These fibers were randomly distributed on the
substrate to form a thin mat and their lengths could reach
several centimeters. The diameter of these fibers was
found in the range of 700 nm to 1 m. After annealing
the sample in air at 600 ÛC, the PVP was removed, and a
well-defined fiber texture kept unchangeable, but the
fibers exhibited shrinkage and diameter was reduced
(Fig. 1b).