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Nanostructured materials play a significant role in numerous advanced and diversified applications many of which exploit their optical properties. Among these are nanostructured substrates for surface-enhanced Raman scattering (SERS). The objective of our study was to contribute to understanding of topological aspects influencing and underlying SERS on nanostructured substrates. To that purpose we fabricated Ag-decorated Si-nanowires (SiNWs) substrates with different fractal and lacunar characteristics. We demonstrated that fractal dimension and lacunarity have a profound influence on SERS enhancement. We discussed the involved interplay between long-range properties of nanostructured substrate, namely its fractal topology, and short-range local features on a nanometer scale related to the distribution of inter-wire gaps (i.e. lacunarity) which strongly affect the local field enhancement, altogether precipitating in significant increase of SERS. Explanation of a strong correlation found to exist between fractal dimension D, lacunarity and SERS enhancement and the observed abrupt increase of SERS at D ≈ 2.54 are provided within the framework of the percolation theory. For a percolated fractal structure a strong enhancement depends on the excitation wavelength resonantly matching the heterogeneity sizes of inter nanowire gaps as characterized with a high lacunarity determining the distribution of localized optical excitations i.e. hot spots.

A method to enhance the optoelectronic properties of thin films containing three-dimensional ordered germanium quantum dots (QDs) coated with metal shell (Al, Ta, and Ti) in alumina matrix is presented. The conditions for the achievement of self-assembled growth of the metal-coated Ge QDs by magnetron sputtering deposition are explored. The influence of the metal shell on the structural, optical, and optoelectronic properties is found to be radical and desirable. First, it reduces Ge oxidation. Second, it enhances overall absorption by an order of magnitude. Third, it enables manipulation of the absorption curve shape in two ways. The Ge absorption peak, useful for photoelectric conversion, can be tuned significantly via control of the Ge energy gap because of the quantum confinement effect. On the other hand, infrared absorption can be controlled by the amount of metal because the geometry of the system can enhance absorption in the core by excitation of plasmon resonances in the shell. The mentioned effects result in a high increase of the photocurrent and quantum efficiency of core–shell nanoparticles compared to simple Ge particles. The experiments are supported by theoretical predictions, showing that the intensity of the incident radiation is strongly amplified in the region around the metal–semiconductor interface upon the excitation of plasmon resonances, hence increasing the probability of photon absorption and, thus, of charge carrier generation in the photo-active material. Therefore, the presented materials are very promising for photoelectric devices.

Spherical microresonators based on whispering gallery modes (WGM) have been used for measuring the concentration of ammonia vapours. Because of their high Q-factors, the WGM microresonators are very sensitive to environmental conditions such as temperature, pressure and moisture. Adding a porous layer of silica (SiO 2 ) onto the sphere's surface makes such sensors sensitive to different kinds of vapours like ethanol, ammonia. etc.

Commercial micrometer silicon (Si) powder was investigated as a potential anode material for lithium ion (Li-ion) batteries. The characterization of this powder showed the mean particle size of approx.75.2 nm, BET surface area of 10.6 m2/g and average pore size of 0.56 nm. Its band gap was estimated to 1.35 eV as determined using UV-Vis diffuse reflectance spectra. In order to increase the surface area and porosity which is important for Li-ion batteries, the starting Si powder was ball-milled and threatened by metal-assisted chemical etching. The mechanochemical treatment resulted in decrease of the particle size from 75 nm to 29 nm, an increase of the BET surface area and average pore size to 16.7 m2/g and 1.26 nm, respectively, and broadening of the X-ray powder diffraction (XRD) lines. The XRD patterns of silver metal-assisted chemical etching (MACE) sample showed strong and narrow diffraction lines typical for powder silicon and low-intensity diffraction lines typical for silver. The metal-assisted chemical etching of starting Si material resulted in a decrease of surface area to 7.3 m2/g and an increase of the average pore size to 3.44 nm. These three materials were used as the anode material in lithium-ion cells, and their electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge-discharge cycles. The enhanced electrochemical performance of the sample prepared by MACE is attributed to increase in pore size, which are large enough for easy lithiation. These are the positive aspects of the application of MACE in the development of an anode material for Li-ion batteries.

A new method for enhancing the Raman scattering signal has emerged recently, based on dielectric enhancement. Especially promising is the dielectric method based on microspheres and photonic nanojet. In this paper, geometrical aspects and the influence of the incident beam parameters on Raman enhancement by silica microspheres were systematically investigated in three steps: by characterizing the incident beam using knife‐edge method, performing horizontal and vertical Raman mapping imaging, and analyzing the results using ray transfer matrix analysis. Maps show a distinct enhancement (hotspot) area caused by the microsphere photonic nanojet and lens effect compared to a plain silicon substrate. Enhancement value on maps was the highest (5.7×) for 0.50 numerical aperture objective, when the incident beam size matched the microsphere diameter, and the focus of the incident beam was below the top of the sphere, so that the output beam focus was at the microsphere–substrate contact area. This geometrical configuration was confirmed as ideal by performing simple ray transfer matrix analysis. The ideal ranges of incident and output beam parameters match with the measured hotspot area. This three‐step process and the usage of vertical Raman mapping have been, for the best of our knowledge, performed for the first time in such configuration. This research introduces a new way of investigating microsphere‐assisted Raman enhancement, offers different approach to microsphere optics research, and improves current knowledge of the influence of the incident beam on the enhancement.

BACKGROUND: It is well known that quantum dot-sensitized solar cells based on nanostructured semiconductor films are considered as a promising alternative to silicon-based solar cells. The aim of this paper is to investigate the structural and morphological properties of CdS/CdSe quantum dot sensitized photoanodes based on nanocrystalline TiO2 thin films considering their performance can reach an efficiency of 2.7%. In particular, quantum dot materials such as CdSe and CdS, which typically have a couple of orders higher absorption than silicon and thin film materials can lead to higher photocurrents and are most effective with liquid electrolyte solar cells. Moreover, CdSe and CdS quantum dots have been shown to be more efficient when combined than as single species. METHODS: TiO2 thin films were prepared on fluorine tin oxide (FTO) glass via the chemical route using commercial Degussa 25 and crystallized at 550oC. Furthermore, a layer of CdS and CdSe nanoparticles was deposited on the titania film by a sequence of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) methods. After preparation, X ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) were employed to investigate the crystallinity of the photoanodes, while Raman and micro-Raman spectroscopy were used to reconfirm the crystalline phase of the materials and sample composition. Surface morphology was investigated using scanning electron microscopy (SEM) while energy dispersive x-ray spectrometry (EDS) was used to analyze the sample stoichiometry. RESULTS: XRD performed for the TiO2 thin film before quantum dot deposition showed strong diffraction peaks at 26o, 34o, 38o and 52o indicating that the FTO substrate is polycrystalline with a mainly tetragonal SnO2 phase while peaks at 25° and 48° degrees revealed that the TiO2 layer is mainly in the anatase phase. Moreover, HR-TEM determined that the crystallite size of titania was around 20nm, while EDS of the deposited film showed that the mole ratio of O to Ti is 2.6:1. After CdS/CdSe quantum dot deposition XRD revealed that CdS exhibits a definite peak at 51° while at 42o we observed a weaker peak corresponding to the CdSe structure. EDS revealed a mole ratio of S to Cd and Se to Cd of almost 1:1 in both cases. HR-TEM showed that the CdS and CdSe quantum dots sizes ranged between 2nm to approximately 10nm. Raman spectroscopy of the TiO2 film revealed peaks at 554 cm-1 and 1092cm-1 corresponding to the FTO substrate, as well as intense peaks at 521cm-1 and 643 cm-1 related to the TiO2 anatase phase. Micro-Raman showed additional Raman active peaks at 142cm-1 and 197 cm-1 related to titania. After CdS/CdSe quantum dot deposition micro-Raman revealed an active peak at 302cm-1 corresponding to CdS while Raman active peaks at 203 cm-1 and 403cm-1 corresponded to CdSe. CONCLUSIONS: The structural properties and morphology of quantum dot sensitized photoanodes revealed that the titania thin films were highly crystalline belonging predominantly in the tetragonalanatase structure, while the CdS/CdS quantum dots were in the cubic phase. Furthermore, scanning electron microscopy (SEM) along with energy dispersive X-Ray mapping EDS showed little contamination as well as high stoichiometry for both the TiO2 substrate as well as the CdS/CdSe quantum dots. Finally, micro-Raman spectroscopy reconfirmed the crystalline phase of the materials and sample composition.

This paper shows steps for silicon nanowires substrates synthesis in detail. The research is focused on experimental techniques optimization while the targeted application was a fabrication of highly sensitive substrates for surface-enhanced Raman spectroscopy (SERS). Horizontal silicon nanowires on top of two-inch wafers were obtained by vapour-liquid-solid growth inside the low-pressure chemical vapour deposition reaction tube. The silicon nanowires morphology was monitored by scanning electron microscope after a short and long growth period which defined an adequate deposition time for SERS applications. Surface-enhanced Raman spectroscopy features were tested on silver nanoparticles decorated substrates and the detection concentration limit of 10− 9 M of rhodamine 6G molecules was reached. Raman spectroscopy showed that the 532 nm laser excitation powers of less than 4 mW (∼0.57 kW/cm2) do not widen the phonon peak or shift its frequency and the nanostructure distribution parameter of 3.7 nm was calculated. The horizontally placed Ag decorated nanowires are proved to be sensitive substrates for surface-enhanced Raman spectroscopy only if the silicon nanowires thickness, length, volume density as well as metal nanoparticle size and distribution are carefully designed.

This paper shows the optimisation of the silicon nanowires (SiNWs) synthesis process and their features which are relevant for numerous sensing applications. In particular, the target was to design SiNWs substrate for surface-enhanced Raman spectroscopy (SERS). The majority of SiNWS has been synthesized by vapour-liquid-solid (VLS) method utilizing Au catalyst. However, in this paper, we show that Ag-Au catalyst system offers advantageous features such as a higher number of SiNWs per unit area, reduced SiNWs thickness and improved diameter distribution. The novel SERS sensor was tested utilizing Mercaptophenylboronic acid (MPBA) and compared with the traditional only Au catalysed system. Furthermore, the SiNWs features based on novel Ag-Au catalyst system were varied employing temperature, SiH4 partial pressure and deposition time. Axial and radial SiNWs growth rates and activation energies are determined and discussed.

Histamine fish poisoning is a foodborne illness caused by the consumption of fish products with high histamine content. Although intoxication mechanisms and control strategies are well known, it remains by far the most common cause of seafood-related health problems. Since conventional methods for histamine testing are difficult to implement in high-throughput quality control laboratories, simple and rapid methods for histamine testing are needed to ensure the safety of seafood products in global trade. In this work, the previously developed SERS method for the determination of histamine was tested to determine the influence of matrix effect on the performance of the method and to investigate the ability of different chemometric tools to overcome matrix effect issues. Experiments were performed on bluefin tuna (Thunnus thynnus) and bonito (Sarda sarda) samples exposed to varying levels of microbial activity. Spectral analysis confirmed the significant effect of sample matrix, related to different fish species, as well as the extent of microbial activity on the predictive ability of PLSR models with R2 of best model ranging from 0.722–0.945. Models obtained by ANN processing of factors derived by PCA from the raw spectra of the samples showed excellent prediction of histamine, regardless of fish species and extent of microbial activity (R2 of validation &gt, 0.99).

The silver (Ag) films were deposited on the monodispersed polystyrene spheres that were drop-coated on hydrophilic glass substrates in order to form a self-assembled 2D monolayer. Thus prepared Ag films over polystyrene nanospheres (AgFONs) were used to record the surface-enhanced Raman scattering (SERS) spectra of rhodamine 6G (R6G) and pyridine (λex = 514.5 nm). AgFONs were prepared by depositing 120, 180 and 240 nm thick Ag layer on the 1000 nm polystyrene spheres and 80, 120, 160 and 200 nm thick Ag layer on the 350 nm spheres as well as on their mixture (350 + 1000 nm). The silver was deposited by electron beam evaporation technique. The best enhancement of the Raman signal for both test molecules was obtained using 180 nm Ag film deposited on the 1000 nm spheres and using 80 nm Ag film deposited on the 350 nm polystyrene spheres. The lowest detectable concentrations of R6G and pyridine were 10−9 mol L−1 and 1.2 × 10−3 mol L−1, respectively. This study has shown that AgFONs could be regarded as good and reproducible SERS substrate for analytical detection of various organic molecules.

A polymer nanocomposite was produced by ultrasonic-assisted dispersion of multiwalled carbon nanotubes (MWCNTs) in a polycarbonate matrix using p-xylene and dichloromethane as the solvents. The filler loading was varied from 1 to 3 wt % in order to examine the effect of MWCNTs on the structure and properties of the composites. The nanocomposites were characterized by DSC, DTA, TGA, UV–vis, FTIR and Raman spectroscopy to evaluate the changes induced by the filler in the polymer matrix. UV–vis, FTIR and Raman spectroscopy measurements confirmed the presence of the dispersed phase in the composite films, while TGA and DSC analysis of the nanocomposites revealed enhanced thermal stability and decreased crystallinity, respectively, as compared to the neat polymer. The proposed composites can find application in a number of everyday products where polycarbonate is the base polymer.

Ge/Si core/shell quantum dots (QDs) recently received extensive attention due to their specific properties induced by the confinement effects of the core and shell structure. They have a type II confinement resulting in spatially separated charge carriers, the electronic structure strongly dependent on the core and shell size. Herein, the experimental realization of Ge/Si core/shell QDs with strongly tunable optical properties is demonstrated. QDs embedded in an amorphous alumina glass matrix are produced by simple magnetron sputtering deposition. In addition, they are regularly arranged within the matrix due to their self-assembled growth regime. QDs with different Ge core and Si shell sizes are made. These core/shell structures have a significantly stronger absorption compared to pure Ge QDs and a highly tunable absorption peak dependent on the size of the core and shell. The optical properties are in agreement with recent theoretical predictions showing the dramatic influence of the shell size on optical gap, resulting in 0.7 eV blue shift for only 0.4 nm decrease at the shell thickness. Therefore, these materials are very promising for light-harvesting applications.

Surface-enhanced Raman scattering (SERS) with near-infrared (NIR) excitation offers a safe way for the detection and study of fragile biomolecules. In this work, we present the possibility of using silver-coated porous silicon photonic crystals as SERS substrates for near-infrared (1064 nm) excitation. Due to the deep penetration of NIR light inside silicon, the fabrication of photonic crystals was necessary to quench the band gap photoluminescence of silicon crystal, which acts as mechanical support for the porous layer. Optimal parameters of the immersion plating process that gave maximum enhancement were found and the activity of SERS substrates was tested using rhodamine 6G and crystal violet dye molecules, yielding significant SERS enhancement for off-resonant conditions. To our knowledge, this is the first time that the 1064 nm NIR laser excitation is used for obtaining the SERS effect on porous silicon as a substrate.

Low threshold coherent emission at 1.5 &micro, m is achieved using Er3+-doped dielectric 1D microcavities fabricated with a Radio Frequency-sputtering technique. The microcavities are composed of a half-wavelength Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of ten, five, and seven pairs of SiO2/TiO2 layers, also doped with Er3+ ions. The morphology of the structure is inspected using scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1.5 &micro, m, respectively. The photoluminescence measurements are obtained using the optical excitation at the third order cavity resonance using a 514.5 nm Ar+ laser or Xe excitation lamp at 514.5 nm, with an excitation angle of 30&deg, The full width at half maximum of the emission peak at 1535 nm decreased with the pump power until the spectral resolution of the detection system was 2.7 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 &micro, W.

Porous silicon has been intensely studied for the past several decades and its applications were found in photovoltaics, biomedicine, and sensors. An important aspect for sensing devices is their long&ndash, term stability. One of the more prominent changes that occur with porous silicon as it is exposed to atmosphere is oxidation. In this work we study the influence of oxidation on the sensing properties of porous silicon. Porous silicon layers were prepared by electrochemical etching and oxidized in a tube furnace. We observed that electrical resistance of oxidized samples rises in response to the increasing ambient concentration of organic vapours and ammonia gas. Furthermore, we note the sensitivity is dependent on the oxygen treatment of the porous layer. This indicates that porous silicon has a potential use in sensing of organic vapours and ammonia gas when covered with an oxide layer.

International audience; All Er3+ doped dielectric 1-D microcavity was fabricated by rf sputtering technique. The microcavity was constituted by half wave Er3+ doped SiO2 active layer inserted between two Bragg reflectors consists of ten pairs of SiO2/TiO2 layers also doped with Er3+ ions. The scanning electron microscopy was used to check the morphology of the structure. Transmission measurements confirm the third and first order cavity resonance at 530 nm and 1560 nm, respectively. The photoluminescence measurements were obtained by optically exciting at the third order cavity resonance using 514.5 nm Ar+ laser with an excitation angle of 30°. The Full Width at Half Maximum of the emission peak at 1560 nm decrease with the pump power until the spectral resolution of the detection system of ∼1.0 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 24 mW was observed with saturation of the signal at above 185 mW of pump power.

Metastable solid solutions of ZrO2-YO1.5 system (from 0 to 100 mol%) were prepared by crystallization of the amorphous precursors, coprecipitated from aqueous solutions of nitrate salts, using two synthesis routes: hydrothermal treatment at 150 °C for 24 h and annealing in the air atmosphere for 2 h at temperatures between 400 and 1200 °C. Thermal behavior of the amorphous precursors were followed by differential scanning calorimetry (DSC), structural analysis of the crystallization product was performed by X-ray powder diffraction (XRPD) and Raman spectroscopy, and the morphology of the crystalline grains was determined by the scanning electron microscope (FE-SEM). It was found that the crystallization temperature of ZrO2-type solid solutions increase with an increase in the YO1.5 content, from 487 °C (0 mol% of YO1.5) to 516 °C (20 mol% of YO1.5). Comparison of the obtained results with the results obtained for mixed oxides of zirconium with different trivalent dopants indicates that the crystallization temperature rises with the increase of dopand content and the difference between the ionic radius of the zirconium and the doped cation. The results of Rietveld refinements show that, regardless of the significant differences in the crystallite size and the morphology of the products obtained by two different synthesis routes, the phase composition and the unit cell parameters of the solid solutions obtained are very similar and depend mostly on the Zr/Y ratio. Crystallization products with YO1.5 content ≥5 mol% contain only one type of solid solution structurally closely related to tetragonal ZrO2 (from 5 to 15 mol% of YO1.5), cubic ZrO2 (from 15 to more than 60 mol% of YO1.5) and cubic Y2O3 (from 70 to 100 mol% of YO1.5). The unit-cell volume of the ZrO2- and Y2O3-type solid solutions increases linearly with the increase in the fraction of the yttrium. This linear dependence continued even after the transitions from ZrO2-type to Y2O3-type lattice.

Iron/titanium oxide nanoparticles with the initial molar ratio [FeIII/(FeIII + TiIV)] ≤ 0.50 were hydrothermally synthesized at 180 °C in an aqueous ammonia solution (pH ≅ 9.6). The titanium and iron precursors were TiCl4 and FeCl3, respectively. The amount of doped iron strongly affected microstructural properties as well as the degree of dispersion of iron in the Fe-Ti-O system. Anatase was the dominant phase in the iron/titanium oxide samples with [Fe/(Fe + Ti)] ≤ 0.25. The average crystallite size of the anatase phase in iron/titanium oxide samples decreased with the increase of iron doping. The results of precise unit-cell parameters measurement, obtained using Rietveld refinements of the powder diffraction patterns with added silicon indicated that the solid solubility limit of FeIII inside the anatase lattice was ∼8 mol%. The appearance of hematite (α-Fe2O3) sextet in the Mössbauer spectrum in the sample doped with 10 mol% of iron confirmed that the solid solubility limit of FeIII in the TiO2 lattice has been overreached. The relative concentrations of α-Fe2O3 in the samples increased with FeIII doping up to 15 mol% of added FeIII and then, quite unexpectedly, the XRD 104 line and Mössbauer sextet of α-Fe2O3 completely disappeared at 0.20 < [Fe/(Fe + Ti)] < 0.30. The EELS (electron energy-loss spectroscopy) analysis confirmed that the sample doped with 30 mol% of FeIII contained no hematite. The FeIII in the samples at 0.20 < [Fe/(Fe + Ti)] < 0.30 segregated not in the form of hematite, but in the form of iron/titanium oxide phase that was poorly crystallized or even amorphous. The α-Fe2O3 again appeared at [Fe/(Fe + Ti)] = 0.50. The diffuse reflectance spectra were used for band gap energy calculations. The band gap energy of the undoped TiO2 sample was 3.1 eV, whereas the band gap energy of Fe-Ti-O samples doped with up to 10% showed a blue shift (3.2 eV). The significant red shift (from 3.2 to 2.4 eV) was observed in the samples with higher iron content (from 10 to 50 mol%).

Silica microspheres were coated using an erbium activated silica hafnia thin film in order to produce microlasers. Lasing was observed and the lasing modes were identified. Only the modes whose electric field is located closest to the surface were found to exhibit lasing.

The field of Raman spectroscopy is constantly under improvement by development of methods of enhancement. One of the latest methods, based on photonic nanojet of a microsphere, has already been proven as simple, reliable and promising method for enhancement of single point micro Raman acquisition, but so far not for imaging. To extend the photonic nanojet method to Raman mapping, we have developed microsphere attached to two perpendicularly connected tapered optical fibers. When the sample is mapped, our two stemmed microsphere stays under the laser beam of the objective, providing enhancement on all points of the image. In addition to the demonstration of the feasibility of such enhancement, the first results reported here with 5-µm two stemmed microsphere on polycrystalline silicon substrate show ~4× signal enhancement of every point, and estimated ~3× resolution enhancement compared to the same setup without the microsphere. Detailed description of fabrication and characteristics of two stemmed microspheres is provided. Mapping images are analyzed and compared to atomic-force and scanning electron microscope images. Also, theoretical calculations of the photonic nanojet are provided. Successful implementation of two stemmed microsphere opens up a gateway and could serve as foundation for future improvements and applications in Raman imaging.

We have developed a reliable RF sputtering techniques allowing to fabricate glass-based one dimensional microcavities, with high quality factor. This property is strongly related to the modification of the density of states due to the confinement of the gain medium in a photonic band gap structure. In this short review we present some of the more recent results obtained by our team exploiting these 1D microcavities. In particular we present: (1) Er3+ luminescence enhancement of the 4I13/2 → 4I15/2 transition; (2) broad band filters based on disordered 1-D photonic structures; (3) threshold defect-mode lasing action in a hybrid structure.

ZnO fibers were prepared by electrospinning of a viscous solution of zinc acetate and polyvinylpyrrolidone in C2H5OH/H2O followed by their calcination at 400 °C. Thus obtained ZnO fibers were hydrothermally processed at 160 °C in aqueous medium containing hydrolyzed zinc acetylacetonate. For short times of electrospinning and relatively short times of hydrothermal processing the uniform ZnO nanorods perpendicular to the axis of electrospun fibers were obtained. The adsorption of zinc hydrolytical products as well as an acetylacetonate group on selected crystal planes was considered responsible for the morphology and size of the ZnO produced. For a longer time (8 h) of hydrothermal processing the recrystallization of ZnO was noticed with the formation of bigger particles elongated along the c-axis with a±b.

Mesoporous Si samples, prepared by anodisation technique with different current densities (0.5–40 mA/cm2), were silver coated by using immersion plating into 10–2 and 10–3 m AgNO3 solutions. It was shown that different porous structures yield formation of different Ag crystals on the surface of mesoporous Si for the same immersion conditions. The effect of immersion time on the morphology of Ag crystals and the corresponding surface-enhanced Raman spectroscopy (SERS) activity were monitored by using the rhodamine 6G dye molecule. A strong difference in the enhancement factor of the SERS signal in the silver-clustered mesoporous silicon in comparison with that in crystalline silicon was found. It was shown that respectable enhancement of the SERS substrates with detection limits of 10−9 m rhodamine 6G is possible to produce by optimisation of anodisation current, concentration of AgNO3 and silver crystals’ growth time. Copyright © 2016 John Wiley & Sons, Ltd.

Microporous and macro-mesoporous silicon templates for surface-enhanced Raman scattering (SERS) substrates were produced by anodization of low doped p-type silicon wafers. By immersion plating in AgNO3, the templates were covered with silver metallic film consisting of different silver nanostructures. Scanning electron microscopy (SEM) micrographs of these SERS substrates showed diverse morphology with significant difference in an average size and size distribution of silver nanoparticles. Ultraviolet–visible–near-infrared (UV-Vis-NIR) reflection spectroscopy showed plasmonic absorption at 398 and 469 nm, which is in accordance with the SEM findings. The activity of the SERS substrates was tested using rhodamine 6G (R6G) dye molecules and 514.5 nm laser excitation. Contrary to the microporous silicon template, the SERS substrate prepared from macro-mesoporous silicon template showed significantly broader size distribution of irregular silver nanoparticles as well as localized surface plasmon resonance closer to excitation laser wavelength. Such silver morphology has high SERS sensitivity that enables ultralow concentration detection of R6G dye molecules up to 10−15 M. To our knowledge, this is the lowest concentration detected of R6G dye molecules on porous silicon-based SERS substrates, which might even indicate possible single molecule detection.

For the sensing application and investigating the nonlinear effects, microresonator structures are very suitable due to their enormous quality factor and small mode volume. These properties can be extended into the mid-infrared region by creating microresonators from chalcogenide glasses, which have large third-order optical nonlinearity. We present the analysis of the nonlinear effects observation in chalcogenide microspheres.

Surface tension induced whispering gallery mode (WGM) micro-resonators can be made in glass with very high quality factor Q. In fact, low losses amorphous glassy dielectrics can be easily shaped in high-surface-quality spheroids by thermal reflow. Since the pioneering works on fused silica microspheres showing several orders of magnitude higher Qs compared to previous findings, a large number of studies have been performed in the last years on glass based microresonators. Main results include frequency conversion through non-linear effects and micro-lasers, filtering and optical switching, RF photonics and sensing. Besides spheres, alternatives shapes like micro-bottles and micro-bubbles have been implemented to improve the resonator performances depending on the application. Other glasses rather than silica have been considered in order to enhance properties like transparency windows and non-linear effects. This presentation will review the main results we obtained on micro-laser sources in erbium doped microcavities, parametric conversion in silica microspheres, and stimulated Brillouin scattering in silica microbubbles. Potentials of coated silica microspheres implemented to add the functionalities of the coating material will be also presented.

International audience; All Er3+ doped dielectric 1-D microcavity are fabricated by RF sputtering technique. The microcavity is composed of half wave Er3+ doped SiO2 active layer inserted, between two Bragg reflectors consisting of seven pairs of SiO2/TiO2 layers also doped with Er3+ ions. The morphology of the structure is inspected with scanning electron microscopy. Transmission measurements show the third and first order cavity resonance at 530 nm and 1535 nm, respectively. The photoluminescence measurements were obtained by optically exciting at the third order cavity resonance using 514.5 nm Ar+ laser with an excitation angle of 30°. The Full Width at Half Maximum of the emission peak at 1535 nm decrease with the pump power until the spectral resolution of the detection system of 2.3 nm. Moreover, the emission intensity presents a non-linear behavior with the pump power and a threshold at about 4 μW.

The main purpose of this paper is to focus on details of the fabrication process of horizontally and vertically oriented silicon nanowires (SiNWs) substrates for the application of surface-enhanced Raman spectroscopy (SERS). The fabrication process is based on the vapor– liquid–solid method and electroless-assisted chemical etching, which, as the major benefit, resulting in the development of economical, easy- to-prepare SERS substrates. Furthermore, we examined the fabrication of Au coated Ag nanoparticles (NPs) on the SiNWs substrates in such a way as to diminish the influence of silver NPs corrosion, which, in turn, enhanced the SERS time stability, thus allowing for wider commercial applications. The substances on which high SERS sensitivity was proved are rhodamine (R6G) and 4-mercaptobenzoic acid (MBA), with the detection limits of 10−8 M and 10−6 M, respectively.

Iron/Titanium oxide nanoparticles with initial molar ratio Fe/(Fe+Ti) = 0.05 (low loading of Fe in TiO2) and Fe/(Fe+Ti) = 0.15 (high loading of Fe in TiO2) were synthesized by a modified sol-gel procedure using Ti(IV)-isopropoxide, FeSO4 ∙ 7H2O and poly(ethylene glycol) (PEG) as starting material. The amount of doped iron strongly affected structural properties as well as the degree of dispersion of iron in the Fe-Ti-O system. The highly-doped sample contained poorly crystallized hydrated iron(III)-sulphates or basic iron(III)-sulphates in a considerable amount. The lowly-doped Fe-TiO2 sample contained about 22 wt % of brookite that had taken up iron virtually in the same proportion as anatase. Contrary to quasi-homogeneous distributions of iron in the lowly-doped Fe-TiO2 sample, the uptake of iron in the highly-doped Fe-TiO2 sample heated at 500 °C is significant, but anatase is free from iron, thus suggesting a heterogeneous distribution of iron. The photocatalytic activity of the highly-doped Fe-TiO2 sample was better than that of the lowly-doped Fe-TiO2 sample, but still below the photoactivity of Degussa P25 reference photocatalyst. This work is licensed under a Creative Commons Attribution 4.0 International License.

Optical microresonators are a very promising component for use in optoelectronics. They have very high quality factors and low mode volumes which makes them suitable for many applications such as lasing, sensing or non-linear optics. We will present our work on microspheres coated with sol-gel Er3+ activated 70SiO2 - 30HfO2. In particular the lasing properties of such microspheres will be presented. Different coating thicknesses will be employed and the peak lasing power will be discussed in respect to the coating thickness. The lasing peaks will be identified in respect to the radial and azimuthal numbers of the whispering gallery modes and the assignments will be discussed in terms of mode selectivity.

Microresonator structures are very suitable for sensing application and the investigation of nonlinear effects, due to their enormous quality factor and small mode volume. These properties can be extended into the mid-infrared region by creating microresonators from chalcogenide glasses, which have a wide window of transparency and a large third-order optical nonlinearity. We present the analysis of the nonlinear effects observation in chalcogenide microspheres created by inert gas heating.

Experimental conditions for the formation of RuO 2 /Ru fibers by electrospinning were investigated. Samples were characterized by the FE SEM, XRD, FT-IR and Raman techniques. Round fibers were produced by electrospinning a viscous polyvinylpyrrolidone (PVP)–C 2 H 5 OH–H 2 O solution, whereas with the addition of RuNO(NO 3 ) 3 , ribbon-like fibers were produced. Heating the ribbon-like fibers of PVP+RuNO(NO 3 ) 3 at 400 °C for 1 h yielded a RuO 2 /Ru composite with the preserved morphology of the precursor. The surface of the ribbon-like RuO 2 /Ru fibers showed a porous nano/microstructure. PVP+RuNO(NO 3 ) 3 foils, produced by freeze-drying the corresponding viscous solution, did not yield ribbon-like fibers upon heating at 400 °C for 1 h. This suggests that the formation of a ribbon-like morphology is the cumulative effect of solvent evaporation during the electrospinning of a viscous solution and the interaction of PVP with RuNO(NO 3 ) 3 .

A simple one-pot synthesis of RuO2 nanoparticles by the thermal decomposition of ruthenium nitrosyl nitrate [Ru(NO)(NO3)3] up to 800 °C was investigated. The RuO2 phase was characterized by XRD, SAXS, FE SEM/EDS, Raman, DTA/TGA and FT-IR techniques. Broadening of prominent diffraction lines (110), (101) and (211) was used to estimate nanocrystallite sizes in RuO2 particles. FE SEM showed the formation of RuO2 plates at 400 °C which consisted of RuO2 nanoparticles of about 15–25 nm in size. At 800 °C RuO2 nanoparticles showed the sintering effect and some of them increased in size to about 200 nm. Raman and FT-IR spectra consolidated the findings. Moreover, DTA curves showed the decomposition and release of NO and NO3− groups to be a stepwise process.

The silver nanoparticles (AgNPs) were synthesized upon γ-irradiation of AgNO3 precursor suspensions in the presence of diethylaminoethyl-dextran hydrochloride (DEAE-dextran) cationic polymer as a stabilizer. The dose rate of γ-irradiation was ~32 kGy h−1, and absorbed doses were 30 and 60 kGy. The γ-irradiation of the precursor suspension at acidic or neutral pH conditions produced predominantly the silver(I) chloride (AgCl) particles, because of the poor solubility of AgCl already present in the precursor suspension. The origin of AgCl in the precursor suspension was due to the presence of chloride ions in DEAE-dextran hydrochloride polymer. The addition of ammonia to the precursor suspension dissolved the AgCl precipitate, and the γ-irradiation of such colourless suspension at alkali pH produced a stable aqueous suspension with rather uniform spherical AgNPs of approximately 30 nm in size. The size of AgNPs was controlled by varying the AgNO3/DEAE-dextran concentration in the suspensions. The surface-enhanced Raman scattering (SERS) activities of synthesized AgNPs were examined using organic molecules rhodamine 6G, pyridine and 4-mercaptobenzoic acid (4-MBA). The NaBH4 was used as SERS aggregation agent. The SERS results have shown that in the presence of synthesized AgNPs, it was possible to detect low concentration of tested compounds.

Features of whispering gallery modes of chalcogenide fiber based microresonators have been studied in a numerical model and in experiment. The second-order group velocity dispersion parameters and intrinsic Q-factors of arsenic sulfide microspheres have been evaluated over the near- and mid-IR spectral ranges. Due to optimization of the microresonators fabrication method, high-Q microresonators have been produced with the maximum Q-factor equal to 7.6 × 106. A tendency of the measured Q-factors increase with a micoresonator size decrease has been revealed.

This study was focused on development of a rapid and sensitive method for histamine determination in fish based on Surface Enhanced Raman Spectroscopy (SERS) using simple and widely available silver colloid SERS substrate. Extraction of histamine with 0.4 M perchloric acid and purification with 1-butanol significantly shortened sample preparation (30 min) and provided clear SERS spectra with characteristic Raman bands of histamine. Principal component analysis effectively distinguished SERS spectra of fish samples with different histamine content. Partial least square (PLS) regression models confirmed reliability of detection and spectral analysis of histamine with SERS. In histamine concentration range 0-200 mg kg-1, significant in legislative and fish quality control aspects, PLS regression model based on spectral range 1139.9- 1643.7 cm-1 showed linear trend with R2pred=0.962, RPD=7.250. Presented protocol for histamine extraction and purification followed by SERS analysis coupled with chemometric approach, enabled development of rapid and inexpensive method for histamine determination in fish.

In this paper we present some results obtained by our consortium regarding rf-sputtered glass-based structures.

The silicon based substrates for surface enhanced Raman spectroscopy (SERS) have been synthesized and tested. The silver-assisted electroless wet chemical etching method has been utilized for silicon nanowires production which has been proved as the promising SERS substrate. The morphology of the silicon nanowires coated with silver nanoparticles has been examined by scanning electron microscopy. The SERS measurements tested on rhodamine 6G molecules indicated the optimal silicon nanowire substrate production obtained for 5 M hydrofluoric acid and 30 mM silver nitrate etching solution. The results show SERS detection limit of 10–8 M rhodamine in aqueous solution. This work is licensed under a Creative Commons Attribution 4.0 International License.

Hard form of carbon obtained by collapsing C60 fullerene molecules at moderate pressure and temperature was investigated using different imaging techniques at spatial resolutions ranging from angstrom to millimeter. Hierarchical granular morphology has been observed from the atomic up to the sample size length scale, revealing scale independent grain size distribution. The unusual fractal-like structure correlates with unique transport and calorimetric properties of this material. Hard carbon can be considered as a bridge between porous and dense amorphous materials.

Acoustic vibrational modes of ZrO2–TiO2 nanoparticles (ZT) have been observed and analyzed by means of low-frequency Raman spectroscopy (LFRS). The low-frequency Raman peak has been observed in the spectra of amorphous as well as of crystalline ZT nanoparticles. The results obtained by the LFRS have been compared to the results obtained by high-resolution transmission electron microscopy (HRTEM). After the method has been tested, the LFRS has been used to investigate the influence of the amount of dopant (Ti4+) and the annealing temperature on size distributions of the ZT nanoparticles. The observed reduction of the particles’ growth-rate with Ti doping was ascribed with increase of defects in nanoparticles. Also, a discontinuity in the particles’ growth-rate at the temperatures between 500 °C and 600 °C was observed. It is at these temperatures that the phase transition from amorphous to nanocrystalline phase occurs.

Light emitting porous silicon samples with different porosities, i.e. crystalline sizes, were produced from the low level doped p-type silicon wafers by the anodization process. The effects of strong phonon confinement, redshift and broadening, were found on the O(Γ) phonon mode of the Raman spectra recorded at non-resonant excitation condition using a near infrared 1064 nm laser excitation wavelength. Similarly, the blueshift of the photoluminescence peak was observed by reducing the crystalline sizes. Vibrational and optical findings were analysed within the existing models of confinement on the vibrational and electronic states of silicon nanocrystals. Since the energy of the photoluminescence peak of small nanocrystals also depends on the oxygen content on the surface of nanocrystals, the surface oxidation states were examined using infrared and energy dispersive spectroscopy. The partial coverage of the surface of nanocrystals was found due to the sample exposure to air. As a consequence, the photoluminescence energy did not increase as would be expected from the quantum confinement model. These results further indicate that the oxygen passivation along with the quantum confinement determines the electronic states of the silicon nanocrystals in porous silicon. Copyright © 2014 John Wiley & Sons, Ltd.

The formation and microstructure of thermal decomposition products obtained in air from Ni(II)-acetate tetrahydrate and Ni(II)-lactate tetrahydrate were investigated using XRD, Raman, UV/Vis/NIR and FE-SEM/EDS techniques. The formation of metallic Ni particles was due to the presence of acetate and lactate groups as reducens and with an increase in the heating temperature the reoxidation of Ni particles occurred. Crystallite sizes of Ni and NiO particles were in nanosize range and with increasing heating temperature the crystallite size of NiO particles was growing. The Raman spectra depended on the microstructure of NiO particles. Raman spectrum features of NiO were temperature dependent. UV/Vis/NIR spectra also showed a certain dependence on the microstructure of NiO samples. The crystal growth of NiO particles and the sintering effect were pronounced at the highest heating temperature.