Scanning tunneling microscopy study on a BC₃ covered NbB₂(0 0 0 1) surface

We have investigated a BC₃ covered NbB₂(0 0 0 1) surface using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and low energy electron diffraction (LEED). The STM images reveal characteristic features of a Moiré pattern reflecting an incommensurate relation of the BC₃ sheet with the substrate: bright protrusions with the periodicity of the substrate lattice are modulated in intensity with the periodicity of the BC₃ lattice. As a result, the surface exhibits nm-scale patchy regions with either the √3 × √3 or the 1 × 1 structure of the substrate. The two-dimensional Fourier transformation pattern of the STM image is consistent with the LEED pattern proving the epitaxial and incommensurate relationship between BC₃ surface sheet and substrate. No feature of a predicted superconducting gap was found in STS spectra measured at 5 K.