Characterization of 2D materials

2D material are promising optoelectronic materials. Their electronic properties can be tuned by engineering its heterostructures. This includes controlling their layers (Single/multi) and/or producing material consisting of different 2D crystals stacked in different fashion.

High resolution scanning transmission electron HAADF micrograph of phase boundary between single layer 2 dimensional MoSe2 and WSe2 crystal. 

-Yuxi Zhang, Anuj Bisht

Gallium Oxide

 Our work on β-Ga2O3 characterizes defect formation in bulk crystals and thin film device structures. We observe how doping and alloying impact these defects and the fundamental material properties. Scanning/transmission electron microscopy (S/TEM) and electron energy loss spectroscopy (EELS) are ideal for understanding these defects as well as atomic and electronic structure.

High entropy oxides are complex oxide systems  with five or more cations in a single lattice. Using the concept of high configurational entropy, novel materials with different compositions are engineered. This leads to unique composition-structure-properties in these materials. In our group, our research is focused on investigation of microstructure, chemistry and defects in these novel High Entropy Oxides at nanoscale regime to correlate the structure-process-properties of these material systems using Scanning/Transmission Electron Microscopy and Electron Energy Loss Spectroscopy.

Atomic resolution STEM image of High Entropy Oxide of Perovskite (ABO3) crystal structure with B site disorder

-Sai Venkata Gayathri Ayyagari

Organic perovskites such as Formamidinium lead iodide (FAPbI3) are promising material for future solar cell due to their high power conversion efficiency and easy-cheap manufacturing. However, they suffer from stability issues. Most of the research related to FaPbI3 are focused around increasing its efficiency and improving its stability. A key to address these issue is to understand and engineer the microstructure and defect in the fabricated FaPbI3 at atomic scale. A challenge posed is the beam damage induced in FaPbI3 when probing it under transmission electron microscope. The image shows the effect of beam damage in FaPbI3.

Bright field TEM micrograph of FaPbI3 perovskites showing beam damage under electron beam exposure during transmission electron imaging at 200 kV. Initial (left) and beam damaged (right). The bubbles in the right image is due to beam damage. 

-Yuxi Zhang, Anuj Bisht