"Smart" Metal-Insulator-Transition and Magnetic Nanocomposite Layers Formed by Ion Beams L. A. Boatner Solid State Division, Oak Ridge National Laboratory Oak Ridge, TN 37831 "Smart" surface nanocomposites consisting of a layer of "active" nanometer precipitates (e.g., metal-insulator-transition or magnetic particles) embedded in a host matrix represent a new materials state with unique properties. These materials are created using ion implantation and thermal processing. In these nanocomposites: each precipitate is generally a faceted single crystal that, in the case of formation in a single-crystal host, is aligned with every other precipitate. In the case of nanoparticle formation in an amorphous host, the particles are generally single crystals that may or may not be faceted and are generally not crystallographically aligned. In either single-crystal or amorphous hosts, the nanoparticles are normally physically isolated from each other by the host matrix - usually by separations whose dimensions are on the order of the nanoparticle size (i.e., there are effectively no inter-particle grain boundaries.) Compound and doped nanoparticles can be created. The "smart" nature of the near-surface nanocomposite layer arises from the use of ion implantation and thermal processing to create "active" precipitates, i.e., precipitates in which large property changes at, for example, a phase transition provide a "feedback" mechanism leading to the "smart" interaction. "Smart" embedded nanocomposite materials have several important advantages over conventional composite materials including: (1) The physical properties of the surface nanocomposite can be optimized by controlling the particle size, (2) Useful properties of two or more materials can be combined into one integrated structure by forming embedded nanocomposite layers at different depths, and (3) Embedded, active nanoparticles are protected from the environment since they are located below the surface of the host material. New physical properties and new effects in these smart nanocomposites arise from the size of the precipitates, nanophase particle-particle, and particle/host interactions.