The effect of inductance-controlled energy release rate on the plasma resistance and size distribution of copper nanoparticles generated by spark-discharge ablation

Spark-discharge ablation (SDA) is a versatile technique for producing nanoparticles with controlled size and composition, high throughput (mg/h), repeatability, and stability. Uniquely small and pure nanoparticles can be produced for different applications in nanotechnology. Nanoparticle properties can be tuned by modifying electrode geometry/spacing, gas flowrate, or circuit parameters. Increasing circuit resistance can reduce nanoparticle mobility diameter but is energy inefficient. Alternatively, changing the circuit inductance can control the energy release rate of individual discharges. Despite its potential importance, the role of inductance on discharge behavior and nanoparticle size distribution remains poorly understood.

We developed a custom SDA generator operated with a 3 L/min nitrogen flow and 3.15 mm diameter copper electrodes (99.95% purity) arranged perpendicular to the gas flow with a 0.67 mm gap separation. One electrode was grounded, while the other was connected to a high-voltage RLC circuit (10 nF capacitance, 7.10 µH inductance, and 3.06 Ω resistance), with a 1 mA charging current. External inductors ranging from 10 to 560 µH were added. Time-resolved voltage and current measurements showed that discharge duration increased monotonically from 7.1 µs (no external inductance) to 60 µs (560 µH). The energy released per discharge ranged from 37 to 80% of the capacitor stored energy (45 mJ).

Analytical fits of the ringing current and voltage yielded an effective constant discharge resistance. A complementary model predicts thermal channel expansion, leading to a time-decreasing plasma resistance governed by discharge frequency, energy, channel geometry, and temperature. Increasing inductance significantly altered light emission and led to deflected thermal channels. Scanning mobility particle spectrometer measurements revealed unimodal size distributions with narrow peaks below 10 nm. External inductance is found to considerably improve the stability and repeatability of the nanoparticle generator as well as increase the nanoparticle production rate with a maximum around 100 µH external inductance.