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SPM Principles

Scanning Capacitance Microscopy

 

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Scanning Capacitance Microscopy is kind of dynamic EFM. Generally [1] in EFM. the cantilever is biased directly by Vtip=Vdc + Vac sin(wt), where Vac is referred to as the driving voltage. Scanning is executed on some height h above the sample surface in according with the profile defined during the first scanning in Semicontact mode. The capacitive force Fcap(z) between the tip and a sample surface at potential Vs is

Fcap(z) =(1/2) (Vtip - Vs)2(dC/dz)

where C(z) is the tip-surface capacitance dependent on tip geometry, surface topography and tip-surface separation z.
   Second harmonic of the capacitive force depends only on (dC/dz) and Vac

Fcap2w(z) =(1/2)(dC/dz) Vac2sin(2wt)

and can be used for acquisition additional information, e.g distribution of the  surface capacity over the sample. For maximization of the second harmonic oscillations the ac frequency w is adjusted to be equal to half of cantilever resonance frequency wr.
 
References
  1. Nanotechnology 12, 485 (2001). 
  2. Appl. Phys. Lett. 52, 1103 (1988). 
  3. J. Appl. Phys. 61, 4723 (1987).  

 

 
 
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