ESCA-studies of the structure and composition of the passive film formed on stainless steels by various immersion times in 0.1 M NaCl solution

This report deals with the structure of the passive film formed on stainless steels during immersion in a 0.1 M NaCl solution for various immersion times. The film was examined using ion etching and Electron Spectroscopy for Chemical Analysis (ESCA).Through the chemical-composition profiles a three-factor model was developed to describe the structure of the passive films: a hydrated layer in contact with the solution, an oxide layer consisting of iron and chromium oxides having maxima at depths of 3 and 10 Å, respectively, and a metallic layer enriched in nickel. There is a smooth transition between the layers, with the thickness of the outer two layers being about 15 A. The maximum concentration of iron in the oxidized state decreases with increasing immersion time concomitant with an increase in both the maximum concentration of chromium in the oxidized state and the maximum concentration of nickel in the metallic state.It is found that air-formed films have similar structures to films formed by exposure to the solution. Longer air exposure thickens the air-formed film, with the maximum of both oxidized iron and chromium nearly equal in magnitude in comparison with the solution formed films. Films formed by short-time exposure only to the solution are somewhat thinner indicating that the total history is important in determining the structure of these passive films, whereas passive films formed by exposures of 15 h to the solution are no longer strongly dependent on prior air exposure.     

ESCA-studies of the surface film formed on stainless steels by exposure to 0.1 M NaCl solution at various controlled potentials

After immersion in a 0.1 M NaCl solution for 1 h at various controlled potentials, the surface films formed on two commercial stainless steels, 18–12 and 29-4-2, have been studied using a surface analysis technique ESCA (Electron Spectroscopy for Chemical Analysis) combined with ion etching. The influence of controlled potential in the lower region, between the OCP and the critical pitting potential, on the structure and chemical composition of the passive film is in limited agreement with the prior work. At higher controlled potentials above the pitting potential, the surface films consist of two components: the passive film and corrosion products. Changes to both oxidized chromium and metallic iron form major differences in the depth profiles in comparison with the previous results with the passive film. At higher controlled potentials oxidized alloying elements tend to the higher oxidation states on the outermost part of surface together with a possibility of enhanced adsorption of chloride ions. There is a great amount of oxidized molybdenum and chloride ions mainly from the corrosion products on the surface at higher applied potential. Their contents increase with the controlled potential.     

Synthesis of Ti-Cr-N thin films by reactive ion-beam mixing of Ti/Cr interfaces

Titanium/chromium interfaces produced by titanium thin film deposition on chromium substrates have been reactively mixed using ion-beams of 2 and 3 keV at room temperature (RT). The ion-beam mixing (IBM) has been analysed using X-ray photoelectron spectroscopy (XPS), angle-resolved X-ray photoelectron spectroscopy (ARXPS) and Monte Carlo TRIDYN simulations. Below ∼2 × 10¹⁶ ions/cm², the IBM kinetic is characterised by a strong decrease of the Ti concentration along with a fast nitrogen incorporation, that can be explained mainly by Ti sputtering and nitrogen implantation. Above that ion dose, the Ti/Cr ratio can be varied in a broad range maintaining nearly constant the nitrogen concentration (∼50%), as a consequence of sputtering, nitruration and mixing effects taking place simultaneously. ARXPS results show that the composition of the ternary films formed by reactive IBM is rather uniform in the near surface region. The comparison of experimental results with those obtained from TRIDYN, that uses pure ballistic mechanisms, suggests that the chemical reaction with the nitrogen partial pressure and processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of Ti/Cr interfaces.     

The influence of hydrogen on the atomic distribution function and electrical resistance of amorphous chromium films

Electrical resistivity of amorphous chromium films (20–37 nm thick) deposited in a hydrogen atmosphere (P _{H 2}=8·10^–6–2·10^–4 hPa) onto a substrate cooled by liquid helium down to 2 K is measured, and electron-diffraction studies have been performed immediately after the quench condensation and after annealing to different temperatures up to 300 K. The preparation method employed permits a considerable hydrogen enrichment of the films to be reached. The maximum hydrogen concentration corresponds approximately to a stoichiometric composition of CrH. It is found that as the maximum concentration is approached the atomic distribution functionG(r) changes remarkably. The interatomic distances increase considerably (by 10%) and the atomic densities decrease. It is quite possible that amorphous chromium hydride is a final state with the maximum hydrogen concentration. For films with intermediate concentration,G(r) is found to vary substantially under annealing up to 90 K. The electron-diffraction and electronmicroscopic data, as well as the variations in resistivity due to annealing, suggest that with annealing up to 90 K, a hydrogen redistribution occurs in the amorphous films, initially homogenous in concentration. We observe also distinct indications of separation into phases with increased and reduced hydrogen contents.     

Perpendicular magnetic anisotropy of ultrathin FeCo alloy films on Pd(0 0 1) surface: First principles study

Using the full potential linearized augmented plane wave (FLAPW) method, thickness dependent magnetic anisotropy of ultrathin FeCo alloy films in the range of 1 monolayer (ML) to 5 ML coverage on Pd(0 0 1) surface has been explored. We have found that the FeCo alloy films have close to half metallic state and well-known surface enhancement in thin film magnetism is observed in Fe atom, whereas the Co has rather stable magnetic moment. However, the largest magnetic moment in Fe and Co is found at 1 ML thickness. Interestingly, it has been observed that the interface magnetic moments of Fe and Co are almost the same as those of surface elements. The similar trend exists in orbital magnetic moment. This indicates that the strong hybridization between interface FeCo alloy and Pd gives rise to the large magnetic moment. Theoretically calculated magnetic anisotropy shows that the 1 ML FeCo alloy has in-plane magnetization, but the spin reorientation transition (SRT) from in-plane to perpendicular magnetization is observed above 2 ML thickness with huge magnetic anisotropy energy. The maximum magnetic anisotropy energy for perpendicular magnetization is as large as 0.3 meV/atom at 3 ML film thickness with saturation magnetization of . Besides, the calculated X-ray magnetic circular dichroism (XMCD) has been presented.     

XPS and AES studies of anodic passive films grown on chromium electrodes in sulphuric acid baths

The surface composition and the thickness of anodic passive films formed on chromium electrodes in sulphuric acid baths have been studied by XPS and AES using Ar⁺—ion sputtering. The results are consistent with a 13–16-Å thick oxide layer of composition close to Cr₂O₃. Some evidence is also given concerning hydrated species located in the outermost part of the passive film.     

Large enhancement of giant magnetoimpedance property in electrodeposited NiFe/Cu wire with copper additive in plating bath

NiFe thin films were electrodeposited on copper wires of diameter. The magnetic and magnetoimpedance (MI) property of the samples were investigated with the variation of copper sulphate additive concentration in the plating bath. Addition of copper ion to the film reduced it’s coercivity values and minimum coercivity was noticed for optimum concentration of 2 mM. This improvement in soft magnetic properties of the film alloy is strongly reflected in the enhancement of the MI (from 111% to 304%). The ac magnetic permeability and MI measured in similar conditions show a strong correlation between them and follows a one-to-one correspondence. Heterogeneous nucleation occurs by copper atoms which establishes a short range order. Magnetic softness increases in good agreement with random anisotropy model.     

The influence of aliovalent impurities on the oxidation kinetics of nickel at high temperatures

The influence of chromium and sodium on the nickel oxidation kinetics has been studied as a function of temperature (1373-1673 K) and oxygen activity (10−10⁵ Pa O₂), using microthermogravimetric techniques. It has been shown that the oxidation of Ni-Cr and Ni-Na alloys, like that of pure nickel, follows strictly the parabolic rate law being thus diffusion controlled. In agreement with the defect model of Ni_1−yO, it has been found that the oxidation rate of the Ni-Cr alloy is higher than that of pure nickel, the reaction rate is pressure independent and the activation energy of this process is lower. This implies that the concentration of double ionized cation vacancies in a Ni_1−yO-Cr₂O₃ solid solution is fixed on a constant level by trivalent chromium ions, substitutionally incorporated into the cation sublattice of this oxide. In the case of the Ni-Na alloy, on the other hand, the oxidation rate is lower than that of pure nickel, the activation energy is higher and the oxidation rate increases more rapidly with oxygen pressure. These results can again be explained in terms of the doping effect, by assuming that univalent sodium ions dissolve substitutionally in the cation sublattice of nickel oxide.     

ESCA studies of Cr-Co alloys

ESCA examination of films formed on Cr-Co alloys after immersion in 0.1M NaCl for 24 h has shown that the thickness of passive films decreased with an increase in chromium content. Surface films consisted of chromium and cobalt oxides as Cr₂O₃ and CoO. The amount of CoO in the surface film of the alloy was decreased with an increase in chromium but Cr₂O₃ was found at a greater depth in the passive film at any composition. Cr₂O₃ was a major component of the surface film when the chromium content in the alloy was 10% or higher. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate. Both Co-10 wt.% Cr and Co-30 wt.% Cr alloys investigated showed a lower corrosion rate than the Co-5 wt.% Cr alloy. Corrosion rate measured could be correlated to the surface film composition and structure as determined by ESCA.     

Improved optical response and photocatalysis for N-doped titanium oxide (TiO2) films prepared by oxidation of TiN

In order to improve the photocatalytic activity, N-doped titanium oxide (TiO₂) films were obtained by thermal oxidation of TiN films, which were prepared on Ti substrates by ion beam assisted deposition (IBAD). The dominating rutile TiO₂ phase was found in films after thermal oxidation. According to the results of X-ray photoelectron spectroscopy (XPS), the residual N atoms occupied O-atom sites in TiO₂ lattice to form TiON bonds. UV-vis spectra revealed the N-doped TiO₂ film had a red shift of absorption edge. The maximum red shift was assigned to the sample annealed at 750 °C, with an onset wavelength at 600 nm. The onset wavelength corresponded to the photon energy of 2.05 eV, which was nearly 1.0 eV below the band gap of pure rutile TiO₂. The effect of nitrogen was responsible for the enhancement of photoactivity of N-doped TiO₂ films in the range of visible light.     

Core-level and valence-band characteristics of carbon nitride films with high nitrogen content

Carbon nitride films with high nitrogen content were prepared by reactive pulsed-laser deposition at nitrogen partial pressures varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increase of the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at. % at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning the core-level and valence-band structures. Some fingerprint information, which shows the role of nitrogen in controlling the electronic structure of carbon nitride films, was found based on the XPS studies. With enhancing the nitrogen incorporation, both the binding energy and the peak intensity of the core-level and the valence-band spectra vary systematically as a function of nitrogen content in the films. Received: 26 June 2000 / Accepted: 26 June 2000 / Published online: 20 September 2000     

Structural, electrical, electronic and optical properties of melanin films

We present thick, uniform and rather flat melanin films obtained using spray deposition. The morphology of the films was investigated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Temperature-dependent electrical resistance of melanin thin films evidenced a semiconductor-like character and a hysteretic behavior linked to an irreversible process of water molecule desorption from the melanin film. X-ray Photoelectron Spectroscopy (XPS) was carried out to analyze the role of the functional groups in the primary and secondary structure of the macromolecule, showing that the contribution of the 5,6-dihydroxyindole-2-carboxylic acid (DHICA) subunit to the molecule is about 35%. Comparison of the optical absorption of the thick (800nm) and thin (80nm) films showed a spectral change when the thickness increases. From in vacuum photoconductivity (PC) measured at controlled temperatures, we suggest that the melanin films exhibit a possible charge transport mechanism by means of delocalized states along the stacked planar secondary structure.     

ESCA studies of Ni-Cr alloys

ESCA examination on Ni-Cr alloys has shown that a thin passive film was formed after 24 h immersion in 0.1 M NaCl. The film contained only chromium oxide in the form of Cr₂O₃. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Both Ni-10 wt. % Cr and Ni-20 wt. % Cr alloys showed a slightly higher corrosion rate than the Ni-40 wt. % Cr alloy.The present ESCA study of the Ni-Cr system is part of our programme which involves an examination of the four binary alloy systems Fe-Si, Cr-Co, Ni-Cr, and Mo-Ni [1]. The aim is to correlate the structure and composition of the passive films formed in 0.1 M NaCl to the corrosion behaviour in the same solution.     

A low temperature study of electron transport properties of tantalum nitride thin films prepared by ion beam assisted deposition

Measurement of electrical resistivity in the temperature range of tantalum nitride films prepared by Ion Beam Assisted deposition and pure tantalum films prepared by electron beam evaporation has been carried out. The tantalum film shows a resistivity minimum at T_m=12 K, whereas tantalum nitride shows a decrease in resistivity with an increase in temperature. An attempt has been made to explain such anomalous behavior by using existing theories.     

High-transparency films for nonlinear integrated optics based on P(VDF-TrFE) and poly(α-methyl styrene) host materials

In search of waveguiding polymer films with both highly efficient NonLinear Optical (NLO) and optimum transmission properties the second harmonic generation of light is measured on poled films of P(VDF-TrFE) blended with 10% PMMA or covered by the polarizable guest-host system PMS, both pure and doped with 2% NLO dye The PMS films turn out to be stable electrets after annealing at about 50°C and poling at room temperature. They are thus particularly easily processable candidates for NLO and waveguiding applications.     

rf reactive co-sputtered Au-Ag alloy nanoparticles in SiO2 thin films

We have studied formation of Au-Ag alloy nanoparticles in sputtered SiO₂ thin films. Silica thin films containing Au-Ag nanoparticles were deposited on quartz substrates using rf reactive magnetron co-sputtering technique. The films heat-treated in reducing Ar + H₂ atmosphere at different temperatures. They were analyzed by using UV-vis spectrophotometry, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) methods for their optical, surface morphological as well as structural and chemical properties. The optical absorption of the Au-Ag alloy nanoparticles illustrated one plasmon resonance absorption peak located at 450 nm between the absorption bands of pure Au and Ag nanoparticles at 400 and 520 nm, respectively, for the thin films annealed at 800 °C. XPS results showed that the alloys were in metallic state, and they had a greater tendency to lose electrons as compared to their corresponding monometallic state. Using lateral force microscopy analysis, we have found that the alloy particles were uniformly distributed on the surface with grain size of about 20 nm.     

Structural stability and electrical conductivity of amorphous Ge-metal alloy films

Stable homogeneous amorphous alloy¹ films of Ge with different concentrations of Al, Cu and Fe have been prepared by the simultaneous vapor deposition technique. Ge-Metal films are amorphous up to a concentration of ～ 40 at.% Al, ～ 20 at.% Cu and ～ 20 at.% Fe. The cyclic annealing and crystallization temperature of these films show that whereas Al increases the stability of the amorphous phase, the addition of Cu and Fe decreases it. The electrical resistivity decreases gradually with increasing Al content. In contrast, a rapid decrease in the electrical resistivity is observed for the Ge-Cu and Ge-Fe systems. The thermoelectric power (TEP) of Ge-Cu and Ge-Fe system assumes small values ～ few μV/deg for concentrations greater than few atomic percent. Ge-Al system exhibits large positive thermoelectric power at all compositions. The temperature dependence of the electrical resistivity of these alloy films show that the addition of Cu and Fe to Ge results in a drastic decrease in the activation energy of conduction whereas the addition of Al increases the activation energy. Ge-Al films exhibit intrinsic like conduction in the temperature range 100–300 K. The Ge-Cu and Ge-Fe films exhibit hopping conduction from 100–300 K and the related density of states is up to 100 times larger than in pure a-Ge films.     

Some properties of vacuum-deposited films of aluminum,nickel, cobalt,copper, and Cu-Cr-Al alloy

An investigation has been made of the electrical and adhesional properties, thermal stability, brazeability, and structure of vacuum-deposited films of aluminum, nickel, cobalt, copper, and a copper-based alloy containing 2.45 wt.% Cr, 4.89 wt.% Al. It was shown that the resistivity of pure metal films is greater than that of the original massive sample. The resistivity of films based on the alloy of the investigated composition is less than that of the original material. The introduction into the original alloy of Cr and Al as alloying elements facilitates reduction of the grain size D and of the height H of the surface microirregularities of the films by comparison with the same parameters for copper-based thin films. Alloying of the original alloy with chromium and aluminum makes possible a substantial improvement in the adhesion of the films to the plastic-laminate substrate and increase in the thermal stability of the alloy-based film elements. Recommendations are made for the practical application of the results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 52–56, August, 1971.In conclusion, the authors wish to express their gratitude to colleagues at the A. A. Baikov Institute of Metallurgy, to Professor A. M. Korol'kov, Doctor of Technical Sciences, and to Junior Scientific Officer E. V. Lysova, for their help given in the execution of this work.     

Synthesis of aqueous dispersion of graphenes via reduction of graphite oxide in the solution of conductive polymer

Graphene sheets were produced by chemical reduction of graphite oxides in the solution of ionic conductive polymer, Nafion. The obtained graphene, coated with Nafion, can be re-dispersed in water, and readily forms stable dispersed state. The polymer-coated graphene had been characterized by FT-IR spectroscopy, UV-vis and X-ray photoelectron spectroscopy (XPS). The PEDOT film with Nafion-coated graphene increased significantly from 0.25 S/cm for pure PEDOT film and reached 12 S/cm. Further, the films of PEDOT doped Nafion-coated graphene had also higher conductivities compared to films doped PSS-coated graphene.