If XRR spectra is taken of the multilayers thin film, say, before and after annealing; then how to compare it? what type of changes are expected if there is interface diffusion or interface sharpening?
Well, in principle you are able to extract from XRR measurement the (electron) density profile in the direction perpendicular to the multilayer and the corresponding roughness. Following the annealing, several things can happen: a new layer of different density appears, the roughness changes, the thickness of the layers changes (gets consumed to form the interface layer), ... Also the critical angle can change if a different density (top) layer is formed. All these should thus reflect into a change of the XRR signal measured. There are several fitting programs to fit reflectivity curves. If you know the
initial structure (have a good fit of your initial sample XRR measurement), you can slightly tune the structure playing with interfacial roughness or introduce extra interface layers (different density) to fit the XRR data of the annealed samples.
You can quickly see such effects you asked using:
http://henke.lbl.gov/optical_constants/multi2.html
It allows to calculate the XRR (varying the energy or the incident angle) from a multilayer playing with different parameters like materials, roughness, interdiffusion thickness
Regards, Cristian
I agree over most of the points to Christian....like formation of a new interfacial layer of different density or surface roughness due to annealing and of course in principle that will change the XRR pattern. However investigating the real change by fitting the XRR data could be extremely tricky. Already two/three materials of different densities and thicknesses will produce two/three oscillations and the critical angle will arise from contributions of different layers. Now any interface state which is few unit cell thick, should produce only a very small effect on critical angle and period of oscillation and could already be in the range of error margin for fitting. Only if the interface roughness increases too much due to annealing and the oscillation is totally or partially destroyed due to this rough interface, you can expect to see a big change in the XRR pattern. In my opinion a cross sectional TEM could be more helpful in determining the real interface state due to annealing.
I do agree with both answers above. Of course XRR can give you the information of the interface diffusion (roughness) once you are able to extract the electron density profile normalized to the surface. But then this part is extremely tricky. How? You can mathematically get the best fit with several models which you think they are scientifically logical. But you do need a microscopy or any complementary characterization to visualize, at the same length-scale you wish, to confirm/identify the best model fit in your X-ray refinement.
I agree with the above posts. However, at XRR energy the optical constants of the newly formed interlayers might not be easily identified, i.e. optical properties in X-ray energy don't change much from the parent material to the new compound. I use EUV instead of XRR as the sensitivity to optical response is much better than XRR. you can still take thickness values from XRR thoguh.
- Badges
- Science topic
- Similar topics
- Linguistics
- Composition Studies
- Publication