Ab initio Design on the Diamond Synthesis Method by Core Excitation

1. YOSHIDA Lab. Hosoya Naoki • Nakayama H and Katayama-Yoshida H • [1] Jpn. J. Appl. Phys. 41 (2002) pp. L817 • [2] J.Phys. Condens. Matter 15 (2003) R1077 Ab initio Design on the Diamond Synthesis Method by Core Excitation

2. Contents • Introduction ・Applications of diamond ・Diamond Synthesis ・Core electron excitation ・Structures of graphite and diamond • Calculated Results ・Ground state ・Core hole state ・Valence hole state • Theoretical prediction • Summary

3. Applications of diamond • Jewel • Diamond anvil cell • Diamond abrasive • Cooling wheel • Semiconductor device • etc… http://kyoto.cc-g.jp/cat10/ http://www.monotaro.com/p/0823/9506/ http://national.jp/product/cooking/rice_cooker/ http://www.cqst.osaka-u.ac.jp/

4. Diamond Synthesis (from graphite) Natural diamond is created in the deep earth. Artificial diamond is created by • High-pressure-high-temperature (HPHT) technique • Chemical vapor deposition (CVD) technique However… Synthetic diamond contains many impurities from catalysts. A new method of the diamond synthesis from graphite by a core electron excitation has been proposed. Hiroshi Katayama-Yoshida, Hiroyuiki Nakayama, Patent : JP2002-156937

5. Core electron excitation e- e- Two holes in the valence band h+ h+ 1s e- e- e- h+ SR : Synchrotron Radiation

6. Structures of graphite and diamond (a) Hexagonal graphite (b) Rhombohedral graphite (c) Cubic diamond A Transition continuously van der Waals bond A A B B B C A C sp3 bond A sp2 bond Hexagonal : 六方晶 Rhombohedral : 菱面体

7. Potential Energy Surface (Ground state) The potential energy surface (PES) in the ground stateand its dependence on the pressure R/c = 1/3 (Rhombohedral graphite) 1/4 (Cubic diamond) In the ground state, a high temperature or a high pressure is necessary in order to cause the transition into diamond structure. 0.1 eV 0.2 eV 0.3 eV

8. Potential Energy Surface (Core hole state) The potential energy surface (PES) in the core hole state andits dependence on the pressure • The graphite structure becomes more stable than diamond structure. • The graphite-to-diamond transition is unlikely to occur. 3.4eV

9. Potential Energy Surface (Valence hole state) The PES in the valence hole state and its dependence on the concentration of holes. • Spontaneous Transition • For higher concentrations than nh = 0.0625/atom, potential barrier disappears !! The graphite becomes completely unstable. • Transition to the diamond structure !!

10. Theoretical prediction ofa new diamond synthesis method by core excitation The diamond created through core excitation does not contain any impurities. The transition to diamond can proceed even at room temperature. (a) Low intensity SR light Both diamond and graphite exists in a matrix. (b) High intensity SR light A diamond single crystal can grow on graphite.

11. Summary • A new method of the diamond synthesis from graphite by a core electron excitation has been proposed. • In the grand state and the core hole state, the graphite structure is stable. • When the holes are excited in the valence band, the graphite structure becomes unstable completely. So,the transition into diamond structure can occur spontaneously with no pressure and no temperature. • This method has some merits.