Alexander Gouralnik

Title : Mg2Si film growth paradigm: How and Why. Perfect Mg2Si films for light and heat conversion into electricity

Abstract:

The narrow band silicide Mg₂Si attracts attention of researchers because it has good perspectives for applications in solar cells and thermoelectric elements, consists of ecologic, abundant and rather cheap components. However, the UHV synthesis of Mg₂Si films on Si surface is problematic: at low T magnesium does not intermix with Si but at high temperatures (HT) the deposited Mg re-evaporates without formation of the film. Basing on the analysis of the deposition kinetics and Mg-Si convex hull, we explain how and why Mg₂Si can be grown on Si at HT. The films obtained by ultra-fast (pulse-type) deposition at T ≈ 400 °C have the best to date quality.

In addition, we demonstrate the rational method of investigation of various temperature-dependent processes on surface or interface. If the sample has a wedge-shaped temperature distribution on the surface, the processes can be studied in the whole T range simultaneously, in a single experiment. Thus, the number of experiments necessary for achieving the result can be radically reduced. As an example, we demonstrate that for the deposition rate of ~ 10000 nm per second the Mg₂Si film forms only on the sample area where T < 484 °C. The mean residence time of a Mg atom on Si(111) at 480 °C is estimated as ~ 10^-6 s. The approach used in our experiments can be suitable for investigations of many T-dependent processes in other systems.

What will audience learn from your presentation?

• Analyses of ab initio calculated convex hull can be useful for creating perspective experimental paradigms and technological approaches.
• The delivered simple method of ultra-fast (pulsed) deposition makes it possible to deposit highly volatile elements on Si surface at high temperatures. Moreover, such films can have better crystal quality.
• The demonstrated method of ultra-fast deposition of Mg onto a Si sample with a temperature gradient immediately yields the precise T limit above which the film does not grow at such deposition rate.
• The paradigm of samples with T gradient can be widely used for studying various temperature-dependent processes on surfaces and interfaces. It allows radical reducing of the time and resources consumed for obtaining the necessary result.

Biography:

Alexander Gouralnik studied physics in Leningrad (St. Petersburg) State University, Russia, and graduated as MS in 1976. He then joined the research Laboratory of Microstructure Control Growth at the Institute of Automation and Control Processes, Far East Branch of the Russian Academy of Sciences (IACP FEB RAS). Now he is studying optics and electro-physics of silicide films and nanostructures on the Si surface. He has published more than 30 research articles in SCOPUS and WOS journals.