[Zurück]

H. Noei, D. Franz, M. Creutzburg, P. Müller, K. Krausert, E. Gránäs, R. Taube, F. Mittendorfer, A. Stierle:
"Monitoring the Interaction of Graphene Supported Ir Clusters by Vibrational Spectroscopy and Desnity Functional Theory Calculations";
The Journal of Physical Chemistry C, 122 (2018), S. 4281 - 4289.

The interaction of carbon monoxide (CO) with
graphene supported Ir cluster (Ir/graphene/Ir(111)) and a
Ir(111) single crystal surface was studied by infrared
reflection−adsorption spectroscopy (IRRAS). The cluster
morphology was characterized by scanning tunneling microscopy
and density functional theory (DFT) calculations
predicted the adsorption frequencies of CO molecules on
the Ir single crystal surface and clusters. After exposing the
clean Ir(111) surface to CO at 195 K, one intense vibrational
band is observed at 2043 cm−1, which is assigned to on top
CO species. This band shifts to a much higher frequency at
2082 cm−1 at higher CO exposure. After exposing clean
graphene/Ir(111) to CO at 195 K, no CO band was observed
in the IR spectra, which confirms a full graphene layer over the Ir(111) surface. However, CO molecules adsorb on Ir clusters
supported on graphene/Ir(111) at 195 K. For the 0.05, 0.1, 0.15, and 0.2 ML Ir clusters, two IR bands were observed at 2060 and
2088 cm−1, 2050 and 2070 cm−1, 2048 and 2070 cm−1, and 2052 and 2070 cm−1, respectively. The IR bands at lower frequencies
are assigned to the CO on one-layer high clusters, and the IR bands at higher frequencies are assigned to the CO adsorption on
two- or several-layer high clusters. The IR frequencies of CO adsorbed on clusters are shifted to lower wavenumbers compared to
those observed on the single crystal surface, which is in agreement with DFT calculations. The IRRAS data recorded after CO
adsorption on Ir clusters at different temperatures demonstrate that CO species are stable up to 350 K, although the intensity of
CO on top one-layer high cluster reduces largely, indicating CO-induced cluster sintering.