The objective of this research is to develop a prediction scheme for dynamic mode atomic force microscopy (DM-AFM) and apply it to enhance the accuracy of topographic measurements. DM-AFM is a powerful imaging and manipulation tool in nanotechnology. Although its operation is based on the dynamic response induced by probe-sample interaction, the interaction itself is not fully understood. The interaction mechanism in DM-AFM should be more completely studied for further advance of this technology. A prediction scheme to investigate the amplitude reduction, phase variation, resonance frequency shift, and bi-stability in DM-AFM is developed and experimentally verified. The developed scheme uses steady state based harmonic balance method for computational time efficiency and it includes continuation methods to detect and estimate the responses in bi-stable regions. The bi-stability in DM-AFM is a consequence of the nature of nonlinear interaction forces. In order to identify the force field, a dynamic force spectroscopy method, based on the probe's amplitude and phase responses, is developed. This method converts the amplitude and phase responses into conservative and damping forces. The converted force-distance curve is used to estimate the elastic modulus of the sample and to estimate and control the force exerted on a sample. In addition, it is used to predict DM-AFM responses more accurately by eliminating the error caused by the discrepancy between the force model and the real force. To aid in practical applications, optimal operation setup and methods for accuracy enhancement in topography measurement are studied and developed. With regard to optimal operation setup, bi-stability as well as force sensitivity and sample damage are investigated. The prediction scheme is also applied to improve the topogphy measurement in bi-stable region. A topography reconstruction method is developed to reduce the topography distortion by compensating for the probe-sample separation error at the amplitude set point. This reconstruction method improves the topography, but it does not eliminate the distortion caused by the Z-scanner tracking error occuring after jumps in bi-stable region. To overcome this problem, probe-sample separation modulation scheme is developed. This operation scheme uses the estimated probe-sample separation as the control feedback and the probe-sample separation does not change with jumps. Topography image obtained with probe-sample separation modulation is free from the distortion by jumps although the operation is in bi-stable region.
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Amplitude, Bi-stable, DM-AFM, Probe-sample|
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