Ammar L Ben, Fakhfakh S, Jbara O, Rondot S
LaMaCop, Faculté des sciences, Sfax, Tunisie.
LISM, UFR Sciences, Reims, Cedex 2, France.
J Microsc. 2017 Mar;265(3):322-334. doi: 10.1111/jmi.12502. Epub 2016 Nov 24.
For studying the electrical properties (charge trapping, transport and secondary electron emission) of the polypropylene-based nanocomposites with different contents of natural clay, the specimens were submitted to electron irradiation of a scanning electron microscope. A device, suitably mounted on the sample holder of the scanning electron microscope, was used to measure two currents (i.e. leakage and displacement currents) induced in the polypropylene-based nanocomposites (polymer nanocomposites) under electron irradiation. The evolution of trapped charge during irradiation for each type of studied polymer nanocomposites is deduced. The amount of trapped charge at the steady state is also determined by measuring the change of secondary electron image size associated to the electron trajectory simulation. It is found, surprisingly, that not only the leakage current increases as a function of clay loading level but also trapped charge. However, this could be related to the increase of conductivity in one hand and to proliferation of interfaces between nanoparticles and neighbouring materials on the other hand. These two processes play crucial role in controlling the carrier transport (through polymer nanocomposites or/and along its surface) closely related to the charge storage and leakage current. Additional experiment using dielectric spectroscopy were performed to show the effect of clay concentration in changing the dielectric relaxation behaviour and to evidence the existence of interfaces between nanoparticles and polymer. The secondary electron emission during electron irradiation is also studied through the total electron yield that is deduced by correlating the measured leakage and displacement currents.
为了研究不同天然粘土含量的聚丙烯基纳米复合材料的电学性质（电荷俘获、传输和二次电子发射），将试样置于扫描电子显微镜下进行电子辐照。使用一个适当地安装在扫描电子显微镜样品台上的装置，来测量在电子辐照下聚丙烯基纳米复合材料（聚合物纳米复合材料）中感应出的两种电流（即漏电流和位移电流）。推导了每种研究类型的聚合物纳米复合材料在辐照过程中俘获电荷的演变情况。通过测量与电子轨迹模拟相关的二次电子图像尺寸的变化，还确定了稳态下的俘获电荷量。令人惊讶地发现，不仅漏电流随粘土负载量的增加而增加，俘获电荷也增加。然而，这一方面可能与电导率的增加有关，另一方面与纳米颗粒和相邻材料之间界面的增多有关。这两个过程在控制与电荷存储和漏电流密切相关的载流子传输（通过聚合物纳米复合材料或/和沿其表面）方面起着至关重要的作用。进行了使用介电谱的额外实验，以显示粘土浓度在改变介电弛豫行为方面的作用，并证明纳米颗粒与聚合物之间界面的存在。还通过将测量的漏电流和位移电流相关联推导出的总电子产额来研究电子辐照期间的二次电子发射。
