## 5 Discussion
In 2004, [PERSON] et al. succeeded in extracting a thin piece of graphene by peeling off the surface of highly oriented anhydrous graphite with adhesive tape and then further peeling off the peeled surface. Since this report was published, the electrical, electronic, mechanical, and scientific properties of graphene have become clear [71]. In particular, the high electron mobility in graphene has been clarified, where electron mobility is a measure of the speed of electrons in a solid. The paper ranked fourth is a review article that focuses on the high electron mobility of graphene and discusses its electrical properties and applications [63]. A theoretical value of 2,000,000 cm\({}^{2}\)/Vs was predicted [64], and an experimental value of 200,000 cm\({}^{2}\)/Vs was obtained [72]. Considering that the electron mobility in silicon is 1000 cm\({}^{2}\)/Vs, the electron mobility of graphene is more than 100 times than in silicon. High electron mobility is an important factor to achieve high-speed transistors, for example. The paper ranked fourth was confirmed to have received 664 citations in 2014. The paper ranked fifth is a comprehensive discussion of the physical properties of graphene. Graphene has a high electron mobility, high thermal stability, and excellent strength. In addition, this paper comprehensively describes the graphene-based applications in field-effect transistors, memory, solar devices, and sensing platforms. This paper had 587 citations in 2014. The sixth article in Table 5 focuses on the methods of structural analysis of nanomaterials. Raman spectroscopy is one of the most effective methods for this purpose. In particular, the Raman spectra of carbon materials shows the G-band peaks derived from graphite structures and the D-band peaks derived from the defects. The ratios of these peaks can be used to evaluate the crystalline purity and defect concentration of nanocarbon materials. This is a review paper focusing on Raman spectroscopy in CNTs and graphene while summarizing related studies. The paper ranked seventh in Table 5 is a review that comprehensively summarizes the prior literature related to the reaction principle of methane catalytic decomposition, the shape of the resulting nanocarbon material, and the formation principle. It is possible to produce hydrogen and carbon using steam reforming methane and a catalyst in a high-temperature section. The hydrogen produced can be used as fuel for fuel cells and has been attracting attention mainly as a means of producing hydrogen. In contrast, because the generated carbon can also be used in direct carbon fuel cells, it is one of the methods attracting attention from the perspective of nanocarbon material production. CNTs are said to be toxic to humans because of their structural similarity to asbestos. Hence, toxicity reduction in other nanocarbons is a popular research topic for the use of nanocarbon materials. This paper [67], ranked eighth in Table 5, is an attempt to provide systematic knowledge in this field, called nanotoxicology. The authors also identified specific challenges for achieving low toxicity. The paper discusses techniques that lead to the biological and toxicological transformation of carbon nanomaterials through chemical changes. The paper by [PERSON] et al. [68] is an exhaustive summary of the history of graphene and its properties, means of production, and impacts on applications in various fields. This includes: electrical devices; optronics devices; scientific sensor nanocomposites; energy storage. As of 2014, there were 506 citations. The paper ranked tenth is entitled \"Carbonaceous nanomaterials for enhancement of TiO\({}_{2}\) photocatalysis\" [69]. Titanium oxide (TiO\({}_{2}\)) is generally used as a photocatalyst material. However, problems have been noted due to its efficiency and narrow response range. The properties can be changed considerably by combining TiO\({}_{2}\) with nanocarbon materials.