Preparing Substrates for Thin-Film Applications

Conversion of the boule into polished substrates requires several operations. The exact number and type of steps involved in this process depend on the material involved and the application for the substrates. The following sequence would be typical for the preparation of singlecrystal substrates of ceramics. 

18 GROWING NANOWIRES AND NANOTUBES BY VAPOR-LIQUID-SOLID AND NOT 

There is great interest in growing single crystals that are smaller than lOOnm in one, two, or three dimensions. The techniques being used are variations on those listed above but deserve separate mention because of the special features involved. The detailed mechaiusms involved in the growth are not fully understood. The essential feature is that the substrate is small. 

The VLS technique has probably attracted most attention. Essentially this is an extension of that used by Wagner and Ellis to grow the original Si whiskers, which were themselves nanowires. Vapor-liquid-solid growth of 

FIGURE 29.19 (a) Graphene sheet illustrating how carbon nanotubes are formed, (b) TIO2 nanotubes, (c) and (d) IrOj nanotubes. 

---