Dipole Absorption Research Articles

Evolution of morphological and optical properties of various AuxPd1−x bimetallic nanostructures by the systematic control of composition

Bimetallic nanostructures (BMNSs) have gained significant attention because of their multi-functionality, site-specific response and electronic heterogeneity along with the additional opportunities to tune physical and optical properties. In this paper, the systematic evolution of AuxPd1−x BMNS is thoroughly investigated in terms of morphological and optical properties through the solid state dewetting on c-plane sapphire. The bilayer composition and deposition order change are coherently tested along with the conventional growth parameter control. By the systematic control of annealing temperature, annealing duration and deposition thickness, the formation of various BMNSs demonstrate sharp distinctions at different AuxPd1−x compositions (x = 0.25, 0.50 and 0.75). In specific, the high Au percentage in the AuxPd1−x bilayers shows an enhanced dewetting due to the higher diffusivity and lower surface energy of Au atoms as compared to the Pd. Furthermore, the deposition order also induces a significant alteration on the dewetting process. Upon annealing, the evolution of BMNSs relies on the combination of atomic diffusion, inter-diffusion, alloying, surface and interface energy minimization and Rayleigh-like instability. Furthermore, the analysis of reflectance spectra demonstrates the development of the quadrupolar and dipolar resonance peaks, absorption band and their shift, induced by the localized surface plasmon resonance (LSPR) of various AuxPd1−x BMNSs. Specifically, the quadrupolar resonance peak is consistent ∼380 nm whereas the dipolar resonance peak and absorption dip are readily blue-shifted and narrowed along with the evolution of isolated and uniform BMNSs.

Position, orientation, and relative quantum yield ratio determination of fluorescent nanoemitters via combined laser scanning microscopy and polarization measurements

We present a universal method of determining the position, 3D orientation, and relative quantum yield ratio (RQYR) of fluorescent nanoemitters (ZnS coated CdSe quantum dots) in a glass slide by combining laser scanning microscopy (LSM) and polarization measurements. The quantum dots were located through LSM intensity maps using azimuthal, radial, and linear incident polarizations. LSM imaging was not sufficient to determine the orientation of the quantum dots due to the isotropic absorption dipole moment. The 3D orientation was obtained through polarization measurement. By combining LSM and polarization measurements, the RQYR of a single molecule was evaluated, allowing us to compare the quantum yield of the nanoemitters.

π-π-Induced aggregation and single-crystal fluorescence anisotropy of 5,6,10b-tri-aza-acephenanthrylene.

The structural origin of absorption and fluorescence anisotropy of the single crystal of the π-conjugated heterocyclic system 5,6,10b-tri-aza-acephenan-thrylene, TAAP, is presented in this study. X-ray analysis shows that the crystal framework in the space group P [Formula: see text] is formed by centrosymmetric dimers of face-to-face mutually oriented TAAP molecules joined by π-π non-covalent interactions. The conformation of the TAAP molecule is stabilized by intramolecular C-H⋯N(sp2), N(sp2)H⋯π(CN), and C-H⋯O(sp2) hydrogen bonds. The presence of weak π-π interactions is confirmed by quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analysis. The analysis of the optical spectra of TAAP in solution and in the solid state does not allow the specification of the aggregation type. DFT calculations for the dimer in the gas phase indicate that the lowest singlet excitation is forbidden by symmetry, suggesting H-type aggregation, even though the overall absorption spectrum is bathochromically shifted as for the J-type. The experimental determination of the permanent dipole moment of a TAAP molecule in 1,4-dioxane solution indicates the presence of the monomer form. The calculated absorption and emission spectra of the crystal in a simple approximation are consistent with the experimentally determined orientation of the absorption and emission transition dipole moments in TAAP single crystals. The electrostatic interaction between monomers with a permanent dipole moment (ca 4 D each) could result in the unusual spectroscopic JH-aggregate behaviour of the TAAP dimer.

Electronic and vibrational spectroscopic (FT-IR and FT-Raman) investigation using ab initio (HF) and DFT (B3LYP and B3PW91) and HOMO/LUMO/MEP analysis on the structure of l-serine methyl ester hydrogen chloride

The vibrational spectroscopy (Fourier Transform Raman and Infrared spectra) of l-serine methyl ester hydrogen chloride (LHCL) have been recorded and the observed vibrational frequencies are assigned and tabulated. The Gaussian hybrid computational calculations were determined by HF and DFT (B3LYP and B3PW91) methods with 6–31++G(d,p) and 6–311++G(d,p) as basis sets. The mulliken and natural charge in the functional group has the maximum magnitude of 0.305 and 0.498 among the hydrogen atoms present in the compound and here, the entire hydrogen atoms exhibit a net positive charge. The change of structure of amino acid due to the addition of subsequent substitutions of methyl, ethyl, carboxylic and hydroxyl chain is investigated. It plays a vital role in the production of different pharmaceutical and cosmetics industries.13C NMR and 1H NMR were calculated by using the gauge independent atomic orbital (GIAO) method with the B3LYP methods and the 6-311 + G(d,p) basis set and nuclear magnetic resonance chemical shifts related to TMS were compared. A study on the optoelectronics properties: absorption wavelengths, excitation energy, oscillator strength, dipole moment and FMO were executed by the HF and DFT methods. UV–Visible spectrum of the present compound is recorded in the region is 200–400 nm and the electronic properties HOMO and LUMO energies are deliberated by TD-DFT method. The polarizability, anisotropy, dipole moment and first order hyperpolarizability of the molecule have been discussed.

The spectroscopic and elastic properties of borosilicate glasses doped with NdF3

NdF3-doped borosilicate glasses were prepared using the high-temperature melt components of ingredients of NdF3 doped borosilicate glasses. Optical transmission spectra were collected in the range of 190–2500 nm to determine different optical parameters such as the direct and the indirect optical band gap, Urbach energy, refractive index and optical dielectric constant. The molar refraction, electronic polarizability, and the optical basicity results have been determined using the measured glass refractive indices. Judd-Ofelt calculations were used to predict the oscillator strength of an electronic dipole absorption transition. The order of the parameters Ω2, Ω4 and Ω6 are Ω2 < Ω4 < Ω6. They were found to decrease with the increase of Nd3+ concentration. In addition, decreasing the parameter Ω6 indicates that the rigidity of glass samples increases with the increase of Nd3+ions. The increase in rigidity, is also confirmed by the increase of the elastic moduli calculated using Makishima and Mackenzie model. This study suggests that the increasing concentration of Nd3+ in the Nd-doped borosilicate glasses not only affect the optical parameters but also increases the glasses rigidity.

Механизмы поглощения терагерцового и инфракрасного излучения в пленках PZT

AbstractTerahertz and IR spectra of dielectric response of dense and porous Pb(Zr,Ti)O_3 films deposited on single-crystal magnesia and alumina substrates and on silicon substrates with a conducting platinum sublayer are measured in the and analyzed. We consider the key mechanisms of electric dipole absorption that give rise to absorption bands observed in experimentally measured reflection and transmission spectra, and discuss the relationship between the type of substrate and the parameters characterizing the absorption bands in the spectra of the prepared PZT films.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time.

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd0.25Ag0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd0.75Ag0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.

Stimulated Raman spectroscopy of 13CF4

CF4 is a powerful greenhouse gas, mostly released in the atmosphere by industries. A careful modeling of its absorption spectrum is required in order to allow accurate atmospheric concentration measurements. For this aim, high resolution Raman spectroscopy is of great help, since it gives access to rovibrational levels that are not directly reachable through dipolar absorption, although they are involved in hot band generation. Following our previous work on 12CF4, we present here a similar investigation of the second isotopologue, 13CF4. The spectra of the ν1 (909.21 cm−1), 2ν1-ν1 (906.77 cm−1), ν1+ν2-ν2 (909.33 cm−1), ν2 (435.47 cm−1), 2ν2 (868.10 cm−1) and 3ν2-ν2 (865.73 cm−1) bands were obtained with a quasi-continuous wave stimulated Raman spectrometer. These six bands were studied at temperatures of 140 and 298 K (for the hot bands). These spectra could be assigned and modeled thanks to the XTDS and SPVIEW software developed in the Dijon group.

Local vs Nonlocal States in FeTiO3 Probed with 1s2pRIXS: Implications for Photochemistry.

Metal–metal charge transfer (MMCT) is expected to be the main mechanism that enables the harvesting of solar light by iron–titanium oxides for photocatalysis. We have studied FeTiO3 as a model compound for MMCT with 1s2pRIXS at the Fe K-edge. The high-energy resolution XANES enables distinguishing five pre-edge features. The three first well distinct RIXS features are assigned to electric quadrupole transitions to the localized Fe* 3d states, shifted to lower energy by the 1s core–hole. Crystal field multiplet calculations confirm the speciation of divalent iron. The contribution of electric dipole absorption due to local p-d mixing allowed by the trigonal distortion of the cation site is supported by DFT and CFM calculations. The two other nonlocal features are assigned to electric dipole transitions to excited Fe* 4p states mixed with the neighboring Ti 3d states. The comparison with DFT calculations demonstrates that MMCT in ilmenite is favored by the hybridization between the Fe 4p and delocalized Ti 3d orbitals via the O 2p orbitals.

High catalytic activity of monometallic Ag, Cu nanostructures in the degradation of acid blue 113 dye: an electron relay effect

This report discusses the observed faster decoloration of an azo dye with an enhanced degradation rate constant achieved using metal nanostructures as a catalyst. Silver and copper nanostructures were synthesized by reducing the corresponding nitrate salts using hydrazine and hexamethylenetetramine (HMTA) in sodium hydroxide (NaOH) solution. The influence of HMTA was clearly evident from the scanning electron microscopy (SEM) images; with increasing concentration it caused agglomeration and the formation of net-like nanostructures. An x-ray diffraction study confirmed the formation of monometallic Ag and Cu nanostructures. The prepared nanostructures exhibited dipole and multipole surface plasmon resonance-related optical absorption bands which were size and shape dependent. The degradation of the azo dye acid blue 113 (AB113) in the presence of sodium borohydride (NaBH4) was taken as model system for studying the catalytic activity of the metal nanostructures. From the optical absorption spectral studies of dye degradation it was observed that the rate constant (k) was of the order of kCu > kAg > kno catalyst. From the dye degradation studies a high catalytic activity was observed for Cu nanostructures with a rate constant of 20.93 × 10–4 s−1.

Photo scattering and absorption cross section in framework of the sdfp-interacting boson model

Low-lying electric dipole strength is an interesting nuclear structure phenomenon which various collective models were employed in order to account for the observed properties of the photoresponse in nuclei. To determine general characteristics of the low-lying dipole strength it is reasonable to use the sdfp-interacting boson model (sdfp-IBM). Dipole strength, photo scattering and absorption cross section of the even–even Z=54 isotopes are calculated in the sdfp-IBM based on dual pairing of affine SU(1,1) Lie algebra and Bethe-ansatz equations. E1 excitations to the spin 1 member of the two-phonon quintuplet excitations (2+⊗3−) are also discussed with respect to the critical point symmetry E(5) in even–even Xe isotopes. SU(1,1) Lie algebra calculations were performed for each dipole using the sdfp-IBM, and the results are compared to the experimental data. The calculations confirm a good agreement for the fragmentation of the E1 strength.

An Experimental and Computational Study of 2-(3-Oxo-3H-benzo[f] chromen-1-ylmethoxy)-Benzoic Acid Methyl Ester

The various methods for studying polarities are based on the use of probe molecules, whose molecular spectral profile is significantly affected by the polarity of the medium. The absorption and emission spectra and dipole moments (µ g and µ e) of 2-(3-oxo-3H-benzo[f]chromen-1-ylmethoxy)-benzoic acid methyl ester (2BME) are studied in solvents of different polarities at room temperature. The determination of dipole moments by solvatochromic shift using various relations and the change in dipole moment (Δµ) were determined using Stokes shift with the variation of the solvent polarity parameter (E T N ). The value of µ e greater than µ g indicating that the probe is more polar in the higher state. DFT and TDDFT theoretical analysis of dipole moment in the vacuum and with solvent, solvent accessible surface (SAS) and molecular electrostatic potential (MEP) are also performed.

Optical Absorption and Emission Mechanisms of Single Defects in Hexagonal Boron Nitride.

We investigate the polarization selection rules of sharp zero-phonon lines (ZPLs) from isolated defects in hexagonal boron nitride (HBN) and compare our findings with the predictions of a Huang-Rhys model involving two electronic states. Our survey, which spans the spectral range ∼550-740 nm, reveals that, in disagreement with a two-level model, the absorption and emission dipoles are often misaligned. We relate the dipole misalignment angle (Δθ) of a ZPL to its energy shift from the excitation energy (ΔE) and find that Δθ≈0° when ΔE corresponds to an allowed HBN phonon frequency and that 0°≤Δθ≤90° when ΔE exceeds the maximum allowed HBN phonon frequency. Consequently, a two-level Huang-Rhys model succeeds at describing excitations mediated by the creation of one optical phonon but fails at describing excitations that require the creation of multiple phonons. We propose that direct excitations requiring the creation of multiple phonons are inefficient due to the low Huang-Rhys factors in HBN and that these ZPLs are instead excited indirectly via an intermediate electronic state. This hypothesis is corroborated by polarization measurements of an individual ZPL excited with two distinct wavelengths that indicate a single ZPL may be excited by multiple mechanisms. These findings provide new insight on the nature of the optical cycle of novel defect-based single-photon sources in HBN.

The stability of the pheromones of xylophagous insects to environmental factors: An evaluation by quantum chemical analysis

The ground and excited states of the pheromone molecules produced by xylophagous insects (the bark beetle Ips typographus L., the black fir sawyer beetle Monochamus urussovi Fisch., and the black pine sawyer M. galloprovincialis Oliv.) were modeled using a quantum chemical method utilizing DFT (density functional theory) with the B3LYP functional. The absorption wavelengths (energies) and dipole moments were calculated; the transitions of electrons from occupied to empty molecular orbitals were considered. The computed data were used to assess the stability of pheromone molecules exposed to environmental factors, such as solar radiation and humidity.

A combined spectroscopic and TDDFT investigation of the solute-solvent interactions of two coumarin derivatives.

The UV/Vis absorption and fluorescence characteristics of 3-cyano-7-hydroxycoumarin [CHC] and 7-amino-4-methyl-3-coumarinylacetic acid [AMCA-H] were studied at room temperature in several neat solvents and binary solvent mixtures of 1,4-dioxane/acetonitrile. The effects of solvent on the spectral properties are analyzed using single and multi-parameter solvent polarity scales. Both general solute/solvent interactions and hydrogen bond interactions are operative in these systems. The solvation of CHC and AMCA-H dyes in 1,4-dioxane/acetonitrile solvent mixtures has been studied. The solutes CHC and AMCA-H are preferentially solvated by acetonitrile and a synergistic effect is observed for both molecules in dioxane/acetonitrile solvent mixtures. In addition, using the solvatochromic method the ground- and the excited-state dipole moments of both the dyes were calculated. The ground- and excited-state dipole moments, absorption and emission maxima and HOMO-LUMO gap were also estimated theoretically using B3LYP/6-311+ G (d,p) level of theory in the gaseous phase, dioxane and acetonitrile solvents. Furthermore, changes in dipole moment values were also calculated using the variation of Stokes shift with the molecular-microscopic empirical solvent polarity parameter ( ETN). The observed excited-state dipole moments are larger than their ground-state counterparts, indicating a substantial redistribution of the electron densities in a more dipolar excited state for both coumarins investigated.

Infrared spectra of thin films of α-crystalline hexafluoroethane: a manifestation of resonant dipole–dipole interaction in the range of fundamental vibrational modes ν5 and ν10

Infrared reflection-absorption spectra of thin films of α-crystalline hexafluoroethane deposited on a gold-plated copper mirror are measured at temperatures of 70 and 80 K. The bands corresponding to strong in the dipole absorption vibrations ν5 and ν10 have complex contours, the shape of which is explained in terms of the resonant dipole–dipole interaction between identical spectrally active molecules of the crystal. Splittings of the complex ν5 and ν10 bands are explained taking into account two effects: the Davydov splitting and the LO–TO splitting of the strong modes. Bands of the asymmetric 13С12СF6 isotopologue in the absorption spectrum of the crystal exhibit an anomalously large isotope shift as compared with the shift in the spectrum of free molecules. This anomaly is explained by intermolecular resonant dipole–dipole interaction of asymmetric 13С12СF6 isotopologue with molecules of the environment, consisting of the most abundant 12C2F6 isotopologue. The correctness of the given interpretation is confirmed calculating these three effects in the model of resonant dipole–dipole interaction.

Probing the Absorption and Emission Transition Dipole Moment of DNA Stabilized Silver Nanoclusters.

Using single molecule polarization measurements, we investigate the excitation and emission polarization characteristics of DNA stabilized silver nanoclusters (C24-AgNCs). Although small changes in the polarization generally accompany changes to the emission spectrum, the emission and excitation transition dipoles tend to be steady over time and aligned in a similar direction, when immobilized in PVA. The emission transition dipole patterns, observed for C24-AgNCs in defocused wide field imaging, match that of a single emitter. The small changes to the polarization and spectral shifting that were observed could be due to changes to the conformation of the AgNC or the DNA scaffold. Although less likely, an alternative explanation could be that several well aligned spectrally similar emitters are present within the DNA scaffold which, due to Förster resonance energy transfer (FRET) processes such as energy hopping, energy transfer, and singlet-singlet annihilation, behave as a single emitter. The reported results can provide more insight in the structural and photophysical properties of DNA-stabilized AgNCs.

Dipole Polarizabilities and Absorption Cross Sections of Two-Particle Nanoclusters of Conductive Homogeneous and Layered Particles with the Degenerate Electron Gas

Frequency dependences of the dipole polarizabilities of clusters consisting of two solid conducting spherical nanoparticles and double-layer metal nanoparticles are investigated versus the geometrical parameters of the system with taking into account the degeneracy of electron gas of its metallic components. It is established that the spectra of the dynamic polarizabilities and absorption cross-sections of clusters have a complex multiresonant structure and strong dependence on the configuration parameters of the cluster, the degree of degeneracy of the metal, and kinetic characteristics of its electron gas. Spectral transformations of the absorption cross-sections of nanoclusters are illustrated under variation of the radii of particles or theirs nuclei, characteristic lengths of the Thomas-Fermi screening, and frequency of electron collisions. The anisotropic nature of absorption of electromagnetic field energy by a cluster is established: it is shown that the value of the absorption cross section depends on the direction of the electric field strength vector relative to the axis of the cluster.

Experimental and Theoretical Studies of the Spectroscopic Properties of Chalcone Derivatives.

Newly synthesized, differently substituted chalcones (1,3-diaryl-2-propen-1-ones) have been studied using steady-state and time-resolved techniques combined with quantum-chemical modelling. To explore spectroscopic structure - property relationships the substituent (acceptor moiety) was chosen according to systematic variation in the Hammett parameter. It was shown that photophysical properties of the studied donor-acceptor (D-A) molecules can be predicted in terms of a simple model from the properties of individual chromophores (composite-model of decoupled moieties: donor (D) and acceptor (A)). The results of spectroscopic measurements also indicate that for investigated D-A fluorophores in medium-polar solvent, the initially populated, locally excited (LE) state (where the fundamental role plays donor moiety (D*-A)) reacts further to produce intramolecular charge transfer (ICT) state. Additionally, the experimental absorption (M ge ) and fluorescence (M eg ) transition dipole moments were calculated on the basis of spectroscopic data and compared with results of our quantum-chemical calculations. The absorption transition dipole moment was found to vary linearly with the Hammett substituent coefficient (σ).

Pressure broadening of the electric dipole and Raman lines of CO2 by argon: Stringent test of the classical impact theory at different temperatures on a benchmark system

A classical approach is applied to calculate pressure broadening coefficients of CO2 vibration–rotational spectral lines perturbed by Ar. Three types of spectra are examined: electric dipole (infrared) absorption; isotropic and anisotropic Raman Q branches. Simple and explicit formulae of the classical impact theory are used along with exact 3D Hamilton equations for CO2–Ar molecular motion. The calculations utilize vibrationally independent most accurate ab initio potential energy surface (PES) of Hutson et al. expanded in Legendre polynomial series up to lmax = 24. New improved algorithm of classical rotational frequency selection is applied. The dependences of CO2 half-widths on rotational quantum number J up to J=100 are computed for the temperatures between 77 and 765K and compared with available experimental data as well as with the results of fully quantum dynamical calculations performed on the same PES. To make the picture complete, the predictions of two independent variants of the semi-classical Robert-Bonamy formalism for dipole absorption lines are included. This method. however, has demonstrated poor accuracy almost for all temperatures. On the contrary, classical broadening coefficients are in excellent agreement both with measurements and with quantum results at all temperatures. The classical impact theory in its present variant is capable to produce quickly and accurately the pressure broadening coefficients of spectral lines of linear molecules for any J value (including high Js) using full-dimensional ab initio - based PES in the cases where other computational methods are either extremely time consuming (like the quantum close coupling method) or give erroneous results (like semi-classical methods).