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

Abstract

W-containing polycrystalline diamond films were produced by a hybrid chemical vapor deposition- powder flowing technique, in order to test the feasibility of using composite diamond-based materials as protective coatings for acceleration grids subjected to ion bombardment. The morphology and structure of the composite layers, deposited on Mo substrates, were investigated by scanning electron microscopy and reflection high-energy electron diffraction. It is found that W insertion substantially lowers the resistivity of the diamond-based layers (around 10−2Ω cm) but does not modify the lattice 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 6×1019 ions/cm2 employed was not sufficient for complete erosion of 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 uncoated Mo samples.