Origin of a superlattice observed in L i0.9 M o6 O17 by scanning tunneling microscopy

We use scanning tunneling microscopy to study the lithium molybdenum purple bronze (Li0.9Mo6O17) at room temperature. Our measurements allow us to identify the single-crystal cleave plane and show that it is possible to obtain clean cleaved surfaces reflecting the crystal structure without the complications of nanoscale surface disorder. In addition to the crystal lattice, we observe a coexisting discommensurate superlattice with wave vectors q=0.5a∗±0.25b∗. We propose that the origin of the superstructure is a surface reconstruction that is driven by cleaving along a crystal plane that contains in-plane MoO4 tetrahedra connected to out-of-plane MoO6 octahedra through corner-sharing oxygens. When combined with spectroscopic measurements, our studies show a promising avenue through which to study the complex physics within Li0.9Mo6O17.