# Diamond-Like Carbon (DLC) Coatings: Classification, Properties, and Applications
## 2 Classification of DLC Coatings
### Stage Diagram  
1. The types of DLC on the ternary graph are shown in Figure 2, which also shows the division of the targets in the combination; i.e., C sp\({}^{3}\), C sp\({}^{2}\), or H [1], according to [PERSON]'s recommended graph [25]. The outline of the stage consists of three main areas: (1) without H a-C along with the left pivot, (ii) sp\({}^{2}\)a-C is commonly lustrous C or a-C produced by dissipation, and (iii) cutting-edge variations of flattering, including uneven magnetron flattering, can make DLCs with an enormous sp\({}^{3}\)substance. At considerably maximum sp\({}^{3}\) content, there is an explicit sort of a-C assigned as tetrahedral shapeless C. This is produced using plasma particles or radiation with high particle splitting and almost no characteristic particle energy [26; 27; 28; 29].  
The second position of the stage outline is in the lower right corner of the figure, where the H content is so high that the material cannot form a fully connected network, and can only form gas molecules [25]. In the center, the area in the material is a-C: H, which is usually produced by the deposition of plasma-enhanced chemical vapors (PECVD) of hydrogen atoms and C, or by the susceptible interference of graphite in air, or from the precursors of hydro C gases [30; 31; 32; 33; 34; 35]. A common PECVD or staggering cycle produces a-C: H, which is located in the area referred to as a-C: H. It can go from the material by including 20 to 25% of H content up to exceptionally high, with H substance of \(\sim\)60% of the total number of atoms. With the improvement of PECVD, it is conceivable to produce high-density plasma. These methods produce thicker a-C: Hs, which we call tetrahedral, hydrogenated invisible C, or ta-C: H [36; 37]. High-density plasma is achieved by working at a lower pressure than typical PECVD and using a magnetic field to generate longer electron path lengths, thus promoting high plasma ionization.  
In addition, since the last decade, researchers have described and revealed the development of high-level accuracy of metal-free C electrocatalysts for oxygen reduction reac  
Figure 2: Ternary phase diagram of the C, H system [1].  
tion (ORR), and this is one of the promising methods for the exploitation and use of renewable and clean energy; however, there still are major challenges to resolve. Meanwhile, the facile synthesis approach is arranged in such a way for three-dimensional (3D) N-doped C with a selected sp\({}^{3}\)/sp\({}^{2}\) interface, which is derived from ionic liquids through shift transformation [38]. However, density functional theory reveals improved performance of ORR, and it can be ascribed to the existence of N dopants at the sp\({}^{3}\)/sp\({}^{2}\)C interface [39; 40; 41; 42; 43; 44; 45].  
Another investigation of DLC coatings was conducted on stainless steel (SS) employing a plasma-based particle-deposition methodology along with two different parameters [46]. Herein, specimens were characterized by several techniques, such as exploitation high-resolution elastic recoil analysis, micro scale X-ray negatron spectrometry, and nano-indentation testing to work out the chemical element content, sp\({}^{2}\)/sp\({}^{3}\) magnitude relation, and mechanical properties of the coating [47; 48].