Friction force microscopy study of annealed diamond-like carbon film

In this paper we introduce mechanical and structural characteristics of diamond-like carbon (DLC) films which were prepared on silicon substrates by radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) method using methane (CH₄) and hydrogen (H₂) gas. The films were annealed at various temperatures ranging from 300 to 900 °C in steps of 200 °C using rapid thermal processor (RTP) in nitrogen ambient. Tribological properties of the DLC films were investigated by atomic force microscopy (AFM) in friction force microscopy (FFM) mode. The structural properties of the films were obtained by high resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the films was obtained using contact angle measurement. XPS analysis showed that the sp³ content is decreased from 75.2% to 24.1% while the sp² content is increased from 24.8% to 75.9% when the temperature is changed from 300 to 900 °C. The contact angles of DLC films were higher than 70°. The FFM measurement results show that the highest friction coefficient value was achieved at 900 °C annealing temperature.     

Evaluation of microstructures and mechanical properties of diamond like carbon films deposited by filtered cathodic arc plasma

Diamond-like carbon (DLC) films were deposited by a cathodic arc plasma evaporation (CAPD) process, using a mechanical shield filter combined with a magnetic filter with enhanced arc structure at substrate-bias voltage ranging from − 50 to − 300 V. The film characteristics were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). The mechanical properties were investigated by using a nanoindentation tester, scratch test and ball on disc wear test. The Raman spectra of the films showed that the wavenumber ranging from 900 to 1800 cm^− 1 could be deconvoluted into 1140 cm^− 1, D band and G band. The bias caused a significant effect on the sp³ content which was increased with the decreasing of I_D/I_G ratio. The XPS spectra data of the films which were etched by H⁺ plasma indicated the sp³ content are higher than those of the as-deposited DLC films. This implied that there is a sp²-rich layer present on the surface of the as-deposited DLC films. The nanoindentation hardness increased as the maximum load increased. A 380 nm thick and well adhered DLC film was successfully deposited on WC-Co substrate above a Ti interlayer. The adhesion critical load of the DLC films was about 33 N. The results of the wear tests demonstrated that the friction coefficient of the DLC films was between 0.12 and 0.2.     

Evaluation of corrosion resistance of diamond-like carbon films deposited onto AISI 4340 steel

The corrosion resistance of amorphous diamond-like carbon (DLC) coatings deposited by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique on AISI 4340 steel substrates was evaluated under saline (5% NaCl) and acid (1700 ppm H₂SO₄) atmospheres. The corrosion process was investigated by surface characterization and electrochemical methods, such as potentiostatic polarization and electrochemical impedance spectroscopy (EIS). DLC coatings effectively protected the substrate after 48 h in a salt fog chamber and after the first Kesternich cycle. For comparison, under the same conditions, titanium nitride (TiN) coatings did not protect the substrate even for 2 h of saline exposure and even for the first Kesternich cycle. Although the DLC coatings resisted well to the corrosive action of the aggressive media, nucleation and growth of homogenous and micro-sized pinholes uniformly distributed on DLC coatings were observed as a result of the corrosion processes. The observed results suggest that the development of techniques which would reduce the porosity of the DLC films could promote further improvement on their corrosion protection ability.     

Effect of pH value on the synthesis and characterization of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>Co<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3−δ</Subscript> powders prepared by the citrate–EDTA complexing method

This study reports the successful preparation of potential candidate Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) oxides for intermediate-temperature solid oxide fuel cells (IT-SOFCs) by a combined citrate-ethylenediaminetetraacetic acid (EDTA) complexing method. The resulting crystal properties, chemical composition, conductivity, and electrochemical properties were studied by X-ray diffraction (XRD), inductively coupled plasma mass spectroscopy (ICP-MS), energy dispersive spectrum (EDS), four-point DC measurement and AC impedance. The X-ray diffraction results of all samples with different pH values reveal a basic perovskite structure. Although samples prepared from different pH solutions have a similar structure, their chemical composition and grain morphologies are different. The optimized composition of BSCF is the sample prepared from the precursor solution with a pH value of 6; this produced highest conductivity at 50.2 S/cm at 400 °C, which is 1.3 times higher than the sample prepared from the precursor solution with a pH value of 9. Electrochemical impedance spectra at an intermediate temperature reveal the better electrochemical performance of BSCF electrode prepared from the solution with pH of 6. The lowest polarization resistance values for charge transfer and oxygen diffusion are 0.07 and 0.11 Ω cm² at 800 °C, respectively.     

Synthesis of polypyrrole film by pulse galvanostatic method and its application as supercapacitor electrode materials

Polypyrrole (PPy) film-coated stainless steel electrodes were prepared from aqueous solution containing 0.5 M p-toluene sulphonic acid and 0.1 M pyrrole using pulse galvanostatic method (PGM) and galvanostatic method (GM). The morphology was characterized by scanning electron microscopy. The electrochemical properties of PPy films were investigated with cyclic voltammetry, charge–discharge tests, and ac impedance spectroscopy. The results showed that the PGM-PPy films exhibited higher specific capacitance, better high-rate discharge ability and lower resistance, and were more promising for applications in supercapacitor than GM-PPy films. The specific capacitance (SC) of PGM-PPy films was 403 F g⁻¹ in 1 M H₂SO₄ electrolyte and 281 F g⁻¹ in 1 M NaNO₃ electrolyte.     

Effects of swift copper (Cu2+) ion irradiation on structural,optical and electrochemical properties of Co3O4-CuO-MnO2/GO nanocomposites powder

The properties of conjugated and irradiated Co₃O₄-CuO-MnO₂/GO nanostructured nanocomposites powder for possible applications in various sphere of life were studied in this research work. The hydrothermal technique was employed to the synthesis of high quality nanocomposite powder and dr. blades technique was employed to construct thin films known as electrodes. The properties of Co₃O₄-CuO-MnO₂/GO nanostructured composite powder (electrodes) were evaluated using SEM, EDS, XRD, FTIR and DRS. The electrochemical properties were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a 1.0 M solution of Na₂SO₄ electrolytic solution with a triple electrodes arrangement. The electrode irradiated with 2.25 × 10¹⁵ ions/cm² offered the highest specific capacitance of 1590 F/g at a scan rate of 10 mV/s. The results of electrochemical studies indicate that the combination of three transition metal oxides with GO irradiated by moderate ions is a noble contender for electrode applications.     

Electrodeposited nanostructured α-Fe2O3 thin films for solar water splitting: Influence of Pt doping on photoelectrochemical performance

Electrochemically deposited α-Fe₂O₃ thin films, whose composition was tuned by Pt doping, were investigated as photoanode for photoelectrochemical water splitting. Morphological and structural characteristics of the nanostructured α-Fe₂O₃ thin films were studied by scanning electron microscopy and X-ray diffraction techniques. The films were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy to determine the effect of Pt doping on the α-Fe₂O₃ structure. The photoelectrochemical performance of the films was examined by linear sweep voltammetry and electrochemical impedance spectroscopy. Results of these studies showed that Pt doping increased the density of small-sized nanoparticles in α-Fe₂O₃ thin films. The Pt doped films exhibited higher photoelectrochemical activity by a factor of 1.4 over un-doped α-Fe₂O₃ films. The highest photocurrent density of 0.56 mA cm⁻² was registered for 3% pt doped film at 0.4 V versus Ag/AgCl in 1 M NaOH electrolyte and under standard illumination conditions (AM 1.5 G, 100 mW cm⁻²). This high photoactivity can be attributed to the high active surface area and increased donor density caused by Pt doping in the film. Electrochemical impedance analysis also revealed significantly low charge transfer resistance of Pt doped films, indicating its superior electrocatalytic activity for water splitting reaction compared to un-doped α-Fe₂O₃ thin films.     

Pitting corrosion protection of low nickel stainless steel by electropolymerized conducting polymer coating in 0·5?M NaCl solution

Conducting polymers of polyaniline (PANi) and poly(o-phenylenediamine) (PoPD) were electropolymerized by cyclic voltammetric technique on low nickel stainless steel (LN SS) in H₂SO₄solution containing aniline and o-phenylenediamine monomers. The coatings were characterized by Fourier transform infrared spectroscopy, UV-visible and scanning electron microscopic techniques and the results are discussed. The corrosion protective properties of PANi and PoPD coatings on LN SS in 0·5 M NaCl were evaluated using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. The potentiodynamic polarization and electrochemical impedance spectroscopic results indicate that the PoPD coating inhibits the corrosion of LN SS in 0·5 M NaCl solution more effectively than PANi.     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.     

Influence of PECVD parameters on the properties of diamond-like carbon films

The properties of diamond-like carbon (DLC) are strongly affected by the amount of carbon atoms bonded in sp² and sp³ electronic hybridizations. Also the amount of incorporated hydrogen and oxygen plays an important role in the final properties of DLC films. Usually, the structure and chemical composition of thin DLC films can be changed by varying the deposition parameters. Therefore, the influence of PECVD process parameters on the properties of DLC films, grown on Si substrates, was investigated in this work.Thin DLC films were deposited in a CH₄/H₂ plasma by using Ar as a gas carrier. Different ratios of gas flows were used as a variable parameter of the PECVD process. The effect of cathodic ion bombardment was also investigated.The chemical composition of DLC specimens was studied by X-ray photoelectron spectroscopy (XPS). The ratio of carbon in sp² and sp³ hybridizations was determined by analyzing the first derivative of Auger C KLL spectra. These results were also confirmed by the measurements of electrical resistivity. The changes of surface morphology and microadhesion were analyzed by Atomic Force Microscopy (AFM).     

Nickle-ion-substituted ceria nanoparticles-based electrochemical sensor for sensitive detection of thiourea

Nickel-substituted ceria nanoparticles (CeO₂:Ni NPs) were prepared by the co-precipitation process under environmental conditions. X-ray diffraction (XRD), field emission-transmission electron microscopy, UV/visible, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy techniques were successfully used to investigate the crystallographic structure, phase purity, morphology, optical properties, chemical composition, and electrocatalytic properties of the as-prepared ceria NPs. XRD pattern shows the formation of single-phase, highly crystalline, and cubic phase nanostructure with an average of 10 nm crystalline size. As observed from TEM micrographs, particles were highly aggregated may be due to the synthesis in aqueous media. The electrochemical properties and sensing performance of the CeO₂:Ni NPs pasted on glassy carbon electrode were measured against different thiourea concentrations. The fabricated electrode revealed excellent electrocatalytic activity against thiourea concentrations as well as characterization in comparison to the bare electrode. The electrode exhibited a linear detection range between 3.56 and 1000 µM, detection limit 3.56 µM, and sensitivity 2.52 µA mL µM^?1 cm^?2 with regression coefficient 0.995. The electrochemical stability, chemical kinetic, and reproducibility were also examined in the presence of thiourea in phosphate buffer solution.

     

Effects of pH on the electrochemical behaviour of titanium alloys for implant applications

The electrochemical behaviour of two commercial titanium alloys Ti-6Al-4 V (ASTM F136) and Ti-13Nb-13Zr (ASTM F1713) was investigated in Ringer physiological solution at two pH values (5.5 and 7.0). The corrosion properties were examined by using electrochemical techniques: Potentiodynamic anodic polarization, cyclic polarization and electrochemical impedance spectroscopy (EIS). The electrochemical corrosion properties of both alloys at different conditions were measured in terms of corrosion potential (E _corr), corrosion current density (i _corr) and passivation current density (i _pass). Equivalent electrical circuits were used to modulate EIS data, in order to characterize alloys surface and better understanding the pH effect on the interface alloy/solution.     

Experimental and theoretical elucidation on the inhibition mechanism of 1-methyl-5-mercapto-1,2,3,4-tetrazole self-assembled films on corrosion of iron in 0.5 M H2SO4 Solutions

The self-assembled films of 1-methyl-5-mercapto-1,2,3,4-tetrazole (MMT) were prepared on the iron surface. By means of electrochemical impedance spectroscopy in 0.5 M H₂SO₄ solutions, the inhibition ability of the film was investigated. Results were discussed through changing the concentrations of the inhibitor and the pH values of the self-assembly solutions. Quantum chemical calculation was applied to elucidate the adsorption mechanism of the inhibitor molecule to iron atom. The study shows that MMT is a good inhibitor for iron in 0.5 M H₂SO₄ solutions. The self-assembled films formed in 10⁻² M acidic solutions have the best protection effect and the inhibition efficiency in 0.5 M H₂SO₄ solutions is 98.0%. Density functional theory proves that MMT molecule is adsorbed on the iron surface by the most negatively charged nitrogen atom and the adsorption can occur spontaneously.     

Wear behaviour and rolling contact fatigue life of Ti/TiN/DLC multilayer films fabricated on bearing steel by PIIID

In order to improve the friction and wear behaviours and rolling contact fatigue (RCF) life of bearing steel materials, Ti/TiN/DLC (diamond-like carbon) multilayer hard films were fabricated onto AISI52100 bearing steel surface by plasma immersion ion implantation and deposition (PIIID) technique. The micro-Raman spectroscopy analysis confirms that the surface film layer possess the characteristic of diamond-like carbon, and it is composed of a mixture of amorphous and crystalline phases, with a variable ratio of sp²/sp³ carbon bonds. Atomic force microscope (AFM) reveals that the multilayer films have extremely smooth area, excellent adhesion, high uniformity and efficiency of space filling over large areas. The nanohardness (H) and elastic modulus (E) measurement indicates that the H and E of DLC multilayer films is about 32 GPa and 410 GPa, increases by 190.9% and 86.4%. The friction and wear behaviours and RCF life of DLC multilayer films specimen have also been investigated by ball-on-disc and three-ball-rod fatigue testers. Results show that the friction coefficient against AISI52100 steel ball decreases from 0.92 to 0.25, the longest wear life increases nearly by 22 times. In addition, wear tracks of the PIIID samples as well as wear tracks of the sliding steel ball were analyzed with the help of optical microscopy and scanning electron microscopy (SEM). The L₁₀, L₅₀, L_a and mean RCF life L of treated bearing samples, in 90% confidence level, increases by 10.1, 4.2, 3.5 and 3.4 times, respectively. Compared with the bearing steel substrate, the RCF life scatter extent of Ti/TiN/DLC multilayer films sample is improved obviously.     

Sol-Gel-Derived Ordered Mesoporous High Entropy Spinel Ferrites and Assessment of Their Photoelectrochemical and Electrocatalytic Water Splitting Performance

The novel material class of high entropy oxides with their unique and unexpected physicochemical properties is a candidate for energy applications. Herein, it is reported for the first time about the physico- and (photo-) electrochemical properties of ordered mesoporous (CoNiCuZnMg)Fe₂O₄ thin films synthesized by a soft-templating and dip-coating approach. The A-site high entropy ferrites (HEF) are composed of periodically ordered mesopores building a highly accessible inorganic nanoarchitecture with large specific surface areas. The mesoporous spinel HEF thin films are found to be phase-pure and crack-free on the meso- and macroscale. The formation of the spinel structure hosting six distinct cations is verified by X-ray-based characterization techniques. Photoelectron spectroscopy gives insight into the chemical state of the implemented transition metals supporting the structural characterization data. Applied as photoanode for photoelectrochemical water splitting, the HEFs are photostable over several hours but show only low photoconductivity owing to fast surface recombination, as evidenced by intensity-modulated photocurrent spectroscopy. When applied as oxygen evolution reaction electrocatalyst, the HEF thin films possess overpotentials of 420 mV at 10 mA cm⁻² in 1 m KOH. The results imply that the increase of the compositional disorder enhances the electronic transport properties, which are beneficial for both energy applications.     

Characterization of Ni0.92V0.08Ox thin films deposited by the pulse sputter method

Based on the use of 8 at.%V-92 at.%Ni alloy target, Ni_0.92V_0.08O_x thin films are deposited via the pulse sputter method to avoid the ferromagnetic disadvantage when using a pure Ni metallic target. Crystallinity, microstructure and electrochromic (EC) properties are investigated systematically by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The optical properties of the Ni_0.92V_0.08O_x films are analyzed by a UV/VIS spectrophotometer (UV–Visible). Electrochromic tests are performed using an electrochemical analyzer. Experimental results indicate that the thickness, chemical composition, microstructure, and electrochromic properties heavily depend on the plasma power and the argon/oxygen ratio. The XPS and XRD analyses reveal that Ni²⁺, Ni³⁺, V⁴⁺ and V⁵⁺ co-exist in the Ni_0.92V_0.08O_x films and form an ideal stoichiometric compound at plasma power above 250 W, demonstrating that V can stabilize the valence state of Ni²⁺. Films deposited at 100 W yields the optimal electrochromic properties, with high optical modulation, high coloration efficiency and the lowest color memory effect at wavelengths of 400, 550 and 800 nm.     

Hydrophobic properties of the ion beam deposited DLC films containing SiOx

Diamond like carbon (DLC) films received considerable interest due to outstanding mechanical and tribological properties as well as chemical inertness and hydrophobicity. That combination is particularly interesting for possible application of the DLC as anti-sticking layers in novel lithographic techniques such as nanoimprint lithography, because Si, quartz and Ni - the most often used materials for imprint stamp formation - have high surface energy and, as a result, bad anti-adhesive properties. In present study, SiO_x containing DLC thin films were synthesized from hexamethyldisiloxane vapor and hydrogen gas mixture by direct ion beam deposition. Anti-sticking properties of the grown DLC thin films were evaluated measuring surface contact angle with water. Chemical composition and structure of the deposited films were investigated by X-ray photoelectron spectroscopy and FTIR spectrometry. Morphology of the films was measured by atomic force microscopy. Effects of hexamethyldisiloxane flux on structure, anti-sticking properties and surface morphology of the SiO_x containing DLC thin films were defined.     

Electrochemical characteristics of Ba0.5Sr0.5Co0.8Fe0.2O3−δ–Sm0.2Ce0.8O1.9 composite materials for low-temperature solid oxide fuel cell cathodes

In this paper, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ–xSm_0.2Ce_0.8O_1.9 (BSCF–xSDC, x = 0–60 wt.%) composite cathodes were prepared by soft chemical methods, and then examined for potential applications in lower temperature solid oxide fuel cells. Both DC polarization and AC impedance spectroscopy measurements indicated that the addition of SDC electrolyte into BSCF remarkably improved the electrochemical properties. The optimum composition was found to be BSCF–30SDC, which exhibited 5.5 times higher polarization current density and 15.1% polarization resistance, compared with the pure-phase BSCF cathode at 550 °C.     

Electrochemical properties of LiCoO2 thin film electrode prepared by ink-jet printing technique

LiCoO₂ thin film electrodes with a thickness of about 1.2 μm were fabricated by an improved ink-jet printing method. LiCoO₂ powder was synthesized via a modified sol-gel method. The LiCoO₂ ink could be easily prepared by an ultrasonic dispersion technique using a commercially available surfactant. The jet printing LiCoO₂ thin films were characterized by X-ray diffraction and Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, charge/discharge cycling and electrochemical impedance spectroscopy. Experimental results showed that the LiCoO₂ thin film electrodes present excellent cycling performance at high discharge rate. At discharge current density of 180 μA/cm² (at this current density, the battery can be fully discharged in 12 min), the initial discharge capacity was 120 mAh/g, and after 100 charge-discharge cycles, the capacity loss was only 5%. It can be even charge-discharged at the current density as high as 384 μA/cm².     

Effect of bias voltage on the electrochemical properties of TiN coating for polymer electrolyte membrane fuel cell

The electrochemical properties of TiN film coated on AISI 316 stainless steel (SS) by the magnetron sputtering physical vapor deposition (PVD) were studied for application as a bipolar plate. The crystal structure and surface morphology of the coatings were examined by x-ray diffractometry (XRD) and atomic force microscopy (AFM), respectively. The corrosion behaviors of the TiN films were investigated by electrochemical methods, including potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) under + 600 mV_SCE application. The electrochemical behavior of the TiN coatings was enhanced with increasing bias voltage due to lower corrosion current density and higher R_ct values during an immersion time of 168 h. This result was attributed to the formation of crystalline-refined TiN(200) at high bias voltage, which increased the coating compactness and the protective efficiency, and decreased passive current density.