Holes in valence bands of nanodiamonds discovered
Nanodiamonds are tiny crystals only a few nanometres in size. Mohamed Sennour, MINES ParisTech.
Dr. Tristan Petit (right side) received a C’Nano award under the category of interdisciplinary research for his doctoral dissertation in late 2014. Credit C'Nano © C'Nano
Researchers hope that their properties might be altered to permit nanodiamonds to be used as catalysts for generating hydrogen from sunlight
Nanodiamonds are tiny crystals only a few nanometres in size. While they possess the crystalline structure of diamonds, their properties diverge considerably from those of their big brothers, because their surfaces play a dominant role in comparison to their extremely small volumes. Suspended in aqueous solutions, they could function as taxis for active substances in biomedical applications, for example, or be used as catalysts for splitting water. But how are the electronic properties of nanodiamonds deposited on a solid-state substrate different from those displayed by nanodiamonds in aqueous solutions? Dr. Tristan Petit working in the HZB team headed by Prof. Emad F. Aziz has now investigated this with the help of absorption and emission spectroscopy at BESSY II. Their results, just published in Nanoscale, demonstrate that nanodiamonds display valence holes in aqueous solutions, which are not observed when characterized as a thin film.
“The interaction between the nanodiamonds and the neighbouring molecules and ions is especially strong in water”, say Petit. The adsorption of active pharmaceutical ingredients on nanodiamonds can be influenced, for example, by adding salts or changing the pH value. Petit and his colleagues have now discovered that the electronic signature of surface states of nanodiamonds in aqueous dispersions are considerably different from those of nanodiamonds on a solid-state substrate.
With the help of micro-jet technology developed by Emad Aziz at HZB, they examined liquid samples in vacuum using X-ray spectroscopy and developed a detailed picture of the filled and unfilled electron states in valence and conduction bands. Their results show that holes, i.e. missing electrons in the valence band, formed on the surfaces of the nanodiamonds in the aqueous dispersion. “This suggests that electrons at the surface of nanodiamonds are donated to the surrounding water molecules”, Petit suggests. The physicists suspect they might also influence the nanoparticles’ chemical, optical, and catalytic properties through changes to their electronic structure. They would like to determine in future studies whether the catalytic effect of nanodiamonds in aqueous environment can be increased in order to split water molecules into oxygen and hydrogen using light.
Reference: Valence holes observed in nanodiamonds dispersed in water, Tristan Petit, Mika Pflüger, Daniel Tolksdorf, Jie Xiao and Emad Flear Aziz, Nanoscale, 2015, DOI: 10.1039/C4NR06639A
Postscript: Dr. Tristan Petit received a C’Nano award under the category of interdisciplinary research for his doctoral dissertation in late 2014. Several research institutions in France have amalgamated under the umbrella organisation C’Nano to conduct research and development on nanomaterials and nanotechnologies.
For his doctoral work, Tristan Petit conducted research at the Laboratoire Capteurs Diamant (CEA LIST Saclay) on properties of nanodiamonds and their potential suitability for cancer treatment. Dr. Tristan Petit has been pursuing research on a team under Prof. Emad Flear Aziz at HZB through a postdoctoral grant from the Alexander von Humboldt Foundation (since summer 2013).
More information on the C’Nano Doctoral awards:
- Green fabrication of hybrid materials as highly sensitive X-ray detectorsNew bismuth-based organic-inorganic hybrid materials show exceptional sensitivity and long-term stability as X-ray detectors, significantly more sensitive than commercial X-ray detectors. In addition, these materials can be produced without solvents by ball milling, a mechanochemical synthesis process that is environmentally friendly and scalable. More sensitive detectors would allow for a reduction in the radiation exposure during X-ray examinations.
- Electrical energy storage: BAM, HZB, and HU Berlin plan joint Berlin Battery LabThe Federal Institute for Materials Research and Testing (BAM), the Helmholtz-Zentrum Berlin (HZB), and Humboldt University of Berlin (HU Berlin) have signed a memorandum of understanding (MoU) to establish the Berlin Battery Lab. The lab will pool the expertise of the three institutions to advance the development of sustainable battery technologies. The joint research infrastructure will also be open to industry for pioneering projects in this field.
- BESSY II: Insight into ultrafast spin processes with femtoslicingAn international team has succeeded at BESSY II for the first time to elucidate how ultrafast spin-polarised current pulses can be characterised by measuring the ultrafast demagnetisation in a magnetic layer system within the first hundreds of femtoseconds. The findings are useful for the development of spintronic devices that enable faster and more energy-efficient information processing and storage. The collaboration involved teams from the University of Strasbourg, HZB, Uppsala University and several other universities.