Supplementary material
In order to estimate the charge transfer quantitatively, we draw on the semi-empirical model for binary metal
alloys described in the work (Watson et al. 1979). According to this model the shift of the binding energy of the core
level ΔEi in the sample relative to metal can calculate by the following formula:
∆𝐸𝑖 = ∆𝐸𝐹 − ∆𝐸𝑟 − (∆𝑛𝑠 𝐹 0 (𝑖, 𝑠) + ∆𝑛𝑑 𝐹 0 (𝑖, 𝑑) − 𝛿𝑛𝐹𝑙𝑎𝑡𝑡 )
(1)
where ∆𝐸𝐹 is the difference of Fermi levels between metal and the sample, ∆𝐸𝑟 is the difference of the final-state
relaxation energies in the presence of a core hole in metal and the sample, and the third term in brackets describes the
change of the inner potential at the electron transfer. Here the Δns, Δnd and 𝛿𝑛 are the changes in the number of the
conductive s and p electrons (s), d electrons (d), and charge on the atom due to the charge transfer on the neighboring
atoms 𝛿𝑛 = ∆𝑛𝑠 + ∆𝑛𝑑 , respectively; F0(i,s) and F0(i,d) are Coulomb integrals between a core electron (i= Ir 4f or Pd
3d) and the d electrons (d) or similar for the s and p electrons (s); Flatt is Madelung -type potential.
The difference of the Fermi level can be estimated as ∆𝐸𝐹 = −𝛥𝛷, where 𝛥𝛷 is the change of the work
function which is, by assumption, linearly dependent on the sample composition of the metal and alloy. The values of
the work functions for polycrystalline Pd and Ir (averaged over faces) are 5.55 eV and 5.59 eV (Holzl and Schulte
1979). This means that for our estimations we can neglect the change of this value.
The results of the theoretical calculations in the work (Castellani et al. 1988) were invoked to estimate the
change of the relaxation energy. Although the data for the Pd-Ir system are missing in this work, it was stated that the
relaxation energy is a smooth function of the composition and determined by Wigner-Seitz radius rs (in Bohr radius).
Because for Ir rs=2.24, we can propose that the relaxation energy for the Pd-Ir system is not so many as for the Pd-Cu
system (for Cu and Pd rs=2.67 and 1.99, respectively). Then, for the system of composition PdIr the relaxation energy
is no more than 0.1 eV for Ir and more than -0.5 eV for Pd. Indeed, our estimation of the change of the relaxation
energy for Pd from the measurement of Auger parameter Δα gives - 0.3 eV relative to the metal according to the
relation (Mason 1983):
Δα = 2ΔEr
(2)
The values of Coulomb integrals for solid Pd( F0(3d,5s) =12.9 eV and F0(3d,4d)=18.4 eV) are taken from the
work (Cho et al. 1995). For Ir atomic Coulomb integrals (F0(4f,6s) = 19.2 eV and F0(4f,5d)=19.9 eV)) are estimated
according to the method described in the work (Watson et al. 1979) taking into account the database (Lu et al. 1972).
Renormalization of Coulomb integrals for Ir due to the change of the wave function in solid has been performed by
analogy with the results in the work (Cho et al. 1995). In result we obtain for solid Ir F0(4f,6s) = 12.7 eV and
F0(4f,5d)=14.5 eV.
Parameter Flatt has been estimated as a charge placed on an atomic sphere from the relation(Cho et al. 1995):
Flatt=e2/r
(3)
where e is an electron charge, r is a metallic radius. For Pd and Ir we obtain Flatt = 10.5 eV and 10.7 eV (rPd = 1.38 Å
and rIr =1.36 Å).
The value Δnd for Ir can be derived from the area of the white line in the Ir L 3 XANES spectrum according to
the method published in the works (Qi et al. 1987; Jeon et al. 1989). In line with these experimental results, the loss of
one 5d electron corresponds to the increase of the white line area in the L 3 edge by 3 eV. Since our experimental data
show the increase of the white line area by 0.8 eV in comparison to Ir metal foil; therefore, for Ir the value Δnd is 0.27. From Equation 1 we obtain for Ir the values Δns = 0.5 and the total charge transfer on Ir δn= 0.23.
For quantitative estimations for Pd we use the electronegativity relation and the experimental shift ΔEPd3d =
0.3 eV. Finally, for Pd Δnd = 0.09, Δns = - 0.32, and δn= - 0.23.
References
Castellani NJ, Leroy DB (1988) Final state core level binding energy shifts in binary alloys. Z Phys B 71:315-319.
Cho EJ, Lee S, Oh SJ, Han M, Lee YS, Whang CN (1995) Unoccupied states and charge transfer in Cu-Pd alloys
studied by bremsstrahlung isochromat spectroscopy, x-ray photoelectron spectroscopy, and LIII absorption
spectroscopy. Phys Rev B 52:16443-16450.
Holzl J and Schulte FK (1979) Work function of metals in Tracts in Modern Physics Springer: Berlin, Germany 85.
Jeon Y, Qi B, Lu F, Croft M (1989) Transition-metal (Au, Pt, Ir, Re) bonding to Al,Si,Ge: X-ray-absorption studies.
Phys Rev B 40:1538-1545.
Lu CC, Carlson TA, Malik FB, Tucker TC, Nestor CW (1972) Relativistic Hartree-Fock-Slater eigenvalues, radial
expectation values, and potentials for atoms potentials for atoms. Atomic Data 3:1-131.
Mason MG (1983) Electron structure of supported small metal clusters. Phys Rev B 27:748-7614.
Qi B, Perez I, Ansari PH, Lu F, Croft M (1987) L2 and L3 measurements of transition-metal 5d orbital occupancy,
spin-orbit effects, and chemical bonding. Phys Rev B 36: 2972-2975.
Watson RE and Perlman ML (1979) X-ray photoelectron spectroscopy application to metals and alloys, in Structure
and Bonding. Springer, Berlin, Germany 24:83-132.