FIM observation of an iron deposited tungsten tip

An iron-deposited tungsten tip was observed with a field ion microscope. The observed features were classified into five types corresponding to the various substrate temperatures. Epitaxial growth was observed at substrate temperatures ranging from 1000C to 5000C, though the parallelism was not perfect. An epitaxially grown film was observed only on one side of a tip cap at a low temperature. The film spread to the entire tip cap at a higher temperature. Diffusivity of the deposited iron was estimated from the observed migration of the iron atoms. Images which implied the formation of an alloy of iron and tungsten were obtained at 550-6600C. When the substrate temperature exceeded 7000C, iron atoms were not observed on the tip cap. These sequential changes corresponding to the substrate temperatures are discussed in relation to the surface diffusion of the deposited iron and substrate tungsten atoms. (Auth.)