TiOxNy coatings grown by atmospheric pressure metal organic chemical vapor deposition

Titanium oxynitride coatings were deposited on various substrates by an original atmospheric pressure metal organic chemical vapor deposition (MOCVD) process using titanium tetra-iso-propoxide as titanium and oxygen precursors and hydrazine as a nitrogen source. The films composition was monitored by controlling the N₂H₄ mole fraction in the initial reactive gas phase. The variation of the N content in the films results in significant changes in morphological, structural and mechanical properties. When a large excess of the nitrogen source is used the resulting film contains ca 17  at % of nitrogen and forms dense and amorphous TiO_xN_y films. Growth rates of these amorphous TiO_1.5N_0.5 coatings as high as 14 μm/h were obtained under atmospheric pressure. The influence of the deposition conditions on the morphology, the structure, the composition and the growth rate of the films is presented. For the particular conditions leading to the growth of amorphous TiO_1.5N_0.5 coatings, first studies on the mechanical properties of samples grown on stainless steel have revealed a high hardness, a low friction coefficient, and a good wear resistance in unlubricated sliding experiments against alumina which make them very attractive as protective metallurgical coatings.     

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.     

Direct deposition of CeO2 films on Ni metal substrate by chemical vapor deposition

Cerium dioxide thin films have been grown in-situ directly on cube textured Ni substrate by metal-organic chemical vapor deposition (MOCVD). At a lower deposition temperature of 400°C, an amorphous film was formed. The texture of crystalline CeO₂ film was changed from (200) orientation to (111) orientation when the deposition temperature was increased from 450°C to 550°C. The growth rate was ~40 nm/min and the rms surface roughness was 50 nm for the CeO₂ film deposited at 450°C for 10 min. Surface roughness of the film was increased with the development of (111) orientation. Deposited CeO₂ film showed a mixed texture of (100)<001> and (100)<011> orientation. Depending on the deposition condition, the transition from (100)<001> texture to (100)<011> orientation was observed.     

Pressure-composition-isotherm behavior of nano-/amorphous Mg<Subscript>2</Subscript>NiH<Subscript>x</Subscript>

It has recently been shown that the hydriding properties of the nanocrystalline metal hydrides are far superior to those of the polycrystalline ones. Especially in the case of the Mg-based hydrogen storage alloys, nanostructural modifications have been studied for the purpose of improving their hydrogenation kinetics. In previous studies, I reported on the successful fabrication of Mg₂NiH_x from Mg and Ni chips with hydrogen induced mechanical alloying (HIMA). Observation of the microstructure showed that the synthesized particles (processed with a 66:1 ball to chips mass ratio and 96 hr HIMA) are composed of amorphous and nanocrystalline composite phases with a grain size of less than 10 nm. The aim of the present work was to examine the hydriding/dehydriding behavior of nanocrystalline metal hydrides using a Sieverts type automatic pressure-composition-isotherm (PCI) apparatus at 393, 423, 453, 483, 513 and 543 K. The specimen was characterized by X-ray diffraction after PCI measurement. The influence of hydrogenation behavior on the phase transition of nano-/amorphous Mg₂Ni is a key factor in commercial application. The particles synthesized at 66:1 BCR and 96 hr HIMA revealed a good hydrogen capacity of 2.25 mass% at 483 K.     

Laser chemical vapor deposition of titanium nitride films with tetrakis (diethylamido) titanium and ammonia system

Wide-area and thick titanium nitride (TiN_x) films were prepared on Al₂O₃ substrate by laser chemical vapor deposition (LCVD) using tetrakis (diethylamido) titanium (TDEAT) and ammonia (NH₃) as source materials. Effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition, microstructure and deposition rate of TiN_x films were investigated. (111) and (200) oriented TiN_x films in a single phase were obtained. The lattice parameter and N to Ti ratio of the TiN_x films slightly increased with increasing P_L and was close to stoichiometric at P_L > 150 W. TiN_x films had a cauliflower-like surface and columnar cross section. The deposition rate of TiN_x films increased from 42 to 90 µm/h at a depositing area of 10 mm by 10 mm substrate, decreasing with increasing P_L and T_pre. The highest volume deposition rate of TiN_x films was about 10² to 10⁵ times greater than those of previous LCVD using Nd:YAG laser, argon ion laser and excimer laser.     

Time-modulated chemical vapor deposition of diamond films

This article investigates the role of substrate temperature in the deposition of diamond films using a newly developed time-modulated chemical vapor deposition (TMCVD) process. TMCVD was used to deposit polycrystalline diamond coatings onto silicon substrates using hot-filament chemical vapor deposition system. In this investigation, the effect of (a) substrate temperature and (b) methane (CH₄) content in the reactor on diamond film deposition was studied. The distinctive feature of the TMCVD process is that it time-modulates CH₄ flow into the reactor during the complete growth process. It was noted that the substrate temperature fluctuated during the CH₄ modulations, and this significantly affected some key properties of the deposited films. Two sets of samples have been prepared, in each of which there was one sample that was prepared while the substrate temperature fluctuated and the other sample, which was deposited while maintaining the substrate temperature, was fixed. To keep the substrate temperature constant, the filament power was varied accordingly. In this article, the findings are discussed in terms of the CH₄ content in the reactor and the substrate temperature. It was found that secondary nucleation occurred during the high timed CH₄ modulations. The as-deposited films were characterized for morphology, diamond-C phase purity, hardness, and surface roughness using scanning electron microscopy, Raman spectroscopy, Vickers hardness testing, and surface profilometry, respectively.     

Structural and mechanical properties of amorphous silicon carbonitride films prepared by vapor-transport chemical vapor deposition

The deposition of amorphous silicon carbonitride (a-SiCN:H) films has been successfully achieved through an in-house developed vapor-transport chemical vapor deposition (VT-CVD) technique in a nitrogenated atmosphere. Polydimethylsilane (PDMS) was used as a single-source precursor for both silicon and carbon, while NH₃ was mixed with argon to ensure the in-situ nitrogenation of the films. The chemical bonding and the atomic composition of the a-SiCN:H films were systematically investigated, as a function of their N content, by means of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). AFM was used to obtain 2-D and 3-D views of the films. The mechanical properties [(hardness (H) and Young's modulus (E)] of the freshly prepared films were investigated by the nanoindentation technique. It is shown that by controlling the NH₃/Ar gas flow ratio in the reactor, a-SiCN:H films with various N contents [(0-27) at.% range] are achieved. On the microstructural level, the increase incorporation of N in the a-SiCN:H films is found not only to lead to C atom substitution by N atoms in the local Si-C-N environment but also to an enhanced incorporation of hydrogen bonded to both Si and N. Furthermore, the increase incorporation of N in the a-SiCN:H films resulted in an increase of the average R_rms surface roughness from 4 to 12 nm. Moreover, the films became porous with pore size and density increase as a result of increasing N at.%. Ultimately, both H and E of the a-SiCN:H films were found to be sensitive to their N content, as they decrease (from ~ 17 GPa and 160 GPa to ~ 13 GPa and 136 GPa, respectively) when the N content is increased from 0 to 27 at.%. The formation of Si-N, Si-H, and N-H bonds at the detriment of the more stiff Si-C bonds is thought to account for the observed lowering of the mechanical properties of the a-SiCN:H films as their N content increased.     

Phase Relations in the System TiO<Subscript>2</Subscript>-V<Subscript>2</Subscript>O<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> under Oxidizing and Reducing Conditions

The target of this work was to investigate the phase development in the catalyst system consisting of TiO₂ (Anatase) and V₂O₅ (Shcherbinaite) under several gas atmospheres. Thus a set of V₂O₅/TiO₂ specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700 °C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525 °C the formation of a Rutile solid solution (Rutile-ss) containing VO _x species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V₂O₅ to V₂O₃ was found by X-ray diffraction measurements. There is no miscibility up to 1300 °C followed by the formation of V₂TiO₅ (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO₂ remains without much alteration. The two phases V₂Ti₇O₁₇ and V₂Ti₃O₉ (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.     

Plasma-enhanced chemical vapor deposition of polyperinaphthalene thin films

Plasma-enhanced chemical vapor deposition (PECVD) has been used to grow corrosion-resistive, semiconducting thin films of the graphite-like polymer polyperinaphthalene (PPN) from 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). Unlike thermal chemical vapor deposition of PPN from PTCDA, where thin film growth is catalyzed by a transition metal substrate, PPN films have been grown by PECVD for the first time on non-catalytic substrates: indium tin oxide (ITO)-coated glass, aluminum and silicon. Films with the same morphology and molecular characteristics have also been grown on steel substrates, where iron functions as a growth catalyst. Potentiodynamic corrosion measurements in pH 5 water show that PPN films on steel provide an effective corrosion protection layer.     

Preparation and characterization of nanostructured Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> and Sn<Subscript>0.5</Subscript>-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Nanostructured Bi₂Se₃ and Sn_0.5-Bi₂Se₃ were successfully synthesized by hydrothermal coreduction from SnCl₂·H₂O and the oxides of Bi and Se. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscope (FESEM). Bi₂Se₃ powders obtained at 180°C and 150°C consist of hexagonal flakes of 50–150 nm in side length and nanorods of 30–100 nm in diameter and more than 1 μm in length. The product obtained at 120°C is composed of thin irregular nanosheets with a size of 100–200 nm and several nanometers in thickness. The major phase of Sn_0.5-Bi₂Se₃ synthesized at 180°C is similar to that of Bi₂Se₃. Sn_0.5-Bi₂Se₃ powders are primarily nanorod structures, but small amount of powders demonstrate irregular morphologies.     

Influence of substrate surface topography in the deposition of nanostructured diamond-like carbon films by high density plasma chemical vapor deposition

In this work, we have studied the influence of the substrate surface condition on the roughness and the structure of the nanostructured DLC films deposited by High Density Plasma Chemical Vapor Deposition. Four methods were used to modify the silicon wafers surface before starting the deposition processes of the nanostructured DLC films: micro-diamond powder dispersion, micro-graphite powder dispersion, and roughness generation by wet chemical etching and roughness generation by plasma etching. The reference wafer was only submitted to a chemical cleaning. It was possible to see that the final roughness and the sp³ hybridization degree strongly depend on the substrate surface conditions. The surface roughness was observed by AFM and SEM and the hybridization degree of the DLC films was analyzed by Raman Spectroscopy. In these samples, the final roughness and the sp³ hybridization quantity depend strongly on the substrate surface condition. Thus, the effects of the substrate surface on the DLC film structure were confirmed. These phenomena can be explained by the fact that the locally higher surface energy and the sharp edges may induce local defects promoting the nanostructured characteristics in the DLC films.     

Structural, morphological and optical properties of Bi2−xSbxSe3 thin films grown by electrodeposition

Ternary single-phase Bi_2−xSb_xSe₃ alloy thin films were synthesized onto Au(1 1 1) substrates from an aqueous solution containing Bi(NO₃)₃, SbCl₃, and SeO₂ at room temperature for the first time via the electrodeposition technique. The electrodeposition of the thin films was studied using cyclic voltammetry, compositional, structural, optical measurements and surface morphology. It was found that the thin films with different stoichiometry can be obtained by controlling the electrolyte composition. The as-deposited films were crystallized in the preferential orientation along the (0 1 5) plane. The SEM investigations show that the film growth proceeds via nucleation, growth of film layer and formation of spherical particles on the film layer. The particle size and shape of Bi_2−xSb_xSe₃ films could be changed by tuning the electrolyte composition. The optical absorption spectra suggest that the band gap of this alloy varied from 0.24 to 0.38 eV with increasing Sb content from x = 0 to x = 0.2.     

Properties and consolidation of nanostructured Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> by pulsed-current-activated sintering

Dense nanophase Ce_0.8Gd_0.2O_1.9 was sintered by a pulsed-current-activated sintering method within 10 min from Ce_0.8Gd_0.2O_1.9 nanopowder made using the co-precipitation method. Sintering was accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense Ce_0.8Gd_0.2O_1.9 with a relative density of up to 96.5% was produced under the simultaneous application of 80 MPa of pressure and a pulsed current. The ionic conductivities and mechanical properties of the Ce_0.8Gd_0.2O_1.9 were investigated.     

Growth and characterization of chemical bath deposited Cd1−xZnxS thin films

Cd_1−xZn_xS (0 ≤ x ≤ 1) thin films have been deposited by chemical bath deposition method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 80 ± 5 °C and after annealed at 350 °C. The structural, morphological, compositional and optical properties of the deposited Cd_1−xZn_xS thin films have been studied by X-ray diffractometer, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) and UV-vis spectrophotometer, respectively. X-ray diffraction analysis shows that for x < 0.8, the crystal structure of Cd_1−xZn_xS thin films was hexagonal structure. For x > 0.6, however, the Cd_1−xZn_xS films were grown with cubic structure. Annealing the samples at 350 °C in air for 45 min resulted in increase in intensity as well as a shift towards lower scattering angles. The parameters such as crystallite size, strain, dislocation density and texture coefficient are calculated from X-ray diffraction studies. SEM studies reveal the formation of Cd_1−xZn_xS films with uniformly distributed grains over the entire surface of the substrate. The EDX analysis shows the content of atomic percentage. Optical method was used to determine the band gap of the films. The photoluminescence spectra of films have been studied and the results are discussed.     

Cold spray of SiC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with soft metal incorporation: A technical contribution

Al + SiC, Al + Al₂O₃ composites as well as pure Al, SiC, and Al₂O₃ coatings were prepared on Si substrates by the cold gas dynamic spray process (CGDS or cold spray). The powder composition of metal (Al) and ceramic (SiC, Al₂O₃) was varied into 1:1 and 10:1 wt.%, respectively. The propellant gas was air heated up to 330 °C and the gas pressure was fixed at 0.7 MPa. SiC and Al₂O₃ have been successfully sprayed producing coatings with more than 50 μm in thickness with the incorporation of Al as a binder. Also, hard ceramic particles showed peening effects on the coating surfaces. In the case of pure Al metal coating, there was no crater formation on hard Si substrates. However, when Al mixed with SiC and Al₂O₃, craters were observed and their quantities and sizes depended on the composition, aggregation and size of raw materials.     

Cu-Al alloy formation by thermal annealing of Cu/Al multilayer films deposited by cyclic metal organic chemical vapor deposition

One of the most important issues in future Cu-based interconnects is to suppress the resistivity increase in the Cu interconnect line while decreasing the line width below 30 nm. For the purpose of mitigating the resistivity increase in the nanoscale Cu line, alloying Cu with traces of other elements is investigated. The formation of a Cu alloy layer using chemical vapor deposition or electroplating has been rarely studied because of the difficulty in forming Cu alloys with elements such as Al. In this work, Cu-Al alloy films were successfully formed after thermal annealing of Cu/Al multilayers deposited by cyclic metal-organic chemical vapor deposition (C-MOCVD). After the C-MOCVD of Cu/Al multilayers without gas phase reaction between the Cu and Al precursors in the reactor, thermal annealing was used to form Cu-Al alloy films with a small Al content fraction. The resistivity of the alloy films was dependent on the Al precursor delivery time and was lower than that of the aluminum-free Cu film. No presence of intermetallic compounds were detected in the alloy films by X-ray diffraction measurements and transmission electron spectroscopy.     

Transport properties of Bi<Subscript>43</Subscript>Se<Subscript>4</Subscript>Te<Subscript>53</Subscript> thermoelectric alloy fabricated by mechanical grinding and pulse discharge sintering

Mechanical grinding followed by pulse discharge sintering was applied to fabricate n-type Bi₄₃Se₄Te₅₃ thermoelectric materials. Calorimetric measurements demonstrated that a Se-rich phase was developed from Bi₂(Se, Te)₃ phase after 10h of milling. However, when the milling time was extended to 25 h or longer, a Te-rich phase was formed. Hall measurements showed that the development of the Se/Te-rich phase considerably increased the carrier concentration but decreased the carrier mobility. The oxygen contamination in the smashed powders was also an important consideration for the degeneration of the figure of merit of the sintered samples.     

Effect of a surface treatment for LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> cathode material in lithium secondary batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode material was surface-treated to improve its electrochemical performance. Al₂O₃ nanoparticles were coated onto the surface of LiNi_1/3Co_1/3Mn_1/3O₂ powder using a sol-gel method. The as-prepared Al₂O₃ nano-particle was identified as the cubic structure of Al₂O₃. XRD showed that the LiNi_1/3Co_1/3Mn_1/3O₂ structure was not affected by the Al₂O₃ coating. With a coating of 3 wt.% Al₂O₃ on LiNi_1/3Co_1/3Mn_1/3O₂, the cyclic-life performance and rate capability were improved. However, heavier coatings (5 wt.%) on LiNi_1/3Co_1/3Mn_1/3O₂ resulted in a considerable decrease of the discharge capacity and rate capability. The thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂ materials was greatly improved by the 3 wt.% Al₂O₃ coating.     

Growth of N-polar GaN on vicinal sapphire substrate by metal organic chemical vapor deposition

The growth and properties of N-polar Ga N layers by metal organic chemical vapor deposition(MOCVD) were reported. It is found that N-polar Ga N grown on normal sapphire substrate shows hexagonal hillock surface morphology. With the misorientation angles increasing from 0.5° to 2.0° toward the a-plane of the sapphire substrate, the number of the hillock becomes less and less and finally the surface becomes flat one on the sapphire substrate with the misorientation angle of 2°. It is also found that the crystalline quality and the strain in the Ga N are greatly influenced by the misorientation angle.     

A study of diamond synthesis by hot filament chemical vapor deposition on Nc coatings

Deposition of diamond films onto various substrates can result in significant technological advantages in terms of functionality and improved life and performance of components. Diamond is hard, wear resistant, chemically inert, and biocompatible. It is considered to be the ideal material for surfaces of cutting tools and biomedical components. However, it is well known that diamond deposition onto technologically important substrates, such as co-cemented carbides and steels, is problematic due to carbon interaction with the substrate, low nucleation densities, and poor adhesion. Several papers previously published in the relevant literature have reported the application of interlayer materials such as metal nitrides and carbides to provide bonding between diamond and hostile substrates. In this study, the chemical vapor deposition (CVD) of polycrystalline diamond on TiN/SiN _x nc (nc) interlayers deposited at relatively low temperatures has been investigated for the first time. The nc layers were deposited at 70 or 400 °C on Si substrates using a dual ion beam deposition system. The results showed that a preliminary seeding pretreatment with diamond suspension was necessary to achieve large diamond nucleation densities and that diamond nucleation was larger on nc films than on bare sc-Si subjected to the same pretreatment and CVD process parameters. TiN/SiN _x layers synthesized at 70 or 400 °C underwent different nanostructure modifications during diamond CVD. The data also showed that TiN/SiN _x films obtained at 400 °C are preferable in so far as their use as interlayers between hostile substrates and CVD diamond is concerned. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.