Nano-Positioning Systems for Atomic Force Microscopy (AFM)

In the last decades, optical limitations of light-based microscopy have been overcome with several super-resolution techniques, such as light-sheet microscopy, where precision motion control equipment plays a key role. 

Even higher resolution can be achieved with high-resolution physical scanning (i.e. scanning probe microscopy, or SPM), where nano-positioning systems become essential.

Atomic force microscopy (AFM), for example, is an advanced method of measuring the 3D surface topology of samples on the sub-nanometer scale. This level of resolution exceeds the optical diffraction limit of the conventional compound microscope by over 1,000 times, necessitating the use of ultra-precise nano-positioning systems to acquire accurate measurement data from sample scanning.

In this blog post, PI explores some of the principles of AFM in more detail. We will also outline some of our nano-positioning systems which have proven instrumental in the growing success of high-technology AFM studies.

Contact mode AFM brings the probe tip into proximity with the surface of a sample which is mounted on a nano-positioning system, such as a piezo stage. This stage moves the sample with multi-axis control (X, Y, Z axes) relative to the tip apex, and helps to maintain a constant tip-sample interaction force as the surface is scanned. The reason this interaction force changes is most commonly due to topological variations, though it may be indicative of any number of complex phenomena occurring at the sub-nanoscale (ferroelectrics for example). An integrated photodiode continually monitors these changes by measuring the position of the cantilever, which bends in response to the Z-orbit of the tip. Probing these sub-nanometer surface variations provides valuable insights for materials characterizations in a broad range of fields.

AFM’s can be designed in different ways. It is common to scan the tip, which is often done with piezo scanner tubes. These tubes are relatively low cost and simple, but are limited in scan range and linearity.  Higher precision can be achieved with flexure guided piezo nano-positioning stages used to scan the sample instead of the tip. Piezo stages with capacitive feedback - which means that capacitive sensors actively provide nanometer precise position control of the piezo stage - can achieve lateral and Z-axis resolutions down to 0.1 nanometers, excellent prerequisites for both atomic force and near-field microscopy. This is true even for sample stages used for measurements of comparatively high lateral scanning ranges – up to 100µm and more, in AFM and confocal Raman microscopy.