Tutorial:Various exercises

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1a The intense rod in the center (qy=0) is the "specular rod", which essentially comes from the reflection of the surface. The rod has oscillations that encode the x-ray reflectivity of the surface: i.e. the oscillations encode the structure of the material in the film-normal direction. (E.g. they represent the film thickness.) The specular rod can be analyzed to determine film thickness, film roughness, etc.

1b The peak comes from some kind of in-plane structure. The qy position tells you the spacing of the structure. Because the peak is a streak without any particular vertical structure, it must mean that the thin-film nanostructure is purely 'in-plane' and not '3D'. In this case, it's a block-copolymer monolayer. There are no layers in the vertical direction; hence no peaks along qz.

2a The "weird stuff" at the top of the image is a detector artifact. The detector became saturated (over-exposed), and so this generates a 'ghost' in another part of the image. In the lower part of the image (near the direct beam), you can see some intense scattering (red) surrounding some areas where the intensity is incorrectly reported as 'zero' (blue areas). This is the saturation, which is duplicated in the top of the image. This artifact only happens with some kinds of detectors (it happens with CCDs, but not with, e.g. pixel-array detectors).

2b There are "lots of peaks" which must mean that the realspace-structure is exceptionally well-defined. The higher-order peaks become extinguished by disorder. The fact that you can see up to 10+ orders means this is a really nice structure! In fact, it is a line-grating made with electron-beam lithography. So the repeating structure is preserved coherently over very large distances.

3a The diffuse ring in the image must come from some kind of fairly disordered structure (since it's broad, and there are no higher-orders). Because this ring is appearing in the wide-angle, it must be from a fairly small-scale structure. In this case, it's the semi-crystalline packing of a polymer. (If the crystallization were better, the ring would be sharper.)

3b The high background is "diffuse scattering", which indicates that there must be some kind of highly disordered structure (which has no well-defined preferred length-scale). In this case, it's because the sample had CNTs dispersed within it, forming fractal structures.

3c The weird black shapes on the right of the image are actually the shadow of a beam obstruction! During the experiment, the sample was placed too close to the edge of the sample-holder, and so one of the screws on the sample-holder showed-up in the experiment. That is literally the shadow of a screw-head and some washers. This is a good reminder of what can go wrong during a measurement!

4a The large number of peaks indicates that the material is crystallized. The peaks are fairly broad, so the crystallites are not so large. But, we see lots of higher-orders, so the crystal unit cell must be quite well-defined. Also, since we see distinct peaks, instead of isotropic rings, this means the material must be oriented with respect to the film normal. This is a small-molecule material: clearly during film casting, it crystallized with a preferential direction. How would we analyze this sample? It depends what we want to know! We could take linecuts across particular peaks to determine grain size. Or we could take linecuts along arcs to determine the orientation distribution. Or we could try to index all the peaks, to determine the unit cell of the material.