School of Mechanical Engineering, Purdue University , West Lafayette, Indiana 47907, United States.
Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
ACS Nano. 2016 Apr 26;10(4):4062-71. doi: 10.1021/acsnano.5b06893. Epub 2016 Mar 21.
Electrostatic force microscopy (EFM) is often used for nanoscale dielectric spectroscopy, the measurement of local dielectric properties of materials as a function of frequency. However, the frequency range of atomic force microscopy (AFM)-based dielectric spectroscopy has been limited to a few kilohertz by the resonance frequency and noise of soft microcantilevers used for this purpose. Here, we boost the frequency range of local dielectric spectroscopy by 3 orders of magnitude from a few kilohertz to a few megahertz by developing a technique that exploits the high resonance frequency and low thermal noise of ultrasmall cantilevers (USCs). We map the frequency response of the real and imaginary components of the capacitance gradient (∂C(ω)/∂z) by using second-harmonic EFM and a theoretical model, which relates cantilever dynamics to the complex dielectric constant. We demonstrate the method by mapping the nanoscale dielectric spectrum of polymer-based materials for organic electronic devices. Beyond offering a powerful extension to AFM-based dielectric spectroscopy, the approach also allows the identification of electrostatic excitation frequencies which affords high dielectric contrast on nanomaterials.
静电 force 显微镜 (EFM) 常用于纳米级介电谱学，即测量材料的局部介电性能随频率的变化。然而，由于用于此目的的软微悬臂梁的共振频率和噪声，基于原子 force 显微镜 (AFM) 的介电谱学的频率范围被限制在几 kHz 以内。在这里，我们通过开发一种利用超小悬臂梁 (USC) 的高共振频率和低热噪声的技术，将局部介电谱学的频率范围从几 kHz 提高到几 MHz，提高了 3 个数量级。我们通过使用二次谐波 EFM 和一个理论模型来绘制电容梯度 (∂C(ω)/∂z) 的实部和虚部的频率响应，该模型将悬臂梁动力学与复介电常数联系起来。我们通过绘制有机电子器件用聚合物基材料的纳米级介电谱来验证该方法。除了为基于 AFM 的介电谱学提供强大的扩展外，该方法还允许识别静电激励频率，从而在纳米材料上提供高介电对比度。
