The development of functional nanomaterials has been a major landmark in the
history of materials science. Nanoparticles with diameters ranging from 5 to
500 nm have unprecedented properties, such as high catalytic activity,
compared to their bulk material counterparts. Moreover, as particles become
smaller, exotic quantum phenomena become more prominent. This has enabled
scientists to produce materials and devices with characteristics that had been
only dreamed of, especially in the fields of electronics, catalysis, and
optics.
But what if we go smaller? Sub-nanoparticles (SNPs) with particle sizes of
around 1 nm are now considered a new class of materials with distinct
properties due to the predominance of quantum effects. The untapped
potential of SNPs caught the attention of scientists from Tokyo Tech, who
are currently undertaking the challenges arising in this mostly unexplored
field. In a recent study published in the Journal of the American Chemical
Society, a team of scientists from the Laboratory of Chemistry and Life
Sciences, led by Dr Takamasa Tsukamoto, demonstrated a novel molecular
screening approach to find promising SNPs.
As one would expect, the synthesis of SNPs is plagued by technical
difficulties, even more so for those containing multiple elements. Dr
Tsukamoto explains: "Even SNPs containing just two different elements have
barely been investigated because producing a system of subnanometer scale
requires fine control of the composition ratio and particle size with atomic
precision." However, this team of scientists had already developed a novel
method by which SNPs could be made from different metal salts with extreme
control over the total number of atoms and the proportion of each element.
Their approach relies on dendrimers, a type of symmetric molecule that
branches radially outwards like trees sprouting form a common center.
Dendrimers serve as a template on which metal salts can be accurately
accumulated at the base of the desired branches. Subsequently, through
chemical reduction and oxidation, SNPs are precisely synthesized on the
dendrimer scaffold. The scientists used this method in their most recent
study to produce SNPs with various proportions of indium and tin oxides and
then explored their physicochemical properties.
One peculiar finding was that unusual electronic states and oxygen content
occurred at an indium-to-tin ratio of 3:4. These results were unprecedented
even in studies of nanoparticles with controlled size and composition, and
the scientists ascribed them to physical phenomena exclusive to the
sub-nanometer scale. Moreover, they found that the optical properties of
SNPs with this elemental proportion were different not only from those of
SNPs with other ratios, but also of nanoparticles with the same ratio. The
SNPs with this ratio were yellow instead of white and exhibited green
photoluminescence under ultraviolet irradiation.
Exploring material properties at the sub-nanometer scale will most likely
lead to their practical application in next-generation electronics and
catalysts. This study, however, is just the beginning in the field of
sub-nanometer materials, as Dr Tsukamoto concludes: "Our study marks the
first-ever discovery of unique functions in SNPs and their underlying
principles through a sequential screening search. We believe our findings
will serve as the initial step toward the development of as-yet-unknown
quantum sized materials." The sub-nanometric world awaits!
Reference:
Takamasa Tsukamoto, Akiyoshi Kuzume, Masanari Nagasaka, Tetsuya Kambe,
Kimihisa Yamamoto. Quantum Materials Exploration by Sequential Screening
Technique of Heteroatomicity. Journal of the American Chemical Society,
2020; 142 (45): 19078 DOI:
10.1021/jacs.0c06653