hno 3 and h 2 so 4 as described in wue p et al surf interface anal 36 497 500 2004 the morphology of the nanofibers was examined by means of sem fig4 a shows the nanofibers in the untreated state the existence of nanosize iron oxide particles which have been embedded in the surface of the nanofibers in the etched samples can be observed fig4 b the spherical etching pits are clearly visible after the iron particles have been removed by washing with acid fig4 c the transmission electron micrograph shown in fig5 a demonstrates the embedding of the iron nanoparticles due to the etching process the surface roughness was increased considerably by etching as the transmission electron micrographs after washing out of the iron nanoparticles show fig5 b c in addition the damage to the wall of the nanofibers can be seen in the high resolution tem shown in fig5 d a spherical hole has been etched into the nanofiber obviously by the outer walls being removed successively the etching over a short period of time results mainly in surface defects without any appreciable changes in the materials properties being observed on the other hand the materials properties can be altered significantly by lengthening the etching time fig6 shows the result of x ray diffraction xrd on nanofibers which have been etched for more than one hour compared to the untreated nanofibers the signal intensity.