A Model for Depth-Profiling Structure in Semi-Crystalline Polymers

Semi-crystalline polymers exhibit sharp and distinct X-ray diffraction peaks from the bulk of the material, but this crystallinity seldom extends completely to the surface. Thus, the surface may have properties which differ significantly from those of the bulk. Grazing incidence X-ray methods intrinsically produce diffraction results in which the depth of penetration varies with the Bragg angle theta. In order to use the full diffraction pattern to measure structure vs. depth, we are faced with the problem of deconvoluting this theta dependence. Our model to test theta deconvolution uses neutron diffraction from an iron plate measured through successive layers of aluminum absorbers to simulate the effects of an amorphous surface layer. This experiment was performed in Bragg and grazing incidence geometries to provide maximum path length variation. Surface layers were simulated by 1 to 6 Al plates (5mm each) on the Fe surface. The results of deconvoluting the Fe neutron diffraction spectrum are presented.