*3.2. Manipulation 3.2. Manipulation*

In the ERATO project, TEM has been used not only as an observation apparatus but also as a tool for the manipulation of nanostructures by electrons on the specimen stage. The 200 keV JEM-2010 TEM has a pole piece with a magnetic field of 10<sup>4</sup> Gauss from top to bottom, where the specimen stage is located slightly above the centre. Based on the kinetic features analysed by Horiuchi et al. [4], the momentum transfer from electrons to nanoparticles is the source of their movement. The spiral trajectory of the electrons causes Al nanoparticles on the specimen stage to experience both a tangential force to rotate and revolve and a centripetal force to migrate, bond, and embed. The features around the specimen stage and the driving forces are illustrated in Figure 4. In the ERATO project, TEM has been used not only as an observation apparatus but also as a tool for the manipulation of nanostructures by electrons on the specimen stage. The 200 keV JEM-2010 TEM has a pole piece with a magnetic field of 104 Gauss from top to bottom, where the specimen stage is located slightly above the centre. Based on the kinetic features analysed by Horiuchi et al. [4], the momentum transfer from electrons to nanoparticles is the source of their movement. The spiral trajectory of the electrons causes Al nanoparticles on the specimen stage to experience both a tangential force to rotate and revolve and a centripetal force to migrate, bond, and embed. The features around the specimen stage and the driving forces are illustrated in Figure 4.

**Figure 4.** Model of the interaction between electrons and particles on the specimen stage in TEM. The magnetic field inside a pole piece is 104 Gauss in a 200 keV TEM. (**a**) Electrons follow a spiral trajectory in the magnetic field to transfer forces or momentum such that (**b**) the tangential force results in rotation and revolution and the centripetal force induces migration to gather, bond, and embed the particles. **Figure 4.** Model of the interaction between electrons and particles on the specimen stage in TEM. The magnetic field inside a pole piece is 10<sup>4</sup> Gauss in a 200 keV TEM. (**a**) Electrons follow a spiral trajectory in the magnetic field to transfer forces or momentum such that (**b**) the tangential force results in rotation and revolution and the centripetal force induces migration to gather, bond, and embed the particles.

### 3.2.1. Migration and Bonding 3.2.1. Migration and Bonding

A set of Al nanodecahedra migrated and bonded to the irradiation centre of the electron beam, as shown in Figure 5. Analysis by superposition before and after irradiation, as shown in Figure 5c, revealed that migration, diameter decrease, A set of Al nanodecahedra migrated and bonded to the irradiation centre of the electron beam, as shown in Figure 5. Analysis by superposition before and after irradiation, as shown in Figure 5c, revealed that migration, diameter decrease, revolution, and bonding occurred in the course of irradiation over 1200 s at 2.1 <sup>×</sup> <sup>10</sup><sup>20</sup> e/cm<sup>2</sup> s s, which was mainly due to the centripetal force, as shown in Figure 4. The bonding step of the two nanoparticles

is shown in Figure 6, where the (111) planes are aligned parallel by rotation before necking (a) and then necking with Σ3 twinning (b) to eventual coalescence (c) [5–7]. aligned parallel by rotation before necking (a) and then necking with 3 twinning (b) to eventual coalescence (c) [5,6].

revolution, and bonding occurred in the course of irradiation over 1200 sec at 2.1 × 1020 e/cm2sec s, which was mainly due to the centripetal force, as shown in Figure 4. The bonding step of the two nanoparticles is shown in Figure 6, where the (111) planes are aligned parallel by rotation before necking (a) and then necking with 3 twinning (b) to

revolution, and bonding occurred in the course of irradiation over 1200 sec at 2.1 × 1020 e/cm2sec s, which was mainly due to the centripetal force, as shown in Figure 4. The bonding step of the two nanoparticles is shown in Figure 6, where the (111) planes are

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eventual coalescence (c) [5,6].

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**Figure 5.** Effects of electron irradiation of a set of Al nanodecahedra inducing migration to the irradiation centre, as well as revolution and rotation. The intensity was 2.1 × 1020 e/cm2 s for (**a**) 0 s and (**b**) 1200 s. A schematic view of the effect is shown in (**c**) [6]. **Figure 5.** Effects of electron irradiation of a set of Al nanodecahedra inducing migration to the irradiation centre, as well as revolution and rotation. The intensity was 2.1 <sup>×</sup> <sup>10</sup><sup>20</sup> e/cm<sup>2</sup> s for (**a**) 0 s and (**b**) 1200 s. A schematic view of the effect is shown in (**c**) [6]. **Figure 5.** Effects of electron irradiation of a set of Al nanodecahedra inducing migration to the irradiation centre, as well as revolution and rotation. The intensity was 2.1 × 1020 e/cm2 s for (**a**) 0 s and (**b**) 1200 s. A schematic view of the effect is shown in (**c**) [6].

neck at 300 s [5,7]. 3.2.2. Rotation and Revolution The force acting on the nanoparticle in the magnetic field was also tangential, as well **Figure 6.** Al nanodecahedra (**a**) bonded by electron irradiation with an intensity of 2.1 × 1020 e/cm2 s after 300 s (**b**) and coalesced after 1500 s (**c**). The (111) planes in two Al nanodecahedra were aligned parallel by rotation and exhibited a 3 coincidence site lattice (CSL) boundary around the neck at 300 s [5,7]. **Figure 6.** Al nanodecahedra (**a**) bonded by electron irradiation with an intensity of 2.1 <sup>×</sup> <sup>10</sup><sup>20</sup> e/cm<sup>2</sup> s after 300 s (**b**) and coalesced after 1500 s (**c**). The (111) planes in two Al nanodecahedra were aligned parallel by rotation and exhibited a Σ3 coincidence site lattice (CSL) boundary around the neck at 300 s [5,7].

aligned parallel by rotation and exhibited a 3 coincidence site lattice (CSL) boundary around the

#### as centripetal, as shown in Figure 4, inducing a clockwise rotation of the nanoparticle on the specimen stage. The speed of rotation measured by the change in angle increased as 3.2.2. Rotation and Revolution 3.2.2. Rotation and Revolution

decrease in the diameter of the particle [6,8].

the irradiation intensity increased for irradiation times less than 1000 sec, as shown in Figure 7. The saturation of the rotation with longer exposure is considered to stem from a decrease in the diameter of the particle [6,8]. The force acting on the nanoparticle in the magnetic field was also tangential, as well as centripetal, as shown in Figure 4, inducing a clockwise rotation of the nanoparticle on the specimen stage. The speed of rotation measured by the change in angle increased as the irradiation intensity increased for irradiation times less than 1000 sec, as shown in Figure 7. The saturation of the rotation with longer exposure is considered to stem from a The force acting on the nanoparticle in the magnetic field was also tangential, as well as centripetal, as shown in Figure 4, inducing a clockwise rotation of the nanoparticle on the specimen stage. The speed of rotation measured by the change in angle increased as the irradiation intensity increased for irradiation times less than 1000 s, as shown in Figure 7. The saturation of the rotation with longer exposure is considered to stem from a decrease in the diameter of the particle [6,8].

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their migration, as shown in Figure 5c.

**Figure 7.** Rotation of Al nanodecahedra and its dependence on the irradiation intensity ranging from 3.0 × 1019 to 3.3 × 1020 e/cm2sec. The diameter of the nanoparticles is 20 nm, denoted on the line as <sup>0</sup> [6]. **Figure 7.** Rotation of Al nanodecahedra and its dependence on the irradiation intensity ranging from 3.0 <sup>×</sup> <sup>10</sup><sup>19</sup> to 3.3 <sup>×</sup> <sup>10</sup><sup>20</sup> e/cm<sup>2</sup> s. The diameter of the nanoparticles is 20 nm, denoted on the line as ϕ<sup>0</sup> [6].

To confirm the effects of the tangential force on the nanoparticle, the magnetic direction in the pole piece was changed from bottom to top by reforming the TEM. Figure 8 shows the revolution behaviour of nanoparticles in both directions of the magnetic field. The clockwise and counterclockwise revolutions of the Al nanoparticles clearly depended on the direction of the magnetic field, and their speed increased as the irradiation intensity increased. The revolution of the nanoparticles was accompanied by

To confirm the effects of the tangential force on the nanoparticle, the magnetic

To confirm the effects of the tangential force on the nanoparticle, the magnetic direction in the pole piece was changed from bottom to top by reforming the TEM. Figure 8 shows the revolution behaviour of nanoparticles in both directions of the magnetic field. The clockwise and counterclockwise revolutions of the Al nanoparticles clearly depended on the direction of the magnetic field, and their speed increased as the irradiation intensity increased. The revolution of the nanoparticles was accompanied by their migration, as shown in Figure 5c. **Figure 7.** Rotation of Al nanodecahedra and its dependence on the irradiation intensity ranging from 3.0 × 1019 to 3.3 × 1020 e/cm2sec. The diameter of the nanoparticles is 20 nm, denoted on the line as <sup>0</sup> [6].

**Figure 8.** Clockwise (+) and counterclockwise (−) revolution of Al nanoparticles during electron irradiation controlled by changing the magnetic field direction. The case shown in Figure 5 induced the clockwise revolution, whereas reversal of the magnetic field (bottom to top) induced the opposite direction of revolution. Here, indicates the diameter of the initial Al particle [8]. **Figure 8.** Clockwise (+) and counterclockwise (−) revolution of Al nanoparticles during electron irradiation controlled by changing the magnetic field direction. The case shown in Figure 5 induced the clockwise revolution, whereas reversal of the magnetic field (bottom to top) induced the opposite direction of revolution. Here, ϕ indicates the diameter of the initial Al particle [8].
