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

1
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. 3 Simulated high resolution TEM images of
(a) patterning and (b) disordered states in Ni3Al
from KMC-generated atomic configurations
Fig. 2 KMC simulations with input from MD are
employed to build a Dynamical phase diagram
1 manuscript to be submitted to Phys. Rev. B 2
manuscript to be submitted to Phys. Rev. B.