The Electronic Structure of Saturated NaCl and NaI

Authors: Héloïse Tissot JeanJacques Gallet Fabrice Bournel Giorgia Olivieri Mathieu G Silly Fausto Sirotti Anthony Boucly François Rochet

Publish Date: 2015/12/30

Volume: 59, Issue: 5-7, Pages: 605-620

PDF Link

Abstract

The near ambient pressure Xray photoelectron spectroscopy set up installed recently at SOLEIL synchrotron facility is used to study the electronic structure of NaCl and NaI saturated solutions formed on a gold substrate The binding energies of the solution constituents are measured with respect to the Fermi level of the gold substrate The C1s binding energy of the aliphatic contaminant floating at the surface of the solution is an evidence that the Fermi level in the metal and in the solution are aligned The use of the Fermi level common energy reference is an added value with respect to previous works realized with microjets that were calibrated in energy with respect to vacuum level We observe that the water valence molecular levels binding energies and hence the Fermi positioning in the gap of the liquid the Na+ 2s binding energy and even the work function are independent of the nature of the anions The secondary electron energy distribution curves show that the work functions of the two solutions are equal within experimental uncertainty We discuss this point considering the different ion distributions at the surface related to the different size and polarizability of the anions and the possible contribution of carbon contaminants We compare the WF values extracted from the secondary electron edges to alternative measurements using the binding energy of the gas phase O1s or 1b1 spectra referenced to the gold Fermi level The ionization energies referenced to the vacuum level that we obtain by adding the work function to the measured binding energies are in good accord with previously published works using microjets obtained however at much lower solute concentration Finally we discuss the origin of the Fermi level pinning in the liquid band gap and consider the possibility that the H+/H2 redox level is aligned with the metal Fermi levelThe authors express their thanks to Dr Jean Daillant director of Synchrotron SOLEIL for enlightening discussions concerning the surface of electrolytes They also much appreciated the very efficient technical support from Christian Chauvet TEMPO beamline SOLEIL This NAPXPS experiment managed by the LCPMR team Université Pierre et Marie Curie was funded by the IledeFrance Region Photoémission Environnementale en IledeFrance SESAME n°090003524 by the Agence Nationale de la Recherche Surfaces under Ambient Pressure with Electron Spectroscopies ANR 08BLAN0096 and by the Université Pierre et Marie Curie Synchrotron SOLEIL supported the integration of the setup to TEMPO beamline LABEX MiChem UPMC also partially funded the experiment HT received a PhD scholarship from Synchrotron SOLEIL

Keywords: