Fig. 1: Optical characterisation of the WS2/WSe2 heterostructure.
From: Confinement of long-lived interlayer excitons in WS2/WSe2 heterostructures
a Illustration of our devices. The SiO2 substrate with nanopillars is in blue, the WSe2 monolayer in red and the WS2 monolayer on top in green. Representative locations on the device are indicated: location L1 is the WS2 monolayer, location L2 is the WSe2 monolayer, location L3 is the flat WS2/WSe2 heterostructure, location L4 is the WSe2 monolayer on a nanopillar and location L5 is the WS2/WSe2 heterostructure on a nanopillar. b Optical image of device A. WSe2 and WS2 monolayers are outlined in red and green, respectively. Scale bar: 4 μm. c Integrated photoluminescence (PL) intensity map of device A under 2.33-eV continuous-wave (CW) excitation at 4 K. Scale bar: 4 μm. d Representative PL spectra under 2.33 eV CW excitation taken at the five locations highlighted in b. The colour coding indicates the origin of PL emission, where green (red) comes from intralayer excitons in WS2 monolayer (WSe2 monolayer), and yellow from interlayer excitons in the WS2/WSe2 heterostructure. In subpanel (i), the PL between 1.3 and 1.5 eV originates from interlayer exciton emission leaking into the detection spot. The multiplicative factors of each PL spectrum are relative to subpanel (iv), WSe2 monolayer spectrum at L4. e PL intensity map under 1.50 eV CW excitation at 4 K, to which only WS2/WSe2 heterostructure regions contribute. Localised PL enhancement and spectrally sharp emission peaks are also seen in device B, for which we choose a smaller stacking angle <7° with respect to high-symmetry alignments (0° or 60°). Scale bar: 4 μm.
