Department of Physics, Stanford University , Palo Alto, California 94305, United States.
SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
ACS Nano. 2016 Apr 26;10(4):4565-9. doi: 10.1021/acsnano.6b00645. Epub 2016 Mar 16.
One prominent structural feature of ionic liquids near surfaces is formation of alternating layers of anions and cations. However, how this layering responds to an applied potential is poorly understood. We focus on the structure of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate (BMPY-FAP) near the surface of a strontium titanate (SrTiO3) electric double-layer transistor. Using X-ray reflectivity, we show that at positive bias the individual layers in the ionic liquid double layer thicken and the layering persists further away from the interface. We model the reflectivity using a modified distorted crystal model with alternating cation and anion layers, which allows us to extract the charge density and the potential near the surface. We find that the charge density is strongly oscillatory with and without applied potential and that with an applied gate bias of 4.5 V the first two layers become significantly more cation rich than at zero bias, accumulating about 2.5 × 10(13) cm(-2) excess charge density.
在离子液体靠近表面的位置，一个显著的结构特征是阴离子和阳离子的交替层形成。然而，这种分层结构对施加的电势如何响应还不太清楚。我们关注的是 1-丁基-1-甲基吡咯烷双（五氟乙基）三氟磷酸盐（BMPY-FAP）在钛酸锶（SrTiO3）电双层晶体管表面附近的结构。我们使用 X 射线反射率法表明，在正偏压下，离子液体双电层中的各个层会变厚，并且分层结构在离界面更远的地方仍然存在。我们使用带有交替的阳离子和阴离子层的改进的扭曲晶体模型来模拟反射率，这使我们能够提取表面附近的电荷密度和电势。我们发现，无论是否施加电势，电荷密度都会发生强烈的振荡，并且在施加 4.5 V 的栅极偏压时，前两层的阳离子比零偏压时丰富得多，积累了约 2.5×10(13)cm(-2)的过剩电荷密度。
