Intensity Redistribution Research Articles

Electronic Stark effect for a single molecule: Theoretical UV response

Abstract Theoretical analysis of optical absorption in the vacuum ultra-violet (VUV) region by single molecules placed in external electrostatic fields reveals characteristic absorption spectra completely at variance with their ‘zero-field’ counterparts consequent to appearance, disappearance, splitting, merging and shifts of absorption bands and extensive intensity redistributions. This ‘molecular electronic Stark effect’ can be tracked through electronic excitations involving frontier orbitals, energy-level splitting and shifts, molecular geometry changes and re-orientation, orbital mutation and migration. The UV spectra predicted herein should provide theoretical grounds for experimental endeavors on appraisal and characterization of the effect.

RESEARCH METHODS OF THE PROPERTIES OF DEFECTIVE ELECTRICAL EQUIPMENT

The properties of electromagnetic fields in real conditions based on the fractal representations of the structure of material and design features of electrical equipment are studied. In calculating, the fractal characteristics methods are being suggested for the detection of redistribution of intensity of electromagnetic field due to the occurrence of diffraction, scattering and interaction with the heterogeneity of the components of equipment.

Anti-staling of high-moisture starchy food: Effect of hydrocolloids, emulsifiers and enzymes on mechanics of steamed-rice cakes

High-moisture rice snacks, such as steamed rice cakes, develop firmness on storage which decreases shelf life significantly. By analogy with lower moisture bread systems, this staling was hypothesised to be due to a combination of starch retrogradation and moisture re-distribution. Therefore, food additives which are commonly used to retard starch retrogradation during bread staling, including enzymes, hydrocolloids and emulsifiers (alpha-amylase, alginate, xanthan, guar gum, carrageenan, carboxymethyl cellulose, distilled monoglyceride, and sodium stearoyl lactylate) were investigated for their anti-hardening effects in high-moisture rice snacks. The results showed that only alginate significantly reduced the firming rate of rice cakes. However, differential scanning calorimetry measurements surprisingly indicated that rice cakes with alginate had higher levels of starch retrogradation than the control after storage for 7 days. Magnetic resonance imaging results were characterised by a redistribution of signal intensity from the edge to the centre of rice cakes and the formation of high intensity regions. These features were stronger with the addition of alginate. We propose that the alginate forms a continuous phase with water that has high mobility, whereas the partially gelatinized starch granules are an included phase distributed within the continuous phase. The reduced hardness of aged rice cakes with alginate is more dependent on the soft continuous phase than the hard starch granules, therefore leading to a softer texture. This mechanism is different to that proposed to operate for lower water content baked systems, therefore hydrocolloid and other anti-staling agents which are effective in bread systems may not be applicable in higher moisture starchy foods.

Light-sheet microscopy with attenuation-compensated propagation-invariant beams.

Scattering and absorption limit the penetration of optical fields into tissue. We demonstrate a new approach for increased depth penetration in light-sheet microscopy: attenuation-compensation of the light field. This tailors an exponential intensity increase along the illuminating propagation-invariant field, enabling the redistribution of intensity strategically within a sample to maximize signal and minimize irradiation. A key attribute of this method is that only minimal knowledge of the specimen transmission properties is required. We numerically quantify the imaging capabilities of attenuation-compensated Airy and Bessel light sheets, showing that increased depth penetration is gained without compromising any other beam attributes. This powerful yet straightforward concept, combined with the self-healing properties of the propagation-invariant field, improves the contrast-to-noise ratio of light-sheet microscopy up to eightfold across the entire field of view in thick biological specimens. This improvement can significantly increase the imaging capabilities of light-sheet microscopy techniques using Airy, Bessel, and other propagation-invariant beam types, paving the way for widespread uptake by the biomedical community.

Impact of Ultrathin Pb Films on the Topological Surface and Quantum-Well States of Bi2Se3 and Sb2Te3 Topological Insulators

The effect of an ultrathin Pb film deposited on the surface of Bi2Se3 and Sb2Te3 compounds on the electronic state structure of topological insulators is studied experimentally by the angle-resolved photoemission spectroscopy (ARPES) technique. The following features are revealed: formation of two-dimensional quantum-well states in the near-surface region, an increase in the binding energy of the Dirac cone and the core levels, and a simultaneous electronic states intensity redistribution in the system in photoemission spectra. The results obtained show that topological states may coexist at the interface between studied materials and a superconductor, which seems to be promising for application in quantum computers.

Competition of the self-activated and Mn-related luminescence in ZnS single crystals

The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of ZnS single crystals thermally doped from ZnS/MnS mixture were studied at 300 and 77 K. PL spectra exhibit bands caused by Mn-related centers and centers of self-activated (SA) emission. Besides intrinsic maximum, a number of narrow peaks corresponded to Mn-related absorption are found in the PLE spectra of both SA and Mn-related emission. A redistribution of SA and Mn-related emission intensities is observed with temperature change. The mechanism of this phenomenon involving free hole trapping by MnZn and the possible position of a ground energy level of substitutional Mn are discussed.

Anomalous Dependence of the Intensity of X-Ray Reflections of Cs2SO4 on the Crystallite Size and Shape

Detailed X-ray and electron microscopy analyses of Cs2SO4 powders consisting of sphere- and platelike crystallites have been carried out. It is established that the intensity distributions of X-ray reflections in both cases radically differ, with the position on the diffraction-angle axis retained in accordance with the PDF-2 database. Electron microscopy microdiffraction investigations of the orientation of developed surfaces of platelike crystallites revealed four different directions; however, these directions could not provide texture amplification of a number of observed (hkl) reflections. It is suggested that the intensity redistribution is based on the sphericity of X-ray waves incident on the sample.

IR Spectroscopic Study of Interatomic Interaction in [(CoFeB)60C40/SiO2]200 and [(CoFeB)34(SiO2)66/C]46 Multilayer Nanostructures with Metal-Containing Composite Layers

This paper presents an IR spectroscopic study of chemical bonds between components of amorphous [(CoFeB)60C40/SiO2]200 and [(CoFeB)34(SiO2)66/C]46 multilayer nanostructures (MNS’s) made up of metal-containing composite layers and different interlayers, which influence their electromagnetic properties. Our results demonstrate that, even though the MNS’s have identical elemental compositions, their IR spectra differ significantly. The reason for this is that the main contribution to the IR spectrum of the [(CoFeB)60C40/SiO2]200 MNS is made by its SiO2 interlayers. The formation of other bonds with oxygen and silicon is blocked by the carbon present in the (CoFeB)60C40 composite layers, as evidenced by the presence of the strongest mode in the IR spectra of this structure, which corresponds to boron carbide, BC. The considerable intensity redistribution to the low-frequency region in the IR spectrum of the [(CoFeB)34(SiO2)66/C]46 MNS, containing carbon interlayers, is due to the incorporation of nominal SiO2 into the metal-containing composite layers and the partial redistribution of oxygen bonds from the SiO2 to the 3d transition metals, resulting in the formation of metal oxides and a silicon suboxide. The interaction of the carbon present in the interlayers between the composite layers with elements of the composite layers, in particular with boron, is considerably weaker in comparison with the other MNS, [(CoFeB)60C40/SiO2]200, which has oxide interlayers.

Аномальная зависимость интенсивности рентгеновских рефлексов Cs-=SUB=-2-=/SUB=-SO-=SUB=-4-=/SUB=- от размера и формы кристаллитов

AbstractDetailed X-ray and electron microscopy analyses of Cs_2SO_4 powders consisting of sphere- and platelike crystallites have been carried out. It is established that the intensity distributions of X-ray reflections in both cases radically differ, with the position on the diffraction-angle axis retained in accordance with the PDF-2 database. Electron microscopy microdiffraction investigations of the orientation of developed surfaces of platelike crystallites revealed four different directions; however, these directions could not provide texture amplification of a number of observed ( hkl ) reflections. It is suggested that the intensity redistribution is based on the sphericity of X-ray waves incident on the sample.

Derivatives of 1,3,5 triaryl-2-pyrazoline with additional heterocyclic moieties in position 1 as potential fluorescent chemosensing compounds for detection of polyvalent metals cations

A series of 1,3,5-triaryl-2-pyrazoline derivatives with pyridine or 8'-hydroxyquinoline fragments in position 1 have been synthesized, some of which also contain a hydroxy group in the ortho-position of benzene ring-3, which makes possible the their OH-group proton phototransfer reaction to the nitrogen atom of pyrazoline cycle. The nitrogen atoms in molecules of the investigated compounds form chelate cavities, binding of the ions of polyvalent metals to which should lead to changes in the spectral characteristics. The spectral-luminescent properties of the synthesized compounds in solvents of different polarity and their interaction with salts of several polyvalent metals in acetonitrile were investigated. The proton phototransfer reaction was shown to result in significant fluorescence quenching, the most prominent for the derivative with the hydroxyquinoline fragment in position 1 of pyrazoline cycle. The proton transfer reaction rate constants vary within the interval of 2-4∙109 s-1 in aprotic solvents of different polarity. The prospects for application of the synthesized derivatives as fluorescent chemosensor compounds for the analysis of polyvalent metals were examined. In most of the studied cases, their interaction with heavy metal ions led to decrease of fluorescence intensity, however for compounds with intramolecular proton phototransfer reaction, no significant quenching by heavy metal ions was observed. The exception was the mercury ions, in the interaction with which compounds with proton phototransfer reaction demonstrated intensity redistribution of their two emission bands on the background of their general fluorescence quenching. The latter circumstance indicates the possibility of application of the modern methods of ratiometric fluorescence detection for the analysis of Hg2+ ions with their help.

Optical properties of magnesium nanorods using time dependent density functional theory calculations.

Plasmonic nanostructures made of Earth-abundant and low-cost metals such as aluminum and magnesium have recently emerged as a potential alternative candidate to conventional plasmonic metals such as gold and silver. Here using computationally efficient time-dependent density-functional theory calculations, we explore optical response modulations of magnesium nanorods via aspect ratio and absolute size variations. We reveal that both the aspect ratio and absolute size of the nanorods are critical for elucidating their optical characteristics. We show that both tuning factors cause significant optical response modulations in the case of thin nanorods (emergence of localized surface plasmon resonances, significant spectral shifting and spectral intensity re-distributions), whereas, very marginal changes in the case of thick nanorods. We believe that our theoretical results would help in the design of magnesium based nano-plasmonic devices.

Theory and practice of electron diffraction from single atoms and extended objects using an EMPAD.

What does the diffraction pattern from a single atom look like? How does it differ from the scattering from long-range potential? With the development of new high-dynamic range pixel array detectors to measure the complete momentum distribution, these questions have immediate relevance for designing and understanding momentum-resolved imaging modes. We explore the asymptotic limits of long-range and short-range potentials. We use a simple quantum mechanical model to explain the general and asymptotic limits for the probability distribution in both real and reciprocal space. Features in the scattering potential much larger than the probe size cause the bright field (BF) disk to deflect uniformly, while features much smaller than the probe size, instead of a deflection, cause a redistribution of intensity within the BF disk. Because long-range and short-range features are encoded differently in the diffraction pattern, it is possible to separate their contributions in differential phase-contrast (DPC) or center-of-mass (CoM) imaging. The shape profiles for atomic resolution CoM imaging are dominated by the shape of the probe gradient and not the highly singular atomic potentials or their local fields. Instead, only the peak height shows an atomic number sensitivity, whose precise dependence is determined by the convergence angle. At lower convergence angles, the contrast oscillates with increasing atomic number, similar to BF imaging. The range of collection angles impacts DPC and CoM imaging differently, with CoM being more sensitive to the upper cutoff limit, while DPC is more sensitive to the lower cutoff.

Nonlinear Spectroscopy of Alkali Atoms in Cold Medium of Astrophysical Relevance

The time-dependent population dynamics of hyperfine (HF) sublevels of n 2 p 3 / 2 atomic states upon laser excitation in a cold medium of alkali atoms is examined. We demonstrate some peculiarities of the absorption HF multiplet formation in D2-line resulting from a long interaction time (∼200 μ s) interaction between light and Na ( n = 3 ) and Cs ( n = 6 ) atoms in a cold and slow sub-thermal ( T ∼ 1 K) beam. We analytically describe a number of D2-line-shape effects that are of interest in spectroscopic studies of cold dusty white dwarfs: broadening by optical pumping, intensity redistribution within components of D2-line HF multiplet for partially closed transitions and asymmetry of absorption lines induced by AC Stark shifts for cyclic transitions.

Nonadiabatic effects in (1~2)1Π–X1Σ+ rovibronic transitions of KRb molecules

Numerical simulation of the effect of intramolecular electrostatic interactions on redistribution of relative intensities in the vibrational structure of (1 ~ 2)1Π–X1Σ+ rotationally resolved transitions of the KRb molecule is performed within the precision nonadiabatic model of coupled vibrational channels. It is established that mutual perturbation of electronically excited states modifies in a nontrivial way a nodal structure of nonadiabatic wavefunction of the (1 ~ 2)1Π complex, which is possible to use for rising efficiency of twostep laser synthesis and stabilization of ultracold ensembles of KRb molecules in the ground electronic state.

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x=0.15, 0.30, 1.16) thin films with oxygen content as low as 0.2 at% are investigated by 4d valence band, shallow 4p core-level and 3d core-level X-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity towards the H 1s - Zr 4d hybridization region at about 6 eV below the Fermi level. For low hydrogen content (x=0.15, 0.30), the films consist of a superposition of hexagonal closest packed metal (alpha-phase)and understoichiometric delta-ZrHx (CaF2-type structure) phases, while for x=1.16, the film form single phase ZrHx that largely resembles that of stoichiometric delta-ZrH2 phase. We show that the cubic delta-ZrHx phase is metastable as thin film up to x=1.16 while for higher H-contents, the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16 film, we find chemical shifts of 0.68 and 0.51 eV towards higher binding energies for the Zr 4p3/2 and 3d5/2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge-transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as function of hydrogen content is discussed in relation to the charge-transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

Generation of equilateral-polygon-like flat-top focus by tightly focusing radially polarized beams superposed with off-axis vortex arrays.

In this paper, the general formula for tightly focusing radially polarized beams (RPB) superposed with off-axis vortex arrays is derived based on Richard-Wolf vector diffraction theory. The off-axis vortex breaks the rotational symmetry of the energy flow along the axial direction and leads to the spatial redistribution of intensity within the focal plane. The dependence of the consequent focal intensity redistribution on the off-axis distance of vortices as well as the numerical aperture of the lens is theoretically studied. Based on this intriguing feature, generation of equilateral-polygon-like flat-top focus (EPFF) with a flat-top area on the level of sub-λ2 is realized. The demonstrated method provides new opportunities for focus shaping and holds great potentials in optical manipulation and laser fabrication.

Theory and Practice of Diffractometry on Single Tungsten Atoms using Electron Microscope Pixel Array Detectors

What does the diffraction pattern from a single atom look like? How does it differ from the scattering from long range potential? With the development of new high-dynamic range pixel array detectors to measure the complete momentum distribution, these questions have immediate relevance for designing and understanding momentum-resolved imaging modes. We explore the asymptotic limits of long range and short range potentials. We use a simple quantum mechanical model to explain the general and asymptotic limits for the probability distribution in both and real and reciprocal space. Features in the scattering potential much larger than the probe size cause the bright-field disk to deflect uniformly, while features much smaller than the probe size, instead of a deflection cause a redistribution of intensity within the bright-field disk. Because long range and short range features are encoded differently in the diffraction pattern, it is possible to separate their contributions in differential phase contrast (DPC) or Center-of-Mass (CoM) imaging. The shape profiles for atomic resolution CoM imaging are dominated by the shape of the probe gradient and not the highly-singular atomic potentials or their local fields. Instead, only the peak height shows an atomic-number sensitivity, whose precise dependence is determined by the convergence angle. At lower convergence angles, the contrast oscillates with increasing atomic number, similar to bright field imaging. The range of collection angles impacts DPC and CoM imaging differently, with CoM being more sensitive to the upper cutoff limit, while DPC is more sensitive to the lower cutoff.

Optical and luminescence spectroscopy of zinc gallate phosphors codoped with manganese and europium ions

ABSTRACTZinc gallate compounds codoped with manganese and europium ions were synthesized using the high-temperature solid-state reaction method. All samples were “characterized” by X-ray diffraction measurements, ultraviolet reflection spectroscopy, and photoluminescence spectroscopy. Structural investigations confirmed that incorporation of europium ions in zinc gallate host leads to distortion of the spinel unit cell and increase in lattice parameter. Manganese ions show the intense excitation in the region of band-to-band transitions. Zinc gallate spinel compounds codoped with manganese and europium ions exhibit emission in the whole spectral region. Among the manganese and europium activator emissions in the “green” and “red” spectral regions, the “blue” emission of spinel matrix was observed. Photoluminescence excitation spectra of europium ions and reflection spectra show similar results in the near-ultraviolet region of the spectra. The optimal concentration of europium activator was determined. Europium doping level leads to redistribution of excitation and emission intensities of zinc gallate codoped samples. The possible energy transfer mechanisms between matrix, manganese, and europium ions are discussed. Overlapping of excitation bands of all types of luminescence gives a possibility to obtain emission in the whole visible spectral range. The Commission Internationale de l’Eclairage chromaticity diagrams confirmed a possible application of the studied zinc gallate spinel compounds codoped with manganese and europium ions for the development of ultraviolet and near-ultraviolet phosphors with flexible emission color in the visible spectral range.

Plasmon–Exciton Coupling at Individual Porphyrin-Covered Silver Clusters

The feasibility to couple surface plasmons with molecular excitations is an intriguing feature of plasmonic–organic hybrid systems. To date, investigations of plasmonic–excitonic coupling have largely focused on ensembles of nanoparticles and on purely optical methods. Here we present a single-particle approach based on laser-spectroscopic photoemission electron microscopy. Localized surface plasmons give rise to photoemission resonances in laser excitation spectra of individual silver nanoclusters. As a most striking manifestation of plasmon–exciton coupling, upon deposition of a thin zinc tetraphenylporphyrin (ZnTPP) film, a second resonance near the ZnTPP Soret band appears in our spectra. In accordance with simulations, spectral repulsion of both resonances as well as intensity redistribution between both modes indicates their plasmonic–excitonic hybrid character.

Spectral broadening and red edge excitation effect in liquid and viscous solutions of DMABN

Effect of intensity redistribution of two fluorescence bands of N,N'-Dimethylaminobenzonitrile in polar solutions of the different viscosity was studied using selective UV irradiation over the red edge of the main absorption band. The effect being depends on temperature and viscosity, indicated eloquently strong inhomogeneous spectral broadening appearing at the red edge excitation. The conformational broadening exists for electronic transitions in the range of the local excited short wavelength band with weak change of electric dipole moments of the solutes. It was found that the spectral conformational broadening may exists independently on the orientational broadening which is due to the change of solute electric dipole moments in polar media and of thermal environmental fluctuations. When different conformers are excited into upper singlet levels, there is no fast dissipation of excitation energy over different conformational sublevels compared to the charge transfer reaction rates. In this case fluorescence and the charge transfer reaction occur from Franck-Condon sublevels with different rates.