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. 2006 Jun 23;91(7):2678–2686. doi: 10.1529/biophysj.106.082412

FIGURE 2.

FIGURE 2

The magnitude of the DEP at various tip-sample distances obtained directly from finite element analysis calculations for a DC electric field is compared to the trend predicted from Eqs. 1 and 2 (λm = 5 nm, ɛm = 5, σm = 0.3 mS/m, λc = 200 nm, ɛc = 70, σc = 360 mS/m, ɛs = 81, σs = 10 mS/m, V = 10 V, and D = 20 μm). The conical AFM tip was modeled by two stacked spheres of radius 35 nm and 100 nm with a cone connecting the midsection of the two spheres. The fit to the data points indicated that the force acting upon the surface relative to the tip-sample distance could be approximated as 137 nN nm/(z + R) − 0.2 nN.