Combinatorial study on submicron Ni-Ti thin films through membrane deflection experiments

Abstract

In order to continuously extend material applications into reduced scales, a number of researches is ongoing to understand the material behaviors in smaller scale regimes. In particular, Nickel-Titanium (Ni-Ti) shape memory alloy is one of the materials that is already widely used in many bulk scale applications, and is still currently attracting numerous interests for small-scale applications. However, integration of this material in the form of thin films is still deemed difficult due to its high compositional sensitivity and the dependency of its properties towards different fabrication methods. Hence, combinatorial high-throughput experiments have been utilized to identify the optimum parameters required in order to fabricate desirable samples. The currently available combinatorial highthroughput approaches utilized in evaluating the mechanical properties are mostly focused on nanoindentations and cantilever beams, but there possesses a need to understand the pure mechanical response of the material itself when subjected to tensile deformation. In this study, membrane deflection experiment was performed with the compositional-spread technique to investigate the mechanical properties of Ni-Ti thin films with submicron thicknesses. The mechanical behaviors of sputter-deposited freestanding Ni-Ti thin films of compositions and thicknesses ranging from 45.7 at. % – 52.7 at. % Nickel and 270 – 530 nm were evaluated. The compositional and microstructural correlations of the initial elastic modulus, transformation stress, recoverable strain, and hysteresis area were observed and cross examined with reported works in literatures. With the results obtained, the compositional ratio of Ni-Ti can then be tailored accordingly based on the requirements of different mechanical responses. In addition, efforts in integrating the high-throughput methodology into the membrane deflection experiment will be demonstrated in the later part of this study.