Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition

A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La_0.7Sr_0.3MnO₃ (LSMO) thin film using atomic force microscope (AFM) is presented. Highly c-axis oriented LSMO thin films were grown on LaAlO₃ (1 0 0) (LAO) substrates by the pulsed laser deposition (PLD) technique. The films were annealed at 800 °C for 12 h in air (pristine films) and subsequently, irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 × 10¹² to 1 × 10¹⁴ ions/cm² and 1 × 10¹¹ to 1 × 10¹² ions/cm² for oxygen and silver ions, respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology such as rms roughness (σ), the surface rms roughness averaged over an infinite large image (σ_∞), fractal dimension (D_F) and the lateral coherence length (ξ) were estimated using the length dependent variance measurements. In case of irradiated films, the surface morphology shows drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine in each case. In case of oxygen ion irradiated films both, σ_∞ and D_F are observed to increase with fluence up to a dose value of 1 × 10¹³ ions/cm². With further increase in dose value both σ_∞ and D_F decreases. In case of silver ion irradiated films, σ_∞ and D_F decrease with increase in fluence value in the range studied.