A process for the halogenation of an aromatic compound wherein the aromatic compound is admixed with a halogenating agent in the presence of an ionic liquid is described. The first dielectric plug has a layer of a first dielectric material and a layer of a second dielectric material formed on the layer of the first dielectric material. An in-stack longitudinal biasing structure for longitudinally biasing the free layer includes a pinned layer, an AFM pinning layer for pinning the pinned layer and a ruthenium spacer layer which is located between the pinned layer and the free layer. The heat sink has a one-piece terraced structure formed by a upper terrace and a lower terrace; the heat sink matches the counterbore to form a firm fit.