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Results for “Optical absorption spectroscopy”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Field intercomparison of a novel optical sensor for formaldehyde quantification

A one-week in situ intercomparison campaign was completed on the Rice University campus for measuring HCHO using three different techniques, including a novel optical sensor based on difference frequency generation (DFG) operating at room temperature. Two chemical derivatization methods, 2,4-dinitrophenylhydrazine (DNPH) and o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA), were deployed during the daylight hours for three- to four-hour time-integrated samples. A real-time optical sensor based on laser absorption spectroscopy was operated simultaneously, including nighttime hours. This tunable spectroscopic source based on difference frequency mixing of two fiber-amplified diode lasers in periodically poled LiNb03 (PPLN) was operated at 3.5315 micrometers (2831.64 cm 1) to access a strong HCHO ro-vibrational transition free of interferences from other species. The results showed a bias of -1.7 and -1.2 ppbv and a gross error of 2.6 and 1.5 ppbv for DNPH and PFBHA measurements, respectively, compared with DFG measurements. These results validate the DFG sensor for time-resolved measurements of HCHO in urban areas.

NASA Discipline Life Sciences Technologies↗
DOE OSTI2025

High-resolution spectroscopy of uranium laser-produced plasma using saturated absorption spectroscopy

High-resolution spectroscopy of laser ablation plumes or laser-produced plasmas (LPPs) is valuable for various applications, including measuring crowded spectral features, determining spectroscopic constants, characterizing plasmas, and performing isotopic analysis. However, various line broadening mechanisms in plasmas limit its use for several applications. Here, in this study, we present the use of saturated absorption spectroscopy (SAS) for Doppler-free linewidth analysis in a uranium LPP. We demonstrate that SAS is effective in obtaining Doppler-free Lamb dip profiles with linewidths on the order of ≤ 20 MHz. The effects of saturation on the Doppler-broadened absorption and Lamb dip profiles at different pressures and probe intensities are quantified, and their impact on measurements of plasma properties is discussed. Finally, we show that the linewidths of the Lamb dips can be used for quantitative estimates of pressure and natural broadening in the plasma.

Absorption spectroscopy↗
DOE OSTI2022

Direct Characterization of Type-I Band Alignment in 2D Ruddlesden–Popper Perovskites

2D Ruddlesden–Popper halide perovskites have attracted considerable attention due to their desirable optoelectronic properties, high chemical and structural tunability, and improved environmental stability. However, the understanding of their structure–properties relationships is still limited. In particular, the energy level positions and band alignments at interfaces involving these materials, which are important features to control in the context of any applications, are still under debate. Here, the electronic structure of high-purity films of BA 2 MA n-1 Pb n I 3n+1 for n = 1–5 (where BA stands for butylammonium and MA for methylammonium) is investigated, using optical absorption, ultraviolet, and inverse photoemission spectroscopies, and density functional theory calculations. Further, this study determines the ionization energy and electron affinity of each compound and demonstrates a type-I band alignment for the BA 2 MA n-1 Pb n I 3n+1 series. This study further describes the evolution of the exciton binding energy as a function of the thickness of the inorganic layers.

2D Ruddlesden–Popper perovskites↗
DOE OSTI2024

Nonthermal Plasma-Stimulated C–N Coupling from CH 4 and N 2 Depends on the Presence of Surface CH x and Plasma-Phase CN Species

Formation of C–N containing compounds from plasma-catalytic coupling of CH 4 and N 2 over various transition metals (Ni, Pd, Cu, Ag, and Au) is investigated using a multimodal spectroscopic approach, combining polarization-modulation infrared reflection–absorption spectroscopy (PM-IRAS) and optical emission spectroscopy (OES). Through sequential experiments utilizing CH 4 and N 2 nonthermal plasmas, we minimize plasma-phase reactions and identify key intermediates for C–N coupling on metal surfaces. Results show that simultaneous CH 4 and N 2 exposure with plasma stimulation produces surface C–N species. However, N 2 –CH 4 sequential exposure does not lead to C–N species formation, while CH 4 –N 2 sequential exposure reveals the presence of CH x surface species and CN radical species as key precursors to C–N species formation. From further analysis using X-ray photoelectron spectroscopy and liquid chromatography–mass spectrometry, the influence of exposure conditions on the degree of nitrogen incorporation and the nature of C–N species formed were revealed. The work highlights the importance of surface chemistry and exposure conditions in surface C–N coupling with plasma stimulation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Supramolecular Assembly of Lanthanide-Binding Tag Peptides for Aqueous Separation of Rare Earth Elements

Selective and eco-friendly separation and purification methods for rare earth elements (REEs) are necessary to meet the increasing demand for these valuable metals, which are extensively used in modern electronics and clean energy technologies. Mining feedstocks consist of REE mixtures as stable trivalent cations (Ln 3+ ) that are difficult to separate due to their identical charge and similar size. Lanthanide-binding tags (LBTs), peptide chelates that coordinate Ln 3+ in binding pockets, show promise as selective, high-affinity extractants. We demonstrate that the LBT variant LBTLLA 5– , designed for high selectivity for Tb 3+ , is an effective extractant, forming complexes with REEs in solution that subsequently organize into self-assembling structures rich in Ln 3+ . These structures condense into aggregates that can be separated, enabling an efficient, all-aqueous, eco-friendly separation process. The self-assembled structures are studied using dynamic light scattering, ζ-potential measurements, transmission electron microscopy, anomalous small-angle X-ray scattering, inductively coupled plasma optical emission spectroscopy, and ultraviolet–visible absorption spectroscopy, which confirm LBTLLA 5– peptide-REE ion binding and the further assembly of micron-scale structures rich in REEs. Molecular dynamics simulations reveal the interactions promoting aggregation as well as the integrity of the binding pocket upon self-assembly. We find that LBTLLA 5– :Ln 3+ complexes recruit excess cations within the macrostructures, and we demonstrate that aggregation and selective separation can be controlled by manipulating the metal-peptide ratio in solution. Furthermore, we demonstrate separation from equimolar mixtures of REE pairs Tb 3+ -Lu 3+ and Tb 3+ -La 3+ , supporting the application of LBT peptides as a platform for the selective separation of REEs.

LBT peptides↗
DOE OSTI2020

Direct Evidence of Photoinduced Charge Transport Mechanism in 2D Conductive Metal Organic Frameworks

Conductive metal organic frameworks (MOFs) represent a promising class of porous crystalline materials that have demon-strated potential in photo-electronics and photocatalytic applications. However, the lack of fundamental understanding on charge transport (CT) mechanism as well as the correlation of CT mechanism with their structure hampered their further development. Herein, we report the direct evidence of CT mechanism in 2D Cu-THQ MOFs and the correlation of temporal and spatial behaviors of charge carriers with their photoconductivity by combining three advanced spectroscopic methods including time resolved optical and X-ray absorption spectroscopy and terahertz spectroscopy. In addition to Cu-THQ, the CT in Cu/Zn-THQ after incorporating Zn2+ guest metal was also examined to uncover the contribution of through space pathway as the presence of the redox inactive 3d10 Zn2+ is expected to perturb the long range in-plane CT. We show that the hot carriers in Cu-THQ generated after photoexcitation are highly mobile and undergo fast localization to a lower energy state (cool carriers) with electrons occupying Cu center and holes in ligands. The cool carriers, which have super long lifetime (> 17 ns) are responsible for the long-term photoconductivity in Cu-THQ and transport through O-Cu-O motif with negligible contribution from interlayer ligand π-π stacking as incorporation of Zn2+ in Cu-THQ significantly reduced photoconductivi-ty. These unprecedent results not only demonstrate the capability to experimentally probe CT mechanism but also provide important insight in the rational design of 2D MOFs for photoelectronic and photocatalytic applications.

14 SOLAR ENERGY↗
DOE OSTI2022

Deciphering the photophysical kinetics, electronic configurations and structural conformations of iridium–cobalt hydrogen evolution photocatalysts

Picosecond optical and X-ray absorption spectroscopies with time-dependent density functional theory revealed the reaction pathways, electronic and structural conformations of Ir–Co hydrogen evolution photocatalysts. The dyad bearing 2-phenylpyridine ancillary ligands produced more photoreduced Co(II) than its 2-phenylisoquinoline analogue. These findings are important for designs of earth-abundant photosensitizers for photocatalytic applications.

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

KS4A-Omics1.0_FspDS682

Soil fungi facilitate the translocation of inorganic nutrients from soil minerals to other microorganisms and plants. This ability is particularly advantageous in impoverished soils, because fungal mycelial networks can bridge otherwise spatially disconnected and inaccessible nutrient hotspots. However, the molecular mechanisms underlying fungal mineral weathering and transport through soil remains poorly understood. Here, we addressed this knowledge gap by directly visualizing nutrient acquisition and transport through fungal hyphae in a mineral doped soil micromodel using a multimodal imaging approach. Here, we observed how a representative of common saprotrophic soil fungi, Fusarium sp. DS 682, exhibited a mechanosensory response (thigmotropism) around obstacles and through pore spaces (~12 μm) in the presence of minerals.This study establishes the significance of fungal biology and nutrient translocation mechanisms in maintaining fungal growth under water and nutrient limitations in a soil-like microenvironment, using a high-throughput multi-omic analysis approach. Data package KS4A-Omics.1.0_FspDS682 (Publication: Fungal Mineral Weathering Mechanisms Revealed Through Direct Molecular Visualization) contents reported here are the first version (1.0) and contain pre- and post-processed data using high throughput data capture technologies for multi-omic analysis and integration, this data package contains raw and post-processed experimental data for X-Ray Absorption Near Edge Structure Spectroscopy (XANES/XRF), Optical Microscopy, Proteomics, Scanning Electron Microscope (SEM), Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-Ray Diffraction Spectroscopy (XRD) files, and X- Ray Photoelectron Spectroscopy (XPS) using EMSL capabilities. This data package DOI contains a comprehensive collection of high-throughput multi-omics data and process metadata catalog. Support files include additional data download contents “Read Me” with dataset descriptor information and data source method application ontologies (see data dictionary section). Reported data download content is structured for compliance with reported guidelines provided by community standard initiatives and publisher stakeholder policies supporting FAIR data principles.

47 OTHER INSTRUMENTATION↗
NASA NTRS1971

Stress corrosion in titanium alloys and other metallic materials

Multiple physical and chemical techniques including mass spectroscopy, atomic absorption spectroscopy, gas chromatography, electron microscopy, optical microscopy, electronic spectroscopy for chemical analysis (ESCA), infrared spectroscopy, nuclear magnetic resonance (NMR), X-ray analysis, conductivity, and isotopic labeling were used in investigating the atomic interactions between organic environments and titanium and titanium oxide surfaces. Key anhydrous environments studied included alcohols, which contain hydrogen; carbon tetrachloride, which does not contain hydrogen; and mixtures of alcohols and halocarbons. Effects of dissolved salts in alcohols were also studied. This program emphasized experiments designed to delineate the conditions necessary rather than sufficient for initiation processes and for propagation processes in Ti SCC.

Harkins, C. G.↗
NASA NTRS1982

Compensation mechanism in liquid encapsulated Czochralski GaAs Importance of melt stoichiometry

It is shown that the key to reproducible growth of undoped semi-insulating GaAs by the liquid encapsulated Czochralski (LEC) technique is the control over the melt stoichiometry. Twelve crystals were grown from stoichiometric and nonstoichiometric melts. The material was characterized by secondary ion mass spectrometry, localized vibrational mode far infrared spectroscopy, Hall-effect measurements, optical absorption, and photoluminescence. A quantitative model for the compensation mechanism in the semi-insulating material was developed based on these measurements. The free carrier concentration is controlled by the balance between EL2 deep donors and carbon acceptors; furthermore, the incorporation of EL2 is controlled by the melt stoichiometry, increasing as the As atom fraction in the melt increases. As a result, semi-insulating material can be grown only from melts above a critical As composition. The practical significance of these results is discussed in terms of achieving high yield and reproducibility in the crystal growth process.

Holmes, D. E.↗
NASA NTRS2000

Growth of Carbon Nanostructure Materials Using Laser Vaporization

Since the potential applications of carbon nanotubes (CNT) was discovered in many fields, such as non-structure electronics, lightweight composite structure, and drug delivery, CNT has been grown by many techniques in which high yield single wall CNT has been produced by physical processes including arc vaporization and laser vaporization. In this presentation, the growth mechanism of the carbon nanostructure materials by laser vaporization is to be discussed. Carbon nanoparticles and nanotubes have been synthesized using pulsed laser vaporization on Si substrates in various temperatures and pressures. Two kinds of targets were used to grow the nanostructure materials. One was a pure graphite target and the other one contained Ni and Co catalysts. The growth temperatures were 600-1000 C and the pressures varied from several torr to 500 torr. Carbon nanoparticles were observed when a graphite target was used, although catalysts were deposited on substrates before growing carbon films. When the target contains catalysts, carbon nanotubes (CNT) are obtained. The CNT were characterized by scanning electron microscopy, x-ray diffraction, optical absorption and transmission, and Raman spectroscopy. The temperature-and pressure-dependencies of carbon nanotubes' growth rate and size were investigated.

Zhu, Shen↗
NASA NTRS2009

Development and Airborne Operation of a Compact Water Isotope Ratio Infrared Spectrometer

A sensitive laser spectrometer, named IRIS (water isotope ratio infrared spectrometer), was developed for the in situ detection of the isotopic composition of water vapour in the upper troposphere and the lower stratosphere. Isotope ratio measurements can be used to quantify troposphere stratosphere exchange, and to study the water chemistry in the stratosphere. IRIS is based on the technique of optical feedback cavity-enhanced absorption spectroscopy. It uses a room temperature near-infrared laser, and does not require cryogenic cooling of laser or detectors. The instrument weighs 51 kg including its support structure. Airborne operation was demonstrated during three flights aboard the European M55-Geophysica stratospheric research aircraft, as part of the AMMA/SCOUT-03 (African Monsoon Multidisciplinary Analysis/Stratospheric Climate links with emphasis on the Upper Troposphere and lower stratosphere) campaign in Burkina Faso in August 2006. The data are discussed with reference to a Rayleigh distillation model. As expected, there is no indication of non-mass-dependent fractionation (also known as mass-independent fractionation) in the troposphere. Furthermore, improvements to the thermal management system and a move to a (cryogen-free) longer-wavelength laser source are discussed, which together should result in approximately two orders of magnitude improvement of the sensitivity

Iannone, Rosario Q.↗
DOE OSTI2023

Effect of electronic transitions on near edge optical properties of off-stoichiometric boron carbide thin films

In the present study, soft x-ray optical properties of off-stoichiometric boron carbide thin films are investigated, and the structure and chemical composition of the film is analyzed using angle dependent x-ray reflectivity and x-ray photoelectron spectroscopy techniques. Energy dependent soft x-ray reflectivity measured at a fixed grazing angle of 1.5° is used to determine the optical constants in the boron K edge region by applying the Kramers–Kronig technique. The measured optical constants show near edge fine features corresponding to σ* and π* resonances. Furthermore, the electronic transitions corresponding to σ* resonance cause a 40%–75% increase in the delta value in the above boron K edge region. The π* transitions corresponding to off-stoichiometric nature of the boron carbide are observed in the absorption spectra near ~ 192.7 eV. Details of the measured soft x-ray optical properties of the off-stoichiometric boron carbide thin film are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Impact of Glass Irradiation on Laser-induced Breakdown Spectroscopy Diagnostics in the Visible and NIR Range

Increased absorption of optical materials arising from the exposure to ionizing radiation must be accounted for to accurately analyze the laser-induced breakdown spectroscopy (LIBS) data retrieved from high-radiation environments. We evaluate this effect on a specifc example that mimics the diagnostics placed within a gas-cooled fast reactor coolant stream. Analysis is performed on the LIBS data measured with 1% Xe gas in an ambient He environment and the measured optical absorption from the gamma- and neutron-irradiated low-OH fused silica and sapphire glasses. No significant change in the number of shots required to reach a 3σ detection level was observed up to 10 Mrad gamma dose and exposure to a 1.7×10 17 n/cm 2 neutron fluence. In contrast, the spectral dependence of absorption results in either a systematic overestimation or underestimation of line intensity ratios, depending on the line of interest selected for analysis. Moreover, if lines from different spectral regions are used to create Boltzmann plots, this attenuation also leads to statistically significant changes in the calculated temperatures for calculations using Xe II lines only, lowering them from 8000±610 K to 6800±810 K for the case of exposure to the 1.7×10 17 n/cm 2 flux, and broadening the temperature range required for a 95% confidence interval. In the case of measuring the Xe spectrum, these effects may be mitigated using only the longer-wavelength spectral region, where radiation-attenuation is relatively small, or through analysis using the iterative Saha-Boltzmann method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

X-ray free electron laser studies of electron and phonon dynamics of graphene adsorbed on copper

Here, we report optical pumping and x-ray absorption spectroscopy experiments at the Pohang Accelerator Laboratory free electron laser that probes the electron dynamics of a graphene monolayer adsorbed on copper in the femtosecond regime. By analyzing the results with ab initio theory we infer that the excitation of graphene is dominated by indirect excitation from hot electron-hole pairs created in the copper by the optical laser pulse. However, once the excitation is created in graphene, its decay follows a similar path as in many previous studies of graphene adsorbed on semiconductors, i.e., rapid excitation of strongly coupled optical phonons and eventual thermalization. It is likely that the lifetime of the hot electron-hole pairs in copper governs the lifetime of the electronic excitation of the graphene.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revealing Hot and Long-Lived Metastable Spin States in the Photoinduced Switching of Solvated Metallogrid Complexes with Femtosecond Optical and X-ray Spectroscopies

An atomistic understanding of the photoinduced spin-state switching (PSS) within polynuclear systems of d 4 –d 7 transition metal ion complexes is required for their rational integration into light-driven reactions of chemical and biological interest. However, in contrast to mononuclear systems, the multidimensional dynamics of the PSS in solvated molecular arrays have not yet been elucidated due to the expected complications associated with the connectivity between the metal centers and the strong interactions with the surroundings. Herein, the PSS in a solvated triiron(II) metallogrid complex is characterized using transient optical absorption and X-ray emission spectroscopies on the femtosecond time scale. The complementary measurements reveal the photoinduced creation of energy-rich (hot) and long-lived quintet states, whose dynamics differ critically from their mononuclear congeners. We report this finding opens major prospects for developing novel schemes in solution-phase spin chemistry that are driven by the dynamic PSS process in compact oligometallic arrays.

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

Adaptive four-level modeling of laser cooling of solids

Laser cooling of rare-earth doped solids has been demonstrated across a wide range of material platforms, inspiring the development of simple phenomenological models such as the four-level model to elucidate the universal properties of laser cooling under various operating conditions. However, these models usually require the input of full absorption spectra that must be provided experimentally or by additional complicated atomic modeling. In this Letter, we propose that a four-level model, when extended to admit effective energy levels adaptive to the pumping photon energy, can accurately predict the cooling efficiency as a function of temperature and pumping frequency using only few inputs such as the absorption coefficient measured at a single frequency and temperature. Our model exploits the quasi-equilibrium properties of the excitation of rare-earth ions for the determination of the effective four energy levels. The model is validated against published experimental results for a span of materials including ytterbium/thulium-doped glass and crystals. With the verified model, we derive explicit expressions for the optimal frequency and the operating bandwidth of pumping lasers. Our model significantly simplifies the modeling process of laser cooling and is expected to stimulate further development of optical refrigeration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗