Zhang Weijie, Chen Yuhang, Xia Xicheng, Chu Jiaru
Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei 230026, China.
Beilstein J Nanotechnol. 2017 Dec 21;8:2771-2780. doi: 10.3762/bjnano.8.276. eCollection 2017.
Harmonic atomic force microscopy (AFM) was employed to discriminate between different materials and to estimate the mixture ratio of the constituent components in nanocomposites. The major influencing factors, namely amplitude feedback set-point, drive frequency and laser spot position along the cantilever beam, were systematically investigated. Employing different set-points induces alternation of tip-sample interaction forces and thus different harmonic responses. The numerical simulations of the cantilever dynamics were well-correlated with the experimental observations. Owing to the deviation of the drive frequency from the fundamental resonance, harmonic amplitude contrast reversal may occur. It was also found that the laser spot position affects the harmonic signal strengths as expected. Based on these investigations, harmonic AFM was employed to identify material components and estimate the mixture ratio in multicomponent materials. The composite samples are composed of different kinds of nanoparticles with almost the same shape and size. Higher harmonic imaging offers better information on the distribution and mixture of different nanoparticles as compared to other techniques, including topography and conventional tapping phase. Therefore, harmonic AFM has potential applications in various fields of nanoscience and nanotechnology.
采用谐波原子力显微镜（AFM）来区分不同材料，并估算纳米复合材料中各组成成分的混合比例。系统研究了主要影响因素，即振幅反馈设定点、驱动频率以及沿悬臂梁的激光光斑位置。采用不同的设定点会引起针尖 - 样品相互作用力的变化，从而产生不同的谐波响应。悬臂梁动力学的数值模拟与实验观测结果具有良好的相关性。由于驱动频率偏离基频共振，可能会出现谐波振幅对比度反转。还发现激光光斑位置如预期那样影响谐波信号强度。基于这些研究，谐波AFM被用于识别多组分材料中的材料成分并估算混合比例。复合样品由形状和尺寸几乎相同的不同种类纳米颗粒组成。与其他技术（包括形貌和传统轻敲相位成像）相比，高阶谐波成像能提供关于不同纳米颗粒分布和混合情况的更好信息。因此，谐波AFM在纳米科学和纳米技术的各个领域具有潜在应用。
