Research

 

The research in nano and molecular systems group is strongly focused on electronic structure and dynamics of atoms, molecules and clusters. To control the properties of matter, one has to have an understanding of the electronic structure. Development of metallic- and catalytic properties, research of novel materials, cluster related surface phenomena and UV induced degradation of environmentally hazardous molecules have been the main research interests of our group.

The strength of the group is to have a theoretically oriented part strongly involved and being able to interplay constantly with the experiments. This provides unique capabilities in comparing quality experimental results with accurate theoretical estimates. The group is also actively involved in developing SR sources and their experimental capabilities in the soft X-ray photon energy range and is nationally a strong unit in the field. The research of the group may be characterized as basic materials research while the new information obtained can find useful applications in many fields of applied science.

Experimental methods:

  • Electron spectroscopy: Detection of electrons emitted from the sample. Gives information about the electronic structure and dynamics of atoms, molecules and clusters.
  • Fluorescence spectroscopy: Fluorescence spectrum represents measured light intensity at different wavelengths emitted by the sample and it can be used to gain information about the properties of the material and processes happening in it.
  • Ion spectroscopy: Using a self-manufactured time-of-flight spectrometer (TOF), one has the ability to study different scattering and fragmentation processes happening in the sample.
  • Coincidence-measurement (PEPICO): Detection of electrons and ions ejected from the same process. With this method one can monitor and get accurate periodic view of the scattering process.
  • Two-color experiments: Provides information about the electron-electron interactions in the sample. Atoms are excited by laser before ionization and the spectrum is compared to the situation where laser-excitation has not been used.

 

Research from atoms to solid:

Atoms and molecules

 

Understanding the properties of matter and modifying them to serve the needs of modern society requires information about the electronic structure of matter.  Using atoms and small molecules as a simpler model systems one can gain some insight into the properties of matter.

 

Clusters (diameter 0.1 nm - 100 nm)

The size and properties of atomic clusters is somewhere between atomic and solid (macroscopic) matter. Particle sizes are usually measured in nanometers. Cluster research is interested in understanding how the properties of everyday materials emerge from those of atoms. The transformation of properties (from atomic- to solid-like) as a function of cluster size is not always smooth and it has some unsuspected deviations, sometimes even new properties are found. Understanding how matter behaves in the nanometer scale has direct applications in modern electronics which nowadays operate on the same scale.  

Solids

In solid matter the electronic states are packed more densely than in the molecules from which energy bands, the allowed energy states, arise. As the system evolves in size from atom to solid, the electron-electron interactions become more significant. The group has studied electronic properties of solids and interactions in the vapour-solid interface with electron spectroscopy.

 

Analysis and theoretical interpretation of experimental results:

Analysis of the experimental results is based on theoretical and computational models of the electronic structure of matter. In atoms the relevant tools are relativistic multiconfiguration theories, allowing for simulation of photon excitation, photoionization, and Auger spectra in great detail, including angular correlations between emitted electrons. In molecules the simulations focus on the electronic levels, and also on the evolution of the molecular bond during electronic excitation and de-excitation processes. Here combination of experimental and computational work allows for mapping the dissociation pathways, providing valuable information of molecular fragmentation processes.

Electronic correlations are visible in the spectra especially as satellite structures: peaks which accompany the main lines and whose origin is in the electron-electron interactions within the target. The intensity and angular correlations of satellites is extremely sensitive to the level of description of the structure and interaction processes. Another way to probe to the internal correlations are the cascade processes: sequential de-excitation processes after an initial excitation.

Simulations of spectroscopic data of large molecules and clusters provide a fruitful arena for electronic structure theories beyond the ab initio all-electron methods applicable to atoms and small molecules. Effective theories of many-electron states can be directly compared by comparison with the synchrotron radiation excited spectra.

 

 

Last updated: 19.1.2017