X-ray diffuse scattering investigation of PTFE surfaces

Christoforos N. Gravalidis ,  Stergios Logothetidis 

Dept. of Physics, Aristotle University of Thessaloniki, 54 124 Thessaloniki, Greece, Thessaloniki 54 124, Greece

Abstract

The surface properties of PTFE are essential for many applications. Especially, the morphology of the surface is critical in the interaction with other solids or liquids. Thus, X-Rays electromagnetic radiation is appropriate in the study of the topography in short length scales, for example in nanoscale. We present an X-Ray Diffuse Scattering XDS technique which can determine, except for the surface roughness, other issues concerning morphology like distribution of in-plane fluctuations and fractal dimension on the surface. The scattering intensity is calculated under Distorted-Wave Born Approximation (DWBA) and depend on quantities related both to 1st and 2nd order surface statistics like, surface roughness σ, lateral correlation length ξ and “Hurst coefficient” or “roughness exponent” h (0<h<1). There are two different scan types for XDS: rocking scan and off-specular reflectivity using the appropriate modification in the intensity. The samples were prepared by spraying a PTFE dispersion directly on preheated Si wafer, at three different spraying times. Afterwards the samples were annealed into inert atmosphere at 340 o C. 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 XRD. The analysis of the XDS rocking scans gave that the mass density is increased with the spraying time and the roughness 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 is 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.

 

Presentation: oral at E-MRS Fall Meeting 2005, Symposium E, by Christoforos N. Gravalidis
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-29 15:34
Revised:   2009-06-07 00:44