Growth of carbon nanofibers and related structures by combined method of plasma enhanced chemical vapor deposition and aerosol synthesis

Growth of carbon nanofibers and nanotubes by combination of aerosol synthesis and plasma-enhanced catalytic chemical vapor deposition with alcohol as carbon precursor is presented. Only a hollow cathode glow discharge (HCGD) is used as gas activation process without any specific heating of the substrate. Specially designed hollow cathode enables the evaporation of catalyst directly on the substrate for catalytic growth. Product of physical vapor deposition process was examined by energy dispersive X-ray spectrometer (EDS). Spectroscopic features of the plasma were monitored by optical emission spectroscopy (OES). Carbon deposition was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Catalytic nanofibers and multi-walled carbon nanotubes with outer diameters 20-60 nm have been observed.     

Optical rib waveguide based on epitaxial Ba0.7Sr0.3TiO3 thin film grown on MgO

Barium strontium titanate (Ba_0.7Sr_0.3TiO₃, abbreviated as BST) thin films were grown on MgO (001) single crystal substrates using pulsed laser deposition. A heteroepitaxial growth relationship of <001> _BST // <001> _MgO was confirmed by X-ray diffraction. The bidimensional structure of a rib waveguide was designed using the effective index method. A BST/MgO rib waveguide was fabricated using photolithography and reactive ion etching techniques. A single-mode near-field output pattern was observed using an end-fire coupling method at a wavelength of 1550 nm, which is consistent with our numerical calculation.     

Hardening behavior of Mn-modified KNN-BT thick films fabricated by aerosol deposition

Highly dense, 30 μm-thick 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ (KNN-BT) lead-free films were successfully fabricated on alumina substrate by aerosol deposition (AD) and the effect of Mn doping (0 mol%, 0.5 mol% and 1.0 mol%) on the film properties was investigated. It was found that low field dielectric constant decreases by 36% for 0.5 mol% Mn doping and 42% for 1 mol% Mn doping. The loss factor was found to reduce by 19% for 0.5 mol% Mn doping and 43% for 1 mol% Mn doping. Based on the high field polarization-electric field measurement, we demonstrate that Mn induces hardening in KNN-BT thick films. The hardening is believed to be due to the pinning of the domains by dipolar defects at domain boundaries.     

Laser-induced synthesis,deposition and etching of materials

The field of laser-induced synthesis, deposition and etching of materials is reviewed with an emphasis on the emerging trends and novel adaptations of the basic laser processing concepts. A number of examples are cited to illustrate the issues involved. These include rapid synthesis of titanium nitride by pulsed laser induced reactive quenching at Ti:liquid NH₃ interface, laser deposition of good quality thin films of such materials as hot oxide superconductors, zinc ferrite, iron oxide, stainless steel, etc. and laser etching of superconductor films.     

A study of ceramic addition in end termination of multilayer ceramics capacitors with cofiring process

The silver paste with ceramics addition as end termination was performed on multilayer ceramic capacitors (MLCC) based on ZnO–B₂O₃ + Zn_0.95Mg_0.05TiO₃ + 0.25TiO₂ ceramic (ZnBO-ZMT′) with Ag95–Pd05 internal electrodes. A green sheet was prepared by tape casting using the ZnBO-ZMT′ powders. Ag95–Pd05 was attached on the green sheet as an internal electrode. After lamination, the green chips were pre-sintered at 800 °C for 1 h, then samples were dipped the external electrodes and were cofired together at 900 °C for 2 h. There is no extra curing process, so the production cost may be cut down and thermal shock of the MLCCs may be reduced. To improve the mismatch between end termination and dielectric body during sintering, the silver paste with different amounts of ceramics, e.g., 20, 30 and 40 wt.%, was added in this study. The mechanical and electrical properties of the MLCCs were investigated subsequently. The results showed that end termination with 40 wt.% ceramic addition has good performances on mechanical properties of MLCC, but equivalent series resistance (ESR) is a little bit higher compared to end termination with 20 and 30 wt.% ceramic addition.     

Preparation of thin epitaxial multilayer YBa2Cu3O7−x (Ag) films by aerosol deposition

Thin-textured YBa₂Cu₃O _y (Ag) films were prepared by a new CVD process consisting of aerosol deposition and low temperature annealing, both operations not exceeding 600°C. MgO and SrTiO₃ single crystals were used as substrates. The stoichiometry of the prepared films was not ideal 1–2–3, having the atomic quotient of copper always lower than 3. For an unoptimized preparation process, the onset temperatures were around 80 K and the zero resistanceT _c values around 70K. Properties of samples obtained by low-temperature annealing are compared with those obtained by high temperature annealing. “Cleaning” effect of vacuum-annealing upon removing the nitrate and hydroxide groups from the prepared films is supposed.     

Large-scale synthesis of nanocrystals of barium titanate and other titanates through solution-phase processes

We reported a large-scale synthesis of nanocrystals of BaTiO₃, SrTiO₃, PbTiO₃, Sr_xBa_1−xTiO₃ through low-temperature and solution-phase processes without any surfactant. The series of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Samples obtained were of high purity, consisting of nanoparticles with fine crystallinity and uniformity as well as good dispersibility in ethanol. This method might also offer an effectively new way to synthesis other titanate nanocrystals with perovskite structure in the future.     

Superhydrophobic polymer films via aerosol assisted deposition — Taking a leaf out of nature's book

Aerosol assisted deposition of three sets of polymer films based on commercially available resins was achieved on various substrates. The films were characterised using a range of methods, including water contact and slip angle to determine water repellent properties. The aerosol assisted deposition inside the chemical vapour deposition reactor was unique in generating a highly rough superhydrophobic surface with water contact angles up to 170°. During the deposition process, two of the polymers were cured resulting in the development of high surface morphology. It was observed that the polymer that did not cure did not develop such a rough surface resulting in a lower water contact angle (∼ 99°). The superhydrophobic films had a Cassie-Baxter type wetting with water failing to penetrate the surface porosity, water spraying on the surface would bounce off. These films had exceptionally low slide angles of ca 1-2° from the horizontal.     

Preparation of Barium Strontium Titanate Ceramic by Sol-Gel Method and Microwave Sintering

The (Ba,Sr)TiO₃ amorphous gel was prepared by sol-gel process and calcined in the 2.45-GHz multimode microwave furnace to synthesize (Ba,Sr)TiO₃ nanopowder. The calcination temperature of the (Ba,Sr)TiO₃ ceramic powders that convert the material into prevoskite phase can be reduced from 1100°C to 900°C, the nanopowder displays the highest sinterability. Using a new kind of insulator materials made of MgAl₂O₄–LaCrO₃, the crack-free and dense (Ba_0.80Sr_0.20)TiO₃ ceramics with fine grain size (<1 µm) were prepared by microwave sintering at 1310°C for 15 min. The fine (Ba,Sr)TiO₃ ceramics sintered by microwave sintering technique display lower dielectric loss than that of conventional samples, indicating a reduction of the influence of defects with the microwave process.     

Microwave synthesis of nano-sized barium titanate

Nano-sized barium titanate powders have been synthesized by microwave processing at 2.45 GHz. Using barium titanyl oxalate (BTO) as a precursor, microwave processing was carried out by heating the precursor to a temperature between 600 °C and 750 °C with different heating rates from 10 °C/min to 20 °C/min without isothermal holding. X-ray diffraction analysis indicates that the decomposed product at 680 °C was pure cubic BaTiO₃. The BET specific surface area of barium titanate powder, after microwave heating to 680 °C, was 14.2 ± 0.5 m²/g, corresponding to an average particle size of 70 nm. This particle size was confirmed by the scanning electron microscopy (SEM). Parallel study shows that the conventional heating in a regular resistance furnace using a similar heating schedule did not result in complete conversion of BTO. This study shows that the microwave processing significantly accelerated the decomposition of barium titanyl oxalate and reduced the temperature of barium titanate nano-powder formation, resulting in nano-sized pure cubic barium titanate powder.     

The incorporation of preformed metal nanoparticles in zinc oxide thin films using aerosol assisted chemical vapour deposition

The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 °C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 °C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented.     

Thickness limit of BaTiO3 thin film capacitors grown on SUS substrates using aerosol deposition method

We fabricated BaTiO₃ thin films with 2.2-0.1 μm thickness on hard stainless steel (SUS) substrates by using the ADM to confirm the causes of dielectric thickness limit showing in BaTiO₃ thin films prepared on SUS substrates and suggest key factors which can overcome the limit. Then, from the measurements of thickness dependence of their dielectric properties, the thickness limit of 0.2 μm was confirmed and to confirm the reason why their dielectric properties could not be measured in the thickness below 0.2 μm, the thickness dependence of leakage current mechanisms in BaTiO₃ films were investigated. As a result, by decreasing the thickness of films from 2.2 to 0.2 μm, the mechanism changed from Poole-Frenkel emission to modified-Schottky emission indicating increase of interface effects. Especially, in the case of 0.2 μm thickness, it was confirmed that the dominant mechanism was Fowler-Nordheim tunneling based on electric field concentration at a high electric field. Consequently, from this investigation of leakage current mechanism, it can be expected that the cause of thickness limits was electric field concentration at rough BaTiO₃/SUS interfaces forming in AD process, and to get over the thickness limit and decrease level of leakage currents, the hard substrates are required to reduce the interface roughness and oxygen vacancies acted as donors should be decreased.     

Molten-salt synthesis of tetragonal micron-sized barium titanate from a peroxo-hydroxide precursor

Barium titanate (BaTiO₃) was produced from an barium-titanate-peroxo-hydroxide precursor material in NaCl-KCl and Na₂SO₄-K₂SO₄ salt mixtures or fluxes at temperatures up to 1080 °C via the molten-salt synthesis (MSS) method. Beside the different salt mixtures several other parameters were studied to determine the effect on the particle morphology. A relatively fast heating rate and a relatively high salt to precursor ratio resulted in a highly faceted morphology. The effect of the salt flux was clearly seen in the morphology of BaTiO₃ obtained by MSS at 1080 °C. Cube-shaped particles were observed for the chloride-flux-grown BaTiO₃ while hexagonal-shaped flat particles were observed for the sulfate-flux-grown BaTiO₃. BaTiO₃ particles produced in the chloride-flux were either {1 0 1} or {0 0 1} faceted. The hexagonal surface of the sulfate-flux-grown BaTiO₃ was {1 1 1} faceted.     

Preparation of Oriented Barium Titanate Thin Films by Combination of Electrophoretic Deposition with Hydrothermal Treatment

Highly oriented barium titanate (BaTiO 3) thin films on Pt substrate were fabricated by combination of electrophoretic deposition with hydrothermal treatment.The structure and morphology of thin films were characterized by X-ray diffraction and field-emission scanning electron microscopy.It is found that the titania precursor film,Ba(OH)2 concentration and hydrothermal temperature play crucial roles in the film morphology and orientation.The BaTiO3 thin films with highly (110) preferred orientation can be f...     

Aerosol deposition of silicon-substituted hydroxyapatite coatings for biomedical applications

Silicon-substituted hydroxyapatite (Si-HA) coatings on commercially pure titanium (Ti) were prepared by aerosol deposition using Si-HA powders. Si-HA powders with the chemical formula Ca₁₀(PO₄)_6 − x(SiO₄)_x(OH)_2 − x, having silicon contents up to x = 0.5 (1.4 wt.%), were synthesized by solid-state reaction of Ca₂P₂O₇, CaCO₃, and SiO₂. The Si-HA powders were characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometry, and Fourier transform infrared spectroscopy. The corresponding coatings were also analyzed by XRD, scanning electron microscopy, and electron probe microanalyzer. The results revealed that a single-phase Si-HA was obtained without any secondary phases such as α- or β-tricalcium phosphate for both the powders and the coatings. The Si-HA coating was about 5 µm thick, had a dense microstructure with no cracks or pores, and showed a high adhesion strength ranging from 28.4 to 32.1 MPa. In addition, the proliferation and alkaline phosphatase activity of MC3T3-E1 preosteoblast cells grown on the Si-HA coatings were significantly higher than those on the bare Ti and pure HA coating. These results revealed the stimulatory effects induced by silicon substitution on the cellular response to the HA coating.     

Chemical liquid deposition process for microstructure fabrication

Scientists and engineers are currently moving into a new era to develop precise and intelligent mini-structures and microsystems. The study of mini-structures and microsystems is a rapidly growing area of research with a great potential to accomplish useful tasks in numerous applications. In this paper, a new fabrication technology for microstructures based on the chemical liquid deposition (CLD) is presented. This technology is based on the following principles: micro-droplets of a cold (room temperature) solution or liquid reactant are sprayed from a nozzle and make contact with a hot substrate, the droplets will evaporate, decompose, or react, and then the reacted solid products will deposit on the substrate. By controlling the motion of the nozzle and the spray time, a desired 3D microstructure of the deposited material can be formed through a layer-by-layer scanning technique. The working principle, available materials as well as the process control and modeling is discussed and some preliminary results are presented.     

Synthesis of epitaxial BaZrO3 thin films by chemical solution deposition

This work reports on the low temperature preparation and characterization of BaZrO₃ (BZO) epitaxial thin films by chemical solution deposition (CSD). The X-ray θ-2θ scan and φ-scan measurements have demonstrated that the BZO films exhibit cube-on-cube epitaxy on (100) MgO substrates, with the full width at half maximum (FWHM) for the ω-scan and φ-scan of 0.35° and 0.46°, respectively. The SEM and AFM analyses revealed that the morphology of the films is strongly correlated with annealing temperature. The root mean square roughness for the film annealed at 600 °C is 3.63 nm, while for the film grown at 1000 °C is 5.25 nm.     

Effect of process parameters and post deposition annealing on the optical, structural and microwave dielectric properties of RF magnetron sputtered (Ba0.5,Sr0.5)TiO3 thin films

Thin films of (Ba_0.5,Sr_0.5)TiO₃ (BST5) in the thickness range 400-800 nm have been deposited by RF magnetron sputtering on to quartz substrates at ambient temperature. All the properties investigated, i.e. structure, microstructure, optical and microwave dielectric, show a critical dependence on the processing and post processing parameters. The surface morphology as studied by atomic force microscopy reveals ultra fine grains in the case of as deposited films and coarse grain morphology on annealing. The as-deposited films are X-ray amorphous and exhibit refractive index in the range 1.9-2.04 with an optical absorption edge value between 3.8 and 4.2 eV and a maximum dielectric constant of 35 at 12 GHz. The dispersion in refractive index fits into the single effective oscillator model while the variation in the optical parameters with oxygen percentage in the sputtering gas can be explained on the basis of packing fraction changes. On annealing the films at 900 °C they crystallize in to the perovskite structure accompanied by a decrease in optical band gap, increase in refractive index and increase in the microwave dielectric constant. At 12 GHz the highest dielectric constant achieved in the annealed films is 175. It is demonstrated that with increasing oxygen-mixing percentage in the sputtering gas, the microwave dielectric loss decreases while the dielectric constant increases.     

电泳沉积法制备钛酸纳米管膜层

采用水热合成法制备钛酸钠纳米管,然后依次与HNO3,正四丁基氢氧化铵水溶液(TBAOH)离子交换后,经过高速离心,将所得沉淀物分散于无水乙醇溶液中,并应用电泳沉积的方法成功地在不锈钢或导电玻璃表面构筑了钛酸纳米管薄膜.采用TEM、XRD、SEM及EDS等对纳米管薄膜的表面形貌、结构和组成等进行表征.结果表明,电泳沉积法制备钛酸纳米管薄膜致密均匀、厚度可控并与基体结合力良好;经高温烧结后,形貌基本保持不变,可望成为一种新的功能材料.文中还对纳米管薄膜的形成机理进行了讨论.     

Enhanced ferroelectric properties of Mg doped (Ba,Sr)TiO3 thick films grown on (001) SrTiO3 substrates

Highly (001)-oriented 1 mol% Mg doped (Ba_0.67,Sr_0.33)TiO₃ (BST) films with a thickness of 1.25 μm were grown on (110) SrRuO₃/(001) SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction measurements reveal that the BST thick films have very high crystalline quality, and have a distorted lattice with a large tetragonality a/c = 1.012. The BST thick films have a remanent polarization (P_r) value as large as 10.1 μC/cm² and a coercive electric field (E_c) value of 65.0 kV/cm. The films possess dielectric constant and loss values of ε_r = 385.36 and tgδ = 0.038 at 1 kHz and room temperature. The leakage currents of the films are on the order of 10^− 5 A/cm² at ± 150 kV/cm. The mechanism for enhancing electric properties of the Mg doped BST films was also discussed.