Figure 3

Controlling layer-by-layer thinning by tuning exposure time. (a) Evolution of layer number (monitored by Raman spectra) with increasing number of scans. For each scan, the laser power is 1.5 mW and the laser exposure time is 0.2 s. The insets show the patterns before and after the 3^rd, 5^th, 7^th, and 13^th laser scan. (b) The AFM image after the 13^th scan. (c) The fluorescence spectra collected before and afer laser thinning. Inset: photoluminescence mapping image at the emission photon energy of 1.8 eV (690 nm) after the 13^th scan. (d) Dependence of the Raman peak interval (between the E_2g and A_1g modes, marking the layer thickness) on the number of laser scans.