Plasma techniques for nanostructured carbon materials synthesis. A case study: carbon nanowall growth by low pressure expanding RF plasma

A short description of approaches for carbon nanostructures synthesis is made and the advantages of using plasma during the growth are presented. As a particular example of a plasma based technique we detail the process of downstream carbon nanowall (CNW) synthesis by a radiofrequency expanding plasma beam. The technique combines magnetron sputtering for catalyst deposition and plasma enhanced chemical vapor deposition (main gas: argon, active gas: hydrogen, precursor gas: acetylene) for carbon growth in a single reactor. The analysis focuses on the correlation between the material properties and the plasma characteristics measured at different points along the flow axis, aiming to reveal the importance of plasma species in the growth process. The material properties were investigated by scanning and transmission electron microscopy, whereas the plasma data were obtained by optical emission spectroscopy, Langmuir probes and mass spectrometry. CNWs with a large area and well isolated from each other are obtained at an optimum distance from the precursor injection point where the plasma presents an enhanced content of carbon nanoclusters. The possible processes responsible for the growth are discussed.