Influence of nanoscale components of the immiscible W–Ba system on the emission characteristics of deposited films

Results on ion-plasma sputtering of composite targets based on the W–Ba system are presented. In freshly deposited W–45 at.% Ba films, X-ray diffraction reveals two diffuse maxima corresponding to two types of amorphous short-range order, interpreted as W-rich and Ba-rich amorphous structural components. Upon thermal treatment, these nonequilibrium components crystallize into a W + BaWO4-containing structure. The structural evolution is considered together with the electrical and thermionic emission characteristics of the films. The results show that preservation of the nanoscale W–Ba mosaic structure and suppression of excessive BaWO4 formation are important for obtaining improved emission performance.