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Raman spectra were obtained using a confocal Raman microscope system (ProMaker). A solid state laser operating at 532.1 nm was used as the excitation source with a laser power of 20 mW, 6 s exposure time and 30 accumulations. X-ray photoelectron spectroscopy (XPS) was performed using the wide-range beamline (BL24A) of the NSRRC in Taiwan. ................
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