  Bi$_2$Se$_3$ and Bi$_2$Te$_3$, and these same surfaces covered with Bi films,
are exposed to Br$_2$ and Cl$_2$ in ultra-high vacuum. Low energy electron
diffraction (LEED) and low energy ion scattering (LEIS) are used to investigate
the surface composition before and after halogen exposure. It is found that
Br$_2$ weakly chemisorbs to the Se- or Te-terminated clean surfaces and light
annealing removes the adsorbates restoring the intact surfaces. In contrast,
halogens dissociatively adsorb onto surfaces covered with an additional bilayer
of Bi, having a p-doping effect. Annealing these halogen-covered surfaces at
130{\deg}C causes Bi atoms to be chemically etched away and the surface reverts
to a Se- or Te-termination. This work shows how halogen adsorption and reaction
can be used to modify the surface termination of such materials.
