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The p-n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. Here, we demonstrate that an atomically thin and sharp heterojunction p-n diode can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) and n-type few-layer molybdenum disulfide (MoS2). Electrical measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic investigation shows distinct layer-number dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron-orbital interaction in TMDs. We believe that these atomically thin heterojunction p-n diodes represent an interesting system for probing the fundamental electro-optical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers.

The characteristics of interaction between six transition-metal porphyrines and the Ag(111) surface are detailed here as resulted from DFT calculations. Van der Waals interactions as well as the strong correlation in 3d orbitals of transition metals were taken into account in all calculations, including the structural relaxation. For each system we investigate four relative positions of the metallic atom on top the surface. We show that the interaction between the transition metal and silver is the result of a combination between the dispersion interaction, charge transfer and weak chemical interaction. The detailed analysis of the physical properties, such as dipolar and magnetic moments and the molecule–surface charge transfer, analyzed for different geometric configurations allows us to propose qualitative models, relevant for the understanding of the self-assembly processes and related phenomena.

The notion of statistical order derives from the disequilibrium concept introduced by López-Ruiz, Mancini, and Calbet thirty years ago. In this effort, it is shown that the disequilibrium is intimately linked to the celebrated Rényi entropy. One also explores this link in connection with the van der Waals gas description.

Molybdenum disulfide quantum dots (MoS2 QDs) are a unique class of zero-dimensional (0D) van derWaals nanostructures. MoS2 QDs have attracted significant attention due to their unique optical, electronic, chemical, and biological properties due to the presence of edge states of these van der Waals QDs for various chemical functionalization. Their novel properties have enabled applications in many fields, including advanced electronics, electrocatalysis, and biomedicine. In this review, the various synthesis techniques, the novel properties, and the wide applications of MoS2 quantum dots are discussed in detail. [ABSTRACT FROM AUTHOR]

Deep‐ultraviolet nonlinear optical (DUV NLO) materials are attracting increasing attention because of their structural diversity and complexity. Using the two‐dimensional (2D) crystal structure prediction method combined with the first‐principles calculations, here we propose layered 18‐membered‐ring (18MR) boron oxide B2O3 polymorphs as high‐performance NLO materials. 18MR‐B2O3 with the AA and AB stackings are potential DUV NLO materials. The superior performing 18MR‐B2O3AB has an unprecedentedly high second harmonic generation coefficient of 1.63 pm V−1, the largest among the DUV NLO materials, three times larger than that of the advanced DUV NLO material KBe2BO3F2 and comparable to that of β‐BaB2O4. Its unusually large birefringence of 0.196 at 400 nm guarantees the phase‐matching wavelength λPM to reach this material's extreme absorption edge of ≈154 nm. [ABSTRACT FROM AUTHOR]

Adhesive and locomotor performances of geckos are inherently linked by specialized morphological and biomechanical features. As such, we predict that conditions that lead to poor adhesive performance (i.e., low resistance to applied force while clinging) also lead to poor locomotor performance and behavior (i.e., slowed running speed, increased frequency and duration of stops, more failed or incomplete runs). In this study, we test the prediction that running speed changes as a function of adhesive performance in variable temperature (12 and 32°C), humidity (30, 55, 70, 80% relative humidity), and substrate wettability (hydrophilic glass, intermediately wetting plexiglass). We also expect other locomotor performance traits and behaviors, such as stopping and avoiding treatment conditions, to change as a function of adhesive performance. The results of this study do not fully support our prediction: gecko locomotor performance does not change as a function of humidity or substrate wettability, unlike adhesive performance. As an anticipated result of ectothermy, geckos run significantly slower and stop more frequently and longer at 12°C than 32°C. At high temperature, geckos required significantly more running attempts on hydrophilic glass than plexiglass to complete the experimental procedure, suggesting that this treatment condition is unfavorable. The results of this study highlight the robust locomotive response of geckos to variation in adhesive performance and environmental conditions, and have significant implications for predictions about habitat use and behavior in their natural environment. Research Highlights: Gecko running speed does not change with variable humidity or substrate, unlike adhesive performance. Geckos run slower and stop often and longer at 12 than 32°C. At 32°C, geckos avoid running on hydrophilic glass. [ABSTRACT FROM AUTHOR]

The discovery of type‐II Weyl semimetal states in layered transition metal dichalcogenides Td‐WTe2 indicates great potential for novel electronic, spintronic, and quantum devices. Theoretically, the interaction between the topological states and the magnetic ordered states of Td‐WTe2 enables the modulation of Weyl semimetal states by an external magnetic field. However, currently, ferromagnetism in layered Td‐WTe2 is still elusive and rarely observed. In this research, ferromagnetic order into WTe2 using magnetic chromium (Cr) doping with a two‐step Te flux strategy is introduced. The Curie temperature (Tc) and the ferromagnetic moment are well tuned with a Cr doping concentration. The Tc of the Cr‐doped layered Td‐WTe2 could be regulated from 182 to 283 K, which is close to room temperature. The saturation magnetic moment could be changed from 2.26 to 4.20 emu g–1, which is stronger than most values reported for these materials. Most intriguingly, the Cr‐doped layered Td‐WTe2 single crystals still exhibit semimetallic behavior and they possess very large magnetoresistance with obvious Shubnikov de Haas (SdH) quantum oscillations and an anomalous Hall effect. The findings offer feasible ways to induce and tune ferromagnetic orders in layered Td‐WTe2 and thus to control its topological phase with external magnetic fields. [ABSTRACT FROM AUTHOR]

The discovery of type‐II Weyl semimetal states in layered transition metal dichalcogenides Td‐WTe2 indicates great potential for novel electronic, spintronic, and quantum devices. Theoretically, the interaction between the topological states and the magnetic ordered states of Td‐WTe2 enables the modulation of Weyl semimetal states by an external magnetic field. However, currently, ferromagnetism in layered Td‐WTe2 is still elusive and rarely observed. In this research, ferromagnetic order into WTe2 using magnetic chromium (Cr) doping with a two‐step Te flux strategy is introduced. The Curie temperature (Tc) and the ferromagnetic moment are well tuned with a Cr doping concentration. The Tc of the Cr‐doped layered Td‐WTe2 could be regulated from 182 to 283 K, which is close to room temperature. The saturation magnetic moment could be changed from 2.26 to 4.20 emu g–1, which is stronger than most values reported for these materials. Most intriguingly, the Cr‐doped layered Td‐WTe2 single crystals still exhibit semimetallic behavior and they possess very large magnetoresistance with obvious Shubnikov de Haas (SdH) quantum oscillations and an anomalous Hall effect. The findings offer feasible ways to induce and tune ferromagnetic orders in layered Td‐WTe2 and thus to control its topological phase with external magnetic fields. [ABSTRACT FROM AUTHOR]

2D materials (2DMs), known for their atomically ultrathin structure, exhibit remarkable electrical and optical properties. Similarly, molecular self-assembled monolayers (SAMs) with comparable atomic thickness show an abundance of designable structures and properties. The strategy of constructing electronic devices through unique heterostructures formed by van der Waals assembly between 2DMs and molecular SAMs not only enables device miniaturization, but also allows for convenient adjustment of their structures and functions. In this review, the fundamental structures and fabrication methods of three different types of electronic devices dominated by 2DM-SAM heterojunctions with varying architectures are timely elaborated. Based on these heterojunctions, their fundamental functionalities and characteristics, as well as the regulation of their performance by external stimuli, are further discussed., (© 2024 Wiley‐VCH GmbH.)

We report a study on the stability, optical absorption and modulated electronic properties of the ZnO(0001-) and MoS 2 Van der Waals heterostructure using density functional theory. We employed a supercell of ZnO/MoS 2 hybrid and specifically explored the effects of creating an interface with the O-terminated face of ZnO while considering the interlayer interaction. We observed an increase in the band gap opening of MoS 2 within the hybrid structure (1.37 eV) is primarily attributed to in-plane strain, with minimal contribution from the identified charge transfer occurring from MoS 2 to ZnO. Notably, the hybrid structure exhibits enhanced photo absorption in the visible and near-infrared regions, highlighting their significance for optoelectronic applications., (© 2024 IOP Publishing Ltd.)

Fe3+δGeTe2(FGT) has proved to be an interesting van der Waals (vdW) ferromagnetic compound with a tunable Curie temperature (TC). However, the underlying mechanism for varyingTCremains elusive. Here, we systematically investigate and compare low-temperature magnetic properties of single crystalline FGT samples that exhibitTCs ranging from 160 K to 205 K. Spin stiffness ( D ) and spin excitation gap (Δ) are extracted using Bloch's theory for crystals with varying Fe content. Compared to Cr-based vdW ferromagnets, FGT compounds have higher spin stiffness values but lower spin wave excitation gaps. We discuss the implication of these relationships in Fe-Fe ion magnetic interactions in FGT unit cells. The itinerancy of magnetic electrons is measured and discussed under the Rhodes-Wohlfarth ratio (RWR) and the Takahashi theory., (Creative Commons Attribution license.)

Nickel phosphorus trisulfide (NiPS 3 ), a van der Waals 2D antiferromagnet, has received significant interest for its intriguing properties in recent years. However, despite its fundamental importance in the physics of low-dimensional magnetism and promising potential for technological applications, the study of magnetic domains in NiPS 3 down to an atomically thin state is still lacking. Here, we report the layer-dependent magnetic characteristics and magnetic domains in NiPS 3 by employing linear dichroism spectroscopy, polarized microscopy, spin-correlated photoluminescence, and Raman spectroscopy. Our results reveal the existence of the paramagnetic-to-antiferromagnetic phase transition in bulk to bilayer NiPS 3 and provide evidence of the role of stronger spin fluctuations in thin NiPS 3 . Furthermore, our study identifies three distinct antiferromagnetic domains within atomically thin NiPS 3 and captures the thermally activated domain evolution. Our findings provide crucial insights for the development of antiferromagnetic spintronics and related technologies.

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, the highly efficient room-temperature nonvolatile magnetic switching is realized by current in a single-material device based on vdW ferromagnet Fe 3 GaTe 2 . Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage., (© 2024 Wiley‐VCH GmbH.)

Quantum emitters are essential components of quantum photonic circuitry envisioned beyond the current optoelectronic state-of-the-art. Two dimensional materials are attractive hosts for such emitters. However, the high single photon purity required is rarely realized due to the presence of spectrally degenerate classical light originating from defects. Here, we show that design of a van der Waals heterostructure effectively eliminates this spurious light, resulting in purities suitable for a variety of quantum technological applications. Single photon purity from emitters in monolayer WSe 2 increases from 60% to 92% by incorporating this monolayer in a simple graphite/WSe 2 heterostructure. Fast interlayer charge transfer quenches a broad photoluminescence background by preventing radiative recombination through long-lived defect bound exciton states. This approach is generally applicable to other 2D emitter materials, circumvents issues of material quality, and offers a path forward to achieve the ultrahigh single photon purities ultimately required for photon-based quantum technologies.

Single-walled carbon nanotube (SWCNT) films exhibit exceptional optical and electrical properties, making them highly promising for scalable integrated devices. Previously, we employed SWCNT films as templates for the chemical vapor deposition (CVD) synthesis of one-dimensional heterostructure films where boron nitride nanotubes (BNNTs) and molybdenum disulfide nanotubes (MoS 2 NTs) were coaxially nested over the SWCNT networks. In this work, we have further refined the synthesis method to achieve precise control over the BNNT coating in SWCNT@BNNT heterostructure films. The resulting structure of the SWCNT@BNNT films was thoroughly characterized using a combination of electron microscopy, UV-vis-NIR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. Specifically, we investigated the pressure effect induced by BNNT wrapping on the SWCNTs in the SWCNT@BNNT heterostructure film and demonstrated that the shifts of the SWCNT's G and 2D ( G ') modes in Raman spectra can be used as a probe of the efficiency of BNNT coating. In addition, we studied the impact of vacuum annealing on the removal of the initial doping in SWCNTs, arising from exposure to ambient atmosphere, and examined the effect of MoO 3 doping in SWCNT films by using UV-vis-NIR spectroscopy and Raman spectroscopy. We show that through correlation analysis of the G and 2D ( G ') modes in Raman spectra, it is possible to discern distinct types of doping effects as well as the influence of applied pressure on the SWCNTs within SWCNT@BNNT heterostructure films. This work contributes to a deeper understanding of the strain and doping effect in both SWCNTs and SWCNT@BNNTs, thereby providing valuable insights for future applications of carbon-nanotube-based one-dimensional heterostructures.

The significance of the van der Waals (vdW) interaction in the adhesion mechanism of geckos to surfaces is estimated quantitatively using dispersion-corrected density functional theory (DFT). A complete survey of the pairwise energies for the elements present in gecko epithelia, soda lime glass and polytetrafluoroethylene (PTFE) shows that the van der Waals interaction plays a minor role in the binding between the atoms in the epithelia and the glass and PTFE substrates. Using a simplified microscopic model for the geckos epithelium, DFT predicts strong (weak) binding between the gecko and glass (PTFE) surfaces, both with and without the vdW interaction. This is in agreement with experimental observations, and is highly suggestive that dispersive interactions only play a minor role in gecko adhesion to glass and PTFE surfaces.

Abstract Tree frogs have the remarkable ability to attach to smooth, rough, dry, and wet surfaces using their versatile toe pads. Tree frog attachment involves the secretion of mucus into the pad-substrate gap, requiring adaptations towards mucus drainage and pad lubrication. Here, we present an overview of tree frog attachment, with focus on (i) the morphology and material of the toe pad; (ii) the functional demands on the toe pad arising from ecology, lifestyle, and phylogenetics; (iii) experimental data of attachment performance such as adhesion and friction forces; and (iv) potential perspectives on future developments in the field. By revisiting reported data and observations, we discuss the involved mechanisms of attachment and propose new hypotheses for further research. Among others, we address the following questions: Do capillary and hydrodynamic forces explain the strong friction of the toe pads directly, or indirectly by promoting dry attachment mechanisms? If friction primarily relies on van der Waals (vdW) forces instead, how much do these forces contribute to adhesion in the wet environment tree frogs live in and what role does the mucus play? We show that both pad morphology and measured attachment performance suggest the coaction of several attachment mechanisms (e.g. capillary and hydrodynamic adhesion, mechanical interlocking, and vdW forces) with situation-dependent relative importance. Current analytical models of capillary and hydrodynamic adhesion, caused by the secreted mucus and by environmental liquids, do not capture the contributions of these mechanisms in a comprehensive and accurate way. We argue that the soft pad material and a hierarchical surface pattern on the ventral pad surface enhance the effective contact area and facilitate gap-closure by macro- to nanoscopic drainage of interstitial liquids, which may give rise to a significant contribution of vdW interactions to tree frog attachment. Increasing the comprehension of the complex mechanism of tree frog attachment contributes to a better understanding of other biological attachment systems (e.g. in geckos and insects) and is expected to stimulate the development of a wide array of bioinspired adhesive applications.

Modern approaches to modelling dispersion forces are becoming increasingly accurate, and can predict accurate binding distances and energies. However, it is possible that these successes reflect a fortuitous cancellation of errors at equilibrium. Thus, in this work we investigate whether a selection of modern dispersion methods agree with benchmark calculations across several potential-energy curves of the benzene dimer to determine if they are capable of describing forces and energies outside equilibrium. We find the exchange-hole dipole moment (XDM) model describes most cases with the highest overall agreement with reference data for energies and forces, with many-body dispersion (MBD) and its fractionally ionic (FI) variant performing essentially as well. Popular approaches, such as Grimme-D and van der Waals density functional approximations (vdW-DFAs) underperform on our tests. The meta-GGA M06-L is surprisingly good for a method without explicit dispersion corrections. Some problems with SCAN+rVV10 are uncovered and briefly discussed.

Models of surface enhancement of molecular electronic response properties are challenging for two reasons: (a) molecule‐surface interactions require a simultaneous solution of the molecular and the surface dynamic response (a daunting task), and (b) when solving for the electronic structure of the combined molecule + surface system, it is not trivial to single out the particular physical effects responsible for enhancement. To tackle this problem, in this work, we apply a formally exact decomposition of the system's response function into subsystem contributions by using subsystem density functional theory (DFT), which grants access to dynamic polarizabilities and optical spectra. In order to access information about the interactions between the subsystems, we extend a previously developed subsystem‐based adiabatic connection fluctuation‐dissipation theorem of DFT to separate the additive from the nonadditive correlation energy and identify the nonadditive correlation as the van der Waals interactions. As an example, we choose benzene adsorbed on monolayer MoS2. We isolate the contributions to benzene's dynamic response arising from the interaction with the surface, and for the first time, we evaluate the enhancements to the effectiveness of C6 coefficients as a function of benzene‐MoS2 distance and adsorption site. We also quantify the spectral broadening of the benzene's electronic excited states due to their interaction with the surface. We find that the broadening has a similar decay law with the molecule‐surface distance as the leading van der Waals interactions (ie, R−6) and that the surface enhancement of dispersion interactions between benzene molecules is less than 5% but is still large enough (0.5 kcal/mol) to likely play a role in the prediction of interface morphologies. [ABSTRACT FROM AUTHOR]

Negative capacitance (NC) provides a path to overcome the Boltzmann limit that dictates operating voltages in transistors and, therefore, may open up a path to the challenging proposition of lowering energy consumption and waste heat in nanoelectronic integrated circuits. Typically, NC effects in ferroelectric materials are based on either stabilizing a zero‐polarization state or slowing down ferroelectric switching in order to access NC regimes of the free‐energy distribution. Here, a fundamentally different mechanism for NC, based on CuInP2S6, a van der Waals layered ferrielectric, is demonstrated. Using density functional theory and piezoresponse force microscopy, it is shown that an unusual combination of high Cu‐ion mobility and its crucial role in determining polarization magnitude and orientation (P) leads to a negative slope of the polarization versus the electric field E, dP/dE < 0, which is a requirement for NC. This mechanism for NC is likely to occur in a wide class of materials, offering new possibilities for NC‐based devices. The nanoscale demonstration of this mechanism can be extended to the device‐level by increasing the regions of homogeneous polarization and polarization switching, for example, through strain engineering and carefully selected electric field pulses. [ABSTRACT FROM AUTHOR]

Quasi 1D gold selenide (AuSe) possesses highly anisotropic crystal structure, excellent electrical conductivity, giant magnetoresistance, and unusual reentrant metallic behavior. We found that AuSe exhibits a near quadratic nonsaturating giant magnetoresistance of 1841% with the magnetic field perpendicular to its in-plane. We also observe unusual reentrant metallic behavior, which is caused by the carrier mismatch in the multiband transport. The atomic structure of quasi one-dimensional (1D) van der Waals materials can be regarded as the stacking of atomic chains to form thin flakes or nanoribbons, which substantially differentiates them from typical two-dimensional (2D) layered materials and 1D nanotube/nanowire array. Here we present our studies on quasi 1D gold selenide (AuSe) that possesses highly anisotropic crystal structure, excellent electrical conductivity, giant magnetoresistance, and unusual reentrant metallic behavior. The low in-plane symmetry of AuSe gives rise to its high anisotropy of vibrational behavior. In contrast, quasi 1D AuSe exhibits high in-plane electrical conductivity along the directions of both atomic chains and perpendicular one, which can be understood as a result of strong interchain interaction. We found that AuSe exhibits a near quadratic nonsaturating giant magnetoresistance of 1841% with the magnetic field perpendicular to its in-plane. We also observe unusual reentrant metallic behavior, which is caused by the carrier mismatch in the multiband transport. Our works help to establish fundamental understandings on quasi 1D van der Waals semimetallic AuSe and identify it as a new candidate for exploring giant magnetoresistance and compensated semimetals. [ABSTRACT FROM AUTHOR]

Density‐functional theory calculations of (TiO2)n clusters (n = 1–5) in the gas phase and adsorbed on pristine graphene as well as graphene quantum dots are presented. The cluster adsorption is found to be dominated by van der Waals forces. The electronic structure and in particular the excitation energies of the bare clusters and the TiO2/graphene composites are found to vary largely in dependence on the size of the respective constituents. This holds in particular for the energy and the spatial localization of the highest occupied and lowest unoccupied molecular orbitals. In addition to a substantial gap narrowing, a pronounced separation of photoexcited electrons and holes is predicted in some instances. This is expected to prolong the lifetime of photoexcited carriers. Altogether, TiO2/graphene composites are predicted to be promising photocatalysts with improved electronic and photocatalytic properties compared to bulk TiO2. [ABSTRACT FROM AUTHOR]

We present a comparative density functional theory (DFT) investigation of the interaction of the iron porphyrin (FeP) molecule with the metallic Co(001) and Cu(001) surfaces, with the aim of elucidating the effect of different choices for the treatment of dispersion. We compare a GGA+U approach, several flavors of dispersion‐augmented terms, and two variants of the vdW‐DF approach, which treats long‐range correlation explicitly. For the Co surface, we find that all approaches predict chemisorption and a high‐spin state, although vdW‐DF functionals generally predict weaker bonds and weaker chemisorption. For the Cu surface, we find that the functionals augmented by pair‐wise dispersion once again predict chemisorption and a preferred HS state, but the vdW‐DF functionals predict physisorption and a LS state. These results demonstrate the importance of careful assessment of the level of theory at which dispersion is treated, as this may have significant quantitative and even qualitative effects on the predictions made. The results also call for additional experimental data for these systems. [ABSTRACT FROM AUTHOR]

Several two-dimensional (2D) materials such as graphene, molybdenum disulfide, or boron nitride are emerging as alternatives for lubrication additives to control friction and wear at the interface. On the other hand, the initiative to accelerate materials discovery through data-driven computational methods has identified numerous novel topologies and families of 2D materials that can potentially be designed as low-friction additives. Hence, generating a structure–property (friction) correlations for 2D material-based additives that present a large variation in atomic composition is the next big challenge. Herein, we present a machine learning (ML) method using the Bayesian modeling and transfer learning approach to predict the maximum energy barrier (MEB) of the potential surface energy (correlated to intrinsic friction) of ten different 2D materials that were previously unexplored for their tribological properties. The descriptors (or properties) required to train the ML model with high accuracy are identified by taking into account the established physical models for dissipation in 2D materials. As a result, a difference of less than 8% in MEB values as predicted via the ML model presented here and the PES profiles generated using molecular dynamics simulations, for a select few 2D materials, was obtained. The model also enabled the identification of material properties that present the highest sensitivity to the corrugated potential, hence enabling the development of design routes for the synthesis of 2D materials with optimal tribological properties. [ABSTRACT FROM AUTHOR]

Neuromorphic computing on the hardware level is promising for performing ever‐increasing data‐centric tasks owing to its superiority to conventional von Neumann architecture in terms of energy efficiency and learning ability. One key aspect to its implementation is the development of artificial synapses that can effectively emulate the multiple functionalities exhibited by their biological counterparts. Here, building on an inorganic ferroelectric gate stack integrated with a 2D layered semiconductor (WS2), a new type of ferroelectricity‐based synaptic transistor that differs from those relying on interface traps or floating gate configuration is reported. By virtue of a 6 nm thick ferroelectric hafnium zirconium oxide by atomic layer deposition and postannealing treatment, the device shows a channel resistance change ratio above 105 corresponding to opposite ferroelectric polarization direction. Furthermore, by applying electrical stimulus to the gate, it demonstrates good capability to mimic various synaptic behaviors including long‐term potentiation, long‐term depression, spike‐amplitude‐dependent plasticity, and spike‐rate‐dependent plasticity. Given the inherent compatibility of the ferroelectric gate stack with existing fabrication technology, and the reliability of ferroelectricity engineering, this work paves the way toward practical implementation of synaptic devices in neuromorphic circuits. [ABSTRACT FROM AUTHOR]

Nanofibrous multifunctional materials have attracted a lot of attention because of the benefits of their special structure. Despite the diverse benefits of nanofibrous materials, their inherent stickiness to any surface is a major obstacle in producing and processing such materials. There are many paragons in which biological models or elements from nature have been biomimetically adapted in various areas in order to resolve technical problems, such as the silent flight of the owl, the lotus effect, or the sticky feet of the gecko. One special example shows us how nanofibers might be handled in the future: cribellate spiders possess a specialized comb, the calamistrum, on their hindmost legs, which is used to process and assemble nanofibers into structurally complex capture threads. Within this study, we were able to prove that these fibers do not stick to the calamistrum because of a special fingerprint-like nanostructure on the comb. This structure prevents the nanofibers from smoothly adapting to the surface of the comb, thus minimizing contact and reducing the adhesive van der Waals forces between the nanofibers and surface. This leads to the spiders' ability of nonsticky processing of nanofibers for their capture threads. The successful transfer of these structures to a technical surface proved that this biological model can be adapted to optimize future tools in technical areas in which antiadhesive handling of nanofibrous materials is required. [ABSTRACT FROM AUTHOR]

These contributions explore interaction modes between the methanethoil (CH3SH) molecule and the Fe(100) surface via implementing accurate density functional theory (DFT) calculations with the inclusion of van der Waals corrections. We consider three adsorption sites over the Fe(100) surface, namely, top(T), bridge (B), and hollow (H) sites as potential catalytic active sites for the molecular and dissociative adsorption of the CH3SH molecule. The molecular adsorption structures are found to occupy either B or T sites with former sites holding higher stability by 0.17 eV. The inclusion of van der Waals corrections refound to slightly alter adsorption energies. For instance, adsorption energies increased by ~0.18 and ~0.21 eV for B and T structure, respectively, in reference to values obtained by the plain generalized gradient approximation (GGA) functional. A stability ordering of the dissociation products was found to follow the sequence (CH4, S) > (CH3, S, H) > (─SCH3, H) > (─CH3, SH). The differential charge density distributions were examined to underpin prominent electronic contributing factors. Direct fission of C─S bond in the CH3SH molecule attains exothermic values in the range 2.0 to 2.1 eV. The most energetically favorable sites for the surface‐mediated fission of the thiol's S─H bond correspond to the structure where the ─SCH3 and H are both situated on hollow sites with an adsorption energy of −2.43 eV. Overall, we found that inclusion of van der Waals functional to change the binding energies more noticeably in case of dissociative adsorption structures. The results presented herein should be instrumental in efforts that aim to design stand‐alone Fe desulfurization catalysts. [ABSTRACT FROM AUTHOR]

The remarkable properties of the gecko adhesive system have been intensively studied. Although many gecko‐inspired synthetic adhesives have been designed and fabricated, few manage to capture the multifunctionality of the natural system. Analogous to previously documented self‐cleaning, recent work demonstrated that gecko toe pads dry when geckos take steps on dry substrates (i.e., self‐drying). Whether digital hyperextension (DH), the distal to proximal peeling of gecko toe pads, is involved in the self‐drying process, had not been determined. Here, the effect of DH on self‐drying was isolated by preventing DH from occurring during normal walking locomotion of Gekko gecko after toe pads were wetted. Our initial analysis revealed low statistical power, so we increased our sample size to determine the robustness of our result. We found that neither DH nor the DH–substrate interaction had a significant effect on the maximum shear adhesive force after self‐drying. These results suggest that DH is not necessary for self‐drying to occur. Interestingly, however, we discovered that shear adhesion is higher on a surface tending hydrophobic compared to a hydrophilic surface, demonstrating that gecko adhesion is sensitive to substrate wettability during the subdigital pad drying process. Furthermore, we also observed frequent damage to the adhesive system during shear adhesion testing post‐drying, indicating that water may compromise the structural integrity of the adhesive structures. Our results not only have behavioral and ecological implications for free‐ranging geckos but also have the potential to influence the design and fabrication of gecko‐inspired synthetic adhesives that can regain adhesion after fouling with water. RESEARCH HIGHLIGHTS: Gecko adhesive pads self‐dry to the same extent with or without digital hyperextension. Shear adhesion after self‐drying is sensitive to substrate wettability and prolonged water exposure may diminish the structural integrity of gecko adhesive setae. [ABSTRACT FROM AUTHOR]

The dimensionless value of critical compressibility factor in the van der Waals theory of gas-liquid critical point is a universal constant, Zc = 0.375. Experimentally measured values of this quantity for simple fluids are considerably smaller than the theory prediction. Van der Waals once assumed that this discrepancy can be removed by taking account of the impact of the molecular pseudo-associations on the fluid criticality but he did not complete a proper modification of his theory following up on this idea. The communication is devoted to the filling of this gap. [ABSTRACT FROM AUTHOR]

We report on the six-body van der Waals interactions within Rydberg atoms. Specifically, we focus on the octahedron case. The results are compared with previous calculations for two to five bodies' interactions. This research is useful for crystal structure in condensed matter physics, such as p-type doping in Silicon or other types of semiconductors. This research is also useful for studying big molecules in chemistry, chemical engineering, and other fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • The primary innovation lies in its comprehensive exploration of the structure and photocurrent characteristics of β-Ga 2 O 3 and GaN two-dimensional materials synthesized via liquid metals. • The focus is on quantitative discussions regarding β-Ga 2 O 3 and GaN photocurrent detectors. • Moreover, the investigation delves into distinctions in photoresponse and recovery times, employing concepts like energy bandgap (Eg) and crystallinity structure. This study uses liquid gallium metal to synthesize two-dimensional gallium oxide and gallium nitride ultra-thin layers. Addressing the challenges of conventional methods, this approach combines liquid metal properties with Polydimethylsiloxane (PDMS) transfer printing, resulting in large-area, highly clean, and low-residue amorphous Ga-based wide bandgap semiconductors. Transformation of amorphous Ga 2 O 3 into crystallized β-Ga 2 O 3 and GaN is achieved through annealing and ammoniation. Comprehensive characterizations confirm successful changes. Photodetector devices are fabricated and characterized, revealing Ga 2 O 3 photosensitive nature with distinct performance metrics. GaN, while exhibiting lower photoresponse, displays rapid photocurrent recovery, making it promising for photodetector applications. This research offers a scalable method for two-dimensional gallium-group semiconductor synthesis, holding potential for diverse optoelectronic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • We report spectroscopic observation and theoretical calculations of a new isomer of (CS 2) 3. • This isomer has C 2 point group symmetry, a structure analogous to that of the noncyclic isomer of (CO 2) 3. • The rotational parameters lie roughly midway between the ab initio and the value obtained using empirical potentials. We report spectroscopic observation and theoretical calculations of a new isomer of (CS 2) 3 as observed in the regions of the ν 3 fundamental band of CS 2 (6.5 μm) and the ν 1 + ν 3 combination band (4.5 μm), using tunable laser sources and a pulsed supersonic slit-jet. The previously observed CS 2 trimer has a barrel-shaped structure with three equivalent monomers and D 3 symmetry. The new isomer consists of a staggered parallel "dimer pair" of equivalent CS 2 monomers with a third CS 2 monomer sitting "on top", similar to the known non-cyclic CO 2 trimer. This structure has C 2 rotational symmetry corresponding to the b inertial axis of the trimer, as proven by observed nuclear spin statistics. Ab initio calculations correctly give the two observed isomer structures and indicate that they lie very close in binding energy. [ABSTRACT FROM AUTHOR]

Building integrated photovoltaic systems have necessitated the development of transparent photovoltaics (TPV). Transparent conducting oxides (TCO) play a vital role in charge carrier transport in TPVs. Their high transparency, electrical conductivity, and tunable work function make them imperative for TPV applications. Here in this work, we develop a room-temperature grown amorphous-InZnO (a-IZO) thin film for the bottom electrode for TPV. The a-IZO film has demonstrated a high average visible transmittance of 84 % over commercial F:SnO 2 (FTO) substrate. A TPV with wide band gap oxide (n-Ga 2 O 3) and a very thin layer of van der Waals material (p-SnS) was fabricated over the a-IZO thin film and commercial FTO substrate for better comparison. A significant enhancement in the current density, open-circuit voltage, and fill factor was recorded. The device with a-IZO electrode showed a bifacial power production feature with a power conversion efficiency of 3.9 % in contrast to FTO electrode-based TPV with 1.5 %. The a-IZO-based TPV also showed a good UV–vis photodetection ability with the highest responsivity of 93 mA/W and the fastest response time of 400 μs. This work suggests that enhanced photovoltaic and photodetection performance is possible using an optimum electrode design. • Amorphous-IZO (a-IZO) thin film of high AVT of 84 % beating commercial FTO was fabricated at room temperature. • Structural frustration between In and Zn causes amorphous structure. • a-IZO thin film has shown high thermal stability up to 500 °C. • a-IZO based Ga 2 O 3 /SnS TPV has shown power conversion efficiency of 3.9 %–2.5 times higher than commercial FTO based TPV. [ABSTRACT FROM AUTHOR]

Van der Waals magnetic materials are promising candidates for spintronics and testbeds for exotic magnetic phenomena in low dimensions. The two-dimensional (2D) limit in these materials is typically reached by mechanically breaking the van der Waals interactions between layers. Alternative approaches to producing large amounts of flakes rely on wet methods such as liquid-phase exfoliation (LPE). Here, we report an optimized route for obtaining monolayers of magnetic cylindrite by LPE. We show that the selection of exfoliation times is the determining factor in producing a statistically significant amount of monolayers while keeping relatively big flake areas (~1 µm2). We show that the cylindrite lattice is preserved in the flakes after LPE. To study the electron transport properties, we have fabricated field-effect transistors based on LPE cylindrite. Flakes are deterministically positioned between nanoscale electrodes by dielectrophoresis. We show that dielectrophoresis can selectively move the larger flakes into the devices. Cylindrite nanoscale flakes present a p-doped semiconducting behaviour, in agreement with the mechanically exfoliated counterparts. Alternating current (AC) admittance spectroscopy sheds light on the role played by potential barriers between different flakes in terms of electron transport properties. The present large-scale exfoliation and device fabrication strategy can be extrapolated to other families of magnetic materials.

Due to their uniquely high surface-to-volume ratio, nanofibers are a desired material for various technical applications. However, this surface-to-volume ratio also makes processing difficult as van der Waals forces cause nanofibers to adhere to virtually any surface. The cribellate spider Uloborus plumipes represents a biomimetic paragon for this problem: these spiders integrate thousands of nanofibers into their adhesive capture threads. A comb on their hindmost legs, termed calamistrum, enables the spiders to process the nanofibers without adhering to them. This anti-adhesion is due to a rippled nanotopography on the calamistrum. Via laser-induced periodic surface structures (LIPSS), these nanostructures can be recreated on artificial surfaces, mimicking the non-stickiness of the calamistrum. In order to advance the technical implementation of these biomimetic structured foils, we investigated how climatic conditions influence the anti-adhesive performance of our surfaces. Although anti-adhesion worked well at low and high humidity, technical implementations should nevertheless be air-conditioned to regulate temperature: we observed no pronounced anti-adhesive effect at temperatures above 30 °C. This alteration between anti-adhesion and adhesion could be deployed as a temperature-sensitive switch, allowing to swap between sticking and not sticking to nanofibers. This would make handling even easier.

The aim of this study is to characterize the behavior of the environmental air using a simple method which can be implemented as a learning media in senior high school or undergraduate students. The method used is experimental which combined with curve fitting. From the curve fitting step, the behavior of the air can be explained. Otherwise, the quantitative data such as Van der Waals constants can also be obtained. From this study obtained that the Van der Waals constants, a and b, of the chosen air samples as large as (11.23 ± 0.84) J.m3/mol2 and (2.04 ± 0.15) × 10-3 m3/mol respectively. These results can be used to predict that the chosen air samples will act as an ideal gas at 636.5 K and 105 Pa in temperature and pressure respectively.Tujuan dari penelitian ini untuk mengetahui perilaku udara sekitar dalam tinjauan sebagai gas ideal atau gas nyata dengan metode sederhana yang dapat diterapkan sebagai media pembelajaran baik di tingkat perguruan tinggi maupun sekolah menengah atas. Metode yang digunakan adalah eksperimen yang dipadukan dengan pencocokan kurva. Informasi terkait kecenderungan perilaku udara sekitar diperoleh dari tahapan pencocokan kurva. Nilai kuantitatif yang berupa konstanta Van der Waals dari sampel udara sekitar juga dapat diperoleh dari persamaan hasil pencocokan kurva yaitu a dan b secara berturut-turut sebesar (11.23 ± 0.84) J.m3/mol2 dan (2.04 ± 0.15) × 10-3 m3/mol. Nilai konstanta yang diperoleh dapat digunakan untuk memprediksi bahwa sampel udara yang diamati akan berperilaku sebagai gas ideal ketika bersuhu 636.5 K dengan tekanan 105 Pa.

The presented work deals with a state behavior of real gas, biogas. Theoretical approach was utilized for processing of this work. Compressibility factor was calculated with help of two equation of state – Van der Waals equation and Redlich‑Kwong equation. Constants a and b of both equations were calculated using geometric average of the constants of pure substances. On the basis of calculated data charts showing the dependence of compressibility factor and the pressure were created. These charts were created for temperatures 20 °C and 40 °C. Statistical analyses of data were carried out. The results showed that compressibility factor reached value from 0.997 to 0.97 (20 °C) and from 0.997 to 0.974 (40 °C) in the case Van der Waals equation and in the range of pressure from 100 kPa to 1000 kPa. In the case of Redlich‑Kwong equation these values were from 0.997 to 0.967 (20 °C) and from 0.997 to 0.974 (40 °C) in the same range of pressures.

The cubic van der Waals equation of state at the critical condition is reduced to a linear function (Vc vs. Tc /Pc coordinates) with one adjustable parameter. It is shown that at the critical point the relation Vc = 3Vo must not hold as van der Waals suggested, but the attractive constant α = Pc Vc2 remains. Selected values of Tc, Pc, Vc compiled by Ihmels where focused on testing the quality of several empirical equations relating critical conditions. It is shown that the obtained critical constants correlation is a general form of the empirical expressions proposed by Young, Meissner, Bird, Grigoras and Ihmels. From the resulting correlation function, a function for the critical compressibility is proposed. The critical volume Vc and the ratio Tc /Pc have been expressed in group contributions.

The main prerequisite for designing electrocatalysts with favorable performance is to examine the links between electronic structural features and catalytic activity. In this work, Ni 2 P as a model electrocatalyst and one of the most potent catalysts for hydrogen evolution reaction (HER) was utilized to develop various Ni 2 P and carbon-based (graphene and N-doped graphene) heterostructures. The characteristics of such structures (Ni 2 P, graphene, N-doped graphene, Ni 2 P/graphene, and Ni 2 P/N-doped graphene), including binding energies, the projected density of states (PDOS), band structure, charge density difference, charge transfer, Hirshfeld charge analysis, and minimum-energy path (MEP) towards HER were calculated and analyzed by density functional theory (DFT) approach. The coupling energy values of hybrid systems were correlated with the magnitude of charge transfer. The main factors driving a promising water-splitting reaction were explained by the data of PDOS, band structures, and charge analysis, including the inherent electronegativity of the N species alongside shifting the Fermi level toward the conductive band. It was also shown that a significant drop occurs in the HER energy barrier on Ni 2 P/graphene compared to the pristine Ni 2 P due to N doping on the graphene layer in the Ni 2 P/N-doped graphene heterostructure., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

The possibility to engineer (GeTe) m (Sb 2 Te 3 ) n phase-change materials to co-host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe) m (Sb 2 Te 3 ) n with GeTe-rich composition is presented. These layered films feature a tunable distribution of (GeTe) m (Sb 2 Te 3 ) 1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe) m (Sb 2 Te 3 ) 1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe) m slab sandwiched in GeTe-rich blocks. That is, the net ferroelectric polarization is confined almost in-plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase-change and ferroelectric switching properties, paving the way for the conception of innovative device architectures., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)