Skip to content

Binary Collision Approximation

Jump to bottom
Jon Drobny edited this page May 31, 2020 · 29 revisions

The binary-collision approximation (BCA) is a set of assumptions that tremendously reduce the computational complexity of simulating ion-material interactions. Ions interact with materials through nuclear and electronic stopping. These assumptions can be summarized as:

  • Particles in the code are "superparticles," and represent many ions or atoms each
  • Energetic particles interact with material atoms through a series of discrete, binary collisions
  • Nuclear collisions occur at mean-free-path distances
  • Between collisions, particles travel in straight lines along which nonlocal electronic stopping is applied
  • Binary collisions are calculated by solving the classical scattering integral for a chosen interatomic potential; local electronic stopping is applied following each collision
  • Material atoms are allowed to transfer momentum to tracked collision partners following any collision, but only collisions that transfer an energy greater than the displacement energy are removed from their original locations
  • Particles are stopped when their kinetic energy drops below a cutoff energy in the material, or when they leave the simulation boundary outside of the material
  • Particles leaving the material experience a locally planar surface binding potential

For an overview of the BCA, see Eckstein[1] or Robinson[2].

BCA for Plasma-Material Interactions

BCA for plasma-material interactions

Plasma-Material Interactions in the PIC-BCA method. Phenomena modelled include: (a) sputtering, (b) ion-driven mixing, (c) vacancy production, (d) implantation, (e) layered composition, (f) ionization and redeposition, (g) reflection as neutrals. Regions of the plasma, including (i) the plasma presheath, (ii) the magnetic presheath, and (iii) the debye or electrostatic sheath are marked along the hPIC/pyPIC field axis.

Electronic Stopping

Local and global coordinates in the binary-collision approximation.

Various formulations of electronic stopping for protons on silicon. Medvedev-Volkov[3] PSTAR[4] Biersack-Varelas[5] Lindhard-Scharff[6] Bethe[7].

Global coordinates in BCA

Local and global coordinates in the binary-collision approximation.

Coordinate system in the BCA as implemented in rustbca.

[1] W. Eckstein, Computer Simulation of Ion-Solid Interactions (1991)

[2] M. T. Robinson, The binary collision approximation: Background and introduction, Rad. Eff. and Def. in Solids (1994)

Clone this wiki locally