Halide adsorption onto Cu(001) electrodes is an ideal system  in which to attempt this measurement, as the halides, Br and Cl, both form simple ordered c(2x2) adlayers on the Cu(001) surface. For both Cl and Br adsorption onto Cu(001) the adsorbates form c(2x2) adlayers, which are simple square structures with a coverage of 0.5 halide atoms per surface Cu atom and adsorption uniquely into the 4-fold Cu hollow site. The c(2x2) cell gives rise to additional surface scattering that is independent from the Cu crystal truncations rods (CTR’s).
In the experiment it is therefore possible to probe the surface Cu atoms, by performing resonant measurements at the ‘anti-Bragg’ positions of the Cu and at the c(2x2) superstructure positions. A shift in the adsorption edge can be seen indicative of a change in the charge state of the surface Cu atoms. More detailed information can be obtained by modelling the experimental data through single atomic charges. Similar experiments were carried out for the Br adsorption on Au(001) and Cuupd halide Au(001) system  for which a difference in bonding, compared to the halide Cu(001) system is expected.
This is the first direct experimental proof of partial charge transfer and subsurface charge distribution at the electrochemical interface. These measurements show that resonant x-ray scattering is an adequate tool to investigate the charge transfer at an electrochemical interface and will shed light on the nature of the chemical bonding at the interface and the role of the double layer.
 Y. Gründer, D. Kaminski, F.Golks ,K. Krug, J. Stettner, O.M. Magnussen et al., PhysRevB. 81 174114 (2010)
 Y. Gründer, P. Thompson, A. Brownrigg, M. Darlington, C.A. Lucas CA. , J. Phys. Chem. C. 116, 6283 (2012)