Integral and local field emission analyses of nanodiamond coatings for power applications

Nanodiamond (ND) powder coatings are very promising for cold cathode applications The suitability of a (di)electrophoretically deposited ND coating (crystallite size: 1-10 nm) for high current applications was analysed depending on three types of Si substrates (flat, rough, Si tip array). DC Field emission (FE) investigations were performed by means of a Field Emission Scanning Microscope (FESM), allowing non destructive measurements of FE properties with a variable lateral resolution R. A decrease of the electrical onset field strength E/sub on/ (0.5 nA) for R=10/100/1000 /spl mu/m from 200/190/109 V//spl mu/m of the flat to /spl ap/67/44/20 V//spl mu/m of the rough, and to /spl ap/7/6.5/4.5 V//spl mu/m of the tip array sample is achieved by the geometrical field enhancement of the structures. The high reproducible current density J(REP)=15 A/cm/sup 2/ for R=10 /spl mu/m of the flat and rough sample exhibits the large potential of the ND coating for power applications. The comparison of FE results obtained by different R proved, however, their non-uniformity due to the /spl mu/m-roughness, resulting in low J/sub REP/ for large areas. In contrast, coated tips show a good uniformity over mm/sup 2/ sized areas with moderate J/sub REP/=0.2 A/cm/sup 2/.