STUDY OF COLUMNAR AMORPHIZATION AND STRUCTURAL SYMMETRY CHANGES PRODUCED BY SWIFT HEAVY-ION IRRADIATION IN YBA2CU3O7-Y THIN-FILMS USING STM

Columnar amorphization and structural symmetry changes produced by 250 MeV Ag+17 ion irradiation in epitaxial thin films of YBa2Cu3O7-y were studied using scanning tunneling microscopy (STM). The columnar amorp hized regions were found to have sizes between 2-3 nm and structural d istortion up to 4-5 nm size around the ion tracks. The change in spaci ng between the nearest columnar defect as a function of ion fluence wa s studied. The observed columnar amorphization is discussed in the fra mework of electronic energy loss of swift heavy ions which excites the electronic system of the materials leading to the deterioration of st ructural symmetry due to energy transfer to lattice via electron-phono n interactions. (C) 1998 Elsevier Science Ltd. All rights reserved.