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By taking advantage of the dual metal substrate of the Ni‐coated Cu foils, the precise control of layer number of graphene by ion implantation has been demonstrated and the layer number of graphene strictly corresponds to the implantation fluence as expected. Besides, the formation mechanism is explored by the experimental analysis in detail and confirmed by the theoretical calculations.

Abstract

Due to the promising utilizations in nanoelectronics, doping‐tunable graphene is paid extensive attentions. Nevertheless, a harmless approach to dope/co‐dope graphene in a controllable and easy way with low cost is still unattainable. Herein, through seeding of 0D N & S dual‐doped graphene quantum dots (N & S dual‐doped GQDs) on a catalytic substrate and then dynamic chemical vapor deposition (CVD), a monolayered dual‐doped graphene film is demonstrated. The concentrations of dopants in graphene are strictly discerned in accordance with preliminary seeding for dual‐doped GQDs. Through the monitoring of growing process, the research elucidates the growth mechanism of the graphene, and unveils that dual‐doped GQDs can serve as the nucleation centers for creating doped‐graphene films by 2D epitaxial growth and thus graphene with designed dopant concentration can be obtained. Finally, the photodetector built on N & S dual‐doped graphene film is found to perform satisfactorily, accompanying high detectivity (≈1.42 × 10¹⁰ cm Hz^1/2 W⁻¹) and responsivity (61 mA W⁻¹), at wavelength of 1550 nm. The research proposes a dexterous approach for synthesizing tunably doped graphene films by the combination of locally controlled nucleation seeds and in situ CVD, which lays the foundation for applying graphene in industries of photonic and electronic devices.

Nature Physics, Published online: 25 October 2019; doi:10.1038/s41567-019-0724-0

Author Correction: Electronic correlations in twisted bilayer graphene near the magic angle

A novel sheet-on-sheet Pd-ZIF/GO (Pd/ZG) catalyst is synthesized by constructing ZIF-L with GO and PVP-Pd nanoparticles (NPs) via a facile in situ method. The in situ introduction of GO promotes the formation of ZIF-L, leading to a higher yield of Pd/ZG, about three times higher than Pd/ZIF-L. We ascribe this to the possible interaction of the oxygen-containing groups on the GO surface with the Zn 2+ cations in ZIF nodes and the PVP wrapped on the Pd surface, resulting in the formation of sheet-on-sheet Pd-ZIF/GO with good Pd dispersion. The Pd/ZG shows superior catalytic performance in the reduction of nitroarenes, and its turnover frequency (TOF) value is five times higher than Pd/ZIF-L. The superior catalytic activity can be ascribed to the uniformly dispersed tiny Pd NPs between ZIF-L and GO nanosheets, fast mass transfer in porous structure, and excellent electron conductivity due to strong interactions among ZIF-L, GO and PVP-Pd. These findings prov...

Stanene has been theoretically predicted to be a 2D topological insulator with a large band gap, potentially hosting quantum spin Hall effect at room temperature. Here, few-layer stanene films have been epitaxially grown on Sb-terminated InSb (1 1 1) surface and their structural and electrical properties are characterized. Scanning tunneling spectrum results reveal a large bulk bandgap in single-layer stanene (over 0.2 eV). Moreover, spectroscopy evidence for a filled edge state near the steps was observed. The gap decreases dramatically with increasing number of layers, and multilayer stanene should become a Dirac semimetal in the bulk limit. The changeover may involve nontrivial topological phase transitions. Clear and reproducible Shubnikov–de Haas oscillations were observed on the single-layer stanene films that were exposed to atmospheric conditions for an extended period of time, showing the possibility for device experiments using nanofabrication and magneto-transport. Ou...

Two-dimensional (2D) layered materials-based field-effect transistors (FETs) are promising for ultimate scaled electron device applications because of the improved electrostatics to atomically thin body thickness. However, compared with the typical thickness of ~5 nm for Si-on-insulator (SOI), the advantage of the ultimate thickness limit of monolayer for the device performance has not been fully proved yet, especially for the on-state at the accumulation region. Here, we present much stronger quantum-mechanical effect at the accumulation region based on the C – V analysis for top-gate MoS 2 FETs. The self-consistent calculation elucidated that the electrons are confined in the monolayer thickness, unlike in the triangle potential formed by the electric field for SOI, the gate-channel capacitance is ideally maximized to the gate insulator capacitance since the capacitive contribution of the channel can be neglected due to the negligible channel thickness. T...

Transition metal dichalcogenides (TMDs) promise to revolutionize optoelectronic applications. While monolayer exfoliation and vapor phase growth produce extremely high quality 2D materials, direct fabrication at wafer scale remains a significant challenge. Here, we present a method that we call ‘lateral conversion’, which enables the synthesis of patterned TMD structures, with control over the thickness down to a few layers, at lithographically predefined locations. In this method, chemical conversion of a metal-oxide film to TMD layers proceeds by diffusion of precursor propagating laterally between silica layers, resulting in structures where delicate chalcogenide films are protected from contamination or oxidation. Lithographically patterned WS 2 structures were synthesized by lateral conversion and analyzed in detail by hyperspectral Raman imaging, scanning electron microscopy and transmission electron microscopy. The rate of conversion was investigated as a functi...

In this study we use nanophotonic effects of graphene to study DNA hybridization: the z −4 nanoscale distance-dependence of the fluorescence lifetime for fluorophores located in the vicinity of graphene is for the first time used to track a DNA hybridization reaction with nanoscale resolution in real time. First, a nanostaircase with ≈2 nm steps from 0 to a total height of 48 nm is used as a nanoruler to confirm the distance dependence law. We find that the axial sensitivity is suited to determine the nanoscale surface roughness of these samples. The proof-of-concept DNA experiments in aqueous medium involve the hybridization of fluorescently labelled DNA beacons attached to CVD grown graphene with complementary (target) DNA added in solution. We track the conformational changes of the beacons statistically by determining the fluorescence lifetimes of the labelling dye and converting them into nanoscale distances from the graphene. In this way, we are able to m...

We study the effect of electric stress, gas pressure and gas type on the hysteresis in the transfer characteristics of monolayer molybdenum disulfide (MoS 2 ) field effect transistors. The presence of defects and point vacancies in the MoS 2 crystal structure facilitates the adsorption of oxygen, nitrogen, hydrogen or methane, which strongly affect the transistor electrical characteristics. Although the gas adsorption does not modify the conduction type, we demonstrate a correlation between hysteresis width and adsorption energy onto the MoS 2 surface. We show that hysteresis is controllable by pressure and/or gas type. Hysteresis features two well-separated current levels, especially when gases are stably adsorbed on the channel, which can be exploited in memory devices.

This work presents a complete analysis of Raman active modes of Sb 2 Se 3 measured by six different excitation wavelengths from NIR to UV, under different polarization configurations and at low temperature. Simultaneous fitting of spectra allowed the deconvolution and identification of the 28 Raman peaks obtained in monocrystalline Sb 2 Se 3 sample from the 30 modes predicted by the group theory analysis for this crystalline structure. Analysis of the spectra measured under different polarization configurations yielded the preliminary assignment of the peaks symmetry, while the measurements under low temperature resulted in a fine resolution of the peaks in Raman spectra. Additionally, evaluation of the spectra of the most probable secondary phases under different excitation wavelengths allowed to define the most appropriate measurement conditions for experimental discrimination of their Raman peaks in the spectra of Sb 2 Se 3

Transition metal dichalcogenide (TMDC) monolayers have attracted great attention due to their unique electronic properties, which promise their applications especially in optoelectronics and valleytronics. A simple and reliable way to fabricate the monolayers is highly desirable for wide applications. Herein, we report a photo-induced exfoliation method for the controllable fabrication of monolayer TMDCs proceeded with the oxidation reaction of TMDCs by the photo-generated holes. The commonly used microscope halogen lamp is sufficient to initiate the exfoliation in pure water. A bulk MoS 2 flake with a surface area of 10 000 µ m 2 and a thickness of 100 nm can be directly exfoliated down to monolayer within four seconds under a 94 nW µ m −2 660 nm laser illumination and by applying 0.1 V potential electrochemically, achieving an astonishing exfoliation speed and efficiency. This method is demonstrated to be applicable also to other semic...

The weak van der Waals interlayer interactions in the transition metal dichalcogenide (TMD) materials have created a rich platform to study their exotic electronic properties through chemical doping or physical gating techniques. We reported bulk superconductivity up to 7.6 K through careful manipulation of the charge carrier density and basal spacing d in the chemically intercalated 2D 1T-SnSe 2 phase. We found, for the first time in the 2D SnSe 2 , that polar organic molecules cointercalated with the alkali metal Li into the basal layers, thus significantly enhancing the superconducting T c . We observed that the T c scales with the basal spacing distance, meanwhile being almost independent of x in Li x (THF) y SnSe 2 system. Our results offers a new general chemical route to study the rich electron correlations and the interplay of charge density...

Structure and symmetry of crystal dictate their physical properties. Reasonable manipulation of those parameters allows designing the materials’ properties in a nonchemical way, like the strain or pressure. Here we report the possibility of manipulating the pseudospin and lifting its degeneracy through the substrate corrugation in graphene, which directly relates to the chirality of Dirac fermions in the low energy regime. By a detailed scanning tunneling microscopy (STM) study that combined with van der Waals heterostructure fabrications, we find the pseudospin degeneracy can be continually lifted that materialized as the gradual wavefunction polarization on the two sublattices by changing graphene’s curvature through a bump. Strikingly, the sublattice polarization shows a linear dependence on the geometry of bumps, which enables to extract a pseudo- g -factor to characterize the pseudospin splitting and geometry. Our results may shine light on engineering the pseudospin, ...

Nanolayered composites are reported to exhibit high strength due to the high density of interfaces. Previously, metal-graphene nanolayered composite had been fabricated by vacuum based deposition of metal layers and wet transfer of graphene layers, both of which are time consuming processes that limit the scalability of the nanolayered composite. In this study, the vacuum based deposition of metal and wet transfer of graphene have been replaced with electrodeposition of metal and roll-based dry transfer of graphene to greatly enhance the scalability of the nanolayered composite fabrication. Fabricated Cu-graphene nanolayered composites with layer spacing of 200 nm, 300 nm, and 400 nm were tested under compression, and the strengths are calculated to be 1.38 GPa, 1.15 GPa, and 1.06 GPa, respectively. The strengths are within the range reported previously for the case of wet transfer and sputter deposited metal, but the new fabrication method has greatly enhanced scalability.

Both carbon nanotube (CNT) and graphene exhibit excellent properties and have many potential applications in integrated circuits, composite materials, thermal management, sensors, energy storage, and flexible electronics. However, their superior properties are confined to one or two dimensions, thus limiting their utility in interconnects or thermal interface materials that require a 3D structure for efficient electron and/or phonon transport. It is conceivable that a combined CNT-graphene structure would provide new opportunities for realizable applications in these and other fields. In recent years, numerous results on synthesis, structural analyses, theoretical modeling, and potential applications of various CNT-graphene heterostructures have been reported. In this review, we summarize the possible structures that can be formed by connecting CNT and graphene. We then report existing experimental efforts to synthesize the heterostructures based on growth method, catalyst desig...