Bottom-up Approach

New bottom-up techniques are being explored as a compliment to traditional top-down methods. In contrast to the removal of excess materials to obtain nanoscale dimensions, bottom-up techniques simply construct the desired features from fundamental building blocks, usually spontaneously through self-assembly without the need for patterning. In the bottom-up approach, materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In molecular recognition, molecules can be designed so that a specific configuration or arrangement is favored due to non-covalent intermolecular forces. Thus, two or more components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.

Bottom-up approaches should be capable of producing devices in parallel and be much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. Nevertheless, there are many examples of self-assembly based on molecular recognition in biology, most notably Watson–Crick base-pairing and enzyme-substrate interactions. The challenge for nanotechnology is whether these principles can be used to engineer new constructs in addition to natural ones, growing these structures in well-designed coordination and fabricating robust structures, etc.