Raman spectroscopy is also widely applied to investigate the optical properties of nanoscale materials
because of its sensitive probe to the local atomic arrangements and vibrations of the materials
[125]. CuO with a monoclinic structure belongs to the space group of the C62
h and shows three acoustic
modes (Au + 2Bu), six IR-active modes (3Au + 3Bu), and three Raman-active modes (Ag + 2Bg)
[29,125]. A typical Raman spectrum of CuO with different particle sizes is shown in Fig. 65. Three Raman
peaks for sample (a) at 288, 330, and 621 cm1 are observed. The peak at 288 cm1 can be assigned
to the Ag mode, and the peaks at 330 and 621 cm1 to the Bg modes [289]. However, a
decrease in grain sizes results in broader Raman peaks of the samples and a slight redshift, which
are mainly due to the size effects. This phenomenon is widely observed for nanoscale CuO