**4. Beta particle interaction with gold nanoparticles**

Charged particles are common by-products of radioactive decay and nuclear reactions and are a primary component of cosmic radiation. Accelerators and ion beams are also common ion sources used in both research and industry. For example, ions are frequently used in radiation damage experiments to simulate material microstructures resulting from neutron radiation exposure in nuclear

reactor environments primarily because it is much less costly and can achieve similar damaged microstructures in a fraction of the time [41]. Accelerators also have a slew of other potential applications ranging from materials analysis (e.g., electron microscopes, Rutherford backscattering) to ion beam modification.

Beta (electron or positron) radiation either incident on or produced in gold will primarily lose its energy via ionization and Bremsstrahlung radiation. As mentioned in the introduction, Bremsstrahlung radiation occurs due to electron acceleration from interaction with an atomic nucleus and results in the production of a photon of energy equal to the energy lost by the electron. This interaction is again Z-dependent and is quite common for high-Z materials like gold [42]. While displacement or knock-on damage resulting from electrons is commonly observed in transmission electron microscopy experiments [43], the significant difference in the masses of an electron and a gold nucleus requires electron energies in excess of 1.35 MeV to create a single Frenkel pair [44]. In many cases the role of the electron beam in altering the nanoparticle stability during these studies is not a result of interaction with the gold atoms itself, but with the organic capping ligands, as a result the stability of the gold nanoparticles to beta radiation is often dictated by the organic capping agent chosen [45]. One of the many examples of gold nanoparticle sintering due solely to electron beam effects can be seen in **Figure 4** [68]. The details of the particle orientation, organic capping, support film, and electron beam condition will alter the sintering rate, particle reorientation, and possible grain boundary character formed during the sintering process. This area is well studied in the electron microscopy community and is not reviewed further in this chapter. Interested readers are referred to the newest edition of the classic Williams and Carter textbook, which contains significant additions discussing a range of electron beam effects [43].

#### **Figure 4.**

*Bright-field TEM images of dodecanethiol-passivated gold nanoparticles with core diameter 4.8 nm (a) before and after focused 200 keV electron beam irradiation with a dose of (b) 7.1, (c) 16.4, (d) 33.7, (e) 73.7, and (f) 149.8 μC/μm2 [68]. Source: https://pubs.acs.org/doi/abs/10.1021/la0533157. American Chemical Society. Reprinted with permission from Y. Chen et al., Langmuir, Vol. 22, pp. 2851, 2006. Copyright 2006 American Chemical Society.*

**59**

*Evolution of Gold Nanoparticles in Radiation Environments*

**5. Light ion interaction with gold nanoparticles**

For the purpose of this chapter, light ions will be defined as energetic particles as light as proton or as heavy as helium ions (alpha particles). Alpha particles are common products of radioactive decay for actinides and other heavy radioactive isotopes, but, along with protons, deuterons, and tritons, they can also result from and induce a number of different nuclear reactions. For example, irradiation of Au-197 with protons with energies of 4.5 MeV or higher can cause a (p,n) reaction resulting in the production of metastable Hg-197m [46]. However, threshold energies of these reactions for gold are, in most cases, sufficiently high and reaction cross sections sufficiently low that these types of interactions rarely occur in practical applications. More often, light ions will interact via ionization and through Coulombic forces. Similar to the other types of interactions discussed, ionization has the potential to result in the emission of characteristic X-rays and other secondary radiations. Coulombic interactions with other atomic nuclei can tend to cause displacement

damage, usually in the form of Frenkel pairs or small, isolated cascades.

nanoparticle structure is lacking in the literature.

**6. Heavy ion interaction with gold nanoparticles**

will be explored in greater detail in the following subsections.

**6.1 Radiation stability of freestanding gold nanoparticles**

In general, the response of nanostructured materials to radiation damage is still poorly understood [29]. Despite the limited understanding in the general field, freestanding gold nanoparticles (usually drop casted onto carbon or silicon nitride TEM

Proton irradiation experiments have commonly been conducted in the context of increasing local dose for proton therapy-based applications [16, 47, 48]. Again, the primary mechanism for this dose enhancement comes from local energy deposition from ionization and secondary radiation that is produced. He irradiation experiments are not typically performed, but the effect can be assumed to be similar. Evidence of the effects of proton and He irradiation on individual gold

Energetic heavy ions, which will be defined as ions heavier than a helium atom, can result from recoil following a nuclear reaction, decay, or fission events, though sources relevant to gold nanoparticle applications will often likely come from particle accelerators. Initiation of nuclear reactions with heavy ion irradiation is improbable, and energy is typically deposited via ionization and Coulombic interaction similar to their less massive counterparts. The primary distinction is that, due to their size, heavy ions are capable of transferring much more energy to the gold atoms they interact with, resulting in large displacement damage cascades (see **Figures 1** and **2**). Cascade clustering, in which several point defects are formed as a result of a single interaction event and coalesce into larger and less mobile defect structures, results in a much more disordered microstructure and production of a smaller fraction of freely migrating defects. Complex interactions between these point- and multi-defect structures can significantly affect their stability and mobility [49]. As alluded to in the introduction, the effects of limited dimensions in the formation of surface cascades and sputtering in gold have been well known for over two decades [50]. At these limited dimensions, the effect of viscous flow during ballistic interactions is thought to have a significant role [50, 51]. These and many other size effects resulting from heavy ion irradiation in gold nanoparticles

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

*Gold Nanoparticles - Reaching New Heights*

modification.

beam effects [43].

reactor environments primarily because it is much less costly and can achieve similar damaged microstructures in a fraction of the time [41]. Accelerators also have a slew of other potential applications ranging from materials analysis (e.g., electron microscopes, Rutherford backscattering) to ion beam

Beta (electron or positron) radiation either incident on or produced in gold will primarily lose its energy via ionization and Bremsstrahlung radiation. As mentioned in the introduction, Bremsstrahlung radiation occurs due to electron acceleration from interaction with an atomic nucleus and results in the production of a photon of energy equal to the energy lost by the electron. This interaction is again Z-dependent and is quite common for high-Z materials like gold [42]. While displacement or knock-on damage resulting from electrons is commonly observed in transmission electron microscopy experiments [43], the significant difference in the masses of an electron and a gold nucleus requires electron energies in excess of 1.35 MeV to create a single Frenkel pair [44]. In many cases the role of the electron beam in altering the nanoparticle stability during these studies is not a result of interaction with the gold atoms itself, but with the organic capping ligands, as a result the stability of the gold nanoparticles to beta radiation is often dictated by the organic capping agent chosen [45]. One of the many examples of gold nanoparticle sintering due solely to electron beam effects can be seen in **Figure 4** [68]. The details of the particle orientation, organic capping, support film, and electron beam condition will alter the sintering rate, particle reorientation, and possible grain boundary character formed during the sintering process. This area is well studied in the electron microscopy community and is not reviewed further in this chapter. Interested readers are referred to the newest edition of the classic Williams and Carter textbook, which contains significant additions discussing a range of electron

*Bright-field TEM images of dodecanethiol-passivated gold nanoparticles with core diameter 4.8 nm (a) before and after focused 200 keV electron beam irradiation with a dose of (b) 7.1, (c) 16.4, (d) 33.7, (e) 73.7, and (f)* 

*with permission from Y. Chen et al., Langmuir, Vol. 22, pp. 2851, 2006. Copyright 2006 American Chemical* 

 *[68]. Source: https://pubs.acs.org/doi/abs/10.1021/la0533157. American Chemical Society. Reprinted* 

**58**

**Figure 4.**

*Society.*

*149.8 μC/μm2*
