BN-carbon and SiO2-carbon nanocomposites as low-field electron emitters

Diamond/sp2-bonded carbon nanocomposites are one of the materials showing very low-field electron emission. In the present work, dielectric/carbon nanocomposites have been prepared in which diamond particles were replaced with insulating particles of SiO2, and BN (in cubic or hexagonal forms). The samples were produced by a pyrolytic carbon deposition inside porous dielectric compact. The average thickness of pyrocarbon shells covering the dielectric particles was varied from 0.4 to 40 nm to find optimal structure for efficient emission. The best samples of the composites showed excellent field emission properties with threshold fields of as low as 0.5-1 V/mum, good surface uniformity and long-term stability that is very similar to diamond/carbon composites. Electronic properties of the emission centers (work function, electrical resistivity, topography and emission intensity) were investigated with a special STM device. No correlation between emission centers location and topography features (tips or pits) was found, rather the centers often correspond to regions with low values of work function and high electrical resistivity. The emission mechanism is considered using quantum properties of nanostructured carbon forms, specifically, taking into account a reduction of the tunneling barrier on insulator/graphite interface due to quantum well effects in thin (two-dimensional) carbon layers on dielectric surface.