  Diamond-like carbon thin films have emerged as durable, chemically stable
optical coatings for many optical and optoelectronics applications due to their
hardness, chemical inertness, and optical transparency. This paper presents a
novel high-energy electron cyclotron resonance ion beam sputter deposition
technique to fabricate pure diamond-like carbon coatings at room temperature.
The chemical composition of the deposited coatings including ratios of sp2/sp3
bonding in the thin films were determined by X-ray photoelectron spectroscopy.
Results indicate that the sp3 percentage ranges from 45% - 85%. The
transmission and reflectance spectra of the coatings were measured from UV to
IR ({\lambda}= 185 to 2500 nm) by utilizing a spectrophotometer. The measured
spectra were analysed by the Tauc method to determine the optical band gap and
Urbach energy and an optical fitting software, which utilizes the model
modified by OJL, to extract the refractive index and extinction coefficient. By
varying the ion energy, the optical properties were found to be n = 2.30 -
2.51, band gap energy = 0.4 - 0.68 eV, and the Urbach energy = 0.33 - 0.49 eV.
This study provides a flexible method for tuning the structural, optical, and
electronic properties of diamond-like carbon coatings by controlling the ion
energy during deposition.
