WF6-CVD tungsten film as an emitter for a thermionic energy converter I. Production, texture and morphology of WF6-CVD tungsten films

The as-deposited WF6-CVD tungsten film consists of columnar grains about 3 µm in diameter and about 30 µm in length. The film has a 100 fiber texture with a clear tendency to the formation of a pseudo-mono-crystal. The overwhelming part of the grains have their 100 axes within 27° of the surface normal. The as-deposited film surface consists of {111} crystal planes. Two hours annealing at 2273 K resulted in grain growth leading to a grain diameter of more than 70 µm. Inspection of etch pits revealed that 62% of the surface area consists of grains which have their 100 axis within 16° of the surface normal.