1,721,081 research outputs found
Fluorinated amorphous carbon thin films: Analysis of the role of the plasma source frequency on the structural and optical properties
No full textDifferent types of fluorinated amorphous carbon (a-C:H:F) thin films were grown by CH4/CF4/Ar mixtures using a 13.56 MHz radio frequency (rf) and a 13.56 MHz rf -2.45 GHz microwave hybrid plasma source. The optical properties of films were carried out by ellipsometric measurement, while x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were exploited to study their structural and vibrational properties. XPS spectra showed that the fluorine incorporation increased with the CF4 partial pressure while fluorine-poorer films were deposited with the rf-microwave hybrid technique., Raman measurements also suggested that with increasing fluorine content, the film microstructure changed from diamond-like to polymer-like.. The mechanism of the a-C:H:F refractive index dependency on the plasma source frequency is investigated in terms of the amount of fluorine incorporation in the films produced. (C) 2001 American Vacuum Society. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Relationship between the optical and mechanical properties of fluorinated amorphous carbon thin films
No full textFluorinated amorphous carbon (a-C:H:F) thin films were grown from CH4/CF4/Ar gas mixtures using a 13.56 MHz radiofrequency (RF) plasma source. The effect of fluorine incorporation on the mechanical properties of the films was investigated by depth sensing indentation, while Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR) and ellipsometry measurements were exploited to study their vibrational, structural and optical properties. While raising fluorine content in the film, visible Raman results show that the sp(2) carbon sites undergo a gradual ordering into graphitic clusters, which are responsible for a higher optical absorption. Nanoindentation measurements showed decreased elasticity of the film, as well as decreased hardness upon fluorine incorporation. A clear correlation between the mechanical properties and the optical constants was found as a function of fluorine content in the film. (C) 2001 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Structural and optical properties of nitrogen and oxygen doped a-C : H coatings
No full textThe deposition and characterization of hydrogenated amorphous carbon films (a-C:H) obtained by radio-frequency plasma enhanced chemical vapor deposition on silicon and on polycarbonate are reported. Small amounts of N-2 and O-2 were added to a CH4-He gas mixture in order to promote the doping of the films. A systematic study of the coating structure and optical and mechanical properties as a function of gas phase composition and applied radio-frequency power is also reported. X-ray photoelectron spectroscopy (XPS) was used to quantify the amount of nitrogen and oxygen incorporation, while the characterization Of sp(2) carbon bonding was performed by Raman spectroscopy. Ellipsometry and UV-Vis-NIR transmission measurements were exploited to relate the refractive index and absorption of light in the visible region to the film composition and the deposition process parameters. The associated variation of the coating hardness was checked by nanoindentation measurements. The results obtained show that oxygen incorporation allows the achievement of an increased film transparency in the visible spectral range, while nitrogen dilution of the methane precursor in the plasma is responsible for the deposition of films that have a higher absorbance in the visible, due to an increased size of graphitic domains. The addition of both doping elements in a small percentage allows the preservation of the characteristic high hardness of a-C:H coatings. (C) 2002 Elsevier Science B.V. All rights reserved. RI Kenny, Jose/F-9372-201
Hydrogen concentrations and mass density obtained by X-ray and neutron reflectivity on hydrogenated amorphous carbon nitride thin films
No full textIn this work, specular reflectivity of neutrons and X-rays was used to determine the scattering-length density profile of nitrogen-doped amorphous carbon films (a-C:H:N) perpendicular to their surface. By the combination of these two techniques, we obtained not only the mass density, but also the concentration of hydrogen. This experimental approach was applied to study the influence of Ar plasma dilution on the properties of a-C:H:N films. The structure (Raman spectroscopy) and chemical structure (X-ray photoelectron spectroscopy) of two series of specimens, deposited with plasma decomposition of CH4/N-2 and CH4/N-2/Ar mixtures, were analysed and the results were correlated to the film hydrogen concentration. The differences observed suggest that as Ar is introduced in the gas mixture, a progressive graphitisation of the films is observed and the mass density decreases. The hydrogen content for films grown in N-2-rich plasma atmosphere is higher with respect to those obtained without nitrogen dilution; otherwise, Ar dilution promotes lower hydrogen incorporation. (C) 2002 Elsevier Science B.V. All-rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Influence of plasma source frequency on composition and density of fluorinated amorphous carbon thin films
No full textDifferent types of fluorinated amorphous carbon (a-C:H:F) thin films were grown from CH(4)/CF(4)/Ar mixtures using a 13.56 MHz radiofrequency and a 13.56 MHz radiofrequency-2.45 GHz microwave hybrid plasma source. Comparison of X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XRR) allowed us to determine the film hydrogen concentration, which depends on the plasma source used, and showed that, independently of the plasma source employed, the fluorine incorporation occurs at the expenses of the hydrogen content. Moreover, films with lower fluorine content were deposited from the radiofrequency-microwave hybrid technique. XRR measurements suggested that with increasing fluorine content, the film density changes indicating a phase transition towards an open and less cross-linked structure. For a fixed gas mixture composition, the deposition of less dense films grown by radiofrequency-microwave hybrid plasma source is probably associated to a different plasma decomposition and lower energy of the bombarding species. (C) 2001 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Effect of catalyst layer thickness and Ar dilution on the plasma deposition of multi-walled carbon nanotubes
No full textThe growth behaviour of carbon nanotubes (CNTs), produced by radio-frequency plasma enhanced chemical vapour deposition, is studied here as a function of a CH4/Ar ratio and Ni catalyst layer thickness. The composition of the plasma mixture was observed as being crucial for the morphology of the nanotubes, indicating a transition from a random to a more uniform orientation, when argon is added to the plasma atmosphere. Scanning tunnelling microscopy shows, as a result of the argon dilution, the formation of a defective structure (i.e. pentagons) at the tip of vertically aligned CNTs while hexagonal atomic arrangement was detected on the sidewall of randomly oriented CNTs deposited by pure methane. The electronic structure of CNTs was then investigated by C Is' photoemission spectroscopy. The results show a shift of the overall spectral to the higher-binding-energy side, indicating the formation of metallic aligned tubes when argon is added to the plasma atmosphere. Experimental results are applied to develop a coherent picture of the relationship between the deposition parameters and the microstructural features, as well as to check the relationship of the electronic properties predicted for nanotubes with the plasma chemical composition. (C) 2003 Elsevier Science B.V. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Effect of fiber surface treatments on thermo-mechanical behavior of poly(lactic acid)/phormium tenax composites
No full textIn the present study, Phormium Tenax fiber reinforced PLA composites were processed by injection molding and twin screw compounding with a fiber content ranging from 10 to 30 wt%. Three surface treatment methods have been used to improve the Phormium Tenax fiber-matrix interfacial bonding that are as follows: (1) aqueous alkaline solution, (2) silane coupling agent, and (3) a combination of alkaline and silane treatment. The mechanical, thermal and morphological properties of the resulting composites were investigated. The results have shown that the moduli of surface treated fiber reinforced composites are lower than the ones obtained for untreated composites (as a consequence of the decrease in fiber modulus caused by the chemical treatments) and no significant increase in strength was observed for any of the composites compared to neat PLA. SEM micrographs of composite fractured surfaces confirmed an improvement in the interfacial strength, which was insufficient nonetheless to significantly enhance the mechanical behavior of the resulting composites. Results from thermogravimetric analysis and differential scanning calorimetry suggest that surface treatment of Phormium affects the ability of PLA to cold crystallize, and the thermal stability of the composites at the different fiber contents was reduced with introduction of alkali and silane treated Phormium fibers
Crystallization and melting behavior of poly(3-butylthiophene), poly(3-octylthiophene), and poly(3-dodecylthiophene)
No full textThe crystallization and melting behavior of poly(3-butylthiophene) (P3BT), poly(3-octylthiophene) (P3OT), and poly(3-dodecylthiophene) (P3DDT) were studied. The equilibrium melting temperatures (Tm0) of these polymers were measured and resulted equal to 321, 230, and 175 °C for P3BT, P3OT, and P3DDT, respectively. The crystallization kinetics was evaluated by the Avrami equation: it proceeds by heterogeneous nucleation with one-dimensional linear growth (n = 1.1−1.8). The effects of the length of the alkyl side chain and of the undercooling were investigated. Phase I, Phase II, and a nematic mesophase were detected in P3BT and P3DDT. In P3BT, Phase I was differentiable from the mesophase on the basis of wide-angle X-ray scattering (WAXS) patterns. This study gives insight, in particular, on the crystallization and melting behavior of P3BT, a polymer not yet well studied. WAXS, small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) were employed as experimental techniques
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