Abstract
The use of resonant soft X-ray reflectivity (RSXRR) in s-polarization is presented with the aim to show how far it is possible to go in the understanding the evolution of the refractive index n(E)=1−δ(E)−iβ(E) of a ultrathin polystyrene film when the RSXRR is measured through the C-edge. We evidence that a direct fit to the data provides a very good estimation of δ(E) and β(E) in a large range of energies. Nevertheless, at some specific energy close to C-edge we observe that it is not possible to obtain a satisfactory fit to the data though the same formalism is applied to calculate the reflectivity. We show that even though we take into account the energy resolution of the incident beam, we still end up with a poor fit at these energies. Incorporating the strong contribution of 2nd order photons appeared near C-edge we could not eliminate the discrepancy. Probably the data normalisations have some impacts on such discrepancies at some specific energies.
Highlights
Low energy XRR is presently becoming more and more attractive as recent advancement in soft X-rays facilities provides access to outstanding soft X-ray reflectometers and some of them equipped with polarized dichroism set-ups
On the contrary to classical XRR carried at high energy (E ∼ 10 keV), resonant soft X-ray reflectivity (RSXRR) is performed at an energy close to 285 eV i.e., in the vicinity of the absorption edge of C to take advantage of the very strong anomalous coefficients f (E) and f”(E) of carbon at this energy and in addition of the resonance observed in the near edge X-ray absorption fine structure (NEXAFS) region for molecular compounds
The measured RSXRR curves (Figure 2a) beautifully show the drastic changes that occur when passing through the edge
Summary
Low energy XRR is presently becoming more and more attractive as recent advancement in soft X-rays facilities provides access to outstanding soft X-ray reflectometers and some of them equipped with polarized dichroism set-ups. This development in technology is of particular interest for all the scientists who are working in the field of soft materials such as polymers or biological samples. For such materials, soft X-rays permit to conduct resonant XRR at the C edge.
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