In this seminar, I will present our latest results on using the molecular beam epitaxy (MBE) method to grow thin films of tantalum-based materials. I will discuss how fine-tuning the growth parameters and procedure, as well as the choice and preparation of substrates, influences the final properties of the films.
The first material is 1T-TaS2 – a polytype widely known for its variety of metastable states. Until now, superconductivity in it was achievable only through precise chemical doping or the application of high hydrostatic pressures. With the protocol we developed, I show how we can grow 10 to 100 nm films of the 1T-TaS2 polytype, which develop and stabilise tensile strain upon cooling to room temperature after growth. The resulting MBE films are fully stable under ambient conditions, do not require special handling, and show a superconducting Tc of 3.8 K.
The second material is alpha-Ta – a prominent candidate for use in superconducting qubit technology. The main limitation of alpha-Ta at the moment is the superconducting Tc, which is much lower in thin films than in the bulk crystal (4.4 K). Using our MBE protocols, we can grow pure alpha-Ta films on insulating substrates ranging in thickness from 10 to 25 nm, with a Tc reaching up to 3.7 K.