Electron transitions in a Ce(iii)-catecholate metal–organic framework

Competitive electron transitions are present in a rare three-dimensional Ce(iii)-catecholate metal–organic framework.

On physical investigation of ball lightnings

Explanations for the long lifetime of spherically symmetric objects in nature and the short lifetime of laboratory plasma are given. A qualitative description of the relativistic model of ball lightning is also given, which is a spherical electric region with strong electric and magnetic fields. The plasma temperature in the zone of the ball-lightning generation is measured by the spectroscopic method. A large ball lightning, the maximum diameter of which is equal to one meter and which stands in the region of its generation, is also registered after the formation and departure of a high-energy ball lightning. The reason for the low emissive power in the optical range characteristic for the atmospheric ball lightning is explained by the absence of electron transitions in the outer proton-containing shell. The absence of electrical breakdown at ultrahigh electric field between the core and the outer shell of the ball lightning and its destruction at the moment when the resulting force becomes nonzero are also explained.

Statistical approach to the process of tunnel ionisation of impurity centres near the heterointerface

To date, the processes of tunnel ionisation of impurities near the interface between two different semiconductors have been comprehensively studied. The most important parameters of the contact electron states of impurities have been determined. However, the calculated expressions for these parameters have been of local nature, as applied to individual impurities. Meanwhile, it is easy to understand that a number of processes, such as the flow of charge carriers and their diffusion through a heterojunction, are clearly statistical in nature. The same applies to the processes of tunnel ionisation of shallow and/or deep impurities near the interface. A statistical approach to the calculation of the parameters of tunnel ionisation of impurities broadens the opportunities for obtaining fundamental information regarding surface electronstates.The aim of this work was to use a statistical approach to study the effect of the heterointerface on the energy spectrum of shallow and deep centres. For this purpose, the expansion of the reflected quasi-classical wave function within the complete system of spherical harmonics and the subsequent extraction of the zero harmonic amplitude (s-component) was used to estimate the minimum distance from the impurity to the heterobarrier and to specify the limitations of the applicability of the results obtained in other works. The article analyses the conditions of the quasi-classical approximation which are used to estimate the order of the value for the minimum height of the potential barrier (pit).This work (with due consideration given to the minimum distance estimate) presents averaged formulas obtained for the energy shift of the ground state and the lifetime of the quasi-stationary state depending on the distance from the heterobarrier. Some qualitatively new considerations can also be found in the article. The distribution of impurity centres near the heterobarrier is assumed to be uniform. The article discusses the role of electron transitions in causing the buffer field effect for both shallow and deep centres. The focus of the article is on the estimates of various physical parameters characterising electron transitions near the heterobarrier.

SYNTHESIS AND SPECTRAL CHARACTERISTICS OF Cu(II), Ni(II) AND Fe(III) NANOSIZED COM­PLEXES ON THE SURFACE OF CARBON QUANTUM DOT

Processes of interaction between carbon quantum dots (CQDs) and solutions of Cu(II) Ni(II) and Fe(III) chlorides in the surface layer have been investigated by electron and IR spectroscopy. When hydrochloric acid is added to the aqueous suspension of CQDs, there is a signi­ficant batochromic shift of the average absorption band (AB) by 1285 cm-1 with a decrease in its intensity to ε = 23.39. The presence of copper in the suspension of CQDs at room temperature leads to a decrease in the intensity of this AB (ε = 21.80), which indicates the interaction of CQDs with metal ions. After heating the suspension for 1 and 3 hours, the gypsochromic shift of this ABs (by 335 cm-1) to 27790 cm-1 with a decrease in intensity depending on the heating time was recorded. Such changes in the UV–Vis Spectrum are due to the redistribution of the electron density of electron transitions n → π *due to the coordination of functional groups with metal ions and the appearance of transitions with charge transfer from ligand to metal (CQD→Cu2+). When heating the suspensions significantly increases the absorption intensity of the AB at 22070 cm-1: from ε = 4.59 to ε = 6.75, which indicates the formation of transitions with charge transfer from ligand to metal (ChTLM) due to the coordination of copper ions with CQD. In the absorption spectra of CQD suspensions with NiCl2 before heating, a hypsochromic shift of AB at 27305 cm-1 by 150 cm-1 and an increase in the intensity of its to ε = 4.95 were registered. That is, Ni(II) ions also form coordination bonds with functional groups on the periphery of the CQD. After heating hydrochloric acid suspensions of CQD with FeCl3, in contrast to the chlorides of previous metals, in the UV-region registered shoulder-shaped AB at 31545 cm-1, the intensity of which increases with heating time (from ε = 9.59 to ε = 12.10), and in the visible region, a weakly intense shoulder-shaped AB at 19345 cm-1 (ε = 3.71 and 4.58), associated with the presence of dd-electron transitions in the metal ion. Such changes in the absorption spectra are explained by the fact that iron may interact with CQD in different ways (in addition to coordination with functional donor groups, the formation of coordination bonds with the π-electron system of conjugated CQDs bonds), which leads to additional weak shoulder-like AB at 31545 cm-1. The IR-spectra data of CQDs showed the presence of a number of characteristic ABs for functionalized CQDs: ν(N–H) at 3260 сm1, (C=O) at 1830, 1840 and 1850 сm1, –С=O(NH) at 1770 сm1, ν(C=N) at 1680 and δ(N–H) at 1640 сm1 and 320-360 см-1 СП ν(Cu–Cl, Ni–Cl, Fe–Cl), which confirms the coordination of metals on the surface of CQDs.

Investigation of the Crystallographic Perfection and Photoluminescence Spectrum of the Epitaxial Films of (Si2)1-x(GaP)x 0 ≤ x ≤ 1 Solid Solution, Grown on Si and GaP Substrates with the Crystallographic Orientation (111)

Epitaxial layers of the solid solution of molecular substitution (Si2)1-x(GaP)x (0 ≤ x ≤ 1) on Si (111) and GaP (111) substrates are grown by liquid-phase epitaxy from an Sn solution-melt. Such graded-gap solid solutions allow the integration of well-established silicon technology with the advantages of III-V semiconductor compounds. The structural features, the distribution of the atoms of the components over the thickness of the epitaxial layer, the photoluminescence spectrum of the (Si2)1-x(GaP)x (0 ≤ x ≤ 1) solid solution, and the electroluminescence of the structure n-GaP-n+-(Si2)x (GaP)1-x (0 ≤ x ≤ 0.01) have been investigated. It is shown that the layers of the solid solution have a perfect single-crystal structure with the crystallographic orientation (111), with the size of subcrystallites ∼ 39 ± 1 nm. The epitaxial layer (Si2)1-x(GaP)x (0 ≤ x ≤ 1) is a graded-gap layer with a smoothly and monotonically varying composition from silicon to 100% GaP. The energy levels of atoms of Si2 molecules which are located 1.47 eV below the bottom of the conduction band of gallium phosphide are revealed. Red emission of n-GaP-n+-(Si2)x(GaP)1-x (0 ≤ x ≤ 0.01) structure which is caused by electron transitions with participation of energy levels of Si2 atoms is detected.

MagnetoPlasmonic Waves/HOMO-LUMO Free π-Electron Transitions Coupling in Organic Macrocycles and Their Effect in Sensing Applications

Optical and magneto-optical surface plasmon resonance (MOSPR) characterization and preliminary sensing test onto single- and multi-layers of two organic macrocycles have been performed; TbPc2(OC11H21)8 phthalocyanine and CoCoPo2 porphyrin were deposited by the Langmuir-Schäfer (LS) technique onto proper Au/Co/Au magneto-optical transducers. Investigations of the MOSPR properties in Kretschmann configuration by angular modulation, gives us an indication about the potential discrimination of two organic macrocycles with absorption electronic transition in and out of the propagating plasmon energy spectral range. An improved molecular vapors sensitivity increase by the MOSPR sensing probe can be demonstrated depending on the overlap between the plasmonic probe energy and the absorption electronic transitions of the macrocycles under investigation. If the interaction between the plasmon energy and molecular HOMO-LUMO transition is preserved, a variation in the complex refractive index takes place. Under this condition, the magneto-plasmonic effect reported as 1/|MOSPR| signal allows us to increase the detection of molecules deposited onto the plasmonic transducer and their gas sensing capacity. The detection mechanism appears strongly enhanced if the Plasmon Wave/HOMO-LUMO transitions energy are in resonance. Under coupling conditions, a different volatile organic compounds (VOC) sensing capability has been demonstrated using n-butylamine as the trial molecule.

A Voltammetric Perspective of Multi-Electron and Proton Transfer in Protein Redox Chemistry: Insights From Computational Analysis of Escherichia coli HypD Fourier Transformed Alternating Current Voltammetry

This paper explores the impact of pH on the mechanism of reversible disulfide bond (CysS-SCys) reductive breaking and oxidative formation in Escherichia coli hydrogenase maturation factor HypD, a protein which forms a highly stable adsorbed film on a graphite electrode. To achieve this, low frequency (8.96 Hz) Fourier transformed alternating current voltammetric (FTACV) experimental data was used in combination with modelling approaches based on Butler-Volmer theory with a dual polynomial capacitance model, utilizing an automated two-step fitting process conducted within a Bayesian framework. We previously showed that at pH 6.0 the protein data is best modelled by a redox reaction of two separate, stepwise one-electron, one-proton transfers with slightly “crossed” apparent reduction potentials that incorporate electron and proton transfer terms (Eapp20 > Eapp10). Remarkably, rather than collapsing to a concerted two-electron redox reaction at more extreme pH, the same two-stepwise one-electron transfer model with Eapp20 > Eapp10 continues to provide the best fit to FTACV data measured across a proton concentration range from pH 4.0 to pH 9.0. A similar, small level of crossover in reversible potentials is also displayed in overall two-electron transitions in other proteins and enzymes, and this provides access to a small but finite amount of the one electron reduced intermediate state.