A gate conductor structure is provided having a barrier region between a N-type device and a P-type device, wherein the barrier region minimizes or eliminates cross-diffusion of dopant species across the barrier region. The barrier region comprises at least one sublithographic gap in the gate conductor structure. The sublithographic gap is formed by using self-assembling copolymers to form a sublithographic patterned mask over the gate conductor structure. According to one embodiment, at least one sublithographic gap is a slit or line that traverses the width of the gate conductor structure. The sublithographic gap is sufficiently deep to minimize or prevent cross-diffusion of the implanted dopant from the upper portion of the gate conductor. According to another embodiment, the sublithographic gaps are of sufficient density that cross-diffusion of dopants is reduced or eliminated during an activation anneal such that changes in Vt are minimized.