(Invited) Improving Nanosynthesis By Means of Pulsed Anodic Arc Discharge

Abstract

Anodic arc discharge operated with a periodic voltage signal shows better performance in nanomaterial synthesis compared to steady DC arc discharge. The main advantages of pulsed arcs consist of improved process control, high arc stability, tailoring of material properties, and growth of high-quality materials thanks to reduced production of macroparticles. This study shows the relevance of pulse frequency (1-5 Hz), duty cycle (10-50%), peak arc voltage (~50 V) and peak arc current (~200 A) on determining arc discharge properties. All arc processes are performed in a helium atmosphere at around 300 Torr. Pulsed arc discharges show ablation rates and average power consumption values of the order of 1 mg/s and 1 kW, respectively, which are competitive with typical values of standard DC anodic arcs. Pulsed arc syntheses of low-dimensional carbon (graphene, nanotubes) and molybdenum disulfide nanomaterials are treated as examples for this new deposition method. Plasma parameters have been estimated by optical emission spectroscopy and fast Langmuir probe diagnostics. Characterization techniques such as Raman spectroscopy, scanning electron microscopy and x-ray diffraction have provided information on structural and morphological properties of the cathode deposit. The basic physical processes during arc discharge are described in terms of a global model that considers the total pressure evolution of the system. Such model provides a scenario for the observed erosion dynamics and optical emission patterns associated to the different arc discharge phases. The electrical properties of pulsed arc discharges have been characterized and related to basic plasma structure. In conclusion, pulsed anodic arc plasmas are promising for the synthesis of nanomaterials with special physical and surface properties suitable for electrical, mechanical and optical applications.