Materials
The Trapping Material Class
New Achlys specific material classes are listed below. These are all based on the concept of the trapping material class which is designed to calculate certain material properties required for use with the Achlys kernels, namely:
The diffusion coefficient,
The trapping reaction rate,
The de-trapping reaction rate for each trap,
These parameters are heavily temperature dependant and so a coupled Temperature variable is often required for these material classes. The other input parameters can be seen from the equations below which are required to calculate values for , , and .
is the diffusivity of the species through some material in units of . This is modelled by an Arhhenius relation as given by Eq. (1).
(1)
, in units of , is the reaction rate for the trapping process and is modelled by Eq. (2) where is the lattice constant in and is the number density of solute sites in the material. (2)
, in units of , is the reaction rate for the de-trapping process from the -th trapping site. This is modelled by the Arrhenius type equation as given by Equation Eq. (3) where E is the energy barrier a trapped atom must overcome to leave the site and is referred to as the attempt frequency. (3)
Extrinsic trap creation
For the case where trapping sites are created over time due to particle bombardment some specialised material classes have been developed.
ExtrinsicTransientTrappingMaterial for the case of ongoing bombardment and trap creation
ExtrinsicStaticTrappingMaterial for constant temperature cases after the creation process has ended
ExtrinsicStaticTrappingMaterialRamptingT for cases with a constant temperature ramp after the creation process has ended, for example in the case of thermal desorption