EK-CER and Wigner RCP researchers show that self-organizing crystal structures form in the surface contamination layer of two-dimensional materials within a few days

The surface coming into contact with ambient air becomes ‘dirty’: various ambient contaminants ‒ water, oxygen, hydrocarbons, etc. ‒ become attached to the surface, leading to a deterioration in or complete loss of the physical and chemical properties of the surface. In the course of this project the researchers used a low-temperature (9K, or around -264 °C) scanning tunneling microscope (STM) imaging to observe the individual molecules making up the contamination layer, as well as their size, internal structure and formation. By using scanning tunneling spectroscopy (STS), X-ray photoelectron spectroscopy (XPS) and infra-red (IR) spectroscopy measurements clear chemical identification of the molecules that make up the self-organizing single layer became possible. An understanding of the molecules making up the surface contamination layer on 2D materials may have a significant influence both on the basic research and on many of the areas the research is applied to, as the self-organizing molecule layer may even dominate the interaction between the surface and its environment.

In order to demonstrate this, the researchers showed that the self-organizing single-layer alkane is also clearly responsible for the development of anisotropic friction domains ‒ something that has been contentious until now ‒ universally observable on the vdW materials, e.g. graphene, graphite, hexagonal boron nitride (hBN) and molybdenum disulfide (MoS₂). To show the transformation of these friction domains in a planned manner and allow observation of their ‘redrawing’, they rotated the long molecules making up the single layer along their long axes in the selected direction of the needle of an atomic force microscope.