Magic-number vacancy clusters in graphite and silicon

M. Hasegawa, Z. Tang, Y. Nagai, T. Shimamura, K. Nakazuru, T. Chiba, M. Saito

Research output: Contribution to journalConference articlepeer-review

2 Citations (Scopus)


Based on positron annihilation experiments combined with first-principles calculations, magic vacancy clusters in two typical covalent materials, graphite (sp2) and Si (sp3), are reported. In the experiments, ample vacancies in graphite and Si samples were introduced by neutron irradiation. The samples were isochronally annealed to high temperature, and then positron lifetime and angular correlation of annihilation radiation (ACAR) were measured. For graphite, it is observed that the longer positron lifetime is stable to higher-dose irradiation and for high-temperature (up to 1500°C) post-irradiation annealing. Especially, both the lifetime and 2D-ACAR distribution are found to agree well with the calculated ones for the V6 of six-membered ring using a first-principles pseudopotential plane-wave method. These findings clearly evidence the magic V6 ring in graphite. For Si, the longer lifetimes corresponding to the magic V6 (puckered) ring and V10 cage (consisting of four V6 rings) were observed after annealing above 500°C, demonstrating vividly the coexisting and evolution of the magic vacancy clusters in Si.

Original languageEnglish
Pages (from-to)132-134
Number of pages3
JournalMaterials Science Forum
Publication statusPublished - 2001
Event12th International Conference on Positron Annihilation - Munchen, Germany
Duration: 2000 Aug 62000 Aug 12


  • First-principles calculations
  • Graphite
  • Magic-number vacancy clusters
  • Positron annihilation
  • Si

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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