Two-dimensional materials and surfactants: exfoliation, controlled stacks, targeted particle growth and functional heterostructures

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Many applications require monodisperse 2D nanocrystals (2DNC). Shape and size determine, e.g., their optoelectronic properties due to quantum confinement in lateral dimensions as well as in the number of layers, and edge structures differ in material character (metallic, semiconducting) and its catalytic activity. Thus, control of size and edges of the 2DNC is necessary for optoelectronic and photocatalytic applications. We aim at controlling 2DNC growth along specific edges by adding surfactants which either passivate or activate reactions with monomers of the colloidal solution, thus controlling the number of layers (from monolayers to stacks), the lateral size, interlayer distance, and the lateral shape of the 2DNC. We will investigate how to attack the basal plane of 2DNC nanodiscs in order to produce toroidal structures, and explore if it is possible to guide synthesis towards specific polytypes. We will investigate the possibility to stack 2DNC monolayers intercalated with surfactants in such way that the electronic properties of the 2DNC monolayers are maintained. Further, we will study electronic interactions of surfactants with 2DNC, in particular with radical surfactants and with charge traps or charge reservoirs.Our research, based on first-principles calculations, will be carried out in close collaboration with two leading experimental groups who will provide in situ spectroscopic data, create 2DNC and suitable surfactants. Initial target materials are metal chalcogenides (TMC), starting from Group 4 and Group 6 transition metal dichalcogenides (TMDC), later extending to noble metal dichalcogenides (Group 10), and 2D COFs (2D polymers). Initially, surfactants serve as means for layer separation, but at the end of the project, we will explore how surfactant functionalization can be exploited as means for control of functionality of the 2DNC. Method implementations carried out in this project, i.e. a multi high-level/low-level method and an automated scheme to compute charge carrier mobilities, will be made publicly available via github, but also be included in the graphical user interface of the Amsterdam Density Functional software package. We collaborate closely with the main developer of the BAND code, which supports DFT calculations with explicit 0D-3D boundary conditions.