Standadization Study On Precise Measurement Of Nanostructures By AFM

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.