Electron injection builds novel crystalline carbons

Charge injection has been widely utilized to tune the energy level of electrons in semiconductors without altering their microscopic structure. Recently, a research team led by Professor ZHU Yanwu from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) has discovered another function of charge injection. By charging C₆₀ molecules periodically arranged in a face center cubic (fcc) lattice with α-Li₃N, a novel long-range ordered porous carbon (LOPC) crystal was thereby formed. The study was published in Nature.  

Different from most elemental crystals in which the building blocks are multifarious atoms, LOPC in this study is composed of C₆₀ molecules, commonly known as fullerenes or buckyballs. LOPC possesses the characteristics of both long-range order in the three-dimensional (3D) crystal and partially broken C₆₀ molecules connected as the building blocks. 

At elevated temperatures and ambient pressure, α-Li₃N donates electrons to C₆₀ molecules, which causes the expansion of the electron cloud surrounding C₆₀. With the help of dipoles that have been formed, electron clouds at adjacent C₆₀ molecules in the fcc lattice overlap, forming covalent bonds (C–C bonds) between C₆₀ molecules. 

The method of chemical activation using potassium hydroxide, which succeeded in reconstructing graphene into 3D carbon, was also adopted by the research team. However, such 3D carbon has a disordered structure since the chemical activation is too violent compared with the method of electron injection from α-Li₃N. The superiority of electron injection has been demonstrated by preserving the periodic stacking of the nanomaterials that serve as the building blocks. 

Many potential applications of LOPC may be explored in the future. For example, due to its high porosity, LOPC could provide abundant liquid or gas diffusion paths, making it a great candidate for catalyst loading. 

The method of electron injection proposed in this study offers a new approach for constructing new materials much like using Lego blocks, thus allowing the precise control of interfaces in crystal structures.