Structural studies of mesoporous alumina membranes by small angle X-ray scattering

Small-angle X-ray scattering (SAXS) has been used to study the structures of mesoporous alumina membranes. These membranes, produced by anodic deposition, have an arrangement of parallel cylindrical pores centred on a disordered hexagonal lattice. The SAXS intensity profile varies over five orders of magnitude, and is a convolution of a structure factor for the 2D distribution of pore axes with a cylinder form factor for the pores. Rotation of the plane of the membrane changes the pattern from a ring structure for channels parallel to the X-ray beam to a set of vertical spots for channels perpendicular to the beam. The oscillatory pattern changes systematically with the anodic deposition voltage, confirming a linear relationship between voltage and pore separation. Initial results are also reported for alumina membranes containing cobalt nanowires in the pore volume. The SAXS technique complements and extends direct-imaging methods such as electron microscopy, which view only the surface structure for a limited area of the sample. The results indicate that the membranes show greater disorder than normally deduced from other techniques.