Site-selective synthesis of onion like carbon from nanodiamond thin film via laser-assisted photothermal process

Abstract

Onion like carbon (OLC) has attracted much attention due to its promising electrochemical properties which originate from its multi sp2 carbon shells that form a spherical nanostructure with uniform size distribution. When utilized as active electrode material in electrochemical cells, it induces fast ionic diffusion and transport rates and can be used in ultrahigh powered supercapacitors. Despite the substantial promise, OLC is typically synthesized by thermal treatment of nanodiamonds (NDs) in a harsh environment (e.g., up to 1800 °C in a high vacuum), which is not feasible for direct synthesis from various substrates. Here, we propose a facile laser-induced site-selective synthesis method of OLC from ND thin film formed by a solution-based process. Spin coating of ultra-dispersed ND ink with uniform size distribution allows preparation of ND thin films of varying thickness on glass and metal substrates. Pulsed laser irradiation in a vacuum transforms the NDs into OLC in an arbitrary area, which is verified by Raman and transmission electron microscopy (TEM) analysis. The laser-synthesized OLC was employed as an active electrode in supercapacitors and demonstrated fast charge and discharge rates, hence exhibiting comparable performance to that of OLC obtained by furnace annealing. We believe that our results open an avenue to explore various electrochemical applications of OLC with designed patterns.