Introduction to Atomic Force Microscopy (AFM)

Lukas Eng from TU Dresden, Germany, emphasizes the complexity of AFM techniques and the necessity of a thorough understanding of the underlying physics to effectively use AFM for material characterization.

Key learning objectives:

Understanding the Principles and Challenges of AFM: The AFM operates by detecting forces between a tip and the sample surface, which can be influenced by various interactions such as van der Waals forces, electrostatic forces, and magnetic forces. Recognizing the influence of different forces and how they interact with the measurement process is crucial. The geometry of the cantilever and the tip's interaction with the sample play significant roles in the accuracy and type of data collected. Differentiating between attractive and repulsive forces is key to avoiding issues like snapping to the surface, which can affect measurement accuracy.

Mastering AFM Operation Modes and Techniques: There are different AFM modes, such as contact mode, tapping mode, and non-contact mode, each suitable for different types of analysis and providing various types of data (e.g., topography, dissipation, electrostatic forces). Choosing the appropriate operation mode and understanding the feedback mechanisms, like AC to DC conversion using a lock-in amplifier, are essential for accurate measurements. The choice of deflection measurement tool—whether optical, capacitive, or piezoresistive—also significantly impacts the measurement outcome and its interpretation.

Recognizing the Impact of Environment and Material Properties: The environment in which AFM is operated, such as vacuum or liquid, and the material properties of the tip and sample, like dielectric constants, can influence the forces measured. For instance, the dielectric constant of the medium can turn attractive van der Waals forces into repulsive forces. Moreover, the force constants of the cantilever and the tip-sample interaction must be balanced to prevent unwanted snapping into the surface. Understanding the physics behind these interactions helps in tailoring the AFM setup and interpreting the results correctly.

These objectives emphasize the complexity of AFM techniques and the necessity of a thorough understanding of the underlying physics to effectively use AFM for material characterization.

This video was recorded with the financial support of the Teaming for Excellence program (European Union Horizon 2020; GA 857543) during the Near-field Optical Nanoscopy Summer School (Donostia- San Sebastian; 6-9 June 2023) organized by neaspec/attocube AG, CIC nanoGUNE BRTA and the ENSEMBLE3 Centre of Excellence.