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A comparative study of the processes of metal-stimulated formation of silicon nanocrystals in SiOx–Sm structures was carried out. Samples with identical oxide matrix stoichiometry and Sm impurity content were formed using two methods: layer-by-layer deposition and coevaporation of SiO and Sm. Studies of PL and IR absorption spectra found that the admixture of samarium in samples of both types accelerates the thermally stimulated decomposition of samarium-doped SiOx films into Si and SiO2 and reduces the transition temperature of silicon nanoparticles from an amorphous state to a crystalline state. However, in (SiOx/Sm)10 multilayers, this effect is more pronounced than in single-layer films obtained using the co-evaporation method. Studying the Raman spectra of (SiOx/Sm)10 multilayers annealed at 750 °C determined that the relative volume fraction of nanocrystals in the silicon phase of the sample is ~ 38%. No line corresponding to the crystalline nc-Si was observed in the Raman spectra of samples deposited by co-evaporation and annealed under the same conditions. For these samples, a narrow line in the Raman spectrum corresponding to crystalline nc-Si appears only after annealing at 970 °C. In this case, the relative fraction of Si nanocrystals in the silicon phase of the sample was ~ 17%, 2.2 times less than for a similar multilayer annealed at 750 °C. This also indicates that, in multilayer (SiOx/Sm)10 samples, the thermally stimulated decomposition of SiOx, as well as the formation and crystallization of silicon nanoparticles, occurs at lower temperatures than in similar samples obtained by coevaporation. A possible mechanism for lowering the crystallization temperature of nc-Si in (SiOx/Sm)10 multilayers is discussed. [ABSTRACT FROM AUTHOR]

The effect of Sm on thermally stimulated decomposition of SiOx and the formation of silicon nanocrystals during high-temperature air annealing was studied by measuring the spectra of photoluminescence (PL), infrared (IR) reflection and transmission and Micro-Raman scattering (RS). The SiOx: Sm films were produced by thermal co-evaporation of silicon monoxide and metallic samarium powders in a vacuum onto polished c-Si and silica substrates. The Sm concentration varied from 0.8 to 2.0 wt. %. In the SiOx: Sm films annealed at 970 ºC, an intense PL band of silicon nanocrystals was found in the 850–900 nm region, the position and intensity of which depend on the samarium concentration. The formation of Si nanocrystals in those films is also confirmed by studying their Raman spectra. At the same time, no Si nanocrystals were found in undoped SiOx films annealed under similar conditions. The analysis of these spectra made it possible to determine the sizes of silicon nanocrystals: 3.7 nm from the PL spectra and 3.6 nm from the Raman spectra. A possible mechanism of thermally stimulated interaction of Sm atoms with the SiOx matrix is discussed. [ABSTRACT FROM AUTHOR]

This work studies the polarization properties of nc-Si nanoparticle radiation in (nc-Si–SiOx–SiOy)n superlattices, formed by successive thermal deposition in a vacuum of solid SiOx and porous SiOy (x < y ≤ 2) nanolayers, and subsequent thermal annealing at 975 °C. Passivation of dangling bonds of silicon atoms at the nc-Si–SiOx interface was carried out by aging in air for 6 months. It was found that, upon excitation of (nc-Si–SiOx–SiOy)n structures with linearly polarized light, the photoluminescence polarization memory effect is observed. It is isotropic in the sample plane. This indicates the presence of anisotropic silicon nanoparticles without preferential orientation in that plane. The spectral dependence of the PL polarization degree (ρ) is investigated at different thicknesses of the active (SiOx) and spacer (SiOy) layers. A dielectric model was used to calculate the asymmetry parameter of the nc-Si in the long-wavelength region of the PL spectrum. The calculations reveal that, with increase in the radiation wavelength (which corresponds to an increase in the size of nc-Si), along with an increase in ρ, the eccentricity of the nanoparticles increases as well. [ABSTRACT FROM AUTHOR]

In this work, the investigations of spectral characteristics and kinetics of photoluminescence (PL) of light-emitting multilayer (nc-Si–SiOx–SiOy)n structures were performed. Such superlattices were formed on c-Si substrates by thermal deposition in vacuum of n = 30–40 pairs of solid SiOx nanolayers and barrier porous SiOy nanolayers (x < y ≤ 2) and subsequent high-temperature annealing and passivation in HF vapor. In this structure, the solid SiOx layers are active, and during annealing, the light-emitting nc-Si silicon nanoparticles are formed in them. It was found that for such samples, the position of PL maximum and its intensity depend on two factors: thickness of the active layers and time of passivation in HF vapor. This makes it possible to control the spectral composition and intensity of PL radiation, changing both the thickness of the initial layers of the superlattices and time of passivation. [ABSTRACT FROM AUTHOR]

The simple way for silver doping of ZnO films is presented. The ZnO films were prepared by reactive rf-magnetron sputtering on silicon and sapphire substrates. Ag doping is carried out by sublimation of the Ag source located at close space at atmospheric pressure in air. Then the ZnO and ZnO–Ag films were annealed in wet media. The microstructure and optical properties of the films were compared and studied by atomic force microscopy (AFM), X-ray diffraction (XRD), photoluminescence (PL) and cathodoluminescence (CL). XRD results indicated that all the ZnO films have a polycrystalline hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. The annealing and Ag doping promote increasing grain's sizes and modification of grain size distribution. The effect of substrate temperature, substrate type, Ag doping and post-growth annealing of the films was studied by PL spectroscopy. The effect of Ag doping was obvious and identical for all the films, namely the wide visible bands of PL spectra are suppressed by Ag doping. The intensity of ultraviolet band increased 15 times as compared to their reference films on sapphire substrate. The ultraviolet/visible emission ratio was 20. The full width at half maximum (FWHM) for a 380 nm band was 14 nm, which is comparable with that of epitaxial ZnO. The data implies the high quality of ZnO–Ag films. Possible mechanisms to enhance UV emission are discussed. [ABSTRACT FROM AUTHOR]

Optical properties of high-frequency Au gratings with a fixed period (296.6 ± 0.5 nm) and a variable modulation depth are studied using measurements of spectral and angular dependence of transmission and reflection of polarized light in order to build the dispersion curves of excited optical modes and to identify their types. It was shown that in gratings with small modulation depth only propagating surface plasmon-polaritons (SPP) modes were observed. With increasing of modulation depth, the intensity of SPP decreases and localized plasmon (LP) resonance appears, which is more intense at small incident angles, and overlaps with the SPP modes. For grating with isolated grooves (nanowires), mostly LP resonance is observed. After additional deposition of gold onto grating with isolated grooves, the intensity of the SPP mode increases again, and the LP band maximum shifts to longer wavelengths. [ABSTRACT FROM AUTHOR]

This study reports on the employment of the interference lithography (IL) technique, using photoresist based on the chalcogenide glass (ChG) films, for fabrication of one-dimensional (gratings) and two-dimensional (arrays) periodic plasmonic structures on the surface of glass plates. The IL technique was optimized for patterning of the Au and Al layers and formation of gratings and arrays with a spatial frequency of 2000 mm. Optical properties of obtained structures were studied using measurements of spectral and angular dependence of transmission and reflection of polarized light. It was shown that the spectral and angular position of the surface plasmon polariton and local surface plasmon resonance, which are observed in these samples, can be adjusted over a wide range by selecting the geometric parameters of structures and technological modes of their manufacturing. [ABSTRACT FROM AUTHOR]

We investigated plasmon-assisted enhancement of emission from silicon nanoparticles (ncs-Si) embedded into porous SiO matrix in the 500- to 820-nm wavelength range. In the presence in the near-surface region of gold nanoisland film, ncs-Si exhibited up to twofold luminescence enhancement at emission frequencies that correspond to the plasmon resonance frequency of Au nanoparticles. Enhancement of the photoluminescence (PL) intensity was attributed to coupling with the localized surface plasmons (LSPs) excited in Au nanoparticles and to increase in the radiative decay rate of ncs-Si . It has been shown that spontaneous emission decay rate of ncs-Si modified by thin Au film over the wide emission spectral range was accelerated. The emission decay rate distribution was determined by fitting the experimental decay curves to the stretched exponential model. The observed increase of the PL decay rate distribution width for the Au-coated nc-Si-SiO sample in comparison with the uncoated one was explained by fluctuations in the surface-plasmon excitation rate . PACS: 78. 67. Bf; 78.55.-m [ABSTRACT FROM AUTHOR]