A detector for an electron multiplier comprising: a substrate comprising a dielectric material, the substrate having a first face and an opposing second face; a charge collector provided adjacent the first face of the substrate; an anode within the substrate, the anode spaced from first face, such that the anode is capacitively coupled to the charge collector, so that charge incident on the charge collector generates an image charge on the anode; and a conduit contact, coupled to the anode and passing through the substrate to the second face of the substrate layer.