Real time reduction of probe-loss using switching gain controller for high speed atomic force microscopy

Area of Science:

• Atomic Force Microscopy
• Surface Science
• Image Processing

Background:

• Tapping mode atomic force microscopy (AFM) is susceptible to probe-loss artifacts, degrading image quality.
• Regions of probe-loss occur when the AFM tip loses contact with the sample surface.
• Existing methods struggle to effectively mitigate these artifacts without compromising imaging performance.

Purpose of the Study:

• To develop and demonstrate a new controller to reduce probe-loss affected regions in AFM images.
• To improve the reliability and feature recovery in tapping mode AFM imaging.
• To enable higher controller gains for faster imaging without performance degradation.

Main Methods:

• A switching gain proportional-integral-differential (PID) controller was implemented.
• The controller gain is dynamically adjusted using a "reliability index" signal derived from cantilever oscillations.
• This signal identifies probe-loss regions in real-time.

Main Results:

• The switching gain controller significantly reduced probe-loss areas in AFM images.
• Imaging of a calibration sample at high speed (240 microm/s) showed improved quality.
• Imaging of plasmid DNA at 60 microm/s demonstrated recovery of previously lost sample features.

Conclusions:

• The developed switching gain controller effectively minimizes probe-loss artifacts in tapping mode AFM.
• This approach allows for faster imaging speeds by enabling higher controller gains.
• The method enhances the fidelity and completeness of AFM-based surface topography data.