I. Petrov

Department of Materials Science and Frederick Seitz Materials Research Laboratory, University of Illinois, 104 S. Goodwin Ave, Urbana, IL 61801

Transition-metal nitrides are well known for their remarkable physical properties including high hardness and mechanical strength, chemical inertness, and electrical resistivities that vary from metallic to semiconducting. As a result, they are widely studied and have become technologically important for applications such as hard wear-resistant coatings, diffusion barriers, and optical coatings. While TiN has received by far the most attention and is presently used commercially in all of the above mentioned applications, the neighboring nitride on the periodic table, ScN, is almost totally unexplored. On the other hand, polycrystalline CrN and TaN are among the most intensively studied at present. There is a need of data on the fundamental properties of these compounds measured on epitaxial layers. We have used ultra-high vacuum reactive magnetron sputter deposition to study the epitaxial growth of stoichiometric B1 NaCl structure ScN, CrN, TaN, and TiN on MgO(001) substrates. In all cases we find that the epitaxial growth is dominated by kinetic surface roughening which results in a periodic array of surface mounds. The mounds evolve with thickness and due to a combination of atomic self-shadowing and limited adatom mobility lead to the formation of cusps and nanopipes. The use of high-flux low-energy ion irradiation during growth enhances adatom mobility and delays the formation of cusps. We report on the relaxed lattice constant, electrical conductivity and hardness of these epitaxial layers.