ZnO thin films prepared on titanium substrate by PLD technique at different substrate temperatures

ZnO thin films were grown by pulsed laser deposition on titanium substrates at different substrate temperatures ranging from 300 to 700 °C. X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS),photoluminescence, and Raman spectroscopy are employed to investigate the change of properties. XRD, XPS, and Raman data showed that the films consisted of TiO₂ at high substrate temperature, which will deteriorate the crystallization quality of ZnO films. The optimum temperature for the growth of ZnO films on the Ti substrate is about 500 °C in this paper. The ZnO films grown on titanium substrate can be used in direct current, microwave, and medical applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparative analysis of the composition, structure, and catalytic activity of the NiO-CuO-TiO2 on Titanium and NiO-CuO-Al2O3 on aluminum composites

The catalytically active oxide structures based on Al and Ti prepared by plasma-electrolytic oxidation (PEO) and additionally modified by impregnation with an aqueous solution of nickel and copper nitrates followed by annealing were studied. The oxide film-metal composites were studied using X-ray diffraction and X-ray spectroscopic analysis, X-ray electron spectroscopy, and electron microscopy. The catalytic activity of the composites in the reaction of CO oxidation was studied. In spite of differences in the elemental composition and morphology, the initial oxide layers on Al and Ti were comparable in terms of activity. Microgranules of size ～ 1 µm and formations from tens to hundreds of nanometers in size were detected on the surface of PEO layers. The modified layers contained crystalline CuO, NiO, and Al₂O₃ or TiO₂ phases. The surface layers of the modified structures about 3 nm in thickness on AMg5 aluminum alloy and VT1-0 titanium had the same elemental composition but exhibited different activity in the reaction of CO oxidation to CO₂.     

Overlayer thickness determination by XPS using the multiline approach

An important analytical application of x‐ray photoelectron spectroscopy is the possibility of determining the overlayer thickness in the nanometer range. The relevant procedure should be based on a realistic theoretical model relating the photoelectron signal intensities, measured for the overlayer and for the substrate, to the overlayer thickness. In the most frequently used procedure, we derive the thickness from the ratio of intensity measured for the overlayer and intensity measured for the substrate. We may expect that the resulting thickness depends on the pair of intensities selected for analysis. This is due to the fact that each calculated intensity has a certain systematic error associated with accuracy of parameters used in calculations. We consider here a possibility of using more than two intensities, for a given element, in the procedure of thickness determination. In this way, we expect that the analysis is more accurate due to the fact that the systematic errors are averaged. In the past, similar approach has been successfully applied to the procedure of surface composition determination. To test the proposed multiline approach, the Au 4f, Ni 2p, and Ni 3p intensities were measured for a series of Ni overlayers deposited on the Au substrate. It has been found that the proposed approach well performs at relatively large overlayer thicknesses. It provides values that are averages of values obtained from other methods. At small overlayer thicknesses, we observe a scatter of thicknesses obtained from different methods which can be due to the discontinuity of the overlayer. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of bath temperatures on the wettability of copper films surface prepared by electroless plating method on beech wood

Copper films were coated on beech wood substrates by electroless plating method. The influence of bath temperature on the copper films properties was studied by varying the bath temperatures 25, 35, 45 and 55 °C. Scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD) pattern, X‐ray photoelectron spectroscopy (XPS), micro Raman spectroscopy and contact angle measurements were used to both characterize the physical and chemical copper films properties and understand the influence of bath temperature on the wettability of copper surface. In our studies, we have found that the gained copper mass significantly increased at 55 °C. The crystalline nature of the coated copper was confirmed by XRD. The presence of Cu₂O and CuO was observed by XPS and micro Raman techniques, which confirms the oxidization of the coated copper surface. Also these characterization techniques have shown the big influence of bath temperature on the morphology, grain size, chemical composition and the film thickness of the coated copper. The wettability was highly influenced by increasing CuO on the coated copper, which is increased by the bath temperature. The contact angle measurements have demonstrated the influence of C―O, O―C?O and CuO components of the surface on the wettability of the samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of the microstructure of the supported catalysts CuO/TiO<Subscript>2</Subscript> and CuO/(CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>) on their catalytic properties in carbon monoxide oxidation

The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO₂ and CuO/(CeO₂-TiO₂) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO₂ catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu²⁺ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO₂ (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO₂-TiO₂) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO₂ catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO₂-TiO₂) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO₂.     

Oxide and carbide formation at titanium/organic monolayer interfaces

X-ray photoelectron spectra (XPS) are reported from a series of buried titanium/organic monolayer interfaces accessed through sample delamination in ultrahigh vacuum (UHV). Conventional characterization of such buried interfaces requires ion-mill depth profiling, an energetic process that frequently destroys bonding information by chemically reducing the milled material. In contrast, we show that delaminating the samples at the metal/organic interface in vacuum yields sharp, nonreduced spectra that allow quantitative analysis of the buried interface chemistry. Using this UHV delamination XPS, we examine titanium vapor deposited onto a C18 cadmium stearate Langmuir-Blodgett monolayer supported on Au, SiO2, or PtO2 substrates. Titanium is widely used as an adhesion layer in organic thick film metallization as well as a top metal contact for molecular monolayer junctions, where it has been assumed to form a few-atoms-thick Ti carbide overlayer. We establish here that under many conditions the titanium instead forms a few-nanometers-thick Ti oxide overlayer. Both TiO2 and reduced TiOx species exist, with the relative proportion depending on oxygen availability. Oxygen is gettered during deposition from the ambient, from the organic film, and remarkably, from the substrate itself, producing substrate-dependent amounts of Ti oxide and Ti carbide "damage". On Au substrates, up to 20% of the molecular-monolayer carbon formed titanium carbide, SiO2 substrates approximately 15%, and PtO2 substrates <5%. Titanium oxide formation is also strongly dependent on the deposition rate and chamber pressure.     

Formation of TiO<Subscript>2</Subscript> and KTiOPO<Subscript>4</Subscript> nanoclusters on the (001) surface of KTiOPO<Subscript>4</Subscript> crystal upon annealing

Morphology and crystallographic characteristics of (001) KTiOPO₄ air-annealed surface were investigated. The autoepitaxy of nanosized KTiOPO₄ islands was revealed in samples annealed at 550°C for 2–20 h. When annealing at 650°C takes ～20 h, the TiO₂ particles are observed to form on the substrate surface. This indicates the onset of the thermal decomposition of KTP at this temperature.     

Preparation of anatase phase titanium dioxide film by non-aqueous electrodeposition

The electrodeposition–annealing route to fabricating thin film of the promising photocatalyst material anatase-titanium dioxide (anatase-TiO₂) has been studied. The sample was deposited with a solution of N,N-dimethylformamide containing titanium compound by controlled-potential technique. SEM image showed the annealed sample at 600 °C for 1 h under air provided a continuous film with a thickness of ca. 350 nm. In this sample, X-ray photoelectron spectrum corresponding to the Ti 2p peak assigned to a chemical bond of TiO₂ and X-ray diffraction peaks assigned to the anatase phase were observed, respectively. Electrochemical oxidation in sodium sulfate solution on this annealed film was enhanced in the presence of UV light radiation. These results confirm the successful synthesis of photocatalytic anatase-TiO₂ film by the electrodeposition and annealing process.     

Thermal stability of anatase TiO2 aerogels

Titanium dioxide (TiO₂) aerogels were prepared with sol–gel ambient pressure drying method by using titanium tetrachloride (TiCl₄) as precursor and tetraethoxysilane as modifier, calcinated at different temperature and characterized by X‐ray diffraction, transmission electron microscopy and small angle X‐ray scattering. The results showed that the TiO₂ aerogels remained amorphous under 500 °C, changed to anatase from 600 °C and further changed to rutile from 900 °C. Between 60 °C and 500 °C, the primary particles within the samples concentrated mainly upon small sizes, enlarged and diverged remarkably above 600 °C. The crystalline grains grew and agglomerated with the rise of the calcination temperature. The TiO₂ aerogels at a temperature higher than 800 °C have better stability than anatase because of the formation of partial Ti―O―Si bonds. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization of TiO2 nanotube arrays prepared via anodization of titanium films deposited by DC magnetron sputtering

Highly ordered TiO₂ nanotube arrays were fabricated on a conducting glass substrate in NH₄HF₂/glycol electrolyte via anodization of titanium film which was deposited by direct current magnetron sputtering (DCMS) at different temperatures. The results showed that Ti films with good homogeneity and high denseness could be formed under the conditions Ar pressure 0.35 Pa, direct current 3.5 A, and 2 h at 300 °C. Characterization of the TiO₂ nanotube arrays was investigated comparatively, by altering anodization time. The surface morphology of the samples changed as the anodization time was prolonged from 10 to 150 min at 30 V. The TiO₂ thin film was amorphous and could be transformed into anatase by annealing at 450 °C. On the basis of UV?Cvisible transmission spectra the bandgap of the thin film was calculated to be 3.12 eV, and its tail extended to 2.6 eV.     

Multilayered Cu–Ti deposition on silicon substrates for chemiresistor applications

Abstract

On the perspective to develop CuO–TiO₂ MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO₂ in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication.     

Synthesis of TiO2 Nanoparticles via a Ti（IV） Complex with Stearic Acid and the Photocatalytic Activity for Organic Oxidation

The nano-sized particles of TiO2 were prepared by thermal decomposition of titanium (IV) tetrabutanoxide complex with stearic acid at 450℃ in the air.It was observed that the amount of stearic acid,used initially for the complex synthesis in 2-propanol at 25℃,had great influence on the physical properties of the prepared TiO2 including crystal structure, the particle size,surface area and the adsorption capacity for organic substrate of a textile dye X3B in eater,and thereafter the photocatalytic activity for the dye oxidation.Some samples displayed lower adsorption capacity for the organic substrate in water than a TiO2 of Degussa p25,but higher photocatalytic activity for the organic oxidation.Possible reason for the observed difference was discussed in the text.     

Preparation and characterization of thin TiO2-films on gold/mica

Flat and highly (111) oriented gold and silver films were prepared by physical vapour deposition (PVD) using optimized deposition parameters. On these films, which were characterized with atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), titanium dioxide films were deposited by electron beam evaporation and dip coating. Dip coating from titanium tetraisopropoxide solutions resulted in films with different morphology and coverage depending on the alkoxide concentration (0.009 mol/L – 0.60 mol/L) and the post-treatment. Scanning electron microscopy (SEM) and AFM revealed that the deposited TiO₂ consists of amorphous, highly porous islands when the applied alkoxide concentration is high (0.05 mol/L – 0.6 mol/L). At higher temperatures these amorphous TiO₂ islands sintered significantly and crystallized to anatase. In contrast, transparent TiO₂ films were obtained from low concentrated alkoxide solutions (< 0.01 mol/L) which covered the whole substrate, similar to electron beam evaporated thin films. Sputter profiles with ion scattering spectroscopy (ISS) indicated that the film thickness is in the range of 2 nm when alkoxide solutions with a concentration of 9 mmol/L are used. The deposition of TiO₂ by electron beam evaporation normally resulted in significantly reduced TiO₂ films, completely oxidized ones were obtained when deposition was performed at elevated oxygen partial pressures (p(O₂) > 2 × 10^–5 mbar).     

Correlation between structural and optical properties of TiO<Subscript>2</Subscript>:ZnO thin films prepared by sol–gel method

We have studied structural and optical properties of thin films of TiO₂, doped with 5% ZnO and deposited on glass substrate (by the sol–gel method). Dip-coated thin films have been examined at different annealing temperatures (350–450 °C) and for various layer thicknesses (89–289 nm). Refractive index, porosity and energy band gap were calculated from the measured transmittance spectrum. The values of the index of refraction are in the range of 1.97–2.44, the porosity is in the range of 0.07–0.46 and the energy band gap is in the range of 3.32–3.43. The coefficient of transmission varies from 50 to 90%. In the case of the powder of TiO₂, doped with 5% ZnO, and aged for 3 months in ambient temperature, we have noticed the formation of the anatase phase (tetragonal structure with 20.23 nm grains). However, the undoped TiO₂ exhibits an amorphous phase. After heat treatments of thin films, titanium oxide starts to crystallize at the annealing temperature 350 °C. The obtained structures are anatase and brookite. The calculated grain size, depending on the annealing temperature and the layer thickness, is in the range of 8.61–29.48 nm.     

Preparation of titanium carbide powders by sol–gel and microwave carbothermal reduction methods at low temperature

Titanium carbide ultrafine powders were prepared from tetrabutyl titanate and sucrose by sol–gel and microwave carbothermal reduction. The influences of reaction temperature and molar ratio of Ti to C on the synthesis of titanium carbide were studied. The results show that excess amount of carbon plays a positive effect on the carbothermal reduction of TiO₂ at low temperature. The inceptive carbothermal reduction temperature of TiO₂ and formation of titanium oxycarbide was below 900 °C, and pure TiC can be prepared at 1,200 °C, which was considerably lower compared to that by conventional carbothermal reduction using a mixture of TiO₂ and carbon powders as raw materials. The morphology and particle size of synthesized TiC powder were examined by field emission-scanning electron microscopy (FE-SEM) and the quantities of the phases of the powders were analyzed by Rietveld refinement method, the particle sizes of the TiC powders synthesized at 1,300 °C distribute over 0.1–0.5 μm.     

Improvement of the oxidation behavior of Ti1-xAlxN hard coatings by optimization of the Ti/Al ratio

The oxidation behavior of cubic Ti_1-xAl_xN films was improved by decreasing the Ti/Al ratio from 50/50 in the direction of the phase transition between cubic and hexagonal structure. Metastable, polycrystalline, single-phase Ti_1-xAl_xN films were deposited on high speed steel (HSS) substrates by reactive magnetron sputtering ion plating (MSIP). The composition of the bulk was determined by electron probe microanalysis (EPMA), the crystallographic structure by thin film X-ray diffraction (XRD). A Ti_1-xAl_xN film with a Ti/Al atomic ratio of 38/62 was deposited in cubic NaCl structure, whereas a further decrease of the Ti/Al ratio down to 27/73 led to a two-phase film with both cubic and hexagonal constituents. The Ti_0.38Al_0.62N film was oxidized in synthetic air for 1 h at 800?°C. The oxidic overlayer was analyzed by X-ray photoelectron spectroscopy (XPS) sputter depth profiling, EPMA crater edge linescan analysis, and secondary neutrals mass spectroscopy (SNMS). Scanning electron microscopy (SEM) micrographs of the cross sectional fracture were taken for morphological examination. With higher Ti content, the Ti_1-xAl_xN formed a TiO_2-x rich sublayer beneath an Al₂O₃ rich toplayer, whereas the oxide layer on the Ti_0.38Al_0.62N film consisted of pure Al₂O₃. The thickness of the oxide layer was determined to 60–80 nm, about a quarter of the oxide layer thickness detected on Ti_0.5Al_0.5N films. The absence of a TiO_2-x sublayer was also confirmed by XRD. The results show a distinct improvement of the oxidation resistance of cubic Ti_1-xAl_xN films by increasing the Al content from x = 0.5 to 0.62, whereas a further increase leads to the hexagonal structure, which is less suitable for tribological applications due to its tendency to form cracks during oxidation.     

Structure and photoluminescence properties of TiO<Subscript>2</Subscript> nanoparticles synthesized from a novel luminescent nano-titanium complex

A new titanium complex [Ti(Me–Q)₂(Cl)₂] (1) is prepared by reacting titanium tetrachloride with 2-methyl-8-hydroxyquinoline in a fast and facile process. The complex is fully characterized based on its ¹H and ¹³C NMR, IR, and UV spectra and elemental analysis. The prepared nanostructured compound is synthesized by the sonochemical method. This new nanostructure is characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), IR spectroscopy, and elemental analysis. Thermal stability of single crystalline and nanosize samples of the prepared compound is studied by thermal gravimetric (TG) and differential thermal analysis (DTA). The prepared complexes both bulk and nanosized are utilized as a precursor for the preparation of TiO₂ nanoparticles by direct thermal decomposition at 600°C in air. The morphology and size of TiO₂ nanoparticles are determined by SEM, powder XRD, and IR spectroscopy and the results show that the TiO₂ nanoparticle size depends on the initial particle size of 1. Photoluminescence (PL) properties of the nanostructured and crystalline bulk prepared complex and their TiO₂ nanoparticle cores are investigated.     

Effect of surface finishing on the formation of nanostructure and corrosion behavior of Ni–Ti alloy

In the present work, we have investigated the formation of nanostructured oxide layers by anodic oxidation on different surface finished (mirror finished, 600 and 400 grit polished) nickel–titanium alloy (Ni–Ti) in electrolyte solution containing ethylene glycol and NH₄F_. The anodized surface has been characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X‐ray photoelectron spectroscopy (XPS). The corrosion behaviors of the Ni–Ti substrate and anodized samples have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks' solution). The results show that the native oxide on the substrate is replaced by nanostructures through anodization process. XPS of Ni–Ti substrate shows the presence of Ni⁰, NiO, Ti⁰ and TiO₂ species, whereas Ni₂O₃ and Ni(OH)₂ and TiO₂ are observed in the samples after anodization. Corrosion resistance of the anodized sample is comparable with that of the untreated sample. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal and X-ray diffraction studies of the solid–solid interactions in CuO–MoO3/MgO system

The solid–solid interactions in pure and MoO₃-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO₃ were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000°C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100°C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO₃ at temperatures starting from 400°C yielding CuMoO₄ which remained stable up to 1000°C. The other portion of MoO₃ interacted with MgO producing MgMoO₄ at temperatures starting from 400°C and remained also stable at 1000°C. The diffraction peaks of Cu₂MgO₃ phase were detected in the diffractograms of pure and MoO₃-doped 0.3CuO/MgO precalcined at 1000°C. The formation of this phase was accompanied by an endothermic peak at 930°C.     

Substrate temperature effects on the structural,compositional, and electrical properties of VO2 thin films deposited by pulsed laser deposition

The vanadium dioxide (VO₂) thin films were deposited on silicon (100) substrate using the pulsed laser deposition technique. The thin films were deposited at different substrate temperatures (500°C, 600°C, 700°C, and 800°C) while keeping all the other parameters constant. X‐ray diffraction confirmed the crystalline VO₂ (B) and VO₂ (M) phase formation at different substrate temperatures. X‐ray photoelectron spectroscopy analysis showed the presence of V⁴⁺ and V⁵⁺ charge states in all the deposited thin films which confirms that the deposited films mainly consist of VO₂ and V₂O₅. An increase in the VO₂/V₂O₅ ratio has been observed in the films deposited at higher substrate temperatures (700°C and 800°C). Scanning electron microscope micrographs revealed different surface morphologies of the thin films deposited at different substrate temperatures. The electrical properties showed the sharp semiconductor to metal transition behavior with approximately 2 orders of magnitude for the VO₂ thin film deposited at 800°C. The transition temperature for heating and cooling cycles as low as 46.2°C and 42°C, respectively, has been observed which is related to the smaller difference in the interplanar spacing between the as‐deposited thin film and the standard rutile VO₂ as well as to the lattice strain of approximately −1.2%.