In this work the density of states close to the Fermi level $E_{\text{F}}$ of the $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ surface is investigated, by means of scanning tunneling spectroscopy (STS). STS spectra are dominated by two features, located at about 0.5 eV below $E_{\text{F}}$ and 0.9 eV above $E_{\text{F}}$. The comparison with ab initio density-functional theory simulations of the surface electronic structure shows a very good agreement and allows assigning the observed features to minority states of the sample surface.

The oxygen-induced effects on the morphology of out-of-equilibrium iron surfaces have been studied by means of scanning tunneling microscopy and spectroscopy applied to either the Fe(001) or the Fe(001)-p(1\ifmmode\times\else\texttimes\fi{}1)O surface. With respect to the pristine Fe(100) surface, step coalescence is observed upon oxygen exposure when the Fe(001)-p(1\ifmmode\times\else\texttimes\fi{}1)O surface is formed, with a final morphology characterized by wide terraces separated by steps bunches. We have also investigated the surfactant properties of the chemisorbed oxygen by comparing Fe/Fe(001) and Fe/Fe(001)-p(1\ifmmode\times\else\texttimes\fi{}1)O homoepitaxy and analyzing the influence of the oxygen overlayer on the growth kinetics. The intralayer mass transport is found to be unaffected by the presence of oxygen, suggesting oxygen-enhanced interlayer mass transport as a mechanism able to explain the surfactant effect. We attribute both phenomena to the presence of a strained FeO overlayer.

We have investigated the formation of scanning tunneling microscopy (STM) atomically resolved images of the $\text{Fe}\left(001\right)\text{−}p\left(1\times 1\right)\text{O}$ surface. The latter is characterized by a high in-plane symmetry for both oxygen and iron atoms, thus representing a very appealing template for understanding how to distinguish between oxygen and metal atoms in STM images of an oxidized metal surface. We report on the occurrence of a corrugation reversal as a function of the tip-sample distance, and we use the conclusions of such an investigation for interpreting the experimental images of an oxygen vacancy created on the surface. Our experimental work, supported by ab initio density-functional theory calculations, allows us to assess the fundamental role of the local potential barrier in determining the STM image formation.