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Plain reactions

A plain reaction can be particle absorption or particle transformation with a given contant sticking coefficient or reaction probability. There is no wall state or surface coverage involved. Reactions which consider the actual surface coverage with different surface materials are described under surface chemistry reactions below. Possible plain reactions are listed in the following:

Simple absorption with sticking coefficient

add_absorption("species", sticking_coefficient);

This simply defines a constant absorption probability of a given species by a sticking coefficient.


# Define a pumping surface for Ar and H2
add_absorption("Ar", 0.2);
add_absorption("H2", 0.05);

Specular reflection

add_specular_reflection("species", probability);

This declares a specular reflection of a given species with a given probability.

Plain reaction with sticking coefficient and reaction products

add_plain_reaction("species", flag, probability, ["rp1", "rp2", ...], [n1, n2, ...]);

This more generalized syntax allows to specify particle absorption and reaction products. The parameters are

  • “species” ⇒ Incoming gas species such as “Ar” or “H2”
  • flag ⇒ Can be 0 or 1. A value of flag==1 means that the incoming species is absorbed, if flag==0 it is reflected at the surface.
  • probability ⇒ A value between [0..1] specifying the reaction probability.
  • [“rp1”, “rp”, ..] ⇒ A comma-separated list of reaction products (use [], if no reaction products are involved)
  • [n1, n2, …] ⇒ The amount of reaction products

Example 1: SiH4 → Si (film growth) + 2 H2 (reaction products given back to the gas volume) with a sticking coefficient of 50%

add_plain_reaction("SiH4", 1, 0.5, ["H2"], [2]);

Example 2: Secondary electron generation with secondary electron coefficient $\gamma=0.1$ by ion impact $Ar^+ \rightarrow Ar + \gamma e^-$

add_plain_reaction("Arplus", 1, 1, ["Ar", "e"], [1, 0.1]);

The emission characteristics of reaction products is by default Maxwellian with a $\cos(\theta)$ like angular distribution. In order to change this behaviour, the same commands for specifying the emission characteristics as in the particle sources can be used.

Example 3: Sputtering with Ar+

add_plain_reaction("Arplus", 1, 1, ["Ar", "e", "Nb", "Ominus"], [1, 0.1, 5, 0.04]);
set_emission_energy("e", 0, 10, 100);     # Electrons are perpendicularly emitted with energies between 0..10 eV 
set_emission_sputter("Nb", 7.39, 1.5);    # Nb is sputtered with Ub=7.39 eV and alpha=1.5
set_emission_sputter("Ominus", 4.5, 1.5); # Creation of negative oxygen ions with a sputter distribution