| Mercury iodide crystal??-HgI2?is an excellent room temperature semiconductor detector material,which is wildly applied in medical imaging?mammography,digital X-ray?,fluorescence analysis,space experiments,non-destructive testing,radiation therapy,environmental protection,military,nuclear industry and other fields.At present,poly-crystalline?-HgI2 film with[001]orientation and uniform size has become a hot issue in the research of medical imaging devices and nuclear radiation detection.The thin film of?-HgI2 poly-crystalline with[001]orientation and satisfied imaging requirements is usually realized by an assisted directional growth method that the growth of seed layer in solution and then grown by vapor phase epitaxy method on the seed layer.Therefore,the analysis of the solution growth mechanism is an interesting subject.Because the electrostatic field has a certain effect on the nucleation,growth and phase transition of the crystal,the controls of the seed layer growth through the introduction of the electrostatic field is a promising idea.In order to determine the growth unit of mercury iodide crystal grown in solution,the existence form of HgI2 was analyzed by UV.The crystal growth unit in the DMSO-H2O-HgI2system is[HgI2]and HgI2·?DMSO?2,the DMF-HgI2-H2O system is[HgI2]and HgI2·?C3H7NO?2,the HgCl2-KI-H2O and HgI2-HI-H2O system is the[HgI2]?[HgI4]2-and[HgI3]-.In order to obtain a continuous HgI2 seed layer,the effects of different electric field strengths and solute concentrations on the morphology of the crystals were studied in the HgI2-HI-H2O system using[HgI2]?[HgI4]2-and[HgI3]-as the growth unit.The results showed that at a constant concentration,the morphology of the crystal changes from a regular tetragonal shape to a“bone shape”that grows in the direction of the electric field as the electric field strength increases.This is the result of the migration of[HgI4]2-and[HgI3]-in the direction of the electric field and bonding of crystals.The electric field has the most prominent control effect on the crystal morphology when the electric field strength is 48V/cm.at a certain electric field strength,the crystal morphology changes from granular into a continuous compact lamellar and dendrite growing in the direction of the electric field.In order to research the effect of electrostatic field on the morphology of HgI2 crystals,the effect of electrostatic field on solution and the effect of electrostatic field on crystal growth were studied respectively.The results show that crystal growth under the influence of an electric field is mainly affected by the crystalline nuclear work and the activation energy of atoms moving from the substrate to the surface of the nuclear.Nucleation energy in electric field is stronger than that without electric field due to the decrease of the concentration in cathode zone,deriving from[HgI4]2-and[HgI3]-of movementfrom cathode zone to anode one in solution.It has been found that[HgI2]and[HgI3]-were both crystal growth units.There exists phase transformation of crystals in both environments,indicating that the electric field environment does not affect the nucleation and growth process of the[HgI2]growth unit.In order to study the metastable?-HgI2 crystal and phase transformation process,the metastable?-HgI2 crystal morphology was calculated by using the Material Studio?MS?software through the BFDH model,and the crystal models of the major crystal planes at six different growth rate ratios have been established,and the habits that may occur during crystal growth have been studied.The rhombohedral and tetragonal metastable?-HgI2 crystals were grown in different solution.The result show that the crystal morphology is consistent with the simulation results,indicating that the micro-environmental changes will affect the crystal habit.The phase transition kinetics of metastable?-HgI2??-HgI2 was studied by phase transition kinetics,which belongs to the first-order transition of structure reconstruction. |
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