Correlation between Surface Structure and Charge Ordering in Magnetite(001) Studied by Scanning Tunneling Microscopy and Spectroscopy

We report the observation on the charge ordering of Fe ions in a magnetite(Fe3O4)(001) film surface by scanning tunneling microscopy and spectroscopy (STM/STS) with a nonmagnetic W tip. The Fe3O4(001) film surface exhibits a B-plane termination with a (√2 x √2)R450 reconstruction. Fe cation rows running along the [110] direction show a wavelike structure. The (√2 x √2)R450 surface reconstruction is originated from the wavelike Fe rows. The current imaging tunneling spectroscopy image shows alternation of two different kinds of current peak with a separation of about 0.6 nm. Each current peak arises from the same local density of states (LDOS) of two Fe ions. The presence of Fe dimers with two different kinds of LDOS provides evidence for the charge ordering of Fe ions with different charge states. STM and STS using a nonmagnetic W tip allow us to correlate the charge ordering pattern with the surface structure