**6.2 Radiation stability of embedded gold nanoparticles**

In addition to the work done on freestanding gold nanoparticles, there have been several studies exploring the response of heavy ion irradiation to particles

**63**

**Figure 8.**

*Evolution of Gold Nanoparticles in Radiation Environments*

embedded in a matrix. The most common matrix that has been used for these studies is amorphous SiOx, as it provides a stark contrast in composition, density, and properties to that of the gold nanoparticles. Similar to the observations in the freestanding nanoparticles, Rizza et al. [61–63] have shown that sputtering plays an important role in the evolution of the embedded particles. In addition to watching the size of the particles decrease, the matrix provides a medium that serves to slow down the travel of the sputtered gold resulting in a satellite structure of smaller gold nanoparticles surrounding the original. The example micrographs and size

*Effects of single 46 keV ions in gold nanoparticles of decreasing size. Note that the magnification is similar for all micrographs. Each pair of micrographs is separated by one frame, about 0.25 s here. (a–c) A single ion strike in a 60-nm nanoparticle created a surface crater, marked by the white arrow. (c) The difference image highlights the change between (a) and (b); features present only in (a) are dark, and newly formed features present only in (b) appear light. (d–f) A single ion creating a crater in a 20-nm nanoparticle. (f) The difference image and (g–i) ~5-nm teardrop-shaped nanoparticle was initially surrounded by a number of previously sputtered particles. (h) The nanoparticle exploded, leaving several particles nearby. (i) Difference image showing the locations of the old and new particles. The white arrow indicates a fragment from (h) that is difficult to see in (i) because it overlapped the original nanoparticle location. Source: https://www.cambridge.org/core/journals/ journal-of-materials-research/article/physical-response-of-gold-nanoparticles-to-single-self-ion-bombardment/ F9933AF9ABAF6D1D3747AE1F8FFB5428. Materials Research Society. Ref. [59], reproduced with permission.*

*DOI: http://dx.doi.org/10.5772/intechopen.80366*

#### **Figure 8.**

*Gold Nanoparticles - Reaching New Heights*

**62**

**Figure 7.**

increased sputtering, sintering, ballistic destruction, and possible ejection demonstrates that the response of gold nanoparticles to heavy ion irradiation is far from that expected by classical theories and models based on bulk sample geometries. As such, significant further investigation is needed before any commercialization in

*Source electron micrographs and discrete 4D electron tomograms of Au nanoparticles irradiated with 3 MeV* 

*Corresponding 3-D tomogram reconstructions, rotated to a different angle from the source micrograph. Source: http://pubs.rsc.org/en/content/articlelanding/2014/cc/c3cc49479a#!divAbstract. The Royal Society of* 

*. (b, d, f)* 

*Cu3+. (a, c, and e) Example micrographs from tilt series at increasing fluences up to ~1015 cm<sup>−</sup><sup>2</sup>*

*Chemistry. Reproduced from [28] with permission of The Royal Society of Chemistry.*

In addition to the work done on freestanding gold nanoparticles, there have been several studies exploring the response of heavy ion irradiation to particles

displacement damage environments is considered.

**6.2 Radiation stability of embedded gold nanoparticles**

*Effects of single 46 keV ions in gold nanoparticles of decreasing size. Note that the magnification is similar for all micrographs. Each pair of micrographs is separated by one frame, about 0.25 s here. (a–c) A single ion strike in a 60-nm nanoparticle created a surface crater, marked by the white arrow. (c) The difference image highlights the change between (a) and (b); features present only in (a) are dark, and newly formed features present only in (b) appear light. (d–f) A single ion creating a crater in a 20-nm nanoparticle. (f) The difference image and (g–i) ~5-nm teardrop-shaped nanoparticle was initially surrounded by a number of previously sputtered particles. (h) The nanoparticle exploded, leaving several particles nearby. (i) Difference image showing the locations of the old and new particles. The white arrow indicates a fragment from (h) that is difficult to see in (i) because it overlapped the original nanoparticle location. Source: https://www.cambridge.org/core/journals/ journal-of-materials-research/article/physical-response-of-gold-nanoparticles-to-single-self-ion-bombardment/ F9933AF9ABAF6D1D3747AE1F8FFB5428. Materials Research Society. Ref. [59], reproduced with permission.*

embedded in a matrix. The most common matrix that has been used for these studies is amorphous SiOx, as it provides a stark contrast in composition, density, and properties to that of the gold nanoparticles. Similar to the observations in the freestanding nanoparticles, Rizza et al. [61–63] have shown that sputtering plays an important role in the evolution of the embedded particles. In addition to watching the size of the particles decrease, the matrix provides a medium that serves to slow down the travel of the sputtered gold resulting in a satellite structure of smaller gold nanoparticles surrounding the original. The example micrographs and size

#### **Figure 9.**

*(a–e) Bright-field TEM micrographs of the time sequence of an embedded nanoparticle evolution under 4 MeV Au irradiation at 300 K at increasing fluences up 8 × 1016 cm<sup>−</sup><sup>2</sup> . (f–j) The corresponding size distributions of nanoparticle and resulting satellites [61]. Source: https://aip.scitation.org/doi/abs/10.1063/1.2402351. American Institute of Physics. Reprinted from G. Rizza et al., Journal of Applied Physics, Vol. 101, pp. 014321, with the permission of AIP Publishing.*

**65**

**7. Future directions**

**Figure 10.**

*Evolution of Gold Nanoparticles in Radiation Environments*

distributions of this transition from the original embedded nanoparticle through this satellite structure to the final clusters of smaller particles can be seen in **Figure 9** [61]. The shape of the particles can also be altered depending on the irradiation condition. Mishra et al. showed that by irradiating gold nanoparticles

*(a) Cross-sectional transmission electron microscopy image of pristine film and (b) cross-sectional transmission electron microscopy image of an irradiated film at 45° beam incident normal with 120 MeV Au [64]. Source: https://aip.scitation.org/doi/10.1063/1.2764556. American Institute of Physics. Reprinted from Y.K. Mishra et al.,* 

beam tilted 45° off normal, elongated embedded nanoparticles can be formed, as seen in **Figure 10** [64]. There are probably many more very unique far-fromequilibrium structures that can originate from embedded gold nanoparticles by varying environmental parameters during the ion irradiation. These structures can be further controlled by combining the radiation damage of the embedded particle with thermal diffusion to study classical Ostwald ripening and other diffusional steps [65, 66]. The evolution of these particles can be understood through a combi-

In addition to the embedding of gold nanoparticles in a ceramic matrix, an effort has also been made to explore the radiation response of polymer matrices embedded with gold and other heavy metal nanoparticles. It has been shown that such materials can serve as easily processible and portable radiation shields [67]. With further study developing on the concepts presented in these examples of ion irradiated embedded gold nanoparticles, a range of complex far-from-equilibrium structures can be envisioned with an even greater number of potential novel applications.

Clearly, the response of both freestanding and embedded gold nanoparticles is drastically different than gold in bulk or thin-film morphologies and is highly dependent on the radiation environment, particle morphology, and surface conditions. Additional work is needed to elucidate the underlying physics governing the increased sputtering and other scaling effects observed in gold nanoparticles [26, 27, 56]. Without a detailed understanding of the mechanisms active when the displacement damage length scale of the radiation event approaches that of the size of the nanoparticle exposed, it will be challenging to employ gold nanoparticles in most radiation environments. If the significant enhancement of sputtering is inherent and cannot be overcome, then the application of gold nanoparticles subject to ionizing radiation may be limited to those environments that produce minimal dose or sputtering yields. Conversely, if properly understood and controlled, the enhanced sputtering yields may also open new fields of study and possible

with the ion

embedded in SiOx with 120 MeV Au to a fluence of 3 × 1013 ions cm−<sup>2</sup>

*Journal of Applied Physics, Vol. 91, pp. 063103, with the permission of AIP Publishing.*

nation of rate theory and Monte Carlo modeling [63].

*DOI: http://dx.doi.org/10.5772/intechopen.80366*

#### **Figure 10.**

*Gold Nanoparticles - Reaching New Heights*

**64**

**Figure 9.**

*permission of AIP Publishing.*

*(a–e) Bright-field TEM micrographs of the time sequence of an embedded nanoparticle evolution under 4 MeV* 

*nanoparticle and resulting satellites [61]. Source: https://aip.scitation.org/doi/abs/10.1063/1.2402351. American Institute of Physics. Reprinted from G. Rizza et al., Journal of Applied Physics, Vol. 101, pp. 014321, with the* 

*. (f–j) The corresponding size distributions of* 

*Au irradiation at 300 K at increasing fluences up 8 × 1016 cm<sup>−</sup><sup>2</sup>*

*(a) Cross-sectional transmission electron microscopy image of pristine film and (b) cross-sectional transmission electron microscopy image of an irradiated film at 45° beam incident normal with 120 MeV Au [64]. Source: https://aip.scitation.org/doi/10.1063/1.2764556. American Institute of Physics. Reprinted from Y.K. Mishra et al., Journal of Applied Physics, Vol. 91, pp. 063103, with the permission of AIP Publishing.*

distributions of this transition from the original embedded nanoparticle through this satellite structure to the final clusters of smaller particles can be seen in **Figure 9** [61]. The shape of the particles can also be altered depending on the irradiation condition. Mishra et al. showed that by irradiating gold nanoparticles embedded in SiOx with 120 MeV Au to a fluence of 3 × 1013 ions cm−<sup>2</sup> with the ion beam tilted 45° off normal, elongated embedded nanoparticles can be formed, as seen in **Figure 10** [64]. There are probably many more very unique far-fromequilibrium structures that can originate from embedded gold nanoparticles by varying environmental parameters during the ion irradiation. These structures can be further controlled by combining the radiation damage of the embedded particle with thermal diffusion to study classical Ostwald ripening and other diffusional steps [65, 66]. The evolution of these particles can be understood through a combination of rate theory and Monte Carlo modeling [63].

In addition to the embedding of gold nanoparticles in a ceramic matrix, an effort has also been made to explore the radiation response of polymer matrices embedded with gold and other heavy metal nanoparticles. It has been shown that such materials can serve as easily processible and portable radiation shields [67]. With further study developing on the concepts presented in these examples of ion irradiated embedded gold nanoparticles, a range of complex far-from-equilibrium structures can be envisioned with an even greater number of potential novel applications.
