Hexagonal arrays of nanoscale holes or metal dots (25nm in diameter and 39nm in period), with orientational order extending over the entire square-centimeter array area, were fabricated on unpatterned silicon wafer substrates using a shear-aligned sphere-forming diblock copolymer template. Since two or more layers of spherical nanodomains are required to achieve alignment in the block copolymer film, but pattern transfer requires a single layer, a multistep etching process was developed, whereby the top layer of a shear-aligned bilayer was evenly removed, leaving the ordered bottom layer as the fabrication template for hole and dot arrays free from grain boundaries.
WS 2 and PEDOT-PSS were individually characterized with the goal of analyzing charge transport across a hetero-junction formed by these two materials. In thermal equilibrium electron flow from the WS 2 conduction band into the polymer LUMO level leads to band bending that creates a potential barrier preventing further current. The measured current-voltage (I DS -V DS ) curve across the hetero-junction was non-linear and asymmetric similar to a diode, with a turn-on voltage of 1.4V and a rectification ratio of 12. The device I-V data were analyzed using the standard thermionic emission model of a Schottky junction and yielded an ideality parameter of 1.9 and a barrier height of 0.58 eV. This facile technique is the first report on a nano-diode fabricated using WS 2 and PEDOT-PSS, opening up the possibility of extending this work to include other layered transition metal dichalcogenides and conducting polymers.
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