Making things is one of the central activities of human life. We spend much of our time fabricating structures of a wide variety of complexities, purposes, sizes, and costs. As a species, we have developed an extensive set of tools and methods for manipulating matter at scales ranging from tenths of nanometers to thousands of kilometers. It is possible, however, to make things a different way: by self-assembly. Defined as the spontaneous generation of order in systems of components, self-assembly is ubiquitous in chemistry as well as in biology, where it generates much of the functionality of the living cell. While self-assembly has yet to be widely used in micro-fabrication, it offers numerous opportunities to:

• Simplify processes
• Develop new processes
• Reduce costs
• Use components too small for robotic manipulation
• Integrate components made using incompatible technologies
• Generate structures in three dimensions and on curved surfaces

Self-assembly describes a general approach to economically assembling atomically precise structures out of atoms and molecules in a pre-defined way with only an initial external input such as heat, light or mechanical agitation. Once initiated, self-assembly processes typically assemble trillions of individual components, such as molecules, into integrated structures possessing specific performance attributes.

The example above shows an extremely thin layer of molecules (‘alkanethiols’) self-assembled onto a metal surface to impart a water beading effect.

It is possible to perform self-assembly on many types of surfaces, such as coatings for glass or textiles which repel water and dirt or prevent corrosion. It can also be performed in solutions, such as polymeric chains which self-assemble as protective sheaths over delicate matter or as intermediaries for the handling of toxic chemicals.

Nano-Terra’s capabilities include two broad categories of self-assembly for both of which our co-founder Prof. Whitesides is a recognized pioneer:

Molecular self-assembly—a recent, but relatively well understood branch of science defined as a process in which nanometer-sized molecules form larger ordered systems; and

Meso-scale self-assembly—an emerging branch of science based on the integration of objects in the micrometer to millimeter size range.

The following image shows an example of meso-scale self-assembly. The image on the left is a plastic substrate with 1500 interconnected ‘receptors’, which was subsequently dropped into a container with water and 1500 silicon cubes. The chemistry on the surface of the cubes and the surface of the receptors was manipulated to make them attract each other over short distances and bond on contact. Gentle shuffling of the container caused the cubes to self-assemble into the receptor sites on the plastic substrate. The four images on the right show a similar approach used to pattern GaAs/GaAlAs LEDs into a cylindrical display in which LEDs were illuminated selectively.

The current top-down manufacturing approach, whereby structures are created, manipulated, and modified by machine, is incapable of offering the combination of complexity and economy of scale that self-assembly demonstrates in nature. Self-assembly offers the promise of waste-free, cost-effective, high-volume production of complex structures with the possibility of error correction at any stage of assembly. While meso-scale self-assembly is still in the early stages of research and development, it, too, promises to play an important role in commercial applications in the near future.