Binding Energy Eb Research Articles

Highly sensitive and selective sensing properties of modified green phosphorene monolayers towards SF6 decomposition gases

Gas sensing properties of pristine, defective and heteroatom substituted green phosphorene (GP) monolayers towards SF6 components such as H2S, SO2, SO2F2, SOF2 are investigated by using van der Waals corrected density function theory calculations. The adsorptions of H2S and SOF2 on pristine GP are found to be exothermic with weak binding energies (Eb) of-0.065 and -0.017 eV respectively, whereas the interactions of SO2 and SO2F2 are endothermic. We found that various vacancy defects and heteroatom substitutions enhance the Eb values of H2S, SO2, SO2F2 and SOF2 to -0.84,-1.04,-0.40and -0.73eV, respectively which are within desired range for efficient gas sensing applications. Presence of selected substituents (Al, B, C, S, Si) and vacancy defects result into measurable variations in electronic properties of GP upon the exposure of sulphur containing gases. We found that B- and S-doped GP systems show selectivity towards H2S and SO2, with Eb values of -0.57eV for H2S and -1.03eV for SO2. We believe that modified GP has potential to be used as excellent sensing material towards SF6 decomposition gases.

Young apple polyphenols as natural α-glucosidase inhibitors: In vitro and in silico studies.

In this study, the inhibitory activity of young apple polyphenols (YAP) on α-glucosidase was investigated. Composition and inhibition analyses suggested that tannic acid (TA), (-)-epicatechin (EC) and phlorizin (PH) were the main active constituents in YAP showing α-glucosidase inhibition. PH was a competitive inhibitor, while YAP, TA and EC were the mixed-type ones. YAP, TA, PH and EC quenched the fluorescence spectrum of α-glucosidase significantly. Interestingly, the constants that indicate binding interaction between α-glucosidase and TA, PH, EC, including reciprocal of competitive inhibition constant (1/Kic), fluorescence quenching constant (KFQ) and binding energy (Eb), were shown similar orders as TA>PH>EC, contrary to IC50 values. This indicates that binding interactions between polyphenols and α-glucosidase caused the enzyme inhibition. Additionally, potential enzyme unfolding by polyphenols interactions indicated by red-shift of maximum emission wavelength is supported by the decrease in α-helix and β-sheet contents of the enzyme. Conclusively, the α-glucosidase inhibition indicates that YAP may have potentials in alleviation of type 2 diabetes symptom.

Light-reflection-induced changes in the line shape of sputtered atoms

The erosion from plasma-facing components has to be monitored in many kind of laboratory and fusion plasmas. For this purpose, spectroscopy is an essential tool. Under certain conditions the particle flux can be calculated from the absolute line intensities of the sputtered material using so-called S/XB values. The impact of light reflection on the emission induced by sputtered particles at the mirror-grade polished surface of tungsten (W) and aluminum (Al) was investigated in a low-density (ne ≈ 2 × 1012 cm−3) and low-temperature (Te ≈ ) argon (Ar) plasma in the linear plasma device PSI-2 using high-resolution spectroscopy. Using the line shape affected by Doppler shift we show that the light reflection has a considerable impact on the number of measured photons and has to be taken into account for calculating particle fluxes. The Al target was sputtered by Ar ions at the incident ion energy of . The measured profile of the Al I line () was compared with a Doppler-shifted emission model based on the Thompson energy distribution function. In this new model, the instrumental broadening and the impact of the Zeeman effect were also taken into account. The parameter for the high-energy fall-off n of the energy distribution function (), the surface binding energy Eb and the surface reflectance were derived by comparing the experimental and the synthetic spectrum. The W target was sputtered by Ar ions at incident ion energies in the range of –. The influence of the ion impact energy on the energy distribution of the sputtered particles was demonstrated.

Investigation on Structural, Relative Stable, and Electronic Properties of Binary AlnLin (n = 2 – 12) Clusters through Density Functional Theory

In the present research, the structural, the relative stable, and the electronic properties of AlnLin (n = 2 – 12) clusters were investigated by density functional theory (DFT). By comparing the calculated values of Al2 and Li2 dimers with experimental ones, the reliability of the proposed method was proved. Furthermore, by considering the values of average binding energy (Eb), vertical ionization potential (VIP), vertical electron affinity (VEA), fragmentation energy (△E), second-order energy difference (△2E), HOMO-LUMO (HL) gap, and chemical hardness (η) were calculated. It was found Fragmentation energy, second-order energy difference, VIP, VEA, the chemical stability and HOMO-LUMO gap exhibit odd-even oscillatory behaviours along with cluster size and have extreme values at n = 5 revealed Al5Li5 cluster yielded excellent stability. Those can be well explained by the density of states (DOS) that Li and Al atoms with stronger covalent bonds. Therefore, Al5Li5 cluster can be used as an ideal candidate for calculating Wilson parameters of Al-Li alloys.

Methylammonium-Mediated Crystallization of Cesium-Based 2D/3D Perovskites toward High-Efficiency Light-Emitting Diodes.

Two-dimensional (2D)/three-dimensional (3D) perovskites have been successfully applied in high-efficiency light-emitting diodes (LEDs) because of their large exciton binding energy (Eb) caused by the quantum and dielectric confinements. Thermal annealing and antisolvent treatments are usually executed in order to promote the crystallization and film quality of perovskites, which add complexity to the device fabrication process. Here, the cesium-based 2D/3D perovskite was prepared by introducing ammonium halide benzamidine hydrochloride (BMCl) as the additive. By further introducing an appropriate amount of MABr and PbBr2, BM2(Cs1-xMAxPbBr3)n-1PbBr4 crystals can be formed rapidly without any additional treatments, while inhibiting the formation of the unfavorable Cs4PbBr6 phase. The optimized 2D/3D perovskite-based LEDs achieved a maximum luminance of 12 367 Cd/m2, a current efficiency of 17.4 Cd/A, and an external quantum efficiency of 5.2%. Our results suggest that appropriate perovskite crystallization can be achieved at room temperature by the regulation of precursor solution, making the perovskite crystallization process easier to control with reduced processing complexity.

ATP Mimics pH-Dependent Dual Peroxidase-Catalase Activities Driving H 2 O 2 Decomposition

Adenosine triphosphate (ATP) is produced mainly in the mitochondrion, and its primary task is to function as a ubiquitous energy currency to meet the cellular metabolic demands in biological system...

Density functional theory study of structural, magnetic and spectral properties of the CrmFen (m + n = 6) and CrmFenCu (m + n = 5) clusters

Using Density functional theory (DFT) to study the geometries, stability, magnetic properties and infrared spectroscopy of CrmFen (m + n = 6) and CrmFenCu (m + n = 5) clusters at the BP86/SDD level. The ground state structures of CrmFen (m + n = 6) and CrmFenCu (m + n = 5) clusters are determined according to the principles of lowest energy and no virtual frequency. On this basis, the structural and chemical stabilities are obtained by the average binding energies (Eb), chemical hardness (η) and HOMO-LUMO energy gap (Eg). The average binding energies show the substitution of a copper atom is beneficial to improve the structural stability; It can be seen Cr4Fe2 and Cr3Fe2Cu have the best chemical stability in the two cluster series from the chemical hardness and HOMO-LUMO energy gap. By calculating the magnetic moment, it is shown that Cr5Fe and CrFe4Cu have large magnetic moments, which can be understood by the spin distribution. Finally, infrared spectroscopy of the clusters are calculated, we find a copper atom substitutes the CrmFen (m + n = 6) does not change the range of vibration frequency a lot because it does not significantly change the molecular structure of the original cluster, but it changes the vibration mode of the original cluster, resulting in the strongest infrared absorption peak intensity of Cr3Fe2Cu being lower than that of Cr3Fe3.

Excited-state engineering of universal ambipolar hosts for highly efficient blue phosphorescence and thermally activated delayed fluorescence organic light-emitting diodes

The development of high-performance universal host materials for both blue electrophosphorescence and thermally activated delayed fluorescence (TADF) is one of the main challenges for organic light-emitting diode (OLED) technology. In this work, based on four quaternary ambipolar hosts with insulated donor-acceptor (D-A) structures, the influence of the excited-state characteristics for these hosts on their device performance was systematically investigated. It was showed that on the premise of the similar electrical properties and excited-state energy levels for positive host-dopant energy transfer (ET), the weak exciton capture ability, embodied as low exciton binding energy (Eb), for the hosts could facilitate the Dexter ET to the dopant through charge migration. Since the charge-transfer -featured excited states and small Eb of blue TADF emitters, in contrast to the blue phosphorescence (PH) counterparts, the influence of the host Eb on the device efficiencies of blue TADF dyes was dramatically enlarged, reflecting the higher sensitivity of the latter to host characteristics. In consequence, 9CzFDBFDPO with the smallest Eb endowed its blue TADF and PH devices with the state-of-the-art performance, e.g. EQE beyond 20% and EQE roll-off within 20% at 500 cd m−2. This work showed that based on the systematically optimized excited-state characteristics, the ambipolar hosts can be competent in both high-efficiency blue PH and TADF OLEDs, which is crucial for their commercial applications.

Achieving Small Exciton Binding Energies in Small Molecule Acceptors for Organic Solar Cells: Effect of Molecular Packing.

Because of strong exciton binding energy (Eb), an exciton dissociation process and extra energy losses are present in organic solar cells relative to inorganic and perovskite solar cells. Here, we calculated the Eb of a series of small molecule acceptors in solid crystals by a self-consistent quantum mechanics/embedded charge approach. The results show that the Eb values are substantially reduced from the gas phase to solid state because of electronic polarization (mainly from the induction effect of charges). Moreover, in contrast to little changes in the gas phase, the Eb in the solid state can vary significantly, indicating an important molecular packing effect. Remarkably, an extremely weak Eb of 0.04 eV is achieved in a three-dimensional packing crystal, which is comparable to the Eb of organo-lead trihalide perovskites. This work underlines the importance of three-dimensional molecular packing for achieving small Eb and will be helpful in reducing energy losses in organic solar cells.

Direct Determination of Band-Gap Renormalization in the Photoexcited Monolayer MoS_{2}.

A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to a large exciton binding energy (E_{b}) and strong renormalization of the quasiparticle band gap (E_{g}) by carriers. The latter has been difficult to determine due to a cancellation in changes of E_{b} and E_{g}, resulting in little change in optical transition energy at different carrier densities. Here, we quantify band-gap renormalization in macroscopic single crystal MoS_{2} monolayers on SiO_{2} using time and angle-resolved photoemission spectroscopy. At an excitation density above the Mott threshold, E_{g} decreases by as much as 360meV. We compare the carrier density-dependent E_{g} with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the band gap.

Effect of electron‐withdrawing groups on photovoltaic performance of thiophene‐vinyl‐thiophene derivative and benzochalcogenadiazole based copolymers: A computational study

AbstractWe report a density functional theory study of the effect of electron‐withdrawing groups such as –F, –CN, –NO2 on the geometrical, optoelectronic, intramolecular charge transfer (ICT), and photovoltaic properties of (E)‐1,2‐bis(5‐alkyl‐[2,3′‐bithiophene]‐2′‐yl)ethene (TVT‐T) based donor‐acceptor (D‐A) copolymers with different acceptor units, that is, benzo[c][1,2,5]thiadiazole, benzo[c][1,2,5]oxadiazole, and benzo[c][1,2,5]selenadiazole. The computed optical absorption spectra of the designed compounds lie in the visible and near‐infrared regions. Of all the studied copolymers, ‐CN substituted and Se‐based compound displays the lowest HOMO‐LUMO (E H ‐ L) gap and optical band gap (E opt). The exciton binding energy (E b) is found to be smaller for O‐incorporated compounds and ‐CN substituted copolymer as well, inferring more ICT. The electron‐hole coherence concentrated over the D‐A units is nearly the same for ‐CN and ‐NO2 substituted compounds, but larger in ‐F derivatives, indicating weak electron‐hole coupling in the formers. Comparatively larger dipole moment (6.421 Debye‐9.829 Debye) and charge transfer length (D CT) (1.976 Å‐3.122 Å) for ‐CN derivatives lead to enhanced ICT properties. The designed donors yield good hole mobilities (0.127‐6.61 cm2 V−1 s−1) and the predicted power conversion efficiencies are calculated to be as high as ~6%‐7% for –CN and –NO2 substituted compounds.

Influence of screening dynamics on excitons in Ga2O3 polymorphs

Exciton binding energies EB measured for α- and β-Ga2O3 crystals seem to be not explainable in the Wannier-Mott picture. However, we demonstrate theoretically that including screening dynamics and effective mass anisotropy, reasonable values EB = 184 meV (α) or 230 meV (β) are derived. Since the binding energies are larger than the phonon frequencies, the exciton formation is so fast that only about 5% of the lattice polarizability contributes to the screening of the electron-hole attraction. Effective dielectric constants possess values between the complete static ones and the electronic high-frequency dielectric constants. They indeed depend on the polymorph.

The Studies on Structure and Stability of CaBn Clusters.

Calcium-boron systems have excellent properties of hardness, strength, and chemical stability, and we studied a series of CaBn clusters to investigate their structures and relative stability. The results showed the most stable structures of CaBn clusters are not planar. The B atoms tend to get together and form the planar ring to stabilize the structure, and the Ca atoms are coordinated to the periphery of the formations. The average binding energy (Eb), fragmentation energy (EF), second-order energy difference (Δ2E), adiabatic detachment energy (ADE), and adiabatic electron affinity (AEA) of the CaBn clusters were calculated to investigate the relative stability and the ability of removing or obtaining an electron. As shown by the results, EF and Δ2E values had obvious odd-even alteration as n increased, which indicated that the formations CaB4, CaB6, and CaB8 were more stable. The ADE values for CaBn clusters with even values of n were higher than those with odd values of n, which indicated CaBn clusters with even values of n had difficultly removing an electron. The AEA values of CaB3 and CaB7 were larger than the others, which meant CaB3 and CaB7 easily obtained an electron. These results provide a useful reference for understanding the formation mechanism and stability of the alkaline earth metal boride as well as guidance for synthesizing the CaBn clusters.

DFT study of small gas molecules adsorbed on undoped and N-, Si-, B-, and Al-doped graphene quantum dots

A theoretical study about the interaction between small gas molecules (H2O, CO, CO2, NH3, and CH4) with graphene quantum dots (GQDs) was performed. To develop gas sensors with ultralow detection levels, the nature of the bonds between the gas molecules and the GQDs should be understood and controlled. It was found that the binding energy (Eb) of the gas molecules with the GQDs can be controlled if the GQDs are doped. In the first part of the investigation, a choice of appropriated exchange/correlation functionals and basis sets was achieved. After this, the pure generalized gradient approximation (GGA) functionals, including the non-local (NL) density-dependent dispersion correction and the atom-pairwise dispersion correction (D3), were employed and found that they described accurately the Eb for the adsorption of water on GQDs. The use of NL and D3 corrected GGA functionals revealed that the Eb for the adsorption of H2O, CO, and NH3 on Si- and Al-doped GQDs can be improved, which indicates that the detection limit for the detection of these gases can be enhanced. To understand the nature of the bonds involved in the adsorption, different approaches were used, such as the quantum theory of atom in molecules and the electron localization function.

Temperature-dependent studies of exciton binding energy and phase-transition suppression in (Cs,FA,MA)Pb(I,Br)3 perovskites

Multiple-cation mixed-halide (Cs,FA,MA)Pb(I,Br)3 perovskites containing cesium, formamidinium (FA), and methylammonium (MA) possess excellent properties for a wide range of optoelectronic applications such as thin-film photovoltaics or lasers. We investigate the role of excitons and the exciton binding energy EB, relevant for the effectiveness of charge separation in solar cells, as well as the temperature-dependent bandgap energy Eg which is used as an indicator for crystal phase transitions. Generalized Elliott fits of absorption spectra offer the possibility to determine both EB and Eg. However, since excitonic effects are non-negligible even at room temperature, a careful and detailed analysis of the spectra is crucial for a correct interpretation. Therefore, an additional evaluation based on a so-called f-sum rule is applied to achieve an improved reliability of the results at higher temperatures. The obtained EB values of 20–24 meV for Cs-containing mixed perovskite compounds are below the ones of 24–32 meV and 36–41 meV for pure methylammonium lead iodide (MAPbI3) and bromide (MAPbBr3), respectively, and, thus, facilitate charge-carrier separation in photovoltaic applications. Furthermore, temperature-dependent (T = 5–300 K) studies of Eg in (Cs,FA,MA)Pb(I,Br)3 indicate a suppressed crystal phase transition by the absence of any phase-transition related signatures such as the well-known jump of about 100 meV in MAPbI3. We verify these results using temperature-dependent electroreflectance spectroscopy, which is a very reliable technique for the direct and non-destructive determination of optical resonances of the absorber layer in complete solar cells. Additionally, we confirm the suppression of the phase transition in Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 by temperature-dependent X-ray diffraction.

Surface Ligand Engineering for Efficient Perovskite Nanocrystal-Based Light-Emitting Diodes.

Lead halide perovskites (LHPs) are emerging as promising materials for light-emitting device applications because of the tunability of the band gap, narrow emission, solution processability, and flexibility. Typically, LHP nanocrystals (NCs) with surface ligands show high photoluminescence quantum yields because of charge-carrier confinement with higher exciton binding energy ( Eb). However, the conventionally used oleylamine (OAm) ligands result in the low electrical conductivity and stability of perovskite NCs (PNCs) because of a long carbon chain without conjugation bonds and weak interaction with the surface of NCs. Here, we report the effect of bulkiness and chain length of ligand materials on the properties and stability of CsPbBr3 PNCs by replacing OAm with other suitable ligands. The effect of the bulkiness of quaternary ammonium bromide (QAB) ligands was systemically studied. The less bulky QAB ligands surrounded the surface of NCs effectively, and brought better surface passivation and less aggregation compared to bulky QAB ligands, and finally the optical property and stability of CsPbBr3 PNCs were enhanced. Furthermore, the electrical property of CsPbBr3 PNCs was optimized by tuning the long-chain length of QAB ligands for balanced charge-carrier transport. Finally, we achieved highly efficient green emissive CsPbBr3 PNC light-emitting diodes (LEDs) by using PNCs with optimized didecyldimethyl ammonium bromide ligands with a current efficiency of 31.7 cd A-1 and external quantum efficiency of 9.7%, which were enhanced 16-fold compared to those of CsPbBr3 LEDs using PNCs with conventional OAm ligands.

4D texture of circular dichroism in soft-x-ray photoemission from tungsten

Photoemission-intensity distributions IRCP/LCP (EB, k) measured for right- and left-circularly polarized soft x-rays revealed a large circular dichroism in angular distribution (CDAD) in the 4D parameter space (EB binding energy, k momentum vector). Full-field k-imaging combined with time-of-flight energy recording at a high-brilliance soft x-ray beamline allowed mapping the CDAD in the bulk Brillouin zone of tungsten and the entire d-band complex within a few hours. CDAD-asymmetries are very high (up to 90%), persist throughout the whole photon-energy range (300–1300 eV) and show a pronounced dependence on momentum k and binding energy EB, visualized as movies or sequences of cuts through the 4D object. One-step photoemission calculations for the same photon energies show fair agreement with the measured results. In addition to the requirement of a ‘handed’ experimental geometry, known from previous experiments on adsorbates and surface states, we find an anti-symmetric behavior of the CDAD with respect to two bulk mirror planes. A new symmetry condition along the perpendicular momentum kz makes CDAD a valuable tool for an unambiguous identification of high-symmetry planes in direct transitions in the periodic zone scheme. Technically, the method provides a circular polarimeter for soft, tender and hard x-rays.

Theoretical Prediction of Size-Dependent Structures and Properties for the Asymmetric Clusters (HBrInN3)n (n = 1–6)

In order to search single-source precursors (SSP) for InN material, the structures, relative stabilities, and electronic properties of small asymmetric clusters (HBrInN3)n (n = 1–6) are systematically investigated at the B3LYP level. The optimized clusters all contain cyclic structures (InNα)n and prefer 3-dimensional configurations for n = 2–6. The uncorrected binding energies (Eb), corrected binding energies (Eb-c) and average corrected binding energies (Eb-c-ave) all reveal that all asymmetric clusters (HBrInN3)n (n = 1–6) can continue to gain energy with the cluster size n increasing. The relative stabilities of clusters (HBrInN3 )n (n= 1–6) are analysed based on the second-order difference of energy (Δ2E) and HOMO–LUMO energy gap (Egap). It is found that the Δ2E exhibits a pronounced even–odd alternation phenomenon with variation of the cluster size n. Compared with monomer HBrInN3, the N–N asymmetric stretching of N3 groups for asymmetric clusters (HBrInN3)n (n = 2–6) shows blue-shifted, however, the N–N symmetric stretching of N3 groups and In–H stretching vibration exhibit red-shifted, respectively. Thermodynamic properties increase linearly with the cluster size n as well as the temperature. The transformations of the clusters (HBrInN3)n (n = 2–6) from the monomer are thermodynamically favorable at 298.2 K judged by Gibbs free energies.

Improvement in hydrogen binding ability of closo-dicarboranes via functionalization and designing of extended frameworks.

Neutral closo-dicarboboranes are reported to have very low H2 binding ability. Herein, we report an improvement in H2 binding energy (Eb) of C2B4H6 by substituting H atoms with different functional groups like X = F, Cl, Br, and XY = BO, CN and NC via quantum-chemical density functional theory based computations. In going from B6H62- to C2B4H6, the Eb value is reduced from 14.6kJmol-1 to 2.7kJmol-1. C2B4X6 and C2B4(XY)6 systems, which can bind a total of eight H2 molecules, with one H2 molecule occupying at each B-B-C face, possess an Eb value per H2 in the range of 4.5kJmol-1 for X = F, 3.9kJmol-1 for X = Cl, 5.9kJmol-1 for X = Br, 6.8kJmol-1 for XY = BO, 5.8kJmol-1 for XY = CN and 5.2kJmol-1 for XY = NC. The improvement in Eb value is found to be the highest in case of C2B4(BO)6, which has the ability to bind 6.6 gravimetric wt% of H2. The situation can be made more favorable by applying an external electric field. Energy decomposition analysis reveals that although the dispersion interaction (ca. 55-65%) has significant role in binding H2 with such types of molecules, contribution from electrostatic and orbital interaction is also considerable. Further, we modeled an extended system by linking C2B4(BO)n through 'C ≡ C' units for H2 storage purpose. The energy difference between the highest occupied and the lowest unoccupied molecular orbitals gradually lessens with the increase in molecular length. Therefore, it can be tuned gradually by controlling the chain length, which may further open up their potency in the field of electronics. Graphical abstract C2B4X6 (X = F, Cl, Br) and C2B4(XY)6 (XY = BO, CN, NC) show enhanced H2 binding ability from C2B4H6. Further, 1D, 2D and 3-D frameworks can be built by joining C2B4(BO)n units via 'C ≡ C' linkage.

Excitonic gain and laser emission from mixed-cation halide perovskite thin films

Organic–inorganic halide perovskites have recently developed into a potential semiconductor coherent light emitter candidate beyond their promise in solar cell applications. However, despite the ample demonstrations of perovskite lasers, experimental results on the origin of optical gain in perovskites are still elusive. Here, we analyze the excitonic gain in the green from mixed-cation halide perovskites Cs0.17[CH(NH2)2]0.83PbBr3 (Cs0.17FA0.83PbBr3) by both low temperature absorption/emission spectroscopies and ultrafast pump–probe transient absorption experiments. The perovskite thin films show a robust excitonic feature up to room temperature, with estimated exciton binding energy E b =43.8 meV, which can be maintained under high electronic excitations that are required for lasers. By using a high-quality (Q=1350) vertical cavity consisting of sputtered dielectric HfO2/SiO2 distributed Bragg reflectors with perovskite optical gain medium embedded inside, we have demonstrated excitonic-gain-enabled optically pumped lasing, with improved threshold of 13.5±1.4 μJ/cm2 and device longevity lifetime >35 h (108 laser shots) at ambient environment under sustained pulsed optical excitations (3.493 eV, τpulse=0.34 ns, 1 kHz). Understanding and exploiting excitonic gain from perovskite thin film materials may help to further boost the performance of perovskite-based lasers.