Let's say I build a parallel plate capacitor using two metal plates with perfectly smooth surfaces. They are separated by some small distance d, with only vacuum between them. I then apply some AC voltage across the plates. Is there some effect which causes loss in the capacitor (equivalent series resistance) that increases as the plates are moved closer and closer together (as d decreases)? More practically, we're talking about d on the order of ~10 microns or so. At some point will the loss become so high that the capacitor will become more of a resistor than a capacitor?