Self‐Assembled NiSe2‐SnSe2 Heterostructures From NiO‐SnO2 Films by Plasma‐Assisted Selenization Process With Efficient Performance of Bifunctional Devices

Abstract Materials with self‐assembly ability can form complex structures spontaneously through entropy or enthalpy‐induced effects and spinodal decomposition, which can positively affect the characteristics of materials. Traditionally, most materials with spinodal decomposition properties require longer processing time and higher power to obtain desirable phases. Instead of utilizing high annealing temperature and a longer duration process, the spinodal decomposition along with a self‐assembly mechanism by a simple plasma‐assisted chemical vapor reaction method with the addition of selenium is demonstrated, namely a plasma‐assisted selenization process, which is capable of synthesizing transition metal dichalcogenides (TMDs) at a lower temperature with a shorter process period. Interestingly, partial to fully selenized surface heterostructure and unique phase engineering in various thicknesses are observed by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. As the thickness of the films decreases, selenization becomes deeper and initially forms a horizontal sandwich structure between the fully selenized and the vertically decomposed oxide parts. In the case of the thinner film, oxide parts are selenized with horizontal phase separation of two separate TMD layers. Furthermore, the controllable structure of the thin film, with tunable electrical properties and phases, is further applied to the hydrogen evolution reaction and gas sensing.