Electron diffraction and imaging of structural changes related with charge density waves in layered materials

Abstract

Abstract Electron diffraction provides us with a powerful and very direct technique for the study of charge density waves. In particular since the diffraction evidence can be directly correlated with high resolution imaging information on the phases, commensurate and incommensurate, and on the interphase boundaries between them. The high atomic scattering power of electrons enables a direct response on changes occuring in very small areas which are usually averaged out by other techniques such as X-ray diffraction and the measurement of physical properties. The diffraction effects to be associated with charge density waves are caused by the periodic lattice distortions and examples will be illustrated for a particular case study: the various CDW-driven phases in transition metal dichalcogenides such as 1T-TaS 2 . The diffraction patterns will be discussed and analysed and in a few cases high resolution images could be obtained which can be interpreted in relation with the charge density waves. A dynamical recording in the electron microscope of the various phases and transitions between them in IT-TaS 2 will be illustrated in a movie where the changes in diffraction patterns as well as in the microstructural images are followed as a function of temperature.