Precise Phase Engineering in Two-dimensional Chalcogenides via Localized External Stimuli

Description

Solid phase transitions can be controlled by macro-/micro scale thermal, mechanical, optical, chemical and other external excitations. First-order phase transition usually follows the classical nucleation theory. The new phase nuclei below the critical radius isinherently unstable and quite challenging to be maintained. The highest precision and spatial resolution on localized control of new phase generation is yet to be reached atomic scale or deep-nm scale, hindering further advancements of nano-/quantum device technologies. To develop the ultrahigh precision, ultrafine atomic resolution and scalable methodologies for phase transition control, in this project we aim to investigate the focused electron beam and scanning probe (tip) electric excitation approaches which can stimulate local atomic phase transitions in polymorphic two-dimensional chalcogenides. We plan to achieve the ultimate atomic-scale (sub-nm) control on the new phases. Particularly, the sub-nm dimension of new phases achieved in this project will greatly reduce the critical nuclei radius in classical nucleation theory by local stimuli. Besides, the phase transition mechanisms will be thoroughly studied via both experiment (TEM/STEM/SPM) and theory (DFT). Our efforts on the source identification will clarify the origins of strain, defect, electric charge/field and so forth for the phase transition. This project will open up new avenues for the atomic-scale or sub-nm scale fabrication and atomic structuring for future quantum or atomic devices.