Effect of HF wet-etching and H2-plasma polishing on the low-temperature growth of carbon nanotubes on stainless-steel substrates

Direct growth of carbon nanotubes (CNTs) on 316 stainless-steel (SS) substrates could facilitate versatile commercial applications. For the successful synthesis of CNTs on SS substrate, hydrofluoric acid (HF) etching renders suitable surface roughness to promote CNT growth. For catalyst preparation and also subsequent CNT growth, H2-plasma treatment plays essential roles. Reversing the aging effect of Fe/Ni from its unwanted oxides of reduced catalytic activity and formation of Fe nanoparticles from the sheet are accomplished using H2-plasma. High-density plasma, along with specific gas precursors with its energetic ions, required for uniform CNT growth is attained by microwave plasma-enhanced chemical vapor deposition. By using CO2, providing suitable oxidizer precursors, in (CH4 + H2) diffuse plasma, necessary ambience for low-temperature nucleation (300 degrees C) and highyield CNT growth is obtained. Reduction in the deposition rate by highly-energetic ion collisions in high-power plasma is resolved by introducing remote plasma configuration using a specially designed mask assembly. Considering the optimum magnitudes of the intensity ratios of D- and 2D-peaks to the G-peak in the Raman spectra of CNTs, a time span of 2 h of HF-etching appears optimum for proper functioning of the Fe/Ni nanoparticle catalyst. Furthermore, H2-plasma polishing is effectively utilized as the last step of pretreatment, leading to the growth of lower-diameter CNTs. Finally, using a shadow mask assembly and weak oxidizing gas, lowtemperature growth of CNTs is successfully accomplished on SS substrates, pretreated by optimum HF-etching and H2-plasma polishing on the Fe-nanoparticle catalyst layer, avoiding the conventional steps of hightemperature annealing for catalyst nanoparticle formation as well as high-temperature nucleation for CNT growth. Even without the use of a separate Fe-catalyst layer, CNT growth is accomplished directly on HF-etched and H2-plasma polished SS substrates, utilizing mostly Fe/Ni nano-grains that originate from the intrinsic composition of SS as the nucleation sites. Use of limited action-steps and of a low-temperature (-300 degrees C) distinguish this as a realistic avenue for commercial production of CNTs.

Automated summary

Direct growth of carbon nanotubes on 316 stainless-steel substrates using hydrofluoric acid etching and H2-plasma treatment is effective for versatile commercial applications. The use of microwave plasma-enhanced chemical vapor deposition allows for high-density plasma and uniform CNT growth.