How AFM Works
Atomic Force Microscopy (AFM) is a high-resolution imaging technique used to analyze surfaces at the nanoscale. Here’s a concise explanation of how it works:
Basic Principles
Probe and Cantilever:
An AFM uses a sharp tip, often made of silicon or silicon nitride, mounted on the end of a flexible cantilever. The tip has a very fine point, typically a few nanometers in diameter.
Interaction with Sample Surface:
The tip is brought very close to the sample surface. Forces between the tip and the sample (such as van der Waals forces, electrostatic forces, or magnetic forces) cause the cantilever to deflect.
Detection of Deflections:
A laser beam is focused on the back of the cantilever and reflected onto a position-sensitive photodetector. As the cantilever deflects, the position of the laser spot on the detector changes, allowing precise measurement of the cantilever’s deflection.
Generating an Image:
The sample is scanned line-by-line under the tip using a piezoelectric scanner, which moves the sample in very small, precise increments. The deflection of the cantilever is recorded at each point.
The recorded deflections are converted into a topographical map of the surface, providing detailed images at the nanoscale.
Modes of Operation
Contact Mode:
The tip is in continuous contact with the surface. This mode provides high-resolution images of hard surfaces but can damage soft samples.
Non-contact Mode:
The tip oscillates near the surface without touching it. This mode is less invasive and suitable for delicate samples.
Tapping Mode:
The tip intermittently contacts the surface. It combines the advantages of contact and non-contact modes, reducing damage while maintaining good resolution.
Applications
Material Science:
Studying the surface roughness, mechanical properties, and composition of materials.
Biology:
Imaging cells, proteins, and other biological structures in their natural environments.
Semiconductors:
Inspecting the surface of microchips and other electronic components for defects.
Nanotechnology:
Manipulating and measuring nanostructures and nanoparticles.
AFM provides three-dimensional surface profiles with atomic-level resolution, making it a powerful tool for researchers in various scientific and engineering fields.
