基于高次谐波原子力显微术的力学特性快速定量测量机理及方法

As the rapid progress in various fields of micro-/nano- science and technology, there have urgent demands in developing methods for fast, quantitative and nondestructive nanomechnical characterization. Multi-harmonic atomic force microscopy (AFM) based approach has shown great potential in meeting such a challenge. However, the quantitative relations between the acquired harmonic amplitude/phase signals and the mechanical properties of the sample have not been clearly understood. In addition, the higher harmonic signals are usually very weak and the low signal-to-noise ratio prevents practical applications. Considering all these current situations and key problems, we propose the systematic investigations on the quantitative nanomechanical measurements based on detecting and analyzing the multi-harmonic responses of dynamic AFM. The major research contents are summarized as follows. First, accurate and systematic models will be constructed, which can link the multi-harmonic signals with the mechanical features of the sample. Various influencing factors will also be considered in the analysis. Second, the enhancement methods of higher harmonic signals will be investigated. Structural design of the AFM cantilevers will be carried out to improve the signal-to-noise ratio at higher harmonics. The optimization methods of assembled cutting structures on the cantilever will be explored to satisfy multiple objectives. Last, data fusion on the series of harmonic AFM images will be studied to enhance the measurement accuracy and provide a more comprehensive view of the mechanical properties of the sample. The proposed approaches of the harmonic AFM cantilever design and the data fusion of multi-harmonic images contain certain novelty. This project can provide new methods and techniques for efficient and accurate AFM based mechanical evaluations at the nanoscale. Furthermore, it can also provide solid theoretical and technical supports for further applications in biology, material science and other fields of nanoscience and nanotechnology.

微纳科技的发展对高分辨、快速、定量的纳米力学特性测量提出了迫切需求，而基于高次谐波检测的原子力显微镜（AFM）方法展现出该方面广泛应用的潜力。本项目针对目前高次谐波响应的振幅/相位与材料力学特性参量间的定量对应关系尚未清楚、谐波信号较为微弱以致限制了成像应用等关键问题，提出开展高次谐波AFM纳米力学特性成像机制的深入研究。主要研究内容包括：明确谐波响应与力学特性及众多影响因素的内在关联，建立精确的分析模型；设计集成微细结构的微悬臂梁，发展多参量多目标优化方法，以实现高次谐波信号的增强；开展各阶次谐波系列图像的数据融合研究，以获得更系统全面、更高精度的纳米力学图像。本项目在高次谐波信号增强和测量数据融合等方面具有新思想。本项目的实施可为亚细胞层面生物科学、材料科学及其他纳米科技的研究提供力学特性测试的新原理和新方法，为拓宽后续多学科交叉应用奠定良好的理论和技术基础。

微纳科技的发展对高分辨、快速、定量的纳米力学特性测量有迫切需求，而基于高次谐波检测的原子力显微术展现出在该方向广泛应用的潜力。本项目针对目前高次谐波响应的振幅/相位与样品局域力学特性参量间的定量对应关系尚未清楚、谐波信号较为微弱以致限制了其成像应用等关键问题，在国家自然科学基金的资助下已完成的主要研究工作包括：1）研制了单孔式、双孔式和编码式等多系列高次谐波增强微悬臂梁，通过材料选择去除来改变常规微悬臂梁的质量分布，从而优化其频率响应特性。2）系统分析了高次谐波原子力显微术成像时设置参数和测量结果间的关联关系，包括反馈振幅、激励频率和检测光斑在微悬臂梁上的位置等。3）进行高次谐波原子力显微术在亚表面成像中的应用分析，并与接触共振、双模态等模式作了对比；研究了液体和大气环境下高次谐波亚表面成像的性能差异。4）提出了基于高斯过程的自适应智能采样方法、结合表面填充扫描路径规划和自适应采样的测量策略以及自适应轮廓跟踪局域扫描测量，可显著提高原子力显微术时间效率并减小数据冗余。5）提出在微悬臂梁背面集成可实现光异常反射的超表面，利用反射角和入射角间的非线性关系使检测激光的反射角在微悬臂梁变形时的变化量相对于入射角变化有放大作用，增强了检测灵敏度。6）进行基于力学特性感知原子力显微术应用于亚表面无损纳米检测的拓展研究，提出样品内部空穴结构分析的理论模型，促进了对接触共振原子力显微术亚表面成像机理的认识，并为成像条件优化提供依据；制备了多层膜系结构并对中间金属功能层进行检测，以此阐明了接触共振原子力显微镜方法的成像影响因素；设计优化了微悬臂梁结构以利于接触共振原子力显微术应用；提出亚表面动态刻蚀过程检测方案，以利于微纳器件研制中的无损纳米检测。本项目研究工作进展较为顺利，完成了各项既定目标，已在国内外学术期刊及会议上发表论文20余篇。