Dislocations in evaporated lead sulphide films

Abstract

Single-crystal films of PbS, oriented with (001) parallel to the film plane, were prepared by evaporation into rocksalt. They were examined in a transmission electron microscope and were found to contain dislocations of three kinds. (i) Screw dislocations with long lines approximately parallel to the ⟨110⟩ directions in the film plane. (ii) Dislocations that took the shortest route through the films and appeared as dots. The majority of these had 1/2a⟨110⟩ Burgers vectors and the Burgers vectors of the remainder were a⟨100⟩. A large fraction of the Burgers vectors lay in the film plane. Some of the dislocations were arranged in low-angle grain boundaries. (iii) Dislocations with lines whose length and orientation suggested that they lay in {110} planos inclined at 45° to (001). Motion of dislocations that corresponded to the operation of the ⟨110⟩ {001} and ⟨110⟩{110}, slip systems occurred while specimens were under observation. Examination of very thin deposits showed that film growth took place by the formation, growth and coalescence of faceted nuclei. The lattices of nuclei were not always in parallel alignment, so it is probable that dislocations were formed in the surfaces on which nuclei coalesced. Holes in almost complete films contained a high concentration of dislocations.