Surface morphology of (Hg,Re)Ba₂CaCu₂O_y thin films prepared by pulsed laser deposition

(Hg,Re)Ba₂CaCu₂O_y thin films have been fabricated on (100) LaAlO₃ by reacting laser deposited Re_0.2Ba₂CaCu₂O_y precursor films with CaHgO₂ in sealed quartz tubes at 780°C for times ranging between 0 h -16 h. The films reacted for more than 2 h exhibit high phase purity (Hg,Re)-1212 and good c-axis texture. Scanning electron microscopy and x-ray diffraction studies showed the existence of small amounts of a-axis oriented grains in all the reacted films. The root-mean-square roughness, measured by atomic force microscopy (AFM), increases initially with increase in heat treatment duration and saturates at ∼ 300 nm after 4 h. The evolution of the surface roughness can be partially explained with a high nucleation density and the appearance of a three-dimensional structure during the initial stages of film growth and crystal coalescence at further growth. Two-dimensional planar growth with a one-unit-cell growth unit in the c direction was observed by AFM.