Investigation of the microstructure, mechanical properties and tribological behaviors of Ti-containing diamond-like carbon films fabricated by a hybrid ion beam method

Diamond-like carbon (DLC) films with various titanium contents were investigated using a hybrid ion beam system comprising an anode-layer linear ion beam source and a DC magnetron sputtering unit. The film composition and microstructure were characterized carefully by X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy, revealing that the doped Ti atoms had high solubility in the DLC films. The maximum solubility was found to lie between about 7 and 13 at.%. When the Ti content was lower than this solubility, the doped Ti atoms dissolved in the DLC matrix and the films exhibited the typical features of the amorphous DLC structure and displayed low compressive stresses, friction coefficients and wear rates. However, as the doped content exceeded the solubility, Ti atoms bonded with C atoms, resulting in the formation of carbide nano-particles embedded in the DLC matrix. Although the emergence of the carbide nano-particles promoted graphitizing due to a catalysis effect, the film hardness was enhanced to a great extent. On the other hand, the hard carbides particles caused abrasive wear behavior, inducing a high friction coefficient and wear rate.     

Surface roughness, mechanical and tribological properties of ultrathin tetrahedral amorphous carbon coatings from atomic force measurements

Atomic force microscope (AFM), lateral force microscope and AFM-based scratch and wear testing techniques were used to evaluate and compare the surface roughness, tribological and mechanical properties of thin (2.7-43 nm) tetrahedral amorphous carbon coatings prepared by pulsed cathodic arc discharge. It was found that surface roughness of ultrathin (2-8 nm) coatings was mainly determined by the roughness of the Si substrate and their average density strongly depended on their thickness. Poor friction, mechanical properties of thinner (2.7-15 nm) coatings can be associated with their low average density. The dense coatings (>15 nm) had lower friction coefficient, better scratch and wear resistance properties that were independent of their thickness. It appears that the over 15-nm coatings studied are feasible for some wear-resistant and tribological applications.     

Effect of thermal annealing on the mechanical properties of low-emissivity physical vapor deposited multilayer-coatings for architectural applications

Low-emissivity (low-E) coatings comprising a stack of multiple physical vapor deposited metallic and dielectric layers play an important role in energy management of modern buildings. The production process of such architectural glazings often requires that the coatings withstand a short-term thermal load of up to 700 °C. Here, we report on thermally-induced variations in the mechanical properties of representative large-area magnetron-sputtered low-E stacks on glass, developed specifically for high temperature stability. Coatings are investigated before and after heat treatment by bulge testing, curvature analyses using Stoney's equation, and nanoindentation. For as-deposited coatings, an in-plane residual compressive stress about 48 MPa and Young's modulus of 120 GPa are found, depending on the type of substrate. Short-term exposure to up to 700 °C converts this situation to in-plane residual tensile stress of > 400 MPa, while Young's modulus decreases to about 105 GPa. These changes in the residual stress state are explained on the basis of structural, topological and dimensional changes in the coating stack. They identified as one of the primary factors governing temperature-resistance of low-E coatings.     

Effect of annealing temperature on the tribological behavior of ZnO films prepared by sol-gel method

The tribological behavior of zinc oxide (ZnO) films grown on glass and silicon (100) substrates by sol-gel method was investigated. Particularly, the as-coated films were post-annealed at different temperatures in air to investigate the effect of annealing temperature. Crystal structural and surface morphology of the films were measured by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). XRD patterns and AFM images indicated that the crystallinity and grain size of the films were enhanced and increased, respectively, with temperature. The tribological behavior of films was evaluated by sliding the ZnO films against a Si₃N₄ ball under 0.5 gf normal load using a reciprocating pin-on-plate tribo-tester. The wear tracks of the films were measured by AFM to quantify the wear resistance of the films. The results showed that the wear resistance of the films could be improved by the annealing process. The wear resistance of the films generally increased with annealing temperature. Specifically, the wear resistance of the films was significantly improved when the annealing temperature was higher than 550° C. The increase in the wear resistance is attributed to the increase in hardness and modulus of the film with annealing temperature.     

Structural and optical properties of thermally evaporated 1,4,8,11,15,18,22,25-octahexylphthalocyanine thin films

Metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine was prepared directly by the cyclotetramerization of 3,6-dihexylphthalonitrile using lithium butoxide in butanol. Thin films of the material were deposited on glass substrates by the thermal evaporation technique. The structure of the films was found to be in the form, and showed a strong peak indicating preferential orientation. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1,4,8,11,15,18,22,25-octahexylphthalocyanine grow in stacks of parallel rows. The spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190–3000 nm. The refractive index, n, and absorption index, k, were found to be independent of annealing at 373 K. The B band absorption occurred at 356 nm, and the Q band showed a doublet at 667 and 739 nm. Other optical parameters, such as absorption coefficient and optical dielectric constant ε, were determined.     

Optical properties and scanning probe microscopy study of some AgAsSSe amorphous films

Doping of AsSSe amorphous films by silver photo-dissolution leads to a decrease of the optical gap and to an increase of the refractive index in forming AgAsSSe films. The difference of the optical gap and refractive index between undoped and doped films has been found in case of Ag₁₅As₂₆S₂₉Se₃₀ film up to 0.37 eV and 0.26, respectively. Transreflectance in far infrared spectral region indicates formation of AgAsS₂ and AgAsSe₂ entities in Ag₁₅As₂₆S₂₉Se₃₀ film. Scanning probe microscopy, namely atomic force microscopy, atomic force acoustic microscopy (AFAM) and Kelvin probe force microscopy (KPFM) was used for studying AgAsSSe films. It was found that silver growth is rather three dimensional and it is reminiscent of the Stranski-Krastanov growth mode. Observed silver protuberances represent silver reservoirs responsible for a local increase of silver content. Hence, the silver growth mode enhances formation of nano/meso inhomogeneities of the surface and near surface density/stiffness, seen in AFAM, and in the surface electric potential, seen in KPFM.     

Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method

ZnO:SiO₂ films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO₂ films are of great interest as catalyst and gas-sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO₂ films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO₂ films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO₂ nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.     

Structural, dielectric and ferroelectric properties of multilayer lithium tantalate thin films prepared by sol-gel technique

Multilayer lithium tantalate thin films were deposited on Pt-Si [Si(111)/SiO₂/TiO₂/Pt(111)] substrates by sol-gel process. The films were annealed at different annealing temperatures (300, 450 and 650 °C) for 15 min. The films are polycrystalline at 650 °C and at other annealing conditions below 650 °C the films are in amorphous state. The films were characterized using X-ray diffraction, atomic force microscopy (AFM) and Raman spectroscopy. The AFM of images show the formation of nanograins of uniform size (50 nm) at 650 °C. These polycrystalline films exhibit spontaneous polarization of 1.5 μC/cm² at an application of 100 kV/cm. The dielectric constant of multilayer film is very small (6.4 at 10 kHz) as compared to that of single crystal.     

Effect of sol concentration on the structural, morphological, optical and photoluminescence properties of zirconia thin films

ZrO₂ thin films were deposited on quartz substrates from 10 wt.%, 20 wt.% and 40 wt.% solutions of Zirconium-n-butoxide in isopropanol by sol-gel dip-coating technique. Higher concentrated sols of 20 wt.% and 40 wt.% exhibited faster gelation, where as 10 wt.% sol remained stable for two months and films synthesized from this sol remained transparent and continuous even for 12 coatings. Ellipsometric study revealed that refractive index of the films increased with increase in sol concentration which is ascribed to the decrease in porosity. X-ray diffraction study showed that a tailoring of grain size from 7.9 to 39.2 nm is possible with increase in sol concentration. Atomic force microscopy studies showed a change in growth mode from vertical to lateral mode with increase in sol concentration. The film surface revealed positive skewness and high kurtosis values which make them favorable for tribological applications. The average optical transmittance in the visible region is highest (greater than 90%) for the film deposited from 10 wt.% sol. The optical band gap decreased from 5.74 to 5.62 eV with increase in the sol concentration. Photoluminescence (PL) spectra of the films exhibit an increase in the emission intensity with increase in sol concentration which substantiates better crystalline quality of the film deposited from 40 wt.% sol and increase in oxygen vacancies. The “Red shift” of the PL spectra with increase in sol concentration originates from the increase in the grain size with sol concentration which makes it suitable for generation of solid state lighting in light emitting diode.     

Effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide composite

The aim of this article was to investigate the effects of vacuum thermal cycling on mechanical and physical properties of high performance carbon/bismaleimide (BMI) composites used in aerospace. The changes in dynamic mechanical properties and thermal stability were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), respectively. The changes in linear coefficient of thermal expansion (CTE) were measured in directions perpendicular and parallel to the fiber direction, respectively. The outgassing behavior of the composites were examined. The evolution of surface morphology and surface roughness were observed by atomic force microscopy (AFM). Changes in mechanical properties including transverse tensile strength, flexural strength and interlaminar shear strength (ILSS) were measured. The results indicated that the vacuum thermal cycling could improve the crosslinking degree and the thermal stability of resin matrix to a certain extent, and induce matrix outgassing and thermal stress, thereby leading to the mass loss and the interfacial debonding of the composite. The degradation in transverse tensile strength was caused by joint effects of the matrix outgassing and the interfacial debonding, while the changes in flexural strength and ILSS were affected by a competing effect between the crosslinking degree of resin matrix and the fiber-matrix debonding.     

Microstructure, mechanical and tribological properties of Ti(C, N)/a-C gradient composite films

Ti(C, N)/a-C composite films with compositional gradient from Ti-TiN-Ti(C, N) to Ti-containing a-C layers have been prepared by closed-field unbalanced magnetron sputtering. Within the composite films, the carbon contents gradually increase and achieve maximum in the a-C layer by increasing the power applied to the graphite targets, the nitrogen contents gradually decrease to zero from Ti(C, N) layer of the interface to a-C layer of the films. In order to achieve a good combination of the mechanical and tribological properties in the composite films, a designed experimental parameter basing on various substrate rotation speeds is also selected. Results show that the compositional gradient result in the microstructure change of composite films where the Ti(C, N) layers consist of fine nanocolumnar Ti(C, N) grains and the a-C layers consist of 2-7 nm TiC nanocrystallites embedded in an amorphous C matrix. The Ti(C, N) layers also exhibit clear multilayer structure where the period thickness gradually decreases as substrate rotation speed increases. Under higher rotation speed, disappearance of the multilayer structure is accompanied with simultaneous increase in the crystallinity of Ti(C, N) layer and also the Ti(C, N) grain size. In the a-C layer, the TiC nanocrystallites embedded in the a-C matrix is produced by the high rotation speeds. The Ti(C, N)/a-C gradient composite films exhibit high microhardness values (~5000 H_V) and low friction coefficient (~ 0.15), which is related to the hard Ti(C, N) layer and self-lubricate a-C layer, respectively. The combination of the Ti(C, N) layer with a-C layer increases the load and the wear resistance capacity of the composite films, which gives satisfactory friction performance in the pin-on-disk tests with a wear rate of 3.7 × 10^− 17 m³/mN.     

Effect of hydrogen plasma treatment on the surface morphology, microstructure and electronic transport properties of nc-Si:H

Hydrogenated nanocrystalline silicon (nc-Si:H) films, deposited by reactive radio-frequency sputtering with 33% hydrogen dilution in argon at 200 °C, were treated with low-power hydrogen plasma at room temperature at various power densities (0.1-0.5 W/cm²) and durations (10 s-10 min). Plasma treatment reduced the surface root mean square roughness and increased the average grain size. This was attributed to the mass transport of Si atoms on the surface by surface and grain boundary diffusion. Plasma treatment under low power density (0.1 W/cm²) for short duration (10 s) caused a significant enhancement of crystalline volume fraction and electrical conductivity, compared to as-deposited film. While higher power (0.5 W/cm²) hydrogen plasma treatment for longer durations (up to 10 min) caused moderate improvement in crystalline fraction and electrical properties; however, the magnitude of improvement is not significant compared to low-power (0.1 W/cm²)/short-duration (10 s) plasma exposure. The results indicate that low-power hydrogen plasma treatment at room temperature can be an effective tool to improve the structural and electrical properties of nc-Si:H.     

Surface morphological, structural, electrical and optical properties of annealed vanadyl tetra tert-butyl 2, 3 naphthalocyanine thin films

Vanadyl Tetra Tert-Butyl 2, 3 Naphthalocyanine (VTTBNc) thin films have been grown at room temperature by physical vapor deposition technique. The article describes the role of air and vacuum annealing on VTTBNc thin film surface morphology, structure, electrical conductivity and optical absorbance on the basis of respective measurements like atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray Diffractogram (XRD), DC electrical conductivity with integrated electrodes and UV-visible absorption spectra.     

Investigation of the tribological behavior and its relationship to the microstructure and mechanical properties of a-SiC:H films elaborated by low frequency plasma assisted chemical vapor deposition

Amorphous hydrogenated silicon carbide (a-SiC:H) coatings are promising candidates for tribological applications in the mechanical and aeronautical industries. Alternately high values of hardness H (15 < H < 32 GPa) and elastic modulus E contribute to their good wear resistance as well as to a low friction coefficient. The latter has been found to vary in the range 0.1 < μ < 0.65, depending upon the microstructure of the layers. The roughness of the films determined by atomic force microscopy is in all cases low (Ra ~ 5 nm). Comparisons between the tests carried out in air and those performed under vacuum conditions point to a substantial role of the adhesive part of the friction coefficient in vacuum. They also highlight the role played by the transfer layer between the film and the pin in producing a low friction coefficient for several coatings. This transfer layer consists chiefly of silicon and oxygen (O/Si ~ 2), whilst low quantities of carbon are also present.     

Effect of temperature on the evolution of diffusivity, microstructure and hardness of nanocrystalline nickel films electrodeposited at low temperatures

Most nickel (Ni) films galvanostatically electrodeposited at 40-50 °C exhibited low hardness about 4 GPa and rough surface. In this article, we have investigated Ni electrodeposition at low temperatures of 5-20 °C in order to enhance the hardness and smoothness of films and performed by potentiostatic mode instead of galvanostatic mode to avoid the low-temperature precipitation of electrolyte agents. Effect of temperature on the evolution of diffusion coefficient, deposition rate, morphology and hardness was studied. Electrodeposition at low temperature without hard-element addition can reduce diffusion rate and produce the fine-grain, smooth morphology and dense film together with compressive residual stress to enhance hardness up to 6.18 GPa at 5 °C. The growth and hardening mechanism of low-temperature electrodeposited Ni were further discussed in details.     

The influence of pH over topography and spectroscopic properties of silica hybrid materials embedding meso-tetratolylporphyrin

Hybrid porphyrin-silica materials consisting in 5,10,15,20-tetratolyl-21H,23H-porphine, encapsulated in silica matrices were obtained by sol-gel method. The hydrolysis and condensation reactions were performed by using tetraethylorthosilicate as precursor, either in one-step acid or in two steps acid-base catalysis, assisted or not by an ultrasonic field. The porphyrin-silica hybrid materials were monitored and characterized by AFM, FT-IR, fluorescence and UV-vis spectroscopy. As a result of porphyrin entrapping into silica gels, a general phenomenon regarding hyperchromic effects of the Q bands, occurs. UV-vis study revealed that during the sol-gel process, major changes regarding porphyrin ring structure occur, especially at acidic pH, when the dicationic species of porphyrin are formed. During acid-base catalyzed method the dye molecules tend to aggregate by π−π and hydrophobic co-facial interactions of sandwich H-type. In acid catalyzed process, the protonation of the porphyrins prevent the formation of aggregates, due to increased electrostatic repulsion between the molecules.     

Comparative study on the structural and catalytic properties of mesoporous hexagonal silica anchored with H3PW12O40: Green synthesis of benzoic acid from benzaldehyde

Mesoporous silica anchored with 25 wt.% 12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) were comparatively characterized on their structures and catalytic activities for benzaldehyde oxidation with H₂O₂. The results revealed that the mesoporous materials retained the typical hexagonal mesopores for the supports of HPW. It was found that HPW exhibited higher dispersion within MCM-41 than those within SBA-15 and other mesoporous molecular sieves. Moreover, the as-prepared materials were found to be the efficient catalysts for the green synthesis of benzoic acid. In particular, HPW/MCM-41 exhibited the best catalytic properties due to its suitable textural and structural characteristics.     

Morphological, optical and electrical properties of samarium oxide thin films

We present here results on samarium oxide thin films, obtained by pulsed laser deposition and by radio frequency assisted pulsed laser deposition. Three different substrate types were used: silicon, platinum covered silicon and titanium covered silicon. The influence of the deposition parameters (oxygen pressure and laser fluence) on the structure and morphology of the thin films was studied. The substrate-thin film interface zone was investigated; the optical and electrical properties (the losses, dielectric constant and leakage currents) were also determined.     

Nonisothermal crystallization behavior and mechanical properties of PEEK/SCF/nano-SiO2 composites

Nonisothermal crystallization of hybrid PEEK composites reinforced with short carbon fibers (SCF) and nano-SiO₂ (1, 1.5 and 2 wt%) was investigated using DSC. Composites were fabricated by melt-mixing process at 400 °C. The Size of the nanoparticles was 13 nm. Samples were cooled from 410 °C to 25 °C with cooling rates of 10, 30, 50 and 70 °C min⁻¹. The onset, peak and end crystallization temperatures were investigated as well as absolute crystallization percentage and crystallization time. Avrami, Ozawa and Ozawa–Avrami equations were fitted to the data in order to investigate the crystallization kinetics. Mechanical behaviors of the composites were examined using nanoindentation and nanoscratching. DSC results revealed that absolute crystallization percentage increases in PEEK/SCF/1%SiO₂ and PEEK/SCF/1.5%SiO₂ samples compared to PEEK/SCF, however it decreases by adding more nano-SiO₂. Ozawa–Avrami is proved to be the best model for describing crystallization behavior of the composites while Avrami equation was suitable for describing a part of the crystallization process. The Avrami and Ozawa–Avrami constants were calculated. Besides, adding SCFs and nano-SiO₂ into PEEK results in a significant decrease in plasticity index, while increases the resistance to plastic deformation of the composite.     

Effects of high hydrogen dilution ratio on surface topography and mechanical properties of hydrogenated nanocrystalline silicon thin films

Hydrogenated nanocrystalline silicon thin films were deposited with high hydrogen dilution ratio by plasma enhanced chemical vapor deposition technique. The effects of high hydrogen dilution on the surface topography and mechanical properties of the films were studied with atomic force microscopy and TriboIndenter nano indenter. The results indicate that the average grain size in films deposited with high hydrogen dilution is about 3.18 ± 0.02 nm. The surface roughness and densification of the films decrease with the increase of hydrogen dilution ratio at certain range, resulting in the enhancement of the elastic modulus E and hardness H. Oppositely, the increase of hydrogen dilution can increase the surface roughness induced by the increase of the cavities on the film surfaces, and lead to the decrease of the elastic modulus and hardness correspondingly. In this paper, the detailed analysis and discussion were carried out to investigate the mechanism of the observed phenomena.