Retaining crystallinity of as-deposited thermoelectric Fe₂VAl-based thin films grown from DCMS and HiPIMS

Abstract

Thermoelectric materials have gained much attention in recent years due to their ability to directly interconvert electrical and thermal energy via the Seebeck/Peltier effect. The efficiency of this process is generally dependent on three parameters—the thermopower, the electrical and thermal conductivity—which are represented together in the dimensionless Figure of Merit ZT. In 2019, Hinterleitner et al. managed to produce thin films of body-centered cubic bcc-Fe2V0.8W0.2Al with an exceptional Seebeck coefficient, but the samples needed to be heat-treated for one week to crystallize from their amorphous state. In this work, we present Fe2VAl-based full-Heusler thin films retaining their crystallinity during sputter deposition. By tuning various parameters, we managed to fabricate films in a bcc-structure on silicon. These films were analyzed using X-ray diffraction, energy dispersive X-ray spectroscopy—confirming that the films are crystalline Heusler-phases with full disorder—and by measurement of transport data. Thermal conductivity of the films was derived from thermoreflectance and specific heat capacity. The measurements suggest a low thermal conductivity and a moderate Seebeck coefficient, resulting in a commendable Figure of Merit.