Thermal stability and electrical properties of Ag–Ti films and Ti/Ag/Ti films prepared by sputtering

Ag–Ti (100 nm) alloy film, and Ti/Ag (100 nm) double-layer and Ti/Ag (100 nm)/Ti triple-layer films were prepared by rf sputtering to investigate the effect of Ti on suppression of agglomeration of the Ag thin film caused by thermal treatment. Scanning electron microscopy revealed that the Ag–Ti and Ti/Ag/Ti films had high thermal stability. X-ray photoelectron spectroscopy analysis showed that the surfaces of both kinds of films were covered with a TiO₂ layer after annealing, which was considered to be the key factor for improvement of the thermal stability of the films. In addition, scratch tests indicated improvement of the adhesive strength of the Ti/Ag/Ti film to the SiO₂ substrate due to the underlying Ti film layer, which effectively promoted suppression of Ag agglomeration. However, the resistivity of the Ag–Ti films increased abruptly with increasing Ti content due to the impurity scattering effect, and minimum usage of the alloying element was required to achieve low resistivity. In contrast, the Ti/Ag/Ti film exhibited both low resistivity and high thermal stability.     

TiOx/Ag/TiOx multilayer for application as a transparent conductive electrode and heat mirror

Amorphous TiO_x films and Ag layer were deposited by electron-beam evaporation on soda-lime glass at room temperature. The details regarding the structure, surface morphology, and optical properties of the as-prepared TiO_x films were examined by X-ray diffraction, scanning electron microscopy, and ultra-violet (UV) -visible-near-infrared (NIR) spectrometry. The TiO_x films exhibit amorphous phase with an optical band gap of 3.35 eV. The polygrains oriented along the (111) and (200) directions in the Ag films were adopted to supply carriers into the TiO_x film and lower the sheet resistance of the stacked layer. The multilayer exhibited a sufficiently large Ag thickness (>15 nm), low resistance, high UV transmittance, visible transmittance, and high NIR reflection. Dependence of Ag thickness, TiO_x bottom-layer, and TiO_x overlayer on the optical and electrical properties of TiO_x/Ag/TiO_x were explored. A figure of merit (FOM) was used to find an optimal structure for a multilayer with superior conductivity and visible transparency. An FOM of 9.8 × 10^?2 (Ω^?1) at the visible wavelength of 550 nm for a TiO_x/Ag/TiO_x stacked layer with an 18-nm-thick Ag and a 20-nm-thick TiO_x was achieved. The TiO_x/Ag/TiO_x sample annealed at 500 °C 10 min also shows a good thermal stability.     

Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate

The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 °C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO₂ film grew at the interface during annealing in moist air, while a TiO₂ layer diffused into the HA films when directly sputtered at 550 °C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.     

Graphene Wrapped TiO2 Based Catalysts with Enhanced Photocatalytic Activity

Reduced graphene oxide (RGO) wrapped titanium dioxide nanocrystals (TiO₂ NCs@RGO) with oxygen vacancies (Vo) and Ti³⁺ defects have been synthesized by electrostatically wrapping GO around TiO₂ NCs followed by thermal annealing at 400 °C. Transmission electron microscope observations have shown that TiO₂ NCs@RGO has a unique crystalline core/crystalline shell structure, which is different from the original amorphous TiO₂ covered TiO₂ NCs. Raman spectroscopy, X‐ray photoelectron spectroscopy, and electron paramagnetic resonance have demonstrated that Vo‐Ti³⁺ species are more readily formed in TiO₂ NCs@RGO than in TiO₂ NCs. As a result, TiO₂ NCs@RGO exhibits enhanced optical absorption in a wide wavelength range from visible light to near IR and red‐shifted absorption edge. In the photocatalytic degradation reaction of methyl orange, the photodegradation rate constant for TiO₂ NCs@RGO is 2.4 times higher than that of TiO₂ NCs. The enhanced photocatalytic performance can be attributed to the improved charge separation at the interface of TiO₂ NCs and RGO layer and the enhanced optical absorption in visible light region due to the donor levels of the defects such as Vo‐Ti³⁺ species. This work establishes a new method for preparing Vo defect contained TiO₂ catalysts.     

Ba<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript> ferroelectric nanofilms on silicon buffered with a TiO<Subscript>2</Subscript> layer

Polycrystalline, 50- to 70-nm-thick barium strontium titanate films of composition Ba_0.8Sr_0.2TiO₃ have been grown on single-crystal silicon substrates by rf ion-beam sputtering. We have determined their structure and composition and detected impurities at the film/substrate interface in the form of titanium silicide islands. The deposition of a 4- to 6-nm-thick TiO₂ buffer layer onto Si by ion-beam sputtering before ferroelectric film growth is shown to prevent uncontrolled formation of impurities near the interface. The buffered heterostructures possess high thermal stability.     

Optimisation of preparation conditions for Ti nanowires and suitability as an antibacterial material

Ultrafine titanium dioxide (TiO₂) nanowires were synthesised using a hydrothermal method with different volumes of ethylene glycol (EG) and annealing temperatures. It shows that sodium titanate nanowires synthesised using 5 and 10 ml EG, which annealed at 400°C produced TiO₂ nanowires that correspond to a photochemically active phase, which is anatase. The influences of annealing temperatures (400–600°C) on the morphological arrangement of TiO₂ nanowires were evident in the field emission scanning electron microscopy. The annealing temperature of 500°C led to agglomeration, which formed a mixture of TiO₂ nanoparticles and nanowires. High thermal stability of TiO₂ nanowires revealed by thermogravimetric analysis and Fourier transform infrared spectroscopy spectrum showed the presence of the Ti–O–Ti vibrations as evidenced due to TiO₂ lattices. An antibacterial study using TiO₂ nanowires toward Escherichia coli and Klebsiella pneumoniae showed large zones of inhibition that indicated susceptibility of the microbe toward TiO₂. Growth kinetic analysis shows that addition of TiO₂ has reduced optical density (OD) suggesting an inhibition of the growth of bacteria. These results indicate TiO₂ nanowires can be effectively used as an antimicrobial agent against gram‐bacteria. The TiO₂ nanowires could be exploited in the medical, packaging and detergent formulation industries and wastewater treatment.Inspec keywords: nanowires, titanium compounds, antibacterial activity, nanomedicine, semiconductor materials, semiconductor growth, nanofabrication, annealing, liquid phase deposition, field emission scanning electron microscopy, nanoparticles, thermal stability, thermal analysis, Fourier transform infrared spectra, microorganismsOther keywords: optimisation, preparation conditions, antibacterial material, ultrafine titanium dioxide nanowires, hydrothermal method, ethylene glycol, annealing temperatures, sodium titanate nanowires, photochemically active phase, anatase, morphological arrangement, field emission scanning electron microscopy, agglomeration, nanoparticles, thermal stability, thermogravimetric analysis, Fourier transform infrared spectroscopy, vibrations, Escherichia coli, Klebsiella pneumoniae, microbe, growth kinetic analysis, optical density, incubation time, bacterial survivability, colony‐forming units, antimicrobial agent, Gram negative bacteria, Gram positive bacteria, temperature 400 degC to 600 degC, TiO₂      

Effect of high-temperature annealing on solid-state reactions in hydroxyapatite/TiO<Subscript>2</Subscript> films on titanium substrates

Hydroxyapatite (HA) films 0.5 and 1 μm thick with a 0.2-μm TiO₂ underlayer have been grown on titanium by rf magnetron sputtering. After annealing in an argon atmosphere at 900, 950, and 1000°C for 30 and 60 min, the phase composition, elemental composition, and surface morphology of the films have been determined by scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. The surface microstructure of the films is shown to depend on annealing temperature. X-ray microanalysis results indicate that, at HA layer thicknesses of both 1 and 0.5 μm, the Ca/P ratio increases with annealing temperature. In addition, the Ca/P ratio in the films produced under identical conditions depends on the film thickness. X-ray diffraction data indicate the presence of reaction intermediates. A TiO₂ interlayer in the HA/Ti system inhibits titanium oxidation, and the reaction intermediates forming during heat treatment improve the adhesion between the titanium and HA.     

Suppression of Cu agglomeration in the Cu/Ta/Si structure by capping layer

Cu/Ta/Si (100) structures deposited by the non-mass separated ion beam deposition system showed a slight resistivity increase at 650 °C due to a Cu agglomeration. To suppress the Cu agglomeration on the Ta layer, a capping layer was deposited on the Cu/Ta/Si structure using Ta or SiO₂ as a suppressor. In the case of the Ta suppressor, the agglomeration of Cu was observed between two distorted Ta films due to the difference in thermal expansion between the Cu film and the Ta film at high temperature. On the other hand, the SiO₂ layer was found to be suitable as a suppressor, and the Cu agglomeration did not occur even after annealing at 650 °C by the suppression of the Cu diffusion.     

TiOx interlayer characterization for sol–gel derived Pb(Zr, Ti)O3 thin films on titanium foil

Pb(Zr, Ti)O₃ films were prepared on titanium foil using sol–gel processing. The films were of large area, crack-free, uniform, with perovskite structure and exhibiting strong adhesion to the titanium foil substrate. Films and the interface region between the film and the substrate were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and dielectric property measurements. The measurements revealed the formation of a TiO_x layer at the interface between the film and the foil. The thickness of the TiO_x interlayer increases with increasing annealing temperature, and was amorphous when annealed below 600 °C. The dielectric properties of films depend on the thickness of the TiO_x interlayer. Films on Ti foil with dielectric constant of 200–400, dielectric loss <5%, leakage current of <1×10^–7 A cm^–2 at 100 kV cm^–1 and breakdown field strength of 0.6–1.13 MV cm^–1 were demonstrated. The TiO_x interlayer resulted in asymmetric C–V hysterisis behavior attributed to trapped charge in the vicinity of the TiO_x interlayer and to elastic mismatch strain.     

Magnesium metallic interlayer as an oxygen-diffusion-barrier between high-κ dielectric thin films and silicon substrate

The deposition of a thin magnesium metallic interlayer on an Si substrate prior to the deposition of an oxide thin film using rf-sputtering was investigated. The deposition of high-κ HfO₂ thin film was more particularly studied and it was demonstrated that the metallic interlayer acts as an oxygen barrier, preventing the formation of a low-κ layer at the high-κ/Si interface during the deposition. A post-deposition annealing treatment performed on the films induced the diffusion of the metal barrier into the HfO₂ film and allowed obtaining a sharp interface. However, the degree of diffusion depends not only on the interlayer thickness, but also on the thickness of the high-κ film. X-ray photoelectron spectroscopy was used to study the degree of oxidation of the Mg interlayer. High resolution transmission electron microscopy and energy filtered transmission electron microscopy were used to characterize the films and the diffusion of the Mg interlayer into the high-κ film after annealing. In this work we will stress on the engineering of the interface via the diffusion of the Mg interlayer during the growth process and on annealing.     

Diffusion barrier performance of nano-structured and amorphous Ru-Ge diffusion barriers for copper metallization

In the experiment, nano-structured and amorphous ultrathin Ru-Ge interlayers (∼15 nm in thickness) were deposited between Cu(Ru) alloy film and Si substrate via co-sputtering functioning as preventive diffusion barrier layers. After annealing at different temperatures, X-ray diffraction and four-point probe method revealed that the amorphous Ru-Ge layer effectively suppressed the Cu diffusion into Si substrate up to a temperature of at least 873 K; however, it is less than 773 K for the nano-structured Ru-Ge layer. A self-formed amorphous multilayer of Ru(RuO_x)/RuGe_xCu_y could be attained by annealing Cu/Cu(Ru)/Ru-Ge(amorphous)/Si system at a very low temperature (even 473 K). The results proved that the amorphous Ru-Ge system could self-form the multilayer diffusion barrier before the diffusion reaction between Cu and Si and improved the thermal stability of the Cu interconnection significantly.     

Suppression of Cu agglomeration in the Cu/Ta/Si structure by capping layer

Cu/Ta/Si (100) structures deposited by the non-mass separated ion beam deposition system showed a slight resistivity increase at 650 °C due to a Cu agglomeration. To suppress the Cu agglomeration on the Ta layer, a capping layer was deposited on the Cu/Ta/Si structure using Ta or SiO₂ as a suppressor. In the case of the Ta suppressor, the agglomeration of Cu was observed between two distorted Ta films due to the difference in thermal expansion between the Cu filmand the Ta film at high temperature. On the other hand, the SiO₂ layer was found to be suitable as a suppressor, and the Cu agglomeration did not occur even after annealing at 650 °C by the suppression of the Cu diffusion.     

The effect of amorphous silicon capping on titanium during TiSi2 formation by RTA

Thin film reactions of the Ti/(1 0 0)Si structure and the amorphous-Si/Ti/(1 0 0)Si structure are performed by rapid thermal annealing (RTA) in argon at temperatures of 500–800° C. Auger depth profiling shows that the as-deposited titanium film of the Ti/(1 0 0)Si structure and the as-deposited amorphous silicon (a-Si) film of the a-Si/Ti/(1 0 0)Si structure exhibit a roughly exponential oxygen distribution decreasing from the surface when exposed to air. An electronic spectroscopy for chemical analysis (ESCA) shows that the oxygen in the a-Si film forms Si0₂ and the oxygen in the titanium film forms titanium oxide. For the Ti/(1 0 0)Si structure, the oxygen tends to be redistributed uniformly throughout the titanium film near the onset of silicide formation during RTA. As silicide formation progresses, the redistributed oxygen is snowplowed back toward the surface owing to oxygen solubility difference between Ti and TiSi₂. Consequently, the oxygen concentration in the unreacted titanium layer increases. This increased oxygen concentration retards the silicide growth even though there remains an unreacted titanium layer. The oxygen redistribution in the titanium film correlates well with the rapid increases in the sheet resistance near the onset of silicide formation. When a-Si is sputter-deposited sequentially on the titanium film without breaking the vacuum, the oxygen in a-Si is not redistributed during RTA. Thus there is no rapid increase in the sheet resistance, and the saturated sheet resistance is lower than that of Ti/(1 0 0)Si structure. The reason is that the conversion of deposited titanium film into TiSi₂ is made completely because the a-Si film on the titanium film prevents oxygen infiltration into the titanium film.     

Investigation of the microstructure and corrosion performance of a nanostructured titania-containing hybrid silicate film on mild steel

A pre-treatment system consisting of a nanostructured titania interlayer loaded with an inhibitor and a hybrid silicate film deposited on the TiO₂ layer is shown to provide protection against active corrosion of mild steel. A nanostructured TiO₂ interlayer was prepared on the mild steel surface via controllable hydrolysis of titanium alkoxide. To further improve this pre-treatment, the hybrid silicate film was synthesized from tetraethylorthosilicate and 3-glycidoxypropyltrimethoxysilane precursors. The morphology and structure of the titania interlayer and hybrid silicate film were characterized with atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. The corrosion performance of the coatings was examined using electrochemical techniques, including potentiodynamic scanning and electrochemical impedance spectroscopy. The TiO₂ nanostructure calcinated/inhibitor/hybrid silicate system shows enhanced corrosion performance, as confirmed by impedance and polarization measurements.     

Fabrication of micro-patterned TiO2 thin films incorporating Ag nanoparticles

A photosensitive TiO₂ thin film embedded with Ag nanoparticles has been prepared from a Ti(OBu)₄–acetylacetone solution, containing dispersed Ag nanoparticles, by the sol–gel method. UV–visible absorption spectra showed that the thin film obtained has two absorption bands, characteristic of the acetylacetone chelate rings and plasmon resonance from Ag nanoparticles. After the irradiation of UV light, the absorption band from the chelate rings almost disappeared, ascribed to structural changes associated with dissociation of the chelate rings. The thin film after the UV irradiation exhibited a broad absorption band in the IR spectrum, indicating that a Ti–O–Ti network was formed in the thin film. HRTEM and EDX spectra revealed that Ag nanoparticles were present and dispersed in the TiO₂ thin film. Micro-patterns of 50 μm dots have been fabricated by UV irradiation through a corresponding photomask, followed by leaching.     

Visible-light-responsive Ag–Si codoped anatase TiO2 photocatalyst with enhanced thermal stability

To utilize visible light more efficiently and enhance the photocatalytic performance of TiO₂, Ag–Si/TiO₂ photocatalyst was synthesized via a two-step method. The obtained materials were characterized by XRD, Raman, TEM, HRTEM, BET, TG–DTA, XPS, ICP as well as UV–vis DRS. All photocatalyst materials held an anatase phase confirmed by XRD, Raman and HRTEM. The Ag–Si/TiO₂ photocatalysts possessed high thermal stability and the phase transformation was retarded to about 900 °C revealed by XRD and TG–DTA. The Ag–Si/TiO₂ particles synthesized via the nonaqueous method were highly monodispersed and the particles size became smaller compared to the un-doped TiO₂, resulting in the enlargement of surface area. In addition, UV–vis light absorption shifted to visible region after Ag doping. XPS results demonstrated that Si weaved into the matrix of TiO₂ and enriched in the surface layer, while Ag dispersed on the surface of TiO₂ particles. The Ag dopant suppressed the recombination of photogenerated electrons and holes, Si enlarged the surface of photocatalysts. Silver and silicon co-doping improved the visible photocatalytic activity, which was evaluated by Rhodamine B (RhB) degradation. The photocatalytic activity of the obtained Ag–Si/TiO₂ sample was much more higher than those of pure TiO₂ and Ag/TiO₂, reaching the maximum at the Ag and Si content of 0.5 mol% and 20.0 mol%, respectively. The improved visible photocatalytic activity may be attributed to the synergetic effects of codoping by silver and silicon.     

Enhancing the photovoltaic performances of dye-sensitized solar-cells by modifying the TiO2 electrode-sensitized dye interface

Enhanced photovoltaic performances of N719 dye-sensitized solar-cells were achieved by modifying the titanium oxide (TiO₂) electrode-sensitized dye interface. Surface of TiO₂ thin film electrode was coated with a calcium oxide (CaO) or lithium fluoride (LiF) thin layer, respectively, in a thermal deposition chamber. As compared to a cell using a bare TiO₂ nanoparticle (NTP) electrode, the solar energy conversion efficiency (η)? was enhanced by 15.1% and 12.8% for the surface of a NTP electrode coated with CaO and LiF, respectively. Moreover, for the surface of a TiO₂ nanotube electrode respectively coated with CaO and LiF, the efficiency was enhanced by 4.8% and 11.6%. This increase in efficiency is attributed to an increase in the adsorption of N719 dye on the CaO or LiF coated TiO₂ thin film electrodes, and the formation of a potential barrier by a CaO or LiF interlayer at the TiO₂ electrode-sensitized dye interface.     

Synthesis and tuning of ordering and crystallinity of mesoporous titanium dioxide film

Synthesis of well-organized and highly crystalline mesoporous titania (TiO₂) film is demonstrated using triblock copolymer (Pluronic P123) as a structure directing template, through the evaporation induced self-assembly (EISA) process. The issue of thermal and structural stability of a mesoporous TiO₂ film was addressed via optimization of annealing temperature and time. An anatase phase, high crystallinity TiO₂ film with ordered pores was obtained at 430 °C after annealing for 15 min. The synthesized film was crack free with TiO₂ nanoparticle size of 10–15 nm, quasi-hexagonal pore diameter in the range of 8–10 nm and film thickness of ~ 150 nm.     

Finite element method simulation of residual stresses in Al2O3–AISI 304 steel joints

Abstract

Thermal residual stresses are very detrimental to the mechanical resistance of metal–ceramic joints and thin metallic foils acting as stress relieving interlayers have been used to reduce their effect. The present work presents finite element method simulations of the residual stress field in Al₂O₃–AISI 304 steel joints using interlayers. Different interlayer materials (Ti, Ni, Mo, and Cu) were considered, either separately or in combination. Calculations show that among the different interlayer materials considered, Cu and Ti/Cu are most effective in reducing the thermal stresses and that this role is determined mainly by the ductility of the interlayer material. The calculated results were validated by shear tests performed on real joints obtained by diffusion bonding and it was concluded that residual stresses control the mechanical resistance of the joints.     

Ag surfactant effects of TiO2 films prepared by sputter deposition

The surfactant effect of Ag on the thin film structure of TiO₂ by radio frequency magnetron sputtering has been investigated. Comparisons between the atomic force microscopy images revealed that the surface roughness of TiO₂ film mediated by Ag was smaller than that of the TiO₂ film without Ag. The surface segregation effect of Ag was confirmed using X-ray photoelectron spectroscopy. The results of X-ray diffraction revealed that the initial deposition of a 0.4 nm thick Ag surfactant layer onto a Fe buffer layer prior to the deposition of the TiO₂ film reduced the rutile (110) growth and enhanced the anatase (100) growth. It was concluded that Ag was an effective surfactant for changing the thin film structure of TiO₂ on the Fe buffer layer. The photocatalytic effect of the fabricated TiO₂ film was also investigated using the remote oxidation process. TiO₂ films with the Ag surfactant exhibited higher photocatalytic activity than conventionally deposited TiO₂ films.