Preparation and properties of graphite grown in vapor phase

Synthetic Metals, 18(1987) 503 507

PREPARATION

AND PROPERTIES

H. MATSUBARA,

503

OF GRAPHITE GROWN IN VAPOR PHASE

Y. YAMAGUCHI ~ J. SHIOYA*and

The Research Association 2-5-21Toranomon,

S. MURAKAMI*

for Basic Polymer Technology,

Minato-ku,

Tokyo

105 (Japan)

ABSTRACT Preparation

conditions

and the electrical

conductivity

prepared by plasma induced chemical vapor deposition were studied.

of carbon films

(plasma CVD) of benzene

It was found that the maximum electrical

conductivity

films was obtained when the benzene flow rate was 7 ml/hr, stainless-steel, 40 W.

the substrate

temperature was

The carbon films were heat-treated

of carbon

the substrate was

I000°C and the plasma power was

at various

temperatures

between

1500°C

and 3300°C and the structure of the film obtained was analyzed by X-ray diffraction analysis

and Raman spectroscopy.

It was found that the carbon film

prepared by plasma CVD could be graphitized pyrolytic

carbons.

treatment

(HTT) of th~ carbon films at 3300°C has tile electrical

of 2. I x 104 S/cm. ~raphitc

Ti~e graphite

at lower temperature

film which was obtained by the bigh telaperature

The highest electrical

films was 9 x 105 S/cm.

than ordinary

conductivity

conductivity

of AsFs intercalated

The stability ~f AsF5 intercalated

graphite

films was also examined.

iNTRODUCTION Preparation

of conductive materials

by pyrolysis

has been attracting much attention recently. prepared by pyrolysis graphitizability.

Vapor grown carbon fibers

conductivity

fibers intercalated

(VGC fibers)

by strong acids like

of 9 x I0 s S/cm, which is higher than that

*Present address: Basic High Technology Laboratories, Ltd., I-I-3 Shimaya, Konohana-ku, Osaka, 554 Japan.

0379-6779/87/$3.50

or hydrocarbons

of benzene by Koyama and Endo [I] are known to have good

Vapor grown graphite

AsF5 showed electrical

of polymers

Sumitomo Electric

industries,

© Elsevier Sequoia/Printed in The Netherlands

504 of copper and silver [2]. contrary,

a preparation

Extensive

studies have been done about VGC.

of a highly conductive

On the

carbon and graphite by plasma CVD

has been little studied. We studied the preparation itizability.

In this paper,

and graphite

of carbon films by plasma CVD and their graphthe preparation

and electrical properties

of carbon

films obtained through plasma CVD method are discussed.

EXPERIMENTAL Plasma CVD was performed with R.F. plasma discharge trode outside a reactor.

apparatus with an elec-

Benzene vapor was used as a raw material

and various metal sheets as substrates.

The conditions

for synthesis

of the preparation were

as follows. Benzene pressure:

133 Pa

Benzene flow rate:

2 ~ 8 ml/h

Plasma power:

20 ~ 80 W (13.56 MHz)

Substrate

800 ~ 1100°C

temperature:

The plasma CVD products were heat-treated atmosphere

using a high temperature

accomplished

at 1500 ~ 3300°C under an argon

resistance

furnace.

Intercalation was

by exposure of carbon and graphite films to AsFs vapor at a

pressure of 8 x 104 Pa at ambient temperature. done by X-ray diffraction

The structural

analysis was

and Raman spectroscopy.

RESULTS AND DISCUSSION Preeparation conditions The main parameters benzene pressure, substrate

of synthesis were substrate

temperature,

plasma power,

The higher the

the larger both the thickness and the electrical

tivities of the products electrical

temperature,

benzene flow rate and substrate material.

conductivities

became.

When the plasma power was increased,

tended to decrease

slightly,

conducthe

but the dependence was

not great. The dependence in Fig.

I.

of the electrical

The maximum electrical

conductivity

on the benzene flow rate is shown

conductivity was obtained at 7 % 8 ml/h.

Carbon films were prepared using eight kinds of metals electrical

conductivities

maximum electrical as shown in Fig. 2. greatly influenced

were measured.

conductivity

Consequently,

It is supposed that the properties by the catalytic

when the benzene flow rate was 7 ml/hr,

substrate

of the carbon film are

action of the substrates conductivity

and their

it was found that the

was obtained with a stainless-steel

It was found that the maximum electrical

substrate

as substrates

during carbonization.

of carbon films was obtained

the substrate was stainless-steel,

temperature was I000°C and the plasma power was 40 W.

the

505

I

I

I

co 10~

O > 10"

S

o S

10~ S ~*o Fe I Ni I Me'~i ;~r ]]a r~b I

10~

I

Cata,ytio

l

action in | Very Slightly Production carbonization) active active of carbide Substrate metal

1

10 Benzene flow rate (m~/h)

Fig.1. Dependence of electical conductivity of vapor grown carbon film on benzene flow rate.

Fig.2. Dependence of electrical conductivity of vapor grown carbon film on substrate. # SS ' Stainless s t e e l .

Stru£tures of vapor grown graAhite films Vapor grown carbon film (VGC film), which was prepared under the condition that the maximum electrical conductivity of carbon films was obtained, was heattreated at 3300°C.

X-ray diffraction patterns and Raman spectra of VGC and

VGG (vapor grown graphite)

films are shown in Fig. 3 and Fig. 4 respectively.

TABLE I Crystal structures of various graphites Samples Vapor grown carbon film HTT-vapor grown graphite film HTT-vapor grown graphite fiber HOPG Graphite single crystal

k.

La(A)

Lc(A)

45 ~ 50 > 1000 > 1000 > 1000 > 1000

30 ~ 70 > 1000 > 1000 > 1000 > 1000

(a)

30 4'0 50 6'0 7'0 8'0 90 160 2O (°) Fig.& X-ray diffraction of vapor grown carbon film (a) and HTT-vapor grown graphite film (b)-

1900180017001 1~01~01400' 131001210011001000 Roman shft (cn7-') Fig,4. Roman spectrum of vapor grown carbon film (a) and HTT-vapor grown graphite film (b).

d(A) 3.406 3.35s 3.359 3.35s 3.354

506 The parameters

of their crystal structures

and Raman spectrum are shown in Table I. to a high degree and that its parameters

determined

by X-ray diffraction

It was found that VGC film crystallized became comparable

to those of a graphite

single crystal.

Properties

of vapor grown graphite film

In Fig. 5, the dependence ature of VGC film prepared pyrolysis

is shown.

of the electrical

The electrical

at 500°C lower than HTT necessary electrical

conductivity

i"

I 1000

.....

VGC fiber

~

VGC film

on the HTT temper-

conductivity

of VGC film rose to 5 x 103 S/cm

for VGC fiber to reach the same level.

The

after 3300°C HTT was 2.1 x 104 S/cm.

7 ............. /--7 ...........

m

conductivities

by plasma CVD and VGC fiber prepared by benzene

/

I

I I I 2000 3000 HTT Temperature ("C)

Fig.5. Electrical conductivities of HTT-vapor grown graphites.

AsFs intercalation The relationship intercalation

between the electrical

is shown in Fig. 6.

several times due to AsF5 intercalation conductivity was 9 x 10 5 S/cm. relationship

conductivities

The electrical

conductivities

increased

and the highest value of electrical

It was found that an approximately

exists and that high electrical

can be reproducibly

before and after

conductivities

conductivities

obtained by AsF5 intercalation

above

linear 1 x I0 s S/cm

of VGG films with electrical

above 5 x 103 S/cm.

Stability The variation of the electrical after AsFs intercalation

conductivity

is shown in Fig. 7.

conductivity

remained almost constant.

conductivity

temporarily

of about 1 x 10 5 S/cm.

under a vacuum and then in air

During pumping,

Upon exposure

became irregular,

the electrical

to air the electrical

and then it stabilized

at the level

507 10 ~

'

o

'

>-~

DCO g u

i

0

10'

>>

Oo

~c ~._o u~

10 6I

V--

o~10 ~

E~IO'

m

103

I

10"

1%o 105

Electrical conductivity before

intercalation O'o (S/cm)

Fig.6. AsF~ intercalation of vapor grown gral~hite films.

lb'

lb ~

t

T

lb ~

10"

Exposure to air

Vacuum start

Time (min)

Fig.7. Stability of electrical conductivity of AsFs-intercalated HTT-vapor grown graphite film.

CONCLUSION (1) Carbon film prepared by plasma CVD is found to exhibit excellent graphitizability. (2) The electrical conductivity of graphite film which was prepared on a stainless-steel substrate by plasma CVD and treated at 3300°C was 2.1 x 104 S/cm. (3) The maximum electrical conductivity of graphite film was 9 x 105 S/cm after AsF~ intercalation. (4) Carbon films prepared by plasma CVD were graphitized at lower temperature than ordinary pyrolytic carbons.

ACKNOWLEDGEMENTS

This work was performed as a part of the R & D Project of Basic Technology for Future Industries sponsored by the Agency of Industrial Science and Technology, Ministry of International Trade and Industry.

REFERENCES I

T. Koyama and M. Endo, Japan. J. AppI. Phys.,

2

J. Shioya, H. Matsubara and S. Murakami, Synth. Met., 14 (1986) 113.

13 (1974)

1175.