Effect of Vacuum Heat Treatment on the Microstructure and Tribological Property of Ti–6Al–4V Alloy with Cu Coating

The effect of vacuum heat treatment on the interface microstructure and tribological property of Cu-coated Ti – 6Al – 4V alloy is investigated herein. After the vacuum heat treatment process, a diffusion layer is formed at the interface between the Cu coating and the Ti – 6Al – 4V substrate. The formed intermetallic compounds at the interface between the Ti – 6Al – 4V substrate and Cu coating are CuTi₂, CuTi, Cu₄Ti₃, and β-Cu₄Ti. The activation energy of intermetallic compound growth in the diffusion zone of Cu-coated Ti – 6Al – 4V is 126.0 kJ mol⁻¹, and the pre-exponential factor is 0.1 m² s⁻¹. The tribological properties of the Cu-coated Ti – 6Al – 4V alloy are best when subjected to diffusion treatment at 700 °C for 300 min, with weight loss reduced by 58.2% compared to the Ti – 6Al – 4V alloy. The wear resistance of the Ti – 6Al – 4V alloy can be enhanced by Cu coating and vacuum diffusion heat treatment, and the formation of the Cu – Ti intermetallic compound contributes to this improvement. These findings offer new insights for further advancements in the tribological properties of titanium alloys.     

TiO2–Cu photocatalysts: a study on the long- and short-range chemical environment of the dopant

In this study, the short- and long-range chemical environments of Cu dopant in TiO₂ photocatalyst have been investigated. The Cu-doped and undoped TiO₂ specimens were prepared by the sol–gel approach employing CuSO₄·5H₂O and Ti(O-iPr)₄ precursors and subjecting the dried gels to thermal treatment at 400 and 500 °C. The photocatalytic activity, investigated by methylene blue degradation under sunlight irradiation, showed a significantly higher efficiency of Cu-doped samples than that of pure TiO₂. The X-ray diffraction results showed the presence of anatase phase for samples prepared at 400 and 500 °C. No crystalline CuSO₄ phase was detected below 500 °C. It was also found that doping decreases the crystallite size in the (004) and (101) directions. Infrared spectroscopy results indicated that the chemical environment of sulfate changes as a function of thermal treatment, and UV–vis spectra showed that the band gap decreases with thermal treatment and Cu doping, showing the lowest value for the 400 °C sample. X-ray absorption fine structure measurements and analysis refinements revealed that even after thermal treatment and photocatalytic assays, the Cu²⁺ local order is similar to that of CuSO₄, containing, however, oxygen vacancies. X-ray photoelectron spectroscopy data, limited to the near surface region of the catalyst, evidenced, besides CuSO₄, the presence of Cu¹⁺ and CuO phases, indicating the active role of Cu in the TiO₂ lattice.     

Fabrication mechanism of nanostructured HA/TNTs biomedical coatings: an improvement in nanomechanical and in vitro biological responses

In this paper, a mechanism for fabrication of nanostructured hydroxyapatite coating on TiO₂ nanotubes is presented. Also, the physical, biological, and nanomechanical properties of the anodized Ti6Al4V alloy consisting TiO₂ nanotubes, electrodeposited hydroxyapatite, and the hydroxyapatite/TiO₂ nanotubes double layer coating on Ti6Al4V alloy implants are compared. Mean cell viability of the samples being 84.63?% for uncoated plate, 91.53?% for electrodeposited hydroxyapatite, and 94.98?% for hydroxyapatite/TiO₂ nanotubes coated sample were in the acceptable range. Merely anodized prototype had the highest biocompatibility of 110?% with respect to the control sample. Bonding strength of hydroxyapatite deposit to the substrate increased from 12?±?2?MPa to 25.4?±?2?MPa using intermediate TiO₂ nanotubes layer. Hardness and elastic modulus of the anodized surface were 956?MPa and 64.7?GPa, respectively. The corresponding values for hydroxyapatite deposit were approximately measured 44.3?MPa and 0.66?GPa, respectively, while the average obtained values for hardness (159.3?MPa) and elastic modulus (2.25?GPa) of the hydroxyapatite/TiO₂ nanotubes double coating improved more than 30?% of the pure hydroxyapatite deposit. Friction coefficient (ξ) of the anodized surface was 0.32?±?0.02. The calculated friction coefficient enhanced from 0.65?±?0.04 for sole hydroxyapatite layer to the 0.46?±?0.02 for hydroxyapatite/TiO₂ nanotubes due to presence of nanotubular TiO₂ intermediate layer.     

Influence of Coating Parameter and Sintering Atmosphere on the Corrosion Resistance Behavior of Electrophoretically Deposited Composite Coatings

The purpose of this study is to synthesize and characterize nanosized titania (TiO₂), zinc oxide (ZnO), and its composite coating on Ti–6Al–4V to enhance its corrosion protection behavior in Ringer's solution. Nanosized powders of TiO₂ and ZnO was characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), and scanning electron microscopy - energy dispersive atomic spectroscopy (SEM-EDAX) analysis. As a result of antibacterial activity, both ZnO and TiO₂/ZnO have produce remarkable inhibition zone on Escherichia coli. The antibacterial activity of composites are due to the combined effect of ZnO on TiO₂. The adherence and surface uniformity of TiO₂/ZnO composite film on titanium implant was examined by optical microscopy and Vickers microhardness test. Corrosion resistant behavior of the coating on titanium implant was investigated by tafel polarization and impedance analysis. The composite coatings on Ti–6Al–4V have produced improved corrosion resistance with a pronounced shift in the anodic corrosion potential (E_corr) with a corresponding less corrosion current density (I_corr) compared to monophase coating. Similar results have been obtained for impedance analysis which indicated a reduction in double layer capacitance (C_dl) and with enhancement in charge transfer resistance (R_ct). These observations suggest improved corrosion resistance property of TiO₂/ZnO composite coating on Ti–6Al–4V.     

Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys

An antibacterial and bioactive titanium (Ti)-based material was developed for use as a bone substitute under load-bearing conditions. As previously reported, Ti metal was successively subjected to NaOH, CaCl₂, heat, and water treatments to form a calcium-deficient calcium titanate layer on its surface. When placed in a simulated body fluid (SBF), this bioactive Ti formed an apatite layer on its surface and tightly bonded to bones in the body. To address concerns regarding deep infection during orthopedic surgery, Ag⁺ ions were incorporated on the surface of this bioactive Ti metal to impart antibacterial properties. Ti metal was first soaked in a 5 M NaOH solution to form a 1 μm-thick sodium hydrogen titanate layer on the surface and then in a 100 mM CaCl₂ solution to form a calcium hydrogen titanate layer via replacement of the Na⁺ ions with Ca²⁺ ions. The Ti material was subsequently heated at 600 °C for 1 h to transform the calcium hydrogen titanate into calcium titanate. This heat-treated titanium metal was then soaked in 0.01–10 mM AgNO₃ solutions at 80 °C for 24 h. As a result, 0.1–0.82 at.% Ag⁺ ions and a small amount of H₃O⁺ ions were incorporated into the surface calcium titanate layers. The resultant products formed apatite on their surface in an SBF, released 0.35–3.24 ppm Ag⁺ ion into the fetal bovine serum within 24 h, and exhibited a strong antibacterial effect against Staphylococcus aureus. These results suggest that the present Ti metals should exhibit strong antibacterial properties in the living body in addition to tightly bonding to the surrounding bone through the apatite layer that forms on their surfaces in the body.     

An extended spectrum bactericidal titanium dioxide (TiO<Subscript>2</Subscript>) coating for metallic implants: in vitro effectiveness against MRSA and mechanical properties

Implant infections remain feared and severe complications after total joint arthroplasty. The incidence of multi-resistant pathogens, causing such infections, is rising continuously, and orthopaedic surgeons are confronted with an ever-changing resistance pattern. Anti-infectious surface coatings aim for a high local effective concentration and a low systemic toxicity at the same time. Antibacterial efficacy and biomechanical stability of a novel broad-spectrum anti-infectious coating is assessed in the present study. Antibacterial efficacy of a sol–gel derived titanium dioxide (TiO₂) coating for metal implants with and without integrated copper ions as antibiotic agent was assessed against methicillin resistant Staphylococcus aureus (MRSA 27065). Both bacterial surface adhesion and growth of planktonic bacteria were assessed with bare and various TiO₂-coated Ti6Al4V metal discs. Furthermore, bonding strength of the TiO₂ surface coating, using standard testing procedures, as well as surface roughness were determined. We found a significant reduction of the bacterial growth rate for the coatings with integrated copper ions, with highest reduction rates observed for a fourfold copper TiO₂-coating. Pure TiO₂ without integrated copper ions did not reduce bacterial growth compared to uncoated Ti6Al4V. The coating was not detached from the substrate by standard adhesive failure testing, which indicated an excellent durability of the implant coating. The TiO₂ coating with integrated copper ions could offer a new strategy for preventing implant-associated infections, with antibacterial properties not only against the most common bacteria causing implant infections but also against multiresistant strains such as MRSA.     

Reduced graphene oxide/Cu<Subscript>2</Subscript>O nanostructure composite films as an effective and stable hydrogen evolution photocathode for water splitting

An efficient photocathode consisting of reduced graphene oxide/Cu₂O/Cu (rGO/Cu₂O/Cu) has been successfully prepared in this work via a facile two step method, consisting of chemical oxidation of a copper foil in alkaline solution using (NH₄)₂S₂O₈ as the oxidizing agent, dipping the prepared samples in graphene oxide (GO) solution and calcination at vacuum to form a rGO layer onto Cu₂O/Cu photocathode, which acts as a protective layer. The products were composed of a thin Cu₂O layer topped with a thin rGO film as the protective coating. The chemical composition and rGO amount in the composite materials were easily controlled by changing the immersion time to enhance PEC performance. UV–Vis spectroscopy, Raman spectroscopy, XRD, SEM, TEM and FTIR spectroscopy were used in the optical and morphological characterization of the graphene oxide and prepared photocathodes. Distinct patches of GO film are formed on the Cu(OH)₂ nanostructure surface, as shown by SEM results. Linear sweep voltammetry and chronoamperometry analysis have been applied in the photoelectrochemical characterizations in the dark and under illumination conditions. Photocurrent density provided by rGO/Cu₂O/Cu photocathode ??2.54 mA cm^??2 is three times greater than that of bare Cu₂O/Cu photocathode ??0.82 mA cm^??2 at 0 V vs. RHE under illumination. Low photostability of 42% is exhibited by bare Cu₂O/Cu photocathode after 200 s irradiation whereas rGO/Cu₂O/Cu photocathode shows approximately 98% of the initial photocurrent density. Therefore, a strategy has been developed in this work for the synthesis of this new photocathode using Cu₂O/Cu as an effective photocathode for photoelectrochemical (PEC) water splitting.     

Synthesis of novel Cu doped anatase TiO<Subscript>2</Subscript> catalysts and assessment of the influence of Nb concentration on the photocatalytic and electrochemical properties

In the present study, Cu doped (Ti_0.8Cu_xO_2?x/2) and (Cu, Nb) co-doped (Ti_0.8Cu_x?y Nb_yO_2?(x?y/2+y)) TiO₂ photocatalysts were fabricated by sol–gel method. The catalysts were polycrystalline in nature with preferential orientation along (101) plane answering to anatase phase of TiO₂. Higher Nb concentration results in the formation of secondary phase (Nb₂O₅). A decrease in average crystallite size was noticed with the addition of Nb concentration in Cu doped TiO₂ photocatalyst. The formation of anatase phase was also fixed by Raman spectra. The TEM photograph confirmed the co-doped TiO₂ photocatalyst in nanometer range of about 15 nm and the particles were in hexagonal shape. The doping of Nb⁵⁺ ions inspired a shift in the absorption threshold towards the visible spectral range (red shift) compared to Cu doped TiO₂ catalyst. The photocatalysts have direct bandgaps of 3.253 to 2.974 eV. Semiconducting properties were investigated through electrochemical impedance spectroscopy. The results indicate that the presence of Nb⁵⁺ ions into Cu doped TiO₂ has enhanced the efficiency of electrochemical conductivity. Photocatalytic performance was assessed from the sample degradation by illuminating methylene blue dye under visible light exposure. It is found that TCN3 photocatalyst bleaches MB much faster than all others. Also it exhibits great improvement of photocatalytic activity (96.86%) within 120 min. The photocatalytic degradation process is explained using the pseudo first order kinetics and it fits well with higher correlation coefficient. All these analyses elucidate that the incorporation of Nb⁵⁺ ions might tune the structural, optical, electrochemical and phocatalytic properties of Cu doped TiO₂ photocatalysts.     

Optimization of annealing treatment and comprehensive properties of Cu-containing Ti6Al4V-xCu alloys

The Ti6Al4V-Cu alloy was reported to show good antibacterial properties, which was promising to reduce the hazard of the bacterial infection problem. For the purpose of preparing Ti6Al4V-Cu alloy with satisfied comprehensive properties, it’s important to study the heat treatment and the appropriate Cu content of the alloy. In this study, high Cu content Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were prepared, and firstly the annealing heat treatments were optimized in the α+β+Ti₂Cu triple phase region to obtain satisfied tensile mechanical properties. Then the effect of Cu content on the tribological property, corrosion resistance, antibacterial activity and cytotoxicity of the Ti6Al4V-xCu alloys were systematically studied to obtain the appropriate Cu content. The results showed that the optimal annealing temperatures for Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were 720, 740 and 760 °C, respectively, which was resulted from the proper volume fractions of α, β and Ti₂Cu phases in the microstructure. The additions of 4.5 wt% and 6 wt% Cu into the medical Ti6Al4V alloy could enhance the wear resistance and corrosion resistance of the alloy, but the addition of 7.5 wt% Cu showed an opposite effect. With the increase of the Cu content, the antibacterial property was enhanced due to the increased volume fraction of Ti₂Cu phase in the microstructure, but when the Cu content was increased to 7.5 wt%, cytotoxicity was presented. A medium Cu content of 6 wt%, with annealing temperature of 740 °C make the alloy possesses the best comprehensive properties of tensile properties, wear resistance, corrosion resistance, antibacterial property and biocompatibility, which is promising for future medical applications.     

Antibacterial efficacy,corrosion resistance,and cytotoxicity studies of copper-substituted carbonated hydroxyapatite coating on titanium substrate

This work elucidated the antibacterial efficacy, corrosion resistance, and cytotoxicity of electroplated copper-substituted hydroxyapatite (CuHAP) coating on titanium (Ti). The fabricated CuHAP coatings were characterized by scanning electron microscopy, energy-dispersive X-ray analysis spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction studies. The CuHAP coating had needle-like apatite crystals, the doping of Cu²⁺ into HAP reduced porosity, and the coating became denser. The CuHAP crystals were carbonated with a few of Cu²⁺ incorporation (about 0.80 wt%). The Cu²⁺ ions were homogenously deposited into HAP films. Potentiodynamic polarisation test revealed that the CuHAP coating provided good barrier characteristics and achieved superior corrosion protection for Ti substrates. The in vitro antibacterial activity of as-prepared CuHAP coating was evaluated against Escherichia coli and was found to be effectively high against bacterial colonization. Bioactivity test conducted by soaking the coatings in simulated body fluid demonstrated that CuHAP coating can quickly induce bone-like apatite nucleation and growth. In vitro biocompatibility tests, MTT, were employed to assess the cytotoxicity of CuHAP coating with osteoblast-like MC3T3-E1 cells. The obtained HAP coating doped with a low content of Cu²⁺ exhibited good cytocompatibility and had no toxicity toward MC3T3-E1.     

Enhanced photovoltaic performance of a dye sensitized solar cell with Cu/N Co-doped TiO<Subscript>2</Subscript> nanoparticles

Pure and Copper/Nitrogen (Cu/N)-codoped TiO₂ photoanodes with various Cu concentrations are prepared via sol–gel route for the photoanode application in dye-sensitized solar cells (DSSCs). All the prepared samples are characterized by X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), UV–Vis spectroscopy (UV–VIS) and Electrochemical Impedance Spectroscopy (EIS). Addition of suitable amount of Cu and N content in TiO₂ can alter its optical and electrical properties by extending absorption in the visible region and band gap reduction. The results show that some of the Ti sites are replaced by Cu atoms while O sites are occupied by N atoms. Upon adequate addition of Cu/N could lead to smaller particle size, higher specific surface area, increased dye adsorption and retarded charge carrier recombination. A significant improvement in the power conversion efficiency is observed in case of optimized 0.3 mol% Cu/N-doped TiO₂ nanoparticles (NPs) based DSSC. This optimized 0.3 mol% Cu/N-doped photoanode accomplished a best power conversion efficiency of 11.70% with a short circuit current density of 23.41 mA cm^?2 which is 41% higher than that of the pure TiO₂ photoanode based DSSC (6.82%).     

In vivo examination of the local inflammatory response after implantation of Ti6Al4V samples with a combined low-temperature plasma treatment using pulsed magnetron sputtering of copper and plasma-polymerized ethylenediamine

Copper (Cu) could serve as antibacterial coating for Ti6Al4V implants. An additional cell-adhesive layer might compensate Cu cytotoxicity. This study aimed at in vitro and in vivo evaluation of low-temperature plasma treatment of Ti6Al4V plates with Ti/Cu magnetron sputtering (Ti6Al4V–Ti/Cu), plasma-polymerized ethylenediamine (Ti6Al4V–PPEDA), or both (Ti6Al4V–Ti/Cu–PPEDA). Ti6Al4V–Ti/Cu and Ti6Al4V–Ti/Cu–PPEDA had comparable in vitro Cu release and antibacterial effectiveness. Following intramuscular implantation of Ti6Al4V–Ti/Cu, Ti6Al4V–PPEDA, Ti6Al4V–Ti/Cu–PPEDA and Ti6Al4V controls for 7, 14 and 56 days with 8 rats/day, peri-implant tissue was immunohistochemically examined for different inflammatory cells. Ti6Al4V–PPEDA had more mast cells and NK cells than Ti6Al4V, and more tissue macrophages, T lymphocytes, mast cells and NK cells than Ti6Al4V–Ti/Cu–PPEDA. Ti6Al4V–Ti/Cu had more mast cells than Ti6Al4V and Ti6Al4V–Ti/Cu–PPEDA. Results indicate that PPEDA-mediated cell adhesion counteracted Cu cytotoxicity. Ti6Al4V–Ti/Cu–PPEDA differed from Ti6Al4V only for mast cells on day 56. Altogether, implants with both plasma treatments had antibacterial properties and did not increase inflammatory reactions.     

Sol–gel preparation and properties of Ag–TiO2 films on surface roughened Ti–6Al–4V alloy

Ag–TiO₂ films (Ag/Ti?=?3·3, 9·1 at-%) were sol–gel coated on Ti–6Al–4V alloy that had been surface roughened by the NaOH–HCl treatment for antibacterial applications. Scanning electron microscopy observation showed that pore size of the surface layer of NaOH–HCl treated Ti–6Al–4V alloy increased with the NaOH concentration. Ag–TiO₂ films on the surface roughened substrate were adherent and crack-free. X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses indicated that Ag existed in metallic state, and the films completely covered the roughened substrate. X-ray diffraction peaks of the substrate and anatase TiO₂ were detected. The Ag–TiO₂ films on the roughened substrate exhibited good adhesion quality and high cohesion strength in the indentation test. The potentiodynamic polarisation test showed that the TiO₂ and Ag–TiO₂ films improved corrosion resistance of the substrate.     

Growth and properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by multiple metallic layer stacks as a function of sulfurization time

In this paper, we report the two stage growth of Cu₂ZnSnS₄ (CZTS) thin films as a function of sulfurization time. First, magnetron sputtered metallic precursors were deposited sequentially (Zn/Cu/Sn/Cu) over rotating glass substrates held at 230?°C. Later, the sputtered precursors were heat treated at 500?°C in the ambiance of sulfur for various time durations in the range, 10–120 min. The sulfur treated samples were examined using various analytical tools to understand the role of sulfurization time on the CZTS growth and properties. From composition and structural analysis, Zn/Cu/Sn/Cu precursors sulfurized for shorter duration (10 and 20 min) revealed severe deficiency of sulfur that resulted in several metallic, bi-metallic and metal sulfide phases. With the increase of sulfurization time to 30 min, sulfur incorporation was enhanced and reached stoichiometric ratio (~50% S) for CZTS growth, however, samples were poorly crystalline in nature and consisted of prominent Cu_2?xS phase as well. The Zn/Cu/Sn/Cu precursors sulfurized for 60 min exhibited prominent CZTS phase without Cu_2?xS phase. Further, rise in sulfurization time to 120 min enabled drastic improvement in crystallinity of CZTS phase. Raman mapping over 60 µm × 60 µm for these films confirmed the homogeneous phase growth of CZTS. XPS study revealed the oxidation states of Cu¹⁺, Zn²⁺, Sn⁴⁺ and S^2? in CZTS films. The optimized films showed high absorption coefficient of 10⁵ cm^?1 with an optical band gap of 1.51 eV. These films showed leaf like grain morphology with high mobility and low resistivity of 18.2 cm²/V-s and 0.7 Ω-cm, respectively.     

Effects of Ti and TiO2 on Combustion Synthesis of (Ti,V)2AlC/Al2O3 Solid Solution Composites

(Ti,V)₂AlC/Al₂O₃ solid solution composites were prepared by solid state combustion simultaneously incorporating reduction reactions of V₂O₅ and TiO₂/V₂O₅ with aluminum. Two reaction systems composed of Ti–V₂O₅–Al–Al₄C₃ and TiO₂–V₂O₅–Al–Al₄C₃ powder mixtures were studied. Combustion exothermicity was enhanced by increasing V₂O₅ and Al, which not only caused an increase in the combustion temperature and reaction front velocity, but also facilitated evolution of the (Ti,V)₂AlC phase. Between two reaction systems, the Ti-containing samples were more energetic and produced (Ti_1–xV_x)₂AlC/Al₂O₃ composites with x = 0.2–0.8. The degree of element substitution was reduced for the samples adopting TiO₂, which yielded Al₂O₃-added (Ti_1–yV_y)₂AlC with y = 0.4–0.8.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Ionic liquid-assisted hydrothermal synthesis of TiO2 nanoparticles and its application in photocatalysis

Anatase TiO₂ nanoparticles have been successfully synthesized at 130 °C for 2 days via ionic liquid-assisted hydrothermal method. The obtained products are characterized using various techniques. The X-ray diffraction data reveal that the nanoparticles are anatase TiO₂. FTIR spectrum shows that the presence of ionic liquid and indicates Ti–O–Ti peak at around 398 cm^?1, and the bands at 1500 and 1600 cm^?1 indicates C–H in-plane vibrations and stretching of imidazolium ring. Raman spectroscopy show bands at 142, 393, 513, and 636 cm^?1 reveal crystalline anatase phase. UV–Vis spectroscopy shows the λ _max at 355 nm corresponding to a band gap of 3.49 eV. TEM images reveal that the average diameters of anatase TiO₂ nanoparticles are in the range 50–100 nm. Anatase TiO₂ exhibited excellent photocatalysis for the degradation of organic dye.     

Cu doping effect on the resistive switching behaviors of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> thin films

Spin-coated Cu_xCo_1?xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, and 0.8) thin films were prepared on Pt/TiO₂/SiO₂/Si substrates. Pt/Cu_xCo_1?xFe₂O₄/Pt structures were fabricated to investigate the effect of Cu doping concentration on the resistive switching behaviors. Structural and morphology characterizations revealed that Cu doping improved the crystallization of the thin films as compared to undoped CoFe₂O₄. Current–voltage characterization showed that all Cu_xCo_1?xFe₂O₄ thin films showed unipolar resistance switching, but the distribution range of the set voltage, reset voltage, and resistances were much reduced by Cu doping. Clear improvement in the stability of these parameters started to appear with x = 0.4, and the optimized performance was observed in the Pt/Cu_0.6Co_0.4Fe₂O₄/Pt structure. The improved stability of the switching parameters was attributed to the enhancement of hopping process between the Fe ions and the Cu ions in the spinel lattice. Our results indicated that appropriate adjustment of the doping elements in oxides can be a feasible approach in achieving stable resistance switching memory devices.     

Preparation of TiO2 thick film by laser chemical vapor deposition method

A TiO₂ film was prepared on Pt/Ti/SiO₂/Si substrate by a laser chemical vapor deposition method. The rutile TiO₂ film with pyramidal grains and columnar cross-section was obtained at a high deposition rate (R _dep = 11.4 μm h^?1). At 300 K and 1 MHz, the dielectric constant (ε _r) and loss (tanδ) of the TiO₂ film were about 73.0 and 0.0069, respectively. The electrical properties of TiO₂ film were investigated by ac impedance spectroscopy over ranges of temperature (300–873 K) and frequency (10²–10⁷ Hz). The Cole–Cole plots between real and imaginary parts of the impedance (Z′ and Z′′) in the above frequency and temperature range suggested the presence of two relaxation regimes that were attributed to grain and grain boundary responses. The ionic conduction in the rutile TiO₂ film was dominated by the oxygen vacancies.     

In-Situ TiB2–TiC–Al2O3 Composite Coating on Aluminum by Laser Surface Modification

To improve the surface hardness of aluminum, in-situ TiB₂–TiC–Al₂O₃ composite coating was deposited on it by pre-placed laser coating process using precursor mixture of (TiO₂ + B₄C) and (TiO₂ + B₄C + Al). Pulsed Nd:YAG laser was used to produce coating track by scanning a laser beam in overlapped condition. Multiple tracks again overlapped to get a wider coating area. Phase constituents and microstructure of the deposited coating were studied by XRD and FESEM analysis. Vickers micro-hardness tester was used to measure micro-hardness of the coating. Results indicate that, in appropriate laser processing condition, coating was obtained with metallurgical bonding to aluminum substrate. XRD and microstructure analysis confirms the formation of TiB₂, TiC, and Al₂O₃ in the coating layer through in-situ reaction of reactant powders. Micro-hardness of the coating was found appreciably higher in comparison to the as-received aluminum substrate, due to presence of hard ceramic particles produced during in-situ reaction and their grain refinement for rapid cooling.