R increase at the beginning of the curve about refnx HOT 7 CLOSED

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I can't see that image unfortunately. If the reflectivity is increasing below the critical edge then it might be due to footprint. Are you measuring on an angular dispersive instrument? At small angles only a fraction of the beam is intercepted by the sample, but as the angle gets larger the sample intercepts more of the beam, and so the signal appears to increase.

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Thanks very much for your reply! This explanation indeed makes sense! Is it possible to consider the dispersal? Or we fit the XRR curve after the critical angle.

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refnx currently doesn't do this kind of correction during a fit. However, it is possible to apply footprint corrections to the original dataset, then fit the amended data.

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May I know how to conduct the footprint corrections? It would be very nice if there is any relevant book or website.

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Do you know the beam profile of the X-ray beam? If so, then one can use refnx.util.beamfrac to estimate the proportion of a Gaussian beam intercepted by the sample for different angles. You then divide through the data by that proportion. Once all the beam is intercepted by the sample the fraction is 1.

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Thank you very much! It really helps a lot. I think I can get the beam profile by scanning without a sample.

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