Ti Vapor Research Articles

Synthesis of [Ca24Al28O64]4+(4e−) single crystal through xenon lamp melting combined with Ti vapor deoxygenation

In this paper, the high-quality [Ca24Al28O64]4+(4e−) (C12A7:e−) single crystal was synthesized by xenon lamp melting combined with Ti vapor treatment. The relative density of the sample is over 99.7%, and the sample's electron density is 1021 cm−3. The results of electron emission performance show that the sample's emission current density is 1.86 A/cm2 when the applied voltage is 3500 V at 1100 °C, and the fluctuation does not exceed 5%. Theoretical calculation results show that C12A7:e− single crystal has a lower work function (2.36 eV). Also, the free electrons in the cage cavity are mainly distributed around the frame oxygen, which is in a weakly bound state. This makes C12A7:e− single crystal have excellent electron emission characteristics. Theoretical calculations provide support for experiments. These laid the foundation for its application in electron emission.

Influence of Ti3SiC2 content on erosion behavior of Cu–Ti3SiC2 cathode under vacuum arc

In this study, a series of Cu–Ti3SiC2 composites with different Ti3SiC2 contents were prepared by spark plasma sintering. Their mechanical properties and electrical resistivity were investigated. Through analyzing the morphology and composition of the eroded regions, the effect of Ti3SiC2 content on the erosion behavior of Cu–Ti3SiC2 cathodes under vacuum arc was studied. Results show that the relative density and bending strength of the Cu–Ti3SiC2 composites decrease with the increasing Ti3SiC2 content, while the opposite holds for hardness and electrical resistivity. The morphology and phase composition of the erosion zone is dominated by the decomposition process and the amount of Ti3SiC2 in the cathode. Cu–Ti3SiC2 cathodes containing 10 mass%Ti3SiC2 or less displayed relatively flat eroded surface morphology. Cathodes with high Ti3SiC2 content suffered more serious erosion with voids, cracks, and severe decomposition of Ti3SiC2, all of which contribute to impairing the arc ablation resistance of the composite. Ti3SiC2 particles decomposed into TiC and Si vapor; eventually, this TiC also decomposed into Ti vapor and C, leaving a considerable amount of C on the arc affected cathode surface. Excess addition of Ti3SiC2 particles not only deteriorates the strength but also the electrical and thermal conductivity of the composite, both of which in turn harms the arc erosion resistance of the material. These results suggest that the optimal Ti3SiC2 content is below 10 mass% in the composite.

Interfaces within biphasic nanoparticles give a boost to magnesium-based hydrogen storage

The use of Mg as hydrogen storage material is hampered by slow sorption kinetics and high thermodynamic stability. This work reports on biphasic Mg–Ti–H nanoparticles that outperform known Mg-based materials in both respects. By exploiting gas-phase condensation of Mg and Ti vapors under He/H2 atmosphere, biphasic nanoparticles are grown, in which the bulk-immiscible MgH2 and TiH2 phases are mixed at the nanoscale. TiH2 conveys catalytic activity for H2 dissociation/recombination and accelerated hydrogen diffusion, while MgH2 provides reversible hydrogen storage. At the remarkably low temperature of 150 °C, hydrogen absorption and desorption are completed in less than 100 s and 1000 s, respectively. Moreover, the equilibrium pressure for hydrogen sorption exhibits a composition-dependent upward shift compared to bulk Mg, resulting in a pressure increase by a factor of about 4.5 in the Ti-richest samples at 100 °C. The enthalpy and entropy of the metal-hydride transformation are both lower in magnitude with respect to the bulk values, suggesting opposite contributions to the free energy change. The results are analyzed by an interface-induced hydride destabilization model, determining an interfacial free energy difference Δγ=(0.38±0.04)Jm−2 between hydride and metal phases at T = 100 °C. These unique composite nanoparticles significantly extend the temperature/pressure window of hydrogen storage applications using Mg-based materials compatible with up-scaling.

Enhanced visible light-driven photodegradation of rhodamine B by Ti3+ self-doped TiO2@Ag nanoparticles prepared using Ti vapor annealing

In recent years, Ti3+ self-doped TiO2 (B-TiO2) exhibits great potential as a photocatalyst. In this work, Ti vapor-assisted annealing is first demonstrated for Ti3+ doping and improving the visible absorption of TiO2. TEM results exhibit the formation of disordered layer, indicating the successful fabricating of B-TiO2. The absorption increase in TiO2 caused by Ti vapor annealing reaches nearly 50% in the visible wavelength range. Benefiting from the absorption increase, the photocatalytic performance of TiO2 after Ti vapor annealing increases by 60–70%. Surface modification of Ag onto B-TiO2 is also carried out to further improve its optical property. Ag-modified Ti3+ self-doped TiO2 (B-TiO2@Ag) exhibits great visible photodegradation behavior to RhB. The RhB degradation rate reaches 97.76% after 60 min of visible light irradiation. Electrochemical performance tests demonstrate that as-prepared TiO2@Ag has lower resistance than W-TiO2. The results indicate that B-TiO2@Ag has great potential in solar photocatalytic degradation of pollutant.

Analysis of Stability of Small Metal Clusters during Metal Vapor Condensation

A statistical analysis of the results of molecular-dynamic calculations of metal (Cu or Ti) vapor condensation in an inert gas (Ar) medium has been performed. Condensation proceeds with the formation of small particles consisting of metal atoms—clusters. The internal energy of the metal cluster—the sum of the kinetic energy of the atoms in the center of mass system and potential energy—is chosen as the key characteristic describing its state. It is shown that the internal energy value gives the possibility for the prediction of the duration of the cluster existence, from birth to decay, i.e., it describes the ability of the cluster to grow. The temporal evolution of the distribution function of the clusters over the internal energy values is presented.

Nucleation of titanium nanoparticles in an oxygen-starved environment. II: theory

The nucleation and growth of pure titanium nanoparticles in a low-pressure sputter plasma has been believed to be essentially impossible. The addition of impurities, such as oxygen or water, facilitates this and allows the growth of nanoparticles. However, it seems that this route requires such high oxygen densities that metallic nanoparticles in the hexagonal αTi-phase cannot be synthesized. Here we present a model which explains results for the nucleation and growth of titanium nanoparticles in the absent of reactive impurities. In these experiments, a high partial pressure of helium gas was added which increased the cooling rate of the process gas in the region where nucleation occurred. This is important for two reasons. First, a reduced gas temperature enhances Ti2 dimer formation mainly because a lower gas temperature gives a higher gas density, which reduces the dilution of the Ti vapor through diffusion. The same effect can be achieved by increasing the gas pressure. Second, a reduced gas temperature has a ‘more than exponential’ effect in lowering the rate of atom evaporation from the nanoparticles during their growth from a dimer to size where they are thermodynamically stable, *. We show that this early stage evaporation is not possible to model as a thermodynamical equilibrium. Instead, the single-event nature of the evaporation process has to be considered. This leads, counter intuitively, to an evaporation probability from nanoparticles that is exactly zero below a critical nanoparticle temperature that is size-dependent. Together, the mechanisms described above explain two experimentally found limits for nucleation in an oxygen-free environment. First, there is a lower limit to the pressure for dimer formation. Second, there is an upper limit to the gas temperature above which evaporation makes the further growth to stable nuclei impossible.

Spatial distribution of Ti vapor admixture ratio in Ar induction thermal plasma torch during Ti feedstock injection

The spatial distribution of the Ti vapor admixture ratio (XTi) was determined together with Ti excitation temperature () from two-dimensional (2D) optical emission spectroscopy (OES) during Ti feedstock injection into an Ar induction thermal plasma (ICTP) torch for Ti nanoparticle synthesis. The XTi is one important parameter affecting ICTP properties such as its electrical conductivity. The value of XTi was estimated from the radiation intensity ratio of the Ar atomic line to the Ti atomic line, and obtained from 2D OES observation. Furthermore the electron density (ne) was also determined from the estimated results of and XTi through the equilibrium composition. These 2D OES results revealed as 2500–4000 K at around the central axis of the ICTP torch, although it was higher than 4000 K in the off-axis region. In the off-axis region, XTi and ne were much higher than in the on-axis region.

Fabrication and electrical transport characteristics of the polycrystalline Ca12Al14O33 electride

The[Ca24Al28O64]4+:4e- (C12A7:e-) electride composed of densely packed, subnanometer-sized cages. This unique structure makes it possess distinctive applications in fields of electronic emission, superconductor, electrochemical reaction. In this paper, we explore a new method to prepare the bulk of C12A7:e- electride. The following areare systematically studied in this work. 1) the condition of preparing bulk of C12A7:e- electride by solid reaction combining spark plasma sintering and reduction with Ti particles at high temperature, CaCO3 and Al2O3 powders are used as raw materials; 2) the first principle calculations of band structure and density of states of the C12A7:e- electride; 3) the analysis of the electrical transport properties of the C12A7:e- electride. The bulk of C12A7:e- electride is successfully prepared by this method, so the results show that the bulk of C12A7:e- electrode with the electron concentration 1018-1020 cm-3 is synthesized at 1100 ℃ and a vacuum pressure of 10-5 Pa for 10-30 h. In the process of Ti reduction, Ti particles become evaporated and deposit on the surface of C12A7, the free O2- atom in the cages diffuse to the sample surface, the Ti vapor reacts with the O2-, forming a loose TiO_x layer. In order to maintain electrical neutrality, the electrons of the free O2- atom leave from the cages, forming the C12A7:e- electride. In addition, the loose TiO_x layer also provides a channel for the diffusion of the O2- atoms in the cage, ensuring the continuation of the reduction reaction. The calculated band structure and density of states of the bulk C12A7:e- electride show that when electrons replace the O2- atoms in the cage, the Fermi level of C12A7:e- crosses over the cage conduction band (CCB). Thus the free movement of the electron is the main reason for the insulator C12A7 to convert into conductor C12A7:e-. At the same time the electrons near the Fermi level in the cages are easy to jump from the CCB to the frame conduction band (FCB). Combination of the above experimental results suggests that the electrons in cages are easier to escape to vacuum under the action of electric field or thermal field, which is the main reason for low work function of C12A7:e-. This way provides an new approach to the realization of the insulator C12A7 converting into C12A7:e- electride. And the C12A7:e- is a good electronic emission material due to low work function, low working temperature, and highly anti-poisoning ability, so this method of preparing bulk C12A7:e- electride provides a good new way to synthesize a new electronic emission material.

Hydrogen Desorption Below 150 °C in MgH2–TiH2 Composite Nanoparticles: Equilibrium and Kinetic Properties

Reversible hydrogen sorption coupled with the MgH2 ↔ Mg phase transformation was achieved in the remarkably low 340–425 K temperature range using MgH2–TiH2 composite nanoparticles obtained by reactive gas-phase condensation of Mg–Ti vapors under He/H2 atmosphere. The equilibrium pressures determined by in situ measurements at low temperature were slightly above those predicted using enthalpy ΔH and entropy ΔS of bulk magnesium. A single van’t Hoff fit over a range extended up to 550 K yields the thermodynamic parameters ΔH = 68.1 ± 0.9 kJ/molH2 and ΔS = 119 ± 2 J/(K·molH2) for hydride decomposition. A desorption rate of 0.18 wt % H2/min was measured at T = 423 K and p(H2) ≈ 1 mbar, i.e., close to equilibrium, without using a Pd catalysts. The nanoparticles displayed a small absorption–desorption pressure hysteresis even at low temperatures. We critically discuss the influence exerted by nanostructural features such as interface free energy, elastic clamping, and phase mixing at the single nanoparticle lev...

Control of Nano-Structure of Photocatalytic TiO2 Films by Oxygen Ion Assisted Glancing Angle Deposition

Control of the nano-structure of TiO2 photocatalytic films by a glancing angle deposition was investigated using an oxygen ion assisted reactive evaporation (OARE) system. The porosity of the film was increased as the incidence angle of Ti vapor increased, and films with clearly separated columnar grains were obtained at an incident angle above 60°. The increase in the porosity led to a significant decrease in UV reflectance and the film deposited at 60° had a large UV absorptance above 80% at 300 nm. The photocatalytic performance of the film, however, did not improve remarkably, since the crystallinity of the film was degraded by the deposition at a high incidence angle above 60°. To improve the crystallinity of the film, control of energy of the incident oxygen ions was attempted. However, only a slight improvement of photocatalytic properties was observed.

Effect of surrounding gas temperature on the morphological evolution of TiO2 nanoparticles generated by laser ablation in tubular furnace

Titanium oxide nanoparticles are synthesized by laser ablation of Ti target in oxygen atmosphere under well-controlled temperature profiles in a tubular furnace. The size and the shape of generated nanoparticles are varied by changing the temperature of furnace. The mobility-based size distributions of generated air-borne nanoparticles are measured using a scanning mobility particle sizer, and the size distributions of primary particles are analyzed by a scanning electron microscope. When the particles are generated by laser ablation at the room temperature, the particles are agglomerates in gas phase with the average mobility diameter of 117 nm and the mean diameter of primary particles of 11 nm. The primary particle diameter increases from 11 to 24 nm by raising the furnace temperature up to 800 °C. Since the mass of Ti vapor ablated from a target is found to be constant regardless of the furnace temperature, this particle growth may be attributed to the reduction in nuclei number as a result of mild quenching at higher temperatures. As the temperature reaches higher than 1,000 °C, the mobility diameter suddenly drops and the primary particle diameter increases due to sintering, and at 1,200 °C the mobility diameter coincides with the primary particle diameter. Since the laser oven method offers an independent control of vapor concentration and the temperature of surrounding atmosphere, it is an effective tool to study the formation process of nanoparticles from primary particles with a given size.

Bottom up deposition of advanced iPVD Cu process integrated with iPVD Ti and CVD Ru

We describe a novel development of bottom up deposition in the advanced Ionized Physical Vapor Deposition (iPVD) Cu process integrated with iPVD Ti and Chemical Vapor Deposition (CVD) Ru. Combination of CVD Ru and iPVD Cu processes provided us void free Cu filling with enlarging Cu grain size. CVD Ru film had superior wettability to Cu without alloy formation. Cu deposition thickness on field area was controlled by adjusting both Cu- and Ar-ion amount. Then Cu migrated on side wall surface toward trench bottom by Ar-ion bombardment and thermal energy avoiding the risk of pinch-off. Cu grain size inside trench was larger than conventional plated Cu. In addition, electrical performance indicated lower wiring resistivity with iPVD Cu filling using CVD Ru liner.

Sn-Doped Starfish-like Nanostructures from TiO2−SiO2 Core−Shell Nanocables and SiO2 Nanowires: Processing, Properties, and Characterization

Starfish-like TiO2:Sn/SiO2:Sn core−shell nanocables with SiO2:Sn nanowires were synthesized on a silicon substrate by thermal evaporation with addition of hydrogen gas at 1000 °C. In this synthesis, SnO2, silica, and Ti powder were used as source materials. The hydrogen gas served to reduce the SnO2 to SnOx (i.e., SnO) vapors and to reduce the silica to SiOx (i.e., SiO) vapors. These vapors, together with Ti vapor, were incorporated into Au liquid droplets (catalyst heads) and seeded the growth of nanostructures (nanocables and nanowires). FESEM images indicated that each catalyst head functioned as a growth site, such that the nanostructures grew in starfish-like forms via a vapor−liquid−solid (VLS) mechanism. HRTEM images revealed that each nanocable was composed of a single-crystalline rutile TiO2:Sn core (about 10−15 nm in diameter) with an amorphous SiO2:Sn shell (about 50−60 nm in thickness). The amorphous SiO2:Sn nanowires also grew densely on the Si substrate from the catalyst heads because of the...

Formation and Characterization of TiO2–SnOx–Sn Composite Nanowires Fabricated by Reduction/Oxidation of Sn and Ti Ions

We demonstrate that TiO2–SnOx–Sn composite nanowires (NWs) can be obtained by the reduction/oxidation of Sn and Ti ions. First, SnO2 nanowires were synthesized on TiO2/alumina substrate by a thermal evaporation through the vapor–liquid–solid (VLS) mechanism. Afterwards, SnO2 NWs/TiO2/alumina was thermally annealed in Ti powder at 1050 °C in a controlled mixture of gaseous argon and hydrogen (H2). The SnO2 nanowires were then decomposed to SnO and H2O vapors, which were together with Ti vapor species to form the TiO2–SnOx–Sn composite nanowires. High-resolution X-ray photoelectron spectroscopy (XPS) evaluated that the as-synthesized TiO2 nanowires mainly consisted of TiO2 with the dopants SnOx and Sn. Through the evaluation of the change in Gibbs free energy, it was found that a spontaneous reaction resulted in the formation of TiO2–SnOx–Sn composite nanowires. The characterization and formation of TiO2–SnOx–Sn composite nanowires are discussed.

Synthesis and Characterization of Single-Phase TiC Nanotubes, TiC Nanowires, and Carbon Nanotubes Equipped with TiC Nanoparticles

Single-phase TiC nanotubes were successfully synthesized for the first time, by the reaction of carbon nanotubes (CNTs) with Ti powder at 1300 °C for 30 h. CNTs equipped with TiC nanoparticles and TiC nanowires were synthesized along with these single-phase TiC nanotubes, and the number ratio of single-phase TiC nanotubes to these other products was very small. According to the core and low-energy electron energy loss spectra taken from CNTs and the CNTs reacted with Ti powder, the ratio of Ti to C in TiC nanowire was higher than that in TiC nanotubes and the ratio in CNT equipped with TiC nanoparticles was the lowest. Three different types of TiC nanomaterials, TiC nanowires, TiC nanotubes, and CNTs equipped with TiC nanoparticles, as well as unreacted CNTs, were observed in this study, possibly because the concentration of Ti vapor decreased with increase in depth from the surface of CNT aggregates. A partly single-crystalline TiC nanotube was also observed.

Controlled growth of high-qualityTiO2 nanowires on sapphire and silica

The vapour–liquid–solid (VLS) growth ofTiO2 nanowires(NWs) was performed using a thermally evaporated Ti source and sputter-deposited Au catalysts under anO2 gas flow. High-densitysingle-crystalline TiO2 NWs having the rutile structure were successfully grown on sapphire (single-crystalα-Al2O3) and quartz(amorphous SiO2) substrates. Ti buffer layers, deposited on the substrates to prevent undesirablereactions between the Ti vapour and substrates, were identified to promote theTiO2 NW growth by providing supplementary Ti vapour to the Au catalysts. Crystallinity ofTiO2 NWs was investigated by x-ray diffraction (XRD) and their morphologicalfeatures were characterized by field emission scanning electron microscopy(FESEM). High-resolution transmission electron microscopy (HRTEM) andselected area electron diffraction (SAED) analyses reveal growth of the rutileNWs having twofold twin structures along the growth direction on Ti/sapphireand the defect-free single-crystalline rutile NWs on Ti/quartz substrates.TiO2 NWs grown on Ti/quartz showed a short-wavelength(∼402 nm) and high-intensity photoluminescence (PL) emission compared to those grown onTi/sapphire substrates. By introducing a Ti buffer layer and using quartz substrates,the crystallinity and PL properties were successfully improved for VLS-grownTiO2 NWs.

The growth and structure of titanium dioxide films on a Re(1 0 −1 0) surface: Rutile(0 1 1)-(2 × 1)

Titanium dioxide films were grown on Re(1 0 −1 0) by Ti vapor deposition in oxygen at T = 830 K and studied by means of low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS) and X-ray diffraction (XRD). The Ti oxide stoichiometry was determined by XPS as Ti:O = 1:2, with the Ti oxidation state (4+). The TiO 2 growth was monitored by means of LEED as a function of film thickness. Extending the coverage from the submonolayer into the multilayer regime gives rise to a p(2 × 2) pattern, a (poorly ordered) (1 × 1), and, finally, a stable (2 × 2) structure, the latter being associated with a homogeneous TiO 2 phase. For normal electron incidence, the (2 × 2) LEED pattern exhibits systematically extinguished beams at ( n ± 1/2, 0) positions, indicating a glide mirror plane. The pg(2 × 2) structure could be explained by both a rutile(0 1 1)-(2 × 1) reconstructed surface and a bulk truncated brookite(0 0 1) surface. Faceting phenomena, i.e. running LEED spots, observed with thin TiO 2 films point to the formation of a rutile(0 1 1)-(2 × 1) surface with two domains and {0 1 1}-(2 × 1) facets and rule out the brookite alternative. Confirmation of this assignment was obtained by an XRD analysis performed at the Berlin synchrotron facility BESSY.

Evolution of the Interface and Metal Film Morphology in the Vapor Deposition of Ti on Hexadecanethiolate Hydrocarbon Monolayers on Au

The combination of in situ X-ray photoelectron spectroscopy, infrared reflection spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry are used to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a CH(3)(CH(2))(15)S/Au{111} self-assembled monolayer (SAM) at ambient temperature. The results show that for a deposition rate of approximately 0.15 Ti atom.nm(-2).s(-1) a highly nonuniform Ti overlayer is produced via a process in which a large fraction of impinging Ti atoms do not stick to the bare SAM surface. The adsorbed atoms form isolated Ti clusters and react with CH(3) groups to form carbide products at the cluster-SAM interfaces. Further growth of Ti clusters appears to be concentrated at these scattered reaction centers. The SAM molecules in the local vicinity are subsequently degraded to inorganic products, progressing deeper into the monolayer as the deposition proceeds to give an inorganic/organic nanocomposite. A continuous overlayer does not form until metal coverage approaches approximately 50 Ti atoms per SAM molecule. These data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic, suffering from both a highly nonuniform contact area and the presence of extensive inorganic products such as nonstoichiometric carbides and hydrides.

Deposition of nanocomposite TiN-Si3N4 thin films by hybrid cathodic arc and chemical vapor process

A hybrid technique is described for the synthesis of nanocomposite TiNSi3N4 thin films based on the reactive deposition of Ti produced from a cathodic arc source and Si from a liquid tetramethylsilane (TMS), precursor. The technique combines both the physical vapour of Ti and chemical vapour of silicon in a nitrogen background pressure in a single system. The influence of the TMS flow rate on the structure and mechanical properties has been investigated. The film structure was found to comprise of TiN crystallites and amorphous Si3N4. The X-ray diffraction data showed that with increasing TMS flow, there is a decrease in the TiN crystalline size from 33 nm to 4 nm. The hardness of the films was found to be strongly dependent on the Si content and reached a maximum value of 41 GPa at ∼5% Si content at a total pressure of nitrogen and TMS of 0.8 Pa. Hardness enhancement was found to arise from the nanostructural change induced due to the addition of an amorphous Si3N4 phase into the film. Transmission electron microscopy (TEM) analysis confirmed the structure of the ncTiN/aSi3N4 composites. Films with 4 at. % or more silicon were found to maintain the hardness after annealing at 500 °C in vacuum.

イオンミキシング蒸着法による（Ｔｉ，Ａｌ）Ｎ薄膜の作製とその特性評価

A few studies on the synthesis of titanium aluminum nitride (Ti,Al)N films have attracted interests, in particular as an alternative to the widely used TiN films, to obtain wear-protective hard coating with higher oxidation resistance at elevated temperature. Here, the (Ti,Al)N films were prepared by depositing Ti and Al metal vapor under simultaneous irradiation of N ions, that is ion mixing and vapor deposition (IVD) technique. With an increase of evaporation Al/Ti and/or transport ratio (Ti + Al)/N, a single-phase of NaCl structure in the films transformed into that of wurtzite structure through a two-phase mixture consisting of NaCl and wurtzite structure. Based on the revelation of two-phase structure, therefore, the optimum preparation conditions for wear- and corrosion-resistive hard coating were identified. The (Ti,Al)N films were also highly resistant against oxidation. Consequently, the results suggest that the Al oxide layers formed on the top of (Ti,Al)N films during elevated temperature oxidation tests protect the films from further oxidation.