Speaker
Description
Surface diffusion and chemical reactions on surfaces are important fundamental processes in catalysis. To fully understand these processes at the atomic scale, real time and real space observations are crucial. Since the first experimental evidence for surface diffusion 100 years ago [1], a variety of methods evolved to study atomic processes on well-defined surfaces. The prominent approach of Scanning Tunneling Microscopy (STM) exhibits remarkable lateral resolution. However, so far time resolution is the limiting factor in STM. Due to the low frame rate, dynamic processes are often not accessible with conventional STM measurements. We show a pathway to increase the frame rate in STM by using custom programmed high-speed electronics and an innovative spiral scan pattern. With our high-speed STM, so far frame rates of up to 120 Hz were achieved. Diffusion processes in dense oxygen adlayers on Ru(0001) at room temperature are observed. For example, the oxygen hopping rate in the O(2x2) adlayer is found to be in the order of 0.1 – 1 Hz, which is 5 to 100 times faster than previously reported literatue values [2]. Theoretical density functional theory (DFT) calculations predict similar hopping rates at 300 K. The proposed diffusion pathway of the oxygen atom includes metastable intermediate states. Thanks to the characteristics of the spiral scan geometry, we could resolve the occupation of such an intermediate state. For data visualization and image analysis we developed fully python based software. In this software, we incorporated automatic and interactive network analysis tools. These tools enable the analysis of future measurements on oxide network formers. The aim is to resolve dynamic structural changes within the atom network as a function of temperature. The dynamic changes could lead to a transformation of the crystalline phase to a vitreous network - or vice versa. Observing and analyzing these structural changes at the atomic scale would lead to more profound understanding of the nature of the vitreous, glassy state.
[1] Volmer, M. and Estermann, I. (1921). Zeitschrift für Physik, 7(1), 13-17
[2] Wintterlin, J. et al. (1997). Surface science, 394(1-3), 159-169 and references therein.
| Abstract Number (department-wise) | MP 05 |
|---|---|
| Department | MP (Meijer) |
