5.2 Nano-Machines

Now we would like to focus on nano-machines. In this case, the use of at least two different materials is unavoidable because we have to deal with movable parts. In our macroscopic world, the design of a simple bearing (which basically can be a drill-hole) and an axle (that can be a cylindrical rod) is not difficult. Both, bearing and axle may consist of the same material. Even if the rod has nearly the same diameter as the drill-hole, the axle is still movable due to the presence of a film of lubricant (water, dirt, air, grease, etc.). If we imagine the same situation at the nanometer realm, both parts would merge together forever.

But there are still other difficulties. Due to the atomic structure, continuous surfaces and shapes are not possible at the nanometer level. Figure 5.5 shows the situation for simple bearings and axles of different diameters. That is, fits for nano-parts, made of crystalline structured materials, like metals or carbon (diamond), have to be designed rather loose.

Figure 5.5: Nano-designing bearings and axles. Tolerances may be kept in a rather narrow range with mechanical engineering, but nano-design allows measures only in certain steps where the step width depends on the according material. Therefore, designing ideal cylindrical shapes and exact fits of axle and bearing is not possible in the nanometer realm.

Rotating parts are of particular interest in connection with nano-machines. The simulation of a rotating nano-structure is quite simple: the first design step is...