Ihr550 spectrometer

A single-crystal 2H-type bulk MoSe₂ flake bought from HQ Graphene was measured by micro-Raman spectroscopy. For the Raman measurement, we used 8 different excitation sources: the 325- and 441.6-nm (3.82 and 2.81 eV) lines of a He-Cd laser; the 457.9-, 488-, and 514.5-nm (2.71, 2.54, and 2.41 eV) lines of an Ar⁺ laser; the 532-nm (2.33 eV) line of a diode-pumped-solid-state laser; the 632.8-nm (1.96 eV) line of a He-Ne laser; and the 784.8-nm (1.58 eV) line of a diode laser. The laser beam was focused onto the flake by using a 50 × objective lens (0.8 N.A.) for all excitation wavelengths except for the 325-nm excitation for which a 40 × uv objective lens (0.5 N.A.) was used. The scattered signal was collected by the same objective lens (backscattering geometry) and was dispersed with a Jobin-Yvon Horiba iHR550 spectrometer. Either a 1200-grooves/mm (630-nm blaze) or a 2400-grooves/mm (400-nm blaze) grating was chosen to acquire the best signal to noise ratio. A liquid-nitrogen-cooled back-illuminated charge-coupled-device detector was used, and thin-film interference filters (RazorEdge Filters) from Semrock were used to reject the Rayleigh-scattered light. The laser power was kept at 100  μW for all the measurement to avoid local heating of the sample. The spectral resolution was below 1 cm⁻¹.

The surface morphology of graphene and GaN films were measured by SEM (Jeol-7500F) and AFM in tapping mode (Bruker Dimension ICON-PT). Raman spectroscopy (Renishaw inVia, 532 nm laser excitation) was performed to characterize the quality of graphene and the stress state of GaN films. The chemical states of graphene were measured by an ESCALab 250 Analytical XPS spectrometer with a monochromatic X-ray source (Al Kα, hν = 1486.6 eV). The binding energies of the spectra were referred to that of the C 1s peak at ~284.8 eV. The crystalline quality of GaN films characterized with a Rigaku Ultima IV XRD with Cu Kα radiation (0.154056 nm), and the structural properties of GaN films were investigated by aberration corrected Thermo Fisher Scientific Titan Cubed Themis G2 transmission electron microscope operated at 300 kV and equipped with Bruker Super-X EDX detector. The PL spectra of InGaN/GaN MQWs were measured by a PL system which includes a He-Cd laser (325 nm, 30 mW) as an excitation source, a Jobin Yvon iHR550 spectrometer, a Syncerity charge coupled device (CCD) and a closed circle helium cryostat.

Variable-excitation
energy PL
measurements were acquired with an Edinburgh Instruments FLS980 photoluminescence
spectrometer at wavelengths of 250 and 275 nm. Confocal PL data was
acquired with a Horiba-Jobin-Yvon iHR550 spectrometer with an excitation
wavelength of 405 nm.