Interface Phenomena in Two-Dimensional Materials

Abstract

The unprecedented technology developments in the 21st century aim at harnessing materials on the molecular or atomic level. Among others, semiconductor technology is pioneering this effort by the fabrication of integrated circuits like computer chips, displays and memory. The continuous downsizing of these structures and resulting performance gains lay the foundation of the digital revolution. The understanding of interfaces – junctions between materials – is crucial for the design and performance of modern electronic devices. The impact of interfaces on the materials properties increases as structures become smaller. Two-dimensional (2D) materials like Graphene that feature virtually only one atomic layer receive tremendous research interest as they push downsizing to the ultimate limit of atomic thickness. The influence between materials and their environment across interfaces now can even determine the properties. However, the understanding of this influence and its consequences remain in their infancy. This dissertation extends the understanding of interfaces by investigations of the influence between 2D materials and their environment. Publication 1 demonstrates the strong impact of the chemical environment on the electronic properties of 2D materials. Oxygen adsorption to a single layer of MoS2 induces an electron transfer across the interface. Publication 2 explores these observations further and establishes the controlled fabrication of flat nanometer-sized platforms (substrates) for 2D materials and the manipulation of their electronic properties. Surface diffusion of adsorbates dominates the growth process on these small scales and can be exploited to fabricate novel nanostructures. Publication 3 extends the spectrum of 2D materials by organic-inorganic mixed crystals. Not deemed feasible before, [C7H10N]3[BiCl5]Cl can be exfoliated to a single layer. The here-discovered novel influence of the crystal thickness on the emission wavelength of the material may enable color tuning in next-generation lighting and display technologies. These results enable a magnitude of new developments and opportunities in research as well as for their applications. The influence on the electronic properties through substrates allows for the creation of internal interfaces that may be used for smaller and more powerful electronic devices.