Nickel containing diamond like carbon thin films

Diamond like carbon (DLC) coatings are well established for multiple applications. The electrical conductivity of DLC or amorphous carbon can be influenced by several orders of magnitude via doping with different metals. Depending on the deposition process hydrogen may be incorporated as well, thereby decreasing the conductivity. Recent investigations of DLC disclose nice piezoresistive properties.Our work was focused on Ni:a-C:H thin films on different substrates by reactive sputtering from a nickel target. Several carbon precursors were added to the sputtering gas to create an amorphous carbon hydrogen network with embedded crystal clusters. In order to optimize the piezoresistive properties we varied various process parameters. The piezoresistive response was monitored by measuring the resistance change during bending. Our Ni:a-C:H films develop gauge factors of approx. 12 in a wide range of process parameters.For sensor applications the temperature coefficient of resistance (TCR) is important as well. It depends on the metal concentration in the thin film and can be adjusted by the concentration of the incorporated nickel. It can be set to approximately zero in a wide temperature range of 80–400 K. The combination of a high gauge factor and a very small TCR is achieved and described in this paper.XRD measurements reveal nickel or nickel carbide clusters with diameters of approx. 8–30 nm depending on the metal concentration. The clusters crystallize in the hexagonal hcp structure which could be transformed into the cubic fcc structure of nickel by thermal annealing in a vacuum.     

Up-scaling the production of modified a-C:H coatings in the framework of plasma polymerization processes

Hydrogenated amorphous carbon (a-C:H) films with silicon and oxygen additions, which exhibit mechanical, tribological and wetting properties adequate for protective coating performance, have been synthesized at room temperature in a small- (0.1 m³) and a large-scale (1 m³) coaters by low-pressure Plasma-Activated Chemical Vapour Deposition (PACVD). Hence, a-C:H:Si and a-C:H:Si:O coatings were produced in atmospheres of tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO), respectively, excited either by radiofrequency (RF – small scale) or by pulsed-DC power (large scale). Argon was employed as a carrier gas to stabilize the glow discharge. Several series of 2–5 μm thick coatings have been prepared at different mass deposition rates, R_m, by varying total gas flow, F, and input power, W. Arrhenius-type plots of R_m/F vs. (W/F)^?1 show linear behaviours for both plasma reactors, as expected for plasma polymerization processes at moderated energies. The calculation of apparent activation energy, E_a, in each series permitted us to define the regimes of energy-deficient and monomer-deficient PACVD processes as a function of the key parameter W/F. Moreover, surface properties of the modified a-C:H coatings, such as contact angle, abrasive wear rate and hardness, appear also correlated to this parameter. This work shows an efficient methodology to scale up PACVD processes from small, lab-scale plasma machines to industrial plants by the unique evaluation of macroscopic parameters of deposition.     

How can H content influence the tribological behaviour of W-containing DLC coatings

In this paper, the influence of the addition of W and H to pure DLC coatings on the structural, mechanical and tribological properties will be presented. The coatings were deposited by r.f. magnetron sputtering from a C target embedded with different numbers of W pellets. Working in non-reactive or reactive atmosphere allowed to deposit H-free or H-containing coatings, respectively, on steel and Si substrates. A Cr adhesion interlayer was interposed between the films and the substrate. Films with W content from 0 to 12 at.% and H incorporated up to a maximum value close to 40 at.% were deposited. All coatings had an amorphous structure, although vestiges of crystallinity could be detected in W-containing films. The addition of W led to a significant hardening of the DLC coating (from ～10 to 18 GPa); inversely, with H incorporation the hardness drop down to values even lower than that of pure DLC films. It was possible to establish a good correlation between the hardness and the residual stresses. In spite of decreasing friction and wear coefficients when alloying DLC with W, almost no difference was found among the W–DLC films whatever the W content was. A similar trend was achieved with the H addition. However, in this case a decrease in the friction coefficient was registered whereas the wear rate increased. The best performance concerning the friction was obtained for an H-containing coating (0.05) whereas, for the wear resistance, H-free W–DLC films were better performing (0.3 × 10^?16 m³ N^?1 m^?1).     

Si-doped carbon nanostructured films by pulsed laser deposition from a liquid target

Ablation of a silicone oil, Dow Corning's DC-705 with laser pulses of sub-ps duration in high vacuum is a novel approach to fabrication of Si-doped carbon nanocomposite films. Gently focused, temporally clean 700 fs pulses @ 248 nm of a hybrid dye/excimer laser system produce power densities of the order of 10¹¹–10¹² W cm^?2 on the target surface. The evolution of the chemical structure of film material is followed by comparing Fourier Transformed Infrared and X-ray Photoelectron spectra of films deposited at temperatures between room temperature and 250 °C. Despite the low thermal budget technique, in the spectrum of films deposited at room temperature the fingerprint of the silicone oil can clearly be identified. With increasing substrate temperature the contribution of the features characteristic of the oil gradually diminishes, but does not completely disappear even at 250 °C. This result is intriguing since the chance of oil droplets to survive in their original liquid form on the hot surface should be minimal. The results of the X-ray Photoelectron Spectroscopy suggest that the chemical structure of the film material resembles that of the oil. Both reflection mode optical microscopy and low magnification Scanning Electron Microscopy reveal that the films are inhomogeneous: areas of lateral dimensions ranging from a few to tens of micrometers, characterized by different contrasts can be identified. On the other hand, surface mapping by Scanning Electron and Atomic Force Microscopy unambiguously proves that all films possess a solid surface consisting of nanoparticles of less than 100 nm dimension, without the presence of any drop of oil. Possible explanations of the puzzling results can be that the films are polymers consisting mainly of the molecules of the target material, or composites of solid C:Si nanoparticles and oil residues.     

Characteristics of Ti–Nb,Ti–Zr and Ti–Al containing hydrogenated carbon nitride films

Nanocomposite Me–C–N:H coatings (Me is TiNb, TiZr or TiAl), with relatively high non-metal/metal ratios, were prepared by cathodic arc method using TiNb, TiZr and TiAl alloy cathodes in a CH₄ + N₂ atmosphere. For comparison purposes, a-C–N:H films were also produced through evaporating a graphite cathode in a similar atmosphere. The films were characterized in terms of elemental and phase compositions, chemical bonds, texture, hardness, adhesion and friction behavior by GDOES, XPS, Raman spectroscopy and XRD techniques, surface profilometry, hardness and scratch adhesion measurements, and tribological tests. The nanocomposite films consisted of a mixture of crystalline metal carbonitride and amorphous carbon nitride. The non-metal/metal ratio in the films composition was found to range between 1.8 and 1.9. For the metal containing nanocomposites, grain size in the range 7–23 nm, depending on the metal nature, were determined. As compared with the a-C–N:H, the Me–C–N:H films exhibited a much higher hardness (up to about 39 GPa for Ti–Zr–C–N:H) and a better adhesion strength, while the coefficients of friction were somewhat higher (0.2–0.3 for Me–C–N:H and 0.1 for a-C–N:H).     

Fabrication of crystallized boron films by laser ablation

Polycrystalline β-rhombohedral boron films mixed with amorphous boron phase have been successfully fabricated on quartz substrates using pulsed laser ablation in a quartz glass tube chamber placed in an electric furnace. The crystallinity of the films strongly depended on the temperature of the furnace and the pressure of background argon gas. High temperature and high pressure in the chamber were suitable for crystallized boron film preparation. The best crystalline films (without B₂O₃ phase formation) were obtained at 1000°C, 100 Pa. XPS measurements demonstrated that the major contaminants were carbon and oxygen, and the atomic ratio of oxygen to boron was 0.05 under the preparation conditions of well-crystallized films. The surface roughness of the films decreased by lowering laser energy to 150 mJ/pulse under the same pressure and temperature conditions.     

Fe-doped SnO2 transparent semi-conducting thin films deposited by spray pyrolysis technique: Thermoelectric and p-type conductivity properties

In this paper, we report structural, electrical, optical, and especially thermoelectrical characterization of iron (Fe) doped tin oxide films, which have been deposited by spray pyrolysis technique. The doping level has changed from 0 to 10 wt% in solution ([Fe]/[Sn] = 0–40 at% in solution). The thermoelectric response versus temperature difference has exhibited a nonlinear behavior, and the Seebeck coefficient has been calculated from its slope in temperature range of 300–500 K. The Hall effect and thermoelectric measurements have shown p-type conductivity in SnO₂:Fe films with [Fe]/[Sn] ≥ 7.8 at%. In doping levels lower than 7.8 at%, SnO₂:Fe films have been n-type with a negative thermoelectric coefficient. The Seebeck coefficient for SnO₂:Fe films with 7.8 at% doping level has been obtained to be as high as +1850 μV/K. The analysis of as-deposited samples with thicknesses ～350 nm by X-ray diffraction (XRD) and scanning electron microscopy (SEM) has shown polycrystalline structure with clear characteristic peak of SnO₂ cassiterite phase in all films. The optical transparency (T%) of SnO₂:Fe films in visible spectra decreases from 90% to 75% and electrical resistivity (ρ) increases from 1.2 × 10^?2 to 3 × 10³ Ω cm for Fe-doping in the range 0–40 at%.     

Tribological behaviour of nanostructured Ti-C:H coatings for biomedical applications

The development of a mechanically stable, functionally graded Ti-doped a-C:H interface layer in combination with a functional a-C:H coating requires a reduction of the brittle phases which induce generally problems in the transitions from Ti to TiC/a-C:H. The core objective of this study was to develop an optimum interlayer between the substrate and the functional top layer for biomedical applications, namely for tooth implants. Since the interlayer may be exposed to the sliding process, in the case of local failure of the top layer it has to fulfil the same criteria: biocompatibility, high wear resistance and low friction.The functional Ti-C:H layers with thickness in the range 2.5–3.5 μm were deposited by a magnetron sputtering/PECVD hybrid process by sputtering a Ti-target in a C₂H₂ + Ar atmosphere in dc discharge regime. The sets of coating samples were prepared by varying the C and H concentrations controlled by the C₂H₂ flow during the deposition process. The tribological properties were evaluated on a pin-on-disc tribometer at room temperature (RT) and at 100 °C using 440C balls with a diameter of 6 mm. The tests at 100 °C were performed to investigate the effect of the sterilization temperature on the tribological properties and the coating lifetime as well. The tribological performance was examined with respect to the friction coefficient, the wear rates of the coating and the counter-parts and the analysis of the wear debris. The Ti/C ratio decreased almost linearly from 4.5 to 0.1 with increasing C₂H₂ flow; the hydrogen content showed a minimum of 5 at.% at C₂H₂ flow of 30 sccm, while for lower flows it was about 10 at.%. The coatings could be divided into three groups based on the C₂H₂ flow: (i) 10–15 sccm, exhibiting severe abrasive damage during the sliding tests, (ii) 20–45 sccm, showing the highest hardness and friction values, and (iii) 52–60 sccm, with moderate hardness and minimal values of the friction coefficient and the wear rate.     

Low energy X-ray radiation impact on coated Si constructions

Low energy X-ray radiation impact on the coated Si structures is discussed in this paper. Experimental sandwich structures consisting of amorphous hydrogenated a:C–H or SiO_x-containing DLC films were synthesized on Si 〈1 1 1〉 wafers using direct ion deposition method and exposed to low energy (medical diagnostic range) X-ray photons. Irradiation of samples was performed continuously or in sequences and protective characteristics of the irradiated DLC films were investigated. Experimental data were used as the input data for Monte Carlo modelling of X-ray scattering effects in the coated silicon constructions, which affect significantly the “signal to noise ratio” in DLC-coated Si structures proposed for their application in medical radiation detectors. Modelling results obtained in the case of DLC coatings were compared to the results of calculations performed for other commonly used combinations coating–detector material.The evaluation method of coated structures for their possible application in medical radiation detector constructions has been proposed in this paper. It is based on the best achieved compatibility between the appropriate mechanical characteristics, coating’s resistance against the radiation damage and the lowest estimated scattering to total dose ratio in the coated radiation sensitive volume.     

Phase equilibria in ternary (carbon dioxide + tetrahydrofuran + water) system in hydrate-forming region: Effects of carbon dioxide concentration and the occurrence of pseudo-retrograde hydrate phenomenon

In the present work, the three- and four-phase hydrate equilibria of (carbon dioxide (CO₂) + tetrahydrofuran (THF) + water) system are measured by using Cailletet equipment in the temperature and pressure range of (272 to 292) K and (1.0 to 7.5) MPa, respectively, at different CO₂ concentration. Throughout the study, the concentration of THF is kept constant at 5 mol% in the aqueous solution. In addition, the fluid phase transitions of L_W–L_V–V → L_W–L_V (bubble point) and L_W–L_V–V → L_W–V (dew point) are determined when they are present in the ternary system. For comparison, the three-phase hydrate equilibria of binary (CO₂ + H₂O) are also measured. Experimental measurements show that the addition of THF as a hydrate promoter extends hydrate stability region by elevating the hydrate equilibrium temperature at a specified pressure. The three-phase equilibrium line H–L_W–V is found to be independent of the overall concentration of CO₂. Contradictory, at higher pressure, the phase equilibria of the systems are significantly influenced by the overall concentration of CO₂ in the systems. A liquid–liquid phase split is observed at overall concentration of CO₂ as low as 3 mol% at elevated pressure. The region is bounded by the bubble-points line (L_W–L_V–V → L_W–L_V), dew points line (L_W–L_V–V → L_W + V) and the four-phase equilibrium line (H + L_W + L_V + V). At higher overall concentration of CO₂ in the ternary system, experimental measurements show that pseudo-retrograde behaviour exists at pressure between (2.5 and 5) MPa at temperature of 290.8 K.     

Observation of possible quantum interference effects in SrRuO3 epitaxial thin films grown by high-oxygen pressure dc sputtering

A careful study of the electronic transport and magnetotransport properties of metallic ferromagnetic SrRuO₃ (SRO) thin films is reported. Epitaxial (～150 nm) SRO films were grown on (001)-oriented SrTiO₃ (STO) substrates by dc sputtering technique at high oxygen pressure. Resistivity measurements were performed up to temperatures as low as 2 K in magnetic fields strengths of up to 9 T, applied perpendicular to the film plane. The films featured excellent metallic behavior at room temperature, with a resistivity, ρ(300 K) < 600 μΩ cm. The presence of minima in the ρ–T plots at ～4 K was clearly detected from these measurements. The 9 T magnetic field did not remove the minima signaling its nonmagnetic origin In addition, the ρ(μ₀H = 9 T,T) minima was slightly shifted to higher temperature and the ρ(μ₀H = 9 T,T ≤ 4 K) was larger when it was compared with ρ(μ₀H = 0 T,T ≤ 4 K). Increasing relevance of quantum corrections to the conductivity as the temperature is lowered has been invocated as possible cause of this anomalous electrical behavior. In this case, effects arising from quantum interference of the electronic wavelength are expected. Weak localization and renormalized electron–electron interaction have been considered as possible sources giving rise to quantum correction to the conductivity.     

The electrodeposition of highly reflective lead dioxide coatings

In the presence of a suitable surfactant, such as hexadecyltrimethylammonium chloride or bromide, highly reflective and hard lead dioxide coatings with a black appearance can be electrodeposited from methanesulfonic acid media at room temperature (295 K). The reflective PbO₂ coatings are compact, adherent to the (vitreous carbon or carbon-polymer) substrate and can be formed at current densities of 10 to 100 mA cm^?2 at a thickness up to several hundred microns. The coatings were characterised by measurement of surface optical reflectance, surface roughness, surface microstructure, phase composition and crystallite size. The reflective PbO₂ films were found to mainly consist of the alpha (orthorhombic) phase with feather-like and orientated microstructures. The crystallite size and surface roughness were in the order of tens of nanometres and their optical reflectance was several orders of magnitude higher than matte coatings produced in the absence of additives.     

Fabrication of hydrophobic fluorinated amorphous carbon thin films by an electrochemical route

A novel electrochemical route for the preparation of hydrophobic fluorinated amorphous carbon (a-C:F) films with nanostructured surfaces on single crystal silicon substrate was reported. The films were investigated in terms of the surface morphology, chemical composition, microstructure and hydrophobic behavior. The results showed that a highly uniform and densely packed bamboo shoot-like nanostructure was obtained without any use of template. The incorporation of fluorine presented mainly in the forms of CF₂ chains and CCF_x (x = 1, 2) in the films. Sessile drop water contact angle measurements showed that the contact angle of a-C:F films deposited by electrochemical route was about 145°, which can be attributed to the lower surface energy of CF_x groups and higher diffusion resistance of the special nanostructured surface to water. Moreover, the related growth mechanism of the resulting films in liquid-phase electrodeposition is discussed as well.     

Room-temperature synthesis and seebeck effect of lead chalcogenide nanocubes

The pure face-centered cubic lead chalcogenide nanocubes have been synthesized in hydrazine hydrate saturated alkaline solution under the conditions of room temperature, ambient pressure, and a short growth time, with advantages of being simple, high yield and cost effective. The size of PbS, PbSe and PbTe nanocubes is 200–300 nm, 50–120 nm, and 30–60 nm, respectively. It was found that the growth steps of lead chalcogenides (especially PbTe) nanostructures could be controlled in the strong hydrazine hydrate alkaline environment. Thermoelectric properties of the films made from the PbS, PbSe and PbTe nanocubes have been investigated comparatively for the first time. The results indicate that the room-temperature Seebeck coefficient value of the PbS, PbSe and PbTe nanocube films is up to 154.4 μV/K, 199.8 μV/K and 451.1 μV/K, respectively.     

Fabrication of highly conductive Ru/a-CNx:H composite films by anode deposit

Ruthenium(0) composite hydrogenated amorphous carbon nitride (Ru/a-CN_x:H) films were deposition on single crystal silicon (1 0 0) substrate by electrochemical deposition technique with acetonitrile as carbon source, and Ru₃(CO)₁₂ as dopant. In the deposited progress, the Si (1 0 0) acted as anode. The relative atomic ratio of Ru/N/C was about 0.28/0.33/1, and Ru nanocrystalline particles about 8 nm were homogeneously dispersed into the amorphous carbon matrix. After doping Ru into a-CN_x:H films, the conductivity of the films were evidently improved and the resistivity drastically decrease from 10⁸ Ω cm to about 100 Ω cm.     

Preparation and properties of cellulose/PE-co-AA blends

Cellulose/polyethylene-co-acrylic acid blends (cellulose concentration 0–50 wt.%) was prepared via mixing their alkaline solutions. The formed suspension was precipitated and dried, where after the morphology as well the thermal and mechanical properties of the blends were characterized by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and Dynamic Mechanical Analyses (DMA). In addition, the melt properties of the blend were studied by rotational rheometer following some injection molding trials as well. The polymers were found to be dispersed homogenously in the blend and the crystallization temperature of the PE-co-AA phase was increased ～6 °C due to the nucleation ability of the cellulose phase. The size of the discontinuous cellulose phase was 5 μm at the most while at higher cellulose concentrations (30–50 wt.%) the polymers formed co-continuous morphology in the blend. This change in the morphology was observed also in their melt properties which showed that the blend reached so called percolation point at ～20 wt.% of cellulose. Finally, the blends were found to be injection moldable over the whole composition range, if only the injection molding became more challenging (i.e. higher mold temperatures and longer mold cooling times were required) after the percholation point.     

The influence of local structure of nanocrystalline Ni films on the catalytic activity

The aim of our investigation was to study the influence of the nanoparticles size (the local structure) in sputter deposited Ni films on hydrogen evolution kinetics. The grain size of Ni-particles (11–100 nm) was controlled by the substrate temperature (from 35 °C to 300 °C). The dependence of the kinetic parameters on the temperature at which the films were deposited was measured in alkaline solution by electrochemical impedance spectroscopy (EIS). It correlates well with the change of the ratio between the nanocrystalline and non-homogenous disordered fraction of the nc-Ni film observable by Grazing incidence small angle X-ray scattering (GISAXS) analysis and ascribed to the intercrystalline matter. The catalytic activity of nanocrystalline nickel (nc-Ni) on the hydrogen evolution reaction (h.e.r.) is markedly greater at larger fraction of the spherical inhomogeneities inside the film. This effect is especially strongly pronounced for the nc-Ni films prepared on the substrates at lower temperatures.     

Thickness dependent physical properties of close space evaporated In2S3 films

In recent years, In₂S₃ is considered as a promising buffer layer in the fabrication of heterojunction solar cells. Film thickness is one of the important parameters that alters the physical characteristics of the grown layers significantly. The effect of film thickness on the structural, morphological, optical and electrical properties of close space evaporated In₂S₃ layers has been studied. In₂S₃ thin films with different thicknesses in the range, 100–700 nm were deposited on Corning glass substrates at a constant substrate temperature of 300 °C. The films were polycrystalline exhibiting strong crystallographic orientation along the (103) plane. The deposited films showed mixed phases of both cubic and tetragonal structures up to a thickness of 300 nm. On further increasing the film thickness, the layers showed only tetragonal phase. With increase of film thickness, both the crystallite size and surface roughness in the films were found to be increased. The optical constants such as refractive index and extinction coefficient of the as-grown layers have been calculated from the optical transmittance data in the wavelength range, 300–2500 nm. The optical transmittance of the films was decreased from 82% to 64% and the band gap varied in the range, 2.65–2.31 eV with increase of film thickness. The electrical resistivity as well as the activation energy was evaluated and found to decrease with film thickness. The detailed study of these results was presented and discussed.     

Electron beam accelerators—trends in radiation processing technology for industrial and environmental applications in Latin America and the Caribbean

The radiation processing technology for industrial and environmental applications has been developed and used worldwide. In Latin America and the Caribbean and particularly in Brazil there are 24 and 16 industrial electron beam accelerators (EBA) respectively with energy from 200 keV to 10 MeV, operating in private companies and governmental institutions to enhance the physical and chemical properties of materials. However, there are more than 1500 high-current electron beam accelerators in commercial use throughout the world. The major needs and end-use markets for these electron beam (EB) units are R and D, wire and electric cables, heat shrinkable tubes and films, PE foams, tires, components, semiconductors and multilayer packaging films. Nowadays, the emerging opportunities in Latin America and the Caribbean are paints, adhesives and coatings cure in order to eliminate VOCs and for less energy use than thermal process; disinfestations of seeds; and films and multilayer packaging irradiation. For low-energy EBA (from 150 keV to 300 keV). For mid-energy EBA (from 300 keV to 5 MeV), they are flue gas treatment (SO₂ and NO_X removal); composite and nanocomposite materials; biodegradable composites based on biorenewable resources; human tissue sterilization; carbon and silicon carbide fibers irradiation; irradiated grafting ion-exchange membranes for fuel cells application; electrocatalysts nanoparticles production; and natural polymers irradiation and biodegradable blends production. For high-energy EBA (from 5 MeV to 10 MeV), they are sterilization of medical, pharmaceutical and biological products; gemstone enhancement; treatment of industrial and domestic effluents and sludge; preservation and disinfestations of foods and agricultural products; soil disinfestations; lignocellulosic material irradiation as a pretreatment to produce ethanol biofuel; decontamination of pesticide packing; solid residues remediation; organic compounds removal from wastewater; and treatment of effluent from petroleum production units and liquid irradiation process to treat vessel water ballast. On the other hand, there is a growing need of mobile EB facilities for different applications in South America.     

Electronic structure and conductivity of nanocomposite metal (Au,Ag, Cu,Mo)-containing amorphous carbon films

In this work, we study the influence of the incorporation of different metals (Me = Au, Ag, Cu, Mo) on the electronic structure of amorphous carbon (a-C:Me) films. The films were produced at room temperature using a species selective bias pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas X-ray diffraction was used to identify the formation of metal nanoclusters in the carbon matrix. The metal content incorporated in the nanocomposite films induces a drastic increase in the conductivity, in parallel with a decrease in the band-gap corrected from Urbach energy. The electronic structure as a function of the Me content has been monitored by X-ray absorption near edge structure (XANES) at the C K-edge. XANES showed that the C host matrix has a dominant graphitic character and that it is not affected significantly by the incorporation of metal impurities, except for the case of Mo, where the modifications in the line shape spectra indicated the formation of a carbide phase. Subtle modifications of the spectral line shape are discussed in terms of nanocomposite formation.