Topographic methods

In this chapter we introduce high resolution diffraction studies of materials, beginning from the response of a perfect crystal to a plane wave, namely the Bragg law and rocking curves. We compare X-rays with electrons and neutrons for materials characterisation, and we compare X-rays with other surface analytic techniques. We discuss the definition and purpose of high resolution X-ray diffraction and topographic methods. We also give the basic theory required for initial use of the techniques. 

The essence of the topographic methods is that they map the interrsity of the diffracted beam over the surface of the crystal. Defects affect the diffracted intensity, so give contrast in the image. The methods are quite sertsitive enough to reveal individual dislocatiorrs, precipitates, magnetic domains and other long-range strain fields but cannot reveal point defects except in dense clusters. 

Lead optimization usually requires smaller libraries, containing some 100-1000 compounds in larger amounts (micro, or better, millimolar quantity). As topographical methods (parallel synthesis) are usually used, compounds do not need tagging and their structure is unambiguously identified by their co-ordinates. They are referred to as focused or optimization libraries. 

Fig. 8. Three X-ray topographic methods (a) back-reflection Berg-Barrett, (b) transmission Berg-Barrett, (c) Borrmann anomalous transmission. In the Laue case X-ray interferometer (d) two coherent beams are produced by the beam splitter the transmission mirror recombines the beams to form one interference pattern at the analyzer.

Surface and interphase characterization by spectroscopy (Auger, X-ray photoelectron, secondary ion mass [Surface chemical analysis ISO 17560 Surface Energy ASTM D5946 Surface Resistivity ASIM D257, IEC60093]), and topographic methods [Surface imperfections ISO 8785]. ... 

Figure I represents a two-dimensional damage distribution of an impact in a 0/90° CFRP laminate of 3 mm thickness. Unlike in ultrasonic testing, which is usually the standard method for this problem, there is no shadowing effect on the successive layers by delamination echos. With the method of X-ray refraction the exact concentration of debonded fibers can be calculated for each position averaged over the wall thickness. Additionally the refraction allows the selection of the fiber orientation. The presented X-ray refraction topograph detects selectively debonded fibers of the 90° direction.

Heights determined by these methods should be regarded as a guide rather than as a mathematically precise decision. The conclusions may need to be modified in the light of particular local circumstances such as valleys, hills and other topographical features. 

Each "tool" has a unique footprint or wear pattern that is a function of its diameter. This wear pattern is eonvolved with the topographic map of material to be removed to create the raster pattern with a dwell time at eaeh raster position. In some implementations, these dwell time methods work very well. A faetor of 10 improvement in surfaee figure is common for the ion beam and MRP methods but there are some definite issues as well. 

Other noncontact AFM methods have also been used to study the structure of water films and droplets [27,28]. Each has its own merits and will not be discussed in detail here. Often, however, many noncontact methods involve an oscillation of the lever in or out of mechanical resonance, which brings the tip too close to the liquid surface to ensure a truly nonperturbative imaging, at least for low-viscosity liquids. A simple technique developed in 1994 in the authors laboratory not only solves most of these problems but in addition provides new information on surface properties. It has been named scanning polarization force microscopy (SPFM) [29-31]. SPFM not only provides the topographic stracture, but allows also the study of local dielectric properties and even molecular orientation of the liquid. The remainder of this paper is devoted to reviewing the use of SPFM for wetting studies. 

Fig. 12 AFM images of a hybrid inorganic-organic xerogel formed via cothermolytic TMP methods using Zr[0Si(0 Bu)3]4 and (EtO)3SiCH2Si(OEt)3. The left image shows a topographical view while that on the right is a top view...

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