The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting . A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification . Here, we show that continuous direct-current (d.c.) with a maximum density of 10 A m can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (10-10 V m) at the conductive nanoscale tip . We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.

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Fouling mechanisms of a light conventional crude were investigated by characterizing the crude oil, performing fouling tests using a bench-scale Alcor hot liquid process simulator (HLPS) unit and characterizing fouling deposits by means of elemental analysis, scanned electron microscopy (SEM), thermogravimetric analysis (TGA), and photoacoustic infrared spectroscopy (PAS-IR). In addition, a mathematical fouling model was developed under a laminar flow regime following Epstein's methodology. Fouling tests were conducted at different temperatures and bulk velocities. Although the asphaltene content in the crude oil is low, the asphaltenes are still unstable because of a high saturate content and this crude oil has a high fouling propensity. On the basis of the fouling test results, fouling model analysis, and characterization of fouling deposits, the fouling mechanism of this crude oil can be explained as follows: In a laminar flow regime, unstable asphaltenes transport to the hot surface, become attached to the surface, and then, through chemical reactions, form fouling deposits. Mass transfer of entrained suspended particulates in the crude oil also contributes to fouling, although it is not the main cause. However, under turbulent flow conditions, such as those that prevail in industrial operations, it is expected that suspended particles would play a greater role in fouling.

Here we report mid infrared (mid-IR) photothermal response of multi layer MoS2 thin film grown on crystalline (p-type silicon and c-axis oriented single crystal sapphire) and amorphous substrates (Si/SiO2 and Si/SiN) by pulsed laser deposition (PLD) technique. The photothermal response of the MoS2 films was measured as changes in the resistance of MoS2 films when irradiated with mid IR (7 to 8.2 μm) source. We show that it is possible to enhance the temperature coefficient of resistance (TCR) of the MoS2 thin film by controlling the interface through proper choice of substrate and growth conditions. The thin films grown by PLD were characterized using XRD, Raman, AFM, XPS and TEM. High-resolution transmission electron microscopy (HRTEM) images show that the MoS2 films grow on sapphire substrate in a layerby-layer manner with misfit dislocations. Layer growth morphology is disrupted when grown on substrates with diamond cubic structure such as silicon due to growth twin formation. The growth morphology is very different on amorphous substrates such as Si/SiO2 or Si/SiN. TheMoS2 film grown on silicon shows a very high TCR (-2.9% K -1 ), mid IR sensitivity (∆R/R=5.2 %) and responsivity (8.7 V/W) as compared to films on other substrates.

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