Analysis of vertical alignment and bending of crystalline α-Fe_2O_3 nanowires using normal and grazing incidence x-ray diffraction intensities

摘要

Owing to the increasing importance of orderly placed nanostructures, the following study was conducted on oriented and disoriented nanowires. Use of grazing incidence x-ray diffraction (GIXRD) and normal x-ray diffraction (XRD) as possible tools to assess their alignment is discussed. The property of crystalline nanowires to grow in a preferred direction over a substrate is made use of, in which deviation in diffraction intensities is measured on a group of oriented and disoriented nanowires. We find that the difference is sufficiently large to predict the spread in orientations away from a reference direction. The observed intensity variation is explained using a modeled view of diffraction geometry with different nanowire orientations. An alignment index A_(nw) has been calculated using (110) and (300) peak intensities in XRD and GIXRD measurements. The values were found to be related to the extent of vertical alignment as observed using scanning electron microscopy (SEM). The difference in diffraction geometry and penetration depth between the two techniques is found to give complementary information on the upper and lower portions of the nanowires, respectively. Analysis of the diffraction patterns also shows that bending of these nanowires occurs preferentially about the c axis as compared to bending in other directions. In the present study samples with crystalline α-Fe_2O_3 nanowires grown on pure Fe substrate by controlled thermal oxidation route have been investigated using GIXRD, XRD, SEM and atomic force microscopy. Morphology of the nanowires is discussed briefly.