Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Agents”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Intelligent Agents for the Optimization of Atomic Layer Deposition

Atomic layer deposition (ALD) is a highly controllable thin film synthesis approach with applications in computing, energy, and separations. The flexibility of ALD means that it can access a massive chemical catalogue; however, this chemical and process diversity results in significant challenges in determining processing parameters that result in stable and uniform film growth with minimal precursor consumption. In situ measurements of the ALD growth per cycle (GPC) can accelerate process development but it still requires expert intuition and time-consuming trial and error to identify acceptable processing parameters. This procedure is made more difficult by the presence of experimental noise in the GPC values and the complexity of ALD surface chemistries. Here, a need exists for efficient optimization approaches capable of autonomously determining processing conditions resulting in optimal ALD film growth. In this work, we present the development of three optimization strategies and compare their performance in optimizing four simulated ALD processes. Furthermore, the effect of noise in the GPC measurements on optimization convergence is studied.

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

Molecular H 2 as the Reducing Agent in Low-Temperature Oxide Reduction Using Calcium Hydride

Low-temperature synthesis is crucial for advancing sustainable manufacturing and accessing novel metastable phases. Metal hydrides have shown great potential in facilitating the reduction of oxides at low temperatures, yet the underlying mechanism—whether driven by H - , H 2 , or atomic H—remains unclear. Here, in this study, we employ in situ electrical transport measurements and first- principles calculations to investigate the CaH 2 -driven reduction kinetics in epitaxial α-Fe 2 O 3 thin films. Intriguingly, samples in direct contact with or separated from CaH 2 powders exhibit similar apparent activation energies for H 2 reduction, although direct contact significantly increases the reduction rate. These findings indicate that molecular H 2 is the dominant reducing species in the low-temperature reduction of oxides using CaH 2 , with a key aspect of the hydrides' superior reducing power attributed to their ability to eliminate residual moisture. This work underscores the critical role of moisture control in enabling effective low-temperature oxide reduction for advanced material synthesis.

Wang, Jiayue [SLAC National Accelerator Laboratory↗
DOE OSTI2025

Criegee Intermediates Compete Well with OH as a Cleaning Agent for Atmospheric Amides

Elucidating the chemical kinetics of stabilized Criegee intermediates (sCIs) in the atmosphere is critically important for climate modeling. Here, we report a class of very rapid bimolecular reactions of two sCIs, namely, CH 2 OO and syn-CH 3 CHOO, with amides. We used electronic structure calculations and kinetics calculations to elucidate a universal mechanism by which the oxygen atom of the carbonyl group in an amide is added to the carbon atom of the COO group in the sCI with simultaneous transfer of the amide hydrogen to the terminal oxygen atom of the carbonyl oxide of the sCI. The barriers for the mechanism are submerged below reactants by ∼9 kcal/mol, which means that the tight transition state is not the rate-determining step, and the rate constants are determined by loose free energy bottlenecks between the reactants and the precursor complexes. We calculate the rate constants due to these loose and barrierless transition states by variable-reaction-coordinate variational transition-state theory. We find that bimolecular reactions of sCIs with amides are very rapid, with rate constants 1 to 5 × 10 –10 cm 3 molecule –1 s –1 , which is a factor of 2 faster than the rate constants of carboxylic acids with sCIs and 10 2 faster than the rate constants of OH reactions with amides. This has the consequence that, under a wide range of conditions, sCIs are the major sink for atmospheric amides, in contrast to the usual assumption that OH radicals are the dominant sinks.

Amides↗