In some reacting flow simulations there may be different types of solid surfaces at which very distinct heterogeneous chemistry takes place. For example, in a plasma etching reactor there might be a wafer composed of silicon and reactor side-walls composed of aluminum. Although the main purpose of the simulation might be to understand the etching chemistry at the wafer, reactions at the walls also serve to create and destroy species. Because chemical reaction mechanisms occurring at the surfaces can be quite different, Pre-processor allows the use of "multiple materials" in input files. This essentially allows the user to specify several different and complete surface reaction mechanisms, one after another (separated by a MATERIAL line). An example of such a Surface Kinetics input file is shown in Example 3.8: Surface Kinetics input file using multiple materials.

Surface Kinetics Pre-processor Input 
MATERIAL WAFER 
SITE/POLY/ SDEN/2.25e-9/
 SI(S) SICL(S) SICL2(S) SICL3(S) 
END 
BULK SI(B)/2.33/ END 
REACTIONS MWOFF 
  CL + SI(S) => SICL(S)              1.0 0.0 0.0 
    STICK 
  CL + SICL(S) => SICL2(S)            0.4 0.0 0.0 
    STICK CL + SICL2(S) => SICL3(S)     0.1 0.0 0.0
    STICK 
END 
MATERIAL WALL 
SITE/METAL/ SDEN/2.25E-9/
  AL(S) ALCL(S) ALCL2(S) 
END 
BULK AL(B)/2.7/ END 
REACTIONS MWOFF 
CL + AL(S) => ALCL(S)             1.0 0.0 0.0 
    STICK 
  CL + ALCL(S) => ALCL2(S)          0.4 0.0 0.0 
    STICK 
  CL + ALCL2(S) + AL(B) => ALCL3 + AL(S)   0.1 0.0 0.0 
    STICK 
    END