# Epitaxial Graphene on 4H-SiC (0001) as a Versatile Platform for Materials Growth: Mini-Review
## 1 Introduction  
The achievement of large area homogeneous monolayer graphene epitaxially grown on the Si face of SiC (0001) [1] has allowed the rapid development of the new class of 2D materials in line with exfoliated graphene and boosted some exciting applications in quantum metrology [2; 3; 4; 5], and environmental sensing [6; 7], which might not be possible using free-standing graphene. It has been demonstrated that epitaxial graphene on SiC, because of its unique structure, distinct from that of other graphene family representatives [8; 9; 10], is a promising material to design the next-generation quantum resistance standard of high precision, which make it possible to calibrate mass. As a breakthrough outcome, recently, the electronic kilogram has been introduced. During the last decade, large efforts have been made to develop epitaxial graphene-based sensors for the detection of NO\({}_{2}\)[11; 12; 13], polar prolic and polar aprotic vapors [14], solvents [15; 16], Hall effect [17; 18], illicit drugs (amphetamine or cocaine) [19], toxic heavy metals (cadmium, lead, and mercury) [20; 21; 22; 23; 24; 25], ultraviolet (UV) light [26], and terahertz waves [27], etc. Notably, the above-listed examples of sensing applications concern only unmodified pristine epitaxial graphene. At the same time, there is a great deal of interest in epitaxial graphene sensitivity improvement by chemical functionalization [28; 29], defect engineering [30; 31], and metal oxide nanoparticle decoration [32; 33; 34].  
Applicability and functionality of epitaxial graphene are attributable, in the first instance, to its transfer-free growth on a native substrate through the Si sublimation process during high-temperature annealing of the SiC substrate in an argon atmosphere. Thepresence of contact between the substrate and graphene is mainly responsible for the observed \(n\)-doping and compression of the topmost graphene layer [35; 36; 37], which is, however, beneficial to promotion of higher reactivity of epitaxial graphene compared to exfoliated counterpart. Indeed, the compressive strain can significantly influence the adsorption capability of graphene with respect to environmental species and individual atoms/molecules [38; 39], while electron doping is regarded as a viable means to increase the reactivity toward oxygen [40]. This creates good prerequisites not only for boosting innovative sensing and catalytic applications but also for the exploitation of epitaxial graphene as a substrate for the growth of other functional materials, such as extremely thin metal layers and nanoparticles, semiconducting films, and insulators with good adhesion. The latter is of relevance in the light of the need to expand the functionality of the epitaxial graphene towards nano-plasmonic sensors for environmental detection/monitoring and field-effect transistor (FET)-based biosensors.  
Although the fundamental properties of epitaxial graphene and physics behind epitaxial-graphene-based devices are well documented in the scientific literature, further progress in implementing epitaxial graphene into realistic applications requires both rethinking of the existing knowledge in this field and systematization of new experimental and theoretical results. The current paper is intended to provide a focused overview of the recent progress in the investigation of the deposition of selected metals and insulators on epitaxial graphene supported by 4H-SiC. Direct current (dc) magnetron sputtering, electrochemical deposition and atomic layer deposition (ALD) methods for thin layer synthesis are presented and discussed. We also highlight the nature of the interrelationships between epitaxial graphene quality and the morphology of deposits. In this mini-review paper, we mainly focus on the generalization of recent studies performed at Linkoping University (Linkoping, Sweden) and CNR-IMM (Catania, Italy).