On January 30th 2014 Vitali Grozovski will defence his doctoral thesis "Adsorption of organic molecules at single crystal electrodes studied by in situ STM method".
Prof. Enn Lust, University of Tartu
Silvar Kallip, PhD, University of Tartu
Prof. Antonio Rodes, University of Alicante, Spain
Nowadays all modern electronic devices like cellphones and computers have trend to be miniaturized, but at the same time offering a higher level of performance. This inevitably leads towards the need for smaller electronic components and memory modules, providing at the same time better performance and higher memory capacity. Bringing a single transistor to the size of one molecule can drastically increase a memory module capacity and decrease the size of single electronic components. This idea has a bright future offering more performance in a smaller package. To understand how it works, one has to consider an ideally flat metal surface, where organic molecules can form a compact single layer, as a result of the adsorption phenomena. Every single molecule in such configuration can be considered as a single transistor and a square centimeter of such memory chip will outperform any present one by a million times in terms of capacity. This is a good example why adsorption studies are important topic in modern science and technology.
Modern surface analysis methods can provide a deep insight over adsorption processes. Therefore, in the present work the state of the art of atomic level surface studies applying the in situ scanning tunneling microscopy (STM) have been implemented. It is capable of visualizing surface structure under atomic resolution and every single molecule adsorbed is visible. This technique provides important information about the state of the surface structure, for example, is it a rough or atomically flat. The great benefit of in situ STM method is that one can observe the changes at the surface in real time, like the visualization of the adsorption of organic molecules under potential control experiment.
During this PhD work several subtopics were considered. The first one was to characterize the surface structure of the antimony (111) single crystal electrode by in situ STM. It was proven, that antimony has a very similar structure to the bismuth (111) single crystal, and both of them are very well suitable objects for adsorption studies of the organic molecules. Bismuth and antimony are also a good substitution as catalytically active materials for replacement of more poisonous and dangerous mercury.
The second topic studied was the adsorption visualization of thiourea at bismuth (111) single crystal electrode. Thiourea is an important compound having wide application in the modern technology. Thiourea is used as a brightening agent in electroplating - giving a very smooth electrodeposited surfaces, and as a corrosion inhibitor - forming adsorbed polymer layers at the metal surfaces. In this work electrochemical in situ STM and impedance spectroscopy was used to study the adsorption kinetics of thiourea at bismuth surface. The thermodynamic adsorption parameters were analyzed and the adsorption limiting stages were defined. In situ STM data revealed that, differently from 4,4'-bipyridine, thiourea does not adsorb in a compact two dimensional layer, but thiourea adsorbs only at the surface defects of bismuth surface.
The third topic studied was 4,4'-bipyridine molecule adsorption at well-defined single crystal bismuth (111) electrode. 4,4'-bipyridine related studies are important due to interesting electronic properties of 4,4-bipyridine molecule, which can be implemented in fabricating as nanoelectronic circuits and high density memory modules. Therefore, in present work the adsorption of 4,4'-bipyridine at bismuth surface was determined by the electrochemical in situ STM method and additionally modeled with the modern computation chemistry approximation - density functional theory. It was found, that experimental data are in good agreement with theoretical calculations and provide an essential information about the 4,4'-bipyridine single layer formation at bismuth (111) single crystal electrode.