“…Each series contains CVs in which the maximum anodisation potential was step-wise increased between 1 and 10 V SHE. Due to the valve metal nature of all species mixed in the library, a typical current rectifying behaviour upon electric field reversal is clearly observable [11]. Ionic species injection into the initial oxide is best observed during the first anodisation step to 1 V (SHE).…”
Section: Resultsmentioning
confidence: 99%
“…These were obtained in accordance with the mixed matter model by a linear combination of pure oxide density values with respect to the species atomic fractions. The values of pure oxide densities used were 9.68, 4.36 and 8.10 g cm −3 for HfO 2 , Nb 2 O 5 and Ta 2 O 5 , respectively [11]. 10.1080/14686996.2018.1498703-F0007Figure 7.Oxide formation factor (in nm V −1 ) mapped as a material constant for the Hf–Nb–Ta thin film combinatorial library.
…”
Section: Resultsmentioning
confidence: 99%
“…This classification and its name are based on their current rectification upon electric field reversal (hence, the name ‘valve’) during metals anodisation under high field conditions. The final anodic oxide thickness is proportional to the applied potential and oxide formation factors of 2.3, 2.6 and 1.8 nm V −1 were measured for Hf, Nb and Ta, respectively [11]. The oxides of the aforementioned pure metals have applications in various fields.…”
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.
“…Each series contains CVs in which the maximum anodisation potential was step-wise increased between 1 and 10 V SHE. Due to the valve metal nature of all species mixed in the library, a typical current rectifying behaviour upon electric field reversal is clearly observable [11]. Ionic species injection into the initial oxide is best observed during the first anodisation step to 1 V (SHE).…”
Section: Resultsmentioning
confidence: 99%
“…These were obtained in accordance with the mixed matter model by a linear combination of pure oxide density values with respect to the species atomic fractions. The values of pure oxide densities used were 9.68, 4.36 and 8.10 g cm −3 for HfO 2 , Nb 2 O 5 and Ta 2 O 5 , respectively [11]. 10.1080/14686996.2018.1498703-F0007Figure 7.Oxide formation factor (in nm V −1 ) mapped as a material constant for the Hf–Nb–Ta thin film combinatorial library.
…”
Section: Resultsmentioning
confidence: 99%
“…This classification and its name are based on their current rectification upon electric field reversal (hence, the name ‘valve’) during metals anodisation under high field conditions. The final anodic oxide thickness is proportional to the applied potential and oxide formation factors of 2.3, 2.6 and 1.8 nm V −1 were measured for Hf, Nb and Ta, respectively [11]. The oxides of the aforementioned pure metals have applications in various fields.…”
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.
“…10, can be found in Ref. [45]. The rate determining step (RDS) in this model could be either ion transport through the interfaces, for example the -oxide/electrolyte [46] or the metal/oxide [47], or within the oxide [48], depending on the material system.…”
Section: Anodization Of Valve Metalsmentioning
confidence: 99%
“…Images from Ref. [45] Although the high field model broadly describes the formation of anodic oxides, it does not capture all the important features of the process, and the final properties of the film are highly dependent on the nature of the mobile metal ions, oxygen, and various ionic electrolyte species as well as the overall crystallinity of the resulting materials. Amorphous oxides (Al, Nb, and Ta) are formed via the transport of both anions and cations with transport numbers close to 0.5 at high field, as indicated by marker studies [49], [50].…”
Manipulating fluids in micro to nano-liter volumes poses significant challenges, due to the dominance of surface forces with increasingly large surface to volume ratios. Commonly, external pumps or precisely micromachined on-chip pumps were used to generate pressure gradients to induce fluid motion. Alternatively, the wettability of a surface can be manipulated by an applied electric field. This phenomenon, known as electrowetting, consists in the spread of a liquid drop placed on an electrode upon application of a voltage. Electrowetting based devices flourished upon the discovery that an added dielectric layer between the drop and a conductive electrode would tolerate the application of large voltages, allowing for significant contact angle change. Several current commercial devices exploiting this effect include electro-optic displays, electronic paper, and variable focus lenses.Additionally, electrowetting has achieved particular prominence in lab-on-a-chip applications, controlling drop transport across patterned electrode structures.Initially, polymers were utilized as the dielectric layer preventing current flow between the fluid and electrode, while providing a hydrophobic surface to minimize the resistance of drop movement.However, these layers were typically in excess of one micron thickness. As a consequence, these layers required over 100 Volts to achieve appreciable contact angle change. This dissertation aims to reduce the voltage dependence for contact angle change by optimization of a dual layer structure utilizing a dielectric and hydrophobic layer. The dielectric layer uses aluminum and tantalum oxides (15-44 nm thick) formed by electrochemical anodization. The electronic and ionic conduction, breakdown characteristics, and dielectric properties of these films were studied in detail, achieving a comprehensive understanding of the charge transport and failure mechanisms. Three hydrophobic layer were investigated: a commercial fluoropolymer Cytop, and two self-assembled monolayers 3
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