12 - Small-scale structures and “nanoscience”

Summary

Introduction

The atomic nature of matter is well documented and appreciated. Solids are made from regular (in the case of crystals) or irregular (for the example of glasses) arrangements of atoms. Nature finds a way to produce various materials by combining constituent atoms into a macroscopic substance.

Imagine the following hypothetical experiment. Suppose that one builds up, for example, a crystal of silicon by starting with a single atom and adding atoms to make a small number of unit cells, repeating the process until a large enough crystallite has formed. A fundamental question is the following: at what stage in this process, i.e. at what size of the crystallite, will it approximately acquire the “bulk” properties? The precise answer to this question may well depend on what exactly one intends to do with the crystal.

While this may sound like a purely thought experiment, remarkable modern fabrication methods are close to being able to achieve this, using at least two independent approaches. Molecular-beam epitaxy (Figure 12.1) is able to grow high-quality crystalline layers one by one with remarkable control. Atomic-resolution methods are already able to deposit atoms selectively on some surfaces (Figure 12.2).