ORIGINAL PAPER Structural and Mechanical Analysis of APCVD Deposited Diamond-Like Carbon Thin Films Ranjan Kumar Ghadai 1 & Soham Das 1 & Kanak Kalita 2 & Bibhu Prasad Swain 3 & João Paulo Davim 4 Received: 17 July 2020 /Accepted: 5 October 2020 # Springer Nature B.V. 2020 Abstract In this study, diamond-like Carbon (DLC) thin film coatings are deposited by atmospheric pressure chemical vapour deposition (APCVD) process by using C 2 H 2 and H 2 as precursor gases on SiO 2 substrates. The morphological, structural, mechanical and composition of the DLC thin film coatings are studied by using field emission scanning electron microscopy (FESEM), Raman spectroscopy, nanoindentation, Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Irrespective of the varying H 2 flow rate, smooth surfaces of the thin film coatings are observed in the FESEM images. The Young’s modulus (E) and hardness (H) of the DLC coating increases with an increase in H 2 flow rate and the maximum E and H are observed as 193.97 GPa and 22.46 GPa respectively. Due to the SiO 2 buffer layer, the residual stress (σ) of the film significantly decreased to a minimum of 1.05 GPa which is much less as compared to the DLC film deposited over the Si substrate. The percentage of sp3 can be calculated from the XPS and it is 58.68% and 70% for the flow rate of H 2 of 0 and 80 sccm respectively. The effect of H 2 flow rate on the morphology, structural, mechanical and composition of the DLC thin film coatings are analyzed and discussed thoroughly along with mechanics behind it. Keywords DLC . APCVD . FESEM . XRD . Raman spectra . XPS 1 Introduction Diamond-like Carbon (DLC) thin film coatings find wide ap- plication in several fields like aerospace, biomedical, electron- ics etc. For example, these coatings are prominently used in engine parts due to their exceptional low coefficient of friction (μ), excellent thermal stability, good wear-resistance and su- perb chemical inertness [1]. Due to such excellent properties, these films are often used as protective films for metals, ceramics, semiconductors and dielectrics [2]. DLC coatings deposited over SiO 2 substrate are quite promising as a chem- ical sensing layer of different nano-devices [3]. Bootkul et al. investigated the arc plasma deposition technique for deposit- ing DLC thin film over SiO 2 /Si substrate with different bias voltage and implemented the DLC coating for selective chem- ical sensors [4]. Smietana et al. deposited DLC thin films over oxidized silicon wafers to investigate the resistivity and vari- ous crystallographic orientations of the films. It was observed from their study that the oxidized silicon substrate enhances the optical properties of the coatings [5]. The properties of CVD deposited DLCs can be altered by varying the deposition process parameters like deposition temperature, deposition techniques, precursor gases, flow rates etc. [6]. Hydrogen (H 2 ) is a light gas with a high diffu- sion coefficient, which can easily diffuse through materials and it acts as a vital factor to enhance the coating resistance at different environments [7]. The key observation of H 2 di- lutions for different materials in the CVD process are as fol- lows: — Fang et al. observed that the H 2 percentage within a- C:H films decreased from 55 to 11% by increasing the H 2 . But, it was observed that the density of sp 3 carbon atoms and surface roughness (R a ) increased with an increase in H 2 [8]. * Kanak Kalita kanakkalita02@gmail.com 1 Department of Mechanical Engineering, Sikkim Manipal Institute of Technology, Sikkim Manipal University, Gangtok, Sikkim 737136, India 2 Department of Mechanical Engineering, Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Avadi, Chennai 600062, India 3 Department of Physics, National Institute of Technology, Manipur 795004, India 4 Department of Mechanical Engineering, University of Aveiro, 3810 193 Campus Santiago, Portugal Silicon https://doi.org/10.1007/s12633-020-00760-3