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Ion bombardment induced self interstitial atom clusters as a precursor of Si amorphization

S. T. Nakagawa, K. Ikuse, T. Abe, T. Ono*, H. J. Whitlow**, and G.Betz*** Okayama Univ. of Science, JAPAN, ** Lund Institute of Technology, Sweden, *** Technische Universität , Austria. Ion bombardment induced self interstitial atom clusters as a precursor of Si amorphization.

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Ion bombardment induced self interstitial atom clusters as a precursor of Si amorphization

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  1. S. T. Nakagawa, K. Ikuse, T. Abe, T. Ono*,H. J. Whitlow**, and G.Betz***Okayama Univ. of Science, JAPAN, ** Lund Institute of Technology, Sweden,***Technische Universität, Austria Ion bombardment induced self interstitial atom clusters as a precursor of Si amorphization COSIRES 2004 June Helsynki

  2. Amorphization mechanism of c-Si regarding SIA-clusterSIA(Self-Interstitial Atom) • Wanted: Dynamic calculations • Methods: • PM(Pixel Mapping) • to analyze the extended defects • MD(classical Molecular dynamics) • to assess the irradiation effect COSIRES 2004 June Helsynki

  3. Static calculations of SIA clusterto define an embryo of amorphization by introducing excess SIA’s • I2: <100> split on (110); Watkins(‘71), Tan(‘81) • : <110> split on (110); Schober(‘89), Chadi(‘92) • : <110> split on (311);Takeda(‘94), Kim(‘97) • I3: right triangle on (111); • Gharaibeh(‘99), Estreicher(‘01), Jones (‘02) • I4: square on (100) plane;Takeda (‘97), Jones (‘02) Internuclear distances; - 5 ~ +10% shift from r0 COSIRES 2004 June Helsynki

  4. Analysis • PM: Pixel Mapping based on crystallography • MD: Molecular Dynamics, based on classical dynamics • - PM +MD - S. T. Nakagawa, Phys. Rev. B 66, 094103/1-7, (2002). S. T. Nakagawa and G. Betz, Nucl. Instr. Meth. B 180, 91-98 (2001). COSIRES 2004 June Helsynki

  5. MD Frame: for the self-irradiation of c-Si MD cube: 32Å cubic (1728 Si atoms) Fixed temperature: 100K Excess SIA’s: 5%, 10% Impact energy: 5keV Interaction (Si-Si): Tersoff potential (T3) COSIRES 2004 June Helsynki

  6. The mapping rule in the PM method SIA S. T. Nakagawa, Phys. Rev. B 66, 094103/1~7, (2002). SIA: an atom left lattice point’s pixel (1) or (2) COSIRES 2004 June Helsynki

  7. Amorphization shown by PM and others g(r): coordination vacancy mapping: local perfection PM: global perfection COSIRES 2004 June Helsynki

  8. The PM can find a co-plane made of SIA’s To find SIA’s on an atomic plane…. by slicing MD box along crystalline plane with low mirror indices (up to 3) The PM can determine the specific orientation of a line interstitial defect To find the meet vector of two co-planes… which defines the line interstitial defects, dimers,… COSIRES 2004 June Helsynki

  9. Calculations At 100K in a MD box [1] Without ion impacts, with excess SIA’s as previous calculations (5%, 10%) [2] With ion impacts, without excess SIA’s as previous experiments (5keV) COSIRES 2004 June Helsynki

  10. To define the range of SIA clusters With excess SIA’s,Without irradiation [1] C-Si at 100K Previous prediction for the “split-I2” - 5%~+10% +5% is the compass of SIA cluster of us: from g(r) COSIRES 2004 June Helsynki

  11. [2] SIA cluster formation along with amorphization (no excess SIA’s in the beginning) C-Si to a-Si Growth of SIA’s COSIRES 2004 June Helsynki

  12. [2] The orientation of SIA dimers at 5keV Si onto Si at 100K (defined by co-planes only with low mirror-indices) <100> <110> <111> <110> on {311} Few of them are expanded. n=25 COSIRES 2004 June Helsynki

  13. [1] vs. [2] Influence of the irradiation effect in the geometry of SIA clusters Dimers SIA induced 5% 10% 5keV no impact (+86 Si) (+173 Si) impacts orientations <100> 5.6% 1.3% 35.2% direction <110> 38.7% 48.0% 40.0% direction <111> 41.8% 44.9% 19.8% direction <112> 14.0% 5.9% 5.0% SIA dimers (average) 5.8 6.5 8.5 (in MD box 1728 Si atoms) 100K (n=25) COSIRES 2004 June Helsynki

  14. Conclusions Purpose: To define extended defects and irradiation effects regarding Si amorphization, using PM and MD The PM can detect planar or line interstitial defects. MD can reveal the intermediate process of extended defect formation. The irradiation can result significant difference from static calculations in SIA cluster formation. The amorphization embryo can be I2: not only <110>, but also <100> and <111> COSIRES 2004 June Helsynki

  15. Other models than SIA clusters: considering vacancies • vacancy-interstitial (V-I) complex; Tang (‘97) • combination of (V-I) + SIA’s; Marqués (‘01) • a di-V and di-I pair; Motooka (‘94) COSIRES 2004 June Helsynki

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