UNIMO Technology UDR-204 Manual de instrucciones descargar pdf (Pagina 281)

Electric Force (EFM) Imaging

Surface Potential Detection—Theory

Rev. B MultiMode SPM Instruction Manual 261

14.5 Surface Potential Detection—Theory

Note: Surface potential detection EFM is only possible using the one of the extender

modules or the NanoScope IV controller. This section does not apply to

microscopes which are not equipped with the Basic or Quadrex Modules, or the

NanoScope IV controller.

The Basic Extender Module allows measurement of local sample surface potential. This is similar

to techniques called Scanning Maxwell Stress Microscopy and Kelvin Probe Microscopy. Surface

potential detection is a two-pass system where the surface topography is obtained in the ﬁrst pass

and the surface potential is measured on the second pass. The two measurements are interleaved,

that is, they are each measured one line at a time with both images displayed on the screen

simultaneously.

A block diagram of the surface potential measurement system is shown in Figure 14.5a. On the ﬁrst

pass, the sample topography is measured by standard TappingMode. In TappingMode the cantilever

is physically vibrated near its resonant frequency by a small piezoelectric element. On the second

pass, the piezo that normally vibrates the cantilever is turned off. Instead, to measure the surface

potential, an oscillating voltage is applied directly to the cantilever tip. This creates an

oscillating electrostatic force at the frequency ω on the cantilever. The oscillating force has the

following amplitude:

where is the vertical derivative of the tip/sample capacitance.

, the dc voltage difference between the tip and the sample,

and

is the amplitude of the oscillating voltage applied to the cantilever tip.

ωtcos

-------

tip

sample

–=

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UNIMO Technology UDR-204 Manual de instrucciones Pagina 281