Comparison of AFM Performance with Active and Passive Isolation
Atomic force microscopy (AFM) is the most widely used SPM technique. AFM operates by dragging an ultra-fine mechanical probe, called a tip, across the surface of a sample. Instead of actually touching the sample, the tip comes near the surface of the sample and interacts with the atomic forces on the surface of the sample. The tip is attached to a cantilever, which is deflected as the tip rasters across the sample surface. A laser is reflected off the back of the cantilever and into a detector that collects information as the probe moves and produces an image of the sample. The resulting image provides an excellent view of the sample’s topography at an extremely high level of resolution. In addition to the original contact mode described above, a number of other modes of operation have been developed for the AFM, including non-contact mode, tapping mode, and force modulation.
The first commercial atomic force microscopes became available in 1988. Since that time, AFM has developed into one of the foremost tools enabling nanotechnology research. AFM has risen to prominence because of its ease of use and unparalleled ability to gather highly accurate topographical data on the nanometer scale. AFMs are now commonplace in university science departments and the research and development departments of large companies. Novel applications of AFM continue to be developed, such as using AFM techniques to diagnose and investigate cancer cells.
AFMs are very sensitive to background vibration present in the environment, even in laboratory settings. Such vibrations can be mitigated by various active and passive isolation solutions. Two situations requiring vibration reduction are presented below. In each case, the active vibration mitigation solution proves to be superior to the passive scheme.
Test Case: Comparing Active and Passive Isolation
Instrument: Digital Instruments MultiMode AFM in refrigerated chamber
Sample: DNA on Mica substrate
Description: Images were taken (shown above) with the AFM on the TS-150 active vibration isolation system from Herzan. Halfway through taking the image, the active isolation was turned off, leaving the built-in passive springs as the method of isolation. The wavy vertical striations in the lower half of the image represent the effects of environmental vibration on the AFM’s imaging capability. This provides a striking comparison of the performance of active vibration cancellation and passive vibration isolation.
Performance Comparison for Interferometry Application
Here is a video of an AFM Probe being imaged using interferometry. The tip is suspended in air in order to measure the amount of noise reaching the probe. This video is taken measuring the quality of application under the following conditions: 1) without vibration isolation, 2) using an optical table, and 3) using a TS-150 active vibration isolation table from Herzan.
You can observe that the noise reaching the probe has almost been completely eliminated.
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