2D material manipulation and growth coupled with atomic-scale imaging

Transmission electron microscopy (TEM) is often carried out separate from other experimental steps, allowing only “post mortem” analysis. However, in this contribution, we will show that combining STEM with capabilities for in situ experimentation directly connected to other experimental and measurement stations not only allows carrying out otherwise difficult or impossible experiments but also can shed light to earlier surprising experimental results.

For example, we will show that the shape of pores that appear in hexagonal boron nitride under electron irradiation depends on the oxygen partial pressure in the microscope column; in ultra-high vacuum, pores assume a circular shape with no clear preference for either N or B termination, whereas under oxygen atmospheres, the characteristic triangular shape becomes apparent.

We also demonstrate that 2D materials can be tailored by incorporating impurity atoms using a two-step process in which vacancies are first introduced using low-energy noble gas irradiation and then filled by evaporating the impurities onto the defect-engineered sample. Similarly created functionalized graphene can also be used as a substrate for truly atomically thin metal structures (metallene) up to 20 nm in size.

Vacuum transfer is also crucial in revealing the relationship between the exact atomic structure of defect-engineered graphene and its mechanical properties. Our correlated experiments reveals–as expected–that ion irradiation leads to softening of the material, but only when measures are taken to remove surface contamination and to prevent it from gathering during the process. Curiously, it turns out that the main contribution to the material softening arises from defect-induced corrugation of the material rather than its general weakening due to the removed bonds.

Finally, we also present small 2D noble gas clusters that can be incorporated within the van der Waals gap of a double layer graphene. This allows the direct imaging of solid and liquid-like van der Waals crystals in STEM, providing a vast playing field for solid state physics research.