I have performed exfoliation experiments with an ultrasonic tip, dissolved MoS2 in DMF and conducted the ultrasonication for 12 hours. I obtained a yellow liquid, which I would expect to have suspended nanosheets. When I go to the Raman spectrometer I do not get characteristic peaks of the material, just noise. I have prepared the sample by dripping a little of the liquid on a SiO2 substrate and placing it in an oven at 66 ° C for 12hrs then I take it to the Raman. Any observation that I am doing wrong or any suggestion? Attached image of my obtained spectra. NOTE. I made measurements with lasers of 532 and 633 nm. I also made measurements to the solid that I precipitated (without exfoliating) and there gave me signals.