ENEA Brindisi Research Centre

In-situ synchrotron X-ray diffraction (XRD) was used to monitor the thermal decomposition (thermolysis) of Cd thiolates precursors embedded in a polymer matrix and the nucleation of CdS nanoparticles. A thiolate precursor/polymer solid foil was heated to 300 degrees C in the X-ray diffraction setup of beamline W1.1 at Hasylab, and the diffraction curves were each recorded at 10 degrees C. At temperatures above 240 degrees C, the precursor decomposition is complete and CdS nanoparticles grow within the polymer matrix forming a nanocomposite with interesting optical properties. The nanoparticle structural properties (size and crystal structure) depend on the annealing temperature. Transmission electron microscopy (TEM) and photoluminescence (PL) analyses were used to characterize the nanoparticles. A possible mechanism driving the structural transformation of the precursor is inferred from the diffraction features arising at the different temperatures.

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymer matrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursors with different carbon chain lengths embedded in TOPAS polymer matrices. Under UV irradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals in the quantum size regime, with size and concentration defined by the number of incident UV pulses, while the host polymer remains macroscopically/microscopically unaffected. The emission of the formed nanocomposite materials strongly depends on the dimensions of the CdS nanocrystals, thus, their growth at the different phases of the irradiation is monitored using spatially resolved photoluminescence by means of a confocal microscope. X-ray diffraction measurements verified the existence of the CdS nanocrystals, and defined their crystal structure for all the studied cases. The results are reinforced by transmission electron microscopy. It is proved that the selection of the precursor determines the efficiency of the procedure, and the quality of the formed nanocrystals. Moreover it is demonstrated that there is the possibility of laser induced formation of well-defined patterns of CdS nanocrystals, opening up new perspectives in the development of nanodevices.

Abstract Carbon nanotubes (CNT) were grown on carbon fibres, both PAN‐ and pitch‐based, by hot filament chemical vapour deposition (HFCVD) using H2 and CH4 as precursors. Nickel clusters were electrodeposited on the fibre surfaces to catalyse the growth, and uniform CNT coatings were obtained on both PAN‐ and pitch‐based carbon fibres. Ni cluster features varied, depending on the deposition parameters, showing on average larger dimensions and denser distribution on pitch fibres. Multi‐walled CNTs with smooth walls and low impurity content were grown. The morphological features, both before and after the growth process, were characterised by SEM. This novel material based on carbon fibres coated with CNT, shows a potential for applications in polymeric matrix composites.

UV laser irradiation of PMMA films containing Cd thiolate precursors results in the spatially selective formation of CdS crystalline nanoparticles in the host matrix. Here we investigate the effect of the irradiation wavelength on the quality of the formed nanocrystals. Fluorescence topography and XPS studies reveal that the polymer matrix contributes to the trap states formation on the surface of the nanocrystals. When the latter are formed upon irradiation at 266 nm, they exhibit broad emission spectra, ascribed to the high degree of photodegradation of the polymer. In contrast, the irradiation at 355 nm does not chemically modify the matrix, resulting in the formation of CdS nanocrystals with narrow emission, i.e. high emission quality. This is further confirmed by fluorescence lifetime topography studies giving a mean fluorescence nanocrystal lifetime as short as 200 ps at room temperature. Thus, the optimized combination of irradiation wavelength with polymer matrix gives nanocomposite materials incorporating nanocrystals of high quality, ready to be used in various optical applications.

Abstract The nucleation of two kinds of crystalline nanoparticles, zinc sulfide (ZnS), and cadmium sulfide (CdS), is achieved directly into specific sites of polymer matrices after their irradiation with UV laser pulses. The starting samples consist of polymers doped with precursors of Zn or Cd thiolate that are proved to decompose after the absorption of UV light, resulting into the nanoparticles formation. The growth of the crystalline nanostructures is followed throughout the irradiation of the samples with successive incident pulses, by different methods, such as transmission electron microscopy, atomic force microscopy, confocal microscopy, and X‐ray diffraction. Special attention is paid to the difference of the formation pathways of the two kinds of nanoparticles studied, because the Cd thiolate precursor exhibits much higher absorption efficiency than the Zn thiolate one, at the applied UV wavelength. Indeed, CdS nanoparticles become evident after the very first incident UV pulses, whereas the formation of ZnS nanocrystals requires rather prolonged irradiation, always through a macroscopically nondestructive procedure for the polymer matrix. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Poly(etherether-ketone) (PEEK) suspensions in ethanol and isopropanol containing also α-alumina and hydroxyapatite powders were studied. An innovative method was used in the study of the quality of suspensions. We studied suspensions by means of zeta potential and grain-size measurements. The comparison amongst the different suspensions was carried out by using statistical and chemometric tools, especially by the use of an explorative test based on the Principal Component Analysis (PCA). The chemometric analysis was performed by involving different combinations of each type of powder and each type of solvent.

Abstract The incorporation of single‐wall carbon nanotubes (SWCNTs) in cadmium arachidate film by means of the Langmuir‐Blodgett (LB) technique was investigated as a function of arachidic acid/SWCNT mass ratio at the air/water interface and in Langmuir‐Blodgett films. The behaviour at the air/water interface shows that SWCNTs act as an independent phase with respect to the cadmium arachidate. Deposition conditions are optimized when the weight ratio between the arachidic acid (AA) and SWCNTs is in the range 0.018:1 to 1:1. The general order of the LB multilayered structure was destroyed by the progressive density increase in SWCNT quantity as evidenced by X‐ray reflectivity (XRR) analysis. Scanning electron microscopy images indicated that when a multilayered structure was formed its layers consisted of SWCNT bundles stacked one over the other. Copyright © 2006 John Wiley & Sons, Ltd.

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.

We investigated by using high resolution x-ray diffraction and glancing incidence x-ray reflectivity InxGa1−xN/GaN and AlxGa1−xN/GaN multiple quantum wells (MQWs) grown by plasma-assisted molecular beam epitaxy on (0001) 6H–SiC substrates covered by a GaN buffer layer. In particular, the macrostrain field is investigated by using a theoretical approach based on the exact calculation of the incidence parameter and an arbitrary strain field and it is directly assessed by measuring the angular separation between the heterostructure and substrate Bragg peaks for several reflections and diffraction geometries. The experimental results reveal non-zero off-diagonal strain components for all the investigated samples, indicating a triclinic deformation of the buffer and the superlattices unit cells. Moreover, we found a coherent interface between the buffer and the AlxGa1−xN/GaN MQW, and a partial relaxation between the GaN buffer and the InxGa1−xN/GaN MQWs. The chemical composition of the ternary alloys has been determined from the strain components by assuming Vegard's law and applying the equilibrium conditions of the elasticity theory. We found a pronounced In-segregation if the MQW was grown under metal-stable flux conditions; in contrast no appreciable segregation effect was observed under nitrogen-stable flux condition. A cumulative interface roughness was found for the samples grown on nitrogen-stable flux condition, exhibiting a strong increase of the rms interface roughness towards the MQW surface.

Composite coatings based on PEEK and Lignin were obtained by EPD. The addition of Lignin had some beneficial effects, the most relevant being an increased coating adhesion on conductive substrates. Before using in EPD suspensions, Lignin was functionalised by a carbonyl group. This functionalisation produced chemical interactions between PEEK powder and Lignin, and, as a consequence, better results in terms of both EPD efficiency and adhesion coating. Moreover, the addition of Lignin increased the hydrophobicity of PEEK coatings when they were thermally treated at temperature lower than the melting point of PEEK.

Poly(etherether-ketone)-alumina coating were deposited by EPD. In order to densify the coatings, conventional thermal treatments were performed at a temperature equal or higher than the melting point of the polymer. The samples treated at the lower temperature showed an increase in the quality of crystallinity of the polymer. As an alternative method, an excimer laser was used to treat the surface of the composite coatings. The laser beam irradiation did not induce any modification in the crystalline structure of the polymer and at the same time did not produce strong degradation of the polymer molecule, also when the laser beam fluence was higher than the ablation limit. The most relevant modification induced by both the treatments was a change in the morphology and the porosity.

A novel material made of carbon fabrics with a uniform threedimensional (3D) distribution of carbon nanotubes (CNTs) on the surface was synthesized by an electrochemical deposition (ELD) process.

The combination of nanoparticles and conducting polymers, known as hybrid conducting nanocomposites, is a new emerging field. The combination of conductive polymers, such as polyaniline (PANI), with conductive carbon nanotubes (CNTs) has already shown some synergistic properties. As a consequence, they have a variety of applications, such as sensors, actuators, touch screens, etc.. Usually PANI and CNTs are combined by using electrochemical synthesis starting with the monomer aniline. In this work PANI-CNTs nanocomposite films were obtained by using different combinations of two methods, Electrochemical Deposition (ELD) and Electrophoretic Deposition (EPD). The samples prepared by using these combined methods were compared with the material prepared by the usual electrochemical synthesis. Therefore, all the films so prepared were characterised and their electrochemical properties were investigated, particularly for evaluating their use as supercapacitor components.

Carbon nanotubes (CNTs) were grown using three different chemical vapor deposition (CVD) processes. Optimized conditions were studied.

The purpose of this study has been to investigate the effects of TiAlN functional coatings in cryo-tribological pin-on-disk experiments. Nowadays, the introduction of new machining technologies for chip removal, both at high speed and in cryogenic conditions, is posing new challenges and opening new horizons to research. As a matter of fact, that in this technology needs to focus on the choice of workpiece materials to be machining and tools coatings used. For the latter, the wear phenomenon has been studied employing pins-on-disk (made by nickel-based alloys) under a liquid nitrogen jet flows simulating cryogenic machining. The coatings used have been of two different types: the coating C1 is a ZrTiAlN quaternary, while the coating C2 is a TiAlN/ZrN. The films were deposited with processes developed by the ENEA Brindisi laboratory using a dual magnetron sputtering and HiPPMS physical deposition technique. The wear measures were acquired employing a full factorial design with two factors: i.e., the test conditions (DRY or CRYO) and the pin coatings (not coated NC, coating C1 or C2). The number of tests was 12 since 2 were the replications. Based on preliminary experimental results, it can be stated that there is a type of coating, i.e., TiAlN/ZrN, that allows for high processing speed, high material removal, and a considerable increase in tool life.

The anisotropy of a short fiber reinforced composite produced by injection molding of basalt fibers and polypropylene matrix has been studied by X-ray microtomography (or micro-CT). Fiber orientation was analyzed using four stereological methods: Mean Intercept Length (MIL), Volume Orientation (VO), Star Volume Distribution (SVD) and Star Length Distribution (SLD). The fabric tensor obtained from micro-CT analysis provided information on the fiber orientation, indicating that fibers were partially aligned in the injection direction.

TiN/ZrN multilayers coatings have been deposited using a reactive R. F. magnetron sputtering process. Nitride layers with different sputtering conditions have been stacked in order to obtain superlattices having different preferred orientations. The deposition rate has been considered as independent parameter which changes the energy and the momentum transfer of the backscattered particles, influencing films structure evolution.

In order to obtain wear resistant coating as well as thermal barrier on metallic substrates by EPD, the conventional high temperature treatments are inapplicable; so we used an alternative method to densify and make the electrophoretic deposit more adherent. In this work we described a novel method to obtain EPD deposits with good density and adherence to stainless steel substrate. At first, we achieved stabilized alumina and alumina-zirconia based suspensions; to improve the adhesion of ceramic coating on metal, some stainless steel substrates were sandblasted, others were coated with titanium bond layers. Then the substrates were coated by EPD; finally, we used the electron beam to treat the ceramic coating-metallic substrate system on the surface; in this way we obtained adherent and dense EPD coatings. In order to evaluate the quality and the microstructure of the coating sintering, the samples were observed by scanning and transmission electron microscopy; pull tests showed the adhesion of treated EPD coating was about one hundred times higher than that of deposited EPD coating.

The proton exchange membrane fuel cells (PEMFC) have been developed mainly as a power source for vehicles, power generation and consumer electronics since they combine high energy conversion efficiency at relatively low temperatures without pollutants emission in the environment. An electrode for a PEMFC is a layered structure composed by a catalyst layer deposited on a porous carbon substrate. The substrate is usually covered by a diffusion layer that enhances the gas and water flow. Platinum nanoparticles supported by carbon microparticles are commonly employed as catalyst layer. In this work an extreme ultra-low loading of Pt catalyst (< 0.02 mg/cm2) has been deposited by magnetron sputtering on gas diffusion electrodes, with different carbon supports (Vulcan and SuperP), in order to enhance the activity of PEM fuel cells. The morphology (shape and grain size) and microstructure have been studied combining field emission scanning electron microscopy (FEG-SEM), grazing incidence synchrotron x-ray diffraction (GIXRD) and x-ray photoelectron spectroscopy (XPS). The results presented here concern the evolution of the cluster size and shape after the ageing, induced by cyclic voltammetry for methanol oxidation reaction.

Extensive efforts are focused on the development of Direct Methanol Fuel Cells, due to the intrinsic advantages of this type of devices for mobile power supply system. One of the major drawback of the DMFC resides in the easy poisoning of the anode electrocatalyst (platinum) by COlike reaction intermediates, which implies the need of high platinum load in order to obtain reasonable performances. The development of platinum alloys is considered one of the promising routes for overcoming this problem: the second metal in fact acts as inhibitor of the Pt poisoning. In this work we have combined the use of unconventional methods to deposit the electrocatalyst nanoparticles with unconventional carbon supports. PtAu alloys have been deposited by sputter deposition process on carbon nanofibers with platelet morphology grown by plasma enhanced chemical vapour deposition on carbon paper. Cyclic voltammetry in H2SO4 was used to determine the electrochemical active surface and the electrocatalytic performance for methanol oxidation reaction. Even at lower Pt load, respect to the ones prepared with commercial catalysts supported on carbon black, the innovative electrodes showed higher performance and stability.