Gel formation during growth of barrier-type anodic films on aluminium

Durán-Romero, Rubén; Ni, Chengyuan; Skeldon, P.; Thompson, G.E.; Wood, G. C.; Shimizu, K.

doi:10.1080/01418639408241798

Cited by 7 publications

(4 citation statements)

References 10 publications

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“…Tungstate ions, on the other hand, have a more limited capacity to stabilize the pH, but can be effective in controlling the pH, just above the film, in the near-neutral range, by reaction with H + ions to form WO 3 when the interfacial pH decreases to about 7 [42] However, possibly of key relevance here, the WO 3 product is able to develop as a relatively continuous gel layer, of hydrated WO 3 , above a barrier-type anodic film, under certain conditions of film growth. A gel layer, about 200 nm thick, has been observed directly above anodic alumina films formed at 1 A m −2 , reasonably close to the conditions of the present experiments [37]. Thus, similar gel formation is considered to occur during anodization of GaAs by the reaction…”

Section: The Efficiency Of Film Growthsupporting

confidence: 90%

“…The simulated spectrum fitted to the measured spectrum assuming a tungstenenriched outer layer of film material of thickness 7 nm, in agreement with the thickness estimated from TEM. From previous analogous work on anodization of aluminium in tungstate electrolytes, a gel may form above anodic films on GaAs by essentially the same interfacial processes as occur above anodic alumina [37]. The tungsten detected by RBS in the thin layer at the surface of the anodic film is possibly contained either within the gel layer or, if the gel layer is rapidly degraded when anodizing is terminated, within a layer of anodic film material contaminated by species derived from tungstate ions.…”

Section: Rutherford Backscattering Spectroscopymentioning

confidence: 84%

“…The tungsten detected by RBS in the thin layer at the surface of the anodic film is possibly contained either within the gel layer or, if the gel layer is rapidly degraded when anodizing is terminated, within a layer of anodic film material contaminated by species derived from tungstate ions. From previous analysis of gels formed above anodic alumina [37], the atomic density of tungsten in a gel is about 1.9×10 27 m −3 , which suggests a gel layer of about 10 nm thickness above the anodic film on GaAs.…”

Section: Rutherford Backscattering Spectroscopymentioning

confidence: 89%

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A high-resolution, analytical study of the anodic film formed on GaAs in a tungstate electrolyte

Habazaki

Skeldon

Ghidaoui

et al. 1996

J. Phys. D: Appl. Phys.

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The anodic film formed in aqueous tungstate electrolyte at , to about 295 nm thickness, on -type GaAs at high faradaic efficiency, about 94%, has been examined by analytical transmission electron microscopy, using ultramicrotomed film sections, Rutherford backscattering spectroscopy, x-ray photoelectron spectroscopy, electron probe micro-analysis and scanning electron microscopy. The film is revealed to be amorphous and to comprise a uniform distribution of units of and across the main film thickness, with possible gallium enrichment in the outermost 10 nm or so of the film. Gallium and arsenic are incorporated into the anodic film at the alloy/film interface in the substrate proportions, without development of a layer enriched either in gallium or in arsenic just beneath the anodic film. The formation ratio for the film is about . The film, formed by migration both of cations and of anions across its thickness, is enriched in arsenic relative to the substrate composition, the level of enrichment suggesting that ions migrate outwards in the film about 2.4 times faster than do ions, based on a cation transport number of 0.2. The ions may be ejected, to the electrolyte, under the electric field, on reaching the film/electrolyte interface, with limited formation of an outer layer of essentially at the film/electrolyte interface, or form a layer of , up to about 10% of the total film thickness, which is thinned after anodizing by exposure to the electrolyte and the rinse water. Significantly, the outer layer of film material developed by the faster migrating ions prevents loss of ions from the film during film growth. However, during prolonged exposure to aqueous conditions in the absence of the field, the film becomes enriched in gallium species due to preferential dissolution of arsenic species. The high faradaic efficiency of film growth is a consequence of the presence of a tungsten-enriched layer, probably a gel composed of hydrated tungsten oxide, which develops at the film/electrolyte interface during film growth. No significant presence of tungsten species within the bulk of the anodic film is detected.

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Section: The Efficiency Of Film Growthsupporting

confidence: 90%

Section: Rutherford Backscattering Spectroscopymentioning

confidence: 84%

Section: Rutherford Backscattering Spectroscopymentioning

confidence: 89%

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A high-resolution, analytical study of the anodic film formed on GaAs in a tungstate electrolyte

Habazaki

Skeldon

Ghidaoui

et al. 1996

J. Phys. D: Appl. Phys.

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“…It is possible that elevated near-surface concentrations of these impurities are present after dissolution in NaOH, since concentrations of elements less reactive than the metal are typically enhanced by dissolution. 35 Aside measurements on aluminum dissolved in NaOH revealed a highly defective layer within about 10 to 20 nm from the oxide/metal interface, within which the concentration of vacancy-type defects was estimated to be on the order of 1%. It is possible that these defects serve as pit nucleation sites, perhaps by disrupting the structure of the overlying protective oxide film.…”

Section: Infroductjonmentioning

confidence: 99%

Development of Surface Impurity Segregation during Dissolution of Aluminum

Hebert

1996

J. Electrochem. Soc.

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Caustic dissolution, when used as a pretreatment for etching of aluminum in chloride solutions, is observed to increase the rate of pit nucleation. Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy were used to measure the composition in the near-surface region of 99.98% purity aluminum after dissolution in 1 N NaOH at room temperature. During dissolution, concentrations of impurities such as Fe, Cu, and Ga were found to accumulate continuously within a layer less than about 10 nm thick adjacent to the surface, because they dissolved more slowly than did aluminum. Impurity concentrations on the order of 1 atom percent (a/o) in this layer, much higher than equilbrium values, were found after 40 min dissolution. It is argued that the large impurity concentrations are consistent with a highly defective region in the metal near the metal/oxide interface, which has been detected using positron annihilation measurements. Dissolution produced a scalloped surface topography with typically 30 nm high ridges separated by 130 nm. A simulation of RBS measurements based on scattering from spherical particles was developed to test for the possibility of preferential impurity segregation to ridges. No such segregation was detected, suggesting that this is not the reason for the strong tendency for pit nucleation to occur on ridges, as has been observed previously. 5. K. Shimizu, G. E. Thompson, G. C. Wood, and Y Xu, Thin Solid Films, 88, 255 (1982 13. P. Skeldon, K. Shimizu, G. E. Thompson, and G. C. Wood, Thin Solid Films, 123, 127 (1985).14. P. Skeldon, K. Shimizu, G. E. Thompson, and G. C. Wood, Surf. Interface Anal., 5, 247 (1983). 15. G. Amsel, C. Cherki, G. Feuillade, and J. P. Nadai, J.Phys. Chem. Solids, 30, 2117Solids, 30, (1961 16. K. Shimizu, P. Skeldon, G. E. Thompson, and G. C. Wood, Surf. Interface Anal., 4, 208 (1981 Acta, 20, 663 (1975). 42. J. J. Randall, W. J. Bernard, and R. R. Wilkinson, ibid., 10, 183 (1965). Development of Surface Impurity Segregation during Dissolution of Aluminum Xiaolin Wu and Kurt HebertDepartment of Chemical Engineering, Iowa State University, Ames, Iowa 50011, USA ABSTRACT Caustic dissolution, when used as a pretreatment for etching of aluminum in chloride solutions, is observed to increase the rate of pit nucleation. Rutherford backscattering spectrometry (EBS) and Auger electron spectroscopy were used to measure the composition in the near-surface region of 99.98% purity aluminum after dissolution in 1 N NaOH at room temperature. During dissolution, concentrations of impurities such as Fe, Cu, and Ga were found to accumulate continuously within a layer less than about 10 nm thick adjacent to the surface, because they dissolved more slowly than did aluminum. Impurity concentrations on the order of 1 atom percent (a/o) in this layer, much higher than equilbrium values, were found after 40 mm dissolution. It is argued that the large impurity concentrations are consistent with a highly defective region in the metal near the metal/oxide interface...

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An electrochemical investigation on the dissolution of bilayered porous anodic alumina

Liao

Ling

et al. 2015

Applied Surface Science

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Gel formation during growth of barrier-type anodic films on aluminium

Cited by 7 publications

References 10 publications

A high-resolution, analytical study of the anodic film formed on GaAs in a tungstate electrolyte

A high-resolution, analytical study of the anodic film formed on GaAs in a tungstate electrolyte

Development of Surface Impurity Segregation during Dissolution of Aluminum

An electrochemical investigation on the dissolution of bilayered porous anodic alumina

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