Nanocrystalline surface layers of WC and SiC are formed by a sequential high-dose metal vapour vacuum arc implantation of carbon and tungsten ions into Si(I 0 0) and subsequent rapid thermal annealing. These layer systems are shown to provide electron field emitter structures with turn-on-fields as low as 15-20 V/mum. The formation of carbide and silicide phases as well as that of cavities at the SiC/Si-substrate interface upon annealing are discussed on the basis of X-ray diffraction, X-ray photo electron spectroscopy, cross-section transmission electron microscopy and HREM measurements.