Crystallinity and texture promotion in WS2 thin films

A systematic study of the promoting effect of various elements on crystallization and texture of tungsten sulfide (WS2) thin films is presented. Best crystallization at relatively low annealing temperatures T-a = 650-750 degrees C is achieved by adding sodium sulfide or nickel to the film, while the strongest texture is achieved with cobalt. An improvement of crystallization and texture is equally achieved with iron, manganese, or cesium. The promoting effect is mostly independent of the way the promoter is added. The promoting element can be added as a thin layer on the substrate or on the top of the WS2 film or it can be codeposited with the WS2 film. Since rheotaxy models cannot satisfactorily explain these results, the possibility of a catalytic growth mechanism is discussed. (C) 1997 American Vacuum Society.