Anisotropy of Radiation Damage in Electron-Bombarded Hexagonal Metals. I. Damage Production and Recovery for Monocrystalline Cobalt, Zinc, and Cadmium

Abstract

Monocrystalline specimens of cobalt, zinc, and cadmium of various crystallographic orientations were irradiated by electrons in the energy range 0.4-1.7 MeV at liquid-helium temperature and the respective electrical-resistivity-change rates and annealing spectra in the stage I were measured. In cobalt, the maximum defect production rate occurred for the specimen bombarded perpendicularly to the (0001) plane, the minimum rates were measured for the (11\ifmmode\bar\else\textasciimacron\fi{}20) samples. The apparent threshold energies for displacement vary between 450 and 500 keV, in the likely order: (0001), (30\ifmmode\bar\else\textasciimacron\fi{}34) and (10\ifmmode\bar\else\textasciimacron\fi{}10), (30\ifmmode\bar\else\textasciimacron\fi{}38), (11\ifmmode\bar\else\textasciimacron\fi{}20). The largest differences in the recovery behavior of cobalt were exhibited at low energies by the (11\ifmmode\bar\else\textasciimacron\fi{}20) and (0001) samples. For zinc, it is difficult to distinguish between different thresholds because of the big angular spread of the electron beam at the relatively low threshold energy of \ensuremath{\sim} 350 keV. The production rates increase in the order (0001), (11\ifmmode\bar\else\textasciimacron\fi{}20), (30\ifmmode\bar\else\textasciimacron\fi{}34). Maximum recovery of the entire state I is observed for the (0001) samples, while the various substages behave quite differently as a function of crystal orientation. In cadmium, complex subthreshold behavior was observed and attributed to impurity effects. After separation of these phenomena, we deduce a minimum ${E}_{d}$ of 630-650 keV for the (0001) orientation; after a size-effect correction, the measured resistivity-change rates are smallest for (0001), followed by (30\ifmmode\bar\else\textasciimacron\fi{}38) and (11\ifmmode\bar\else\textasciimacron\fi{}20). Two recovery regions are observed in the stage I: 4-6 and 6-9\ifmmode^\circ\else\textdegree\fi{}K; at low energies, the recovery of the (30\ifmmode\bar\else\textasciimacron\fi{}38) sample is smallest in the first region, and at high energies, it is maximal in both regions.