スライド 1

Ab initio Design on the
Diamond Synthesis Method
by Core Excitation
Nakayama H and Katayama-Yoshida H
[1] Jpn. J. Appl. Phys. 41 (2002) pp. L817
[2] J.Phys. Condens. Matter 15 (2003) R1077
YOSHIDA Lab.
Hosoya Naoki
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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
2
Applications of diamond

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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/
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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
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Core electron excitation
ee-
h+ h+
1s
h+ e-
SR : Synchrotron Radiation
Two holes
in the valence band
e- e-
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Structures of graphite and diamond
(a) Hexagonal graphite
A
(b) Rhombohedral graphite
(c) Cubic diamond
Transition continuously
van der Waals bond
A
A
B
B
B
C
A
C
sp3 bond
sp2 bond
A
Hexagonal : 六方晶
Rhombohedral : 菱面体
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Potential Energy Surface (Ground state)
The potential energy surface (PES)
in the ground state and
its dependence on the pressure
R/c = 1/3 (Rhombohedral graphite)
1/4 (Cubic diamond)
0.1 eV
0.2 eV
In the ground state,
a high temperature or a high pressure
is necessary in order to cause the
transition into diamond structure.
0.3 eV
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Potential Energy Surface (Core hole state)
The potential energy surface (PES)
in the core hole state and its dependence
on the pressure
3.4 eV
The graphite structure becomes more
stable than diamond structure.
The graphite-to-diamond transition is
unlikely to occur.
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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 !!
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Theoretical prediction of
a 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.
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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.
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