Programs in Physics & Physical Chemistry
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|Manuscript Title: TRIDYN: binary collision simulation of atomic collisions and dynamic composition changes in solids.|
|Authors: W. Moller, W. Eckstein, J.P. Biersack|
|Program title: TRIDYN (VERSION 3.1)|
|Catalogue identifier: ABFH_v1_0|
Distribution format: tar.gz
|Journal reference: Comput. Phys. Commun. 51(1988)355|
|Programming language: Fortran.|
|Operating system: COS 1.16.|
|RAM: 91K words|
|Word size: 64|
|Keywords: Solid state physics, Atomic collisions, Collision cascades, Binary collision Approximation, Ion ranges, Ion reflection, (preferential) Sputtering, Ion mixing.|
Nature of problem:
A beam of fast ions (energy range app. 1 eV/amu to 100 KeV/amu) entering a solid substance is slowed down and scattered due to electronic interaction and nuclear collisions. Along its path, an individual projectile may create fast recoil atoms which in turn may initiate collision cascades of moving target atoms. These may either leave the surface (be sputtered) or be deposited at a site different from their original one. Together with the projectiles being deposited in the substance, this results in local composition changes. In the case of large implantation fluences, these phenomena will cause collisional mixing in layered substances, changes of the surface composition due to preferential sputtering, and the establishment of a stationary range profile of the implanted ions.
The paths of the individual moving particles and their collisions are modelled by means of the binary collision approximation for an amorphous substance, using a screened Coulomb potential for nuclear collisions and local or nonlocal free-electron-gas approximations for the electronic energy loss. For each nuclear collision, the impact parameter, the azimuthal deflection angle and the species of the collision partner are determined from random numbers. A proper scaling is chosen so that each incident projectile ('pseudoprojectile') represents an interval of implantation fleunce. Subsequent to the termination of each pseudoprojectile and its associated collision cascades, the local partial densities of the constituents are rearranged according to their atomic volumes. In order to make advantage of vector processing, the the time-consuming sections of the code have been written in vectorized form, where possible.
The running time depends strongly on the problem chosen and is mainly influenced by the number of pseudoprojectiles, their energy and their atomic species. For the test example of 1 keV Ne atoms incident on Ta2O5, a calculation with 6 . 10**4 pseudoprojectiles corresponding to a fluence of 6 . 10**16 Ne/cmsq requires 18 min on the CRAY-XMP computer.
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