Quantum Dots embedded in decoupled Graphene Nanoribbons

The goal of the project is to study electronically decoupled graphene-nanoribbons (GNRs) and decoupled optically active quantum dots based on GNRs on coinage metals such as copper, silver and gold. Growth of these graphene-nanostructures is already well established on those metal surfaces. However, since generally metals show good electronical conductivity, significant electronical interaction between the graphene-nanostructures and the metal substrate occurs. Thus, in order to study the electronical properties of the graphene-nanostructures more efficiently a decoupling from the metal substrate is a necessity. Up to now, this task remains still a challenge. Therefore, insulating thin films will be grown on the metal surface followed by a placement of the graphene-nanostructures on those films. The experiments will be carried out in an ultra-high vacuum chamber equipped with a low-temperature scanning tunnelling microscope. This microscope enables a rastering of the surface by a metal tip while measuring a current (tunnelling current) between tip and surface. Thus the electronical surface structureopography and electronical states of the graphene nanostructures can be determined. These studies show a huge potential for a deeper understanding of the physical properties of electronically decoupled graphene-nanostructures and future technologically relevant applications such as light emitting diodes, photodetectors, displays etc.

Since the discovery of graphene in 2004, which was awarded with the Nobel Prize in physics in 2010, research on ultrathin 2D films has become a subject of tremendous interest. 2D materials in general are characterized by an atomic thick layer, which mostly differ in physical and chemical properties from their bulk structure. In my project I focused on finding suitable, insulating 2D materials, which can be used as a decoupling layer, shielding the electronically conducting metal substrate, for a further study of physically interesting, electronically decoupled molecular structures (e.g. Graphene Nanoribbons). A material with promising electronic and magnetic properties down to the two-dimensional limit is NiBr2 (nickel-di-bromide). Therefore, as the starting point of my project, the investigation on the growth behavior of 2D NiBr2 on Au(111) (gold single crystal surface) was chosen. We managed to grow stable 2D layers of NiBr2 on Au(111) and characterized the system with surface sensitive methods. One highlight was finding evidence of an intrinsic magnetic character of 2D NiBr2. 2D materials, exhibiting magnetism, are very rare, bearing huge potential for future nano-technological applications (e.g. spintronics). In order to understand magnetism in 2D materials in detail, the use of quantum mechanics is crucial. Since our first results on the growth behavior of NiBr2 on Au(111) were scientifically of great achievement we tried to combine this quantum mechanical system with an other quantum system, namely superconductivity. The idea was to construct an overall, new exotic quantum state of matter. Therefore, we performed further measurements of NiBr2 on the superconducting material NbSe2 (niobium-di-selenide). The growth of 2D NiBr2 on NbSe2 resulted in nice 2D island structures and indeed showed interesting quantum behavior at the direct interface between NiBr2 and NbSe2. These quantum states at the edges are a hot topic within the science community and do not just have huge scientific relevance but as well have great potential for future quantum technological applications