Title : In search of metastable forms of Carbon
Abstract:
Metastable forms of matter often possess properties superior to those of their ground state. A case in point is diamond vs. graphite. Yet, in practice, many predicted metastable structures are dismissed as hard-to-realize. We introduce a method that can enhance the realizability of a targeted metastable structure against the ground state in the potential energy surface and directly guide its experimental synthesis. This is done by selecting a proper precursor according to the building block of the targeted structure and forming topological assemblies of the precursor molecules. The method is applied to realize metastable forms of carbon, which is one of the most fascinating elements in the periodic table. The unique properties of carbon emerge from its ability to form diverse spn (1 < n < 3) bonds, graphite with sp2 and diamond with sp3 bonding being the most common forms. The discovery of zero-dimensional (0D) carbon fullerenes, one-dimensional (1D) chain-like carbyne and carbon nanotube, and two-dimensional (2D) graphene, all with novel properties characteristic of their reduced dimensionality and size, has ushered a new era in carbon science. In recent years many new metastable forms of carbon exhibiting a mixture sp1, sp2 and/or sp3 bonding pattern have also emerged. In this talk I will focus on the carbon allotropes that have been studied in our group. These include functionalized C60 fullerenes for hydrogen storage, semi-hydrogenated graphene for metal-free ferromagnet, 3D metallic carbon made of hybridized sp2 and sp3 bonded atoms, and a Cairo-tilling inspired quasi-2D penta-graphene made only of carbon pentagons. I will highlight the discovery of a new carbon allotrope, named U-carbon, that is composed of carbon atoms forming sp2 and sp3 bonds. Arranged in four- and six-membered rings, U-carbon is metallic and magnetic. Theoretical studies were carried out using a multi-scale first-principles approach while experiment was conducted using a chemical vapor deposition of the targeted organic precursor molecule. Potential applications of some of these carbon allotropes will be discussed.
Audience take away:
• How to search for metastable states of matter that can be realized in practice?
• How the discovery of new carbon allotropes can enrich science and technology?
