Images of oxygen (upper row) and nitrogen atoms (lower row) in a carbon network, produced at the microscopy laboratory of the University of Vienna. Among the expected configurations, oxygen is also found with three neighbors, as well as in a ‘pair’ configuration with another oxygen. Image: Christoph Hofer and Jannik Meyer.The identification of new chemical bonds is crucial for the design of new material structures. A team led by Jani Kotakoski at the University of Vienna in Austria and Jannik Meyer at the University of Tübingen in Germany has now found unexpected new configurations of oxygen and nitrogen in graphene. They report their findings, and present direct images of the actual atoms, in a paper in Nature Communications.
Life as we know it is based on just a handful of different types of atoms, among them carbon, nitrogen and oxygen. The complexity of life derives from the ability of these elements to connect to each other via chemical bonds to form larger structures. Knowing these possible bonding structures allows scientists both to understand the building blocks of life and to design completely new structures.
Each type of atom can make a characteristic number of bonds depending on the number of available electrons. Chemistry textbooks say that carbon can have up to four bonds, nitrogen up to three and oxygen only one or two. Now, Kotakoski, Meyer and their team have studied the bonding of a large number of nitrogen and oxygen atoms using state-of-the-art scanning transmission electron microscopy. This was made possible by embedding the atoms in the one-atom-thick carbon material known as graphene.
The study revealed that the nitrogen and oxygen atoms bind to their neighbors in a rich variety of configurations. For the most part, it confirmed the textbook picture, which could now be illustrated with direct images of actual atoms: nitrogen atoms were bound to two or three carbon atoms, while most oxygen atoms had two carbon neighbors.
"What really surprised us, however, was the additional presence of structures with oxygen bonded to three carbon neighbors," says Christoph Hofer, the lead author of the paper. "Until now, the exception of oxygen with three bonds was only known in an unusual highly charged state, referred to as oxonium, which is difficult to stabilize." In the current study, however, the structures were remarkably stable, allowing them to be imaged by the microscope.
The study also revealed a ‘paired oxygen’ configuration, where two oxygen atoms occupy neighboring sites in the graphene lattice but do not create a bond. In addition to providing new insights to the building blocks of life, these new bonding configurations may also lead to the development of new materials.
Overall, the study provides a comprehensive overview of the different bonding configurations for nitrogen and oxygen, illustrated directly through images of the individual atoms. While the textbook concept of bonding for carbon, nitrogen and oxygen was mostly confirmed, these common elements can obviously still yield surprises even after decades of study.
This story is adapted from material from the University of Vienna, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.