Kinetics and the crystallographic structure of bismuth during liquefaction and solidification on an insulating substrate

Here we study the kinetics of liquefaction and solidification of thin bismuth films grown on the insulating substrate by the pulsed laser deposited (PLD) and molecular beam epitaxy (MBE) and investigated by in situ electron and X-ray diffraction. By PLD, we can grow films similar to those obtained using MBE, studied by ex-situ AFM, KPFM, XRR, and XRD. The liquefaction-solidification transition is monitored in real-time by RHEED and synchrotron XRD, resulting in a dewetting phenomenon and the formation of spherical droplets which size depends on the initial film thickness. Studying this phase transition in more detail, we find instantaneous liquefaction and solidification, resulting in formation of the nanodots oriented with a (110) crystallographic plane parallel to the substrate. Furthermore, we propose a two-step growth mechanism by analyzing the recorded specular diffraction rods. Overall, we show that the PLD and MBE can be used as a method for the highly controlled growth of Bi nanostructures, including their crystallographic orientation on the substrate. Bi the orientation and Bi nanostructures' melting and solidification kinetics. Deposition at low temperatures ~40 K leads to the formation of uniform Bi (110) films, and subsequent rise of the temperature leads to their smoothening and finally change of the crystal structure towards Bi(111). Just before reaching the melting point, Bi films show rapid dewetting into nanodots and subsequently liquefy. The solidification of the nanodots is observed well below the melting point of Bi due to its supercooled state. The liquid Bi solidifies into nanodots oriented with the (110) crystallographic plane perpendicular to the substrate. The direct deposition above 220 K leads to the formation of faceted nanocrystals having the (110) orientation. The presented results show a plethora of different scenarios for the growth of controlled Bi nanostructures, thereby controlling the shape, size, and crystallographic orientation.