Chemical vapor deposition of titanium nitride at low temperatures

A new method is proposed for making titanium nitride (TiN) films at substrate temperatures between about 400 and 700°C. The films are formed from TiCl₄ and NH₃ by chemical vapor deposition. The method is versatile with growth rates of up to 0.1 μm s⁻¹ possible. The optical properties of the films are measured and fitted theoretically using the Drude theory to obtain the plasma frequency of the films. A modification of the Drude theory according to Maxwell Garnett explains a decreased reflectance in the IR region for the thinner films. Use of the films as heat mirrors and other applications are discussed.     

Initiated chemical vapor deposition of biopassivation coatings

Organosilicon polymers show great utility as both biocompatible and electrically insulating materials. In this work, thin films of a novel organosilicon polymer are synthesized by initiated CVD utilizing trivinyl-trimethyl cyclotrisiloxane as a monomer and terbutyl peroxide as a free radical generating initiator. Use of an initiator allows for formation of polymer films at filament temperatures as low as 250 °C which allows for retention of all siloxane ring moieties within the resulting polymer. The all-dry deposition process generates a highly crosslinked matrix material in which over 95% of the vinyl moieties present on the monomer units have been reacted out to form linear polymerized hydrocarbon chains. The material possesses an electrical resistivity of 4 × 10¹⁵ Ω cm. In addition, biased soak testing of material samples in a simulated biological environment demonstrates retention of electrical material properties for greater than 2 years.     

Thick boride coatings by chemical vapor deposition

In this paper we describe an experimental study of the chemical vapor deposition (CVD) of TiB₂ by the hydrogen reduction of TiCl₄ and BCl₃ with the purpose of obtaining very thick (more than 100 μm) and uniform coatings. The optimum deposition conditions were as follows: temperature, 900–950 °C; source gas ratios, $\text{[}\text{Ti}\text{]/[}\text{B}\text{] =}\text{1}\text{2}$ and $\text{[}\text{H}\text{]/[}\text{Cl}\text{] =}\text{6}\text{1}$. With these conditions, deposition rates greater than 25 μm h^-1 were obtained. The composition was very uniform with an excess of boron over stoichiometry (probably in the form of free boron). A small amount of chlorine remained incorporated in the deposit probably as TiCl₂ (0.05 wt.% at 950 °C). The coatings were very hard (about 3700 kgf mm^-2) and hardness was uniform through the thickness. With careful control of the deposition parameters, the CVD of uniform coatings with thickness of 1 mm or more appears feasible.     

Thermal barrier coatings produced by chemical vapor deposition

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to prepare TBCs due to excellent conformal coverage and columnar microstructure. This paper reviews the fabrication of YSZ films by conventional thermal CVD and plasma CVD intended for TBCs. A new laser CVD developed by our group with a high deposition rate of 660 µμh^-1 was also briefly introduced.     

Thermal barrier coatings produced by chemical vapor deposition

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to prepare TBCs due to excellent conformal coverage and columnar microstructure. This paper reviews the fabrication of YSZ films by conventional thermal CVD and plasma CVD intended for TBCs. A new laser CVD developed by our group with a high deposition rate of 660 μm h⁻¹ was also briefly introduced.     

Kinetics of titanium nitride coatings deposited by thermo-reactive deposition technique

In this study, the growth kinetics of titanium nitride layer deposited on pre-nitrided AISI 1020 steel samples by thermo-reactive diffusion (TRD) techniques in a solid medium was reported. Steel was at first tufftrided and then titanium nitride coating treatment was performed in a powder mixture consisting of ferro-titanium, ammonium chloride and alumina at 1173, 1223 and 1273 K for 1-4 h. Titanium nitride layer thickness on the titanium nitride coated AISI 1020 steel ranged from 5.5 to 19.2 μm depending on treatment time and temperature. Layer growth kinetics was analyzed by measuring the depth of titanium nitride layer as a function of time and temperature. The kinetics equation of the reaction has also been determined with Arhenius equation K=K_oexp(−Q/(RT). The result showed that the diffusion coefficient (K) of the process increased with treatment temperature. Activation energy (Q) for TRD process was calculated as 187.09 kJ/mol. The diffusion coefficients (K) changed between 6.637×10⁻¹¹ and 2.097×10⁻¹⁰ cm²/s depending on the process temperature.     

Formation of technological protective coatings by chemical vapor deposition

We perform the theoretical substantiation of the choice of modifiers of the processes of thermal treatment used to form nanometer and thin-film technological protective coatings (nanolayers), which give new properties to the metal surfaces of the products. This technological procedure is quite new, very promising, and does not require significant changes in the existing technological schemes. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 51–55, September–October, 2006.     

Low-temperature plasma-enhanced chemical vapor deposition of tungsten and tungsten nitride

Tungsten and tungsten nitride layers have been deposited by plasma-enhanced chemical vapor deposition (PECVD). Tungsten layers deposited at low deposition temperatures T150 °C using this method showed good uniformity over dielectric and silicon substrate areas. As the deposition temperature decreased, the silicon consumed during the deposition reaction decreased, at T150 °C no silicon consumption was measurable. PECVD tungsten nitride layers were deposited directly on oxidized silicon substrates with no requirement for a nucleation layer. As the NH₃ flow rate was increased, whilst maintaining all other parameters constant, deposited layers were found to change from metal tungsten to tungsten-rich amorphous layer to W₂N. The resistivity of the layers was found to be high compared to published literature for higher-temperature deposited layers. The high resistivity is attributed to the incorporation of fluorine into the layer at low deposition temperatures. A deposition process was established for smooth amorphous tungsten-rich W _x N layers at 150 °C.     

Investigation of the interlayers between cemented carbides and titanium carbide coatings obtained by chemical vapor deposition

Data are presented on the microstructure, microhardness and chemical composition of the interlayers between cemented carbides and chemically vapor-deposited TiC coatings. The carbon: metal ratios of the cubic carbides across the interlayers were obtained by Auger depth profile analysis. The mechanisms of nucleation and diffusional growth of the η-carbide skeleton at the upper layer of the substrate are discussed. It is proposed that a cubic carbide phase acts as a carbon donor and thus inhibits the localized formation of the η-carbide skeleton and retains the integrity of the surrounding network.     

Effective growth of boron nitride nanotubes by thermal chemical vapor deposition

Effective growth of multiwalled boron nitride nanotubes (BNNTs) has been obtained by thermal chemical vapor deposition (CVD). This is achieved by a growth vapor trapping approach as guided by the theory of nucleation. Our results enable the growth of BNNTs in a conventional horizontal tube furnace within an hour at 1200?°C. We found that these BNNTs have an absorption band edge of 5.9?eV, approaching that of single h-BN crystals, which are promising for future nanoscale deep-UV light emitting devices.     

Low pressure chemical vapor deposition of niobium coatings on graphite

Niobium coatings were prepared on graphite by low pressure chemical vapor deposition using niobium chloride and hydrogen as the reactant gases. The effects of deposition temperature on the morphology, phase, and deposition rate of niobium coatings were studied. The as-deposited niobium coatings were characterized by scanning electron microscopy and X-ray diffraction. The results indicate that the niobium coatings exhibit a granular hillock structure at 850-900 °C while a laminar structure at 950-1100 °C. The deposition is dominated by surface chemical kinetics with an apparent activation energy of 93.2 kJ/mol at 850-950 °C, while it is dominated by mass transport with an apparent activation energy of 7.9 kJ/mol at 950-1050 °C. At temperatures below 1100 °C, the deposited coatings mainly contain niobium. At temperatures above 1100 °C, the deposited coatings mainly contain niobium carbides. Considering the deposition kinetics and interfacial reactions, the deposition temperature should be controlled below 950 °C.     

Double-walled boron nitride nanotubes grown by floating catalyst chemical vapor deposition

One-dimensional nanostructures exhibit quantum confinement which leads to unique electronic properties, making them attractive as the active elements for nanoscale electronic devices. Boron nitride nanotubes are of particular interest since, unlike carbon nanotubes, all chiralities are semiconducting. Here, we report a synthesis based on the use of low pressures of the molecular precursor borazine in conjunction with a floating nickelocene catalyst that resulted in the formation of double-walled boron nitride nanotubes. As has been shown for carbon nanotube production, the floating catalyst chemical vapor deposition method has the potential for creating high quality boron nitride nanostructures with high production volumes.     

Reactor length-scale modeling of chemical vapor deposition of carbon nanotubes

Chemical Vapor Deposition (CVD) of carbon nanotubes from a gas mixture consisting of methane (carbon precursor) and hydrogen (a carrier gas) in the presence of cobalt, nickel or iron catalytic particles in a cylindrical reactor is modeled at the reactor length-scale by solving a continuum-based coupled boundary-layer laminar-flow hydrodynamics, heat-transfer, gas-phase chemistry and surface chemistry problem. The model allows determination of the gas-phase fields for temperature, velocity, and various species as well as the surface-species coverages and the carbon deposition rate. Various available experimental and theoretical assessments are used to construct the necessary database for gas-phase and surface chemistry and gas-phase transport parameters. A reasonably good agreement is found between the model predicted and the experimentally measured carbon nanotubes deposition rates over a relatively large range of processing conditions.     

Synthesis and characterization of indium nitride nanowires by plasma-assisted chemical vapor deposition

High-quality indium nitride (InN) nanowires were synthesized in a high temperature furnace on Au-coated Si substrates through the reaction of indium metal vapor with highly reactive nitrogen radicals generated by N₂ plasma. Highly-reactive nitrogen radicals provided a wide process window for the synthesis of InN nanowires by lowering the process temperature to avoid the decomposition of InN. X-ray diffraction, transmission electron microscopy and Raman spectra further showed that the as-synthesized InN nanowires were perfect single crystallites of wurtzite structure with the growth direction along [110].     

Wafer scale homogeneous bilayer graphene films by chemical vapor deposition

The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. However, bilayer graphene samples have been limited to μm(2) size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. × 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.