  Elemental phosphorous is believed to have several stable allotropes that are
energetically nearly degenerate, but chemically reactive. To prevent chemical
degradation under ambient conditions, these structures may be capped by
monolayers of hexagonal boron nitride ({\em h}-BN) or graphene. We perform {\em
ab initio} density functional calculations to simulate scanning tunneling
microscopy (STM) images of different layered allotropes of phosphorus and study
the effect of capping layers on these images. We find that protective
monolayers of insulating {\em h}-BN allow to distinguish between the different
structural phases of phosphorus underneath, even though the images are filtered
through only nitrogen atoms that appear transparent. No such distinction is
possible for phosphorus films capped by semimetallic graphene that masks the
underlying structure. Our results suggest that the real-space imaging
capability of STM is not hindered by selected capping layers that protect
phosphorus surfaces.
