A hybrid quantum-classical theory for predicting terahertz charge-transfer plasmons in metal nanoparticles on graphene.

Metal nanoparticle (NP) complexes lying on a single-layer graphene surface are studied with a developed original hybrid quantum-classical theory using the Finite Element Method (FEM) that is computationally cheap. Our theory is based on the motivated assumption that the carrier charge density in the doped graphene does not vary significantly during the plasmon oscillations. Charge transfer plasmon (CTP) frequencies, eigenvectors, quality factors, energy loss in the NPs and in graphene, and the absorption power are aspects that are theoretically studied and numerically calculated. It is shown the CTP frequencies reside in the terahertz range and can be represented as a product of two factors: the Fermi level of graphene and the geometry of the NP complex. The energy losses in the NPs are predicted to be inversely dependent on the radius R of the nanoparticle, while the loss in graphene is proportional to R and the interparticle distance. The CTP quality factors are predicted to be in the range ∼10-100. The absorption power under CTP excitation is proportional to the scalar product of the CTP dipole moment and the external electromagnetic field. The developed theory makes it possible to simulate different properties of CTPs 3-4 orders of magnitude faster compared to the original FEM or the finite-difference time domain method, providing possibilities for predicting the plasmonic properties of very large systems for different applications.

Intense charge transfer plasmons in golden nanoparticle dimers connected by conductive molecular linkers.

Golden nanoparticle dimers connected by conjugated molecular linkers 1,2-bis(2-pyridyl)ethylene are produced. The formation of stable dimers with 22 nm diameter nanoparticles is confirmed by transmission electron microphotography. The possibility of charge transfer through the linkers between the particles in the dimers is shown by the density functional theory calculations. In addition to localized plasmon resonance of solitary nanoparticles with a wavelength of 530 nm, the optical spectra exhibit a new intense absorption peak in the near-infrared range with a wavelength of ∼780 nm. The emergent absorption peak is attributed to the charge-transfer plasmon (CTP) mode; the spectra simulated within the CTP developed model agree with the experimental ones. This resonant absorption may be of interest to biomedical applications due to its position in the so-called transmission window of biological tissues. The in vitro heating of CTP dimer solution by a laser diode with a wavelength of 792 nm proved the efficiency of CTP dimers for achieving a temperature increase of ΔT = 6 °C, which is sufficient for hyperthermia treatment of malignant tumors. This indicates the possibility of using hyperthermia to treat malignant tumors using the material we synthesized.

Infrared bound states in the continuum: random forest method.

In this Letter, we consider optical bound states in the continuum (BICs) in the infrared range supported by an all-dielectric metasurface in the form of subwavelength dielectric grating. We apply the random forest machine learning method to predict the frequency of the BICs as dependent on the optical and geometric parameters of the metasurface. It is found that the machine learning approach outperforms the standard least square method at the size of the dataset of ≈4000 specimens. It is shown that the random forest approach can be applied for predicting the subband in the infrared spectrum into which the BIC falls. The important feature parameters that affect the BIC wavelength are identified.

Charge transfer plasmons in the arrays of nanoparticles connected by conductive linkers.

Charge transfer plasmons (CTPs) that occur in different topology and dimensionality arrays of metallic nanoparticles (NPs) linked by narrow molecular bridges are studied. The occurrence of CTPs in such arrays is related to the ballistic motion of electrons in thin linkers with the conductivity that is purely imaginary, in contrast to the case of conventional CTPs, where metallic NPs are linked by thick bridges with the real optical conductivity caused by carrier scattering. An original hybrid model for describing the CTPs with such linkers has been further developed. For different NP arrays, either a general analytical expression or a numerical solution has been obtained for the CTP frequencies. It has been shown that the CTP frequencies lie in the IR spectral range and depend on both the linker conductivity and the system geometry. It is found that the electron currents of plasmon oscillations correspond to minor charge displacements of only few electrons. It has been established that the interaction of the CTPs with an external electromagnetic field strongly depends on the symmetry of the electron currents in the linkers, which, in turn, are fully governed by the symmetry of the investigated system. The extended model and the analytical expressions for the CTPs frequencies have been compared with the conventional finite difference time domain simulations. It is argued that applications of this novel type of plasmon may have wide ramifications in the area of chemical sensing.

Engineering novel tunable optical high-Q nanoparticle array filters for a wide range of wavelengths.

The interaction of non-monochromatic radiation with arrays comprising plasmonic and dielectric nanoparticles has been studied using the finite-difference time-domain electrodynamics method. It is shown that LiNbO3, TiO2, GaAs, Si, and Ge all-dielectric nanoparticle arrays can provide a complete selective reflection of an incident plane wave within a narrow spectral line of collective lattice resonance with a Q-factor of 103 or larger at various spectral ranges, while plasmonic refractory TiN and chemically stable Au nanoparticle arrays provide high-Q resonances with moderate reflectivity. Arrays with fixed dimensional parameters make it possible to fine-tune the position of a selected resonant spectral line by tilting the array relative to the direction of the incident radiation. These effects provide grounds for engineering novel selective tunable optical high-Q filters in a wide range of wavelengths, from visible to middle-IR.

Collective lattice resonances in arrays of dielectric nanoparticles: a matter of size.

Collective lattice resonances (CLRs) in finite-sized $ 2D $2D arrays of dielectric nanospheres have been studied via the coupled dipole approximation. We show that even for sufficiently large arrays, up to $ 100 \times 100 $100×100 nanoparticles (NPs), electric or magnetic dipole CLRs may differ significantly from the ones calculated for infinite arrays with the same NP sizes and interparticle distances. The discrepancy is explained by the existence of a sufficiently strong cross-interaction between electric and magnetic dipoles induced at NPs in finite-sized lattices, which is ignored for infinite arrays. We support this claim numerically and propose an analytic model to estimate a spectral width of CLRs for finite-sized arrays. Given that most of the current theoretical and numerical researches on collective effects in arrays of dielectric NPs rely on modeling infinite structures, the reported findings may contribute to thoughtful and optimal design of inherently finite-sized photonic devices.

Suppression of surface plasmon resonance in Au nanoparticles upon transition to the liquid state.

Significant suppression of resonant properties of single gold nanoparticles at the surface plasmon frequency during heating and subsequent transition to the liquid state has been demonstrated experimentally and explained for the first time. The results for plasmonic absorption of the nanoparticles have been analyzed by means of Mie theory using experimental values of the optical constants for the liquid and solid metal. The good qualitative agreement between calculated and experimental spectra support the idea that the process of melting is accompanied by an abrupt increase of the relaxation constants, which depends, beside electron-phonon coupling, on electron scattering at a rising number of lattice defects in a particle upon growth of its temperature, and subsequent melting as a major cause for the observed plasmonic suppression. It is emphasized that observed effect is fully reversible and may underlie nonlinear optical responses of nanocolloids and composite materials containing plasmonic nanoparticles and their aggregates in conditions of local heating and in general, manifest itself in a wide range of plasmonics phenomena associated with strong heating of nanoparticles.

[Experience in the use of synchrotron radiation for the x-ray study of biopolymers]. / Opyt ispol'zovaniia sinkhrotronnogo izlucheniia dlia rentgenograficheskogo issledovaniia biopolimerov

The results of methodical work, carried out on the sources of synchrotron radiation (SR) with the aim of using SR as a powerful source of X-rays for studying biopolymer structure, are presented. The questions of monochromatization are considered. The technique designed for photoregistration of diffraction patterns within the wide range of scattering angles is described. X-ray diffraction patterns of feather ceratin, collagen and striated muscle are obtained with exposure periods ten times less than those in the case of X-ray tubes. The high resolution of diffraction lines, the absence of parasitic phone and the presence of reflections within the wide range of scattering angles are characteristic of these patterns.

[X-ray diffraction study of adaptive changes in the structure of dense phase juice from the duodenum]. / Rentgenograficheskoe issledovanie adaptivnykh izmenenii struktury plotnoi fazy soka dvenadtsatiperstnoi kishki.

Low-angle X-ray diffraction patterns of canine duodenal juice precipitates taken at two stages of digestion, after 20 h fasting and after food stimulation have been obtained. Both diffraction patterns are due to glycoproteins. However, the glycoproteins contained in the precipitate after food stimulation occur in the native form while in fasting animals they are partially degraded.

[Roentgenographic study of the duodenal juice components in the dog]. / Rentgenograficheskoe izuchenie komponentov soka dvenadtsatiperstnoi kishki sobaki.

It is shown that X-ray pattern rich in reflections that we have received earlier from concentrated canine duodenal juice is the sum of the patterns arising from both mucin macromolecules and from unknown component of the juice. The functional role of the duodenal juice regularity observed is discussed.

[Effect of thiol reagents on the structure of mucus glycoproteins (mucins)]. / Vliianie tiolovykh reagentov na strukturu glikoproteinov slizi (mutsinov).

The structure of both native mucins and subunits obtained by thiol reduction was studied by small-angle X-ray diffraction. X-ray pattern from the subunits significantly differs from that of the native mucins in the number, spacings and width of the reflections observed. Decrease in the number of the reflections and increase of their width pointed out that isolated subunits are less regular structure than the whole mucin molecule. This may be due to the two reasons: 1) conformation of the subunits in native molecule differs from that of in isolate state; 2) native mucin molecule is not a simple polymer, formed by the subunits.