Field Emission Properties Of One-dimensional SiC Nanocrystal/Amorphous Composite

In the thesis,we systematically investigated the synthesis and field emission properties of One-dimensional SiC Nanocrystal/Amorphous Composite (SiC nanofiber), including the comparison of field emission properties with carbon nanotubes and the influence of diameter variation on the absolute field amplification factor of SiC nanofibers. Besides, we also studied the room-temperature luminescent properties of SiC nanofiber.We used multi-walled carbon nanotubes as templates to synthesize vertically aligned diameter controllable SiC nanofiber arrays. The SiC nanofibers have unique"tree like"morphology. XPS and HR-TEM characterization showed that SiC nanofiber is a composite of amorphous a-Si1-xCx matrix with SiC nanocrystallites embedded in it. We use a two direction diffusion mechanism to explain the formation of the"tree like"morphology.The SiC nanofibers have show novel electron field-emission behavior with a turn-on field as low as 1.1 V/μm. Electrons are emited from the tube tips at low applied fields, while at high fields, they are also emited from the"branches"located on the side-wall (tip-side emission model). Comparing with carbon nanotubes, the SiC nanofibers have better filed emission properties, not only because the"branches"at the side-wall can act as emitters, but also a result of intrinsic reason that SiC has lower work function than graphite (carbon nanotubes). We use a universal relationship between the electrodes gap d and the field amplification factorβto calculate the absolute field amplification factorβ0 of SiC nanofibers with different diameters, the result show the tendency that the absolute field amplification factorβ0 increases with the nanofiber diameters diminishing.At room-temperatures, we observed strong photoluminescence (PL) from SiC nanofibers with a sharp peak locate at 675 nm, the full width at half maximum was 9.1nm, which shows good homochromatic properties. Using the quantum confinement model, we calculated the band gap of 3.8nm size SiC nanocrystallites is 2.7eV (457nm), which was in good agreement with our PLE result (449nm). Combined with the theoretical calculation, we used a"three level"model to explain the mechanism of the PL from SiC nanofibers: carriers excited from the core of nanocrystallites relax to interface state, and then recombine there. We also perform H2 plasma treatment on our SiC nanofiber samples. After the treatment, the PL peak blue shift to 520nm, while PLE peak retain the same location. This result confirms our conclusion on the PL mechanism.