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Controlling the dynamic responses of different ordered phases has stimulated extensive research interests. Here, the implementation of a charge‐density‐wave (CDW) for terahertz detection is reported and its extremely high sensitivity driven by CDW distortion is demonstrated. The collective excitation combined with the strong interaction with long‐wavelength photons opens up novel feasibility toward realistic exploration of many‐body states for imaging and sensing applications.

Abstract

The quantum behavior of carriers in solid is the foundation of modern electronic and optoelectronic technology, but it is still facing huge challenges within inherited single‐particle quantum processes working at the millimeter wave/terahertz (THz) band. Here, a straightforward strategy for the direct detection of millimeter wave/THz photons in a sub‐wavelength metal‐TaSe₂‐metal structure under strong interaction with a localized field of surface plasmon is proposed. By breaking the inversion symmetry under the perturbations of electric field and atomic reconstruction from van der Waals integration, the nonequilibrium electronic states under a radiant field can be manipulated in a collective fashion, leading to a large photocurrent responsivity over 40 A W⁻¹ and noise equivalent power less than 1 pW Hz^−1/2 even at room temperature. A more than 40‐fold enhancement in responsivity is achieved when transitioning from the normal phase to the CDW phase. The findings shed fresh light on the understanding of the delicate balance in the charge‐ordered phase, and facilitate the exploitation of a correlated electron system for optoelectronic applications in fields of security, remote sensing, and imaging.

Nature Nanotechnology, Published online: 02 September 2019; doi:10.1038/s41565-019-0536-5

Few-layer micas show proton permeation across the sheet, exceeding that of graphene and hBN by one to two orders of magnitude.

Great progress has been achieved in the research field of topological states of matter during the past decade. Recently, a quasi–1-dimensional bismuth bromide, Bi4Br4, has been predicted to be a rotational symmetry-protected topological crystalline insulator; it would also exhibit more exotic topological properties under pressure. Here, we report a thorough...

Sea energy harvesting with carbon nanomaterials is an attractive renewable energy utilization strategy. Recently, studies with the focus on electric energy generation with various graphene-based materials combined with ionic fluids have been reported. However, reliable materials for the energy generation from the mechanical movements of seawater are still a challenge. In the present work, a wrinkled graphene based highly sensitive and stable electric generator has been developed and applied to multiple seawater movements with superior performances. The electric generation mechanism from the mechanical movements of seawater including droplet movement, boundary shift, and continuous flow is explored, and the corresponding electric generation performances are evaluated. The results suggest that the surface wrinkle nanostructure of graphene can enable energy harvesting from continuously flowing ionic liquid due to the drifting of adsorbed ions and ion accumulation in the wrinkles. B...

Quantum spin Hall (QSH) insulator with large gap is highly desirable for potential spintronics application. Here we realize electrically tunable QSH insulator with large gap in van der Waals heterobilayer of monolayer transition metal dichalcogenide (TMD) and hexagonal boron arsenide (BAs), in particular the WSe 2 /BAs heterobilayer. When the type II band alignment gets inverted in an electric field, the hybridization by interlayer hopping between the spin-valley locked valence band edges in TMD and the BAs conduction band edges leads to a stacking-configuration dependent topological band inversion. In the non-interacting limit, the double spin degeneracy of BAs leaves an un-hybridized conduction band inside the gap, so the heterobilayer is a spin-valley locked metal instead of a QSH insulator. With the Coulomb interaction accounted in the double-layer geometry, the interaction with the hybridization induced electric dipole shifts this un-hybridized conduction band upwa...

Violet phosphorus (VP), also known as Hittorf’s phosphorus (HP), is promised a next-generation 2D material with black phosphorus (BP). It is an intermediate in the process of synthesizing blacks starting with red phosphorus (RP), and has a unique activity. This VP does not show up in both red and black, and has a catalytic reduction performance. This catalytic performance was further enhanced by the partially oxidized P=O structure and showed a recyclable performance by reducing the 30 mg l −1 high concentration dye in a few minutes. The properties of the synthesized materials were confirmed by XRD, TEM, SEM, EDS, UV–vis–NIR spectrophotometer, FT-IR, EPR and Raman spectroscopy techniques. Dye materials were quantitatively analyzed by UV–vis-spectrophotometer using 4-nitrophenol, methylene blue (MB), rhodamine B, and the catalytic activity was measured. The amorphous VP had a very strong negative charge and the P=O structure acted as a redox functional group. The object...

Twisted bilayer graphene with a twist angle of exactly 30° (30°-TBG) is a unique two-dimensional (2D) van der Waals (vdW) system because of its quasicrystalline nature. Here we report, for the first time, scanning tunneling microscopy (STM) measurements of the quasicrystalline 30°-TBG that was obtained in a controllable way by using transfer-assisted fabrication of a pair of graphene sheets. The quasicrystalline order of the 30°-TBG, showing a 12-fold rotational symmetry, was directly visualized in atomic-resolved STM images. In the presence of high magnetic fields, we observed Landau quantization of massless Dirac fermions, demonstrating that the studied 30°-TBG is a relativistic Dirac fermion quasicrystal. Because of a finite interlayer coupling between the adjacent two layers of the 30°-TBG, a suppression of density-of-state (DOS) at the crossing point between the original and mirrored Dirac cones was observed. Moreover, our measurements also observe strong intervalley scatte...

The strong light–matter interaction in two dimensional (2D) materials portends an untapped potential for fiber lasers in the long sought-after terahertz to mid-infrared spectral range. Here, the broadband nonlinear optical properties of zero-gap 2D Ti 2 CT x MXene—a class of 2D transition metal carbides that exhibit high laser damage threshold—is discussed. Using the open aperture Z -scan method, for the first time the broadband saturable absorption properties of Ti 2 CT x in the 800–1560 nm spectral range are demonstrated. Specifically, it is shown that the high absorption and low saturation intensity of Ti 2 CT x make it an ideal saturable absorber for mode-locked fiber lasers operating at 1565 and 1051 nm, which exhibited pulse widths of 5.3 ps and 164 ps, respectively. Additionally, a Ti 2 CT x saturable absorber was used as a Q-switcher to realize a pulsed f...

Cancer phototherapy (PT) including photodynamic therapy (PDT) and photothermal therapy (PTT) has attracted extensive interest due to its non-invasive and region-specific nature. In order to enhance the efficacy, we have fabricated various nanocomposites consisting of a photosensitizer (chlorin e 6 (Ce6), pheophorbide a (Pa) or bacteriopheophorbide a (bPa)) for PDT and a two-dimensional nanosheet (graphene or MoS 2 ) for PTT by a one-pot protocol through liquid phase exfoliation. In addition, an anticancer drug (doxorubicin (DOX) or irinotecan (Ir)) was loaded on the nanosheet in the same way for comparison. The nanocomposites demonstrated stability when dispersed in water except for MoS 2 –Ir. We observed that MoS 2 -Ce6 killed cancer cells over ten times more effectively than other Ce6-loaded nanocomposites.

Atomically-thin magnetic crystals have been recently isolated experimentally, greatly expanding the family of two-dimensional materials. In this Article we present an extensive comparative analysis of the electronic and magnetic properties of ##IMG## [http://ej.iop.org/images/2053-1583/6/4/045042/tdmab2f06ieqn001.gif] , based on density functional theory (DFT). We first show that the often-used ##IMG## [http://ej.iop.org/images/2053-1583/6/4/045042/tdmab2f06ieqn002.gif] approaches fail in predicting the ground-state properties of this material in both its monolayer and bilayer forms, and even more spectacularly in its bulk form. In the latter case, the fundamental gap decreases by increasing the Hubbard- U parameter, eventually leading to a metallic ground state for physically relevant values of U , in stark contrast with experimental data. On the contrary, the use of hybrid functionals, which naturally take int...

Designing the nature-driven 3D scaffold is essential for reconstructing of the injured brain in association with stem cell replacement therapy. In this paper, we developed brain cortex-mimetic 3D hybrid scaffolds and applied them to a motor-cortectomy rat model. Graphene oxide bacterial cellulose (GO-BC) hybrid scaffold integrated GOs stably and homogeneously within BC nanofibrous building blocks made of BC and amphiphilic comb-like polymers (APCLP). Density functional theory calculations and molecular dynamics simulations revealed higher binding energies between GO-BC and APCLP than between GO or APLCP with BC. The monodispersed human neural stem cells (F3 cells) incorporated within the GO-BC scaffold generated a large number of differentiated neurons with robust neurite outgrowths and possible synapse formation in vitro . In corticectomized rats and nude mice, highly sensitive photoacoustic signals visualized the GO-BC at the implant site. Moreover, the implanted F3 cell...

A multibeam interference model is developed to analyze irregular scattering‐type scanning near‐field optical microscopy images of polaritons induced by small sample size or complex edges. This model extracts the polariton wave vectors and ratio of scattering rate to reflectivity at edge, which is important for studying van der Waals nanomaterials smaller than 10 µm and designing integrated nanophotonic devices.

Abstract

Van der Waals (vdW) materials are among the most promising candidates for photonic integrated circuits because they support a full set of polaritons that can manipulate light at deep subdiffraction nanoscale. It is possible to directly probe the propagating polaritons in vdW materials in real space via scattering‐type scanning near‐field optical microscopy, such that the wave vector and lifetime of the polaritons can be extracted from as‐measured interference fringes by Fourier analysis. However, this method is unsuitable for clutter interference patterns in samples exhibiting inadequate fringes due to small size (less than 10 µm) or complex edges that are often encountered in nanophotonic devices and new material characterization. Here, a multibeam interference model is developed to analyze complex images by disentangling them into periodic patterns and residue. By employing phase stationary approximation, polariton wave vector can be derived from offset ratio of the center point, and the ratio of polariton reflection and scattering rates at the edge is obtained from the ratio of the periodic and aperiodic patterns. This method can be widely used in the optical characterization of new vdW materials that are difficult to synthesize into large crystals, as well as nanophotonic integrated devices with unique boundaries.

Various theoretical and experimental researches regarding the mechanism of degradation and passivation strategies are proposed and reported to overcome the problem of the ambient instability of phosphorene. Here, not only an extensive summary of these passivation strategies but also an overview of the fabrication methods, challenges, and suitable applications of phosphorene are provided.

Abstract

Phosphorene as a rising star is a monolayer or few‐layer form of black phosphorus (BP), which is used as a 2D material, in addition to graphene. This monoelemental 2D material has gained considerable attention in the fields of electronics, optoelectronics, and biomedicine due to its extraordinary physical properties. However, as both theoretical and experimental works show, the intrinsic instability of phosphorene under ambient conditions is a major challenge in practical applications. Various theoretical and experimental researches regarding the mechanism of the degradation and passivation strategies are proposed and reported to overcome the problem of the ambient instability of phosphorene. These strategies have enabled researchers to conduct fundamental studies on phosphorene's extraordinary properties. Here, not only an extensive summary of these passivation strategies but also an overview of the fabrication methods, challenges, and suitable applications of phosphorene are provided.

Porous carbon nitrides enable “facile functionalization” when its domain is wetted by solution of metal halides with mobile cations/anions. During the wetting process, each cavity can be functionalized by a unit of metal halide, endowing the systems with various desirable properties for potential applications in multiferroicity, piezoelectronics, valleytronics, and photovoltaics.

Abstract

Ab initio calculation evidence has shown that two‐dimensional (2D) carbon nitrides may enable “facile functionalization” when a domain of carbon nitride is wetted by a solution of metal halides with mobile cations/anions. During the wetting process, each cavity can be functionalized by a unit of metal halide. Compared with prevailing functionalization or doping strategies through either high‐temperature diffusion of source ions or ion implantation by using accelerators, such a room‐temperature “wet‐lab” functionalization approach is more facile and efficient. The wet‐lab functionalization not only can facilitate isolation of the 2D monolayer, but also, with applying different metal halides, enable various new and desirable properties for broad applications, e.g., 2D magnetism and 2D ferroelectricity with high piezoelectric coefficient. The latter can be implemented in spin‐independent valleytronics for non‐volatile electrical manipulations. Notably, tunable bandgaps, ranging from 1.0 to 2.5 eV, can be realized by controlling the metal‐halide functionalization density, while the separation of electrons/holes can be facilitated by the ferroelectric polarizations and heterostructure band alignments. Moreover, multifunctional domains like P/N doped or magnetic/ferroelectric domains can be selectively constructed through such solution‐processed functionalization with different halides, followed by seamless integration into a single sheet of carbon nitride, akin to the P/N channels in silicon wafers.

The doping of three‐dimensional (3D) graphene has emerged as a topic of interest because of attempts to combine its large available surface area and superior catalytic, structural, chemical, and biocompatible characteristics that can be induced by doping. This review provides an overview of the scalable chemical‐vapor‐deposition‐based growth of doped 3D graphene materials and their applications in various contexts.

Abstract

Graphene doping principally commenced to compensate for its inert nature and create an appropriate bandgap. Doping of 3D graphene has emerged as a topic of interest because of attempts to combine its large available surface area—arising from its interconnected porous architecture—with superior catalytic, structural, chemical, and biocompatible characteristics that can be induced by doping. In light of the latest developments, this review provides an overview of the scalable chemical vapor deposition (CVD)‐based growth of doped 3D graphene materials as well as their applications in various contexts, such as in devices used for energy generation and gas storage and biosensors. In particular, single‐ and multielement doping of 3D graphene by various dopants (such as nitrogen (N), boron (B), sulfur (S) and phosphorous (P)), the doping configurations of the resultant materials, an overview of recent developments in the field of CVD, and the influence of various parameters of CVD on graphene doping and 3D morphologies are focused in this paper. Finally, this report concludes the discussion by mentioning the existing challenges and future opportunities of these developing graphitic materials, intending to inspire the unveiling of more exciting functionalized 3D graphene morphologies and their potential properties, which can hopefully realize many possible applications.

An ultraflexible and stretchable affinity nanosensor consisting of aptamer‐functionalized graphene on a 2.5‐µm Mylar substrate is presented. Aptamer‐biomarker binding induces a measurable change in the carrier concentration of the graphene for determination of the biomarker concentration. The device is shown to incur no visible mechanical damage, and maintain consistent electrical properties and biomarker responses under large bending, twisting, and stretching deformations.

Abstract

An ultraflexible and stretchable field‐effect transistor nanosensor is presented that uses aptamer‐functionalized monolayer graphene as the conducting channel. Specific binding of the aptamer with the target biomarker induces a change in the carrier concentration of the graphene, which is measured to determine the biomarker concentration. Based on a Mylar substrate that is only 2.5‐µm thick, the nanosensor is capable of conforming to underlying surfaces (e.g., those of human tissue or skin) that undergo large bending, twisting, and stretching deformations. In experimental testing, the device is rolled on cylindrical surfaces with radii down to 40 µm, twisted by angles ranging from −180° to 180°, or stretched by extensions up to 125%. With these large deformations applied either cyclically or non‐recurrently, the device is shown to incur no visible mechanical damage, maintain consistent electrical properties, and allow detection of TNF‐α, an inflammatory cytokine biomarker, with consistently high selectivity and low limit of detection (down to 5 × 10⁻¹² m). The nanosensor can thus potentially enable consistent and reliable detection of liquid‐borne biomarkers on human skin or tissue surfaces that undergo large mechanical deformations.

Devices made from two-dimensional (2D) materials such as graphene and transition metal dichalcogenides exhibit remarkable electronic properties of interest to many subdisciplines of nanoscience. Owing to their 2D nature, their quality is highly susceptible to contamination and degradation when exposed to the ambient environment. Protecting the 2D layers by encapsulation between hexagonal boron nitride (hBN) layers significantly improves their quality. Locating these samples within the encapsulant and assessing their integrity prior to further processing then becomes challenging. Here we show that conductive scanning probe techniques such as electrostatic force and Kelvin force microscopy make it possible to visualize the encapsulated layers, their charge environment and local defects on the sub-micrometer scale. Our techniques are employed without requiring electrical contact to the embedded layer, providing valuable feedback on the device’s local electronic quality prior to any...