In-Situ TEM Study of the Thickness Impact on the Crystallization Features of a Near Equal-Atomic TiNi Thin Film Prepared by Planar Magnetron Sputtering

Abstract

In-situ TEM studies were conducted to reveal the crystallization features of equi-atomic TiNi amorphous thin films. The TiNi amorphous thin film crystallization procedure can be divided to be two types: the in-homogenous nucleation and growth mode in the ultra thin regions and the homogenous polymorphous mode in the thick areas. In the thin regions, the thickness controls the in-homogenous nucleation mode. The formed nano-crystallites in the thin areas are with a size of 5–20 nm while in the homogenous nucleation and growth mode, the grain size drops to the range of sub-micron level. In general, the stabilized grain size is a function of thin film thickness and can be described as G=kx, where x is the thickness in nano-meter and k is a constant related to lattice parameter. An intermediate phase forms through the crystallization procedure in the thick region. The intermediate phase possesses a cubic structure with lattice parameter of a=9.03 A. The intermediate phase transforms to the stable B2 phase when the specimen being kept above the crystallization temperature for some time. The crystallization sequence in the thick region is determined to be: TiNi amorphous → intermediate phase → B2 + Ti₃Ni₄.