The influence on immersion time of titanium conversion coatings on electrogalvanized steel

The study aims to replace chromate treatments of electrogalvanized steels by immersing the electrogalvanized steel in a titanium trichloride (TiCl₃) bath. The influence of immersion time on surface morphology and corrosion resistance of the titanium conversion coatings was investigated. The titanium conversion coating prepared for 300 s immersion time with a uniform structure has the most excellent anticorrosive performance. Furthermore, the coating comprises a loose outer layer and a dense inner layer structure with a thickness of 150 nm. X-ray photoelectron spectroscope analysis shows that the coating consisted of Zn and Ti oxides and/or hydroxides.     

Structure and chemical bonds in reactively sputtered black Ti-C-N-O thin films

The evolution of the nanoscale structure and the chemical bonds formed in Ti-C-N-O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O₂ + N₂ gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro-Raman spectroscopy, but it was not the only effect associated to the increase of the O₂ + N₂ partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitrogen than to carbon. This gives rise to the appearance of amorphous carbon coexisting with poorly crystallized titanium oxynitride. The evolution of the films colour is explained on the basis of these structural changes.     

Self-patterned Nano Structures in Structurally Gradient Epitaxial La0.5Ba0.5CoO3 Films

Highly epitaxial La_0.5Ba_0.5CoO₃ (LBCO) thin films with sharp interface and a thickness of 200 nm were epitaxially grown on (001) SrTiO₃ substrates using pulsed laser deposition. High-resolution transmission electron microscopy and electron diffraction analysis revealed that the films have a triple-layered structure. The first layer, close to the film/substrate interface, has a thickness of ~ 6 nm and is a defect free single crystal disordered cubic structure (a = 3.882 Å) which has a lattice mismatch of − 0.59% with respect to the substrate. The second layer which dominates the film structure has a single crystal disordered cubic structure (a = 3.854 Å) which has a lattice mismatch of − 1.31% with respect to the substrate. The third layer located on the top of the film has a thickness of several nanometers and consists of 112-type ordered tetragonal structure. The cubic structures in the first and second layer have an orientation relationship of (001)_LBCO//(001)_STO and < 100 > _LBCO//< 100 > _STO with respect to the substrate. Self-patterned 3-dimensional nano structures with a dimension range from 2 to 10 nm were formed in the second and third layers. These nano structures were formed by the enclosure of anti-phase boundary planes which are parallel to the {100} of the cubic structure. Epitaxial LBCO thin films with such nano structures are hard ferromagnetic with a large coercive field value and magnetoresistance effect value (~ 24%), and exhibit semiconductor behavior at temperatures < 300 K.     

Highly c-axis oriented AlN layers grown on c-plane sapphire substrates by radio-frequency sputter epitaxy at 1080 °C

Aluminum nitride (AlN) single-crystalline layers were grown on c-plane sapphire substrates by radio-frequency magnetron sputter epitaxy using N₂/Ar mixture ambient gas and 5-N grade Al target. The crystalline structures of the AlN layers depending on substrate temperature and N₂ composition ratio in ambient gas, were predominantly studied. The crystalline quality of the AlN layer was improved by elevating substrate temperature, and the full-widths at half-maximum (FWHMs) of X-ray rocking curves (XRC) for both symmetric and asymmetric planes of AlN layers grown at N₂ composition ratio of around 25%, became low. The FWHMs of XRC for (0002) diffraction of the AlN layers grown at 1080 °C, were less than 20 arcsec. The surface root-mean-square roughness of such highly c-axis oriented AlN layer was determined by atomic force microscopy, and was increased from 0.6 nm to 1.3 nm when AlN layer thickness was varied from 0.15 to 0.7 μm.     

Structural modifications and enhanced Raman scattering from multiwalled carbon nanotubes grown on titanium coated silicon single crystals

Multiwalled carbon nanotubes (MWCNTs) were grown on 10 nm iron (Fe) film by microwave plasma enhanced chemical vapor deposition using titanium (Ti) film as an interlayer. The Ti interlayer of thickness 5 nm-20 nm was sandwiched between Fe and silicon (Si) using thermal evaporation. Enhanced Raman response was observed in MWCNTs with increasing Ti interlayer thickness. This was related with the plasmonic effects occurring at the interface of the CNTs and the metallic support in a three layer system (Ti-Fe-CNTs). The increase in the G mode optical strength is attributed to surface enhanced resonance Raman scattering. Moreover, the increase in the D-mode and 2D-mode intensity is explained on the basis of double resonance effects. The crystallinity in the samples was calculated using I_D/I_G ratio. It was found that that I_D/I_G ratio decreases in three layer system with increasing Ti interlayer thickness as compared to a two layer (Fe-CNTs) system as reported earlier.     

Al and Ti/Al contacts on n-GaN

Al(60 nm) and Ti(40 nm)/Al(160 nm) metal layers have been deposited by thermal evaporation onto n-GaN epitaxial layers grown by metal organic chemical vapour deposition (MOCVD) on a c-plane sapphire substrate. The samples have been annealed at 300, 400, 700 or 900 °C for 10 min in vacuum. The microstructural and electrical properties of the contacts have been investigated by electron microscopy, X-ray diffraction and by current-voltage measurements. As-deposited Al and Ti/Al contacts were rectifying with Schottky barrier heights below 0.35 eV and 0.38 eV, respectively. After heat treatment at 300 °C and 400 °C both contacts exhibited linear current-voltage characteristics. After annealing at 700 °C Al contacts became rectifying with a barrier height of 0.42 eV, while Ti/Al contacts remained nearly linear at the same temperature. The electrical characteristics and XRD analysis indicated that the upper metal in Ti/Al contact diffused in the Ti layer already during deposition. Cross-sectional transmission electron microscopy revealed that in the case of Ti/Al contacts, the continuity of the Ti layers ceased when annealing above 700 °C. X-ray diffractions showed, that a Ti₂N interface phase formed in Ti/Al contacts at 700 and 900 °C, and an AlN interface phase developed in the same contact at 900 °C.     

Hybrid nanostructures of titanium-decorated ZnO nanowires

Hybrid nanostructures of titanium (Ti)-decorated zinc oxide (ZnO) nanowire were synthesized. Various thick Ti films (6 nm, 10 nm, and 20 nm) were coated to form a titanium oxide (TiO) coating layer around ZnO nanowires. Transmission electron microscope analysis was performed to verify the crystallinity and phases of the TiO layers according to the Ti-coating thickness. Under UV illumination, a bare ZnO nanowire showed a conventional n-type conducting performances. With a Ti coating on a ZnO nanowire, it was converted to a p-type conductor due to the existence of electron-captured oxygen molecules. It discusses the fabrication of Ti-decorated ZnO nanowires including the working mechanisms with respect to UV light.     

Electrodeposition of gold thin films from 1-butyl-1-methylpyrrolidinium dicyanamide Au solutions

The electrodeposition of gold from a HAuCl₄.3H₂O solution in 1-butyl-1-methyl-pyrrolidinium dicyanamide is reported in the present paper. A cyclic voltammetry study of the electrochemical behaviour of the plating solution showed that the reduction of gold occurs by a two-step process. Gold thin films were obtained by electrodeposition on nickel substrates under potentiostatic control at a constant potential of − 1 V, for temperatures from 293 to 353 K and deposition times of 1500 and 4500 s. The films prepared at 293 and 333 K consist of 9-15 nm diameter polyhedral particles aggregated in clusters 50-250 nm in diameter. The films deposited at 353 K consist of a quasi-continuous film of nanoparticles covered by nanosized dendrites. This morphology evolves towards a globular structure with increasing deposition time.     

Coercivity variation in exchange-coupled Fe/FePt bilayer with perpendicular magnetization

The soft/hard Fe/FePt film with perpendicular magnetization has been deposited on a glass substrate. The (001) oriented L1₀ FePt film was obtained when annealed by rapid thermal process at 800 °C and a Fe layer was deposited at room temperature with thicknesses of 2 nm to 20 nm. Controlling the Fe layer thickness allowed modification of the hysteresis loops from out-of-plane rigid magnet to in-plane exchange-spring like magnet due to the nanometer scale interface coupling. When the Fe layer thickness increased to 2 nm, the out-of-plane coercivity is reduced to 5.9 kOe but the remanence ratio (0.98) is still high. The Fe (2 nm)/FePt film shows perpendicular magnetization with linear in-plane hysteresis loop. The remanence ratio is reduced to 0.85 when the Fe layer thickness increased to 5 nm. When the Fe layer thickness was varied up to 10-20 nm, the in-plane hysteresis loop shows exchange-spring like behavior with two-step magnetization reversal processes. The films with perpendicular coercivity were moderated by the thickness of soft magnetic layer.     

Textured strontium titanate layers on platinum by atomic layer deposition

Formation of textured strontium titanate (STO) layers with large lateral grain size (0.2-1 μm) and low X-ray reflectivity roughness (~ 1.36 nm) on Pt electrodes by industry proven atomic layer deposition (ALD) method is demonstrated. Sr(t-Bu₃Cp)₂, Ti(OMe)₄ and O₃ precursors at 250 °C were used to deposit Sr rich STO on Pt/Ti/SiO₂/Si ∅200 mm substrates. After crystallization post deposition annealing at 600 °C in air, most of the STO grains showed a preferential orientation of the {001} plane parallel to the substrate surface, although other orientations were also present. Cross sectional and plan view transmission electron microscopy and electron diffraction analysis revealed more than an order of magnitude larger lateral grain sizes for the STO compared to the underlying multicrystalline {111} oriented platinum electrode. The combination of platinum bottom electrodes with ALD STO(O₃) shows a promising path towards the formation of single oriented STO film.     

Structural and mechanical properties of titanium and titanium diboride monolayers and Ti/TiB2 multilayers

Nano-multilayers represent a new class of engineering materials that are made up of alternating nanometer scale layers of two different components. In the present work a titanium (Ti) monolayer was combined with titanium diboride (TiB₂) to form a Ti/TiB₂ nano-multilayer. Designed experimental parameters enabled an evaluation of the effects of direct current bias voltage (U_b) and bilayer thickness (Λ) during multilayer deposition on the mechanical properties of reactively sputtered Ti/TiB₂ multilayer films. Their nanostructures and mechanical properties were characterized and analyzed using X-ray photoelectron spectroscopy (XPS), low-angle and high-angle X-ray diffraction (XRD), plan-view and cross-sectional high-resolution transmission electron microscopy (HRTEM), and microindentation measurements. Under the optimal bias voltage of U_b = − 60 V, it was found that Λ (varied from 1.1 to 9.8 nm) was the most important factor which dominated the nanostructure and hardness. The hardness values obtained varied from 12 GPa for Ti and 15 GPa for TiB₂ monolayers, up to 33 GPa for the hardest Ti/TiB₂ multilayer at Λ = 1.9 nm. The observed hardness enhancement correlated to the layer thickness, followed a relation similar to the Hall-Petch strengthening dependence, with a generalized power of ∼ 0.6. In addition, the structural barriers between two materials (hcp Ti/amorphous TiB₂) and stress relaxation at interfaces within multilayer films resulted in a reduction of crack propagation and high-hardness.     

Deposition of c-axis orientation aluminum nitride films on flexible polymer substrates by reactive direct-current magnetron sputtering

Aluminum nitride (AlN) piezoelectric thin films with c-axis crystal orientation on polymer substrates can potentially be used for development of flexible electronics and lab-on-chip systems. In this study, we investigated the effects of deposition parameters on the crystal structure of AlN thin films on polymer substrates deposited by reactive direct-current magnetron sputtering. The results show that low sputtering pressure as well as optimized N₂/Ar flow ratio and sputtering power is beneficial for AlN (002) orientation and can produce a highly (002) oriented columnar structure on polymer substrates. High sputtering power and low N₂/Ar flow ratio increase the deposition rate. In addition, the thickness of Al underlayer also has a strong influence on the film crystallography. The optimal deposition parameters in our experiments are: deposition pressure 0.38 Pa, N₂/Ar flow ratio 2:3, sputtering power 414 W, and thickness of Al underlayer less than 100 nm.     

Crystallization of amorphous AlN and superhardness effect in VC/AlN nanomultilayers

VC/AlN nanomultilayers with various AlN layer thicknesses have been prepared by multi-target magnetron sputtering. Microstructure evolution and mechanical properties of the multilayers have been investigated. Under the “template effect” of cubic VC, as-deposited amorphous AlN has been crystallized to cubic structure with AlN layer thickness < 1 nm, correspondingly the multilayers exhibit coherent growth and obtain significantly enhanced hardness with the maximum of 40.1 GPa. A further increase of AlN layer thickness causes the formation of amorphous AlN, which blocks the coherent growth of the multilayers, resulting in a rapid decline of hardness.     

Titanium diffusion in gold thin films

In the present study, diffusion phenomena in titanium/gold (Ti/Au) thin films occurring at temperatures ranging between 200 and 400 °C are investigated.The motivation is twofold: the first objective is to characterize Ti diffusion into Au layer as an effect of different heat-treatments. The second goal is to prove that the implementation of a thin titanium nitride (TiN) layer between Ti and Au can remarkably reduce Ti diffusion.It is observed that Ti atoms can fully diffuse through polycrystalline Au thin films (260 nm thick) already at temperatures as a low as 250 °C. Starting from secondary ion mass spectroscopy data, the overall diffusion activation energy ΔE = 0.66 eV and the corresponding pre-exponential factor D₀ = 5 × 10^− 11 cm²/s are determined. As for the grain boundary diffusivity, both the activation energy range 0.54 < ΔE_gb < 0.66 eV and the pre-exponential factor s₀D_gb0 = 1.14 × 10^− 8 cm²/s are obtained. Finally, it is observed that the insertion of a thin TiN layer (40 nm) between gold and titanium acts as an effective diffusion barrier up to 400 °C.     

Application of plasma polymerized siloxane films for the corrosion protection of titanium alloy

Organosilicon film and SiO_x-like film are deposited on titanium alloy (Ti6Al4V) surfaces by atmospheric pressure (~ 10⁵ Pa) dielectric barrier discharge to improve its corrosion resistance in Hanks solution. Hexamethyldisiloxane (HMDSO) is used to be the chemical precursor. The organosilicon film deposited in Ar/HMDSO system has high growth rate (75 nm/min) and low surface roughness (3 nm), while the SiO_x-like film deposited in Ar/O₂/HMDSO system has lower growth rate (35 nm/min) and slightly higher surface roughness (9 nm). The potentiodynamic polarization tests show that both the two siloxane films coated Ti6Al4V samples have more positive corrosion potential and one order of magnitude lower corrosion current density than the substrate, indicating the corrosion resistance of Ti6Al4V can be improved by depositing siloxane film on its surface. In particular, as the surface is more compact and cross-linked, the SiO_x-like film has better corrosion resistance than the organosilicon film.     

Biophotofuel cell anode containing self-organized titanium dioxide nanotube array

We made a biophotofuel cell consisting of a titanium dioxide nanotube array photosensitive anode for biomass decomposition, and a low-hydrogen overpotential metal, Pt, as the cathode for hydrogen production. The titanium dioxide nanotubes (TiO₂ NTs) were prepared via electrochemical oxidation of pure Ti in NaF solutions. Scanning electron microscopy was used to analyze the morphology of the nanotubes. The average diameter, wall thickness and length of the as-prepared TiO₂ NTs were 88 ± 16 nm, 10 ± 2 nm and 491 ± 56 nm, respectively. Such dimensions are affected by the NaF concentration and the applied voltage during processing. Higher NaF concentrations result in the formation of longer and thicker nanotubes. The higher the voltage is, the thicker the nanotubes. The photosensitive anode made from the highly ordered TiO₂ NTs has good photo-catalytic property, as can be seen from the test results of ethanol, apple vinegar, sugar and tissue paper decomposition under ultraviolet (UV) radiation. It is concluded that the biophotofuel cell with the TiO₂ nanotube photoanode and a Pt cathode can generate electricity, hydrogen and clean water depending on the pH value and the oxygen presence in the solutions.     

Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration–in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 °C, 800 °C and 900 °C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700 °C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800 °C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700 °C to parabolic law at 900 °C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900 °C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.     

A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B₂ structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti-B-N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B_0.29N_0.46 was found to have a phase composition of 72-79 mol.% nc-(Ti,Al)(N,B)_1 − x+ 21-28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B_0.66N_0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure-property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.     

NH4Cl-assisted low temperature synthesis of anatase TiO2 nanostructures from Ti powder

A simple, low temperature and low cost method, which was based on heating the mixture of Ti and NH₄Cl powders in air at 300 °C, has been developed for the controlled synthesis of anatase TiO₂ nanostructures including irregular nanoparticle aggregates, curved nanowires built up by the oriented attachment of nanoparticles, and nanoplates constructed with nanoparticles. The characterization results from X-ray diffraction and Raman spectra indicated that the as-obtained products were anatase TiO₂. Field emission scanning electron microscope images revealed that the products obtained for 3, 10 and 16 h comprised, in turn, irregular nanoparticle aggregates (8-55 nm), curved nanowires built up by the oriented attachment of nanoparticles (~ 9 nm), and nanoplates constructed with nanoparticles (~ 8 nm).     

The estimation of corrosion behaviour of ZrTi binary alloys for dental applications using electrochemical techniques

Titanium and zirconium are in the same group in the periodic table of elements and are known to have similar physical and chemical properties. Both Ti and Zr usually have their surfaces covered by a thin oxide film spontaneously formed in air. However, the cytotoxicity of ZrO₂ is lower than that of TiO₂ rutile. Treatments with fluoride are known as the main methods to prevent plaque formation and dental caries. The corrosion behaviour of ZrTi alloys with Ti contents of 5, 25 and 45 wt.% and cp-Ti was investigated for dental applications. All samples were tested by linear potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) performed in artificial saliva with different pH levels (5.6 and 3.4) and different fluoride (1000 ppm F⁻) and albumin protein (0.6%) contents. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology of the test materials after linear potentiodynamic polarisation. The corrosion current densities for the ZrTi alloys increased with the titanium content. The Zr5Ti and Zr25Ti alloys were susceptible to localised corrosion. The role that Ti plays as an alloying element is that of increasing the resistance of ZrTi alloy to localised corrosion. The presence of 0.6% albumin protein in fluoridated acidified artificial saliva with 1000 ppm F⁻ could protect the cp-Ti and ZrTi alloys from attack by fluoride ions.