 |
|
|
|
|
|
|
|
|
||||
|
|
|
||||||||||
| Diffusion | ||||||||||||
| Two
Solutions to Fick's Second Law
· Two diffusion conditions are of major interest: * A fixed mass of material is deposited on the surface and it is allowed to diffuse into the bulk * The surface concentration of the diffusing species is kept constant as it diffuses into the bulk. · The solution of Fick's second law for these two conditions gives rise to different profiles for the diffusing species. · For a fixed mass, M, of A-atoms deposited on the surface of a B -matrix the surface concentration of A-atoms decreases as diffusion proceeds but the total area under the concentration spatial profile is constant. · For a fixed surface concentration of A-atoms diffusing into an B-matrix the concentration in the sample increases with time until the complete sample is at the surface concentration. |
||||||||||||