**Acknowledgements**

This work has been financed by the European Commission under projects of Horizon 2020 program BET-EU (proposal 692373), ERC Start Grant NewFun (proposal 640598), and SYMBIOTIC (proposal 665046 and 60643); the FEDER funds through the COMPETE 2020 Programme and Portuguese Science Foundation (FCT-MEC) through the Projects EXCL/ CTM-NAN/0201/2012, EXPL/CTM-NAN/1184/2013, UID/CTM/50025/2013 and PTDC/CTM-ENE/5125/2014. A. T. Vicente acknowledges the support from the Portuguese Foundation for Science and Technology (FCT) and MIT-Portugal through the scholarship SFRH/ BD/33978/2009. D. Gaspar acknowledges the support from AdvaMTech PhD program scholarship PD/BD/52627/2014. M. J. Mendes acknowledges support from EU FP7 Marie Curie Action (FP7- PEOPLE-2013-IEF) through the DIELECTRIC PV project (Grant No. 629370). A. Araújo acknowledges the FCT through the scholarship SFRH/BD/85587/2012. The authors want to thank their colleagues Ana Pimentel for DSC-STA measurements, Daniela Gomes for SEM images acquisition, and Rita Branquinho for helping with 3D profilometer data acquisition.
