How can the MEMS heating + biasing TEM sample holder be used to investigate non-equilibrium phase changes in 2D materials?

Pawan Kumar, Eric A. Stach, Deep Jariwala, and their colleagues from University of Pennsylvania studied, for the first time, direct visualization of structural transformations in MoS2 2D materials at elevated temperatures. They used the Hummingbird Scientific MEMS heating + biasing TEM sample holder to visualize these transformations at the atomic scale with aberration-corrected scanning transmission electron microscopy (STEM).

Annealing of 2D MoS2 at different heating rates shows different phase transformations from MoS2 to either a highly ordered crystalline island structure that is composed of both 2H and 3R phases (a-d) or to nanocrystalline and amorphous regions (a, e-g). 

The researchers report a strong correlation between the resulting structures after using different heating rates in their annealing experiments. Specifically, fast heating rates resulted in a highly ordered, sub-10 nm size crystalline islands that are composed of both 2H and 3R phases. On the other hand, slow heating rates resulted in nanocrystalline and amorphous regions. They explain the different phases observed using different heating rates by differences in the rate of evaporation and redeposition of sulfur from the 2D MoS2 flakes. The Hummingbird Scientific MEMS heating + biasing TEM sample holder enabled ultrafast heating at 25 °C/sec providing valuable insights that can lead to the development of new methods to synthesize 2D layered nanostructures with unique electronic or optical properties.

Reference: Pawan Kumar, James P. Horwath, Alexandre C. Foucher, Christopher C. Price, Natalia Acero, Vivek B. Shenoy, Eric A. Stach and Deep Jariwala,  npj 2D Mater Appl 4, 16 (2020). DOI: 10.1038/s41699-020-0150-2

Full paper  From npj 2D Materials and Applications under the Creative Commons license

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