In-depth Investigation of Hg₂Br₂ Crystal Growth and Evolution

Physical vapor transport (PVT) has frequently been adopted for the synthesis of mercurous bromide (Hg₂Br₂) single crystals for acousto-optic modulators. However, thus far, very few in-depth studies have been conducted that elucidate the growth process of the Hg₂Br₂ single crystal. This paper reports an in-depth investigation regarding the crystal growth and evolution behavior of the Hg₂Br₂ crystal with facet growth mode. Based on the experimental and simulation results, the temperature profile conditions concerning the seed generation and seed growth could be optimized. Next, the PVT-grown Hg₂Br₂ crystals (divided into single crystal and quasi-single crystal regions) were characterized using various analysis techniques. The single-crystal Hg₂Br₂ was found to possess a more uniform strain than that of the quasi-single crystal through a comparison of the X-ray diffraction data. Meanwhile, the binding energy states and electron backscatter diffraction images of the as-synthesized Hg₂Br₂ crystals were similar, regardless of the crystal type. Furthermore, Raman spectroscopy and transmission electron microscopy analyses provided information on the atomic vibration mode and atomic structures of the two kinds of samples. The synergistic combination of the simulation and experimental results used to verify the growth mechanism facilitates the synthesis of high-quality Hg₂Br₂ crystals for potential acousto-optic tunable filter device applications.