LabAdviser/314/Microscopy 314-307/SEM/Nova/Micro 4-point probe: Difference between revisions
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s1= s2 = s3 = s, the resistivity is given by: | s1= s2 = s3 = s, the resistivity is given by: | ||
ρ = 2aπsV/I | (1) ρ = 2aπsV/I | ||
where a is the thickness correction factor for thicknesses t equal to or less than half the probe spacing (t/s < 0.5): | where a is the thickness correction factor for thicknesses t equal to or less than half the probe spacing (t/s < 0.5): | ||
a = 0.72t/s | (2) a = 0.72t/s | ||
Substituting Eq. 2 in Eq. 1 we get: | Substituting Eq. 2 in Eq. 1 we get: | ||
ρ = 2aπsV/I = 4.53V/I | (3) ρ = 2aπsV/I = 4.53V/I | ||
If both sides of Eq. 3 are divided by t we get: | If both sides of Eq. 3 are divided by t we get: | ||
Rs = ρ/t = 4.53V/I | (4) Rs = ρ/t = 4.53V/I | ||
which we refer to as sheet resistance. When the thickness t is very small respect to the spacing s, Rs is the preferred measurement quantity, being independent of any geometrical dimension and therefore a function of the material alone. | which we refer to as sheet resistance. When the thickness t is very small respect to the spacing s, Rs is the preferred measurement quantity, being independent of any geometrical dimension and therefore a function of the material alone. | ||