The plasmon enhancement of carbon dots (CDs) photoluminescence (PL) in thin-film structures with metal nanoparticles is of interest in their practical applications in sensors and light-emitters. This paper investigates CDs in the thin-film structures with nanogranulated silver films with different thickness. CDs in an aqueous solution were precipitated by spin-coating over the surface of annealed Ag films coated previously by a polymer layer. The IR, optical density and PL spectra of free-CDs and in thin-film structures with Ag films were studied. The PL intensity enhancement of CDs was demonstrated in the thin-film structures with Ag films due to absorption cross-section enhancement and the action of the Purcell effect. The improvement of thin-film structures producing technology will contribute to PL enhancement of CDs and the development of new thin-film sensors, light-emitters and other devices on their base.

SummarySilver nanostructures are of interest to be used in hybrid thin‐film structures with various materials. In this work, we analyse 3D AFM images of granulated silver film nanostructures prepared by thermal evaporation. The advanced AFM data study aims to understand how film thickness and postannealing affect the nanostructure morphology changes. For the first time, the evaluation of surface statistical parameters and fractal geometry were used to characterise the nanostructure morphology of Ag island films. The samples with gravimetric thickness of 2, 4 and 10 nm were analysed before and after annealing at 200°C for 10 min. The statistical processing revealed the essential variation of parameters with Ag film thickness increment and as a postannealing result. The nonmonotonic variation of surface roughness, skewness and fractal dimensions were found. It is caused by the features of the film growth process with the thickness increment and thermally activated diffusion of Ag nanoparticles during annealing.Lay DescriptionSilver nanostructures are of great scientific interest due to their unique properties and wide applicability. In this work, we analyse microscopic 3D images of silver nanostructures deposited on quartz in vacuum chamber. Such thin‐film nanostructures consisted of silver nanoparticles attached to the surface of quartz substrate. We aimed at studying how effective film thickness and postannealing affect the nanostructure shapes and forms. Effective thickness is the equivalent thickness of a smooth film. For this purposes we used special parameters called statistical parameters and fractal geometry to investigate nanostructures. The samples with effective thickness of 2, 4 and 10 nm were analysed before and after annealing at 200°C for 10 min. It has been shown, that effective Ag film thickness and postannealing results in variation of nanostructures forms. We have shown that the variation of statistical parameters were nonmonotonic. It is caused by the features of the film growth process with the thickness increment and thermally activated diffusion of Ag nanoparticles during annealing.

n this work, we studied changes in the spectra of optical density, photoluminescence (PL) and Raman spectra of hybrid thin-film structures based on a-C: H and granular silver films before and after annealing of samples at 200 ° C. The hypsochromic shift of the main plasmon peak, the formation of double resonance spectra, and an increase in the band intensity were observed after annealing of samples with the gravimetric Ag film thickness of 10 nm. The influence of both the morphology of the nanostructure of Ag films and the features of the electronic structure of a-C: H films were observed on the plasmon enhancement of the PL and Raman spectra. For samples based on a-C:H with an optical gap Eg = 0.4 eV, a more effective PL enhancement was observed after annealing of the samples. At the same time, in the samples with Eg = 2.7 eV, the PL intensity practically did not change, remaining higher. The amplification of resonant Raman scattering was selective. It was associated with scattering by polycyclic aromatic groups predominant in the structure of the a-C: H film with a narrower optical gap.

The changes occurring in the optical density, photoluminescence (PL), and Raman scattering (RS) spectra of thin-film structures based on a-C:H and granulated silver films after annealing of samples at 200°C are studied. A hypsochromic shift of the main plasmon peak, formation of double resonance spectra, and an increase in band intensities were observed after annealing of samples with a 10-nm gravimetric thickness of the Ag film. It is shown that both the Ag film nanostructure morphology and the a-C:H film electronic structure affect the plasmon enhancement of PL and Raman spectra. A more efficient PL enhancement was observed after annealing of samples based on a-C:H with optical band gap E g = 0.4 eV. At the same time, the initially higher PL intensity of samples with E g = 2.7 eV almost did not change. The enhancement of resonance RS had a selective character. It was related to scattering by polycyclic aromatic groups, which are dominant in the structure of the a-C:H film with a narrower optical band gap.

In this work, double plasmon resonances in hybrid structures comprising Ag nanoparticles (NPs) and amorphous hydrogenated carbon films (a-C:H) have been studied. Granulated silver films with a gravimetric thickness of 10 nm were thermally deposited on top or underneath a-C:H films fabricated by plasma-assisted chemical vapour deposition on a quartz substrate. Two plasmon bands with comparable intensities have been observed in the hybrid structures optical density spectrum after annealing at 200 degrees C. On the other hand, in the absence of the amorphous hydrogenated carbon film the short-wavelength peak in the optical density spectrum of the same Ag film is hardly observable. In addition, plasmon-enhanced photoluminescence of the a-C:H film being excited close to the spectral dip at the wavelength of 405 nm was observed. The nature of double plasmon resonance spectra were discussed and explained by the resonance interaction of plasmons excited in Ag NPs with excitons in a-C:H.

It has been shown the possiblity of threshold voltage reducing of dynamic light scattering effect in LC cells. The decrease of the threshold voltage has occurred due to the use of electrodes with metal-dieletric-semiconduxtor micro-structures containing gold nanoparticles. The enhancement of the electrode efficiency contributes to an increase in the conductivity of the cells and to a decrease in the intensity of passed light in the low-voltage region.

The regularities study of a-C:H film photoluminescence (PL) enhancement by localized surface plasmon resonance (LSPR) in hybrid structures with nanogranulated Ag film was the main aim of this work. We have compared the PL spectra of two thin-film hybrid structures in which the a-C:H optical gap was 2.7 eV and 0.4 eV. The a-C:H films with the thickness of similar to 50 nm were deposited on quartz substrates using the chemical vapor deposition of toluene vapor in glow discharge plasma. The nanogranulated silver film by 10 nm thickness was deposited on all a-C:H film by the thermal evaporation method at the same time. The optical density spectra and the surface morphology of Ag nanoparticles (NPs) by AFM as well as the PL spectra of a-C:H in the hybrid structures at the visible range and room temperature were obtained. It has been shown that PL intensity of wide gap a-C:H in the hybrid structure increased fourfold but the narrow-gap film sevenfold against the intensity of initial films at excitation wavelength 405 nm. The intensity of dipole and quadrupole mode peaks increased in the optical density spectra after annealing of the hybrid structures at 200 degrees C. This fact was connected with the form and size changes of Ag NPs. The blue shift of PL maximum to 498 nm and the twentyfold enhancement of PL intensity of the hybrid structure with the narrow-gap a-C:H was observed after annealing. The mechanism of plasmon-enhanced of a-C:H PL in hybrid structures with Ag NPs was discussed. Obtained results can find practice applications in both light-emitting devices and biosensor chip.

The possibility of reducing the threshold of the effect of dynamic light scattering in liquid-crystal cells has been demonstrated. The threshold lowering is favored by using electrodes with metal–insulator–semiconductor microstructures containing gold nanoparticles. The increase in the efficiency of the electrodes leads to a higher cell conductivity and weaker light intensity at low voltages.

In this work, the optical constant films of amorphous hydrogenated carbon (a-C: H) and a hybrid structure based on it with a granulated gold film before and after their annealing at 300 °C were studied by spectral ellipsometry. The dispersions n (λ) and k (λ) of the a-C:H film were established using the Cauchy approximation and its thickness. The spectral features of the Au plasmon nanoparticle layer deposited on the a-C:H surface were modeled as an effective medium and a Lorentz oscillator. The parameters of the films and their thickness were determined by fitting the calculated spectra to the ellipsometric spectra  (λ) and  (λ). The obtained data were used to determine the parameters of the Lorentz oscillator in the model of a-C:H / Au two-layer structure. As a result of the a-C:H / Au structure annealing, the intensity of the maxima in the spectra n and k increased, their position shifted to the blue region, and the half-width of the bands decreased. The observed changes in the ellipsometric spectra are completely consistent with the spectrophotometric data of this structure.

Optical сonstants of an amorphous hydrogenated carbon (a-C:H) film and its hybrid structure with granular gold film before and after annealing at 300°C have been investigated by spectral ellipsometry. Dispersions n(λ) and k(λ) of the a-C:H film and its thickness have been identified using the Cauchy approximation. The spectral features of the layer of Au plasmon nanoparticles deposited on the a-C:H surface have been modeled in the form of an effective medium and Lorentz oscillator. The parameters of the films and their thickness have been determined by fitting the calculated spectra to the ψ(λ) and Δ(λ) ellipsometric spectra. The obtained data have been used to determine the Lorentz oscillator parameters in the model of an a‑C:H/Au two-layer structure. The intensity of the maxima in the n and k spectra increased, their position shifted to the blue region, and the half-width of the bands decreased as a result of the a-C:H/Au structure annealing. The observed changes in ellipsometric spectra are fully consistent with the spectrophotometric data of this structure.

Spectra of optical density of granulated 2-nm-thick gold films deposited on the surface of thin films of amorphous hydrogenated carbon (a-C:H) on quartz substrates are investigated. A shift of the peak corresponding to the localized surface plasmon resonance toward the shorter wavelengths by 32 nm upon an increase in the optical bandgap of the a-C:H films from 0.8 to 2.4 eV is demonstrated. Simultaneously, an increase in intensity and narrowing of the plasmon-resonance band in spectra of gold nanostructures is observed. This fact indicates that formation of the granulated gold films on the surface of a-C:H films depends on the specific structural properties of the latter.

Localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs) in a granulated film with thickness 2 nm was investigated at the interface of two amorphous hydrogenated carbon (a-C:H) films with optical gap 0.67 eV and 2.7 eV. In these hybrid structures, a blue shift of the LSPR wavelength was observed in contrast with Au NPs on quartz surface at a room temperature. The annealing of such hybrid structures at 200 degrees C resulted in forming spheroid Au NPs with the dimensions about 11 nm which promotes increasing blue shift of the LSPR spectra. The intensity of the LSPR peak increased significantly after annealing at 300 degrees C, but Au NPs film morphology and LSPR peak position have not changed. After annealing at 400 degrees C the LSPR peak intensity in hybrid structure with a narrow gap a-C:H film decreased dramatically but did not change in the sample with a wide gap a-C:H. The observed changes in the LSPR spectra as a result of hybrid structures annealing are associated with the difference in the electronic and atomic structure of a-C:H thin films, as shown by their studies using Raman spectroscopy.

Background: The luminescence amplification of semiconductor quantum dots (QD) in the presence of self-assembled gold nanoparticles (Au NPs) is one of way for creating biosensors with highly efficient transduction. Aims: The objective of this study was to fabricate the hybrid structures based on semiconductor CdSe/ZnS QDs and Au NP arrays and to use them as biosensors of protein. Methods: In this paper, the hybrid structures based on CdSe/ZnS QDs and Au NP arrays were fabricated using spin coating processes. Au NP arrays deposited on a glass wafer were investigated by optical microscopy and absorption spectroscopy depending on numbers of spin coating layers and their baking temperature. Bovine serum albumin (BSA) was used as the target protein analyte in a phosphate buffer. A confocal laser scanning microscope was used to study the luminescent properties of Au NP/QD hybrid structures and to test BSA. Results: The dimensions of Au NP aggregates increased and the space between them decreased with increasing processing temperature. At the same time, a blue shift of the plasmon resonance peak in the absorption spectra of Au NP arrays was observed. The deposition of CdSe/ZnS QDs with a core diameter of 5 nm on the surface of the Au NP arrays caused an increase in absorption and a red shift of the plasmon peak in the spectra. The exciton-plasmon enhancement of the QDs' photoluminescence intensity has been obtained at room temperature for hybrid structures with Au NPs array pretreated at temperatures of 100 degrees C and 150 degrees C. It has been found that an increase in the weight content of BSA increases the photoluminescence intensity of such hybrid structures. Conclusion: The ability of the qualitative and quantitative determination of protein content in solution using the Au NP/QD structures as an optical biosensor has been shown experimentally.

In the present study, the polarisation-independent dynamic light scattering (DLS) in a nematic liquid crystal (LC) with a negative dielectric anisotropy has been compared in two operating modes by applying DC voltage or AC voltage to LC cells with a vertical and hybrid alignment. The attenuation of light transmittance and the DLS optical threshold without polarizers as well as a phase retardation of LC bend-splay deformation and a Fredericks threshold voltage with polarizers have been determined. Diffuse scattering of a light beam and broadband transmittance spectra of LC cells have been examined using the DC voltage in the interval of 0-40V. Multi-domain structures and turbulent flows in the LC cells have been observed by polarisation optical microscope. The results show that the enhancement of the diffuse scattering of light in the LC cells correlate with ion density increase. The largest attenuation of the light intensity in the LC cells with a vertical alignment was 16.4dB at a wavelength of 650nm with a minimum decay time equal to 2.5ms at DC voltage of 60V. Our study has been shown that switching from a diffuse light scattering state to a transparent state can be twice accelerated by applying AC voltage with high frequency to LC cells. [GRAPHICS] .

Изучены спектры оптической плотности гранулированных пленок золота толщиной 2 nm, осажденных на поверхность тонких пленок аморфного гидрогенизированного углерода (a-C : H) на кварцевых подложках.Показан сдвиг пика локализованного поверхностного плазмонного резонанса в коротковолновую область спектра на 32 nm при увеличении ширины оптической щели a-C : H

Local fields of metal nanoparticles can change quantum dots (QDs) absorption and luminescence. In this work, we have investigated the interaction of granulated Ag NPs films with CdSe/ZnS semiconductor QDs in hybrid structure with a-C:H thin films. We have studied hybrid structure with two a-C:H films on a quartz substrate having wider optical gap of 2.1 eV and narrow gap of 0.7 eV. The distribution of Ag NPs on the a-C:H was more ordered unlike a pure quartz surface. Homogeneous films of Ag NPs on a-C:H surface have narrower picks of LSPR in spectra. The intensity magnifying and the blue shift of the LSPR peak of Ag NPs on 31 nm in the spectra has been observed with an increase in the optical gap of a-C:H film. We have also compared how the properties of a-C:H films in hybrid structures with Ag NPs affect the absorption and luminescence of CdSe/ZnS quantum dots. The absorption maximum for the QDs on Ag NPs/a-C:H surface was higher than on Ag NPs on pure quartz. The red shift of the absorption peak was observed. We have observed photoluminescence quenching of the CdSe/ZnS QDs on the surfaces of the studied hybrid structures. The greatest quenching of QD luminescence was observed on quartz substrate. A less significant quenching of the CdSe/ZnS QDs luminescence was obtained in the sample with a-C:H film having a wider optical gap.

We investigated the dielectric losses and the ionic currents in the nematic liquid crystal (NLC) doped with semiconductor quantum dots (QDs) of CdSe/ZnS core - shell type and covered with trioctylphosphine oxide (TOPO) molecules. The dielectric loss tangent of the NLC composites increased with increasing the QDs concentration from 0.1 to 0.3wt%. The density of mobile ions in the composites increased linearly and the average values of ions mobility in the composites decreased with increasing the QDs concentration. The fast ions with the mobility of about 10(-10)m(2)/Vs and the slow ions with the mobility of about 10(-11)m(2)/Vs were detected in the NLC composites. The growth of the content of slow ions took place with increasing the QDs concentrations. Increasing the dielectric loss tangent was observed with increasing the duration of sonication time of the NLC composites to prepare homogeneous suspensions. The fragmentation of the CdS/ZnS shell as a result of the sonication may lead to the appearance of the slow ions in the NLC composites.[GRAPHICS].

We have compared optical and electrical properties as well as the electro-optical characteristics of the pure and doped LC with 0.1wt% of TiO2 nanoparticles and the CdSe/ZnS quantum dots (QDs) with core sizes of about 5nm and different core shells. A significant difference in the IR absorption spectra and the low-frequency dielectric spectra of LC composites was not observed. The addition of 0.1wt% nanoparticles caused no significant change in the order parameter or dielectric anisotropy of the LC. The addition of QDs increased the ion density by an order of magnitude compared to the pure LC and LC doped TiO2 due to the shell disruption of nanoparticles. The rotational viscosity evaluated by the test of electrical response of LC cells was twice bigger in case of LC doped with QDs. It has been shown the change in the rotational viscosity correlated with the ion density in the LC. An increase in the electrical conductivity was observed for the LC doped QDs. TiO2 nanoparticles significantly reduced the conductivity in high electric fields. Optical response time of LC cell with QDs was about twice less than with the pure LC and equal to 0.76ms for the variation of phase retardation on 2π. It is connected with an increase in the pretilt angle of LC director in the cell with QDs and decrease in the anchoring energy. Increasing the dynamic viscosity and reducing the anchoring energy contributed to slowing the switching of the LC cell with the QDs during the relaxation process. TiO2 nanoparticles had smaller effect on electro optical characteristics of the LC cell and quench the photoluminescence of LC less effectively than QDs due to insignificant changes in the LCs properties.

The structure of granular silver films at the interface of liquid crystal (LC) cells and their influence on LC molecule orientation and ionic contamination are examined. Granular silver films were deposited on a glass substrate covered with an ITO electrode and a-C:H thin films. The morphology structure of the silver films was changed after their annealing at 200 °C. The silver granules became spheroidal with an average diameter of -30 nm and the channel area between them increased. The change in the structure of the Ag films led to an increase in the phase retardation and a decrease in the pretilt angle of the LC director from 51° to 7°. The density of ionic impurities in the LC cell with the annealed silver film was three times more than in the LC cell with the unannealed film. The impact of the alignment of the LC molecules at the surface of the granular silver films on the intensity of the plasmonic peak and its red shift in the absorption spectra is shown.