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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Capture of Single Silver Nanoparticles in Nanopore Arrays Detected by Simultaneous Amperometry and Surface-Enhanced Raman Scattering

The attoliter volumes and confinement abilities of zero-dimensional nanopore-electrode arrays (NEAs) hold considerable promise for examining the behavior of single nanoparticles. In this work, we use surface-enhanced Raman scattering (SERS) in tandem with amperometry in order to monitor single Ag Raman-sentinel nanoparticles transported to and captured in single nanopores. To that end, highly ordered solid-state NEAs were fabricated to contain periodic arrays of nanopores, each housing a single recessed Au-ring electrode. These were used to electrostatically capture and trap single silver nanoparticles (AgNPs) functionalized with the electrochemically stable Raman reporter, 1,4-bis(2-methylstyryl)benzene (bis-MSB). Transport and capture of the bis-MSB-tagged AgNPs in the nanopores was followed by simultaneous amperometry and SERS signals characteristic of AgNP oxidation and enhanced Raman scattering by bis-MSB at silver–gold hot spots, respectively. The frequency and magnitude of oxidation-current spikes increased with stepwise increases in DC voltage, and characteristic bis-MSB SERS spectra were observed. Under AC excitation, on the other hand, two distinctly different types of SERS signals were observed, independent of frequency and amplitude: (1) strong, transient (<10 s) spectra and (2) slow (>100 s) monotonically diminishing spectra. We hypothesize that the former behavior results from AgNP aggregates, whereas the latter occurs as a result of multiple incomplete AgNP-oxidation events in succession. Here, these results show that attoliter-volume NEAs are competent for acquiring concurrent SERS spectra and for amperometry of single nanoparticles and that together these measurements can illuminate the collision dynamics of nanoparticles in confined environments.

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

Tuning Electrogenerated Chemiluminescence Intensity Enhancement Using Hexagonal Lattice Arrays of Gold Nanodisks

Electrogenerated chemiluminescence (ECL) microscopy shows promise as a technique for mapping chemical reactions on single nanoparticles. The technique’s spatial resolution is limited by the quantum yield of the emission and the diffusive nature of the ECL process. To improve signal intensity, ECL dyes have been coupled with plasmonic nanoparticles, which act as nanoantennas. Here, we characterize the optical properties of hexagonal arrays of gold nanodisks and how they impact the enhancement of ECL from the coreaction of tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate and tripropylamine. Here, we find that varying the lattice spacing results in a 23-fold enhancement of ECL intensity because of increased dye-array near-field coupling as modeled using finite element method simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High dynamic range CdTe mixed-mode pixel array detector (MM-PAD) for kilohertz imaging of hard x-rays

A hard x-ray, high-speed, high dynamic range scientific x-ray imager is described. The imager is based on the mixed-mode pixel array detector (MM-PAD) readout chip coupled to a 750 µm thick cadmium telluride (CdTe) sensor. The full imager is a 2 × 3 tiled array of MM-PAD sensor/readout chip hybrids. CdTe improves detection for high energy x-rays as compared to silicon sensors, enabling efficient x-ray imaging to extend to >100 keV. The detector is capable of 1 kHz imaging and in-pixel circuitry has been designed to allow for well depths of greater than 4 × 10 6 80 keV x-rays. Here, a charge integrating front-end allows for quantitative measurement of high flux x-ray images beyond the capabilities of photon counting detectors. Detector performance is summarized and experimental measurements are presented.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2019

Detection of random noise and anatomy of continuous seismic waveforms in dense array data near Anza California

We develop a methodology to separate continuous seismic waveforms into random noise (RN), not random noise (NRN) produced by earthquakes, wind, traffic and other sources of ground motions, and an undetermined mixture of signals. The analysis is applied to continuous records from a dense seismic array on the San Jacinto fault zone. To detect RN signals, we cut hourly waveforms into non-overlapping 1 s time windows and apply cross-correlations to separate RN candidates from outliers. The cross-correlation coefficients between different RN candidates fall into a tight range (i.e. 0.09–0.35), while cross-correlation coefficients of RN candidates with NRN signals (e.g. seismic or air-traffic events) are lower. The amplitude spectra of RN candidates have a well-defined level, while the amplitude spectra of other signals deviate from that level. Using these properties, we examine the amplitude spectra of moving time windows and cross-correlation coefficients with RN templates in each hour. The hourly RN is quasi-stationary and the results cluster tightly in the parameter space of cross-correlation coefficients and L2 norm deviations from the mean spectra of RN candidates. Time windows with parameters in this tight cluster are identified as RN, windows that deviate significantly from the RN cluster are identified as NRN and windows with values in between are identified as mixed signals. Several iterations on each hourly data are used to update and stabilize the selection of RN templates and mean noise spectra. For the days examined, the relative fractions of RN, NRN and mixed signals in local day (night) times are about 26 (42 percent), 40 (33 percent) and 34 percent (25 percent), respectively.

Geochemistry & Geophysics↗
DOE OSTI2023

Realization of a wide steering end-fire facet optical phased array using silicon rich silicon nitride

The design, fabrication, and characterization of a 16-element optical phased array (OPA) using a high index (n = 3.1) silicon-rich silicon nitride (SRN) is demonstrated. Here, we present one-dimensional beam steering with end-fire facet antennas over a wide steering range of >115° at a fixed wavelength of 1525 nm. A beam width of 6.3° has been measured at boresight, consistent with theory. We demonstrate SRN as a viable material choice for chip-scale OPA applications due to its high thermo-optic coefficient, high optical power handling capacity [negligible two-photon absorption (TPA)], wide transparency window, and CMOS compatibility.

Nejadriahi, Hani↗
DOE OSTI2018

Microseismic Event Detection Using Multiple Geophone Arrays in Southwestern Utah

We conducted four geophone array experiments in southwestern Utah between July 2016 and October 2017 to characterize regional levels of microseismicity. Each experiment comprised between 48 and 93 geophones and recorded continuously for ~30 days. Using a new frequency domain array-based detector and a traditional STA/LTA detector, we identified 242 earthquakes. We were able to precisely locate 203 of these earthquakes using HYPOINVERSE. During the same time period the University of Utah Seismograph Stations (UUSS) catalog contained 68 earthquakes in the study area, therefore, we were able to locate 135 additional events. We estimate local magnitudes for events using maximum peak-to-trough amplitude and epicentral distance. As expected, our detection threshold becomes lower with higher station density. We find sparse seismicity across the study area apart from two areas that contain clustered and more frequent activity (Dog Valley and Cove Fort), which together account for roughly 70% of the recorded seismicity. A third prominent cluster in the central Mineral Mountains contains about 15% of the recorded seismicity. Lastly, the remainder of the detected seismicity is spread across the study area.

58 GEOSCIENCES↗
DOE OSTI2021

Multielectrode Array Sensors to Enable Long-Duration Corrosion Monitoring and Control of Concentrating Solar Power Systems

Molten mixtures of MgCl2-KCl-NaCl are promising heat transfer fluid (HTF) candidates for the next generation of concentrating solar power systems (Gen3 CSP), because of their low cost, high decomposition temperature, and favorable heat transfer characteristics. However, if the chemistry of the salts is not properly controlled, molten chlorides can cause corrosion of high-temperature metal alloys, such as Inconel (R), in CSP systems. Here we demonstrate a corrosion monitoring system that can be used to monitor the health of the structural alloys over long durations. The monitoring system includes a multielectrode array voltammetry sensor that measures the redox potential of molten MgCl2-KCl-NaCl mixture as well as the presence of corrosion products and impurities. The sensors have been successfully operated in static molten salt environments for long durations, and are capable of detecting corrosion products, such as Cr2+ and Fe2+, quantitatively at low concentrations (i.e., approximately 100 ppm) with less than 4% error.

Concentrated solar power↗