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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Quantum Imaging of Ferromagnetic van der Waals Magnetic Domain Structures at Ambient Conditions

Recently discovered 2D van der Waals magnetic materials, and specifically iron–germanium–telluride (Fe5GeTe2), have attracted significant attention both from a fundamental perspective and for potential applications. Key open questions concern their domain structure and magnetic phase transition temperature as a function of sample thickness and external field, as well as implications for integration into devices such as magnetic memories and logic. Here we address key questions using a nitrogen-vacancy center based quantum magnetic microscope, enabling direct imaging of the magnetization of Fe5GeTe2 at submicrometer spatial resolution as a function of temperature, magnetic field, and thickness. This quantum imaging technique provides noninvasive, high-sensitivity measurements with high spatial resolution under ambient conditions, making it particularly well suited for probing 2D magnets. We employ spatially resolved measures, including magnetization variance and cross-correlation, and find a significant spread in transition temperature yet with no clear dependence on thickness down to 15 nm. We also identify previously unknown stripe features in the optical as well as magnetic images, which we attribute to modulations of the constituting elements during crystal synthesis and subsequent oxidation. Our results suggest that the magnetic anisotropy in this material does not play a crucial role in their magnetic properties, leading to a magnetic phase transition of Fe5GeTe2 which is largely thickness-independent down to 15 nm. Our findings could be significant in designing future spintronic devices, magnetic memories, and logic with 2D van der Waals magnetic materials.

Bindu, Bindu [Hebrew University of Jerusalem, Isra↗
DOE OSTI2019

Tailoring Fluorescence Emissions, Quantum Yields, and White Light Emitting from Nitrogen-doped Graphene and Carbon Nitride Quantum Dots

Highly fluorescent N-doped graphene quantum dots (NGQDs) and graphitic carbon nitride quantum dots (CNQDs, g-C 3 N 4 ) were synthesized using a solid-phase microwave-assisted (SPMA) technique. The SPMA method, based on the pyrolysis of citric acid and urea with different recipes, is capable of producing quantum dots with coexisting NGQDs and CNQDs at 280°C within only five minutes. The photoluminescence (PL) emissions from NGQD and CNQDs are strongly dependent on excitation wavelength and the solvent type, i.e., water, ethanol, and N-methyl pyrrolidinone. The unique design of the quantum dots possesses a multiple chromophoric band-gap structure, originated from the presence of g-C 3 N 4 , defect-related emissive traps, and grain boundaries. Thus, an appropriate excitation wavelength induces a conjugated π electron system to fulfill the most probable absorption band, resulting in wavelength-dependent emissions including ultraviolet, visible and infrared light. Here, the quantum yield of the NGQD and CNQD samples can attain as high as 68.1%. Accordingly, one light-emitting device using the combination of the NGQD and CNQD powders embedded polymeric film can emit white-like light with high power conversion efficiency.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

A dedicated compression device for high resolution X-ray tomography of compressed gas diffusion layers

We present an experimental approach to study the three-dimensional microstructure of gas diffusion layer (GDL) materials under realistic compression conditions. A dedicated compression device was designed that allows for synchrotron-tomographic investigation of circular samples under well-defined compression conditions. The tomographic data provide the experimental basis for stochastic modeling of nonwoven GDL materials. A plain compression tool is used to study the fiber courses in the material at different compression stages. Transport relevant geometrical parameters, such as porosity, pore size, and tortuosity distributions, are exemplarily evaluated for a GDL sample in the uncompressed state and for a compression of 30 vol.%. To mimic the geometry of the flow-field, we employed a compression punch with an integrated channel-rib-profile. It turned out that the GDL material is homogeneously compressed under the ribs, however, much less compressed underneath the channel. GDL fibers extend far into the channel volume where they might interfere with the convective gas transport and the removal of liquid water from the cell.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Nonlinear optical parameters of nonparabolic semiconductor plasmas: Influence of energy dependent effective mass

An investigation is carried out in III-V compound semiconductor when a strong transverse magnetic field is applied. By considering the heating effect of carriers, an analytical investigation is made for n-InSb in which the nonlinearity arises due to dependence of effective mass on electronic temperature. At optical frequencies the temperature dependence part of momentum transfer collision frequency is assumed to be negligibly small. The linear and nonlinear parts of optical parameters are evaluated through the first and third order susceptibility of InSb sample. The analysis reveals that the nonlinear part of refractive index increases with intensity which leads to self-focusing of the beam. Thus by adjusting the doping concentration pump frequency and intensity, one may achieve desired nonlinearity in the crystal. Hence n - InSb sample establishes its potentials as candidate material for fabrication of cubic nonlinear devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Non-invasive low charge electron beam time-of-arrival diagnostic using a plasmonics-enhanced photoconductive antenna

The use of a plasmonics-enhanced photoconductive antenna (PCA) optically gated by a near infrared (NIR) pulse enables non-invasive time-of-arrival measurements of a low charge electron beam with respect to the NIR reference, achieving picosecond resolution. The measured signal values show the expected scaling with the beam charge and distance from PCA to the beam axis, as the PCA samples the electric field of the passing electron beam. We operate the device with an NIR spot size much larger than the PCA active-area, resulting in a very simple optical setup and alignment procedure, making the plasmonics-enhanced PCA a preferred alternative to more complex timing diagnostics for applications requiring non-invasive picosecond or sub-picosecond timestamping.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

DR-RINS: Digital real-time relative intensity noise suppressor for pump–probe spectroscopy and microscopy

Relative intensity noise (RIN) inherent in fiber lasers poses a serious obstacle to their use in pump–probe spectroscopy and imaging. RIN can be removed through an analog balanced detector, or, as we have previously shown, software adaptive noise cancellation (ANC) on digitized signals. One major drawback to software ANC is the added time required for digitizing and post-processing. In this article, we describe a design for ANC on a field-programmable gate array (FPGA), making use of high-level synthesis tools and fixed-point arithmetic to achieve real-time laser RIN suppression at 25 MHz sample rates. Unlike the software-ANC approach, the FPGA-ANC device can serve as a dedicated drop-in denoiser, placed between the detectors and a commercial lock-in amplifier. We demonstrate its application to transient absorption spectroscopy and microscopy, lowering the noise floor to ~17 dB above the shot noise limit. Furthermore, we demonstrate a dramatic improvement in data acquisition time from ~6 h to ~5 min in a real-time imaging scenario.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

First measurement of S/XB values of Re I visible emission lines

A spectroscopic parameter, so called S/XB (the number of ionization events per photon or inverse photon efficiency), is experimentally determined for Re I visible emission lines (488.9, 527.1, and 527.6 nm) at an electron temperature range of ~2–8 eV in the PISCES-B linear plasma device. Our standard mass loss method was applied, where a pure Re sample was sputtered by Ar plasma. In addition, a new alloy method was developed, where a W-3.3 at% Re alloy sample was used. In the new method, the sputtered flux ratio of Re and W atoms is assumed to be the same as the elemental composition because of the very similar sputtering yields. In this work, good agreement in measured Re I S/XB values is obtained between the standard mass loss and new alloy methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Imaging propagative exciton polaritons in atomically thin WSe 2 waveguides

The exciton polariton (EP) is a half-light and half-matter quasiparticle that is promising for exploring both fundamental quantum phenomena as well as photonic applications. Van der Waals materials, such as transition-metal dichalcogenide (TMD), emerge as a promising nanophotonics platform due to its support of long propagative EPs even at room temperature. However, real-space studies have been limited to bulk crystal waveguides with a thickness no less than 60 nm. Here, we report the nano-optical imaging of the transverse-electric EPs in WSe 2 nanoflakes down to a few atomic layers, which can be turned on and off by tuning the polarization state of the excitation laser. Unlike previously studied transverse-magnetic modes that exist only in bulk TMD waveguides, we found that the transverse-electric EPs could reside in ultrathin WSe 2 samples, owing to the alignment of the electric field with the in-plane dipole orientation of two-dimensional excitons. Furthermore, we show that the EP wavelength and propagation length can be largely controlled by varying laser energy and sample thickness. These findings open opportunities to realize near-infrared polaritonic devices and circuits truly at the atomically thin limit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Exploring possible ferromagnetism of the LaAl O 3 / SrTi O 3 interface

We report on extensive investigations of magnetism at the n -type LaAl O 3 / SrTi O 3 interface performed by utilizing a spectrum of local and integrative analytical techniques: Scanning superconducting quantum interference device microscopy, polar Kerr magnetometry, ferromagnetic resonance, and magnetic torque magnetometry. The samples originated from the same wafers. For nominally fully oxidized samples, we find that the mere presence of the conducting interface does not induce magnetism to values exceeding already present magnetic signals originating from the substrates, irrespective of the measurement technique. With the controlled introduction of oxygen vacancies, however, the different analytical techniques with their inherently different sensitivities and potential interactions with possible magnetic moments in the samples yield different results concerning the existence of magnetism. These unexpected differences obtained with the various measurement techniques are a possible source of the disagreement in the literature about the existence of ferromagnetism at LaAl O 3 / SrTi O 3 interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Vela Hotel Program: The AEC's Space-Based Nuclear Detection and Treaty Verification Program [Slides]

Early Interest in "Detection": "I would suggest that the best way to get reliable information in a short time would be to send from the States a man qualified to do the testing of the samples on the spot. This man should be officially a representative of the State Department, and his detecting devices, such as small portable Geiger Counters, could then go into Switzerland in the diplomatic pouch via air from Southern Italy. This man could then contact, through the Embassy, suitable people who could collect the water samples without arousing too much curiosity. A fishing trip in a boat would probably give the best disguise, as the fisherman could carry a water bottle in his lunch basket, and fill it after drinking the original contents. The water should be collected from the center of the river, to get the swiftest flowing water, so that the holdup could be minimized. In the lake, the water should be collected as near to the suspected site as possible, or as near to each of the inlet rivers as can be done. Speed in getting from the collection point to the counting room is of great importance, as you are, no doubt, aware." - Luis Alvarez to Major Furman, May 1944.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Secured fault detection in a power substation

Systems and methods for fault detection and protection in electric power systems that evaluates electromagnetic transients caused by faults. A fault can be detected using sampled data from a first monitored point in the power system. Detection of fault transients and associated characteristics, including transient direction, can also be extracted through evaluation of sample data from other monitored points in the power system. A monitoring device can evaluate whether to trip a switching device in response to the detection of the fault and based on confirmation of an indication of detection of fault transients at the other monitored points of the power system. The determination of whether to trip or activate the switching device can also be based on other factors, including the timing of receipt of an indication of the detection of the fault transients and/or an evaluation of the characteristics of the detected transients.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Secured fault detection in a power substation

Systems and methods for fault detection and protection in electric power systems that evaluates electromagnetic transients caused by faults. A fault can be detected using sampled data from a first monitored point in the power system. Detection of fault transients and associated characteristics, including transient direction, can also be extracted through evaluation of sample data from other monitored points in the power system. A monitoring device can evaluate whether to trip a switching device in response to the detection of the fault and based on confirmation of an indication of detection of fault transients at the other monitored points of the power system. The determination of whether to trip or activate the switching device can also be based on other factors, including the timing of receipt of an indication of the detection of the fault transients and/or an evaluation of the characteristics of the detected transients.

Cui, Tao↗
DOE OSTI2024

DIRECT RF SAMPLING BASED LLRF CONTROL SYSTEM FOR C-BAND LINEAR ACCELERATOR

Low Level RF (LLRF) control systems of linear accel- erators (LINACs) are typically implemented with hetero- dyne based architectures, which have complex analog RF mixers for up and down conversion. The Gen 3 Radio Fre- quency System-on-Chip (RFSoC) device from AMD Xilinx integrates data converters with maximum RF frequency of 6 GHz. This enables direct RF sampling of C-band LLRF signal typically operated at 5.712 GHz without any analogue mixers, which can significantly simplify the system architec- ture. The data converters sample RF signals in higher order Nyquist zones and then up or down convert digitally by the integrated data path in RFSoC. The closed-loop feedback control firmware implemented in FPGA integrated in RF- SoC can process the base-band signal from the ADC data path and calculate the updated phase and amplitude to be up- mixed by the DAC data path. We have developed a C-band LLRF control RFSoC platform with direct RF sampling, which targets Cool Copper Collider (𝐶3) and other C or S band LINAC research and development projects. In this paper, the architecture of the platform will be described. We have optimized the configuration of the data converter and characterized performance of them with RF pulses. The test results for some of the key performance parameters for the LLRF platform with our custom solid-state amplifier, such as phase and amplitude stability, will be discussed in this paper.

Liu, C↗
DOE OSTI2016

Investigation of HCl-based surface treatment for GaN devices

Surface treatments of GaN in HCl-based solutions are studied by X-ray photoelectron spectroscopy (XPS) and electrical characterization of fabricated GaN surfaces. A dilute-HCl treatment (HCl:H{sub 2}O=1:1) at room temperature and a boiled-HCl treatment (undiluted HCl) at 108°C are made on high-temperature annealed n-GaN. From the XPS study, removal of surface oxide by the dilute-HCl treatment was found, and more thoroughly oxide-removal was confirmed in the boiled-HCl treatment. Effect of the surface treatment on electrical characteristics on AlGaN/GaN transistor is also studied by applying treatment processes prior to the surface SiN deposition. Increase of drain current is found in boiled-HCl treated samples. The results suggest that the boiled-HCl treatment is effective for GaN device fabrication.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Site and endmember spectra of terrestrial vegetation and soils for the Colorado Headwaters Ecological Spectroscopy Study, June-July 2025

This dataset provides site and endmember spectra collected during the 2025 Colorado Headwaters Ecological Spectroscopy Study (CHESS) campaign. The site spectra were collected to help validate airborne hyperspectral data acquired by the National Ecological Observatory Network's aerial observation platform (NEON AOP). Endmember spectra were collected to augment existing spectral libraries with additional samples of bare surfaces and non-photosynthetic vegetation. All measurements were acquired with an Analytical Spectral Devices (ASD) FieldSpec4 Hi-Res NG (Next Generation) spectroradiometer, which records radiance at 1nm (nanometer) intervals from the ultraviolet to the short-wave infrared (350-2500 nm). The dataset includes spectra measured at meadow sites where the CHESS team also collected vegetation samples for trait analyses. The site spectra were collected with the ASD FieldSpec4 palm grip attachment using an 8° field-of-view foreoptic. Site spectra are integrated measurements of the entire surface within the foreoptic’s field of view. For site-level spectra, the sun is the illumination source. A Spectralon panel mounted on a tripod was used for instrument optimization and white reference measurements for all site spectra. Site spectra were acquired within two hours of solar noon and within 48 hours of a NEON AOP overflight. Site spectra are labeled by date, sampling area, and site number according to the naming conventions of the CHESS campaign’s data management plan. The dataset also contains endmember spectra in the following categories: photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), bare (soil/rock), and flowers. Endmember measurements were acquired using either the contact probe or the leaf clip attachments of the ASD FieldSpec4. In these configurations, the bulb inside the spectrometer provides the light source for the measurements. The spectrometer was optimized and white reference measurements were recorded using the circular white pucks attached to the contact probe and leaf clip. Because they do not rely on solar illumination, contact probe and leaf clip measurements were collected during a broader time frame than the palm grip site spectra. Some endmembers were measured at CHESS meadow sites, while others were collected within the larger sampling area or in nearby locations (e.g. Gothic Townsite) with similar characteristics. Radiance, reflectance, and metadata files are split into three subfolders according to measurement type: proximal/palm grip (prx), contact probe (cp), and leaf clip (lc). Radiance spectra are provided in ASD file format (.asd file extension). All ASD files can be opened using the provided scripts. Metadata is provided in two formats: CSV file format (no geolocation) and GEOJSON file format (includes geolocation for each spectra). The dataset includes a set of pre-processed reflectance spectra as CSV files (yyyymmdd_rfl.csv). The python scripts and jupyter notebook used to calculate reflectance spectra from the ASD radiance data is included here and was previously published at: https://doi.org/10.3334/ORNLDAAC/2446. There is also a folder of JPEG photographs corresponding to selected spectra. We include a protocol document with detailed steps for ASD FieldSpec4 assembly and operations. This data additionally contains a file level metadata (flmd.csv) and data dictionary (dd.csv) file. Geospatial information: Geospatial data for mapping measurement site locations are in the files CHESS_polygons_lai_UTM.geojson, CHESS_polygons_shrub_UTM.geojson, and CHESS_polygons_meadow_UTM.geojson in the companion geospatial package for the 2025 CHESS campaign, ‘CHESS 2025: Location data for field observations and sampling’ (Henderson et al., 2026). CHESS Project Description: The Colorado Headwaters Ecological Spectroscopy Study (CHESS) comprised a multi-week airborne remote sensing and field observation campaign in the Upper Gunnison Basin, Colorado, conducted in June and July of 2025. Airborne remote sensing was conducted by the National Ecological Observatory Network Airborne Observation Platform (NEON AOP), concurrent with a field campaign run by the Rocky Mountain Biological Laboratory (RMBL), the Lawrence Berkeley National Laboratory (LBNL) and SLAC National Accelerator Laboratory Watershed Function Science Focus Area (SFA), and NASA-JPL (Jet Propulsion Laboratory) Earth Surface Mineral Dust Source Investigation (EMIT) program. Between June 10 and July 18, 2025, the NEON AOP flight team collected high-resolution aerial imaging spectroscopy and Light Detection and Ranging (LiDAR) data over three domains: the Upper East River (CRBU), Almont Triangle (ALMO), and the Upper Taylor Basin (UPTA). In coordination with the flights, a field campaign acquired ground-truth observations, including observations of vegetation composition, foliar traits, forest demography, and subsurface properties in 18 core sampling areas within the domains. Additional surface water observations were taken at over 380 point locations. All CHESS campaign datasets can be found within the CHESS ESS-DIVE data portal: https://data.ess-dive.lbl.gov/portals/chess. Funding Acknowledgment: This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004) and was funded by EMIT Extended Mission Phase E Science.

2018 NEON and 2025 CHESS Campaigns↗
DOE OSTI2019

Ce-Doping and Reduction Annealing Effects on Magnetic Properties of Pr{sub 2-x}Ce{sub x}CuO{sub 4} Nanoparticles

Magnetic properties of reduced T’-Pr{sub 2-x}Ce{sub x}CuO{sub 4} (T’-PCCO) nanoparticles with x = 0, 0.10, and 0.15 have been investigated. The T’-PCCO samples were synthesized by the chemically dissolved method with HNO{sub 3} as dissolving agents and by the succeeding calcination at 1000 °C for 15 h in air. The reduced T’-PCCO samples were obtained by the reduction annealing at 700 °C for 10 h in Argon atmosphere and at 700 °C for 12 h in vacuum. Rietveld analyses of the X-ray diffraction (XRD) patterns for all the samples have revealed dependences of the c-axis length and the crystal size on the Ce doping and the reduction annealing. XRD analyses and transmission electron microscopy (TEM) images have confirmed T’-PCCO nanoparticles with the size of around 40–100 nm. Magnetic properties of all the T’-PCCO nanoparticles were studied by a superconducting quantum interference device (SQUID) showing a dominant paramagnetic feature with very weak ferromagnetism in the as-synthesized samples at room temperature. It has changed to a pure paramagnetic feature after the reduction annealing in argon atmosphere and an enhanced ferromagnetism through vacuum annealing. This is probably due to the change in the number of oxygen vacancies through the defect recovery and the removal of excess oxygen after both reduction annealing processes, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Ultrafast (1‐5 sec) Lamination of Perovskite Solar Cells With Self‐Encapsulation Using Rapid Joule Heating

Perovskite solar cells (PSCs) are traditionally fabricated using sequential layer‐by‐layer deposition, in which each layer of the device is processed on top of the preceding layer. This constrains the processing techniques and selection of transport layer materials that can be used in the solar cell. To overcome these challenges, two half‐cells can be processed independently and then diffusion‐bonded through a lamination process. However, current lamination processes for perovskite solar cells suffer from relatively long process times, which can limit throughput when moving toward high‐volume manufacturing. In this study, a custom platform was designed for rapid‐joule heating of perovskite materials and devices. This enabled more than a 99% reduction in lamination time from 26 min to 1 s. Perovskite samples that were laminated in 1 s exhibited comparable values of percent bonded area, interfacial toughness, grain domain size, and X‐ray diffraction spectra to those laminated in greater than 10 min. As a proof‐of‐concept, 18.3% efficient devices were successfully laminated in 5 s. A transient heat transfer model was developed to describe the relationship between the perovskite temperature and the electrical power supplied to the heaters, establishing a baseline for predicting processing conditions in large‐scale manufacturing systems. Ultra‐fast lamination provides a pathway toward scalable roll‐to‐roll or sheet‐to‐sheet manufacturing of PSCs.

heat transfer↗
DOE OSTI2016

Studies on magnetic properties of chemically synthesized crystalline calcium ferrite nanoparticles

Spinel-type ferrites have taken a very important role for modern electronic industry. Most of these ferrites exhibit low-loss dielectric properties, high resistivity, low eddy current and also high temperature ferromagnetism. Calcium ferrite is one such important metal oxide which is environmentally safe, chemically stable, low cost and greatly abundant. This outstanding material of calcium ferrite is synthesized by a simple chemical precipitation method using NaOH as the precipitating agent. Ferric chloride anhydrous (FeCl{sub 3}) and Calcium chloride dihydrate (CaCl{sub 2}.2H{sub 2}O) were used as iron and calcium sources respectively. The samples were heated at 200°C for 8h to obtain homogeneous powder of Calcium ferrite. The powders were characterized by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Transmission electrical microscopy (TEM), and Fourier transform infrared spectroscopic (FTIR) measurements. The polycrystalline nature of the sample was confirmed by X-ray diffraction study. The magnetic properties of the sample were investigated by vibrating sample magnetometer (VSM) measurements. Magnetization curve of the prepared sample depicts that as synthesized calcium ferrite nanoparticles have saturation magnetic moment of 1.74 emu/g and the coercivity of 35.08 Oe with superparamagnetic behavior. The synthesized calcium ferrite nanoparticles with such magnetic properties will be a candidate material for different applications in electronics and exploring its functionality in the field of recently developing semiconductor device physics and spintronics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗