Special Seminar
Name: Dr. Vojtech Kundrat
Affiliation: Weizmann Institute of Science
Title: Mechanism of WS2 nanotube formation revealed by in-situ/ex-situ imaging
Date & Time: Wednesday, 28th February at 11.00 a.m.
Venue: Rajarshi Bhattacharya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
Metal dichalcogenide nanotubes, and in particular those made of WS2, are known for over 30 years and have been investigated extensively. They usually come in multiwall form with a diameter spanning the range of 20-150 nm and an aspect ratio that can exceed 100. Synthesis of macroscopic amounts of such nanotubes has been demonstrated in past.1 The tungsten suboxide W18O49 nanowhiskers are converted to WS2 nanotubes by high-temperature reaction in the stream of a gaseous mixture of H2S and H2.
Scanning and transmission electron microscopy (SEM and TEM) play a crucial role in the structural characterization of nanomaterials. Various tools related to electron microscopy are available and under development for a deep understanding of reactions and nanostructures. The mReactor2 technology allows in-situ observation of high-temperature heterogeneous reactions within a scanning electron microscope in a low-pressure atmosphere (up to 500 Pa). For the current work, the expedient SEM with a fitted mReactor was further developed for in-situ observation of sulfidation reactions. The coupling of in-situ sulfidation in SEM and sequential ex-situ TEM, both on the Micro Electromechanical System (MEMS) chip3, revealed the mechanism of the WS2 nanotube formation. Subsequent to the presentation of the modified mReactor and the experimental results, the growth mechanism of the nanotubes is discussed in light of the new growth environment in-depth.
References:
1 A. Rothschild, J. Sloan and R. Tenne, J. Am. Chem. Soc. 2000 122, 5169-5179.
2 L. Novák, J. Stárek, T. Vystavěl, L. Mele, Microsc Microanal 2016 22, 184.
3 L. Mele, S. Konings, P. Dona, F. Evertz, C. Mitterbauer, P. Faber, R. Schampers, J. R. Jinschek, Microsc. Res. Tech. 2016 79, 239.