Summer Research Fellowship Programme of India's Science Academies

Solvent exfoliation of transition metal dichalcogenides

Tonipe Anuradha

Silver Jubilee Govt. Degree College, Kurnool, A.P.

Dr. Ranjan Datta

Associate professor, International Center for Material Science, Jawaharlal Nehru Center for Advanced Scientific Research, Banglore.


Transition metal dichalcogenides (TMDs) exhibit diverse properties that depend on their composition and they can be semiconductors (MoS2, WS2, ReS2), semi-metals (WTe2, TiSe2) and superconductors (NbSe2, TaS2). TMDs which are semiconductors of the type MX2 where M is a transition metal (Mo or W) and X is a chalcogen atom (such as S, Se or Te) have unique properties similar to graphene. The hexagonal layers of metal atoms (M) sandwiched between two layers of chalcogen atoms, the bonding between these trilayer sheets is covalent, adjacent sheets stack via Van der waals interactions. We have chosen MoS2, WS2, ReS2 due to their many electronic and optoelectronic device applications. Transmission electron microscope (TEM) is a microscopy technique in which a beam of electrons transmitted through a specimen and direct structure and diffraction pattern can be recorded. The specimen is most often an ultra thin section less than 100 nm thick on a suspension grid. The image, then magnified and focused onto an imaging device, is known as a fluorescent screen. Using the TECNAI 200 kV TEM, we obtained images and electron diffraction pattern of these three different samples. Here in this project exfoliation to mono and a few layers is done by sonication process. Sonication means the act of applying sound energy to agitate the particles in the sample. It converts an electrical signal into a physical vibration to break substances apart. Sonication uses ultrasonic waves of 20 kHz. Preparation of the sample is done by using “ultrasonic bath sonicator.” This method uses ultrasonic frequencies of 20 kHz to agitate the sample. Due to weak van der Waals forces between the layers, they layers separate out and we will get the electron transparent sample for TEM imaging. After sonication , we dropped the sample on the holey carbon grid followed by heating under a lamp for 2-3 hours and then images a were recorded in a TEM. This project also includes the analysis of the lattice parameters from diffraction pattern. The analysis contains calculations related to interplanar spacing and the lattice parameters.

Keywords: TMDs, ultrasonication,TEM,lattice parameter, interpalnar spacing,sample

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