Bubble distribution in shaped sapphire grown from molybdenum crucibles using the micro-pulling down technique

Abstract

As a function of the capillary die geometry for fibers (ϕ: 1 mm) and rods (ϕ: 3 mm), the bubble distribution and size have been studied. It is discussed how the pulling rate and the capillary die design impact the bubble propagation during sapphire crystallization from molybdenum crucibles using the micro-pulling down (μ-PD) technique. At a low pulling rate (v = 0.25 mm min⁻¹), for both fibers and rods, the crystallization interface is flat, the bubble concentration is low, and they are regularly distributed in the periphery of the crystals.