Fig. 2: Straining suspended WSe2 monolayers by electrostatic forces.
From: Strain control of hybridization between dark and localized excitons in a 2D semiconductor
a Schematic of the device and measurement scheme. Applying a voltage VG between a WSe2 monolayer suspended over a hole and the Si backgate mechanically strains the WSe2. We probe the strain by recording PL spectra from a small region at the centre of the suspended WSe2 where the strain is spatially homogeneous and biaxial in nature. b Microscope image of a typical device. Inset: Room temperature PL map of the neutral exciton at 1.66 eV in the unstrained (VG = 0V) suspended WSe2 membrane. c PL spectra as a function of VG at T = 100 K taken with the laser focused at the centre of the device. Selected spectra are shown in (d). Neutral exciton (\({X}^{0}\), 1.738 eV), positively charged trion (\({X}^{+}\), 1.713 eV), negatively charged intervalley trion (\({X}_{T}^{-}\), 1.708 eV), and negatively charged intravalley trion (\({X}_{S}^{-}\), 1.701 eV) appear at the energies close to what is reported in literature for high-quality hBN encapsulated devices 41,43,44,45. Changes in intensity and peak position for −70 V < VG < +70 V closely resemble those in encapsulated devices, showing that charging dominates the device behaviour for this regime. The near-zero VG position of the charge neutrality point and the disappearance of the \({X}^{0}\) peak outside of the −50 V < VG < +10 V region confirm the good optical quality of our samples.
