Ultrasmall and Monolayered Tungsten Dichalcogenide Quantum Dots with Giant Spin-Valley Coupling and Purple Luminescence

Kaiyu Zhang; Lin Fu; Weili Zhang; Hongzhe Pan; Yuanyuan Sun; Chuannan Ge; Youwei Du; Nujiang Tang

doi:10.1021/acsomega.8b01125

Ultrasmall and Monolayered Tungsten Dichalcogenide Quantum Dots with Giant Spin-Valley Coupling and Purple Luminescence

ACS Omega. 2018 Sep 28;3(9):12188-12194. doi: 10.1021/acsomega.8b01125. eCollection 2018 Sep 30.

Authors

Kaiyu Zhang¹, Lin Fu¹, Weili Zhang¹, Hongzhe Pan¹, Yuanyuan Sun², Chuannan Ge^{1

3}, Youwei Du¹, Nujiang Tang¹

Affiliations

¹ National Laboratory of Solid State Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing 210093, China.
² School of Physics & Electronic Engineering, Linyi University, Linyi 276005, China.
³ School of Physics & Electronic Engineering, Jiangsu Second Normal University, Nanjing 210013, China.

Abstract

Monolayered tungsten dichalcogenide quantum dots (WS₂ QDs) have various potential applications due to their large spin-valley coupling and excellent photoluminescence (PL) properties. What is expected is that with the decrease in lateral size of QDs, the stronger quantum confinement effect will dramatically strengthen the spin-valley coupling and widen the band gap. However, ultrasmall monolayered WS₂ QDs prepared by ion intercalation unavoidably undergo the problem of structural defects, which will create defect levels and significantly change their properties. In this study, we report that by annealing defective monolayered WS₂ QDs in sulfur vapor, pristine monolayered WS₂ QDs with an ultrasmall lateral size of ca. 1.8-3.8 nm can be obtained. The results show that the ultrasmall monolayered WS₂ QDs exhibit a giant spin-valley coupling of ca. 821 meV. Moreover, the pristine ultrasmall monolayered WS₂ QDs show purple PL centered at 416 nm, and the defect PL peaks in defective WS₂ QDs can be effectively removed by annealing. All of these results afford the ultrasmall monolayered QDs various applications such as in optoelectronics, spintronics, valleytronics, and so on.