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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Ternary molecular switching in a single-crystal optical actuator with correlated crystal strain

A growing portfolio of single-crystal optical actuators is forging a new class of photonic materials that hold prospects for quantum technologies. Ruthenium-based complexes that exhibit this phenomenon via SO 2 -linkage photoisomerisation are of particular interest since they display multiple metastable states, once induced by green light; yet, complete photoconversion into each SO 2 -isomeric state is rarely achieved. We discover a new complex, trans-[Ru(SO 2 )(NH 3 ) 4 (4-bromopyridine)]tosylate 2 , that produces 100% photoconverted η 1 -OSO isomeric crystal structures at 90 K, which fully transition into η 2 -(OS)O photoisomers upon warming to 100 K, while the dark-state η 1 -SO 2 structure is wholly recovered by heating the crystal to room temperature. Crystal structures and optical-absorption profiles of each state are captured via in-situ light-induced single-crystal X-ray diffraction and optical-absorption spectroscopy. Results show that both photoisomeric species behave as optical switches, but with distinct optical properties. The photoisomerisation process causes thermally-reversible micro- and nanoscopic crystal strain, as characterised by optical microscopy and in-situ light-induced atomic-force microscopy.

actuators↗
DOE OSTI2021

Single-Crystal Optical Actuation Generated by 100% SO 2 Linkage Photoisomerization in a Ruthenium-Based Coordination Complex

Single-crystal optical actuators are emerging as a new field of materials chemistry because of their wide-ranging potential applications, from light-induced molecular motors to photosensing technologies. Ruthenium-based coordination complexes that contain sulfur dioxide linkage photoisomers have shown particular promise as optical actuators, given that they may exhibit either optical switching or nano-optomechanical transduction in their single-crystal form. The type of single-crystal optical actuation observed in a specific compound within this family of complexes depends upon the nature of the ligand that lies trans to this SO 2 linkage photoisomer, since this governs the type and extent of photoisomer (η 2 -(OS)O or η 1 -OSO) that will form upon the application of light. We report the discovery of a new complex, trans-[Ru(SO 2 )(NH 3 ) 4 (3-iodopyridine)]tosylate 2 (1), which forms an η 1 -OSO photoisomer with 100% photoconversion upon the application of 505 nm light. The photoisomerization process in the ruthenium-based cation of 1 stimulates rotation and translation of the toluenic constituent of its neighboring anion, thereby affording nano-optomechnical transduction. We show that this η 1 -OSO photoisomer transitions to its more thermally stable η 2 -(OS)O photoisomer with an activation energy, E a , of 11(2) kJ/mol using thermally activated single-crystal optical absorption spectroscopy. The application of external light with different wavelengths to 1 is also shown to cause a variation in its optical absorption spectral characteristics. Here, this suggests that the photophysical properties of 1 may be tunable with light.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

Spectroscopy-Based Characterization of Single Wall Carbon Nanotubes

We present the initial results of our combined investigation of Raman scattering and optical absorption spectroscopy in a batch of single wall carbon nanotubes (SWNTs). The SWNT diameters are first estimated from the four radial breathing mode (RBM) peaks using a simple relation of omega(sub RBM) = 248/cm nm/d(sub t)(nm). The calculated diameter values are related to the optical absorption peaks through the expressions of first interband transition energies, i.e., E(sup S)(sub 11) = 2a gamma/d(sub t) for semiconducting and E(sup S)(sub 11) = 6a gamma/d(sub t) for metallic SWNTs, respectively, where a is the carbon-carbon bond length (0.144 nm) and gamma is the energy of overlapping electrons from nearest neighbor atoms, which is 2.9 eV for a SWNT. This analysis indicates that three RBM peaks are from semiconducting tubes, and the remaining one is from metallic tubes. The detailed analysis in the present study is focused on these three peaks of the first absorption band by determining the values of the representative (n,m) pairs. The first step of analysis is to construct a list of possible (n,m) pairs from the diameters calculated from the positions of the RBM peaks. The second step is to compute the first interband transition energy, E(sub 11), by substituting the constructed list of (n,m) into the expression of Reich and Thomsen, and Saito et al. Finally, the pairs with the energies closest to the experimental values are selected.

Namkung, Min↗
DOE OSTI2021

Investigations of radiation damaged arranged scintillating particle composites

Composites consisting of periodically arranged scintillating particles within an acrylic (poly methyl methacrylate) matrix are excellent templates for the gamma-insensitive detection of fast neutrons. In order to study the impact of radiation damage on acrylic-based scintillating particle composites, we exposed acrylic samples to different doses of fast neutrons up to 119.7 kGy and investigated the change in optical characteristics using optical absorption spectroscopy in the 200–800 nm wavelength range. The experimental results are compared to coupled MCNP6 and optical ray-tracing (FRED) simulations, and qualitative agreement is found. Neutron-induced radiation damage in the acrylic matrix manifests as a red-shift in the ultra-violet absorption edge of the acrylic and a corresponding decrease in the light propagation efficiency, which leads to detector performance degradation. We show for the first time that the effects of radiation damage can be mitigated by the use of wavelength-shifting coatings. We predict that composites with wavelength-shifting coatings can enable neutron detectors with high tolerance against neutron-induced radiation damage, a property that is particularly desired for neutron detection in high radiation environments.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Origin of the Bandgap Bowing in ZNSe(1-x)Te(x) Alloys

Photomodulated reflection and optical absorption spectroscopies were used to measure the composition and hydrostatic pressure dependencies of interband optical transitions in ZnSe(1-x)Te(x) alloys. On the Te-rich side, the bandgap reduction and the reduction in the pressure dependence of the bandgap are well explained by the band anticrossing interaction between the ZnTe conduction band states and the Se localized state located at 2.85 eV above the valence band top of ZnTe. On the Se-rich side, an interaction between the degenerate Gamma valence bands of ZnSe and the localized Te state located at 0.1 eV above the valence band top of ZnSe is proposed to generate the bandgap reduction and the rapid increase of the spin-orbit splitting with increasing Te concentration. A linear interpolation between these two models accounts for the composition and pressure dependencies of the bandgap in the entire composition range.

Walukiewicz, W.↗
NASA NTRS1976

Electron-impact excitation of UF6 at an electron energy of 20 eV in the energy-loss range of 0-10 eV

A technique combining electron impact excitation and optical absorption spectroscopy was applied to UF6. The crucial features of the experiment were that: (1) the electron optics was differentially pumped relative to the scattering chamber and (2) the target UF6 beam was condensed on a liquid nitrogen cold trap placed immediately above the scattering center. Energy loss spectra are presented at an incident electron energy of 20 eV and at scattering angles between 20 and 135 degrees. It is shown that no transitions are found below the first-detected feature at 3.0 eV and an optically forbidden excitation is found at 4.2 eV. A fairly strong optical absorption at 4.8 eV is observed to 'fill-in' at a scattering angle of 20 degrees but is practically absent at higher angles.

Chutjian, A.↗
NASA NTRS2016

Utilization of O4 Slant Column Density to Derive Aerosol Layer Height from a Space-Borne UV-Visible Hyperspectral Sensor: Sensitivity and Case Study

The sensitivities of oxygen-dimer (O4) slant column densities (SCDs) to changes in aerosol layer height are investigated using the simulated radiances by a radiative transfer model, the linearized pseudo-spherical vector discrete ordinate radiative transfer (VLIDORT), and the differential optical absorption spectroscopy (DOAS) technique. The sensitivities of the O4 index (O4I), which is defined as dividing O4 SCD by 10(sup 40) molecules (sup 2) per centimeters(sup -5), to aerosol types and optical properties are also evaluated and compared. Among the O4 absorption bands at 340, 360, 380, and 477 nanometers, the O4 absorption band at 477 nanometers is found to be the most suitable to retrieve the aerosol effective height. However, the O4I at 477 nanometers is significantly influenced not only by the aerosol layer effective height but also by aerosol vertical profiles, optical properties including single scattering albedo (SSA), aerosol optical depth (AOD), particle size, and surface albedo. Overall, the error of the retrieved aerosol effective height is estimated to be 1276, 846, and 739 meters for dust, non-absorbing, and absorbing aerosol, respectively, assuming knowledge on the aerosol vertical distribution shape. Using radiance data from the Ozone Monitoring Instrument (OMI), a new algorithm is developed to derive the aerosol effective height over East Asia after the determination of the aerosol type and AOD from the MODerate resolution Imaging Spectroradiometer (MODIS). About 80 percent of retrieved aerosol effective heights are within the error range of 1 kilometer compared to those obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) measurements on thick aerosol layer cases.

Air Pollution↗
DOE OSTI2025

WO 3 /CuWO 4 Ratio Controls Open-Circuit Photovoltage and Photocurrent in Type II Heterojunction Solar Fuel Photoelectrodes

WO 3 /CuWO 4 photoelectrodes for the oxygen evolution reaction benefit from a type II heterojunction for charge separation. However, the impact of the WO 3 /CuWO 4 ratio on the photocurrent and the photovoltage is not clear. To probe the effect of composition, Cu x W 1-x O y thin films with variable W:Cu ratio were prepared on FTO by reactive magnetron co-sputtering of W and Cu, followed by air annealing at 500ºC. EDS, XRD, Rietveld refinement, and Raman spectroscopy confirm the presence of crystalline WO 3 and CuWO 4 in the W rich films and increasing amounts of amorphous copper oxides in the Cu rich films. Bandgaps were determined by optical absorption spectroscopy, surface photovoltage spectroscopy (SPS), and photoaction spectra and are found to decrease from 2.7 eV to 1.2 eV with increasing copper oxide content. SPS reveals n-type semiconductor photoanode behavior for WO 3 /CuWO 4 samples and p-type photocathode behavior for CuO x rich films. Photoelectrochemical experiments confirm stable water oxidation with Faraday efficiency near unity for all W rich films and photocurrents that are increasing with CuWO 4 content. Optimal performance is seen for WO 3 /CuWO 4 mixed phases containing 47-75 mass% CuWO 4 . These compositions maximize charge separation at the type II heterojunction interface between the two materials. Additionally, according to incident photon to current efficiency (IPCE) data, the WO 3 improves photon conversion below 350 nm, while CuWO 4 improves conversion at 450-525 nm. Overall, this work shows for the first time how the WO 3 /CuWO 4 ratio controls the photovoltage and the photocurrent in type II heterojunction solar fuel photoelectrodes, and how copper oxides in the copper rich films severely degrade the performance. Furthermore, these results are useful in the context of bulk-heterojunction electrodes for the conversion of solar energy into fuels.

CuWO4↗
DOE OSTI2021

Relaxation timescales and electron-phonon coupling in optically pumped $\mathrm{YBa_2Cu_3O_{6+\mathcal{x}}}$ revealed by time-resolved Raman scattering

Time-resolved measurements provide a new way to disentangle complex interactions in quantum materials due to their different timescales. We used pump-probe Raman scattering to investigate the apical oxygen vibration in $\mathrm{YBa_2Cu_3O_{6+\mathcal{x}}}$ under nonequilibrium conditions. Time dependence of the phonon population demonstrated strong electron-phonon coupling. Most importantly, the phonon shifts to a higher energy due to transient smearing of the Fermi surface in a remarkable agreement with diagrammatic theory. Here we also discuss insights into photoinduced superconductivity reported at lower doping that follow from these results.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-Temperature 2D Optical Relaxation Visualizes Enhanced Oxygen Exchange Kinetics at Metal-Mixed Conducting Oxide Interfaces

Solid-state heterointerfaces are of interest for emergent local behavior that is distinct from either bulk parent compound. One technologically relevant example is the case of mixed ionic/electronic conductor (MIEC)–metal interfaces, which play an important role in electrochemistry. Metal–MIEC composite electrodes can demonstrate improved catalytic activity vs single-phase MIECs, improving fuel cell efficiency. Similarly, MIEC surface reaction kinetics are often evaluated using techniques that place metal current collectors in contact with the surface under evaluation, potentially altering the response vs the native surface. Here, techniques enabling direct and local in situ observation of the behavior at and around such heterointerfaces are needed. Here, we develop a spatially resolved optical transmission relaxation (2D-OTR) method providing continuous evaluation of local, high-temperature, controlled atmosphere defect kinetics across a ~1 cm2 sample area simultaneously in a contact-free manner. We apply it to observe the spatial variance of oxygen incorporation and evolution rates at ~525–620 °C, in response to step changes in oxygen partial pressure, on MIEC SrTi 0.65 Fe 0.35 O 3–x films as a function of distance from porous Pt and Au layers. Using this model geometry, we find significant enhancements in kinetics adjacent to the metals that decay over a few millimeter distance. To extract kinetic parameters, we fit the short-term optical data (initial portion of relaxations) with an exponential decay function appropriate for surface-exchange-limited kinetics, yielding apparent surface exchange coefficients (k chem ) with spatial resolution, decreasing with distance from the metal. To understand the kinetic processes governing the complete (long-term) optical relaxations, we performed COMSOL simulations, which demonstrated that a combination of laterally varying k chem and in-plane diffusion controls the observed kinetics over the full time range. Further support for spatially varying kchem comes from demonstrations of changing surface and bulk chemistry vs distance from the metal–MIEC interface, by X-ray photoelectron and optical absorption spectroscopies, respectively. Although microporous Pt and Au are not excellent electrodes in isolation, both metals exert a synergistic effect on the oxygen surface exchange rate in the presence of the mixed conducting film.

36 MATERIALS SCIENCE↗
NASA NTRS1986

A mobile system for active otpical pollution monitoring

The remote monitoring of atmospheric pollutants can now be performed in several ways. Laser radar techniques have proven their ability to reveal the spatial distribution of different species or particles. Classical optical techniques can also be used, but yield the average concentration over a given path and hence no range resolution. One such technique is Differential Optical Absorption Spectroscopy, DOAS. Such schemes can be used to monitor paths that a preliminary lidar investigation has shown to be of interest. Having previously had access to a mobile lidar system, a new system has been completed. The construction builds on experience from using the other system and it is meant to be more of a mobile optical laboratory than just a lidar system. A complete system description is given along with some preliminary usage. Future uses are contemplated.

Sunesson, A.↗
NASA NTRS2005

Chirality Characterization of Dispersed Single Wall Carbon Nanotubes

Raman scattering and optical absorption spectroscopy are used for the chirality characterization of HiPco single wall carbon nanotubes (SWNTs) dispersed in aqueous solution with the surfactant sodium dodecylbenzene sulfonate. Radial breathing mode (RBM) Raman peaks for semiconducting and metallic SWNTs are identified by directly comparing the Raman spectra with the Kataura plot. The SWNT diameters are calculated from these resonant peak positions. Next, a list of (n, m) pairs, yielding the SWNT diameters within a few percent of that obtained from each resonant peak position, is established. The interband transition energies for the list of SWNT (n, m) pairs are calculated based on the tight binding energy expression for each list of the (n, m) pairs, and the pairs yielding the closest values to the corresponding experimental optical absorption peaks are selected. The results reveal that (1, 11), (4, 11), and (0, 11) as the most probable chiralities of the semiconducting nanotubes. The results also reveal that (4, 16), (6, 12) and (8, 8) are the most probable chiralities for the metallic nanotubes. Directly relating the Raman scattering data to the optical absorption spectra, the present method is considered the simplest technique currently available. Another advantage of this technique is the use of the E(sup 8)(sub 11) peaks in the optical absorption spectrum in the analysis to enhance the accuracy in the results.

Namkung, Min↗
DOE OSTI2020

Systematic Assessment of Retrieval Methods for Canopy Far-Red Solar-Induced Chlorophyll Fluorescence Using High-Frequency Automated Field Spectroscopy

Remote sensing of solar-induced chlorophyll fluorescence (SIF) offers potential to infer photosynthesis across scales and biomes. Many retrieval methods have been developed to estimate top-of-canopy SIF using ground-based spectroscopy. However, inconsistencies among methods may confound interpretation of SIF dynamics, eco-physiological/environmental drivers, and its relationship with photosynthesis. Using high temporal- and spectral resolution ground-based spectroscopy, we aimed to (1) evaluate performance of SIF retrieval methods under diverse sky conditions using continuous field measurements; (2) assess method sensitivity to fluctuating light, reflectance, and fluorescence emission spectra; and (3) inform users for optimal ground-based SIF retrieval. Analysis included field measurements from bi-hemispherical and hemispherical-conical systems and synthetic upwelling radiance constructed from measured downwelling radiance, simulated reflectance, and simulated fluorescence for benchmarking. Fraunhofer-based differential optical absorption spectroscopy (DOAS) and singular vector decomposition (SVD) retrievals exhibit convergent SIF-PAR relationships and diurnal consistency across different sky conditions, while O2A-based spectral fitting method (SFM), SVD, and modified Fraunhofer line discrimination (3FLD) exhibit divergent SIF-PAR relationships across sky conditions. We find that such behavior holds across system configurations, though hemispherical-conical systems diverge less across sky conditions. O 2 A retrieval accuracy, influenced by atmospheric distortion, improves with a narrower fitting window and when training SVD with temporally local spectra. This may impact SIF-photosynthesis relationships interpreted by previous studies using O 2 A-based retrievals with standard (759–767.76 nm) fitting windows. Fraunhofer-based retrievals resist atmospheric impacts but are noisier and more sensitive to assumed SIF spectral shape than O 2 A-based retrievals. We recommend SVD or SFM using reduced fitting window (759.5–761.5 nm) for robust far-red SIF retrievals across sky conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Ultrafast Jahn‐Teller Photoswitching in Cobalt Single‐Ion Magnets

Abstract Single‐ion magnets (SIMs) constitute the ultimate size limit in the quest for miniaturizing magnetic materials. Several bottlenecks currently hindering breakthroughs in quantum information and communication technologies could be alleviated by new generations of SIMs displaying multifunctionality. Here, ultrafast optical absorption spectroscopy and X‐ray emission spectroscopy are employed to track the photoinduced spin‐state switching of the prototypical complex [Co(terpy) 2 ] 2+ (terpy = 2,2′:6′,2″‐terpyridine) in solution phase. The combined measurements and their analysis supported by density functional theory (DFT), time‐dependent‐DFT (TD‐DFT) and multireference quantum chemistry calculations reveal that the complex undergoes a spin‐state transition from a tetragonally elongated doublet state to a tetragonally compressed quartet state on the femtosecond timescale, i.e., it sustains ultrafast Jahn‐Teller (JT) photoswitching between two different spin multiplicities. Adding new Co‐based complexes as possible contenders in the search for JT photoswitching SIMs will greatly widen the possibilities for implementing magnetic multifunctionality and eventually controlling ultrafast magnetization with optical photons.

36 MATERIALS SCIENCE↗
NASA NTRS2014

Global Free-tropospheric NO2 Abundances Derived Using a Cloud Slicing Technique from AURA OMI

We derive free-tropospheric NO2 volume mixing ratios (VMRs) by applying a cloud-slicing technique to data from the Ozone Monitoring Instrument (OMI) on the Aura satellite. In the cloud-slicing approach, the slope of the above-cloud NO2 column versus the cloud scene pressure is proportional to the NO2 VMR. In this work, we use a sample of nearby OMI pixel data from a single orbit for the linear fit. The OMI data include cloud scene pressures from the rotational-Raman algorithm and above-cloud NO2 vertical column density (VCD) (defined as the NO2 column from the cloud scene pressure to the top of the atmosphere) from a differential optical absorption spectroscopy (DOAS) algorithm. We compare OMI-derived NO2 VMRs with in situ aircraft profiles measured during the NASA Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign in 2006. The agreement is generally within the estimated uncertainties when appropriate data screening is applied. We then derive a global seasonal climatology of free-tropospheric NO2 VMR in cloudy conditions. Enhanced NO2 in the free troposphere commonly appears near polluted urban locations where NO2 produced in the boundary layer may be transported vertically out of the boundary layer and then horizontally away from the source. Signatures of lightning NO2 are also shown throughout low and middle latitude regions in summer months. A profile analysis of our cloud-slicing data indicates signatures of lightning-generated NO2 in the upper troposphere. Comparison of the climatology with simulations from the global modeling initiative (GMI) for cloudy conditions (cloud optical depth less than10) shows similarities in the spatial patterns of continental pollution outflow. However, there are also some differences in the seasonal variation of free-tropospheric NO2 VMRs near highly populated regions and in areas affected by lightning-generated NOx.

NO2↗
NASA NTRS2014

Global Free Tropospheric NO2 Abundances Derived Using a Cloud Slicing Technique Applied to Satellite Observations from the Aura Ozone Monitoring Instrument (OMI)

We derive free-tropospheric NO2 volume mixing ratios (VMRs) and stratospheric column amounts of NO2 by applying a cloud slicing technique to data from the Ozone Monitoring Instrument (OMI) on the Aura satellite. In the cloud-slicing approach, the slope of the above-cloud NO2 column versus the cloud scene pressure is proportional to the NO2 VMR. In this work, we use a sample of nearby OMI pixel data from a single orbit for the linear fit. The OMI data include cloud scene pressures from the rotational-Raman algorithm and above-cloud NO2 vertical column density (VCD) (defined as the NO2 column from the cloud scene pressure to the top-of-the-atmosphere) from a differential optical absorption spectroscopy (DOAS) algorithm. Estimates of stratospheric column NO2 are obtained by extrapolating the linear fits to the tropopause. We compare OMI-derived NO2 VMRs with in situ aircraft profiles measured during the NASA Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign in 2006. The agreement is generally within the estimated uncertainties when appropriate data screening is applied. We then derive a global seasonal climatology of free-tropospheric NO2 VMR in cloudy conditions. Enhanced NO2 in the free troposphere commonly appears near polluted urban locations where NO2 produced in the boundary layer may be transported vertically out of the boundary layer and then horizontally away from the source. Signatures of lightning NO2 are also shown throughout low and middle latitude regions in summer months. A profile analysis of our cloud slicing data indicates signatures of uplifted and transported anthropogenic NO2 in the middle troposphere as well as lightning-generated NO2 in the upper troposphere. Comparison of the climatology with simulations from the Global Modeling Initiative (GMI) for cloudy conditions (cloud optical thicknesses > 10) shows similarities in the spatial patterns of continental pollution outflow. However, there are also some differences in the seasonal variation of free-tropospheric NO2 VMRs near highly populated regions and in areas affected by lightning-generated NOx. Stratospheric column NO2 obtained from cloud slicing agrees well with other independently-generated estimates, providing further confidence in the free-tropospheric results.

NO2↗
DOE OSTI2022

Spectroscopic investigation of historical uranium glasses

Here, we present spectroscopic investigations of uranium in two historical glasses. A 1920's-1930's Art Deco (Bagley Carnival) green soda-lime-silica uranium glass bowl and a 1930's-1940's (Thomas Webb) yellow full lead crystal uranium glass vase were studied using optical absorption spectroscopy, XRF and SEM-EDX, X-band EPR and High- Energy Resolution Fluorescence-Detected (HERFD)-XANES. Uranium speciation may be different in the two glasses. Uranium occurs as uranyl groups (UO 2 2+ ) with minority reduced uranium species, mostly as U(V), more important in the Webb glass than in the Bagley glass. The differences between the two glasses arise from the fining procedure and result from the presence of other multivalent elements and differences in base glass composition. Electron Paramagnetic Resonance (EPR) spectra show the presence of an incipient signal close to g~2, partially annealed by heating to 550 °C, which we assign to a small concentration of radiation-induced defects caused by uranium decay. The presence of multivalent glass components in addition to U (As + Cu + Fe in the Bagley glass and Sb + Fe in the Webb glass) can trap the electron-hole pairs generated by the presence of uranium. This may explain the weakness of this signal in these glasses that anyway received a limited radiation dose since their fabrication. The low activity of these glasses, close to the background radiation, confirms that there is no danger to exhibiting them in museums.

36 MATERIALS SCIENCE↗