AFM FAQs

A: AFM is a high-resolution scanning probe microscopy (SPM) technique. It maps surface topography and material properties down to the sub-nano scale using a physical probe attached to a flexible cantilever.

A: A sharp tip scans across a sample surface. A laser reflects off the back of the cantilever onto a position-sensitive photodetector. As surface features deflect the cantilever, a feedback system adjusts the vertical position (Z) to maintain constant force or amplitude, constructing a 3D height map.

A: AFM provides true 3D surface topography (Z-height data) without requiring vacuum environments or conductive sample coatings. SEM uses an electron beam to capture 2D surface images and typically requires a high-vacuum chamber and conductive samples

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Contact Mode: The tip drags directly across the surface. Best for hard, flat samples.

Tapping Mode (AC Mode): The cantilever oscillates near its resonant frequency, touching the surface intermittently. Reduces shear forces and protects soft samples.

Non-Contact Mode/Nap Mode: The tip oscillates above the surface, detecting van der Waals forces without physical contact.

A: Yes. AFM can function in aqueous environments, making it ideal for imaging biological samples, like living cells or DNA, in physiological conditions.

A: Almost any solid material, including polymers, biological cells, semiconductor wafers, ceramics, and thin films. Samples must be firmly attached to a substrate to prevent movement during scanning.

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Scan Speed: Scanning a single image generally takes minutes, though high-speed AFMs exist.

Image Range: Maximum vertical height (Z-range) and maximum field of view (X-Y) are limited compared to optical microscopes.

Tip Artifacts: A dull, contaminated, or damaged tip causes image distortion through tip convolution.

A: Biological samples must be immobilized on ultra-flat substrates, such as cleaved mica, glass cover slips, or silicon wafers. Modifiers like poly-L-lysine or silanes are often used to chemically bond negatively charged molecules (e.g., DNA, proteins) to the surface so they aren't swept away by the probe.

A: SMFS uses functionalized tips (e.g., coated with specific ligands or antibodies) to pull individual biomolecules off a surface or receptor, measuring rupture forces and mapping chemical binding affinity at the single-molecule level.

A: If the radius of curvature of the probe tip is larger than or comparable to the surface feature size, the resulting image reflects the geometry of the tip rather than the sample. This makes surface features appear wider than they are.

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Streaks/Paraboloids: Usually caused by a contaminated tip picking up debris, or proportional/integral (P/I) feedback gains being set too low or too high.

Thermal Drift: Slow, continuous image distortion caused by ambient temperature changes or thermal expansion of scanner components.

Double Peaks: Indicates a broken or split tip scanning the surface with two points simultaneously.