Ankur Goswami

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS 2 multilayers

The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting1–3. 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 rectification2. Here, we show that continuous direct-current (d.c.) with a maximum density of 106 A m−2 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 (MoS2). 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 (105−106 V m−2) at the conductive nanoscale tip4. 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.A large triboelectric direct current can be generated via the nanoscale sliding friction of a conductive-AFM tip on a MoS2 thin film.

Erratum to: Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition

The correspondence author in the original version of this article was unfortunately wrongly written on page 3571 and the first page of the ESM.Instead of Ankur Goswami1, Priyesh Dhandaria1, Soupitak Pal2, Ryan McGee1, Faheem Khan1, Željka Antić1, Ravi Gaikwad1, Kovur Prashanthi1, and Thomas Thundat1 (✉)It should read Ankur Goswami1 (✉), Priyesh Dhandaria1, Soupitak Pal2, Ryan McGee1, Faheem Khan1, Željka Antić1, Ravi Gaikwad1, Kovur Prashanthi1, and Thomas Thundat1 The email address of the correspondence author in the original version of this article was unfortunately wrongly written on the page 3571 and the first page of the ESM.Instead of Address correspondence to thundat@ualberta.caIt should read Address correspondence to agoswami@ualberta.ca

Energy Harvesting Using Droplet

Abstract Energy harvesting becomes increasingly important from free mechanical vibration for running self-sustained wireless electronics, remote sensors, and power portable devices, which have emerged over the past decades. Transducers using the principle of electromagnetic induction defined by Faradays law are predominantly used as energy harvesters since their inception. Furthermore, piezoelectric energy harvesters are becoming one of the matured technologies that satisfy the above demand to a significant extent. However, despite a large potential of variable capacitor in energy harvesting, it remains as an infant till date. Nevertheless, numerous articles have been devoted to harvest energy using the concept of variable capacitance utilizing the motion of conductive (mercury) and dielectric (water) droplets. Applying the concept stated above using the idea of reverse electrowetting on dielectric, bulge instability, and water motion active transducer energy harnessing have been possible as shown in several literatures. By rolling the droplet on thin dielectric (known as electret) superhydrophobic surfaces (e.g., Teflon, Parylene, Cytop, etc.) using nonresonant free-vibration energy harvesting was demonstrated by various authors. In this chapter, we will revisit the concept of energy harvesting from electrets by using the above ideas of moving droplets.

Preferentially Oriented TiO2 Nanotube Arrays on Non-Native Substrates and Their Improved Performance as Electron Transporting Layer in Halide Perovskite Solar Cells

Anodically formed TiO2 nanotube arrays (TNTAs) constitute an optoelectronic platform that is being studied for use as a photoanode in photoelectrocatalytic cells, as an electron transport layer (ETL) in solar cells and photodetectors, and as an active layer for chemiresistive and microwave sensors. For optimal transport of charge carriers in these one-dimensional polycrystalline ordered structures, it is desirable to introduce a preferential texture with the grains constituting the nanotube walls aligned along the transport direction. Through x-ray diffraction analysis, we demonstrate that choosing the right water content in the anodization electrolyte and the use of a post-anodization zinc ion treatment can introduce a preferential texture in sub-micron length transparent TNTAs formed on non-native substrates. The incorporation of 1.5 atom% of Zn in TiO2 nanotubes prior to annealing, was found to consistently result in the strongest preferential orientation along the [001] direction. [001] oriented TNTAs exhibited a responsivity of 523 A W-1 at a bias of 2 V for 365 nm photons, which is among the highest reported performance values for ultraviolet photodetection using titania nanotubes. Furthermore, the textured nanotubes without a Zn2+ treatment showed a significantly enhanced performance in halide perovskite solar cells that used TNTAs as the ETL.

Thermomechanical analysis of picograms of polymers using a suspended microchannel cantilever

Microchannel cantilevers are an emerging platform for physical characterization of materials at the picogram level. Here we report on detecting multiple thermal transitions in picogram amounts of two well-known polymers, semicrystalline poly(L-lactide) (PLA) and amorphous poly(methylmethacrylate) (PMMA), using this platform. The polymer samples, when loaded inside the cantilever, affect its resonance frequency due to changes in its total mass and stiffness. When taken through a thermal cycle, the resonance response of the cantilever further changes due to multiple thermal transitions of the samples. Continuous monitoring of the resonance frequency provides information about β-transition (Tβ), glass transition (Tg), crystallization (Tc), and melting (Tm) of the confined polymer samples. The measured Tg, Tc, and Tm for PLA were ∼60, 78, and 154 °C, respectively, while the Tg and Tβ for PMMA were 48 and 100 °C, respectively. These results are in an agreement with the data obtained from differential scanning calorimetry (DSC). Because of its high sensitivity, this technique is capable of detecting the weaker β-transitions that cannot be observed with conventional DSC.