Offsets in Electrostatically Determined Distances: Implications for   Casimir Force Measurements
  The imperfect termination of static electric fields at semiconducting surfaces has been long known in solid state and transistor physics. We show that the imperfect shielding leads to an offset in the distance between two surfaces as determined by electrostatic force measurements. The effect exists even in the case of good conductors (metals) albeit much reduced. 
S.K. Lamoreaux and A.O. Sushkov
quant-ph