Atomic control over 2D materials via ion beam manipulation

The focus of this project is to use an old method from the modern semiconductor industryion irradiationto adjust the atomic structure of new materials in a controlled manner. We will specifically focus on two-dimensional materials, which have gained a large amount of interest due to their unique properties over the last decade. In Nature, such materials form stacked crystals, similar to sheets of paper in a paper stack, from which individual layers can be extracted. An example of such a material is graphite, which consists of layers of carbon atoms arranged in a honeycomb pattern. A single sheet of graphite, the one-atom-thick crystal of carbon atoms, is called graphene, and although it is far from being the only one, it is the best known two-dimensional material to date. With careful control over irradiation parameters, it is possible to selectively modify even atomically thin materials, for example by changing some of the carbon atoms in graphene with other elements. Due to different mass, number of electrons and different electrostatic potential, these foreign atoms will affect many material properties. Success in this project will provide us with a new method for tailoring novel materials so that they will fulfill the demands of specific applications in various fields.

Since the discovery of graphene, a one-atom-thick material consisting of carbon atoms, in 2004, research of other similarly thin materials has lead to the development of a completely new research field within materials science. Many of the discovered so-called 2D materials exist normally in a stacked form, like a stack of papers, similar to how several graphene layers build graphite, the material well-known as the "lead" of a pencil. The large interest in them arises partially from the fact that many of their properties differ from normal materials, because of quantum-mechanical confinement of their electrons to two dimensions, which leads to many unique properties that can be used in applications. Despite many interesting properties of 2D materials, harnessing their full potential also requires being able to alter them in a controlled manner. Such alteration is often done with ion irradiation within the modern-day semiconductor industry. However, due to the thin structure, this technology is not directly transferable for 2D materials. The goal of this stand-alone research project was to make ion irradiation also suitable for tailoring the structure of 2D materials. The main outcomes from the project were a new way to prepare atomically clean 2D materials, their controlled alteration with low-energy ion irradiation, new methods for their automated atomic-scale imaging and the successful introduction of single atoms and few-atom clusters into them. With these advances, the project outcomes can be expected to have a significant impact to technical development in many fields ranging from catalysis and green energy production to quantum information technology.