Field emission (FE) has been extensively explored from various exotic low dimensional carbon nanomaterials, such as amorphous carbon films, 1 single and multiwalled carbon nanotubes (CNTs), 2 tubular graphitic cones, 3 vertically aligned nanowalls, 4 few-layered graphene (FLG) nanoflakes, 5,6 and, more recently, from doped and pristine graphene. 7,8 Graphene, a two-dimensional monatomic plane layer of hexagonally arrayed sp 2-hybridized carbon atoms forms the backbone of all the above-mentioned carbon nanostructures. 9 The highly desirable properties of graphene, such as atomic thickness, excellent electrical conductivity, and high aspect ratio, make it an ideal candidate for field emission applications. 7-9 Also, as compared to CNTs, the presence of a large number of edges may render graphene superior for electron tunneling. 7 Although FE in CNTs is highly efficient, it has been shown that heteroatom doping by elements, such as nitrogen, can further reduce the effective tunneling potential barrier, thereby reducing the turn-on field and significantly increasing the electron emission current. 10,11 Nitrogen acts as an electron donor in CNTs because it has five valence electrons and causes a shift in the Fermi level (E F) to the conduction band and increases the electron density of states (DOS). In the case of graphene, theoretical studies have shown that substitutional heteroatom doping can modulate the band structure of graphene, leading to a metal-semiconductor transition, thereby expanding the applications of graphene. 12,13 Although Malesevic et al. 5 and Qi et al. 6 have shown the field emission behavior of pristine and Ar plasma-treated FLG nanoflakes, respectively, to the best of our knowledge, until now, there ' EXPERIMENTAL SECTION The synthesis of FLGs was carried out in a SEKI MPECVD deposition system, equipped with a 1.5 kW, 2.45 GHz microwave source. The substrates used were bare n-type heavily doped Si wafers (resistivity < 0.005 Ω cm) (10 mm  10 mm). Prior to growth, the substrates were pretreated with N 2 plasma at 650 W at 40 Torr while the substrate temperature was maintained at 900°C. Synthesis was then carried out using CH 4 /N 2 (gas flow

Interconnected conducting porous graphene as supercapacitive material as well as current collector for integrated metal-free microsupercapacitor (MSC) having ultra-long cycle life and outstanding capacitive performance.

Many-body states like excitons, biexcitons, and trions play an important role in optoelectronic and photovoltaic applications in 2D materials. Herein, we studied carrier dynamics of excitons and trions in monolayer MoS2 deposited on a SiO2/Si substrate, before and after Au NP deposition, using femtosecond transient absorption spectroscopy. Luminescence measurements confirm the presence of both an exciton and trion in MoS2, which are drastically quenched after deposition of Au NPs, indicating electron transfer from photoexcited MoS2 to Au. Ultrafast study reveals that photogenerated free carriers form excitons with a time scale of ∼500 fs and eventually turn into trions within ∼1.2 ps. Dissociation of excitons and trions has been observed in the presence of Au, with time scales of ∼600 fs and ∼3.7 ps, respectively. Understanding the formation and dissociation dynamics of the exciton and trion in monolayer MoS2 is going to help immensely to design and develop many new 2D devices.

Among catalysts based on non‐noble metals, Mo‐based materials are important for hydrogen evolution because of their low cost, good conductivity, and catalytic efficiency. This study demonstrates a facile two‐step synthesis of Mo2N nanostructures assembled from 5–8 nm particles with graphitic carbon nitride as the nitrogen source. These Mo2N nanostructures of various morphologies (hexagons, triangles, and nanowires) show a very high activity and stability in acidic media during water electrolysis. Their nanostructures were characterized by using powder XRD, electron microscopy, N2 gas adsorption analysis, and X‐ray photoelectron spectroscopy. Hydrogen evolution reaction parameters, which include the Tafel slope, charge transfer resistance, and stability, were analyzed by using linear sweep voltammetry and electrochemical impedance spectroscopy. Thin hexagonal sheets of Mo2N show the highest apparent electrocatalytic activity (current density of 197 mA cm−2geometric at −400 mV vs. the reversible hydrogen electrode) and excellent stability in an acidic medium with a small onset potential of 90 mV and a Tafel slope of 145 mV decade−1. The lowest Tafel slope was observed for Mo2N nanowires.

Hotspot engineering has the potential to transform the field of surface-enhanced Raman spectroscopy (SERS) by enabling ultrasensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer molybdenum disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the unpassivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions, creating hotspots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with a large SERS enhancement (∼104) at the hotspots for RhB concentrations as low as ∼10–10 M. The single-step laser-etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electrochemical deposition, e-beam lithography, nanoimprinting, or photolithography. Whereas we have focused our study on MoS2, this concept could, in principle, be extended to a variety of 2D material platforms.