As shown in Fig 1A and 1B, MoS2 nanosheets (MSNs) were found to present as flower-like flakes that showed a layered crystal structure. It has been reported that MSNs seemed to become transparent when the layer number decreased, since the MSNs became thin enough for light to pass through . Herein, we also found that some parts of the bulk MSNs looked transparent (Fig 1A and 1B, indicated with red circles and arrows), since some of the MSN flakes were very thin. We further characterized the chemical components of the MSNs we used. The EDS results indicated that the MoS2 samples only contained sulfur and molybdenum atoms without any significant impurities (see Fig 1C and S1 Table). Raman spectroscopy has been widely applied to characterize the structural properties of MSNs and it has been possible to determine the number of layers, as the vibrational spectrum is sensitive to sample thickness and by inference, to the number of layers . In our work, the MSNs were thus further characterized by Raman spectroscopy (Fig 1D). As shown in Fig 1D, the Raman spectrum of the MSNs had two prominent peaks (383 cm-1 and 409 cm-1), corresponding to the in-plane (E12g) mode and the out-of-plane (A1g) mode, respectively . The spacing between the E12g and A1g modes was about 26 cm-1, which suggested that the used MSNs were composed of bulk MoS2 [14, 33].