Applying grazing incidence X-ray reflectometry (XRR) to characterising nanofilms on mica

Molecularly smooth mica has hitherto not been widely used as a substrate for the X-ray reflectometry (XRR) technique. That is largely due to the difficulty of achieving flatness over a sufficiently large area of mica. Here we show that this difficulty can be overcome by slightly bending the mica substrate over an underlying cylinder; the enhanced rigidity of the bent mica sheet along the axis of the cylinder provides sufficient flatness along this axis for XRR measurements. To test this method, we have employed it to characterise three types of nanofilms on mica in air: (A) Cr-Au thin films; (B) a surface-grown zwitterionic polymer brush; and (C) a Langmuir-Blodgett (LB) phospholipid monolayer, using a table-top X-ray reflectometer. Fitting the obtained reflectivity curves with the standard Parratt algorithm allows us to extract the structural information of the nanofilms (both thickness and apparent roughness). Our simple method points to how XRR may be exploited as a useful characterisation tool for nanofilms on mica.