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Raman Tweezers (RT) were exploited to trap and characterize polystyrene microbeads floating within a complex medium obtained by the digestion of a mussel which is considered a bioindicator for microplastics pollution.

Radiation pressure is used to push gold nanorods on multilayer graphene and create hybrid active surfaces for surface-enhanced Raman spectroscopy (SERS) in liquid. As a proof of concept, ultrasensitive detection of bovine serum albumin is shown and the aggregation kinetics is studied as a function of the irradiation time. We compare the results on graphene with experiments on glass and gold surfaces. Optical aggregation on graphene occurs on time scales of 20 min, ca. 3.5 times slower than on glass. No stable aggregation is obtained on gold. We attribute the differences to the destabilization effect of the standing wave produced on the metallic substrates, due to their higher reflectivity, and to the reduced thermophoretic effects, related to the higher heat dissipation. Despite the slowdown of the aggregation kinetics, the usage of graphene as substrate offers manifold benefits: an almost negligible fluorescence background when using near-infrared light (785 nm), the absence of thermal absorption as well as the possibility to easily functionalize the surface to enhance the affinity with the analytes. Our results enlarge the spectrum of materials that can be used for optical aggregation and SERS detection of biomolecules, highlighting the importance of controlling the physical properties of the surfaces. Graphic abstract: [Figure not available: see fulltext.]

The preparation and characterization of a hybrid composite, based on carbon cloth (CC) matrix functionalized with two-dimensional (2D) MoS2 flakes and MoO3, and its use for developing an electrochemical sensor for the determination of riboflavin (RF) is here reported. The 2D-MoS2-MoO3CC composite was prepared by depositing 2D-MoS2 nanosheets, obtained by liquid phase exfoliation (LPE), on the surface of a carbon cloth fiber network, previously functionalized with a layer of molybdenum oxide (α-MoO3) by radio-frequency magnetron reactive sputtering technique. The 2D-MoS2-MoO3CC composite was characterized by scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX), and Raman spectroscopy. An electrochemical sensor has been then fabricated by fixing a slice of the 2D-MoS2-MoO3CC composite on the working electrode of a screen-printed carbon electrode (SPCE). The 2D-MoS2-MoO3-CC/SPCE sensor display good electrochemical characteristics which have been exploited, for the first time, in the electroanalytical determination of riboflavin (RF). The sensitivity to RF, equal to 0.67 µA mM−1 in the linear range from 2 to 40 µM, and a limit of detection (LOD) of 1.5 µM at S/N = 3, demonstrate the promising characteristics of the proposed 2D-MoS2-MoO3-CC/SPCE electrochemical sensor for the determination of riboflavin.

In recent years, considerable effort has been devoted to the synthesis and characterization of two-dimensional materials. Liquid phase exfoliation (LPE) represents a simple, large-scale method to exfoliate layered materials down to mono- and few-layer flakes. In this context, the contactless trapping, characterization, and manipulation of individual nanosheets hold perspectives for increased accuracy in flake metrology and the assembly of novel functional materials. Here, we use optical forces for high-resolution structural characterization and precise mechanical positioning of nanosheets of hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide obtained by LPE. Weakly optically absorbing nanosheets of boron nitride are trapped in optical tweezers. The analysis of the thermal fluctuations allows a direct measurement of optical forces and the mean flake size in a liquid environment. Measured optical trapping constants are compared with T-matrix light scattering calculations to show a quadratic size scaling for small size, as expected for a bidimensional system. In contrast, strongly absorbing nanosheets of molybdenum disulfide and tungsten disulfide are not stably trapped due to the dominance of radiation pressure over the optical trapping force. Thus, optical forces are used to pattern a substrate by selectively depositing nanosheets in short times (minutes) and without any preparation of the surface. This study will be useful for improving ink-jet printing and for a better engineering of optoelectronic devices based on two-dimensional materials.

We demonstrate optical trapping of plasmonic silica-gold mesocapsules and their use as local SERS probes in Raman tweezers. These novel hybrid dielectric-metal particles, designed for optoplasmonic applications, are mesoscopic porous silica shells embedding gold nanospheres in their inner wall. We observe a high trapping efficiency due to plasmon-enhanced optical trapping of the gold component. Furthermore, we develop an accurate model of optical trapping of this hybrid system in the T-matrix framework studying how the plasmon-enhanced optical forces scale with gold nanoparticle number in the mesocapsule. The relevance of effective optical trapping in hollow plasmonic mesocapsules is twofold for detection and delivery technologies: positioning and activation processes. In fact, the presented system allows for the opportunity to drag and locate cargo mesocapsules embedded with specific molecules that can be activated and released in situ when a precise localization is required. (Graph Presented).

Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment is limited by the intrinsic difficulties of the techniques currently used for the detection, quantification, and chemical identification of small particles in liquid (light scattering, vibrational spectroscopies, and optical and electron microscopies). Here we introduce Raman Tweezers (RTs), namely optical tweezers combined with Raman spectroscopy, as an analytical tool for the study of micro- and nanoplastics in seawater. We show optical trapping and chemical identification of sub-20 mu m plastics, down to the 50 nm range. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Being a microscopy technique, RTs also permits one to assess the size and shapes of particles (beads, fragments, and fibers), with spatial resolution only limited by diffraction. Applications are shown on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin ecocorona. Coupled to suitable extraction and concentration protocols, RTs have the potential to strongly impact future research on micro and nanoplastics environmental pollution, and enable the understanding of the fragmentation processes on a multiscale level of aged polymers.

Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment and their impact on the biota compartment is limited by the intrinsic difficulties of conventional analytical techniques (light scattering, FT-IR, Raman, optical and electron microscopies) in the detection, quantification and chemical identification of small particles in liquid samples. Here we propose the use of optical tweezers, a technique awarded in 2018 with the Nobel prize, as an analytical tool for the study of micro- and nano- plastics in sea water. In particular, we exploit the combination of optical tweezers with Raman spectroscopy (Raman Tweezers, RTs) to optically trap plastic particles with sizes from tens of µm down to 90 nm and unambiguously reveal their chemical composition. RTs applications are shown on particles made of the most common plastic pollutants, including polyethylene, polypropylene, nylon and polystyrene, that are artificially fragmented and aged directly in seawater. RTs allow us to assess the size and shapes of microparticles (beads, fragments, fibers) and can be applied to investigate particles covered with organic layers. Furthermore, operating at the single particle level, RTs enable unambiguous distinction of plastic particles from marine microorganisms and seawater minerals, overcoming the capacities of standard Raman spectroscopy in liquid, limited to average measurements. Coupled to suitable extraction and concentration protocols, RTs could have a strong impact in the study of the fate of micro and nanoplastics in marine environment, as well as in the understanding of the fragmentation processes on a multi-scale level.

Two-dimensional molybdenum disulphide nanosheets (2D-MoS2) were prepared by liquid-phase exfoliation and used to modify screen-printed carbon electrodes (SPCE), in order to develop an electrochemical sensor for the simultaneous determination of dopamine (DA) and tyrosine (Tyr) in presence of uric acid (UA). To demonstrate the layered morphology, the synthesized molybdenum disulphide nanostructures, have been characterized by Raman and SEM in both liquid dispersion and after deposition on SPCE. The performances of the 2D-MoS2-SPCE electrode have been tested and optimized in terms of sensitivity, reaching high sensitivity values of 1044 μA mM−1 cm−2 for DA and 321 μA mM−1 cm−2 for Tyr, selectivity against UA and high stability. The simultaneous detection of these biomolecules is the first study so far reported with the use of 2D-MoS2-based sensors. The promising characteristics of the developed electrodes suggest 2D-MoS2 as a versatile, low cost and easy to produce material for the next generation of electrochemical sensors of a variety of important biomolecules.

Optical forces are used to aggregate plasmonic nanoparticles and create SERS-active hot spots in liquid. When biomolecules are added to the nanoparticles, high sensitivity SERS detection can be accomplished. Here, we pursue studies on Bovine Serum Albumin (BSA) detection, investigating the BSA-nanorod aggregations in a range from 100 mu M to 50 nM by combining light scattering, plasmon resonance and SERS, and correlating the SERS signal with the concentration. Experimental data are fitted with a simple model describing the optical aggregation process. We show that BSA-nanorod complexes can be optically printed on non-functionalized glass surfaces, designing custom patterns stable with time. Furthermore, we demonstrate that this methodology can be used to detect catalase and hemoglobin, two Raman resonant biomolecules, at concentrations of 10 nM and 1 pM, respectively, i.e., well beyond the limit of detection of BSA. Finally, we show that nanorods functionalized with specific aptamers can be used to capture and detect Ochratoxin A, a fungal toxin found in food commodities and wine. This experiment represents the first step towards the addition of molecular specificity to this novel biosensor strategy.

Strategies for in-liquid molecular detection via Surface Enhanced Raman Scattering (SERS) are currently based on chemically-driven aggregation or optical trapping of metal nanoparticles in presence of the target molecules. Such strategies allow the formation of SERS-active clusters that efficiently embed the molecule at the “hot spots” of the nanoparticles and enhance its Raman scattering by orders of magnitude. Here we report on a novel scheme that exploits the radiation pressure to locally push gold nanorods and induce their aggregation in buffered solutions of biomolecules, achieving biomolecular SERS detection at almost neutral pH. The sensor is applied to detect non-resonant amino acids and proteins, namely Phenylalanine (Phe), Bovine Serum Albumin (BSA) and Lysozyme (Lys), reaching detection limits in the μg/mL range. Being a chemical free and contactless technique, our methodology is easy to implement, fast to operate, needs small sample volumes and has potential for integration in microfluidic circuits for biomarkers detection.

Due to its exceptional physical properties, synthetic diamond is an ideal material for the realization of UV and X-ray detectors to be used for the characterization of laser-generated plasmas. Diamond detectors are able to operate at high temperatures and in the presence of high fluxes of ionizing radiation, where traditional silicon-based detectors usually fail. In this paper, we report on Raman and electro-optical characterization of a structure consisting of intrinsic diamond/boron-doped diamond homoepitaxially grown by chemical vapor deposition onto a commercial high pressure high temperature Ib-type diamond substrate using a 1% CH4/H2 gas mixture. A metal–insulator–semiconductor (MIS) diode was obtained by thermally evaporating an aluminum contact on the growth surface of the intrinsic layer. The detection capability of this device operating in transverse configuration was measured in the deep UV spectral range. The device sensitivity has been estimated at different biasing voltages and at two wavele...

UV/vis absorption and time-resolved fluorescence measurements on alcoholic solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS(4)) in neutral and acid form have been performed as a function of the alcohol polarity. These solutions show a peculiar behavior that mimics porphyrin in confined water solutions. In alcohols, TPPS(4) exhibits a metastable phase showing the formation of new species in analogy with the confined water environment of AOT microemulsions. Various species have been detected at different pH values and on aging the solutions. Under neutral pH conditions, the porphyrin is present as free base monomer (S415) with a small amount of H-dimeric species (S400). On aging, the S415 leads to the formation of a new species (S423), which has been assigned as a J-type dimer of the neutral porphyrin. The species S400 and S423 are not present in bulk water solution but are typical of TPPS(4) in confined water. On decreasing pH, the S415 almost immediately converts into the diacid form (S438), which evolves toward red-shifted J-aggregates (S490) and blue-shifted H-aggregates (S420). On decreasing alcohol polarity, the kinetic evolution from fresh to aged solution and from the monomeric diacid species to H- and J-aggregates speeds up. Exploiting the amphiphilic character of short chain alcohols and widely varying their polarity, we were able to enhance in bulk conditions the peculiar behavior observed in close proximity to the microemulsion wall.

The crucial role of precursor gas (PG) and of catalyst support (CS) in the growth of multi-walled C nanotubes (MWCNTs) by iron-catalysed chemical vapour deposition (CVD) is evidenced. This is accomplished by comparing structural and morphological properties of MWCNTs synthesised by the use of different PGs (ethane and isobutane) and CSs (silica and alumina). The results of analyses, carried out on catalysts and C deposits by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermo-gravimetry (TG) and X-ray diffraction (XRD), demonstrate that Al2O3-supported catalysts are more efficient than SiO2-supported ones in decomposing hydrocarbons. The use of i-C4H10 as PG allows reducing Fe-encapsulation and improving yield (YC) and selectivity, so as the large-scale production (YC > 900 wt.%) of high-quality nanotubes can be operated even at moderate reaction temperature (600 °C) after proper calibration of Fe-load (29 wt.%) and catalyst reduction temperature (500 °C).

Wetting phenomena in porous silicon layers are experimentally investigated by Raman scattering. The experimental results show a reversible blue-shift of Raman spectra of wetted porous silicon layers with respect to the unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions.

Multiwalled carbon nanotubes (MWCNTs) were synthesised by chemical vapour deposition (CVD) in a C 2 H 6 +H 2 atmosphere over 20%Fe/SiO 2 catalysts. The influence of synthesis temperature, flow-rate and flow ratio of the reactant gases, the amount of catalyst employed and the catalyst reduction temperature on the abundance and crystalline perfection of product was analysed by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy. The changes in yield and crystalline perfection, as monitored by Raman G' band relative intensity, were correlated with the variations of synthesis temperature, the diverse catalyst surface area and H 2 /C supply ratio attained by varying growth conditions. In the range examined, the lowering of catalyst reduction-temperature turns out to be beneficial for both yield and crystalline perfection of the MWCNTs. All the other growth parameters produce opposite effects so the best compromise has to be sought.

In this paper, porous silicon (PS) layers of different porosity and thickness have been investigated by Raman spectroscopy. The estimation of built-in strain in PS is reported. Moreover, wetting phenomena in PS layers have been also investigated. The results prove a reversible blue shift of Raman spectra of wetted PS layers with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the PS layer and the bulk silicon substrate in wetting conditions. Copyright © 2008 John Wiley & Sons, Ltd.

Optical trapping of hybrid core–shell gold–polymer particles is studied. Optical forces are measured for different gold core size and polymer shell thickness, revealing how a polymer shell increases the trapping efficiency with respect to the bare gold nanoparticles. Data are in agreement with calculations of optical trapping based on electromagnetic scattering theory in the T-matrix approach. The scaling behaviour of optical forces with respect to the ratio between polymer layer thickness and the whole particle radius is found and discussed.

Polycrystalline (pCVD) and single crystal (scCVD) diamond films grown from Chemical Vapour Deposition (CVD), if sufficiently pure at Raman analysis, are very good materials for beam or flux monitors inside accelerators or nuclear reactors. This is because they are very hard to damage in high radiation fields and very resistant to high temperatures. Films of pCVD diamond are, however, not so good as spectroscopy detectors due to inhomogeneities induced by their growth in grains with the consequent presence of grain boundaries which worsen their energy resolution. The latter can be significantly improved by growing scCVD diamond films onto HPHT synthetic diamond substrates. We have shown that it is possible to measure the density of defects inside diamond specimens using as probes suitable penetrating nuclear radiations. With the preliminary results reported here we'll show that, bombarding CVD diamond films grown at Roma 'Tor Vergata' with energetic protons and 4 He, Li-6 and C-12 ions produced in the accelerators of Catania laboratories, the pulse height defects are higher than those in silicon detectors and likewise well described by a power law in the deposited energy. Furthermore, we'll show that pulse heights for the same particles seem to depend on the duration of the measurement, thus exhibiting a sort of depolarization of the insulator when exposed to the electric voltage which makes it a particle detector. (c) 2006 Elsevier B.V. All rights reserved.

The mid-range structure of glasses of the glass-forming system xNb(2)O(5)-(60 - x)P(2)O(5)-40Na(2)O, with x varying from 0 to 40, has been investigated by Raman spectroscopy and electro-optical Kerr measurements. It was found that the mid-range inhomogeneities in the glasses under study vary with x and their compositions and structures dramatically differ from the gross glass composition. It is shown that inhomogeneities with the 8NaNbO(3) + (Nb(2)O(5)·P(2)O(5)) composition are responsible for the electro-optical sensitivity of the glasses. The electro-optical structural elements of the inhomogeneities of this type are assumed to be fragments of the quasicubic lattice of crystalline NaNbO(3) demonstrating a rather high electro-optic Kerr coefficient. The obtained results are discussed in terms of the concepts of constant stoichiometric groupings and crystal motifs.

The recognition of some globular proteins was carried out in aqueous solution, at micromolar concentrations, by using an uncharged symmetrical cobalt-porphyrin (Co-P). By means of UV/Vis, induced circular dichroism, and fluorescence spectroscopy techniques, it was ascertained that the interactions between specific amino acid residues and Co-P occurred on the protein surface. In particular, spectroscopic evidence showed the formation of supramolecular complexes without disruption of the native structure of the proteins and, furthermore, that signal changes were characteristic of each Co-P/protein system, so that they could be used as a highly sensitive analytical tool for protein recognition. The relative association constants were proportional to the protein molecular masses (and then to the number of amino acid residues).

A rapid method to detect the addition of reconstituted mandarin oils to natural mandarin essential oils is suggested. The method is based on the ratio of the two enantiomers of limonene determined by GC using an on-line coupling of non-chiral and chiral capillary columns. The ratio of (−)-limonene and (+)-limonene in the genuine mandarin oils was 2.2 to 97.8, while in reconstituted oils the same ratio was 13.4 to 86.6. Addition of reconstituted oils increases the ratio of (--) to (+)-limonene in genuine oils enabling the detection of additions of even 5% of reconstituted oils to genuine mandarin oils.

The tetraanionic water soluble meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) can be easily embedded into Nafion®, obtaining membranes which exhibit interesting optical properties strongly dependent both on the aggregation extent and on the organic solvent used for the re-cast procedure.

In this paper, niobium-phosphate glasses doped with rare earths (Er and Sm) are investigated by Raman scattering. The goal of Raman characterization is twofold: (a) to perform a fine structural characterization of the synthesized glasses and (b) to measure the Raman gain coefficient of the samples and to compare it with fused silica. The results reveal the presence of NbO6 octahedra and Nb–O–P–Nb–O mixed chains. A broadening of bandwidth and a significant enhancement (∼24 times) in gain coefficient G with respect to conventional silica glasses are also demonstrated.

Catalytic activity of iron based catalysts in the production of multi-walled carbon nanotubes (MWCNTs) has been investigated. The effect of the carbon source (ethane or isobutane), catalyst support (Al2O3 or SiO2), iron loading, catalyst reduction temperature and reaction temperature on yield and quality of carbon products has been examined. The structural and morphological properties of catalyst and carbon products obtained have been analyzed by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD). The iron-based catalysts supported on alumina seem to be efficient systems for the production of carbon nanotubes from chemical vapor deposition (CVD) of isobutane with very interesting yields. The opportune calibration of reaction parameters, such as iron loading and reaction temperature, can in fact drive the synthesis toward the formation of high quality CNTs.

Three-layer structures consisting of intrinsic/B-doped homoepitaxial CVD diamond grown onto commercial HPHT Ib substrates have been studied by means of Raman spectroscopy and photoluminescence (PL). The intrinsic layers have been deposited, at fixed methane to hydrogen ratio (1%), by systematically changing the substrate temperature (620-820 °C). Raman measurements point out the excellent crystalline quality and phase purity of the samples. Moreover, flat PL spectra in a wide energy range (1.7 eV-2.7 eV) indicate also their great purity. As the free-exciton recombination can be used to further probe the quality of synthetic diamond, measurements of free-exciton emission at room temperature have been also performed. The excitation was produced by a 5 ns pulsed tunable laser irradiation. The results have been compared with the detection characteristics of simple alpha-particle detector prototypes based on the analyzed samples. A clear correlation between excitonic emission and detector sensitivity is demonstrated. On the basis of these results, low methane concentrations (approx. 1% CH4/H2) in the deposition gas mixture and intermediate substrate temperatures (approx. 720 °C-770 °C) have been identified as the best working conditions of our growth reactor.

We performed experiments on the synthesis of carbon nanotubes (CNTs) by iron-catalyzed chemical vapor deposition (CVD) in C 2 H 6 + H 2 atmosphere. We varied flow-rates of reactant gases (ethane: 30–120 sccm, hydrogen: 0–120 sccm), as well as their ratio, in order to study the evolution of the growth kinetics. We used scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy to investigate the morphologies, dimensions and crystalline structure of the samples. Our results demonstrate the crucial role played by H 2 in the enhancement of C diffusion-rate and in the consequent development of ordered and smooth graphene layers. A faster growth-rate is achieved by the increase of C 2 H 6 flow-rate. However, if H 2 flow-rate is not adequately enhanced, the improvement is only apparent. The excess of C supplied gives rise to deposition of amorphous carbon onto the CNT walls, and to the co-production of different nanostructures. A substantial agreement is found with results reported for CVD growth of CNTs by the use of different catalysts, reactants and gas-flowing setups.

The stress in porous silicon during exposition to a liquid is investigated by an approach based on Raman scattering. When the porous silicon structure is exposed to isopropanol or ethanol, a reversible blue shift of the Raman spectra is observed. The blue shift of Raman scattering is ascribed to the contraction induced by the liquids that fill the pores.

The action of molecular interaction between a fluid and an adsorbent results in adsorption and wetting phenomena. However, the adsorbent is also submitted to the action of the molecular forces. In order to provide a large adsorption capacity, adsorbents with a large specific surface area are preferable. For this reason, for the study of adsorption phenomena, porous silicon is a material of great interest. Wetting phenomena in porous silicon layers are experimentally investigated by Raman scattering. The experimental results prove a reversible blue-shift of Raman spectra of wetted porous silicon layers with isopropanol or ethanol with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions. The use of two liquids having quite similar density and surface tension resulted, as expected, in quite comparable blue shift of the peak. This effect may be conveniently used in sensing applications of liquids on porous silicon layers.

The achievement of high yields seems to be one of the most pressing demands for large-scale production of carbon nanotubes (CNT). In this work, a demonstration is given in which in the synthesis of CNT by chemical vapour deposition (CVD) higher yields are attained at the expense of crystalline quality and purity of CNT, thus suggesting that an accurate balance of competing factors is necessary for the optimisation of the preparation process. This is accomplished by comparatively discussing the results of morphologic and structural analysis carried out on multi-walled C nanotubes (MWCNT), prepared at 750 °C by CVD in C2H6–H2 mixture over 20% Fe/SiO2 catalyst, in order to clarify the role of the gas mixture composition on the issue of CNT synthesis. The results of Raman analysis, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) observations are correlated with yield variations and understood in the light of current assessments on CNT growth. Higher ethane/hydrogen flow ratios result in enhanced carbon deposit with amorphous-phase inclusions. Among the values investigated, a dilution of ethane in hydrogen at 50% may represent the best compromise between yield and quality of reaction products.

In this work, it is shown that some Raman-active modes may be detected, below 500cm−1, in the spectrum of nanotubes synthesized by iron catalyzed chemical vapor deposition. By comparatively discussing results of Raman, high-resolution transmission electron microscopy, and thermogravimetric analyses, demonstration is given that these spectral features originate from scattering by nanoparticles of iron catalyst encapsulated within the tubes under nonstationary growth regime. Their intensity progressively weakens with increasing carbon supply rate until bands disappear as stationary conditions are reached.

The infrared (IR) absorption dependence on visible light illumination has been measured in doped and undoped hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films grown by plasma enhanced chemical vapour deposition. The measurements were made by a highly sensitive technique which exploits properly designed a-Si1−xCx:H/ZnO test waveguides for lengthening the interaction region between the IR and visible (VIS) radiations in the material. Experimental data show that boron doping strongly enhances the VIS light induced variation of the IR absorption, whereas the increase in carbon content has a quenching effect on the phenomenon. The a-SiC:H films have been also characterized by photoluminescence measurements. The spectra are dominated by a photoluminescence band, ranging between 1.4 eV and 1.9 eV. This band is enhanced by the increase in carbon content, while is strongly quenched with increasing B-doping level. On the basis of these results, a correlation is found between the measurements of optical absorption, photo-induced absorption and photoluminescence. The type and the density of defects induced in the films by the different growth conditions have been recognized as the origin of the different behaviors observed.

In this work, we report on the structural characterization of homoepitaxial Microwave Plasma Enhanced CVD diamond grown onto Ib diamond substrates by varying systematically the methane to hydrogen ratio in the gas mixture (1–7% CH 4 ). X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements pointed out the excellent crystalline quality and phase purity of the specimens. PL measurements in the 1.7–2.7 eV energy range have shown completely flat spectra, excluding the presence of nitrogen-related optical centers. Such results show that the homoepitaxial CVD diamond can be grown, at moderate microwave power (720 W), and at growth rates not too low (∼ 1 μm/h) preserving a good quality. Moreover, the homoepitaxial crystals exhibited a strong free-exciton recombination radiation at room temperature even at the highest methane concentration used (7%). Preliminary measurements of the lifetime of the free exciton at room temperature have been also performed. The excitation was produced by a 5 ns pulsed laser irradiation at energies above the diamond band gap. The results have been compared with the structural properties of the samples and correlated with the growth conditions.

In this paper, we report on the characterization of homoepitaxial CVD diamond grown onto HPHT Ib diamond substrates by varying systematically the methane to hydrogen ratio in the deposition gas mixture (1–7%) and the microwave power (520–720 W). Growth rates up to approximately 2.2 μm/h have been achieved. X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements point out an excellent crystalline quality and phase purity of the homoepitaxial specimens even at the highest CH 4 concentration used. Completely flat PL spectra registered in a wide energy range (1.7–2.7 eV) exclude impurity contamination of the diamond samples. Such results show that homoepitaxial CVD diamond can be grown, at moderate microwave power and with moderate growth rate, preserving a good crystalline quality.

The aim of the present work is the characterization of decorated pottery samples from Caltagirone (Sicily, Italy), a renowned production centre of this kind of artwork. These fragments were found during archaeological excavations and were attributed to historical periods extremely far in time from each other (from XVIII century b.C. to XVI a.C.). Therefore, we expect that the manufacture techniques result rather different over so long time. The measurements, performed by Fourier Transform-InfraRed (FT-IR) absorbance and micro-Raman scattering, allowed us a non-destructive study of so precious artefacts. Some pigments were identified, various elements of ceramic paste and glazed layer were characterized.

Synthetic diamond has been proven as an important material for advanced electronic applications, such as those encountered in high energy physics and astrophysics. In fact, diamond transparency to visible light, its high carrier mobility, high breakdown field and strong resistance to chemical attack and radiation damage have suggested the potential application of this material for ‘solar-blind’ UV detectors which have to operate in extreme environments. To avoid the possible problems connected with the presence of grain boundaries in polycrystalline diamond films, a great effort has been devoted to the optimization of the growth process leading to high-quality single-crystal diamond on diamond substrates (homoepitaxy). In this view, characterization studies play a crucial role, because they provide the feedback for the optimization of the deposition process, in order to obtain the best quality material. In this work, a characterization study of homoepitaxial diamond grown by chemical vapor deposition (CVD) on synthetic diamond substrates is presented. The samples have been deposited in a CVD tubular reactor using a CH 4 –H 2 gas mixture (1–7%) at approximately 560 °C substrate temperature. The growth rate ranged between 0.9 μm/h and 2.2 μm/h, microwave powers between 520 W and 720 W. The crystalline quality of the diamond layer has been studied by means of Raman spectroscopy. Photoluminescence has been used to study the nature and the distribution of impurities, having energy levels in the diamond band gap, which influence negatively the electronic quality of the material. The results have been compared with electro-optical characterization of UV detectors for astrophysics based on the analyzed diamond samples. The growth parameters which guarantees both high material quality and optimal device response have been determined.

This work reports on the development and characterization of large area (1 cm2) vacuum UV CVD diamond photodetectors to address the requirements of space missions where pixel and 2D arrays are used. The quality of the CVD diamond was characterized by photoluminescence and Raman spectroscopy. The performance of these devices in the dark and under illumination was investigated and the results compared to those from small area detectors based on similar material. Planar and transverse electrode configurations were used in order to evaluate the possibility of producing imaging detectors. The spectral analysis of the photocurrent was measured as a function of several functional parameters and experimental conditions.

High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition (CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement of the best results was made possible. The films were deposited using a CH4-H2 gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 °C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than 2.4 cm-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at higher methane concentrations.

Silicon nanoparticles obtained by ball-milling of a 50% porosity silicon layer have been optically trapped when dispersed in a water–surfactant environment. We measured the optical force constants using linearly and radially polarized trapping beams finding a reshaping of the optical potential and an enhanced axial spring constant for the latter. These measurements open perspectives for the control and handling of silicon nanoparticles as labeling agents in biological analysis and fluorescence imaging techniques. (Some figures may appear in colour only in the online journal)

In this paper, the optical dispersion properties and the Raman gain of sodium phosphate glasses containing niobium oxide at increasing concentrations have been systematically investigated, with the aim of establishing a potential enhancement of the Raman gain and its bandwidth with respect to silica. A broadening of the bandwidth and a higher peak Raman gain (approximately 17 times) than in silica glass have been observed at high niobium oxide molar content. Our findings point out that sodium-niobium-phosphate glasses could be utilized for the realization of Raman amplifiers.

Optical forces are used to position and aggregate nanoparticles for different applications. In particular, plasmonic enhanced optical forces are exploited to direct gold nanorods surrounded by biomolecules to create hot-spots on demand in a liquid buffered environment. This enables protein detection at the 10 nM level. Furthermore, optical forces on liquid phase exfoliated layered materials (hBN, MoS2, WS2) are studied and used to push and aggregate nanostructures in specific patterns.