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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.

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 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.

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.

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.

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.

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.

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.

Carbon nanoparticles produced by CO 2 laser pyrolysis have been investigated using morphological and structural probes such as high-resolution scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and electron diffraction, as well as chemical probes, such as gas chromatography–mass spectrometry and fast atom bombardment–mass spectrometry. The produced particles resulted to have a spherical shape and a diameter of about 50 nm with graphitic domains of the order of 80 A. They contain appreciable fractions of polycyclic aromatic hydrocarbons, which can be extracted with toluene, as well as fullerene units. The implications of these results for the use of carbon nanopowders in the carbon nanotube synthesis are also discussed.

Carbon nanotubes films have been prepared by low-velocity spraying of carbon nanosized particles on heated Si substrate. Studies reveal that by properly choosing the deposition temperature, well-aligned carbon nanotubes are self-assembled from the particles without a catalyst. Raman scattering and reflection high-energy electron diffraction show that the tubes are bundles of single-wall nanotubes.

In this work the preparation of ceramic matrix composites with improved mechanical properties and reduced process time and cost has been investigated. A combination of liquid and vapour infiltration processes has been developed for producing SiC(fibers)/C/SiC composites. 2D-woven Nicalon fibers were coated with pyrolitic carbon and stacked to form flat panel preforms. Chemical vapour infiltration was achieved using methyltrichlorosilane (MTS) as SiC precursor in a hot wall reactor under isothermal (1050°C) and isobaric (20torr) conditions. The solution infiltration was achieved using polycarbosilane (PCS) as SiC precursor along with laser formed SiC nanopowders. Pyrolysis was performed in inert atmosphere up to 1100°C. Various combinations of the two routes were tested in order to optimise the composite properties. A short vapour infiltration run was used to form a uniform SiC deposit on the fibers that were subsequently filled by several cycles of liquid infiltration/pyrolysis. CVI was also effective to fill the submicron porosity resulting from PCS to SiC transformation. Scanning Electron Microscopy (SEM) is presented for the description of the morphology of the composites. Mercury porosimetry along with SEM, was used to evaluate the infiltration yield and the quality of the deposit in the various steps of the process. The mechanical behavior of the composites was investigated by flexural tests. Fibers push-in by microindentation measurements were performed to characterize the fiber/matrix interface and to investigate how it is affected by the pyrocarbon coating on the fibers. On the basis of the obtained results, a preparative process for SiC/SiC composites can be optimized by the proper use of both liquid and vapour infiltration. Reaxys Database Information

Visible-light emitting nanocomposite Si/diamond polycrystalline layers, produced by means of a hybrid CVD/powder-flowing technique, have been investigated by atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED), Raman spectroscopy, photoluminescence (PL), and electron spin resonance (ESR). The room temperature emission of the layers at 1.7 eV and 2.0-2.4 eV is dominated by the optical properties of the inserted Si nanoparticles (mean diameter 3.3 ± 0.5 nm). The density of the ESR active centers is N = (4 ± 2) x 10 19 cm -3 with g = 2.0025 (T= 300 K). A study of the temperature-dependent changes in the nature and localization of paramagnetic centers has been carried out by comparing the ESR signals taken at 300 K, 30 K, and 4.2 K. The ESR results suggest that the active centers originate from the dangling bonds induced in sp 3 -coordinated C atoms by insertion of the Si nanoparticles. The g-factor anisotropy, detected at 4.2 K, is consistent with the peculiarities of dipole-dipole interactions in structures with low dimensionality.

Single-walled carbon nanotubes (SWCN) have been produced treating nanosized graphitic powders with atomic hydrogen fluxes in a purpose-designed reactor. The Fe-catalyzed synthesis process yielded rather dense networks of nanotubes forming continuous layers adherent to the substrates. Raman spectroscopy in the 140–250 cm −1 region, high-resolution transmission electron microscopy and reflection electron diffraction in selected area configuration have been used to define the structural details of the nanotubes. The analysis evidenced a nanotubes population belonging prevalently to the ( n ,0) achiral symmetry subclass. This new experimental approach for SWCNs growth provides promising conditions for maximizing yields and generating selected tubular configurations.