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Summary Two-dimensional (2D) graphdiyne (GDY) is a promising floating-gate material for flexible optoelectronic flash memory owing to its fascinating electrical and optical properties. However, research in GDY-based flash memory is still in its infancy owing to the huge challenge in the synthesis of large-area and ultrathin GDY films with high quality and uniformity. Here, an electric double-layer-confined strategy is proposed to synthesize a wafer-scale GDY film with thickness of 1 nm. Then, a two-terminal top-floating-gated optoelectronic memory with multibit storage capability is investigated using GDY as a photoresponsive top-floating gate. Benefiting from the excellent charge storage capability and high photoresponse of GDY, this device exhibits over 256 distinct storage levels (8 bits) with signal-to-noise ratios larger than 100. Moreover, the fully 2D material and two-terminal architecture endows the device with robust bending stability for over 1,000 bending circles, paving the way to develop wearable electronics.

The microscopic structure of a macroscopic material assembled from a nanoscale determines its performance in practical functional applications. The rapid, effective, and in situ characterization of...

Mixed dimensional van der Waals (vdW) heterostructures constructed by one-dimensional (1D) and two-dimensional (2D) materials exhibit extra degree of freedom to modulate the electronic and optical properties due to the combination of different dimensionalities. The charge transfer at the interface between 1D and 2D materials plays a crucial role in the optoelectronic properties and performance of the heterostructure-based devices. Here, we stacked single-walled carbon nanotubes (SWNTs) on monolayer WS2 for a mixed dimensional vdW heterostructure, and investigated the local modulation of excitions and trions in WS2 by SWNTs. Different directions of charge transfer between SWNTs and WS2 are evidenced by the photoluminescence (PL) spectra of WS2. The PL intensity can be either enhanced or weakened by individual SWNTs. In our work, the PL intensity of WS2 is enhanced and the exciton peak position heterostructure is red-shifted about 3 meV due to the charge transfer from WS2 to an individual SWNT (SWNT#1). The change of PL by another SWNT (SWNT#2) can not be well-resolved in far-field, but scanning near-field optical microscope (SNOM) measurements show that the PL intensity of WS2 is weakened by the SWNT. The peak position of exciton is blue-shifted by ~ 1 meV while that of trion is redshifted by ~ 1 meV due to the charge transfer from the SWNT to WS2. These results give insight into the charge transfer at the interface of SWNT/WS2 heterostructure, and can be useful for design of optoelectronic devices based on mixed dimensional vdW heterostructures.

Quantitative analysis is a demanding challenge for surface-enhanced Raman scattering (SERS). A number of methods have been developed using different SERS-active substrates for quantitative detection of certain species. However, for a target analyte that is mixed with other molecules, the competitive adsorption of other molecules on the SERS substrate becomes the major disturbance to quantitative analysis or even qualitative detection. Whether it is possible to quantitatively detect a single analyte in a mixture of molecules using SERS has remained unclear. In this work, we explored the possibility of quantitative detection of multiple analytes by using graphene-based SERS (G-SERS). Graphene provides an atomically flat surface for homogeneous adsorption of molecules, and its own Raman scattering intensity can serve as internal standard in SERS for quantitative analysis. Our results show that the adsorption constants, the concentration and the Raman scattering cross sections of competing species are the most important factors to be considered. The findings could be helpful for quantitative analysis of target analyte in practical complex systems.

Twisted bilayer graphene (tBLG) has recently attracted growing interest due to its unique twist-angle-dependent electronic properties. The preparation of high-quality large-area bilayer graphene with rich rotation angles would be important for the investigation of angle-dependent physics and applications, which, however, is still challenging. Here, we demonstrate a chemical vapor deposition (CVD) approach for growing high-quality tBLG using a hetero-site nucleation strategy, which enables the nucleation of the second layer at a different site from that of the first layer. The fraction of tBLGs in bilayer graphene domains with twist angles ranging from 0° to 30° was found to be improved to 88%, which is significantly higher than those reported previously. The hetero-site nucleation behavior was carefully investigated using an isotope-labeling technique. Furthermore, the clear Moiré patterns and ultrahigh room-temperature carrier mobility of 68,000 cm2 V−1 s−1 confirmed the high crystalline quality of our tBLG. Our study opens an avenue for the controllable growth of tBLGs for both fundamental research and practical applications., The synthesis of twisted bilayer graphene with controllable angles is challenging. Here, the authors devise a chemical vapor deposition approach using a hetero-site nucleation strategy that affords twist angles ranging from 0° to 30°.

Molecular chirality transfer and amplification is at the heart of the fundamental understanding of chiral origin and fabrication of artificial chiral materials. We investigate here the nonlinear amplification effect in the chiral transfer from small molecules to assembled plasmonic nanoparticles. Our results show clearly a recognizable nonlinear behavior of the electronic and plasmonic circular dichroism activities, demonstrating the validity of the "majority-rules" principle operating in both the three-dimensional interface-confined molecularly chiral environment and the assembled plasmonic nanoparticles. Such twin "majority-rules" effects from the self-assembled organic-inorganic nanocomposite system have not been reported previously. By establishing a direct correlation between the dynamic template of the molecularly chiral environment and the nonlinear chiral amplification in the nanoparticle assemblies, this study may provide an insightful understanding of the hierarchical and cooperative chiral information transfer from molecular levels to nanoscales.

We propose a technique of Raman spectroscopy to characterize the excitonic nature and to evaluate the relative contribution of the two kinds of electron/exciton-phonon interactions that are observed in two-dimensional transition-metal dichalcogenides (TMDCs). In the TMDCs, the electron/exciton-phonon interactions mainly originate from the deformation potential (DP) or the Frohlich interaction (FI) which give the mutually different Raman tensors. Using a circularly polarized light, the relative proportion of the DP and the FI can be defined by the ratio of helicity-polarized intensity that is observed by MoS2. By this analysis, we show that the excitonic FI interaction gradually increases with decreasing temperature, contributes equally to DP at ∼230 K, and dominates at lower temperatures. The excitonic effect in the Raman spectra is confirmed by modulating the dielectric environment for the exciton and by changing the laser power.

Mg and its alloys generally exhibit the poor corrosion and wear resistances, which greatly limits their industrial applications. Inspired from an ordered layered structure within natural nacre, the homogeneous reduced graphene oxide/poly (vinyl alcohol) (RGO/PVA) coating is successfully fabricated on Mg alloy surface in the current study, through a facile spin-assisted layer-by-layer assembly (SA-LBL) technology. The hybrid hydrogen/covalent bond networks form between PVA chains and RGO sheets, resulting in a compact lamellar “bricks-and-mortar” structure. The microstructure of hybrid coating is strongly influenced by the cross-linking effect of PVA molecule, whose suitable content is beneficial to generating the densely stacked lamellar coating with excellent binding strength and reduced intrinsic defects, which can significantly improve its corrosion resistance. And the water molecules can hardly diffuse into the hybrid coating, leading to a long-term stability of samples in aqueous solution, ethanol and N, N-dimethylformamide. Besides, the high hardness and good lubricant effect of RGO sheets confer the hybrid coatings outstanding wear-resistant properties. Therefore, the bio-inspired RGO coating with a certain amount of PVA allows it to have a superior barrier effect and maintain the lubrication, which can provide an integrated protection for the corrosion and wear behaviors of Mg alloy.

Anisotropic two-dimensional (2D) materials exhibit lattice-orientation dependent optical and electrical properties. Carriers doping of such materials has been used to modulate their energy band structures for opto-electronic applications. Herein, we show that by stacking monolayer rhenium disulfide (ReS2) on a flat gold film, the electrons doping in ReS2 can affect the in-plane anisotropic Raman enhancement of molecules adsorbed on ReS2. The change of enhancement factor and the degree of anisotropy in enhancement with layer number are sensitively dependent on the doping level of ReS2 by gold, which is further confirmed by Kelvin probe force microscopy (KPFM) measurements. These findings could open an avenue for probing anisotropic electronic interactions between molecules and 2D materials with low symmetry using Raman enhancement effect.

Graphene has received abundant attentions in many applications because of its extraordinary properties. Liquid-phase exfoliation is one of the most important methods to obtain graphene from graphite. However, due to strong van der Waals interaction force, it is still extremely challenging to further improve the exfoliation efficiency. Here we report that by carrying out reductions with the oxygenic functional groups on the pristine graphite edges using hydrazine hydrate and hydrogen at 800 °C as a pretreatment approach, the exfoliation efficiency can be improved by ∼37% using a lithium-assisted liquid-phase exfoliation approach. The change of the functional groups is characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The graphene sheets show high degree of structural integrity and few defects. A thin film is prepared from the exfoliated graphene by vacuum assisted filtration and treated by annealing and mechanical compression. The graphene thin film shows a high thermal conductivity of 1707 W m−1 K−1, which is superior to that of common metal materials, such as Cu and Al.

We study the roles of graphene acting as a buffer layer for growth of an AlN film on a sapphire substrate. Graphene can reduce the density of AlN nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in AlN and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AlN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry.

Manipulating the polarization of light at the nanoscale is essential for the development of nano-optical devices. Owing to its corrugated honeycomb structure, two-dimensional (2D) layered black phosphorus (BP) exhibits outstanding in-plane optical anisotropy with distinct linear dichroism and optical birefringence in the visible region, which are superior characteristics for ultrathin polarizing optics. Herein, taking advantage of polarized Raman spectroscopy, we demonstrate that layered BP with a nanometer thickness can remarkably alter the polarization state of a linearly-polarized laser and behave as an ultrathin optical polarization element in a BP-Bi2Se3 stacking structure by inducing the exceptionally polarized Raman scattering of isotropic Bi2Se3. Our findings provide a promising alternative for designing novel polarization optics based on 2D anisotropic materials, which can be easily integrated in microsized all-optical and optoelectronic devices.

Controlled synthesis of structurally anisotropic rhenium diselenide (ReSe2) with macroscopically uniform and strictly monolayer thickness as well as tunable domain shape/size is of great interest for electronics-, optoelectronics-, and electrocatalysis-related applications. Herein, we describe the controlled synthesis of uniform monolayer ReSe2 flakes with variable morphology (sunflower- or truncated-triangle-shaped) on SiO2/Si substrates using different ambient-pressure chemical vapor deposition (CVD) setups. The prepared polycrystalline ReSe2 flakes were transferred intact onto Au foil electrodes and tested for activity in the hydrogen evolution reaction (HER). Interestingly, compared to the compact truncated-triangle-shaped ReSe2 flakes, their edge-abundant sunflower-shaped counterparts exhibited superior electrocatalytic HER activity, featuring a relatively low Tafel slope of ∼76 mV/dec and an exchange current density of 10.5 μA/cm2. Thus, our work demonstrates that CVD-grown ReSe2 is a promising two-dimensional anisotropic material for applications in the electrocatalytic HER.

Two-dimensional (2D) layered materials have attracted tremendous attention and led to a prosperous development in both fundamental investigation and device applications in various fields, such as nanoelectronics, flexible devices, sustainable energy and catalysts. The precise characterization of the structure and properties of 2D materials is in urgent need. Raman scattering spectroscopy is one of the most popular characterization tools that is convenient, rapid and non-invasive. It provides information on both the lattice structure from the frequency of phonon modes and the electronic band structure through the intensity due to electronic resonance Raman scattering. Although a few morphological characterization tools can image 2D materials with atomic resolution, Raman scattering measurements are more tolerant to the conditions of sample preparation such as the substrate and less technically demanding, and have been one of the routine tools for the characterization of 2D materials. In this review, we focus on the characterization of 2D materials using Raman scattering spectroscopy, in particular, the revealing of differences from primitive 2D materials, such as defects, doping effects, van der Waals heterostructures and the interaction with molecules. The characteristic Raman features of such differences and the corresponding interpretation will be discussed. We hope that this review will be useful for wide research communities of materials, physics, chemistry and engineering.

Towards future applications, like nanoelectronic devices, techniques to obtain single-walled carbon nanotubes (SWNTs) with specific electronic types (semiconducting or metallic ones) are urgently required. Herein, we developed a rational approach for the preferential etching of either metallic or semiconducting SWNTs assisted by selective adsorption of molecules onto the corresponding SWNTs. The adsorbed molecules were easily oxidized under a temperature below the threshold for the etching of SWNTs, and the heat generated during oxidation could accelerate the etching process of nearby SWNTs. Based on this design, we could obtain semiconducting-enriched or metallic-enriched SWNT arrays with a purity of 93% and 86% assisted by the adsorption of different molecules. Further in-situ observation by polarized optical microscope ensured the acceleration of the etching process of SWNTs adsorbed by the molecular igniters. Our method combines the advantages of solution separation (high selectivity and diversity) and gas-phase etching (clean and high efficiency), providing more feasibility in obtaining SWNT horizontal arrays with uniform properties.

As gas-phase etching has become an important method to obtain single-walled carbon nanotubes (SWCNTs) with specific electronic structures, numerous etchants were studied in the past decades. However, the understanding of the dynamic process as well as the etching state is still limited. Herein, we investigated the etching process of SWCNTs at the level of the individual tube in real time using an improved polarized optical microscope equipped with a miniature chemical vapor deposition (CVD) system. Experiments showed a universal etching behavior in a SWCNT oxidation process under different etchants (O2, H2O, and CO2), that is, the random appearance of etching sites and the self-terminating phenomenon. We built a new etching model at the level of the individual tubes to describe the etching rate. Based on this model, a new constant R, the ratio of etching rates between metallic and semiconducting SWCNTs, was defined to describe the etching selectivity. Optical spectroscopy was used to identify the chiralit...

Architectural windows are a major cause of thermal discomfort as the inner glazing during cold days can be several degrees colder than the indoor air. Mitigating this, the indoor temperature has to be increased, leading to unavoidable thermal losses. Here we present solar thermal surfaces based on complex nanoplasmonic antennas that can raise the temperature of window glazing by up to 8 K upon solar irradiation while transmitting light with a color rendering index of 98.76. The nanoantennas are directional, can be tuned to absorb in different spectral ranges, and possess a structural integrity that is not substrate-dependent, and thus they open up for application on a broad range of surfaces. © 2017 American Chemical Society. Funding Agencies|VR, Vetenskapsrådet; SSF, Stiftelsen för Strategisk Forskning; 2009 00971; 248154, FP7, Seventh Framework Programme; 309127, FP7, Seventh Framework Programme; RMA08-0109, SSF, Sjögren’s Syndrome Foundation; KVA, Royal Swedish Academy of Sciences

The semiconductor industry is increasingly of the view that Moore's law-which predicts the biennial doubling of the number of transistors per microprocessor chip-is nearing its end. Consequently, the pursuit of alternative semiconducting materials for nanoelectronic devices, including single-walled carbon nanotubes (SWNTs), continues. Arrays of horizontal nanotubes are particularly appealing for technological applications because they optimize current output. However, the direct growth of horizontal SWNT arrays with controlled chirality, that would enable the arrays to be adapted for a wider range of applications and ensure the uniformity of the fabricated devices, has not yet been achieved. Here we show that horizontal SWNT arrays with predicted chirality can be grown from the surfaces of solid carbide catalysts by controlling the symmetries of the active catalyst surface. We obtained horizontally aligned metallic SWNT arrays with an average density of more than 20 tubes per micrometre in which 90 per cent of the tubes had chiral indices of (12, 6), and semiconducting SWNT arrays with an average density of more than 10 tubes per micrometre in which 80 per cent of the nanotubes had chiral indices of (8, 4). The nanotubes were grown using uniform size Mo2C and WC solid catalysts. Thermodynamically, the SWNT was selectively nucleated by matching its structural symmetry and diameter with those of the catalyst. We grew nanotubes with chiral indices of (2m, m) (where m is a positive integer), the yield of which could be increased by raising the concentration of carbon to maximize the kinetic growth rate in the chemical vapour deposition process. Compared to previously reported methods, such as cloning, seeding and specific-structure-matching growth, our strategy of controlling the thermodynamics and kinetics offers more degrees of freedom, enabling the chirality of as-grown SWNTs in an array to be tuned, and can also be used to predict the growth conditions required to achieve the desired chiralities.

The poor corrosion and wear resistances hinder the industrial applications of magnesium and its alloys. In this paper, a new graphene oxide (GO) coating is fabricated on the surface of extruded Mg-Zn-Ca alloy, via the silane coupling agent. The GO coating has fully covered the Mg substrate through the chemical reactions, and formed an overlapped multilayer structure by interlocked effects. Electrochemical measurements indicate that the anti-corrosion performance can be remarkably improved by silane/GO coating, because the stable covalent bonds within the coating effectively restrict the penetration of electrolyte into the Mg surface, representing an excellent corrosion barrier effect. The GO coating drastically promotes the wear resistance, due to the superior bonding between the Mg substrate and GO sheets with high hardness and good lubricant effect.

Due to the single-molecule sensitivity and the capability of chemical fingerprints recognition, surface-enhanced Raman scattering (SERS) has been an attractive analytical technique used in various fields. However, SERS sensing still suffers from several problems, including the heterogeneous adsorption of molecules on SERS substrates, the spectral fluctuation of molecules, the photo/chemical reactions of molecules in direct contact with metal, and the continuum spectral background originated from fluorescence or photocarbonization. Such problems greatly hinder its practical applications, in particular, in SERS quantification. Graphene, the star of the two-dimensional (2D) materials family, can be used for Raman enhancement, termed as graphene-based surface-enhanced Raman scattering (G-SERS). In this review, we will introduce the discovery of graphene-enhanced Raman scattering (GERS), the chemical enhancement, and its extension to other 2D materials beyond graphene. Then we will concentrate on graphene-base...

The incident and scattered light engaged in the Raman scattering process of low symmetry crystals always suffer from the birefringence-induced depolarization. Therefore, for anisotropic crystals, the classical Raman selection rules should be corrected by taking the birefringence effect into consideration. The appearance of the 2D anisotropic materials provides an excellent platform to explore the birefringence-directed Raman selection rules, due to its controllable thickness at the nanoscale that greatly simplifies the situation comparing with bulk materials. Herein, a theoretical and experimental investigation on the birefringence-directed Raman selection rules in the anisotropic black phosphorus (BP) crystals is presented. The abnormal angle-dependent polarized Raman scattering of the Ag modes in thin BP crystal, which deviates from the normal Raman selection rules, is successfully interpreted by the theoretical model based on birefringence. It is further confirmed by the examination of different Raman modes using different laser lines and BP samples of different thicknesses.

Due to the in-plane structural anisotropy, two-dimensional (2D) layered materials with low symmetry exhibit unique crystalline-axis dependent properties, including the optical, mechanical and electrical properties. Raman spectroscopy, in particular, polarized Raman spectroscopy, has been used as a rapid and non-invasive technique to study the composition, structure and symmetry of 2D anisotropic layered materials. In this chapter, the recent advances on the Raman spectroscopic studies of anisotropic 2D materials are summarized. The Raman selection rules and the structural symmetry will be discussed, followed by the overview of the polarized Raman scattering studies of anisotropic 2D materials cataloged by crystal symmetries.

A trilayer single-crystalline GDY film on graphene was prepared through a solution-phase van der Waals epitaxial strategy., Graphdiyne (GDY) is an ordered two-dimensional (2D) carbon allotrope comprising sp- and sp2-hybridized carbon atoms with high degrees of π-conjugation, which features a natural band gap and superior electric properties. However, the synthesis of one- or few-layer GDY remains challenging because of the free rotation around alkyne-aryl single bonds and the lack of thickness control. We report the facile synthesis of an ultrathin single-crystalline GDY film on graphene through a solution-phase van der Waals epitaxial strategy. The weak admolecule-substrate interaction at the heterojunction drastically relaxes the large lattice mismatch between GDY and graphene. It allows the fast in-plane coupling of admolecules and slow out-of-plane growth toward the formation of an incommensurately stacked heterostructure, which is composed of single-layer graphene and few-layer ABC-stacked GDY, as directly observed by electron microscopy and identified from Raman fingerprints. This study provides a general route not only to the bottom-up synthesis of intriguing 2D acetylenic carbon allotropes but also to the device fabrication for the direct measurement of their intrinsic electrical, mechanical, and thermal properties.

Graphdiyne is predicted to have a natural band gap and simultaneously possesses superior carrier mobility, which makes it potential for electronic devices. Synthesis of ultrathin graphdiyne film is highly demanded. In this work, we proposed an approach for synthesis of ultrathin graphdiyne film using graphene as a surface template, which can induce confined reaction on substrate. With all-carbon, conjugated, atomically flat structure, graphene has a strong interaction with the graphdiyne system, resulting the formation of continuous flat ultrathin graphdiyne film with thickness less than 3 nm. Raman spectra, grazing incidence X-ray diffraction, and transmission electron microscopy characterization all confirmed the features of graphdiyne. Furthermore, this strategy was also extended to the hexagonal boron nitride (hBN) surface with resembling structure, serving as a perfect dielectric layer. Field-effect transistor devices based on graphdiyne film grown on hBN were fabricated directly, and electrical transport measurements demonstrate the good conductivity with p-type characteristics of the as-obtained graphdiyne film.

β-Graphdiyne (β-GDY) is a two-dimensional carbon material with zero band gap and highly intrinsic carrier mobility and a promising material with potential applications in electronic devices. However, the synthesis of continuous single or ultrathin β-GDY has not been realized yet. Here, we proposed an approach for ultrathin β-GDY-like film synthesis using graphene as a template because of the strong π–π interaction between β-GDY and graphene. The as-synthesized film presents smooth and continuous morphology and has good crystallinity. Electrical measurement reveals that the film presented a conductivity of 1.30 × 10–2 S·m–1 by fabricating electronic devices on β-GDY grown on a dielectric hexagonal boron nitride template.

The striking in-plane anisotropy remains one of the most intriguing properties for the newly rediscovered black phosphorus (BP) 2D crystals. However, because of its rather low-energy band gap, the optical anisotropy of few-layer BP has been primarily investigated in the near-infrared (NIR) regime. Moreover, the essential physics that determine the intrinsic anisotropic optical property of few-layer BP, which is of great importance for practical applications in optical and optoelectronic devices, are still in the fancy of theory. Herein, we report the direct observation of the optical anisotropy of few-layer BP in the visible regime simply by using polarized optical microscopy. On the basis of the Fresnel equation, the intrinsic anisotropic complex refractive indices (n-iκ) in the visible regime (480-650 nm) were experimentally obtained for the first time using the anisotropic optical contrast spectra. Our findings not only provide a convenient approach to measure the optical constants of 2D layered materials but also suggest a possibility to design novel BP-based photonic devices such as atom-thick light modulators, including linear polarizer, phase plate, and optical compensator in a broad spectral range extending to the visible window.

Semiconducting single‐walled carbon nanotubes (s‐SWNTs) are regarded as an important candidate for infrared (IR) optical detection due to their excellent intrinsic properties. However, the strong binding energy of excitons in s‐SWNTs seriously impedes the development of s‐SWNTs IR photodetector. This Communication reports an IR photodetector with highly pure s‐SWNTs and γ‐graphdiyne. The heterojunctions between the two materials can efficiently separate the photogenerated excitons. In comparison to device fabricated only with s‐SWNTs, this IR detector shows a uniform response in the whole channel of the device. The response time is demonstrated to be below 1 ms. The optimal responsivity and detectivity approximately reach 0.4 mA W−1 and 5 × 106 cmHz1/2 W−1, respectively.

Graphyne (GY) is a new type of carbon allotrope, which is viewed as a rapidly rising star in the carbon family referred to as 2D carbon allotropes due to its extraordinary properties. Considering the dynamic nature of the alkyne metathesis reaction, a hydrogen-substituted graphyne (HsGY) film is successfully synthesized on a gas/liquid interface using 1,3,5-tripynylbenzene (TPB) as the precursor. The synthesized HsGY film is used as a sulfur host matrix to be applied in lithium-sulfur batteries (LSBs). The HsGY@S electrode is prepared using S8 as sulfur source and presents excellent electrochemical performance.

The identification of the crystalline axis of anisotropic black phosphorus (BP) is key for the study of its physical properties and for its optical and electronic applications. Herein, we show that by applying an in-plane uniaxial strain and measuring the changes of Raman shifts, the crystalline axis of BP can be reliably determined. The strain effects on Raman shifts are angle-dependent, which can be expressed as a combination of Raman responses under zigzag and armchair strains. Different from previous polarized optical spectroscopic means, the proposed method does not rely on the laser polarization, the excitation wavelength, the sample thickness and the material of the stretchable substrate. Besides, the effective strain applied on BP from the stretched substrate is estimated, showing that only 20% to 40% of the strain can be effectively transferred to BP flakes from polyethylene terephthalate substrates. Our method provides not only an effective and universal approach to identify the crystalline orientation of layered BP, but also a model to extract additional information in strain-related studies, and can be extended to other 2D anisotropic materials., 28 pages, 10 figures. There are some incorrect description would cause misunderstanding

A strategy and implementation for efficiency enhancement of optimized high performance organic solar cells by a plasmonic nanostructured Ag rear electrode is presented. This enhancement is achieved by tuning the surface plasmon resonance of the nanostructures to the active layer absorption tail, which generates enhanced absorption by light scattering, as verified by experiment and simulation. © 2013 WILEY-VCH Verlag GmbH and Co.

Corrugation is a ubiquitous phenomenon for graphene grown on metal substrates by chemical vapor deposition, which greatly affects the electrical, mechanical, and chemical properties. Recent years have witnessed great progress in controlled growth of large graphene single crystals; however, the issue of surface roughness is far from being addressed. Here, the corrugation at the interface of copper (Cu) and graphene, including Cu step bunches (CuSB) and graphene wrinkles, are investigated and ascribed to the anisotropic strain relaxation. It is found that the corrugation is strongly dependent on Cu crystallographic orientations, specifically, the packed density and anisotropic atomic configuration. Dense Cu step bunches are prone to form on loose packed faces due to the instability of surface dynamics. On an anisotropic Cu crystal surface, Cu step bunches and graphene wrinkles are formed in two perpendicular directions to release the anisotropic interfacial stress, as revealed by morphology imaging and vibrational analysis. Cu(111) is a suitable crystal face for growth of ultraflat graphene with roughness as low as 0.20 nm. It is believed the findings will contribute to clarifying the interplay between graphene and Cu crystal faces, and reducing surface roughness of graphene by engineering the crystallographic orientation of Cu substrates.

Correction for ‘Spotting the differences in two-dimensional materials – the Raman scattering perspective’ by Shishu Zhang et al., Chem. Soc. Rev., 2018, DOI: 10.1039/c7cs00874k.

Controllable synthesis of carbon nanotubes (CNTs) is of great importance in its further application, which attracts broad attention. As growth and etching are the two sides in the process of material crystallography and the control of the competition between them forms the foundation for modern technology of materials design and manufacture, the understanding on etching process of carbon nanotubes is still very unclear because technically it is of great challenge to characterize the dynamics in such small one-dimensional (1D) scale. Here the real-time investigation on the etching process of CNTs is reported, by the hot-wall chemical reactor equipped with a polarized optical microscope. It is discovered that the CNT etching behavior in air is totally of random, including the etching sites, termination sites, and structure dependence. Combining with the dynamic simulation, it is revealed that the random behavior reflects the unique "self-termination" phenomenon. A structure-independent etching propagation barrier of 2.4 eV is also obtained, which indicates that the etching propagation process still follows the conventional Kinetic Wulff construction theory. The results represent the new knowledge on the etching process in carbon nanotube and can contribute to its selective enrichment. Furthermore, the "self-termination" phenomenon may be a universal behavior in 1D process.

The decontamination of water polluted with heavy metal ions is of worldwide concern. Among various treatment approaches to remove metal ions from water, adsorption is regarded as an efficient method, and a variety of materials have been applied as adsorbents for the removal of metal ions from polluted water. Recently, carbon nanomaterials have been examined as alternative adsorbents due to their high specific surface areas, high removal efficiency, and strong interactions with metal ions. Graphdiyne, a new kind of carbon allotrope composed of sp- and sp2-hybridized carbon atoms, has attracted great interest due to its impressive properties. Graphdiyne is considered to be a promising candidate for the adsorption of heavy metal ions as the acetylenic links in graphdiyne strongly interact with metal ions. Herein, graphdiyne is used as an adsorbent to remove lead ions from water. The interaction between lead ions and graphdiyne is explored by X-ray photoelectron spectroscopy and Raman spectroscopy. The maximum adsorption capacity calculated by the Langmuir isotherm model is 470.5 mg g−1. Graphdiyne is also synthesized on copper foam and used as a filter to eliminate lead ions from water. The filter shows high performance with a removal efficiency of 99.6% and can be recovered through treatment with acidic solution.

Quantitative surface-enhanced Raman spectroscopy (SERS) with ultrahigh sensitivity will significantly promote its practical application in many fields, such as environment monitoring, food safety, and drug detection. However, the challenges that remain unresolved, particularly in the low concentration levels, arise from the instability of the SERS spectra and the uncertainty of the number of detected molecules. Herein, a graphene-based, flexible, and transparent substrate for SERS quantification is reported, wherein the 2D single-crystalline nature of graphene promises the homogeneous adsorption of molecules, facilitating the determination of the number of molecules, the separation of molecules from metal, which ensures the stability of the Raman signals, and an internal standard for the calibration of SERS intensities. The in situ quantification of probe molecules is demonstrated in an aqueous solution down to the detection limit of 10−8m, and the real-time, in situ monitoring of the release process of rhodamine B molecules, which mimics practical application, for example, the controlled release of medicine, is shown. The results open up an avenue for reliable SERS quantification for practical applications with high efficiency and low cost.

β-Graphdiyne (β-GDY) is a member of 2D graphyne family with zero band gap, and is a promising material with potential applications in energy storage, organic electronics, etc. However, the synthesis of β-GDY has not been realized yet, and the measurement of its intrinsic properties remains elusive. In this work, β-GDY-containing thin film is successfully synthesized on copper foil using modified Glaser-Hay coupling reaction with tetraethynylethene as precursor. The as-grown carbon film has a smooth surface and is continuous and uniform. Electrical measurements reveal the conductivity of 3.47 × 10-6 S m-1 and the work function of 5.22 eV. TiO2 @β-GDY nanocomposite is then prepared and presented with an enhancement of photocatalytic ability compared to pure TiO2 .