Department of Materials Science and Engineering, University of Virginia , 395 McCormick Road, Charlottesville, Virginia 22904, United States.
ACS Appl Mater Interfaces. 2017 Dec 6;9(48):42278-42286. doi: 10.1021/acsami.7b07366. Epub 2017 Nov 17.
The electrowetting-on-dielectric behavior of Cytop/Tantalum oxide (TaOx) bilayers is studied by measuring their response vs applied voltage and under prolonged periodic cycling, below and above the threshold voltage V corresponding to the breakdown field for the oxide. TaOx exhibits symmetric solid state I-V characteristics, with electronic conduction dominated by Schottky, Poole-Frenkel emission; conduction is attributed to oxygen vacancies (6 × 10 cm), resulting in large currents at low bias. Electrolyte/Metal Oxide/Metal I-V characteristics show oxide degradation at (<5 V) cathodic bias; anodic bias in contrast results in stable characteristics until reaching the anodization voltage, where the oxide thickens, leading eventually to breakdown and oxygen production at the electrode. Electrowetting angle vs applied voltage undergoes three different stages: a parabolic variation of contact angle (CA) with applied voltage, CA saturation, and rebound of the CA to higher values due to degradation of the polymer layer. The contact angle remained stable for several hundred cycles if the applied voltage was less than V; degradation in contrast is fast when the voltage is above V. Degradation of the electrowetting response with time is linked to charge accumulation in the polymer, which inhibits the rebound of the CA when voltage is being applied.
双层 Cytop/氧化钽 (TaOx) 的电润湿介电行为通过测量其在低于和高于对应于氧化物击穿场的阈值电压 V 的外加电压下的响应以及在长时间周期性循环下进行研究。TaOx 表现出对称的固态 I-V 特性，电子传导由肖特基、普尔-弗兰克尔发射主导；传导归因于氧空位（6×10^17 cm^-3），导致在低偏压下出现大电流。电解质/金属氧化物/金属 I-V 特性显示在 (<5 V) 阴极偏压下氧化物降解；相比之下，阳极偏压导致特性稳定，直到达到阳极氧化电压，此时氧化物变厚，最终导致电极处的击穿和氧气产生。外加电压下的接触角（CA）经历三个不同阶段：接触角随外加电压呈抛物线变化、CA 饱和以及由于聚合物层降解导致 CA 反弹到更高值。如果外加电压低于 V，则接触角在几百个循环内保持稳定；相比之下，当电压高于 V 时，降解速度很快。随着时间的推移，电润湿响应的退化与聚合物中的电荷积累有关，这会抑制施加电压时 CA 的反弹。
