vdW Interactions Research Articles

Measuring interfacial thermal resistance across carbon nanotubes with in-situ electron microscopy: Unexpected reduction upon detachment and two orders of magnitude variations across diverse morphologies

The dynamic mechanical processes can notably impact the van der Waals (vdW) interaction at nanoscale contact interface and further interfacial thermal transport, but the experimental study is challenging. Here, by integrating a movable nanoprobe within an electron microscope, we dynamically adjusted the contact and detachment processes of vdW contact between two carbon nanotubes (CNTs), while measuring the thermal contact resistance (TCR) in situ with a nanofabricated thermal sensor. The TCR was found to span approximately two orders of magnitude at the moments when two CNTs just came into contact or detached. Surprisingly, during the initial stage of detachment, we observed that TCR unexpectedly further decreased by 65% instead of increasing. This decrease is attributed to the subtle alteration of exact contact interface in the circumferential direction, induced by the real-time observed rotation during the detachment process. A two-order magnitude difference in TCR for the diverse morphologies in static equilibrium between the same pair of CNTs due to the non-uniformity of the CNT surface structures can also support it. Our work provides valuable insights for dynamically modulating nanoscale interfacial thermal transport in various applications.

Computational Insights for Interactions between nsP2 and nsP3 of CHIKV and Hormones through DFT Computations and Molecular Dynamics Simulations.

The non-structural protein (nsP2 & nsP3) of the Chikungunya virus (CHIKV) is responsible for the transmission of viral infection. The main role of non-structural proteins are involved in the transcription process at an early stage of the infection. In this work, authors have studied the impact of nsP2 and nsP3 of CHIKV on hormones present in the human body using a computational approach. The ten hormones of chemical properties such as 4-Androsterone-2,17-dione, aldosterone, androsterone, corticosterone, cortisol, cortisone, estradiol, estrone, progesterone and testosterone were taken as a potency. From the molecular docking, the binding energy of the complexes is estimated, and cortisone was found to be the highest negative binding energy (-6.57 kcal/mol) with the nsP2 and corticosterone with the nsP3 (-6.47 kcal/mol). This is based on the interactions between hormones and nsP2/nsP3, which are types of noncovalent intermolecular interactions categorized into three types: electrostatic interactions, van der Waals (vdW) interactions, and hydrogen-bonding (H-bonding) interactions. To validate the docking results, additional molecular dynamics simulations and MM-GBSA methods were performed. The change in enthalpy, entropy, and free energy were calculated using MM-GBSA methods. The nsP2 and nsP3 of CHIKV interact strongly with the cortisone and corticosterone with free energy changes of -20.55 & -36.08 kcal/mol, respectively. Methods: The crystal structures of 3TKR and 3GPO proteins of nsP2 and nsP3 were extracted from the RCSB Protein Data Bank. Initially, unnecessary atoms like extra cations or anions and missing explicit hydrogen atoms were removed and added from the native domain of nsP2 and nsP3. The alignment of coordinated in the native domain was performed using Chimera and Notepad++ tools. The molecular docking of protein and ligand was performed usingAutoDock tool; it is essential for the prediction of the orientation of the ligand into the cavity of the target protein based on binding affinity. Based on thermodynamic parameters, MD Simulations were employed to calculate the change in binding free energies of various complexes followed by a change in enthalpy and entropy with time. According to MD production, the CPPTAJ and PTRAJ programs were used to analyse the trajectories, such as dynamic stability (RMSD), residual fluctuation (RMSF), compatibility, and hydrogen bonds of the newly formed complexes. After that, the Density Functional Theory (DFT) were used to calculate the electronic properties of selected molecules by Gaussian 16 on applying the B3LYP method with the 6-311G (d, p) basis set.

One-Dimensional Van Der Waals V2Se9 As a Conversion-Type Anode Material for Advanced Li Rechargeable Batteries

Volume expansion of active materials during lithium storage is one of the main issues in Li-ion batteries (LIBs) that should be addressed. In particular, large volume changes and particle cracking are problematic for electrode materials based on conversion reaction, which are considered attractive anode materials with high energy densities. In this study, a one-dimensional van der Waals (1D vdW) material, V2Se9, is proposed as a conversion-type anode material for LIBs. The V2Se9 electrode material has a 1D chain molecular structure with vdW interactions between chains to form a bulk crystal structure. The spaces between the 1D chains act as structural buffers and provide short Li+ diffusion paths that can improve the electrochemical performance of the electrode materials. The V2Se9 electrode exhibits a high reversible capacity of 563.3 mAh g-1 at 100 mA g-1 and a high rate capability of 109.1 mAh g-1 at 3200 mA g-1. The capacity retention of V2Se9 electrodes is 83.72 % after 100 cycles. Synchrotron X-ray diffraction and X-ray absorption spectroscopy reveal the formation of Li2Se and V metal, indicating that Li ion storage occurs via the conversion reaction. The structural stability of V2Se9 is demonstrated using SEM measurements of the discharged and charged V2Se9 electrodes during cycling. These results demonstrate the reaction mechanism of V2Se9 and highlight the potential of 1D vdW materials as high-performance anode materials in LIBs.

(Invited) Deformable Electronics Based on Strain-Engineered Van Der Waals Materials

Materials exhibit drastically different physical and chemical properties as their dimensionality varies. Atomically-thin van der Waals (vdW) materials possess unique mechanical, electrical, optical, and thermal characteristics, originated from quantum confined low-dimensionality and a lack of dangling bond. In particular, strong in-plane covalent bonding and weak interlayer vdW interaction of two-dimensional (2D) vdW materials enable exceptional combination of mechanical properties, such as high Young’s modulus, high in-plane strength, and ultralow bending stiffness at a level of cell membrane. Moreover, mechanical strain can induce modulation of electronic and phononic band structures of 2D vdW materials more effectively due to mechanical resilience and high surface-to-volume ratio. For these reasons, deformation engineering has garnered substantial interest in mechanics, materials and electronics communities as a new tuning knob for emerging phenomena and functionalities of 2D vdW materials. In this talk, I will discuss deformation engineering of 2D vdW materials – (1) active and dynamic deformation strategies, including in-plane interfacial slippage and out-of-plane structural deformation, (2) deformation strain induced phenomena, and (3) emerging device concepts based on deformation engineering of 2D vdW materials.

Molecular insights reveal how the glycolipids in cell membrane mitigates nanomaterial's invasion

Nanomaterial-cellular membrane interaction is crucial for the cytotoxicity of such materials in theoretical investigations. However, previous research often used cellular membrane models with one or few lipid types, which deviates significantly from realistic membrane compositions. Here, employing molecular dynamics (MD) simulations, we investigate the impact of a typical nanomaterial, boron nitride (BN), on a cellular membrane model based on the realistic small intestinal epithelial cell (SIEC) membrane. This membrane contains a complex composition, including abundant glycolipids. Our MD simulations reveal that BN nanosheet can partially insert into the SIEC membrane, maintaining a stable binding conformation without causing obvious structural changes. Dynamic analyses suggest that van der Waals (vdW) interactions drive the binding process between BN and the SIEC membrane. Further simulation of the interaction between BN nanosheet and deglycosylated SIEC membrane confirms that BN nanosheet cause significant structural damage to deglycosylated SIEC membranes, completely inserting into the membrane, extracting lipids, and burying some lipid hydrophilic heads within the membrane interior. Quantitative analyses of mean squared displacements (MSD) of membranes, membrane thicknesses, area per lipid, and order parameters indicate that BN nanosheet causes more substantial damage to deglycosylated SIEC membrane than to intact SIEC membrane. This comparison suggests the molecular mechanism involved in mitigating BN invasion by SIEC membrane that the polysaccharide heads of glycolipids in the SIEC membrane form a significant steric hindrance on membrane surface, not only hindering the insertion of BN, but also resisting the lipid extraction by BN. Free energy calculations further support this conclusion. Overall, our MD simulations not only shed new light into the reduced impact of BN nanosheet on the realistic SIEC membrane but also highlight the importance of glycolipids in protecting cell membranes from nanomaterial invasion, contributing to a deeper understanding of nanomaterial-realistic cell membrane interactions.

The peeling behavior of compliant nano-films in adhesive contact with a planar rigid substrate: Insights from molecular dynamics and continuum mechanics

Peeling compliant nano-films from supporting substrates is crucial in the mechanical exfoliation and transfer processes. However, the peeling behavior, especially concerning the peeling stiffness and peak peeling force, exhibits intricate interplay with the geometric and material properties of nano-films, as well as interfacial interactions, which have yet to be fully elucidated. In this work, both classical molecular dynamics (MD) simulations and continuum analysis are adopted to investigate the entire peeling process of compliant nano-films from a planar rigid substrate. Considering the atomic structure and van der Waals (vdW) interactions at the interface, we establish a continuum mechanics model to describe the entire peeling process, encompassing the initial, transitional, steady-state, and unstable peel-off stages. The theoretical predictions are reasonably consistent with the results obtained by MD simulations. The effects of film length and interface toughness on the peeling process, the peeling stiffness and peak peeling force, are thoroughly investigated, and a phase diagram for the peeling deformation modes is quantitatively constructed. Finally, dimensional analysis yields scaling relations for the peak peeling force in terms of the length and bending stiffness of compliant nano-films, as well as the governing parameters for interfacial vdW interactions. These results contribute to a better understanding of the peeling mechanics of various two-dimensional nano-films (e.g., graphene, hexagonal boron nitride, and molybdenum disulfide) adhered to substrates.

Computational and experimental characterisation of a new (R)-camphor-Thiazolidinone derivative: A combined approach for structure optimisation and activity prediction

This study describes the synthesis, characterisation, in-silico exploration, and theoretical investigation of a novel 5-Methyl-2-(((1S,4R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)hydrazono)thiazolidin-4-one 3. The structure of the synthesised derivative was successfully confirmed using high-resolution mass spectrometry (HRMS) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. In addition, a concise theoretical study was employed to elucidate the experimentally observed stability of the compound. On the computational level, this investigation utilised DFT, molecular docking, and molecular dynamics simulations for the (R)-camphor-thiazolidinone derivative. The optimised structure of compound 3 was predicted with the DFT/B3LYP method with the 6–311++G(d,p) basis set. The theoretical vibrational modes were assigned and found to be consistent with the observed FT-IR spectrum. The simulated NMR values exhibited good agreement with the experimental NMR chemical shifts, with the deviations of 0.5113 and 3.816 ppm for the 1H and 13C, respectively. The UV–vis spectra indicated the n → π* and π → π* transitions in compound 3, with confirmation of intermolecular charge transfer (ICT) from the FMOs and NBO analyses. The MEP surface, Mulliken, and NPA analyses confirm the presence of reactive sites within compound 3. NCI-RDG studies revealed the presence of van der Waals (vdW) interactions and the absence of hydrogen bonding within the studied molecule. The molecular docking analysis indicates that compound 3 exhibits a strong inhibitory effect on the targeted protein 6HQO, which, in turn, is associated with breast cancer. The molecular dynamics analysis validates the accuracy of the docking results.

Excitonic Properties versus Structure Stability Trade‐Off in Halide Perovskite Photovoltaics Caused by van der Waals Interactions

Lead halide perovskites, and their derivatives, are among the most promising photovoltaic materials for third generation solar cells. Despite the large number of available works on some of these materials, excitonic properties whose assessment has been challenging are less investigated. These include quantitative measures of excitonic properties variations with van der Waals (vdW) interactions. Consistent comparisons of how vdW interactions affect phononic and optical properties are also desirable. This work focuses on cubic phases of with X = Cl, Br, I, and MA = methylammonium, using density functional theory simulations including vdW interactions. These cause 30%–38% increase of absolute cohesive energies and 15%–37% reduction of ionic/vibrational contributions to static dielectric constants, along with 10%–29% reduction of exciton Bohr radii and 29%–107% increase of exciton binding energies. The effects on band gaps, frequency‐dependent dielectric functions, and exciton effective masses are less pronounced. Within the Mott–Wannier exciton model, the results suggest a trade‐off between photovoltaic performance and structure stability. The results can help assess stability, feasibility, and performance of hybrid photovoltaic materials.

Substrate Induced van der Waals Force Effects on the Stability of Violet Phosphorus

AbstractSince the first isolation of graphene, the importance of van der Waals (vdW) interactions has become increasingly recognized in the burgeoning field of layered materials. In this work, infrared nanoimaging techniques and theoretical modeling are used to unravel the critical role played by interfacial vdW interactions in governing the stability of violet phosphorus (VP)—a recently rediscovered wide bandgap p‐type semiconductor—when exfoliated on different substrates. It is demonstrated that vdW interactions with the underlying substrate can have a profound influence on the stability of exfoliated VP flakes and investigate how these interactions are affected by flake thickness, substrate properties (e.g., substrate hydrophilicity, surface roughness), and the exfoliation process. These findings highlight the key role played by interfacial vdW interactions in governing the stability and physical properties of layered materials, and can be used to guide substrate selection in the preparation and study of this important class of materials.

Novel two-dimensional HfSi2N4 monolayer with excellent bandgap modulation and electronic properties modulation.

The bandgap modulation and electronic properties modulation of two-dimensional HfSi2N4 monolayer induced by strain, electric field and atomic adsorption are studied by first principles. The HfSi2N4 monolayer was found to be dynamically, thermally, and mechanically stable at equilibrium, and it is a direct semiconductor with a bandgap of 1.87eV. The bandgap of the HfSi2N4 monolayer can be precisely modulated by strain. Under the action of strain, HfSi2N4 monolayer not only transforms from direct semiconductor to indirect semiconductor, but also improves the absorption of visible light. An external electric field in the 0-0.5eV/Å range can also modulate the bandgap of HfSi2N4 monolayer from 1.87eV to 0eV, and most importantly, at an external electric field of 0.5eV/Å, HfSi2N4 monolayer shows the characteristics of spin gapless semiconductor. The calculated adsorption energy shows that the structures of H, O and F atoms adsorbed by HfSi2N4 monolayer can all exist stably. The bandgap of the configuration after adsorption of O and F atoms is significantly reduced compared with that of HfSi2N4 monolayer. Furthermore, the HfSi2N4 monolayer after adsorption of H and F atoms is transformed into a magnetic semiconductor. METHOD: All calculations were performed using Vienna ab initial simulation package, The electronic structure, mechanical properties, electronic properties and other properties were carried out using generalized gradient approximation (GGA-PBE), supplemented by HSE06 and GGA + U. The total-energy and force convergence are less than 10-6eV and 0.001eV/Å, respectively. The vacuum on the z-axis is selected20Å. The vdW interactions were corrected using the Grimme scheme (DFT-D3).

The selective adsorption mechanism of benzene over water on nitrogen-doped activated carbon regulated by methyl functional groups

Improving the adsorption capacity of activated carbon (AC) for volatile organic compounds (VOCs) in humid conditions, while suppressing the interference of water molecules on the adsorption process, is significant for maximizing the effectiveness of AC as an adsorbent for efficient VOC removal. This paper investigates the impact of water on benzene adsorption by nitrogen-doped activated carbon (ACN), the hydrophobicity of different nitrogen-doped types, and the effects of methyl on the selective adsorption of benzene by ACN. The investigation is based on experiments and DFT simulations, and the corresponding mechanisms were elucidated through the force field-based energy decomposition analysis (EDA-FF), the independent gradient model based on Hirshfeld partition (IGMH), and the atoms in molecules (AIM). Under the coexistence of benzene and water, a van der Waals (vdW) interaction occurs between the adsorbed water molecules and benzene molecules, which seriously impairs benzene adsorption on ACN. Pyridine and pyrrole N enhance the adsorption of water by increasing the electrostatic interaction between water molecules and AC. Methyl group reduces hydrophilicity by increasing the repulsion of pyridine and pyrrole nitrogen with water. The selective adsorption of benzene on ACN was improved by enhancing the dispersion effect with benzene. The experimental results showed that after ACN modification with the methyl, benzene adsorption was completely restored to the situation when there was no water interference. This confirms that nitrogen-methylation is an effective method for enhancing benzene adsorption by AC while suppressing water interference.

Discovery and Manipulation of van der Waals Polarons in Sb2O3 Ultrathin Molecular Crystal.

Manipulating single electrons at the atomic scale is vital for mastering complex surface processes governed by the transfer of individual electrons. Polarons, composed of electrons stabilized by electron-phonon coupling, offer a pivotal medium for such manipulation. Here, using scanning tunneling microscopy and spectroscopy (STM/STS) and density functional theory (DFT) calculations, we report the identification and manipulation of a new type of polaron, dubbed van der Waals (vdW) polaron, within mono- to trilayer ultrathin films composed of Sb2O3 molecules that are bonded via vdW attractions. The Sb2O3 films were grown on a graphene-covered SiC(0001) substrate via molecular beam epitaxy. Unlike prior molecular polarons, STM imaging observed polarons at the interstitial sites of the molecular film, presenting unique electronic states and localized band bending. DFT calculations revealed the lowest conduction band as an intermolecular bonding state, capable of ensnaring an extra electron through locally diminished intermolecular distances, thereby forming an intermolecular vdW polaron. We also demonstrated the ability to generate, move, and erase such vdW polarons using an STM tip. Our work uncovers a new type of polaron stabilized by coupling with intermolecular vibrations where vdW interactions dominate, paving the way for designing atomic-scale electron transfer processes and enabling precise tailoring of electron-related properties and functionalities.

Exploring Methane Storage Capacities of M2(BDC)2(DABCO) Sorbents: A Multiscale Computational Study

A promising solution for efficient methane (CH4) storage and transport is a metal–organic framework (MOF)-based sorbent. Hence, searching for potential MOFs like M2(BDC)2(DABCO) to enhance the CH4 storage capacity in both gravimetric and volumetric uptakes is essential. Herein, we systematically elucidate the adsorption of CH4 in M2(BDC)2(DABCO) or M(DABCO) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) MOFs using multiscale simulations that combined grand canonical Monte Carlo simulation with van der Waals density functional (vdW-DF) calculation. We find that, in the M(DABCO) series, Mg(DABCO) has the highest total CH4 adsorption capacities, with mtot= 231.39 mg/g at 298 K, for gravimetric uptake, and Vtot= 231.43 cc(STP)/cc, for volumetric uptake. The effects of temperature, pressure, and metal substitution on enhancing CH4 storage are evaluated, and we predict that the volumetric CH4 storage capacity on M(DABCO) could meet the DOE target at temperatures of ca. 238 K–268 K and pressures of 35–100 bar. The interactions between CH4 and M(DABCO) are dominated by the vdW interactions, as shown by the vdW-DF calculations. The Mg, Mn, Fe, Co, and Ni substitutions in M(DABCO) result in a stronger interaction and thus, a higher CH4 storage capacity, at higher pressures for Mg, Mn, Ni, and Co and at lower pressures for Fe. This work may provide guidance for the rational design of CH4 storage in M2(BDC)2(DABCO) MOFs.

Quantitative assessment of thermal resistance in graphene field-effect transistors based on a phonon hydrodynamics and van der Waals coupling approach

In the progressive miniaturization of graphene field-effect transistors (GrFETs), pronounced thermal boundary resistance (TBR) and increasing ballistic-diffusive thermal resistance pose formidable challenges to thermal management. Quantitative analysis of thermal resistance is crucial for advancing efficient thermal designs in GrFETs using state-of-the-art technology. The inherently low-dimensional structure nature of graphene means that thermal conduction in GrFETs, governed by phonon hydrodynamic transport and van der Waals (vdW) interactions, cannot be accurately described by traditional Fourier's law-based models or the single-mode relaxation time approximation. This study introduces an innovative thermal simulation framework that addresses these challenges by incorporating phonon hydrodynamics equations and considering weak vdW coupling. Our findings indicate that thermal conduction in GrFETs is predominantly facilitated by flexural (ZA) phonons, and their thermal transport efficiency is significantly influenced by substrate perturbations. Specifically, the TBR in GrFETs is closely associated with the weak vdW coupling between ZA phonons and substrate atoms. Furthermore, this study employs dimensionless thermal resistance ratios and Knudsen numbers to explore the impact of silicon's geometric dimensions, heat source size, and ballistic phenomena on the substrate's thermal resistance. These insights provide substantial theoretical support for the development of efficient thermal management strategies in GrFETs.

Nanosheets adsorption and antiviral activity of Favipiravir drug against envelope proteins of yellow fever virus: DFT and molecular docking simulation study

Our previous research investigated the delivery of Favipiravir (FAV) drug through the encapsulation of FAV into 1D nanomaterials (NMs), AlN, BN, and carbon nanotubes, now we evaluated the possibility of using 2D NMs carbon nanosheets (GPNS), boron nitride nanosheets (BNNS), and aluminum nitride nanosheets (AlNNS) as drug delivery systems. The adsorption of FAV drug in its two tautomeric forms over the surfaces of these NSs is conducted. The adsorption energies are in the range of − 0.681 to − 2.469 eV. FAV binds to BNNS and GPNS through stacking interactions, while it chemisorbs to AlNNS. NCI and QTAIM analyses confirmed the dominance of vdW interactions. The recovery times over NSs were shorter than those inside NTs, and they indicated that NSs are better for drug release while NTs bind better and have larger adsorption energies. MD simulations revealed that FAV showed a good level of resistance to yellow fever virus (YFV) infections.

Epitaxial growth of highly atomically ordered Pt-Fe nanoparticles from carbon nanotube bundles as durable oxygen reduction electrocatalysts

Intermetallic Pt-based nanoparticles have displayed excellent activity for the oxygen reduction reaction (ORR) in fuel cells. However, it remains a great challenge to synthesize highly atomically ordered Pt-based nanoparticle catalysts because the formation of an atomically ordered structure usually requires high-temperature annealing accompanied by grain sintering. Here we report the direct epitaxial growth of well-aligned, highly atomically ordered Pt3Fe and PtFe nanoparticles (<5 nm) on single-walled carbon nanotube (SWCNT) bundles films. The long-range periodically symmetric van der Waals (vdW) interactions between SWCNT bundles and Pt-Fe nanoparticles play an important role in promoting not only the alignment ordering of inter-nanoparticles but also the atomic ordering of intra-nanoparticles. The ordered Pt3Fe/SWCNT catalyst showed enhanced ORR catalytic performance of 2.3-fold higher mass activity and 3.1-fold higher specific activity than commercial Pt/C. Moreover, the formation of an interlocked interface and strong vdW interaction endow the Pt-Fe/SWCNT catalysts with extreme long-term stability in potential cycling and excellent anti-thermal sintering ability.

2D Exfoliation Chemistry Towards Covalent Pseudo-Layered Phosphate Framework Derived by Radical/Strain-Synergistical Process.

2D compounds exfoliated from weakly bonded bulk materials with van der Waals (vdW) interaction are easily accessible. However, the strong internal ionic/covalent bonding of most inorganic crystal frameworks greatly hinders 2D material exfoliation. Herein, we first proposed a radical/strain-synergistic strategy to exfoliate non-vdW interacting pseudo-layered phosphate framework. Specifically, hydroxyl radicals (⋅OH) distort the covalent bond irreversibly, meanwhile, H2O molecules as solvents, further accelerating interlayered ionic bond breakage but mechanical expansion. The innovative 2D laminar NASICON-type Na3V2(PO4)2O2F crystal, exfoliated by ⋅OH/H2O synergistic strategy, exhibits enhanced sodium-ion storage capacity, high-rate performance (85.7 mAh g-1 at 20 C), cyclic life (2300 cycles), and ion migration rates, compared with the bulk framework. Importantly, this chemical/physical dual driving technique realized the effective exfoliation for strongly coupled pseudo-layered frameworks, which accelerates 2D functional material development.

2D Exfoliation Chemistry Towards Covalent Pseudo‐Layered Phosphate Framework Derived by Radical/Strain‐Synergistical Process

Abstract2D compounds exfoliated from weakly bonded bulk materials with van der Waals (vdW) interaction are easily accessible. However, the strong internal ionic/covalent bonding of most inorganic crystal frameworks greatly hinders 2D material exfoliation. Herein, we first proposed a radical/strain‐synergistic strategy to exfoliate non‐vdW interacting pseudo‐layered phosphate framework. Specifically, hydroxyl radicals (⋅OH) distort the covalent bond irreversibly, meanwhile, H2O molecules as solvents, further accelerating interlayered ionic bond breakage but mechanical expansion. The innovative 2D laminar NASICON‐type Na3V2(PO4)2O2F crystal, exfoliated by ⋅OH/H2O synergistic strategy, exhibits enhanced sodium‐ion storage capacity, high‐rate performance (85.7 mAh g−1 at 20 C), cyclic life (2300 cycles), and ion migration rates, compared with the bulk framework. Importantly, this chemical/physical dual driving technique realized the effective exfoliation for strongly coupled pseudo‐layered frameworks, which accelerates 2D functional material development.

Impact of the nature of the linker on the 2D and 3D organization of lipid-phenalenone conjugates

A series of phenalenone-lipid conjugates (1A, 1B, 1C, 2) have been synthesized to compensate for the poor water solubility of the photosensitizer phenalenone (PN) and promote the formation of nano-assemblies. We show that the organization and structure of monolayers upon compression strongly depend on the nature of the linker connecting PN to the lipid backbone, and the number of C18 chains. Monolayer properties at the air-water interface were analyzed by surface pressure measurements, Brewster angle and atomic force microscopies, grazing incidence X-ray diffraction, and X-ray reflectivity. Whereas conjugate 1C (ester bond) organizes into multilayers upon compression, conjugates 1A, 1B, and 2 form stable monolayers whose structure is controlled by van der Waals (vdW) interactions between C18 chains, intermolecular H-bonding involving the linker, and for 1B, π-π stacking of PN moieties. Conjugate 1A (amide-triazole linker) is structured into a rectangular network of chains with an order that extends only to the molecule of the adjacent cell. Conjugate 1B (amide bond) forms two incommensurate networks, one for the chains and the other for the headgroups. The distance between molecules in the next near neighbor chain lattice and the sufficient degree of freedom of PN groups allow the latter to pile up via π-π interactions below the chains in a rectangular cell. Conjugate 2 with its double chain adopts a similar behavior to that of a saturated phospholipid. Strong vdW interactions predominate and allow, at high surface pressure, hexagonal packing with no chain tilt. The distance between molecules prevents PN stacking. The identified PN derivative structures explain the linker’s impact on the formation and stability of nano-assemblies.

One-dimensional van der Waals material SbPS4 with large bandgap for UV sensing applications

UV sensors possess high importance for modern electronics such as environmental monitoring, health diagnostics, and optoelectronic devices. Thus UV-sensing-materials with high stability has drawn significant interest for next generation UV sensors. Herein, a simple synthesis method of SbPS4 has been proposed. Then the SbPS4 crystals are effectively delaminated by micromechanical exfoliation into a few-nanometer-scale nanowires, which is the first demonstration of the material’s possibility of exfoliation down to one-molecular-layer thickness. Weak van der Waals (vdW) interaction within the crystal lattice can be easily overcome. The exfoliated SbPS4 nanowires showed one-dimensional tube structure, and the work function of SbPS4 showed strong thickness dependence and was confirmed through Scanning Kelvin probe microscopy. The bandgap of 2.54 eV of SbPS4, showed great sensitivity to UV lights, depicting SbPS4 as a promising future UV sensing material for future optoelectronic application.