Room-Temperature Quantum Hall Effect in Graphene

Supramolecular Chiral 2D Materials and Emerging Functions

Chiral materials are widely applied in various fields such as enantiomeric separation, asymmetric catalysis, and chiroptical effects, providing stereospecific conditions and environments. Supramolecular concepts to create the chiral materials can provide an insight for emerging chiro-optical properties due to their well-defined scaffolds and the precise functionalization of the surfaces or skeletons. Among the various supramolecular chiral structures, 2D chiral sheet structures are particularly interesting materials because of their extremely high surface area coupled with many unique chemical and physical properties, thereby offering potential for the next generation of functional materials for optically active systems and optoelectronic devices. Nevertheless, relatively limited examples for 2D chiral materials exhibiting specific functionality have been reported because incorporation of molecular chirality into 2D architectures is difficult at the present stage. Here, a brief overview of the recent advances is provided on the construction of chiral supramolecular 2D materials and their functions. The design principles toward 2D chirality and their potential applications are also discussed.

3D Graphene Materials: From Understanding to Design and Synthesis Control

Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C₆₀ and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.

Linear interband optical refraction and absorption in strained black phosphorene

Strain effects have been widely addressed in monolayer black phosphorus (MBP) due to its significant influence on the orbital hybridization of atoms. In this theoretical contribution, we use the tight-binding model, the Harrison rule and the Kubo formula to describe the optical refraction and absorption of MBP in detail. The analytical study of the band gap in strained MBP demonstrates electronic phase transitions from semiconductor-to-semimetal/metal and semiconductor-to-insulator, in which both the compressive and tensile strains act linearly on the band gap alterations. The critical strains corresponding to these phase transitions are fully characterized as well. Our calculations show that the variation of the refraction inflections and absorption peaks depends on the strained band gap, however; the band gap changes under out-of-plane strains are different than the in-plane ones. The conditions under which this discrepancy is significant and/or negligible are investigated. Moreover, the dedication of minimal/maximal optical refraction and/or absorption in MBP to both in-plane and out-of-plane strains are fully addressed. Our theoretical results clarify the strain-induced interplay between the band gap and optical properties to propose a wide range of applications in nano-optoelectronics.

Distinguishing strain, charge and molecular orbital induced effects on the electronic structure: graphene/ammonia system

Molecular adsorption at the surface of a two-dimensional material poses numerous questions regarding the modification to the band structure and interfacial states, which of course deserve full attention. In line with this, first principles density functional theory is employed on a graphene/ammonia system. We identify the effects on the band structure due to strain, charge transfer and presence of molecular orbitals (MOs) of NH3for six adsorption configurations. Induced-strain upon ammonia-adsorption opens the band gap (Eg) of graphene due to the breaking of translational symmetry. The charge transfer/MOs of NH3shifts the equilibrium Fermi energy (EF). TheEgandEFvalues and charge density distribution are dependent on the adsorption configuration, where the MO structure of NH3plays a crucial role. The presence of MOs of N or H-originated pushes the unoccupied states of graphene towardsEF. NH3forms an interfacial occupied state originating from N2pbelow theEFwithin ∼1.6 to 2.2 eV for all configurations. These findings enhance fundamental understanding of graphene/NH3system.

Heat capacity in doped graphene under magnetic fields: the role of spin splitting

We study the electronic heat capacity in doped graphene under magnetic fields. The partition function is calculated considering only the thermal excitations in the last occupied energy levels. Due to the large energy separation between the Landau levels (LLs) and the Zeeman splitting, at low temperatures the heat capacity is dominated by the spin excitations in the last occupied LL. Correspondingly the heat capacity oscillates with maximum amplitude at half filling of each LL. At higher temperatures the inter-LLs excitations dominate the heat capacity, with maximum amplitude at full filling factors. The oscillation amplitudes are compared with the phonon heat capacityCp. It is shown that the spin induced heat capacity oscillations have a maximum amplitude approaching 3% ofCp, whereas for the inter-LLs excitations the maximum amplitude is only 0.1% ofCp. These amplitudes decrease in the presence of impurities, although the effect is appreciable if the LLs broadening is bigger than the excitation energies.

Tunable Schottky barrier in InTe/graphene van der Waals heterostructure

The structures and electronic properties of InTe/graphene van der Waals heterostructures are systematically investigated using the first-principles calculations. The electronic properties of InTe monolayer and graphene are well preserved respectively and the bandgap energy of graphene is opened to 36.5 meV in the InTe/graphene heterostructure. An n-type Schottky contact is formed in InTe/graphene heterostructure at the equilibrium state. There is a transformation between n-type and p-type Schottky contact when the interlayer distance is smaller than 3.56 Å or the applied electric field is larger than -0.06 V Å^-1. In addition, the Schottky contact converts to Ohmic contact when the applied vertical electric field is larger than 0.11 V Å^-1 or smaller than -0.13 V Å^-1.

Synthesis of Atomically Thin Hexagonal Diamond with Compression

Atomically thin diamond, also called diamane, is a two-dimensional carbon allotrope and has attracted considerable scientific interest because of its potential physical properties. However, the successful synthesis of a pristine diamane has up until now not been achieved. We demonstrate the realization of a pristine diamane through diamondization of mechanically exfoliated few-layer graphene via compression. Resistance, optical absorption, and X-ray diffraction measurements reveal that hexagonal diamane (h-diamane) with a bandgap of 2.8 ± 0.3 eV forms by compressing trilayer and thicker graphene to above 20 GPa at room temperature and can be preserved upon decompression to ∼1.0 GPa. Theoretical calculations indicate that a (-2110)-oriented h-diamane is energetically stable and has a lower enthalpy than its few-layer graphene precursor above the transition pressure. Compared to gapless graphene, semiconducting h-diamane offers exciting possibilities for carbon-based electronic devices.

A Comprehensive Review of Integrated Hall Effects in Macro-, Micro-, Nanoscales, and Quantum Devices

A comprehensive review of the main existing devices, based on the classic and new related Hall Effects is hereby presented. The review is divided into sub-categories presenting existing macro-, micro-, nanoscales, and quantum-based components and circuitry applications. Since Hall Effect-based devices use current and magnetic field as an input and voltage as output. researchers and engineers looked for decades to take advantage and integrate these devices into tiny circuitry, aiming to enable new functions such as high-speed switches, in particular at the nanoscale technology. This review paper presents not only an historical overview of past endeavors, but also the remaining challenges to overcome. As part of these trials, one can mention complex design, fabrication, and characterization of smart nanoscale devices such as sensors and amplifiers, towards the next generations of circuitry and modules in nanotechnology. When compared to previous domain-limited text books, specialized technical manuals and focused scientific reviews, all published several decades ago, this up-to-date review paper presents important advantages and novelties: Large coverage of all domains and applications, clear orientation to the nanoscale dimensions, extended bibliography of almost one hundred fifty recent references, review of selected analytical models, summary tables and phenomena schematics. Moreover, the review includes a lateral examination of the integrated Hall Effect per sub-classification of subjects. Among others, the following sub-reviews are presented: Main existing macro/micro/nanoscale devices, materials and elements used for the fabrication, analytical models, numerical complementary models and tools used for simulations, and technological challenges to overcome in order to implement the effect in nanotechnology. Such an up-to-date review may serve the scientific community as a basis for novel research oriented to new nanoscale devices, modules, and Process Development Kit (PDK) markets.

Supported and Suspended 2D Material-Based FET Biosensors

Field Effect Transistor (FET)-based electrochemical biosensor is gaining a lot of interest due to its malleability with modern fabrication technology and the ease at which it can be integrated with modern digital electronics. To increase the sensitivity and response time of the FET-based biosensor, many semiconducting materials have been categorized, including 2 dimensional (2D) nanomaterials. These 2D materials are easy to fabricate, increase sensitivity due to the atomic layer, and are flexible for a range of biomolecule detection. Due to the atomic layer of 2D materials each device requires a supporting substrate to fabricate a biosensor. However, uneven morphology of supporting substrate leads to unreliable output from every device due to scattering effect. This review summarizes advances in 2D material-based electrochemical biosensors both in supporting and suspended configurations by using different atomic monolayer, and presents the challenges involved in supporting substrate-based 2D biosensors. In addition, we also point out the advantages of nanomaterials over bulk materials in the biosensor domain.

High-contrast optical microscopy of graphene sheets

In the way of making graphene an industry-friendly material, it must be mass-produced with high-quality and reduced cost over large areas. Assisted by machine-learning techniques, rapid, nondestructive and accurate determination of large graphene sheets on SiO₂ /Si substrates has been made possible in recent years by the optical microscopy method. Optimization of the substrate to achieve the maximum contrast can further extend the application of the optical microscopy method for quality control of the mass-produced graphene. Graphene/n₂ /n₃ three-layer structures, where n₂ and n₃ are refractive indices, are routinely used for identifying the number of graphene layers by optical reflection microscopy. In this paper, two analytical equations are derived that can be easily used for high-contrast optical imaging of graphene sheets without any need to resort to the cumbersome numerical methods. One of the equations is derived for choosing the best material with refractive index n₂ that when coated on a substrate with refractive index n₃ , maximizes the optical contrast. The other equation is derived for finding the best thickness of the SiO₂ layer in graphene/SiO₂ /Si structures, which are in common use for fabrication of graphene-based devices. The results are implemented in a MATLAB GUI, see Supporting Information, to assist the users in using the equations.

High-resolution optical micro-spectroscopy extending from the near-infrared to the vacuum-ultraviolet

Optical characterization of small samples over a wide spectral range with rapid data acquisition is essential for the analysis of many material systems, such as 2D van der Waals layers and their heterostructures. Here, we present the design and implementation of a tabletop micro-spectroscopy system covering the near-infrared to the vacuum-ultraviolet (1.2 eV-6.8 eV or ∼1.0 μm to 185 nm) using mostly off-the-shelf components. It can measure highly reproducible local reflectance spectra with a total integration time of a few minutes and a full-width-half-maximum spot size of 2.7 by 5.6 μm. For precise positioning, the design also allows simultaneous monitoring of the measurement location and the wide-field image of the sample. We demonstrate ultra-broadband reflectance spectra of exfoliated thin flakes of several wide-gap 2D materials, including ZnPS₃, hexagonal BN, and Ca(OH)₂.

Viral Filtration Using Carbon-Based Materials

Viral infections alone are a significant cause of morbidity and mortality worldwide and have a detrimental impact on global healthcare and socio‐economic development. The discovery of novel antiviral treatments has gained tremendous attention and support with the rising number of viral outbreaks. In this work, carbonaceous materials, including graphene nanoplatelets and graphene oxide nanosheets, were investigated for antiviral properties. The materials were characterized using scanning electron microscopy and transmission electron microscopy. Analysis showed the materials to be two‐dimensional with lateral dimensions ranging between 1 and 4 µm for graphene oxide and 110 ± 0.11 nm for graphene nanoplatelets. Antiviral properties were assessed against a DNA virus model microorganism at concentrations of 0.5, 1.0 and 2.0 wt/v%. Both carbonaceous nanomaterials exhibited potent antiviral properties and gave rise to a viral reduction of 100% across all concentrations tested. Graphene oxide nanosheets were then incorporated into polymeric fibres, and their antiviral behaviour was examined after 3 and 24 hr. A viral reduction of 39% was observed after 24 hr of exposure. The research presented here showcases, for the first time, the antiviral potential of several carbonaceous nanomaterials, also included in a carrier polymer. These outcomes can be translated and implemented in many fields and devices to prevent viral spread and infection.

Review of fabrication methods of large-area transparent graphene electrodes for industry

Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes; it has low sheet resistance, high optical transmission and is flexible. Whereas the most common transparent electrode material, tin-doped indium-oxide (ITO) is brittle, less transparent and expensive, which limit its compatibility in flexible electronics as well as in low-cost devices. Here we review two large-area fabrication methods for graphene based transparent electrodes for industry: liquid exfoliation and low-pressure chemical vapor deposition (CVD). We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results. State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5, slightly over the minimum required for industry of 35, while CVD reaches as high as 419.

Probing the low-temperature limit of the quantum anomalous Hall effect

Quantum anomalous Hall effect has been observed in magnetically doped topological insulators. However, full quantization, up until now, is limited within the sub-1 K temperature regime, although the material's magnetic ordering temperature can go beyond 100 K. Here, we study the temperature limiting factors of the effect in Cr-doped (BiSb)2Te3 systems using both transport and magneto-optical methods. By deliberate control of the thin-film thickness and doping profile, we revealed that the low occurring temperature of quantum anomalous Hall effect in current material system is a combined result of weak ferromagnetism and trivial band involvement. Our findings may provide important insights into the search for high-temperature quantum anomalous Hall insulator and other topologically related phenomena.

Single-step fabrication and work function engineering of Langmuir-Blodgett assembled few-layer graphene films with Li and Au salts

To implement large-area solution-processed graphene films in low-cost transparent conductor applications, it is necessary to have the control over the work function (WF) of the film. In this study we demonstrate a straightforward single-step chemical approach for modulating the work function of graphene films. In our approach, chemical doping of the film is introduced at the moment of its formation. The films are self-assembled from liquid-phase exfoliated few-layer graphene sheet dispersions by Langmuir-Blodgett technique at the water-air interfaces. To achieve a single-step chemical doping, metal standard solutions are introduced instead of water. Li standard solutions (LiCl, LiNO3, Li2CO3) were used as n-dopant, and gold standard solution, H(AuCl4), as p-dopant. Li based salts decrease the work function, while Au based salts increase the work function of the entire film. The maximal doping in both directions yields a significant range of around 0.7 eV for the work function modulation. In all cases when Li-based salts are introduced, electrical properties of the film deteriorate. Further, lithium nitrate (LiNO3) was selected as the best choice for n-type doping since it provides the largest work function modulation (by 400 meV), and the least influence on the electrical properties of the film.

Neural computing in four spatial dimensions

Relationships among near set theory, shape maps and recent accounts of the Quantum Hall effect pave the way to neural networks computations performed in higher dimensions. We illustrate the operational procedure to build a real or artificial neural network able to detect, assess and quantify a fourth spatial dimension. We show how, starting from two-dimensional shapes embedded in a 2D topological charge pump, it is feasible to achieve the corresponding four-dimensional shapes, which encompass a larger amount of information. Synthesis of surface shape components, viewed topologically as shape descriptions in the form of feature vectors that vary over time, leads to a 4D view of cerebral activity. This novel, relatively straightforward architecture permits to increase the amount of available qbits in a fixed volume.

Stable halogen 2D materials: the case of iodine and astatine

Two-dimensional (2D) materials have applications towards electronic devices, energy storages, and catalysis,et al. So far, most of elemental 2D materials are composed based on groups IIIA, IVA or VA. To expand the 2D material family, the orbital hybridization becomes a key factor to determine stability. Here we predict that sp2d3hybridization of the outmost electrons in iodine and astatine can build up 2D triangle lattices, delta-iodiene and delta-astatiene, using first-principles calculations. Each atom is connected by σ bonds with nearest 6 atoms and the π bonds are thus introduced. The band gaps can approach zero because of interaction of unpaired single electron between each atom, if the identical bond length is reduced. By inducing compression strain, the Dirac points or topological nontrivial points can be created in the delta-iodiene and delta-astatiene. Our discovery paves a new way to construction of 2D materials.

Strong anisotropy and layer-dependent carrier mobility of two-dimensional semiconductor ZrGeTe4

Layered ZrGeTe4is a new type of ternary anisotropic semiconductor. The strong in-plane anisotropy may give us another degree of freedom for controlling electrical and optical properties, and designing advanced nanodevices. Using first-principles calculations, physical properties such as band structure, phonon vibration, and carrier mobility of layered ZrGeTe4from bulk to monolayer were investigated. The bulk and few-layer ZrGeTe4are predicted as indirect bandgap semiconductors, but the monolayer ZrGeTe4turns out to be a direct band gap semiconductor with moderate value of 1.08 eV. Electronic structure calculations reveal that the van der Waals interaction is the main reason of causing the transition from indirect band gap to direct one. Phonon calculations demonstrate that the layered ZrGeTe4is mechanically stable and anisotropic. In orders of magnitude, the predicted average carrier mobility of ZrGeTe4(∼103cm2V-1s-1) is between that of graphene (∼105) and MoS2(∼102), and the anisotropy of electronic mobility is similar to that of black phosphorus, while hole mobility varies with the numbers of layers.

Chern-Simons Current of Left and Right Chiral Superspace in Graphene Wormhole

Starting from the basic definitions of Chern-Simons current, it is possible to calculate its values with a quantum machine learning approach, the so-called supersymmetric support Dirac machine. The related supercurrent is generated from the coupling between three states of the quantum flux of a modified Wilson loop of Cooper pairs. We adopt the Holo-Hilbert spectrum, in frequency modulation, to visualize the network as the coupling of convolutional neuron network in a superstatistic theory where the theory of superconductors is applied. According to this approach, it is possible to calculate the number of carbon atoms in the spinor network of a graphene wormhole. A supercurrent of Cooper pairs is produced as graviphoton states by using the Holo-Hilbert spectral analysis.

Recent Advancement in Bio-precursor derived graphene quantum dots: Synthesis, Characterization and Toxicological Perspective

Graphene quantum dots (GQDs), impressive materials with enormous future potential, are reviewed from their inception, including different precursors. Considering the increasing burden of industrial and ecological bio-waste, there is an urgency to develop techniques which will convert biowaste into active moieties of interest. Amongst the various materials explored, we selectively highlight the use of potential carbon containing bioprecursors (e.g. plant-based, amino acids, carbohydrates), and industrial waste and its conversion into GQDs with negligible use of chemicals. This review focuses on the effects of different processing parameters that affect the properties of GQDs, including the surface functionalization, paradigmatic characterization, toxicity and biocompatibility issues of bioprecursor derived GQDs. This review also examines current challenges and s the ongoing exploration of potential bioprecursors for ecofriendly GQD synthesis for future applications. This review sheds further light on the electronic and optical properties of GQDs along with the effects of doping on the same. This review may aid in future design approaches and applications of GQDs in the biomedical and materials design fields.

Copper-doped induced ferromagnetic half-metal zirconium diselenide single crystals

Two-dimensional (2D) magnetic layered materials have attracted considerable attention in memory storage devices due to their exciting magnetic ordering. Herein, the electronic and magnetic properties of high-quality single crystals zirconium diselenide and copper (Cu)-doped zirconium diselenide as grown via chemical vapor transport technique combined with first principle density functional theory calculations were investigated. A semimetallic state is recognized for Cu_0.052Zr_0.93Se₂ as measured through resistance versus temperature measurements and angle resolved photoemission spectroscopy (ARPES). The magnetic measurement shows diamagnetic semiconducting behaviour for ZrSe₂, whereas Cu_0.052Zr_0.93Se₂ exhibits ferromagnetic character via applying perpendicular magnetic field. Cu_0.052Zr_0.93Se₂ reveals the room temperature magnetic moment ∼0.0125 emu g^-1, while the Curie temperature is ∼363.49 K. Furthermore, first principle density functional theory (DFT) calculations show energetically long range ferromagnetic ordering in a half-metallic Cu-doped ZrSe₂, while a diamagnetic state in case of ZrSe₂ agrees well with experiment results. These results suggest that due to strong interaction elements at the octahedral site of zirconium atoms when replaced by copper atoms, which can change the spin ordering of electrons and make zirconium vacancy, while their magnetic moment is increased. Very importantly the half-metallic character of Cu_0.052Zr_0.93Se₂ promotes much spin polarized electrons around the Fermi level, suggesting significant potential in future memory devices and spintronic applications.

Graphene Oxide Nanofiltration Membranes Containing Silver Nanoparticles: Tuning Separation Efficiency via Nanoparticle Size

Three types of graphene oxide/silver nanoparticles (GO/AgNPs) composite membranes were prepared to investigate size-effect of AgNPs on nanofiltration ability. The size of AgNPs was 8, 20, and 33 nm, which was characterized by UV-visible spectroscopy and transmission electron microscopy. The morphology and structure of GO and GO/AgNPs composite membranes were characterized by atomic force microscopy, scanning electron microscopy, and X-ray diffraction. The filtration performance of membranes were evaluated on a dead-end filtration device. When the size of AgNPs is 20 nm, the GO/AgNPs composite membrane has the highest water flux (106.1 L m⁻² h⁻¹ bar⁻¹) and rejection of Rhodamine B (RhB) (97.73%) among three types of composite membranes. The effect of feed concentration of dye solution and the flux of common solvent was also investigated. The mechanism was discussed, which demonstrated that both interlaying spacing and defect size influence the filtration ability of membrane, which is instructive to future study.

Effects of Graphene on Larix olgensis Seedlings and Soil Properties of Haplic Cambisols in Northeast China

We investigated the impacts of graphene application at different concentrations on the growth and physiological characteristics of Changbai larch (Larix olgensis A. Henry) seedlings and the chemical properties and enzyme activities of Haplic Cambisols under these seedlings. The aim is to evaluate the environmental effects of graphene on the afforestation species and the zonal forest soils of Northeast China. Seedlings receiving 0 (CK), 25, 50, 100, 250, or 500 mg L−1 graphene were incubated for 30, 40, or 50 days. Low concentrations (25–50 mg L−1) of graphene increased the dry masses of root, stem, and leaf; however, high concentrations (100–500 mg L−1) inhibited them. Compared with those under 0 mg L−1 graphene, the root length, surface area, volume, and average diameter all increased during the early stages of incubation (i.e., 30 and 40 days) under low concentration of graphene (<50 or 100 mg L−1) and decreased at higher graphene concentration (>100 mg L−1); at 50 days, they were significantly inhibited. At 30 days, graphene decreased superoxide dismutase (SOD) and peroxidase (POD) activities, as well as pigment, soluble protein, and proline contents, and the decline increased with increasing graphene concentration; at 40 and 50 days, the above parameters increased initially and then decreased, reaching a maximum at 50 mg L−1. The changes in relative conductivity and malondialdehyde (MDA), superoxide anion and hydrogen peroxide contents were the opposite of those in the physiological indexes mentioned above. Therefore, graphene caused different degrees of oxidative stress in L. olgensis seedlings. At 30 days, graphene generally increased the organic matter, hydrolytic nitrogen, and available phosphorus and potassium contents of Haplic Cambisols, but these parameters decreased at 40 and 50 days. Graphene generally decreased acid phosphatase, urease, dehydrogenase, and catalase activities. Therefore, when graphene reaches a certain content level in this soil, it may also affect nitrogen and phosphorus cycling.

Crystal Chemistry and Bonding Patterns of Bismuth-Based Topological Insulators

Bismuth is gaining importance as a key element of functional quantum materials. The effects of spin-orbit coupling (SOC) are at the heart of many exciting proposals for next-generation quantum technologies, including topological materials for efficient information transmission and energy-saving applications. The "heavy" element bismuth and its compounds are predestined for SOC-induced topological properties, but materials design is challenged by a complex link between them and the chemical composition and crystal structure. Nevertheless, a lot can be learned about a certain property by testing its limits with compositional and/or structure modifications. We survey a handful of topological bismuth-based materials that bear structural and chemical semblance to the early topological insulators, antimony-doped elemental bismuth, Bi₂Se₃ and Bi₂Te₃. Chemical bonding via p orbitals and modular structure underlie all considered bismuth chalcogenides, subhalides, and chalcogenide halides and allow us to correlate the evolution of chemical bonding and structure with variability of the topological properties, although materials design should not be regarded as a building blocks set. Over the past decade, material discoveries have unearthed a plethora of topological properties, and bismuth is very fertile as a progenitor of a rich palette of exotic quantum materials, ranging from strong and weak 3D and crystalline topological insulators over topological metals and semimetals to magnetic topological insulators, while preserving the general layered structure motif.

Mo2B, an MBene member with high electrical and thermal conductivities, and satisfactory performances in lithium ion batteries

Owing to their high specific area, good flexibility and many other unique properties, two-dimensional (2D) materials have attracted extensive attention in the recent two decades. As an analogy to the well-studied MXenes, MBenes also emerged. In this work, Mo₂B, an MBene member, is predicted both in H- and T-type configurations from first-principles calculations. Structural, mechanical, electronic, and thermal properties, and performances in lithium ion batteries (LIBs) for both configurations are investigated. The H-type Mo₂B is found to be the stable structure, which can be transformed into the T-type by applying strains. The elastic constants c ₁₁ in the H- and T-type Mo₂B are respectively calculated to be 187.5 and 157.6 N m^-1, which are higher than that in the previously reported Mo₂C. The electronic thermal conductivity and electrical conductivity are investigated based on the semiclassical Boltzmann transport theory. The electrical conductivities for both structures are of the order of 10⁶ Ω^-1 m^-1. Because of the large phonon contributions, the thermal conductivities in the H- and T-type Mo₂B are much higher than that of the synthesized Mo₂C. Based on a 5 μm flake length, the phonon thermal conductivities at room temperature are calculated to be 146 and 141 W m^-1 K^-1 respectively for the H- and T-type configurations. The T-type Mo₂B shows promising performances in LIBs. The theoretical volumetric capacity is as high as 2424 mA h cm^-3, and the migration energy barrier is as low as 0.0372 eV. These data imply that Mo₂B has widespread applications, such as in conductive films and anode materials.

Two-Dimensional (001) LaAlO3/SrTiO3 Heterostructures with Adjustable Band Gap and Magnetic Properties

Very recently, freestanding crystalline perovskite films as thin as a single unit cell have been successfully synthesized, which expands the opportunities for research and applications of low-dimensional materials with novel functionalities. In this work, we constructed a series of two-dimensional (2D) (001) LaAlO₃/SrTiO₃ heterostructures and systematically investigated their atomic and electronic properties by means of first-principles calculations. Our results show that (1) nonstoichiometry leads to ferromagnetism at the interfaces of the systems; (2) half-metallicity can be realized by introducing slight hole-doping; and (3) a semiconductor-to-metal transition can be triggered by applying a moderate (within 3%) out-of-plane strain. Besides, based on in-depth analysis of the electronic structures, we propose that the orbital hybridization of interfacial O and Ti atoms may play a crucial role in determining the above interesting phenomena. Our findings are expected to stimulate further experimental researches on the related 2D perovskite heterostructures and to be beneficial for the design of new multifunctional electronic devices.

Topological and transport properties of graphene-based nanojunctions subjected to a magnetic field

We study the topological properties of finite-size S-shaped graphene junctions with distinctive edge features subjected to the perpendicular magnetic field, using the tight-binding model. The quantum confinement and edge effects induced by the specific junction give rise to significant modifications in the Hofstadter spectra of the bent flakes, when compared to those of their perfect forms. Moreover, the results show that in absence of a magnetic field, the sharpest zigzag-edged corners support the edge states rather than the others, but the magnetic field leads to the localization of the edge states along the whole perimeter of the flakes. Furthermore, based on the Green's function method, we investigate the electron transport through our proposed junctions. We show that, under magnetic flux, one can effectively control the energy gap and the conductance around the Fermi energy. Moreover, the transitions between metallic, semimetallic, and semiconducting phases are possible by the magnetic flux in the S-shaped junctions.

Pseudo chiral anomaly in zigzag graphene ribbons

As the three-dimensional analogs of graphene, Weyl semimetals display signatures of chiral anomaly which arises from charge pumping between the lowest chiral Landau levels of the Weyl nodes in the presence of parallel electric and magnetic fields. In this work, we study the pseudo chiral anomaly and its transport signatures in graphene ribbon with zigzag edges. Here 'pseudo' refers to the case where the inverse of width of zigzag graphene ribbon plays the same role as magnetic field in three-dimensional Weyl semimetals. The valley chiral bands in zigzag graphene ribbons can be introduced by edge potentials, giving rise to the nonconservation of chiral current, i.e. pseudo chiral anomaly, in the presence of a longitudinal electric field. Further numerical results reveal that pseudo magnetoconductivity of zigzag graphene ribbons is positive and has a nearly quadratic dependence on the pseudofield, which is regarded as the transport signature of pseudo chiral anomaly.

A New Filler for Epoxy Resin: Study on the Properties of Graphite Carbon Nitride (g-C3N4) Reinforced Epoxy Resin Composites

In this study, graphitic carbon nitride (g-C3N4) as a novel filler was used for fabricating epoxy nanocomposites. The static mechanical, dynamic thermal-mechanical properties and thermostability of as-prepared g-C3N4/epoxy nanocomposites were significantly ameliorated compared with that of the pure epoxy matrix. The tensile modulus and flexural modulus of g-C3N4/epoxy nanocomposites increased by 31.81% and 28.28%, respectively. Meanwhile, the tensile and flexural strength was also improved by 16.02% and 12.67%, respectively. The g-C3N4/epoxy nanocomposites exhibited an increased storage modulus and glass transition temperature. The markedly improved mechanical and viscoelasticity properties were attributed to the stronger interfacial interaction caused by enlarged contact area and increased chemical bonding, and enhanced mechanical interlocking on the interface. The loss factor of epoxy nanocomposites also raised by 40% due to the comprehensive effect of frication caused by the relative slip between nanosheets, micro-constrained layer damping structure and the reversible cycle of breakage and re-established of the hydrogen bond. Meanwhile, the 10% weightlessness temperature (Tinitial), semi weightlessness temperature (Thalf) of g-C3N4/epoxy nanocomposites have increased by about 15 °C and 14 °C, respectively.

Graphene/Semiconductor Heterostructure Wireless Energy Harvester through Hot Electron Excitation

Recharging the batteries by wireless energy facilitates the long-term running of the batteries, which will save numerous works of battery maintenance and replacement. Thus, harvesting energy form radio frequency (RF) waves has become the most promising solution for providing the micropower needed for wireless sensor applications, especially in a widely distributed 4G/5G wireless network. However, the current research on rectenna is mainly focused on the integrated antenna coupled with metal-insulator-metal tunneling diodes. Herein, by adopting the plasmon excitation of graphene and quantum tunneling process between graphene and GaAs or GaN, we demonstrated the feasibility of harvesting energy from the 915 MHz wireless source belonging to 5G in the FR1 range (450 MHz-6 GHz) which is also known as sub-6G. The generated current and voltage can be observed continuously, with the direction defined by the built-in field between graphene and GaAs and the incident electromagnetic waves treated as the quantum energy source. Under the RF illumination, the generated current increases rapidly and the value can reach in the order of 10^-8-10^-7 A. The harvester can work under the multiple channel mode, harvesting energy simultaneously from different flows of wireless energy in the air. This research will open a new avenue for wireless harvesting by using the ultrafast process of quantum tunneling and unique physical properties of graphene.

Single-atom metal-modified graphenylene as a high-activity catalyst for CO and NO oxidation

Herein, the adsorption behaviors and interactions of different gas species on single-metal atom-anchored graphenylene (M–graphenylene, M = Mn, Co, Ni, and Cu) sheets were investigated by first-principles calculations.

Progress in the functional modification of graphene/graphene oxide: a review

Graphene and graphene oxide have attracted tremendous interest over the past decade due to their unique and excellent electronic, optical, mechanical, and chemical properties. This review focuses on the functional modification of graphene and graphene oxide. First, the basic structure, preparation methods and properties of graphene and graphene oxide are briefly described. Subsequently, the methods for the reduction of graphene oxide are introduced. Next, the functionalization of graphene and graphene oxide is mainly divided into covalent binding modification, non-covalent binding modification and elemental doping. Then, the properties and application prospects of the modified products are summarized. Finally, the current challenges and future research directions are presented in terms of surface functional modification for graphene and graphene oxide.

Graphene and graphene oxide have attracted tremendous interest over the past decade due to their unique and excellent electronic, optical, mechanical, and chemical properties.

On the comparison of oxygen and sulfur transfer reactivities in phosphine and phosphorene: the case of R3Sb(X) carriers (X = O or S)

Functionalization is one of the most powerful tools in materials science for the development of new and innovative materials with tailored properties purposefully designed to enhance the overall stability of the system. This is particularly true for exfoliated black phosphorus, which suffers from easy decomposition by air and moisture, hampering its highly desirable applications, especially in electronics. The present work suggests an innovative approach to the functionalization process of this 2D-material based on the selective introduction of chalcogen atoms on the material surface through a reaction with suitable molecular precursors such as stibine chalcogenides (R3Sb(X), X = O or S; R = organyl group). These molecules may readily act as chalcogen-transfer agents and, upon releasing the chalcogen atom atop the bP surface, leave stable stibines (R3Sb) as byproducts, which may be easily removed from the functionalized bP surface. The work provides an overview of all the possible structural, electronic and energy aspects associated with the chalcogen-atom transfer from the stibine to phosphorus based compounds, exemplified by trialkyl phosphines and single layer exfoliated black phosphorus, i.e. phosphorene, Pn. In both cases the oxygen transfer is more exergonic than the sulfur transfer, with the associated free energy barrier for the phosphine process being higher. Although the sulfur transfer for the Pn is found to be endergonic (ca. +3.6 kcal mol-1), the process may surely occur at high temperature. The evolution of the band structure upon the chalcogen transfer has been depicted in detail.

Metallic bands in chevron-type polyacenes

We present electronic structure calculations based on a single-parameter plane wave expansion method for basic graphene building blocks, namely n-oligophenylenes and n-oligoacenes, revealing excellent agreement with density-functional theory. When oligophenylene molecules are joined through meta (zigzag) or ortho (chevron) junctions, the resulting molecular dimers and polymers exhibit a semiconducting character. While zigzag dimers of oligoacenes also exhibit gapped electronic structures, their chevron-phase features a sharp metallic band at the Fermi energy. This zero-point-energy state, which transforms into Dirac-like band in chevron polymers, survives at the outer elbows of the dimer irrespective of the molecular length, and has the same origin as reported for the polyacetylene and topologically induced edge states at edge-decorated graphene nanoribbons. These findings assist the engineering of topological electronic states at the molecular level and complement the toolbox of quantum phases in carbon-based nanostructures.

We present electronic structure calculations based on a single-parameter plane wave expansion method for molecular nanostructures revealing excellent agreement with density functional theory and predicting metallic bands for chevron molecular dimers.

The bond charge current in the monolayer graphene superlattice with hopping beyond nearest neighbor

In this paper, we systematically investigate the transportation properties of the zigzag nano-ribbon graphene in a local potential barrier/well with electrons hopping between and beyond nearest neighbor. When the local potential is present, the conductance exhibits novel periodic oscillation plateaus around increasing quantized conductance. The oscillation plateau hops down with the quantized conductance until vanishes with increasing local potential barrier. Furthermore, when a small voltage is applied between the two terminals of the conductor, the local current presents periodic oscillation in the barrier region. In contrast, when a local potential well is applied, the conductance shows irregular oscillation, exhibiting incommensurate oscillations of local current inside and outside the well. Finally, similar phenomena persists when more local potentials are applied to the system. We expect our studies can facilitate the design of relevant electronic devices.

Transfer of transition-metal dichalcogenide circuits onto arbitrary substrates for flexible device applications

Transition-metal dichalcogenide (TMD) materials with two-dimensional layered structures and stable surfaces are well suited for transparent and flexible device applications. In order to completely utilize the advantages of thickness control and fabrication of various heterostructure stacks, we proposed a transfer method of TMD field-effect transistors (FETs) and TMD complementary metal-oxide-semiconductor (CMOS) circuits from a Si/SiO2 substrate to a flexible substrate. We compared the characteristics of transferred MoS2 and WSe2 FETs with those of the corresponding devices transferred after channel passivation with an Al2O3 layer on a flexible substrate. Al2O3 passivation further stabilized the transfer of the entire device with electrodes. A CMOS circuit with MoS2 and WSe2 materials could be successfully transferred to a polyethylene terephthalate substrate after the channel passivation. This implies that TMD circuits can be easily fabricated on polymer substrates, which makes them suitable for use in semiconductor processes, for various applications.

A Hexanuclear Niobium Cluster Compound Crystallizing as Macroscopic Tubes

Compounds with ordered structures in one or two dimensions are exciting materials and investigated intensively in many different areas of science. Many activities have been put into the preparation of low‐dimensional nano‐scaled structures and many compounds in this size regime are known. Contrary, the number of known compounds that have low‐dimensional macroscopic sized structures that form directly in a chemical reaction is very limited. Here, we present the synthesis of the niobium cluster compound [(Et₂O)₂H]₂[Nb₆Cl₁₈], crystals of which grow in form of large hexagonal empty tubes of several centimeter length and diameters in the range of 2 mm. The single‐crystal X‐ray structure of this compound has been refined. Under warming, the compound readily eliminates diethyl ether molecules and decomposes. From a closer look at the crystallization process a step‐by‐step scheme of the procedure of the tube growth is proposed. The overall conclusion from this proposal is that a crucial balance between the cluster solution concentration, the crystal growth speed and the ether diffusion speed results in the formation of macroscopic crystal tubes.

Room temperature strain-induced Landau levels in graphene on a wafer-scale platform

Graphene is a powerful playground for studying a plethora of quantum phenomena. One of the remarkable properties of graphene arises when it is strained in particular geometries and the electrons behave as if they were under the influence of a magnetic field. Previously, these strain-induced pseudomagnetic fields have been explored on the nano- and micrometer-scale using scanning probe and transport measurements. Heteroepitaxial strain, in contrast, is a wafer-scale engineering method. Here, we show that pseudomagnetic fields can be generated in graphene through wafer-scale epitaxial growth. Shallow triangular nanoprisms in the SiC substrate generate strain-induced uniform fields of 41 T, enabling the observation of strain-induced Landau levels at room temperature, as detected by angle-resolved photoemission spectroscopy, and confirmed by model calculations and scanning tunneling microscopy measurements. Our work demonstrates the feasibility of exploiting strain-induced quantum phases in two-dimensional Dirac materials on a wafer-scale platform, opening the field to new applications.