Chemistry Reference
In-Depth Information
Fig. 21 STM topographic images of CO molecules on 2 ML MgO/Ag(001) imaged with (a)a
metallic and (b) a CO-covered tip (3
3nm
2
, 150 mV, 3 pA). The CO(tip)
CO(sample)
interaction leads to a ringlike appearance of the adsorbates in (b). (c) STM image of a
CO-saturated Au island taken with a CO-covered tip (4
4nm
2
, 100 mV, 3 pA). CO-induced
contrast is only revealed at the perimeter of the Au island [
66
]
Fig. 22 (a) STM topographic image and (b-d) corresponding second-derivative maps of a planar
Au island saturated with CO (7.0
5.5 nm
2
, 10 pA). Due to the metallic tip state, the CO
molecules are not resolved on the island but give rise to distinct energy-loss features at the island
perimeter (c, d). The second-derivative contrast vanishes at bias voltages away from the CO
vibrational modes (b), (e-h) corresponding information for single Au atoms [
66
,
94
]
As mentioned before, no CO is visible on the aggregate in topographic images
taken with a metallic tip. However, CO-related loss signals emerge in the d
2
l/dV
2
maps and produce a bright/dark brim around the island at positive/negative sample
bias (Fig.
22c, d
). Control measurements taken at bias values above or below the
CO frustrated rotation did not produce any d
2
l/dV
2
contrast (Fig.
22b
). The local-
ization of the inelastic signals along the perimeter therefore corroborates the CO
attachment to edge and corner atoms of the Au islands. For comparison, we show
similar information for a single Au atom with adsorbed CO. Here we see a very
similar spectral response indicating the a-top position of CO on the Au monomer
(Fig.
22e-h
).
