Contrast Transfer Function-Based Exit-Wave Reconstruction and Denoising of Atomic-Resolution Transmission Electron Microscopy Images of Graphene and Cu Single Atom Substitutions by Deep Learning Framework

The exit wave is the state of a uniform plane incident electron wave exiting immediately after passing through a specimen and before the atomic-resolution transmission electron microscopy (ARTEM) image is modified by the aberration of the optical system and the incoherence effect of the electron. Although exit-wave reconstruction has been developed to prevent the misinterpretation of ARTEM images, there have been limitations in the use of conventional exit-wave reconstruction in ARTEM studies of the structure and dynamics of two-dimensional materials. In this study, we propose a framework that consists of the convolutional dual-decoder autoencoder to reconstruct the exit wave and denoise ARTEM images. We calculated the contrast transfer function (CTF) for real ARTEM and assigned the output of each decoder to the CTF as the amplitude and phase of the exit wave. We present exit-wave reconstruction experiments with ARTEM images of monolayer graphene and compare the findings with those of a simulated exit wave. Cu single atom substitution in monolayer graphene was, for the first time, directly identified through exit-wave reconstruction experiments. Our exit-wave reconstruction experiments show that the performance of the denoising task is improved when compared to the Wiener filter in terms of the signal-to-noise ratio, peak signal-to-noise ratio, and structural similarity index map metrics

In Situ Scanning Transmission Electron Microscopy Study of MoS2 Formation on Graphene with a Deep-Learning Framework

Atomic-scale information is essential for understanding and designing unique structures and properties of two-dimensional (2D) materials. Recent developments in in situ transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable research to provide abundant insights into the growth of nanomaterials. In this study, 2D MoS2 is synthesized on a suspended graphene substrate inside a TEM column through thermolysis of the ammonium tetrathiomolybdate (NH4)(2)MoS4 precursor at 500 degrees C. To avoid misinterpretation of the in situ STEM images, a deep-learning framework, DeepSTEM, is developed. The DeepSTEM framework successfully reconstructs an object function in atomic-resolution STEM imaging for accurate determination of the atomic structure and dynamic analysis. In situ STEM imaging with DeepSTEM enables observation of the edge configuration, formation, and reknitting progress of MoS2 clusters with the formation of a mirror twin boundary. The synthesized MoS2/graphene heterostructure shows various twist angles, as revealed by atomic-resolution TEM. This deep-learning framework-assisted in situ STEM imaging provides atomic information for in-depth studies on the growth and structure of 2D materials and shows the potential use of deep-learning techniques in 2D material research

Unconventional assemblies of bisacylhydrazones: The role of water for circularly polarized luminescence

Understanding the precise molecular arrangement of chiral supramolecular polymers is essential not only to comprehend complex superstructures like proteins and DNA but also for the development of next-generation optoelectronic materials, including materials displaying high-performance circularly polarized luminescence (CPL). Herein, we report the first chiral supramolecular polymer systems based on hydrazone???pyridinium conjugates comprising alkyl chains of different lengths, which afforded control of the apparent supramolecular chirality. Although supramolecular chirality is governed basically by the remote chiral centers of alkyl chains, helicity inversion was achieved by controlling the conditions under which the hydrazone building blocks underwent aggregation (i.e., solvent compositions or temperature). More importantly, the addition of water to the system led to aggregation-induced hydrazone deprotonation, which resulted in a completely different self-assembly behavior. Structural water molecules played an essential role, forming the assembly's channel-like backbone, around which hydrazone molecules gathered as a result of hydrogen bonding interactions. Further co-assembly of an achiral hydrazone luminophore with the given supramolecular polymer system allowed the fabrication of a novel CPL-active hydrazone-based material exhibiting a high maximum value for the photoluminescence dissymmetry factor of ???2.6 ?? 10???2

Study on Atomic Layer Formation and Oxidation of Two-Dimensional Molybdenum Disulfide

Department of Materials Science and Engineeringclos