Characterization of carbon -molecule -metal junctions by cyclic voltammetry, Raman spectroscopy and X-ray photoelectron spectroscopy

Nitroazobenzene (NAB) diazonium salts were reduced with cyclic voltammetry scans to derivatize pyrolyzed photoresist (PPF) surfaces. This process resulted in covalently bonded NAB on the PPF surface, as shown by XPS and Raman spectroscopy. Junction top contacts were fabricated by using various deposition conditions and metal layers including titanium, copper, aluminum, silver and gold.;Junction low voltage resistance, current density and properties of aging molecular junctions will be discussed, along with their role in electron injection for NAB. The PPF/NAB/Ti/Au junctions are examples of monolayer molecular electronic devices with covalent bonding between the contacts and the molecular layer. Electron transfer through the molecular layer was found to be a strong function of molecular structure as well as molecular thickness.;The pressure in the electron beam chamber during metal deposition was found to have a large effect on junction resistance in titanium junctions, and to a lesser extent with copper junctions. Both high and low oxide junctions are discussed with titanium being the most commonly used metal. Electronic and Raman characterization of different metal top contact molecular junctions was performed. Raman intensity ratios were used to characterize reduction of the NAB molecular layer with different metal top contacts. XPS characterization was used to show the surface bonding between the molecule and metal contact, as well as oxide characterization in the junction metal contact. Depth profiling using Argon ion sputtering was used to determine depth-resolved composition inside fabricated molecular junctions.;Five different metals were used with PPF/NAB(3.7nm). Aluminum junctions were shown to have low conductivity, and high resistance compared to other metals. Titanium junctions deposited at high oxide conditions exhibited semiconductor properties with asymmetric i/V curves that included hysteresis and rectification. At lower deposition pressures, Ti, Cu, Ag and Au all showed symmetric, conductive i/V curves. Ti, Cu and Ag were found to form covalent metal-N bonds at the NAB/metal interface. At higher deposition pressures, the metal oxides present in the top contact contributed significantly to the observed i/V curves for Al, Ti, and to a lesser extent with Cu.