**3. Graphene and its derivatives**

Graphene is a stable 2D material based on carbon (C). It has been very successful, since it is composed of van der Waals type layers which are one or few atoms thick [1]. It has attracted designers due to its exceptional electronic properties. In addition, graphene is one million times thinner than paper, transparent, and the strongest material in the world. Gapless graphene strongly interacts with light from terahertz to ultraviolet (mainly, photodetectors) range [3]. Graphene has a very high carrier mobility (15,000 cm2 /Vs for graphene on SiO2 substrate and 200,000 cm2 /Vs for suspended graphene) and low losses through the Joule effect. Unfortu‐ nately, graphene has zero band gap, which disqualifies it due to its low on/off ratio required by FETs for applications in digital circuits.

For example, graphene has been chemically modified into different versions such as graphane [9], graphone [10], graphyne [10], graphdiyne [10], fluorographene [11], or graphXene [12]. Graphyne is better than graphene in directional electronic properties and charge carriers. Graphone (partially hydrogenated) and graphane (100% hydrogenation of graphene with stoichiometry CH) have applications in nanoelectronics and spintronics due to the presence of band gap and magnetic properties [1]. Graphone with hydrogen coverage of 8% reaches a band gap of ∼1.0 eV due to the rehybridization from sp2 to sp3 , and other authors have reported a band gap of 1.25 eV for different coverage [13]. Therefore, the size of the band gap depends exclusively on the H/C ratio, where band gaps of up to 1 eV are obtainable. Graphane achieves a band gap of 3.5 eV (insulating behaviour), although theoretically it achieves a value of 4.5 eV [13–14]. The presence of configuration changes from sp2 to sp3 configuration, should lead to a band gap of 3.12 eV. Unfortunately, graphane has an optical band gap different from the electronic band gap, which is not expected for direct band gap materials. FETs based on graphane and/or graphone present large *Ion* and *Ion*/*Ioff* ratios [2], reduced band‐to‐band tunnelling, without disadvantages such as lithography and patterning requirements for conventional circuit integration [9]. Graphyne (allotrope of graphene with one atom thick planar sheet of sp and sp2 bonded carbon atoms arranged in a crystal lattice) and graphdiyne (allotrope of graphene containing two acetylenic linkages in each unit cell rather the one linkage as in graphyne), thanks to their crystalline structures, present tunable band gap giving place to semiconducting materials [10]. The band gap is increased with the reduction in the ribbon width and the number of sheets involved. Graphyne ribbons have band gaps in the semiconducting range from 0.59 to 1.25 eV. A tensile strain of 0.15 increases the band gap in 1 eV, while a compressive strain of 0.1 reduces the band gap in 0.3 eV. For strain‐free graphdiyne, its band gap is 0.47 eV, while with strain it varies from 0.28 to 0.71 eV. Graphdiyne with low doping levels of boron nitride (BN) increases its band gap by 1 eV, and the trend is linear with the increasing dopant concentration [15]. When BN replaces all carbon atoms, a new material is formed, which is called BNdiyne with band gap of 4.39 eV (achieving an insulating behav‐ iour) [10]. Fluorographene (FG), which results due to the exposure of graphene to atomic F, has an excellent behaviour as an insulator and possesses a high thermal and chemical stability [11]. It presents an optical band gap of 3.0 eV and an electrical band gap of ∼3.5 eV (electrical insulator). Graphene can be made to interact with Group IA and Group VIIA elements to form materials called graphXenes [12]. These materials present a range of band gap between 0 and 6.4 eV. Therefore, metallic, semiconducting, and insulating behaviours are presented, and it is obtained through a mixture of sp2 /sp3 systems. Combinations, such as C2HCl0.5F0.5 and C2HCl, show semiconducting behaviour, while combinations C2HF and C2F2 show insulating behav‐ iour [12].
