Generating intense electric fields in 2D materials by dual ionic gating

The application of an electric field through two-dimensional materials (2DMs) modifies their properties. For example, a bandgap opens in semimetallic bilayer graphene while the bandgap shrinks in few-layer 2D semiconductors. The maximum electric field strength achievable in conventional devices is limited to ≤0.3 V/nm by the dielectric breakdown of gate dielectrics. Here, we overcome this limit by suspending a 2DM between two volumes of ionic liquid (IL) with independently controlled potentials. The potential difference between the ILs falls across an ultrathin layer consisting of the 2DM and the electrical double layers above and below it, producing an intense electric field larger than 4 V/nm. This field is strong enough to close the bandgap of few-layer WSe2, thereby driving a semiconductor-to-metal transition. The ability to apply fields an order of magnitude higher than what is possible in dielectric-gated devices grants access to previously-inaccessible phenomena occurring in intense electric fields

High-Power-Density Energy-Harvesting Devices Based on the Anomalous Nernst Effect of Co/Pt Magnetic Multilayers

The anomalous Nernst effect (ANE) is a thermomagnetic phenomenon with potential applications in thermal energy harvesting. While many recent works studied the approaches to increase the ANE coefficient of materials, relatively little effort was devoted to increasing the power supplied by the effect. Here, we demonstrate a nanofabricated device with record power density generated by the ANE. To accomplish this, we fabricate micrometer-sized devices in which the thermal gradient is 3 orders of magnitude higher than conventional macroscopic devices. In addition, we use Co/Pt multilayers, a system characterized by a high ANE thermopower (∼1 μV/K), low electrical resistivity, and perpendicular magnetic anisotropy. These innovations allow us to obtain power densities of around 13 ± 2 W/cm3. We believe that this design may find uses in harvesting wasted energy, e.g., in electronic devicesThis work was supported by the Spanish Ministry of Science and Innovation through the projects PID2019-108075RB-C31 and MCIN/FEDER RTI2018-097895-B-C41. G.L.-P. acknowledges financial support from the Spanish Ministry of Science and Innovation through the Juan de la Cierva program (FJCI-2017-32370). J.M.-M. acknowledges the Spanish Ministry of Science, Innovation and Universities through FPU Program No. FPU18/01738

Controlled dynamic screening of excitonic complexes in 2D semiconductors

We report a combined theoretical/experimental study of dynamic screening of excitons in media with frequency-dependent dielectric functions. We develop an analytical model showing that interparticle interactions in an exciton are screened in the range of frequencies from zero to the characteristic binding energy depending on the symmetries and transition energies of that exciton. The problem of the dynamic screening is then reduced to simply solving the Schrodinger equation with an effectively frequency-independent potential. Quantitative predictions of the model are experimentally verified using a test system: neutral, charged and defect-bound excitons in two-dimensional monolayer WS2, screened by metallic, liquid, and semiconducting environments. The screening-induced shifts of the excitonic peaks in photoluminescence spectra are in good agreement with our model

Controlled assembly of artificial 2D materials based on the transfer of oxo-functionalized graphene

Functionalized 2D materials have unique properties, but are currently not used for the assembly of van der Waals heterostructures. Here, we present the controlled transfer of artificially synthesized, polar and highly transparent oxo-functionalized graphene, which can decouple graphene layers

Publisher Correction: Controlled dynamic screening of excitonic complexes in 2D semiconductors

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