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.     

Single-step fabrication of nanolamellar structured oxide ceramic coatings by metal-organic chemical vapor deposition

Oxide ceramic coatings in the system Y2O3-Al2O3-ZrO2 were fabricated in laboratory scale by using a MOCVD unit. A hot wall reactor was used along with different precursor feeding systems. Most experiments were carried out by using powder flash evaporation including a screw feeder for precursor powder delivery. For comparison, further samples were fabricated by using band flash evaporation and continuous evaporation from a crucible. Oxygen was used in all cases as reactant gas. Aluminium-tris-2,4-pentanedione (Al(acac)3), yttrium-tris-2,2,6,6-tetramethyl-3,5-heptanedione (Y(thd)3) and zirconium-tetrakis-2,2,6,6-tetramethyl-3,5-heptanedione (Zr(thd)4) were applied as metal-organic precursors because of their similar vaporization behaviour under the given conditions. The coating stoichiometry was varied from pure alumina to complex ternary compositions in the system Y2O3-Al2O3-ZrO2. Both kinds of ternary coatings fabricated by using flash evaporation methods show a nanolamellar microstructure in the as deposited state. Heat treating experiments at 1200 degrees C for up to 5 days enhance the lamellar character of the coating deposited by using powder flash evaporation. The lamellar microstructure is due to alternating YSZ enriched layers and YAG enriched layers in this state. However, the coating fabricated by using band flash evaporation shows a dense interpenetrating network of YSZ and YAG after heat treating instead of a lamellar microstructure observed in the as deposited state.     

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.     

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.     

Low temperature deposition of tin oxide films by inductively coupled plasma assisted chemical vapor deposition

Well-crystallized tin oxide films were successfully synthesized without additional heating by inductively coupled plasma assisted chemical vapor deposition (ICP-CVD). The degree of crystallization was affected by the ICP power and hydrogen flow rate. The substrate temperature was increased only up to 423-453 K by plasma heating, which suggests that the formation of the SnO₂ crystals was not caused by plasma heating, but by enhanced reactivity of precursors in high density plasma. The micro-hardness of deposited tin oxide films ranged from 5.5 to 11 GPa at different hydrogen flow rates.     

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.     

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.     

Plasma-assisted deposition of metal and metal oxide coatings

A combination of physical vapour deposition and plasma-assisted chemical vapour deposition techniques were used to deposit Cu-, Ni- and Sn-rich SnO/SnO2 coatings on metal and ceramic substrates. Cu and Ni were deposited on Al alloy 6061 substrates and Ni deposition was also performed on glass microscope slides and commercially pure alumina substrates. Sn-rich SnO/SnO2, on the other hand, was coated on stainless steel and pure Cu substrates. A direct-current plasma system was used to deposit the pure metals in vacuum with a resistively heated tungsten boat that was coated with alumina. All samples were sputtered for 20 min in an argon:hydrogen (1:1) atmosphere at a pressure of 300 mTorr. To reduce contamination and oxidation of both substrates and deposited layers, Cu and Ni coatings were made with argon:hydrogen (2:1) carrier gas. Sn-rich tin oxide coatings were deposited in a pure argon atmosphere (no hydrogen) to allow for the oxidation of Sn deposits on the stainless steel and copper substrates. Investigations of coated surfaces by scanning electron microscopy and X-ray diffraction showed coatings to be smooth, continuous and pure. Deposition rates showed this application to provide a very high rate when compared with chemical vapour deposition and metal–organic chemical vapour deposition techniques. Scratch tests results prove good attachment of the coatings to their respective substrates. © 1998 Chapman & Hall     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.     

Transparent conducting indium oxide thin films grown by low-temperature metal organic chemical vapor deposition

We have grown indium oxide thin films on silicon substrates at low temperature by metal organic chemical vapor deposition. Polycrystalline film growth could only be obtained at temperatures below 400 °C. Above 400 °C, metallic indium deposition dominated. We have investigated the effect of substrate temperature and reactor pressure on the film growth and structural properties in the range of 250-350 °C and 5 ^? 10³-4 ^? 10⁴ Pa. The film grown at 300 °C exhibited a resistivity of about 3.6 × 10^− 3 Ω cm and a maximal optical transmittance of more than 95% in the visible range. The film showed an optical band gap of about 3.6 eV.     

磁场辅助等离子体增强化学气相沉积

本文根据螺线管线圈内部磁场的分布规律，以及磁场对等离子体内部电子的作用原理，设计了磁场辅助的等离子体增强化学气相沉积（PECVD）系统，并且研究了在PECVD系统中获得均匀磁场的方法。而后，以SiH4和N2为反应气体，在低气压下沉积了SiN薄膜。测量了SiN薄膜的沉积速率，折射率，表面形貌等参数。验证了磁场分布的均匀性，分析了磁场在等离子体增强化学气相沉积系统中的作用。     

Effects of argon and oxygen flow rate on water vapor barrier properties of silicon oxide coatings deposited on polyethylene terephthalate by plasma enhanced chemical vapor deposition

Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O₂ flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m²/day and was decreased after depositing the silicon oxide (SiO_x) coatings. The minimum WVTR, 0.47 g/m²/day, was observed at Ar and O₂ flow rates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm^− 1 and Si-O-Si stretching at 1000-1150 cm^− 1 varied depending on the Ar and O₂ flow rates. The contact angle of the SiO_x coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O₂ flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO_x morphology and the water vapor barrier performance with the Ar and O₂ flow rates. The roughness of the deposited coatings increased when either the O₂ or Ar flow rate was increased.     

Scratch resistant optical coatings on polymers by magnetron-plasma-enhanced chemical vapor deposition

The magnetron-plasma-enhanced chemical vapor deposition (magPECVD) provides silicon-organic thin films for optical, electrically insulating or diffusion barrier coating applications. With process pressures of ≤ 1 Pa this technology is well adapted to the sputtering process of optical interference coatings and also facilitates an inline-process implementation. This paper describes the deposition process for scratch resistant coatings on polycarbonate (PC) and allyl diglycol carbonate substrates. Based on the optical, chemical and mechanical characterization of single magPECVD thin films of varied chemical composition, several types of layer stacks (e.g. of gradient or alternating hardness distribution) were deposited with varied total thickness on PC substrates. Abrasion test results indicate two main effects: the resistance against scratches of high load abrasion (50 N) mainly depends on the total coating thickness. The durability against scratches of low load abrasion (5 N) shows a clear advantage for the multilayer design in contrast to homogeneous single layers even of higher thickness. Finally a 5-layer antireflective system was reactively sputtered onto the magPECVD coating and successfully passed adhesion and environmental tests.     

Interrupted cutting tests of cemented carbide tools coated by physical vapor deposition and chemical vapor deposition techniques

Refractory compound coatings prolong the life of cemented carbide inserts. The structure of these coatings is vastly different when the same coating is produced by chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods. TiC and HfN coatings were applied to cemented carbide tools by both CVD and PVD processes. The coated inserts were tested under interrupted cutting conditions using slotted bar tests. The CVD-coated inserts failed after a few (less than 100) cycles whereas the PVD-coated inserts lasted well past 2000 cycles without failure as did the uncoated inserts. PVD coatings have a much greater fracture toughness than CVD coatings due to their very fine-grained microstructure with a distribution of fine cavities which act as crack stoppers. In contrast, CVD coatings have a fully dense microstructure with a large grain size which does not have much fracture toughness. Another reason for the difference in behavior is the much lower deposition temperature (about 500°C) used in the PVD process as compared with the much higher deposition temperature (about 1000°C) used in the CVD process. Chemical attack of the cemented carbide substrate occurs at high deposition temperatures, thus weakening the area near the coating-substrate interface.     

Graphene synthesis by thermal chemical vapor deposition using solid precursor

We report single layer to few layer graphene on polycrystalline nickel by chemical vapor deposition at ambient pressure using solid precursor, camphor. Investigating at a wide range of temperature, it was observed that 870 °C is better for the deposition of single layer graphene on nickel substrate. The percentage of single layer on the substrate reduced significantly with decreasing the deposition temperature. The full width half maximum of the synthesized single layer graphene was 21 cm^?1 and Raman intensity ratio of 2D to G peak was almost nine. The film was transferred to insulating substrate and measured transmittance was 85 %. Raman spectroscopy, Raman mapping, SEM and UV–visible spectrometer measurement were performed for characterization.     

Superhydrophilic and tribological improvements of polymeric surfaces via plasma enhanced chemical vapor deposition ceramic coatings

The main object of this study is the treatment of polymeric (PVC, PC) surfaces with the aim of inducing enhanced superhydrophilic characteristics together with nanohardness features; this would allow polymeric surfaces to have longer durability and prevent the accumulation of dirt on the surface which could disable the proper use of these polymeric surfaces. Indeed plastic surfaces are difficult substrates to be covered effectively and functionalized, mainly due to their high sensitivity to heat treatments and irradiation in the UV-Vis range together with their inert behavior. Their functionalization is achieved through the deposition of ceramic coatings such as titania (TiO2), on the polymeric surfaces via PECVD (Plasma Enhanced Chemical Vapor Deposition) at low temperatures. Characterizations are carried out by contact angle analysis for the superhydrophilic characteristics, and by nanoindentation analysis for the tribological features. A cold PECVD discontinuous method allowed us to improve nanohardness, reaching a value of 1.39 GPa which is nearly ten times higher than that of the uncoated polymeric substrate, and seems a promising solution for improving uniformity of the coatings. Superhydrophilic behavior of the activated TiO2 surfaces showed contact angle values lower than 10 degrees.     

High-speed oxide coating by laser chemical vapor deposition and their nano-structure

Oxide thick films, partially yttria-stabilized zirconia (YSZ) and titania (TiO₂), were prepared by laser chemical vapor deposition (LCVD). The assistance of laser tremendously increased the deposition rate for YSZ and TiO₂ films up to 660 and 2500 μm/h, respectively. The increase in the deposition rate was accompanied by plasma formation around the deposition zone, and the plasma was observed over critical values of laser power and substrate pre-heating temperature. A wide variety of morphologies of films from feather-like columnar to dense microstructures were obtained depending on deposition conditions. The columnar structure contained a large amount of nano-pores at columnar boundary and inside grains. These columnar structure and nano-pores were advantageous for applying YSZ films to thermal barrier coatings.     

Tuning of electrical and structural properties of indium oxide films grown by metal organic chemical vapor deposition

Tuning of structural and electrical properties of indium oxide (In₂O₃) films by means of metal organic chemical vapor deposition is demonstrated. Phase selective growth of rhombohedral In₂O₃(0001) and body-centered cubic In₂O₃(001) polytypes on (0001) sapphire substrates was obtained by adjusting the substrate temperature and trimethylindium flow rate. The specific resistance of the as-grown films can be tuned by about two orders of magnitude by varying the growth conditions.