Control and Modification of Nanostructured Materials by Electron Beam Irradiation

Abstract

I have proposed a bottom-up technology utilising irradiation with active beams, such as electrons and ions, to achieve nanostructures with a size of 3–40 nm. This can be used as a nanotechnology that provides the desired structures, materials, and phases at desired positions. Electron beam irradiation of metastable θ-Al₂O₃, more than 10¹⁹ e/cm²s in a transmission electron microscope (TEM), enables the production of oxide-free Al nanoparticles, which can be manipulated to undergo migration, bonding, rotation, revolution, and embedding. The manipulations are facilitated by momentum transfer from electrons to nanoparticles, which takes advantage of the spiral trajectory of the electron beam in the magnetic field of the TEM pole piece. Furthermore, onion-like fullerenes and intercalated structures on amorphous carbon films are induced through catalytic reactions. δ-, θ-Al₂O₃ ball/wire hybrid nanostructures were obtained in a short time using an electron irradiation flashing mode that switches between 10¹⁹ and 10²² e/cm²s. Various α-Al₂O₃ nanostructures, such as encapsulated nanoballs or nanorods, are also produced. In addition, the preparation or control of Pt, W, and Cu nanoparticles can be achieved by electron beam irradiation with a higher intensity.

1. Introduction

The size range of several tens of nanometres represents a transition region from “top-down” to “bottom-up” processes in nanotechnology. The author has proposed a bottom-up technology utilising active beam irradiation to achieve nanostructures with a size of 3–40 nm. Recent developments in focusing and scanning technologies for active beams, such as electrons or ions, in tabletop apparatuses enable the evolution and control of various types of nanostructures, which can provide desirable hybrid structures, materials, and phases at the desired positions on the nanometre scale.

The source of the electron beam used by the author’s group is a transmission electron microscope (TEM) equipped with either an LaB₆ filament or a field emission gun. Although TEM has been widely used as an analysis tool for studying nanostructure and element distributions, we consider a specimen stage of 3 mm in diameter as a reaction field, and focused electrons with an intensity more than 50 times higher than that used under normal observation conditions. The electron irradiation intensity ranged from 5×10¹⁹ to 4 × 10²³ e/cm²s (8 × 10⁴–6 × 10⁸ A/m²) in our experiment, and we succeeded in producing oxide-free nanoparticles via electron irradiation of the oxide and facilitated their subsequent manipulation.

In this paper, three topics on the manipulation and control of ceramics and metals by electron beam irradiation are discussed: (1) the preparation of Al nanoparticles and their nanostructure evolution starting from metastable Al₂O₃, (2) their manipulation by electrons, and (3) the effects of electron irradiation on other nanoparticles, such as Cu, Pt, and W, to prepare nanofilms. This review is based on papers published between 1995 and 2005.

2. Electron Excited Reaction Field

2.1. Overview

In the “Exploratory Research for Advanced Technology” (ERATO) “Tanaka Solid Junction Project,” JST [1], held in 1993–1998, I commenced an innovative challenge to fabricate nano-/microstructures by irradiation with an energy beam such as electrons and ions, based on the proposed concept of an “excited reaction field.” One of the characteristics of such field is that the beams are obtained on the specimen stage of a TEM for electrons, and on the milling/thinning stage for ions. In other words, observation or specimen preparation apparatuses are utilised for their beam source and excited reaction fields. Irradiation with these energy beams has the following merits: first, it facilitates the selection of the site/energy/reaction. Second, it can induce nonequilibrium/catalytic reactions, making it possible to manipulate atomic clusters, synthesise nanomaterials, control the nanostructure and phase, and modify the nanospace.

2.2. Effects of Electron Beam Irradiation on θ-Al₂O₃

The normal electron beam intensity for observation by a TEM equipped with an LaB₆ filament is on the order of 10¹⁸ e/cm²s (1600 A/m²) for bright-field imaging and 5 × 10¹⁶ e/cm²s s (80 A/m²) for selected area diffraction measured by a fluorescent plate. We increased the electron beam density by increasing the current in the condenser lens to between 10¹⁹ and 10²² e/cm²s to enable electron irradiation of the nanomaterials.

When an electron beam irradiates metastable θ-Al₂O₃ particles at an intensity of 10²⁰ e/cm²s in a TEM, successive reactions occur: ① Al nanoparticle inducement, ② rotation, revolution, and migration to coalesce/embed, and ③ formation of onion-like fullerenes and Al intercalation, as shown in Figure 1. Furthermore, ④ θ- or δ-Al₂O₃ nanostructures are obtained under flashing-mode irradiation (rapid switching between 10¹⁹ and 10²² e/cm²s).

3. Nanostructure Evolution

3.1. Al Nanoparticles

The starting material consists mainly of a metastable θ-Al₂O₃ monoclinic structure accompanied by orthorhombic δ-Al₂O₃ (Al₂O₃ allotrope), and it is different from stable α-Al₂O₃ with a trigonal structure. The θ-Al₂O₃ powder was synthesised using the vaporised metal combustion method (Admatechs Company Limited) [2].

Electron irradiation (2.1 × 10²⁰ e/cm²s for 50 s) of one θ-Al₂O₃ particle with a diameter of 100 nm on the φ3 mm specimen stage of the TEM led to the formation of Al nanoparticles with a diameter of 2–20 nm and a stable α-Al₂O₃ particle, as shown in Figure 2 [3]. The TEM used was a JEOL JEM-2010 equipped with an LaB₆ filament and a specimen chamber under a vacuum of 10⁻⁷ Pa, obtained by a direct coupling sputter ion pump. Under these conditions, the electrons cut the Al-O bond in θ-Al₂O₃, which was followed by the loss of oxygen to the vacuum and Al atom recombination to form nanoparticles, as schematically shown in Figure 3. In the electron-irradiated area, transformation or rearrangement from θ-Al₂O₃ to stable α-Al₂O₃ also occurred.

θ- and δ-Al₂O₃ appear as low-temperature phases in the allotropic transformation from γ-Al₂O₃ to α-Al₂O₃ upon heating. The starting powder used in this experiment was obtained by melting Al metal powder, vaporisation, collision of droplets, and quenching into the metastable phase [2]. The powder particles had a spherical shape with an average diameter of approximately 10 µm. No stable α-Al₂O₃ structure was observed by X-ray diffraction, and an equilibrium thermodynamic consideration was invalid for metastable θ-Al₂O₃, where the binding energy for Al-O was lower than that for α-Al₂O₃. The reaction was expected to proceed via a nonequilibrium route. Electron irradiation promoted the decomposition of metastable θ-Al₂O₃, recombination of Al atoms, loss of a part of oxygen atoms into vacuum, and transformation to stable α-Al₂O₃, as shown in Figure 3, which resembles one stile of the electron-stimulated desorption.

Al nanoparticles have a twinned decahedron structure surrounded by {111} surfaces, which has been reported in typical face-centred cubic noble metals, such as Au, Pt, or Ag, whereas no report has been published on Al because of its easily oxidised surface. Decahedra appeared with diameters in the range of 10–20 nm, and further electron irradiation of a set of nanodecahedra enabled their manipulation, as discussed in the next section.

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 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.

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, revolution, and bonding occurred in the course of irradiation over 1200 s at 2.1 × 10²⁰ e/cm²s 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) [5,6,7].

3.2.2. Rotation and Revolution

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].

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.

3.2.3. Embedding

The forces discussed in Section 3.2.1 and 3.2.2 manipulate the nanoparticles to cause migration and embedding into the substrate. Figure 9 shows an example of an Al nanoparticle embedded in the α-Al₂O₃ matrix following electron irradiation at 10²⁰ e/cm²s, which is attributed to an epitaxial relationship between the two substances. This technique can be utilised for the implantation of catalysts, such as Pt nanoparticles, at the desired position in a matrix [9].

3.3. Fullerene and Intercalation

A series of nanostructures were formed on the amorphous carbon nanofilm of the specimen mesh, which was suspended on a Cu grid. Electron irradiation induced the formation of an onion-like fullerene nanostructure under the Al nanoparticles by the catalysis effect and promoted the intercalation of Al atoms between the graphite shells.

3.3.1. Onion-Like Fullerene

Giant onion-like fullerenes were induced from the amorphous carbon nanofilms under the Al nanodecahedra by electron beam irradiation, as shown in Figure 10. A catalytic reaction nucleated a graphitic flake along the edge of the Al nanoparticle, and prolonged electron irradiation induced the growth of the fullerene, shrinking of the nanoparticles, and intercalation of Al atoms between the shells, as shown in Figure 11 and Figure 12 [5,10].

3.3.2. Intercalation

To verify Al atom intercalation into the graphitic shells, an analysis using energy dispersive spectroscopy (EDS), for which the JEM-2010 TEM was equipped, was conducted on the electron irradiated specimen. Figure 13 shows the presence of Al atoms in the circled area of 7 nm in diameter, accompanied by C and Cu in the grid. Moreover, the expansion of the graphite (002) lattice spacing confirmed the presence of Al atoms between the layers, as shown in Figure 14. However, the growth saturated below the composition of Al₂C₆ owing to the blocking effect of the coexisting Cu atoms or the constraint of passing through multiple carbon layers. Electron energy loss spectra (EELS) also suggested the partial replacement of carbon atoms by Al or Cu atoms through σ bond, sp², decrease, as shown in Figure 15 [10,11,12].

4. Al₂O₃ Derivatives

Continuous electron irradiation of metastable θ-Al₂O₃ at 2.1 × 10²⁰ e/cm²s produced Al nanoparticles and stable α-Al₂O₃ particles, as shown in Figure 2. When the intensity and area of electron irradiation changed abruptly (i.e., flashing of the beam), other-shaped nanosized aluminium oxides were obtained. In this section, I present the oxide derivatives of Al₂O₃ oxides with different shapes and phases.

4.1. α-Al₂O₃ Nanorods

Although α-Al₂O₃ with a polygonal shape was deposited beside θ-Al₂O₃ by the recombination of Al and O atoms, the α-Al₂O₃ nanorods shown in Figure 16 grew from the surface of the parent α-Al₂O₃. The rods had a faceted structure surrounded by {100} surfaces and grew in the {110} direction. Figure 16 was obtained in situ, in which the nanorods grew without an amorphous oxide film.

4.2. δ-, θ-Al₂O₃ Nanoballs/Nanowires

When metastable Al₂O₃ was irradiated by electrons with a higher density over a short time, the structure was retained, but a different nanostructure was also obtained. Kameyama and Tanaka abruptly switched between intensities of 5.5 × 10²² and 5 × 10¹⁹ e/cm²s in a so-called “flashing mode,” maintaining each state for 0.1 s, which facilitated the formation of θ-, δ-Al₂O₃ nanorods/nanoballs, as shown in Figure 17, respectively [13].

Both θ-Al₂O₃ nanowires and nanoballs grown using flashing-mode electron beam irradiation are shown in Figure 17. They connected and grew toward the irradiation centre from the original θ-Al₂O₃ particle surface. The nanowire and nanoball had a (111)//(101) epitaxial relationship, as shown in Figure 18. The θ-Al₂O₃ nanoball was a sphere of 30 nm in diameter covered with an amorphous Al-O layer, suggesting that the impact of a higher irradiance electron beam resulted in a temperature rise of approximately 400 °C, reaction, and rapid cooling without phase transformation. The δ-Al₂O₃ nanowires and nanoballs shown in Figure 19 were obtained by applying the same flashing electron beam to δ-Al₂O₃ particles. The diameter of the δ-Al₂O₃ particles was 20 nm, which was slightly smaller than that of the θ-Al₂O₃ particles, and no explicit epitaxy relation was observed.

4.3. Al₂O₃ Nanoparticle Encapsulation

The surface of the Al₂O₃ particles was easily covered by an amorphous hydrocarbon layer through a reaction with residual gases in the TEM, where CO, H₂O, and H₂ remained even in a highly evacuated atmosphere. When the particles were irradiated by electrons through the outer layer, their inner volume was pulverised into smaller nanoparticles. An example is shown in Figure 20, for the case in which δ-Al₂O₃ particles with 200 nm in diameter were transformed into δ- and α-Al₂O₃ nanoballs with 2–20 nm in diameter, encapsulated by a hydrocarbon skin. This structure was generated by irradiation with an intensity of 1.6 × 10²⁰ e/cm²s, which was as high as that used for nanoparticle preparation and manipulation. Nanoparticle encapsulation technology may be applicable to drug delivery systems in medicine [15].

5. Other Nanoparticles

5.1. W Nanoparticles and Manipulation

In Section 2, a novel method for preparing oxide-free Al nanoparticles from metastable oxides using electron beam irradiation was discussed. This method can be extended to other nanoparticles of easy oxide-forming elements, such as W. W has a heavier specific weight of 19.3 g/cm³, and W-O has a larger bonding enthalpy such that a higher electron irradiation intensity is required to obtain W nanoparticles from WO₃. Although the fundamental electron optics in the TEM were the same as those used for Al nanoparticles, electrons from the field emission source provided a higher intensity of 10²³ e/cm²s than the 10²⁰e/cm²s obtained from the LaB₆ filament. Using a Hitachi HF-2000 TEM equipped with a field emission gun with an intensity of 4 × 10²³ e/cm²s, Tamou and Tanaka reported the formation of W nanoparticles with an average diameter of 4.3 nm, as shown in Figure 21. The EELS spectra showed no oxygen atoms on the W surface, as shown in Figure 22 [16].

5.2. W Migration to Bond and Fullerene Formation

Further electron irradiation of two W nanoparticles, obtained as in Figure 21 at 1.9 × 10²¹ e/cm²s, which is an irradiation 10 times higher than that used to form Al as shown in Figure 6, induced migration, bonding, and coalescence, as shown in Figure 23 [16]. Graphitic shells also nucleated beneath the W nanoparticles from the amorphous carbon film and grew to onion-like fullerene, which is the same phenomenon observed with Al nanoparticles shown in Figure 10, Figure 11 and Figure 12 [16].

5.3. Bonding of Pt and Cu Nanoparticles

Electron irradiation of a group of Pt and Cu nanoparticles induced bonding to form nanofilms, as shown in Figure 24, Figure 25 and Figure 26. In these cases, nanoparticles were prepared by Ar ion sputtering with a diameter of 10 nm for Pt and 50 nm for Cu. The irradiation intensity for Pt was the same as that for Al, whereas it was 100 times higher for Cu. Bonded Pt/Pt mainly showed three stable Σ3 twin boundaries. The Cu particles migrated to the irradiation centre and bonded, as shown in Figure 26 and Figure 27. The driving force was also the momentum transfer from electrons in the pole piece of the TEM, as shown in Figure 4 and Figure 5 [17,18,19,20].

6. Nature of Nanoparticle Manipulation and Nanostructure Modification by Electron Beam Irradiation

6.1. Temperature Rise in Al Nanoparticle Manipulation

In Section 3.2, various types of manipulation of Al nanoparticles on the TEM specimen stage were explained. These were migration, bonding, rotation, revolution, and embedding of the nanoparticles, and the driving forces were explained as tangential and centripetal forces, as shown in Figure 4. Another possibility of manipulation is the temperature rise caused by electron irradiation to induce their movement. Xu and Tanaka [10] estimated the temperature rise at the stage as 10° C at most, based on Equation (1) using Fisher’s theory [21]:

Tm − Tg = r²I₀ΔE[a₀ + ln(R/r)²]/4kz,

(1)

where Tm is the maximum temperature of the carbon film, Tg is the temperature of the Cu support grid, namely Tm−Tg is the temperature rise by electron beam irradiation, r is the radius of the irradiation beam, I₀ is the intensity of the irradiation beam (10²⁰ e/cm²s), ΔE is the energy loss of the incident electron in the carbon film, when it is <1000 nm thick, a₀ is Euler’s constant (0.5772), R is the distance between the irradiation beam centre and the Cu grid bar, k is the thermal conductivity of carbon, and z is the thickness of the carbon film (20 nm).

The heating effect in the localised area under the irradiation condition of 10²⁰ e/cm²s can be a minor effect, and the Lorenz force or the momentum transfer from electrons and ionised atoms is the major effect of the manipulation. This effect is clearly supported by the counterclockwise revolution caused by the magnetic field change, as shown in Figure 8 [8].

6.2. Temperature Rise in Al₂O₃ Nanocomplex and W Nanoparticles

When θ-Al₂O₃ was irradiated at a density of 10¹⁹–10²⁰ e/cm²s, Al and α-Al₂O₃ were formed, as shown in Figure 2 and Figure 16, where the reaction proceeded with a small temperature increase of the order of 10 °C, as shown in Section 6.1. On the contrary, the flashing mode of electron irradiation by rapid switching between intensities of 5.5 × 10²² and 5 × 10¹⁹ e/cm²s was applied to θ- and δ-Al₂O₃ to induce Al₂O₃ nanoball/nanowire complexes, as shown in Figure 17 and Figure 19 [13]. The higher electron beam intensity increased the temperature by more than 300 °C, as calculated through I₀ in Equation (1) by maintaining 5.5 × 10²² e/cm²s even in a short time of less than 0.1 s. This temperature increase was also predicted by Yokota et al. [22]. Rapid and concentrated heat input at the localised resulted in an Al-O recombined nanoball/nanowire complex with epitaxy at the interface, as shown in Figure 18 [14].

Heavy atoms such as W required a higher irradiation intensity of 4 × 10²³ e/cm²s to obtain W nanoparticles, as shown in Figure 21 [16]. Although the binding energy of W–O in the starting material WO₃ was smaller than that of Al–O, the W atom is ten times heavier than the Al atom, and required a higher energy for sputtering. A temperature rise was also expected in this irradiation condition, but no melting was observed because of its higher melting point, 3680 K.

6.3. Lorentz Force in Nanoparticle Manipulation

To discuss the mechanism of nanoparticle manipulation in a TEM, the interaction between electrons and nanoparticles on the specimen stage in the magnetic field was analysed. The TEM used in this study was 200 keV JEM-2010, which 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 plane. In Figure 4, the electron trajectory is illustrated schematically by Horiuchi et al. [4], and the Lorentz forces F₁ and F₂ arise from the magnetic components Br and Bz, respectively, with spirally running electrons. The specimen stage is located between planes 1 and 2, and Al, W, Pt, and Cu nanoparticles experience both a tangential force to rotate and revolve and a centripetal force to migrate, bond, and embed. The momentum transfer from electrons to nanoparticles is the source of this movement.

The Lorentz force exerted on one electron, F_e, was roughly estimated by Equation (2)

F_e = m_ev_e²/r,

(2)

where m_e is the mass of one static electron as 9.1094 × 10⁻³¹ kg, v_e is the velocity of electrons, considering the relativistic effects at 200 kV as v_e = v₂₀₀ 1.3914 = 2.900 × 10⁸ m/s, and r is the distance between the nanoparticle and the irradiation centre. When assuming the experimental case of Al nanoparticles shown in Figure 5, r = 60 nm, the Lorentz force from one electron F_e was 1.277 × 10⁻⁶ N. The total Lorentz force, F, to the Al nanoparticle of 20 nm in diameter with an irradiation time of 1200 s at 10²⁰ e/cm²s was estimated to be 9.63 × 10⁵ N. Although this is the maximum value, which occurs when electrons travel from plane 1 to 2 and the driving force of nanoparticle manipulation changes the direction from tangential to centripetal, it is too high for nanoparticle movement. The author proposes the following reasons: although the electron density was measured on the fluorescent plate beneath the stage, accelerated electron velocity decreased while travelling inside a TEM, and electrons lost their kinetic energy through ionisation of the wall by their impact. The Lorentz force decreased by at least 1/100. The existence of a friction force between nanoparticles and a substrate carbon film could also be one of the causes. The effective cross-section of the nanoparticle might be considered, which decreases the impact of the electrons.

The Lorentz force for nanoparticle manipulation is also valid for W, Pt, and Cu, as shown in Figure 23, Figure 24, and Figure 26. Although the time to bond is different depending on the density of the weight, electron irradiation focusing to the localised region will be a candidate technology for fabricating circuits or functional dots by nanoparticle arrays.

7. Summary of the Nanostructure Evolution and Manipulations in the Electron Excited Field

Research conducted by my group on nanostructure evolution by electron beam irradiation from 1995 to 2005 was reviewed. I have utilised electron beams in TEM to synthesise nanomaterials and manipulate their nanostructures, in addition to observing and analysing nanostructures. An overview of the effects of electron irradiation is presented in Figure 28 and Figure 29, where the abscissa is expressed as the electron irradiation intensity on a logarithmic scale. The electron beam was focused for synthesis and manipulation up to 10¹⁹–10²⁴ e/cm²s, which is higher than 10¹⁶ e/cm²s generally used for electron diffraction and 10¹⁸ e/cm²s used for bright-field imaging.

Figure 28 shows that electron irradiation of metastable θ-Al₂O₃ provides oxide-free Al nanoparticles, rod-like α-Al₂O₃, and encapsulated nanoparticles, whereas flashing mode provides θ-, δ-Al₂O₃ nanoball/nanowire complexes. The formation of W nanoparticles from WO₃ requires a higher intensity of more than 10²³ e/cm²s. Electrons traveling in a spiral trajectory in the magnetic field of the pole piece transfer momentum to the Al nanoparticles enable various types of manipulation, such as migration, bonding, rotation, revolution, embedding, fullerene formation, and intercalation. The intensity is also more than 100 times higher than that of normal observation conditions, as shown in Figure 29. The combination of such syntheses and manipulation will provide more complicated nanostructures for future applications.

8. Recent Development in Control and Manipulation of Nanostructured Materials

In this review, pioneering works by the author’s group published in 1995–2005 are summarised as a tool for nanomaterial control and manipulation at the TEM room temperature stage. In these works, mediate-accelerating keV was initially used, followed by accompanying magnetic field, and focusing electrons to the localised area. Although there are several works on the effects of electron irradiation, reviews on this topic are scarce. For example, lattice defects such as point defects or stacking faults are introduced as radiation damage in the region of MeV electron irradiation, for which an ultra-high voltage TEM has been used as an experimental simulation. Krasheninnikov et al. published an excellent review paper on the effects of ion and electron irradiation, collecting more than 680 papers [23], which contained derivation and simulation for nanostructured materials. Accompanying magnetic field and focusing electrons to the localised area in TEM are unique technologies for manipulation, which were partly covered in the papers by Zheng et al. [24] and Andres et al. [25]. Zheng et al. reported that the trapping force for one nanoparticle was on the order of 10⁻⁹ N in the electron density gradient of 10¹⁸⁻¹⁹ e/cm²s [24] which is the same order of magnitude as discussed in Section 6.3. Simulation by first-principle theory using the density of state is important for predicting the formation, growth, and coalescence of nanoparticles [25].

9. Conclusions

The author’s group succeeded in inducing the formation of Al nanoparticles by electron irradiation of metastable θ-Al₂O₃, followed by manipulation of the nanoparticles. A series of phenomena was observed without heating using high-resolution TEM (HRTEM), with an electron beam intensity as low as 10^19–20 e/cm²s. The typical morphology of the nanoparticles was that of a nanodecahedron surrounded by (111) surfaces with twins. Electron beam irradiation of a group of Al nanoparticles promoted their rotation, revolution, and migration to the irradiation centre, resulting in bonding and embedding into an α-Al₂O₃ matrix. The driving force is considered to be the momentum transfer from electrons spiralling across the pole piece of the HRTEM in a strong magnetic field to the Al nanoparticles. When nanoparticles were placed on an amorphous carbon film, onion-like fullerene nucleated and grew beneath them, and finally, a metallofullerene or Al-atom-intercalated structure was formed by electron irradiation.

To develop the manipulation technology for other types of nanoparticles, an electron beam was used to irradiate Cu nanoparticles of 10–50 nm in diameter at an irradiation intensity of 5.5 × 10²² e/cm²s, Pt nanoparticles at 1.0–3.3 × 10²⁰ e/cm²s, and W nanoparticles derived from WO₃ at 9 × 10²⁰ to 4 × 10²³ e/cm²s. The behaviour of Cu, Pt, and W nanoparticles under electron irradiation was similar to that of Al, and a nanofilm was finally formed. The CSL boundary structures at the bonded interface of Cu nanoparticles were found to be unstable Σ7 and Σ13b, which are different from the stable Σ3 obtained in Al and Pt with weaker electron beam irradiation.

The possible scientific contribution of electron irradiation is the synthesis of materials in a metastable state through a nonequilibrium reaction in vacuum, as well as the induction of hybridised nano-/mesostructures. It also enables the study of the nature of materials in a pristine and controlled environment, for example, without the formation of an oxide. From the viewpoint of application to devices, nanosized balls, dots, wires, and tube-forming three-dimensional structured circuits may be used as elements of nanodevices, and chemically active points embedded in the substrate for use as a catalyst can be achieved by the manipulation of electron irradiation. With respect to industrial applications, our technologies will contribute to the development of micro- and nanoelectromechanical systems, memories, photonics, battery electrodes, H₂ storage, and more.