Surface atomic structure characterization of SnSe and black phosphorus using selected area uLEED-IV via LEEM

Selected area diffraction intensity-voltage ($\mu$LEED-\textit{IV}) analysis via low energy electron microscopy (LEEM) has the combined functionality of atomic surface structure determination and $\mu$m area selectivity, making it ideal for structural investigations of 2-D materials. SnSe thin films have been predicted and observed to be topological crystalline insulators. Previous studies suggested that SnSe has a preferred Se-terminated surface configuration. Using $\mu$LEED-\textit{IV}, we determined that SnSe has, on the contrary, a stable Sn termination. This surface is stabilized through an oscillatory interlayer relaxation, which agrees with previous DFT predictions. Black phosphorus (BP) has an intrinsic layer-dependent bandgap ranging from 0.3 eV to 2 eV. Previous STM and DFT studies suggested BP surfaces have a buckling of 0.02 \AA\ to 0.06 \AA. We experimentally determined that the surface buckling of BP to be near 0.2 \AA. We further propose, using DFT calculations, that this large surface buckling is induced by the presence of surface defects. The influence of this surface buckling on the electronic structures of BP is under investigation.