Dynamics of laser-induced microcone formation on germanium in an oxidizing atmosphere and a vacuum

Abstract

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 µm, pulse half-width of 1 ms), microcones with a maximum height of 235 µm in a vacuum and 590 and 840 µm 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)∘ in a vacuum and (35±3)∘ 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.