Electron irradiation dislocations

Cherns, D., Jenkins, M. L., White, S. (1980). The structure of dislocations in quartz under electron irradiation. Proc. EMAGS 79, 121-22. Bristol Institute of Physics. 

Laser vaporisation of h-BN under nitrogen at high pressure also leads to BN nanotubes, which apparently grow from disordered BN material [173]. In this case the tubes are poorly crystaUine, possibly due to dislocations and defects within the hexagonal framework. However, further high electron irradiation is capable of annealing such a defect [173]. 

Yang, Z., Sakaguchi, N., Watanabe, S., and Kawai, M. 2011 Dislocation loop formation and growth under in sim laser and/or electron irradiation. Sci. Rep. 190 1-4. 

Dislocations can also act as sites for local amorphiza-tion of a ceramic because the bonds are already distorted at the core. This is a case of a phase transformation being initiated at a dislocation. An example of this occurring in quartz during electron irradiation is shown in Figure... 

Nagai et al. have reported results from the study of Fe-0.3 wt% Cu, Fe-0.15 wt% Cu and Fe-0.05 wt% Cu alloys irradiated at 8.3 x 10 n/cm E > 1 MeV at -300 °C (the irradiation time was 144 hours) - see Fig. 9.31. As a result of CDB and positron hfetime measurements on irradiated and annealed samples, the authors reported the formation of microvoids (-10 vacancies), dislocation loops and Cu-mono-vacancy complexes. They considered that the micro-voids were decorated with Cu in all the alloys studied, and that in all cases the micro-voids were almost completely coated with Cu. After electron irradiation, ° vacancy clusters and single vacancies surrounded by Cu (v-Cu , where n > 6) were observed in electron-irradiated Fe-Cu, vacancy clusters were observed in Fe-Ni and Fe-P, but no vacancy clustering in Fe-C, Fe-Si or Fe-Mn was observed. 

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

Particle irradiation effects in halides and especially in alkali halides have been intensively studied. One reason is that salt mines can be used to store radioactive waste. Alkali halides in thermal equilibrium are Schottky-type disordered materials. Defects in NaCl which form under electron bombardment at low temperature are neutral anion vacancies (Vx) and a corresponding number of anion interstitials (Xf). Even at liquid nitrogen temperature, these primary radiation defects are still somewhat mobile. Thus, they can either recombine (Xf+Vx = Xx) or form clusters. First, clusters will form according to /i-Xf = X j. Also, Xf and Xf j may be trapped at impurities. Later, vacancies will cluster as well. If X is trapped by a vacancy pair [VA Vx] (which is, in other words, an empty site of a lattice molecule, i.e., the smallest possible pore ) we have the smallest possible halogen molecule bubble . Further clustering of these defects may lead to dislocation loops. In contrast, aggregates of only anion vacancies are equivalent to small metal colloid particles. 

These results indicate that the radiation induced defects such as some point defects, dislocations and lattice distortions have no influence on the protonic conduction. However, the electronic conduction is modified by sub-band annihilation in gap between valence and conduction bands after neutron irradiation [2, 6, 7],... 

The strong bonding in valence crystals results in the failure of these crystals to demonstrate, on irradiation, quasichemical changes such as depolymerization. Unlike metals, however, valence crystals have no conduction electrons. This permits them to retain electronic dislocations as well as atomic displacement. The trapping of dislocated electrons in the crystal by potential wells such as those created by atomic vacancies results in coloration of the normally transparent valence crystals. 

Irradiation of ionic crystals results in atomic and electronic dislocations. The trapping of displaced electrons by anion vacancies results in the absorption of visible and near ultraviolet light, which give these crystals their characteristic colors. These pseudoatomic electrons and their vacancies are called color centers. 

The process is remarkably similar to CS-plane growth under the influence of the electron beam discussed above. In this case sodium ions are leaving the crystal, possibly as sodium atoms after combining with one of the irradiating electrons. They do not leave at random, but seem to file out via a dislocated part of the structure where... 

There are three circumstances which make a geometrical reason for an altered catalytic activity probable. If the substrate is a metal with a clean surface, any change upon irradiation must be attributed to atomic point defects or dislocations since electronic defects are excluded by the conductivity of metals. Since dislocations are produced or destroyed by radiation only under special circumstances, the normal explanation for a metal is vacancies, subsurface interstitials, or multiple defects. If, with any nonmetallic type of solid, a catalytic activity is introduced only or especially by heavy-particle bombardment and if the induced activity is little changed by annealing at low temperature, then the arrangement of the atoms rather than the presence or absence of electrons must be important. Finally, if the induced catalytic effect depends... 

The role of crystal imperfections in the dimerization of substituted anthracenes has been described in the case of l,8-dichloro-9-methylanthracene.178 Similar studies have now been conducted for the 10-methyl isomer.179 In order to explain how the topochemically forbidden / -dimer (head to tail) is produced from irradiation in the solid phase, optical and electron microscopic examinations of the (010) faces of the orthorhombic crystals of the monomer have been carried out, together with differential-enthalpic and dielectric measurements. Again it is shown that the dimer nuclei appear at emergent dislocations. 

In the silver halides Mott and Gurney suggested a mechanism for the formation of colloidal Ag [167]. A conduction-band electron produced by irradiation is first trapped at a lattice imperfection which may be a silver atom or ion, a chemical impurity, or a trapping site along a dislocation. The trapped electron then attracts a Ag interstitial ion to form a Ag atom. Following this, electrons and Ag " interstitials are trapped at the site in proper sequence to cause the buildup of a colloidal silver particle. This mechanism requires the presence and mobility of silver ions, and it is further required that the hole motion be sufficiently small that trapped electrons are not annihilated by electron-hole recombinations. 

Nanoscale clusters of metals or voids, which may be formed with irradiation (cf. Bjo as, 2012 Dubinko, 2012), interacts with dislocations at their boundaries in addition to DLs and branches inside the crystal. The formation of such permanent dislocation inside the material may give it superior hardness and yield strength, because it is not easy to move such dislocations (Kittle, 1996). That is why irradiated material is hardened (cf. Dubinko et al., 2009). Interaction of the radiation-induced electron cloud with nearby defect site may occur under certain conditions, while synthesis of new chemical compounds is dependent on the TDs of the inorganic material. Such effect may help in development of new materials or deterioration of an efQdent material. 

---