Fabrication And Characterization Of Rare-Earth Boride Nanostructures For Application In Field-Emission Electron Sources

Rare-earth hexaborides such as lanthanum hexaboride（La B₆）,cerium hexaboride（Ce B₆）,samarium hexaboride（Sm B₆）and other materials have low work function,low thermal evaporation rate,high electrical conductivity,high melting point and high chemical stability and other excellent characteristics and performance,especially can be used to fabricate a cold field emission point electron source with high emission brightness,stable emission current,and longer operating life,which is a very promising field emission cathode materials.Theory analysis and experiments have shown that alkaline-earth barium（Ba）-doped rare-earth hexaboride nanomaterials have lower work functions and better physicochemical properties,and thus the field emission function of multifaceted rare-earth hexaboride materials at the nanometer size can be higher.At present,the preparation of Ba element-doped poly（rare earth hexaboride）nanomaterials are mainly nanoparticles,and the controlled synthesis of one-dimensional nanowires is still difficult.In this paper,the La_xBa_1-xB₆ and Sm_0.8Ba_0.2B₆ nanowires structures were successfully prepared mainly by chemical vapor deposition process,and carried out a series of characterizations.At the same time,and the La_xBa_1-xB₆ and Sm_0.8Ba_0.2B₆ nanowires were investigated.The main studies include:（1）La_xBa_1-xB₆ nanowires with uniform size,large growth area and diameters in the range of 70-120 nm were successfully prepared by a green and efficient chemical vapor deposition method,and the effects of reaction temperature,reaction time and catalyst factors on the nanostructure morphology were investigated.The results showed that a reaction temperature of 1200°C and a reaction time of 25 min were the most suitable conditions for the growth of La_xBa_1-xB₆ nanowires.The crystal structure characterization results showed that the prepared La_xBa_1-xB₆ nanowires were single-crystal nanowires with simple cubic structure.Finally,according to the microscopic morphology and crystal structure of La_xBa_1-xB₆ prepared in this experiment,the vapor-liquid-solid phase（VLS）growth mechanism of the synthesized La_xBa_1-xB₆ nanowires was discussed in conjunction with the conventional growth mechanism of one-dimensional nanomaterials.（2）Sm_0.8Ba_0.2B₆ nanowires with diameters in the range of 20-100 nm were successfully prepared by a green and efficient chemical vapor deposition method for the first time,and the effect of reaction time on the nanostructure morphology was investigated.The results showed that a reaction time of 30 min was the most suitable condition for the growth of Sm_0.8Ba_0.2B₆ nanowires.The crystal structure characterization results all indicate that the prepared Sm_0.8Ba_0.2B₆ nanowires are single-crystal nanowires with simple cubic structure.Based on the morphology and crystal structure of the nanowires prepared in this experiment,it is suggested that the growth of Sm_0.8Ba_0.2B₆ nanowires can be explained by a VLS-like growth mechanism.These results provide a material basis for further development of field emission nanowire point electron sources with low work functions.