Photocatalytic reaction of activated TiO2 can be directly used for water splitting to produce hydrogen for fuel cell. TiO2 thin films have been deposited using sol-gel method and subsequently heat-treated at 500 degrees C to form anatase phase. Ar+ or N+ ions with energy of 30 keV were implanted in anatase TiO2 thin films with different ion doses in order to modify the band gap for visible light absorbance. UV-Vis spectroscopy was used to check the efficiency for absorbing visible light while structural and surface modifications caused by implantation were studied by using FT-IR and SEM respectively in the TiO2 films. The ion-beam modified samples were found to be more efficient to absorb visible light in comparison to pure TiO2 films. This efficiency of absorption increases with the implantation dose without any structural changes studied from FT-IR analysis. Ar+ ions caused the formation of defect energy levels in the band gap while N+ ions efficiently narrowed the band gap of TiO2 thin film in the visible light region. The results are further discussed in terms of defect formation caused by ion implantation. (C) 2009 Elsevier B.V. All rights reserved.

Cr- or Fe-ion-doped TiO2 thin films have been synthesized by radio-frequency magnetron sputtering and a sol–gel method to study hydrogen generation by photocatalytic water-splitting under visible light irradiation. The doping method, dopant concentration, charge transfer from metal dopants to TiO2, and type of dopants used for modification of TiO2 were investigated for their ability to enhance photocatalytic activity. UV–Visible spectra show that the metal-doped-TiO2 obtained by sputtering is much more efficient than that obtained by the sol–gel technique at inducing a red shift of the absorption edge in the visible light range. Low concentration metal ion doping must be done near the conducting indium tin oxide (ITO) – TiO2 interface to avoid the formation of recombination centers for photo-generated electron–hole pairs. H2 production rate (μmol/h) is higher for Fe-doped TiO2 (15.5μmol/h) than for Cr-doped TiO2 (5.3μmol/h) due to the ability of Fe ions to trap both electrons and holes, thus avoiding recombination, while Cr can only trap one type of charge carrier. A constant H2 generation rate is obtained for long periods of time by all the investigated TiO2 films because of the separate evolution of H2 and O2 gases, thus eliminating the back-reaction effect.

TiO2 thin films have been synthesized by radio-frequency magnetron sputtering and sol–gel method to study the hydrogen generation by photocatalytic water splitting under visible light irradiation. Photoelectrochemical cell with chemical bias, involving photo-anode in form of TiO2 film deposited on conducting indium tin oxide (ITO) film and Pt as cathode, is developed. The effect of conducting ITO layer on photo-voltage is studied by varying the thickness of ITO films. Constant H2 generation rate is obtained for long period of time by both the TiO2 films because of the separated evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Sputter-deposited film as compared to sol–gel-synthesized film showed better H2 generation rate, mainly explained in terms of the higher visible light absorption achieved by oxygen vacancies created in the TiO2 film by the energetic target ions during deposition in pure Ar gas pressure.

Zn alloys are able to surpass the performance of electrogalvanised or hot-dip Zn (at same thickness) for corrosion protection of car bodies. In particular, vacuum deposited Zn alloy layers have higher protection power on non-painted steel surfaces as compared with pure Zn layers. In the present work the Zn–Mn system was investigated: Zn/Mn alloys of different compositions as well as Zn/Mn multilayers of 5–6 μm total thickness were prepared on low alloy steel by ion beam assisted deposition (IBAD). The equipment contained two electron beam evaporators and a slit extraction ion source, delivering ions of 100–1500 eV energy. The corrosion behaviour of the samples was evaluated by standard salt spray tests (SST). The composition and microstructure of the coatings was studied by scanning electron microscopy (SEM) and EDX-depth profiling. The behaviour of the coating/substrate system is discussed in comparison with ‘state of the art’ Zn-coatings (EZ) produced by electrogalvanizing. Generally speaking, the performance of the optimised coatings is as good or better than the reference standard.

In this work we have studied the ion beam etching rates of PTFE by changing N-ion fluence at different sample temperatures. PTFE substrates were irradiated with 160 keV N ions to a dose range between 1×1014 and 4×1016 ions/cm2. The treated samples were examined by visible (514.5 nm) Raman spectroscopy as well as by scanning electron microscopy. Mechanical properties of the implanted layers were assessed by scratch-testing in conjunction with profilometry. Radiation cross-linking and polymer degradation by chain scission are competing processes in this type of polymer depending on the irradiation temperature. Flexible-chain polymers are easier to cross-link than rigid-chain polymers like PTFE, however, the latter can be cross-linked if temperature is high enough. It is shown that ion irradiation at room temperature even in the low dose range leads only to chain scission while at temperatures higher than the glass transition, evidence for cross-linking and consequent stiffening are found.

The ternary compound TiAlN coating has been known to be superior to binary compound TiN in protecting tools, which may be damaged by high thermal load. In the present study, TiAlN coatings are deposited on stainless (AISI 316L) and carbon steel substrates by using DC sputtering technique. The structure of TiAlN coatings with different Al contents is studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that the structure evolves from the cubic B1 type of TiN to the hexagonal phase of AlN when the Al content increases from 0 to 70 at.%. The oxidation behavior of deposited TiAlN coatings with different Al concentrations are investigated at oxidation temperatures ranging from 300 to 800 °C using energy-dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis. It is concluded that the oxidation resistance is enhanced at first and then decreases with increasing Al content, the addition of 40 at.% Al leading to the best anti-oxidation effect. Coatings of same composition exhibit the best barrier performance to hydrogen permeation.

Considerable efforts have been made to improve the physical and chemical properties of a large number of polymers by ion implantation, and the enhancement of various properties was attributed to different mechanisms like chain scission, cross-linking and carbonization. It was observed that ion implantation can also improve the surface properties of polytetrafluoroethylene (PTFE) but the mechanisms for such enhancement are not completely clear yet. In this work we have studied the adhesion of Au thin films on PTFE. The PTFE substrates were implanted with 160 keV N ions to a dose range between 1×1014 and 1×1017 ions/cm2. The treated samples were examined by visible (514.5 nm) and FT infrared (1064 nm) Raman spectroscopy as well as by scanning electron microscopy. Ion implantation on PTFE in the low dose range leads to the splitting of weaker CC bonds; in the intermediate dose range sputter loss effects are dominant, and at higher doses, the microstructure strongly evolves and double CC bonds are created. Before and/or after the ion pretreatment, the specimens were coated (with a sputtering technique) with 150 nm thick Au films. Adhesion properties of the films were assessed by conventional scratch- and scotch-tape tests in conjunction with optical microscopy. In the case of pre-deposited coatings, enhanced adhesion occurs only if the implanted dose is lower than 2×1014 ions/cm2, in connection with the formation of dangling bonds in the polymer (‘chemical’ adhesion), as confirmed by contact angle measurements. In the case of post-deposited coatings, enhanced adhesion occurs in the whole dose range. In the medium-high dose range, the enhanced adhesion can be related to the development of surface topography of the polymer substrate (‘mechanical’ adhesion).

The metallisation of glass for decorative and/or functional purposes is now a well-established technique. The most popular methods are electroplating or sputter deposition. In order to obtain suitable adhesion, substrate pretreatment is a substantial part of a vapour-deposited coating that generally cannot be dispensed with. The pretreatment costs can reach the same order of magnitude as those associated with the actual coating process, or can even exceed them. In this work we studied the adhesion of Au thin films on glass. The substrates were pretreated by an ion-beam-mixing step, consisting of the deposition of Au/C bilayers or C/Au/C multilayers followed by Xe+ implantation. After such preparation, the specimens were further coated (using a sputtering machine) with 150-nm-thick Au or Au-alloy films. Adhesion properties of the films were examined using a scratch tester in conjunction with scanning electron microscopy. It was observed that, without the ion-beam-mixing pretreatment, the coatings were poorly adherent. Strong adhesion enhancement was observed in the pretreated samples. The key mechanism envisaged to explain this is related to the formation of mixed SiC–Au phases at the interface region. Moreover, the mechanical properties of the pure and alloyed Au films were quantified by nano-indentation, and hardness results are in good agreement with a simple rigid-sphere model of substitutional hardening.

Hexagonal boron nitride thin films (h-BN) were deposited by RF magnetron sputtering on 160-keV N+-implanted polycarbonate (PC) substrates at fluences ranging between 1 and 8×1015 N+ cm−2. Before coating deposition, the PC substrates were treated by plasma ion etching in the deposition chamber. Plasma treatment of the polycarbonate ensured good adhesion of the h-BN coating on virgin and ion-implanted PC substrates. For implantation fluences up to 2×1015 N+ cm−2, the h-BN layers deposited exhibited lower levels of intrinsic stresses and better resistance to delamination under scratch testing compared to the coating deposited on the virgin PC substrate. This result can be related to the formation, by ion implantation, of a PC surface layer with improved thermal and mechanical properties. The thermal expansion coefficient of this surface layer matches well with that of the h-BN thin films, thus limiting the level of the thermal intrinsic stresses in the coating. Moreover, surface hardening of the PC, induced by the ion beam, produced less substrate deformation than in the virgin PC substrate under a scratch test load, thus reducing the level of mechanical stresses in the h-BN coating. For implantation fluences greater than 2×1015 N+ cm−2 the h-BN layers deposited delaminate at low scratch test loads, indicating embrittlement of the PC surface layer.

In the present work, various Zn-Cr alloy coatings were deposited on automobilistic steels by a vacuum process, in which Zn and Cr are evaporated from resistance heated sources. After ion etching, different Zn:Cr evaporation rates were applied to produce several compositions in the films until a final coating thickness of 4 mu m was obtained. The coatings were characterized with respect to morphology (SEM), structure (XRD) and hardness (by nanoindentation). The structure changed from the hexagonal Zn-Cr solid solution to a cubic (bcc) phase as the amount of Cr in the coating increased. Nanoindentation tests showed that the presence of Cr can significantly change coating hardness: this effect can be correlated with compositional and microstructural changes. To optimise the adhesion, the necessity of a multistage pre-treatment of the steel substrates was recognized. Further to Ar+ sputter cleaning of the substrates, the deposition of a thin Cr interlayer is necessary. It was observed that, without suitable pre-treatments, the coatings are poorly adherent.Salt spray corrosion tests revealed that even small Cr additions are able to significantly improve the corrosion resistance of Zn coatings. The time for red rust to appear is very long (at least four times) when compared to pure Zn vapour deposited, or steel sheet electroplated with Zn (reference specimens). The generation of protective corrosion products which can suppress cathodic reaction is considered an important factor for that improvement. (C) 2000 Elsevier Science S.A. All rights reserved.

The use of polymeric materials is often limited by low hardness, poor wear resistance and wettability considerations. The area of mechanical changes caused by ion beam treatments has been explored only to a limited extent for polymers despite their growing usage in automotive, biomedical and aerospace applications, in which traditionally metals have been used.Polycarbonate (PC) specimens were subjected to medium-high energy (160 keV) nitrogen ion implantation at different dosage. Ion irradiation, even at low fluence, can improve surface properties in a well controlled way. A colour change from amber to dark brown with increasing fluence is associated with the ion implantation process. Hardness and elastic modulus, as measured by a nanoindenter, increase dramatically with increasing N dose.The surface property improvement can be explained by cross-linking phenomena, responsible for the formation of a three-dimensionally connected rigid network. Such hypothesis is confirmed by TOF-SIMS analyses of untreated and ion bombarded specimens.Too high implanted fluence may induce progressive degradation of the PC surface. Should the thickness of the ion-modified layer be too low for a specific application, it is possible to extend the ion irradiation treatment by plasma or ion beam assisted deposition of hard semi-transparent top layers. Using such a method the advantages of both the techniques can be retained to obtain PC surfaces with optimum wear resistance properties. (C) 1998 Elsevier Science S.A.

To produce smooth ceramic surfaces, with the aim to improve their mechanical capabilities, e.g. thermal shock, erosion and corrosion behaviour, various beam techniques (laser, electron, ion) can be used. Each presents favourable and less favourable aspects. If the surface of a solid is subjected to irradiation by high-intensity pulsed ion beams (HIPIBs), the intensity of the pulse can be set sufficiently high to bring the solid surface to a high temperature, i.e. the melting point or higher, thus enabling glazing applications to be performed.In our experiments, HIPIBs were generated in a rod plasma injector machine, equipped with coaxial grid-type electrodes. Several pulses of plasma, containing ions from a discharge in a nitrogen atmosphere, were used to irradiate sintered SiC substrates. The energy density of the pulses was in the range 4-6 J cm(-2). The ion energy was estimated to be 10 keV. The samples were analysed by Auger electron spectroscopy and scanning electron microscopy. An improved tribological behaviour of the treated surfaces was found without deterioration of the bulk properties.

The effect of nitrogen implantation into pure aluminium has been extensively explored, taking into account the variation of several physical and technological properties of the implanted layer. In particular, the formation of aluminium nitride, which occurs under specific choices of the implantation parameters, is associated with an increase in hardness. In this work, we consider two Al alloys (Al-7075 and Al-2011), frequently employed in the mechanical industry, with properties strongly dependent on the thermomechanical treatment.Molecular nitrogen bombardment at 150 keV (75 keV N+) was employed, up to a total dose of 3 x 10(17) N cm(-2), varying the substrate temperature from 373 to 473 K. The samples were then characterized with respect to composition, structure, morphology, microhardness, scratch resistance (also performing multi-pass testing) and friction coefficient.The results were interpreted within the framework of micromechanical models describing the hardness of thin coatings deposited onto soft substrates; the microhardness of the implanted layer increased by a factor of five.It appears that nitrogen-implanted aluminium alloy layers, in spite of their shallow thickness, behave better than hard TiN-coated surfaces. Care must be taken to implant bath alloys at the lowest possible temperature to avoid degradation of the substrate properties.