Shape memory alloys offer the highest work output per unit volume among smart materials and have both high actuation stress and large recoverable strain. Miniaturization of materials and devices requires shape memory actuation which is uncompromised at a small scale. However, size effects need to be understood in order to scale shape memory actuation with the minimum size critical to device design. Controlling material quality and properties is essential in fabrication of shape memory alloys into nanometer regime. This work demonstrates a novel fabrication technique, biased target ion beam deposition (BTIBD), which uses additional adatom energy in order to fabricate high-quality nickel-titanium (NiTi) alloys thin films with nanometer thickness. These fabricated ultrathin NiTi films provide insight into the size scale dependence of shape memory functionality at nanoscale regime. BTIBD provides additional adatom energy to the growing film in order to fundamentally tailor the film growth mode for quality and properties. An independent ion beam source is customized in BTIBD to provide low-energy ions (tens of eV) during growth of films on substrates. Pure Ti and pure Ni targets are co-sputtering in BTIBD to fabricate NiTi thin films. The prepared NiTi films are continuous, and the thickness ranges from several tens to a few hundreds nanometers. The composition is controllable over the range of Ni-rich (>50.5 at% Ni), near-equiatomic, and Ti-rich (

The need for high performance microelectromechanical systems (MEMS) has driven the industry to research ultra-thin shape memory alloy (SMA) films, specifically for microactuators capable of rapid actuation [1]. Biased target ion beam deposition (BTIBD) is a novel technique that can produce high quality films with thicknesses less than 1000 [2]. Nickel-titanium (NiTi) thin films with different composition ranges (Ni-poor/Ti-rich, near equiatomic NiTi, and Ni-rich), various thicknesses, and post-deposition annealing were deposited using BTIBD by Dr. Huilong Hou at the Penn State University [2 4]. The shape memory effect in NiTi films can be detected by measuring the thin film stress as a function of temperature. Stress measurements during heating and cooling were made on a variety of films using laser-based system that measures substrate. Additionally, cyclic tests, up to 100 heating-cooling cycles, were conducted to evaluate the stability of the phase transformation in subset of the deposited films. In several films that were 800 nm thick, thermal stress measurements showed a distinct hysteresis indicative of a functional shape memory effect in these films. These same films also showed that the effect was repeatable even after 100 temperature cycles.

This book, the first dedicated to this exciting and rapidly growing field, enables readers to understand and prepare high-quality, high-performance TiNi shape memory alloys (SMAs). It covers the properties, preparation and characterization of TiNi SMAs, with particular focus on the latest technologies and applications in MEMS and biological devices. Basic techniques and theory are covered to introduce new-comers to the subject, whilst various sub-topics, such as film deposition, characterization, post treatment, and applying thin films to practical situations, appeal to more informed readers. Each chapter is written by expert authors, providing an overview of each topic and summarizing all the latest developments, making this an ideal reference for practitioners and researchers alike.

With this grant we explored the properties that result from combining the effects of nanostructuring and shape memory using both experimental and theoretical approaches. We developed new methods to make nanostructured NiTi by melt-spinning and cold rolling fabrication strategies, which elicited significantly different behavior. A template synthesis method was also used to created nanoparticles. In order to characterize the particles we created, we developed a new magnetically-assisted particle manipulation technique to manipulate and position nanoscale samples for testing. Beyond characterization, this technique has broader implications for assembly of nanoscale devices and we demonstrated promising applications for optical switching through magnetically-controlled scattering and polarization capabilities. Nanoparticles of nickel-titanium (NiTi) shape memory alloy were also produced using thin film deposition technology and nanosphere lithography. Our work revealed the first direct evidence that the thermally-induced martensitic transformation of these films allows for partial indent recovery on the nanoscale. In addition to thoroughly characterizing and modeling the nanoindentation behavior in NiTi thin films, we demonstrated the feasibility of using nanoindentation on an SMA film for write-read-erase schemes for data storage.