Department of Materials Engineering
    School of Engineering
    The University of Tokyo

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last update, 17 Jul, 2017   

Thanks to the recent progress in high-performance computational environments,
the range of applications of computational metallurgy is expanding rapidly.
Our recent works have focused on understanding physics and chemistry
during synthesis and processing of materials by numerical modelling.
Our target ranges from base materials such as iron and steel to
advanced materials such as carbon nanotubes, graphene.

1. Large-scale MD simulation of solidification and grain growth
2. Dewetting dynamics of metal thin film on substrate
3. Metal-catalyzed growth of carbon nanotubes and graphene
4. Interaction of graphenes with a turbostratic orientational relationship
5. Structure of semiconductor/bio-interface
6. Nanocluster dynamics in fast rate epitaxy
7. Phase transition in nanoparticles
8. Kinetics of heterointerface during phase transformation of iron and steel
9. Phase-field modelling of electrochemical process

Large-Scale MD Simulation of Solidification and Grain Growth

Continuous processes of homogeneous nucleation and solidification are
spontaneously achieved from an undercooled iron melt
without any phenomenological parameter in large-scale MD simulations [1-3],
which are performed on the GPU supercomputer.

[1] Y. Shibuta, K. Oguchi, T. Takaki, M. Ohno, Scientific Reports, 5 (2015) 13534.

[2] Y. Shibuta, S. Sakane, T. Takaki, M. Ohno, Acta Materialia, 105 (2016) 328-337.

[3] Y. Shibuta, S. Sakane, E. Miyoshi, S. Okita, T. Takaki, M. Ohno
Nature Communications, 8 (2017) 10.

(collaborative work with Kyoto Institute of Technology and Hokkaido University, Japan)

Moreover, grain growth in nanometer scale is closely investigated with a combination of
a large-scale MD simulation and a comprehensive post-analysis technique [4].
Then, a topological equation for the growth kinetics of 3D indivisual grains is derived.

[4] S. Okita, Y. Shibuta, ISIJ International, 56 (2016) 2199-2207.

Dewetting dynamics of metal thin film on substrate

Dewetting is one of the dominant factors determining the morphology of metal thin films and
nanoparticles on the substrate.It is essential to understand a fundamental aspect of dewetting
from the atomistic point of view [5] since it is essential to control the morphology of nanoparticles
on the substrate for the better use of catalytic metal as nanoparticles.
Moreover, dewetting is positively used for the formation of suspended graphene nanoribbons [6].

[5] Y. Maekawa, Y. Shibuta, Chemical Physics Lettes, 658 (2016) 30-36.

[6] H. Suzuki, T. Kaneko, Y. Shibuta, M. Ohno, Y. Maekawa, T. Kato
Nature Communications, 7 (2016) 11797.

(collaborative work with Tohoku University, Japan)

Metal-Catalyzed Growth of Carbon Nanotubes and Graphene

It is empirically known that the yield and quality of the carbon nanotubes and graphene
products strongly depend on a choice of carbon source molecules and additive.
Therefore, it is important to understand the dissociation process of carbon source molecules.
We have investigated the dissociaton of methane on the nickel(111) surface
to understand the initial stage of graphene growth via a CVD technique
by ab initio molecular dynamics simulation [7].

[7] Y. Shibuta, R. Alifin, K. Shimamura, T. Oguri, F. Shimojo, S. Yamaguchi,
Chem. Phys. Lett. 565 (2013) 92-97.

(selected as Editor's Choice Articles and Highly Cited Research 2016)
(collaborative work with Kumamoto University, Japan)

Moreover, dissociation of ethanol on a nickel cluster is investigated to reveal
the bond dissociation mechanism of carbon source molecules during carbon nanotube synthesis [8].
It was found that C-C bonds in only CHxCO fragments are dissociated on the nickel cluster,
whereas there is no preferential structure among the fragments for C-O bond dissociation.

[8] T. Oguri, K. Shimamura, Y. Shibuta, F. Shimojo, S. Yamaguchi,
Chem. Phys. Lett. 595-596 (2014) 185-191.

(collaborative work with Kumamoto University, Japan)

One of the unsolved issues is to understand a key factor determining a chirality of the carbon nanotubes.
The role of catalytic metals on carbon nanotube and graphene growth is investigated by
focusing on the orientation relationship between graphite network and crystalline metal surface [9].

[9] Y. Shibuta, J.A. Elliott, Chem. Phys. Lett. 472(2009)200-206.

(collaborative work with University of Cambridge, UK)

Interaction of Graphenes with a Turbostratic Orientational Relationship

It is well known that the AB stacking order between graphene layers in graphite is energetically
stable. However, there is little information on the interaction between the graphite layers
with a turbostratic orientational relationship (OR).
Interaction of two rigid defect-free graphene sheets with various turbostratic ORs is investigated.
It is revealed turbostratic orientations diminish the energy for translational displacement to zero. [10]

[10] Y. Shibuta, J.A. Elliott, Chem. Phys. Lett. 512 (2011) 146-150.

(collaborative work with University of Cambridge, UK)

Structure of Semiconductor/Bio-Interface

It is essential to elucidate the electrical double layer (EDL) structure including
biomolecules for controlling biointerfacial functions in biosensing devices.
The effect of double-stranded DNA (ds-DNA) on the EDL structure at the SiO2/NaClaq
interface in a concentrated solution is investigated by MD simulation [11].

[11] Y. Maekawa, Y. Shibuta, T. Sakata, Chem. Phys. Lett. 619 (2015) 152-157.

(collaborative work with Prof. Sakata's group in Dept. Mater. Eng, Univ. Tokyo.)

Nanocluster Dynamics in Fast Rate Epitaxy

The dynamics of Si nanoclusters during epitaxial growth is investigated [12].
Several nm sized Si cluster formed during rapid cooling is found to deform
instantaneously upon impingement on a Si(100) substrate at the same time
with the spontaneous ordering of the atomic structure to that of the substrate.

[12] L.W. Chen, Y. Shibuta, M. Kambara, T. Yoshida, Chem. Phys. Lett. 564 (2013) 47-53.

(collaborative work with Prof. Kambara's group in Dept. Mater. Eng, Univ. Tokyo.)

Phase Transition in Nanoparticles

Phase transition in metal nanoparticles is an interesting issue since it is different from that in bulk metal.
In addition to experiments over many years, molecular dynamics simulation contributes
to interpret thermodynamic properties in the nanoparticles.
Solidification and melting of metal nanoparticles are closely investigated.
It is confirmed that the depression of the melting point of nanoparticles is proportional
to the inverse of particle radius. [13]

[13] Y. Shibuta, T. Suzuki, J. Chem. Phys. 129(2008)144102.

Kinetics of Heterointerface during Phase Transformation of Iron and Steel

The kinetics of the (110)bcc//(111)fcc heterointerface of iron during the fcc-bcc phase transformation
has been investigated [14]. The various orientation relationships (ORs) between Nishiyama-Wasserman
(N-W) and Kurdjumow-Sachs (K-S) ORs, which are experimentally observed, were examined.
The planar propagation of the heterointerface was observed in the case of the N-W and near N-W ORs,
whereas a fast needlelike growth after planar growth was observed in the case of the K-S and near K-S ORs.

[14] S. Tateyama, Y. Shibuta, T. Suzuki, Scripta Materialia 59(2008)971-974.

Phase-Field Modelling of Electrochemical Process

A phase-field (PF) model for electrochemical processes, in which cations were driven by an electrostatic
potential coupled with a thermodynamic potential, was formulated on the basis of the PF model
for binary alloys. Using this model, Cu electrodeposition from CuSO4 solution has been investigated [15].

[15] Y. Shibuta, Y. Okajima, T. Suzuki, Sci. Tech. Adv. Mater. 8(2007)511-518.

Above methodology is now employed for application of the electrorefining process of materials.
Morphology of uranium electrodeposits on cathode with respect to applied voltage, zirconium concentration
in the molten salt and the size of primary deposit during pyroprocessing is systematically investigated [16].
It is found that there is a threshold zirconium concentration in the molten salt demarcating planar
and cellular/needle-like electrodeposits, which agrees with experimental results.

[16] Y. Shibuta, T. Sato, T. Suzuki, H. Ohta, M. Kurata, J. Nuclear Materials. 436(2013) 61-67.

(collaborative work with JAEA and CRIEPI, Japan)