Phase transitions and structural regulation of low-dimensional condensed-matter

Low-dimensional condensed matter has been widely used in nano electronics, sensors, ion batteries, solar cells, energy collection/storage, micro/nano electromechanical fields, etc. The relationship between its microstructure and physical properties is the core content of condensed matter physics research. At low dimensional scales, the structures of condensed matter are extremely sensitive to external environments including mechanical stress, temperature, electric field, etc. Therefore, we can finely tune the structures and physical properties in a multi-parameter space, thereby realizing a series of novel quantum states. Clarifying the atomistic phase transition mechanisms under the external fields is a key step in achieving the above objectives. Transmission electron microscopy has become an indispensable tool for characterizing the microstructure of low dimensional materials. The development of in situ transmission electron microscopy technology with high temporal and spatial resolution provides an excellent platform for dynamically characterizing the structure and chemical composition evolution of low-dimensional materials under external stimuli (stress field, temperature field, and electric field). In this review, we briefly introduce our recent progress on investigating the structural stability of low-dimensional materials: (1) Anelasticity of CuO nanowires induced by phase transformation and structural stability of ZnO materials subjected to the mechanical stress; (2) structural stability of low-dimensional W and Cu2Se materials at high temperatures; (3) the influence of Na+ migration on the structural stability of low-dimensional frame structure sodium tungsten bronze under electric fields; (4) the effect of high-energy electron beam irradiation on structural stability of sodium tungsten bronze. The relevant results clarify the atomic-scale phase transition mechanisms of low-dimensional condensed matter and provide a reference for structural modulation by applying different external fields. In addition, there are still many areas that need to be explored. (1) This review only focuses on the influence of a single external field. In practical work, devices may be affected by multiple physical fields such as combined stress/temperature or stress/electric field. The development of multifunctional specimen holders could promote in situ electron microscopy technology in the future. (2) The current research focuses on the atomic structure of condensed matter. In the future, we need to combine electronic holography, segmented annular all field (SAAF) and other technologies to characterize the localized electronic structures. (3) Establishing the correlation between microstructures and macroscopic physical properties requires the continued development of large-scale and multi-scale structural characterization methods, which can provide comprehensive understanding of the microstructure-property interplay.