Plasmon-enhanced optical absorption with graded bandgap in diamond-like carbon (DLC) films

Diamond-like carbon (DLC) films with tunable optical bandgap (Eg) were successfully deposited on glass and n-Si (100) substrates by radio frequency (RF)-sputtering technique in different argon (Ar) and acetylene (C2H2) plasmas. The bandgap of the films can be tuned from 1.41 to 1.28 eV, which correlates with the sp2 content, which increases from 56.3 to 63.7 %, respectively. The different ratios of sp2/sp3 lead to different bandgaps of the DLC films. Plasmonic nanoparticles of silver (Ag) were also embedded in the DLC matrix by reactive magnetron sputtering to study the enhancement of light absorption in DLC films. The absorption coefficient significantly increased when the DLC films were incorporated with 10 at.% of silver nanoparticles. Raman and X-ray photoelectron spectroscopy (XPS) studies were utilized to determine the bonding nature and sp2/sp3 ratios of DLC–Ag films.