Fig. 2: Thermomigration of Au in Si.

a Calculated and experimental alloy droplet velocity in silicon normalised by the temperature gradient in the host, as a function of 1/T for several metals. Theory and data for Au in Si after Cline and Anthony^39,52, with experimental data from two droplets in the present study (solid lines-orange for the gradient of 4500 K cm⁻¹ and blue for the gradient of 5500 K cm⁻¹). b Si fibre core welded to a single crystal Si substrate (using geometry of Fig. 1e) after thermomigration removal of a thin Au layer at the interface (inset close-up of weld region, scale bar 50 µm), and (c) Infrared transmission of Si fibres after removal of gold that was introduced by thermomigration (orange) and that was included in the preform when drawing the fibre (blue). The black dashed curve shows a scaled transmission profile of a 5 mm thick uncoated Si window (Thorlabs), to allow comparison of spectral features.