A solution-gate field effect transistor (SGFET) has been fabricated on few-layer graphene (FLG). The ideally polarizable graphene/aqueous electrolyte interface allows the capacitive charging of the surface by hydroxyl (OH-) and hydroxonium ions (H3O+). The conductivity versus gate potential curve exhibits "V" shaped ambipolar transfer characteristics of graphene, with hole and electron mobilities of 3600 cm2/Vs and 2100 cm2/Vs, respectively. The shift of the negative gate potential with pH shows a supra-Nernstian response of 99 meV/pH. Our work points to the potential application of graphene in ultrafast and ultralow noise chemical or biological sensors.

Graphene has attracted a lot of interest for fundamental studies as well as for potential applications. Till now, micromechanical cleavage (MC) of graphite has been used to produce high-quality graphene sheets on different substrates. Clear understanding of the substrate effect is important for the potential device fabrication of graphene. Here we report the results of the Raman studies of micromechanically cleaved monolayer graphene on standard SiO 2 (300 nm)/Si, single crystal quartz, Si, glass, polydimethylsiloxane (PDMS), and NiFe. Our data suggests that the Raman features of monolayer graphene are independent of the substrate used; in other words, the effect of substrate on the atomic/electronic structures of graphene is negligible for graphene made by MC. On the other hand, epitaxial monolayer graphene (EMG) on SiC substrate is also investigated. Significant blueshift of Raman bands is observed, which is attributed to the interaction of the graphene sheet with the substrate, resulting in the change of lattice constant and also the electronic structure.

As a unique two-dimensional nanomaterial, layered black phosphorus (BP) nanosheets have shown promising applications in electronics. Although mechanical exfoliation was successfully used to prepare BP nanosheets, it is still a challenge to produce novel BP nanostructures in high yield. A facile top-down approach for preparation of black phosphorus quantum dots (BPQDs) in solution is presented. The obtained BPQDs have a lateral size of 4.9±1.6 nm and thickness of 1.9±0.9 nm (ca. 4±2 layers). As a proof-of-concept application, by using BPQDs mixed with polyvinylpyrrolidone as the active layer, a flexible memory device was successfully fabricated that exhibits a nonvolatile rewritable memory effect with a high ON/OFF current ratio and good stability.

The fabrication of epitaxial graphene (EG) on SiC substrate by annealing has attracted a lot of interest as it may speed up the application of graphene for future electronic devices. The interaction of EG and the SiC substrate is critical to its electronic and physical properties. In this work, Raman spectroscopy was used to study the structure of EG and its interaction with SiC substrate. All the Raman bands of EG blue shift from that of bulk graphite and graphene made by micromechanical cleavage, which was attributed to the compressive strain induced by the substrate. A model containing 13 × 13 honeycomb lattice cells of graphene on carbon nanomesh was constructed to explain the origin of strain. The lattice mismatch between graphene layer and substrate causes the compressive stress of 2.27 GPa on graphene.We also demonstrate that the electronic structures of EG grown on Si and C terminated SiC substrates are quite different. Our experimental results shed light on the interaction between graphene and SiC substrate that are critical to the future applications of EG.

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for HER when nanoscale MoS 2 is used, [ 1 ] albeit bulk MoS 2 is suggested to be inactive towards HER. [ 2 ] Thus most studies have focused on designing thin layered/nanostructured MoS 2 nanomaterials with most exposed edges for HER. To this end, amorphous MoS 2,[ 3 ] MoS x nanosheets [ 4 ] were found to outperform bulk MoS 2 signifi cantly; layer-dependent attributes, [ 5 ] the correlation with intrinsic low conductivity out-of-plane, and phasedetermined performance have also been studied. [ 6 ] These fi ndings have stimulated the work of sulfi de of earth-abundant metals, e.g., WS 2 [ 7 ] and its analogues, selenides, [ 8 ] resulting in a big family of chalcogenides of fi rst-row transition metals. [ 9 ] Reviews [ 6b , 7c , 10 ] have been conducted from different perspectives and can be referred to accordingly. Unfortunately, the best performing MoS 2 catalyst still lacks the competitiveness of Pt. Furthermore, improvements in performance relies heavily on the basis that moly bdenum/tungsten chalcogenides (sulfi de, selenide) are nanostructured with abundant S-edges and are thin layered (preferable single layer). These requirements may severely constrain their application in large-scale production. Thus, it is imperative to continue the search for new inexpensive catalysts that can rival the performance of Pt while being suitable for large-scale hydrogen production.It was only recently discovered that hydrogen evolution proceeds via a similar pathway to that of hydrogenation (hydrotreating process), e.g., hydrodesulfurization (HDS), where a reversible ad/desorption of hydrogen on catalyst is critical for achieving fast kinetics. This correlation broadens the scope of search for new catalysts. Hence, phosphides, previously employed as catalysts for HDS, were found to be active towards HER, e.g., Ni 2 P [ 11 ] has been reported to achieve a better performance than the state-of-the-art MoS 2 .[ 11c ] This pivotal work [ 11c ] was followed by a variety of studies applying phosphide as catalysts for HER. This class of electrocatalyst with superb electrocatalytic activities has thus opened up a new avenue in the search of non-noble metal catalysts for HER. Here, we focus our discussion on the recent developments of synthesis methodology of phosphides for HER. Based on different synthetic routes of phosphides, we then make a comparative survey of their activities, which are evaluated in terms of experimental metrics of over-potential ( η ) at a certain current density ( j ), Tafel slope coupled with exchange current density ( j o ) extrapolated from the plot of η vs. Log 10 ( j ), and turnover frequency (TOF). In conjunction with experimental results, Hydrogen evolution by means of electrocatalytic water-splitting is pivotal for effi cient and economical production of hydrogen, which relies on the development of inexpensive, highly active catalysts. In addition to sulfi des, the search for non-noble metal catalysts has been mainly directed at phosphides due to the superb activity of phosphides for hydrogen ev...

Chemical vapour deposition of two-dimensional materials typically involves the conversion of vapour precursors to solid products in a vapour-solid-solid mode. Here, we report the vapour-liquid-solid growth of monolayer MoS, yielding highly crystalline ribbons with a width of few tens to thousands of nanometres. This vapour-liquid-solid growth is triggered by the reaction between MoO and NaCl, which results in the formation of molten Na-Mo-O droplets. These droplets mediate the growth of MoS ribbons in the 'crawling mode' when saturated with sulfur. The locally well-defined orientations of the ribbons reveal the regular horizontal motion of the droplets during growth. Using atomic-resolution scanning transmission electron microscopy and second harmonic generation microscopy, we show that the ribbons are grown homoepitaxially on monolayer MoS with predominantly 2H- or 3R-type stacking. Our findings highlight the prospects for the controlled growth of atomically thin nanostructure arrays for nanoelectronic devices and the development of unique mixed-dimensional structures.

The concept of using single molecules as key building blocks for logic gates, diodes and transistors to perform basic functions of digital electronic devices at the molecular scale has been explored over the past decades. However, in addition to mimicking the basic functions of current silicon devices, molecules often possess unique properties that have no parallel in conventional materials and promise new hybrid devices with novel functions that cannot be achieved with equivalent solid-state devices. The most appealing example is the molecular switch. Over the past decade, molecular switches on surfaces have been intensely investigated. A variety of external stimuli such as light, electric field, temperature, tunneling electrons and even chemical stimulus have been used to activate these molecular switches between bistable or even multiple states by manipulating molecular conformations, dipole orientations, spin states, charge states and even chemical bond formation. The switching event can occur either on surfaces or in break junctions. The aim of this review is to highlight recent advances in molecular switches triggered by various external stimuli, as investigated by low-temperature scanning tunneling microscopy (LT-STM) and the break junction technique. We begin by presenting the molecular switches triggered by various external stimuli that do not provide single molecule selectivity, referred to as non-selective switching. Special focus is then given to selective single molecule switching realized using the LT-STM tip on surfaces. Single molecule switches operated by different mechanisms are reviewed and discussed. Finally, molecular switches embedded in self-assembled monolayers (SAMs) and single molecule junctions are addressed.