Embossing of silicon with an ultrashort laser pulse diffracted by a bubble in liquid

• Published in: Applied surface science 2023-04, Vol.615, p.156212, Article 156212
• Main Authors: Romashevskiy, S.A., Ignatov, A.I., Zhakhovsky, V.V., Eganova, E.M., Pershina, E.A., Inogamov, N.A., Ashitkov, S.I.
• Format: Article
• Language: English
• Subjects: Bubble; Diffraction; Liquid; Melting; Silicon; Ultrashort laser pulses
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2022.156212

Laser-assisted nanostructuring of silicon interfaces provides a unique procedure for leading-edge technologies. We report on a new embossing technique with tightly focused Gaussian-shaped ultrashort laser pulses near the ablation threshold in liquid. We take advantage of a primary microbubble for controllable spatial-modulation of light intensity of succeeding pulses. Such a bubble, generated in liquid near the molten silicon surface by the first pulse, serves as an obstacle for the second pulse following with a sub-millisecond time delay, to produce a diffraction ring pattern. Variation of laser intensity can be utilized to guide the diffraction patterns. Thus the various annular patterns deeply embossed up to hundreds nanometers on the surface are produced with high reproducibility. Morphology of modified surface layer is investigated in detail using atomic-force microscopy, as well as scanning and transmission electron microscopies. Full-wave EM modeling of laser beam diffraction by the bubbles with various radii and shapes shows that the peak intensity in silicon is up to 1.7 times higher than in bubble-free liquid. Atomistic simulation of ultrafast heating with such a diffraction peak reveals that an annular microdimple surrounded by rims is formed by high-gradient pressure in molten silicon to be frozen after several nanoseconds. [Display omitted] •Method of surface embossing with a pair of ultrashort laser pulses in liquid.•3D EM modeling of laser beam diffraction by a pre-produced bubble in liquid.•Embossing of molten Si by laser-induced high-gradient pressure followed by freezing.•High reproducibility of various annular patterns controlled with laser intensity.