Investigation on morphology and structural properties of 2D carbon nanostructure grown via 150 MHz PECVD

Abstract

A 150 MHz very high frequency plasma enhanced chemical vapor deposition (150 MHz VHF-PECVD) system was utilized to fabricate two-dimensional carbon nanostructure from the mixture of CH4 and H2. Morphology and structural properties of the grown nanostructure were investigated by means of microscopic imaging, Raman spectroscopy and X-ray diffraction technique. FESEM imaging had revealed two different carbon nanowalls (CNW), namely wavy-like and dense structure. A significant change in the film density and wall size were observed when H2 flow rate and substrate temperature were varied. It was found that a suitable intermixing of H2 and CH4 is necessary for synthesizing good quality CNW. A limited or excessive amount of H2 flow produced CNW having high defects density and poor surface coverage due to variation in the concentration of H radicals. In addition, a drastic change in film morphology was observed at growth temperature between 750 °C to 850 °C due to high rate of surface reactions. The growth of CNW was found to be more efficient at smaller electrode spacing due to better flux of hydrocarbon radicals towards the substrate surface. Typical characteristics of CNW were observed from strong D band, narrow bandwidth of G band and single broad peak of 2D band of Raman spectra indicating the presence of disordered nanocrystalline graphite structure with high degree of graphitization. The occurrence of strong peak at [002] plane with interplanar distance of 0.34 nm confirmed the growth of 2D highly graphitized CNW. It can be concluded that a capacitively coupled 150 MHz VHFPECVD is a promising alternative technique for CNW fabrication due to its capability to dissociate CH4 to CHx and H radicals more efficiently.