In-depth Investigation of Hg2Br2 Crystal Growth and Evolution

Abstract

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.

Growth and Temperature-Dependent Mechanical and Thermal Properties of One-Dimensional Chain Structure Hg2Br2 Crystals for Infrared Acousto-Optic Device Application

“…As discussed in our previous work, the large temperature difference of 30 °C between the upper zone (350 °C) and lower zone (320 °C) facilitates the single nucleus formation . However, Hg 2 Br 2 crystals grown at a low-temperature field (black line in Figure b 350 °C/320 °C) showing a rough surface during the growth (1# crystal in Figure c) are identified as a quasi-single crystal . Once the rough surface formed in the nucleation stage, it is hard to evolve to the smooth surface no matter how we adjust the growth parameters.…”

“…Cho et al. deeply analyzed the effect of the ampoule position, the temperature gradient, and the temperature of the bottom heater on the nucleation and crystal growth by using the experiment and simulation . Our group also reported that the temperature field, growth rates, and vapor transport distances are key factors for obtaining high-quality crystals.…”

“…The Hg 2 I 2 crystal has a high M 2 value (3200 × 1.5 × 10 –18 s 3 /g) and wide spectral transmission range (0.5–40 μm), but large-size crystals with high quality are difficult to be obtained because of the severe layered characteristics . The Hg 2 Br 2 crystal has excellent acousto-optic properties, the M 2 value (2600 × 1.5 × 10 –18 s 3 /g) of which is about 2.5 times that of the Hg 2 Cl 2 crystal, and it has a wide transmission range (0.4–30 μm) . Moreover, the Hg 2 Br 2 crystal has a low acoustic velocity and attenuation coefficient, and the AOTF based on the Hg 2 Br 2 crystal has large separation and acceptance angle owing to the large birefringence of crystals. ,,, …”

“…11 The Hg 2 Br 2 crystal has excellent acoustooptic properties, the M 2 value (2600 × 1.5 × 10 −18 s 3 /g) of which is about 2.5 times that of the Hg 2 Cl 2 crystal, and it has a wide transmission range (0.4−30 μm). 12 and acceptance angle owing to the large birefringence of crystals. 6,8,13,14 Up to now, some research studies have been carried out on Hg 2 Br 2 crystal growth, property characterization, and device fabrication.…”

“…18 Cho et al deeply analyzed the effect of the ampoule position, the temperature gradient, and the temperature of the bottom heater on the nucleation and crystal growth by using the experiment and simulation. 12 Our group also reported that the temperature field, growth rates, and vapor transport distances are key factors for obtaining high-quality crystals. Research studies of both Cho et al and our group found that the large temperature gradient limits the supersaturation area for nucleation, thus favoring the formation of the Hg 2 Br 2 single crystal at the tip of an ampoule.…”