Diamond-based composite layers as protective coatings for ion beam extraction systems

W-containing polycrystalline diamond films were produced by a hybrid chemic al vapor deposition-powder flowing technique, in order to test the feasibil ity of using composite diamond-based materials as protective coatings for a cceleration grids subjected to ion bombardment. The morphology and structur e of the composite layers, deposited on Mo substrates, were investigated by scanning electron microscopy and reflection high-energy electron diffracti on. It is found that W insertion substantially lowers the resistivity of th e diamond-based layers (around 10(-2)Omega cm) but does not modify the latt ice parameters of the host diamond matrix. The performance of such coatings for shielding Mo grids from ion-induced sputtering was tested using 1 keV Ar+ beams. The Auger electron spectroscopy spectra indicated that the dose of 6 X 10(19) ions/cm(2) employed was not sufficient for complete erosion o f the composite layers, for which sputtering yields in the range of 0.6-0.9 atoms/ion were measured. The secondary electron emission induced by 1.5-4. 0 keV Ar+ ions was investigated and compared with the emission from uncoate d Mo samples. (C) 2001 American Vacuum Society.