Radiation-induced amorphization can proceed by sev­eral different mechanisms, including direct impact amorphization and gradual accumulation of lattice defects and chemical disorder that eventually causes destabilization of the crystalline matrix.213 Figure 36 shows an example of the microstructure near the crystalline to amorphous transition dose in ion-irradiated SiC, where the amorphization is induced by gradual buildup of radiation defects.209

At intermediate doses, amorphous islands gradu­ally emerge from the initially crystalline matrix in SiC irradiated at low temperatures. Direct amorphization within individual displacement cas­cades has been observed in several intermetallic,334 semiconductor,12,335 and ceramic insulator15,336,337 materials. In many other materials, extensive chemi­cal disordering from displacement cascades or point defects precedes amorphization.3,76,87 The chemical disordering can be monitored either on the nanoscale dimensions (e. g., due to individual displacement cas­cades) by techniques such as transmission electron microscopy,12,338 or an integrated average value by various techniques including X-ray diffraction, TEM, and Rutherford backscattering spectrometry.76,339 As previously noted in Section 1.03.3.8, the intense ionization associated with swift heavy irradiation can lead to amorphization either directly within ion tracks, or by a cumulative process involving chemical disordering before amorphization due to multiple overlapping ion tracks.