Meta-stable Sites in Amorphous Carbon Meta-stable Sites in Amorphous Carbon Generated by Rapid Quenching of Liquid Generated by Rapid Quenching of Liquid

DiamondDiamond

Seung-Hyeob Lee, Seung-Cheol Lee, Kwang-Ryeol Lee, Kyu-Hwan Lee, and June-Gunn Lee

Future Technology Research Division, Korea Institute of Science and Technology,P.O. Box, 131 Cheongyang, Seoul, Korea

Introductions Introductions Diamond like Carbon (DLC)

High density and hardness Optically transparent Chemically inertness High–electronic quality Wide range of physical properties Lower deposition temperature

Synonyms a-C:H : hydrogenated amorphous carbon a-C : amorphous carbon ta-C : tetrahedral amorphous carbon

Application Protective coatings for semiconductor or mechanical deviceElectronic devices

Application Protective coatings for semiconductor or mechanical deviceElectronic devices

Tetrahedral Amorphous Carbon Tetrahedral Amorphous Carbon (ta-C)(ta-C) Properties

Particular form of amorphous carbon High ratio of sp3 hybridization bonding (>80%) High hardness and wear resistance with optical

transparency Smooth surface

Similar properties of diamondLower synthesis temperature Enable to various applications

High residual compressive stress Poor adhesion

Advantages

Disadvantages

In order to overcome the disadvantages, we should understand the structural properties of ta-C in atomic scale using computer simulation.

In order to overcome the disadvantages, we should understand the structural properties of ta-C in atomic scale using computer simulation.

Amorphous Structure Amorphous Structure GenerationGeneration

Methodologies that can make an amorphous phase Rapid quenching of liquid carbon Interstitial addition of carbon atom in diamond High-energy carbon ion bombardment In many cases, a new peak near the second

peak was observed from radial distribution function (RDF). The new peak is considered to be a meta-stable site of carbon The role of the meta-stable site in the amorphous carbon structure has not been understood.We investigated the role and the

structural dependence of the meta-stable site in amorphous carbon.

We investigated the role and the structural dependence of the meta-stable site in amorphous carbon.

Purposes and Approaches of Purposes and Approaches of this workthis work

Investigation of the meta-stable site of

an amorphous carbon

Investigation of the meta-stable site of

an amorphous carbon

Calculation of the properties of crystal diamond to check the validity

Generation of an amorphous carbon structure Rapid quenching of liquid carbon Ion bombardment into a crystalline carbon Using the simulation program XMD 2.5.29 with empirical potential

proposed by Tersoff

Investigation of meta-stable site of the amorphous carbon structure

Properties of Crystal DiamondProperties of Crystal Diamond Calculated the crystal diamond

Interatomic Potential : Tersoff Potential J. Tersoff, Phys. Rev. Lett., 61 (1988) 2879.

Time Step : ~10-15 sec XMD ver. 2.5.29

PropertiesProperties CalculatedCalculated MeasuredMeasured

Lattice Parameter 3.565 A 3.567 A

C11 1058 GPa 1080 GPa

C12 130 Gpa 130 GPa

g (100) 7.67 Jm-2 9.2 Jm-2

g (110) 5.03 Jm-2 6.5 Jm-2

g (111) 4.11 Jm-2 5.3 Jm-2

g (211) 6.03 Jm-2 7.5 Jm-2

0 2000 4000 6000 8000 10000

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

D

ensi

ty o

f at

om [A

-3]

Temperature [K]

Number of atom 1728 512

0 2000 4000 6000 8000 10000

-1.20E-011

-1.10E-011

-1.00E-011

-9.00E-012

-8.00E-012

-7.00E-012

-6.00E-012

-5.00E-012

Total Energy potential Energy

Ene

rgy

[erg

]

Timestep [100 K/0.8e-13sec]

Melting the Diamond LatticeMelting the Diamond Lattice Methodology

Forming the diamond lattice (lattice parameter = 3.565 Å)

Increasing the temperature from 0 K to 10000 K

Heating rate : 1.25 K/fs

The periodic boundary condition : X-Y-Z axis

The crystal diamond melted between 7000 ~ 8000 K.

Z

Y

X

Suddenly increasing region

8000K

4000K

10000K

6000K

1 2 3 4 5

0

20

40

g(r

)

r (A)

Amorphization of Carbon Amorphization of Carbon StructureStructure Methodology

Melted the diamond structure lattice sufficiently (10000K)

Decreasing the temperature with different cooling rate to 0 K.

Instantaneous freezing to 0 K 1.25 K/fs ~ 6.25 K/fs

In the amorphous structure, first and second nearest peak were observed at 1.52 Å and 2.52 Å

We observed a small peak near the 2nd nearest peak, when the cooling rate is larger than 6 K/fs

Substantial number of atoms were placed at a meta-stable site at about 2.2 Å

Spontaneous Quenching

6.25 K/fs

2.50 K/fs

1.25 K/fs

0 20 40 60 80 100

-1.10E-011

-1.00E-011

-9.00E-012

-8.00E-012

-7.00E-012

-6.00E-012

-5.00E-012

Total Potential 1.25 K/fs 2.5 K/fs 6.25 K/fs Spontaneous quenching

Ene

rgy

[erg

]

Timestep [100 K/0.8e-13sec]

1 2 3 4 5

0

20

40

g(r

)

r (A)

Carbon Atom Bombardment Carbon Atom Bombardment Methodology

Bombarding atom Beam energy : 1 ~ 100 eV (10, 40, 70, 100) Time step : 0.155 ~ 0.5 fs / Time interval :

500 fs Stabilization

time : 10 ps

Formation of a meta-stable site became significant as the kinetic energy increased

The more smeared peaks implied the higher degree of disorder

100 eV

70 eV

40 eV

10 eV

0 2000 4000 6000 8000 10000 12000

-1.10E-011

-1.05E-011

-1.00E-011

-9.50E-012 10eV 40eV 70eV 100eV

To

tal E

ne

rgy

[erg

]

Timestep

0 2000 4000 6000 8000 10000 12000-1.12E-011

-1.10E-011

-1.08E-011

-1.06E-011

-1.04E-011

-1.02E-011

-1.00E-011 10eV 40eV 70eV 100eV

Po

ten

tial E

ne

rgy

[erg

]

Timestep

1 2 3 4 5

0

4

8

12

16

g(r

)

r (A)

Relaxation by AnnealingRelaxation by Annealing Methodology

After spontaneous Quenching to 0K

Annealing at an elevated temperature : 300 K ~ 1500 K

Heating time : 2.4 ps

As the annealing temperature was increased, the meta-stable phase peak at 2.2 Å was significantly decreased

The atoms occupied at the meta-stable site were relaxed by thermally activated process

1500 K

1200 K

900 K

600 K

300 K

0 20 40 60 80

-1.04E-011

-1.03E-011

-1.02E-011

-1.01E-011

-1.00E-011

-9.90E-012

-9.80E-012

Total energy 300K 600K 900K 1200K 1500K

Potential Energy 300K 600K 900K 1200K 1500K

Ene

rgy

[erg

]

Timestep [1 step/ 0.8e-12sec]

Heat-up stage Holding stage

0 20 40 60 80

-1.04E-011

-1.03E-011

-1.02E-011

-1.01E-011

-1.00E-011

-9.90E-012

-9.80E-012

Temperature 300K 600K 900K 1200K 1500K

Potential Eenergy

Total Eenergy

En

erg

y [e

rg]

Timestep [1 step/ 0.8ps]

Energy behaviorEnergy behavior

At the heat-up stage, the potential energy was decreased due to the atomic rearrangement when the heat-up temperature is sufficiently high. But total energy was kept almost constant because increasing temperature was cancelled out by the decreasing potential energy.

At the holding stage, both total and potential energy decreased as the relaxation process continued

Methodology After spontaneous Quenching to 0K Annealing at an elevated temperature to 300 K ~

1500 K Heat-up time 2.4 ps / Relaxation (Holding) time 4 ps

Activation Energy CalculationActivation Energy CalculationFrom meta-stable to stable sitesFrom meta-stable to stable sites

0 5 10 15 20 25 30 351E10

1E11

dI/

dt

1/T [K-1]

Methodology In case of relaxation rate contr

ol system, the relaxation rate was characterized by decrease in the peak intensity at 2.2 Å

Linear dependence of logarithm of relaxation kinetics was thus governed by Arrhenius type reaction

So, we calculate the activation barrier of the meta-stable site

Activation energy( ) = 4.8x10-14 erg/atom ms stE

Summaries & ConclusionsSummaries & Conclusions

Structure of amorphous carbon generated by rapid

quenching of the liquid was investigated by MD

simulation.

We observed that a meta-stable site exists at 2.2 Å,

and the atomic population of the site increased as the

quenching rate increased.

The activation barrier of the site was 4.8 x 10 –14

erg/atom.

We observed the similar meta-stable site when carbon

atoms of high kinetic energy bombarded to the

diamond lattice.