Pattern shapes, effects

Kiihamaki J, Franssila S (1999) Pattern shape effects and artefacts in deep silicon etching. J Vac Sci Technol A17 2280... 

In the powder diffraction technique, a monochromatic (single-frequency) beam of x-rays is directed at a powdered sample spread on a support, and the diffraction intensity is measured as the detector is moved to different angles (Fig. 1). The pattern obtained is characteristic of the material in the sample, and it can be identified by comparison with a database of patterns. In effect, powder x-ray diffraction takes a fingerprint of the sample. It can also be used to identify the size and shape of the unit cell by measuring the spacing of the lines in the diffraction pattern. The central equation for analyzing the results of a powder diffraction experiment is the Bragg equation... 

Effects of Masking Geometry and Process Parameters on Pattern Shape... 

The average d-spacings of the iron diffraction peaks are very close to those of pure elemental iron as indicated in Fig. 2.15. This result is in good agreement with the conclusions reached from the other two methods of structural analysis discussed above. There is one difference, however, between the diffraction patterns of pure iron powder and that of the catalyst, namely, the line shape is significantly and reproducibly different. The theory of paracrystallinity was developed " from this line shape effect, which is the only experimental evidence in support of the idea that the bulk of an active ammonia synthesis catalyst may be different from iron powder. 

The infrared spectra of a set of 2-thiazolylthioureas are reported in Ref. 486. The ultraviolet spectra of l-aryl-3-(2-thiazolyl)thioureas are characterized by two bands of approximate equal intensity around 282 and 332 nm (492). For l-alkyl-3-(2-thiazolyl)thioureas these bands are shifted to 255 and 291 nm, respectively (492). The shape of the spectrum is modified further when l.l -dialkyl-3-(2-thiazolyl)thioureas are considered (491). Fragmentation patterns of various 2-thiazolylthioureas have been investigated (100, 493), some of which are shown in Scheme 158. Paper and thin-layer chromatography provide an effective tool for the analysis of these heterocyclic thioureas (494. 495). 

Various geometric coring patterns ki polyurethanes (171,175) and ki latex foam mbber (176) exert significant influences on thek compressive behavior. A good discussion of the effect of cell size and shape on the properties of flexible foams is contained ki References 60 and 156. The effect of open-ceU content is demonstrated ki polyethylene foam (173). 

What this adds up to is simply the fact that your study of organic chemistry must integrate the general with the specific. You must not only learn general patterns but also how to apply them to specific molecules, and you must also learn the behavior of specific molecules in order to see where patterns come from. These skills can be learned in a variety of ways, but one of the most effective learning techniques is to study models of molecules that duplicate their size, shape, stability, and other chemically important properties. That is where this workbook comes in. 

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