Atomic-Scale Strain Field Mapping Methods for HR-TEM and HR-STEM Images

Abstract

Atomic-scale strain mapping has become increasingly vital for investigating deformation mechanisms and the governing principles of solid materials. This is due to the significant impact of atomic-scale strain on the physical, chemical, and mechanical properties of nanomaterials that comprise functional devices such as nanoelectronics, communication devices, electromechanical systems, and sensors. The advent of advanced electron microscopes has enabled the acquisition of high-magnification images with atomic resolution, providing an exceptional platform for measuring the atomic-scale strain of solid materials. However, accurate and unified strain mapping methods and standards for evaluating atomic-scale strain distribution remain scarce. Consequently, a unified strain mapping framework is proposed for atomic-scale strain measurement. Utilizing finite deformation analysis and the least-squares mathematical method, two types of atomic-scale strain field mapping methods have been developed, including the phase analysis-based methods (PAD and PAS) and the peak matching-based strain mapping method (PMS) for high-resolution scanning transmission electron microscope images. The prototypical 2D materials, graphene and molybdenum disulfide, serve as the subjects for the strain field mapping research, conducted through both simulation and experimentation. Upon comparing the theoretical strain mapping results of single-layer graphene and molybdenum disulfide with and without defects, it is demonstrated that the proposed strain mapping methods, particularly the PMS method, can accurately describe the large deformation surrounding a significant strain gradient.