A parametric study to unravel the alignment mechanism of carbon nanotubes during its plasma-assisted growth

Abstract

The alignment and catalyst-assisted growth mechanism of carbon nanotubes (CNTs) in a hydrogen-diluted methane plasma are demonstrated in the present work. The consequence of plasma parameters (plasma density and temperature) and bias potential of the substrate on the sheath electric field is examined. The role of the electric field in the plasma sheath to provide the necessary electrostatic force and its repercussion on the carbon nanotubes alignment in the plasma are studied by taking into contemplation the steady state fluid equations, kinetics of the plasma sheath, charged species dynamics (positive ions and electrons) and neutral atoms in a reactive plasma, kinetics of the catalyst particle, and creation of atomic species of carbon and hydrogen over the surface of catalyst nanoparticle and incorporating various processes vital for the growth of carbon nanotube in plasma. Taking into deliberation the initial conditions and the glow discharge parameters determined experimentally for the model, the numerical solutions for the equations are obtained. The outcomes of the studies revealed that the alignment of the nanotube depends on the force exerted at the tip of CNTs, i.e., the catalyst nanoparticle. This force is a consequence of the plasma sheath electric field which is dependent on the plasma parameters and the bias voltage at the substrate. This electrostatic force is also dependent upon the dimensions of the nanotube growing in the plasma environment and modifies itself continuously conferring to the instantaneous nanotube measurement and alignment during the growth. The present study can be apprehended to manufacture carbon nanotubes aligned vertically in plasma for better applications in the areas of field emission devices. The results of the present study have been assessed and compared with the existing experimental observations which accredit the proposed mechanisms.