4.7 Article

Anisotropic defect distribution in He+-irradiated 4H-SiC: Effect of stress on defect distribution

Journal

ACTA MATERIALIA
Volume 211, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2021.116845

Keywords

Silicon carbide; Irradiation effect; Swelling; Defects; TEM

Funding

  1. JSPS KAKENHI [JP19K22035, JP19H00799]
  2. Project for promoting public utilization of advanced research infrastructure (Program for supporting introduction of the new sharing system) [JPMXS0420100519]
  3. Nanotechnology Platform program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan

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Anisotropic swelling in hexagonal alpha-SiC induced by irradiation was found to degrade the mechanical properties of the material. By introducing an anisotropic swelling condition in 4H-SiC using selected-area He+ irradiation, researchers observed an anisotropic distribution of defects which could potentially enhance the understanding of SiC's mechanical properties.
Irradiation-induced anisotropic swelling in hexagonal alpha-SiC is known to degrade the mechanical properties of SiC; however, the associated physical mechanism and microstructural process remain insufficiently understood. In this study, an anisotropic swelling condition where the surface normal direction was allowed to freely expand with constraint in the lateral direction was introduced in 4H-SiC using selected-area He+ irradiation, and the internal defect distribution was investigated using transmission electron microscopy (TEM) and advanced scanning TEM. The defect distribution was compared to that in non-selected-area He+-irradiated 4H-SiC and electron-irradiated TEM-foil 4H-SiC. An anisotropic defect distribution was observed in the selected-area He+-ion-irradiated 4H-SiC, with interstitial defects preferentially redistributed in the surface normal direction ([0 004]) and negative volume defects (such as vacancies and/or carbon antisite defects) dominantly located in the lateral directions ([11 (2) over bar0] and [10 (1) over bar0]). This anisotropy of the defect distribution was substantially lower in the non-selected-area He+-irradiated and electron-irradiated samples. The stress condition in the three samples was also measured and analyzed. In the selected-area He+-irradiated 4H-SiC, compressive stress was introduced in the lateral directions (([10 (1) over bar0] and [11 (2) over bar0])), with little stress introduced in the surface normal direction ([0 004]); this stress condition was introduced at the beginning of ion irradiation. The compressive stress likely inhibits the formation of interstitial defects in the lateral directions, enhancing the anisotropy of the defect distribution in SiC. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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