Electrochemically deposited polypyrrole films and their characterization

Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H₂O and NaBF₄ aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (< 30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm^− 3 KCl_(aq) at 295 K was ≈ 1 × 10⁶ Ω cm, while the resistivity of the oxidised membrane was 2700 Ω cm.     

Improvement in corrosion resistance of CrN coated stainless steel by conformal TiO2 deposition

A conformal titanium dioxide (TiO₂) layer was deposited onto chromium nitride (CrN) coated stainless steel by atomic layer deposition technique, and the electrochemical corrosion test on the CrN single-layer and TiO₂/CrN double-layer coated sample was carried out. The equilibrium corrosion potential of the double-layer coated sample shifted positively compare to that of the single-layer coated one. Moreover, the corrosion current density decreased significantly with the TiO₂ deposition, revealing that better corrosion resistance was obtained after the deposition of the TiO₂ layer. The improvement in corrosion resistance after the TiO₂ deposition was attributed to the blocking of the through-thickness cracks or pinholes in the CrN layer.     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

Influence of EDTA concentration on the structure and properties of SnS films prepared by electro-deposition

Tin sulfide (SnS) thin films were deposited onto indium tin oxide (ITO) glass substrates by cathodic electro-deposition from aqueous solution containing ethylene diamine tetraacetate acid (EDTA). Because EDTA can slow the deposition rate of Sn through formation of Sn chelates, it is possible to obtain stoichiometric SnS films with good quality by adding EDTA to the deposition bath. The deposited films were characterized with X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometer. The as-deposited films are mainly polycrystalline SnS with orthorhombic crystalline structure, and they show good uniformity and surface coverage with root mean square (RMS) roughness of 45.36-62.39 nm and grain sizes of 100-300 nm. Raman microscopy shows that the films have bands at around 190 and 218 cm^− 1 belonging to A_g mode of SnS. The concentration ratio of EDTA and Sn²⁺ (EDTA/Sn²⁺) has some influence on the structure, phase, Raman shift and optical properties of the deposited films. When the EDTA/Sn²⁺ is less than 0.5, the films have a Raman shift at around 306 cm^− 1 due to Sn₂S₃. XPS analysis also shows that there exists a Sn₂S₃ phase in the deposited films. When the EDTA/Sn²⁺ equals 1/1, there is only the SnS phase in the deposited films. With an increase of the EDTA/Sn²⁺ from 0.1 to 1, the direct band gap of the films is decreased from 1.75 eV to 1.43 eV. Therefore EDTA/Sn²⁺ = 1/1 is good for depositing SnS films.     

Effect of RF deposition power on the properties of Al-doped TiO2 thin films

The Al-doped TiO₂ (TiO₂:Al) films were deposited by simultaneous RF (Radio Frequency) magnetron sputtering of TiO₂ and DC (Direct Current) magnetron sputtering of Al. The advantage of this method is that the Al content could be independently controlled. TiO was more favorable to form and the deposited films became nonstoichiometric by increasing RF power density. The morphologies of TiO₂ and TiO₂:Al films were significantly affected by RF power density. The nonlinear refractive index of TiO₂:Al film on the glass substrate was measured by Moiré deflectometry, and was of the order of 10^− 8 cm² W^− 1. Compared with TiO₂ film, TiO₂:Al film had smaller grain size, lower porosity, higher linear refractive index, lower stress-optical coefficient and higher VIS-IR transmission.     

The electroplated palladium-copper alloy film on 316L stainless steel and its corrosion resistance in mixture of acetic and formic acids

Palladium-copper alloy films (Cu 2.93-5.66 at.%) were deposited on 316L stainless steel by electroplating. The films showed good adhesive strength and increased surface micro-hardness. In boiling mixture of 90% acetic acid + 10% formic acid + 400 ppm Br⁻ under stirring (625 r/min), the Pd-Cu films showed better corrosion resistance than Pd film. The Pd-5.66%Cu films showed the lowest corrosion rate almost three orders of magnitude lower than that of 316L matrix. The increased corrosion resistance of Pd-Cu films was attributed to the improved passivity, better barrier effect, increased surface hardness and the effect of Cu to resist pitting.     

High-repetition rate pulsed laser deposition of ZrC thin films

ZrC thin films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a high-repetition rate excimer laser working at 40 Hz. The substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that the films were crystalline. Films deposited under residual vacuum or 2 × 10^− 3 Pa of CH₄ atmosphere exhibited a (200)-axis texture, while those deposited under 2 × 10^− 2 Pa of CH₄ atmosphere were found to be equiaxed. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES), showed the usual high oxygen contamination of carbides. Once the topmost − 3-5 nm region was removed, the oxygen concentration rapidly decreased, being around 3-4% only in bulk. Scanning electron microscopy (SEM) investigations showed a smooth, featureless surface morphology, corroborating the roughness values below 1 nm (rms) obtained from simulations of the X-ray reflectivity (XRR) curves. From the same simulations we also estimated films mass density values of around 6.32-6.57 g/cm³ and thicknesses that correspond to a deposition rate of around 8.25 nm/min. Nanoindentation results showed a hardness of 27.6 GPa and a reduced modulus of 228 GPa for the best quality ZrC films deposited under an atmosphere of 2 × 10^− 3 Pa CH₄.     

Influence of oxygen partial pressure on electrical and optical properties of Zn0.93Mn0.07O thin films

The Zn_1−xMn_xO (x = 0.07) thin films were grown on glass substrates by direct current reactive magnetron cosputtering. The influence of oxygen partial pressure on the structural, electrical and optical properties of the films has been studied. X-ray-diffraction measurement revealed that all the films were single phase and had wurtzite structure with c-axis orientation. The experimental results indicated that there was an optimum oxygen partial pressure where the film shows relative stronger texture, better nano-crystallite and lower surface roughness. As the oxygen partial pressure increases, the carrier concentration systematically decreases and photoluminescence peaks related to zinc interstitials gradually diminish. The minimal resistivity of 70.48 Ω cm with the highest Hall mobility of 1.36 cm² V⁻¹ s⁻¹ and the carrier density of 6.52 × 10¹⁶ cm⁻³ were obtained when oxygen partial pressure is 0.4. All films exhibit a transmittance higher than 80% in the visible region, while the deposited films showed a lower transmittance when oxygen partial pressure is 0.4. With the increasing of oxygen partial pressure, the peak of near-band-edge emission has firstly a blueshift and then redshift, which shows a similar trend to the band gap in the optical transmittance measurement.     

Conductive and transparent Bi-doped ZnO thin films prepared by rf magnetron sputtering

Bi-doped ZnO thin films were grown on glass substrates by ratio frequency (rf) magnetron sputtering technique and followed by annealing at 400 °C for 4 h in vacuum (~ 10^− 1 Pa). The effect of argon pressure on the structural, optical, and electrical properties of the Bi-doped films were investigated. The XRD patterns show that the thin films were highly textured along the c-axis and perpendicular to the surface of the substrate. Some excellent properties, such as high transmittance (about 85%) in visible region, low resistivity value of 1.89 × 10^− 3 W cm and high carrier density of 3.45 × 10²⁰ cm^− 3 were obtained for the film deposited at the argon pressure of 2.0 Pa. The optical band gap of the films was found to increase from 3.08 to 3.29 eV as deposition pressure increased from 1 to 3 Pa. The effects of post-annealing treatments had been considered. In spite of its low conductivity comparing with other TCOs, Bi-doping didn't appreciably affect the optical transparency in the visible range of ZnO thin films.     

Enhanced electrical properties of Pb(Zr0.80Ti0.20)O3 thick films prepared by a modified sol-gel technique

Ferroelectric Pb(Zr_0.80Ti_0.20)O₃ thick films (5.0 μm) were grown on Pt/Ti/SiO₂/Si substrates by a modified sol-gel technique. In this process, PZT nanopowders were prepared via sol-gel, and then these powders were dispersed in a precursor sol to form a slurry. Slurry and PZT precursor solution were spin-coated alternately to form uniform and crack-free thick films. The microstructure and electrical properties of the PZT thick films were investigated. The results in this work show that the PZT thick films possess typical polycrystalline perovskite structures, good pyroelectric coefficient (8.0 × 10^− 8C/cm² K), high remnant polarization (30 μC/cm²), and low coercive field (50 kV/cm).     

Optical and electrical properties of zinc oxide thin films with low resistivity via Li-N dual-acceptor doping

Zinc oxide thin films with low resistivity have been deposited on glass substrates by Li-N dual-acceptor doping method via a modified successive ionic layer adsorption and reaction process. The thin films were systematically characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, ultraviolet-visible spectrophotometry and fluorescence spectrophotometry. The resistivity of zinc oxide film was found to be 1.04 Ω cm with a Hall mobility of 0.749 cm² V⁻¹ s⁻¹ and carrier concentration of 8.02 × 10¹⁸ cm⁻³. The Li-N dual-acceptor doped zinc oxide films showed good crystallinity with prior c-axis orientation, and high transmittance of about 80% in visible range. Moreover, the effects of Li doping level and other parameters on crystallinity, electrical and ultraviolet emission of zinc oxide films were investigated.     

Low temperature growth of nanocrystalline TiO2 films with Ar/O2 low-field helicon plasma

TiO₂ thin films were deposited on silicon wafer substrates by low-field (1 < B < 5 mT) helicon plasma assisted reactive sputtering in a mixture of pure argon and oxygen. The influence of the positive ion density on the substrate and the post-annealing treatment on the films density, refractive index, chemical composition and crystalline structure was analysed by reflectometry, Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD). Amorphous TiO₂ was obtained for ion density on the substrate below 7 × 10¹⁶ m^− 3. Increasing the ion density over 7 × 10¹⁶ m^− 3 led to the formation of nanocrystalline (~ 15 nm) rutile phase TiO₂. The post-annealing treatment of the films in air at 300 °C induced the complete crystallisation of the amorphous films to nanocrystals of anatase (~ 40 nm) while the rutile films shows no significant change meaning that they were already fully crystallised by the plasma process. All these results show an efficient process by low-field helicon plasma sputtering process to fabricate stoichiometric TiO₂ thin films with amorphous or nanocrystalline rutile structure directly from low temperature plasma processing conditions and nanocrystalline anatase structure with a moderate annealing treatment.     

Corrosion resistance of Al ion implanted AZ31 magnesium alloy at elevated temperature

The Al ion implantation into AZ31 magnesium alloy was carried out in a MEVVA 80-10 ion implantation system at an ion energy of 40-50 keV with an ion implantation dose ranging from 2 × 10¹⁶ to 1 × 10¹⁷ ions/cm² at an elevated temperature of 300 °C induced by an ion current density of 26 μA/cm². The concentration-depth profile of implanted Al in AZ31 alloy measured by Rutherford backscattering spectrometry (RBS) is a Gaussian-type-like distribution in a depth up to about 1200 nm with the maximum Al concentration of about 8 at.%. The X-ray diffraction (XRD) analysis revealed the formation of α-Mg(Al) phase, intermetallic β-Mg₁₇Al₁₂, and MgO phase on the Al ion implanted samples. The potentiodynamic anodic polarization curves of the Al ion implanted samples in the 0.01 mol/l NaCl solution with a pH value of 12 showed increases of the corrosion potential and the pitting breakdown potential, and a decrease of the passive current density, respectively. The Al ion implanted samples with 6 × 10¹⁶ ions/cm² achieved the high pitting breakdown potential to about − 480 mV (SCE). In the 0.08 mol/l NaCl solution with pH = 12, the Al ion implanted samples with 1 × 10¹⁷ ions/cm² showed an increased pitting breakdown potential to about − 1290 mV (SCE), from around − 1540 mV (SCE) of unimplanted samples. It is indicated that different corrosion mechanisms are responsible for improvement in corrosion resistance of the AZ31 magnesium alloy in the NaCl solutions with the varied concentrations.     

Capacitance behaviour of passive films on ferritic and austenitic stainless steel

The electrochemical behaviour of passive films formed on one austenitic stainless steel (AISI 304) and one ferritic stainless steel (AISI 446) in solutions with pH between 0.6 and 8.4 was studied by capacitance measurements and photocurrent spectroscopy. Compositional characterization of the passive films was done by X-ray photoelectron spectroscopy. The capacitance increases with decreasing pH. Doping densities evaluated from Mott-Schottky plots are in the range 2-6 × 10²⁰ cm⁻³ and increased with the pH in the neutral/alkaline range while in pH 0.6, values above 10²¹ cm⁻³ were found. The bandgap energy indicates two transitions, at 2.5-2.8 and 3.2 eV. The analytical data reveal that, as the pH increased, the films become enriched in Fe(II) and Fe(III), whereas the Cr(III) gradually decreases. The films formed at very low pH had a behaviour that contrasts with that of the films formed in the neutral/alkaline media. The films are described by a bilayer structure, with hydroxides in the outer layer and a spinel type oxide in the inner layer.     

Corrosion studies of stainless steel protected by a TiO2 thin film deposited on a sulfonate-functionalized self-assembled monolayer

Thioacetate hexadecyltrimethoxysilane was deposited on SiO₂-coated stainless steel to form a thioacetate-functionalized monolayer. In situ oxidation of the thioacetate yielded a sulfonate-functionalized monolayer. Solution deposition of TiO₂ on this monolayer covered the stainless steel with a thin layer of the metal oxide (5-10 nm). Cyclic voltammetry (CV) and potentiostatic current transient demonstrated the efficiency of the corrosion protection in sodium chloride media, including protection against pitting corrosion.     

Filtered vacuum arc deposition of undoped and doped ZnO thin films: Electrical, optical, and structural properties

Filtered vacuum (cathodic) arc deposition (FVAD, FCVD) of metallic and ceramic thin films at low substrate temperature (50-400 °C) is realized by magnetically directing vacuum arc produced, highly ionized, and energetic plasma beam onto substrates, obtaining high quality coatings at high deposition rates. The plasma beam is magnetically filtered to remove macroparticles that are also produced by the arc. The deposited films are usually characterized by their good optical quality and high adhesion to the substrate. Transparent and electrically conducting (TCO) thin films of ZnO, SnO₂, In₂O₃:Sn (ITO), ZnO:Al (AZO), ZnO:Ga, ZnO:Sb, ZnO:Mg and several types of zinc-stannate oxides (ZnSnO₃, Zn₂SnO₄), which could be used in solar cells, optoelectronic devices, and as gas sensors, have been successfully deposited by FVAD using pure or alloyed zinc cathodes. The oxides are obtained by operating the system with oxygen background at low pressure. Post-deposition treatment has also been applied to improve the properties of TCO films.The deposition rate of FVAD ZnO and ZnO:M thin films, where M is a doping or alloying metal, is in the range of 0.2-15 nm/s. The films are generally nonstoichiometric, polycrystalline n-type semiconductors. In most cases, ZnO films have a wurtzite structure. FVAD of p-type ZnO has also been achieved by Sb doping. The electrical conductivity of as-deposited n-type thin ZnO film is in the range 0.2-6 × 10^− 5 Ω m, carrier electron density is 10²³-2 × 10²⁶ m^− 3, and electron mobility is in the range 10-40 cm²/V s, depending on the deposition parameters: arc current, oxygen pressure, substrate bias, and substrate temperature. As the energy band gap of FVAD ZnO films is ∼ 3.3 eV and its extinction coefficient (k) in the visible and near-IR range is smaller than 0.02, the optical transmission of 500 nm thick ZnO film is ∼ 0.90.     

Pulsed laser deposition of anatase and rutile TiO2 thin films

The investigation deals with the preparation of both anatase and rutile thin films from a sintered rutile target of TiO₂ by pulsed laser ablation technique. Microstructural characterization of the sintered target was carried out using X-ray diffraction and AC impedance spectroscopy. Thin films of titania were deposited on (111) Si substrates at 673 K in the laser energy range 200-600 mJ/pulse at two different conditions: (i) deposition at 3.5 × 10^− 5 mbar of oxygen, and (ii) deposition at an oxygen partial pressure of 0.1 mbar. The influence of laser energy and oxygen addition on the film growth has been studied. X-ray diffraction analysis of the films indicated that the films are single phasic and nano crystalline. Titania films deposited in the energy range 200-600 mJ/pulse at a base pressure of 5 × 10^− 5 mbar are rutile with particle sizes in the range 5-10 nm, whereas the films formed at the oxygen partial pressure 0.1 mbar are anatase with particle sizes in the range 10-24 nm. In addition, at higher energies, a significant amount of particulates of titania are found on the surface of the films. The change in the microstructural features of the films as a function of laser energy and oxygen addition is discussed in relation with the interaction of the ablated species with the background gas.     

H2S and O2 influence on the corrosion of carbon steel immersed in a solution containing 3 M diethanolamine

Aqueous solutions with 3 mol L⁻¹ (M) diethanolamine (DEA) concentration are extensively used in the gas processing industry to remove acid gases. However, the degradation of the DEA and the formation of heat-stable salts (HSS) lead to severe corrosion problems. Even worse, equipment corrosion can be magnified by the unavoidable presence of sulphide acid and dissolved oxygen as a result of hydrocarbon (natural gases and crude oil) processing. The aim of this work is to study the combined corrosion effects of DEA, sulphide acid and oxygen on carbon steel. Electrochemical methods revealed that in the 3 M DEA medium without oxygen, corrosion processes are modulated by adsorbed DEA film formation. Furthermore, it was shown that the addition of oxygen and 15 × 10⁻³ mol L⁻¹ (15 mM) H₂S produced the formation of an adherent film on the carbon steel surface. Chemical analyses by EDAX revealed a homogeneous film of corrosion products composed of iron oxide and sulphide formed in DEA solution containing O₂ and H₂S, respectively. Equivalent circuits were used to estimate the parameters associated with ion diffusion through the formed corrosion films. The results showed that the presence of H₂S induced the formation of thin iron sulphide films that provide protective properties to the metal. It is concluded that the presence of oxygen in a sweetening plant should be avoided as DEA degradation can be produced with the subsequent decrease in chelating process efficiency and the increase in corrosion problems.     

Parametric study of nitrided AISI 304 austenite stainless steel prepared by plasma immersion ion implantation

This paper investigates the characteristics of plasma immersion nitrogen-ion implanted AISI 304 austenite stainless steel against such processing parameters as bias voltage (5-20 kV), substrate temperature (300-500 °C), and implantation fluence (1.4 × 10¹⁸-4.2 × 10¹⁸ cm^− 2). Characteristics of the as-implanted specimens under investigation included elemental depth profile, hardness depth profile, crystallographic structure, and corrosion behavior and were determined using glow discharge spectrometry (GDS), the Vickers hardness tester, X-ray diffractometry (XRD), and the potentiodynamic polarization test, respectively. The results show that nitrogen depth profiles strongly depend on these processing parameters and closely relate to the corresponding chromium depth profiles. The hardness depth profiles increase and widen as substrate temperature, bias voltage, and implantation fluence increase. In particular, an improvement in hardness is accompanied by a reduction in corrosion resistance when substrate temperature reaches 500 °C. The corrosion-resistance degrader, CrN, precipitates as substrate temperature exceeds 450 °C, a phenomenon which is clearly evident in the chromium depth profiles as well as the XRD results.     

Transparent conducting oxide films of heavily Nb-doped titania by reactive co-sputtering

Niobium-doped titania (TNO) films of various Nb content were deposited on glass and silicon substrates by reactive co-sputtering of Ti and Nb metal targets. Nb content in the TNO films was varied from 0 to ∼13 at.% (atomic percent), corresponding to Ti_1−xNb_xO₂ with x = 0-0.52, by modulating the Nb target power from 0 to 150 W (Watts). The influence of ion bombardment on the TNO films was investigated by applying an RF substrate bias from 0 to 25 W. The as-deposited TNO films were all amorphous and insulating, but after annealing at 600 °C for 1 h in hydrogen, they became crystalline and conductive. The annealed films crystallized into either pure anatase or mixed anatase and rutile structures. The as-deposited and the annealed films were transparent, with an average transmittance above 70%. Anatase TNO film (Ti_1−0.39Nb_0.39O₂) with Nb 9.7 at.% exhibited a dramatically reduced resistivity of 9.2 × 10⁻⁴ Ω cm, a carrier density of 6.6 × 10²¹ cm⁻³ and a carrier mobility around 1.0 cm² V⁻¹ s⁻¹. In contrast, the mixed-phase Ti_1−0.39Nb_0.39O₂ showed a higher resistivity of 1.2 × 10⁻¹ Ω cm. This work demonstrates that the anatase phase, oxygen vacancies, and Nb dopants are all important factors in achieving high conductivities in TNO films.