Atomically precise manufacturing is the production of materials, structures, devices, and finished goods in a manner such that every atom has a specified location relative to the other atoms, and in which there are no defects, missing atoms, extra atoms, or incorrect atoms. Molecules are atomically precise objects and, as such, are essentialbuilding blocks in atomically precise manufacturing. Novel molecular designs can, themselves, be considered atomically precise products; for example, enzyme-like catalysts can be crafted to accelerate chemical reactions. Beyond synthesis techniques to create single molecules, the key challenge of atomically precise manufacturing is in the assembly of molecular building blocks into larger and more complex objects that are also atomically precise. The two known methods for doing this are self-assembly and positional assembly. Molecules that have been designed or have evolved to bind together, typically along conformal surfaces, will self-assemble under the right conditions. In the production of atomically precise membranes, molecules can arrange themselves on the surface of a liquid and then be chemically bound to each other. Complex atomically precise self-assembled objects are also possible: striking examples include the robot-like Enterobacteria phage T4 and the bacterial flagellar motor. In these cases, free-floating "parts" in solution self-assemble into three-dimensional objects. Self-assembly APM is experimentally accessible today. In non-biological systems, the positional assembly of a single atom to a single molecule was first demonstrated by Ho and Lee at Cornell Universityin 1999 using a scanning tunneling microscope. In this seminal work, a single carbon monoxide molecule on the tip of an STM was moved to a single iron atom sitting on the surface of a crystal and chemically bound by applying electric current. In August 2015, the United States Department of EnergyAdvanced Manufacturing Office invited researchers to their Workshop on Integrated Nanosystems for Atomically Precise Manufacturing to gather information for accelerating the development of APM. "A fundamentally new approach to INFAPM structures and applications, tools, and demonstration is needed to realize the enormous savings potential of atomic-scale, defect-free manufacturing." There are two assembly approaches for achieving an atomic precision. The first approach is tip-based positional assembly using scanning probe microscopes, which would also include Joseph W. Lyding's selective deprotection and atomic layer epitaxial deposition. The second approach is an integrated nanosystems using molecular machine components. "Both approaches have considerable challenges to implementation, including positional accuracy, repeatability, working tip design and synthesis, suitable building block design, transport of molecules to the working tip, and scalability."
