Two projects in the PRELUDIUM BIS 2 programme

PhD students led by prof. Mariusz Zdrojek and prof. Marek Wasiucionek will have a chance to take part in a project financed under the PRELUDIUM 2 programme of the National Science Center.

Prof. Zdrojek: Novel van der Waals heterostructures for next-generation nano and optoelectronics.

Two-dimensional materials are atomically thick layers and promising candidates for basic building blocks of new generation nanoelectronics. The best-known example of 2D material is graphene: first to be discovered, Nobel prize-winning, an atomically thin sheet of carbon atoms. Today we know several hundreds of different kinds of 2D materials with various electrical, optical, and thermal properties. This variability combined with their often unusual properties is the key to their applications. This project will focus on how various 2D layers interact with each other by stacking them into artificial, not found in nature towers called van der Waals heterostructures. The project's goal is confirmation of the hypothesis that we can build new devices with specific, needed properties by choosing the right layers, modifying, and stacking them. This approach, when material properties are designed for a particular application, is called material on demand. This project will specifically look into two areas of building electronic devices: electrical contacts, which are the link for the signal between our 3D world and 2D device, and passivation, which deals with protecting the device from the environment. These are essential and unresolved problems that we need to deal with before using 2D materials in the electronic industry. With contacts, we will study how to minimize contact resistance and the nature of electronic transport between metallic contact and 2D layer. We will use various experimental techniques to understand and find the best solution for contacting devices made from 2D materials and van der Waals heterostructures. With passivation, we will study how its presence influences the device performance, find the differences between currently used and new materials for this purpose, and use this knowledge to further improve our device. Expected final results include the building of well-optimized specific devices like field-effect transistors or photodetector. During the project, knowledge about the interaction between layers will be gained and used to design crucial components of electronic devices like contacts and passivation. This project will confirm the hypothesis that with proper design, combination, and modification of 2D layers, one can build highly efficient electronic devices which can be used in the future electronic application.

Prof. Wasiucionek: Complementary experimental and numerical studies on stabilization mechanism of high-temperature delta-Bi2O3 phase down to room temperature confined in amorphous matrix

Today’s technology requires new ‘tailored-on-demand’ materials, which should be optimized to best perform in given applications. It has been long recognized that the properties of these materials depend not only on their bulk chemical and phase composition, but also on their microstructure, especially at nanosized scale. One of many strategies to produce new application-oriented materials is to stabilize their high-temperature advantageous (e.g. highly conducting) crystalline phases down to room temperature, using different synthetic strategies. These are cases of -AgI (an excellent Ag+ ionic conductor, stable at >147C) and -Bi2O3 (an excellent O2- ionic conductor, stable in a 730-825C temperature range). In both cases it is possible to stabilize these phases down to room temperature in form of nanosized crystallites embedded inside respective glassy matrices. Unfortunately, the mechanisms of such stabilization have not yet been reliably and ultimately established. One can only find partial studies on special cases of those phenomena. In this project we plan to fill that fundamental gap by exploring in detail the mechanisms of stabilization of - Bi2O3 down to room temperature. We feel obliged to do that, because we had experimentally discovered that stabilization effect in our studies on thermal nanocrystallization of bismuthate glasses [1]. Therefore, this will be a natural continuation of our previous work. We plan to establish the mechanism of stabilization of -Bi2O3 by carrying out an integral vast program of complementary experimental and computer-modelling studies. The experimental side will include syntheses and many methods which should give a complete information on the structure, phase composition, local order, thermal properties, microstructure at scales of tens nm and below, electrical transport, interfacial structure and dynamics. The numerical calculation side will be focused on finding stability conditions for -Bi2O3 nanoclusters and nanocrystallites embedded inside a glassy phase. The studies will be carried out in cooperation with leading academic and research centers in Poland, Europe (Germany, France) and USA. The experimental methods will include temperature dependent X-ray diffraction, differential thermal analysis (DTA), differential scanning calorimetry (DSC), synchrotron radiation-based XANES/EXAFS absorption spectroscopies, solid state nuclear magnetic resonance spectroscopy (MAS NMR), scanning- and high-resolution transmission microscopies (SEM and HR-TEM), and impedance spectroscopy (IS). Numerical modelling will use molecular dynamics (MD) and/or density functional theory (DFT) approaches. We strongly believe that the ambitious program of these studies will enable us to present a complete, reliable and well-evidenced mechanism of the stabilization of nanocrystallites of a high temperature phase (here - Bi2O3) down to room temperature. We are also convinced that the conclusions of this project will be valuable for other systems in which a high-temperature phase can be stabilized down to room temperature.