Systems approach based solution to fundamental limitations in unraveling spatial and temporal regimes in nano-interrogation and nano-positioning
De, Tathagata (2008) Systems approach based solution to fundamental limitations in unraveling spatial and temporal regimes in nano-interrogation and nano-positioning. PhD thesis, Iowa State University.
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A design scheme that achieves an optimal tip-sample force regulation with an ideal topography image reconstruction is presented. It addresses the problem of obtaining accurate sample profiles when scanning at high bandwidth while maintaining a constant cantilever-tip sample force in atomic force microscopes. It is shown that the proposed scheme provides a faithful replica of the sample at all relevant scanning speeds limited only by the inaccuracy in the model for the atomic force microscope. This provides an improvement over existing designs where the sample profile reconstruction is typically bandwidth limited. The experimental results corroborate the theoretical development. Conventional imaging signals such as the amplitude signal and the vertical piezo-actuation signal cannot identify the areas of probe loss, where dynamic atomic force microscopy based image where the cantilever fails to be an effective probe of the sample. A real-time methodology is developed to determine regions of probe loss. It is experimentally demonstrated that probe-loss affected portion of the image can be unambiguously identified by a real-time signal called reliability index. Reliability index, apart from indicating the probe-loss affected regions, can be used to minimize probe-loss affected regions of the image, thus aiding high speed AFM applications. A new immobilization technique for quantitative imaging and topographic characterization of living yeast cells in solid media using Atomic force microscope (AFM) is presented. Unlike previous techniques, proposed technique allows almost complete cell surface to be exposed to environment and studied using AFM. Apart from the new immobilization protocol, in this report, for the first time, high resolution height imaging of live yeast cell surface in intermittent contact mode is presented. High resolution imaging and significant improvement in operational stability facilitated investigation of growth patterns and evolution of surface morphology in quantitative terms. Growth rate of mother cell and budding cell showed distinct patterns over the imaging time.
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