Growth of nanocrystalline graphite on sapphire by implantation of large carbon clusters from SNICS source

Abstract

Nano-crystalline graphite (NCG) structures on insulating layers have been grown via implantation of kilo-electron-volt (keV) energetic carbon clusters (Cn) on sapphire (Al2O3) and post-implantation thermal annealing conditions. The clusters were produced using a source of negative ion using Cesium sputtering (SNICS) with graphite and carbon nanotubes (CNT) as cathode materials. The Graphite cathode exhibited high currents for most of the cluster sizes. However, the CNT cathodes showed higher yields for relative heavy clusters (n = 16, 18, and 20). Also, carbon clusters as large as n ~ 56 were observed from the SNICS source. The Sapphire substrates were implanted with carbon cluster (Cn, n = 18) ions at 11 keV (~611 eV per carbon atom) with fluences of 1.1 × 1015 C18-clusters/cm2 (~2 × 1016 carbon atoms/cm2). Ion impact craters and surface build-ups were observed. Further, we have studied the carbon bonding characteristics by Raman Spectroscopy (RS) on as-implanted and annealed implanted samples. We have observed well-developed disorder (D), graphite (G), and 2D peaks from the optimized samples, indicating the formation of nano-crystalline graphite (NCG) structures on the surface. The ratio of D and G peaks in the RS spectra suggests that the nano-crystalline cluster diameter or in-plane correlation length is about 10–16.5 nm. The Crystal size approaches a maximum value with increasing post-implantation thermal annealing temperature. We have studied the growth of NCG by X-ray Photoelectron Spectroscopy (XPS) for the chemical bonding and distribution. The average sizes of crystalline NCGs were also estimated using Grazing Angle X-ray Diffraction (GAXRD) Spectrometry. The surface morphology of the implanted samples was investigated using Atomic Force Microscopy (AFM).