Thin Solid Films 428(2003) 269–272

0040-6090/03/$ - see front matter� 2002 Elsevier Science B.V. All rights reserved.PII: S0040-6090Ž02.01229-4

Apparatus development for diamond synthesis from acetone vapor withlow energy consumption

Fumitomo Onishi, Kaoru Gyoda, Yoshiki Takagi*

Teikyo University of Science and Technology, 2525 Yatsusawa, Uenohara-machi, Kitatsuru-gun, Yamanashi Prefecture 409-0193, Japan

Abstract

We synthesized diamond via gaseous phase of vaporized acetone. Molecular acetone decomposes to two methyl radicals withthermal activation. We propose here a new method for diamond synthesis with these methyl radicals from molecular acetone.With this method, we successfully synthesized diamond particles on Si substrates with shorter experimental time and lower energyconsumption than conventional methods. With liquid carbon sources, such as acetone, impurity elements will be easily substitutedin synthesized diamond thin film, which has wide applications for the future electronic devices. Nickel, boron and phosphorusdoping will be presented.� 2002 Elsevier Science B.V. All rights reserved.

Keywords: Diamond synthesis; Liquid carbon sources; Diamond-like-carbon

1. Introduction

For a few years, we had been concentrated on adevelopment of completely closed diamond synthesizingsystem aimed for microgravity experiments. Recentlywe started the new method with graphite heater ascarbon source. With this method, a completely closedsystem is successfully performed. At the same time, westarted another new method with liquid carbon sources.With this method, pseudo-closed system is performed.In this paper, experimental results with liquid carbonsources will be presented.The conventional techniques for depositing diamond

at low pressure utilize a flow of a hydrocarbon–hydro-gen gas mixturew1x with complicated gas line tointroduce reaction gas into a reaction chamber andevacuating reactant gas from it. Beside that, thesetechniques require a complicated method for generationof atomic hydrogen, such as a plasmaw2x, hot tungstenfilament w3,4x, or flame w5x. Therefore, these types offlow systems are considered to be impracticable formounting on a spacecraft.For few years, we had been concentrated on devel-

oping completely closed diamond synthesizing systemaimed for microgravity conditionsw6–9x. Recently we

*Corresponding author. Tel.:q81-554-63-4411; fax:q81-556-63-4431.

E-mail address: takagi@ntu.ac.jp(Y. Takagi).

started the new method with graphite heater as carbonsourcew10,11x. With this method, a completely closedsystem is successfully performed.In situ analysis of gaseous species in a reaction

chamber by using gas chromatography and possiblereaction model is reported elsewherew12,13x.Fabisiak et al. reported diamond synthesis on various

substratesw14x. They used thermal filament method withacetone and hydrogen mixture gas flow system.Okoshi et al. synthesized diamond-like carbon from

laser abrasion with frozen acetonew15x.One acetone molecule has two methyl groups, which

has a very important role on diamond synthesis withgaseous reactions. Acetone molecule reacts with hydro-gen molecules and produces two methane molecules andone carbon mono-oxide.

2. Experimental

We used liquid carbon source, such as acetone,methanol, ethanol, ethylene glycol and tertiary butylalcohol. One molecule of these five liquid carbonsources has 2, 1, 2, 2 and 4 methyl groups, respectively.So it is expected that diamond will be synthesized withrelatively low activation energy consumption.Tungsten filament was set perpendicular to substrate

on the center of the reaction chamber. After air wasevacuated from the chamber, liquid carbon source was

270 F. Onishi et al. / Thin Solid Films 428 (2003) 269–272

Fig. 1. Particles synthesized from acetone.Fig. 3. Particles synthesized from ethanol.

Fig. 2. Particles synthesized from methanol. Fig. 4. Particles synthesized from ethylene glycol.

introduced on the chamber and vaporized to 1 Torr withroom temperature, and then hydrogen gas was intro-duced until it reached 51 Torr in total pressure. After allvalves were closed, filament heated up and then diamondsynthesis was started. Temperature of filament was 22008C measured with the two-colored pyrometer(CHINO,Tokyo, Japan, model IR-AQ) through a silica glasswindow on the chamber. Substrate temperature was 7808C measured with K-type thermocouple attached to thesubstrate. Synthesizing time was 60 min, distancebetween substrate and filament was 2.5 mm, and sup-plied electric power was 200 W. Substrates were siliconsingle crystal with p-type(1 0 0) with 10=30 mm in2

size. Experimental apparatus, we used for this study,was shown and explained elsewherew16x.

3. Results and discussion

3.1. Five liquid carbon sources

Figs. 1–5 show SEM photographs of particles synthe-sized from acetone, methanol, ethanol, ethylene glycoland tertiary butyl alcohol, respectively.Fig. 6 shows Raman spectra for particles synthesized

from these five liquid carbon sources.Raman spectra of particles synthesized from tertiary

butyl alcohol and acetone had characteristic diamondpeaks on approximately 1333 cm , but from methanol,y1

ethanol and ethylene has no diamond peaks. And spectrafrom tertiary butyl alcohol had diamond-like-carbon(DLC) peak on 1550 cm .y1

271F. Onishi et al. / Thin Solid Films 428 (2003) 269–272

Fig. 5. Particles synthesized from tertiary butyl alcohol.

Fig. 6. Raman spectra for particles synthesized from liquid carbonsources(top to bottom: tertiary butyl alcohol, acetone, methanol, eth-ylene glycol, and ethanol).

Fig. 8. Particles synthesized from nickel doped.

Fig. 9. Particles synthesized from phosphorus doped.

Table 1EPMA analysis for boron doped

Boron doped

Particle Substrate

C (at.%) 99.98 44.42Si (at.%) 0.02 54.59O (at.%) 0.00 0.98B (at.%) 0.00 0.00

Fig. 7. Particles synthesized from boron doped.

3.2. Impurity doping on liquid acetone

We tried impurity doping on liquid acetone. For borondoping we used Boric Acid(H BO ), for nickel, Nickel3 3

(II) Hydroxide (Ni(OH) ), and for phosphorus, Phos-2

phorus(V) Oxide (P O ), respectively. Figs. 7–9 show2 5

SEM photographs and Tables 1–3 show EPMA results

272 F. Onishi et al. / Thin Solid Films 428 (2003) 269–272

Table 2EPMA analysis for nickel doped

Nickel doped

Particle Substrate

C (at.%) 55.1 36.4Si (at.%) 25.2 45.8O (at.%) 19.0 17.8Ni (at.%) 0.75 0.00

Table 3EPMA analysis for phosphorus doped

Phosphorus doped

Particle Substrate

C (at.%) 99.99 0.00Si (at.%) 0.01 98.93O (at.%) 0.00 1.07P (at.%) 0.00 0.00

of particles synthesized from boron doping, nickel dop-ing and phosphorus doping experiments, respectively.With these results, we confirmed that nickel element

was successfully doped on diamond particles. But, wecould not confirm boron or phosphorus doping withEPMA. We are trying to identify boron and phosphoruselements with other analytical methods.

4. Conclusions

As liquid carbon sources, acetone, methanol, ethanol,ethylene glycol, tertiary butyl alcohol were tested fordiamond synthesis. Diamond was synthesized from thefirst and the last ones. And from other three liquidcarbon sources, DLC was synthesized.

With EPMA results, we confirmed that Ni elementswere substituted on diamond crystal lattice, but boronand phosphorus elements were not observed.With optical microscope, we observed that boron-

doped particle has slightly blue coloring. For borondoped particles, as boron element is light and the dopedamount must be very low. So with EPMA analysis, weconfirmed no boron or phosphorus elements on diamondlattice.

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