Plasma and Material Processes in Atmospheric Pressure Plasmas
The primary purpose of this project is to develop an understanding of the synergy of plasma and nanoscale material processes in carbon, boron nitride (BN), and hybrid B-C-N nanostructure synthesis, including but not limited to, fullerenes, nanotubes and nanofibers. The focus of this project is on the fundamental and interdisciplinary science associated with the synthesis of nanoparticles and nanostructures by atmospheric pressure arc discharges.
We utilize a helium DC arc discharge with a vaporized anode at atmospheric pressure, or anodic arc, which has been successfully applied to the synthesis of a broad class of nanomaterials, including but not limited to carbon nanoparticles and nanostructures and metal nanoparticles. Figure 1 shows the schematic of an atmospheric pressure arc plasma.
Figure 1: Schematic of atmospheric pressure arc plasma using graphite electrodes
Carbon neutral atoms evaporate from the anode, which is heated by plasma electrons. The ions created by ionization will then deposit to the cathode.
In addition, the arc technique was previously attempted, although less successfully, for synthesis of BN, B-C-N and carbon nitride nanostructures. The scope of the research includes comprehensive experimental and theoretical studies of three common major steps for arc synthesis of carbon, boron nitride, and hybrid B-C-N nanostructures:
Our integrated approach for characterization of synthesis processes is as follows: i) spatial and temporal measurements of plasma properties will provide an input for modeling of atomistic processes; ii) modeling results of formation of nanoparticles and nanostructures will be validated by in-situ diagnostics of nanoparticles and nanostructures synthesized in plasma; iii), synthesized nananomaterials will be extracted from the plasma during the arc and collected after the synthesis process. The extracted and collected materials will be then characterized by ex-situ material evaluation to validate in-situ measurements and provide an additional input for modeling.
A comprehensive set of plasma and nanoparticle diagnostics is employed to provide the dataset needed to validate and further develop theoretical models and codes of nanostructure growth.
In this project, we perform measurements of the arc source properties to understand the particle and heat flux from the arc plasma for nanosynthesis. Important measured quantities are:
1) ablation rate of the anode materials,
2) power absorbed by the arc plasma and electrodes,
3) temperatures of electrodes, ambient gas, and arc chamber,
4) profile of established gas-flow velocity,
5) profile of electric potential,
6) distribution of electron temperature and plasma density,
7) temperatures and densities of active elements such as carbon atoms, C2, and C3 species, and densities of atomized catalyst metals and boron atoms (for synthesis of, for example, BN and
8) densities and characteristic size of catalyst nanoparticles and nanostructures, and
9) nanoparticle charge.
For these measurements, the LPN-PPPL is currently equipped with a variety of diagnostic techniques including: fast camera imaging, infrared cameras, bolometers, thermocouples, floating and swept Langmuir probes, Optical Emission Spectroscopy, and Laser Induced Incandescence (LII). In addition, advanced laser diagnostics, including Laser Induced Fluorescence (LIF), Coherent Rayleigh-Brillouin Scattering (CRBS), and Mie scattering are now under development as a key part of this project. These diagnostics are calibrated with a microplasma nanoparticle source with prescribed properties and dimensions developed by Prof. M. Sankaran’s group at Case Western Reserve University. A shielded electrostatic probe developed by Prof. M. Keidar’s group at The George Washington University is developed to measure the charge of synthesized nanoparticles in plasma and extract nanoparticles. This probe is equipped with a movable shutter to control the flux of nanoparticles and nanostructures to the probe collector. These laser and probe-based techniques are expected to provide spatially resolved measurements in the arc plasma and surrounding nanoparticle formation regions.