Image of the Month

June 2016

Origin of a superlattice observed in Li0.9Mo6O17 by scanning tunneling microscopy


Figure 1: Zoomed 5 nm image. Using Fourier filtering of the larger raw image, the superlattice is removed, and only the crystal lattice remains. Specifically, in filtering, we selected all of the crystallographic Bragg peaks connected by reciprocal lattice vectors appearing in the FFT. (PHYSICAL REVIEW B 93, 045430 (2016))

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.

Ling Fu,1  Aaron M. Kraft,1  Martha Greenblatt,2  and Michael C. Boyer1,*  (Phys. Rev. B 93, 045430 (2016))

1 Department of Physics, Clark University, Worcester, Massachusetts 01610, USA

2 Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854, USA

Images and data graciously provided by Michael Boyer, Clark University, Worcester, Massachusetts.

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