# Diamond-Like Carbon (DLC) Coatings: Classification, Properties, and Applications
### Historical Background of DLC  
Indistinct DLC coatings reveal exceptionally smooth surfaces, resistance to wear, and low-friction behavior. Nowadays, DLC films are utilized globally in a wide range to improve apparatuses and segment quality, particularly for automobile applications [5; 6; 7; 8; 9], with greater than 100 million covered parts for every year and a market volume of approximately EUR 100 million.  
In 1953, [PERSON] introduced C-films using acetylene gas instead of tungsten-cobalt alloy [10]. The significant outcome of the experiment was to achieve a thin sheet of tungsten carbide (WC) produced by glow discharge in the presence of hydrocarbons at low temperatures. In continuation of the same work, it was observed that black hard formless layers were set up at the cathode pole as long as the flow rate of current was low. However, thick (\(\upmu\)m) hard films were recognized as diamonds after performing X-ray diffraction (XRD) [11]. In 1951, [PERSON] and [PERSON] [12] investigated direct current (DC) through the glow-discharge process in a benzene (C\(\upmu\)H) atmosphere. However, they analyzed only the film grown on the discharged anode, and the films had a yellow color and comparatively low-density. Hereafter, [PERSON] [13; 14] investigated that more films with high density were deposited on the cathode compared to the anode, which showed that positive particles had larger cross-sections than negatively charged particles. [PERSON] [13] found that the films' growth rate significantly depended on the substrate geometries, while those protecting the substrate were charged under ion-bombardment then stopped the film growth. The term DLC was initially introduced by [PERSON] and [PERSON] [15] in 1971, the layers were formed at ambient temperature, making use of ion beam deposition technique, which involves C, argon (Ar) particles, and a graphite electrode. After examination, it was determined that films showed optical transparency, resistance to wear, and electrical and chemical flow. The film structure was described as partly crystalline, having lattice parameters the same as diamond. In 1971, [PERSON] et al. reported improvement of cutting performance of paper-cutting blades by employing DLC coatings. When the blades were tested for wear, they found a decrease in frictional coefficient [16]. [PERSON] et al. [17] investigated DLC coating performance like [PERSON] and [PERSON] [15]. [PERSON] and [PERSON] [18] organized hard and protecting coatings of up to 4 \(\upmu\)m thickness on various metal surfaces utilizing the ion beam deposition method of [PERSON], but used a gas combination of ethylene (C\(\upmu\)H) along with 5% Ar. The protective layer required to holds a positive charge attaining maximum thickness should be normal. [PERSON] [19] clarified this, expecting that secondary electrons produced at the boundary of the domed aperture compensate for the positive charge. Later, the result was confirmed for a DC-based particle plating a-C: H measure on protecting glass substrates [20]. Throughout the tenure, new techniques like responsive filtering and cathodic circular segment measures as changes of diamond-like indistinct C-based films were made. Now, a maximum utilization, particularly in the automobile, has been set up, and, for example, for diesel infusion system, DLC coatings are essential.