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Multiwalled carbon nanotube (MWCNT)-based chemiresistors were electrochemically decorated with Au and Pd nanoparticles (NPs), resulting in an improvement in the detection of gaseous pollutants as compared to sensors based on pristine MWCNTs. Electrophoresis was used to decorate MWCNTs with preformed Au or Pd NPs, thus preserving their nanometer-sized dimensions and allowing the metal content to be tuned by simply varying the deposition time. The sensing response of unmodified and metal-decorated MWCNTs was evaluated towards different gaseous pollutants (e.g., NO2, H2S, NH3 and C4H10) at a wide range of concentrations in the operating temperature range of 45–200 °C. The gas sensing results were related to the presence, type and loading of metal NPs used in the MWCNT functionalization. Compared to pristine MWCNTs, metal-decorated MWCNTs revealed a higher gas sensitivity, a faster response, a better stability, reversibility and repeatability, and a low detection limit, where all of these sensing properties were controlled by the type and loading of the deposited metal catalytic NPs. Specifically, in the NO2 gas sensing experiments, MWCNTs decorated with the lowest Au content revealed the highest sensitivity at 150 °C, while MWCNTs with the highest Pd loading showed the highest sensitivity when operated at 100 °C. Finally, considering the reported gas sensing results, sensing mechanisms have been proposed, correlating the chemical composition and gas sensing responses.

An electrophoretic process is proposed to deposit electrochemically-preformed Au or Pd NPs, with controlled size, directly on MWCNTs-based chemiresistors to improve the detection of aromatic pollutants, compared to pristine ones. The sensing properties of pristine and functionalized MWCNTs were evaluated at an operating temperature of 40°C towards various concentrations of one aromatic pollutant, belonging to the dangerous BTEX class of compounds, m-Xylene. The sensing performance was related to the metal used in the functionalization process. Metal-doped MWCNTs sensors exhibited a very high gas sensitivity to m-Xylene even at low (80 ppb) concentration at low operating temperature (40°C), good reversibility and repeatability, with the sensing properties controlled by the type of deposited metal catalyst. The results indicate that Metal-modified MWCNT-based chemiresistive gas sensors has good potential in practical applications, due to its remarkable performance, low power consumption, and facile synthesized methods. © 2017 Materials Research Society.

Pristine and electrochemically Pd-modified ZnO nanorods (ZnO NRs) were proposed as active sensing layers in chemiresistive gas sensors for hydrocarbon (HC) gas detection (e.g., CH4, C3H8, C4H10). The presence of Pd nanoparticles (NPs) on the surface of ZnO NRs, obtained after the thermal treatment at 550 °C, was revealed by morphological and surface chemical analyses, using scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The effect of the Pd catalyst on the performance of the ZnO-based gas sensor was evaluated by comparing the sensing results with those of pristine ZnO NRs, at an operating temperature of 300 °C and for various HC gas concentrations in the range of 30–1000 ppm. The Pd-modified ZnO NRs showed a higher selectivity and sensitivity compared to pristine ZnO NRs. The mean sensitivity of Pd-modified ZnO NRs towards the analyzed HCs gases increased with the length of the hydrocarbon chain of the target gas molecule. Finally, the evaluation of the selectivity revealed that the presence or the absence of metal nanoparticles on ZnO NRs improves the selectivity in the detection of specific HCs gaseous molecules.

A one-step electrochemical method based on sacrificial anode electrolysis (SAE) was used to deposit stabilized gold nanoparticles (Au NPs) directly on the surface of nanostructured ZnO powders, previously synthesized through a sol–gel process. The effect of thermal annealing temperatures (300 and 550 °C) on chemical, morphological, and structural properties of pristine and Au-doped ZnO nancomposites (Au@ZnO) was investigated. Transmission and scanning electron microscopy (TEM and SEM), as well as X-ray photoelectron spectroscopy (XPS), revealed the successful deposition of nanoscale gold on the surface of spherical and rod-like ZnO nanostructures, obtained after annealing at 300 and 550 °C, respectively. The pristine ZnO and Au@ZnO nanocomposites are proposed as active layer in chemiresistive gas sensors for low-cost processing. Gas-sensing measurements towards NO2 were collected at 300 °C, evaluating not only the Au-doping effect, but also the influence of the different ZnO nanostructures on the gas-sensing properties.

The applications and innovations related to the ultraviolet field are today in strong growth. To satisfy these developments which go from biomedical to the large equipment like the Storage Ring Free Electron Laser, it is crucial to control with an extreme precision the optical performances, in using the substrates and the thin film materials impossible to circumvent in this spectral range. In particular, the reduction of the losses by electromagnetic diffusion, Joule effect absorption, or the behavior under UV luminous flows of power, resistance to surrounding particulate flows... become top priority which concerns a broad European and international community. Our laboratory has the theoretical, experimental and technological tools to design and fabricate numerous multilayer coatings with desirable optical properties in the visible and infrared spectral ranges. We have extended our expertise to the ultraviolet. We present here some results on high reflectivity multidielectric mirrors towards 250 nm in wavelength, produced by Ion Plating Deposition. The latter technique allows us to obtain surface treatments with low absorption and high resistance. We give in this study the UV transparent materials and the manufacturing technology which have been the best suited to meet requirements. Single UV layers were deposited and characterized. HfO2/SiO2 mirrors with a reflectance higher than 99% at 300 nm were obtained. Optical and non-optical characterizations such as UV spectrophotometric measurements, X-Ray Diffraction spectra, Scanning Electron Microscope and Atomic Force Microscope images were performed

In the present study, Au-surfactant core-shell colloidal nanoparticles (NPs) with controlled dimension and composition were synthesized by sacrificial anode electrolysis. Transmission electron microscopy (TEM) revealed that Au NPs core diameter is between 8 and 12 nm, as a function of the electrosynthesis conditions. Moreover, surface spectroscopic characterization by X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nanosized gold phase. Controlled amounts of Au NPs were then deposited electrophoretically on carbon nanotube (CNT) networked films. The resulting hybrid materials were morphologically and chemically characterized using TEM, SEM (scanning electron microscopy) and XPS analyses, which revealed the presence of nanoscale gold, and its successful deposition on CNTs. Au NP/CNT networked films were tested as active layers in a two-pole resistive NO2 sensor for sub-ppm detection in the temperature range of 100–200 °C. Au NP/CNT exhibited a p-type response with a decrease in the electrical resistance upon exposure to oxidizing NO2 gas and an increase in resistance upon exposure to reducing gases (e.g. NH3). It was also demonstrated that the sensitivity of the Au NP/CNT-based sensors depends on Au loading; therefore, the impact of the Au loading on gas sensing performance was investigated as a function of the working temperature, gas concentration and interfering gases.

Colloidal Au and Pd nanoparticles (NPs) were directly electrochemically synthesized, by sacrificial anode electrolysis (SAE), on hydrothermal ZnO nanostructures, previously desiccated; further, the functionalized ZnO nanostructures were subjected to thermal annealing at 550°C to obtain stable ZnO nanorods (NRs), superficially decorated by naked metal NPs. The both pristine and metal functionalized ZnO NRs were proposed as active layer in chemiresistive sensors for environmental monitoring to detect pollutant gases (e.g. NO2, C4H10). The effect of the presence and of the chemical nature of the deposited metal NPs on the performance of ZnO NRs-based gas sensor (e.g. sensitivity, selectivity and recovery) was evaluated, comparing the sensing results with those of pristine ZnO NRs. In particular, the gas sensing properties of pristine and metal-functionalized ZnO NRs were studied at an operating temperature of 300°C towards a various range of concentration of different gaseous pollutants. © 2017 Materials Research Society.

Nanosized platinum-gold alloys clusters have been deposited on gas diffusion electrode by sputter deposition. The deposits were characterized by FE-SEM, TEM and XPS in order to verify the formation of alloy nanoparticles and to study the influence of deposition technique on the nanomorphology. The deposition by sputtering process allowed a uniform distribution of metal particles on porous surface of carbon supports. Typical island growth mode was observed with the formation of a dispersed metal nanoclusters (mean size about 5 nm). Cyclic voltammetry was used to determine the electrochemical active surface and the electrocatalytic performance of the PtAu electrocatalysts for methanol oxidation reaction. The data were re-calculated in the form of mass specific activity (MSA). The sputter-catalyzed electrodes showed higher performance and stability compared to commercial catalysts.

Networked films of carbon nanotubes (CNTs) have been grown by CVD technology onto low-cost miniaturized alumina substrates. The sidewalls of the CNTs films have been modified by spray-coating with two different metalloporphyrins (MPPs) consisting of a TetraPhenylPorphyrin coordi-nated by a central metal of zinc (Zn-TPP) and manganese (Mn-TPP) for enhanced sensitivity and tailored specificity. Hazardous gases such as NO2, NH 3, H2S, SO2, and CO have been detected with various responsiveness in the range of concentration from 0.1 to 1000 ppm. The response of the chemiresistors in terms of p-type electrical conductance has been investigated as a function of the thickness of the functionalizing MPPs; and the effect of the temperature ranging from 20 to 150 °C on the sensor response has been addressed as well. A response of the CNT-sensor functionalized by 2 layers of Mn-TPP has been measured as 0.025% towards 0.5 ppm NO 2, at 150 °C.

Networked films of carbon nanotubes (CNTs) have been grown by Chemical Vapor Deposition (CVD) technology onto cost-effective alumina substrate, coated by Cobalt nanocatalyst for growing the CNTs. The sidewalls of the CNTs films have been functionalized by spray-coating with two different metalloporphyrins (MPP), consisting of a Tetraphenylporphyrin coordinated by a central metal of zinc (Zn-TPP) and manganese (Mn-TPP). The surface-modification of the CNTs with layers of Zn-TPP and Mn-TPP provides enhanced sensitivity and broad selectivity to volatile organic compounds (VOCs). The chemical interactions of these MPP-modified CNTs films with different tested VOCs (alcohols, esters, aromatics, ketones) have been investigated using the miniaturized two-pole chemiresistors technique. The sensor response in terms of p-type electrical conductance in the MPP-modified CNTs-chemiresistors exhibits a good sensing performance, at room temperature. The findings show a VOC adsorption occuring by sensing characteristics of response-concentration relationships as a combined Langmuir-Henry behaviour

Carbon nanotube (CNT) networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF–PECVD) technology onto low-cost alumina substrates, coated by nanosized Fe-catalyst for growing CNTs, to perform chemical detection of hazardous gases, at an operating sensor temperature in the range 25–150 °C. The morphology and structure of the CNT networks have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The carbon nanotubes were “forest-like” with ropes vertically-aligned to the substrate surface. A dense network of bundles of multiple tubes consisting of multi-walled carbon nanostructures appears with a maximum length of 7–10 μm and single-tube diameter varying in the range of 5–35 nm. Surface functionalizations of the vertically-aligned CNT networks with nominally 5 nm thick Pt-, Ru- and Ag-nanoclusters, prepared by magnetron sputtering, provide higher sensitivity for significantly enhanced gas detection of NO 2 , H 2 , ethanol and toluene up to a low limit of sub-ppm level. The measured electrical conductance of the functionalized CNTs upon exposures of a given oxidizing and reducing gas is modulated by a charge transfer model with p-type semiconducting characteristics. Functionalized CNT gas sensors exhibited better performances compared to unmodified CNTs, making them highly promising candidates for environmental air monitoring applications, at ppb-level of toxic gas detection.

We investigate the impact of the tailored load of gold (Au) nanoclusters functionalizing the sidewalls of the carbon nanotubes (CNTs) networks on gas sensing performance of a chemiresistor, operating at a working temperature in the range of 20–250 °C. CNTs networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) technology onto low-cost alumina substrate, provided with 6 nm nominally thick cobalt (Co) growth-catalyst. Nanoclusters of Au have been deposited by sputtering onto CNTs networks with a controlled loading of equivalent thickness of 2.5, 5 and 10 nm. Microstructure and morphology of the CNTs have been characterized by FE-SEM and TEM with diameter of the bundles of nanotubules of 10–40 nm. CNTs and Au-modified CNTs exhibit a p-type response with a decrease in electrical resistance upon exposure to oxidizing NO 2 gas and an increase in resistance upon exposure to reducing gases (NH 3 , CO, N 2 O, H 2 S, SO 2 ). Negligible response has been found for CNTs and Au-modified CNTs sensors exposed to CO, N 2 O, SO 2 . In the contrast, significantly enhanced gas response of NO 2 , H 2 S and NH 3 , up to a low limit of sub-ppm level, has been measured for Au-functionalized CNTs-chemiresistors. Highest gas sensitivity to NO 2 , H 2 S and NH 3 has been found by CNTs functionalized with Au loading of 5 nm, at 200 °C. An optimal operating temperature for each Au-modified CNTs-sensor exposed to NO 2 gas has been recorded. Good repeatability of the electrical response to 200 ppb NO 2 is also reported, at 200 °C. These results demonstrate the efficiency of the CNTs-chemiresistors functionalized with Au nanoclusters for selective air-pollutants environmental monitoring applications.

A gas chemiresistor, fabricated onto alumina using multi-walled carbon nanotubes (MWCNTs) networked films grown by radiofrequency plasma enhanced chemical vapor deposition (RF-PECVD) technology, is described for high-performance gas detection, at an operating temperature of 200 °C. Functionalizations of MWCNTs tangled bundle-films with nominally 5-nm thick Pt- and Pd-nanoclusters, prepared by magnetron sputtering, provide higher sensitivity for significantly enhanced gas detection of NO2, H2S, NH3, CO, up to a low limit of sub-ppm level. The measured electrical conductance of the functionalized MWCNTs upon gas exposures is modulated by charge transfer with p-type semiconducting characteristics. Pt- and Pd-nanoclusters functionalized MWCNTs gas sensors exhibited better performances compared to unfunctionalized MWCNTs, making them promising candidates for air-pollutants environmental monitoring. Simple electronic interface for the chemiresistor has been developed with a voltage output of the sensor signal.

The SrFeCo0.5Oy system combines high electronic/ionic conductivity with appreciable oxygen permeability at elevated temperatures. This system has potential use in high-temperature electrochemical applications such as solid oxide fuel cells, batteries, sensors, and oxygen separation membranes. Dense ceramic membranes of SrFeCo0.5Oy are prepared by pressing a ceramic powder prepared by using a sol–gel combustion technique. Oxygen and hydrogen permeation at high temperature on this material are studied. Measurements are conducted using a time-dependent permeation method at the temperature in the range of 1073–1273 K with oxygen- and hydrogen-driving pressures in the range (3×102)–(1×105) Pa (300–1000 mbar). The maximum oxygen-permeated flux at 1273 K is 6.5×10−3 mol m−2 s−1. The activation energies for the O2-permeation fluxes and diffusivities are 240 and 194 kJ/mol, respectively. Due to the high fragility, the high temperature for the measurements and the high oxygen permeation through such material, a special membrane holder, and compression sealing system have been designed and realized for the permeation apparatus.

Multiwalled carbon nanotube (MWCNT) films have been deposited by using plasma-enhanced chemical vapor deposition (PECVD) system onto alumina substrates, provided with 6 nm thick cobalt (Co) growth catalyst for remarkably improved gas sensing, at working temperature in the range of 100–. Functionalization of the MWCNTs with nanoclusters of gold (Au) sputtering has been performed to modify the surface of carbon nanotube networked films for enhanced and specific gas detection up to sub-ppm level. It is demonstrated that the gas sensitivity of the MWCNT-based sensors depends on Au-loading used as surface-catalyst. The gas response of MWCNT-based chemiresistor is attributed top-typeconductivity in the Au-modified semiconducting MWCNTs with a very good short-term repeatability and faster recovery. The sensor temperature of maximum sensitivity of the Au-functionalized MWCNTs is found to decrease with increasing Au-loading on their surface, and continuous gas monitoring at ppb level of is effectively performed with Au-modified MWCNT chemiresistors.

Multiwalled carbon nanotube (MWCNT)-based gas sensors were decorated by an electrophoretic deposition of electrochemically preformed gold nanoparticles (Au NPs) with controlled size and loading, for the detection of gaseous pollutants at sub-ppm concentrations and operating temperature in the range of 100-200 °C. The effects of the tailored Au content on the sensitivity and selectivity of MWCNT-based gas sensors were evaluated towards the NO2 monitoring, and also towards some interfering reducing gases, such as NH3 and H2S. Gas sensing measurement revealed the highest NO2 response up to sub-ppm level by using MWCNTs functionalized by the lowest Au content; instead, the worse NO2 response was obtained by modified MWNTs containing the highest Au loading. Moreover, the control of the deposited gold loading has allowed to control the MWCNT sensing response; specifically the increase of gold content on MWCNT has reduced the selectivity and sensitivity towards NO2 gas, and, on the contrary, at the same time it has improved those towards H2S and NH3 interfering gases. Finally, binary gas mixtures (NO2/H2S and NO2/NH3) were performed to evaluate the detection of the targeted NO2 gas, simulating possible real-world conditions. © 2015 Elsevier B.V. All rights reserved.

A calibration procedure for the detection efficiency of energy dispersive X-ray spectrometers (EDS) used in combination with scanning electron microscopy (SEM) for standardless electron probe microanalysis (EPMA) is presented. The procedure is based on the comparison of X-ray spectra from a reference material (RM) measured with the EDS to be calibrated and a reference EDS. The RM is certified by the line intensities in the X-ray spectrum recorded with a reference EDS and by its composition. The calibration of the reference EDS is performed using synchrotron radiation at the radiometry laboratory of the Physikalisch-Technische Bundesanstalt. Measurement of RM spectra and comparison of the specified line intensities enables a rapid efficiency calibration on most SEMs. The article reports on studies to prepare such a RM and on EDS calibration and proposes a methodology that could be implemented in current spectrometer software to enable the calibration with a minimum of operator assistance.

Sputter deposition was investigated as a tool for manufacturing proton-exchange membrane fuel cell (PEMFC) electrodes with improved performance and better catalyst utilization vs. commercial electrode. Nanosized (diameter 2–5 nm) platinum clusters were deposited on gas diffusion electrodes (carbon paper + PTFE/C diffusive layer). The activity for methanol oxidation was increased about 14 times compared to commercial catalyst, with loading − 2 . SEM–FEG characterization and cyclic voltammetry were carried out to study the morphology, and the behavior of the Pt clusters as cathodic electrocatalyst of a polymer electrolyte fuel cell.

Carbon nanotubes (CNTs) were grown on nickel catalysts by hot filament chemical vapour deposition (HFCVD) using H 2 and CH 4 as gas precursors. CNTs with different characteristics were observed varying some growth parameters, such as the substrate temperature, the total pressure and the methane concentration. These parameters were optimised in order to obtain untangled CNTs with high density and smooth walls. Catalyst nanoparticles were obtained through the clustering of Ni thin films deposited by sputtering techniques. CNTs grown on samples with the silicon native oxide or with a SiO 2 coating between Si substrate and Ni film were compared. Catalytic layers and CNTs were characterised by SEM and XPS.

Controlled amounts of colloidal Au nanoparticles (NPs), electrochemically pre-synthesized, were directly deposited on MWCNTs sensor devices by electrophoresis. Pristine and Au-functionalized MWCNT networked films were tested as active layers in resistive gas sensors for detection of pollutant gases. Au-modified CNT-chemiresistor demonstrated higher sensitivity to NO2 detecting up to sub-ppm level compared to pristine one. The investigation of the cross-sensitivity towards other pollutant gases revealed the decrease of the sensitivity to NO2 with the increase of Au content, and, on the other side, the increase of that to H2S; therefore the fine tune of the metal loading on CNTs has allowed to control not only the gas sensitivity but also the selectivity towards a specific gaseous analyte. Finally, the sensing properties of Au-decorated CNT sensor seem to be promising in environmental and automotive gas sensing applications, based on low power consumption and moderate operating temperature.

Stabilized Au NPs were directly deposited on nanostructured ZnO and ZrO2 by a simple one-step strategy based on sacrificial anode electrolysis. The annealed nanocomposites are proposed as active layers in resistive gas sensors for low-cost processes. Results on the performance of gas sensors based on pristine and Au-doped MOx nanostructured thin films, used for the detection of NO2 gas, were reported at an operating temperature of 300°C, evaluating the effects of the MOx chemical composition and morphology, and the Au-doping.

The sensing properties of tetra-tert-butyl copper phthalocyanine (ttb-CuPc) toward toluene at room temperature are reported in this manuscript. Thin films of ttb-CuPc were obtained by thermal evaporation. The similarities between powdered and layered material have been con.rmed by FTIR analysis. Taking into consideration the interactions involved between material and the target gas, Quartz Crystal Microbalance (QCM) was chosen as transducer. The key role of tertiary butyl groups grafted at the periphery of the phthalocyanine ring on toluene sensitivity has been firstly established. Despite reproducible frequency shifts for toluene exposures at the same concentration, sensor drifts were observed and attributed to temperature effects on quartz crystal. Such thermal in.uence on sensor responses has been minimized by short exposure times and temperature compensation on sensor signal. The strong affinity of ttb-CuPc to toluene as compared to other phthalocyanines, the repeatability of sensor responses, the reversibility of involved gas/material interactions, a resolution higher than 10 ppm and a threshold of detection lower than 35 ppm have been established from experiments. The partial selectivity has been also highlighted toward others gases like CO, NO2, H2S and xylene. At last, the relevance of metallo-phthalocyanine thin films as sensitive coatings on QCM devices to detect volatile organic compounds in real-time situation will be discussed. © 2015 Elsevier B.V. All rights reserved.

The standing-wave electric field pattern that forms inside an optical coating as a consequence of laser irradiation is one of the factors influencing the coating laser-induced damage threshold. The influence of the standing-wave electric field profile on the damage resistance to ultraviolet radiation of hafnium dioxide (HfO2) thin films was investigated in this work. To this end, HfO2 thin films of different thicknesses deposited by the electron beam evaporation technique at the same deposition conditions were analyzed. Laser damage thresholds of the samples were measured at 308 nm (XeCl laser) by the photoacoustic beam deflection technique and microscopic inspections. The dependence of the laser damage threshold on the standing-wave electric field pattern was analyzed.

Laser damage studies at 248 nm (KrF excimer laser) have been performed on HfO 2 films of 300 nm thickness deposited on silica substrates by the Xe ion-assisted electron beam evaporation technique. The assistance parameters (ion mass, energy and current density) have been adjusted to investigate the effect of the Xe-ion momentum transfer parameter P on the film optical and structural properties. Then, the dependence of laser damage fluence on film properties has been studied. Higher laser damage fluences have been found for the HfO 2 films deposited at lower P values and characterized by a fully crystalline structure with the grain of smaller size and randomly oriented.

In this work, we investigate the optical and the structural properties of Ag films by means of spectrophotometric techniques and X-ray diffraction methods in the low- and high-angle regimes. The coatings were grown by radio frequency magnetron sputtering on (100)-oriented silicon substrates. Several sets of samples were produced by varying the sputtering pressure (0.15–0.9 Pa) and changing the sputtering power supply in the range of 25–100 W. In particular, the dependence of the coating optical features, surface roughness, texture and residual stress on the parameter β, proportional to the momentum transferred to the growing film from the energetic particles bombarding it, was pointed out. The results indicate that the Ag films are polycrystalline with a moderate [111] texture and compressive in-plane stress was measured for all the investigated samples. The behavior of the stress with the momentum parameter can be summarized as follows: (i) the compressive stress increases in the range 0 1000 V2s/A.

It is well known that energetic particle bombardment during diamond-like carbon film growth has a significant influence on the resulting film stress, optical transparency, hardness and chemical inertness. It has been commonly recognised that many of the desirable properties of carbon films arise from the sp 3 tetragonal bonding component. Therefore, it is essential to have a deeper knowledge of the role of ion energy on the evolution of the diamond-like phase. In this work, we propose a parameter ( P ) as a key for the understanding of the nucleation and growth mechanism, which takes into account the number of recoiled atoms and their transfer momentum by argon ion assistance, compared to all atoms present in the volume, described by ion range, plus the atoms coming from the graphite-sputtered target. Thin films of a-carbon were deposited by the dual ion beam sputtering technique. An argon ion beam sputters a graphite target and a second one assists the film during the growth. Sets of samples were produced with different momentum transferred by the assistance beam ( P ). A spectrophotometric analysis in the visible range is performed to determine the Tauc optical gap E g , the refractive index and the extinction coefficient. The results show that the films not assisted exhibit a lower density and consequently a low refractive index ( n =1.8 in the visible range), while increasing the momentum transfer parameter ( P ) the refractive index increases suggesting a densification of the material. The same trend is observed for the Tauc optical gap. In order to get further information on the evaluation of density due to the assistance, X-ray reflectivity measurements have been performed and correlated to the optical results.

A chloride-based inorganic sol-gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO 2 sol. SnCl 4 was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO 2 lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO 2 grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO 2 grain size very close to that of pure SnO 2 .

The investigation of the surface and interface of a multilayer coating is a key factor for producing high quality optical device. In this work, we present a non-destructive technique as X-ray reflectivity to study deeply the chemical and structural quality of the multilayer. XPS depth profile analysis and AFM images have been used to evaluate the chemical intermixing and the surface roughness in order to verify the X-ray results.

Hafnium oxide (HfO2) films were deposited on silica and glass substrates by ion (Xe+) assisted deposition with increasing ion momentum transfer to the growing film. The relationship among the ion momentum values, the crystalline phase and the refractive index (packing density) has been worked out by means of X-ray diffraction and spectrophotometric analysis. Compaction of the films by ion beam assistance is clearly evidenced by the changes in their microstructure. A three steps transition from a random monoclinic phase, via amorphous phase, up to an highly phase oriented (fiber texture), as a function of ion momentum, has been found.

The main limitation in using plastics for optical components is the softness of their surface, which is responsible for low impact and abrasion resistance and for weak adhesion between the film and the substrate. Protecting the substrate with a hard film can increase the impact resistance of polymeric lenses. However, deposition of thin films on chemically cleaned plastic substrates has resulted in fast delamination of the coating. This paper discusses the problems associated with coated plastics, it presents the ion assistance as one of the solutions and it finally identifies the relevant parameters. A hard oxide layer with additional ion pre-treatment is proposed as protection for plastic optics. The adhesion between the film and the substrate has been evaluated by a scratch-test and the hardness has been calculated by measuring the radius of the stylus track.

Silica thin films have been deposited by a dual-ion-beam sputtering technique using argon or xenon ions mixed with oxygen ions in the assisting beam and the role of the assisting-ion-beam parameters on the laser-damage-threshold at 308 nm (XeCl laser) has been investigated. It is shown that a proper choice of these parameters allows a considerable increase of the laser-induced damage threshold. Lower damage thresholds (1 J/cm 2 ) were found for the xenon/oxygen assisted samples. Whereas, the highest damage threshold (8 J/cm 2 ) was found for the argon-ion assisted sample and its value was also much higher than that (2.9 J/cm 2 ) of the non-assisted films. Damage thresholds have been determined by the photoacoustic mirage technique and it is demonstrated that this technique can provide useful information on the mechanisms responsible for laser damage.

SiO2 films have been deposited by ion-beam sputtering techniques either without assistance or with Ar-ion assistance and the role of the substrate temperature during the deposition process on the film damage threshold by laser light at the wavelength of 308 nm (XeCl) has been investigated. The photoacoustic probe beam deflection technique has been used to determine damage thresholds and it is shown that this technique provides valuable information on the mechanisms leading to laser damage. It has been found that the samples deposited by the Ar-ion beam sputtering technique are characterized by higher damage thresholds at lower temperatures of the substrate than the SiO2 films deposited without ion assistance.

Dual ion-beam sputtering deposition is a very promising technique for fabricating optical coatings thanks to its very good control of the deposition parameters. Unfortunately, the different sputtering yields of the elements composing the films modify the stoichiometry and, consequently, may cause an increase of the absorption in the UV range and an undesirable variation of the refractive index. In this work we investigate the influence of ion-beam assistance on some oxide materials: SiO 2 , ZrO 2 , and HfO 2 . The sputtering yield has been measured by varying the mass (Ar, Xe) and energy (100–1000 eV) of the bombarding ions. The yield measurements were compared with the calculated yields using Sigmund's model. Different screening functions for different characteristic energy ranges were necessary to fit the experimental results.

We present an X-ray reflectivity study of thin TiN and TiOxNy films grown on Si(100) substrate by the dual-ion-beam-sputtering technique. The thickness range of the deposited films varies between 25 and 35 nm. We demonstrate that low-angle X-ray reflectivity is a powerful tool for studying the early stages of growth and the surface and interface properties of these films. We found that an oxidation of the TiN film surface occurs, yielding a 2 nm thick TiO2 film, if the films are exposed to air after the growth. Furthermore, an interface layer 1.5 nm thick with electron density near that of SiO2 is present at the substrate–film interface. The thickness of the interface layer increases by more than three times after 7–8 months (aging). The formation of the oxide layers is independent of the growth mode, i.e. growth with and without ion assistance. In addition, the formation of a TiO2 surface layer is also observed for TiOxNy films. The samples synthesized by employing ion-beam assistance show a much lower surface roughness (∼0.8 nm) compared to the samples deposited without ion-beam assistance (∼1.5 nm). This finding demonstrates that films with improved structural and surface properties can be obtained by using dual-ion-beam-sputtering. © 1997 Elsevier Science S.A. All rights reserved.

Nanocrystalline aluminium (n-Al), prepared by mechanical attrition in an inert atmosphere and in form of cold consolidated bars, has been investigated by transmission electron microscopy. The effects of three final thinning techniques of preparation for TEM, ion-milling, electrochemical jet-polishing and "powders", have been compared. The most representative samples prove to be those prepared by putting some powder on a carbon film coated grid. Information about the grain sizes for samples prepared by the different techniques and samples before and after a thermal treatment (500 K) has been obtained. We have also reported our high-resolution images of interfaces.

A sensors array based on two different types of chemical sensors such as tin dioxide commercial sensors and carbon nanotubes innovative sensors developed in the ENEA laboratories to monitor gases (e.g., CO, NO 2, SO 2, H 2S and CO 2) of relevance in polluted air has been analyzed. Measurements of chemical sensing of the sensors array have been performed in laboratory to create a database for applying artificial neural networks (ANNs) algorithms to quantify gas concentration of individual air pollutants and binary gas-mixture. A total number of 3,875 data-samples based on 413 distinct gas concentrations measured by 14 gas sensors has been used in the database. The ANN performance has been assessed for each targeted air-pollutant. The lowest normalized mean square error (NMSE) of 6%, 9% and 11% has been achieved for NO 2, SO 2 and CO 2, respectively. In the contrast, NMSE as high as 28% and 39% has been measured for CO and H 2S, respectively. The aim of this study is the selection of an optimal set of gas sensors in the array for enhanced environmental measurements of gas concentration in real-scenario. © 2012 Springer Science+Business Media, LLC.

In this work, the use of unconventional reference materials to determine experimentally the Cliff-Lorimer factor for EDS quantitative analysis with a TEM is checked by means of an alternative experimental procedure. The k-factor is determined by the extrapolation method based on pure elements, by measuring the normalized X-ray intensities emitted by thin films of pure gold and pure silver of different thickness, accurately measured by X-ray reflectivity. The goal of this work is to confirm the value of the k-factor previously obtained by the use of unconventional reference materials consisting of a bi-layer of pure gold on pure silver. The current result is in accordance with the previous one when considering their error bars, however, their relative difference is about 13 %, probably due to some uncertainties in mass thickness measurements. The mass thickness measurement of the layers of pure elements needs to be performed by different methods in order to reduce its uncertainty.

A portable sensor-system based on solid-state gas sensors has been designed and implemented as proof-of-concept for environmental air-monitoring applications and malodours olfactometric control. Commercial gas sensors (metal-oxides, n-type) and nanotechnology sensors (carbon nanotubes, p-type) are arranged in a configuration of array for multisensing and multiparameter devices. Wireless sensors at low-cost are integrated to implement a portable and mobile node, that can be used as early-detection system in a distributed sensor network. Real-time and continuous monitoring of hazardous air-contaminants (e.g., NO 2, CO, SO 2, BTEX, etc.) has been performed by in-field measurements. Moreover, monitoring of landfill gas generated by fermentation of wastes in a municipal site has been carried out by the portable sensor-system. Also, it was demonstrated that the sensor-system is able to assess the malodours emitted from a municipal waste site and remarkably compared to the olfactometry method based on a trained test panel. © 2012 Springer Science+Business Media, LLC.

In this work, carbon nanomaterials have been prepared by CVD technology onto alumina substrates, coated by nanosized Co-catalyst at different thickness (2.5 nm and 7.5 nm) and used for a simple gas sensor device. The surface has been functionalized with sputtered Pt-nanocluster at a tuned loading of 8, 15 and 30 nm. The response of the chemiresistors in terms of p-type electrical conductance has been investigated as a function of the thickness of the Pt-nanoclusters towards different gases (NO 2, NH 3, CO, CH 4, CO 2). Furthermore, the effect of the temperature ranging from 20°C to 250°C on the sensor response has been addressed as well. Additionally, a short-term stability of the carbon nanomaterials based sensor towards NO 2 gas detection has been investigated for a 2-month period. The gas sensors based on Pt-modified carbon nanomaterials exhibit higher sensitivity compared to unmodified material, fast response, reversibility, repeatability, moderate drift of the baseline signal, sub-ppm range detection limit. © 2012 Springer Science+Business Media, LLC.

A Quartz Crystal Microbalance (QCM) gas sensor coated with carbon nanotubes (CNTs) layered films as chemically interactive nanomaterial is described. A QCM resonator integrated on AT-cut quartz substrate has been functionally characterized as oscillator at the resonant frequency of 10 MHz. The CNTs have been grown by chemical vapor deposition (CVD) system onto alumina substrates, coated with 2.5 nm thick Fe catalyst, at a temperature of 750°C in H 2/C 2H 2 gaseous ambient as active materials for gas sensors. CNTs multilayers, with and without buffer layer of cadmium arachidate (CdA), have been prepared by the Langmuir-Blodgett (LB) technique to coat at the double-side the QCM sensors for organic vapor detection, at room temperature. It was demonstrated that the highest mass sensitivity has been achieved for CNTs multilayer onto CdA buffer material due to the greatest gas adsorbed mass. The sensing properties of the CNTs-sensors at enhanced mass sensitivity have been investigated for different vapors of ethanol, methanol, acetone, m-xylene, toluene and ethylacetate in a wide range of concentration from 10 to 800 ppm. The CNTs-based QCM-sensors exhibit high sensitivity (e.g., 5.55 Hz/ppm to m-xylene of the CNTs-multilayer) at room temperature, fast response, linearity, reversibility, repeatability, low drift of the baseline frequency, potential sub-ppm range detection limit. © 2012 Springer Science+Business Media, LLC.

The real market penetration of polymer electrolyte fuel cells is hindered by the high cost of this technology mainly due to the expensive platinum catalyst. Two approaches are followed to reduce the cost: one way is to increase the Pt utilization efficiency reducing at the same time the total load and the other way is to increase the catalytic activity of the catalyst/support assembly. In this work, the increase of utilization efficiency is addressed by optimizing the catalyst distribution on the uppermost layer of the electrode via electrodeposition and sputter deposition, while the improvement of the catalyst activity is pursued by nanostructuring the catalysts and the carbon-based supports. A very low Pt loading 0.006 mg cm 2 was obtained by sputter deposition on electrodes that exhibited a mass specific activity for methanol oxidation reaction better than a commercial product. Carbon nanofibers used as catalyst support of electrodeposited platinum nanoparticles resulted in improved mass specific activity and long term stability compared to conventional carbon-based supports. Finally, PtAu alloys developed by sputter deposition were found more efficient than commercial PtRu catalyst for the methanol oxidation reaction. In conclusion, polymer electrolyte membrane fuel cell electrode based on nanomaterials, developed by combining physical and chemical deposition processes, showed outstanding electrochemical performance. DOI: 10.1115/1.4003629

A portable sensor-system based on solid-state gas sensors has been designed and implemented as proof-of-concept for environmental air-monitoring applications, malodours olfactometric control and landfill gas monitoring. Commercial gas sensors and nanotechnology sensors are arranged in a configuration of array for multisensing and multiparameter devices. Wireless sensors at low-cost are integrated to implement a portable and mobile node, that can be used as early-detection system in a distributed sensor network. Real-time and continuous monitoring of hazardous air-contaminants (NO 2, CO, PAH, BTEX, etc.) has been performed in field measurements by comparison of chemical analyzers from environmental protection governmental agency (ARPA-Puglia). In addition, experimental campaigns of the integrated portable sensor-system have been realized for assessment of malodours emitted from an urban waste site. The results demonstrate that the sensor-system has a potential capacity for real-time measurements of air-pollutants, malodours from waste site, and control of landfill gas. © 2011 American Institute of Physics.

Thermoelectric power (TEP) of the carbon nanotubes (CNTs) films, grown by radiofrequency plasma-enhanced chemical vapor technology onto silicon substrates, has been measured. Two different metal contacts of Cr–Al and Cr–Au have been fabricated for the CNTs-based thermocouples and preliminarily investigated. The CNTs-based thermocouples exhibit large values of TEP due to the Schottky barriers at semiconducting CNTs-metal junctions. The highest TEP of 40.7 ?V/K has been achieved for the thermocouple CNTs/Cr–Al. This value is enhanced of about 2 times compared to single-walled CNTs bundles reported in literature (Collins et al. Science 287:1801–1804, 2000), and comparable to isolated suspended single-walled carbon nanotubes with Pt-electrodes reported in literature (Yu et al. Nano Lett 5(9):1842–1846, 2005) as well. The CNTs-thermocouples exhibit linear relationship for the output voltage versus temperature in the range from 20 to 70°C by providing an interesting nanomaterial for energy applications and temperature and/or radiation microsensors.

Carbon nanotubes (CNTs) networked films have been grown by chemical vapor deposition (CVD) technology onto miniaturized low-cost alumina substrates, coated by nanosized Co-catalyst for growing CNTs, to perform chemical detection of toxic gasses (NO2 and NH3), greenhouse gasses (CO 2 and CH4) and domestic safety gasses (CO and C 2H5OH) at an operating sensor temperature of 120 °C. The morphology and structure of the CNTs networks have been characterized by scanning electron microscopy (SEM). A dense network of bundles of multiple tubes consisting of multi-walled carbon nanostructures appears with a maximum length of 1-5 μm and single-tube diameter varying in the range of 5-40 nm. Surface modifications of the CNTs networks with sputtered Platinum (Pt) nanoclusters, at tuned loading of 8, 15 and 30 nm, provide higher sensitivity for significantly enhanced gas detection compared to un-decorated CNTs. This could be caused by a spillover of the targeted gas molecules onto Pt-catalyst surface with a chemical gating into CNTs layers. The measured electrical conductance of the functionalized CNTs upon exposures of a given oxidizing and reducing gas is modulated by a charge transfer model with p-type semiconducting characteristics. The effect of activated carbons as chemical filters to reduce the influence of the domestic interfering alcohols on CO gas detection has been studied. Functionalized CNT gas sensors exhibited better performances compared to unmodified CNTs, making them highly promising candidates for functional applications of gas control and alarms. © 2011 Elsevier B.V. All rights reserved.

Networked carbon nanotubes (CNTs) films have been grown by chemical vapor deposition (CVD) technology onto miniaturized Co-coated alumina substrates for NO2 and NH3 gas sensing applications, at a sensor temperature of 150°C. The sidewalls of the CNTs films have been modified by spray-coating with two different metalloporphyrins (MPPs) consisting of a TetraPhenylPorphyrin coordinated by a central metal of zinc (Zn-TPP) and manganese (Mn-TPP) for enhanced sensitivity and tailored specificity. It was demonstrated that the gas sensitivity of the MPPs-modified CNTs-sensors significantly improved by a factor up to four-times through a catalytic effect of the MPPs. The gas sensing properties of CNTs-sensors, including MPPs-modified CNTs, are characterized by a change of the electrical conductivity in a model of charge transfer with a semiconducting p-type character. A response of the CNTs-sensor functionalized with 2 spray-layers of Mn-TPP has been measured as 0.43% to 0.5 ppm NO2, and as 0.09% to 10 ppm NH3, at 150°C. The MPPs-functionalized CNTs-sensors exhibit high sensitivity, fast response, reversibility, good repeatability, sub-ppm range detection limit.