The microstructural evolution of ultrananocrystalline diamond films due to P ion implantation and annealing process-dosage effect

• P-ion implantation/annealing (PIA) processes markedly enhance the conductivity of UNCD films.
• Conduction mechanism is explained by the formation of interconnected graphitic filaments.
• A model for P-ions to diamond interaction was proposed to explain the PIA processes.

The effect of microstructural evolution on the electrical properties of UNCD films, which were P-ion implanted and annealed, was systematically investigated. The electrical resistivity of the UNCD films was markedly lowered when the UNCD films were implanted with P-ions of sufficient dosage (> 1 × 1014 ions/cm2) and followed by annealing at 800 °C for 30 min, but the electronic field emission (EFE) behavior was not enhanced. The incident P-ions mainly alter the granular structure of the region in UNCD films where the P-ions reside, the “interacting zone”, which is found at about 300 nm beneath the surface of the films. In this “interacting zone”, coalescence of diamond grains occurred and the nano-graphitic clusters were induced, forming interconnected graphitic filaments and resulting in the decrease in surface resistance. However, the UNCD-to-Si interfacial resistance remained at large value that hindered the efficiency for the electron transport crossing the interface of the UNCD films. These microstructural evolution processes account for very well the phenomenon that in spite of enhanced conductivity of the UNCD films along the film's surface due to P-ion implantation and annealing processes, the EFE properties for these UNCD films were not improved.