2 research outputs found
Gold Fusion: From Au<sub>25</sub>(SR)<sub>18</sub> to Au<sub>38</sub>(SR)<sub>24</sub>, the Most Unexpected Transformation of a Very Stable Nanocluster
The
study of the molecular cluster Au<sub>25</sub>(SR)<sub>18</sub> has
provided a wealth of fundamental insights into the properties
of clusters protected by thiolated ligands (SR). This is also because
this cluster has been particularly stable under a number of experimental
conditions. Very unexpectedly, we found that paramagnetic Au<sub>25</sub>(SR)<sub>18</sub><sup>0</sup> undergoes a spontaneous bimolecular
fusion to form another benchmark gold nanocluster, Au<sub>38</sub>(SR)<sub>24</sub>. We tested this reaction with a series of Au<sub>25</sub> clusters. The fusion was confirmed and characterized by
UV–vis absorption spectroscopy, ESI mass spectrometry, <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy, and electrochemistry.
NMR evidences the presence of four types of ligand and, for the same
proton type, double signals caused by the diastereotopicity arising
from the chirality of the capping shell. This effect propagates up
to the third carbon atom along the ligand chain. Electrochemistry
provides a particularly convenient way to study the evolution process
and determine the fusion rate constant, which decreases as the ligand
length increases. No reaction is observed for the anionic clusters,
whereas the radical nature of Au<sub>25</sub>(SR)<sub>18</sub><sup>0</sup> appears to play an important role. This transformation of
a stable cluster into a larger stable cluster without addition of
any co-reagent also features the bottom-up assembly of the Au<sub>13</sub> building block in solution. This very unexpected result
could modify our view of the relative stability of molecular gold
nanoclusters
Molecular Beam Epitaxy of Highly Crystalline MoSe<sub>2</sub> on Hexagonal Boron Nitride
Molybdenum
diselenide (MoSe<sub>2</sub>) is a promising two-dimensional
material for next-generation electronics and optoelectronics. However,
its application has been hindered by a lack of large-scale synthesis.
Although chemical vapor deposition (CVD) using laboratory furnaces
has been applied to grow two-dimensional (2D) MoSe<sub>2</sub> cystals,
no continuous film over macroscopically large area has been produced
due to the lack of uniform control in these systems. Here, we investigate
the molecular beam epitaxy (MBE)Â of 2D MoSe<sub>2</sub> on hexagonal
boron nitride (hBN) substrate, where highly crystalline MoSe<sub>2</sub> film can be grown with electron mobility ∼15 cm<sup>2</sup>/(V s). Scanning transmission electron microscopy (STEM) shows that
MoSe<sub>2</sub> grains grown at an optimum temperature of 500
°C are highly oriented and coalesced to form continuous film
with predominantly mirror twin boundaries. Our work suggests that
van der Waals epitaxy of 2D materials is tolerant of lattice mismatch
but is facilitated by substrates with similar symmetry