Speed of fragments ejected by an expanding liquid tin sheet

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Amer Physical Soc
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We experimentally investigate the speed of fragments produced by ligament breakup in the laser-induced deformation of tin microdroplets into axisymmetric sheets. The experiments were carried out covering a wide range of droplet diameters and laser-pulse energies. In addition to fragments produced by end-pinching, we also observe fragments shed via Rayleigh-Plateau breakup of long ligaments at late times. A double-frame backlit camera was used to obtain the speeds of the fragments u(f) and the time of their detachment t(d). We show that by normalizing u(f) to the initial expansion speed of the sheet R-0, all data collapse onto a single, universal curve that is a function of the dimensionless time t(d)/tau(c) only, where tau(c) is the capillary time. This universal curve is explicitly independent of the droplet's Weber number. The collapse of u(f) is supported by energy conservation arguments. Our findings enable the prediction of the instantaneous speed and position of the fragments shed from liquid tin targets used in state-of-the-art extreme ultraviolet nanolithography, facilitating the design of effective mitigation strategies against microparticulate debris.
© 2022 American Physical Society. We thank Alexander Klein for providing the double-frame camera utilized in this study. This work was carried out at the Advanced Research Center for Nanolithography (ARCNL), a publicprivate partnership of the University of Amsterdam (UvA), the Vrije Universiteit Amsterdam (VU), the Dutch Research Council (NWO), and the semiconductor equipment manufacturer ASML. This project received funding from the European Research Council (ERC) through Starting Grant No. 802648 and is part of the Vidi research program with Project No. 15697, which is financed by NWO.