Center-cross pattern

Some crystals exhibit a texture called a center-cross pattern, the origin of which was, at one time, a subject of controversy, as to whether the origin was by growth or by plastic deformation. The center-cross pattern is schematically illustrated in Fig. 9.12 it corresponds to a texture shown by the growth sectors of two coexisting crystal faces, lll and 100. This pattern indicates that the arms of the cross correspond to the growth sectors of 100, which disappear at the later stage of... 

Figure 9.12. Growth sector showing a center-cross pattern formed by the growth of smooth 111 and rough 100 interfaces.

The shape and size of the devices to be bonded define dispensing patterns. Patterns for square die are simpler than for rectangular die, and patterns may vary within each category as die size increases. Simple dot dispense patterns are used for small square die (less than 5 mm per side), but the volume must be estimated so that the circular area of the adhesive will spread to the edge of the die and produce a fillet. Square die, larger than 20 mm per side, still require a center dot, but must also be supplemented with a cross-pattern and other dots in order for the adhesive to flow uniformly (Fig. 4.8). The lines should extend far enough so that, once the die is placed, its bonded surface will be completely covered. Typically, this involves... 

Fig. 68. (a) Body-centered tetragonal ThCr Sij type crystal structure. Spheres without pattern, with simple cross pattern and with complex pattern show the Th, Cr and Si atoms, respectively (b) Brillouin zone of the body-centered tetragonal crystal lattice for da > /2. The rectangular parallelepiped which is equivalent to the Brillouin zone is indicated by the dashed lines. 

Fig. 16.1. He scattering pattern of reconstructed Au(lll). Schematic representation of the full diffraction pattern. The crosses indicate the diffraction peak locations expected for the unreconstructed surface. The center spots D and K are off by AG=0.054 A, which is larger than the bulk value 2.515 A, indicating a contraction in this direction. The spot sizes [except the (112) groups] are proportional to the intensity. (Reproduced from Harten et al., 1985, with permission.)...

RGURE 8-14 X-ray diffraction pattern of DNA. The spots forming a cross in the center denote a helical structure. The heavy bands at the left and right arise from the recurring bases. 

---