Wedge cleaving

Fig. 8. A slice, h cm thick, is cleaved from a solid by pushing in a wedge...

Cleavage of bulk crystals to expose clean, defined lattice planes is possible for brittle substances. Some materials, like mica or highly oriented pyrolytic graphite (HOPG) that exhibit a layered structure, are readily cleaved by just peeling off some layers or using a razor blade. For other materials the so-called double-wedge technique can be used (Fig. 8.8). 

Fig. 4.1. Schematic of cleaving for (a) cross-section and (b) plan-view samples. A final grinding slightly away from the (100) direction with rough sand paper creates many scratches. A sharp wedge is easily formed by cleaving along these scratches.

Even at normal incidence, the transmission spectra may be relatively sensitive. To demonstrate this. Fig. 7.13 shows the vOH band of water adsorbed on NaCl(lOO) at -27°C, which is lower than the freezing point of a saturated NaCl solution, and a pressure of 0.2 mbar (35% RH) [358]. The spectrum was recorded by the multiple-transmission technique. For this purpose, 11 crystals cleaved along the (100) faces of NaCl were collected in a pile with spacers of 0.1-mm Ta wire, so that the NaCl faces did not touch each other. To reduce reflection from the external air-NaCl boundary, wedged silicon windows were attached to both ends of the pile. Comparison of the band position of adsorbed water with that of water in various phases (the top of Fig. 7.13) suggests that at this temperature the adlayer is mostly in the liquid state. On this basis, the surface coverage can be evaluated by introducing the absorption index of bulk water in the modified BLB relationship ... 

Variations of these three techniques are used to make plan-view lamellae. In the methods based on the trench and the lift-out techniques, the samples are cleaved or polished and placed end-on to the EIB. In the methods based on the wedge technique, the wedge is rotated by 90° before being fixed to the side of the TEM grid. 

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