Origin of multi-level switching and telegraphic noise in organic nanocomposite memory devices.

The origin of negative differential resistance (NDR) and its derivative intermediate resistive states (IRSs) of nanocomposite memory systems have not been clearly analyzed for the past decade. To address this issue, we investigate the current fluctuations of organic nanocomposite memory devices with NDR and the IRSs under various temperature conditions. The 1/f noise scaling behaviors at various temperature conditions in the IRSs and telegraphic noise in NDR indicate the localized current pathways in the organic nanocomposite layers for each IRS. The clearly observed telegraphic noise with a long characteristic time in NDR at low temperature indicates that the localized current pathways for the IRSs are attributed to trapping/de-trapping at the deep trap levels in NDR. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems

Semiconductor-less vertical transistor with I-ON/I-OFF of 10(6)

Semiconductors have long been perceived as a prerequisite for solid-state transistors. Although switching principles for nanometer-scale devices have emerged based on the deployment of two-dimensional (2D) van der Waals heterostructures, tunneling and ballistic currents through short channels are difficult to control, and semiconducting channel materials remain indispensable for practical switching. In this study, we report a semiconductor-less solid-state electronic device that exhibits an industry-applicable switching of the ballistic current. This device modulates the field emission barrier height across the graphene-hexagonal boron nitride interface with ION/IOFF of 106 obtained from the transfer curves and adjustable intrinsic gain up to 4, and exhibits unprecedented current stability in temperature range of 15–400 K. The vertical device operation can be optimized with the capacitive coupling in the device geometry. The semiconductor-less switching resolves the long-standing issue of temperature-dependent device performance, thereby extending the potential of 2D van der Waals devices to applications in extreme environments. © 2021, The Author(s).1

Regioselective Introduction of Heteroatoms at the C-8 Position of Quinoline N-Oxides: Remote C-H Activation Using N-Oxide as a Stepping Stone

Reported herein is the metal-catalyzed regioselective C-H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.11711741sciescopu

Rhodium(III)-catalyzed C-C bond formation of quinoline N-oxides at the C-8 position under mild conditions

The Rh(III)-catalyzed C-8 selective direct alkylation and alkynylation of quinoline N-oxides has been developed. The reactions proceeded highly efficiently at room temperature over a broad range of substrates with excellent regioselectivity and functional group tolerance. This development demonstrates the synthetic utility of the N-oxide directing group as a stepping stone for remote C H functionalization of quinolines.11311301sciescopu

Engineering Active Sites of 2D Materials for Active Hydrogen Evolution Reaction

Abstract Hydrogen evolution reaction (HER) is a promising clean and sustainable energy source with zero carbon emissions. Numerous studies have been conducted with versatile low dimensional materials, and the development of highly active electrochemical catalysts for HER is one of the most important applications of the materials in these studies. Despite such extensive research, the physical origin of the active catalytic performance of low dimensional materials remains unclear, and is distinguished from that of classical transition metal‐based catalysts. Here, recent studies on the intrinsic catalytic activity of 2D semimetals are reviewed, particularly among transition metal dichalcogenides (TMDs), highlighting promising strategies for the design of materials to further enhance their catalytic performance. One attractive approach for active HER involves fabricating single‐atom catalysts in the framework of TMDs. The electrochemical reaction at a catalytic atom for hydrogen evolution has typically been described by the Sabatier principle. Recent studies have focused on optimizing the Gibbs free energy for hydrogen adsorption via down‐sizing, alloying, hybridizing, hetero‐structuring, and phase boundary engineering, mostly with TMDs. The unique advantages of TMDs and their derivatives for HER are summarized, suggesting promising research directions for the design of low dimensional electrochemical catalysts for efficient HER and their energy applications

Regioselective Introduction of Heteroatoms at the C‑8 Position of Quinoline <i>N</i>‑Oxides: Remote C–H Activation Using <i>N</i>‑Oxide as a Stepping Stone

Reported herein is the metal-catalyzed regioselective C–H functionalization of quinoline <i>N</i>-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of <i>N</i>-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C–H activation using <i>N</i>-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated

Rhodium(III)-Catalyzed C–C Bond Formation of Quinoline <i>N</i>‑Oxides at the C‑8 Position under Mild Conditions

The Rh­(III)-catalyzed C-8 selective direct alkylation and alkynylation of quinoline <i>N</i>-oxides has been developed. The reactions proceeded highly efficiently at room temperature over a broad range of substrates with excellent regioselectivity and functional group tolerance. This development demonstrates the synthetic utility of the <i>N</i>-oxide directing group as a stepping stone for remote C–H functionalization of quinolines

Flexible Molecular-Scale Electronic Devices Composed of Diarylethene Photoswitching Molecules

The electrical properties of diarylethene photoswitching molecular devices on flexible substrates are studied. When exposed to UV or visible light, diarylethene molecular devices show two electrical states (a high and a low conductance state) with a discrepancy of an order of magnitude in the level of current between the two states. The diarylethene flexible molecular devices exhibit excellent long-time stability and reliable electrical characteristics in both conductance states when subjected to various mechanical stresses