Ammonia adsorption on iron phthalocyanine on Au(111): Influence on adsorbatesubstrate coupling and molecular spin
Cristina Isvoranu, Bin Wang, Evren Ataman, Karina Schulte, Jan Knudsen, Jesper N.
Andersen, Marie-Laure Bocquet, and Joachim Schnadt
Supplementary Information
Adsorption geometry of FePc on Au(111): N 1s XAS
XAS experiments (Figure S1) performed on monolayer of FePc show that the FePc
molecules are oriented with the molecular plane parallel to the Au(111) surface. According to
the dipole selection rule, the resonances in the N 1s x-ray absorption spectra correspond to
excitations from the atomic N 1s core orbitals to unoccupied π* and/or σ* molecular orbitals,
with maximum intensity when the electric field vector E is oriented along the final state
orbital.S1 In the present case, the maximum intensity of the π* resonances is observed for
grazing photon incidence with respect to the sample surface (65° from the surface normal)
and the minimum intensity for normal incidence (0° with respect to surface normal). The
opposite angular dependence is observed for the σ* resonance intensities. This information,
together with the knowledge that FePc are planar molecules, with the π* orbitals
perpendicular to the molecular plane and the σ* orbitals in the molecular plane, prove a flat
geometry of the FePc molecules on the Au(111) surface. The double peak feature at around
399.5 eV present in the normal incidence geometry was also observed in previous studies of
ours involving mono- and multilayers of FePc on HOPGS2 and Au(111)S3 and has also been
reported in literature before.S4-S6 A DFT study performed on an isolated FePc molecule
assigned the feature to a low-lying * resonanceS6 in agreement with the here observed angle
behavior.
Figure S1. N 1s XAS spectra for an FePc monolayer on Au(111) taken in two different
geometries, with the photon beam in normal incidence with respect to the sample (0° with
respect to surface normal), and grazing incidence (65° with respect to surface normal). The
angular dependence of the resonances shows a flat geometry of the FePc molecules on the
Au(111) surface. The measurements were carried out in Auger yield at a photon energy
resolution of around 160 meV.
Comparison of mono- and multilayers of FePc
Figure S2 shows a comparison of the C 1s and N 1s x-ray photoelectron spectra of the FePc
mono- and multilayers. In both cases, the mono- and multilayers spectra basically show the
same line shape, only the peak position is approximately 0.4 eV higher in binding energy for
the multilayer.
Figure S2. Comparison of the N 1s and C 1s x-ray photoelectron spectra obtained on monoand multilayer FePc. A polynomial background was subtracted from all spectra.
Adsorption geometry of FePc on Au(111) after adsorption of NH3: N 1s XAS
N 1s XAS measurements performed after adsorption of 5 L of ammonia (Figure S3), which
corresponds to a coverage lower than the iron saturation coverage, show that the FePc
molecules remain flat on the Au(111) surface. The two new resonances at 400.8 and 402.7
eV, observed in normal incidence geometry, are attributed to ammonia orbitals.
Figure S3. N 1s x-ray absorption spectra obtained on NH3/FePc/Au(111) (NH3 dose 5L,
lower than the dose necessary to obtain iron saturation). Two geometries were used for the
experiments, grazing photon incidence (65° incidence) and normal photon incidence (0°
incidence) with respect to the surface normal.
Influence of NH3 adsorption on the macrocycle: C 1s XPS
The C 1s spectra in Figure S4 show that after ammonia adsorption shifts occur for both the
low-binding energy peak of the benzene carbon atoms and the higher binding energy peak of
the nitrogen-bonded carbon atoms. The low-binding energy peak remains at the shifted
position even for increasing coverages, while the high binding energy peak shifts back to its
original position. While it is difficult to elucidate the exact reason for the observed binding
energy shifts, in particular the shift of the low-binding energy component suggests that there
might exist ammonia species or small ammonia clusters weakly bonded to the isoindole units
of the molecule.
Figure S4. C 1s photoelectron spectra of one monolayer of FePc on Au(111) before and after
adsorption of different amounts of ammonia (up to 20 L as indicated). A Shirley background
was subtracted from the spectra. The bottom spectrum is the C 1s photoelectron spectrum for
an FePc monolayer.
Evaluation of water contamination
The level of water contamination upon NH3 dosing is quantitatively evaluated in Fig. S5.
Figure S5. O 1s and C 1s photoelectron spectra after dosing 5 L NH3. The spectra are
essentially raw data, but all measurement-dependent parameters have been normalized out.
The intensities are directly comparable, and, taking into account that one phthalocyanine
molecule contains 32 carbon atoms, it is found that the contamination level is approximately
one water molecule per three phthalocyanine molecules. This was the worst level of water
contamination observed in our measurements; in all other measurements the level of
contamination was lower.
(S1) J. Stöhr, NEXAFS Spectroscopy (Springer, Berlin, Heidelberg, New York, 1996).
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and J. Schnadt, J. Chem. Phys. 131, 214709 (2009).
(S3) C. Isvoranu, E. Ataman, K. Schulte, J. Knudsen, J. N. Andersen, and J. Schnadt, unpublished work.
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