Electronic structure of nanomaterials
The electronic and chemical structure of carbon materials are highly dependent on the hybridization of carbon atoms, but also on their functionalization and their nanostructure. We are also very interested in the effect of solvation on their electronic and chemical properties.
Several classes of materials are investigated in our group:
Diamond is a wide bandgap semiconductor (5.5 eV), which has exceptional electronic properties, such as a negative electron affinity when its surface is hydrogenated. It can also be doped by heteroatoms such as boron, nitrogen or phosphorus. Nevertheless, the impact of nanostructuration (nanoparticles, nanoporous diamond) and doping on the diamond electronic properties are not fully understood yet. We are probing different kind of diamond materials using X-ray absorption and emission spectroscopies at the carbon K edge to probe unoccupied and occupied electronic states, respectively, and gain new insights into the link between structure and electronic properties.
We are also probing nanodiamonds directly in solution using microjet and flow cell systems to observe the effect of solvation on their electronic structure. In particular, we have found that graphitic surface states are reacting with water molecules, inducing the formation of holes in the diamond valence band .
Many different carbon dots and graphene quantum dots, having mainly amorphous or graphitic hybridization have been reported in the literature. However, only few information are currently available on their electronic structure. We are currently applying soft X-ray spectroscopies on these materials.
Carbon-containing 2D materials
In addition to fully carbon-based nanomaterials, we are also interested in the characterization of hybrid 2D nanomaterials. We are investigating polymeric carbon nitride (C3N4), which is a promising photocatalyst for solar fuel production. We are also investigating electronic properties of titanium carbide (Ti3C2) which has been proposed as an outstanding material for electrochemical storage.
Characterization of nanomaterials in solution with X-ray absorption spectroscopy
Methods to probe nanoparticle dispersions based on liquid microjet or transmission flow cell systems have been applied to diamond nanoparticles [1-2]. Nevertheless, only highly concentrated and stable dispersions can be characterized with these methods.
We are developing a new flow cell using holey membrane, which dramatically enhanced the X-ray transmission in the water window. X-ray absorption spectroscopy in fluorescence yield is possible with this approach, which has been demonstrated on TiO2 nanoparticles so far .
-  T. Petit, M. Pflüger, D. Tolksdorf, J. Xiao, E. F. Aziz. Valence holes observed in nanodiamonds dispersed in water. Nanoscale (2015) DOI: 10.1039/C4NR06639A
-  T. Petit, H. Yuzawa, M. Nagasaka, R. Yamanoi, E. Osawa, N. Kosugi, E. F. Aziz. Probing Interfacial Water on Nanodiamonds in Colloidal Dispersion. J Phys. Chem. Lett. (2015) DOI: 10.1021/acs.jpclett.5b00820
-  T. Petit, J. Ren, S. Choudhury, R. Golnak, S. S. N. Lalithambika, M. F. Tesch, J. Xiao, E. F. Aziz, X-Ray Absorption Spectroscopy of TiO2 Nanoparticles in Water Using a Holey Membrane-Based Flow Cell, Advanced Materials Interfaces, (2017). DOI: 10.1002/admi.201700755