Abstract The use of silicon nanoparticles for lithium-ion batteries requires a precise control over both their average size and their size distribution. Particles larger than the generally accepted critical size of 150 nm fail during lithiation because of excessive swelling, while very small particles (<10 nm) inevitably lead to a poor first cycle coulombic efficiency because of their excessive specific surface area. Both mechanisms induce irreversible capacity losses and are detrimental to the anode functionality. In this manuscript we describe a novel approach for enhanced growth of nanoparticles to ∼20 nm using low-temperature flow-through plasma reactors via pulsing. Pulsing of the RF power leads to a significant increase in the average particle size, all while maintaining the particles well below the critical size for stable operation in a lithium-ion battery anode. A zero-dimensional aerosol plasma model is developed to provide insights into the dynamics of particle agglomeration and growth in the pulsed plasma reactor. The accelerated growth correlates with the shape of the particle size distribution in the afterglow, which is in turn controlled by parameters such as metastable density, gas and electron temperature. The accelerated agglomeration in each afterglow phase is followed by rapid sintering of the agglomerates into single-crystal particles in the following plasma-on phase. This study highlights the potential of non-thermal plasma reactors for the synthesis of functional nanomaterials, while also underscoring the need for better characterization of their fundamental parameters in transient regimes.
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Nanosynthesis by atmospheric arc discharges excited with pulsed-DC power: a review
Abstract Plasma technology is actively used for nanoparticle synthesis and modification. All plasma techniques share the ambition of providing high quality, nanostructured materials with full control over their crystalline state and functional properties. Pulsed-DC physical/chemical vapour deposition, high power impulse magnetron sputtering, and pulsed cathodic arc are consolidated low-temperature plasma processes for the synthesis of high-quality nanocomposite films in vacuum environment. However, atmospheric arc discharge stands out thanks to the high throughput, wide variety, and excellent quality of obtained stand-alone nanomaterials, mainly core–shell nanoparticles, transition metal dichalcogenide monolayers, and carbon-based nanostructures, like graphene and carbon nanotubes. Unique capabilities of this arc technique are due to its flexibility and wide range of plasma parameters achievable by modulation of the frequency, duty cycle, and amplitude of pulse waveform. The many possibilities offered by pulsed arc discharges applied on synthesis of low-dimensional materials are reviewed here. Periodical variations in temperature and density of the pulsing arc plasma enable nanosynthesis with a more rational use of the supplied power. Parameters such as plasma composition, consumed power, process stability, material properties, and economical aspects, are discussed. Finally, a brief outlook towards future tendencies of nanomaterial preparation is proposed. Atmospheric pulsed arcs constitute promising, clean processes providing ecological and sustainable development in the production of nanomaterials both in industry and research laboratories.
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- Award ID(s):
- 1747760
- NSF-PAR ID:
- 10389749
- Date Published:
- Journal Name:
- Nanotechnology
- Volume:
- 33
- Issue:
- 34
- ISSN:
- 0957-4484
- Page Range / eLocation ID:
- 342001
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Advances in nanoscience have enabled the synthesis of nanomaterials, such as graphene, from low‐value or waste materials through flash Joule heating. Though this capability is promising, the complex and entangled variables that govern nanocrystal formation in the Joule heating process remain poorly understood. In this work, machine learning (ML) models are constructed to explore the factors that drive the transformation of amorphous carbon into graphene nanocrystals during flash Joule heating. An XGBoost regression model of crystallinity achieves an
r 2score of 0.8051 ± 0.054. Feature importance assays and decision trees extracted from these models reveal key considerations in the selection of starting materials and the role of stochastic current fluctuations in flash Joule heating synthesis. Furthermore, partial dependence analyses demonstrate the importance of charge and current density as predictors of crystallinity, implying a progression from reaction‐limited to diffusion‐limited kinetics as flash Joule heating parameters change. Finally, a practical application of the ML models is shown by using Bayesian meta‐learning algorithms to automatically improve bulk crystallinity over many Joule heating reactions. These results illustrate the power of ML as a tool to analyze complex nanomanufacturing processes and enable the synthesis of 2D crystals with desirable properties by flash Joule heating. -
The use of plasma processes in nanomaterial synthesis is limited by a lack of understanding of the effects of plasma treatment on the morphology and other properties. Here, we studied the effects of atmospheric plasma treatment on the morphology and optical properties of Ag nanoparticles. The Ag nanoparticles were deposited on substrates by injecting an aerosol into flowing argon gas and then treated with a low-temperature atmospheric plasma jet. After plasma treatment, the mean Ag nanoparticle diameter reduced to an average of 5 nm, which was accompanied by a blue shift of ~70 nm in the peak of the surface plasmon resonance; these results are similar to those obtained by thermal treatment at elevated temperatures. The reduction in nanoparticle size is explained by the redox reaction that occurs on the nanoparticle surface, which is evident from the presence of AgO and Ag2O Raman peaks in the treated sample. The surface charge changed as a result of plasma treatment, as indicated by a large change in the zeta potential from +25.1 ± 4 mV for the untreated sample to −25.9 ± 6 mV after 15 min of plasma treatment. Surface-enhanced Raman spectroscopy of the plasma-treated films was carried out with the fluorescent dye Rhodamine 6 G, which showed a ~120-fold enhancement in the signal intensity relative to the untreated substrates. We, therefore, conclude that cold-plasma treatment modified the surface morphology of the Ag nanoparticles, thereby enhancing their optical properties. This technique could be applied to a wide range of nanoparticle systems used in biosensing applications.more » « less
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High-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and precise timing are required. The switches allow operation in the megaampere, megavolt regime while maintaining low insertion losses. Currently, there is a lack of detailed plasma measurements in these switches, yet such measurements are needed to elucidate the detailed physics, which include a range of processes such as laser breakdown, streamer formation and growth, current flow, plasma evolution, and cooling. Detailed spatially- and temporally resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems. This contribution presents laser Thomson scattering measurements of the electron number density and temperature evolution in a HV-LTS. The switch was operated at 6 kV with current flow for a duration of 145 ns and a peak current density of 0.2 MA/cm2 into a matched load. The Thomson scattering diagnostic system uses a 532 nm probe from an Nd:YAG laser allowing a temporal resolution of ∼10 ns. We find that during the switch current pulse, the plasma electron temperature rose from a starting value of 8.1 ± 1.6 eV (due to cooling of the earlier trigger laser plasma) to a peak value of 26 ± 5 eV with an associated increase in the electron density from 8.6 ± 1.7 × 1017 to 3.1 ± 0.6 × 1018 cm−3.
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1361-6528/ac6bad
