Synthesis of uniform single layer WS2 for tunable photoluminescence

• Published in: Scientific reports 2017-11, Vol.7 (1), p.1-8, Article 16121
• Main Authors: Park, Juhong, Kim, Min Su, Cha, Eunho, Kim, Jeongyong, Choi, Wonbong
• Format: Article
• Language: English
• Subjects: 140/133; 140/146; 639/301/357/1018; 639/925/357/1018; Chemical vapor deposition; Humanities and Social Sciences; Luminescence; multidisciplinary; Optical properties; Photons; Science; Science (multidisciplinary); Thinning; Tungsten
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-16251-2

Two-dimensional transition metal dichalcogenides (2D TMDs) have gained great interest due to their unique tunable bandgap as a function of the number of layers. Especially, single-layer tungsten disulfides (WS 2 ) is a direct band gap semiconductor with a gap of 2.1 eV featuring strong photoluminescence and large exciton binding energy. Although synthesis of MoS 2 and their layer dependent properties have been studied rigorously, little attention has been paid to the formation of single-layer WS 2 and its layer dependent properties. Here we report the scalable synthesis of uniform single-layer WS 2 film by a two-step chemical vapor deposition (CVD) method followed by a laser thinning process. The PL intensity increases six-fold, while the PL peak shifts from 1.92 eV to 1.97 eV during the laser thinning from few-layers to single-layer. We find from the analysis of exciton complexes that both a neutral exciton and a trion increases with decreasing WS 2 film thickness; however, the neutral exciton is predominant in single-layer WS 2 . The binding energies of trion and biexciton for single-layer WS 2 are experimentally characterized at 35 meV and 60 meV, respectively. The tunable optical properties by precise control of WS 2 layers could empower a great deal of flexibility in designing atomically thin optoelectronic devices.