09:30 - 10:30 Plenary Speaker

Beyond Structural Materials Engineering

Thomas Heine

Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, GER

Quantum confinement is one of the design principles in nanotechnology. Well-known examples are quantum dots, which are nanocrystals whose electronic band gaps depend crucially on their spatial extension. Thus, it is possible to create light emitting devices with the colour defined by the diameter of the quantum dot. Latest applications include large-scale displays and lasers.

In my presentation I will show that quantum confinement is not restricted to quantum dots and optoelectronic applications. I will show how quantum confinement can be exploited as strategy for the rational design of functional nanomaterials.

The first examples are taken from the field of layered materials, where quantum confinement can be used to tailor the band gap, but also the character of the band gap. For example, transition metal dichalcogenides $\ce{MX_2}$ ($\ce{M}$=$\ce{Mo, W}$, $\ce{X}$=$\ce{S, Se}$) are indirect band gap semiconductors as bulk and multilayer phases, but direct band gap semiconductors with appreciable photoluminescence signal as single-layer material. These ultrathin materials are also called two-dimensional crystals. We have added a few members to the family of 2D materials, including noble metal dichalcogenides, 2D clays, $\ce{GeP3}$, and recently semiconducting 2D polymers. All of them show very strong interlayer quantum confinement effects.

In the final part of my presentation I will show how quantum confinement can be exploited to separate isotopes of light-weight elements, e.g. hydrogen or helium. I will present two independent mechanisms that have been realized in metal-organic frameworks (MOFs): MOFs with well-defined apertures that are about the same size as the effective diameter as the dihydrogen isotopologue show a so-called kinetic quantum sieving effect, where the diffusion of heavier isotopologues is favoured. On the contrary, chemical affinity sieving is observed for materials with strong adsorption sites, such as undercoordinated metal ions. Here, the isotopologues have different zero-point energy contributions to the adsorption energy. Using this effect, separation coefficients of 10 and higher can be achieved even at temperatures above 100 K.