CVD grown MoSe2 monolayers were electrically characterized at room temperature in a field effect transistor (FET) configuration using an ionic liquid (IL) as the gate dielectric. During the growth, instead of using MoO3 powder, ammonium heptamolybdate was used for better Mo control of the source and sodium cholate added for lager MoSe2 growth areas. In addition, a high specific capacitance (∼7 μF/cm2) IL was used as the gate dielectric to significantly reduce the operating voltage. The device exhibited ambipolar charge transport at low voltages with enhanced parameters during n- and p-FET operation. IL gating thins the Schottky barrier at the metal/semiconductor interface permitting efficient charge injection into the channel and reduces the effects of contact resistance on device performance. The large specific capacitance of the IL was also responsible for a much higher induced charge density compared to the standard SiO2 dielectric. The device was successfully tested as an inverter with a gain of ∼2. Using a common metal for contacts simplifies fabrication of this ambipolar device, and the possibility of radiative recombination of holes and electrons could further extend its use in low power optoelectronic applications.

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with swelling-induced resistance changes of the films signaling the presence of vapors. To identify and classify vapors, arrays of such vapor sensing elements have been constructed. Each element contained a different organic polymer as the insulating phase. The differing gas-solid partition coefficients for the various polymers of the detector array produced a pattern of resistance changes that was used to classify vapors and vapor mixtures. The performance of this system towards DNT, the predominant signature in the vapor phase above land mines, has been evaluated in detail, with robust detection demonstrated in the laboratory in less than 5 s in air at DNT levels in the low ppb range.

The effect of polymer side chain on extrusion-based direct-write 3D printing and rheology is examined. Longer side chain length improves printability at ambient temperatures.

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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