2021 Fiscal Year Research-status Report
Investigation of growth dynamics of faceted grain/grain/melt grain boundary junction during directional solidification of Si
| Project/Area Number |
21K20343
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| Research Institution | Tohoku University |
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Principal Investigator |
CHUANG LUCHUNG 東北大学, 金属材料研究所, 助教 (90911123)
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| Project Period (FY) |
2021-08-30 – 2023-03-31
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| Keywords | Crystal growth / In situ observation / Silicon / Grain boundary / Solid/melt interface |
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| Outline of Annual Research Achievements |
This project started last October. I have achieved two advances for performing experiments in this study. One is the development of the technique for cutting oriented crystal seeds accurately. The oriented seeds are used to create coincidence site lattice grain boundaries (CSL GBs) with accuracies of better than 1 degree. The other advance is the modification of current crystal growth furnace. The thermocouples with higher operating temperature have been installed on the furnace. The temperature control loop has been re-designed and improved. Both the temperature gradient and the cooling rate of the crystallization process can now be controlled with high precision. These two advances pave the way for following in-situ experiments.
The Si seeds for generating Σ9 GBs are prepared. Preliminary tests showed that the Si seeds can be partly melted without loss of the initial crystallinity and the solid/melt interface are able to move steadily due to the improved controllability of the modified furnace. The in-situ experiments for Σ9 GBs are just beginning and data collection is continuing. Before the seeds were prepared successfully with satisfying accuracy, I tested the ability of the modified furnace with bulk Si and Ni-Si alloy. This process generated interesting observations, and I have published these results.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
A procedure has been developed for cutting oriented Si seeds. All four types of symmetrical Σ9 GBs are able to be generated artificially now. The deviation from the perfect CSL GBs is less than ±1 degree determined by EBSD. Necessary Si seeds are ready for experiments. For the modification of the crystal growth furnace, the thermocouples have been replaced by B-type ones for better thermal tolerance. The furnace structure has been changed to allow the new thermocouples to directly measure the temperature of the samples. The parameters of the temperature controllers have been optimized to satisfy the stability and precision required by the directional solidification process. I tested the heating and cooling process repeatedly to ensure the reproducibility of the desired temperature profile. Testing of the modified furnace was time-consuming, but the experimental conditions can be well-controlled now.
Before the seeds were successfully prepared, I used bulk Si and Ni-Si alloy to test the ability of the modified furnace. Some good results have been published in journal and reported in conference.
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| Strategy for Future Research Activity |
The temperature gradient and cooling rate are controllable for directional solidification now. I am going to observe the faceted grooves of Σ9 GBs either under different gradients at same growth velocity or under same gradient at different growth velocities. The combination of the experimental conditions would quantitatively reveal how the dynamic interfacial morphology responds to different thermal environments and improve our knowledge of the growth behavior of GBs. The kinetic coefficients will be calculated for each configuration of Σ9 GBs. The Σ27 GB is the research topic for the next year.
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| Causes of Carryover |
I started using the budget from last October. I only bought part of the materials needed for experiments. In the following year, I will purchase more Si wafers, quartz crucibles, Ar gas, and other materials when the experiments are continued.
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