Materials Computation Center, University of Illinois Duane D. Johnson and Richard Martin, NSF DMR-03-25939 Nanoscale Patterning of Chemical Order Induced By Ion Beam Processing Pascal Bellon and graduate student Jia Ye Chemically ordered phases are commonly used in engineered alloys, e.g., to optimize mechanical and magnetic properties. Simulations show that nonequilibrium processing by ion beams can induce the spontaneous formation of patterns of ordered domains with tunable sizes at the nanometer scale, which would be ideal for high-density magnetic storage media applications. We have combined molecular dynamics simulations (MD) (collaboration R.S. Averback), kinetic Monte Carlo simulations (KMC), and electron microscopy contrast simulations (collaboration J. Zuo). We have identified the conditions required for, and the nature of nanoscale patterning of L12 order in Ni3Al. 1 We have also introduced a new criterion to distinguish patterning of order from short range order state, using a Gaussian-Lorentzian decomposition of the structure factor. 2 Fig. 1 MD simulations of energetic displacement cascades in Ni3Al (Ni: blue, Al: gray) Fig. 2 KMC simulations with input from MD are employed to build a Dynamical phase diagram Fig. 3 Simulated high resolution TEM images of (a) patterning and (b) disordered states in Ni3Al from KMC-generated atomic configurations 1 manuscript to be submitted to Phys. Rev. B ; 2 manuscript to be submitted to Phys. Rev. B.