Figure 5: Illustrating the optical absorption measurement of SiNW arrays along with bulk Si (a) Optical absorption spectrum of p-type Si(111) wafer. (b) Absorption measurement of nanowire arrays using 0.0 2 M Cu(NO3)2 with etching time 1 hour. (c) Absorption image of Cu treated nanowires film using 0.02 M Cu(NO3)2 with etching time 2 hours. (d) Absorbance of nanowires film with etching time 2 hours with 0.05 M Cu(NO3)2.