Tailoring of 2D materials beyond graphene

This project aims to understand and manipulate two-dimensional structures beyond graphene in a pursuit for establishing materials with tailored properties for future applications. The discovery of graphene in 2004 soon lead to the separation of other mono-layers from their conventional layered bulk crystals, e.g., hexagonal boron nitride (h-BN) and molybdenum disulphide (MoS 2 ) with a promise for many more especially in the family of transition metal dichalcogenides. We also recently discovered a novel two- dimensional silica (SiO 2 ) glass structure which grew on a graphene support. Also first controversial reports of silicene a graphene-like two-dimensional silicon structure have been recently published. Several fundamental scientific questions related to this new class of materials are waiting to be answered, but also the prospect of novel applications is enthralling. Overall, the relatively young field of two-dimensional materials is quickly gaining momentum. Our past research among graphene and other carbon nanostructures has highlighted the importance of incorporating atomistic simulations and state-of-the-art atomic resolution microscopy and spectroscopy techniques to obtain complete understanding of these materials and especially ways to manipulate them. Within this project, we plan to extend our previous work to new frontiers including single-layer transition metal dichalcogenides and other novel materials. We further aim at developing post-synthesis methods for controlling the properties of these materials to pave the way for actual applications in future electronics. Our goals can be divided into following broad themes: 1) Study of dynamic morphological modifications in two-dimensional materials to gain control over their atomic structure; 2) Post-synthesis manipulation of these materials by adding foreign atoms and molecules; 3) Assessing the relationship between the actual atomic structure and the mechanical and electronic properties for reproducible manipulation to obtain materials with tailored properties. This project will strengthen the bonds between experiments and theoretical research by allowing an expert on modelling of defects and dynamics of carbon nanomaterials Dr. Jani Kotakoski to join the recently established experimental group of Prof. Jannik C. Meyer at the University of Vienna. This project will incorporate in the same research group a state-of-the-art electron microscopy setup and atomic-scale understanding of the relevant processes occurring in the microscope to allow University of Vienna to assume a unique position in the highly competitive field of physics of low-dimensional materials. While the team at University of Vienna will significantly benefit from the additional expertise, this project also allows Dr. Kotakoski to strengthen his knowledge on the experimental methods including sample growth and preparation, electron microscopy as well as engineering. Overall, the project will have a significant impact both on personal level for the involved researchers as well as more broadly on the Austrian excellence and visibility in research topics involving low-dimensional materials and development of nanoelectronics.

It has been said that crystals are like people: defects are what makes them interesting. One of the reasons for this is that the presence of irregularities in the atomic structure affects the properties of the material. In this project, we have studied defects in a new class of materials: two-dimensional (2D) structures, which only consist of one layer of atoms. Since controlled introduction of defects brings control over the material properties, this can be used to create structures which can be later utilized in specific applications, such as nanometer-scale electronic devices.The main method used to create defects in our project was particle irradiation, in which energetic particles are passed through the material to create changes in the atomic structure.For irradiation with electrons, we used the recently installed scanning transmission electron microscopy device (Nion UltraSTEM 100) at the University of Vienna. For irradiation with ions, we relied on our international collaborators in Germany, Finland and Israel. During the project, we have been able to establish conditions for using both electron and ion irradiation to transform the crystalline graphene structure (which looks like a chicken wire made out of carbon atoms) into amorphous network, where carbon atoms form rings of different sizes, not dissimilar to mosaic art. Since these modifications can be made with high precision only to specifically selected areas, these methods give a high promise for creating nanometer-scale electronic devices, which only consist of carbon atoms. We have also studied defects in non-carbon 2D materials, directly observed for the first time a diffusion path of a defect, as well as developed significant advances on different areas of microscopy of 2D structures.