**1. Introduction**

Graphene is a 2D form of graphite which can be used in electronics and other branches of technique due to its interesting parameters [1–3]: high electron mobility—in literature, the published value was at 1.5 × 108 m2 /Vs, very low resistivity (1 × 10−4 Ωm), metallic and semiconductive character, low absorption of white light (2.3%), low noise, quantum Hall effect, and so on. These important parameters predestine graphene for substitution of silicon in future microelectronics. Application of graphene is expected for construction of field effect transistor (FET) transistors, transparent conductive electrodes, gas and biosensors, lithium batteries, memory structures, super capacitors, and other structures [2]. The so-called single-layer graphene (SLG) shows the widest application; so the preparation of few layer graphenes (FLG) can be usually simpler.

Graphene is grown by many technological processes. The method of mechanical exfoliation or cleavage was one of the first methods, used by Geim and Novoselov, for the preparation of the graphene films [4–6]. This method comes from mechanical splitting of thin pieces of

graphite from the oriented pyrolytic graphite. The main disadvantage of the method is that it produces only small pieces of graphene—graphene flakes.

Today, many methods are used for graphene growth. Graphene is very frequently prepared by a chemical vapor deposition (CVD) method [7–9]. Thin foils of Cu, Ni, or other metals are used as substrates. The method is scalable (graphene films with large dimension can be prepared), but the graphene film must be transferred onto a dielectric substrate for the next application (e.g., SiO2 /Si). Temperature or plasma CVD processes are used in practice.

The next method is a high-temperature decomposition of SiC, which is sometimes called as an epitaxial growth of graphene (EG) [10–12]. In the method silicone atoms sublimate from the surface of SiC substrate at high temperature—1100–1600°C in high vacuum and remaining carbon creates graphene. The method can be used for industrial growth of graphene due to full-wafer technology. Careful control of the sublimation process has recently led to the growth of very thin graphene film over the SiC surface, with only single graphene layer.

The vacuum sublimation of SiC usually produces graphene films with small crystallinity (30–200 nm) [13, 14] due to surface SiC roughening and creation of deep pits. The preparation of graphene by decomposition of SiC in an argon atmosphere of about 100 kPa gives better layers. This method gives SLG films with greater domain sizes. Graphene parameters can be also improved by increasing the growth temperature (up to 2000°C) since SiC decomposition occurs at 1500°C under argon atmosphere rather than at 1150°C in vacuum.

A special sort of method of graphene preparation is the so-called transfer-free method [15]. The method comes from a metal/C/SiO2 /Si structure. The synthesis of graphene is based on a metal-catalyzed crystallization of amorphous carbon (a-C) by thermal annealing. Polymer layer [16] and thin SiC layer [17] are used very frequently as the carbon source instead of a-C. Carbon atoms diffuse into a metal layer at elevated temperatures followed by their precipitation as graphene during the cool-down step.

The graphene growth on SiC substrates at relatively low temperature is very perspective [18]. The technique applies the Ni/SiC system as a basic structure. The method is very promising for the transfer of graphene layers from the SiC substrate to other substrates (mainly on dielectric one). By the annealing of the Ni/SiC system, carbon-rich products can be obtained at the Ni-SiC interface, and the graphene film is segregate on the top of the Ni layer.

This method has been developed by various groups of authors in many ways. The Ni(200 nm)/SiC structure was applied in the work [18]. Graphene was grown on the structure surface by annealing at 750°C (the speed of 25°C per second), with follow-up cooling with no specified velocity. The prepared graphene showed the FLG character. The results of the mentioned work are in discrepancy with the results of works [19, 20], where only thin Ni films (from single to tens nm) were applied. Heating speed was slightly lower (4°C per second), and cooling velocity was approximately 20°C per second. Prepared graphene had a character of FLG and SLG. Authors of work [21] elaborated with the Ni/SiC structure, where the thickness of nickel layer did not exceed the value of 100 nm. The annealing of the structure produced at 1100°C for 300 s (heating and cooling velocities were not specified; a rapid thermal process was used). After the annealing process, the created silicide layer was etched off, and a thin graphene film of FLG type remained on the silicon carbide substrate. Lastly, the modificated method described in the study [22] is also valuable. A 50 nm-thick amorphous silicon carbide layer was used here. The layer was deposited onto the SiO2 / Si substrate, and after that, the SiC layer was covered with 500 nm of Ni. Annealing was done by an Rapid Thermal Annealing (RTA) process at 1100°C for 30 s. The formed silicide was etched off, and the graphene film was detected on the SiO<sup>2</sup> surface. Co as a metal can be used too instead of Ni [23]. The segregation method can be applied in case of metal combination for reduction of carbon solubility and thus modification of the segregation process itself. Ni/Cu metallization was used in Ref. [24] for the preparation of graphene films in silicon carbide-based Micro Electro Mechanical Systems (MEMS) and Nano Electro Mechanical Systems (NEMS) devices.
