Wieligor and coworker stress the role of the laser power. "Silicon carbide is a material that effectively absorbs light, including the incident laser light. During this process the sample's temperature increases and this may cause frequency shifts. This effect may overlap with shifts due to other effects and must be separated. … To reduce laser induced heating effects, during" their studies, Wieligor and coworkers "applied a very small laser power of 0.01 W, and to collect spectra of high signal to noise ratio" they "used long exposure times." . Moreover, Wieligor and coworkers observe that "with decreasing grain size the intensity of the Raman lines of SiC was decreasing, the LO and TO peaks became increasingly broader and asymmetric, and their frequency shifted". The researchers also remember that , "observed asymmetric broadening of Raman lines and frequency shifts when the crystal size was decreasing. They explained these effects in terms of the phonon confinement model". Nemanich and coworkers investigated BN microcrystalline samples.