Session: Research Posters

Paper Number: 114153

114153 - Non-Linear Behavior of Raman Linewidth of Wse2 

In recent years, abundant studies have been done on the extraordinary properties of graphene and transition-metal dichalcogenides (TMDs). One of the more interesting features which scientists have focused on is the electronic structure of low-dimensional TMDs compared to their bulk phases. The direct bandgap of monolayer TMDs intrigues the possibility of producing two-dimensional (2D) materials and contributes to their optoelectronic application possibilities. Among them, WSe2 is a promising candidate due to high figures of merit such as having a seebeck coefficient as high as 680 μV/K. WSe2 has a layer-dependent trend and as a result has attracted a lot of research on electron transport in WSe2. At room temperature WSe2 shows low thermal conductivity. On the other hand, phonon transport has received less attention and there is too little experimental data that investigates phonon scattering properties in few-layer WSe2. The large gap prediction between the computational data in thermal conductivity of WSe2 samples is an outstanding motivation to do more experimental data on phonon scattering for a few layers of WSe2. Since experimental assessment of the in-plane thermal conductivity of WSe2 is so important to understand the phonon scattering behavior of this 2D material. In this work, we focused on the Raman spectra of WSe2 and studied the full width half Maximum (FWHM) of each spectrum to bridge the gap between the theoretical prediction and experimental data.

We have performed experimental investigation on the FWHM of WSe2 at varying temperature conditions. Bulk crystals of WSe2 were mechanically exfoliated onto Si/SiO2 to form the few layer of WSe2. Raman spectra were obtained through a 514 nm laser with the low power intensity to avoid overheating and damaging the flakes. Theoretical calculations for linewidth were performed with through Matlab to fit the Lorentzian, semi-quantitative, and Kelemens model to our experimental result. Our data focuses solely on the in-plane E2g1 mode as the A1g mode had a very low intensity and contributed no significant data. Measurements for WSe2 Lorentzian fit FWHM at a temperature range of 100K to 500K were obtained through experimentation rather than theoretical calculations and simulations. Results show that the temperature dependent FWHM is actually a combination of both anharmonic phonon-scattering and lattice thermal expansion. Past works have failed to cite the lattice thermal expansion as a contributing factor, resulting in an inaccurate linear fit. Understanding that both these processes are key contributors to the FWHM of WSe2 yields a more accurate non-linear fit for our data. Our future work consists of similar experiments and analysis of temperature dependent FWHM of other two-dimensional materials. This work will shed light on discovering the fundamental mechanisms of phonon dispersions in 2D materials.

Presenting Author: Elham Easy Stevens Institute of Technology

Presenting Author Biography: PhD student at Stevens Insitute of Technology.

Authors:

Elham Easy Stevens Institute of Technology
Xian Zhang Stevens Institute of Technology