Smaller than ever: Exploring the unusual properties of quantum-sized
materials

Date:
November 12, 2020
Source:
Tokyo Institute of Technology
Summary:
Scientists have synthesized sub-nanometer particles with
precisely controlled proportions of indium and tin using specific
macromolecular templates called dendrimers. Through a screening
process spanning different metallic ratios, they discovered
unusual electronic states and optical properties originating from
size-miniaturization and elemental- hybridization. Their approach
could be a first step in the development of sub-nanoparticles
with unique functionalities and characteristics for electronic,
magnetic, and catalytic applications.



FULL STORY ==========================================================================
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!

========================================================================== Story Source: Materials provided by Tokyo_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. 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 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/11/201112100903.htm

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