Van Der Waals Research Articles

Computational study of the encapsulation of an organic polluant with beta-CD, in vacuum and in water

This article reports the results of a theoretical study of the host/guest inclusion complex involving a herbicide called Diuron in β-cyclodextrin. Various computational techniques were used to determine the structure, geometry and stability energies of the complex. The analysis of the diuron/β-CD inclusion complex was performed both in vacuum and in water in a 1:1 ratio. The DFT/B97-3C method was used to obtain the structures of the complexes and to calculate their stability energies. The specific configurations were determined using nuclear magnetic resonance spectroscopy. The interaction bonds were investigated and the formation of conventional hydrogen bonds was detected by AIM analysis. The nature of the interactions was further elucidated using the method of non-covalent interactions (NCI). This showed that hydrogen bonds and van der Waals interactions contribute significantly to the formation of the inclusion complex. To gain more insight into the absorption and emission energies of the investigated complex, the gap energy (EHOMO-ELUMO) was calculated.

Three‐Dimensional VTe2/MXene/CNT Ternary Architectures for the Development of High Performance Microsupercapacitors

AbstractRapid advancements in portable electronics have created a demand for ultrathin power sources. Microsupercapacitors (MSCs) are becoming a competitive and advantageous option for these applications. It is widely recognized that to develop MSCs with exceptional performance, electrode materials having two‐dimensonal (2D) permeable channels, structural scaffolds with high‐conductivity and large surface area are suitable. Vanadium ditelluride (VTe2) stands out as an ideal material platform in this context. Its unique combination of metallic properties and exfoliative characteristics‐stemming from the conducting Te–V–Te layers held together by weak van der Waals interlayer interactions‐ renders it highly promising for high‐performance MSCs. This study is the first to report that the restacking issues and electrochemical performance of VTe2 can be successfully avoided by the simultaneous incorporation of MXene and CNT to form a ternary hybrid. Here, a laser‐induced graphene (LIG)‐based MSC utilizing VTe2/MXene/CNT as the active electrode material is fabricated. This MSC achieve fabrications an outstanding maximum energy density of 6.84 µWh cm−2 and a power density of 304.7 µW cm−2. This significant achievement demonstrates the potential of this LIG‐based MSC to advance the design of high‐performance micro‐energy storage devices.

The synergistic immunomodulatory activity of Lycium barbarum glycopeptide and isochlorogenic acid A on RAW264.7 cells.

Regulation of the immune system to maintain homeostasis in the organism has become a focus of research, and the synergistic effect of multi-component complexes will effectively improve the immunomodulatory activity. The present study aimed to investigate the interaction and synergistic immunomodulatory activity of isochlorogenic acid A (IAA) and Lycium barbarum glycopeptide (LbGp). The results obtained indicated that non-covalent intermolecular interactions were employed to form the LbGp-IAA complex, with a binding ratio of 135.15 mg g-1. The formation of LbGp-IAA complex altered the conformation of LbGp, and IAA was mainly bound to LbGp by van der Waals forces and hydrogen bonds. In addition, LbGp-IAA promoted the proliferation of RAW264.7 cells. The IAA and LbGp interaction had a synergistic effect on the promotion of phagocytosis and the expression of nitric oxide, tumor necrosis faction-α and interleukin-1β, which improved the immunomodulatory effect of LbGp. Furthermore, the combination of LbGp and IAA synergistically inhibited lipopolysaccharide-induced inflammatory response. In summary, the binding of IAA enhanced the immunomodulatory activity of LbGp and coordinated the immune response, and did not trigger an inflammatory response, which was potentially attributed to the alteration of spatial structure of LbGp through the binding of IAA. The results provide new perspectives for the study of glycopeptide-polyphenol interactions. © 2024 Society of Chemical Industry.

Ultrafast Charge Transfer-Induced Unusual Nonlinear Optical Response in ReSe2/ReS2 Heterostructure.

Ultrafast charge transfer in van der Waals heterostructures can effectively engineer the optical and electrical properties of two-dimensional semiconductors for designing photonic and optoelectronic devices. However, the nonlinear absorption conversion dynamics with the pump intensity and the underlying physical mechanisms in a type-II heterostructure remain largely unexplored, yet hold considerable potential for all-optical logic gates. Herein, two-dimensional ReSe2/ReS2 heterostructure is designed to realize an unusual transition from reverse saturable absorption to saturable absorption (SA) with a conversion pump intensity threshold of approximately 170 GW/cm2. Such an intriguing phenomenon is attributed to the decrease of two-photon absorption (TPA) of ReS2 and the increase of SA of ReSe2 with the pump intensity. Based on the characterization results of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, femtosecond transient absorption spectrum, Kelvin probe force microscopy, and density functional theory calculation, a type-II charge-transfer-energy level model is proposed combined with the TPA of ReS2 and SA of ReSe2 processes. The results reveal the critical role of ultrafast interfacial charge transfer in tuning the unusual nonlinear absorption and improving the SA of ReSe2/ReS2 under different excitation wavelengths. Our finding deepens the understanding of nonlinear absorption physical mechanisms in two-dimensional heterostructure materials, which may further diversify the nonlinear optical materials and photonic devices.

Ferroelectric Polarization Enhanced Optoelectronic Synaptic Response of a CuInP2S6 Transistor Structure.

Neuromorphic computing can simulate brain function and is a pivotal element in next-generation computing, providing a potential solution to the limitations brought by the von Neumann bottleneck. Optoelectronic synaptic devices are highly promising tools for simulating biomimetic nervous systems. In this study, we developed an optoelectronic neuromorphic device with a transistor structure constructed using ferroelectric CuInP2S6. Essential synaptic behaviors in this device are observed in response to light and electrical stimuli. The optoferroelectric coupling is revealed, and the highly tunable gate modulation of the charge carrier is realized in a single device. On this basis, the light adaptation of the biological eyes and smarter Pavlovian dogs was implemented successfully and enhanced by ferroelectric polarization. The gate voltage application promotes the migration of additional Cu+ ions in the in-plane direction, thus enhancing the synaptic performance of electrical stimulation. Meanwhile, the processing ability of convolutional kernel noise images in ferroelectric devices has been achieved. Our results offer the important observation and application of ferroelectric polarization-enhanced synaptic properties of a transistor structure and have great potential in promoting the development of two-dimensional van der Waals materials and devices.

Potential toxicity of Graphene (Oxide) quantum dots to human intestinal fatty acid binding protein (HIFABP) via obstructing the protein’s openings

Graphene quantum dots (GQDs) have garnered significant attention across numerous fields due to their ultrasmall size and exceptional properties. However, their extensive applications may lead to environmental exposure and subsequent uptake by humans. Yet, conflicting reports exist regarding the potential toxicity of GQDs based on experimental investigations. Therefore, a comprehensive understanding of GQD biosafety requires further microscopic and molecular-level investigations. In this study, we employed molecular dynamics (MD) simulations to explore the interactions between GQDs and graphene oxide quantum dots (GOQDs) with a protein model, the human intestinal fatty acid binding protein (HIFABP), that plays a crucial role in mediating the carrier of fatty acids in the intestine. Our MD simulation results reveal that GQDs can be adsorbed on the opening of HIFABP, which serves as an entrance for the fatty acid molecules into the protein’s interior cavity. This adsorption has the potential to obstruct the opening of HIFABP, leading to the loss of its normal biological function and ultimately resulting in toxicity. The adsorption of GQDs is driven by a combination of van der Waals (vdW), π-π stacking, cation-π, and hydrophobic interactions. Similarly, GOQDs also exhibit the ability to block the opening of HIFABP, thereby potentially causing toxicity. The blockage of GOQDs to HIFABP is guided by a combination of vdW, Coulomb, π-π stacking, and hydrophobic interactions. These findings not only highlight the potential harmful effects of GQDs on HIFABP but also elucidate the underlying molecular mechanism, which provides crucial insights into GQD toxicology.

Anomalous Pressure-Induced Blue-Shifted Emission of Ionic Copper-Iodine Clusters: The Competitive Effect between Cuprophilic Interactions and Through-Space Interactions.

Developing ionic copper-iodine clusters with multiple emitting is crucial for enriching lighting and display materials with various colors. However, the luminescent properties of traditional ionic copper-iodine clusters are often closely associated with low-energy cluster-centered triplet emission, which will redshift further as the Cu⋅⋅⋅Cu bond length decreases. This article utilizes a pressure-treated strategy to achieve an anomalous pressure-induced blue-shifted luminescence phenomenon in ionic Cu4I6(4-dimethylamino-1-ethylpyridinium)2 crystals for the first time, which is based on dominant through-space charge-transfer (TSCT). Herein, we reveal that the more advantageous through-space interactions in the competition between cuprophilic interactions and through-space interactions can lead to a blue-shifted luminescence. High-pressure angle-dispersive X-ray diffraction and high-pressure infrared experiments show that the enhanced through-space interactions mainly originate from forming new intermolecular C-H⋅⋅⋅I hydrogen bonds and the enhancement of van der Waals interactions between organic cations and anionic clusters. Theoretical calculations and experimental studies of excited-state dynamics confirm that the blue-shifted emission is due to the increased energy gap between the excited triplet and ground states caused by the electron delocalization under stronger through-space interactions. This work deepens previous understanding and provides a new avenue to design and synthetic ionic copper-iodine clusters with high-energy TSCT emission.

Light-modulated van der Waals force microscopy

Atomic force microscope generally works by manipulating the absolute magnitude of the van der Waals force between tip and specimen. This force is, however, less sensitive to atom species than to tip-sample separations, making compositional identification difficult, even under multi-modal strategies or other atomic force microscopy variations. Here, we report the phenomenon of a light-modulated tip-sample van der Waals force whose magnitude is found to be material specific, which can be employed to discriminate heterogeneous compositions of materials. We thus establish a near-field microscopic method, named light-modulated van der Waals force microscopy. Experiments discriminating heterogeneous crystalline phases or compositions in typical materials demonstrate a high compositional resolving capability, represented by a 20 dB signal-to-noise ratio on a MoTe2 film under the excitation of a 633 nm laser of 1.2 mW, alongside a sub-10 nm lateral spatial resolution, smaller than the tip size of 20 nm. The simplicity of the light modulation mechanism, minute excitation light power, broadband excitation wavelength, and diversity of the applicable materials imply broad applications of this method on material characterization, particularly on two-dimensional materials that are promising candidates for next-generation chips.

Anomalous Pressure‐Induced Blue‐Shifted Emission of Ionic Copper‐Iodine Clusters: The Competitive Effect between Cuprophilic Interactions and Through‐Space Interactions

AbstractDeveloping ionic copper‐iodine clusters with multiple emitting is crucial for enriching lighting and display materials with various colors. However, the luminescent properties of traditional ionic copper‐iodine clusters are often closely associated with low‐energy cluster‐centered triplet emission, which will redshift further as the Cu⋅⋅⋅Cu bond length decreases. This article utilizes a pressure‐treated strategy to achieve an anomalous pressure‐induced blue‐shifted luminescence phenomenon in ionic Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 crystals for the first time, which is based on dominant through‐space charge‐transfer (TSCT). Herein, we reveal that the more advantageous through‐space interactions in the competition between cuprophilic interactions and through‐space interactions can lead to a blue‐shifted luminescence. High‐pressure angle‐dispersive X‐ray diffraction and high‐pressure infrared experiments show that the enhanced through‐space interactions mainly originate from forming new intermolecular C−H⋅⋅⋅I hydrogen bonds and the enhancement of van der Waals interactions between organic cations and anionic clusters. Theoretical calculations and experimental studies of excited‐state dynamics confirm that the blue‐shifted emission is due to the increased energy gap between the excited triplet and ground states caused by the electron delocalization under stronger through‐space interactions. This work deepens previous understanding and provides a new avenue to design and synthetic ionic copper‐iodine clusters with high‐energy TSCT emission.

Electrically reconfigurable MoO3/InSe van der Waals heterojunctions

Abstract Van der Waals (vdW) heterojunctions formed by stacking different layers of two-dimensional atomic crystals with atomically sharp interface and versatile band alignment have been considered as promising candidates for construction of nanoelectronic and nanophotonic devices. Here, we demonstrate the electrically reconfigurable behavior in MoO3/InSe vdW heterojunction with a type-III broken-gap band alignment. The electrical reconfigurability is enabled by the ambipolar transport property of InSe, which is achieved through the use of Pt as contact electrodes. By electrostatically doping the indium selenide (InSe), the reconfigurable MoO3/InSe heterojunctions can be converted between p-n and n+-n junctions. As a current rectifier, the MoO3/InSe heterojunction shows rectification ratios of ~ 107 and ~104 for forward and backward bias conditions, respectively. As a photodetector, the MoO3/InSe heterojunction shows stable photo-switching behavior with a ~105 on/off ratio and an ultralow dark current (≈10 fA).The response time is measured to be 500 μs and 300 μs for rise and fall processes, respectively. These results highlight the role of MoO3 with high electron affinity in construction of vdW heterostructure with type-III band alignment and provide a new platform for high performance optoelectronic devices.

Tailoring the Charge Transfer‐Driven Oxidation in van der Waals Ferroelectric NbOI2 Through Hetero‐Interface Engineering

Abstract2D transition metal halide oxides (TMHOs) have attracted much interest due to their intriguing ferroelectrics and excellent nonlinear optics, however, their susceptibility to oxidation makes their basic research and practical application a challenge. Therefore, it is crucial to understand the oxidation mechanism and explore effective strategies for protection. Here, taking van der Waals (vdWs) ferroelectric NbOI2 as an example, oxidation mechanisms and tuning the oxidation behaviors of NbOI2 and its heterostructures by a variety of in situ experiments and first‐principles calculations are discovered. The ambient‐pressure X‐ray photoelectron spectra reveal a self‐limiting oxidation in isolated NbOI2, driven by spontaneously formed iodine vacancies that react with oxygen molecules due to their lower formation and adsorption energies. For the heterostructures with a lower Fermi level (such as WSe2) than transition state VI@NbOI2 (NbOI2 rich in I‐vacancies), the charge transfer from NbOI2 to WSe2 drives the continuous and complete oxidation of NbOI2 flakes. Moreover, the heterostructures with a higher Fermi level (such as graphene) than VI@NbOI2 can weaken the oxidation of NbOI2. By linking the energy band structures to oxidation behavior, the work offers a new oxidation mechanism of 2D air‐sensitive materials and a crucial strategy for improving their chemical stability.

Large Magnetic Anisotropy in van der Waals Ferromagnet Fe3GaTe2 above Room Temperature.

Discoveries of above-room-temperature intrinsic ferromagnetism in two-dimensional (2D) van der Waals (vdW) materials offer a platform for studying fundamental 2D magnetism and spintronic devices, especially the recently discovered above-room-temperature 2D vdW Fe3GaTe2 (FGaT). However, the magnetic mechanism in FGaT remains elusive. Here, a detailed investigation using magnetic force microscopy on the thickness-dependent magnetic behavior of FGaT single crystals is reported. The Heisenberg exchange interaction constant (J) at room temperature is determined to be 1.32836 × 10-12 J/m. Our study combining angle-resolved photoemission spectroscopy and density functional theory suggests that the high Curie temperature in FGaT is attributed to the shift of the localized Fe d band toward the Fermi level as well as the enhanced magnetic exchange effect due to the strong itinerant ability of Fe. This work sheds light on the understanding of magnetism in FGaT and provides a promising platform to investigate the mechanisms of 2D magnetic materials.

A high-performance selenium nanoflake-based avalanche photodetector

Photodetectors are now indispensable in our daily lives, and there is a pressing need to explore new materials and mechanisms that can push the boundaries of device performance. Two-dimensional (2D) van der Waals (vdW) semiconductors have emerged recently as a promising material platform with exceptional optoelectronic properties, making them particularly suitable for high-performance photodetectors. However, photoinduced carrier generation in conventional 2D vdW photodetectors are usually limited, and new mechanisms need to be introduced to enhance device performance. Herein, we report a high-performance avalanche photodetector based on selenium (Se) nanoflakes. Our device achieves a high photoresponsivity (R) and specific detectivity (D*) of 361 A·W−1 and 2.4 × 1012 Jones, respectively. These figures of merit are two orders of magnitude higher than that in conventional Se photoconductive photodetectors. As a large bandgap vdW semiconductor, the Se channel allows the application of an extremely large bias voltage across it, and the resulting high electric field leads to the avalanche multiplication of carriers, which lays the groundwork for the improved device performance.

Gate-Controlled Potassium Intercalation and Superconductivity in Molybdenum Disulfide.

Intercalation of guest ions into a van der Waals (vdW) gap in layered materials is a powerful route to create novel material phases and functionalities. Ionic gating is a technique to control the motions and configuration of ions for both intercalation and surface electrostatic doping. The advance of ionic gating enables the in situ probe of dynamics of ion diffusion, carrier doping, and transport properties. Here we performed in situ resistivity and Raman experiments on the potassium ion (K+) intercalation of single-crystal MoS2 and constructed a temperature-carrier density phase diagram. The K+-intercalation induces a structural transition from the prismatically coordinated phase to the octahedrally coordinated phase, where anisotropic three-dimensional superconductivity and a possible charge density wave state were observed. The present ionic gating offers a comprehensive view of the intercalated phases and proves that the electrostatically induced superconductivity is distinct from that in the intercalated phase.

Flexibility, Dispersion Property, and Giant Sunlight Absorption of Monolayer MX2 (M = Zr, Hf; X = S, Se) and Related Janus MXY (M = Zr, Hf; X = S, Y = Se)

IVB–VIA transition metal dichalcogenides (TMDs) MX2 (M = Zr, Hf; X = S, Se) and related Janus MXY (M = Zr, Hf; X = S, Y = Se) have garnered significant attention due to their unique optoelectronic properties. To further explore their potential in flexible photonics, their mechanical, band dispersion, and optical dielectric properties using orbital hybrid theory are investigated. The results reveal that the out‐of‐plane linear compression resistance of these materials is considerably lower than their in‐plane resistance, primarily because van der Waals interactions are much weaker compared to ionic bond interactions. This characteristic makes them less susceptible to external pressure and torsional forces, positioning them as promising candidates for flexible optoelectronic devices. Furthermore, the presence of multiple energy bands at the same momentum state suggests a tendency toward metal–insulator transitions. Notably, the materials exhibit a high photon flux, indicating robust photoelectric conversion capabilities, making them suitable for applications in photoelectric transducers. This study not only deepens the understanding of the optoelectronic and mechanical properties of IVB–VIA TMD materials, but also offers theoretical guidance for the development and application of flexible optoelectronic devices based on IVB‐VIA TMDs and related Janus materials.

Designing a 2D van der waals oxide with lone-pair electrons as chemical scissor

Abstract 2D van der Waals (vdW) materials are known for their intriguing physical properties, but their rational design and synthesis remain a great challenge for chemists. In this work, we successfully synthesized a new non-centrosymmetric oxide, i.e. InSbMoO6, with Sb3+ lone-pair electrons serving as chemical scissor to generate its 2D vdW crystal structure. Monolayer and few-layer InSbMoO6 flakes are readily obtained via facile mechanical exfoliation. They exhibit strong second-harmonic generation (SHG) response with an effective second-order nonlinear optical susceptibility $\chi _{{\rm{eff}}}^{{\rm{(2)}}}\ $of 32.4 pm·V−1. Meanwhile, the SHG response is in-plane anisotropic and directly proportional to the layer thickness, independent of layer parity. In addition, the InSbMoO6 flakes exhibit excellent thermal and atmospheric stability, along with pronounced anisotropy in Raman spectroscopy. This work implies that using lone-pair electrons as chemical scissor is an effective strategy for designing and synthesizing new 2D vdW materials for integrated photonic applications.

Spectrum of Tunneling Transport through Phonon-Coupled Defect States in a Carbon-Doped Hexagonal Boron Nitride Barrier.

Defects in hexagonal boron nitride (h-BN) play important roles in tunneling transport through the h-BN barrier. Here, using carbon-doped h-BN (h-BN:C) as a tunnel barrier containing defects in a controlled manner, we investigated tunneling transport through defects in the h-BN:C/graphene heterostructures. Defect-assisted tunneling through a specific kind of carbon-related defect was observed in all measured devices, where the defect level was always located at ∼0.1 eV above the graphene's charge neutrality point. We revealed a phonon-assisted inelastic process in the defect-assisted tunneling, in which carriers tunnel through the defect with phonon emission. Furthermore, when the h-BN:C barrier was thick (12 layers, ∼4 nm), sequential tunneling through two defects became dominant, where the phonon-assisted inelastic process shows substantial effects between the two defects. This study reveals the contribution of phonons to defect-assisted tunneling transport, which is essential for the development of defect-related van der Waals (vdW) electronic techniques.

Van der Waals Heterojunction Based Self-Powered Biomimetic Dual-Mode Sensor for Precise Object Identification.

The design and fabrication of materials that can concurrently respond to light and gas within the dual-modal recognition domain present a significant challenge due to contradictory structural requirements. This innovative strategy introduces a type-I heterojunction, combining the properties of Sb2Te3 and WSe2 nanosheets, to overcome these obstacles. The heterojunction is prepared through a precise stacking approach to create a single-side barrier on the valence band and a near-zero offset on the conduction band. The resulting Sb2Te3/WSe2 heterojunction demonstrates unparalleled performance, showcasing the best integrated photoelectric and gas sensing performance in a single device to date. Based on the above features, the heterojunction successfully integrates visual and olfactory sensing performance, achieving the first biomimetic visual-olfactory dual-mode recognition in a single device. This simulation increased the accuracy of distinguishing electric and fuel-powered cars from ≈50% to ≈96%. This work introduces a novel approach to creating efficient, self-powered sensing materials, paving the way for next-generation biomimetic dual-model devices with broad applications in environmental protection, medical care, and other fields.

Narrowband Electroluminescence from Color Centers in Hexagonal Boron Nitride.

Defects in wide bandgap materials have emerged as promising candidates for solid-state quantum optical technologies. Electrical excitation of single emitters may lead to scalable on-chip devices and therefore is highly sought after. However, most wide bandgap materials are not amenable to efficient doping, posing challenges for electrical excitation and on-chip integration. Here, we demonstrate narrowband electroluminescence from visible and near-infrared color centers in hexagonal boron nitride (hBN). We harness van der Waals tunnel junctions of graphene-hBN-graphene. Charge carriers are electrically injected into hBN, exciting localized defects that emit nonclassical light, as characterized by the second order correlation measurement. Remarkably, the devices operate at room temperature and produce robust, narrowband emission spanning from visible to the near-infrared. Our work marks an important milestone in vdW materials and their promising attributes for integrated quantum technologies and on-chip photonic circuits.

Multifunctional optoelectronic devices based on two-dimensional tellurium/MoS2 heterojunction

Two-dimensional van der Waals heterojunctions consisted of p–n-type semiconductors have been rapidly developed owing to their built-in electric field which can facilitate the separation of photogenerated electron–hole pairs and properties like current rectification and negative differential transconductance. Benefitting from these advantages, we have prepared an air-stable multifunctional p-tellurium (Te)/n-MoS2 heterostructure working both as a self-driven broadband photodetector and as an optically switchable complementary metal-oxide-semiconductor inverter. For photodetection, this device exhibits wavelength-modulated positive/negative optical response with large responsivity (1.51 A/W at 520 nm and 642.92 mA/W at 1550 nm, Vds = 0 V) and fast response speed, showcasing its prospects for optical encoding communication. Moreover, the device has been demonstrated to function as an inverter that will be shut down by illumination. Our multifunctional device possesses the compactness of integrated modules, widens the application scope of Te-based heterojunctions, and provides a reference for the application of Te-based devices in the field of integrated circuits.