Physical Properties of Elastocaloric Materials

University of Maryland

Composition, thickness & resistance are sample’s parameters critical for the discovery of new elastocaloric materials.

Characterizing physical properties of composition, thickness, and resistance is a major expertise at University of Maryland, which supports the discovery of new elastocaloric materials.  It is well known that properties of elastocaloric materials can change dramatically with minute change in the stoichiometry of the material. For instance, a small shift in composition near the equiatomic NiTi can lead to significant change in the martensitic transformation temperature. Thus, it is crucial that we are able to accurately determine the (local) composition of different materials. Measuring and mapping compositions is also of paramount importance for combinatorial investigation. Each combinatorial library wafer contains up to hundreds of thin film samples whose composition is continuously changing. Because the goal of such high-throughput experimentation is to track how physical properties such as the lattice constant, the transformation temperature, and the latent heat change as a function of continuously changing composition, we need to be able to accurately determine the compositions of all samples on combinatorial libraries.  JEOL 8900R wavelength-dispersive x-ray spectroscopy (WDS) is particularly suitable for determining composition of thin films and bulk materials in an accurate manner.

Other measurement instrumentation available at UMD for measuring various properties include a Signatone WL250 automated probe station, which is able to measure electrical resistance for a library of materials in a high-throughput manner. A Dektak profilometer is used to measure the thickness of deposited thin films with accuracy on the order of 10 nm. In addition, for processing/annealing thin film and bulk samples, we have an AJA high vacuum chamber and a Lindberg/Blue M high temperature furnace.