RESEARCH ARTICLE
◥NANOPARTICLES
Oriented attachment induces fivefold twins by
forming and decomposing high-energy
grain boundaries
Miao Song^1 , Gang Zhou^2 , Ning Lu^3 *, Jaewon Lee1,4, Elias Nakouzi^1 , Hao Wang^2 , Dongsheng Li^1 †
Natural and synthetic nanoparticles composed of fivefold twinned crystal domains have distinct
properties. The formation mechanism of these fivefold twinned nanoparticles is poorly understood.
We used in situ high-resolution transmission electron microscopy combined with molecular dynamics
simulations to demonstrate that fivefold twinning occurs through repeated oriented attachment
of ~3-nanometer gold, platinum, and palladium nanoparticles. We discovered two different mechanisms
for forming fivefold twinned nanoparticles that are driven by the accumulation and elimination of strain.
This was accompanied by decomposition of grain boundaries and the formation of a special class of
twins with a net strain of zero. These observations allowed us to develop a quantitative picture of the
twinning process. The mechanisms provide guidance for controlling twin structures and morphologies
across a wide range of materials.
T
winning in materials occurs when two
crystals that share the same crystal
lattice plane intergrow through certain
symmetry operations. Crystallographic
twins are widespread, being found in a
wide range of materials that include minerals
(such as rutile and wurtzite) ( 1 , 2 ), metals [such
as copper (Cu), silver (Ag), and gold (Au)] ( 3 , 4 ),
and ceramics [barium titanate (BaTiO 3 )] ( 5 ).
Twinning leads to a variety of structures and
morphologies that affect physical and chemi-
cal properties. For example, the stress of five-
fold twins (5-FTs) substantially increases the
Young’s modulus of nanowires ( 6 ), whereas
multitwinned Cu nanowires exhibit excellent
methane selectivity during reduction of car-
bon dioxide ( 7 ). Multiply twinned structures
have attracted substantial attention for ap-
plications in crystal growth ( 8 ), mechanical
engineering ( 9 ), biomedical diagnosis ( 10 ),
optics ( 11 ), and catalysis ( 12 ).
Understanding the properties of these
twinned materials required determining the
formation mechanisms that enables control
of the growth and the final shape. Fivefold
twins are a common multiply twinned struc-
ture that was discovered nearly 200 years ago
( 13 , 14 ), and the formation mechanisms and
potential applications have been widely studied
( 15 , 16 ). However, the underlying formation
mechanisms are unclear and subject to debate
because of the challenges of making direct
observations of the formation process at the
atomic scale. Proposed formation mechanisms
include (i) direct nucleation through atom-by-
atom addition on the basis of theoretical simu-lations ( 17 ), (ii) the successive twining and
growth of tetrahedral units ( 4 , 18 , 19 ), and (iii)
partial dislocation slipping ( 20 ). Experimental
studies were mainly based on morphology evo-
lution, in contrast to the decahedral symmetry
of 5-FTs ( 4 , 18 , 19 ). Furthermore, in these ex-
perimental studies, the particles had already
undergone twinning by the time they were
observed ( 18 , 20 ). Oriented attachment (OA)
of particles, which is a candidate pathway for
5-FT formation, was observed directly during
the formation of twin interfaces ( 21 ). We pri-
marily focused on face-centered cubic Au nano-
particles (NPs) as a model system with which to
investigate the twinning process at the atomic
scale. In order to observe the onset of twinning,
we chose small (~3 nm) Au NPs because of the
size effect on 5-FTs, which are stable with the
size of 3 to 14 nm owing to thermodynamics
( 22 – 24 ). Twinning exists in Au NPs of≥3nm
in our experiment (fig. S1, B and E) ( 25 ).Multiply twinned structures formed
through OA
We drop-cast spherical Au NPs (~3 nm) (fig.
S1) embedded in an organic matrix of 1-
dodecanethiol (fig. S2) on a transmission elec-
tron microscope (TEM) grid. The organics
decomposed under electron-beam (e-beam)
irradiation and the surface of the Au NPs
self-adjusted to decrease the surface energyRESEARCH
Songet al.,Science 367 ,40–45 (2020) 3 January 2020 1of6
(^1) Physical and Computational Sciences Directorate, Pacific
Northwest National Laboratory, Richland, WA 99352, USA.
(^2) Division of Titanium Alloys, Institute of Metal Research,
Chinese Academy of Sciences, Shenyang 110016, China. 3
Department of Materials Science and Engineering, University
of Michigan, Ann Arbor, MI 48109, USA.^4 Department of
Biomedical, Biological and Chemical Engineering, University
of Missouri, Columbia, MO 65211, USA.
*These authors contributed equally to this work.
†Corresponding author. Email: [email protected]
Fig. 1. Examples of resulting crystal structures after OA processes of Au NPs.(A) Formation of a
single crystal. (B) Formation of a twin structure with a twin boundary. (CtoF) Formation of crystals with
multiple twin interfaces, including (C) parallel twin interfaces, (D) crossed twin interfaces with an angle
of ~109° betweenS3s and a concave surface angle of ~89°, (E) crossed twin interfaces with an angle of ~70°
betweenS3s and a concave surface angle of ~98°, and (F) crossed twin interfaces with an angle of ~71°
betweenS3s and a concave surface angle of ~149°.