Study On Dislocation Structure Of KDP Crystal And Growth Mechanism Of KDP(101)Faces

KDP crystal is an excellent non-linear optical crystal.Currently,the production of KDP crystal has been industrialized and the aperture made from large-scale KDP crystal has been successfully applied onto the Inertial Confinement Fusion system.However,we still don't know quite much about how the crystal grows;and the low quality of large-scale crystal promotes the necessity of investigation of the growth mechanism.For these reasons,we characterized kinds of phenomenon occur during crystal growth,especially the dislocation mechanism.The main experiment content and conclusions are introduced as below:1 The topography of etch pit on KDP(101)surface is characterized and the orientation of dislocation line is measured by optical method.The etch pit at dislocation terminal presents a shape of pyramid,dislocation source locates at the tip of pyramid.Cut off a crystal slice of(101)face,by searching groups of etch pits of the same pattern on upper and lower surface,we can identify a bunch of dislocations penetrate the slice and calculate the dislocation orientation.In our experiment,we obtain 7 groups of distinguishable dislocations,and predict that there exist dislocations with Burgers Vector of[103],[102]and[101].2 Characterization of Step Bunching phenomenon.(101)face has a remarkable attraction to anion in solution.By doping metaphosphate,the pining effect of anion occurred and steps bunching phenomenon was observed,the bunching degree increases to 2 times than those without doping.3 Two dimensional nucleus are observed on crystal grows under large undercooling.AFM measurement shows that the height of 2D nucleus is 0.5 um,the same as the interplaner distance of(101)surface.No special profile was found on 2D nucleus.4 Dislocation growth mechanism of KDP crystal is intensively investigated.The growth spiral on(101)surface is characterized,which presents a topography of regular triangular spiral.The formation of the growth spiral is explained from the aspect of atom arrangement on(101)face.Also,we found the growth spiral are multi-spirals with different number of layers;model of screw dislocation in KDP crystal is constructed to explain the relationship between dislocation's Burgers Vector and the layer number of spiral due to the dislocation.Our work provides an intuitive view of how KDP crystal grows,and explains some fundamental issue of crystal growth.More issues remain to be solved.