Amorphous Ti Research Articles

Growth and Properties of CVD Ti–P–O Films Obtained from the CO2 ∕ H2-Added and CO2 ∕ H2-Free Systems

Amorphous titanium phosphate (Ti–P–O) films were prepared by low-pressure chemical vapor deposition (CVD) using a mixture of titanium tetrachloride and trimethyl phosphite under the coexistence of and at a flow rate of 50 sccm for each (the -added system) or devoid of and (the -free system). The growth rate and the ratio in films increased with the increase in deposition temperature and the input for the -added system but remained unchanged for the -free system. Different growth mechanisms are proposed to elucidate the different growth behaviors. A new viewpoint for the generation of intrinsic stress in thin films is suggested, based upon the internal stress changing with the input for the -free Ti–P–O films at the same film thickness and composition. Three composition zones for the amorphous Ti–P–O films, based upon the compositional analysis and property measurement, are proposed to explain the measured electrical properties.

Preparation of Li 4Ti 5O 12 spherical particles for rechargeable lithium batteries

Spherical Li 4Ti 5O 12 particles were prepared via an emulsion-gel process. The preparation of spherical Li 4Ti 5O 12 such as the concentrations of the starting materials and heat treatment were optimized. The particle size distribution of the Li 4Ti 5O 12 prepared under optimized condition was very narrow, and the particle size was 0.45 μm. It was found that a short heat treatment in an infrared furnace was useful to crystallize amorphous Li Ti O powders without aggregation of particles or morphology change. The obtained Li 4Ti 5O 12 had the spinel structure, and was phase pure. The prepared Li 4Ti 5O 12 exhibited a high discharge capacity of 160 mA h g −1 at the potential of 1.5 V versus Li/Li +, and the charge–discharge cycle stability was excellent.

Peculiarities of structural state and hydrogen storage properties of Ti–Zr–Ni based intermetallic compounds

Structural states of the Ti–Zr–Ni based melt-spun ribbons have been investigated by means of the X-ray diffraction analysis. The ribbon structural state was found to be strongly affected by the production conditions. A small amount of Si (0.2–0.3 at.%) in the Ti–Zr–Ni alloy leads to the formation of an amorphous or a mixed amorphous-quasicrystalline state in the ribbons produced at the different hardening rates. The amorphous-quasicrystalline structural state of the ribbons is stable during annealing up to temperatures of 400 ° C but some changes in its parameters take place. The uncoated by Pd amorphous and amorphous-quasicrystalline Ti–Zr–Ni ribbons have the property of absorbing a large amount of hydrogen. Changes in the amorphous and quasicrystalline subsystems have a reversible character: the structural states of the ribbons after natural dehydrogenation practically fully returns to the initial one.

Mesoporous and amorphous Ti–silicas on the epoxidation of vegetable oils

For the epoxidation oleic acid methyl ester, different kinds of Ti–MCM-41 materials and Ti–amorphous silicas were compared. Catalytic activity was explained in terms of chemical and textural features of the denoted materials. Further examinations were made of the behavior of reaction temperature and different solvents, Ti-loading of the catalysts, and their re-usability and stability. Mesoporous materials like MCM-41 used as a Ti-support have the advantage of its higher surface area toward amorphous Ti SiO 2. The structure of Ti–MCM-41 was not observed to play any important role in the activity. Ti SiO 2 proved to be a truly heterogeneous catalyst and could be reused at least four times. The epoxidation system TBHP/Ti SiO 2 has not been reported so far in the literature for the epoxidation of vegetable oils and their transesterification products. Based on the results presented here, this system could have a great potential for industrial use.

STRUCTURE AND PROPERTIES OF TITANIUM–POLYMER THIN FILM NANOCOMPOSITES

Thin film titanium/poly-para-xylylene nanocomposites with controlled Ti content are prepared by vacuum coevaporation and cocondensation of Ti and paracyclophane. The structure and chemical composition of as-deposited samples and the changes of electrical resistivity, which they undergo upon heating, are studied by atomic force microscopy, optical absorption spectroscopy, and the temperature coefficient of the electrical resistivity. It is shown that vacuum coevaporation results in the production of nanocomposite thin films with average Ti particle size of 10–50 nm. The inorganic phase is shown to be amorphous Ti for the samples with high metal content, whereas for the low-filled nanocomposites it consists of amorphous titanium oxide. Two types of kinetics of the nanocomposite oxidation process have been found and modeled by (i) inverse logarithmic and (ii) logarithmic functions depending on the metal content within the thin film. After a long preconditioning period in air the electrical conductivity of the thin film nanocomposites was carefully investigated by two-probe DC measurements. A strong correlation between the concentration of Ti in the thin films and the electrical conductivity dependency on temperature is found and modeled by a heterogeneous model of conductivity.

Comparative study of polycrystalline Ti, amorphous Ti, and multiamorphous Ti as a barrier film for Cu interconnect

Ultrathin (10nm) Ti films with various structures were deposited by physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. CVD-Ti films with low-temperature(<500°C) plasma-enhanced chemical vapor deposition using TiCl4 and H2 as reactants is an amorphous structure. This result is different from PVD-Ti films deposited by magnetron sputtering, which have a columnar structure. Ammonia plasma was further employed to post-treat the CVD-Ti barrier layer to improve barrier properties. An amorphous Ti(N,H) layer was formed on the surface of the CVD-Ti layer after ammonia plasma post-treatment. The resultant films had a bilayered amorphous Ti(N,H)∕Ti structure. Furthermore, the effective resistivity of the resultant Ti(N,H)∕Ti film decreased to 122μΩcm. The thermal stability of Cu∕PVD-Ti∕Si and Cu∕CVD-Ti∕Si contact systems was evaluated by thermal stressing at various annealing temperatures. For the Cu∕PVD-Ti∕Si, the highly copper titanium compound was formed after 450°C annealing. The PVD Ti barrier failed initially due to the reaction of Cu and the Ti barrier, in which Cu atoms penetrated into the Si substrate after annealing at high temperature. However, no copper-titanium and copper-silicide compounds were found for amorphous Ti and plasma-treated Ti[Ti(N,H)∕Ti] barriers, even after annealing at 500 and 600°C, respectively. Improved barrier capability against Cu diffusion was found for the Ti(N,H)∕Ti barrier layer because the Cu∕Ti(N,H)∕Ti∕n+-p junction diodes retained low leakage current densities even after annealing at 500°C for 1h. Ti(N,H)∕Ti barrier layers present lengthened grain structures to effectively impede Cu diffusion, thus acting as much more effective barriers than conventional Ti and TiN films.

Reaction-induced phase separation from supersaturated solid solution to nitride in thin films

For the development of an advanced fabrication process aimed for nano-structured coating, a combination process of ion beam sputtering (IBS) and ion implantation has been conducted on Ti–X–N films. Non-equilibrium Ti–V and Ti–Si films have been prepared by IBS, and then followed by N + implantation into the films to investigate low-temperature reaction-induced nano-phase separation in ternary Ti–V–N and Ti–Si–N systems. Ti–12 at.% V and Ti–20 at.% Si have been deposited on (001)Si substrate with thickness 150 nm by IBS. The structural change due to the N-implantation has been evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. The cross-sectional TEM images of the as-deposited films respectively show nano-crystalline bcc Ti–V and amorphous Ti–Si. N-implantation with a dose of 5.0×10 17 ion/cm 2 induces affected zones consisting of equi-axed grains on the surface of the Ti–Si and Ti–V films. The selected area diffraction pattern (SAED) from the affected zone shows the direct formation of fcc–TiN during N-implantation. The N concentration has been measured by the XPS depth profiling. The N concentration in Ti–V and Ti–Si films are ∼30 at.% N average and 60 at.% N maximum. The compositional gradient of N against the depth of the film suggested that the introduction of equi-axed grains was mainly due to the chemical reaction of Ti–N in proportion to the N concentration. The decreasing of Si concentration in Ti–Si film during N-implantation suggests that the segregation of Si might simultaneously occur with the preferential nitriding of Ti. The structural difference between N-implanted Ti–V and Ti–Si is mainly attributed to the difference in miscibility of V and Si into TiN.

Formation of titanium nitride by mechanical milling and isothermal annealing of titanium and boron nitride

The formation of titanium nitride with rock salt structure (δ-TiN x ) was studied by mechanical milling of a mixture of Ti and hexagonal boron nitride (h-BN) powders and isothermal annealing of the mixture after milling for 70 h under argon atmosphere. The mole ratio of Ti to h-BN is 22:78. In the milling process, an amorphous Ti–N alloy was formed firstly by a diffusion reaction between Ti and BN, and then the amorphous Ti–N alloy transformed into δ-TiN x driven by mechanical milling. However, in the annealing process, a Ti(N) solid solution was formed firstly by incorporation of N into Ti, and the N content in the Ti(N) increased with increasing annealing temperature. When the N content exceeded the solubility limit of the Ti(N) at some annealing temperature, the Ti(N) decomposed into δ-TiN x and Ti(N) with the solubility limit. No self-sustaining reaction occurs in the present work. No TiB 2 is observed to form in the two processes. The thermodynamic and kinetic mechanisms of formation of the δ-TiN x are discussed.

Behavior of cultured human umbilical vein endothelial cells on titanium oxide films fabricated by plasma immersion ion implantation and deposition

Our previous research results have shown that Ti–O films with appropriate characteristics possessed good blood compatibility. In this paper, we synthesized Ti–O films using plasma immersion ion implantation and deposition (PIII-D) and investigated the characteristics and the biological behavior of cultured human umbilical vein endothelial cells (HUVEC) onto film surface. The structure and composition of the Ti–O films were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atom force microscopy (AFM). The surface energy was measured by a contact angle method. The in vitro HUVEC-cultured investigation of Ti–O film surface justified that the biological behavior of HUVEC on different structure surfaces was significantly different. The adherence and growth of HUVEC to crystalline Ti–O film surface were much better than that of amorphous Ti–O film. The mechanism based on the relationship between the film characteristics and biological behavior of endothelial cells (ECs) is discussed.

Effect of amorphous–crystalline interfaces on the martensitic transformation in Ti 50Ni 25Cu 25

A partially crystallized amorphous Ti 50Ni 25Cu 25 melt-spun ribbon showing spherical particles in martensite has been investigated. Microstructural observations support the hindering of the martensitic transformation as well as the production of additional autoaccommodated structures nearby the interface compared with the ones used inwards.

Structure of multi-grain spherical particles in an amorphous Ti50Ni25Cu25 melt-spun ribbon

Microstructural observations of crystalline particles created by controlled thermal treatments in an initially amorphous Ti 50 Ni 25 Cu 25 melt-spun ribbon have been carried out by means of transmission electron microscopy (TEM). After annealing at temperatures close to the crystallization temperature during short times (10 min at 693 K), a low dispersion of micrometric particles embedded in the amorphous matrix is obtained. Their lattice structure is cubic (austenite) and many of them exhibit a single crystallographic orientation, although particles with several grains have also been observed. In the latter case, each grain grows radial and simultaneously from the center of the particle, producing a spherical crystalline area divided in several crystallographic grains. Most of them show rather planar interfaces between adjacent grains in TEM images and twinning relationships in selected area electron diffraction patterns (SAEDP). However, the directions of the twinning planes in the SAEDP do not match with the traces of the interfaces between the corresponding grains observed in the TEM images. The experimental results indicate that the growth of the particular grains does not occur independently, and suggest that additional topological conditions yield the interfaces different from the twinning planes.

A study of amorphous Ti–Ni alloys by X-ray photoelectron spectroscopy

Amorphous thin films of Ti–Ni alloys with 48, 50, and 51.5% atomic nickel concentration have been studied by X-ray photoelectron spectroscopy (XPS). The films were prepared by rf magnetron sputtering technique. The 2p core levels and the X-ray excited Auger regions of titanium and nickel were investigated. The aluminum anode was employed as the source of X-ray excitation. The experimental shifts were found to be positive for both titanium and nickel, indicating that the criterion of electronegativity cannot be used to determine the direction of charge transfer in these films. The Auger parameters (APs) were determined from the binding energies (BEs) of the 2p 3/2 core levels and the most prominent peak in the Auger regions. The Auger parameter data show that the metallic nature to the films comes mainly from titanium. The shift in the Auger parameter is found to be positive for titanium and negative for nickel, suggesting a charge transfer from nickel to titanium. The chemical shifts have been calculated by subtracting the relaxation shifts from the experimental core level shifts. These shifts were observed to be negative for titanium and positive for nickel, establishing the direction of charge transfer from nickel to titanium. This direction of charge transfer was also confirmed by calculating the charges on the ionized atoms using a simple electrostatic model. These values are observed to be positive for titanium and negative for nickel, in complete agreement with the earlier conclusions. The data on the Auger parameter, the chemical shifts, and the charge on the ions show similar trend. The Shirely and Tougaard backgrounds under the core level peaks were also estimated. The difference between these backgrounds when normalized with respect to the elemental values provides information on the density of states at the Fermi level. A decrease in the density of states at the Fermi level was observed both for titanium and nickel in the films. This is in agreement with the observed increase in the unoccupied density of states at the Fermi level studied in the earlier investigations.

Twinned b.c.c. spherical particles in a partially crystallized Ti 50Ni 25Cu 25 melt-spun ribbon

Some micrometric spherical particles containing several b.c.c. grains are obtained from an initially amorphous Ti 50Ni 25Cu 25 melt-spun ribbon after a controlled thermal treatment. The microstructure and crystallography of these crystalline particles have been investigated by TEM, showing that each of the grains grows to the same distance from the center of the particle, keeping the isotropic growth of the entire system. The number of grains in each particle is variable, but self-accommodating arrangements have always been found. Most of the grains show {112} B2 (sometimes {114} B2) planes unchanged when moving to an adjacent grain, as typical twin crystals. However, the interfaces between adjacent grains usually do not match with these invariant planes. The morphology and self-accommodating arrangements found in these multi-grain particles are unusual for b.c.c. structures, but resemble in some way the case of multiple twinned particles present in other materials, as the five-fold twinned structures in f.c.c. systems.

Formation of nanocrystals in Ti 78Fe 15Si 7 amorphous alloy with a wide supercooled liquid region

An as-quenched amorphous Ti 78Fe 15Si 7 alloy with a large supercooled liquid region (61 K) was investigated using X-ray diffraction, differential scanning and transmission electron microscopy (TEM). This amorphous alloy transforms into primary nano-sized β-Ti phase particles (<20 nm) of spherical shape upon a first exothermic reaction. The remaining amorphous phase transforms to the Ti 2Fe phase followed by the Ti 5Si 3 phase upon the second and third exothermic reaction. The tensile fracture strength was 1318 MPa for the amorphous alloy and increased up to 1876 MPa for a volume fraction of 15% primary β-Ti phase.

Crystallization studies of amorphous melt-spun Ti50Ni25Cu25

Amorphous ribbons of the ternary shape memory alloy Ti 50 Ni 25 Cu 25 crystallize polymorphously upon heating. The subsequent growth proceeds isotropic resulting in the formation of perfectly spherical grains in an amorphous matrix at intermediate stages of the transformation. These experimental results match exactly with the idealized preconditions that are employed in various models describing nucleation- and growth kinetics at deep undercooling. Therefore, amorphous Ti 50 Ni 25 Cu 25 is an ideal candidate to study the crystallization by calorimetry in conjunction with microstructure analyses and to compare the results with theoretical predictions. It was found, that the isothermal crystallization process of Ti 50 Ni 25 Cu 25 near the glass transition can be adequately described by Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetics using an Avrami exponent of n = 3. Kissinger analysis of non-isothermal crystallization using different heating rates revealed an activation energy of Q a = 374 kJ/mol.

Reactive oxo-titanium species in titanosilicate molecular sieves: EPR investigations and structure–activity correlations

The structure of the reactive oxo-titanium species (hydroperoxo-, peroxo-, and superoxo-titanium) in titanosilicate molecular sieves (TS-1, Ti- β, amorphous Ti–SiO 2, and TiMCM-41), generated on interaction with aqueous H 2O 2 or urea–H 2O 2 adducts, was investigated by electron paramagnetic resonance (EPR) and diffuse reflectance UV–visible (DRUV–visible) spectroscopies and magnetic susceptibility measurements. Two types of superoxo-titanium species (A and B) were identified in TS-1 and amorphous Ti–SiO 2. An additional oxo species, A′, was also detected over Ti- β. TiMCM-41 generated, mainly, the B-type species. DRUV–visible spectroscopy and magnetic susceptibility measurements suggest the coexistence of both the superoxo- and hydroperoxo-titanium species. The A-type oxo-titanium species originate from the framework Ti sites having a tetrapodal (SiO) 4Ti structure located inside the pores, while the B-type species originate predominantly from tripodal (SiO) 3Ti(OH) structures, also located in the framework, probably at the external surface. The local structural environment of the Ti 4+ ions, solvent, and temperature influence the concentration of these oxo-titanium species. The concentration of the A-type species decreased in the order: TS-1>Ti- β>amorphous Ti–SiO 2. The B type varied as follows: TiMCM-41>amorphous Ti–SiO 2>Ti- β>TS-1. In the oxidation of styrene, the A-type species correlate with styrene oxide formation, while the presence of B-type species lead to nonselective products. Experimental evidence is given for the involvement of the hydroperoxo-titanium species in olefinic epoxidations (styrene to styrene oxide) and the superoxo-titanium in aromatic hydroxylations (phenol to hydroquinone and catechol).

Optical and crystallisation behaviour of TiO 2 and V/TiO 2 thin films prepared by plasma and ion beam assisted methods

This paper reports the synthesis of TiO 2 and V/TiO 2 thin films, prepared by plasma enhanced and ion beam induced chemical vapour deposition procedures. Thin films with different contents of vanadium from a few to some tenth percents of this element have been prepared. Vanadium oxide thin films were also prepared for comparison. Morphological, structural and chemical characterisation of the samples was carried out by means of several techniques including scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Optical properties of these samples were studied by ellipsometry and ultraviolet–visible absorption spectroscopy. It has been shown that the absorption threshold of V/TiO 2 thin films shifts continuously towards the visible by increasing the V content. On the basis of this behaviour it is proposed the use of these thin films as optical filters in the UV–vis region of the spectrum. In the ‘as prepared’ samples vanadium is homogeneously distributed within an amorphous Ti–O structure. After annealing in air at T>673 K, both segregation of vanadium as vanadium oxide and crystallisation of the TiO 2 into the rutile structure take place. It is realised that infrared spectroscopy can be a complementary technique of XRD to determine the crystallisation behaviour of the samples. The observed structural modifications are accompanied by a change in the light absorption properties of the films that can now be interpreted as due to the superposition of the absorption spectra of TiO 2 and vanadium oxide. In the ion beam assisted films, only slight changes in their refraction index ( n) are found as a function of the vanadium content and/or the annealing treatments. The changes were greater for the less compact films obtained by plasma deposition, indicating that the main parameter controlling the value of n is the density of the films.

The influence of TiN on cosputtered (Ti+Si) blanket film

X-ray diffraction, transmission electron microscopy and Auger spectroscopy were used to study the formation of TiSi 2 from a cosputtered (Ti+Si) film with and without TiN capping. In all cases, a metal rich silicide identified as Ti 5Si 3, was the first phase to form from the amorphous (Ti+Si) regardless if a TiN overlayer was or was not present. At temperatures of 923 K and below it only Ti 5Si 3 was observed in all specimens. C54 TiSi 2 formation is enhanced in specimens having a TiN capping and its formation occurs at lower temperatures and at a faster rate at some appropriate temperature than in specimens without TiN. The effect of tensile stress induced by the TiN layer is suggested as the reason of C54 TiSi 2 formation.

607 ナノ結晶 TiAl の超塑性鍛造とニアネット形状制御

This article describes the evaluation of high-speed superplastic forging and near-net-shape control in nanocrystalline titanium aluminide. The process analysis of isochronal forging at a constant displacement rate permits us to derive the strain rate sensitivity exponent (m) of approximately 0.4 on the basis of the constitutive equation of ε^m=Aδ(1/d)*exp(-Q/kT) for full density nanocrystalline (Ti_<50>Al_<50>)_<90>Fe_<10> with the average crystallite size of 20 nm. For the full density amorphous Ti_<50>Al_<50> sample, the isochronal forging under the constant load leads to a relatively high plastic strain rate of approximately 1×(10)^<-2>s_<-1> at 977K during Newtonian viscous flow that is given by a relation of η=η_0 exp(Q_v/kT) in a supercooled liquid. The apparent activation energy (Q) for nanocrystalline Ti_<50>Al_<50> is derived at 113 kJ・mol^<-1> that is a nearly quarter of the value (467 kJ・mol^<-1> ) of the amorphous alloy. The near-net-shape forging is successfully achieved for the amorphous and nanocrystalline TiAl by using a specially designed carbon plunger.

Scanning tunneling microscopy and in situ spectroscopy of ultra thin Ti films and nano sized TiO x dots induced by STM

Scanning tunneling microscopy and scanning tunneling spectroscopy (STM/STS) of a titanium (Ti) amorphous film and titanium oxide dots were investigated at room temperature and in ambient air by scanning tunneling microscope (STM). A smooth amorphous Ti film (3 nm thick) with an area of 1 μm×1 μm was chosen and imaged by STM. Tunneling current versus bias spectra for the film are symmetric to the origin in the STS measurements. Ultra thin films were oxidized at different positions by applying different voltage pulses ranging from 3.5 to 5 V for a period of 5 s. The subsequent images of STM show that the higher the bias applied to the film, the larger the dot. The in situ STS measurements were used, for the first time, to study the contaminant-free TiO x dots just as induced by STM. The in situ corresponding tunneling current versus bias spectrum was preceded by formation of a dot and followed by imaging the dot. STS I– V curves exhibit that the formed TiO x dots are n-type semiconductors. A transformation from slight asymmetry to drastic asymmetry of STS curves and increase in band gap indicate that nano-TiO x dots exhibit metallic to semiconducting behaviors with increase in the voltage pulse applied to sample.