Solvent-Induced Degradation of Electrochemically Exfoliated Vanadium Selenide Visualized by Electron Microscopy.

Recently discovered two-dimensional ferromagnetic materials (2DFMs) have rapidly gained much interest in the fields of spintronics and computing, where they may prove powerful tools for miniaturizing devices such as magnetic tunnel junctions and spin-transfer torque memory bits. In addition, heterojunctions and twisted bilayer stacks of such materials may yield exotic spin textures. However, preparation of such devices is complicated by the air sensitivity of many 2DFMs. Here, we report details on the preparation of few-to-monolayer flakes of vanadium selenide (VSe2) using electrochemical exfoliation in propylene carbonate. We also present a detailed study of the effects of air on the structure and magnetic properties of bare and passivated VSe2 after different concentrations of surface passivation treatment. We characterized the microstructure of holes in the VSe2 flakes and the formation of new compounds arising from air exposure, solvent exposure during the exfoliating process, and deliberate electron beam irradiation (sculpting). We sculpt VSe2 flakes while retaining the 1T-VSe2 lattice structure, opening the door for top-down patterned high-resolution 2DFM nanostructures. Additionally, investigation of the magnetic response of nanosheets using magnetic force microscopy (MFM) showed that the oxidation-induced damage only affects the surface fields locally and does not quench large-scale magnetic signal. The findings of this study pave the way toward practical incorporation of 2D ferromagnetic materials in nanoelectronics.

Devices for Nanoscale Guiding of DNA through a 2D Nanopore.

We fabricate on-chip solid-state nanofluidic-2D nanopore systems that can limit the range of motion for DNA in the sensing region of a nanopore. We do so by creating devices containing one or more silicon nitride pores and silicon nitride pillars supporting a 2D pore that orient DNA within a nanopore device to a restricted geometry, yet allow the free motion of ions to maintain a high signal-to-noise ratio. We discuss two concepts with two and three independent electrical connections and corresponding nanopore chip device architectures to achieve this goal in practice. Here, we describe device fabrication and transmission electron microscope (TEM) images, and provide simulated translocations based on the finite element analysis in 3D to demonstrate its merit. In both methods, there is a main 2D nanopore which we refer to as a "sensing" nanopore (monolayer MoS2 in this paper). A secondary layer is either an array of guiding pores sharing the same electrode pair as the sensing pore (Method 1) or a single, independently contacted, guiding pore (Method 2). These pores are constructed parallel to the "sensing" pore and serve as "guiding" elements to stretch and feed DNA into the atomically thin sensing pore. We discuss the practical implementation of these concepts with nanofluidic and Si-based technology, including detailed fabrication steps and challenges involved for DNA applications in solution.

Simple and rapid gas sensing using a single-walled carbon nanotube field-effect transistor-based logic inverter.

Single-walled carbon nanotubes (SWCNTs) are promising candidates for gas sensing applications, providing an efficient solution to the device miniaturization challenge and allowing low power consumption. SWCNT gas sensors are mainly based on field-effect transistors (SWCNT-FETs) where the modification of the current flowing through the nanotube is used for gas detection. A major limitation of these SWCNT-FETs lies in the difficulty to measure their transfer curves, since the flowing current typically varies between 10-12 and 10-3 A. Thus, voluminous and energy consuming systems are necessary, severely limiting the miniaturization and low energy consumption. Here, we propose an inverter device that combines two SWCNT-FETs which brings a concrete solution to these limitations and simplifies data processing. In this innovative sensing configuration, the gas detection is based on the variation of an electric potential in the volt range instead of a current intensity variation in the microampere range. In this study, the proof of concept is performed using NO2 gas but can be easily extended to a wide range of gases.

Tuning bimetallic catalysts for a selective growth of SWCNTs.

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst's chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticles. By using the as-synthesized SWCNTs as a channel material infield effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results.

All-solution-processed inverted quantum-dot light-emitting diodes.

Quantum dots are a promising new candidate for the emissive material in light-emitting devices for display applications. The fabrication of such devices by solution processing allows considerable cost reduction and is therefore very attractive for industrial manufacturers. We report all solution-processed colloidal quantum-dot light-emitting diodes (QLEDs) with an inverted structure. The red, green, and blue devices showed maximum luminances of 12 510, 32 370, and 249 cd/m(2) and turn-on voltages of 2.8, 3.6, and 3.6 V, respectively. We investigate the effect of a surfactant addition in the hole injection layer (HIL), with the aim of facilitating layer deposition and thereby enhancing device performance. We demonstrate that in the device structure presented in this study, a small amount of surfactant in the HIL can significantly improve the performance of the QLED.