Simultaneous generation of direct- and indirect-gap photoluminescence in multilayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>MoS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> bubbles
Hailan Luo, Xuanyi Li, Yanchong Zhao, Rong Yang, Lihong Bao, Yufeng Hao, Yu-nan Gao, Norman N. Shi, Yang Guo, Guodong Liu, Lin Zhao, Qingyan Wang, Zhongshan Zhang, Guangyu Zhang, Jiatao Sun, Yuan Huang, Hongjun Gao, Xingjiang Zhou
Abstract
Transition metal dichalcogenide (TMD) materials have received enormous attention due to their extraordinary optical and electrical properties, with ${\mathrm{MoS}}_{2}$ being one of the most representative examples. As the thickness increases from monolayer to multilayer, the photoluminescence (PL) of ${\mathrm{MoS}}_{2}$ is gradually quenched due to the direct-to-indirect band gap transition. How to enhance PL response and decrease the layer dependence in multilayer ${\mathrm{MoS}}_{2}$ remains a challenge. In this work, we report simultaneous generation of three PL peaks at around 1.3, 1.4, and 1.8 eV on multilayer ${\mathrm{MoS}}_{2}$ bubbles. The temperature dependent PL measurements indicate that the two peaks at 1.3 and 1.4 eV come from phonon-assisted indirect-gap transitions while the peak at 1.8 eV comes from the direct-gap transition. The weakening of interlayer coupling on multilayer ${\mathrm{MoS}}_{2}$ bubbles, which may account for the emergence of PL peaks, is confirmed by the low-frequency Raman spectroscopy. Using first-principles calculations, the band structure evolution of multilayer ${\mathrm{MoS}}_{2}$ under strain is studied, from which the origin of the three PL peaks of ${\mathrm{MoS}}_{2}$ bubbles is further confirmed. Moreover, PL standing waves are observed in ${\mathrm{MoS}}_{2}$ bubbles that create Newton-Ring-like patterns. This work demonstrates that the bubble structure may provide new opportunities for engineering the electronic structure and optical properties of layered materials.