Local Lattice Deformation of Tellurene Grain Boundaries by Four-Dimensional Electron Microscopy

Abstract

Two-dimensional (2D) tellurene is a promising competitor for the fabrication of ultrathin optoelectronic devices belonging to a new family of monoelemental 2D materials. The precise fabrication and characterization of tellurene and its lattice defects is of utmost importance to determine device reliability and predict functionality, yet it remains experimentally challenging. The rapid growth of the four-dimensional scanning transmission electron microscopy (4D-STEM) technique as well as postprocessing tools now allows for structural analysis with nanometer-scale resolution over a broad range of length scales. Here, we use 4D-STEM to reveal the three-dimensional (3D) atomic structure of the characteristic grain boundary in 2D tellurium formed through a new microwave-enabled chemical self-assembly. Strain and lattice parameter maps permit the reconstruction of the roughness of the grain boundary and suggest that its formation is promoted by a wedge of helical atomic chains along the [0001] crystallographic direction. The observation of wrinkles at the grain boundary is found to be the dominant relaxation mechanism. Insights into the formation mechanism are elucidated by mapping the lattice parameters as the first demonstration of local in-plane and out-of-plane unit cell variation in a nanometer-by-nanometer real-space array.

Anisotropic Properties of Tellurium Nanoflakes Probed by Polarized Raman and Transient Absorption Microscopy: Implications for Polarization-Sensitive Applications

“…The nanoplate was obtained on soft mica layers via the epitaxy method. So far, monolayer and few-layer Te nanoflakes can be fabricated by several strategies, such as physical vapor deposition (PVD), , liquid phase exfoliation, and hydrothermal synthesis. − …”

A Close Look at Molecular Self-Assembly with the Transmission Electron Microscope

“…Four-dimensional scanning transmission electron microscopy (4D-STEM) is a scanning-probe electron diffraction technique (see section ) in which a converged electron beam scans across the sample generating a 2D image, where each pixel contains a 2D diffraction pattern, resulting in a 4D data set. , This technique can be used to obtain a wide range of structural information including nanoscale variation in crystal orientation, structural order, grain boundaries, and material phase. , For example, it is possible to produce an orientation map of a specific region within a sample by assigning each pixel of the raster scan to a crystalline orientation based on the directionality and features in each diffraction pattern (Figure i). 4D-STEM has been used to study polymers, − biomolecules, , and porous frameworks. , One benefit of 4D-STEM is the ability to finely control electron flux and cumulative dose through careful selection of electron current, probe size, probe dwell time, and interprobe position distance .…”

Adaptative Diffraction Image Registration for 4D-STEM to optimize ACOM Pattern Matching

“…19,20,21 This 4D-STEM data analysis method based on the ACOM system of NanoMegas (Astar) 22,23,24,25 uses pattern matching of a scanning nano-diffraction dataset with libraries of diffraction patterns simulated from known structures extracted from CIF files. This method enables to construct crystalline phase and orientation maps to determine crystallinity 26,27 , microstructures 28 , structural deformation 29 , and grain boundaries 30 using scanning nanodiffraction with precession mode in a nanometer resolution. 31,32,33 The recent use of high-speed cameras, pixelated detectors 34 such as CMOS cameras 35, and hybrid-pixel detectors 10 enabled better compromises between signal-over-noise and dwell time of acquisition.…”