Identifying the organisation of electrons in matter
Electronic structure defines how electrons organise within matter. It provides vital insights into the origin of physical properties down to the atomic scale. Quantifying electronic structure experimentally can be used to define atomic electron configurations, oxidation state, the type of chemical bonds, the coordination symmetry of bound atoms and the quantum spin and orbital contributions to magnetic properties.
- Timothy Burrow
- Rasmus Tang Christiansen
- Myron Huzan
- Nathan Alcock
- Jiafu Xian
Our research group specialise in the application of both X-ray and inelastic neutron spectroscopies for the study of electronic structure. We apply a broad range of X-ray techniques including X-ray absorption near-edge fine structure (XANES), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). We apply dichroism for some of these methods, including X-ray magnetic circular dichroism (XMCD) and X-ray linear dichroism. It is an important part of our research to back experimental results with theoretical simulations. This enables us to obtain a fundamental understanding of experimental sensitivities to electronic structure and facilitates precise quantification of physical properties. We utilise atomic multiplet theory, time-dependent density functional theory and ab. initio. quantum chemistry methods to simulate spectra and identify precise descriptions of electronic structure.
X-ray absorption spectroscopies are ideally suited for accessing electronic structure since by tuning the x-ray energy it is possible to measure the excitation of core-electrons into the lowest energy unoccupied orbitals. Since the absorption edge energy is specific for any given element, element-specific electronic structure can be obtained in crystalline and non-crystalline environments. X-ray absorption spectroscopy can therefore provide important information concerning the electronic and geometric structure of an analyte in solid, liquid or even gaseous forms. Combining X-ray absorption with emission spectroscopy makes it possible to measure both the lowest energy unoccupied orbitals and the highest energy occupied orbitals, providing a holistic picture of the frontier molecular orbitals or Fermi level.
Inelastic neutron spectroscopy
Neutrons have a quantum spin of a half but carry no charge and are therefore highly penetrating in matter. We apply inelastic neutron scattering to study the spin dynamics of molecular-based magnetic compounds.
Specific projects currently underway include:
- the electronic structure and magnetisation dynamics of single-ion dopants in solid-state crystals (see Figure 1).
- the study of spin dynamics within molecules that exhibit valence delocalisation
- the characterisation of molecular-based switchable magnetism
- the determination of f-block element electronic structure and bonding
As a society we have a responsibility to develop chemical tools to control and treat the hazardous situations that arise from exploiting fission for energy production. The industrial use of nuclear fission creates a multitude of radioactive, f-block element waste that is a major challenge to treat, store, and ultimately clean up. The ‘f’ in f-block comes from the name given to the outer electron shell for these elements.
The first of this series of elements, known as the lanthanides, remain radioactive for a relatively short period of time, while the second series, known as the actinides, remain active for many tens of thousands of years. The development of ways to separate actinides from lanthanides would considerably reduce the volume of radioactive waste to be stored.
However chemical tools for selectively extracting f-block elements are limited by our lack of knowledge about their chemistry. The challenge in overcoming this limitation comes from a lack of suitable experiments to understand how f-block elements form bonds with other elements. However recent advances in the use of intense X-rays, generated at Diamond, open possibilities to extract rich information about f-block element bonding.
This proposed research programme will develop X-ray spectroscopy methods to differentiate how f-block elements engage in chemical bonding. This information will help society by providing information vital for treating radioactive waste, but will also be relevant to many other areas where f-block elements are used, such as within consumer electronic devices and the automotive industry.