Ultrashort Pulsed Laser Induces Graphene on Woods and Leaves for Green Electronics

In recent years, we have witnessed a tremendous demand for electronic devices that leads to a massive amount of electronic waste and rapid exhaustion of non-renewable resources. Accordingly, green electronics has received much attention to minimize the negative impact of electronic waste and pave the way toward the sustainable development of our society. Functional nanomaterials are essential components in green electronics in which graphene is highly attractive owing to outstanding electrical, mechanical, and thermal properties. Graphene has been used in various advanced applications ranging from academia to industry. Until now, graphene can be synthesized via liquid-phase exfoliation, mechanical exfoliation, chemical vapor deposition, and reduction of graphene oxide. Nevertheless, there is a lack of an efficient, low-cost, and eco-friendly synthesis method to realize the full potential of graphene.<br/> <br/>Herein, we have developed a facile fabrication of pre-designed graphene electrodes on arbitrary woods and leaves in ambient conditions utilizing ultraviolet femtosecond laser pulses. Compared with conventional lasers, the femtosecond laser shows distinct advantages due to ultrashort pulse durations, extremely high peak intensities, and nonlinear interactions with carbon materials. The mechanism of LIG formation was extensively studied in which the heat accumulation of repetitive laser pulses increases the base temperature at the laser-irradiated area to carbonize the precursors, and the intense ultrashort laser pulses induce sufficiently high temperature to transform amorphous carbon into LIG. The formation of LIG was confirmed and characterized using electrical measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction (XRD). The resultant LIG electrodes on woods and leaves exhibited sheet resistances of 10 and 23.3 Ω/sq, respectively. Especially, the sheet resistance of LIG electrodes could be easily controlled via the laser writing parameters. SEM images revealed three-dimensional porous structures formed during the laser-induced carbonization and graphitization processes. These porous structures possess a high active surface area which enhances ion diffusion and is beneficial for sensing and energy storage applications. High-resolution TEM images showed graphene flakes with a typical lattice spacing of 0.355 nm. In order to demonstrate the potential of LIG on woods and leaves, we fabricated green graphene thermistors, micro-supercapacitors, and pseudo-capacitors. The as-produced devices exhibit comparable or better performance than other state-of-the-art graphene-based devices. Thus, the use of low-cost, abundant, renewable, and biodegradable green materials not only allows the mass production and commercialization of green electronics but also develops a sustainable future.