Center for Functional Nanomaterials Seminar

The transport characteristics of nano-electronic devices are determined not only by the electronic properties of isolated nanostructures, but also by the details of contact barriers and parasitic conduction pathways. Because nanoparticle and single molecule devices require the use of nano-scale gaps, a major concern is that the electronic behavior of such devices may be greatly influenced by residual nanoscale metal particles. We have developed a feedback controlled electromigration (FCE) process for creating nanogaps at room temperature, which allows characterization of a bare nanogap before putting a nanostructure into the nanogap. To permit the use of transmission electron microscopy (TEM) to image the gaps, nanogaps are fabricated on free-standing transparent SiNx membranes and are found to be clear of any apparent debris. Real-time TEM of nanogap formation by FCE reveals a remarkable degree of crystalline order. Crystal facets appear during FCE indicating a layer-by-layer, highly reproducible electromigration process that avoids thermal runaway and melting. These high-quality nanogaps are used as electrodes for dielectrophoretic assembly of Au nanoparticles and the resulting devices are characterized by a combination of transport measurements at room temperature and 4 K and by inspection with TEM. To extend the value of FCE, a technique is developed for simultaneously fabricating large numbers of nanogaps in a single processing step in a balanced simultaneous process that utilizes a novel arrangement of nanoscale shorts with resistances <4 Ω between junctions.