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.     

Determination of the surface composition of palladium-nickel alloy film catalysts using Auger electron spectroscopy

Palladium-nickel films evaporated in UHV on room temperature substrates form alloys of good bulk homogeneity as indicated by X-ray diffraction. The average composition of the outermost 3 to 5 atom layers has been determined from the intensities of the high energy 848 eV nickel and 330 eV palladium Auger electrons. This average composition is in close agreement with the bulk composition determined by X-ray diffraction, X-ray fluorescence and atomic absorption spectrophotometry. If the nickel concentration is determined from the intensity of the low energy 61 eV nickel Auger electrons, when the analysis refers more critically to the first 1 to 3 atom layers, then a surface enrichment of palladium is indicated for all alloy compositions. From the decrease in the relative intensities of the low energy and high energy nickel Auger electrons with increasing palladium concentration it may be deduced that the enrichment of palladium in the first atom layer is higher than in the second and third layers and that a complete monolayer of palladium is formed for bulk concentrations of 65 at% or more. The experimental observations are in qualitative agreement with theoretical predictions of surface composition from bulk thermodynamic data. The palladium-nickel alloys form a range of surface compositions which can be controlled by changing the bulk composition and which are useful for studying catalytic activity as a function of composition. The alloy films are stable under electron irradiation in the AES analysis in UHV but air exposed films analysed in a residual pressure of 1.3 microPa water vapour show a decrease in palladium surface concentration on irradiation indicating a diffusion of nickel to the surface to form an overlayer of nickel oxide.     

Detection of excess crystalline As in GaAs: Nation oxide overlayers by Raman scattering

Laser Raman spectroscopy was employed as a non-destructive probe for the detection and monitoring of crystalline arsenic in the native oxide films formed during heating of GaAs in air at various temperatures. Spectroscopy of oxide films formed after successive heating and etching treatments could confirm the location of arsenic to be near the top of the GaAs: native oxide overlayer.     

Microstructural investigation of nickel silicide thin films and the silicide-silicon interface using transmission electron microscopy

This article discusses the results of transmission electron microscopy (TEM)-based investigation of nickel silicide (NiSi) thin films grown on silicon. Nickel silicide is currently used as the CMOS technology standard for local interconnects and in electrical contacts. Films were characterized with a range of TEM-based techniques along with glancing angle X-ray diffraction. The nickel silicide thin films were formed by vacuum annealing thin films of nickel (50 nm) deposited on (100) silicon. The cross-sectional samples indicated a final silicide thickness of about 110 nm. This investigation studied and reports on three aspects of the thermally formed thin films: the uniformity in composition of the film using jump ratio maps; the nature of the interface using high resolution imaging; and the crystalline orientation of the thin films using selected-area electron diffraction (SAED). The analysis highlighted uniform composition in the thin films, which was also substantiated by spectroscopy techniques; an interface exhibiting the desired abrupt transition from silicide to silicon; and desired and preferential crystalline orientation corresponding to stoichiometric NiSi, supported by glancing angle X-ray diffraction results.     

Optical Properties of Nonstoichiometric Silicon Oxide SiOx (x < 2)

Optics and Spectroscopy - The optical properties of amorphous nonstoichiometric silicon oxide (SiOx) films of variable composition (x = 0.62–1.92) formed by plasma-enhanced chemical vapor...     

Investigation of ultrathin iron and iron/nickel layers prepared from Langmuir-Blodgett films

Oxidic and metallic iron and iron/nickel multilayers, formed after thermal and chemical treatment of Langmuir-Blodgett films, were investigated. Reduced iron-stearate multilayers were compared with evaporated films concerning their phase composition and their lateral homogeneity. The sequence of metallic and oxidic iron in the films after reduction was determined. Oxidic iron/nickel mixed layers can be prepared from Langmuir-Blodgett films, in which a magnetically non-ordered Fe³⁺ phase exhibiting a distribution of the quadrupole splitting is observed. After reduction of such layers, two metallic iron phases appear dependent on the nickel concentration. The hyperfine field distribution of the magnetically ordered metallic phase can be evaluated using a method proposed by Rancourt.     

Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

Characterisation of nickel silicide thin films by spectroscopy and microscopy techniques

This article discusses the formation and detailed materials characterisation of nickel silicide thin films. Nickel silicide thin films have been formed by thermally reacting electron beam evaporated thin films of nickel with silicon. The nickel silicide thin films have been analysed using Auger electron spectroscopy (AES) depth profiles, secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectroscopy (RBS). The AES depth profile shows a uniform NiSi film, with a composition of 49-50% nickel and 51-50% silicon. No oxygen contamination either on the surface or at the silicide-silicon interface was observed. The SIMS depth profile confirms the existence of a uniform film, with no traces of oxygen contamination. RBS results indicate a nickel silicide layer of 114 nm, with the simulated spectra in close agreement with the experimental data. Atomic force microscopy and transmission electron microscopy have been used to study the morphology of the nickel silicide thin films. The average grain size and average surface roughness of these films was found to be 30-50 and 0.67 nm, respectively. The film surface has also been studied using Kikuchi patterns obtained by electron backscatter detection.     

Comparative study of transport properties relevant to a textured sol-gel PZT coating on Ni substrate

In this work, the preparation of PbZr_0.52Ti_0.48O₃ (PZT) thin films for piezoelectric applications on untextured and (200) textured nickel foil substrates is reported. Transport properties of the nickel substrate relevant to the sintering of PZT and their interaction with PZT are also reported in this paper. Sols of PZT were prepared and used to deposit films of thickness between 150–1000 nm by dip coating. PZT could be sintered to full density at <750 °C in air. Catastrophic oxidation of the Ni substrate could be avoided either by pre-oxidising a textured Ni foil or by the use of un-oxidised textured Ni foil. The PZT film obtained was also textured while the amount of nickel oxide formed was negligible and could not be detected by field emission electron microscopy, and barely detectable by X-ray diffraction. The films thus produced show a step forward in developing piezoelectric devices using more economic routes. Paper presented at the Patras Conference on Solid State Ionics - Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Analysis of protective oxide films on copper—nickel alloys by photoelectron spectroscopy

Photoelectron spectroscopy was used to determine the elemental composition of thin films formed on 70:30 cupronickel exposed to sodium chloride solutions at different impressed electrochemical potentials. At anodic potentials below the passivation potential, ?0.350 V versus SCE under the experimental conditions, either no film or a film containing copper and nickel in the same ratio as the alloy existed on the alloy. At the passivation potential the spectrum of the passive film indicated primarily nickel oxide and was very similar to the spectrum obtained from a pure nickel specimen passivated in the same environment.