Electromechanical coupling in anodic niobium oxide: Electric field-induced strain, internal stress, and dielectric response

Abstract

Seemingly, contradictory results have been reported so far for electrostriction in anodic oxides. Furthermore, no definitive agreement could be obtained with theory. In this paper, in situ techniques are combined to elucidate electrostriction in anodic niobium oxide. The dependence of strain, internal stress, and dielectric constant on the electric field is measured by, respectively, spectroscopic ellipsometry, curvature, and impedance measurements. The through-thickness strain is tensile and proportional to the square of the electric field. The in-plane internal stress is compressive and proportional to the square of the electric field at low field values. The internal stress is predicted relatively well by the Maxwell stress because of the weak dependence of the dielectric constant on the volume change of the oxide. The dielectric constant decreases with the electric field, the dependence being quadratic. While the evolution of the strain and stress with the electric field can be ascribed to the dependence of the dielectric constant on strain, the dependence of the dielectric constant on the electric field contains an explicit strain and electric field dependence. A mechanism for the latter is proposed

Tailoring of the Solid State Properties of Al–Nb Mixed Oxides: A Photoelectrochemical Study

“…Furthermore, it is chemically stable over a wide range of pH. A very high, field-dependent dielectric constant is reported for anodic niobia (ε ∼ 57), − which makes this oxide a very appealing high k material, even if the use of Nb 2 O 5 as a dielectric may be limited by its poor blocking character. Starting from these considerations, Al–Nb mixed oxides are anticipated to have properties that lie between those of pure Al 2 O 3 and Nb 2 O 5 , which suggests that an improvement on the low ε value of Al 2 O 3 and a lowering of the high leakage current of Nb 2 O 5 could be achieved.…”

On the Origin of Damped Electrochemical Oscillations at Silicon Anodes (Revisited)

“…As the evolution of the internal stress was shown to be the result (and not the cause) of such a transition, it can be expected that it is the electricfield-induced or so-called electrostrictive component of the internal stress that is affected at the transition. [14,17,18] In short, the application of an electric field to a dielectric induces a reversible electrostatic stress, which encompasses two distinct though interlinked contributions. The latter indeed implies that the growth-induced internal stress component, which results from a thickness increase of anodised silicon either at the electrolyte or substrate side, stays unaffected.…”

“…We have already performed a number of dedicated experimental studies in the past unravelling the contribution of electrostriction as a reversible, field-induced component of the total internal stress in anodic oxide films. [14,17,18] In short, the application of an electric field to a dielectric induces a reversible electrostatic stress, which encompasses two distinct though interlinked contributions. The first one, usually referred to as the Maxwell stress, results from the Coulombic attraction between charges of opposite sign located on both sides of the dielectric.…”

Downstream analytics quantification of ion release during high-voltage anodisation of niobium

“…Many properties of Nb anodic oxide films during and after anodisation have been investigated in the past. This includes electronic properties [24], optical properties [25], anodic luminescence [19], photoelectrochemical properties [25,26], composition changes [27,28], growth kinetics [17,29], corrosion properties [30,31] and evolution of internal stress [32]. During all these studies, the question of Nb dissolution during anodisation itself was overlooked.…”