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Supported metal particles probed individually: An STM study
Niklas Nilius1
Department of Physics, University of Oldenburg, Germany
[email protected]
Metal deposits on oxide supports are the active chemical elements in most heterogeneous catalysts and therefore in the focus of research for decades. Their characterization is often realized by non-local spectroscopic techniques, which generates problems due to the unavoidable
size and shape distribution of particles on surfaces. The scanning tunneling microscope
(STM) enables a local view on metal particles and provides a versatile toolbox to probe their
atomic structure, electronic properties as well as optical response.
In my talk, I survey multiple characterization schemes of metal particles with the STM. Using
thin-film oxide supports, e.g. MgO, the nucleation and growth regime of ad-metals is examined, putting special emphasis on the role of oxide defects. I demonstrate how strain patterns
arising in oxide films can be exploited to produce self-assembled particle arrays with high
quality [1]. Conductance spectroscopy with the STM is the method of choice to probe the
electronic structure of metal deposits. In the size limit below 100 atoms, the particles are governed by quantum-well states, the energy and orbital shape of which can be approximated
with simple particle-in-a-box models [2]. A particularly interesting class of electronic states
develops at the boundary of metal deposits that host excess charges due to electron exchange
with the support. The states are highly susceptible to interact with adsorbates and are of relevance for the chemical response of the ad-particles. I will discuss how small shifts in the energy of these states can be used to analyze the nature of molecule-metal interactions, being
either of physisorptive or chemisorptive character [3]. A short outlook into possibilities to
probe the optical properties of single metal particles with STM luminescence-spectroscopy
will conclude my talk.
(a) Topographic
and (b) conductance maps of an
Au particle on
showing the bias
evolution of
patterns inside
the island
(11×11 nm2).
[1] S. Benedetti , F. Stavale , S. Valeri , C. Noguera, H.-J. Freund , J. Goniakowski, N. Nilius, Adv. Funct.
Mat. 23, 75 (2013).
[2] X. Lin, N. Nilius, H.-J. Freund, M. Walter, P. Frondelius, K. Honkala, H. Häkkinen, Phys. Rev. Lett.
102, 206801 (2009).
[3] C. Stiehler, F. Calaza, W.-D. Schneider, N. Nilius, H.-J. Freund, Phys. Rev. Lett. 115, 036804 (2015).
Semester Test Study Questions
Semester Test Study Questions