Figure 4

Simulation results for the solution of (3.1) and (3.2), using two species, with initial fractions $f_1=0.3$, $f_2=0.7$, and respective etching rates $A_1=1$, $A_2=2$. The vertical axis represents the fraction of exposed sites at a number of different times; the horizontal axis represents depth into the crystal ($n=0$ is the top of the crystal). The Gaussian-like curves represent the fraction of vacant sites at level n, that is, ${\psi }_n$; dashed curves represent the fraction of vacant sites of species 1 at level n, that is, ${\psi }_n^1$; dot-dash curves represent fraction of vacant sites of species 2 at level n, that is, ${\psi }_n^2$. The vertical lines represent the asymptotic approximation (3.27) for the position of the wavefront, $n_w\sim 1.54t$, neglecting its diffusion.