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As the scan speed of the atomic force microscope (AFM) operating in intermittent contact mode is increased, the likelihood of artifacts appearing in the image is increased due to the probe tip losing contact with the sample. This paper presents an analysis of the effects of probe loss and a new method, switched gain resonant control, of reducing the problem of probe loss when imaging at high speed. The switched gain resonant controller is implemented to switch the cantilever quality Q factor according to the sample profile during the scan. If the controller detects that the probe has lost contact with the sample the cantilever Q factor is increased leading to a faster response of the feedback controller, expediting the resumption of contact. A significant reduction in image artifacts due to probe loss is observed when this control technique is employed at high scan speeds.
Date of Publication: Nov. 2012