세미나

Microscopic investigation of model catalyst systems using STM: from a single molecule to nanostructures

Hyun Jin Yang, Ph. D.
hyunjin.yang@lgensol.com , hyunjin.yang@gmail.com
Surface analysis team, Center for Analytical Sciences, LG Energy Solution

Heterogeneous catalysis has been a long-standing subject of surface chemistry, employing the elements of heterogeneous catalysts, i.e. molecules, metallic catalysts and oxide supports, in the form of well-defined surfaces. Scanning tunneling microscopy (STM) has been one of the most powerful tool in atomic scale imaging, revealing not only atomic structures on surfaces, but also spectroscopic information. In this presentation, three model-catalyst studies ranging from molecular adsorption on metal to oxide nanostructures using low-temperature STM will be introduced.
The first part is about how intermolecular interaction of CO molecules chemisorbed on Pt(111) affects the adsorption sites and overlayer structures, eventually to the spectroscopic property of a single molecule inside overlayer structures. Molecularly resolved STM images and single-molecule action spectroscopy reveal the domains of overlayer structure comprised from combination of ontop-adsorbed primary species and bridge-adsorbed secondary species, and shifted vibrational energy of the bridge-adsorbed species due to neighboring interactions.
The second part is about the CeO2(111)-(√3×√3)R30° reconstructed nanoislands prepared under slightly-oxygen-deficient condition, which indicating the formation of Ce=O termination supported by electronic-state imaging with STM, diffraction (LEED), vibrational spectroscopy (HREELS) and DFT calculations. The last part is about various structures of two-atom-thin SiO2 film prepared on metal surfaces, showing crystalline structure to amorphous one. Atomically resolved STM images of bilayer silica beautifully show what ‘amorphous’ structure is, and nanoscale images of the film shows different phases and their interfaces. These case studies not only exhibit the correlation between nanoscale imaging and surface spectroscopies, but also expose hidden information in the bulk spectroscopic information by means of nanoscale imaging.

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