Liquid phase regrowth of 〈110〉 nanodiamond film by UV laser annealing of PTFE to generate dense CVD microdiamond film

Abstract

Herein we report the conversion of polytetrafluoroethylene (PTFE) into 〈110〉 nanodiamonds via a melting route using pulsed laser annealing (PLA). The converted nanodiamond (ND) film is used as a seed layer to grow dense microdiamond coating synthesized by chemical vapor deposition. We utilize an ArF excimer laser with a photon energy of 6.4 eV to decompose PTFE (bandgap: 6.0 eV). Initial laser pulses result in photochemical decomposition of PTFE, and PTFE is converted to an amorphous carbon film. This amorphous carbon film, when subjected to additional laser pulses melts, and when this melt is quenched from an undercooled state at rates exceeding 109 K/s, it undergoes first-order phase transformation into the ND film. Notably, the obtained NDs are phase pure, exhibiting full width at half maxima (FWHM) of 1.23 cm−1 and demonstrating 〈110〉 out of plane orientation characterized by Raman spectroscopy and transmission electron microscopy, respectively. The average ND size is ~28.5 nm (range: 5-30 nm) determined by scanning electron microscopy and X-ray diffraction. The COMSOL simulations substantiate the use of nanosecond laser pulses with an energy density in the range of 0.6–0.8 J/cm2 to fully convert ~ 50% crystalline PTFE into ND film. The CVD microdiamonds grew densely on the ND seed layer as compared to reduced graphene oxide confirmed by SEM and Raman analysis. This innovative method of ND fabrication by UV irradiation of PTFE opens up opportunities for generating selective coatings of advanced polymer-diamond composites and doped nanodiamonds for quantum computing and biomedical applications.