Electronic Gap Research Articles

(Digital Presentation) Electronic and Optical GAP Evaluation By Oxygen Tuning in MOSE2

In this study, a simple and fast electrochemical method was employed to synthesis molybdenum diselenide thin film. Molybdenum diselenide films have been electrodeposited on FTO substrates from an ammoniacal solution of H2MoO4 and SeO2. We fabricated thin films composed of MoSe2, MoO2 and MoO3 elements by adjusting some electrodeposition factors, e.g., deposition time and potential. The Structural characterizations of the electrodeposited films were investigated by SEM, Scanning tunneling spectroscopy (STS), Raman spectroscopy and UV-Visible spectroscopy. And also, Electronic and optical gap have been measured by STS and UV-Vis spectra, respectively.

High-Throughput Prediction of the Band Gaps of van der Waals Heterostructures via Machine Learning

Van der Waals heterostructures offer an additional degree of freedom to tailor the electronic structure of two-dimensional materials, especially for the band-gap tuning that leads to various applications such as thermoelectric and optoelectronic conversions. In general, the electronic gap of a given system can be accurately predicted by using first-principles calculations, which is, however, restricted to a small unit cell. Here, we adopt a machine-learning algorithm to propose a physically intuitive descriptor by which the band gap of any heterostructures can be readily obtained, using group III, IV, and V elements as examples of the constituent atoms. The strong predictive power of our approach is demonstrated by high Pearson correlation coefficient for both the training (292 entries) and testing data (33 entries). By utilizing such a descriptor, which contains only four fundamental properties of the constituent atoms, we have rapidly predicted the gaps of 7140 possible heterostructures that agree well with first-principles results for randomly selected candidates.

Efficient blue light-responsed dithienylethenes with exceptional photochromic performance

Three novel dithienylethenes modified by bifluoroboron β-diketonate fragments have been successfully developed. Upon blue light irradiation, they reached photostationary state within 2–5 s, as well as 100% conversion ratio and photocyclization quantum yield of > 0.70. Such fascinating photochromism were endowed by collaborative role of electron-withdrawing effect of BF2bdk group to reduce HOMO-LUMO electronic gap for the open isomer, together with intramolecular hydrogen bonds and CH-π interactions favoring antiparallel conformation fixation. Moreover, they displayed specific discrimination and photoswitchable bacterial imaging for S. aureus.

Intermolecular charge-transfer complexes between chlorothiazide antihypertensive drug against iodine sigma and picric acid pi acceptors: DFT and molecular docking interaction study with Covid-19 protease

The interaction of chlorothiazide (CH) as donor (D) with picric acid (PA) and iodine (I2) as π- and σ-acceptors (A), respectively, gives charge-transfer (CT) complexes as a final products. The reaction of donor and acceptors were studied spectrophotometrically. The complexes are generally of the n-π* and n-σ* types, with the ground state wave function primarily characterized by the non-bonding structure. For the micro determination of chlorothiazide using picric acid and iodine as acceptors, the ideal conditions encouraging the formation of complexes are thoroughly explored. It was discovered that the stoichiometry of the molecular structure is 1:1 (D:A). The equilibrium constant and the molar extinction coefficient were calculated using Benesi-Hildebrand and its modifications. DFT/TD-DFT calculations with B3LYP/LanL2DZ and 6-311G++ level of theory were used to provide comparable theoretical data along with electronic energy gap of HOMO→LUMO. Molecular docking calculations have been performed between CT complexes and Covid-19 protease (6LU7) to study the interaction between them and their inhibitory effect.

Ab Initio Study of Graphene/hBN Van der Waals Heterostructures: Effect of Electric Field, Twist Angles and p-n Doping on the Electronic Properties.

In this work, we study the structural and electronic properties of boron nitride bilayers sandwiched between graphene sheets. Different stacking, twist angles, doping, as well as an applied external gate voltage, are reported to induce important changes in the electronic band structure near the Fermi level. Small electronic lateral gaps of the order of few meV can appear near the Dirac points K. We further discuss how the bandstructures change applying a perpendicular external electric field, showing how its application lifts the degeneracy of the Dirac cones and, in the twisted case, moves their crossing points away from the Fermi energy. Then, we consider the possibility of co-doping, in an asymmetric way, the two external graphene layers. This is a situation that could be realized in heterostructures deposited on a substrate. We show that the co-doping acts as an effective external electric field, breaking the Dirac cones degeneracy. Finally, our work demonstrates how, by playing with field strength and p-n co-doping, it is possible to tune the small lateral gaps, pointing towards a possible application of C/BN sandwich structures as nano-optical terahertz devices.

Oxidation Potential Gap (ΔEox): The Hidden Parameter in Redox Chemistry

AbstractOxidative biaryl coupling of aryls with different electronic features generally fails. However, this has not been systematically studied via theoretical analysis, and thus, the crucial factor governing coupling efficiency remains unclear. Herein, we propose that the “oxidation potential gap (ΔEox)” is a key parameter in predicting the efficiency of an intramolecular oxidative coupling reaction, with ΔEox defined as a difference in the oxidation potentials of the relevant aromatic rings. Our experimental and computational analyses revealed that the efficiency of an aromatic intramolecular coupling reaction correlates with the activation energy (ΔE≠) of C−C bond formation of the radical cation intermediates. Furthermore, ΔE≠ correlates with ΔEox. Therefore, we demonstrate the tuning of ΔEox by attaching cleavable extra electron‐donating/‐withdrawing groups, enabling the rational synthesis of a phenanthridone skeleton using aromatic rings with an electronic gap.

Oxidation Potential Gap (ΔEox ): The Hidden Parameter in Redox Chemistry.

Oxidative biaryl coupling of aryls with different electronic features generally fails. However, this has not been systematically studied via theoretical analysis, and thus, the crucial factor governing coupling efficiency remains unclear. Herein, we propose that the "oxidation potential gap (ΔEox )" is a key parameter in predicting the efficiency of an intramolecular oxidative coupling reaction, with ΔEox defined as a difference in the oxidation potentials of the relevant aromatic rings. Our experimental and computational analyses revealed that the efficiency of an aromatic intramolecular coupling reaction correlates with the activation energy (ΔE≠ ) of C-C bond formation of the radical cation intermediates. Furthermore, ΔE≠ correlates with ΔEox . Therefore, we demonstrate the tuning of ΔEox by attaching cleavable extra electron-donating/-withdrawing groups, enabling the rational synthesis of a phenanthridone skeleton using aromatic rings with an electronic gap.

Floquet electronic bands and transport in magic-angle bilayer graphene

We theoretically study Floquet band structures and transport properties of twisted bilayer graphene at the magic-angle under the irradiation of variously polarized light. The magic-angle bilayer graphene is depicted by the newly proposed ten-band tight-binding model and the iterative continued fraction method is adopted to facilitate the calculations of electronic properties in the low-frequency regime. The transitions between Floquet sidebands induce discontinuous electronic bands and energy gaps which further give rise to the antiresonances in longitudinal conductivity calculated by the Kubo formula. Furthermore, significant Hall conductivity is generated by circularly polarized light and its magnitude and sign are sensitive to light polarization as well as photoinduced bandgap-opening, offering a feasible way to tune Hall conductivity by manipulating light polarization. We finally take into account the interplay between light irradiation and short-range disorder, and reveal that disorder scattering remarkably enhances the photoinduced Hall conductivity and can be viewed as an extrinsic source to Hall conductivity.

Simple development of eco-friendly dye-sensitized solar cells via controlling thickness of TiO2 nanoparticles and viscosity of electrolyte: Experimental study and DFT calculations

The pigments (N3 dye, anthocyanin, and oleandrin) that absorb light in the visible region, change electrolyte viscosity KI/I2 by adding polyethylene glycol (PEG), and the painting method of TiO2 using the spray and doctor-blade methods was studied. The ultraviolet–visible (UV–VIS) spectra of natural dyes showed strong bands in the visible regions at 350–450 nm. The Fourier-transform infrared (FTIR) spectra confirmed the formation of the N3-triodide complex which was not observed for the other natural dyes. The impact of the changing of viscosity by the addition of PEG improved the current flow in dye-sensitive solar cells (DSSCs). Scanning electron microscopy (SEM) images showed a homogenous and thin film of TiO2 by using the spray method. The efficiency of N3-DSSCs jumped and reached 0.2770% by the sprayed method in PEG-KI/I2 electrolyte. The efficiencies of 0.195 and 0.089 % for BB and NO-DSSCs were recorded in PEG-KI/I2 electrolytes, respectively. A low-cost carbon counter electrode was used in fabricating for DSSCs. The reduction in the values of RSH (shunt resistance) had a negative impact on the performance of DSSCs. Density functional theory (DFT) calculations were studied for optimized geometry of the three dyes. The chemical potential µ of N3 was greater than that of anthocyanin, and oleandrin which reflects the ability of electrons to exchange with TiO2. The Eg (energy gap) of N3 got to a height that slowed the rate of recombination of electron-hole of dye. The electronic chemical potential (µ) and energy gap (Eg) are effective to improve the efficiency of DSSCs.

Covalent Triazine Frameworks with Defective Accumulation Sites: Exceptionally Modulated Electronic Structure for Solar-Driven Oxidative Activation of Peroxymonosulfate.

Precisely tailoring the electronic structure and surface chemistry of metal-free covalent triazine frameworks (CTFs) for efficient photoactivation of oxyanions is environmentally desirable but still challenging. Of interest to us in this work was to construct artificial defective accumulation sites into a CTF network (CTF-SDx) to synchronously modulate both thermodynamic (e.g., band structure) and kinetic (e.g., charge separation/transfer/utilization and surface adsorption) behaviors and probe how the transformation affected the subsequent activation mechanism of peroxymonosulfate (PMS). With the incorporation of terminal cyano (-CN) groups and boron (B) dopants, the delocalized CTF-SD underwent a narrowed electronic energy gap for increased optical absorption as well as a downshifted valence band position for enhanced oxidation capacity. Moreover, the localized charge accumulation regions induced by the electron-withdrawing -CN groups facilitated the exciton dissociation process, while the adjacent electron-deficient areas enabled strong affinity toward PMS molecules. All of these merits impelled the photoactivation reaction with PMS, and a 15-fold enhancement of bisphenol-A (BPA) removal was found in the CTF-SD2/PMS/vis system compared with the corresponding pristine CTF system. Mechanistic investigations demonstrated that this system decomposed organics primarily through a singlet oxygen-mediated nonradical process, which originated from PMS oxidative activation over photoinduced holes initiated by an electron transfer process, thereby opening a new avenue for designing an efficient PMS activation strategy for the selective oxidation of organic pollutants.

Phonon-Limited Mobility in h-BN Encapsulated AB-Stacked Bilayer Graphene.

The weak acoustic phonon scattering in graphene monolayer leads to high mobilities even at room temperatures. We identify the dominant role of the shear phonon mode scattering on the carrier mobility in AB-stacked graphene bilayer, which is absent in monolayer graphene. Using a microscopic tight-binding model, we reproduce experimental temperature dependence of mobilities in high-quality boron nitride encapsulated bilayer samples at temperatures up to ∼200 K. At elevated temperatures, the surface polar phonon scattering from boron nitride substrate contributes significantly to the measured mobilities of 15 000 to 20000 cm^{2}/Vs at room temperature and carrier concentration n∼10^{12} cm^{-2}. A screened surface polar phonon potential for a dual-encapsulated bilayer and transferable tight-binding model allows us to predict mobility scaling with temperature and band gap for both electrons and holes in agreement with the experiment.

Copper(II) Schiff base complex derived from salen ligand: structural investigation, Hirshfeld surface analysis, anticancer and anti-SARS-CoV-2

This work deals with the synthesis and characterization of copper(II) complex [Cu(salen)(H2O)](1) of salen-type Schiff base ligand derived from the condensation of 5-bromo-2-hydroxy-3-methoxybenzaldehyde and ethylenediamine in EtOH. This complex was characterized by different spectroscopic and physicochemical methods. Single crystal X-ray crystallography study revealed that Cu(II) in complex (1) is five-coordinate and adopts a distorted square pyramidal geometry. A DFT calculation was employed to evaluate the optimized electronic structure, HOMO-LUMO, energy gap, and global parameters. A detailed structural and non-covalent interaction on the complex is investigated by single crystal structure analysis and computational approaches. The strength of the interaction and 3D topology of the crystal packing are visualized through an energy framework. Hirshfeld surface and 2D fingerprint plots have been explored in the crystal structure of the complex. The anticancer properties of copper(II) complex was studied against the selected cancerous cell lines of breast cancer, cervical cancer, colon cancer and hepatocellular carcinoma. Additionally, molecular docking and MD simulations was performed on the complex to predict the binding mode and interactions between the ligand and the main protease of the SARS-CoV-2 (PDB ID: 7CBT and 7D1M). The molecular docking calculations of the complex (1) with SARS-CoV-2 virus revealed the binding energy of –8.1 kcal/mol and –7.5 kcal/mol with an inhibition constant of 3.245 µM and 2.318 µM at inhibition binding site of receptor towards 7CBT and 7D1M main protease (Mpro), respectively. Besides this, molecular docking results (–7.6 kcal/mol, 3.196 µM) towards Escherichia coli PBP2 targets (PDB ID: 6G9S) was also studied. Communicated by Ramaswamy H. Sarma

Highly tunable and strongly bound exciton in MoSi2N4 via strain engineering

Motivated by the recently synthesized layered material MoSi2N4, we investigated excitonic response of quasiparticle of monolayer MoSi2N4 by using G0W0 and Bethe-Salpeter equation (BSE) calculations. With a dually sandwiched structure consisting of a central MoN2 layer analogue of 2H-MoS2 capped with silicon-nitrogen (SiN) honeycomb outer layers, MoSi2N4 possesses frontier orbitals confined at the central MoN2 layer with similar sub-valley at K-point as 2H-MoS2. The valley splitting (~130 meV) due to the spin-orbital coupling (SOC) gives rise to a doublet in the spectrum. Excitons in MoSi2N4 shows a strong binding energy up to 0.95 eV with the optical bandgap of 2.44 eV. Both electronic and optical gaps are highly sensitive to tensile strains and become redshift albeit a marginal change of exciton binding energy. With the protection of capped SiN layers, quantum confined excitons in MoSi2N4 without the need of additional passivation layer like BN would provide a bright new platform for robust emission with partially screened disturbance from environment.

Direct and alternating magnon spin currents across a junction interface irradiated by linearly polarized laser

The developments in the field of quantum optics raise expectations that laser-matter coupling is a promising building block for magnonics. Here, we propose a method for the generation of direct and alternating spin currents of magnons across the junction interface irradiated by linearly polarized laser. In a junction of ferromagnetic insulators with a large electronic gap, the spin angular momentum is exchanged during the tunneling process of magnons across the junction interface. The advanced technology in the field of plasmonics and metamaterials realizes that spins irradiated by the laser field interact only with the magnetic component of the laser through the Zeeman coupling. Using an analytic perturbation theory, we provide a general formula for magnon transport induced by the inversion symmetry breaking across the junction interface. Then, we show that those spin currents are enhanced by the ferromagnetic resonance, and the period of the ac spin current is one-half of that of the laser magnetic field. Finally, we estimate the magnitude of the spin current, and find that it will be within experimental reach.

Synthesis, experimental and theoretical analyses of bis(2-ethylphenyl)phosphorodithioates of nickel(II)

Bis(2-ethylphenyl)dithiophosphates of nickel(II) of the composition [{(2-C2H5)C6H4O}2PS2]2Ni (1) and [{(2-C2H5)C6H4O}2PS2(C5H5N)]2Ni (2) were isolated successfully and characterized by experimental and theoretical analyses. Single crystal X-ray diffraction analysis of the complex (2) exhibits that nickel atom is hexa-coordinated with four sulfur atoms of dithio moiety at the equatorial position and two nitrogen atoms of pyridine on axial position. In addition, several non-covalent interactions were also observed that assist to form supramolecular architecture. An exhaustive investigation of the Hirshfeld surface (HS) analysis enables contributions to the crystal packing of the complex (2). The non-covalent interactions were identified using HS and two dimensional finger print plot (2D-FP) analysis. DFT/TD-DFT studies were also used to provide comparable theoretical data along with MEP map and electronic energy gap of HOMO→LUMO.

Highly anisotropic mechanical and optical properties of 2D NbOX2 (X = Cl, Br, I) revealed by first-principle

In the latest experimental success, NbOI2 two-dimensional (2D) crystals with anisotropic electronic and optical properties have been fabricated (Adv. Mater. 33 (2021), 2101505). In this work inspired by the aforementioned accomplishment, we conduct first-principles calculations to explore the mechanical, electronic, and optical properties of NbOX2 (X = Cl, Br, I) nanosheets. We show that individual layers in these systems are weakly bonded, with exfoliation energies of 0.22, 0.23, and 0.24 J m−2, for the isolation of the NbOCl2, NbOBr2, and NbOI2 monolayers, respectively, distinctly lower than those of the graphene. The optoelectronic properties of the single-layer, bilayer, and bulk NbOCl2, NbOBr2, and NbOI2 crystals are investigated via density functional theory calculations with the HSE06 approach. Our results indicate that the layered bulk NbOCl2, NbOBr2, and NbOI2 crystals are indirect gap semiconductors, with band gaps of 1.79, 1.69, and 1.60 eV, respectively. We found a slight increase in the electronic gap for the monolayer and bilayer systems due to electron confinement at the nanoscale. Our results show that the monolayer and bilayer of these novel 2D compounds show suitable valence and conduction band edge positions for visible-light-driven water splitting reactions. The first absorption peaks of these novel monolayers along the in-plane polarization are located in the visible range of light which can be a promising feature to design advanced nanoelectronics. We found that the studied 2D systems exhibit highly anisotropic mechanical and optical properties. The presented first-principles results provide a comprehensive vision about direction-dependent mechanical and optical properties of NbOX2 (X = Cl, Br, I) nanosheets.

Effect of Molar Concentration on the Structural and Optical Properties of the Cd2SnO4 Thin Films

In this paper, cadmium stannate (Cd2SnO4) thin films at four different molar concentrations (1:1, 2:1, 3:1, and 4:1) were prepared at a temperature of (400 oC) using a chemical spray pyrolysis technique and have a thickness of about 400±10 nm. XRD patterns of the prepared thin films showed that the thin films have both a polycrystalline and a cubic structure. FE-SEM and AFM were used to investigate the surface morphology of Cd2SnO4 thin films. The measurement of absorbance and transmittance spectra for films in the range of 300–900 nm was part of the optical properties research. The effect of various molar concentrations of these films on transmittance was investigated, and the results revealed a decrease in transmittance. The allowed direct electronic transmission optical energy gap was calculated, and it was discovered that it decreases as the molar concentrations increase, with a value ranging between (2.61-2.91) eV.

Monitoring flame soot maturity by variable temperature Raman spectroscopy

Flame-formed soot nanoparticles are known to possess different nanostructures as a function of a large variety of combustion operative parameters, including particle residence time in flames, flame stoichiometry, fuel chemical composition, temperature and pressure. This implies that important properties (e.g., soot oxidation reactivity, optical and electronic gap) may be different depending on the way soot particles are generated. Hence, it is beneficial to develop diagnostic methods that are sensitive to such differences among the various kinds of soot particles. In this work we investigate by off-line variable-temperature Raman spectroscopy two types of soot particles, namely just-nucleated and aged/mature particles, with a different size and maturity degree. The results obtained for soot particles have been compared and discussed with those found for other related carbon materials. As the Raman spectra are recorded at increasing sample temperature, from 300 to 525 K, both soots display a linear downshift of the position of the two main Raman modes (D and G bands). Just-nucleated soot particles exhibit the strongest temperature dependence of the position of the G band. Based on results from density functional theory calculations, interpreted by a simple empirical model, the observed temperature coefficient differences can be ascribed to differences in the nanostructural order of the two soot samples, which causes a different thermal expansion behavior.

Multiple low-energy excitons and optical response of [formula omitted] double perovskite Ba[formula omitted]ScTaO[formula omitted

Large bandgap insulators are considered promising for applications such as photocatalysts, dielectric resonators and interference filters. Based on synchrotron X-ray diffraction, diffuse reflectance measurement and density functional theory, we report the crystal structure, optical response, and electronic properties of the synthesized d0 double perovskite Ba2ScTaO6. In contrast to earlier prediction, the electronic bandgap is found to be large, ∼4.66eV. The optical response is characterized by the presence of multiple exciton modes extending up to the visible range. A detailed investigation of the direct gap excitons based on the Elliot formula is presented. Density functional theory based investigation of the electronic properties within generalized gradient approximation severely underestimates the electronic gap. To reach a quantitative agreement, we consider different available flavors of the modified-Becke–Johnson exchange–correlation potential and discuss their effects on the electronic and optical properties.

Effects of Mechanical Deformation on the Opto-Electronic Responses, Reactivity, and Performance of Conjugated Polymers: A DFT Study.

The development of polymers for optoelectronic applications is an important research area; however, a deeper understanding of the effects induced by mechanical deformations on their intrinsic properties is needed to expand their applicability and improve their durability. Despite the number of recent studies on the mechanochemistry of organic materials, the basic knowledge and applicability of such concepts in these materials are far from those for their inorganic counterparts. To bring light to this, here we employ molecular modeling techniques to evaluate the effects of mechanical deformations on the structural, optoelectronic, and reactivity properties of traditional semiconducting polymers, such as polyaniline (PANI), polythiophene (PT), poly (p-phenylene vinylene) (PPV), and polypyrrole (PPy). For this purpose, density functional theory (DFT)-based calculations were conducted for the distinct systems at varied stretching levels in order to identify the influence of structural deformations on the electronic structure of the systems. In general, it is noticed that the elongation process leads to an increase in electronic gaps, hypsochromic effects in the optical absorption spectrum, and small changes in local reactivities. Such changes can influence the performance of polymer-based devices, allowing us to establish significant structure deformation response relationships.