Idus 401

A hBN-encapsulated WSe₂ monolayer was obtained by sequentially transferring a bottom hBN flake, ML WSe₂, and top hBN flake, which were mechanically exfoliated from bulk crystals, onto a quartz substrate [14 (link)]. In the PL experiments, an objective lens with a numerical aperture of 0.5 was used to collect PL signals and to focus the laser beam onto the sample with a spot size of about 1 μm. The spot size was measured by both the knife edge method and charge-coupled device (CCD) intensity. The collected emission was sent to a spectrometer (Acton Research Corporation SpectroPr-275) equipped with a thermoelectrically cooled CCD (Andor iDus 401, Abingdon, UK). The sample was kept at a temperature of 80 K inside an optical cryostat (Linkam Scientific, Tadworth, UK), in which motorized motion was used to enable spatially resolved PL mapping. Laser power was in the range 50–300 μW. In the PL excitation measurements, we used a home-built broadband Ti:sapphire laser that covers a wavelength range of 660–980 nm.

A WITec Alpha300R+ confocal Raman microscope equipped with a Zeiss W Plan-Apochromat VIS-IR 100×/0.9 objective, a 785 nm excitation diode laser (Toptica, Munich, Germany), and an UHTS 300 spectrometer (WiTec, Ulm, Germany) using a −75 °C cooled CCD camera (ANDOR iDus 401, Belfast, UK) was used. A fiber with 100-μm diameter was used as a pinhole.

The measurements
were performed using a bespoke Raman system consisting of a monochromatic
laser (HeNe, ThorLabs) with a beam splitter and a long-pass filter
(RazorEdge, Semrock), an inverted optical microscope (IX71, Olympus),
a spectrograph (SP-2300i, Princeton Instruments), and a CCD camera
(iDus 401, Andor).^{55 (link),68 (link)−70 (link)} A 50×
objective was used to focus the laser (532 nm wavelength, 5 mW incident
power regulated by an attenuator) and collect the Raman and fluorescence
signals with an exposure time of 2 s in an accumulation mode (10 accumulations).
The CCD camera was calibrated over the spectral window using the Raman
spectrum of toluene. To take spatial variability into consideration,
an average signal from 10 different spots on the sample was reported.