Nanostructures

Design Software for Atomically Precise Nanotechnologies

Computer-aided design of structures on an ordinary scale can ignore atoms, and this is a major simplification. A piece of steel, for example, can typically be treated as a homogenous and isotropic material. The dimensions and angles of a steel component can be chosen freely: With few limitations, a steel plate can be of any thickness, and a smooth groove can be cut across its surface at any angle.

On a length scale of nanometers, however, accurate control of the shape and properties of a component requires precise control of the arrangement of its constituent atoms, and atoms aren’t available in fractional sizes. A smooth plate of a particular crystalline material, for example, can have one of only a limited number of thicknesses, and these are determined by its lattice structure. Likewise, smooth surfaces can exist only at particular angles, the ones that align with lattice planes. The choice of size, shape, and material are interlinked.

In ordinary engineering, the designer chooses the shape of a component. In atomically precise engineering, the designer chooses the way atoms are to be linked (subject to many constraints!), and interatomic forces then choose the shape of the component. Design and modeling become more tightly linked: Rather than using physical models only to evaluate the behavior of a structure of an assigned shape, physical models must be applied earlier, when searching for a structure that will assume an acceptable shape. (I’ll have an update on Nanoengineer-1 in a few weeks.)

What I said above focused on atomically precise structures based on a materials having crystalline order, but these much easier to design than to make. The linkage between design and modeling becomes tighter for theeasier-to-make, harder-to-design structures that are of practical interest today, as I’ll be discussing later.