The dynamics of laser-induced microcone formation on the (111) surface of single-crystal germanium in a vacuum and an oxidizing atmosphere at an irradiation energy below the threshold for melt removal from the irradiation region under the effect of vapor pressure were studied using high-speed video recording. As a result of single-exposure irradiation with a laser pulse with an irradiation spot diameter of 1 mm (wavelength of 1.06 mu m, pulse half-width of 1 ms), microcones with a maximum height of 235 mu m in a vacuum and 590 and 840 mu m in air and. oxygen at atmospheric pressure, respectively, were obtained. The dynamic contact angle between the melt and its solid phase was measured as (13 +/- 3)degrees in a vacuum and (35 +/- 3)degrees in air. The increase in the dynamic wetting angle in the oxidizing atmosphere is associated with a Ge oxidation reaction on the surface of the melt and the adjacent solid phase with the formation of the oxide GeO, which is volatile at the melting temperature of Ge. A microcone formation model is proposed in which the increase in the microcone height is due to an increase in the dynamic wetting angle. (C) 2020 Optical Society of America
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