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Radiation-induced color centers locally produced in lithium fluoride (LiF) are successfully used for radiation detectors. LiF detectors for extreme ultraviolet radiation, soft and hard X-rays, based on photoluminescence from aggregate electronic defects, are currently under development for imaging applications with laboratory radiation sources, as well as large-scale facilities. Among the peculiarities of LiF-based detectors, noteworthy ones are their very high intrinsic spatial resolution across a large field of view, wide dynamic range, and versatility. LiF crystals irradiated with a monochromatic 8 keV X-ray beam at KIT synchrotron light source (Karlsruhe, Germany) and with the broadband white beam spectrum of the synchrotron bending magnet have been investigated by optical spectroscopy, laser scanning confocal microscopy in fluorescence mode, and confocal Raman micro-spectroscopy. The 3D reconstruction of the distributions of the color centers induced by the X-rays has been performed with both confocal techniques. The combination of the LiF crystal capability to register volumetric X-ray mapping with the optical sectioning operations of the confocal techniques has allowed performing 3D reconstructions of the X-ray colored volumes and it could provide advanced tools for 3D X-ray detection.

We report micro-Raman spectroscopy, high-resolution scanning electron microscopy (HR-SEM) and atomic force microscopy (AFM) investigation of changes in chemical vapor deposition grown single-layer ...

Nanocomposite films with high electrical conductivity and UV sensitivity were prepared by integration of DNA-modified graphene nanoplatelets (GNPs) with a polymer matrix made of poly(3,4-ethylenedioxythio-phene):poly(styrenesulfonate) (PEDOT:PSS). The exceptional electrical properties and mechanical strength of graphene were used to enhance the PEDOT:PSS properties and stability, whereas DNA molecules are sensitive to UV and have an exfoliating effect on the GNPs in aqueous solution. GNP-DNA/PEDOT:PSS films were exposed to radiation in the energetic UV-C band (254 nm), and their properties investigated before and after irradiation. Several techniques, including scanning electron microscopy, optical contact angle, electrical impedance and Raman spectroscopies, were used to characterize the nanocomposites and to investigate their sensitivity to UV. In particular, Raman microscopy mapping was used to analyze the chemical structure of the films and its modification at molecular level upon exposure to UV-C radiation. Results of these investigations are useful for the application of the GNP-DNA/PEDOT:PSS films in ultra-small and lightweight UV sensor devices for use in space environment, for example during extravehicular activities (EVA), or for industrial settings on Earth that are characterized by high levels of UV-C radiation.

The toughness mechanisms of epoxy-based nanocomposites reinforced by double-walled carbon nanotubes (DWCNT) are investigated using Raman microscopy mapping. Maps of the residual strain of the carbon nanotubes were generated for the fracture surfaces obtained after tensile loading. By imaging through different microscope objectives, Raman mapping allowed to determine the distribution of the nanotube residual strain, indicating tension or compression, in different sampling volumes near the fracture surface. The G′ band with its high sensitivity to nanotube diameter variations, and not overlapping with the characteristic epoxy Raman lines, was selected for the mapping. Results provide a quantitative analysis of the nanotube bridging and pull-out mechanisms identified by scanning electron microscopy (SEM) inspection of the fracture surfaces.

The main characteristics of the ENEA Discharge Produced Plasma (DPP) Extreme Ultraviolet (EUV) source are presented together with results of irradiations of various materials. The DPP EUV source, based on a Xe-plasma heated up to a temperature of 30 ÷ 40 eV, emits more than 30 mJ/sr/shot at 10 Hz rep. rate in the 10 ÷ 18 nm wavelength spectral range. The DPP is equipped with a debris mitigation system to protect particularly delicate components needed for patterning applications. The ENEA source has been successfully utilized for sub-micrometer pattern generation on photonic materials and on specifically designed chemically amplified resists. Details down to 100 nm have been replicated on such photoresists by our laboratory-scale apparatus for contact EUV lithography. Preliminary EUV irradiations of graphene films aimed at modifying its properties have been also performed. © 2019 SPIE.

The integration of surface sensing elements providing an in situ monitoring of the UV-induced degradation effects in composite materials and structures is crucial for their applications in hostile environments characterized by high levels of radiation, such as space. In this work, the electrical response of a novel UV-sensitive nanocomposite film was investigated using electrical resistance tomography (ERT). The conductivity changes measured at the irradiated surfaces were compared with results from morphology analysis by scanning electron microscopy (SEM) and surface analytical techniques, such as Raman microscopy. Highly conductive and UV-sensitive nanocomposite coatings were prepared by embedding the graphene and deoxyribonucleic acid (DNA) component in a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) matrix. The coatings were deposited onto carbon-reinforced laminated structures fabricated by resin transfer molding process using an aerospace-grade epoxy resin. Two different irradiation conditions were tested by exposing the nanocomposite surfaces to UV-C irradiances of 2.6 and 4.0 mW/cm2. Results show that the ERT technique has great potential for the in situ health monitoring of carbon-based materials and structures for aerospace applications, which are subject to degradation by UV-C radiation: it allows mapping of the conductivity changes occurring at the surface of the graphene/DNA/PEDOT:PSS coatings during irradiation.

The self-assembly of double-stranded DNA (dsDNA) segments on two variations of graphene surfaces having nano-platelets with different lateral sizes and thicknesses was investigated using surface-enhanced Raman spectroscopy (SERS) and electrical impedance spectroscopy (EIS) techniques. Due to the strong local field-enhancement, the SERS signals from functional molecules bound to the graphene edges and from DNA moieties were recorded. Relative intensities of specific Raman modes were used as contrast parameters to build Raman signal intensity maps. The observed variation in the SERS signal intensity was related to the different configuration (tilted or flattened) in which dsDNA segments are assembled on the carbon surface, depending on the graphene platelet size. EIS was used to characterize the conductive properties of nano-structured films containing pristine or DNA-functionalized graphene nano-platelets. Results from the EIS analysis supported the SERS findings and confirmed that SERS mapping is a reliable method for a rapid monitoring of the procedures used to interface DNA with graphene surfaces. The present study, linking DNA anchoring morphology to the conductive properties of nano-structured hybrid films, contribute to define a new approach in the optimization of biosensor design. © 2016 Elsevier Ltd

Carbon nanotubes (CNTs) and graphene are at the center of a significant research effort due to their unique physical and chemical properties, which promise high technological impact. For the future development of all the foreseen applications, it is of particular interest the study of binding interactions between carbon nanostructures and functional groups. An appropriate method is the surface-enhanced Raman spectroscopy (SERS), which provides a large amplification of Raman signals when the probed molecule is adsorbed on a nanosized metallic surface. In this chapter, we present a review of principal results obtained applying SERS for the characterization of pristine and functionalized CNTs and graphene. The obtained results encourage us to consider SERS as a powerful method to obtain a rapid monitor of the procedures used to interface graphene and nanotubes.

In this work, we combined AFM, FE-SEM and Raman spectroscopy to study the commercially available CVD grown graphene on Cu and Si substrate. SEM and AFM provide topographic information, show a network of out of plane deformations, 'wrinkles', whereas Raman spectroscopy which can give information on structural properties of the graphene films, such as the number of layers and level of disorder, by observing the peaks, indicates a I2D/IG ratio smaller than the value expected for mono-layer graphene. © 2018 Author(s).

Multi-walled nanotube (MWNT) functionalisation was investigated by surface-enhanced Raman spectroscopy (SERS). The MWNTs were deposited as dilute dispersions on SERS-active substrates. We used nano-structured gold surfaces with various morphologies for our measurements. The surface enhancement effect was used to amplify the Raman signal from functional molecules bound to the nanotube walls. The recorded spectral features allowed for discrimination between the differently functionalised MWNTs. Although the present study is limited to a few examples, our measurements indicate the higher specificity obtained by the SERS approach and its possible use for a systematic study of functionalisation effects on MWNT structures. © the Owner Societies 2015.

Surface-enhanced Raman spectroscopy (SERS) measurements on 1,3,5-trinitroperhydro-1,3,5-triazine were performed with a table-top micro-Raman system exciting the analyte with a diode laser emitting at 785nm. The main Raman features of 1,3,5-trinitroperhydro-1,3,5-triazine were clearly identified, and a careful optimization of acquisition parameters was performed in order to increase the overall sensitivity of the apparatus. The amount of the sampled substance was determined through the analysis of high-resolution scanning electron microscope images of the substrate covered with the residual explosive and resulted to be of the order of few tens of picograms. This value demonstrates the applicability of commercial substrates to the ultrasensitive surface-enhanced Raman spectroscopy detection of explosives, allowing for their identification in real time. Copyright © 2013 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site.

Methods for rapid identification of explosives and their associated compounds at trace level quantities are needed for security screening applications. In this paper, we apply the surface-enhanced Raman spectroscopy (SERS) to detect and identify traces (as low as tens of pg) of pentaerythritol tetranitrate (PETN), ethylene glycol dinitrate (EGDN), cyclotrimethylene-trinitramine (RDX) and trinitrotoluene (TNT) using commercially available substrates (Klarite®, Renishaw diagnostics). High quality spectra were achieved within 10 s with a compact Raman spectrometer. Principal component analysis (PCA) of the data was performed to understand what factors affected the spectral variation across the samples. It was found that 76% of the spectral variation was explained by the first three PCs. Score plots for these components showed that the energetic materials can be clearly classified on the basis of SERS spectra also at trace level quantity. Our measurements further demonstrate the potential for using SERS as fast, in situ analytical tool for safety devices, with a sensitivity which competes and, in some cases, overcomes other techniques. Copyright © 2013 John Wiley & Sons, Ltd.

Surface-enhanced Raman spectroscopy (SERS) measurements of some common military explosives were performed with a table-top micro-Raman system integrated with a Serstech R785 miniaturized device, comprising a spectrometer and detector for near-infrared (NIR) laser excitation (785 nm). R785 was tested as the main component of a miniaturized SERS detector, designed for in situ and stand-alone sensing of molecules released at low concentrations, as could happen in the case of traces of explosives found in an illegal bomb factory, where solid microparticles of explosives could be released in the air and then collected on the sensor’s surface, if placed near the factory, as a consequence of bomb preparation. SERS spectra were obtained, exciting samples in picogram quantities on specific substrates, starting from standard commercial solutions. The main vibrational features of each substance were clearly identified also in low quantities. The amount of the sampled substance was determined through the analysis of scanning electron microscope images, while the spectral resolution and the detector sensitivity were sufficiently high to clearly distinguish spectra belonging to different samples with an exposure time of 10 s. A principal component analysis procedure was applied to the experimental data to understand which are the main factors affecting spectra variation across different samples. The score plots for the first three principal components show that the examined explosive materials can be clearly classified on the basis of their SERS spectra.

The detection of explosives and their associated compounds for security screening is an active area of research and a wide variety of detection methods are involved in this very challenging area. Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most sensitive tools for the detection of molecules adsorbed on nano-scale roughened metal surface. Moreover, SERS combines high sensitivity with the observation of vibrational spectra of species, giving complete information on the molecular structure of material under study. In this paper, SERS was applied to the detection of very small quantities of explosives adsorbed on industrially made substrates. The spectra were acquired with a compact Raman spectrometer. Usually, a high signal-to-noise (S/N) spectrum, suitable for identification of explosive molecules down to few hundreds of picograms, was achieved within 30 s. Our measurements suggest that it is possible to exploit SERS using a practical detection instrument for routine analysis. Copyright © 2010 John Wiley & Sons, Ltd.

Visible-light emitting nanocomposite Si/diamond polycrystalline layers have been produced by means of a hybrid CVD/powder-flowing technique. These films are of great interest for optoelectronic applications, but it has been experienced that the structural and optical properties of such composite materials depend dramatically on both concentration and distribution of Si defects. In this work Micro-Raman spectroscopy, Scanning Electron Microscopy (SEM), Photoluminescence (PL), and Cathodoluminescence (CL) techniques have been employed to explore the 1.68 eV Si-related centers in polycrystalline CVD diamond films. The spatial distribution of these defects inside the diamond lattice has been studied by performing a series of CL, PL and Raman mapping with a sub- and micrometric resolution. The results allowed to correlate the emission features with the crystallographic orientation, evidencing more intense luminescence signals from (100) faces of diamond crystallites. As regards the Si distribution, the PL analysis evidenced that Si centers are preferentially located in proximity of the dislocations in the diamond crystal lattice. Moreover, the Raman signal shift of diamond peak position indicates that the Si centers give rise to a slight compressive stress, dependent on the Si concentration. Overall, the investigations carried out confirm that this CVD approach affords versatility with regards the insertion of Si centers inside the diamond lattice together with the insertion of Si nanoparticles in the diamond matrix and is suitable for production of purpose-designed optical layers.

The second-order susceptibility tensor χ(2)(2ω;ω, ω) of a carbon nanotube (CNT) surface was determined as a function both of the average tube orientation and CNT topology distribution. The transformation properties of the hyperpolarizability β tensor, as rooted in the CNT isogonal symmetry point group, make non-vanishing only the chiral component of χ(2)(2ω;ω, ω), thus denying second harmonic generation (SHG) in racemic samples. Nevertheless, the rupture of the CNT spatial symmetry due to local deformations and to finite size can act as a source for SHG even in racemic samples. The study of SHG polarization and of the anisotropic dependence of the signal intensity on the angle Ω between the surface normal and the exciting laser beam direction are proposed as methods to discriminate between the two contributions. An experimental test of such a statement was performed on a sample grown by the laser annealing technique. A massive presence of chiral CNTs with strong local deformations was revealed by the low- and medium-wavenumber Raman spectra measured on the sample. The SHG polarization and the anisotropic dependence of the signal intensity as a function of Ω were studied experimentally, allowing the racemic nature of the investigated sample to be elucidated. Copyright © 2005 John Wiley & Sons, Ltd.

In this work, we report a simple method of producing single walled carbon nanotubes by CO 2 laser – annealing of cold pressed pellets of silicon carbide nano-particles. The surface morphology of the treated samples was observed by field emission scanning electron microscopy, whereas the modification induced in the lattice structure was examined by Raman scattering spectroscopy. All the measurements indicate that, due to the laser irradiation, nanotubes grow on the SiC particles surface, without a preferential alignment.

The properties of the carbon nanotubes (CNTs) hyperpolarizability β due to π electrons is studied by using the formalism of the irreducible representations of CNT space symmetry group (G). The main contribution to the second order nonlinearity is demonstrated to come from electrons at the origin of the Brillouin zone (k=0). Within this scheme, a description based on the isogonal point group associated to G accounts for the relevant properties of β.

The growth of carbon nanotubes usually requires a catalyst (typically Ni, Co or Fe). Although these catalysts promote the growth of nanotubes, they also require complex purifying treatments to remove them, which damage and dope the final product. Alternative catalyst-free growth of nanotubes films, as needed for electronic applications, was achieved by laser-annealing of amorphous SiC in vacuum at a relatively low temperature. In this work, we present the main results obtained and give some relevant examples of such carbon systems. The formation mechanism of carbon nanotube films is also discussed.

The role played by symmetry properties of a carbon nanotube in the generation of second harmonic radiation is studied by using the formalism of irreducible representation of the symmetry point group. Experimental results of second harmonic generation in a carbon nanotube sample are discusses in view of the theoretical prediction obtained.

Femtosecond pulses of a Cr:forsterite laser are used to study second- and third-harmonic generation in a layer of single-wall carbon nanotubes produced by low-velocity spraying. The harmonic amplitude in our experiments scales as ( I p ) n as a function of the pump intensity I p , with n = 2 and 3 for the second and third har- monics, respectively. This scaling law holds up to pump intensities on the order of 10 12 W/cm 2 . The ratio of the maximum signal to the averaged background in the spectra of the second and third harmonics is estimated as 50 and 30, respectively. The second and third harmonics produced by a linearly polarized pump field are also linearly polarized, with their polarization vectors oriented along the polarization direction of the pump field. The capabilities of nonlinear-optical methods for structural and morphological analysis of carbon nanotubes are discussed, as well as ways to create solid-state carbon-nanotube generators of optical harmonic. © 2004 MAIK "Nauka/Interperiodica".

Non-linear optical response of single-wall carbon nanotubes, produced without catalyst, was investigated. Third-order susceptibility Degenerate Four Wave Mixing measurements have been performed on thick film of nanotubes deposited onto quartz substrate. Results are presented as measured in the nanosecond time scale at 532 nm. The second-order hyperpolarizability γ was estimated to be as large as 1.6 × 10 −29 e.s.u.

Carbon nanotube films produced on a Si(1 0 0) substrate without any metal catalyst were used as electrodes in galvanic cells. The electrochemical mechanism of hydrogen evolution, storage and oxidation was studied using cyclic voltammetry and galvanostatic polarisation. Cyclic voltammetry showed that hydrogen is easily produced on the carbon nanotube surface, but a significant overvoltage was observed for hydrogen oxidation. The kinetics of hydrogen evolution influenced the quantity of hydrogen stored in the nanotube, which increased with increasing discharge currents.

The effect of thermal processing at 1050 °C of a dispersed film of carbon nanoparticles deposited on a Si substrate with a native SiO 2 layer has been studied by scanning electron microscopy and scanning photoelectron spectromicroscopy. It has been found that the thermal processing results in formation of pyramidal-shaped defects of 2–7 μm with strongly reduced SiO 2 content with silicon wires of diameter ranging between 30 and 50 nm decorating the pyramid walls. The nucleation of the Si nanowires occurs via reduction of the native oxide layer by the nanosized carbon particles, without the need of metal catalysts and at temperatures relatively lower than that used in similar techniques.

Second- and third-harmonic generation in single-wall carbon nanotube layers produced by low-velocity spraying was studied experimentally with the use of amplified 75 fs pulses of Cr:forsterite laser radiation within the range of pump pulse intensities up to the breakdown threshold. Harmonic-generation processes are shown to be ideally suited for the non-linear spectroscopy and structure analysis of carbon nanotubes, in many ways supplementary to Raman spectroscopy. The second- and third-harmonic yields scale as quadratic and cubic functions, respectively, of the pump pulse energy up to pump intensities of 1012 W cm−2, indicating the perturbative regime of non-linear-optical interactions and suggesting a convenient calibration for the second and third harmonics employed as spectroscopic probes. Comparison of harmonic-generation data with absorption spectra of carbon-nanotube layers reveals an important role of quantum confinement effects in the non-linear coherent scattering of light from carbon nanotubes. Femtosecond pulses of Cr:forsterite laser radiation also generate the fifth optical harmonic at 251 nm in the glass substrate of carbon-nanotube samples, which can be employed for UV spectroscopy and subwavelength-resolution non-linear microscopy of carbon nanotubes. Copyright © 2003 John Wiley & Sons, Ltd.

In this Letter, we report a new method for the fabrication of carbon nanotubes (CNT) and nanowires where amorphous hydrogenated carbon nano-particles were used as precursor, without metal catalyst addition. In particular, depending on the process parameters, we obtained single walled nanotubes (SWNTs) with mean diameter 1.2 nm and carbon nanowires with mean diameter 250 nm. A discussion on the possible growth mechanism is also reported.

Recent advances in nanotechnology and nanostructured materials offer the possibility to improve the mechanical properties of composite structures in terms of toughness and stiffness. In particular, in aerospace applications research efforts are focused on the design of advanced composite materials reinforced with carbon nanotubes (CNTs) that combine weight saving with multifunctional properties, including thermal, mechanical and electromagnetic ones. It is well known that carbon nanoparticles enhance the fracture strength, the modulus, and the yield strength of a polymer matrix through different mechanisms. However, despite the large amount of investigations on CNT-based composites and their relevant properties, there is a lack of understanding of the mechanisms leading to the failure of these materials under impact or static loads, which limits their use in practical applications. In this work, we present an experimental investigation of the fracture mechanisms of aerospace grade epoxy composites reinforced with multi-walled CNTs bridging the mechanical characterization with non-destructive methods, such as optical spectroscopy and electron microscopy. Our results show that it is possible to link the failure mechanisms of the nanostructured composite at the interface between the CNT and the epoxy matrix, namely cracking, pull-out and telescopic failure, with the molecular fingerprint of the carbon structure at the fracture surface after mechanical testing. © 2014 The Authors. Published by Elsevier Ltd.

The surface enhanced Raman spectroscopy (SERS) is one of the most sensitive tools for trace analysis and the fabrication of effective and robust SERS substrates is the subject of intensive research in view of their possible applications. In this Letter, the SERS activity of an ordered structure of inverted pyramids (Klarite, Ltd) was examined by using nitro-based explosives, as Raman probe molecules. Enhancement factors up to 106 and detection limits of tens of pg were measured with an excellent run to run reproducibility. These findings provide new opportunities for the utilization of SERS for analytical detection at trace level. © 2013 Elsevier B.V. All rights reserved.

We report the results of Raman measurements on some common military explosives and explosives precursors deposited on clothing fabrics, both synthetic and natural, in concentration comparable to those obtained from a single fingerprint or mixed with similar harmless substances to detect illegal compounds for smuggling activities. Raman spectra were obtained using an integrated portable Raman system equipped with an optical microscope and a 785-nm laser in an analysis of

Light-emitting layers of silicon quantum dots embedded in a diamond matrix have been prepared by using a new hybrid chemical vapour deposition-powder flowing technique. The polycrystalline diamond matrix is grown by thermal activation of CH 4 -H 2 mixtures. The silicon nanoparticles used for the synthesis of the diamond-based composites were prepared by CO 2 laser pyrolysis of SiH 4 -He mixtures in a gas flow reactor with controlled atmosphere. During the matrix deposition, the powder-flowing apparatus drives the silicon nanoparticles across the active area of the substrate, where diamond is growing. A strong room temperature emission is observed from composite films with characteristics dependent on the size distribution of the inserted silicon particles. We report details of the synthesis procedure and emission features of composite diamond films, whose properties promise high technological impact.

Linear (visible photoluminescence) and non-linear (third-order susceptibility) optical properties have been measured for laser-synthesized crystalline Si nanoparticles. The observed luminescence is compared to similar measurements on nanocomposite aerogels prepared integrating the Si-nanoparticles into a continuous silica phase by sol–gel processing. The results show that incorporation of the Si-nanoparticles into a silica matrix by sol–gel technology is not detrimental to the PL (photoluminescence) emission intensity. The effect on the nanocomposites of annealing in air (at temperatures in the range of 300–500°C) has been investigated by means of PL and Raman spectroscopy. The obtained results indicate that the oxidation treatment induces the bleaching of the smaller luminescent particles and is not effective in reducing the average size. Micro-Raman mapping and TEM analysis of the nanocomposites have shown the presence of agglomerated nanoparticles (in the sub-micrometer range), as confirmed by dynamic light scattering (DLS) measurements on colloidal suspensions of the as-synthesized powders.

We report on the production of single-wall carbon nanotubes from nanosized graphite powders and atomic hydrogen using a novel growth technique. The individual nanotubes produced during the process form rather thick layers of bundles deposited onto the iron-coated Si substrates. Raman spectroscopy in the 150–250 cm−1 region and reflection electron diffraction in selected area configuration have been used to define the geometrical details of the nanotubes. The proposed growth methodology is found to yield prevalently nanotubes belonging to the (n, 0) zigzag achiral subclass, with a diameter distribution function centred at about 1.6 nm.

a new hybrid CVD-powder flowing technique has been adopted in order to grow diamond-based composite materials in form of thin films, coatings and free-standing layers. We report details of the synthesis procedure that allows to control incorporation of nanometer-sized powdered species (metals and semiconductors ) in form of aggregates, clusters or nanosized dispersions inside a polycrystalline diamond matrix. The focus is on microstructure and actual properties (electrical, optical) connected with the deposition procedure of some representative nanocomposite layers. The electrical behaviour of Nd-containing diamond films and the room-temperature emission in the 2.0-2.4 eV region by the Si-containing films are reported and discussed.

Silicon nanoparticles have been synthesized by heating reactant gases with a 500 W CO2 laser. A technique based on scattering of He–Ne laser light by particulates in a reaction flame has been developed for probing the particle size evolution during the process, in order to scale down the particle diameter (under 10 nm). The optical and structural properties of laser-synthesized silicon nanopowders obtained in different runs are reported. © 1998 John Wiley & Sons, Ltd.

The oxidation of nanocrystalline silicon powder (average crystallite size of 87 A), prepared by laser-driven pyrolysis of SiH4, has been studied by X-ray diffraction and transmission electron microscopy. In a previous study the Si particles were shown to form perfect isolated near-spherical ‘single crystals’ that are stable up to 1073 K under high vacuum conditions. We have measured the size reduction of the Si nanoparticles in a flow of oxygen as a function of the degree of oxidation. The results are in agreement with model calculations for a shell-wise oxidation of silicon surface layers to amorphous silicon oxide. An oxidation to 50 vol.% implies a size reduction of 20% and tenfold improved visible photoluminescence intensity. Preliminary kinetic studies at 656 Kin oxygen indicate a self-limiting type of oxidation, which is reached for an oxide layer thickness of ≈6.8 A

In the development of advanced ceramic nanocomposites, the production of titanium-based nanopowders has assumed importance, especially since recent results showed that mechanical properties of SiC matrices could be significantly improved by the incorporation of TiC second phase and vice versa. Nanosized TiC and TiC/SiC powders were synthesized by CO2 laser-induced reactions. A TiCl4 and hydrocarbons mixture was irradiated for titanium carbide production; the addition of SiH4 gave rise to the composite powders. The results of the powder characterization, obtained mainly by X-ray photoelectron spectroscopy, X-ray-induced Auger Spectroscopy and X-ray diffraction, are discussed in detail to correlate the reaction parameters to the composition and morphology of the products. Both TiC and SiC/TiC nanopowders showed a high reactivity to the air exposure, as evinced by the surface oxidation of the particles. Nevertheless, a quite good yield was obtained for nanocomposites of β-SiC matrix with the addition of up to 20% TiC phase.

In this work we report the results of RS measurements on some common military explosives and some of the most common explosives precursors deposited on clothing fabrics, both synthetic and natural, such as polyester, leather and denim cotton at concentration comparable to those obtained from a single fingerprint. RS Spectra were obtained using an integrated portable Raman system equipped with an optical microscope, focusing the light of a solid state GaAlAs laser emitting at 785 nm. A maximum exposure time of 10 s was used, focusing the beam in a 45 μm diameter spot on the sample. The substances were deposited starting from commercial solutions with a Micropipetting Nano-Plotter, ideal for generating high-quality spots by non-contact dispensing of sub-nanoliter volumes of liquids, in order to simulate a homogeneous stain on the fabric surface. Images acquired with a Confocal Laser Scanning Microscope provided further details of the deposition process showing single particles of micrometric volume trapped or deposited on the underlying tissues. The spectral features of each substance was clearly identified and discriminated from those belonging to the substrate fabric or from the surrounding fluorescence. Our results show that the application of RS using a microscope-based apparatus can provide interpretable Raman spectra in a fast, in-situ analysis, directly from explosive particles of some μm3 as the ones that it could be found in a single fingerprint, despite the contribution of the substrate, leaving the sample completely unaltered for further, more specific and propaedeutic laboratory analysis. The same approach can be envisaged for the detection of other illicit substances like drugs. © 2013 SPIE.

Nanoscale SiC powders, produced by laser synthesis from gaseous precursors, have been successfully used to prepare sintered pellets. All the sintered samples showed the low temperature β-SiC structures and presented an enhanced thermal conductivity (> 20%) with respect to materials prepared from commercial powders. Samples hardness and toughness, comparable with commercial products, confirmed the good samples quality. The thermal shock tests have been performed by irradiating the pellets with a Nd-YAG pulsed laser (pulse duration and energy: 0.25 μs and 0.18 J or 0.4 ms and 0.65 J). The laser fluence (power density) was increased by reducing the spot size, up to the appearance of a visible surface damage. The threshold values for the structural damage were quantified using a heat flux parameter φabs√tp. The measured threshold value rose from ca. 20 MW/m2 √s for the best materials prepared from commercial SiC powders to ca. 24 MW/m2√s for the newly developed β-SiC.

Microstructural properties of nanosized particles produced by CO 2 laser synthesis from gaseous precursors, are studied by different techniques. Results on the characterization of binary (SiC and Si 3 N 4 ) and ternary (Si/C/N) ultrafine powders are presented. The evolution of the chemical composition and microstructure, after heat treatments in different atmospheres, is investigated in order to study and to improve the stability of these materials.

Second- and third-harmonic generation in single-walled carbon nanotube films is experimentally investigated with the fundamental 1064nm radiation from a Q-switched Nd:YAG laser. Measurements were performed both on commercially available carbon nanotubes and on samples of carbon nanotubes grown with a catalyst-free method. Third-harmonic generation was observed in both samples while only the sample grown with a catalyst-free method generated a second-harmonic signal. The quantum yield of second- and third-harmonic signal was proven to scale, respectively, with the second and third power of the pump pulse energy up to intensities of 109W∕cm2.