Preparation of epitaxial ScF₃ thin films – a negative thermal expansion material

Scandium trifluoride (ScF₃) is known for a pronounced negative thermal expansion over a wide range of temperature, from 10 K to 1100 K. The structure of ScF₃ can be described as an ABX₃ perovskite with an empty A-site. Growing films of ScF₃ allows for tuning the lattice constant, the thermal expansion, and the construction of devices based upon differential thermal expansion. We have investigated the growth of ScF₃ films on oxide and fluoride substrates using pulsed laser deposition (PLD). There are several unique features to this material that pose challenges for PLD growth: poor adhesion of ScF₃ pressed powder targets, a narrow stability range, and complex interfaces between fluorides and oxides. Nonetheless, we have found growth routes for producing films with very good epitaxy and narrow mosaic. This report describes the growth and initial characterization of high quality ScF₃ films.