Phase Engineering of Palladium Selenide Using Chalcogen Flux Control

Palladium selenides, relatively unexplored platinum group metal chalcogenides, have been attracting significant interest due to their versatility in different applications and their numerous stable phases with different crystal structures. Most vapor-based bottom-up growth approaches using furnaces have resulted in the layered PdSe2 phase due to the reactions occurring in a saturated chalcogen vapor environment, in which PdSe2 is the most stable phase. Here, we show that precise control over the Pd/Se stoichiometry can be achieved through tuning the chalcogen flux, both incoming and outgoing, resulting in control over the local Se concentration on the growth substrate. Increasing temperatures are used to increase the outgoing flux of Se, leading to a phase transition from PdSe2 to Pd17Se15. Increasing the incoming flux of Se, through high mass loading, is then used to tune the reaction back to the growth of the PdSe2 phase. Detailed material characterization is performed to prove the different crystal structures and show the ability to tailor the Pd/Se family across two stable phases, with one being layered (PdSe2) and the other being three-dimensional (3D) bulk (Pd17Se15). Finally, we demonstrate the lifecycle of phase tuning by transforming PdSe2 into Pd17Se15 and then back again, through control of temperature and Se mass loading. These results open pathways for exploring the solid-state properties of this family of Pd-Se materials in optoelectronics and catalysis, which have been limited to date for vapor-based furnace growth approaches on substrates.