<p>Carbon-based nanomaterials, such as graphene and carbon nanotubes (CNTs), are promising for the energy-related applications including lithium-ion batteries (LIBs) and supercapacitors. Those graphitized nanocarbon are usually synthesized at elevated temperatures. However, from a view point of the green (environmentally friendly) process, even the energy-related nanomaterials should be synthesized at lower temperatures, ideally at room-temperature (RT).</p><p></p><p>Ar⁺ ion irradiation onto the solid surfaces entails the formation of various shapes of surface nanostructures, such as well-known conical nanostructures at RT. Such a formation of conical structures is dramatically enhanced by the simultaneous supply of C during the Ar⁺ ion irradiation [1]. The composition of the ion-irradiated surfaces is readily controllable by a simultaneous supply of the “third” material during the ion irradiation [2, 3]. By the simultaneous C and Ni supply during the Ar⁺ ion irradiation to Au substrate, for instance, the conically textured Au surface was covered with C layers with a dispersion of Ni nanoparticles (NPs), and the C layers showed the spontaneous local graphitization [4]. Very interestingly, the Ni NP including C thus prepared at RT showed the excellent supercapacitor property [4]. Surprisingly, the NPs were still metallic in the C matrix even after the long exposure to air.</p><p></p><p>Encouraged by this fact, we challenged the synthesis of Li including C nanocomposites by the ion irradiation method. In this case also, the metallic Li was clearly visible by high resolution transmission electron microscope, with a lattice distance of 0.24 nm corresponding to the (110) plane of Li after the exposure to air without any glovebox [5], and the solid electrolyte interphase (SEI) was instantaneously formed at the very initial stage of the charge-discharge cycles [1]. So, the ion-induced C-Li can be attractive as the anode material for the LIB battery for easy and safe handling.</p><p></p><p>By pre-coating C layers also, Ar⁺ ion irradiation onto Au substrate induced the enhanced formation of conical protrusions. Au conical arrays thus prepared were used as a substrate for the surface enhanced Raman spectroscopy, and the ultrafast and ultrasensitive detection of COVID-19 virus was achieved [6]. Thus, the C-based nanocomposites fabricated by ion-irradiation method at RT are promising for the energy- and bio-related applications.</p><p></p><p>[1] W. M. Lin, et al., Appl. Surf. Sci. 613 (2023) 156011. [2] S. Sharma, et al., Carbon, 132 (2018) 165. [3] M. Z Yusop, et al., ACS Nano 6 (2012) 9567. [4] T. Akiyama, et al., RSC Adv. 12 (2022) 21318. [5] S. Sharma, et al., Nanomaterials, 10 (2020) 1483. [6] Y. Yang, et al., Nano-Micro Lett. 13 (2020) 109.</p><p>This work was partially supported by JSPS Grant-in-Aid for Scientific Research (B) Grant No. 20H02618.</p>