Clusters of gold nanoparticles look just like a multiple-strand necklace.
“The research on gold nanoparticles is a field of both fundamental and applied importance” explains Academy Professor Kari Rissanen of the Department of Chemistry at the University of Jyväskylä.
X-ray crystallography is the most powerful method for molecular-structure determination of these nanosystems, but obtaining good quality single crystals suitable for accurate X-ray analysis has been the bottleneck in this demanding research.
This problem has now been successfully addressed thanks to an electrochemical strategy called electrocrystallization.
X-ray single crystal diffraction analysis of gold nanoclusters - structures composed of a core formed of dozens gold atoms capped and protected by a layer of molecules - has the intrinsic limitation that good quality single crystals are very difficult to obtain.
The team has developed an electrochemical method that allows growing high-purity crystals in large quantities and very high crystallographic quality. By allowing a very small current to flow between two electrodes, dense forests of millimeter-long single crystals can be generated directly onto the electrode surface.
The breakthrough nature of this electrocrystallization method - continues Professor Maran - was put in practice by the single crystal X-ray crystallographic determination of the structures of four different nanoclusters each formed of 25 gold atoms.
Not only did these successful results validate the efficacy of the electrochemical technique, but also led to the discovery that one of these clusters crystallizes by forming needles consisting in parallel chains of interconnected gold nanoclusters, just like a multiple-strand necklace made of gold "pearls" of only a few nanometers.