CSIC and Nano-Bio Spectroscopy Group University of the Basque Country UPV/EHU Department of Experimental Physics, Freie Universität, Berlin Abt. Physikalische Chemie, Fritz-Haber-Institut, Berlin Michael Meyer, M. Bertin, U. Bovensiepen and M. Wolf Properties of photoinduced states in water covered Alkali atoms on a Cu(111) surface A. Iacomino, A. Perez Paz, A. Rubio ETSF YRM 2013 Budapest - Hungary

Outline Motivations & Objectives Measurements & Experimental data Theoretical analysis Conclusions & ongoing work

ETSF YRM 2013 Budapest - Hungary Motivations 1.Water ice has plenty of sites for excess electrons from Cu(111) surface, thus promoting chemical reactions

ETSF YRM 2013 Budapest - Hungary Motivations 1.Water ice has plenty of sites for excess electrons from Cu(111) surface, thus promoting chemical reactions 2.Alkali metals donate electrons to the Cu(111) and decrease the work function, thus increasing electron excitation from the surface control reactivity towards electronegative molecules

ETSF YRM 2013 Budapest - Hungary Motivations 1.Water ice has plenty of sites for excess electrons from Cu(111) surface, thus promoting chemical reactions 2.Alkali metals donate electrons to the Cu(111) and decrease the work function, thus increasing electron excitation from the surface control reactivity towards electronegative molecules 3. Low coverages regime under UHV conditions are easier to control than liquids and gases solutions atmospheric pollution reactions stratospheric ionizing radiation and ozone depletion geminal stage of heterogeneous photocatalysis

ETSF YRM 2013 Budapest - Hungary Objectives - We need an electron reservoir → metal Cu(111) - Excitations in the desired energy window → alkali atoms - Long lifetime of excitations → wait and see Alkali on Cu(111) reduce  → lower photon energy Excited states couple with CB bands and quickly decay --> need gap above E F - Cu(111) gap at Γ

ETSF YRM 2013 Budapest - Hungary Measurements Time Programmed Desorption Work Function variation vs Exposure -we know the number of water molecules adsorbed on alkalis No dissociation of water below critical alkali coverage (  crit ~ 0.2 ML) We still do not know the configuration of adsorption How do polar molecules like water interact with the positively charged alkali ions? preferential binding at Alkali ions

ETSF YRM 2013 Budapest - Hungary Theoretical Approach DFT code: Quantum-ESPRESSO (PW representation, Ultrasoft PP) Slabs in supercell: 5x5 Cu(111), 6 layers (Cu fcc -> cu111 hcp) Minimum size of solvation shell to stabilize an excess charge Alkalis Coverage: 1/25=0.04 Na → 0.09 ML (1ML = 3/2 x 3/2) K → 0.16 ML (1ML = 2x2) Cs → 0.16 ML (1ML = 2x2) Water Coverages: 1 H2O x Alk Atm → BL water 6 H2O x Alk Atm → 0.28 BL water WARNING: Critical alkalis Coverage for water dissociation is 0.2 ML

ETSF YRM 2013 Budapest - Hungary Optimized Structures - H 2 O molecules are in plane - H atoms toward surface Cu - 1 H 2 O on top of alk less stable - Alk lifted up - 1 st water shall: 5 H 2 O molecules others through H bonds Ice on Cu(111)

ETSF YRM 2013 Budapest - Hungary How Geometry affects the charge redistribution Δρ=ρ tot -(ρ surf +ρ cl ) Δρ=ρ tot (3H 2 O)-ρ tot (0) - electron donation and redistribution is quite unaffected by water addition

ETSF YRM 2013 Budapest - Hungary How to explain experimental findings

ETSF YRM 2013 Budapest - Hungary (Boltzmann-like) Population distributions = 2

ETSF YRM 2013 Budapest - Hungary (Boltzmann-like) Population distributions = 2 1- Fix overall density 2- Consider only irreducible combinations 3- Discriminate in Energy (most/least stables) 4- Attribute fictitious T (T=293 K ~ 25 meV) 5- Attribute weight 1 to max stable 6- Total ΔΦ and final e - peaks from averages

ETSF YRM 2013 Budapest - Hungary (Boltzmann-like) Population distributions

ETSF YRM 2013 Budapest - Hungary (Boltzmann-like) Population distributions s states wet states

ETSF YRM 2013 Budapest - Hungary (Boltzmann-like) Population distributions + configurations s states wet states

ETSF YRM 2013 Budapest - Hungary