  We study the effect of chiral-tunneling in Bernal and Rombhohedral stacked
trilayer-graphene (3LG). Based on the chirality of the electronic bands, at the
K-point, (Rombhohedral) Bernal-3LG exhibits 100% (50%) transparency across a
heterojunction. Utilizing this property, we further investigate the effect of
electron collimation in 3LG. Due to the difference in the Berry's phase, we
show that, Rombhohedral-3LG is a better electron collimator, compared to
monolayer and Bernal-bilayer graphene. Since, Bernal-3LG can be decomposed into
two separate channels consisting of a monolayer and a modified Bernal-bilayer
graphene; the Bernal-3LG is weaker electron collimator, compared to
Rombhohedral-3LG.
