Nguyen Thanh Mai
北海道大学

大学院工学研究院

材料科学部門Synthesis, fine structure, and formation mechanism of metal and metal alloy nanoparticles
via sputtering onto liquid polymers「液体高分子へのスパッタリングによる金属・合金ナノ粒子の合成、微細構造、生成機構」

Solid solution alloy (SSA) nanoparticles are particles in nanoscale regime containing a single
phase of metals completely miscible in solid state. They offer a tool to realize new and/orsynergistic properties which single constituents do not have. However, it is challenging tosynthesize SSA nanoparticles of various metal systems, especially those contain miscibility gapsor intermetallics in the bulk. Recently developed vacuum sputter deposition onto a non-/lowvolatile liquid has some unique features. The sputter deposition generates metal atoms/clusters
from the bulk metals and allows for random combinations and alloying. Meanwhile, the low
volatile liquid can capture and control particle growth to form nanoparticles. Hence, the particle
formation by this technique is unique compared to that in chemical synthesis and/or bulk alloy
fabrication. We have been using sputter deposition onto liquid polymer to synthesize metal andSSA nanoparticles and aiming to elucidate the fine alloy structures and particle growth mechanism.
Fine-structure of sputtered binary nanoparticles
Using co-sputter deposition onto liquid polyethylene
glycol (PEG) (Fig. 1), we attained binary SSA nanoparticles
of below 3 nm for various metals no matter they are miscible(e.g., Au/Ag), form intermetallics (e.g., Au/Cu, Ag/Pt, Cu/Pd,Cu/Pt), or possess a large miscibility gap (e.g., Au/Pt) in thebulk. Their composition was varied in almost entire range byFig. 1. Co-sputtering onto PEGadjusting the sputter currents. XRD
results reveals fcc structure of Au/Ptnanoparticles with the (111) peak shift
from that of Au to Pt for an increase ofPt atom % (Fig. 2a, Langmuir 2020).
Fine structure analysis with atomic
resolution high-angle annual dark Fig. 2. (a) XRD and STEM-EDS maps of SSA Au/Pt andfield (HAADF) imaging in scanning- (b) intensity line profile of a SSA Au/Cu nanoparticle.
electron microscope (STEM) coupledwith energy dispersive X-ray spectra (EDS) further confirmed SSA structure in a single Au/Pt
nanoparticle (Fig. 2a). In intermetallic systems, such as Au/Cu, the sputtered nanoparticles
exhibited a random mixing, e.g., Au and Cu, in atom columns (Fig. 2b, Langmuir 2017),
suggesting the formation of SSA instead of intermetallics. These small SSA nanoparticles are inon-going study and expected to deliver interesting catalytic properties.
Particle growth mechanism
The particle growth in liquid was traced. By measuring particle size for various deposition
period and time, we obtained experimental evidence of the particle growth in both the surface andinside the liquid. Besides, impact of the liquids on size, structure, composition distribution, andaggregation of nanoparticles was elucidated. The physiochemical properties of the liquids,
particularly their binding strength to particles relatively compared with metal-metal interaction,
were demonstrated as a control factor. Small particles and stable dispersions were obtained withstronger binding strength of the liquid to metal, which is in line with the trend in chemical synthesis.
Acknowledgements:
This research was carried out at Laboratory of Novel Materials Hybrid Engineering, Graduate
School of Engineering, Hokkaido University with guidance of Professor Tetsu Yonezawa andcontribution of many past and present students. My sincere thanks go to all of those involved inthis research. I am also acknowledge great contribution from our collaborators. It is my honor to
be awarded the Encouragement Award. With this award as an encouragement, we will work harderto further develop complex alloy nanoparticles with multiple metal elements, address theirstructure and novel catalytic properties.
References: [1] Nguyen et al. Sci. Technol. Adv. Mater. 2018, 19, 883; [2] Nguyen et al. Mater.
Lett. 2016, 171, 75; [3] Nguyen et al. Langmuir 2017, 33, 12389; [4] Deng et al. Langmuir 2020,36, 3004; [5] Zhu et al. Langmuir 2021, 37, 6096; [6] Deng et al. Langmuir 2019, 35, 8418; [7]Nguyen et al. ACS Sustain. Chem. Eng. 2020, 8, 18167.