Microscopic Study of the Spinodal Decomposition of Supported Eutectic Droplets During Cooling: PtGe/Ge{110}

Abstract

We embarked on an in situ low-energy electron microscopy, photo-electron emission microscopy, and selected area low-energy electron diffraction study during the cooling of huge eutectic droplets through the critical stages of the eutectic transition. On this journey through uncharted waters, we revealed an expected initial shrinking of the exposed area of the droplet, followed by an unanticipated expansion. We attribute this behavior to an initial fast amorphization of the interface between the droplet and surface, followed by the recrystallization of Ge expelled from the droplet at the interface. As a major surprise, we discovered the emergence of extensive “spaghetti”-like patterns, which are rationalized in terms of parallel Ge ripples oriented along, mainly, [−554] and [−55–4] directions. They emerge during spinodal decomposition when passing the eutectic temperature of the system. Their sides are defined by Ge{111} and Ge{11–1} vicinals covered with Pt-modified (√3 × √3) superstructures. The distance between adjacent ripples is about 18 nm.

Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene

“…The eutectic droplet formation process is extensively discussed in [38][39][40]. Upon returning to room temperature, the spinodal decomposition of these droplets occurs, leading to a crystalline Ge 2 Pt phase and a distinct pure Ge phase [26,37,38]. This process results in the formation of germanene layers on Ge 2 Pt(101), which are separated by a buffer layer, as elaborated in [29].…”

“…Subsequently, the system is heated just above 1047 K to create Ge 0.78 Pt 0.22 eutectic droplets. The eutectic droplet formation process is extensively discussed in [38][39][40]. Upon returning to room temperature, the spinodal decomposition of these droplets occurs, leading to a crystalline Ge 2 Pt phase and a distinct pure Ge phase [26,37,38].…”