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We observe that an Au interlayer markedly enhances the electrical field emission (EFE) properties of ultrananocrystalline diamond (UNCD) films on Si substrates. The EFE properties of UNCD/Au/Si films can be turned on at a lower field and attain a higher current density than in UNCD films grown on Si substrates without an Au interlayer. Transmission electron microscopy reveals that the Au interlayer induces the formation of SiC clusters, preventing the formation of a resistive amorphous carbon layer that nucleates the diamond clusters. This improves the diamond-to-substrate interfacial conductivity. Moreover, there is an abundant nano-graphite phase, which is presumably induced by the coalescence of nano-sized diamond clusters. The percolation of the nano-graphite clusters helps transport electrons, improving the conductivity of the UNCD films. We believe that the simultaneous increase in the conductivity of the UNCD-to-Si interface and the bulk of the UNCD films is the main factor enhancing electrical conductivity and EFE properties of the films. [ABSTRACT FROM AUTHOR]

Enhanced electron field emission (EFE) properties for ultrananocrystalline diamond (UNCD) films grown on silicon substrate were achieved, especially due to the high dose N ion implantation. Secondary ion mass spectroscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy measurements indicated that the N ion implantation first expelled H-, induced the formation of disordered carbon (or defect complex), and then induced the amorphous phase, as the ion implantation dose increased. The postimplantation annealing process healed the atomic defects, but converted the disordered carbon to a stable defect complex, and amorphous carbon into a more stable graphitic phase. The EFE characteristics of the high dose (>1015 ions/cm2) ion-implanted UNCD were maintained at an enhanced level, whereas those of the low dose (<1014 ions/cm2) ion-implanted ones were reverted to the original values after the annealing process. Ion implantation over a critical dose (1×1015 ions/cm2) was required to improve the EFE properties of UNCD films. [ABSTRACT FROM AUTHOR]

Effects of pretreatment on the nuclei formation of ultrananocrystalline diamond (UNCD) on Si substrates were studied. Either precoating a thin layer of titanium (∼400 nm) or ultrasonication pretreatment using diamond and titanium mixed powder (D&T process) enhances the nucleation process on Si substrates markedly, and the UNCD nuclei formed and fully covered the Si substrate, when deposition was processed using the microwave-plasma-enhanced chemical-vapor deposition process for 10 min. In contrast, during the same period, ultrasonication pretreatment using diamond powders (D process) can only form large UNCD clusters, which were scarcely distributed on Si substrates. The analyses using x-ray diffractometer, secondary ion mass spectroscopy, and electron spectroscopy for chemical analysis reveal that the titanium layer reacted with carbon species in the plasma, forming crystalline TiC phase, which facilitates the subsequent formation of UNCD nuclei. The beneficial effect of Ti layer on enhancing the nucleation of UNCD is presumably owing to high solubility and high diffusivity of carbon species in Ti materials, as compared with those of Si materials. [ABSTRACT FROM AUTHOR]