NER: Molecular Electronics and Spintronics in Self-Assembled Monolayer Devices

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This NER proposal is a collaborative effort among researchers with diverse expertise in Organic Materials Science and Chemistry (Burtman); Optics, Optoelectronics, and Magneto-transport (Vardeny), and device Physics (both). The two co-PI.s have worked together for two years and have successfully built a set-up for growing self-assembled monolayers (SAM). We are therefore experienced in all aspects of the proposed studies. Intellectual Merit: The goal of this proposal is to demonstrate and study electronic and spintronics processes in molecular devices made of SAM mixtures of conducting and insulating molecules with anchoring thiol end groups, upon tailoring the transport process between isolated molecules with 1D-like transport and aggregates with 2D-like transport. SAM diodes will be fabricated from solution mixtures of molecular wires (1,4 benzene-dimethane-thiol, Me-BDT) with two anchoring thiol end groups, and molecular insulators (pentathiol, PT) with one anchoring thiol end group, at different ratio, r of wires/insulators on metallic ferromagnetic (FM) and non-FM electrodes that include gold and cobalt. At r 10-3 the Me-BDT molecules should be isolated in the insulating PT matrix, whereas they would form two-dimensional (2D) aggregates at r 0.1. We propose to check (i) the Me-BDT bonding to the opposite electrodes; (ii) Me-BDT molecular surface density, and (iii) Me-BDT molecular aggregate formation, using titration techniques of molecular tags that are borrowed from other Applied Science subfields. These measurements include optical absorption, vibrational spectroscopy, AFM microscopy, and electrochemical charge counting. Using the fabricated SAM devices we will be able to study the charge transport properties of isolated and aggregated Me-BDT conducting molecules from the device I-V and differential conductance characteristics, measured at different temperatures. In addition spin transport properties of Me-BDT molecules and aggregates will be also obtained using magnetoresistance (MR) measurements, where the I-V characteristic of Co-based SAM devices will be studied as a function of an external magnetic field. From these measurements we expect to be able to clearly separate devices based on isolated molecular wires from those based on 2D molecular wire aggregates; a phase transition at a certain rc value is anticipated. All the necessary equipment for the SAM growth and set-ups for the device fabrication and testing are already in our laboratory. We have obtained preliminary results that show the feasibility of the proposed studies. Broader Impact: These pilot research studies, if successful would show an alternative method of studying charge and spin transport in single molecules, and in molecular aggregates that show charge delocalization, using SAM devices. Our measurements have the potential to substantially advance the molecular electronic field using a reliable measurement technique. In addition the integration of our large arsenal of experimental efforts, including SAM growth, optics, magneto-optics, and device fabrication, processing and testing, will serve to efficiently educate the post-doctoral associate, and graduate and undergraduate students who will be involved in the highly interdisciplinary research projects. This proposal is in the subfield of Nanoscale Devices and System Architecture.