Van Der Waals Contacts Research Articles

Forming Stable van der Waals Contacts between Metals and 2D Semiconductors.

High-performing 2D electrical and optical devices can be realized by forming an ideal van der Waals (vdW) metal contact with weak interactions and stable interface states. However, the methods for applying metal contacts while avoiding damage from metal deposition present challenges in realizing a uniform, stable vdW interface. To overcome this problem, this study develops a method for forming vdW contacts using a sacrificial Se buffer layer. This study explores this method by investigating the difference in the Schottky barrier height between the vdW metal contact deposited using a buffer layer, a transferred metal contact, and a conventional directly deposited metal contact using rectification and photovoltaic characteristics of a Schottky diode structure with graphite. Evidently, the Se buffer layer method forms the most stable and ideal vdW contact while preventing Fermi-level pinning. A tungsten diselenide Schottky diode fabricated using these vdW contacts with Au and graphite as the top and bottom electrodes, respectively, exhibits excellent operation with an ideality factor of ≈1, an on/off ratio of >107 , and coherent properties. Additionally, when using only the vdW Au contact, the electrical and optical properties of the device can be minutely modulated by changing the structure of the Schottky diode.

In silico studies of the interaction of the minor groove binder Hoechst 33258 with B-DNA

Interaction of the minor groove binder, Hoechst 33258, with the Dickerson-Drew DNA dodecamer sequence has been investigated using docking, MM/QM, MM/GBSA and molecular dynamics computations to study the modes of binding and the interactions responsible for the binding. Besides the original Hoechst 33258 ligand (HT), a total of 12 ionization and stereochemical states for the ligand are obtained at the physiological pH and have been docked into B-DNA. These states have one or the other or both benzimidazole rings in protonated states, apart from the piperazine nitrogen, which has a quaternary nitrogen in all the states. Most of these states are found to exhibit good docking scores and free energy of binding with B-DNA. The best docked state has been taken further for molecular dynamics simulations and compared with the original HT. This state is protonated at both benzimidazole rings besides the piperazine ring and hence has very highly negative coulombic interaction energy. In both cases, there are strong coulombic interactions, but these are offset by the almost equally unfavorable solvation energies. Thus, the nonpolar forces, particularly van der Waals contacts, dominate the interaction, and the polar interactions highlight subtle changes in the binding energies, leading to more highly protonated states having more negative binding energies. Communicated by Ramaswamy H. Sarma

Structural and FTIR spectroscopic studies of matrix-isolated 3-thio-1,2,4-triazole complexes with dinitrogen. First experimental evidence for the UV-induced formation of thiol⋯N2 complexes

Complexes of 3-thio-1,2,4-triazole (ST) with N2 were studied theoretically by the B3LYP-D3 method and experimentally by FTIR spectroscopy combined with the matrix isolation technique and UV laser irradiation. The computational results show that ST interacts specifically with dinitrogen in several different ways. For the 1:1 complexes of the most abundant ST thione tautomer, three stable minima have been located on the potential energy surface. The two most stable structures, containing both the N-H⋯N hydrogen bond and the S⋯N van der Waals contact, were detected experimentally in the argon matrix after deposition. Interestingly, it was found that laser irradiation at λ = 270 nm, apart from generating the thiol tautomer of ST, also leads to the formation of its corresponding complexes, characterized by N-H⋯N hydrogen bonds. What is more, it appeared that the efficiency of hydrogen atom transfer in ST complexed with N2 is lower than in the monomeric form.

Relationship between changes in interface characteristics and external voltage under compressing force in metal–graphene–metal stacks

Metal–graphene–metal (M–G–M) stacks have provided new specific methods for the integration of two-dimensional (2D) materials into three-dimensional (3D) electronic devices, such as transistors, supercapacitors, memristors and others. Intentional control of the local electronic properties in the stacks is the primary problem to be solved when developing hybrid structures with 2D and 3D elements. In order to do this, the physical mechanisms and processes that define the properties of the stacks must be thoroughly understood. This report introduces an approach based on the force curve analysis in terms of the interface characteristics in the M–G–M stack. In the study, the stack was produced by pressing the platinum probe of a scanning probe microscope into the surface of a gold-supported graphene monolayer, and the force curve was measured under applied direct current voltage. Based on the model of the van der Waals contact, the equilibrium interface distances and the built-in potential were obtained from the experimental results. The equilibrium state was proved to be weakly dependent on the applied voltage below a threshold level. Above this level, irreversible changes and the effect of the history of the tests were detected. The proposed method is acceptable to quantitatively describe the most essential characteristics in a local area of the M–G–M stack, essential for the construction of nano-scaled electronic devices.

Synthesis, single crystal X-ray structure determination, Hirshfeld surface analysis, interaction energies, and density functional theory calculations of N,N'-(cyclohexane-1,4-dicarbonothioyl)bis(4-methylbenzamide)

The present research offers convenient synthesis, molecular and crystal structures of C2 symmetric N,N'-(cyclohexane-1,4-dicarbonothioyl)bis(4-methylbenzamide). The synthesized bis-amide crystallized in monoclinic crystal system, having space group of P 21/c with a = 17.8669 (14) Å, b = 6.3495 (5) Å, c = 9.6195 (7) Å, β = 101.567 (8)°, Z = 2 and V = 1069.13 (15) Å3. The asymmetric unit contains cyclohexane ring located on an inversion center, one dicarbonothioyl and one methylbenzamide group. In the crystal structure, the N–H···O, C–H···O and C–H···S hydrogen bonds link the molecules, enclosing R21(6), R22(16) and R22(22) ring motifs, into three-dimensional architecture. Hirshfeld surface (HS) analysis revealed the prevailing significance of hydrogen bond contacts. HS analysis suggested prominent contributions for crystal packing encompasses H…H (49.6%), H…C/C…H (18.9%) and H…S/S…H (16.0%). Hydrogen bonding and van der Waals contacts are the dominant interactions in the crystal packing. The respective volume of the crystal voids and the percentage of free spaces in the unit cell is calculated as 117.87 Å3 and 11.02% indicating the absence of any large cavity within the crystal and the associated stability of the crystal. Evaluation of the electrostatic, dispersion and total energy frameworks revealed that stabilization is dominated by dispersion energy contribution. Moreover, optimized molecular structure, using density functional theory at B3LYP/6-311G(d,p) level, were compared with the experimentally determined ones. HOMO–LUMO energy gap was determined, frequencies and molecular electrostatic potential surface were calculated at the B3LYP/6–311G level to predict sites for electrophilic and nucleophilic attacks. The significant charge polarity, half molecule spread of HOMO and LUMO impart bis-amide nucleophilic as well as electrophilic behavior with relative potency depending upon the nature of the attacking molecule.

Enhanced enzymatic activity and conformational stability of catalase in presence of tetrahedral DNA nanostructures: A biophysical and kinetic study

The emergence of DNA nanotechnology has shown enormous potential in a vast array of applications, particularly in the medicinal and theranostics fields. Nevertheless, the knowledge on the biocompatibility between DNA nanostructures and cellular proteins is largely unknown. Herein, we report the biophysical interaction between proteins (circulatory protein bovine serum albumin, BSA, and the cellular enzyme bovine liver catalase, BLC) and tetrahedral DNA (tDNA), which are well-known nanocarriers for therapeutics. Interestingly, the secondary conformation of BSA or BLC was unaltered in the presence of tDNAs which supports the biocompatible property of tDNA. In addition, thermodynamic studies showed that the binding of tDNAs with BLC has a stable non-covalent interaction via hydrogen bond and van der Waals contact, which is indicative of a spontaneous reaction. Furthermore, the catalytic activity of BLC was increased in the presence of tDNAs after 24 h of incubation. These findings indicate that the presence of tDNA nanostructures not only ensures a steady secondary conformation of proteins, but also stabilize the intracellular proteins like BLC. Surprisingly, our investigation discovered that tDNAs have no effect on albumin proteins, either by interfering or by adhering to the extracellular proteins. These findings will aid in the design of future DNA nanostructures for biomedical applications by increasing the knowledge on the biocompatible interaction of tDNAs with biomacromolecules.

Intrinsic Electronic Properties of BN-Encapsulated, van der Waals Contacted MoSe2 Field-Effect Transistors

Two-dimensional (2D) semiconductors have attracted considerable interest for their unique physical properties. Here, we report the intrinsic cryogenic electronic transport properties in few-layer MoSe2 field-effect transistors (FETs) that are fully encapsulated in ultraclean hexagonal boron nitride dielectrics and are simultaneously van der Waals contacted with gold electrodes. The FETs exhibit electronically favorable channel/dielectric interfaces with low densities of interfacial traps (< 1010 cm−2), which lead to outstanding device characteristics at room temperature, including near-Boltzmann-limit subthreshold swings (65 mV/dec), high carrier mobilities (53–68 cm2⋅V−1⋅s−1), and negligible scanning hystereses (< 15 mV). The dependence of various contact-related parameters with temperature and carrier density is also systematically characterized to understand the van der Waals contacts between gold and MoSe2. The results provide insightful information about the device physics in van der Waals contacted and encapsulated 2D FETs.

Biological Evaluation and Computational Studies of Methoxy-flavones from Newly Isolated Radioresistant Micromonospora aurantiaca Strain TMC-15.

This study aims to determine UV-B resistance and to investigate computational analysis and antioxidant potential of methoxy-flavones of Micromonospora aurantiaca TMC-15 isolated from Thal Desert, Pakistan. The cellular extract was purified through solid-phase extraction and UV-Vis spectrum analysis indicated absorption peaks at λmax 250nm, 343nm, and 380nm that revealed the presence of methoxy-flavones named eupatilin and 5-hydroxyauranetin. The flavones were evaluated for their antioxidant as well as protein and lipid peroxidation inhibition potential using di(phenyl)-(2,4,6-trinitrophenyl) iminoazanium (DPPH), 2,4-dinitrophenyl hydrazine (DNPH), and thiobarbituric acid reactive substances (TBARS) assays, respectively. The methoxy-flavones were further studied for their docking affinity and interaction dynamics to determine their structural and energetic properties at the atomic level. The antioxidant potential, protein, and lipid oxidation inhibition and DNA damage preventive abilities were correlated as predicted by computational analysis. The eupatilin and 5-hydroxyauranetin binding potential to their targeted proteins 1N8Q and 1OG5 is - 4.1 and - 7.5kcal/mol, respectively. Moreover, the eupatiline and 5-hydroxyauranetin complexes illustrate van der Waals contacts and strong hydrogen bonds to their respective enzymes target. Both in vitro studies and computational analysis results revealed that methoxy-flavones of Micromonospora aurantiaca TMC-15 can be used against radiation-mediated oxidative damages due to its kosmotrophic nature. The demonstration of good antioxidant activities not only protect DNA but also protein and lipid oxidation and therefore could be a good candidate in radioprotective drugs and as sunscreen due to its kosmotropic nature.

ZBTB7A regulates primed-to-naïve transition of pluripotent stem cells via recognition of the PNT-associated sequence by zinc fingers 1-2 and recognition of γ-globin -200 gene element by zinc fingers 1-4.

ZBTB7A, a transcription factor containing a tandem array of four Cys2-His2 zinc fingers (ZFs), is vital for multiple physiological events through directional binding to different genomic loci. Our previously determined crystal structure of ZBTB7A in complex with a GCCCCTTCCCC sequence revealed that all four ZFs (ZF1-4) are involved in binding to γ-globin -200 gene element to repress fetal haemoglobin expression. Recently, it has been reported that ZBTB7A drives primed-to-naïve transition (PNT) of pluripotent stem cells through binding to a 12-bp consensus sequence ([AAGGACCCAGAT], referred to as PNT-associated sequence). Here, we report a crystal structure of ZBTB7A ZF1-3 in complex with the PNT-associated sequence. The structure shows that ZF1 and ZF2 primarily contribute to recognizing the GACCC core sequence mimicking the half part (GCCCC) of γ-globin -200 gene element via specific hydrogen bonding and van der Waals contacts. The mutations of key residues in ZF1-2 remarkably reduce their binding affinities for the PNT-associated sequence in vitro and cannot restore epiblast stem cells to the naïve pluripotent state in vivo. Collectively, our studies demonstrate that ZBTB7A mainly employs its ZF1-2 to recognize the PNT-associated sequence but recognizes γ-globin -200 gene element via ZF1-4, providing insights into the molecular mechanism for the diversity of ZBTB7A's genomic localization.

Graphene‐Enhanced Metal Transfer Printing for Strong van der Waals Contacts between 3D Metals and 2D Semiconductors

Abstract2D semiconductors have shown great potentials for ultra‐short channel field‐effect transistors (FETs) in next‐generation electronics. However, because of intractable surface states and interface barriers, it is challenging to realize high‐quality contacts with low contact resistances for both p‐ and n‐ 2D FETs. Here, a graphene‐enhanced van der Waals (vdWs) integration approach is demonstrated, which is a multi‐scale (nanometer to centimeter scale) and reliable (≈100% yield) metal transfer strategy applicable to various metals and 2D semiconductors. Scanning transmission electron microscopy imaging shows that 2D/2D/3D semiconductor/graphene/metal interfaces are atomically flat, ultraclean, and defect‐free. First principles calculations indicate that the sandwiched graphene monolayer can eliminate gap states induced by 3D metals in 2D semiconductors. Through this approach, Schottky barrier‐free contacts are realized on both p‐ and n‐type 2D FETs, achieving p‐type MoTe2, p‐type black phosphorus and n‐type MoS2 FETs with on‐state current densities of 404, 1520, and 761 µA µm−1, respectively, which are among the highest values reported in literature.

Fully Printed Organic Phototransistor Array with High Photoresponse and Low Power

Organic phototransistors (OPTs) as optical chemical sensors have progressed excitingly in recent years, mainly due to the development of new materials, new device structures, and device interfacial engineering. Exploiting the maximum potential of low-cost and high-throughput fabrication of organic electronics and optoelectronics requires devices that can be manufactured in a fully printed way that also have a low operation voltage. In this work, we demonstrate a fully printed fabrication process that enables the realization of a high-yield (~90%) and low-voltage OPT array. By solution printing of a high-quality organic crystalline thin film on the pre-printed electrodes, we create a van der Waals contact between the metal and organic semiconductor, resulting in a small subthreshold swing of 445 mV dec−1 with a signal amplification efficiency over 5.58 S A−1. Our OPTs thus exhibit both a low operation voltage of −1 V and a high photosensitivity over 5.7 × 105, making these devices suitable for a range of applications requiring low power consumption. We further demonstrate the capability of the low-voltage OPT array for imaging and show high imaging contrasts. These results indicate that our fabrication process may provide an entry into integrated and low-power organic optoelectronic circuits fabricated by scalable and cost-effective methods for real-world applications.

Large Scale Fabrication of Graphene Based Nano‐Electromechanical (NEM) Contact Switches with Sub‐0.5 Volt Actuation (Adv. Phys. Res. 4/2023)

Nano-Electromechanical Contact Switches Nano-electromechanical (NEM) contact switches based on graphene–graphene van der Waals contacts are demonstrated by Jothiramalingam Kulothungan and Karthi Kandhasamy in article number 2200050. Graphene–graphene NEM contact switches with ultra-low pull-in voltage and significant improvement in the contact lifetime are achieved using the graphene on gold electrode as a contact material. The graphene NEM contact switches with graphene as a contact material exhibits an ultra-low pull-in voltage of < 0.5 V and high contact lifetime, suitable for a new generation of energy efficient electronics.

A Methodology of Fabricating Novel Electrodes for Semiconductor Devices: Doping and Van der Waals Integrating Organic Semiconductor Films.

Electrodes are indispensable components in semiconductor devices, and now are mainly made from metals, which are convenient for use but not ideal for emerging technologies such as bioelectronics, flexible electronics, or transparent electronics. Here the methodology of fabricating novel electrodes for semiconductor devices using organic semiconductors (OSCs) is proposed and demonstrated. It is shown that polymer semiconductors can be heavily p- or n-doped to achieve sufficiently high conductivity for electrodes. In contrast with metals, the doped OSC films (DOSCFs) are solution-processable, mechanically flexible, and have interesting optoelectronic properties. By integrating the DOSCFs with semiconductors through van der Waals contacts different kinds of semiconductor devices can be constructed. Importantly, these devices exhibit higher performance than their counterparts with metal electrodes, and/or excellent mechanical or optical properties that are unavailable in metal-electrode devices, suggesting the superiority of DOSCF electrodes. Given the existing large amount of OSCs, the established methodology can provide abundant electrode choices to meet the demand of various emerging devices.

Pharmacological Chaperones and Protein Conformational Diseases: Approaches of Computational Structural Biology.

Whenever a protein fails to fold into its native structure, a profound detrimental effect is likely to occur, and a disease is often developed. Protein conformational disorders arise when proteins adopt abnormal conformations due to a pathological gene variant that turns into gain/loss of function or improper localization/degradation. Pharmacological chaperones are small molecules restoring the correct folding of a protein suitable for treating conformational diseases. Small molecules like these bind poorly folded proteins similarly to physiological chaperones, bridging non-covalent interactions (hydrogen bonds, electrostatic interactions, and van der Waals contacts) loosened or lost due to mutations. Pharmacological chaperone development involves, among other things, structural biology investigation of the target protein and its misfolding and refolding. Such research can take advantage of computational methods at many stages. Here, we present an up-to-date review of the computational structural biology tools and approaches regarding protein stability evaluation, binding pocket discovery and druggability, drug repurposing, and virtual ligand screening. The tools are presented as organized in an ideal workflow oriented at pharmacological chaperones' rational design, also with the treatment of rare diseases in mind.

Integration of Self-Passivated Topological Electrodes for Advanced 2D Optoelectronic Devices.

With the rapid development of two-dimensional semiconductor technology, the inevitable chemical disorder at a typical metal-semiconductor interface has become an increasingly serious problem that degrades the performance of 2D semiconductor optoelectronic devices. Herein, defect-free van der Waals contacts have been achieved by utilizing topological Bi2 Se3 as the electrodes. Such clean and atomically sharp contacts avoid the consumption of photogenerated carriers at the interface, enabling a markedly boosted sensitivity as compared to counterpart devices with directly deposited metal electrodes. Typically, the device with 2D WSe2 channel realizes a high responsivity of 20.5AW-1 , an excellent detectivity of 2.18×1012 Jones, and a fast rise/decay time of 41.66/38.81ms. Furthermore, high-resolution visible-light imaging capability of the WSe2 device is demonstrated, indicating its promising application prospect in future optoelectronic systems. More inspiringly, the topological electrodes are universally applicable to other 2D semiconductor channels, including WS2 and InSe, suggesting its broad applicability. These results open fascinating opportunities for the development of high-performance electronics and optoelectronics.

Resolving Interface Barrier Deviation from the Schottky–Mott Rule: A Mitigation Strategy via Engineering MoS2–Metal van der Waals Contact

The Schottky barrier (SB) in the ultraclean van der Waals contact between two-dimensional (2D) MoS2 and three-dimensional (3D) indium (In) strikingly deviates from the Schottky-Mott limit (SML). Herein, on the basis of first-principles calculation, the origin of the SB deviation is brought to bear, as well as a strategy for mitigating the SB deviation. In light of the good agreement between the SB and the corrected SB by interface potential difference (ΔV) and Fermi -level shift (ΔEF) based on the SML, the SB deviation is attributed to the combined effects of ΔV and ΔEF. Furthermore, when a Au, Sc, or Ti thin film is coated on the back side of In, the SB deviation and the sum of ΔV and ΔEF decrease similarly. Importantly, in the Ti coating situation, the SB is reduced to 0.12 eV, notably smaller than the value of 0.30 eV in the Au coating case. This interface engineering can be generalized to regulate the SB between a 2D semiconductor and a 3D alloy.

Suppressed Fermi Level Pinning and Wide-Range Tunable Schottky Barrier in CrX3 (X = I, Br)/2D Metal Contacts

CrX3 (X = I, Br) monolayers exhibit outstanding performance in spintronic devices. However, the Schottky barrier at the CrX3/electrode interface severely impedes the charge injection efficiency. Herein, we propose two-dimensional (2D) metals as electrodes to form van der Waals (vdW) contact with CrX3 monolayers and systematically explore the contact properties of CrX3/metal by density functional theory (DFT) calculations. The results demonstrate that the strongly suppressed Fermi level pinning (FLP) effect and the wide-range tunable Schottky barrier can be achieved in CrX3/metal contacts. Specifically, the n-type and the p-type Schottky contacts can be realized in CrX3/metal contacts by choosing 2D metal electrodes with different work functions. Importantly, the pinning factors for CrX3/metal contacts are exceptionally larger than other commonly studied 2D semiconductors, indicating the strongly suppressed FLP in CrX3/metal contacts, which leads to the wide-range tunable Schottky barrier. Our findings provide guidance to the choice of electrodes and promote the development of CrX3-based spin devices.

3-Methyl-2-(methyl-sulfan-yl)-5,5-diphenyl-3,5-di-hydro-4H-imidazol-4-one.

In the title mol-ecule, C17H16N2OS, the di-hydro-imidazolone ring is slightly puckered and the methyl-sulfanyl group is nearly coplanar with it. In the crystal, two sets of C-H⋯O hydrogen bonds form corrugated layers of mol-ecules parallel to the ac plane. The layers pack with normal van der Waals contacts between them.

Quantitative chirality in the binding of androgens to their receptor

Chirality is a binary yes/no molecular property that nevertheless can be described by a continuous chirality measure function. Chirality measure values can be understood as sensitive descriptors of molecular shape. In this study, we evaluated the role of quantitative chirality (measures) in binding of androgens to their receptor. We demonstrate that a simple Quantitative Structure-Activity Relationship equation correlating the binding affinity with the partial charges of pharmacophoric oxygen atoms is significantly improved upon introducing quantitative chirality descriptors as additional variables. In such models, the charge descriptors account for the strength of the formed hydrogen bonds. However, the picture is completed by the chirality measures that indirectly contain information on the geometries of the hydrogen bond networks and subtle differences in the van der Waals contacts connected with different local or global shapes of the molecules. The model case studied here (11 simple and very similar steroids) proves that both global and local chirality is important in the androgen binding to their receptors.

Coupled-oscillator model for hybridized optical phonon modes in contacting nanosize particles and quantum dot molecules

Modification of optical phonon spectra in contacting nonpolar nanoparticles compared to single particles is studied. Optical phonons in dielectric and semiconducting particles obey the Euclidean metric Klein-Fock-Gordon equation with Dirichlet boundary conditions. This equation is supposed to be solved numerically for manifolds of cojoined spheres. It is proposed to replace this problem with the simpler-to-solve coupled-oscillator model (COM), where an oscillator is attributed to each phonon mode of a particle and the particle overlap leads to the appearance of additional couplings for these oscillators with the magnitude proportional to the overlap volume. For not too big overlaps, this model describes solutions of the original eigenvalue problem with a quantitative level of accuracy. In particular, it works beyond isotropic $s$ modes in dimers, which has been demonstrated for $p$ modes in dimers and for tetramers. It is proposed to apply the COM for the description of recently manufactured dimer nanoparticles and quantum dots. The obtained results are in agreement with the dynamical matrix method for optical phonons in nanodiamonds. The dynamical matrix method is also used to demonstrate that the van der Waals contacts between faceted particles lead to very small modifications of the optical phonon spectra, which therefore could be neglected when discussing the propagation of vibrational excitations via a nanopowder. The possibility to distinguish between dimerized and size-distributed single particles from their Raman spectra is also considered. The proposed COM paves a way towards the description of propagation of vibrational modes in the ensembles of particles in contact including tight agglomerates, nanocrystal solids, and porous media.