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Structure and UV absorption of QCCs: Carbonaceous dust analogues
Adv. Space Res. Vol. 24, No. 4, pp.523-526,1999 Q 1999 COSPAR. Published by Elsevier Science Ltd. All rights resewed Printed in Great Britain 0273-1177/99 $20.00 + 0.00 PII: SO273-1177(99)00095-2
Pergamon
www.elsevier.nl/locate/asr
STRUCTURE AND UV ABSORPTION CARBONACEOUS DUST ANALOGUES S. Wada,‘, C. Kaito2,
S. Kimura’,
OF QCCs:
and A.T. Tokuna.ga”
l-5-1 Chofugaoka, Chofu-shi, Tokyo 18% ‘Dept. of Chemistry, Univ. of Electra-Co,m.munications. 8585, Japan ‘Department of Physics, University of Ritsumeikan, Nojicho, Kusatsu, Shiga, 525-77, Japan 31nstitute for Astronomy, Univ. of Hawaii, 2680 Woodlawn Dr., Honolul,u, HI 96822, USA
ABSTRACT “Quenched Carbonaceous thesized in the laboratory
Composites (QCCs)” from a hydrocarbon
are carbonaceous interstellar dust analogues synplasma. We produced new types of carbonaceous
condensates from the ejecta of plasma with mixtures of methane and hydrogen as source gases. We find that QCC with an absorbance peak at 220 nm is composed of onion-like spherules, and QCCs with an absorbance peak at 230-240 nm are composed of polyhedral particles. The onion-like QCC contains
aromatic
hydrogen bonds, and it shows the 3.3 and 11.4 pm absorption
with an absorbance
peak at 230-240
nm is composed
suggests that the carrier of the interstellar interstellar
of ribbons
220 nm extinction
diffuse emission bands.
bands.
with bent graphitic
The QCC
layers.
band might also be an emitter
This of the
01999 COSPAR. Published by Elsevier Science Ltd.
INTRODUCTION The interstellar
extinction
curve and infrared
about composition of interstellar centered at 217.5 nm is observed
emission
bands provide us with direct
of the maximum absorption and the width of the absorption band have been observed, central wavelength is fairly constant (Fitzpatrick & Massa 1986). Many types of carbon
and other
nm feature.
was first proposed
absorption graphite
Graphite feature
particles
the problems
(Stecher predicted
in identifying
We have produced
information
dust. As has been known for some time, an absorption feature in the interstel1a.r extinction curve. Variations in the wavelength
carbonaceous
materials
as a candidate
have been proposed in the discovery
& Donn 1965, Draine & Lee 1984).
although
to explain
paper
the
the 217
for the 217 nm
However, the 217 nm peak of small
by theory has not been confirmed experimentally.
A good summary
of
the 217 nm feature is given by Draine (1989).
carbonaceous
materials
that
a.re named
Quenched
Carbona,ceous
Composites
(QCCs). They are condensates of hydrocarbon plasma produced in a vacuum. A brown-black carbonaceous material named “dark-QCC” wa.s obtained from the material produced directly in the plasma beam. The dark-QCC s h ows a 220 nm a.bsorbance peak in uv spectrum, with a peak wavelength that is very close to that of interstellar dust, and Sakata et al. (1983, 1994) have suggested QCC as a laboratory analogue for an interstellar carbonaceous dust. A review of QCC materials was presented by Tokunaga & Wada (1997).
523
524
S. Wada
0'
etal.
1
I
I
200
300
400
500
Wavelength (nm) Fig. 1. UV-visible spectra. of the QCCs normalized at the a.bsorbance peak. (a) QCC made from source gas of 0% Hz, 100% CH4, (b) QCC made from source gas of 50% Hz, 50% CH4, (c) QCC made from source gas of 70% Hz, 30% CH4. We have produced
new types of carbonaceous
condensates
from the ejecta of plasma with mixtures
of methane and hydrogen as source gases. These materials showed an ultraviolet absorbance peak at various wavelengths. Our objective is to understa.nd the cause of the 220 nm peak in the QCCs and to obtain insight into the nature of interstellar dust. In this report, images obtained
with a high resolutioil
and infrared absorption
electron
microscope
we will present lattice fringe
as well as uv-visible
absorption
spectra
spectra.
EXPERIMENTS The experimental in the plasmic
setup was reported
beam
by Sakata
et al. (1994).
W e collected
using various ratios of H2/CH4 as source gases.
QCCs
A difference
on substrates from previous
experiments is that we controlled the flow-rates of source gases instead of keeping the gas pressure constant in the plasma chamber. All of the measurements of the QCCs were done after washing with acetone to remove organic molecules with low-molecular weight. High-resolution transmission electron microscopic (HRTEM) images of the QCCs were obtained a Hitachi H-9000 HRTEM
electron
micro grid.
We measured
U3300 spectrophotometer We needed samples
microscope.
The QCCs on the substrates
the uv-visible
and Perkin-Elmer
with different
thickness
FTIR
were stripped
and infrared spectra spectrometer
in ea.& measurement.
by
off and put on a
of the QCCs with a Hitachi
(Spectrum
2000).
The samples that were used for
obtaining the uv spectrum were not thin enough for the HRTEM observation. However, we could observe their structure clearly at the edges of the aggregates in the QCC sample. We prepared other samples to obtain good uv-visible spectra and infrared spectra. RESULTS
AND DISCUSSION
525
Structureand UVAbsorptionof QCCs
Fig. 2. Images of high-resolution
electron
microscopy
of the QCCs.
The peaks in the absorbance
at (a) 220 nm, (b) 233 nm, (c) 241 nm, and (d) 249 nm, respectively. in the left bottom
of each images.
Their diffraction
are located
patterns
are shown
The scale of the ilnages is shown in (a).
In Figure 1, we present absorption spectra of three kinds of QCCs. The QCC which has a 217-225 nm peak is produced from a plasma of pure methane as a source gas. When hydrogen gas is added to the methane gas, the QCC produced shows an absorbance peak at longer wavelengths. With a source gas of 70% Hz and 30% CH4, the QCC shows an absorbance peak at 243-250 nm. We obtained
HRTEM
images
of 10 samples with various peak wavelengths. Figure QCC js with various peak wavelengths.
four that
typical images of the has a peak at 220 nm is compdsed
that
shown
particles is often
in Figure
la).
of many
rather
than
HRTEM.
Many
onion-like
spherical.
particle
onion-like
spherules
(this
sample
corresponds
The
spherules
is composed
QCC
that
wa.s not wa.shed
are also observed
although
with they
acetone
was also observed
are somewhat
unclear
of the presence of much organic molecules. The shape of the particles changes from onion-like spherules to concentric polyhedral QCCs which have a peak at 230-240 nm (Figure 2b a.nd 2~). Each particle is slightly spherules patterns are seen. In Figure
of the onion-like QCC. In the QCC showing a. 249 nm absorbance are observed (Figure 2d). Flat gra.phitic particles are not observed; 3, we present
(2) a source
infrared
spectra.
gas of 70% Hz and
the QCC showing might
a 249 nm peak.
also be an emitter
of the QCCs formed
30% CH,.
formed from 100% CH4 is presented in the spectrum of the QCC showing band
to
of concentric shells. The size of onion-like A central va.cant core 2-3 nm in diameter in the QCC ranges from 5 to 15 nm in diameter. observed in the particles. Some cores are very round, although most QCC cores are very
distorted
Each
In Figure 2, we present 2a shows that the QCC
An infra.red
particles in the bigger than the
peak, many ribbon-like only ribbon-like features
from (1) a source
spectrum
by
because
of a filmy
gas of 100% CH4, and material
(filmy-QCC)
for comparison. A 3.3 pm peak and a 11.4 pm peak is present a 220 nm pea.k, while both are not detected in-the spectrum of
This suggests
of the interstellar
that, the carrier diffuse
emission
of the interstellar
220 nm extinction
bands.
Small graphite units have been expected to be present in interstellar dust because the calculated absorbance peak is 217 nm when particle size is very small. However, as shown in our experiment, the peak is still located at 243-250 nm in the QCC composed of short graphitic bent layers. On the
S. Wada et al
526
3.4
3.2
Fig.
3. Infrared
absorption
spectra.
and 30% CH4. Each spectrum different. The filmy-&CC shown in (1) and (2).
other
hand,
It shows
is shifted
the spectrum
simultaneously.
This
vertically.
of the onion-like peak
suggests
of the diffuse
that
QCC
the carrier
infrared
emission
In summary, (1) the QCCs produced with in the ultraviolet, and (2) th e concentration these
QCCs.
The vertical
expansion
At present,
we have
onion-like &CC. An important fairly constant is still unsolved.
not
absorbance
(2) QCC formed
from 70% Hz
of the left and right figures are
similarity peaks
of the interstellar
to that
caused
of interstellar
by aromatic
220 nm extinction
dust.
C-H
band
bonds
might
also
bands. various particle shapes show different absorbance of aromatic hydrogen bonds apparently changes
yet determined
problem
14
not in the plasmic beam as for. the samples
shows many
and infrared
12
from 100% CH4.
(1) QCCs formed
is formed on the walls of the apparatus;
a 220 nm absorbance
be an emitter
10
the cause
is why in the interstellar
of the
peaks among
220 mn absorption
medium
in the
the absorbance
peak
is
REFERENCES Draine,
B; T. and H. M. Lee, Optical
pp, 89-108 (1984). Draine, B.T., On the interpretation dola & A.G.G.M.
Tielens,
properties
135, pp.
An analysis
carbonaceous
(1983). Sakata,
A., S. Wada,
of Quenched
composite
account
A. T. Tokunaga,
Carbonaceous
Composite
313-327,
on the shapes
2175 A bump, ApJ, 307, pp. 286294 (1986). Sakata, A., S. Wada, Y. Okutsu, H. Shintani, artificial
graphite
and silicate
of the X2175 A f ea t ure, in Interstellar
IAU Symp.,
The Netherlands (1989). Fitzpatrick, E.L. and D. Massa,
of interstellar
Kluwer
and Y. Nakada.,
for UV interstellar
T. Narisawa, Derivatives:
Publishers, extinction
Does a. 2,200 A hump extinction?
H. Nakagawa, Comparison
Dust, eds., L.J. Allaman-
Academic
of the ultraviolet
ApJ, 285,
grains,
curves.
pp.
Ultraviolet
to the “217 Nanometer”
I-The
observed
Nature, 301,
and H. Ono,
Dordrecht,
in an
493-494 Spectra
Interstellar
Absorption Feature, ApJ, 430, pp. 311-316 (1994). Stecher, T. P. and B. Donn, On graphite and interstellar extinction, ApJ, 142, pp. 1681-1683 (1965). Tokunaga, A. T. and S. Wada, Quenched Carbonaceous Composite: A Laboratory Analog for Carbonaceous Material in the Interstellar Medium, in Adw. Space Res. 19, pp.1009-1017, 1997 COSPAR, Published by Elsevier Science Ltd. (1997).
Pergamon
www.elsevier.nl/locate/asr
STRUCTURE AND UV ABSORPTION CARBONACEOUS DUST ANALOGUES S. Wada,‘, C. Kaito2,
S. Kimura’,
OF QCCs:
and A.T. Tokuna.ga”
l-5-1 Chofugaoka, Chofu-shi, Tokyo 18% ‘Dept. of Chemistry, Univ. of Electra-Co,m.munications. 8585, Japan ‘Department of Physics, University of Ritsumeikan, Nojicho, Kusatsu, Shiga, 525-77, Japan 31nstitute for Astronomy, Univ. of Hawaii, 2680 Woodlawn Dr., Honolul,u, HI 96822, USA
ABSTRACT “Quenched Carbonaceous thesized in the laboratory
Composites (QCCs)” from a hydrocarbon
are carbonaceous interstellar dust analogues synplasma. We produced new types of carbonaceous
condensates from the ejecta of plasma with mixtures of methane and hydrogen as source gases. We find that QCC with an absorbance peak at 220 nm is composed of onion-like spherules, and QCCs with an absorbance peak at 230-240 nm are composed of polyhedral particles. The onion-like QCC contains
aromatic
hydrogen bonds, and it shows the 3.3 and 11.4 pm absorption
with an absorbance
peak at 230-240
nm is composed
suggests that the carrier of the interstellar interstellar
of ribbons
220 nm extinction
diffuse emission bands.
bands.
with bent graphitic
The QCC
layers.
band might also be an emitter
This of the
01999 COSPAR. Published by Elsevier Science Ltd.
INTRODUCTION The interstellar
extinction
curve and infrared
about composition of interstellar centered at 217.5 nm is observed
emission
bands provide us with direct
of the maximum absorption and the width of the absorption band have been observed, central wavelength is fairly constant (Fitzpatrick & Massa 1986). Many types of carbon
and other
nm feature.
was first proposed
absorption graphite
Graphite feature
particles
the problems
(Stecher predicted
in identifying
We have produced
information
dust. As has been known for some time, an absorption feature in the interstel1a.r extinction curve. Variations in the wavelength
carbonaceous
materials
as a candidate
have been proposed in the discovery
& Donn 1965, Draine & Lee 1984).
although
to explain
paper
the
the 217
for the 217 nm
However, the 217 nm peak of small
by theory has not been confirmed experimentally.
A good summary
of
the 217 nm feature is given by Draine (1989).
carbonaceous
materials
that
a.re named
Quenched
Carbona,ceous
Composites
(QCCs). They are condensates of hydrocarbon plasma produced in a vacuum. A brown-black carbonaceous material named “dark-QCC” wa.s obtained from the material produced directly in the plasma beam. The dark-QCC s h ows a 220 nm a.bsorbance peak in uv spectrum, with a peak wavelength that is very close to that of interstellar dust, and Sakata et al. (1983, 1994) have suggested QCC as a laboratory analogue for an interstellar carbonaceous dust. A review of QCC materials was presented by Tokunaga & Wada (1997).
523
524
S. Wada
0'
etal.
1
I
I
200
300
400
500
Wavelength (nm) Fig. 1. UV-visible spectra. of the QCCs normalized at the a.bsorbance peak. (a) QCC made from source gas of 0% Hz, 100% CH4, (b) QCC made from source gas of 50% Hz, 50% CH4, (c) QCC made from source gas of 70% Hz, 30% CH4. We have produced
new types of carbonaceous
condensates
from the ejecta of plasma with mixtures
of methane and hydrogen as source gases. These materials showed an ultraviolet absorbance peak at various wavelengths. Our objective is to understa.nd the cause of the 220 nm peak in the QCCs and to obtain insight into the nature of interstellar dust. In this report, images obtained
with a high resolutioil
and infrared absorption
electron
microscope
we will present lattice fringe
as well as uv-visible
absorption
spectra
spectra.
EXPERIMENTS The experimental in the plasmic
setup was reported
beam
by Sakata
et al. (1994).
W e collected
using various ratios of H2/CH4 as source gases.
QCCs
A difference
on substrates from previous
experiments is that we controlled the flow-rates of source gases instead of keeping the gas pressure constant in the plasma chamber. All of the measurements of the QCCs were done after washing with acetone to remove organic molecules with low-molecular weight. High-resolution transmission electron microscopic (HRTEM) images of the QCCs were obtained a Hitachi H-9000 HRTEM
electron
micro grid.
We measured
U3300 spectrophotometer We needed samples
microscope.
The QCCs on the substrates
the uv-visible
and Perkin-Elmer
with different
thickness
FTIR
were stripped
and infrared spectra spectrometer
in ea.& measurement.
by
off and put on a
of the QCCs with a Hitachi
(Spectrum
2000).
The samples that were used for
obtaining the uv spectrum were not thin enough for the HRTEM observation. However, we could observe their structure clearly at the edges of the aggregates in the QCC sample. We prepared other samples to obtain good uv-visible spectra and infrared spectra. RESULTS
AND DISCUSSION
525
Structureand UVAbsorptionof QCCs
Fig. 2. Images of high-resolution
electron
microscopy
of the QCCs.
The peaks in the absorbance
at (a) 220 nm, (b) 233 nm, (c) 241 nm, and (d) 249 nm, respectively. in the left bottom
of each images.
Their diffraction
are located
patterns
are shown
The scale of the ilnages is shown in (a).
In Figure 1, we present absorption spectra of three kinds of QCCs. The QCC which has a 217-225 nm peak is produced from a plasma of pure methane as a source gas. When hydrogen gas is added to the methane gas, the QCC produced shows an absorbance peak at longer wavelengths. With a source gas of 70% Hz and 30% CH4, the QCC shows an absorbance peak at 243-250 nm. We obtained
HRTEM
images
of 10 samples with various peak wavelengths. Figure QCC js with various peak wavelengths.
four that
typical images of the has a peak at 220 nm is compdsed
that
shown
particles is often
in Figure
la).
of many
rather
than
HRTEM.
Many
onion-like
spherical.
particle
onion-like
spherules
(this
sample
corresponds
The
spherules
is composed
QCC
that
wa.s not wa.shed
are also observed
although
with they
acetone
was also observed
are somewhat
unclear
of the presence of much organic molecules. The shape of the particles changes from onion-like spherules to concentric polyhedral QCCs which have a peak at 230-240 nm (Figure 2b a.nd 2~). Each particle is slightly spherules patterns are seen. In Figure
of the onion-like QCC. In the QCC showing a. 249 nm absorbance are observed (Figure 2d). Flat gra.phitic particles are not observed; 3, we present
(2) a source
infrared
spectra.
gas of 70% Hz and
the QCC showing might
a 249 nm peak.
also be an emitter
of the QCCs formed
30% CH,.
formed from 100% CH4 is presented in the spectrum of the QCC showing band
to
of concentric shells. The size of onion-like A central va.cant core 2-3 nm in diameter in the QCC ranges from 5 to 15 nm in diameter. observed in the particles. Some cores are very round, although most QCC cores are very
distorted
Each
In Figure 2, we present 2a shows that the QCC
An infra.red
particles in the bigger than the
peak, many ribbon-like only ribbon-like features
from (1) a source
spectrum
by
because
of a filmy
gas of 100% CH4, and material
(filmy-QCC)
for comparison. A 3.3 pm peak and a 11.4 pm peak is present a 220 nm pea.k, while both are not detected in-the spectrum of
This suggests
of the interstellar
that, the carrier diffuse
emission
of the interstellar
220 nm extinction
bands.
Small graphite units have been expected to be present in interstellar dust because the calculated absorbance peak is 217 nm when particle size is very small. However, as shown in our experiment, the peak is still located at 243-250 nm in the QCC composed of short graphitic bent layers. On the
S. Wada et al
526
3.4
3.2
Fig.
3. Infrared
absorption
spectra.
and 30% CH4. Each spectrum different. The filmy-&CC shown in (1) and (2).
other
hand,
It shows
is shifted
the spectrum
simultaneously.
This
vertically.
of the onion-like peak
suggests
of the diffuse
that
QCC
the carrier
infrared
emission
In summary, (1) the QCCs produced with in the ultraviolet, and (2) th e concentration these
QCCs.
The vertical
expansion
At present,
we have
onion-like &CC. An important fairly constant is still unsolved.
not
absorbance
(2) QCC formed
from 70% Hz
of the left and right figures are
similarity peaks
of the interstellar
to that
caused
of interstellar
by aromatic
220 nm extinction
dust.
C-H
band
bonds
might
also
bands. various particle shapes show different absorbance of aromatic hydrogen bonds apparently changes
yet determined
problem
14
not in the plasmic beam as for. the samples
shows many
and infrared
12
from 100% CH4.
(1) QCCs formed
is formed on the walls of the apparatus;
a 220 nm absorbance
be an emitter
10
the cause
is why in the interstellar
of the
peaks among
220 mn absorption
medium
in the
the absorbance
peak
is
REFERENCES Draine,
B; T. and H. M. Lee, Optical
pp, 89-108 (1984). Draine, B.T., On the interpretation dola & A.G.G.M.
Tielens,
properties
135, pp.
An analysis
carbonaceous
(1983). Sakata,
A., S. Wada,
of Quenched
composite
account
A. T. Tokunaga,
Carbonaceous
Composite
313-327,
on the shapes
2175 A bump, ApJ, 307, pp. 286294 (1986). Sakata, A., S. Wada, Y. Okutsu, H. Shintani, artificial
graphite
and silicate
of the X2175 A f ea t ure, in Interstellar
IAU Symp.,
The Netherlands (1989). Fitzpatrick, E.L. and D. Massa,
of interstellar
Kluwer
and Y. Nakada.,
for UV interstellar
T. Narisawa, Derivatives:
Publishers, extinction
Does a. 2,200 A hump extinction?
H. Nakagawa, Comparison
Dust, eds., L.J. Allaman-
Academic
of the ultraviolet
ApJ, 285,
grains,
curves.
pp.
Ultraviolet
to the “217 Nanometer”
I-The
observed
Nature, 301,
and H. Ono,
Dordrecht,
in an
493-494 Spectra
Interstellar
Absorption Feature, ApJ, 430, pp. 311-316 (1994). Stecher, T. P. and B. Donn, On graphite and interstellar extinction, ApJ, 142, pp. 1681-1683 (1965). Tokunaga, A. T. and S. Wada, Quenched Carbonaceous Composite: A Laboratory Analog for Carbonaceous Material in the Interstellar Medium, in Adw. Space Res. 19, pp.1009-1017, 1997 COSPAR, Published by Elsevier Science Ltd. (1997).