# Laser Synthesized Graphene and Its Applications
## 2 Laser Synthesis of Graphene
The authors of this study have investigated an even wider range of both polymers and natural materials and have concluded that virtually any carbon source can be either converted to graphene or firstly transformed into amorphous carbon and then converted to graphene [46]. By multiple laser passes, they found that polymers with high melting temperature or that are cross-linked were directly converted into graphene, whilst vinyl polymers and other natural materials were first converted to amorphous carbon and then to graphene. Moreover, the initial conversion to amorphous carbon could be obtained by any method, not just by laser irradiation [46]. The same multi-pass approach was later proposed by the same group to obtain LIG from an acrylate-based positive photoresist [47]. A two-step approach was also proposed by [PERSON] et al. [48] starting from silk fabric, as they first heated the material to 350 \({}^{\circ}\)C and then exposed the same to a laser scribing process to obtain LIG, as witnessed by Raman spectroscopy. Because lignin is a common industrial byproduct, [PERSON] et al. demonstrated the direct conversion of such material to graphene using laser writing [49]. Molecular dynamics (MD) simulations have been carried out on the laser irradiation of PI, showing that at temperatures above 2400 K, pressures above 3 GPa are induced, allowing the formation of graphene clusters containing rings formed by five, six, or seven elements [50]. Such clusters, still according to MD simulations, have non-carbon atoms bonded at the edges, suggesting that these could allow the formation of intermediates that ultimately induce the formation of rings [50]. While we have discussed how a controlled atmosphere allows the formation of LIG which could not otherwise be formed, such an approach was also used to control or improve the properties of LRG and LIG. The first report of such an approach was published in 2010 by [PERSON] et al. [14], who used direct laser writing by a continuous laser at 663 nm in air to make patterns by oxidative burning of GO films, then irradiating in N\({}_{2}\) atmosphere to obtain LRG. Thus, in this case, while laser irradiation in air caused GO etching, in N\({}_{2}\) atmosphere it caused GO reduction [14]. [PERSON] et al. irradiated GO films with 355 nm and 532 nm continuous laser in air and N\({}_{2}\), and noted by Raman spectroscopy that irradiation in N\({}_{2}\) atmosphere yielded rGO with less disorder [51]. Further studies were expanded to other atmospheres such as Ar and argon/H\({}_{2}\) (95:5) using a 405 nm continuous laser source [52]. Here, it was found by Raman spectroscopy that while Ar atmosphere produces better rGO than N\({}_{2}\), the results obtained in Ar/H\({}_{2}\) are the most promising due to the presence of 5% H\({}_{2}\) that makes the atmosphere slightly reducing and thus more suitable for GO reduction (Figure 4) [52]. The Ar-based environments were subject to further investigation relative to the LS conditions. It was found that the slower the laser writing speed (1.2 mm/s), the worse the conditions for reducing GO, while the fastest speed (5.9 mm/s) was optimal for Ar/H\({}_{2}\) atmosphere and an intermediate one (2.7 mm/s) was optimal for Ar. It was also found that a second laser pass yields a further improvement in GO reduction [53]. [PERSON] et al. investigated the formation of LIG from PI in different atmospheres [54]. While from Raman spectroscopy they also observed a better graphene quality in Ar or H\({}_{2}\) atmosphere, they also studied the surface properties of the obtained GO by contact angle measurements. It was found that while the produced samples generally show superhydrophilicity, with contact angle close to zero, when irradiating in a chamber with Ar or H\({}_{2}\) the material becomes superhydrophobic, with contact angle close to 150\({}^{\circ}\) (Figure 5) [54].