| Doping by ion implantation is an effective method for improving conductive properties of diamond films, which is expected to enhance the overall performance of cold cathode materials of field emission display. Therefore, 80 ke V Ag ions was implanted into polished free-standing diamond( FSD_P) films and intrinsic FSD films at a fluence of 5.0 × 1016 ions/cm2 in this thesis, subsequently annealed at different atmospheres and temperatures to have a better electron field emission(EFE) properties of diamond films. The microstructures were characterized by field emission scanning microscopy, atomic force microscopy, grazing incidence X-ray diffraction, laser Raman spectroscopy and X-ray photoelectron spectroscopy, while the electric properties and EFE properties were investigated through Hall Effect and high vacuum field emission test. The effects of Ag ion implantation, annealing atmospheres and annealing temperatures were systematically studied. The main contents and results are as follows:(1) FSD_P films implanted with Ag ions were annealed at 500 ℃ under Ar atmosphere. The impacts of Ag implantation and temperature treatment on the microstructures and EFE properties of FSD_P films were scientifically studied. The results show that Ag nanoparticles(NPs) and graphite phases are introduced by Ag ion implantation near the surface of FSD_P films, providing a conductive path for the transport of electrons, which enhances the electric properties of the implanted FSD_P films with a high carrier mobility(16.24 cm2V-1s-1) and low turn on field(E0 = 18 V/μm). After 500 ℃ annealing, the implanted damages have been restored, and Ag NPs have uniformly grown, resulting in a current density of 101.15 μA/cm2 at the applied field of 25.79 V/μm.(2) FSD films implanted with Ag ions were respectively annealed at 500 ℃ under four atmospheres, namely Ar, N2, H2 and O2. The effects of annealing atmosphere on the microstructures and EFE properties of the implanted FSD films were systematically investigated. It turns out that some sp3 carbon bonds of FSD films are broken during ion implantation, becoming sp2 carbon bonds and other dangling bonds. The implanted FSD films are etched under Ar annealing atmosphere, resulting in a disappearance of graphite phases. And Ag NPs grow bigger and partially evaporate from the surface of FSD fims. No obvious change occurs about its conductivity. After annealing in N2 and H2 atmospheres, the Ag NPs are uniformly dispersed upon the near surface of FSD films, and amorphous carbons become to graphite phases. Especially, the formation of nanographite phases has been attained under N2 atmospheres, which significantly decreases its turn on field(E0 = 4.08 V/μm) with a current density of 78.34 μA/cm2 at the applied field of 7.28 V/μm. However, after annealing in O2 atmosphere, there are a distinct agglomeration and growth of Ag NPs, and Ag O has appeared. Because of the evident oxidation, there is a selective evaporation and decomposition of sp2 carbon bonds. Therefore, it is not favorable for the improvement of EFE properties of FSD films under O2 annealing atmosphere.(3) FSD films implanted with Ag ions were respectively annealed at 300 ~ 700 ℃ under four atmospheres, namely Ar, N2, H2 and O2. Raman measurement was conducted to analyze the thermal evolution of phase components of Ag implanted FSD films under different annealing atmospheres. Results indicate that, Ar and O2 annealing atmosphere is not conducive to the retention of graphite phase in FSD films. The graphite phases have disappeared respectively at 500 ℃ and 400 ℃ and above, leaving only little amorphous carbon in the FSD films. After annealing in N2 and H2 atmospheres, amorphous carbon converts to stable graphite phase as the temperature increased, and obtained nanographite phases at 500 ℃ and 600 ℃, respectively. The difference is that H2 atmosphere can remain stable nano-graphite in FSD films annealing at higher temperatures, while N2 atmosphere has a reverse phase transition trend to sp3 carbon phase. Consequently, the significance is obviously there for the improvement of microstructure and EFE properties of FSD films by regulating the annealing atmosphere and temperature. |
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