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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Catalytic Reaction Intermediates Revealed with Femtosecond M-edge XANES (Final Technical Report)

The major goals of this work were to measure the electronic structure of earth-abundant catalysts at key steps in their catalytic cycles using ultrafast UV/Visible, Extreme Ultraviolet, and X-ray spectroscopy. Our central idea was that by using these sophisticated probes, we could uncover hidden reaction mechanisms and provide guidance for catalyst design. A second major goal was the development of Extreme Ultraviolet (XUV) spectroscopy as an accessible, tabletop probe of transition metal electronic structure. Spectra in this 30-100 eV energy range probe 3d→3p transitions in 3d metals and 5p/4f→5d transitions in 5d metals, and share the oxidation state, spin state, and ligand field specificity of hard X-ray spectroscopy. The Vura-Weis group previously established the basic utility of this technique for measuring the excited-state cascades of transition metal chromophores, and in this grant we intended to extend its scope to catalytic intermediates.

36 MATERIALS SCIENCE↗
DOE OSTI2023

From Femtoseconds to Gigaseconds: The SolDeg Project to Analyze and Mitigate the Performance Degradation of a-Si:H/c-Si Heterojunction Solar Cells

We pursued two major projects. In the first, we studied the degradation of a-Si/c-Si Heterojunction cells. We substantially expanded our previously developed SolDeg platform, and incorporated hydrogen into it. We also expanded the capabilities of SolDeg by developing a three channel model for a very efficient way to determine long term junction dynamics. The first main result was that we identified hydrogen drifting away from the interface as a key degradation channel. The second was that we developed and proposed the concept of a “reverse silicon density gradient” in the a-Si layer that had the promise of reducing degradation by up to 80%. In the second project, we studied the degradation of TOPCon solar cells. We again identified a key degradation channel, which in these cells was the formation of pinholes across the oxide layer. We then again were able to develop and to propose a way to dramatically reduce degradation by discovering that tuning the hydrogen concentration forms a sharp and deep minimum of the recombination current.

14 SOLAR ENERGY↗
DOE OSTI2020

Parallel Broadband Femtosecond Reflection Spectroscopy at a Soft X-Ray Free-Electron Laser

X-ray absorption spectroscopy (XAS) and the directly linked X-ray reflectivity near absorption edges yield a wealth of specific information on the electronic structure around the resonantly addressed element. Observing the dynamic response of complex materials to optical excitations in pump–probe experiments requires high sensitivity to small changes in the spectra which in turn necessitates the brilliance of free electron laser (FEL) pulses. However, due to the fluctuating spectral content of pulses generated by self-amplified spontaneous emission (SASE), FEL experiments often struggle to reach the full sensitivity and time-resolution that FELs can in principle enable. Here, we implement a setup which solves two common challenges in this type of spectroscopy using FELs: First, we achieve a high spectral resolution by using a spectrometer downstream of the sample instead of a monochromator upstream of the sample. Thus, the full FEL bandwidth contributes to the measurement at the same time, and the FEL pulse duration is not elongated by a monochromator. Second, the FEL beam is divided into identical copies by a transmission grating beam splitter so that two spectra from separate spots on the sample (or from the sample and known reference) can be recorded in-parallel with the same spectrometer, enabling a spectrally resolved intensity normalization of pulse fluctuations in pump–probe scenarios. We analyze the capabilities of this setup around the oxygen K- and nickel L-edges recorded with third harmonic radiation of the free electron laser in Hamburg (FLASH), demonstrating the capability for pump–probe measurements with sensitivity to reflectivity changes on the per mill level.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Femtosecond time-domain phase comparator

Phase shift in test device is measured by summing output of mixer with ramp voltage and comparing time interval between zero crossings of summed signal and ramp reference frequency. Circuit can be used to test devices at other frequencies by changing only signal source, phase splitter, and mixer; divider and time-interval counter need not be driven by oscillator.

Donahoe, T.↗