## 1 Introduction  
Diamond-like carbon (DLC) is a general term for amorphous carbon consisting of sp\({}^{2}\) and sp\({}^{3}\) carbon-carbon hybrid bonds [1]. According to whether hydrogen-containing diamond-like carbon films are present, they can be divided into two categories: hydrogen-containing diamond-like carbon films (a-C: H) and hydrogen-free diamond-like carbon films (a-C). In addition to carbon atoms with sp\({}^{3}\) and sp\({}^{2}\) bonds, hydrogen-containing diamond-like films also contain a certain number of hydrogen elements. Hydrogen-free diamond-like carbon films mainly contain carbon atoms with sp\({}^{3}\) and sp\({}^{2}\) bonds and do not contain hydrogen elements. The unique microstructure of DLC endows it with excellent optical, tribological, mechanical, and biocompatibility properties [2; 3; 4]. These characteristics provide DLC with broad prospects for applications in fields such as biomedicine, optics, and tribology. Importantly, DLC distinguishes itself from other carbonaceous materials, such as carbon nanotubes and graphene, by obviating the necessity for intricate surface treatments or reliance on metal catalysts during thin film deposition, thereby rendering the process eminently practicable at ambient room temperature. The methods for preparing diamond-like carbon films can be divided into two categories: physical vapor deposition (PVD) and chemical vapor deposition (CVD). PVD methods mainly include DC magnetron sputtering deposition [5], high-power pulse magnetron sputtering [6], vacuum evaporation method [7], etc. These methods mainly evaporate or sputter carbon source materials into carbon atoms or ions through physical means and then deposit them on a substrate to form diamond-like carbon films. For example, the vacuum evaporation method heats the carbon source material to an evaporative state, and carbon atoms are deposited on the substrate to form a thin film during the evaporation process. The sputtering rule involves using high-energy ions to bombard carbon source materials, causing them to eject carbon atoms or ions, and then deposit them on the substrate. CVD is currently the most commonly used method for preparing diamond-like carbon films. This method mainly decomposes carbon source gases (such as methane, acetylene, etc.) into carbon atoms through chemical reactions and deposits them on a substrate to form a thin film. According to different reaction conditions, CVD methods can be divided into various types, such as hot-filament chemical vapor deposition (HFCVD) [8], plasma-enhanced chemical vapor deposition (PECVD) [9], and so on. The advantages of chemical vapor deposition methods in preparing DLC thin films can be summarized as follows: the active particles in the plasma (such as ions, electrons, and free radicals) can significantly increase the reaction rate, thereby accelerating the deposition rate of the thin film; DLC thin films prepared by RF-PECVD have advantages such as a smooth surface, high hardness, and structure similar to that of diamonds. At the same time, it has a high sp\({}^{3}\) bond content, which helps to improve the mechanical properties and stability of the films; by adjusting process parameters such as RF power, gas flow rate, and reaction chamber pressure, the thickness, structure, and performance of the thin films can be easily controlled to meet different application requirements. Various metal elements were doped with DLC films in the reported literature to adjust the structure and properties of DLC films. [PERSON] et al. prepared Ni DLC and controlled the Ni content and nanoparticle size by adjusting the power. They analyzed the effect of elemental Ni on the structure and optical properties of diamond-like carbon films and found that the optical bandgap (Eg) decreased from 4.58 eV to 3.66 eV with increasing applied power [10]. [PERSON] et al. controlled Cu content and nanoparticle size by changing the DC current range and analyzed the effects of Cu content changes on the structure, hardness, and optical properties of a film.