X-Ray diffuse scattering investigation of polytetrafluoroethylene surfaces

We present the X-Ray Diffuse Scattering (XDS) technique which can determine, except for the surface roughness, the distribution of in-plane fluctuations and fractal dimension on the surface. The scattering intensity is calculated using Distorted-Wave Born Approximation (DWBA) and depends on the quantities related both to 1 st and 2 nd order surface statistics like, surface σ, lateral correlation length ξ and Hurst coefficient or roughness h (0 < h < 1). The samples were prepared by spraying a PTFE dispersion directly on preheated Si wafer, at three different spraying times, following by an annealing process. The aim of this work is to study the effect of spray duration on the surface morphology. Firstly, the amorphization induced due to the annealing was observed by X-ray diffusion measurements. The analysis of the XDS rocking scans gave that the mass density is increased with the spraying time and the is almost the same. However, the surface morphology described also by the distribution of the vertical fluctuations, through the correlation length ξ, showed that the narrow distribution was realized at middle, while broad one at long or short spraying times. Furthermore, the surface exponent h, calculated by XDS off-specular scan, is constant and low, meaning that the low smoothness of the surface is not affected by the spraying time.