Monolayer of PtSe2 on Pt(1 1 1): is it metallic or insulating?

Motivated by the recent synthesis of a PtSe2 monolayer by direct selenization of a Pt(1 1 1) substrate and in order to reproduce ARPES experimental results, we investigate if the PtSe2 film could have grown directly on top of the Pt substrate or if some buffer structure separates both of them. We calculate the electronic properties for different growth possibilities and come to the conclusion that the experimental outcome is not compatible with the growth of a PtSe2 monolayer directly on top of the Pt(1 1 1) substrate.

Effect of halogen dopants on the properties of Li2O2: is chloride special?

There is consensus on the fact that one of the main limitations of Li air batteries (LABs) is the insulating character of Li2O2 and that it becomes crucial to explore new conduction paths. Recent studies indicate that doping with chloride increases the ion conductivity of Li2O2, although to a much lesser extent than expected if chloride is assumed to be a donor dopant [Gerbig et al., Adv. Mater., 2013, 25, 3129]. Subsequently, it has been shown that the addition of lithium chloride, LiCl, to the battery electrolyte increases its discharge capacity, while this effect is not observed with other halogens [Matsuda et al., J. Phys. Chem. C, 2016, 120, 13360]. This fact was attributed to an increase in the conductivity of Cl-doped Li2O2, but still the responsible mechanism is not clear. In this work, we have performed first principle calculations to study the effect of the different halogens (F, Cl, Br, I) as substitutional defects on the electronic and transport properties of Li2O2. We have calculated the formation energies of the different defects and impurities and we analysed how they affect the activation barriers and diffusion coefficients. We have demonstrated that the chloride does not behave like a donor dopant, thus explaining the meager increase of the ionic conductivity experimentally observed, and neither does it promote polaron formation and mobility. We have also found that chloride does not present any special behaviour among the halogen series. Our results reveal that all the studied configurations associated with the halogen defects do not derive metallic states nor extra polarons that would increase considerably the electronic conductivity. This is mainly due to the ionic characteristics of the Li2O2 crystal and the capability of the oxygen dimers to adapt its valence rather than to the nature of the dopant itself.

A Two-Dimensional Manganese Gallium Nitride Surface Structure Showing Ferromagnetism at Room Temperature.

Practical applications of semiconductor spintronic devices necessitate ferromagnetic behavior at or above room temperature. In this paper, we demonstrate a two-dimensional manganese gallium nitride surface structure (MnGaN-2D) which is atomically thin and shows ferromagnetic domain structure at room temperature as measured by spin-resolved scanning tunneling microscopy and spectroscopy. Application of small magnetic fields proves that the observed magnetic domains follow a hysteretic behavior. Two initially oppositely oriented MnGaN-2D domains are rotated into alignment with only 120 mT and remain mostly in alignment at remanence. The measurements are further supported by first-principles theoretical calculations which reveal highly spin-polarized and spin-split surface states with spin polarization of up to 95% for manganese local density of states.