Real-Time Visualization and Mechanistic Insights of Semiconductor Nanocrystal Transformations via In-Situ Transmission Electron Microscopy

Semiconductor nanocrystals exhibit tunable optical and electrical properties, making them promising candidates for a range of technological applications. However, their performance can be significantly affected by structural evolution under various environmental and chemical conditions. In this presentation, we will highlight the use of in-situ transmission electron microscopy (in-situ TEM) to directly visualize and elucidate the underlying mechanisms of nanocrystal transformations.
First, we will discuss the moisture-induced degradation of quantum-sized semiconductor nanocrystals.¹ By monitoring structural changes in real time, in-situ liquid-phase TEM enabled us to capture intermediate amorphous phases and trace the reaction pathways that drive irreversible degradation. The advanced liquid cells developed in this study allowed us to investigate, on a single-particle level, changes in crystal structure at the atomic scale as well as compositional changes triggered by moisture exposure.
Second, we will present the off-stoichiometry-driven phase transitions of two-dimensional (2D) CdSe nanocrystals.² Using in-situ TEM, we observed the transformation from the hexagonal wurtzite structure to the cubic zinc blende phase. These findings underscore the delicate balance of stoichiometry and atomic rearrangement in determining the final crystal structure. Interestingly, we captured unique phenomena such as domain coalescence and separation during the transformation. The ability to visualize these transitions in real time opens new avenues for precisely tuning nanocrystal properties through compositional engineering.
Our work provides critical insight into the dynamic structural evolution of semiconductor nanocrystals and emphasizes the importance of in-situ TEM as a powerful tool for probing the nexus between environmental factors, stoichiometry, and phase stability. These insights will pave the way for more robust and tunable nanomaterials in next-generation optoelectronic applications.

REFERENCE
1. H. Ma, S. Kang, S. Lee, G. Park, Y. Bae, G. Park, J. Kim, S. Li, H. Baek, H. Kim, J.-S. Yu, H. Lee, J. Park and J. Yang, ACS Nano, 17, 13734(2023), doi:10.1021/acsnano.3c03103
2. H. Ma, D. Kim, S. I. Park, B. K. Choi, G. Park, H. Baek, H. Lee, H. Kim, J.-S. Yu, W. C. Lee, J. Park and J. Yang, Adv. Sci., e2205690, (2023), doi:10.1002/advs.202205690.