Thin Solid Films, Vol.558, 125-133, 2014
Evolution and change of He bubbles in He-containing Ti films upon thermal treatment studied by small-angle X-ray scattering and transmission electron microscopy
Evolution and change of He bubbles in magnetron sputtering prepared He-containing Ti films under thermal treatment are studied by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and X-ray diffraction. Incorporation of He introduces a large number of He-vacancy clusters and some voids in the films, and significantly increases SAXS intensity and causes anisotropic scattering. The change of He induced defects during annealing is affected by thermal diffusion and migration of trapped He to the surface and between interfaces of He induced defects within the films. Annealing at 200 and 400 degrees C reduces intensity and anisotropy of SAXS, in accord with observed shrinking and disappearance of the voids. The simultaneous growth of non-uniformly distributed He bubbles to the sizes of 1-2 nm and a population level of 10(5)/mu m(3) are detected in the temperature range. The changes are explained by migration and coalescence mechanisms, which requires low apparent activation energy. Inconsistence between TEM and SAXS observations is noted and attributed to thinning induced internal stress relaxation of TEM specimen. Remarkable enlargement of He bubbles, associated with increased SAXS intensity and fractal dimension, is observed after 600 degrees C annealing, indicating involvement of Ostwald Ripening (OR) mechanism. The OR process dominates at 800 degrees C, where the high temperature provides activation energy for accelerated He dissociation from small bubbles into larger ones, and generating textured microstructure and agglomerated bubble clusters. The inhomogeneous bubble size distribution observed at this temperature covers a broad range of about 10-50 nm and possessing a population density level of 10(3)/mu m(3). (C) 2014 Elsevier B.V. All rights reserved.
Keywords:Helium bubbles;Bubble evolution;Small-angle X-ray scattering;Transmission electron microscopy;Thermal treatment;Magnetron sputtering;Titanium-helium films