Room-Temperature Negative Differential Resistance in Graphene Field Effect Transistors: Experiments and Theory

In this paper we demonstrate experimentally and discuss the negative differential resistance (NDR) in dual-gated graphene field effect transistors (GFETs) at room temperature for various channel lengths, ranging from 200 nm to 5 μm. The GFETs were fabricated using chemically vapor-deposited graphene with a top gate oxide down to 2.5 nm of equivalent oxide thickness (EOT). We originally explain and demonstrate with systematic simulations that the onset of NDR occurs in the unipolar region itself and that the main mechanism behind NDR is associated with the competition between the specific field dependence of carrier density and the drift velocity in GFET. Finally, we show experimentally that NDR behavior can still be obtained with devices of higher EOTs; however, this comes at the cost of requiring higher bias values and achieving lower NDR level

High-Temperature Phase Transitions Preceding the Decomposition of Mixed Valence Aluminum Titanate Pseudobrookite

Dark blue single crystals of Al1.753+Ti1.04+Ti0.253+O5 were grown with a novel synthesis method based on the reaction of a Ti3+/Ti4+-containing langbeinite melt and porous α-alumina crucible. The obtained needles crystallize in the pseudobrookite structure and, upon heating, undergo two reversible phase transitions, from orthorhombic Cmcm to C2/m first and subsequently to C2 symmetry. Like the known aluminum titanate pseudobrookites, anisotropic thermal expansion is observed. The temperature evolution of the crystal structure reveals insights into the mechanism leading to the decomposition of the pseudobrookites above 725 °C. The magnetic and electrical properties are discussed and compared to other reported aluminum titanate pseudobrookites

Nanopore Integrated Nanogaps for DNA Detection

A high-throughput fabrication of sub-10 nm nanogap electrodes combined with solid-state nanopores is described. These devices should allow concomitant tunneling and ionic current detection of translocating DNA molecules. We report the optimal fabrication parameters in terms of dose, resist thickness, and gap shape that allow easy reproduction of the fabrication process at wafer scale. The device noise and current voltage characterizations performed and the influence of the nanoelectrodes on the ionic current noise is identified. In some cases, ionic current rectification for connected or biased nanogap electrodes is also observed. In order to increase the extremely low translocation rates, several experimental strategies were tested and modeled using finite element analysis. Our findings are useful for future device designs of nanopore integrated electrodes for DNA sequencing

In Situ Electric Field Skyrmion Creation in Magnetoelectric Cu₂OSeO₃

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore’s law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu₂OSeO₃. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications

In Situ Electric Field Skyrmion Creation in Magnetoelectric Cu₂OSeO₃

Exploiting additional degrees of freedom in solid-state materials may be the most-promising solution when approaching the quantum limit of Moore’s law for the conventional electronic industry. Recently discovered topologically nontrivial spin textures, skyrmions, are outstanding among such possibilities. However, the controlled creation of skyrmions, especially by electric means, remains a pivotal challenge in technological applications. Here, we report that skyrmions can be created locally via electric field in the magnetoelectric helimagnet Cu₂OSeO₃. Using Lorentz transmission electron microscopy, we successfully write skyrmions in situ from a helical-spin background. Our discovery is highly coveted because it implies that skyrmionics can be integrated into modern field effect transistor based electronic technology, in which very low energy dissipation can be achieved and, hence, realize a large step forward toward its practical applications

Diuron Sorbed to Carbon Nanotubes Exhibits Enhanced Toxicity to Chlorella vulgaris

Carbon nanotubes (CNT) are more and more likely to be present in the environment, where they will associate with organic micropollutants due to strong sorption. The toxic effects of these CNT-micropollutant mixtures on aquatic organisms are poorly characterized. Here, we systematically quantified the effects of the herbicide diuron on the photosynthetic activity of the green alga Chlorella vulgaris in presence of different multiwalled CNT (industrial, purified, pristine, and oxidized) or soot. The presence of carbonaceous nanoparticles reduced the adverse effect of diuron maximally by <78% (industrial CNT) and <34% (soot) at 10.0 mg CNT/L, 5.0 mg soot/L, and diuron concentrations in the range 0.73–2990 μg/L. However, taking into account the measured dissolved instead of the nominal diuron concentration, the toxic effect of diuron was equal to or stronger in the presence of CNT by a factor of up to 5. Sorbed diuron consequently remained partially bioavailable. The most pronounced increase in toxicity occurred after a 24 h exposure of algae and CNT. All results point to locally elevated exposure concentration (LEEC) in the proximity of algal cells associated with CNT as the cause for the increase in diuron toxicity

The Role of Transport Agents in MoS₂ Single Crystals

We report resistivity, thermoelectric power, and thermal conductivity of MoS₂ single crystals prepared by the chemical vapor transport (CVT) method using I₂, Br₂, and TeCl₄ as transport agents. The material presents low-lying donor and acceptor levels, which dominate the in-plane charge transport. Intercalates into the van der Waals gap strongly influence the interplane resistivity. Thermoelectric power displays the characteristics of strong electron–phonon interaction. A detailed theoretical model of thermal conductivity reveals the presence of a high number of defects in the MoS₂ structure. We show that these defects are inherent to CVT growth method, coming mostly from the transport agent molecules inclusion as identified by total reflection X-ray fluorescence analysis (TXRF) and in-beam activation analysis (IBAA)