【作者】 王春梅；

【导师】 胡钧；

【作者基本信息】 上海交通大学 ， 生物医学工程， 2009， 博士

【摘要】 本论文重点研究应用原子力显微镜(AFM)对纳米结构(纳米颗粒/纳米材料/单个生物分子等)的形貌进行精确检测的方法学,其目标是发展与AFM针尖形貌精确测量相关的方法学、发展适用于纳米结构的形貌校正/重构模型和适用于AFM的图像处理新技术,进而有助于发展、建立并制定标准化的检测方法和过程,提高对纳米结构的测量分辨率和测量精度。纳米结构的测量标准化是当前国际纳米科技领域的重点研究内容之一。作为纳米检测技术的基本工具之一,AFM已经在研究纳米尺度物质的结构和特性方面取得了显著的进展,但在规范统一并可溯源性的标准化测量方面还处在起步的探索阶段.。当前实现基于AFM的精确测量存在许多困难和挑战,影响对样品纳米结构的定量表征,其中包括:1)AFM实验得到的图像是针尖形貌与样品结构的卷积/膨胀结果,目前还缺乏有效的方法精确标定针尖本身的形貌;2)针尖样品间相互作用的复杂性直接影响AFM的实验测量结果,当前还无法判断并单一区分这些相互作用;3)对于柔软的纳米结构,当前的针尖样品卷积模型还没有将形变考虑在内;4)此外,AFM仪器本身的特性(扫描管的非线性漂移、噪声等)以及针尖的安装方式等都会以不同的程度和方式影响测量结果。针对这些问题,本论文的主要研究内容包括两方面:1)基于新发展的有望成为一种标准物质的Tip Characterizer (Tip-C),从组装过程对Tip-C成功制备的影响、Tip-C作为标准样品的可行性以及测量误差分析及优化等方面研究利用Tip-C精确测量针尖形貌的方法;2)基于精确测量的针尖形貌,对几种纳米结构(纳米金颗粒、碳纳米管和DNA分子)进行测量校正,研究校正模型的可行性及修正方案,以实现对纳米结构的精确测量。针对应用Tip-C开展AFM针尖精确测量的主要研究结果包括:1)新发展的Tip-C可用于无损测量有效针尖形貌,有望进一步发展成为表征针尖形貌的标准样品;2)提出动态模式下AFM针尖的倾斜振动因作为一个影响因子耦合在卷积模型中,由此建立了动态模式下针尖-样品的卷积物理模型;3)对探针-Tip C相互作用主要参数(成像力、表面结构、反馈等)进行了系统分析,研究了相应参数下测量到的针尖形貌的规律性变化,提出可把相位作为标准样品测量评判的关键参数之一;4)结合Tip-C的特殊结构设计和测量变化规律,提出量化实验误差的实验性判据;5)建立了针尖倾斜振动方式下测得的振幅-相位-距离曲线的振动空间和表面拓扑结构之间的关系,并用于定量分析针尖-样品相互作用变化;5)由针尖稳态振动方程、针尖-样品相互作用DMT模型和已知针尖-样品平均力方程,建立了独立的悬臂参数组和样品参数组之间的近似关系,理论研究了Asp的优化条件,建立的量化关系有助于在固定样品情况下指导多种悬臂的优化参数设置与调节。针对典型纳米结构精确测量的主要研究结果包括:1)对Au和DNA的形貌校正表明,去卷积操作能极大地提高测量的可靠度,但是由于纳米结构的形变等因素,需要针对性进行测量方法和测量条件的优化;2)针对截面为类弧形的柔软纳米结构,提出基于接触点的修正Garcia校正模型,基于此模型校正后的CNT的形貌特征与TEM的检测结果具有可比性。结合其他AFM技术,有可能表征出包含内壁层数在内的CNT完整结构信息;3)提出基于VSPFM技术和Tip-C的柔软纳米结构精确测量的普适方案,并有针对性地将图像处理中的配准和叠加算法应用于该方案面临的漂移和噪声问题,提示图像处理算法可能对AFM精确测量起到重要作用。应用AFM实现纳米结构的精确测量及其标准化是一项多因素影响的系统性工作,目前还缺乏相关的基础性标准,还处在探索研究阶段。本论文的研究内容和发展的方法不仅为从事AFM测量的研究者所关注,Tip-C的部分工作也已包含在相关国际标准化组织和机构(ISO等)研究和制定纳米标准的工作计划中。希望通过进一步的国际合作和深入研究,加速AFM精确测量纳米结构的标准化研究,及早发展并制定出与AFM相关的检测技术标准,从而规范有效地提高对纳米结构的研究、开发、应用和风险控制的水平。更多还原

【Abstract】 The thesis focuses on methodology developments of precise morphology measurement of nanostructures, which including single nano-particles, nano-materials, single biomolecules in this thesis, by atomic force microscope (AFM). The main goals of our research are listed here as : 1) developing the precise measurement methodologies and processes for characterizing probe shape; 2) developing correction/reconstruction model applicable for nanostructures; 3) developing suitable image process techniques for applying AFM in single bio-molecules. Furthermore, the study helps to develop and establish the standardized measurement procedure, improving the measurement resolution and precision of nanostructures.Metrology standardization of nanostructures is one of the most essential facets in nano-science and nanotechnology. As one of the basic and popular measurement tools at nano-scale, AFM has been widely used in characterizing nanostructures’morphology and other Physical Chemistry properties. However, AFM is still in the initial stage for realizing traceable and standardized measurement. There are still many unsolved problems and challenges in realizing precise measurement by AFM, including: 1) AFM image is the convolution/dilation result of probe shape and sample geometry, and there is no effective way to characterize accurate probe shape now; 2) the complex tip-sample interaction directly influence the final measurement, and how to discriminate these interactions are still very difficult; 3) the deformation in measuring soft nanostructures not only calls for new measurement technique but also for new ideas about convolution model; 4) measurement is also affected by scanner’s thermal drift, noise, cantilever’s installation and others.For the above problems, the main topics of this thesis includes two aspects: 1) based on a new developed tip characterizer (Tip-C) which might be made as a kind of certified reference materials (CRMs), exploring the measurement methodology for obtaining precise probe shape from the fabrication effect to Tip-C preparation, feasibility of Tip-C as a CRM and measurement uncertainty analysis and optimization; 2) based on precisely characterized probe shape, correcting several nanostructures’(Au, CNT and CNT) morphology, analyzing the reliability of correction/reconstruction model and proposing the solutions for realizing precise measurement of nanostructures by AFM.The study results focused on the precise characterization of probe shape by Tip-C includes: 1) New developed Tip-C can characterize effective probe shape without any damage, thus making it feasible for becoming a potential CRMs; 2) establishing the convolution model in dynamic mode by additionally introducing the probe’s tilt oscillation behavior; 3) systematically exploring the tendency change of probe shape under some main factors, including image force, structure, feedback and so on, that might affect probe-Tip C interaction, and proposing the phase should be one of the critical estimation parameters for imaging quality; 4) suggesting the experimental criterion for estimation the measurement error based on the special designed structure in Tip-C and known measurement change; 5) establishing the relative position relationship between amplitude-phase-distance curve and surface topography by considering the tilted oscillation, and applying it to the analysis of different tip-sample interaction from the structure; 5)establishing the approximation relationship between separated experimental set parameters of cantilever and sample parameters, and suggesting the optimized Asp setting based on the relationship. The study also helps establish guidance of optimizing parameter setting of various types of cantilevers.The results focusing on the precise measurement of nanostructures includes:1) The morphology correction of Au and DNA shows that deconvolution operation can improve measurement reliability, especially for rigid sample. However, further methodology should be considered due to the deformation; 2) establishing the modified Garcia model applicable for nanostructures having arc cross section,and corrected morphology of CNT based on this model is comparable to TEM observation. Combing with other AFM technique, it is possible to characterize complete structure information including inner layers; 3) Proposing general reconstruction solution to soft nanostructures based on VSPFM technique and Tip-C based probe shape characterization. Image registration and time averaging algorithms were applied in reducing the drift and noise problems in the solution, indicating that image processing might be crucial to AFM based precise measurement.The standardization of precise morphology measurement by AFM is a systematic work affected by multi-factors, and now there are still not basic standards for it, calling for experts to attend the AFM standardization work. The research and developed method in the thesis attracts most of the researchers engaged in it, and partial work on Tip-C was now included in ISO new working items. It is hopeful that through the further international collaboration and researches, standardization work in AFM can be advanced. The establishment of measurement standards helps promote and regulate the study to nanostructures.更多还原