Electrochemistry on binary valve metal combinatorial libraries: niobium-tantalum thin films

Mardare, Andrei Ionut; Ludwig, Alfred; Savan, Alan; Hassel, Achim Walter

doi:10.1016/j.electacta.2014.02.138

Cited by 14 publications

(19 citation statements)

References 29 publications

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“…Slightly elongated surface grains, with about 100 nm equivalent diameter, are grouped in domains for high Nb amounts and almost equal Hf and Ta concentrations. This type of microstructure has previously been observed in both Nb–Ta and Hf–Nb binary thin film libraries (for Nb amounts around 66 at.%) which indicate that surface domains formation may be triggered by the presence of Nb [23,24]. Additionally, the study of a Hf–Ta binary library revealed that amorphisation of alloys occurs at equal amounts of Hf and Ta [25].…”

Section: Resultssupporting

confidence: 61%

“…The transition between hexagonal Hf and tetragonal Ta occurs through a relatively large amorphous compositional zone. However, mixing the cubic phase of Nb with either tetragonal Ta or hexagonal Hf results in very narrow amorphous regions, as binary studies have shown [23,24]. Depending on the composition, the transitions between cubic and either tetragonal or hexagonal phases are sharp.…”

Section: Resultsmentioning

confidence: 99%

“…Screening of a Hf–Nb library showed the effect of Nb as a cubic phase stabiliser in metallic alloys and a remarkably high electrical permittivity of mixed Hf–Nb anodic oxides [23]. Semiconducting properties of Nb 2 O 5 were imprinted on mixed oxides grown anodically on Nb–Ta combinatorial libraries, with relatively high charge carrier densities, while the dielectric constants remained at high values [24]. Screening of a Hf–Ta combinatorial library showed strong amorphisation of the parent metal alloys, which had a direct impact on the electrochemical properties of the mixed anodic oxides [25].…”

Section: Introductionmentioning

confidence: 99%

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Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

Mardare

Kollender

et al. 2018

Science and Technology of Advanced Materials

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A thin film combinatorial library deposited by co-sputtering of Hf, Nb and Ta was employed to characterise fundamental properties of the Hf-Nb-Ta system. Compositional mappings of microstructure and crystallography revealed similarities in alloy evolution. Distinct lattice distortion was observed upon addition of hexagonal Hf, leading to amorphisation of alloys containing more than 32 at.% Hf and less than 27 and 41 at.% Nb and Ta, respectively. Volta potential and open circuit potential mappings indicated minimal values for the highest Hf concentration. Localised anodisation of the library by scanning droplet cell microscopy revealed valve metal behaviour. Oxide formation factors above 2 nm V−1 were identified in compositional zones with high amounts of Nb and Ta. Fitting of electrochemical impedance spectroscopy data allowed electrical permittivity and resistivity of mixed oxides to be mapped. Their compositional behaviours were attributed to characteristics of the parent metal alloys and particularities of the pure oxides. Mott–Schottky analysis suggested n-type semiconductor properties for all Hf–Nb–Ta oxides studied. Donor density and flat-band potential were mapped compositionally, and their variations were found to be related mainly to the Nb amount. Synergetic effects were identified in mappings of Hf-Nb-Ta parent metals and their anodic oxides.

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Section: Resultssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

Mardare

Kollender

et al. 2018

Science and Technology of Advanced Materials

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“…In previous work, a similar library was characterized and signicant changes were observed depending on the Nb-Ta alloy composition. 17 The declared aim to investigate the dielectric properties of the anodic oxides grown on the Nb-Ta parent metal alloys by ellipsometry requires a surface as smooth as possible. Surface roughness increases the complexity of the required optical layer model by the need of additional surface layers and can induce depolarization effects, which are difficult to model.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

et al. 2016

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“…The current decrease is associated with the reduction of the electric field strength in the barrier layer present beneath the porous layer, being typical in anodizing of valve metals. 23,24 The CV curve similar to the higher basic phosphate electrolyte is also observed in the lower basic phosphate electrolyte ( Fig. 1b), although the constant current density between 1 and 5 V vs. Pt in the lower basic phosphate electrolyte is much lower than that in the higher basic phosphate electrolyte.…”

Section: Methodsmentioning

confidence: 55%

Diffusion-controlled Growth of TiO<sub>2</sub> Mesoporous Anodic Films in Hot Phosphate/glycerol Electrolytes

et al. 2018

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This paper reports unusual diffusion-controlled growth of TiO 2 mesoporous anodic films on titanium in hot phosphate/glycerol electrolytes. The formation behavior was investigated by cyclic voltammetry (CV) between 0 and 5 V vs. Pt at 433 K. The current density became almost constant above 1.5 V vs. Pt during the positive potential sweep, and was maintained even during the negative potential sweep. This is contrast to a drastic decrease in current density in changing the direction of potential sweep from the positive to negative in fluoride-containing ethylene glycol electrolyte. The constant current density between 1.5 and 5 V vs. Pt increased with an increase in the basicity of the hot phosphate electrolyte, suggesting that the rate-determining step of the film formation in the hot phosphate electrolyte was diffusion process of oxygen sources in the electrolyte, not the ion migration in the thin barrier layer under the high electric field. When CV measurements were conducted to higher potentials up to 20 V vs. Pt, anatase was developed above 7 V vs. Pt, leading to generate oxygen gas. The film morphology was also potential-dependent and the diffusion current was also influenced by the film morphology as well as oxygen gas generation.

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Electrochemistry on binary valve metal combinatorial libraries: niobium-tantalum thin films

Cited by 14 publications

References 29 publications

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

Basic properties mapping of anodic oxides in the hafnium–niobium–tantalum ternary system

Spectroscopic ellipsometry for compositionally induced bandgap tuning of combinatorial niobium–tantalum anodic oxides

Diffusion-controlled Growth of TiO<sub>2</sub> Mesoporous Anodic Films in Hot Phosphate/glycerol Electrolytes

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