基于开尔文探针力显微镜的纳米复合材料次表面成像分析

Analysis of KPFM-Based Subsurface Imaging of Nanocomposites

针对聚合物纳米复合材料次表面结构高分辨无损检测的需求，应用开尔文探针力显微镜（KPFM）对聚合物中导电填充物进行次表面纳米成像．首先，建立探针一纳米颗粒一基质体系的静电相互作用理论模型，分析聚合物中金属颗粒检测的成像机理；其次，通过有限元软件模拟并结合理论模型，系统研究针尖与样品间距、针尖半径等因素的影响；最后，制作聚合物和碳纳米管复合材料样品并进行基于KPFM的内部碳纳米管成像实验验证．结果表明：当针尖半径大约为1．5倍颗粒直径、间距较小时，成像效果较好；相较而言，探针锥角对成像结果影响不显著；KPFM对相对介电常数在3～10之间、颗粒直径越大、掩埋深度越小的内部纳米颗粒成像效果越好．

Subsurface imaging, performed with Kelvin probe force microscopy（ KPFM）, was investigated to identify conductive fillers embedded in polymer aiming to satisfy the need of high-resolution imaging of nanocomposites without damage. In this paper a theoretical model, describing the electrostatic interaction in the tip-particle-matrix system, was proposed to analyze the mechanism. Parameters such as tip-sample distance, radius of tip, and so forth were studied systematically by using finite element analysis （FEA） and theoretical model. Experiment validation was performed on a polyimide nanocomposite with carbon nanotubes buried inside. The results show that to obtain better subsurface images, a tip with a radius 1.5 times greater than the particle＇ s and a small tip-sample distance are preferred. Comparatively, the cone angle of the tip exerts less effect on electrostatic forces. Subsurface imaging on samples with relative die- lectric constants in the range of 3-10, large particle radius and small buried depth is much easier.