Controlling wrinkles nanopatterns induced by femtosecond laser

Surface structuring is a critical technique used to modify the topography of material surfaces at the micro and nanoscale, aiming to enhance their physical, chemical, or biological properties. In this study, we investigate the variation in the amplitude and periodicity of wrinkles produced by femtosecond laser irradiation on amorphous GeTe film capped with a SiN layer, deposited on Si substrate. Different samples with SiN layer of thickness ranging from 10 nm to 50 nm with a step size of 10 nm were produced. After the deposition process by magnetron sputtering, a residual compressive stress develops in the SiN layer. Two stress states were obtained by varying the deposition process conditions for the SiN layer: low stress (from 428 to 650 MPa) and high stress (from 958 to 1070 MPa). An Yb-fiber femtosecond laser (Satsuma, Amplitude) delivering 350 fs pulses at 1030 nm with an average power of 4W is used to trigger the melting of the GeTe layer. The liquid layer produced allows the SiN stress to be released, leading to the formation of surface wrinkle patterns. Furthermore, because they are the result of mechanical instabilities, without specific constraints, the patterns produced are completely random. From a theoretical point of view, it has been shown that their periodicity can be tuned via the mechanical properties of the SiN capping layer, thickness and residual stress, offering precise control. Utilizing a laser flat top beam profile produces wrinkles with uniform periodicity. AFM and batch-wise FFT on differential interference contrast optical microscopy measurements were performed to quantify wrinkle height and periodicity, respectively.