also crystallized in the same hexagonal structure. The average crystallite size was estimated from the most intense XRD peak [(1 0 1)] to be about 33 nm by using Scherrer's formula [23]. Fig. 3 shows the Raman spectra of ZnO nanofibers annealed at 500 1C and 550 1C for 90 min. The strong Raman peak near 437 cm 1 corresponds to Eh2igh phonon mode of wurtzite ZnO and the peak located at 385 cm 1 corresponds to A1-TO mode. The peak located at $581 cm 1 (E1-LO) has been attributed to O-vacancy defects presentin the crystal [24]. The star marked peaks in the figure are due to multiple phonon scattering processes. It can be noticed that except the E2-high peak, the position of the rest shift slightly with increase in annealing temperature. The decrease in the intensity and the broadening of the E2-high peak with increasing temperature indicate a variation in defect concentration with temperature as proposed earlier [24]. It is evident that annealing at higher temperatures reduces the defect concentration in these nanostrucures. The Raman spectra also confirm the existence of a single hexagonal wurtzite phase with no other impurity phase as depicted by the XRD patterns.