Electronic Transition Probabilities Research Articles

Effect of alloying on the carrier dynamics in high-performance perovskite solar cells

High-efficiency solar cells often require light absorbers prepared from alloys, such as CdTe1−xSex, CuInxGa1−xSe2, Cu2ZnSnS4−xSex, and (CsxFA1−x)Pb(I1−yBry)3. However, how alloying affects solar cell performance is poorly understood, and determining common features associated with alloying is of significant interest. Herein, we studied the correlation between the A/X site compositional ratio and the photo-generated carrier dynamics using mixed halide perovskites (CsxFA1−x)Pb(IyBr1−y)3 as examples. Nonadiabatic molecular dynamics calculations demonstrated that charge carrier recombination is highly sensitive to the compositional ratio at the A/X-site. The enhanced lifetime is attributable to the suppression of atomic fluctuations, the weakening of electron-phonon coupling, and a reduction in the electron-transition probability between band edges. The optimal Br concentration was determined to be ∼18%, in agreement with experimental observations. This study not only advances our understanding of why mixed perovskites usually exhibit superior experimental photoelectric properties, but also provides a route for optimizing the carrier lifetimes and efficiencies of perovskite solar cells.

Effect of inter-wall coupling on the electronic structure and optical properties of group-III doped SiCNTs

The inter-wall coupling mechanism is studied by comparing the group-III doped on the inner and outer walls of DWSiCNTs and SWSiCNTs differs in band structure and optical properties. For DWSiCNTs, B and Ga atoms doping the outer wall is easier to dope, while Al and In doping the inner wall is easier to achieve. DWSiCNTs doped with group-III atoms enhances the inter-wall coupling, and the coupling effect of the inner wall doped DWSiCNTs is stronger than that of the outer wall doped. The inner wall doping has a more obvious regulatory effect on the inter-wall coupling of DWSiCNTs. The absorption and photoconductivity show that in the visible and ultraviolet bands, the intrinsic conductivity peaks of DWSiCNTs are larger and wider. This is because the coupling effect increases the electron transition probability of doped DWSiCNTs, making the carrier concentration greater than SWSiCNTs, and the minority carrier lifetime is longer.

SPECTROSCOPY OF A NON-L TROSCOPY OF A NON-LUMINESCEN UMINESCENT ASSOCI T ASSOCIATE OF INDIGO CARMINE IN SOLUTIONS

Introduction. The food dye Indigo Carmine (E-132) was subjected to spectroscopic studies. It is shown that conditions for their participation in Association processes are created in aqueous and binary mixtures of solvents. The absorption bands against the background of the hypochromic effect in their electronic spectra are determined. Experimentally and by quantum chemical calculations, it is established that the dipole moments of the Indigo Carmine dye in the excited state increase up to 40 % and they contribute to the appearance of a strong dipole-dipole interaction, which results in the unification of Monomeric molecules into an associate. The interaction force (van der Waals) leads to resonant splitting of electronic States and changes in the probability of electron transition from the main excited levels of dye molecules. Research methods. The choice of binary mixtures of solvents was due to the fact that in one of the components of the solvents the dyes under study dissolved well, in the other they practically did not dissolve

ADSORPTION-INDUCED INCREASING SPECULARITY OF CONDUCTION ELECTRONS’ SURFACE SCATTERING

We present a review of our investigations on the increasing specularity of surface scattering of conduction electrons on the W(011), Mo(011), and W(001) surfaces after covering the surfaces with well-ordered (sub)monolayers of adsorbed hydrogen or deuterium. The degree of the specularity of surface scattering was estimated on the base of measurements of magnetoresistance of single-crystalline plates, cooled with liquid He, under ultra-high vacuum conditions, and in a strong magnetic field. The structures of adsorbed hydrogen and deuterium layers were determined from LEED patterns. It is found that the magnetoresistance non-monotonically depends on submonolayer hydrogen coverage and degree of the ordering of adsorbed layers, showing a drastic increase of the specularity (which is higher than for the atomically-clean surfaces!) after the formation of the well-ordered [Formula: see text]-H structures and a pronounced increase of the specularity after the formation of the well-ordered [Formula: see text]-2H structure. Changes in the magnetoresistance induced by the ordering of structures of adsorbed H(D) layers are found to corroborate with the adsorption-induced transformation of Fermi contours of surface electronic states obtained in performed DFT calculations. The increase of the specularity of the scattering caused by the ordering of the surface structures is attributed to the decrease of the probability of electronic transitions between the surface and bulk electronic states induced by surface scattering.

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Molecular docking, quantum chemical computational and vibrational studies on bicyclic heterocycle “6-nitro-2,3-dihydro-1,4-benzodioxine”: Anti-cancer agent

The heterocyclic aromatic compounds are primarily used to make pharmaceutical and agrochemicals. In addition, these compounds can be chosen as antioxidants, corrosion inhibitors, electro and opto-electronic devices, polymer material, dye stuff, developers, etc. On the account of this, the heterocyclic aromatic 6-nitro-2,3-dihydro-1,4-benzodioxine (6N3DB) was chosen and the structure is optimized to predict the important properties of it. The structural parameters such as bond length and bond angle have been obtained by DFT/B3LYP/6-311++G(d,p) basis set to know the geometry and orientation of 6N3DB. The molecule has been characterized by FT-IR and FT-Raman spectroscopic techniques to predict the functional groups, vibrational modes and aromatic nature of 6N3DB. The chemical shifts of 1H and 13C have been obtained experimentally and compared with the theoretical data. The parameters such as the band gap between HOMO-LUMO orbitals, λmax, and electron transition probability in frontier orbitals have been estimated to know the NLO and corrosion inhibition activity. HOMO-LUMO orbital diagram has been obtained for different energy levels and their band gap energies have been compared with UV–vis band gap values. The chemical significance of the molecule has been explained using ELF, LOL, and RDG. The binding energy and intermolecular energy values indicate that the title compound possesses anti-cancer property through hydrolase inhibition activity.

Prediction of the Kinetic Properties of Sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) Solid Solution: an Ab Initio Approach

In the present paper, the interaction of electrons with different types of defects in sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) solid solution is considered. Analysis is carried out by using the short-range scattering models for electron interaction with eight kinds of point lattice defects. Calculation of the electron transition probabilities was made based on the wave function and self-consistent potential energy which were evaluated with the help of ABINIT code. For crystals with impurity concentrations 9.4 × 1014 – 1×1018 cm−3, the temperature dependencies of electron mobility and Hall factor in the range 15–1200 K are calculated. A comparative analysis of two competing approaches has been made: a short-range approach and a long-range approach (relaxation time approximation). It was found that these two approaches yield to essential qualitative and quantitative differences for theoretical temperature dependencies of electron mobility.

Ultrasensitive Plasmon-Free Surface-Enhanced Raman Spectroscopy with Femtomolar Detection Limit from 2D van der Waals Heterostructure.

Two-dimensional (2D) materials have been promoted as an ideal platform for surface-enhanced Raman spectroscopy (SERS), as they mitigate the drawbacks of noble metal-based SERS substrates. However, the inferior limit of detection has limited the practical applicability of 2D material-based SERS substrates. Here, we synthesize uniform large-area ReOxSy thin films via solution-phase deposition without post-treatments and demonstrate a graphene/ReOxSy vertical heterostructure as an ultrasensitive SERS platform. The electronic structure of ReOxSy can be modulated by changing the oxygen concentration in the lattice structure, obtaining efficient complementary resonance effects between ReOxSy and the probe molecule. In addition, the oxygen atoms in the ReOxSy lattice generate a dipole moment on the thin-film surface, which increases the electron transition probability. These synergistic effects outstandingly enhance the Raman effect in the ReOxSy thin film. When ReOxSy forms a vertical heterostructure on a graphene as the SERS substrate, the enhanced charge-transfer and exciton resonances improve the limit of detection to the femtomolar level, while achieving remarkable flexibility, reproducibility, and operational stability. Our results provide important insights into 2D material-based ultrasensitive SERS based on chemical mechanisms.

Modulation of the spin-orbit interaction and the transition probability of polaron in disk quantum dot under electromagnetic field

This work presents the important role played by the spin-orbit interaction in nanostructures such as disk quantum dot when subjected to an external field. Here by using the LLP variational method, the Rashba effect on polaron in this nanostructure with Gaussian confinement potential under electromagnetic field is investigated. The polaron ground, first excited state energy and the electron transition probability are derived. Results show that the external electromagnetic field highly modulates the spin-orbit coupling strength αr, the polaron energies and transition probability. The polaron transition probability splits in two branches due to the splitting of the eigenstates energies. Our study also reveals that DQD properties can be adjusted by the external field. Therefore, the transport and the optical properties of the quantum dot can be controlled by turning the spin-orbit coupling.

Structural design of cubic Sr,V:CeFeO3 thin films with a strong magneto-optical effect and high compatibility with a Si substrate.

This paper focuses on strong magneto-optical thin films that closely match a Si substrate. The orthorhombic perovskite crystal structure of CeFeO3 was optimized to a cubic perovskite structure by introducing strontium and vanadium ions into lattice. The cubic Ce1-xSrxFe1-xVxO3 (x = 0.3, 0.5, 0.7) thin films with high quality and high growth orientation were prepared on a Si substrate by using the RF magnetron sputtering method. Moreover, the birefringence effect, which may weaken the magneto-optical effect, should not occur in the cubic thin film. The calculation results based on density functional theory show that the increased electronic transition probability is attributed to the strong spin-coupling between the hybrid Ce3+ 4f and Fe3+/V4+ 3d states. The magnetic circular dichroism ellipticity |ΨF| of the Ce0.7Sr0.3Fe0.7V0.3O3 thin film is up to 4300 deg. cm-1, which indicates a strong magneto-optical effect. Therefore, the cubic Ce1-xSrxFe1-xVxO3/Si film with high Ce3+ concentration is expected to be a new candidate for integrated magneto-optical devices.

Spin Polarization of Nonequilibrium Conduction Electrons in Magnetic Junctions

An original equation for nonequilibrium spin polarization in magnetic junctions based on dynamic equations for magnetic moment was obtained. Spatial nonuniformity of the distribution of carriers is taken into account in the equations, and the magnetic moment is averaged over the ensemble of nonequilibrium spin-injected electrons. The solution to the dynamic equations for the magnetic moment is used to estimate the probability of spin-flip electron transitions upon spin injection, and the solution to the equation for the nonequilibrium spin polarization in magnetic junctions is used to calculate frequencies of photon emission or absorption at energies corresponding to the energy of effective exchange splitting of spin subbands.

Novel method of high-efficient synergistic catalyze ammonia borane hydrolysis to hydrogen evolution and catalytic mechanism investigation

In the study, we have successfully prepared β-SiC NWs, Pt-Ru/β-SiC NWs as the high-efficient catalysts to synergistic catalytic AB hydrolysis to hydrogen evolution. In addition, the mechanism of the Pt-Ru nanoclusters modified the band structure of the β-SiC NWs and the synergistic catalytic AB hydrolysis are addressed clearly, and proposed a newly possible mechanism of photocatalytic AB hydrolysis to produce hydrogen. The orbital hybridizations of Pt-3d-orbitals, 4s-orbitals and Ru-3d-orbitals, 4s-orbitals, 4p-orbitals to the β-SiC result in the variation of band structure and band gap, the experiment results show the band gap of β-SiC NWs, Pt/β-SiC NWs and Ru/β-SiC NWs are 2.36 eV, 1.97 eV and 1.74 eV, respectively. Pt-Ru nanocluster’s modification is beneficial to increase the transition probability of photo-induced electrons and the separation of photo-electron and hole pairs, and then improve the photocatalytic quantum efficiency. Pt-Ru/β-SiC NWs both obtained higher catalytic activity in the light irradiation condition compare with in dark condition, the reaction required time decreased by 2′26″ and 4″12′. The experimental results above confirm the synergistic photocatalytic AB hydrolysis and conventional metal catalyze AB hydrolysis exist in the Pt-Ru/β-SiC NWs catalytic AB hydrolysis reaction system. Ru/β-SiC NWs have a perfect reusability due to the required time of completed reaction only extended by 0′58″ even experiencing ten life cycles. In addition, the previous mechanism of AB photocatalytic hydrolysis which believes the reaction is related to the dissolved oxygen in the solution have proved to be inaccurate via demonstration experiment, and have proposed a newly possible mechanism of photocatalytic AB hydrolysis to produce hydrogen through the inference of the especial Lewis structure of AB.

The effect of electron-phonon interaction on the formation of reverse currents of p-n-junctions of silicon-based power semiconductor devices

The article represents the physical processes and mechanisms that accompany the work of the real p-n-junction. The nature of the reverse and forward currents of p-n-junctions is studied as the basis for the operation of these devices. The new model of recombination in space charge region of p-n-junction has been developed. This model made it possible to develop a new method for processing current-voltage characteristics and determining the parameters of recombination centers in semiconductor devices including electron-phonon interaction parameters. The probability of electronic transitions is calculated. It takes into account the electron-phonon interaction and explains the rapid build-up of reverse currents as the applied voltage increases. The mechanisms of formation of the reverse current of the p-n-junction were discussed and it was concluded that the current is determined by the generation with the participation of deep centers and electron-phonon interaction.

High magneto-optical performance of GdFeO3 thin film with high orientation and heavy Ce3+ doping

Abstract In this paper, GdFeO3 thin films with high orientation and heavily Ce3+ doping were deposited by radio frequency magnetron sputtering with a matching substrate. The effects of substrates and Ce3+ doping on the structure, magnetic and magneto-optical properties of thin films were investigated. As a result, Ce3+ doping can not only increase the saturation magnetization but also greatly enhance the magnetic circular dichroism signals of Ce:GdFeO3 thin films. Based on the density functional theory calculation, it can be found that the probability of electron transition between Ce3+ 4f and Fe3+ 3d and the difference in the absorption of right and left circularly polarized light increase, which results in the strong magneto-optical effect of Ce:GdFeO3/STO thin films.

Electronic states, spectroscopic parameters, transition probabilities, and radiative lifetimes of the scandium monosulfide cation, ScS+: A theoretical contribution

High-level CASSCF/MRCI calculations with cc-pV5Z basis sets were employed to characterize a manifold of electronic states of the monosulfide cation ScS+ correlating with the three-lowest dissociation channels. The global energetic picture provided by the potential energy curves makes evident a region, especially above 35,000 cm−1, of high density of electronic states that presents a challenge for both experimentalists and computational chemists to assign properly the electronic transitions. For the lowest-lying singlet and triplet states, a whole set of spectroscopic parameters are provided. Additionally, data on dipole moment functions, transition dipole moment functions, radiative transition probabilities and lifetimes are also evaluated for a subset of singlet states, namely, X 1Σ+, B 1Π, C 1Π, G 1Σ+, H 1Π, I 1Π, and J 1Σ+, for which we identified favorable transitions to be investigated experimentally. Our results are sufficiently accurate and reliable to guide and motivate spectroscopists to investigate further this species.

Scattering of conduction electrons on the W(001) surface covered with the ordered deuterium monolayer

Specularity of the scattering of conduction electrons at the W(001) surface covered with an ordered deuterium (D) monolayer is shown to be higher than that for the clean W(001)−(2×2)R45o reconstructed surface. In the course of experiments, we measured changes in the transversal magnetoresistance induced by adsorption and ordering the D submonolayers on a thin W(001) plate. The obtained experimental data have been compared with Fermi contours of surface electronic states (SES) calculated for both the clean reconstructed W(001) surface and that covered with the D-monolayer. It has been found that transformations of the surface electronic structure, induced by the ordered monolayer of adsorbed D, lead to an almost twice decrease in the probability of electronic transitions between the surface and bulk electronic states. This effect has been assumed to be the reason for the considerable increase in specularity of the surface scattering of conduction electrons.

Insight into nuclear midshell structures by studying K isomers in rare-earth neutron-rich nuclei

Inspired by the newly discovered isomeric states in the rare-earth neutron-rich nuclei, high-$K$ isomeric states in neutron-rich samarium and gadolinium isotopes are investigated within the framework of the cranked shell model (CSM) with pairing correlation treated by a particle-number-conserving (PNC) method. The experimental multi-particle state energies and moments of inertia are reproduced quite well by the PNC-CSM calculations. A remarkable effect from the high-order deformation $\varepsilon_{6}$ is demonstrated. Based on the occupation probabilities, the configurations are assigned to the observed high-$K$ isomeric states. The lower $5^-$ isomeric state in $^{158}$Sm is preferred as the two-proton state with configuration $\pi\frac{5}{2}^{+}[413]\otimes\pi\frac{5}{2}^{-}[532]$. More low-lying two-particle states are predicted. The systematics of the electronic quadrupole transition probabilities, $B(E2)$ values along the neodymium, samarium, gadolinium and dysprosium isotopes and $N=96,98,100,102$ isotones chains is investigated to reveal the midshell collectivities.

The Green’s function technique for numerical simulations of multichannel electron transfer reactions in electron-donor-acceptor complexes

A method for numerical solution of diffusion equations with delta-localized coupling terms is proposed and applied to the stochastic model of multichannel electron transfer (ET) reaction in the Debye polar solvent. The Green’s function for the model equations is calculated using the Laplace transform technique for the time-dependent reaction fluxes between the reactant and product states. Two computational schemes for ET simulations are suggested: (a) the particle-based Brownian algorithm, (b) the grid scheme, utilizing the probabilities of the diffusion-assisted electronic transitions. The suggested schemes are shown to be more efficient than the previously developed recrossing-algorithm (the RABS method) in the solvent-controlled ET regimes and for slow processes accompanied by rare reactive events. Test simulations with the QM2L code are carried out and demonstrate an accuracy of the method. The results of the simulations agree well with known analytical expressions for the rate of thermal ET and the quantum yield of nonequilibrium multichannel ET in different regimes from the nonadiabatic (the Fermi Golden Rule) limit to the solvent-controlled reactions.

Electronic and optical properties of strained noble metals: Implications for applications based on LSPR

The localized surface plasmon resonance (LSPR) of noble metal nanoparticles provides a means to significantly enhance light-matter interaction. Thus, it is recently introduced into photovoltaics and photocatalysis for enhancing the transformation of solar light, where the efficiency of intra- and inter-band electron transitions fundamentally affects the overall performance of the systems. Considering the commonness and tunability of strain in nanoparticles, in this work we examine its potential effects on the intra- and inter-band electron transitions and related plasmonic properties of noble metals by the first-principles calculations and Drude theory. It is meaningful to find that strain can significantly modulate the electronic structures of noble metals that are closely related to the sp intra- and d–sp inter-band electron transitions. As a consequence, compressive strain notably increases the intra-band, but decrease the inter-band electron transition probabilities in the visible and near-infrared spectral range. Moreover, it significantly increases the near-field enhancement and light absorption efficiency for the LSPR in the visible and near-infrared range. Whereas the effect of tensile strain is exactly opposite. These results are very useful as guides in optimizing the nanostructure design for higher solar energy conversion efficiency and optoelectronic devices based on the LSPR of noble metals.

Calculation of transition matrix element, |MAB|, in a triboelectric nanogenerator (TENG) system

Abstract The aim of this paper is to calculate the transition matrix element (MAB), which is one of the parameters related to quantum mechanical charge exchange to describe the microscopic transition process on the contact interface in a triboelectric nanogenerator (TENG) system. It is well known that |MAB| squared (|MAB|2) is correlated to the transition probability of electrons through the barrier between two materials. In particular, the potential barrier between the metal and the polymer is reflected by the electric field resulting from the tribocharges via triboelectrification. Based on the derived formula for |MAB|, a numerical analysis is performed to understand the electron transfer pattern. As a result, it is determined that |MAB| is reduced exponentially at a fixed distance, d, as the electronic energy state, E, is farther away from the Fermi-energy level (EF). In contrast, |MAB| slowly increases as the triboelectric charge density, σ, increases. That is, electrons near EF can influence |MAB| during the charge transfer process. As |MAB| differs among tribomaterials, further study into material selection could enhance TENG performance.