(Invited) Deformation of 2D Semiconductors By Interfaces with Organic Materials

Abstract

2D semiconducting materials gather attention for realizing atomically thin optoelectronic devices and a platform for emerging quantum phenomena. Especially monolayer 2D materials are fascinating because of their ultrathin crystalline structure with various physicochemical characteristics such as direct-band gap and asymmetric crystalline structures. In this presentation, I will show our recent results related to the deformation of transition metal chalcogenides (TMDCs) morphology by interfaces with organic materials.The mechanical exfoliation method is a simple method to prepare TMDCs and has been widely applied in many research studies. However, the exfoliated TMDCs on substrates show a bunch of bulk flakes and very few target monolayers. In the worst case, the exfoliated monolayer is surrounded by bulk flakes and is difficult to apply for fabricating devices. We developed a method of selectively removing bulk flakes, furthermore, isolating monolayer TMDCs on substrates. The method uses ultrasonication in organic solvents with a consideration of surface chemistry. Surprisingly, bulk flakes are selectively removed, and the adjacent monolayers can be effectively isolated on substrates. [1]Monolayer TMDCs show emission properties because of their direct-band gap nature. The emission strength, e.g., photoluminescence (PL) intensity, is often low. The limitation factor includes various parameters, for example, the over-carrier concentration is one limiting factor in sulfur-based compounds (MoS2 and WS2). So far, p-type doping to reduce the electron concentration is demonstrated to enhance their PL intensity, however, the method is not applicable to selenium-based compounds, such as MoSe2 and WSe2. In addition, a universal method to enhance PL intensity for the selenium-based compounds is still few. We found a general PL enhancement method for both sulfur- and selenium-based compounds, MoS2, WS2, MoSe2, and WSe2, by applying a hydrocarbon, paraffin. The method simply uses paraffin on the surface of TMDCs. I would show the details of the results and methods in the presentation. [2]REF:[1] T. Nakamoto, et al., " Selective isolation of mono to quad layered 2D materials via sonication-based solution engineering", ChemRxiv, 2022, DOI: 10.26434/chemrxiv-2022-lgp8l[2] T. Nakahara, et al., " Spontaneous crystal fluctuation in hydrocarbon polymer–coated monolayer MoS2, MoSe2, WS2, and WSe2 with strong photoluminescence enhancement", ChemRxiv, 2023, DOI: 10.26434/chemrxiv-2023-gxzqw