Boron nitride coatings by chemical vapor deposition from borazine

Boron nitride coatings were prepared from borazine as the single source precursor containing stoichiometric boron and nitrogen by hot-wall chemical vapor deposition (CVD) in a low deposition temperature range from 800 °C to 900 °C, with a total pressure of 1 kPa. The chemical and phase compositions, morphologies and structures of the coatings were investigated. The coatings deposited at 800 °C still contained some residual N-H, whereas the coatings prepared at 900 °C were comparatively pure BN. The surface of the as-deposited coatings exhibited a pebble-like and compact structure, and the cross-sectional morphology of the coatings showed a laminar structure. While the as-deposited coatings had a turbostratic structure as evidenced from the XRD and TEM examinations, the turbostratic BN crystallized into hexagonal BN by heat treatment at temperatures above 1400 °C. The as-deposited coatings had a preferential orientation near the coating/graphite substrate interface in which the (002) basal planes organized parallel to the surface of the substrate.     

Hydroxyapatite coating on titanium substrate by electrophoretic deposition method: Effects of titanium dioxide inner layer on adhesion strength and hydroxyapatite decomposition

Nanosized hydroxyapatite (HA) powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V substrates. The powders were calcined before the deposition process in order to obtain crack-free coating surfaces. As an inner layer between Ti6Al4V substrate and HA coating, nanosized titanium dioxide (TiO₂) powders were deposited, using different coating voltages, in order to connect substrate and HA tightly. Moreover, this layer is considered to be acting as a diffusion barrier, reducing the HA decomposition due to ion migration from the metal substrate into the HA. After the sintering stage, adhesion strengths of coatings were measured by shear testing, phase changes were studied by X-ray diffraction, and coating morphology was analyzed through scanning electron microscopy observations. Results showed that usage of the TiO₂ inner layer prevented HA decomposition. Furthermore, decreasing the voltage used in TiO₂ deposition resulted in crack-free surfaces and increased adhesion strength of the overall coating.     

Development of a novel cathodic plasma/electrolytic deposition technique part 1: Production of titanium dioxide coatings

A new atmospheric pressure plasma electrolytic deposition process has been developed for the production of crystalline titanium dioxide films on metal substrates. The process occurs in a liquid precursor composed of titanium tetraisopropoxide and absolute ethanol. A plasma discharge is created and confined around the cathode in a superheated vapour sheath surrounded by the liquid phase, inducing the production of a nano-crystalline TiO₂ coating at the surface of the cathode. The analysis of the structure and composition of these TiO₂ coatings have been carried out by Scanning Electron Microscopy, Transmission Electron Microscopy, Raman and X-Ray Photoelectron Spectroscopies and X-Ray Diffraction. The produced crystalline titanium dioxide coatings are very adherent to the substrate and present a dendritic-like structure. We have moreover demonstrated that it is possible to adjust easily its composition by a post-processing calcination. Such characteristics make these films very interesting for photocatalysis, solar cells and gas sensing applications, and promise therefore some useful industrial benefits.     

Thermal plasma chemical vapor deposition of wear-resistant, hard Si-C-N coatings

Wear-resistant, hard Si-C-N coatings were synthesized in a triple torch plasma reactor using a thermal plasma chemical vapor deposition process. In this reactor, three dc plasma torches were angled so that their jets converge to form a highly chemically reactive region at the substrate. Vaporized hexamethyldisilazane (HMDSN) was injected through a central injection probe, while nitrogen or hydrogen gases were added through the torches to the argon plasma.Various dissociation, recombination and intermediate reactions were considered to determine what major species exist in the gas phase during the deposition of Si-C-N films. Reactant flow rates were varied to evaluate the thermodynamic equilibrium compositions across a linear temperature profile above the substrate and to identify the species that lead to the production of wear-resistant, hard Si-C-N films.A series of experiments were conducted at low HMDSN flows (∼ 1 sccm) and varying hydrogen and nitrogen flows. Films were characterized by micro X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Indentation tests were conducted on the polished film cross-sections, while wear tests were carried out on the film surfaces. At substrate temperatures below 1000 °C, amorphous Si-C-N films were deposited, while higher temperatures produced crystalline composite films of α- and β-Si₃N₄ and α- and β-SiC. Films produced with hydrogen at low HMDSN flows displayed non-columnar morphology and therefore had higher wear-resistance, indicating the benefit of low reactant-to-plasma gas flow concentrations on film growth. At low HMDSN flows, low nitrogen-to-hydrogen ratios had also shown an increase in film linear density. Small variations in mechanical properties and wear were observed between films grown under low N:H flow ratio conditions (smooth film surfaces). Wear-resistance of films with columnar structures from high N:H conditions was significantly lower, while the hardness was unobtainable. This result indicates the importance of film morphology on mechanical performance.     

Antibacterial properties of vacuum plasma sprayed titanium coatings after chemical treatment

Implant-related infection is one of the common clinical complications that cause high rates of mortality and morbidity in orthopedic surgery. Endowing implant antibacterial properties is a useful method to reduce such infection. In this paper, vacuum plasma sprayed titanium coatings were treated by NaOH solution firstly, and then antimicrobial silver was introduced into the coatings by immersing in 0.02 mM (denoted as CA1), 0.06 mM (denoted as CA2) and 0.1 mM (denoted as CA3) Ag⁺ containing calcification solution. Antibacterial property of the treated titanium coatings was examined by employing three types of bacteria stains, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. X-Ray diffraction and scanning electron microscopy were used to observe the phase composition and surface morphology of the modified titanium coatings. Results showed that all of the three kinds of coatings exhibited more than 90.00% antibacterial ratio except CA1 to Staphylococcus aureus which is 63.30%. The release of silver in physiological environment was monitored and it was found that the excellent antibacterial property of the treated coatings was attributed to the release of silver.     

Formation of mullite coatings on silicon-based ceramics by chemical vapor deposition

Dense, uniform, mullite coatings have been deposited by chemical vapor deposition on SiC substrates, using a AlCl₃-SiCl₄-CO₂-H₂ system. The typical coating microstructure consisted of a thin layer of nanocrystallites of γ-Al₂O₃ in vitreous silica at the coating-substrate interface, with columnar mullite grains over this interfacial layer. The composition of the coating was graded such that the outer surface of the coating was highly alumina rich. The changes in the coating microstructure with processing parameters are discussed. The ability of mullite to incorporate such large composition variations is discussed in the light of vacancy formation as theAl/Si ratio is increased and the ordering of these vacancies leads to changes in lattice parameters. The formation of domains was studied by measuring the spacing of superlattice spots in electron diffraction patterns and the relationship between domain size andAl/Si ratio is discussed.     

Synthesis of titanium nano-particles via chemical vapor condensation processing

In the present study, titanium nano-particles have been synthesized using chemical vapor condensation (CVC) process. Reaction of sodium and titanium tetrachloride vapors in the tube furnace resulted in the production of titanium nano-particles that were encapsulated in sodium chloride. Dried Argon gas was employed as a carrying agent. Titanium nano-particles were contained in an ethanol bath. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) were employed for analysis and characterization of nano-particles. The size of primary particles was smaller than 100 nm and secondary particles were submicron agglomerations.     

Thermal conductivity of titanium dioxide films grown by metal-organic chemical vapor deposition

We studied the effect of the microstructures on the thermal conductivity of the titanium dioxide (TiO₂) films. TiO₂ films were grown by MOCVD, their morphologies were observed using a scanning electron microscope (SEM). The chemical composition was determined through Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) measurements. The thermal conductivity of the in-plane direction was measured using an alternating current calorimetric method (laser-heating Angstrom method) in the temperature range of 300 to 470 K. The authors fabricated a TiO₂ film with extremely low thermal conductivity (~ 0.5 Wm^− 1 K^− 1), in which a feather-like texture is regularly arranged in the direction perpendicular to the heat flow. The origins of the extremely low thermal conductivity were studied from a microstructural viewpoint.     

Formation of aluminide coatings on Fe-based alloys by chemical vapor deposition

Aluminide and Al-containing coatings were synthesized on commercial ferritic (P91) and austenitic (304L) alloys via a laboratory chemical vapor deposition (CVD) procedure for rigorous control over coating composition, purity and microstructure. The effect of the CVD aluminizing parameters such as temperature, Al activity, and post-aluminizing anneal on coating growth was investigated. Two procedures involving different Al activities were employed with and without including Cr–Al pellets in the CVD reactor to produce coatings with suitable thickness and composition for coating performance evaluation. The phase constitution of the as-synthesized coatings was assessed with the aid of a combination of X-ray diffraction, electron probe microanalysis, and existing phase diagrams. The mechanisms of formation of these CVD coatings on the Fe-based alloys are discussed, and compared with nickel aluminide coatings on Ni-base superalloys. In addition, Cr–Al pellets were replaced with Fe–Al metals in some aluminizing process runs and similar coatings were achieved.     

Syntheses of carbon nanomaterials by radio frequency plasma enhanced chemical vapor deposition

We report a simple and effective method for syntheses of carbon nanomaterials, including a hybrid CNTs/cobalt particles shelled with graphitic layers, pure CNTs, a CNTs/carbon nanosheets (CNSs) composite and pure CNSs, on O₂-thermal etched Co substrate films, in discharging different mixed gases (CH₄/H₂, CH₄/H₂/O₂, CH₄/Ar and CH₄/Ar/O_2, respectively), using radio frequency plasma enhanced chemical vapor deposition (PECVD). Being etched by O₂ during the pretreatment stage, Co thin film transformed into small CoO particles and consequently the deoxidization of CoO particles may occur in PECVD process when different reactive gases are used to obtain various carbon nanomaterials. We find that the reactive gases govern the degree of how the CoO particles can be deoxidized and determine the final carbon nanomaterial products. In this work, the possible growth mechanisms for obtaining various carbon nanomaterials have been explored.     

直流等离子体-热丝化学气相沉积金刚石薄膜的研究

通过在传统热丝化学气相沉积装置中引入直流等离子体,设计了直流等离子体-热丝化学气相沉积金刚石薄膜的设备,设备中既包括相互独立的灯丝电压和施加的偏压。通过调节偏压可以控制所形成的等离子体的偏流。在这一改进的系统中研究了金刚石薄膜形核和生长过程,利用扫描电子显微镜（SEM）、X射线衍射（XRD）分析了金刚石的样品,结果表明,施加偏压不仅能大大促进金刚石的形核密度（10^10cm^-2）、提高金刚石薄膜的生长速率,金刚石薄膜的取向也随机取向变为（111）定向生长。     

Effective parameters on diameter of carbon nanotubes by plasma enhanced chemical vapor deposition

The effective parameters on the diameter of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) were presented.Among lots of influential parameters,the effects of the catalytic film thickness and the pretreatment plasma power on the growth of CNTs were investigated.The results show that the size of catalytic islands increases by increasing the thickness of catalytic layer,but the density of CNTs decreases.The pretreatment duration time of 30 s is the optimal condition for growing CNTs with about 50 nm in diameter.By increasing the pretreatment plasma power,the diameter of CNTs decreases gradually.However,the diameter of CNTs does not change drastically from 80 to 120 W.The uniformly grown CNTs with the diameter of 50 nm are obtained at the pretreatment plasma power of 100 W.     

Influence of substrate pre-treatments on the growth of SixNyHz thin films by plasma enhanced chemical vapor deposition

A two-step plasma enhanced chemical vapor deposition procedure has been developed to produce high quality Si_xN_yH_z films for quantum cascade laser applications. The procedure consists in exposing the GaAs substrate to a controlled N₂ plasma previous to the silicon nitride film deposition. The pre-treatment causes the formation of a thin GaN film that passivates the GaAs wafer. The method has been optimized varying RF power, N₂ flow rate and process time of the pre-treatments and monitoring their effects on the resulting chemical composition and dielectric properties of the nitride overlayers, by means of infrared spectroscopy, X-ray photoelectron spectroscopy and electric characterizations. A narrow window in the pre-treatment RF power, N₂ flux and time values, improves the composition, structural and dielectric properties of the silicon nitride overlayers. The best result has been found depositing the silicon nitride films on GaAs wafer after 2 min of N₂ plasma treatment with a power of 20 W and a 50 cm³/min flow rate.     

Fast chemical vapor deposition of microcrystalline silicon by applying magnetic field to hollow electrode enhanced radio frequency glow plasma

Fast chemical vapor deposition of microcrystalline silicon by applying magnetic field to hollow electrode enhanced radio frequency (rf) glow plasma has been investigated. We have already developed a plasma generation technique called hollow electrode enhanced rf glow plasma transportation (HEEPT). In this study, we equipped a HEEPT system with a hollow cylinder shaped permanent magnet around an orifice prepared at the center of the counter electrode. The plasma was characterized by plasma emission spectroscopy. Silicon thin films were deposited on a glass substrate. It was found that increasing the magnetic flux density resulted in increasing plasma emission intensity, film deposition rate, and crystallinity. The maximum deposition rate of 6.9 nm/s was achieved with high crystallinity and photo-sensitivity at a plasma excitation frequency of 13.56 MHz, a substrate temperature of 300 °C and a magnetic flux density of 75 mT. Our results indicate that the magnetic field is effective in promoting fast chemical vapor deposition of microcrystalline silicon thin films with photo-sensitivity using the HEEPT technique. We consider that the effectiveness is due to a decrease of electron temperature caused by drift motion of electrons in the magnetic field inside the orifice.     

Raman spectroscopy investigations of TiBxCyNz coatings deposited by low pressure chemical vapor deposition

TiB_xC_yN_z coatings have been prepared applying LPCVD and characterized using SEM/EDX, XRD, and Raman micro-spectroscopy. It has been shown that first-order, defect-induced Raman spectra of good quality can be obtained from TiB_xC_yN_z coatings, even if buried within a multilayer stack. The Raman peak assignments fit well with previous work on TiC_1 − xN_x. Even small changes in the B:C:N ratio result in systematical shifts of the Raman peaks. With increasing nitrogen content, the acoustical phonons shift to lower frequencies. A high correlation of the Raman shifts with lattice constants derived from XRD has also been found. Additionally, intensity and FWHM of the Raman peaks also change going from carbon- to nitrogen-rich coatings. The sensitivity of the TA peak Raman shifts to changes of the investigated basic coating properties is largest for N-rich coatings. Looking at the full range of coatings the dependence of the Raman shifts is slightly nonlinear.The present work establishes Raman microscopy as a complementary non-destructive technique compared to XRD for studying coatings like TiB_xC_yN_z. Structural, optical and chemical properties can be determined with considerably higher spatial resolution.     

CO addition in low-pressure chemical vapour deposition of medium-temperature TiCxN1-x based hard coatings

TiC_xN_1-x base layers with Al₂O₃ top layers, both grown by chemical vapour deposition (CVD), are state-of-the-art in metal cutting with cemented carbide inserts. In order to influence the microstructure and properties of the base layer, five different TiC_xN_1-x coatings were grown by medium-temperature CVD with increasing CO fractions in the TiCl₄–CH₃CN–H₂–N₂–CO feed gas using an industrial-scale low-pressure CVD system. With the CO fraction in the feed gas rising up to 2.2 vol.%, oxygen contents of 2.2. at.% could be detected, which are distributed homogeneously over the coating thickness. The originally equiaxed TiC_xN_1-x grains with preferred {110} orientation obtained without CO addition change to randomly distributed plate-like grains, while the grain size decreases to the sub-micron range. Also the surface roughness decreases with rising CO addition. The incorporation of oxygen leads to a homogenous distribution of dislocations within the TiC_xN_1-x grains and to an increasing density of twin boundaries. The residual tensile stress shows a minimum of 200 ± 47 MPa, while the hardness increases to 29.1 ± 1.3 GPa and the elastic modulus reaches a maximum 569 ± 29 GPa for CO fractions of 1.5 vol.% in the feed gas.     

Electrophoretic deposition of hydroxyapatite coatings on titanium from dimethylformamide suspensions

Hydroxyapatite powders were prepared by a chemical precipitation method and electrophoretically deposited on pure Ti surgical substrates. The powders were suspended in dimethylformamide (DMF). The zeta potential, electromobility and the conductivity of the HA suspension was characterized at various pH values to identify the most stable dispersion conditions. The effect of applied voltage and deposition time on deposition rate, deposition thickness and coating morphology were studied. The coating morphology and composition were characterized by scanning electron microscopy (SEM). The crystalline phase of HA before and after electrophoretic deposition was examined using X- ray diffraction (XRD). Transition electron microscope (TEM) indicated that HA consisted of needle-shaped crystallites.     

Nanocrystalline titanium nitride films prepared by electrophoretic deposition

Homogeneous and adhesive nanocrystalline TiN thin films are fabricated on Ti substrates by electrophoretic deposition in an aqueous suspension containing TiN powders at room temperature. X-ray diffraction confirms the formation of TiN films and the film color varies with deposition time. The current-time curves are recorded during deposition and the surface morphology and cross-sectional images are investigated by scanning electron microscopy (SEM). The film thickness is around 6.1 μm after 10 min deposition and increases with deposition time. The adhesion strength is characterized by the ultrasonic vibration method and peel-off test. Our results suggest that electrophoretic deposition is a practical and facile technique to prepare nanocrystalline TiN films that are particularly suitable for the decorative coating industry.     

Characterization of GaSb Films by Metalorganic Chemical Vapour Deposition

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Formation of wedge-shaped carbon film by chemical vapor deposition method and observation using transmission electron microscopy

Unusual morphologies of carbon nanofibers (CNFs) fabricated by the microwave plasma-enhanced chemical vapor deposition method were confirmed by transmission electron microscopy. In particular, the presence and distribution of wedge-shaped carbon films, consisting of amorphous carbon and CNFs, were observed by three-dimensional electron tomography (3D-ET), and their growth mechanisms were modeled. High-resolution transmission electron microscopy (HRTEM) revealed the presence of amorphous carbon on carbon nanofibers. Wedge-shaped carbon films are most likely caused by the bridging of individual CNFs by amorphous carbon from plasmarized carbon. The combination of 3D-ET and HRTEM clearly provides a successful strategy for determining 3D morphologies with characteristic sizes on the nanometer scale.