed to use both electrical and thermal energy from a nuclear power plant (NPP). The system is designed to consume 10 MWe DC in electrolysis mode while producing hydrogen from demineralized feedwater. In fuel cell mode, the same stacks produce 2.37 MWe DC of electricity by reacting hydrogen and oxygen, while generating water as a byproduct which is recycled to be used later in the electrolysis mode. The system detailed in this specification is a high-temperature steam electrolysis (HTSE) system when operated in the electrolysis mode. HTSE systems have the benefit of producing hydrogen at a higher efficiency than conventional low-temperature electrolysis (LTE) systems. In this report it is assumed that some of the heat required for HTSE operation comes from an NPP. Heat extraction from an NPP for use in electrolysis mode of the rSOC system allows preheating and vaporization of feedwater before recuperators and trim heaters raise the feed temperature to the approximately 800 °C before entering the solid oxide stacks. The purpose of an rSOC system in a utility company setting is to employ energy arbitrage with a dispatchable demand load which can consume excess electricity generation during times of low grid demand / high generation and can produce electricity for the grid during times of high grid demand / low generation. There is a wide range of energy storage technologies that could be used for utility-scale energy arbitrage (utility-scale battery storage is considered the baseline technology), the object of this work is not to compare and contrast rSOC technology with any of these other technologies, but only to present this preliminary design for consideration and for use in future conceptual or front end engineering design (FEED) work. This document is not meant to be a final specification or definitive description of the rSOC system, but it is meant to showcase preliminary process modeling results, provide boundary conditions and interface requirements such as input feed and utility stream flowrates, temperatures, and pressures as well as thermal and electrical energy requirements, and output conditions in both electrolysis mode and fuel cell mode. These results are intended to inform the future development of a conceptual demonstration-scale study to assess the technical and economic feasibility of a future demonstration of an rSOC integrated project at an NPP.

08 HYDROGEN↗
DOE OSTI2022

Characterization of the structure and chemistry of the solid–electrolyte interface by cryo-EM leads to high-performance solid-state Li-metal batteries

Solid-state lithium-metal (Li 0 ) batteries are gaining traction for electric vehicle applications because they replace flammable liquid electrolytes with a safer, solid-form electrolyte that also offers higher energy density and better resistance against Li dendrite formation. Solid polymer electrolytes (SPEs) are highly promising candidates because of their tunable mechanical properties and easy manufacturability; however, their electrochemical instability against lithium metal (Li 0 ), mediocre conductivity, and poorly understood Li 0 /SPE interphases have prevented extensive application in real batteries. In particular, the origin of the low Coulombic efficiency (CE) associated with SPEs remains elusive, as the debate continues as to whether it originates from unfavored interfacial reactions or lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-electromicroscopy (cryoEM) imaging and spectroscopic techniques to characterize the structure and chemistry of the interface between Li 0 and a polyacrylate-based SPE. Contradicting the conventional knowledge, we find that no protective interphase forms, owing to the sustained reactions between deposited Li dendrites and polyacrylic backbones and succinonitrile plasticizer. Due to the reaction induced volume change, large amounts of cracks form inside the Li dendrites with a stress corrosion-cracking behavior, indicating that Li0cannot be passivated in this SPE system. Based on this observation, we then introduce additive engineering leveraging on the knowledge of liquid electrolytes, and demonstrate that the Li 0 surface can be effectively protected against corrosion using fluoroethylene carbonate (FEC), leading to densely packed Li 0 domes with conformal and stable solid-electrolyte interphases (SEIs) films. Owing to the high room temperature ionic conductivity of 1.01 mS/cm -1 , the high transference number of 0.57 and the stabilized lithium electrolyte interface, this improved new SPE delivers an excellent lithium plating/stripping CE of 99% and 1800 hours of stable cycling in Li||Li symmetric cells (0.2 mA/cm -2 , 1mAh/cm -2 ). Furthermore, this improved cathodic stability along with the high anodic stability enables record high cycle life of >2000 cycles for Li||LiFePO 4 and >400 cycles for Li||LiCoO 2 full cells.

25 ENERGY STORAGE↗
DOE OSTI2022

Non‐Traditional Positively‐Biased Narrow‐Band Perovskite Single‐Crystal Photodetectors Enabled by Interfacial Engineering

Abstract The positive bias in theory narrows down the depletion region and thus results in significant charge injection, which should be detrimental to charge generation and collection performance for traditional photodetectors. Here, instead, it is found that the external quantum efficiency (EQE) is increased by more than 50 times when the photodetector is positively biased. A positive bias of +6 V drives ion migration of Br − and Cs + towards the anode and cathode, respectively, leading to self‐doping within bulk single crystals to form an advantageous p‐i‐n junction for better charge collection in the devices. Meanwhile, the injected holes are allowed to tunnel through the cesium lead bromide/fullerene interface to reach the cathode which also significantly contributes to the enhancement of EQE in the forward‐biased devices. The positively‐biased narrow‐band (full width at half maxima (FWHM) = 16 nm) photodetectors exhibit a specific detectivity of 6.5 × 10 10 Jones at 550 nm, along with the −3 dB cutoff frequency of 2776 Hz. By manipulating charge injection and ion migration using interfacial engineering, a class of non‐traditional, positively‐biased, and highly narrow‐band photodetectors is demonstrated, which offers an alternative design strategy for imaging, biosensing, automatic control, and optical communication.

Li, Junchi↗
DOE OSTI2022

On the broadband vibration isolation performance of nonlocal total-internal-reflection metasurfaces

The concept of a nonlocal elastic metasurface has been recently proposed and experimentally demonstrated in Zhu et al. (2020). When implemented in the form of a total-internal-reflection (TIR) interface, the metasurface can act as an elastic wave barrier that is impenetrable to deep subwavelength waves over an exceptionally wide frequency band. The underlying physical mechanism capable of delivering this broadband subwavelength performance relies on an intentionally nonlocal design that leverages long-range connections between the units forming the fundamental supercell. This paper explores the design and application of a nonlocal TIR metasurface to achieve broadband passive vibration isolation in a structural assembly made of multiple dissimilar elastic waveguides. The specific structural system comprises shell, plate, and beam waveguides, and can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. The study also reports the results of an experimental investigation that confirms the significant vibration isolation capabilities afforded by the embedded nonlocal TIR metasurface. We report these results are particularly remarkable because they show that the performance of the nonlocal metasurface is preserved when applied to a complex structural assembly and under non-ideal incidence conditions of the incoming wave, hence significantly extending the validity of the results presented in Zhu et al. (2020). Results also confirm that, under proper conditions, the original concept of a planar metasurface can be morphed into a curved interface while still preserving full wave control capabilities.

42 ENGINEERING↗
DOE OSTI2021

Demonstrating SolarPILOT’s Python API Through Heliostat Optimal Aimpoint Strategy Use Case

SolarPILOT is a software package that generates solar field layouts and characterizes the optical performance of concentrating solar power (CSP) tower systems. SolarPILOT was developed by the National Renewable Energy Laboratory (NREL) as a stand-alone desktop application but has also been incorporated into NREL’s1 System Advisor Model (SAM) in a simplified format. Prior means for user interaction with SolarPILOT have included the application’s graphical interface, the SAM routines with limited configurability, and through a built-in scripting language called “LK.” This paper presents a new, full-featured, Python-based application programmable interface (API) for SolarPILOT, which we hereafter refer to as CoPylot. CoPylot provides access to all SolarPILOT’s capabilities to generate and characterize power tower CSP systems seamlessly through Python. Supported capabilities include (i) creating and destroying a model instance with message reporting tools; (ii) accessing and setting any SolarPILOT variable including custom land boundaries for field layouts; (iii) programmatically managing receiver and heliostat objects with varied attributes for systems with multiple receiver or heliostat types; (iv) generating, assigning, and modifying solar field layouts including the ability to set individual heliostat locations, aimpoints, soiling rates, and reflectivity levels; (v) simulating solar field performance; (vi) returning detailed results describing performance of individual heliostats, the aggregate field, and receiver flux distribution; and, (vii) exporting Python-based model instances to multiple file formats. CoPylot enables Python users to perform detailed CSP tower analysis utilizing either the Hermite expansion technique (analytical) or the SolTrace ray-tracing engine. In addition to CoPylot’s functionality, Python users have access to the over 100,000 open-source libraries to develop, analyze, optimize, and visualize power tower CSP research. This enables CSP researchers to perform analysis that was previously not possible through SolarPILOT’s existing interfaces. This paper discusses the capabilities of CoPylot and presents a use case wherein we demonstrate optimal solar field aiming strategies.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2020

Primal interface debonding formulation for finite strain isotropic plasticity

In this work, a framework is developed for modeling ductile damage of nonlinear materials whose plastic deformation is characterized using rate independent classical plasticity. This method relies on the assumption that the free energy can be decomposed into elastic, plastic and damage parts. A thermodynamically consistent method is derived which satisfies the second law of thermodynamics in the Clausius–Duhem inequality form. The dissipation associated with plasticity takes place in the domain only, while damage dissipation is localized to the interface. The method is developed using Variational Multiscale ideas to obtain definitions of the interface fluxes within a primal formulation analogous to the Discontinuous Galerkin method, which ensures weakly vanishing interface gap prior to reaching a damage initiation criterion. The local nonlinear problem to calculate both plastic deformation gradient and damage variable follows an incremental approach similar to classical plasticity return mapping algorithm. This elastoplastic damage formulation is developed for material undergoing finite strain, and it naturally accommodates a trapezoidal traction separation law (TSL) whose shape can be varied to model either ductile interface behavior or brittle interface behavior. The formulation's performance is assessed through modeling a patch test and a compact tension specimen.

42 ENGINEERING↗
DOE OSTI2021

Large intrinsic anomalous Hall effect in SrIrO 3 induced by magnetic proximity effect

The anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, by skew or side-jump scattering due to chiral features of the disorder scattering, or by an intrinsic contribution directly linked to the topological properties of the Bloch states. Here we show that the AHE can be artificially engineered in materials in which it is originally absent by combining the effects of symmetry breaking, spin orbit interaction and proximity-induced magnetism. In particular, we find a strikingly large AHE that emerges at the interface between a ferromagnetic manganite (La 0.7 Sr 0.3 MnO 3 ) and a semimetallic iridate (SrIrO 3 ). It is intrinsic and originates in the proximity-induced magnetism present in the narrow bands of strong spin-orbit coupling material SrIrO 3 , which yields values of anomalous Hall conductivity and Hall angle as high as those observed in bulk transition-metal ferromagnets. These results demonstrate the interplay between correlated electron physics and topological phenomena at interfaces between 3d ferromagnets and strong spin-orbit coupling 5d oxides and trace an exciting path towards future topological spintronics at oxide interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fully Transparent GaN Homojunction Tunnel Junction-Enabled Cascaded Blue LEDs.

A sidewall activation process was optimized for buried magnesium-doped p-GaN layers yielding a significant reduction in tunnel junction-enabled light emitting diode (LED) forward voltage. This buried activation enabled the realization of cascaded blue LEDs with fully transparent GaN homojunction tunnel junctions. The initial optimization of buried p-GaN activation was performed on PN junctions grown by metal organic chemical vapor deposition (MOCVD) buried under hybrid tunnel junctions grown by MOCVD and molecular beam epitaxy. Next the activation process was implemented in cascaded blue LEDs emitting at 450 nm, which were enabled by fully transparent GaN homojunction tunnel junctions. The tunnel junction-enabled multi-active region blue LEDs were grown monolithically by MOCVD. This work demonstrates a state-of-the-art tunnel junction-enabled cascaded LED utilizing homojunction tunnel junctions which do not contain any heterojunction interface.

42 ENGINEERING↗
DOE OSTI2026

Roadmap on advanced and / real-time characterisation of solid state materials and devices for energy applications

A strong societal and political drive is motivating the development and optimization of novel energy conversion and storage systems for decarbonization. The successful implementation of solid state devices such as fuel cells and secondary batteries depends, however, on achieving ambitious targets in terms of performance, reliability and cost competitiveness. Research and technology are addressing these needs through a holistic approach including exploration of new materials and nanoarchitectures, as well as system engineering. These significant efforts require the support of appropriate characterization tools capable of assessing nanometer-scale phenomena such as concentration profiles of ionic and electronic charges, local chemical compositions and their evolution over time across interfaces. This roadmap provides an overview of selected advanced characterization techniques for energy materials and devices. Specific focus is put on in situ/operando methods for probing electrochemical phenomena in real-time under realistic working conditions. Experts in the field provide an extensive review of the current state of the art in 2025 and the current and future challenges for the characterization of local chemistry and kinetics in the bulk of the material, in nanoarchitectures (e.g. thin films) and at the interfaces (e.g. grain boundaries, phase contacts, solid/liquid and solid/gas interfaces) . The aim is to provide a detailed guide to the techniques, describing opportunities and bottlenecks for their practical deployment and examples of successful applications.

25 ENERGY STORAGE↗
DOE OSTI2022

In-plasma photo-assisted etching of Si with chlorine aided by an external vacuum ultraviolet source

Photo-assisted etching of p-type Si was previously found to occur in a chlorine-containing, Faraday-shielded, inductively coupled plasma (ICP), and this was attributed to the vacuum ultraviolet (VUV) light generated by the plasma. Other causes for the very high etching rates were ruled out, including ion bombardment. In the present study, the substrate in the main Cl2/Ar ICP was subjected to extra VUV light that was generated in an independently controlled, auxiliary Ar/He ICP in tandem with the main ICP. The ICPs were separated by a tungsten mesh and a bundle of high-aspect-ratio quartz tubes in a honeycomb configuration. There was no measurable perturbation of the main plasma by the auxiliary plasma. The etching rate was found to be enhanced by 11%–51% with the additional VUV light provided by the auxiliary ICP. With absolute measurements of the auxiliary ICP photon flux at the sample surface, as described elsewhere, incredibly large etching yields of 90–240 Si atoms per photon were obtained. It is argued that etching is not a result of electron–hole pair formation but is instead ascribed to a photocatalytic chain reaction.

42 ENGINEERING↗
DOE OSTI2025

A high-resolution molecular spin-photon interface at telecommunication wavelengths

Optically addressable electronic spins in polyatomic molecules are a promising platform for quantum information science, with the potential to enable scalable qubit design and integration through atomistic tunability and nanoscale localization. However, optical state- and site-selection are an open challenge. Here, in this work, we introduce an organo-erbium spin qubit in which narrow (megahertz-scale) optical and spin transitions couple to provide high-resolution access to spin degrees of freedom with telecommunication-frequency light. This spin-photon interface enables demonstration of optical spin polarization and readout that distinguishes between spin states and magnetically inequivalent sites in a molecular crystal. Operation at frequencies compatible with mature photonic and microwave devices provides an opportunity for engineering scalable, integrated molecular spin-optical quantum technologies.

Weiss, Leah R. [University of Chicago, IL (United ↗
DOE OSTI2026

or-topas: Operations Research Toolkit for Pyomo Alternative Solutions

SAND2026-16702O OR-TOPAS: Operations Research Toolkit for Pyomo Alternative Solutions is a tool that enhances optimization applications defined by the Pyomo modeling library. It offers functions to generate optimal or near-optimal solutions, operating independently of Pyomo’s solver interface. Users can configure these functions with specific solver names and options, resulting in a custom solution object that returns a list of solutions. The OR-TOPAS library includes methods tailored to the properties of the model, such as binary integer programs versus linear programs, and specific solver interfaces like Gurobi. It does not provide models for specific applications, but it is applicable to a wide range of Pyomo optimization models. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Siirola, John [Sandia National Lab. (SNL-CA), Live↗
DOE OSTI2023

Local Modification of Cast Aluminum Alloys via the Cast-and-Print Process

Casting of aluminum alloys is a cost-effective way to mass manufacture bulk aluminum parts for automotive applications. However, the casting process requires filling of a mold, which imposes some limitations on the geometries that can be successfully cast and limits parts to be a uniform material. Therefore, we proposed that a hybrid casting plus additive manufacturing approach, Cast-and-Print, which could be used to locally modify the properties and geometry of cast parts to create difficult-to-cast, functional features. Here, we report the results of the properties of deposited materials on cast substrate, the properties of the interface of the deposited and cast material, and the application of the Cast-and-Print method to deposit rivet tabs on high-pressure die cast plates. Ultimately, the approach appears viable, but there are engineering challenges present to reliable additive processing of aluminum wires that need to be overcome for successful implementation of the technology.

42 ENGINEERING↗
DOE OSTI2024

A Scalable & Non-Destructive Characterization Strategy to Study Semiconductor/Dielectric Interfaces and Predict Wafer-Level Device Performance

The defect density present at the dielectric-semiconductor interface in an MOS structure directly influences the channel carrier characteristics in semiconductor devices, especially in wide bandgap material systems used in power devices. While these trap defects are typically quantified through electrical characterization of MOS-capacitor test structures, this treatment offers very little insight into the physical nature of interface defects. Such shortcomings demand a physical characterization strategy to guide fabrication optimization. X-ray photoelectron spectroscopy (XPS) is suggested as a viable technique to determine chemical data for dielectric interfaces formed using atomic layer deposition (ALD) on GaN substrates. Previously, 1-D XPS characterization has confirmed the presence of a Ga x O y interlayer between ALD dielectrics and the GaN substrate. In this work, XPS data is serially collected to form 2-D images of an ALD-Al 2 O 3 /GaN interface as a proof-of-concept experiment for in-situ XPS quality monitoring during ALD processing. The information provided by this work reveals some of the challenges for incorporating XPS characterization as an in-situ strategy during fabrication of GaN-based devices. Separately, electrical mapping of a 2-D array of ALD-Al 2 O 3 /GaN MOS-capacitor devices provide a means to quantify the spatial variations in interface quality across a single wafer. Physical characterization techniques, such as time-of-flight secondary ion mass spectroscopy, provide additional chemical information about the Al 2 O 3 /Ga x O y /GaN structure that complement the electrical mapping results. This analysis shows that a higher Ga x O y content correlates with higher interface state defects for trap energies deep in the band gap.

42 ENGINEERING↗
DOE OSTI2025

Elucidating the Role of Electric Fields in Fe Oxidation via an Environmental Atom Probe

Abstract We quantify the effects of intensely applied electric fields on the Fe oxidation mechanism. The specimen are pristine Fe single crystals exposing a variety of surface structures identified by field ion microscopy. These crystals are simultaneously exposed to low pressures of pure oxygen gas, on the order of 10 −7 mbar, while applying intense electric fields on their surface of several tens of volts per nanometer. The local composition of the different surface structures is probed directly and in real time using an Environmental Atom Probe and successfully compared with first principles‐based models. We found that rough Fe{244} and Fe{112} facets are more reactive toward oxygen than compact Fe{024} and Fe{011} facets. Results demonstrate that the influence of an electric field on the oxidation kinetics depends on the timescales that are involved as the system evolves toward equilibrium. The initial oxidation kinetics show that strong increases in electric fields facilitate the formation of an oxide. However, as one approaches equilibrium, high field values mitigate this formation. Ultimately, this study elucidates how high externally applied electric fields can be used to dynamically exploit reaction dynamics at the nanoscale towards desired products in a catalytic reaction at mild reaction conditions.

Lambeets, Sten V. [Physical and Computational Scie↗