High-Energy Excimer Annealing of Nanodiamond Layers

Here, we aimed to achieve exposure of a nanodiamond layer to a high-energy excimer laser. The treatment was realized in high-vacuum conditions. The carbon, in the form of nanodiamonds (NDs), underwent high-temperature changes. The induced changes in carbon form were studied with Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction (XRD) and we searched for the Q-carbon phase in the prepared structure. Surface morphology changes were detected by atomic force microscopy (AFM) and scanning electron microscopy (SEM). NDs were exposed to different laser energy values, from 1600 to 3000 mJ cm^-2. Using the AFM and SEM methods, we found that the NDs layer was disrupted with increasing beam energy, to create a fibrous structure resembling Q-carbon fibers. Layered micro-/nano-spheres, representing the role of diamonds, were created at the junction of the fibers. A Q-carbon structure (fibers) consisting of 80% sp³ hybridization was prepared by melting and quenching the nanodiamond film. Higher energy values of the laser beam (2000 and 3000 mJ cm^-2), in addition to oxygen bonds, also induced carbide bonds characteristic of Q-carbon. Raman spectroscopy confirmed the presence of a diamond (sp³) phase and a low-intensity graphitic (G) peak occurring in the Q-carbon form samples.