Understanding Solvent Effects on the Properties of Two-Dimensional Transition Metal Dichalcogenides

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have emerged as attractive direct bandgap semiconducting materials with remarkable properties. Recently, TMDC-based electronic and optoelectronic systems have been demonstrated with various chemical doping and functionalization approaches for modulating their physical properties and enhancing device performances. However, the dependence of intrinsic properties of TMDCs on diverse solvents, which are used necessarily in fabrication processes and chemical doping, remains largely unaddressed. Here we report a charge transfer mechanism in TMDCs by commonly used solvents such as chloroform, toluene, acetone, and 2-propanol, which significantly changes the physical properties of monolayer MoS2 and WSe2. We find that the relative difference in electronegativity between solvents and TMDCs drives the transfer of electrons from or to the TMDCs, which results in photoluminescence (PL) enhancement or quenching depending on the change of carrier density in TMDCs. The analysis of exciton and trion spectral weights in MoS2 as a function of solvent electronegativity provides evidence of charge transfer. Finally, conductive atomic force microscopy (C-AFM) on TMDCs before and after immersion in the solvents further supports the charge transfer mechanism and resulting changes in carrier density. Our results highlight the importance of selection of solvents for solution-processed 2D TMDC devices and systems.

The influence of two-dimensional organic adlayer thickness on the ultralow frequency Raman spectra of transition metal dichalcogenide nanosheets

“…The PL intensity of 1L AA-MoS 2 nanosheet was greatly decreased more than 90% even after being incubated in acetone environment for 0.5 h (Fig. 1o), which further confirmed the n-type doping of MoS 2 nanosheet by acetone adlayer [7,16]. As the incubation time increased from 1 to 1.5 h, the PL intensity of 1L AA-MoS 2 nanosheet was slightly .…”

“…Meanwhile, the CPD between 1L MoS 2 and SiO 2 substrate was increased to −13 mV as shown in Fig. 1h, indicating the 1L MoS 2 was n-doped by acetone adlayer (referred to as AA-MoS 2 ) [16,29,41]. The thickness of acetone adlayer was further increased to 0.8 nm after 1 h incubation (Fig.…”

“…S20), respectively. In contrast to acetone and ethanol, chloromethane was considered as p-type dopant [16]. As one kind of chloromethane, dichloromethane (DCM) has a saturated vapor pressure of 47.4 kPa at 22°C and is a bit more volatile than acetone.…”

“…In addition to graphene, physisorbed molecules also largely influenced the properties of 2D transition metal dichalcogenides (TMDCs). It has been reported that physisorbed p-type dopants enhanced while n-type dopants decreased the photoluminescence (PL) intensity of single-layer (1L) MoS 2 [7,16]. The photoresponsivity and mobility of MoS 2 nanosheet-based devices were highly influenced by physisorbed adsorbates on MoS 2 nanosheets at ambient condition, such as H 2 O and O 2 molecules [8,20,21].…”

Rapid visualization of grain boundaries in monolayer MoS2 by multiphoton microscopy

“…25). Further, there have been several recent reports about the effects of chemical doping on the optical and electronic properties of MoS 2 (refs 26, 27, 28, 29). These studies show that both chemical doping by various solvents and laser treatment can significantly modify the PL of monolayer MoS 2 .…”