Florencia Marchini

Surface Porphyrins Metalate with Zn Ions from Solution.

Controlling the metalation of surface porphyrins is a critical process in porphyrin-based devices. Indeed, surface porphyrins are known to metalate in ultrahigh vacuum from codeposited metal atoms or substrate atoms; however, it is not yet known if surface porphyrins could metalate from ions in solution, that is, the most likely environment for porphyrin-based devices. Using X-ray photoelectron spectroscopy we have studied the metalation of monolayers and multilayers of a free-base tetraphenyl porphyrin adsorbed on Au(111) with ions in solution. We found that full metalation with Zn(2+) can be achieved already at room temperature in contrast with the elevated temperatures required for metalation with codeposited metal atoms.

Tuning the electronic properties at the surface of BaBiO3 thin films

The presence of 2D electron gases at surfaces or interfaces in oxide thin films remains a hot topic in condensed matter physics. In particular, BaBiO3 appears as a very interesting system as it was theoretically proposed that its (001) surface should become metallic if a Bi-termination is achieved (Vildosola et al., PRL 110, 206805 (2013)). Here we report on the preparation by pulsed laser deposition and characterization of BaBiO3 thin films on silicon. We show that the texture of the films can be tuned by controlling the growth conditions, being possible to stabilize strongly (100)-textured films. We find significant differences on the spectroscopic and transport properties between (100)-textured and non-textured films. We rationalize these experimental results by performing first principles calculations, which indicate the existence of electron doping at the (100) surface. This stabilizes Bi ions in a 3+ state, shortens Bi-O bonds and reduces the electronic band gap, increasing the surface conductivity. Our results emphasize the importance of surface effects on the electronic properties of perovskites, and provide strategies to design novel oxide heterostructures with potential interface-related 2D electron gases.