• Nano-continuum Design Optimization

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• Atomic Force Microscopy (AFM)
  • ■ Surface sensing

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 AFM uses a cantilever with very sharp tip to scan over a sample surface. As the tip approaches the surface, attractove fprces between the surface and the tip cause the cantilver to deflect towards surcace. However, as the cantilever is brought even closer to the surface, when contacted, repulsive force causes the fcantilever to deflect away from the surface.

■ Detection method

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 A laser beam is used to detect cantilever deflections toward and away from the surface. By reflecting an incident beam off the flat top of the cantilever, any deflections will cause slight changes in the direction of the reflected beam. A position-sensitive photodiode(PSPD) is used to track the changes.                                                              

■ Imaging


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 AFM images the topography of a sample surface by scanning the cantilever over a region of interest. The deflection of cantilever influenced by smaple surface is detected by PSPD. By using the feedback loop to control the height of the tip above the surface, maintaining constant laser postion, the topography of the sample is obtained.


■ Contact mode


 Contact mode is a standard AFM technique where the sample topograph is measured by monitoring the deflection of the cantilever as the probe scans across the sample. A feedback loop maintains a constatnt deflection by vertically moving the scanner at each data point.


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■ Tapping mode


 Tapping mode is kind of intermittent contract mode. In tapping mode, the sample topography is measured by monitoring the amplitude of oscillation of the cantilever, A piezo stack excites the cantilever substrate vertically, causing a constant sinusoidal amplitude. The feedback loop maintains a constant oscillation amplitude by vertically moving the scanner at each data point.

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■ ScanAsyst


 ScanAsyst is a imaging mode with automatic image optimization technology. ScanAsyst is based on the Peak Force Tapping mode which uses the force curve at every pixel in image as a feedback signal for imaging. Unlike Tapping mode, where imaging force is a compex function of the setpoint and other variables, Peak Force Tapping provides direct force control. Furthermore, it does not resonate the cantilver so that the cantilever turning is not required.


■ AFM Images 


   - Gold Nano Particles


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