Effective Polarizability Research Articles

Study of H2O Polarizability Based on Data on Rovibrational Line Shifts by Buffer Gas Pressure

The study of the vibrational dependence of H2O polarizability α is based on the comparison of experimental and calculated line shifts induced by argon, nitrogen, and air pressure in different H2O vibrational bands. The dependence of α on the internal coordinate θ, which describes large-amplitude bending vibration in the molecule, is expressed by a power series. The coefficients of the power series were selected so as to ensure the best agreement between the calculated matrix elements 〈ψn|α(θ)|ψn〉 and the polarizability values α(n) derived from the analysis of experimental H2O absorption line shifts in nν2 vibrational bands by nitrogen, oxygen, air, and argon pressure. The rotational contributions in the effective H2O polarizability are calculated and discussed. The α(θ) representation found is compared with ab initio calculations.

Cylindrical micro and nanowires: Fabrication, properties and applications

The state of the art in cylindrical nano and micro wires is reviewed with particular emphasis on the latest research trends. We analyze some of the key properties for prospective applications including magnetic anisotropy and micromagnetic structure, spin-caloritronics, domain wall dynamics and its control by transverse magnetic field and induced anisotropy, high frequency impedance and magnetic control of the electric polarizability, shape-memory and magnetocaloric effects in Heusler alloys wires. Cylindrical nanowires present specific magnetic domain configurations as complex vortex and transverse domains while the magnetization reversal typically involves propagation of Bloch-point domain walls. Such magnetic behavior offers new perspectives for applications in advanced technologies including spintronics, logic devices and novel magnetic recording media, functionalization and bioengineering and sensor devises. In particular, rapidly solidified glass-coated amorphous nanowires and submicron wires which constitute a novel class of ultrathin soft magnetic materials are attractive for future micro and nano sensors.Amorphous and nanocrystalline microwires prepared by rapid quenching from the melt can present quite peculiar magnetic properties, like spontaneous magnetic bistability associated with single and large Barkhausen jump and magnetoimpedance effect. Magnetic properties of amorphous microwires are related to the value and sign of the magnetostriction constant since the magnetoelastic anisotropy is one of the main sources of the magnetic anisotropy. As-prepared microwires with positive magnetostriction constant show generally rectangular hysteresis loops and fast domain wall propagation. In the case of low and negative magnetostriction, the wires demonstrate inclined hysteresis loops and large magnetoimpedance. To refine the magnetic structure, the easy anisotropy can be adjusted by annealing in the presence of a magnetic field and/or mechanical stress. Thus, the magnetic bistability in negative magnetostriction wires can be induced by annealing. Minimizing the magnetoelastic anisotropy either by adjusting the chemical composition with a low magnetostriction coefficient or by heat treatment is an appropriate route for enhancing the domain wall velocity. Tailoring the magnetic anisotropy by stress-annealing is also a promising method of the optimization of the domain wall dynamics in magnetic microwires.Soft magnetic properties and tunable magnetic structure of amorphous microwires are responsible for the magnetoimpedance effect, which preserves a high sensitivity up to GHz frequencies. This opens up novel applications based on the electric polarization of a finite-length microwire depending on the wire surface impedance near the antenna resonance, including embedded wireless sensing elements, self-sensing composites and selective microwave materials.Heusler alloys demonstrate the huge variety of physical properties that can be obtained by simple change in composition. Naturally, the efforts have been made to produce Heusler-based nano and micro wires to take advantage of variety of their physical properties in a miniature form. In this review, the emphasis is made on Heusler alloy glass-coated microwires.

Effective dipolar polarizability of amorphous arrays of size-dispersed nanoparticles.

Inhomogeneity of nanoparticle size, shape, and distribution is ubiquitous and inherent in fabricated arrays or may be a deliberate attempt to engineer the optical response. It leads to a spread of polarizabilities of interacting elements and phases of scattered light, and quantitative understanding of these effects is important. Focusing on random/amorphous arrays of optical antennas, we combine T-matrix calculations and an analytical approach based on an effective dipolar polarizability within a film of dipoles framework to quantify the spectral response as a function of the particle inhomogeneity and stochastic clustering. The interplay of position-dependent stochastic coupling and size distribution of antennas determines the optical properties of such arrays as a function of mean/standard deviation of diameter and minimum separation. The resonance wavelength, amplitude, and scattering-to-absorption ratio exhibit oscillations around their size-averaged values with periods and amplitudes given by average structural factors.

Lattice Resonances in Optical Metasurfaces With Gain and Loss

Periodic lattices of strongly scattering objects coupled to active media are of central importance in applied nanophotonics, serving as light-emitting metasurfaces of tailored emission properties and promising an attractive platform for testing novel physical concepts and realization of unprecedented light-shaping functions. We provide an overview of the semianalytical Green function method with Ewald lattice summation applied to the investigation of surface lattice resonances in periodic arrays of resonant nanoscatterers with gain and loss. This theory is meant as a minimal model for plasmonic lattices and metasurfaces with gain: minimal in complexity, yet sufficiently rich to be a self-consistent, fully retarded multiple scattering model. It enables to include the electromagnetic interactions between electric and/or magnetic point dipoles of arbitrary orientation and arrangement, taking into account retardation and tensorial nature of these interactions and including radiation damping. It gives access to the far-field observables (reflection/transmission), as well as to the photonic band structure of guided modes. At the same time, it does not violate the optical theorem, as opposed to the commonly used tight-binding or quasi-static models. After extending the lattice Green function formalism to include gain and loss in the unit cell, we demonstrate the effects of parity-time (PT) symmetry breaking in active-lossy plasmonic arrays: the emergence of exceptional points, nontrivial topology of photonic bands, diverging effective unit-cell polarizability, and spin polarization in the PT-broken phase.

Relaxation of atomic temperature anisotropy in a one-dimensional optical lattice enhanced by dynamic control of the aspect ratio

We study the relaxation dynamics of temperature anisotropy between longitudinal and transverse motions of $^{87}\mathrm{Rb}$ atoms in a one-dimensional optical lattice. The temperature imbalance is established by Raman sideband cooling applied along the lattice axis. At low temperature, a large difference between the longitudinal and transverse vibration frequencies limits the relaxation. We transform the trap potential by phase modulating the lattice beam to reduce the anisotropy and thereby enhance cross-dimensional sympathetic cooling. An extension of classical theory, which incorporates the quantization of the atomic motion, explains the experimental results well. We also report that effects of trap anharmonicity and atomic vector polarizability on broadening of the Raman sideband cancel each other at a particular lattice depth, which greatly facilitates sideband cooling.

Helicity maximization in a planar array of achiral high-density dielectric nanoparticles

We investigate how a periodic array composed of achiral isotropic high-refractive index dielectric nanospheres generates nearfield over the array surface reaching helicity density very close to its upper bound. The required condition for an array of nanospheres to generate “optimally chiral” nearfield, which represents the upper bound of helicity density, is derived in terms of array effective electric and magnetic polarizabilities that almost satisfy the effective Kerker condition for arrays. The discussed concepts find applications in improving chirality detection based on circular dichroism (CD) at the surface level instead of in the bulk. Importantly, the array would not contribute to the generated CD signal when used as a substrate for detecting chirality of a thin layer of chiral molecules. This eliminates the need to separate the CD signal generated by the array from that of the chiral sample.

Polarizability effects in atomic nuclei

This work sheds light upon how the atomic nucleus polarizes throughout the nuclear chart. Deviations from the well-known behavior of the nuclear dipole polarizability — which smoothly increases with increasing atomic mass number — are investigated. Relative enhancements are found for light nuclei as the nuclear symmetry energy decreases and, within a nucleus, as its excitation energy increases. These two properties are related by a diminishing binding energy of the nuclear system. Contrarily, hindrances of nuclear polarizability are observed in the photo-neutron cross-section data and photon-strength functions of semi-magic nuclei with [Formula: see text], 50 and 82, which support the presence of shell effects at low-lying excitations and — assuming validity of the Brink-Axel hypothesis — at high-excitation energies up to the quasi-continuum region. These features assign the nuclear dipole polarizability as a sensitive measure of the long-range correlations of the nuclear force, and provide a new spectroscopic probe to investigate collective phenomena, shell closures, and the elusive nuclear symmetry energy. Particular cases of quadrupole collectivity are also discussed in terms of the available, and yet so scarce, information on nuclear polarizability (e.g. Sn and Ni isotopes).

Nanobismuth enhanced plasmonic, emission and Faraday rotation properties of diamagnetic tellurite glasses

Bismuth has played important roles in metal and condensed matter physics. This paper reports the influence of Bi nanoparticle to diamagnetic tellurite glass-forming, structure, spectra andproperties. 30 nm hexagonal pure Bi nanoparticles (NPs) presented an obvious SPR effect around 275 nm, broad emission FWHM (200 nm) and superparamagnetic behavior. Successfully incorporated of nanobismuth (<5%) into glass and the BiNPs modifications on TeO4, TeO3 and NBOs structure has been confirmed through FT-IR, Raman spectra, DSC and Urbach energy measurement. UV–visible spectra showed SPR peak of BiNPs at 508 (glass) and 700 nm (metal-glass) with gradually increased intensities and gradually broadened cross-sections with doping amount. The visible and infrared luminescence show characteristic emission of BiNPs at 460 nm, 730 nm, 910 nm and 1150 nm respectively. All samples exhibited diamagnetic property and the magnetization increased with the doping amount due to the diamagnetic nature of host and dopant. The increased polarizability and intense SPR effect enhanced Faraday rotation and a large Verdet constant (0.1828 min/G.cm) at 633 nm was obtained for 5%BiNPs doped glass which also exhibited large thermal stability and good luminescence performance.

Structure and microwave dielectric properties of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 ceramics

Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al1/2Nb1/2)4+ substitution on the dielectric properties of Li2Mg3TiO6 ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al1/2Nb1/2)4+ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (εr) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τf|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li2Mg3Ti0.92(Al1/2Nb1/2)0.08O6 sample exhibited outstanding dielectric characteristics:εr = 15.256, Q × f = 174,300 GHz and τf = −19.97 ppm/°C.

Extraordinary Properties of Alcohols from the Homologous Series of Methanol

Non-trivial properties of thermodynamic quantities such as the density, the critical and triple point temperatures, and their ratio, as well as the optical and dielectric properties, have been analyzed for primary alcohols from the methanol series. The aim is to reveal relationships among their values measured at the same temperatures for alcohols with different ordinal numbers m’s in the methanol series. It is shown that the non-monotonic character of the temperature dependences of alcohol densities is associated with methanol rather than ethanol, as may seem at first glance. The critical temperature of methanol also deviates from the quasilinear dependence of the critical alcohol temperatures on m. With the growing m, the ratio between the critical and triple-point temperatures for alcohols is shown to tend to the corresponding value for water. Simple linear dependences of the electronic and effective static polarizabilities of alcohol molecules on m are established. The transverse and longitudinal components of the polarizability tensor for alcohol molecules are found. The dipole moments of the closest neighbor molecules in the alcohols are proved to anticorrelate, i.e. to orient in opposite directions.

Optical spectra of organic dyes in condensed phases: the role of the medium polarizability.

When designing molecular functional materials, the properties of the active specie, the dye, must be optimized fully accounting for the presence of a surrounding medium (a solvent, a polymeric matrix, etc.) that may largely alter the dye behavior. Here we present an effective model to account for the effects of the medium electronic polarizability on the spectral properties of charge-transfer dyes. Different classes of molecules are considered and the proposed antiadiabatic approach to solvation is contrasted with the adiabatic approach, currently adopted in all quantum chemical approaches to solvation. Transition frequencies and band-shapes are addressed, and the role of the medium polarizability on symmetry-breaking phenomena is also discussed.

Activity Trends in Desoxy Anthrapyrazoles: The Influence of Molar Volume, Polarizability and Lipophilicity of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; C&amp;lt;sub&amp;gt;5&amp;lt;/sub&amp;gt; Side Chains on Their Anticancer Response

QSAR methodology was used to assess the effects of lipophilicity (logP), molar volume (MV) and polarizability (pl) of the side chains at N2 and C5 of 20 known desoxy anthrapyrazoles on their in vitro anticancer activity expressed as the negative logarithm of the inhibitory concentration of 50% of L1210 murine leukemia cell line (1/logIC50). The main data set shows poor correlations between biological response and the descriptors with exception of MV of the C5 side chain, where a moderate correlation was discerned ( =0.60, n = 18, two outliers). To extract more information regarding mechanism, the main data set was visually classified to three clusters depending on N2 side chain. Cluster 1 containing six 5-substituted 2-[(2-hydroxyethyl) amino] ethyl anthrapyrazoles; cluster 2 contains ten 5-subsitutes 2-(diethyl amino) ethyl anthrapyrazoles and cluster 3 contains four anthrapyrazoles with miscellaneous substituents at both N2 and C5. For cluster 1, MV and pl of C5 show high correlation with biological response (R2’s = 0.75 and 0.72 respectively) while logP gives a weak correlation (R2 = 0.44). For cluster 2, the correlations of logP and pl of C2side chain are higher (=0.66 and 0.62 respectively) compared with MV (=0.16). Cluster 3 shows very poor correlation with all descriptors (~0.3). This indicates mechanistic distinction between the three clusters. Derived descriptors which represent the difference between the descriptors of N2 and C5 side chains where used to explore the presence of interplay between these descriptors in affecting variability of the biological response.

Large optical polarizability causing positive effects on the birefringence of planar-triangular BO3 groups in ternary borates.

The structure-property relationship of photoelectric functional materials has been recognized as a hot topic. The study of the inner link between the band gaps and birefringence of optical materials is extremely crucial for the design and creation of novel optical devices, but still remains rather unexplored. In this work, taking a series of borates with only planar-triangular BO3 groups, α-/β-TM3(BO3)2 (TM = Zn, Cd), Cd2B2O5, and M3(BO3)2 (M = Hg, Mg, Ca, Sr) as the research subject, the comprehensive relationship between their electronic structures and linear optical properties has been systematically investigated. Through combining experimental measurements and theoretical calculations, the effect of optical polarizability on the birefringence of these borates was clarified. Based on the present discussion, the relationship between the O (2p) bandwidth of the highest valence band and the HSE06 band gaps is opposite. Meanwhile, a method involving the determination of so-called optical permittivity Δε to evaluate the magnitude of birefringence Δn is found to be feasible. A large Δε makes a positive contribution to Δn. In addition, the experimentally measured band gaps and IR vibrations are in good agreement with theoretical results for the compounds α-Cd3(BO3)2 and Cd2B2O5.

Polarizable MD simulations of ionic liquids: How does additional charge transfer change the dynamics?

Both experimental and computational evidence exist that Coulomb interactions between the molecular ions in ionic liquids are significantly damped by almost a factor of two. This circumstance is often used to justify charge scaling. However, as polarizable MD simulations are also capable of explaining the reduced Coulomb interaction between the ionic liquid ions [C. Schröder, Phys. Chem. Chem. Phys., 2012, 14, 3089], the question arises, if the reduced Coulomb interactions are due to a charge transfer between the molecules or due to an overall effect of induced dipolar interactions. We aim to contribute to this discussion using polarizable MD simulations of 1-ethyl-3-methylimidazolium tetrafluoroborate including a new model for treating charge transfer between the cations and anions. The diffusion time scales are not changed significantly with the inclusion of charge transfer, but individual ions show a strong dependence on charge transfer amounts. Ions which have transferred more charge, and have a charge with a smaller magnitude, diffuse slower. The charge transfer model shows a slightly larger conductivity, despite having smaller charges, and shows a much stronger contribution of the anions to the conductivity. With charge transfer, the anions become the dominant species for charge transport, while the polarizable models show a roughly equal contribution from the anions and the cations.

Polarizability and isotope effects on dispersion interactions in water

True understanding of dispersion interaction in solution remains elusive because of difficulty in the precise evaluation of its interaction energy. Here, the effect of substituents with different polarizability on dispersion interactions in water is discussed based on the thermodynamic parameters determined by isothermal titration calorimetry for the formation of discrete aggregates from gear-shaped amphiphiles (GSAs). The substituents with higher polarizability enthalpically more stabilize the nanocube, which is due to stronger dispersion interactions and to the hydrophobic effect. The differences in the thermodynamic parameters for the nanocubes from the GSAs with CH3 and CD3 groups are also discussed to lead to the conclusion that the H/D isotope effect on dispersion interactions is negligibly small, which is due to almost perfect entropy-enthalpy compensation between the two isotopomers.

Polarizability of the Active Site in Enzymatic Catalysis: Cytochrome c.

Anisotropic polarizability of the heme in cytochrome c is found to be a major factor in suppressing the activation barrier of protein electron transfer (catalytic effect). Polarizability couples to the electric field of protein and water to enhance fluctuations of the electron-transfer energy gap and the corresponding variance reorganization energy λvar. The reorganization energy observable by kinetic measurements λr = (λSt)2/λvar is composed of λvar and the Stokes-shift reorganization energy λSt. It is lowered compared to the usually reported λSt due to polarizability of the active site leading to λvar > λSt. The coupling of electrostatic protein-water fluctuations to the polarizable active site is accounted for here by empirical valence-bond diagonalization of the active-site Hamiltonian along the simulation trajectory. We show that recent simulations employing this technique, which failed to find the effect of polarizability on electron-transfer kinetics, were erroneous in neglecting the diagonal dipole moments in the Hamiltonian matrix and failing to rotate the electric field produced by the protein-water medium into the molecular frame of the active site. We find that anisotropy of the tensor of polarizability difference in the two oxidation states of the heme matches anisotropy of the second-rank tensor constructed from the electric field at the active site. Exposure of the heme to water from only one side carries significant catalytic function, directly leading to the field anisotropy and the corresponding depression of the activation barrier.

Hydrogen Bonds with Chalcogens: Looking Beyond the Second Row of the Periodic Table

Compared to conventional hydrogen bonds like (O–H···N, N–H···O, O–H···O, N–H···N), hydrogen bonds involving heavier chalcogens like sulfur, selenium, and tellurium have been considered weaker owing to less electronegativity of these elements. However, various instances exist to prove that these hydrogen bonds (H bonds) are of similar strength of conventional hydrogen bonds, although the nature of hydrogen bonding could be different depending on a combination of electronegativity, polarizability, and dispersion effects. We have presented a plethora of such H bonds that have been investigated over past several decades through high-resolution laser spectroscopy, microwave spectroscopy, and quantum chemical calculations. These H bonds not only play important roles in biological systems, but are increasingly being tuned in nature and strength to construct artificial models that can aid our mechanistic understanding of non-covalent interactions and also help in modulation of activity, detection, and combat of diseases. We have discussed how these interactions could be exploited for applications in crystal engineering, superconductivity, gas capture, and field-effect transistor studies.

Illusion mechanisms with cylindrical metasurfaces: A general synthesis approach

We explore the use of cylindrical metasurfaces in providing several illusion mechanisms including scattering cancellation and creating fictitious line sources. We present the general synthesis approach that leads to such phenomena by modeling the metasurface with effective polarizability tensors and by applying boundary conditions to connect the tangential components of the desired fields to the required surface polarization current densities that generate such fields. We then use these required surface polarizations to obtain the effective polarizabilities for the synthesis of the metasurface. We demonstrate the use of this general method for the synthesis of metasurfaces that lead to scattering cancellation and illusion effects, and discuss practical scenarios by using loaded dipole antennas to realize the discretized polarization current densities. This study is the first fundamental step that may lead to interesting electromagnetic applications, like stealth technology, antenna synthesis, wireless power transfer, sensors, cylindrical absorbers, etc.

Brownian Motion and Large Electric Polarizabilities Facilitate Dielectrophoretic Capture of Sub-200 nm Gold Nanoparticles in Water.

Dielectrophoresis can move small particles using the force resulting from their polarization in a divergent electric field. In liquids, it has most often been applied to micrometric objects such as biological cells or latex microspheres. For smaller particles, the dielectrophoretic force becomes very small and the phenomenon is furthermore perturbed by Brownian motion. Whereas dielectrophoresis has been used for assembly of superstructures of nanoparticles and for the detection of proteins and nucleic acids, the mechanisms underlying DEP of such small objects require further study. This work presents measurements of the alternating-current (AC) dielectrophoretic response of gold nanoparticles of less than 200 nm diameter in water. An original dark-field digital video-microscopic method was developed and used in combination with a microfluidic device containing transparent thin-film electrodes. It was found that the dielectrophoretic force is only effective in a small zone very close to the tip of the electrodes, and that Brownian motion actually facilitates transport of particles towards this zone. Moreover, the fact that particles as small as 80 nm are still efficiently captured in our device is not only due to Brownian transport but also to an effective polarizability that is larger than what would be expected on basis of current theory for a sphere in a dielectric medium.

Diffusional Encounter Rate Constants for Xanthone and 2-Naphthoic Acid by Flash Photolysis Experiments and Brownian Dynamics Simulations: Substantial Effects of Polarizability of the Triplet State.

Diffusional encounter rate constants, for xanthone and 2-naphthoic acid molecules in their triplet states with xanthone or 2-naphthoic acid molecules in their triplet or singlet states, were determined using nanosecond laser flash photolysis spectroscopy. Simultaneously, Brownian dynamics simulations were used to compute these rate constants for assumed models of encountering molecules. Altogether, a global fit to transient absorption progress curves, reporting populations of triplet state xanthone and triplet state 2-naphthoic acid molecules, allowed us to determine six diffusional encounter rate constants from our experiments. The most important result of this study is the detection of substantial effects of the electric polarizability of molecules in their triplet state, visible for xanthone triplet and 2-naphthoic acid ground states, a homo triplet-triplet annihilation of 2-naphthoic acid, and a hetero triplet-triplet annihilation for xanthone and 2-naphthoic acid.