Impact and characterisation of heavy ion tracks on epitaxial growth

Abstract

The possibility of influencing the epitaxial relationship by heavy ion tracks has been investigated for high temperature superconducting films YBa2Cu3O7−δ (YBCO) on single crystalline MgO (100) substrates. The tracks are formed by irradiation with 120 MeV 197Au ions at incidence angles of 1.5° and 1.9° from the surface plane. AFM images of irradiated surfaces reveal the presence of channels which are on average 130 nm long and 6 nm wide. The length of the surface tracks is described by cutting a 4.3 nm deep trench diagonally at an angle of 1.9° relative to the track axis. The measured apparent depth of 1 nm agrees with this assumption due to our finite tip radius of about 20 nm. YBCO films grow on non-irradiated substrates with the in-plane epitaxial relationship YBCO[100]t MgO[100]. Heavy ion irradiation as described above with a fluence of 1013 Au ions/cm2 parallel to the (110) plane resulted in an almost complete change in epitaxial alignment, yielding YBCO[100] t MgO[110]. In contrast, the in-plane orientation of YBCO did not change if the same density of tracks was created parallel to the MgO (100) plane. Although the results demonstrate the influence of heavy ion channels on the in-plane orientation, attempts to rotate the film axis by 20° on MgO substrates failed.