Honeycomb Boron on Al(111): From the Concept of Borophene to the Two-Dimensional Boride

A great variety of two-dimensional (2D) boron allotropes (borophenes) were extensively studied in the past decade in the quest for graphene-like materials with potential for advanced technological applications. Among them, the 2D honeycomb boron is of specific interest as a structural analogue of graphene. Recently it has been synthesized on the Al(111) substrate; however it remains unknown to what extent does honeycomb boron behave like graphene. Here we elucidate the structural and electronic properties of this unusual 2D material with a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and DFT calculations. We demonstrate that in contrast to graphene on lattice-mismatched metal surfaces, honeycomb boron cannot wiggle like a blanket on Al(111), but rather induces reconstruction of the top metal layer, forming a stoichiometric AlB2 sheet on top of Al. Our conclusions from theoretical modeling are fully supported by X-ray absorption spectra showing strong similarity in the electronic structure of honeycomb boron on Al(111) and thick AlB2 films. On the other hand, a clear separation of the electronic states of the honeycomb boron into π- and σ-subsystems indicates an essentially 2D nature of the electronic system in both one-layer AlB2 and bulk AlB2.

Osmotic Transport at the Aqueous Graphene and hBN Interfaces: Scaling Laws from a Unified, First-Principles Description

Osmotic transport in nanoconfined aqueous electrolytes provides alternative venues for water desalination and "blue energy" harvesting. The osmotic response of nanofluidic systems is controlled by the interfacial structure of water and electrolyte solutions in the so-called electrical double layer (EDL), but a molecular-level picture of the EDL is to a large extent still lacking. Particularly, the role of the electronic structure has not been considered in the description of electrolyte/surface interactions. Here, we report enhanced sampling simulations based on ab initio molecular dynamics, aiming at unravelling the free energy of prototypical ions adsorbed at the aqueous graphene and hBN interfaces, and its consequences on nanofluidic osmotic transport. Specifically, we predicted the zeta potential, the diffusio-osmotic mobility, and the diffusio-osmotic conductivity for a wide range of salt concentrations from the ab initio water and ion spatial distributions through an analytical framework based on Stokes equation and a modified Poisson-Boltzmann equation. We observed concentration-dependent scaling laws, together with dramatic differences in osmotic transport between the two interfaces, including diffusio-osmotic flow and current reversal on hBN but not on graphene. We could rationalize the results for the three osmotic responses with a simple model based on characteristic length scales for ion and water adsorption at the surface, which are quite different on graphene and on hBN. Our work provides fundamental insights into the structure and osmotic transport of aqueous electrolytes on 2D materials and explores alternative pathways for efficient water desalination and osmotic energy conversion.

Ternary Conductance Switching Realized by a Pillar[5]arene-Functionalized Two-Dimensional Imine Polymer Film

Nowadays, most manufacturing memory devices are based on materials with electrical bistability (i. e., "0" and "1") in response to an applied electric field. Memory devices with multilevel states are highly desired so as to produce high-density and efficient memory devices. Herein, we report the first multichannel strategy to realize a ternary-state memristor. We make use of the intrinsic sub-nanometer channel of pillar[5]arene and nanometer channel of a two-dimensional imine polymer to construct an active layer with multilevel channels for ternary memory devices. Low threshold voltage, long retention time, clearly distinguishable resistance states, high ON/OFF ratio (OFF/ON1/ON2=1 : 10 : 10³ ), and high ternary yield (75 %) were obtained. In addition, the flexible memory device based on 2DP_TPAZ+TAPB can maintain its stable ternary memory performance after being bent 500 times. The device also exhibits excellent thermal stability and can tolerate a temperature as high as 300 °C. It is envisioned that the results of this work will open up possibilities for multistate, flexible resistive memories with good thermal stability and low energy consumption, and broaden the application of pillar[n]arene.

Plasmon-Mediated 2D/2D Phase Junction for Improved Photocatalytic Hydrogen Generation Activity

A phase junction fabricated by two crystalline phases of the same semiconductor is a promising photocatalyst with efficient charge transfer and separation. However, the weak light absorption and uncontrolled phase junction interface limit the generation and separation of photogenerated carriers. Herein, a two-dimensional (2D)/2D phase junction was prepared by growing orthorhombic WO₃ ultrathin nanosheets on hexagonal WO₃ nanosheets through a one-step hydrothermal method. The orthorhombic/hexagonal WO₃ possesses large-area phase junction interfaces, rich reactive sites, and built-in electric field, which greatly accelerate the photogenerated charge separation and transfer. Thus, the orthorhombic/hexagonal WO₃ displayed excellent photocatalytic hydrogen generation activity from water splitting under light irradiation (λ > 420 nm), which is 2.16 and 2.85 times those of orthorhombic and hexagonal WO₃ phase components. Furthermore, Au nanoparticles (about 4.5 nm in diameter) were deposited on both orthorhombic and hexagonal WO₃ nanosheets to form a plasmon-mediated phase junction. The hybrids exhibit prominent visible-light absorption and efficient charge transfer, leading to a further improved photocatalytic hydrogen generation activity. Further characterization studies demonstrate that superior photoactivity arises from the excellent visible-light-harvesting ability, appropriate band structure, and high-efficiency and multichannel transferring processes of photogenerated carriers.

Refractive Index Modulation in Monolayer Molybdenum Diselenide

Two-dimensional transition metal dichalcogenides are promising candidates for ultrathin light modulators due to their highly tunable excitonic resonances at visible and near-infrared wavelengths. At cryogenic temperatures, large excitonic reflectivity in monolayer molybdenum diselenide (MoSe₂) has been shown, but the permittivity and index modulation have not been studied. Here, we demonstrate large gate-tunability of complex refractive index in monolayer MoSe₂ by Fermi level modulation and study the doping dependence of the A and B excitonic resonances for temperatures between 4 and 150 K. By tuning the charge density, we observe both temperature- and carrier-dependent epsilon-near-zero response in the permittivity and transition from metallic to dielectric near the A exciton energy. We attribute the dynamic control of the refractive index to the interplay between radiative and non-radiative decay channels that are tuned upon gating. Our results suggest the potential of monolayer MoSe₂ as an active material for emerging photonics applications.

Abnormal Phase Transition and Band Renormalization of Guanidinium-Based Organic-Inorganic Hybrid Perovskite

Low-dimensional organic-inorganic hybrid perovskites have attracted much interest owing to their superior solar conversion performance, environmental stability, and excitonic properties compared to their three-dimensional (3D) counterparts. Among reduced-dimensional perovskites, guanidinium-based perovskites crystallize in layered one-dimensional (1D) and two-dimensional (2D). Here, our studies demonstrate how the dimensionality of the hybrid perovskite influences the chemical and physical properties under different pressures (i.e., bond distance, angle, vdW distance). Comprehensive studies show that 1D GuaPbI₃ does not undergo a phase transition even up to high pressures (∼13 GPa) and its band gap monotonically reduces with pressure. In contrast, 2D Gua₂PbI₄ exhibits an early phase transition at 5.5 GPa and its band gap follow nonmonotonic pressure response associated with phase transition as well as other bond angle changes. Computational simulations reveal that the phase transition is related to the structural deformation and rotation of PbI₆ octahedra in 2D Gua₂PbI₄ owing to a larger degree of freedom of deformation. The soft lattice allows them to uptake large pressures, which renders structural phase transitions possible. Overall the results offer the first insights into how layered perovskites with different dimensionality respond to structural changes driven by pressure.

Gate Control of Spin-Layer-Locking FETs and Application to Monolayer LuIO

A recent 2D spinFET concept proposes to switch electrostatically between two separate sublayers with strong and opposite intrinsic Rashba effects, exploiting the spin-layer-locking mechanism in centrosymmetric materials with local dipole fields. Here, we propose a novel monolayer material within this family, lutetium oxide iodide (LuIO). It displays one of the largest Rashba effects among 2D materials (up to k_R = 0.08 Å^-1), leading to a π/2 rotation of the spins over just 1 nm. The monolayer was predicted to be exfoliable from its experimentally known 3D bulk counterpart, with a binding energy lower than graphene. We characterize and simulate the interplay of the two gate-controlled parameters for such devices: doping and spin channel selection. We show that the ability to split the spin channels in energy diminishes with doping, leading to specific gate-operation guidelines that can apply to all devices based on spin-layer locking.

Thermodynamic Perspective on the Oxidation of Layered Materials and Surface Oxide Amelioration in 2D Devices

Surface oxidation is an unneglectable problem for 2D semiconductors because it hinders the practical application of 2D material-based devices. In this research, the oxidation of layered materials is investigated by a thermodynamic approach to verify their oxidation tendency. It was found that almost all 2D materials are thermodynamically unstable in the presence of oxygen at room temperature. Two potential solutions for surface oxidation are proposed in this work: (i) the conversion of the surface oxides to functional oxides through the deposition of active metals and (ii) the recovery of original 2D materials from the surface oxides by 2D material heterostructure formation with the same chalcogen group. Supported by thermodynamic calculations, both approaches are feasible to ameliorate the surface oxides of 2D materials by the appropriate selection of metals for deposition or 2D materials for heterostructure formation. Thermodynamic data of 64 elements and 75 2D materials are included and compared in this research, which can improve gate insulator or electrode contact material selection in 2D devices to solve the surface oxidation issue. For instance, yttrium and titanium are good candidates for surface oxide conversion, while zirconium and hafnium chalcogenide can trigger the recovery of original 2D materials from their surface oxides. The systematic diagrams presented in this work can serve as a guideline for considering surface oxidation in future device fabrication from various 2D materials.

Selective Oxygen and Hydrogen Functionalization of the h-BN/Rh(111) Nanomesh

We present detailed studies on the covalent adsorption of molecular oxygen and atomic hydrogen on the hexagonal boron nitride (h-BN) nanomesh on Rh(111). The functionalization of this two-dimensional (2D) material was investigated under ultra-high vacuum conditions using synchrotron radiation-based in situ high-resolution X-ray photoelectron spectroscopy, temperature-programmed X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. We are able to provide a deep insight into the adsorption behavior and thermal stability of oxygen and hydrogen on h-BN/Rh(111). Oxygen functionalization was achieved via a supersonic molecular beam while hydrogen functionalization was realized using an atomic hydrogen source. Adsorption of the respective species was observed to occur selectively in the pores of h-BN leading to spatially defined modification of the 2D layer. The adsorption of the observed molecular oxygen species was found to be an activated process that requires high-energy oxygen molecules. Upon heating to 700 K, oxygen functionalization was observed to be almost reversible except for small amounts of boron oxides evolving due to the reaction of oxygen with the 2D material. Hydrogen functionalization of h-BN/Rh(111) was fully reversed upon heating to about 640 K.

Lanthanide-Doped Topological Nanosheets with Enhanced Near-Infrared Photothermal Performance for Energy Conversion

Two-dimensional inorganic semiconductor materials have aroused tremendous research interest and found their potential in resolving the present urgent global issues, such as cancer therapy and fresh water shortage. Particularly, the near-infrared (NIR) photothermal conversion efficiency is a significant parameter in photothermal therapy. However, lack of an effective improvement strategy and their relatively low NIR phothermal conversion efficiency would restrict their wide and further application. Here, this work reports that enhanced NIR photothermal conversion is achieved in topological Bi₂Se₃ nanosheets by introducing a lanthanide dopant. Specifically, lanthanide Pr-doped Bi₂Se₃ nanosheets possess a photothermal conversion efficiency of 49.5%, which is higher than those of undoped Bi₂Se₃ nanosheets (31.0%) and numerous reported photothermal materials. The electronic structure of Pr-doped Bi₂Se₃ nanosheets was also analyzed by first-principles simulation. Furthermore, an interfacial evaporation system based on the developed nanosheets has been established, demonstrating a superior solar-thermal conversion efficiency of 91.5% and a water evaporation rate of 1.669 kg m^-2 h^-1 under 1 sun irradiation. The present work would provide new insights for the increase in the efficiency of photothermal materials.

Exfoliated Bi2Te3-enabled membranes for new concept water desalination: Freshwater production meets new routes

Water scarcity forces the science to find the most environmentally friendly propulsion technology for supplying plentiful freshwater at low energy costs. Membrane Distillation well meets criteria of eco-friendly management of natural resources, but it is not yet competitive on scale. Herein, we use a dichalchogenide compound (Bi₂Te₃) as a conceivable source to accelerate the redesign of advanced membranes technologies such as thermally driven membrane distillation. A procedure based on assisted dispersant liquid phase exfoliation is used to fill PVDF membranes. Key insights are gained in the crucial role of this topological material confined in hydrophobic membranes dedicated to recovery of freshwater from synthetic seawater. Intensified water flux together with reduced energy consumption is obtained into one pot, thereby gathering ultrafast production and thermal efficiency in a single device. Bi₂Te₃-enabled membranes show ability to reduce the resistance to mass transfer while high resistance to heat loss is opposite. Permeate flux is kept stable and salt rejection is higher than 99.99% during 23 h-MD test. Our results confirm the effectiveness of chalcogenides as frontier materials for new-concept water desalination through breakthrough thermally-driven membrane distillation, which is regarded as a new low-energy and sustainable solution to address the growing demand for access to freshwater.

Boosted Solar Light Absorbance in PdS2/PtS2 Vertical Heterostructures for Ultrathin Photovoltaic Devices

Transition-metal dichalcogenides (TMDs) represent a class of materials whose archetypes, such as MoS2 and WS2, possess exceptional electronic and optical properties and have been massively exploited in optoelectronic applications. The layered structure allows for their exfoliation to two-dimensional samples with atomic thickness (≲ 1 nm), promising for ultrathin, ultralight devices. In this work, by means of state-of-the-art ab initio many-body perturbation theory techniques, we focus on single-layer PdS2 and PtS2 and propose a novel van der Waals heterostructure with outstanding light absorbance, reaching up to 50% in the visible spectrum and yielding a maximum short-circuit current of 7.2 mA/cm2 under solar irradiation. The computed excitonic landscape predicts a partial charge separation between the two layers and the momentum-forbidden lowest-energy state increases the carrier diffusion length. Our results show that the employment of vertical heterostructures with less conventional TMDs, such as PdS2/PtS2, can greatly boost light absorbance and favor the development of more efficient, atomic-thin photovoltaic devices.

Toward Low-Temperature Solid-Source Synthesis of Monolayer MoS2

Two-dimensional (2D) semiconductors have been proposed for heterogeneous integration with existing silicon technology; however, their chemical vapor deposition (CVD) growth temperatures are often too high. Here, we demonstrate direct CVD solid-source precursor synthesis of continuous monolayer (1L) MoS₂ films at 560 °C in 50 min, within the 450-to-600 °C, 2 h thermal budget window required for back-end-of-the-line compatibility with modern silicon technology. Transistor measurements reveal on-state current up to ∼140 μA/μm at 1 V drain-to-source voltage for 100 nm channel lengths, the highest reported to date for 1L MoS₂ grown below 600 °C using solid-source precursors. The effective mobility from transfer length method test structures is 29 ± 5 cm² V^-1 s^-1 at 6.1 × 10¹² cm^-2 electron density, which is comparable to mobilities reported from films grown at higher temperatures. The results of this work provide a path toward the realization of high-quality, thermal-budget-compatible 2D semiconductors for heterogeneous integration with silicon manufacturing.

Super-Resolution Nanolithography of Two-Dimensional Materials by Anisotropic Etching

Nanostructuring allows altering of the electronic and photonic properties of two-dimensional (2D) materials. The efficiency, flexibility, and convenience of top-down lithography processes are, however, compromised by nanometer-scale edge roughness and resolution variability issues, which especially affect the performance of 2D materials. Here, we study how dry anisotropic etching of multilayer 2D materials with sulfur hexafluoride (SF₆) may overcome some of these issues, showing results for hexagonal boron nitride (hBN), tungsten disulfide (WS₂), tungsten diselenide (WSe₂), molybdenum disulfide (MoS₂), and molybdenum ditelluride (MoTe₂). Scanning electron microscopy and transmission electron microscopy reveal that etching leads to anisotropic hexagonal features in the studied transition metal dichalcogenides, with the relative degree of anisotropy ranked as: WS₂ > WSe₂ > MoTe₂ ∼ MoS₂. Etched holes are terminated by zigzag edges while etched dots (protrusions) are terminated by armchair edges. This can be explained by Wulff constructions, taking the relative stabilities of the edges and the AA' stacking order into account. Patterns in WS₂ are transferred to an underlying graphite layer, demonstrating a possible use for creating sub-10 nm features. In contrast, multilayer hBN exhibits no lateral anisotropy but shows consistent vertical etch angles, independent of crystal orientation. Using an hBN crystal as the base, ultrasharp corners can be created in lithographic patterns, which are then transferred to a graphite crystal underneath. We find that the anisotropic SF₆ reactive ion etching process makes it possible to downsize nanostructures and obtain smooth edges, sharp corners, and feature sizes significantly below the resolution limit of electron beam lithography. The nanostructured 2D materials can be used themselves or as etch masks to pattern other nanomaterials.

Rise of silicene and its applications in gas sensing

Reviewing a subject is done to provide an insight into theoretical and conceptual background of the study. Looking back into the history of an emerging field and summarizing it in a few pages is a herculean task. Anyway, it was imperative to write a few words about the rise of silicene, its properties, and its applications as gas sensors. Currently, silicene is a growing field of interest. It is probably one of the most studied materials nowadays and scientists and researchers are studying it because of its intriguing electronic properties and potential applications in nanoelectronics. Various experimental and theoretical investigations are going on worldwide to explore the various aspects of this field. It is essential to review the literature based on investigations by various scientists in this field.

Width Dependent Elastic Properties of Graphene Nanoribbons

The mechanical response of graphene nanoribbons under uniaxial tension, as well as its dependence on the nanoribbon width, is presented by means of numerical simulations. Both armchair and zigzag edged graphene nanoribbons are considered. We discuss results obtained through two different theoretical approaches, viz. density functional methods and molecular dynamics atomistic simulations using empirical force fields especially designed to describe interactions within graphene sheets. Apart from the stress-strain curves, we calculate several elastic parameters, such as the Young’s modulus, the third-order elastic modulus, the intrinsic strength, the fracture strain, and the Poisson’s ratio versus strain, presenting their variation with the width of the nanoribbon.

A Plasmon-Enhanced SnSe2 Photodetector by Non-Contact Ag Nanoparticles

The 2D layered materials are promising candidates for broadband, low-cost photodetectors. One deficiency of 2D materials is the relatively low absorbance of light, limiting the applications of the 2D photodetectors. Doping of plasmonic nanoparticles into 2D materials may enhance the optical absorbance owing to the localized surface plasmonic resonance (LSPR) effect; however, considerable defects may be introduced into the 2D materials at the same time, resulting in certain degradation of device performance. Here, a novel design of 2D photodetectors with enhanced photoresponsivity by non-contact plasmonic nanoparticles (NPs) is proposed, consisting of a hybrid structure of few-layer SnSe₂ transferred a fused silica (SiO₂ ) plate with embedded Ag NPs. The system of Ag NPs-in-SiO₂ shows strong LSPR effect with significantly enhanced optical absorption, acting on SnSe₂ in a non-contact configuration. Benefiting from well-preserved intrinsic features of SnSe₂ and LSPR effect, the responsivity of the photodetector is enhanced by 881 times with the bias voltage of 0.1 V, which is superior to previously reported results of plasmon-enhanced 2D photodetectors. Moreover, the SiO₂ with embedded Ag NPs is recyclable and can be easy to be recombined with different 2D materials. This work offers additional strategy for development of efficient, low-cost 2D photodetectors by using plasmonic NPs.

Surface Diffusion and Epitaxial Self-Planarization for Wafer-Scale Single-Grain Metal Chalcogenide Thin Films

Although wafer-scale single-grain thin films of 2D metal chalcogenides (MCs) have been extensively sought after during the last decade, the grain size of the MC thin films is still limited in the sub-millimeter scale. A general strategy of synthesizing wafer-scale single-grain MC thin films by using commercial wafers (Si, Ge, GaAs) both as metal source and epitaxial collimator is presented. A new mechanism of single-grain thin-film formation, surface diffusion, and epitaxial self-planarization is proposed, where chalcogen elements migrate preferentially along substrate surface and the epitaxial crystal domains flow to form an atomically smooth thin film. Through synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy, the formation of single-grain Si₂ Te₃ , GeTe, GeSe, and GaTe thin films on (111) Si, Ge, and (100) GaAs is verified. The Si₂ Te₃ thin film is used to achieve transfer-free fabrication of a high-performance bipolar memristive electrical-switching device.

Paraffin-Enabled Compressive Folding of Two-Dimensional Materials with Controllable Broadening of the Electronic Band Gap

The capability to manipulate the size of the electronic band gap is of importance to semiconductor technology. Among these, a wide direct band gap is particularly helpful in optoelectronic devices due to the efficient utilization of blue and ultraviolet light. Here, we reported a paraffin-enabled compressive folding (PCF) strategy to widen the band gap of two-dimensional (2D) materials. Due to the large thermal expansion coefficient of paraffin, folded 2D materials can be achieved via thermal engineering of the paraffin-assisted transfer process. It can controllably introduce 0.2-1.3% compressive strain onto folded structures depending on the temperature differences and transfer the folding product to both rigid and soft substrates. Exemplified by MoS₂, its folded multilayers demonstrated blue-shifts at direct gap transition peaks, six times stronger photoluminescence intensity, almost double mobility, and 20 times higher photoresponsivity over unfolded MoS₂. This PCF strategy can attain controllable widening band gap of 2D materials, which will open up novel applications in optoelectronics.

CVD-Grown 2D Nonlayered NiSe as a Broadband Photodetector

Two-dimensional (2D) materials have expansive application prospects in electronics and optoelectronics devices due to their unique physical and chemical properties. 2D layered materials are easy to prepare due to the layered crystal structure and the interlayer van der Waals combination. However, the 2D nonlayered materials are difficult to prepare due to the nonlayered crystal structure and the combination of interlayer isotropic chemical bonds, resulting in limited research on 2D nonlayered materials with broad characteristics. Here, a 2D nonlayered NiSe material has been synthesized by a chemical vapor deposition method. The atomic force microscopy study shows that the grown NiSe with a thin thickness. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy results demonstrate the uniformity and high quality of NiSe flakes. The NiSe based photodetector realizes the laser response to 830 nm and 10.6 μm and the maximum responsivity is ~6.96 A/W at room temperature. This work lays the foundation for the preparation of 2D nonlayered materials and expands the application of 2D nonlayered materials in optoelectronics fields.

Real-Time Biomonitoring Device Based on 2D Black Phosphorus and Polyaniline Nanocomposite Flexible Supercapacitors

Flexible energy storage devices are becoming significantly important to power wearable and portable devices that monitor physiological parameters for many biomedical applications. Many hybrid nanomaterials based on 2D materials are used in order to improve the performance of flexible energy storage devices. Here, a hybrid nanocomposite is synthesized through in situ polymerization of aniline in the presence of black phosphorus (BP) nanoflakes. This nanocomposite, polyaniline (PANI)@BP, is employed to fabricate flexible supercapacitor (FSC) electrodes. PANI@BP FSCs can provide a power source for biometric devices. The generated signal can be transmitted to a smartphone in real time via wireless communication. Such a compact and lightweight integrated device has been used to track a human heart beat while powered by PANI@BP FSC. These findings are providing a promising example of a flexible energy storage device that can be integrated with different real-time health monitoring devices.

Ultrathin Multibridge Channel Transistor Enabled by van der Waals Assembly

Multibridge channel field-effect transistors (MBCFETs) enable improved gate control and flow of a large drive current and they are regarded as promising candidates for next-generation transistor architecture. However, in achieving a larger drive current with a thinner channel, limitations arise from the decrease in mobility when the thickness of the Si nanosheet is less than 5 nm. In addition, an increase in the leakage current is unavoidable when a large number of channels are stacked. Here, a 2D ultrathin MBCFET is demonstrate, constructed based on 2 nm/2 nm MoS₂ channels. The normalized drive current (23.11 µA*µm µm^-1 ) in each level channel of this MBCFET exceeds that of the latest seven-level-stacked Si MBCFET, while the leakage current is only 0.4% of this value, with the subthreshold swing reaching 60 mV dec^-1 and an on/off ratio reaching up to 4 × 10⁸ at room temperature. Furthermore, the drive current of this 2D ultrathin MBCFET can be further increased by regulating the polarity of the operation voltage to reduce the injection barrier. The combination of 2D materials and an MBC structure has the potential for use in high-performance and low-power-consumption electronics.

Arsenene Nanodots with Selective Killing Effects and their Low-Dose Combination with ß-Elemene for Cancer Therapy

Arsenical drugs have achieved hallmark success in treating patients with acute promyelocytic leukemia, but expanding their clinical utility to solid tumors has proven difficult with the contradiction between the therapeutic efficacy and the systemic toxicity. Here, leveraging efforts from materials science, biocompatible PEGylated arsenene nanodots (AsNDs@PEG) with high monoelemental arsenic purity that can selectively and effectively treat solid tumors are synthesized. The intrinsic selective killing effect of AsNDs@PEG is closely related to high oxidative stress in tumor cells, which leads to an activated valence-change of arsenic (from less toxic As⁰ to severely toxic oxidation states), followed by decreased superoxide dismutase activity and massive reactive oxygen species (ROS) production. These effects occur selectively within cancer cells, causing mitochondrial damage, cell-cycle arrest, and DNA damage. Moreover, AsNDs@PEG when applied in a multi-drug combination strategy with β-elemene, a plant-derived anticancer drug, achieves synergistic antitumor outcomes, and its newly discovered on-demand photothermal properties facilitate the elimination of the tumors without recurrence, potentially further expanding its clinical utility. In line of the practicability for a large-scale fabrication and negligible systemic toxicity of AsNDs@PEG (even at high doses and with repetitive administration), a new-concept arsenical drug with high therapeutic efficacy for selective solid tumor therapy is provided.

Intercalation Strategy in 2D Materials for Electronics and Optoelectronics

Intercalation is an effective approach to tune the physical and chemical properties of 2D materials due to their abundant van der Waals gaps that can host high-density intercalated guest matters. This approach has been widely employed to modulate the optical, electrical, and photoelectrical properties of 2D materials for their applications in electronic and optoelectronic devices. Thus it is necessary to review the recent progress of the intercalation strategy in 2D materials and their applications in devices. Herein, various intercalation strategies and the novel properties of the intercalated 2D materials as well as their applications in electronics and optoelectronics are summarized. In the end, the development tendency of this promising approach for 2D materials is also outlined.

Moiré, Euler and self-similarity - the lattice parameters of twisted hexagonal crystals

A real-space approach for the calculation of the moiré lattice parameters for superstructures formed by a set of rotated hexagonal 2D crystals such as graphene or transition-metal dichalcogenides is presented. Apparent moiré lattices continuously form for all rotation angles, and their lattice parameter to a good approximation follows a hyperbolical angle dependence. Moiré crystals, i.e. moiré lattices decorated with a basis, require more crucial assessment of the commensurabilities and lead to discrete solutions and a non-continuous angle dependence of the moiré-crystal lattice parameter. In particular, this lattice parameter critically depends on the rotation angle, and continuous variation of the angle can lead to apparently erratic changes of the lattice parameter. The solutions form a highly complex pattern, which reflects number-theoretical relations between formation parameters of the moiré crystal. The analysis also provides insight into the special case of a 30° rotation of the constituting lattices, for which a dodecagonal quasicrystalline structure forms.