In a bold statement that raised questions about a billion-dollar industry, Mike Kelly, professor and nanotechnology scientist at the Center for Advanced Photonics and Electronics at the University of Cambridge, said that structures with a diameter of 3 nm or less cannot be mass produced using a top-down approach. This statement, which appears in a paper published in the Institute of Physics' journal Nanotechnology, raises a major question concerning the billions of dollars that are poured into nanotechnology each year in the hope that the latest technology developed in the lab can make the transition to a manufactured product on the market. Nanotechnology, which is built on the ability to control and manipulate matter at the atomic and molecular levels, has far-reaching applications, including delivering drugs into the body, increasing the efficiency of solar panels, and improving methods of food packaging. The overall goal when entering nanotechnologies into the market is low-cost, high-volume manufacturability, but at the same time, the materials' properties must be highly reproducible within a prespecified limit, which Kelly said cannot happen below the 3-nm limit when trying to make arrays. The top-down approach to manufacturing uses external tools to cut and shape large materials such that they contain many smaller features. Its alternative, the bottom-up approach, involves piecing together small units, usually molecules, to construct whole materials, much like putting together a jigsaw puzzle; this process, however, is too unpredictable for defect-free mass production of arrays. Kelly used statistical evaluation of vertical nanopillars, which have been suggested for uses in sensors and displays, as an example to demonstrate his theory. He states that the proof comes in two stages. The first is the variation in size of various components that results when materials are mass produced on such a small scale. As a result of this variation, the properties of the material will vary to such an extent that it cannot function to full capacity within an array. “If I am wrong, and a counterexample to my theorem is provided, many scientists would be more secure in their continued working, and that is good for science,” Kelly said. “If more work is devoted to the hard problem of understanding just what can be manufactured and how, at the expense of more studies of things that cannot be manufactured under the conditions of the present theorem, then that too is good for science and for technology.” For more information, visit: www.iop.org