Influence of the substrate material on the optical properties of tungsten diselenide monolayers

Abstract

Monolayers of transition-metal dichalcogenides such as WSe 2 have become increasingly attractive due to their potential in electrical and optical applications. Because the properties of these 2D systems are known to be affected by their surroundings, we report how the choice of the substrate material affects the optical properties of monolayer WSe 2 . To accomplish this study, pump-density-dependent micro-photoluminescence measurements are performed with time-integrating and time-resolving acquisition techniques. Spectral information and power-dependent mode intensities are compared at 290K and 10K for exfoliated WSe 2 on SiO 2 /Si, sapphire (Al 2 O 3 ), hBN/Si 3 N 4 /Si, and MgF 2 , indicating substrate-dependent appearance and strength of exciton, trion, and biexciton modes. Additionally, one CVD-grown WSe 2 monolayer on sapphire is included in this study for direct comparison with its exfoliated counterpart. Time-resolved micro-photoluminescence shows how radiative decay times strongly differ for different substrate materials. Our data indicates exciton-exciton annihilation as a shortening mechanism at room temperature, and subtle trends in the decay rates in correlation to the dielectric environment at cryogenic temperatures. On the measureable time scales, trends are also related to the extent of the respective 2D-excitonic modes' appearance. This result highlights the importance of further detailed characterization of exciton features in 2D materials, particularly with respect to the choice of substrate.

On the impact of Vertical Alignment of MoS2 for Efficient Lithium Storage

“…Above a certain Mo thickness (3 nm), the preferential growth in vertically aligned has been reported for no more than 25 nm thick MoS 2 29 . VA-MoS 2 has shown stable electrocatalytic activity for the hydrogen evolution reaction (HER) 28, 30, 31 . However, the intriguing question of its performance as an ion-storing device remains unanswered.…”

Advances in Functional Nanomaterials Science

“…Monolayers of TMDs have enough contrast to be identified visually on the transparent substrate, with a few bright spots representing multilayered material or debris (such monolayer systems were subject of a comparative study in ref. [32]. The yellow line indicates a Raman line scan and optical contrast extraction, both not shown here).…”

“…Adapted under the terms of the CC-BY Creative Commons Attribution 3.0 International Licence (http://creativecommons.org/licenses/by/3.0/). [32] Copyright 2017, IOP Publishing Ltd. Lower right inset: Schematic illustration of a possible hybrid functional nanomaterials system for optoelectronics consisting of optically excited core-shell colloidal QDs (nanoparticles) with their 0D excitons (indicated as two-level system with confined electrons and holes, solid and open circles, respectively) deposited onto a sub-nanometer-thin graphene monolayer; adapted under the terms of the CC-BY Creative Commons Attribution 4.0 International Licence (http://creativecommons.org/licenses/by/4.0/). [33] Copyright 2016, Springer Nature.…”

“…Recently, it had been analyzed and discussed how the properties of monolayer TMDs are affected by the surroundings. [32,123,124,[126][127][128][129][130][131] In this context, the impact of the substrate and environment on optical properties of 2D semiconductors and its implications on 2D-systems design were studied by Arash Rahimi-Iman (Philipps-Universität Marburg) and co-workers. Comparative studies used monolayer WSe 2 and heterostructures comprising WSe 2 and hexagonal-BN as primary platform for microphotoluminescence investigations among other spectroscopic studies.…”

“…Comparative studies used monolayer WSe 2 and heterostructures comprising WSe 2 and hexagonal-BN as primary platform for microphotoluminescence investigations among other spectroscopic studies. [32,128,130,131] Naturally, when envisioning devices and structures based on 2D materials, the study of ultrafast charge transfer in 2D semiconductors and heterostructures becomes very important. The significance of ultrafast charge transfer (on the sub-ps scale) and plasmonic hot carrier injection (approximately on the ps scale) in 2D semiconductors or heterostructures will further increase, as it reportedly had led to new photophysical properties, such as correlated fluorescence blinking [90] (Figure 6) and charge-induced second-harmonic generation (SHG).…”