Adsorbates on Tio2(110) – What can low Temperature STM Experiments add?
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Date: 07-21-2006
Start Time:
11:00am
End Time: 12:00pm
Speaker: Dr. Markus Lackinger
From:
University of California, Irvine
Location: 414 Schapiro/CEPSR
Hosted by:
Center for Integrated Science
Abstract:
Cryogenic temperatures and a UHV environment provide the conditions for stable STM operation, facilitating high resolution imaging, local spectroscopy, and single atom / molecule manipulation. Combination of these experimental capabilities was utilized to study the interaction of adsorbates with oxygen vacancies on TiO2(110). This type of point defect is common for reducible transition metal oxides and greatly influences their surface chemistry. Since their unexpected catalytic activity was discovered, Au-nanoparticles on TiO2(110) have received considerable attention. Deposition of Au at low temperature inhibits thermally activated diffusion and aggregation, thus leads to adsorption of single Au-atoms. Two different distinctive adsorption sites have been identified through STM imaging and manipulation: Au-atoms either adsorb on bridge sites between five-fold coordinated Ti atoms or in oxygen vacancies, i.e. substituting the missing bridging oxygen atom. Moreover, another characteristic property of oxygen vacancies on TiO2(110) was revealed: When a porphyrin derivative is laterally manipulated to the vicinity of an oxygen vacancy, the peak-position of molecular orbital related resonances in dI/dV spectra shifts to lower energies. This behaviour is consistent with a positive charge localized at the vacancy sites.