Highly Stable Near-Unity Photoluminescence Yield in Monolayer MoS₂ by Fluoropolymer Encapsulation and Superacid Treatment

Abstract

Recently, there has been considerable research interest in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) for future optoelectronic applications. It has been shown that surface passivation with the organic nonoxidizing superacid bis(trifluoromethane)sulfonamide (TFSI) produces MoS and WS monolayers whose recombination is at the radiative limit, with a photoluminescence (PL) quantum yield (QY) of ∼100%. While the surface passivation persists under ambient conditions, exposure to conditions such as water, solvents, and low pressure found in typical semiconductor processing degrades the PL QY. Here, an encapsulation/passivation approach is demonstrated that yields near-unity PL QY in MoS and WS monolayers which are highly stable against postprocessing. The approach consists of two simple steps: encapsulation of the monolayers with an amorphous fluoropolymer and a subsequent TFSI treatment. The TFSI molecules are able to diffuse through the encapsulation layer and passivate the defect states of the monolayers. Additionally, we demonstrate that the encapsulation layer can be patterned by lithography and is compatible with subsequent fabrication processes. Therefore, our work presents a feasible route for future fabrication of highly efficient optoelectronic devices based on TMDCs.

Synergetic photoluminescence enhancement of monolayer MoS2via surface plasmon resonance and defect repair

“…2a also conrms that the TFSI treatment does not affect the morphology of MoS 2 , which is consistent with the previous reports. 20,33 The density of Au NPs of all our samples was about 440 NPs/mm 2 (as shown in Fig. S4 in the ESI †), which is a proper density that could enhance the lightabsorption in MoS 2 as we previously reported.…”

“…47 The high populations of excitons leads to a high biexcitionic recombination, which results in a sublinear dependence of PL intensity with the incident power. 20,33,34,47 In our experiments, the laser power was 3.9 mW and the spot diameter was about 1 mm. So, the power density was about 10 2 W cm À2 , much larger than 10 À2 W cm À2 .…”

“…To obtain higher material performance, improving both the light absorption process and light emission process are vital. So far, many efforts have been made to improve the PL intensity of monolayer MoS 2 , including surface plasmon resonance (SPR) based on metallic nanoantennas, [21][22][23][24][25][26][27][28] nanocavities, 29 doping via chemical treatments, [30][31][32] passivation engineering, 20,33,34 and electrical tuning. 35,36 Among these methods, the PL intensity of MoS 2 monolayer was improved by either enhancing the excitation eld [21][22][23][24][25][26][27][28] or improving the QY.…”

“…35,36 Among these methods, the PL intensity of MoS 2 monolayer was improved by either enhancing the excitation eld [21][22][23][24][25][26][27][28] or improving the QY. 20,33,34 Note, compared to the effect of LSPR of Au NPs, the suspension effect on MoS 2 on Au NPs could be negligible. As reported in previous work that weak enhancement was realized in the condition of MoS 2 on Au NPs wrapped in thick HfO 2 which maintained the morphology of Au NPs and have much weaker LSPR effect, 28 also the results of suspended MoS 2 on thick Al 2 O 3 /Au indicated that a suspension of MoS 2 would not cause a high PL enhancement factor.…”

Light Sources and Photodetectors Enabled by 2D Semiconductors

“…Indeed, large exciton binding energies have been observed for ultrathin layered TMDs such as 1L MoS 2 , WS 2 , MoSe 2 , and WSe 2 . Meanwhile, stable exciton emission with high quantum efficiency in 2D semiconductors prepared by both mechanical exfoliation and chemical vapor deposition (CVD) techniques has been obtained via superacid treatment at RT . Thus, developing highly efficient light‐emitting devices based on 2D semiconductors is practical and promising.…”