Real-Time 3D Visualization of the Formation of Micrograting Structures Upon Direct Laser Interference Patterning of Ge

Abstract

Direct Laser Interference Patterning (DLIP) is a versatile technique that enables the fabrication of periodic micro- to nanometric scale structures over large areas in a variety of materials. The periodically modulated excitation pattern can be exploited to trigger a range of complex processes, including heating, melting, ablation, and matter reorganization. In this work, a novel strategy is developed to combine deep-ultraviolet (UV) DLIP (λ = 193 nm, τ = 23 ns) and real-time optical reflectivity and diffraction techniques to unravel the formation dynamics of grating structures with periods down to Λ = 740 nm. Applied to crystalline Ge wafers, single-pulse topography modulation profiles with amplitudes up to 85 nm can be imprinted. Moreover, the dynamics of the melting and solidification processes, as well as the surface topography deformation, can be followed in real-time. Combined with a model, changes in topography over time with ns resolution can be obtained. The results unambiguously reveal that the formation process of the 3D structures can only be understood when taking both Marangoni convection and thermocapillary waves into account. The technique presented here has the potential to unravel the formation dynamics of a wide range of periodic structures in other materials.