The movement of the stages was controlled by MATLAB codes programmed in our lab. In a typical plasmonic heating scanning, the scanning area was 20 μm x 20 μm with a 40-pixel × 40pixel resolution. The laser expose time at each pixel was 500 milliseconds. The laser power was adjusted with an NDC-100C-4M filter (Thorlabs, Newton, NJ, USA). The Raman spectra were collected using a Princeton Instruments SCT-320 spectrometer with an 1800 lines/mm grating at the same time as the laser-induced plasmonic heating. The peak of Si at 520.4 cm -1 was used as the calibration for all the Raman spectral analyses.