Characteristics of surface nano-structural modifications in nitrogen ion implanted W as a function of temperature

Abstract

The surface modifications of tungsten massive samples (0.5 mm foils) made by nitrogen ion (30 keV; 1 x 10 18 N + cm -2 ) implantation are studied by XRD, AFM, and SIMS. XRD patterns clearly showed WN 2 (0 1 8) (rhombohedral) very close to W (2 0 0) line. Crystallite sizes obtained from WN 2 (0 1 8) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. These morphological changes are similar to those observed for thin films by increasing substrate temperature (i.e. structure zone model (SZM)). Surface roughness variation with temperature, showed a decrease with increasing temperature. The density of implanted nitrogen ions, and the depth of nitrogen ion implantation in W are studied by SIMS. The results show a minimum for N + density at a certain temperature consistent with XRD results (i.e. Iw ( 2 0 0) /Iw (2 1 1) ). This minimum in XRD results is again similar to that obtained for different thin films by Savaloni et al. [Physica B, 349 (2004) 44; Vacuum, 77 (2005) 245] and Shi and Player [Vacuum, 49 (1998) 257].