Room-Temperature Quantum Hall Effect in Graphene

Barut-Girardello coherent states for anisotropic 2D-Dirac materials

We construct the Barut-Girardello coherent states for charge carriers in anisotropic 2D-Dirac materials immersed in a constant homogeneous magnetic field which is orthogonal to the sample surface. For that purpose, we solve the anisotropic Dirac equation and identify the appropriate arising and lowering operators. Working in a Landau-like gauge, we explicitly construct nonlinear coherent states as eigenstates of a generalized annihilation operator with complex eigenvalues which depends on an arbitrary function f  of the number operator. In order to describe the anisotropy effects on these states, we obtain the Heisenberg uncertainty relation, the probability density, mean energy value and occupation number distribution for three different functions f . For the case in which the anisotropy is caused by uniaxial strain, we obtain that when the stress is applied along the x-axis of the material surface, the probability density for the nonlinear coherent states is smaller compared to when the material is stressed along the orthogonal axis.

Intact Crystalline Semiconducting Graphene Nanoribbons from Unzipping Nitrogen-Doped Carbon Nanotubes

Unzipping carbon nanotubes (CNTs) may offer a valuable route to synthesize graphene nanoribbon (GNR) structures with semiconducting properties. Unfortunately, currently available unzipping methods commonly rely on a random harsh chemical reaction and thereby cause significant degradation of the crystalline structure and electrical properties of GNRs. Herein, crystalline semiconducting GNRs are achieved by a synergistic, judiciously designed two-step unzipping method for N-doped CNTs (NCNTs). NCNTs are effectively unzipped by damage-minimized, dopant-specific electrochemical unzipping and subsequent sonochemical treatment into long ribbon-like nanostructures with crystalline basal planes. Owing to the nanoscale dimension originating from the dense nucleation of the unzipping reaction at highly NCNTs, the resultant GNRs demonstrate semiconducting properties, which can be exploited for chemiresistor-type gas-sensing devices and many other applications.

Induced growth of quasi-free-standing graphene on SiC substrates

Free-standing graphene grown on SiC substrates is desirable for micro- and nano-electronic device applications. In this work, an induced growth method to fabricate quasi-free-standing graphene on SiC was proposed, where graphene nucleation sites were generated on the SiC substrate and active carbon sources were subsequently introduced to grow graphene centered along the established nucleation sites. The structure and morphology of the cultivated graphene were characterized by using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Compared to the traditional epitaxial growth methods on SiC substrates, this approach shows a significant reduction of the buffer layer. This study provides an efficient method for growing quasi-free-standing graphene on SiC substrates and is believed to be able to broaden the application of graphene in electronic devices as SiC is an intrinsically outstanding wide bandgap semiconductor.

Quasi-free-standing graphene on a SiC substrate was directly prepared by using the induced graphene growth method.

Schottky barrier modulation of a GaTe/graphene heterostructure by interlayer distance and perpendicular electric field

Two-dimensional materials have recently been the focus of extensive research. Graphene-based vertical van der Waals heterostructures are expected to design and fabricate novel electronic and optoelectronic devices. Monolayer gallium telluride is a graphene-like nanosheet synthesized in experiment. Here, the electronic properties of GaTe/graphene heterostructures are investigated under the interlayer coupling and the applied perpendicular electric field. The results show that the electronic properties of GaTe and graphene are preserved, and the energy bandgap of graphene is opened to 13.5 meV in the GaTe/graphene heterostructure. It is found that the n-type Schottky contact is formed in the GaTe/graphene heterostructure, which can be tuned by the interlayer coupling, and the applied electric field. Moreover, a transformation from n-type to p-type Schottky contact is observed when the interlayer distance is smaller than 3.15 Å or the applied electric field is larger than 0.05 V Å^-1. These properties are fundamental to the design of new Schottky nanodevices based on the GaTe/graphene heterostructure.

A comparative study of the thermoelectric performance of graphene-like BX (X = P, As, Sb) monolayers

The electronic and phonon transport properties of graphene-like boron phosphide (BP), boron arsenide (BAs), and boron antimonide (BSb) monolayers are investigated using first-principles calculations combined with the Boltzmann theory. By considering both the phonon-phonon and electron-phonon scatterings, we demonstrate that the strong bond anharmonicity in the BAs and BSb monolayers can dramatically suppress the phonon relaxation time but hardly affect that of electron. As a consequence, both systems exhibit comparable power factors with that of the BP monolayer but much lower lattice thermal conductivities. Accordingly, a maximum ZT value above 3.0 can be realized in both BAs and BSb monolayers at optimized carrier concentration. Interestingly, very similar p - and n-type thermoelectric performance is observed in the BSb monolayer along the zigzag direction, which is of vital importance in the fabrication of thermoelectric modules with comparable efficiencies.

Phosphorene and Black Phosphorus: The 31P NMR View

This work aims at characterizing for the first time the ³¹P spin interactions determining the nuclear magnetic resonance (NMR) properties of solid black phosphorus (bP) and of its few-layer exfoliated form (fl-bP). Indeed, the knowledge of these properties is still very poor, despite the great interest received by this layered phosphorus allotrope and its exfoliated 2D form, phosphorene. By combining density functional theory (DFT) calculations and solid-state NMR experiments on suspensions of fl-bP nanoflakes and on solid bP, it has been possible to characterize the ³¹P homonuclear dipolar and chemical shift interactions, identifying the network of ³¹P nuclei more strongly dipolarly coupled and highlighting two kinds of magnetically nonequivalent ³¹P nuclei. These results add an important missing piece of information to the fundamental chemico-physical knowledge of bP and support future extensive applications of NMR spectroscopy to the characterization of phosphorene-based materials.

Self-Confined Growth of Ultrathin 2D Nonlayered Wide-Bandgap Semiconductor CuBr Flakes

2D planar structures of nonlayered wide-bandgap semiconductors enable distinguished electronic properties, desirable short wavelength emission, and facile construction of 2D heterojunction without lattice match. However, the growth of ultrathin 2D nonlayered materials is limited by their strong covalent bonded nature. Herein, the synthesis of ultrathin 2D nonlayered CuBr nanosheets with a thickness of about 0.91 nm and an edge size of 45 µm via a controllable self-confined chemical vapor deposition method is described. The enhanced spin-triplet exciton (Z_f , 2.98 eV) luminescence and polarization-enhanced second-harmonic generation based on the 2D CuBr flakes demonstrate the potential of short-wavelength luminescent applications. Solar-blind and self-driven ultraviolet (UV) photodetectors based on the as-synthesized 2D CuBr flakes exhibit a high photoresponsivity of 3.17 A W^-1 , an external quantum efficiency of 1126%, and a detectivity (D*) of 1.4 × 10¹¹ Jones, accompanied by a fast rise time of 32 ms and a decay time of 48 ms. The unique nonlayered structure and novel optical properties of the 2D CuBr flakes, together with their controllable growth, make them a highly promising candidate for future applications in short-wavelength light-emitting devices, nonlinear optical devices, and UV photodetectors.

Strong magnetophonon oscillations in extra-large graphene

Van der Waals materials and their heterostructures offer a versatile platform for studying a variety of quantum transport phenomena due to their unique crystalline properties and the exceptional ability in tuning their electronic spectrum. However, most experiments are limited to devices that have lateral dimensions of only a few micrometres. Here, we perform magnetotransport measurements on graphene/hexagonal boron-nitride Hall bars and show that wider devices reveal additional quantum effects. In devices wider than ten micrometres we observe distinct magnetoresistance oscillations that are caused by resonant scattering of Landau-quantised Dirac electrons by acoustic phonons in graphene. The study allows us to accurately determine graphene’s low energy phonon dispersion curves and shows that transverse acoustic modes cause most of phonon scattering. Our work highlights the crucial importance of device width when probing quantum effects and also demonstrates a precise, spectroscopic method for studying electron-phonon interactions in van der Waals heterostructures.

Increasing the size of mesoscopic devices based on van der Waals heterostructures triggers additional quantum effects. Here, the authors observe distinct magnetoresistance oscillations in graphene/h-BN Hall bars only in devices wider than 10 μm due to resonant scattering of charge carriers by transverse acoustic phonons in graphene.

Optical interband transitions in strained phosphorene

In this paper, we have concentrated on the orbital and hybridization effects induced by applied triaxial strain on the interband optical conductivity (IOC) of phosphorene using a two-band Hamiltonian model, linear response theory and the Kubo formula. In particular, we study the dependence of the electronic band structure and of the IOC of a phosphorene single layer on the modulus and direction of the applied triaxial strain. The triaxial strain is included in a model through the introduction of strain-dependent hopping parameters using the Harrison rule. Among the various configurations for applying the triaxial strain, considerable findings are presented here in three classes: (i) uniform, (ii) in-plane uniform and (iii) non-uniform triaxial strain. The main consequence of applying triaxial strain is that of increasing and decreasing the band gap depending on the considered class of study, resulting in a blue shift and red shift of the interband optical transitions, respectively. Our results show that a pure blue shift independent of the strain modulus as well as strain sign (tensile or compressive) emerges when applying non-uniform triaxial strain. The overall feature of our outcomes is tailoring the edge-dependent optical responses of phosphorene in the presence of triaxial strain, which provides the required conditions of tuning the optical properties of phosphorene for future experimental research.

Electrochemical aptasensor for activated protein C using a gold nanoparticle - Chitosan/graphene paste modified carbon paste electrode

In this work, a selective and simple electrochemical aptasensor was developed for the detection of activated protein C by employing methylene blue (MB) as a redox indicator. An activated protein C aptamer (APC-apt) was covalently immobilized on the surface of a carbon paste electrode modified with gold nanoparticle - chitosan /graphene paste (AuNPs-Chi/Gr). The AuNPs-Chi/Gr paste increased electrochemical peak current and immobilized the aptamer on the electrode surface. The process of aptasensor construction and successful immobilization of the aptamer on the electrode surface was confirmed by electrochemical cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was used to determine the methylene blue peak current. By replacing APC instead of MB at the electrode surface, the cathodic current of the MB decreases, and this decrease corresponds to the APC concentration. Under optimum conditions, the APC concentration was detected in the range from of 0.1 ng·mL^-1 to 40 μg·mL^-1 with a relatively low detection limit of 0.073 ng·mL^-1. This method was then applied to the determination of APC in human serum samples. The results revealed that this strategy can be used to measure other proteins in biological samples.

Strain engineering of optical activity in phosphorene

Optical activity is one of the most fascinating fields in current physics. The strong anisotropic feature in monolayer phosphorene leads to the emergence of non-trivial optoelectronic physics. This paper is devoted to a detailed analysis of strain effects on the optical activity of phosphorene ranging from low-optical-field to high-optical-field. To do so, a numerical study of the two-band tight-binding model is accomplished using the Harrison rule and the linear response theory. Although the transparency of phosphorene confirms at all frequencies independent of the strain modulus and direction, on average, from low- to high-optical-field limit, the polarization of the reflected wave at critical strains becomes circular and the ellipse axis tends to a rotation of 180°. It is found that the maximum absorption takes place at high-energy transitions, which quantitatively depends strongly on the strain modulus and direction. Furthermore, a detailed investigation of compressive and tensile strains results in the dominant contribution of the in-plane compressive and out-of-plane tensile strains to the reflected/transmitted light for low- and intermediate-optical-field ranges, whilst both contribute for the high-optical-field limit. However, overall, in-plane compressive and out-of-plane tensile strains come in to play a role in the absorption spectra. Thereby, the quality of the determined reflection, transmission and absorption waves depends on the regarded regime of the optical field, strain modulus, and strain orientation. These findings if sufficient can be performed and/or tuned experimentally, and a vast number of phosphorene-based optoelectronic devices can be achieved.

Recent advances in graphene-based nanomaterials: properties, toxicity and applications in chemistry, biology and medicine

This review (with 239 refs.) summarizes the progress that has been made in applications of graphene-based nanomaterials (such as plain graphene, graphene oxides, doped graphene oxides, graphene quantums dots) in biosensing, imaging, drug delivery and diagnosis. Following an introduction into the field, a first large section covers the toxicity of graphene and its derivatives (with subsections on bacterial toxicity and tissue toxicity). The use of graphene-based nanomaterials in sensors is reviewed next, with subsections on electrochemical, FET-based, fluorescent, chemiluminescent and colorimetric sensors and probes. The large field of imaging is treated next, with subchapters on optical, PET-based, and magnetic resonance based methods. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical Abstract Schematic presentation of the potential applications of graphene-based materials in life science and biomedicine, emphatically reflected in some vital areas such as DNA analysis, biological monitoring, drug delivery, in vitro labelling, in vivo imaging, tumor target, etc.

Large magnetoresistance and large magnetothermopower effect in the Dirac material EuMn0.8Sb2

In this article, the structure, transport and magnetic properties were studied in details for EuMn_0.8Sb₂ crystals with the orthorhombic structure and Mn deficiencies. It was found that the temperature dependence of the resistivity exhibits a metallic behavior in the whole measuring temperature range, different from that in the crystals without Mn deficiencies. A large positive magnetoresistance (MR) (∼127% at 2 K and  ∼25% at 300 K, in 9 T field) was observed, which can be ascribed to the combination of semiclassical MR and quantum limit MR of Dirac electrons. We also observed the high mobility of the carriers and large magnetothermopower effect at low temperatures, and two magnetic transitions emerging at  ∼24 K and  ∼10 K, respectively, corresponding to the antiferromagnetic ordering and canted arrangement of the Eu moments. Our findings shed new light on the intrinsic properties of EuMn_0.8Sb₂ and demonstrate the existence of Dirac fermions.

Complementary Dual-Channel Gas Sensor Devices Based on a Role-Allocated ZnO/Graphene Hybrid Heterostructure

Here, we present a new approach to dual-channel gas sensors on the basis of a role-allocated graphene/ZnO heterostructure, formed by the complementary hybridization of graphene and a ZnO thin film. The method enables cyclic and reproducible gas response as well as high gas response. The role allocation of graphene and ZnO was verified by studying the electrical transport properties of the heterostructure. The results indicated that the ZnO top layer and graphene bottom layer act as a gas adsorption layer and a carrier conducting layer, respectively. The charge interactions of the heterostructures were systematically explored by monitoring changes in transfer characteristics at room temperature and elevated temperature ( T = 250 °C) after introducing 20 ppm NO₂. These results can be understood in terms of the dual-channel effect of the graphene/ZnO heterostructures. Remarkably, an abrupt and reliable gas response under periodic NO₂ gas injection was unambiguously achieved by the heterostructure-based gas sensors and as ∼30 times higher than those of a graphene-based gas sensor. These proposed heterostructures represent a fundamental building block of a complementary hybrid gas sensor with highly sensitive and reproducible gas response.

Stacking stability of C2N bilayer nanosheet

In recent years, a 2D graphene-like sheet: monolayer C₂N was synthesized via a simple wet-chemical reaction. Here, we studied the stability and electronic properties of bilayer C₂N. According to a previous study, a bilayer may exist in one of three highly symmetric stacking configurations, namely as AA, AB and AB′-stacking. For the AA-stacking, the top layer is directly stacked on the bottom layer. Furthermore, AB- and AB′-stacking can be obtained by shifting the top layer of AA-stacking by a/3-b/3 along zigzag direction and by a/2 along armchair direction, respectively, where a and b are translation vectors of the unit cell. By using first-principles calculations, we calculated the stability of AA, AB and AB′-stacking C₂N and their electronic band structure. We found that the AB-stacking is the most favorable structure and has the highest band gap, which appeared to agree with previous study. Nevertheless, we furthermore examine the energy landscape and translation sliding barriers between stacking layers. From energy profiles, we interestingly found that the most stable positions are shifted from the high symmetry AB-stacking. In electronic band structure details, band characteristic can be modified according to the shift. The interlayer shear mode close to local minimum point was determined to be roughly 2.02 × 10¹² rad/s.

Pseudospin-1 Physics of Photonic Crystals

We review some recent progress in the exploration of pseudospin-1 physics using dielectric photonic crystals (PCs). We show some physical implications of the PCs exhibiting an accidental degeneracy induced conical dispersion at the Γ point, such as the realization of zero refractive index medium and the zero Berry phase of a loop around the nodal point. The photonic states of such PCs near the Dirac-like point can be described by an effective spin-orbit Hamiltonian of pseudospin-1. The wave propagation in the positive, negative, and zero index media can be unified within a framework of pseudospin-1 description. A scale change in PCs results in a rigid band shift of the Dirac-like cone, allowing for the manipulation of waves in pseudospin-1 systems in much the same way as applying a gate voltage in pseudospin-1/2 graphene. The transport of waves in pseudospin-1 systems exhibits many interesting phenomena, including super Klein tunneling, robust supercollimation, and unconventional Anderson localization. The transport properties of pseudospin-1 systems are distinct from their counterparts in pseudospin-1/2 systems, which will also be presented for comparison.

Low Contact Barrier in 2H/1T' MoTe2 In-Plane Heterostructure Synthesized by Chemical Vapor Deposition

Metal-semiconductor contact has been a critical topic in the semiconductor industry because it influences device performance remarkably. Conventional metals have served as the major contact material in electronic and optoelectronic devices, but such a selection becomes increasingly inadequate for emerging novel materials such as two-dimensional (2D) materials. Deposited metals on semiconducting 2D channels usually form large resistance contacts due to the high Schottky barrier. A few approaches have been reported to reduce the contact resistance but they are not suitable for large-scale application or they cannot create a clean and sharp interface. In this study, a chemical vapor deposition (CVD) technique is introduced to produce large-area semiconducting 2D material (2H MoTe₂) planarly contacted by its metallic phase (1T' MoTe₂). We demonstrate the phase-controllable synthesis and systematic characterization of large-area MoTe₂ films, including pure 2H phase or 1T' phase, and 2H/1T' in-plane heterostructure. Theoretical simulation shows a lower Schottky barrier in 2H/1T' junction than in Ti/2H contact, which is confirmed by electrical measurement. This one-step CVD method to synthesize large-area, seamless-bonding 2D lateral metal-semiconductor junction can improve the performance of 2D electronic and optoelectronic devices, paving the way for large-scale 2D integrated circuits.

Ab Initio Study of the Electronic, Vibrational, and Mechanical Properties of the Magnesium Diboride Monolayer

Magnesium diboride gained significant interest in the materials science community after the discovery of its superconductivity, with an unusually high critical temperature of 39 K. Many aspects of the electronic properties and superconductivity of bulk MgB 2 and thin sheets of MgB 2 have been determined; however, a single layer of MgB 2 has not yet been fully theoretically investigated. Here, we present a detailed study of the structural, electronic, vibrational, and elastic properties of monolayer MgB 2 , based on ab initio methods. First-principles calculations reveal the importance of reduction of dimensionality on the properties of MgB 2 and thoroughly describe the properties of this novel 2D material. The presence of a negative Poisson ratio, higher density of states at the Fermi level, and a good dynamic stability under strain make the MgB 2 monolayer a prominent material, both for fundamental research and application studies.

Lithographic band structure engineering of graphene

Two-dimensional materials such as graphene allow direct access to the entirety of atoms constituting the crystal. While this makes shaping by lithography particularly attractive as a tool for band structure engineering through quantum confinement effects, edge disorder and contamination have so far limited progress towards experimental realization. Here, we define a superlattice in graphene encapsulated in hexagonal boron nitride, by etching an array of holes through the heterostructure with minimum feature sizes of 12-15 nm. We observe a magnetotransport regime that is distinctly different from the characteristic Landau fan of graphene, with a sizeable bandgap that can be tuned by a magnetic field. The measurements are accurately described by transport simulations and analytical calculations. Finally, we observe strong indications that the lithographically engineered band structure at the main Dirac point is cloned to a satellite peak that appears due to moiré interactions between the graphene and the encapsulating material.

A Perspective on Recent Advances in Phosphorene Functionalization and Its Applications in Devices

Phosphorene, the 2D material derived from black phosphorus, has recently attracted a lot of interest for its properties, suitable for applications in materials science. The physical features and the prominent chemical reactivity on its surface render this nanolayered substrate particularly promising for electrical and optoelectronic applications. In addition, being a new potential ligand for metals, it opens the way for a new role of the inorganic chemistry in the 2D world, with special reference to the field of catalysis. The aim of this review is to summarize the state of the art in this subject and to present our most recent results in the preparation, functionalization, and use of phosphorene and its decorated derivatives. We discuss several key points, which are currently under investigation: the synthesis, the characterization by theoretical calculations, the high pressure behavior of black phosphorus, as well as its decoration with nanoparticles and encapsulation in polymers. Finally, device fabrication and electrical transport measurements are overviewed on the basis of recent literature and the new results collected in our laboratories.

Effects of site asymmetry and valley mixing on Hofstadter-type spectra of bilayer graphene in a square-scatter array potential

Under a magnetic field perpendicular to an monolayer graphene, the existence of a two-dimensional periodic scatter array can not only mix Landau levels of the same valley for displaying split electron-hole Hofstadter-type energy spectra, but also couple two sets of Landau subbands from different valleys in a bilayer graphene. Such a valley mixing effect with a strong scattering strength has been found observable and studied thoroughly in this paper by using a Bloch-wave expansion approach and a projected [Formula: see text] effective Hamiltonian including interlayer effective mass, interlayer coupling and asymmetrical on-site energies due to a vertically-applied electric field. For bilayer graphene, we find two important characteristics, i.e. mixing and interference of intervalley scatterings in the presence of a scatter array, as well as a perpendicular-field induced site-energy asymmetry which deforms severely or even destroys completely the Hofstadter-type band structures due to the dependence of Bloch-wave expansion coefficients on the applied electric field.

Helical edge states of topological photonic crystals with line defects

Topologically protected edge states of honeycomb photonic crystals (PCs) have been extensively studied in recent years. Here we propose several optimized two-dimensional PC configurations with distinct line defects introduced by breaking the C₆ symmetry of each topological lattice along the interfaces between two different topologies. The spin-flipping nature of the defect modes of these PC configurations is measured, which is expected to offer a novel realization mechanism of quantum spin Hall effect. The line defects can be treated as unidirectional air waveguides due to the characteristic topological properties. We manipulate the coupling effect of two helical edge states with tunable waveguide widths. It shows that the air waveguide has possibility for practical applications because of its suppression of backward scattering and considerable transmission efficiency.

A Facile Method for Batch Preparation of Electrochemically Reduced Graphene Oxide

The electrochemical reduction of graphene oxide (GO) is an environmentally friendly and energy-saving method for improving the characteristics of GO. However, GO films must be coated on the cathode electrode in advance when usingthis technique. Thus, the formed electrochemically reduced GO (ERGO) films can be used only as sensing or conductive materials in devices because mass production of the flakes is not possible. Therefore, this study proposes a facile electrochemical reduction technique. In this technique, GO flakes can be directly used as reduced materials, and no GO films are required in advance. A 0.1 M phosphate buffered saline solution was used as the electrolyte, which is a highly safe chemical agent. Experimental results revealed that the as-prepared GO flakes were electrochemically reduced to form ERGO flakes by using a -10 V bias for 8 h. The ratio of the D-band and G-band feature peaks was increased from 0.86 to 1.12, as revealed by Raman spectroscopy, the π-π stacking interaction operating between the ERGO and GO has been revealed by UV-Vis absorption spectroscopy, and the C⁻O ratio was increased from 2.02 to 2.56, as indicated by X-ray photoelectron spectroscopy. The electrical conductivity of the ERGO film (3.83 × 10^-1 S·cm^-1) was considerably better than that of the GO film (7.92 × 10^-4 S·cm^-1). These results demonstrate that the proposed electrochemical reduction technique can provide high-quality ERGO flakes and that it has potential for large-scale production.

Graphitic carbon nitride (g-C3N4) nanosheets functionalized composite membrane with self-cleaning and antibacterial performance

Membrane fouling significantly impedes membrane performance and thus short lifespan of the membrane. Membranes that functionalized with photocatalytic activity are deemed as an effective and novel approach to settle membrane fouling. The membranes with self-cleaning and antibacterial performance were fabricated via facilely filtering g-C₃N₄ nanosheets onto polyacrylonitrile (PAN) porous substrates. The g-C₃N₄ nanosheets were exfoliated by acid etching and ultrasound treatment, and the exfoliated nanosheets was verified by Fourier transform infrared spectra, Atomic force microscopy and X-ray diffraction. The g-C₃N₄ nanosheets functionalized composite membranes have a water permeability of 11.70 L m^-2 h^-1 bar^-1 and a good antibacterial activity. In addition, the membranes could be restored their original permeability and their surfaces were close to initial color even after three cycles rejecting dyes and post treatment under irradiation with visible light. Besides, the degradable and antimicrobial mechanisms of the membranes were investigated respectively. These g-C3N4 nanosheets composite membranes with self-cleaning and antimicrobial properties have a potential feasibility in water treatment, and provide an alternative method for fabricating self-cleaning membranes.

Polymeric Graphene Bulk Materials with a 3D Cross-Linked Monolithic Graphene Network

Although many great potential applications are proposed for graphene, till now none are yet realized as a stellar application. The most challenging issue for such practical applications is to figure out how to prepare graphene bulk materials while maintaining the unique two-dimensional (2D) structure and the many excellent properties of graphene sheets. Herein, such polymeric graphene bulk materials containing three-dimensional (3D) cross-linked networks with graphene sheets as the building unit are reviewed. The theoretical research on various proposed structures of graphene bulk materials is summarized first. Then, the synthesis or fabrication of these graphene materials is described, which comprises mainly two approaches: chemical vapor deposition and cross-linking using graphene oxide directly. Finally, some exotic and exciting potential applications of these graphene bulk materials are presented.

Electrical Property of Graphene and Its Application to Electrochemical Biosensing

Graphene, a single atom thick layer of two-dimensional closely packed honeycomb carbon lattice, and its derivatives have attracted much attention in the field of biomedical, due to its unique physicochemical properties. The valuable physicochemical properties, such as high surface area, excellent electrical conductivity, remarkable biocompatibility and ease of surface functionalization have shown great potentials in the applications of graphene-based bioelectronics devices, including electrochemical biosensors for biomarker analysis. In this review, we will provide a selective overview of recent advances on synthesis methods of graphene and its derivatives, as well as its application to electrochemical biosensor development. We believe the topics discussed here are useful, and able to provide a guideline in the development of novel graphene and on graphene-like 2-dimensional (2D) materials based biosensors in the future.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

The Thermal, Electrical and ThermoelectricProperties of Graphene Nanomaterials

Graphene, as a typical two-dimensional nanometer material, has shown its unique application potential in electrical characteristics, thermal properties, and thermoelectric properties by virtue of its novel electronic structure. The field of traditional material modification mainly changes or enhances certain properties of materials by mixing a variety of materials (to form a heterostructure) and doping. For graphene as well, this paper specifically discusses the use of traditional modification methods to improve graphene’s electrical and thermoelectrical properties. More deeply, since graphene is an atomic-level thin film material, its shape and edge conformation (zigzag boundary and armchair boundary) have a great impact on performance. Therefore, this paper reviews the graphene modification field in recent years. Through the change in the shape of graphene, the change in the boundary structure configuration, the doping of other atoms, and the formation of a heterostructure, the electrical, thermal, and thermoelectric properties of graphene change, resulting in broader applications in more fields. Through studies of graphene’s electrical, thermal, and thermoelectric properties in recent years, progress has been made not only in experimental testing, but also in theoretical calculation. These aspects of graphene are reviewed in this paper.

New 2D Structural Materials: Carbon-Gallium Nitride (CC-GaN) and Boron-Gallium Nitride (BN-GaN) Heterostructures-Materials Design Through Density Functional Theory

New class of ternary nanohetrostructures have been proposed by mixing 2D gallium nitride (GaN) with graphene and 2D hexagonal boron nitride (BN) with an aim towards desgining innovative 2D materials for applications in electronics and other industries. The structural stability and electronic properties of these nanoheterostructures have been analyzed using first-principles based calculations done in the framework of density functional theory. Different structure patterns have been analyzed to identify the most stable structures. It is found to be more energetically favorable that the carbon atoms occupy the positions of the nitrogen atoms in a clustered pattern in CC-GaN heterostructures, whereas boron doping is preferred in the reverse order, where isolated BN and GaN layered configurations are preferred in BN-GaN heterostructures. These 2D nanoheterostructures are energetically favored materials with direct band gap and have potential application in nanoscale semiconducting and nanoscale optoelectronic devices.

Strong-correlation induced high-mobility electrons in Dirac semimetal of perovskite oxide

Electrons in conventional metals become less mobile under the influence of electron correlation. Contrary to this empirical knowledge, we report here that electrons with the highest mobility ever found in known bulk oxide semiconductors emerge in the strong-correlation regime of the Dirac semimetal of perovskite CaIrO₃. The transport measurements reveal that the high mobility exceeding 60,000 cm²V⁻¹s⁻¹ originates from the proximity of the Fermi energy to the Dirac node (ΔE < 10 meV). The calculation based on the density functional theory and the dynamical mean field theory reveals that the energy difference becomes smaller as the system approaches the Mott transition, highlighting a crucial role of correlation effects cooperating with the spin-orbit coupling. The correlation-induced self-tuning of Dirac node enables the quantum limit at a modest magnetic field with a giant magnetoresistance, thus providing an ideal platform to study the novel phenomena of correlated Dirac electron.

Electron correlation normally makes electrons less mobile, but it is still not clear when correlation becomes very strong in Dirac semimetals. Here, Fujioka et al. report a very high electron mobility exceeding 60,000 cm²V⁻¹s⁻¹ in correlated Dirac semimetal of perovskite CaIrO3, due to the enhanced electron correlation nearby the Mott transition.

Structure and Properties of Single-Layer MoS₂ for Nano-Photoelectric Devices

To meet the need for preparing high-performance nano-optoelectronic devices based on single-layer MoS₂, the effects of the heating method (one-step or two-step heating) and the temperature of the MoO₃ source on the morphology, size, structure, and layers of an MoS₂ crystal grown on a sapphire substrate using chemical vapor deposition are studied in this paper. The results show that MoS₂ prepared by two-step heating (the heating of the S source starts when the temperature of the MoO₃ source rises to 837 K) is superior over that of one-step heating (MoO₃ and S are heated at the same time). One-step heating tends to form a mixture of MoO₂ and MoS₂. Neither too low nor too high of a heating temperature of MoO₃ source is conducive to the formation of MoS₂. When the temperature of MoO₃ source is in the range of 1073 K to 1098 K, the size of MoS₂ increases with the rise in temperature. A uniform large-sized triangle with a side length of 100 μm is obtained when the heating temperature of MoO₃ is 1098 K. The triangular MoS₂ crystals grown by the two-step heating method have a single-layer structure.

The multidimensional brain

Brain activity takes place in three spatial-plus time dimensions. This rather obvious claim has been recently questioned by papers that, taking into account the big data outburst and novel available computational tools, are starting to unveil a more intricate state of affairs. Indeed, various brain activities and their correlated mental functions can be assessed in terms of trajectories embedded in phase spaces of dimensions higher than the canonical ones. In this review, I show how further dimensions may not just represent a convenient methodological tool that allows a better mathematical treatment of otherwise elusive cortical activities, but may also reflect genuine functional or anatomical relationships among real nervous functions. I then describe how to extract hidden multidimensional information from real or artificial neurodata series, and make clear how our mind dilutes, rather than concentrates as currently believed, inputs coming from the environment. Finally, I argue that the principle "the higher the dimension, the greater the information" may explain the occurrence of mental activities and elucidate the mechanisms of human diseases associated with dimensionality reduction.

Influence of composition on the external quantum efficiency of reduced graphene oxide/carbon nanoparticle based photodetector used for human body IR detection

Here, we developed an efficient infrared (IR) detector comprising reduced graphene oxide (RGO) and carbon nanoparticles (CNPs) for detecting human body IR radiation under ambient conditions. The RGO/CNP nanocomposite thin-film based photodetectors were assembled via a simple solution-phase cost-effective route with different concentrations of RGO solution while keeping CNP concentration constant. Three RGO/CNP nanocomposite photodetector devices were fabricated with three different concentrations of RGO (keeping CNP concentration constant) and their photoresponse properties have been studied. The devices showed a sharp response to IR radiation emitted by the human body at room temperature having a wavelength of nearly 780 nm. I–V characteristics, radiation current responsivity, and time response curves as well as their external quantum efficiencies have been studied and explained. We measured two important parameters, namely, IR responsivity (R_λ) and external quantum efficiency (EQE) of RGO/CNP based IR detector devices. Our annotations show that R_λ and EQE increase with increasing concentration of GO in RGO/CNP nanocomposites as expected. This simple and inexpensive approach based on the integration of RGO and CNP could also be useful for the design of other potential optoelectronic devices such as photosensors for use in auto-doors to permit the entrance of human bodies only and in spaceships or robots to identify the existence of humans on Mars and the Moon.

We report an efficient infrared (IR) detector comprising reduced graphene oxide (RGO) and carbon nanoparticles (CNPs) for detecting human body IR radiation under ambient conditions.

The Quantum Hall Effect in the Era of the New SI

The quantum Hall effect (QHE), and devices reliant on it, will continue to serve as the foundation of the ohm while also expanding its territory into other SI derived units. The foundation, evolution, and significance of all of these devices exhibiting some form of the QHE will be described in the context of optimizing future electrical resistance standards. As the world adapts to using the quantum SI, it remains essential that the global metrology community pushes forth and continues to innovate and produce new technologies for disseminating the ohm and other electrical units.

Pseudospin-1 Physics of Photonic Crystals

We review some recent progress in the exploration of pseudospin-1 physics using dielectric photonic crystals (PCs). We show some physical implications of the PCs exhibiting an accidental degeneracy induced conical dispersion at the Γ point, such as the realization of zero refractive index medium and the zero Berry phase of a loop around the nodal point. The photonic states of such PCs near the Dirac-like point can be described by an effective spin-orbit Hamiltonian of pseudospin-1. The wave propagation in the positive, negative, and zero index media can be unified within a framework of pseudospin-1 description. A scale change in PCs results in a rigid band shift of the Dirac-like cone, allowing for the manipulation of waves in pseudospin-1 systems in much the same way as applying a gate voltage in pseudospin-1/2 graphene. The transport of waves in pseudospin-1 systems exhibits many interesting phenomena, including super Klein tunneling, robust supercollimation, and unconventional Anderson localization. The transport properties of pseudospin-1 systems are distinct from their counterparts in pseudospin-1/2 systems, which will also be presented for comparison.

Electrically and Optically Tunable Responses in Graphene/Transition-Metal-Dichalcogenide Heterostructures

Heterostructures involving layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) are not only fundamentally interesting to explore emerging properties at atomically thin limit, but also technically important to achieve novel optoelectronic devices. However, achieving tunable optoelectronic properties and clarifying interlayer processes (charge transfer, energy transfer) in 2D heterostructures have remained part of the key challenges so far. Here, by fabricating heterostructures of graphene and monolayer TMDCs (n-type MoS₂ and p-type WSe₂), we demonstrate both electrically and optically tunable responses of the heterostructures, revealing the critical interface processes between graphene and TMDCs. In MoS₂/graphene heterostructures, electron transfer from MoS₂ to graphene is observed, and gate-tunable interface relaxation induces the electrically controlled photoluminescence (PL), whereas in WSe₂/graphene heterostructures, electron transfer from graphene to WSe₂ is observed, and the PL is tuned by carrier density, which can be controlled by the gate voltage. The interlayer process can also be modulated by laser intensity, which enables photoinduced doping on graphene and optically tunable electrical characteristics of graphene. Combining the tunable Fermi level of graphene and strong light-matter interaction of monolayer TMDCs, our demonstrations are important for the design of multifunctional and efficient optoelectronic devices with TMDC/graphene heterostructures.