Robust atomic force microscopy using multiple sensors.

Area of Science:

• Surface science
• Nanotechnology
• Control engineering

Background:

• Atomic force microscopy (AFM) typically uses cantilever deflection for imaging and property estimation.
• Amplitude-modulation AFM (AM-AFM) and contact-mode AFM rely on regulating cantilever deflection for topography.
• Existing methods face limitations in bandwidth and robustness due to complex dynamics.

Purpose of the Study:

• To propose and evaluate an augmented control design for AFM using an additional vertical z-piezo motion sensor.
• To improve imaging bandwidth and robustness in AFM, particularly in AM-AFM.
• To leverage piezo motion sensor data for enhanced control not available from deflection signals alone.

Main Methods:

• Developed a control design scheme augmenting deflection-based control with a vertical z-piezo motion sensor feedback.
• Employed H∞ control framework for designing the piezo-sensor based feedback.
• Evaluated the augmented design in both AM-AFM and contact-mode AFM experiments.

Main Results:

• The two-sensor design in AM-AFM substantially improved robustness to modeling uncertainties, eliminating sensitivity peaks without reducing bandwidth.
• Contact-mode AFM imaging showed over 30% improvement in bandwidth and over 20% in robustness to modeling uncertainties.
• The augmented design demonstrated significant enhancements in imaging bandwidth and overall system robustness.

Conclusions:

• Augmenting AFM control with a z-piezo motion sensor offers significant improvements in imaging performance.
• The proposed method enhances robustness and bandwidth, overcoming limitations of traditional deflection-based control.
• This dual-sensor approach provides a more reliable and efficient method for AFM imaging and analysis.