A method for immersion based inspection, the method includes: receiving an article that comprises a wafer and a transparent element, wherein a first fluid substantially fills a space between an upper surface of the wafer and the transparent element; and inspecting the wafer by utilizing a lens that contacts a second fluid element that also contacts the transparent element. A first group of capacitance versus voltage curves of a capacitor is measured. The end stop structures include at least one of high density polyethylene, to medium density polyethylene, polypropylene, a cyclic olefin copolymer, a high density material, or a high modulus material and may optionally include low density polyethylene or linear low density polyethylene.