Dislocation hollow cores observed on surfaces of molecular organic thin films: P-nitrophenyl nitroxyl nitroxide radical

We have studied by means of tapping mode atomic force microscopy ex situ grown surfaces of highly-oriented α-phase thin films of the molecular organic radical p-nitrophenyl nitroxyl nitroxide. The films are grown by thermal evaporation of the precursor radical in high vacuum on glass and NaCl(001) substrates. The surfaces reveal a complex nanometer-scale morphology formed by a random distribution of dislocations identified as spirals (screw dislocations) of opposite sign interacting in pairs. Each spiral emerges from a hollow core with a diameter of ca 15-20 nm. The dislocation density is rather high due to the way in which the films grow under the given experimental conditions. The out-of-plane growth of the films is governed by the Frank-Read source mechanism. © 1998 Elsevier Science B.V. All rights reserved.