Temperature-dependent XPS studies on Ga-In alloys through the melting-point

Gallium indium alloys are known to be liquid at remarkably low temperatures. Herein, we provide X-ray photoelectron spectroscopy (XPS) studies and DFT-based ab-initio molecular dynamics (MD) calculations on the composition of the liquid alloy surface. We find that alloying Ga and In in ratios close to the eutectic composition results in only minor signal shifts of the corresponding In core levels. The topmost surface layer of the liquid alloy exhibits significant In enrichment for all measured temperatures, between 300 K to 800 K the observed enrichment slightly decreases with increasing temperature. This behavior is seen in both temperature-dependent XPS and ab-initio MD simulations. Furthermore, we investigate changes in the surface composition during the liquid-to-solid phase transition by time-dependent XPS during cooling of the alloy sample. The surface of the alloy presents an advantageous nucleation site, where we regularly observe the precipitation of indium. During cooling, the precipitation processes were followed by both XPS and by monitoring the sample temperature/heating power.