Study of Short-Range Order in Supercooled Liquid Silicon by Beam-Line Electrostatic Levitation (BESL)*

Previous studies of the liquid structure of supercooled Si by x- ray diffraction using electromagnetic and aerodynamic levitation have produced conflicting results. We describe a BESL technique that obtains complete diffraction patterns in 0.1 s using high- energy synchrotron x-rays, allowing the evolving structures of supercooled liquids to be measured continuously. Contrary to some molecular dynamic simulation studies, no first order liquid- liquid phase transition was observed in supercooled liquid Si over the measured temperature range (1100 $^{\circ}$C to 1600 $^{\circ}$C). The coordination number remained constant, in conflict with earlier measurements. Modeling suggests that the A5 structure of liquid Si distorts continuously toward cubic diamond structure with decreasing temperature.