Ab initio Design on the Diamond Synthesis Method

by Core Excitation

YOSHIDA Lab.

Hosoya Naoki

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Nakayama H and Katayama-Yoshida H

[1] Jpn. J. Appl. Phys. 41 (2002) pp. L817

[2] J.Phys. Condens. Matter 15 (2003) R1077

Contents

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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

Applications of diamond

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Jewel Diamond anvil cell Diamond abrasive Cooling wheel Semiconductor device

etc…

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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 : JP2002-1569374

Core electron excitation

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e-

h+1s

e- e- e-

h+ h+

e-

Two holesin the valence band

SR : Synchrotron Radiation

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Structures of graphite and diamond

(a) Hexagonal graphite (b) Rhombohedral graphite (c) Cubic diamond

sp2 bond

sp3 bond

A

B

A

A

A

B

C

van der Waals bond Transition continuously

A

B

C

Hexagonal : 六方晶Rhombohedral : 菱面体

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The potential energy surface (PES)

in the ground state and

its dependence on the pressure

In the ground state,

a high temperature or a high pressure

is necessary in order to cause the

transition into diamond structure.

Potential Energy Surface (Ground state)

R/c = 1/3 (Rhombohedral graphite)

1/4 (Cubic diamond)

0.3 eV

0.2 eV

0.1 eV

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The graphite structure becomes more stable than diamond structure.

The graphite-to-diamond transition is unlikely to occur.

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 PES in the valence hole state and

its dependence on the concentration of holes.

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For higher concentrations than nh = 0.0625/atom,

potential barrier disappears !!

The graphite becomes completely unstable.

Potential Energy Surface (Valence hole state)

Transition to the diamond structure !!

Spontaneous Transition

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.

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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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