Birck Nanotechnology Center and School of Mechanical Engineering, Purdue University, West Lafayette, IN 47904-2088, USA.
Nanotechnology. 2013 Apr 5;24(13):135701. doi: 10.1088/0957-4484/24/13/135701. Epub 2013 Mar 12.
The characterization of dispersion and connectivity of carbon nanotube (CNT) networks inside polymers is of great interest in polymer nanocomposites in new material systems, organic photovoltaics, and in electrodes for batteries and supercapacitors. We focus on a technique using amplitude modulation atomic force microscopy (AM-AFM) in the attractive regime of operation, using both single and dual mode excitation, which upon the application of a DC tip bias voltage allows, via the phase channel, the in situ, nanoscale, subsurface imaging of CNT networks dispersed in a polymer matrix at depths of 10-100 nm. We present an in-depth study of the origins of phase contrast in this technique and demonstrate that an electrical energy dissipation mechanism in the Coulomb attractive regime is key to the formation of the phase contrast which maps the spatial variations in the local capacitance and resistance due to the CNT network. We also note that dual frequency excitation can, under some conditions, improve the contrast for such samples. These methods open up the possibility for DC-biased amplitude modulation AFM to be used for mapping the variations in local capacitance and resistance in nanocomposites with conducting networks.
在新型材料体系、有机光伏以及电池和超级电容器电极中，对聚合物内部碳纳米管（CNT）网络的分散和连通性进行描述具有重要意义。我们专注于一种使用振幅调制原子力显微镜（AM-AFM）的技术，该技术在吸引力操作模式下使用单模和双模激励，在施加直流尖端偏置电压后，通过相位通道，可以对分散在聚合物基体中的 CNT 网络进行原位、纳米级、次表面成像，深度为 10-100nm。我们对该技术中相位对比的起源进行了深入研究，并证明库仑吸引力作用下的能量耗散机制是形成相位对比的关键，该相位对比映射了由于 CNT 网络导致的局部电容和电阻的空间变化。我们还注意到，在某些条件下，双频激励可以提高此类样品的对比度。这些方法为使用带有直流偏置的振幅调制 AFM 来映射具有导电网络的纳米复合材料中的局部电容和电阻变化开辟了可能性。
