CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
COOLING RATE THRESHOLD IN TRANSFORMATION OF C60
FULLERENE TO AMORPHOUS DIAMOND AND HIGHLY
DISORDERED CARBON IN SCARQ EXPERIMENTS
Tomotaka Homae1, Atsushi Okamoto1, Kazutaka G. Nakamura1, Ken-ichi Kondo1,
M asatake Yoshida2, Keiji Hirabayashi3, and Keisuke Niwase4
Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori,
Yokohama 226-8503, Japan
2
National Institute of Advanced Industrial Science and Technology, 1-1 Higashi, Tsukuba,
Ibaraki 305-8565, Japan
3
Canon Inc., 3-30-2 Shimomaruko, Ohta, Tokyo 146-8501, Japan
4
Hyogo University of Teacher Education, 942-1 Shimokume, Yashiro, Hyogo 673-1494, Japan
Abstract C60 films on gold substrates (film thickness of 6-20 jim) were prepared. These films were
shock compressed to 48 GPa and recovered using "shock compression and rapid quenching (SCARQ)"
technique. The recovered samples were amorphous diamond, when the initial thickness of the sample
was less than 10 |im, and disordered carbon, when the initial thickness was 20 jam. The temperature
history of the sample was estimated by one-dimensional thermal diffiision analysis. It was revealed
that there was a lower limit of cooling rate for recovery of amorphous diamond. The chemical bond
change of carbon after shock compression was also discussed.
of the sample and the heat conductivity is high, will
be shock-compressed, the maximum shock
temperature of the sample and the another material
should be different.
The low-compressible
material work as a heat sink and the sample is
cooled rapidly by heat conduction. For example,
diamond synthesis from graphite powder mixed
with copper powder have already been developed
[1]. Hirai et al. improved this technique and
called it "SCARQ" (Shock Compression And Rapid
Quenching) technique [2].
In this improved
technique, thin sample is sandwiched by metal disks
and shock compressed. New carbon phases such
as n-diamond [3], amorphous diamond [4], and
nanocrystalline diamond ceramics [5] were
INTRODUCTION
Shock compression and recovery technique is
very useful for exploring new carbon phases,
because it brings the sample to extremely high
pressure and temperature conditions, although the
duration of shock compression is short. But, if the
high shock temperature continues after arrival of a
release wave, the transformed carbon phase
retransforms to sp2 bonded carbon phase. A
technique, which allows rapid cooling the sample
during the compression followed by quenching the
metastable phase, was developed to deal with this
problem. If a sample is in contact with another
material, whose compressibility is lower than that
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superimposing the disks face to face, was inserted
into a capsule made of stainless steel. Thus, the
initial thickness of the samples were 6 fim, 10 jim,
and 20 jam. The capsule was put into a protective
assembly and subjected to shock loading with a 3
mm-thick stainless steel flyer accelerated by an
explosive plane-wave generator.
The flyer
velocity was estimated to be approximately 2.0
km/s. The shock pressure and a duration were
estimated to be 48 GPa and 800 ns, respectively.
successfully obtained. In the case of the thin-film
uniform sample, the temperature history of the
sample may be estimated easily with aid of
one-dimensional thermal diffusion analysis.
C60 fullerene is considered as the promising
initial material for exploring the new phase of
carbon. When tapped C60 fullerene powder was
shock compressed to more than 27 GPa, highly
disordered carbon was recovered [6]. On the other
hand, when C^ fullerene was shock compressed to
55 GPa and cooled rapidly using SCARQ technique
[2], amorphous diamond [4] and/or nanocrystalline
diamond ceramics [5] were obtained. These
results suggest that the cooling rate of the shocked
sample may dictate what kind of carbon phase will
be recovered, but the details are unknown. The
transition paths from C^ fullerene to amorphous
diamond and to highly disordered carbon are also of
interest.
In the present work, C60 fullerene films
(thickness of 6-20 jam) sandwiched by gold disks
were
shock
compressed
to
48
GPa.
Temperature-history of the sample was estimated by
the one-dimensional thermal diffusion analysis.
The relation between the cooling rate of the sample
and the recovered samples and the change of the
carbon chemical bond after the shock compression
was discussed.
i
I
4^VUW^^
1000 1100 1200 1300 1400 1500_ 1600 1700 1800
Raman Shift (cm"1)
Figure 1. Raman spectrum of deposited film.
TEMPERATURE-HISTORY CALCULATION
The shock-compressed state was calculated first
on the basis of the conservation of mass,
momentum, and energy, the Hugoniot equations of
state of gold and carbon (initial density of 1.77
g/cm3, as substitute for C60 fullerene) [7], and the
Mie-Griineisen equation of state involving Debye's
theory.
Single shock was assumed and the
openings between the films were neglected. Since
the heat conduction during the shock compression
EXPERIMENTAL METHOD
A commercial grade C60 fullerene purified to
99.9% was used as starting material. The CM
films for the present investigation were prepared by
vacuum deposition on gold disks (12 mm in
diameter and 100 |mi in thickness). €50 was
heated to 400 °C under vacuum (1 x 105 torr).
Sublimed C60 was cooled by the gold disk, which
was placed over the crucible, and deposited. The
deposition rate was about 1 mm/h and the prepared
films were approximately 3 jim, 5 fxm, and 10 jam
thick. Spectrum of deposited film shows only a
peak at around 1469 cm"1, which is assigned to Ag2
pentagonal pinching mode of C60 fullerene crystal
(Figure 1). The gold disks were used as heat sinks
in this experiments because gold has relatively low
reactivity with carbon and the gold lattice constant
differs from that of known carbon phase such as
diamond. A sandwich of C60 films, made by
was neglected because the rate of pressure increase
is significantly higher than the rate of heat
conduction for actual sample thickness of
micrometers and tens of micrometers, the two-step
process can be assumed. The changes of the
sample temperature after the shock compression
were calculated on the basis of one-dimensional
thermal diffusion analysis.
Thermodynamic
parameters of gold and diamond at room pressure
and room temperature were used for calculation.
Figure 2 shows the calculated results for the
temperature history at the center of various
thickness (3-40 jam) diamond sample sandwiched
by 100 ^m-thick gold disks. As the density of the
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C60 fullerene crystal is 1.65 g/cm3 and the density of
the diamond crystal is 3.51 g/cm3, if initial C60 film
transforms to diamond under shock compression,
the thickness reduces to one-half of its initial value.
Thus, the initial thickness of 6 um, 10 um, and 20
um in this experiment correspond to 3 urn, 5 um,
and 10 um in Figure 2, respectively. It is obvious
that the thickness of the sample is thinner, the
cooling rate is higher. For example, cooling rate
of first 100 ns after shock compression is 3.2 x 108
K/s, 5.8 x 109 K/s, 1.5 x 1010 K/s in the case of
thickness of 3, 5, and 10 mm, respectively. At 800
ns after shock compression, corresponding to the
arrival of the release wave, the temperature of the
diamond is estimated to be 2590 K, 1510 K, and
1160 K, in the case of thickness of 3, 5, and 10 mm,
respectively.
03 mm
Figure 3. Recovered sample (a) initial thickness of 10 jam (b)
initial thickness of 20 jim. Some of the sample exfoliated from
the gold substrate when the recovery capsule was opened (looks
white in these pictures).
200
400
600
Time (ns)
800
1000
Figure 2.
Temperature history calculation based on
one-dimensional thermal diffusion analysis.
RESULTS
The recovered samples were studied using a
optical microscope. When the initial thickness of
the sample was 6 um and 10 um, the recovered
sample was transparent and were tile-like fragments
whose size was less than 100 um (Figure 3 (a)).
The gold substrate can be seen through the sample.
In the case of 20 um thickness, the recovered
sample was black, unsettled shape, and size of a
couple of mm (Figure 3 (b)).
Transparent
recovered samples show no Raman peaks and a
broad photoluminescence peak (Figure 4 (a)).
Since these characteristics are in agreement with
that of the amorphous diamond reported previously
[4], these samples are identified as amorphous
1000 1500 2000 2500 3000 3500 4000 4500 5000
Raman Shift (cm"1)
Figure 4. Raman spectra of recovered samples, (a) initial
thickness of 6 jam and (b) initial thickness of 20 jam.
diamond.
In contrast, black recovered samples show G
(1580 cm"1) and D (1360 cm'1) Raman peaks of sp2
bonded carbon (Figure 4 (b)). Since the intensity
of D peak is comparable to that of G peak, these
recovered sample are identified as sp2 bonded
highly disordered carbon [8]. All of the recovered
samples show no Raman peak around 1469 cm"1,
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problem.
which is assigned to Ag2 pentagonal pinching mode
of C60 fullerene crystal and observed before the
shock compression (Figure 1 (b)).
Shock compression
to 50 GPa
DISCUSSION
The samples of three initial thickness were shock
compressed, but the maximum pressure and the
temperature were almost identical, because initial
thickness of the sample does not affect the
maximum pressure and temperature. As shown in
the model calculation (Figure 2), the dominant
difference is the cooling rate of the sample.
Lower
High
cooling rate
cooling rate
Highly disordered carbon
As these samples were shock compressed to
diamond stable region (up to 48 GPa and 2000 K),
it is supposed that during the shock compression, all
of these samples transformed into sp3 bonded
carbon. If the cooling rate was high enough and the
sample was cooled enough before the release wave
arrived, this sp3 bonded carbon was recovered as
amorphous diamond without crystal growth. In
contrast, if the cooling rate was lower and the
sample was exposed to high temperature and
normal pressure after the release wave arrived, this
sp3 bonded carbon transformed into sp2 bonded
carbon without crystal growth, as graphite, because
the duration of high temperature acting was not
long enough for the crystal growth. In this case,
the recovered sample was highly disordered carbon
(Figure 5).
It is obvious that the lower limit of the cooling
rate and upper limit of the initial thickness of the
sample to recover amorphous diamond are exist.
This threshold must depend on the shock duration.
But when the shock duration is about 1 ms, which is
typical value for shock compression apparatus of
many laboratories, the upper limit of the initial
sample thickness is between 10 and 20 |im. In
general, this fact implies that one cannot recover
quenched metastable materials thicker than 20 jam
using the shock-compression and recovery
technique.
The way of the designing temperature-history of
the shock compression was established. But it is not
revealed what is more effective for quenching and
recovering the metastable phase: the cooling rate of
first several tens of ns or the temperature of the
sample at the time of the arrival of the release wave.
Further experiments are required to deal with this
Amorphous diamond
Figure 5. Transition path from CGO fullerene to amorphous
diamond or highly disordered carbon.
ACKNOWLEDGEMENTS
This work was supported by Core Research for
Evolutional Science and Technology (CREST)
program of Japan Science and Technology
Corporation (JST).
The authors thank M.
Hasegawa for his experimental help.
REFERENCES
1. Trueb, L. E, J. Appl Phys. 39, 4707-4716 (1968).
2. Hirai, H., and Kondo, K., Science 253, 772-774 (1991).
3. Hirai, H., and Kondo, K., Proc. Jpn. Acd. 67(B), 22-26
(1991).
4. Hirai, H., and Kondo, K., Appl Phys. Lett. 64 (1994)
1797-1799.
5. Hirai, HL, Kondo, K., Kim, M., Koinuma, H.,
Kurashima, K., and Bando, Y, Appl. Phys. Lett. 71,
3016-3018(1997).
6. Yoo, C. S., Nellis, W. J., Science 254, 1489-1491
(1991).
7. Marsh, S. P., LASL Shock Hugoniot Data, University of
California Press, Berkeley, 1980.
8. Knight, D. S., and White, W. B., J. Mater. Res. 4, 385393 (1989).
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