November 2013. Intellectual Merit. Although manufacture of silicon computer chips with increasingly smaller features over the past 30 years has led to the development of ever smaller, faster, and more powerful computers, fundamental physics tells us that for dimensions smaller than about 12 nanometers (12 nm) or about half a millionth of an inch, conventional silicon technology will encounter fundamental limitations. If we are to continue the advance in computing capability beyond 2015, we will need to develop new concepts. Engineers understand how electrons flow through conventional materials primarily through well-known laws such as Ohm’s Law: electrical current equals the applied voltage divided by the material resistance. Although Nanotechnology makes it possible for us to make things of dimensions much smaller than 12 nm, at these dimensions the normal laws for electrical conduction must break down. In order to build useful electronic devices of these nanoscale dimensions, we must develop new understanding. The Columbia Center for Electron Transport in Molecular Nanostructures has been seeking fundamental understanding for how electrons flow through dimensions smaller than 12 nm. Through this understanding we will be able to generate new concepts for electronic computer devices that will allow for continued growth of our computational capabilities. In our research program we have studied electrical conduction in single molecules by allowing them to react in a controlled way with gold atoms at the tip of a tiny gold wire. We have found that, in general, current does not flow very well in these molecules, but our theory does describe the observations well. However based on our research, we have been able to create special molecules that conduct perfectly – that means at the "quantum limit" for conductance – as perfectly as a chain of gold atoms. This discovery provides one key capability for the potential use of single molecules as tiny electronic devices such as transistors. Similarly by reacting molecules with the ends of tiny carbon nanotube electrodes we have measured directly electrical conduction in the molecules. Not only has this second set of experiments yielded additional scientific understanding for molecular conduction, we discovered that a change in the orientation within of a single molecule can change the electrical conduction significantly. Using this observation we discovered that we can detect the presence of a single fragment of DNA, the basic building block of biology. Thus we can use simple and direct electrical conduction measurement to learn details about biological structures. The Columbia Nanocenter was one of the discoverers of graphene – a single sheet of carbon atoms placed in a hexagonal configuration that is only one atom thick. Theoretical physics suggested that electrical current could flow through graphene sheets in a way analogous to the flow of light through air, with electrons moving at a constant speed without any loss. We were amongst the first to verify that this theoretical result can be achieved in our graphene materials, over significant distance. This concept has led us to propose and build new electronic circuits which operate or respond at very high speed. In addition we have discovered in graphene a number of truly new and unusual effects for electrical conduction in the presence of magnetic fields. These experiments may in fact lead to the use of totally new ways to carry out information processing. Broader Impact. The Columbia Nanocenter has provided a basis for major positive impact upon society. The discovery and our experimental work on graphene has created entirely new concepts for electronic devices beyond silicon, including demonstrated devices that function far better than conventional electronics. Graphene devices will become important for the evolution of the electronics industry with applications for computers, but also other high speed electronic components needed for cell phone operation, for advanced radar, and for other technologies impacting our lives. Through our partnership with the Semiconductor Industry Association we are actively bringing these concepts to fruition. Molecular conduction may provide the basis for new kinds of electronic devices including for example direct electrical measurement of DNA structures that characterize disease including cancer. We have generated a new company to explore these opportunities. The Columbia Nanocenter has also made significant impact on higher education, preparing several members of underrepresented minorities as faculty members at leading Colleges and Universities.
