A group of sub-nano-sized substances with a size of about 1 nanometer, in which a few atoms to about several tens of atoms are accumulated, is attracting attention as a post-nanomaterial because the combinations of 118 kinds of elements and the number of atoms is infinite, so there are unknown substances with various functions. Dr. Yamamoto took on the challenge of this unexplored nanoscience and pioneered science and technology that handles atoms with atomic precision. He has created many new substance groups called superatoms and sub-nanoparticles of multi-element alloy, and is pioneering new material chemistry for next-generation. "Atom hybrid" is his original science to create sub-nanoparticles by precisely controlling the number of atoms and elemental composition using a new type of polymer called "dendrimer" that independently developed as a template by himself.
1. Establishment of precision metal accumulation method
His group is to independently develop more than 30 types of rigid, dendritic polymers (phenylazomethine dendrimers). He discovered for the first time in the world a phenomenon in which metal ions are regularly accumulated radially and stepwise in this polymer according to the basic gradient of the coordination sites (multi-step radial complexation). Of the 118 elements in the periodic table, excluding radioactive elements, highly toxic elements, and rare gas elements, almost all 67 elements out of 70 practical elements can be accumulated in the dendrimer with atomic precision. Furthermore, his group have achieved more than 250 patterns of different element accumulation in the dendrimer, and have also succeeded in precise accumulation of up to 10 elements. His unique dendrimers enable the control of the number of atoms and the atomic composition ratio, which has been considered difficult until now, and realizes precise assembling technology for various atoms.
2. Creation of sub-nanoparticles by atom hybrid
His group have developed a method (atom hybrid method) to create sub-nanoparticles of multi-element alloy with controlled atomic composition using dendrimers as a template. They have created a library of over 230 types of sub-nanoparticles. Many new material groups such as superatoms, sub-nano particles of multi-element alloy, and borophene atomic sheets have been synthesized. They demonstrate that the atom hybrid method is an excellent method for constructing new quantum functions.
3. Development of sub-nano catalysts
They have developed atomic-precision sub-nanoparticles into catalysts, clarified the activity of each atomic composition, and discovered many sub-nano catalysts that far surpass the activity of bulk metals and nano catalysts. They found sub-nano catalyst with the specific high activity, such as Pt19 for four-electron reduction of oxygen, Pt10 for alkane hydrogenation, Pt16Cu32Au12 for aerobic oxidation of indane, Pt27Pd2 for hydrogen oxidation, and Rh32Fe28 for nitro reduction.
4. Theoretical development of sub-nanoparticles
On the basis of the material library of many synthesized sub-nanoparticles, his group discovered a periodicity of sub-nanoparticles. He has proposed a new periodic table of sub-nanomaterials, which is attracting attention in the material science community. This led to the theoretical discovery that superdegenerate sub-nanoparticles (Zn20, Mg20, Cd20) with higher symmetry than spherically symmetric atoms, overturning conventional wisdom.
5. Observation of atom dynamics
He is developing a technology to visualize the movement of metal atoms (atomic dynamics) in sub-nanoparticles using the STEM with a low accelerating voltage and 6th-order spherical aberration correction. His group have succeeded in observing the state that is not found in nano or bulk solids. Furthermore, by developing a new observation method using AI (MTANN) and image tracking system, they have succeeded in element identification for each atom. As a result, gold, silver, and copper, which normally do not form homogeneous alloys due to phase separation in the bulk, exist as AuAgCu triatomic molecules in the sub-nano region for the first time in the world. Furthermore, they have visualized the dynamics of bond formation and cleavage of a large number of heteroatom dimers on graphene.
Thus, Professor Yamamoto's great contributions deserves well to the Chemical Society of Japan (CSJ) Award.