High Resolution Imaging by Atomic Force Microscopy (AFM)

Since its invention, AFM has become a technique of choice for the study of surfaces in materials science, nanotechnology and life sciences. To a great extent, it is its nanometer-level high resolution that has led to its tremendous popularity. Although new advanced uses of AFM have been developed, like molecular force measurement or mapping of a sample's magnetic characteristics, high resolution surface topography remains the main application of AFM.

The tip: the AFM core

The tip, with its control system, is the core of the AFM and largely determines its performances. Usually made of silicon or silicon nitride, the tip is like a nanofinger that gently scans the sample surface. It must be very sharpened to accurately survey the humps and troughs of the sample.

Three modes of operation

AFM can operate in three modes: contact, tapping and non contact. The contact mode utilizes the repulsive forces between the tip and the sample. The tapping mode, the most commonly used, makes the lever and the tip vibrate at its resonance frequency. The feedback system then follows the variations of the vibration amplitude, due to the tip-sample interaction. Finally, the non contact mode makes use of the attractive forces, but it is rarely used.

AFM, a versatile instrument

AFM has found applications in an impressive number of domains. In electronics and in the semiconductor business, technicians and engineers use the AFM to examine surface defects or to measure wafer roughness. In optics, AFM serves to measure the surface finish (or roughness) of a lens. In life sciences, AFM is the ideal tool to imagine proteins or DNA.

Benefits:

- Works with all types of samples (insulating, conductor, biological, etc)

- Excellent resolution (inferior to the nm)

- Can quantify roughness

Applications:

- Surface topography

- Roughness measurements

- 3D imaging.

Jean-Sebastien Tasse is business development manager - industry at the Thin Film Research Laboratory (GCM), a materials analysis laboratory based in Montreal, Canada. The GCM offers a comprehensive range of analytical services to industry including chemical analyses, microscopy and mechanical testing. For more information: http://www.gcmlab.ca/services-to-companies.php