As the current silicon complimentary metal-oxide-semiconductor (CMOS) technology continues to increase the speed, capacity and computational power of modern computers, it approaches the fundamental limit at which processors can no longer be made smaller, faster and cheaper. This collaborative project will investigate single-molecule electronic devices as fundamental building blocks for molecular nanocomputing, an emerging technology for the next generation of information systems beyond CMOS integrated circuitry. By bringing together the complimentary expertises in organic synthesis (the Yu group at the University of Chicago), device fabrication and electrical characterization (the Tao group at the Arizona State University), and nanoscale theory/modeling (the Oleynik group at the University of South Florida) into a synergistic effort, the team will focus on the development of innovative computer technologies at the atomic and molecular levels using fundamental principles of nanoscience and engineering. This high-risk, high-return area of research promises revolutionary advances in developing faster and smaller computer chips beyond conventional silicon CMOS technology.
The research program includes three major thrusts: (1) to synthesize new "designer" molecules that will function as diodes, transistors, switches and information storage elements and with the help of theory/modeling to establish a structure/property relationship between a molecule's chemical nature and resulting electronic properties. (2) to assemble these "designer" molecules into nanocircuitry using STM, conducting AFM, and electrochemical break junctions for electrical characterization of single-molecule devices, and to control the electron transport in these molecules using electrochemical gating combined with the guidance from theory. (3) to develop fundamental operational principles of specific molecular devices using the theory of electron and hole resonant tunneling conduction, and to investigate molecule/electrode contacts, negative differential resistance switches, molecular field effect and bipolar transistors. The tightly coupled, vertically integrated research and educational activities will provide a unique opportunity to nurture the next generation of scientists and engineers who will put the science beyond Moore's law into practice.
This NSF grant explored fundamental science of novel single-molecule electronic devices including single-molecule diodes, transistors, switches, molecular memory, and logic elements, designed at the level of atoms with the goal to control, manipulate and harness quantum phenomena, thus advancing science beyond Moore’s law. The USF team developed theoretical foundations of molecular electronics, which include theory and modeling of charge and heat transport through molecules. The fundamental mechanisms of heat and charge transfer, established in this project were used to obtain structure-property relationship by calculating current-voltage characteristics of specific molecules, and to provide guidance for experimental teams concerning the structures that exhibit desirable diode, transistor or switching effects. Our experimental collaborators from the University of Chicago and Arizona State University focused on the synthesis of new "designer" molecules, design molecular diodes, transistors, switches and information storage elements, and their electrical characterization. It was found that the fundamental mechanism of charge transfer in single molecule devices is resonant tunneling, which allows the charge carriers (electrons and/or holes) to be easily transmitted through the charged states of the molecule (positive molecular ion – for holes and negative molecular ion – for electrons). The resonant tunneling theory was used to develop theory of single molecular rectification and switching in single molecules. A method for experimental determination of resonant electron and/or hole conductance mechanisms has been proposed which includes measurements of heat released in metallic electrodes by methods of nanocalorimetry. The classical theory of image potential has been extended to include quantum effects of electron-plasmon interactions. Photon emission upon plasmon excitation by the current in resonant molecular tunnel junctions has been predicted. The first-principles density functional theory calculations have been performed to elucidate the atomic and electronic structure of the molecular junctions. A theory of inelastic resonant tunneling in single molecules has been developed, and applied to investigate thermal stability of the single molecular electronic devices during current flow. Due to emergence of graphene, an atom-thick layer of carbon, as a new promising electronic material, the USF team initiated a seed project on graphene nanoelectronics. Theoretical modeling of a 1-dimensional topological defect in graphene, showed that the line defect constitutes a metallic wire, several atom across, entirely embedded in an otherwise perfect graphene sheet. Broader impacts. This project provided theoretical base for development of novel class of electronic materials based on single molecules, which are actively explored for developing future generations of electronic devices. The new concept of resonant tunneling through charged molecular states is a significant advance which allows to predict characteristics of new elements of electronic circuitry built from molecular-scale components. The concerted joint theory-experiment effort has led to the important discovery of the molecular diode, which was published in Nature Chemistry journal. The discovery of one-dimensional line defect in graphene opens up a new opportunity to develop atomic-scale, molecular nanoelectronics based on all-carbon material. This work was published in Nature Nanotechnology journal and highlighted at the main NSF webpage www.nsf.gov/news/news_summ.jsp?cntn_id=116705. Educational activities within this project were directed towards extensive training of two graduate students and a postdoctoral scholar in the new area of molecular electronics. A series of training workshops for students and postdocs were conducted aimed at performing large-scale atomistic simulations of molecular electronics using density functional theory and molecular dynamics codes run at state-of-the art massively parallel computational Teragrid facilities supported by NSF. Five undergraduate students, supported by the REU supplements to this grant participated in the research activities performed within this project.
