High-temperature In-situ Raman Spectroscopy Studies On LiB₃O₅ And Monolayer MoS₂ Crystal Growth

Functional crystals are the fundament materials for our modern sciences and technologies.Both the growing the current functional crystals and exploring new crystal materials are important for the further development of modern material sciences.Among the current abundant function materials,LBO（lithium tri-borate）,as a nonlinear optical material,has been widely used in various fields,such as national defense,scientific research and life science,due to its excellent properties;monolayer MoS₂crystals are a research hotspot in semiconductor research field,as the next-generation semiconductor basic material replace single crystal silicon in the further.In this paper,we have designed an in-situ investigation system,that combined by a high-temperature crystal growth micro-furnace and a confocal Raman spectrometer,and investigated the growth processes of LBO and monolayer MoS₂crystals at high temperature using the in-situ probing system.The large-sized LBO single crystals have successfully grown via the molybdenum trioxide（MoO₃）flux method,but we still unclear the MoO₃ solvent-solution mechanism and molecule dynamic processes of LBO crystal growth.These has become an obstacle for the further development of LBO crystals.Basing on the in-situ experiments,we studied structure units of the high-temperature MoO₃ flux,and proposed the growth process of LBO crystals at the molecular level using Raman spectroscopy.The main conclusions were listed as below:（1）At the high temperature,the molybdenum-oxygen polyhedron structure exists in the melt independently and does not react with the boron-oxygen structure in the system;（2）The molybdenum-oxygen polyhedron in the high-temperature solution prevents the interconnection of boron-oxygen structures,reduces the viscosity of the melt,and facilitates the transport of ions in the solution;（3）MoO₃ exists in the form of molybdenum-oxygen polyhedron at high temperature.The accumulation of molybdenum-oxygen polyhedron in the crystal growth region increases the regional negative charge and promotes the movement of Li⁺to the crystal growth region.Monolayer MoS₂ crystals with the size of sub-millimeter have been growth via chemical vapor deposition（CVD）on the single crystal silicon substrate.However,the growth details,such as nucleation and raw material supplement,are not clear.This may be one of the reasons to the further growth why the crystal no longer grows after reaching a certain size during the growth process.The crystal nucleation and raw material supplement during the monolayer MoS₂ crystal growth process were obtained through the in-situ investigations,which were listed as below:（1）The growth and decomposition of two-dimensional MoS₂crystals occurred at the same time via a reversible reaction;（2）The monolayer MoS₂ growth was also influenced by raw materials,the gas environment and the growth temperature.Among them,when using a molybdenum trioxide melt as the molybdenum source,it is found that when sulfur vapor contacts the molybdenum source,an intermediate（MoO₂）is formed first,and then the intermediate is vulcanized to form molybdenum disulfide.