Discharge Optical Emission Spectroscopy Depth Research Articles

Formation of Nanoporous NiFe2O4 Oxide Films By Anodizing of Fe-Ni Alloy

Anodizing of metals and alloys has attracted increased attention for the formation of nanostructured oxide films with self-ordered morphologies. The anodizing researches have been conducted mainly on valve metals, including aluminum, magnesium, titanium, zirconium, niobium and tantalum, because of ready formation of thick anodic films on these metals. Recent findings of organic electrolytes containing fluoride have expanded the anodizing studies to non-valve metals; nanoporous and nanotubular anodic films are now available even on iron and stainless steel 1-3. The nanoporous and nanotubular α-Fe2O3 films have been formed by anodizing of iron and subsequent heat treatments, and such oxide films are of interest for photoelectrochemical water splitting 4. Further functional oxide films will be formed by anodizing of iron alloys. In the present study, we examined the formation of nanoporous anodic films on an Fe-Ni alloy. The oxygen evolution properties of the anodic oxide films were also examined. An Fe-Ni invar alloy plate containing 41 mass% nickel was used in this study. For comparison, a high purity (99.99%) iron plate was also used. The specimens were anodized at 40 V in ethylene glycol electrolyte containing 0.1 mol dm-3 NH4F and 0.5 mol dm-3 H2O at 293 K. For anodizing of iron, the H2O concentration was increased to 1.5 mol dm-3 because the detachment of an oxide film formed at the H2O concentration of 0.5 mol dm-3 proceeded during heat treatment. After anodizing, heat treatment of the specimens was conducted in an argon atmosphere at temperatures between 673 K and 873 K to remove fluoride species in the anodic films and increase the crystallinity of the oxide films. During anodizing of the Fe-Ni alloy at 40 V the current density exceeded 200 A m-2, which was approximately 4 times that of iron in the same electrolyte. Because of the high current density, the film growth rate on the Fe-Ni alloy was as high as 0.3 μm min-1 and a 3-μm-thick anodic film was formed by anodizing only for 10 min. The anodic film exhibited a cylindrical nanoporous morphology, which was similar to that formed on iron. However, the pore size and the interpore distance for the Fe-Ni alloy were smaller than those on iron. The as-anodized specimens contained fluoride species in the anodic films, as confirmed by glow discharge optical emission spectroscopy depth profile analysis. The heat treatment of the anodized alloy in argon atmosphere at 873 K removed fluoride species and a crystalline spinel phase was developed. When anodized iron specimens were heat-treated in the argon atmosphere at 673 and 773 K, α-Fe2O3 phase was also detected by XRD as well as the Fe3O4 phase. The a-Fe2O3phase disappeared at 873 K. The oxygen evolution reaction (OER) was examined in 0.1 mol dm-3 KOH solution by anodic polarization measurements. For the iron specimens, the OER activity increased with an increase in the heat treatment temperature from 773 K to 873 K. The presence of α-Fe2O3heat-treated at 773 K may be associated with the lower OER activity. The alloy specimen heat-treated at 873 K showed further enhanced activity, confirming the beneficial effect of nickel incorporation into the anodic oxide for enhancing the OER activity.

Determination of the Interface Roughness between Ni-Coated Layer and Cu Substrate by Glow Discharge Optical Emission Spectroscopy Depth Profiling

The depth profiles of Ni-coated copper substrates polished by different mesh size sandpapers were measured by the glow discharge optical emission spectroscopy (GDOES) depth profiling technique. The measured depth profiles were well fitted by the MRI-CRAS model developed recently on the basis of the Mixing-Roughness-Information depth (MRI) model and the CRAter-Simulation (CRAS) model, taking into account the pronounced crater effect upon GDOES depth profiling. The crater effect upon depth profiling was characterized quantitatively and the interface roughness values between the coated Ni layer and the Cu substrates were determined and compared with the ones measured by AFM.

Degradation mechanisms of Ta and Ta?Si diffusion barriers during thermal stressing

The degradation mechanisms of 10 nm thick Ta and Ta73Si27 diffusion barriers deposited between Cu and SiO2 are compared by means of X-ray reflectometry, glancing angle X-ray diffraction, glow discharge optical emission spectroscopy depth profiling and transmission electron microscopy analysis. Annealing the samples at Tan=600 °C for tan=1 h results in a diffusion of Ta atoms through the Cu capping layer to the sample surface, particularly in the case of the pure Ta barrier. During longer heat treatment (tan>1 h), microstructural changes occur within both barrier types. Whereas the amorphous Ta–Si layer starts to crystallize into Ta5Si3, the initially grown metastable β-Ta of the pure Ta film transforms into the equilibrium α-Ta phase. Analyzing the diffusion rate of Cu atoms into the substrate, the Ta73Si27 barrier shows an enhanced thermal stability compared to the pure Ta film.

Degradation mechanisms of Ta and Ta–Si diffusion barriers during thermal stressing

The degradation mechanisms of 10 nm thick Ta and Ta 73Si 27 diffusion barriers deposited between Cu and SiO 2 are compared by means of X-ray reflectometry, glancing angle X-ray diffraction, glow discharge optical emission spectroscopy depth profiling and transmission electron microscopy analysis. Annealing the samples at T an=600 °C for t an=1 h results in a diffusion of Ta atoms through the Cu capping layer to the sample surface, particularly in the case of the pure Ta barrier. During longer heat treatment ( t an>1 h), microstructural changes occur within both barrier types. Whereas the amorphous Ta–Si layer starts to crystallize into Ta 5Si 3, the initially grown metastable β-Ta of the pure Ta film transforms into the equilibrium α-Ta phase. Analyzing the diffusion rate of Cu atoms into the substrate, the Ta 73Si 27 barrier shows an enhanced thermal stability compared to the pure Ta film.

Deposition of TiN, TiC and Ti 1− xAl xN coatings by pulsed d.c. plasma enhanced chemical vapour deposition methods

Unipolar and bipolar pulsed d.c. plasma enhanced chemical vapour deposition techniques have been used under various process conditions to deposit hard crystalline (Ti,Al)N, TiC and TiN coatings on steel and WC/Co hard metal substrates at temperatures between 500 and 700°C. As process gases mixtures of titanium tetrachloride (TiCl 4), aluminium trichloride (AlCl 3) and nitrogen or methane/hydrogen/argon were applied. The golden, violet grey or dark grey coloured TiN, (TiAl)N, TiC coatings deposited by varying the substrate temperature, plasma power density, excitation mode, and titanium to aluminium ratio in the gas phase were investigated with respect to their composition and structure. At substrate temperatures up to 700°C and gas mixture ratios of Ti/Al=0.3–0.5 using the unipolar pulsed d.c. method cubic (Ti,Al)N coatings with different aluminium and titanium content could be deposited. At constant gas phase ratios and plasma parameters an increased substrate temperature resulted in an increased titanium content. For the bipolar d.c. excitation mode higher aluminium trichloride concentration had to be used in order to obtain the same composition as for the unipolar case. Besides the cubic (Ti,Al)N phase, hexagonal AlN was found in samples prepared at 700°C and 4 mbar by XRD measurements. The crystallite size of the (Ti,Al)N coatings deposited by unipolar and bipolar activation were estimated to be approximately 10 nm. The hardness HV[0.02] was found to be in the range of 25–30 GPa for Ti 1− x Al x N, up to 32 GPa for TiN, and up to 40 GPa for TiC. Coating thickness and element composition were determined by glow discharge optical emission spectroscopy depth profile analysis.

Glow discharge optical emission spectroscopy – a powerful tool for the study of compositional non-uniformity in electrodeposited films

The potential of glow discharge optical emission spectroscopy for the analysis of thin films on metals is examined using the example of electrodeposited Ni–P, about 0.53 μm thick. The glow discharge optical emission spectroscopy depth profiles reveal layering of the deposited material with a good correlation between the sequence of layers in the composition profile and that observed by transmission electron microscopy.