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Site‑selective synthesis of onion like carbon from nanodiamond thin film via laser‑assisted photothermal process Yoonsoo Rho1 · Heuiseok Kang2 · Costas P. Grigoropoulos1 · Kyung‑Tae Kang2  Received: 31 May 2020 / Accepted: 2 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

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 lasersynthesized 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. Keywords  Onion like carbon · Nanodiamond · Laser annealing · Photothermal process · Supercapacitors

1 Introduction Onion like carbon (OLC) is a zero-dimensional (0D) carbon derivative consisting of concentric multi-fullerene shells [1] that exhibit high chemical stability and electrical conductivity due to s­ p2 carbon bonding. Thus, various applications based on the promising properties of OLC have been explored, including electrochemical devices [2–7], gas storage [8], and solid lubricants [9]. When applied in electrochemical devices, its exohedral nanopores (e.g., positive curvature) allow fast ionic transport and diffusion, allowing the realization of ultrahigh powered supercapacitors [2–7]. Various synthesis methods have been introduced, including * Kyung‑Tae Kang [email protected] 1



Laser Thermal Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA



Micro/Nano Process Group, Korea Institute of Industrial Technology, Ansan‑si, Gyeonggi‑do 15588, Republic of Korea

2

e-beam irradiation [1, 10], pulsed laser beam annealing [11, 12], resonant excitation of molecules [11, 12] and furnace annealing of detonated nanodiamonds (NDs) [4, 5, 13–16]. Among these methods, thermal treatment of the detonated NDs has shown reliable and scalable production of OLC with