ABSTRACT
Nature has developed remarkably powerful methods for assembling exceptionally complex objects such as animals and plants from relatively simple initial components. In some respects, this assembly resembles the majority of the manufacturing done by humans in the sense that the fi nal object, such as an automobile, is built up from a number of smaller and simpler components. This is known as bottom-up fabrication. In contrast, many of the smallest and most sophisticated devices fabricated by humans, such as microprocessors (which contain roughly one billion transistors in a <1 cm2 area), utilize top-down lithographic fabrication processes. In this latter case, material is selectively removed from a homogeneous layer similar to the manner in which a sculptor carves a face out of clay. Topdown approaches are prevalent at submicron length scales because of the diffi culty of positioning
and connecting such small components. Yet this is precisely what nature has accomplished for millions of years. The critical feature that enables natural self-assembly is that no external forces or central control are required. Self-assembly occurs spontaneously as a result of innate interactions of the components that cause them to naturally associate into a predefi ned, complex structure. Thus, self-assembly refers to processes in which one simply mixes together sets of smaller components that then form more sophisticated, predefi ned, and desired structures without the need for any external intervention or driving forces.
