Study on transport mechanism of carriers that go across the contact interface in insulating composite

使用绝缘复合材料的电气和电子设备和其他设备的电气化程度越高，其绝缘层所施加的强电场就越大。绝缘子-绝缘子界面的电荷交换速率受载流子输运方向和载流子种类的影响。这种不对称特性在RE-EVA和环氧氧化铝等绝缘复合材料中广泛存在，对于了解复合材料的绝缘性能似乎非常重要。为了阐明聚合物在费米能级、电离势、电子亲和和有效电子或空穴传导能级等电子能级基础上的不对称性质，讨论了聚合物中电子能级的估计方法。本文利用接触电位差XPS、空气中UPS和光注入电流估算了绝缘聚合物中的电子能级，并研究了估算值之间的相关性。结合开尔文法测得的功函数和XPS谱测得的结合能，估计了聚-2-乙烯基吡啶- co - stirene、PMMA（聚甲基丙烯酸甲酯）、PS（聚苯乙烯）和PVK（聚- n -乙烯基-咔唑）的电离能。在PVK中，光注入电流法测得的电子能级与开尔文法和XPS法测得的电子能级一致。然而，在PS和PMMA中，用该方法估计的电子能级与开尔文法和XPS法估计的价带上边缘不一致，而对应于有助于空穴传导的有效给体能级。UPS在空气中的测量似乎能够观察到费米能级附近的电子能级的尾部，这是负责接触带电的。聚合物表面的电子态容易因水或其他分子的吸附、形态的改变等而发生改变。另一方面，聚合物与基准材料（Au或ITO）之间的接触电位差随着聚合物的UV处理而减小。这说明开尔文法对观察聚合物表面电子态在热处理和紫外处理下的变化具有很高的灵敏度，这可能与聚合物被热或紫外降解有关。这项研究似乎有助于建立估计绝缘聚合物中电子能级的方法。少

The more electrical and electronic apparatus and other equipment using insulating composites are nimiaturized, the more strong electric fields apply their insulating layr. The charge-exchange rate at the insulator-insulator interface in insulating composites is affected by the direction of carrier transport and carrier species. Such asymmetric characteristics are widely seen in insulating composites e. g. RE-EVA and epoxy-alumina and seem very important to understand the insulation performance of composites. In order to clarify the asymmetric properties on the basis of electronic levels, such as Fermi level, ionization potential, electron affinity and effective electron or hole conduction levels, the methods for estimating electronic levels in ploymers were discussed. In this paper, electronic levels in insulating polymers were estimated by contact potential defference XPS,UPS in air and photoinjection current and the correlation among the estimated levels was investigated.Ionization p … More otential (Poly-2-Vinyl Pyridine-Co-Stirene), PMMA (polymethyl-methacrylate), PS (polystirene) snd PVK (Poly-N-Vinyl-carbazole) were estimated by adding the work function measured by Kelvin method and binding energy estimated from the XPS spectrum. In PVK,the electronic level estimated by photoinjection current method was consistent with that by Kelvin method and XPS.However, In PS and PMMA,the electronic level estimated by that did not coincide with the upper edge of valence band estimated from Kelvin method and XPS and corresponded to effective donor level which contribute to hole conduction. The UPS measurement in air seemed to be able to observe tail of electronic levels near Fermi level which were responsible for contact electrification.The electronic states on polymer surface were easily changed by adsorption of water or other molecules, change in morphology and so on. On the other hand, the contact potential difference between polymers and reference materials (Au or ITO) decteases with UV treatment for polymers. This shows that Kelvin method is highly sensitive to observe the change of the electronic states on polymer surface with heat and UV treatment which might be related to degradation of polymers by heat or UV.It seems that this investigation contributed to the establishment of the methods for estimating electronic levels in insulating polymers. Less