Abstract
Two-dimensional (2D) transition metal dichalcogenide semiconductors are promising candidates for next-generation nanoelectronics and optoelectronics thanks to their unique lattice structures. They show strong layer-number-dependent properties which may be tailored and harnessed for diverse functionalities and applications. Among various strategies for controlling their optical and electronic properties, external light-irradiation may be utilized in conjunction with a uniform layer of photoswitchable molecules. Diarylethene (DAE), for example, can transform between two configurations, open- and closed-ring isomers under visible and UV light, respectively. In this presentation, we show that optoelectronic properties of monolayer molybdenum disulfide (MoS2) functionalized with a 2-nm-thick DAE layer can be modulated by photo-irradiation and that such photoswitchability depends on the layer number of the TMD. We discovered that photoluminescence emission from monolayer MoS2 is quenched after UV exposure while electric conductivity is enhanced. However, no such changes were observed with two- or three-layer MoS2. Density functional theory (DFT) calculations revealed that hole transfer is facilitated between monolayer MoS2 and closed-form DAE but not with open-ring isomer. In contrast, both bilayer and trilayer MoS2 do not support any charge transfer at the hybrid interface due to the band energy alignment. Of considerable utility is that this scheme can be exploited to control different layer numbers of TMD flakes and that the photoswitchability may also be repeated and cycled. Lastly, we will compare photoswitchable phenomena of MoS2-DAE with those of MoSe2-DAE hybrids and elucidate underlying mechanisms. Given the vast library of photochromic molecules, this approach may be extended to many other 2D TMD families towards photo-controlled 2D optoelectronic devices.