Surface Species

) node adds detailed surface chemistry to the model. The species can either be surface species (for example, Si(s)) or bulk species (for example, Si(b)). Surface species are not available directly from the context menu, they can only added via a surface reaction. By entering a surface reaction formula containing surface species, the surface species will appear in the Model Builder. The selection for the surface species is locked, and automatically derived from any participating surface reactions. In addition, when all participating surface reactions are deleted in the Model Builder, the corresponding surface species will also be deleted.

Enter a formula for the surface species. The symbols (s) and (b) are reserved to denote surface species or bulk species, respectively. So, to create a silicon surface species simply type Si(s). To create a silicon bulk species type Si(b). COMSOL Multiphysics automatically renames the species to a valid name, for example Si_surf or Si_bulk.

Enter the molecular weight (SI unit: kg/mol) of the surface or bulk species. The default value is , which means that the surface species properties are computed from the values given in the text fields below. There is preset transport data available for some of the typical surface species encountered in plasma processing. Selecting one of these fills in the correct values for the molecular weight and thermodynamic properties automatically.

If the species is a surface species then this section is available.

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Enter the σ (dimensionless) of the species. The default value is 1. This accounts for the fact that larger molecules can occupy more than one active site on a surface.

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The Zk,0 (dimensionless) is the initial fraction of the total sites which is occupied by the species. This must be a number between 0 and 1.

If the species is a bulk species then enter the density (SI unit: kg/m3). The default value is 2329 kg/m3 corresponding to the density of silicon.