Alpha 300r system

The Raman measurements of the TBG samples were performed using many different laser lines, in the near IR, visible and UV ranges, for samples with different twisting angle θ. Experiments in the visible range were performed in a DILOR XY triple-monochromator spectrometer equipped with a N₂-cooled charge-couple device detector, a 1800 g/mm diffraction grating, and using an Ar/Kr with 12 laser lines in the visible range. The NIR Raman measurements were performed on a home-made setup, including an iHR-550 Horiba spectrometer equipped with a liquid-nitrogen-cooled silicon CCD detector. A tunable CW Ti:sapphire laser filtered using tunable laser line filters^{21 (link)} was used for excitation. The scattered light was collected through a ×100 objective (NA = 0.95) using a backscattering configuration. The 3.41 eV Raman spectra were obtained using a Dilor UV Raman spectrometer equipped with a cooled CCD and an argon-ion laser. The laser power on the sample was kept lower than 1 mW with ×40 objective to avoid heating. The Raman spectra at 3.00 eV were obtained using a Jobin-Yvon-Horiba T64000 Raman spectrometer equipped with a cooled CCD with a krypton-ion laser. The laser power on the sample was limited to 0.5 mW with ×100 objective. In the case of G/h-BN heterostructures, the measurements were performed in Witec Alpha 300R system using 633 nm as a pump laser.

For steady-state photoluminescence measurements, the sample was performed on the WITec Alpha 300 R system and excited using a continuous-wave 532-nm laser focused to a spot size of 1.5 μm. The sample temperature was kept at 6 K. The pressure of the low-temperature test system is below 10^–5 pa, and the temperature is cooled by compressing helium gas. When the temperature is stable at 6 K, the PL spectrum test of the sample is carried out. The model of the cryogenic refrigeration system is C04-005-044, which comes from the Cryo Industries of America.

All Raman spectra and maps were taken using a WITec Alpha300R system. The laser excitation wavelength and grating density were 532 nm laser line and 600 mm⁻¹, respectively. The laser beam size was ~500 nm and the laser power on the sample was adjusted to around 0.75 mW to avoid laser-induced heating. Atomic force microscopy (AFM) topography image was obtained using Veeco Digital Instrument Nanoscope III in tapping mode.

Raman measurements were carried out using a WITec alpha300 R system equipped with a He–Ne laser (λ = 633 nm at 30 mW of power) and a high sensitivity back-illuminated Newton CCD camera. An air Olympus MPLAN (50×/0.76NA) objective was used. Time-series spectra were obtained in the 500–3800 cm⁻¹ range by 10 scans with an integration time of 10 s and a resolution of 3 cm⁻¹. Measurements were performed at T = 333 K using a THMS600 Linkam stage with a temperature stabilization of ±0.5 °C within intervals of 300 s. All data were manipulated by performing a baseline correction and cosmic ray removal. The spectrometer's monochromator was calibrated using the Raman scattering line of a silicon plate (520.7 cm⁻¹).

All-optical data were measured on the WITec Alpha 300R system, which has 50× objective lenses and a light spot of nearly 1 μm. Before the optical measurement, the pressure in the cryogenic chamber should be kept below 10⁻⁵ Pa, and then the chamber was heated to 350 K for 20 min to remove the water vapor. Finally, optical measurements were performed on the WITec Alpha 300R Raman system when the sample temperature reached 8 K. The model number of the cryogenic refrigeration system is C04-005-044 from Cryo Industries of America. The excitation light source of the SHG signal was a 1064 nm pulsed laser, and the excitation wavelength of the excitation light source measured by other data was 532 nm (2.33 eV). The angle data shown in Fig. 1e is fitted by a sine function, y = y₀ + A*sin (B*α + φ), where y is the intensity of SHG, y₀, A, B are constants, α is the angle of rotation of the half-wave plate, and φ is a fitting parameter defining the relative orientation of TMD crystal lattices. The twist angle between the two monolayers can be deduced by fitting the resulting function.

To analyze the SERS efficiency of the different AuFoN samples, p-aminothiophenol (p-ATP) was used as a known Raman reporter, which is covalently bound to gold surfaces. To obtain uniformly coated surfaces, the samples were immersed for 24 h in 10^–4 M p-ATP in ethanol solution followed by rinsing the samples several times in ethanol. SERS measurements on the AuFoN substrates made of different-sized PS spheres were performed on a Witec Alpha 300R system, using 633 nm and 785 nm excitation lasers and an objective with NA = 0.4. Laser power and integration times/spectrum were 0.25 mW and 10 s (average of 6 accumulations) for the 633 nm laser, respectively, and 2.62 mW and 6 s (average of 6 accumulations) for the 785 nm laser.