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Diamond particles synthesized with graphite spark method in two seconds
Superlattices and Microstructures 40 (2006) 526–529 www.elsevier.com/locate/superlattices
Diamond particles synthesized with graphite spark method in two seconds Takayuki Hirai c , Toru Kawai a , Yoshiki Takagi a,∗ , Osamu Shimizu b , Yoshihisa Suda b , Yoshinori Kanno c , Kiyoshi Kuribayashi a , Tsuyosi Hayashi a a Teikyo University of Science and Technology, 2525 Yatsuzawa, Uenohara-city, Yamanashi-pref. 409-0193, Japan b MITSUBISHIPENCIL CO., LTD. 5-23-37 Higashioi Shinagawa-ku, Tokyo 140-8537, Japan c University of Yamanashi, 4-4-37 Takeda, Kofu-city, Yamanashi-pref. 400-8510, Japan
Received 25 September 2006; accepted 29 September 2006 Available online 22 November 2006
Abstract A wide bandgap semiconductor, diamond, has recently emerged as important and promising materials for a wide field of optoelectronic and electronic applications. With graphite spark method in hydrogenic atmosphere, we successfully synthesized diamond particles in 3–5 µm diameter in only ten seconds and in 1–2 µm diameter in two seconds. The resultant particles were observed with SEM (Scanning Electron Microscope) images, and confirmed as diamond by sharp peak on 1331 cm−1 with Raman spectrometer. With this study, we searched for precursors with various experimental conditions, such as hydrogen pressures and/or graphite temperatures. For gaseous species identification, OES (Optical Emission Spectroscopy) results will be reported on this presentation, and the preliminary synthesis mechanism for ‘spark method’ will be presented. c 2006 Elsevier Ltd. All rights reserved.
Keywords: New growth methods; Plasma chemistry; High-deposition rates; Diamond; Spark method
1. Introduction CVD diamond has properties that are very similar to those of natural diamond. Diamond has many extreme properties making it ideal as a semiconductor material for many high-power, ∗ Corresponding author. Tel.: +81 554 63 6851; fax: +81 554 63 4431.
E-mail address: [email protected] (Y. Takagi). c 2006 Elsevier Ltd. All rights reserved. 0749-6036/$ - see front matter doi:10.1016/j.spmi.2006.09.027
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high-frequency or high-temperature applications. These properties include: a very high electric breakdown field strength, high mobility of both electrons and holes and the highest room temperature thermal conductivity of any materials. However, due to the inconsistent crystal quality of both natural and synthetic diamonds, the development of electronic devices in diamond has been severely limited up to now [1,2]. Therefore we developed a new method of diamond film synthesis at a low price and simple process. The depositions were performed with a conventional spark apparatus (model JEE-5B, JEOL, Japan), with the chamber sized 200 mm in radius and 250 mm in height, which originally designed for non-conductive sample pretreatment for SEM analysis. With this spark apparatus, specimens were coated with carbon fine particles in a few seconds, and specimens were kept in low temperature. But carbon fine particles were spread over all directions. To synthesize diamond particles, we installed additional tubing for hydrogen gas. We used two graphite rods, one with straight cut and other with sharpened top. Hydrogen gas was installed up to relatively low pressures. Silicon wafer substrate was set 5–10 mm beneath the rods. Applied electric current was kept at 50 A in ten seconds. We called this new method ‘Spark method’. With graphite spark method in hydrogen atmosphere, we successfully synthesized diamond particles in 3–5 µm diameter in only ten seconds and in 1–2 µm diameter in two seconds. The process was run in hydrogen atmosphere on different types of substrates: silicon and non-alkaline glass under several variations of geometric arrangements of substrates and graphite rods, distances between substrates and graphite rods 5–10 mm and upside down position of substrates to graphite rods. The resultant particles were confirmed as diamond by sharp peaks on 1331 cm−1 with Raman spectrum and by particle shape with SEM (Scanning Electron Microscope) image [3,4]. With this study, we searched for precursors in various experimental conditions, such as graphite temperatures. The result was that we found that with a graphite rod at critical temperature nuclei started to form. The preliminary synthesis mechanism for ‘spark method’ will be presented. 2. Experimental We used solid carbon source, such as graphite rods (model PFC, MITSUBISHI PENCIL CO., LTD, Japan). We used two graphite rods, one with a straight cut, the other sharpened like a screw driver top. They were attached to each other. Reaction chamber is shown in Fig. 1. The substrate was set perpendicular to the graphite rods at the centre of the reaction chamber. After air was evacuated from the chamber, the hydrogen was introduced until the pressure reached 1.3 × 104 Pa. After all valves were closed, the graphite rods were heated and diamond synthesis was started, so this method can be considered as a closed system. The temperature of a graphite rod top was 1800–2400 ◦ C measured with the two-coloured pyrometer (model IR-AQ 2CS, CHINO corporation, Japan) through a silica glass window on the chamber wall. Substrate temperature was under 500 ◦ C measured with a K-type thermocouple attached to the substrate. Synthesizing time was within 2 s, the distance between the substrate and graphite rod top was 5 mm, and supplied electric power was about 200 W. Substrates were silicon single crystal with p-type (100) with 10 × 3 mm2 in size. The experimental apparatus we used for this study was shown and explained elsewhere [5]. 3. Results and discussion We synthesized at various temperatures by using several types of graphite rod tops. At first, the starting temperature was 1800 ◦ C, up to every 100 ◦ C, whence Si substrate was unchanged.
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Fig. 1. Reaction chamber.
Fig. 2. Particles synthesized at 2000 ◦ C ((a) × 1500, (b) × 15 000).
Fig. 3. Particles synthesized at 2200 ◦ C ((a) × 1500, (b) × 15 000).
Diamond and graphite particles were not synthesized below 1900 ◦ C. Figs. 2–4 show SEM photographs of particles synthesized at 2000 ◦ C, 2200 ◦ C, and at 2400 ◦ C kept in 2 s, respectively. In the vicinity of 2000 ◦ C, graphite particles were generated and small submicron diamond particles (under about 0.3 µm) were produced at 2200 ◦ C. Many diamond particles being 1–2 µm in size were synthesized extensively by keeping temperature at 2400 ◦ C in 2 s.
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Fig. 4. Particles synthesized at 2400 ◦ C kept in 2 s ((a) × 1500, (b) × 15 000).
Fig. 5. Raman spectra (top to bottom; 1–2 µm particle, submicron particle).
3.1. Raman spectra Two types of Raman spectra were observed and shown in Fig. 5. In the case of 1–2 µm particles, the symbolic peak was 1330 cm−1 , and FWHM (full width at half maximum) was 9.4 cm−1 . On the other hand, the peak top of submicron particles was 1327 cm−1 , and FWHM was 11.3 cm−1 . 4. Conclusions We successfully synthesized the diamond particles on Si substrate within a shorter experimental time at lower substrate temperature with lower energy consumption than conventional methods. The diamond particles were synthesized at high speed. With this method, we could perform the highest growth rate of CVD methods. However, a small amount of diamond particles only were synthesized. As a next stage, we have to synthesize the diamond film by this method. References [1] Y. Gurbuz, O. Esame, I. Tekin, W.P. Kang, J.L. Davidson, Solid State Electronics 49 (2005) 1055. [2] J. Isberg, J. Hammersberg, D.J. Twitchen, A.J. Whitehead, Diamond and Related Materials 13 (2004) 320. [3] T. Hirai, Y. Takagi, O. Shimizu, Y. Suda, T.V. Semikina, Proc. 15th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, 2004, p. 5.1.15. [4] T.V. Semikina, Y. Takagi, T. Hirai, T. Kawai, O. Shimizu, Y. Suda, Proc. 16th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes and Nitrides, 2005, p. 5.2.13. [5] K. Gyoda, Y. Tanaka, Y. Takagi, Mat. Res. Soc. Symp. Proc., vol. 749, Materials Research Society, 2003.
Diamond particles synthesized with graphite spark method in two seconds Takayuki Hirai c , Toru Kawai a , Yoshiki Takagi a,∗ , Osamu Shimizu b , Yoshihisa Suda b , Yoshinori Kanno c , Kiyoshi Kuribayashi a , Tsuyosi Hayashi a a Teikyo University of Science and Technology, 2525 Yatsuzawa, Uenohara-city, Yamanashi-pref. 409-0193, Japan b MITSUBISHIPENCIL CO., LTD. 5-23-37 Higashioi Shinagawa-ku, Tokyo 140-8537, Japan c University of Yamanashi, 4-4-37 Takeda, Kofu-city, Yamanashi-pref. 400-8510, Japan
Received 25 September 2006; accepted 29 September 2006 Available online 22 November 2006
Abstract A wide bandgap semiconductor, diamond, has recently emerged as important and promising materials for a wide field of optoelectronic and electronic applications. With graphite spark method in hydrogenic atmosphere, we successfully synthesized diamond particles in 3–5 µm diameter in only ten seconds and in 1–2 µm diameter in two seconds. The resultant particles were observed with SEM (Scanning Electron Microscope) images, and confirmed as diamond by sharp peak on 1331 cm−1 with Raman spectrometer. With this study, we searched for precursors with various experimental conditions, such as hydrogen pressures and/or graphite temperatures. For gaseous species identification, OES (Optical Emission Spectroscopy) results will be reported on this presentation, and the preliminary synthesis mechanism for ‘spark method’ will be presented. c 2006 Elsevier Ltd. All rights reserved.
Keywords: New growth methods; Plasma chemistry; High-deposition rates; Diamond; Spark method
1. Introduction CVD diamond has properties that are very similar to those of natural diamond. Diamond has many extreme properties making it ideal as a semiconductor material for many high-power, ∗ Corresponding author. Tel.: +81 554 63 6851; fax: +81 554 63 4431.
E-mail address: [email protected] (Y. Takagi). c 2006 Elsevier Ltd. All rights reserved. 0749-6036/$ - see front matter doi:10.1016/j.spmi.2006.09.027
T. Hirai et al. / Superlattices and Microstructures 40 (2006) 526–529
527
high-frequency or high-temperature applications. These properties include: a very high electric breakdown field strength, high mobility of both electrons and holes and the highest room temperature thermal conductivity of any materials. However, due to the inconsistent crystal quality of both natural and synthetic diamonds, the development of electronic devices in diamond has been severely limited up to now [1,2]. Therefore we developed a new method of diamond film synthesis at a low price and simple process. The depositions were performed with a conventional spark apparatus (model JEE-5B, JEOL, Japan), with the chamber sized 200 mm in radius and 250 mm in height, which originally designed for non-conductive sample pretreatment for SEM analysis. With this spark apparatus, specimens were coated with carbon fine particles in a few seconds, and specimens were kept in low temperature. But carbon fine particles were spread over all directions. To synthesize diamond particles, we installed additional tubing for hydrogen gas. We used two graphite rods, one with straight cut and other with sharpened top. Hydrogen gas was installed up to relatively low pressures. Silicon wafer substrate was set 5–10 mm beneath the rods. Applied electric current was kept at 50 A in ten seconds. We called this new method ‘Spark method’. With graphite spark method in hydrogen atmosphere, we successfully synthesized diamond particles in 3–5 µm diameter in only ten seconds and in 1–2 µm diameter in two seconds. The process was run in hydrogen atmosphere on different types of substrates: silicon and non-alkaline glass under several variations of geometric arrangements of substrates and graphite rods, distances between substrates and graphite rods 5–10 mm and upside down position of substrates to graphite rods. The resultant particles were confirmed as diamond by sharp peaks on 1331 cm−1 with Raman spectrum and by particle shape with SEM (Scanning Electron Microscope) image [3,4]. With this study, we searched for precursors in various experimental conditions, such as graphite temperatures. The result was that we found that with a graphite rod at critical temperature nuclei started to form. The preliminary synthesis mechanism for ‘spark method’ will be presented. 2. Experimental We used solid carbon source, such as graphite rods (model PFC, MITSUBISHI PENCIL CO., LTD, Japan). We used two graphite rods, one with a straight cut, the other sharpened like a screw driver top. They were attached to each other. Reaction chamber is shown in Fig. 1. The substrate was set perpendicular to the graphite rods at the centre of the reaction chamber. After air was evacuated from the chamber, the hydrogen was introduced until the pressure reached 1.3 × 104 Pa. After all valves were closed, the graphite rods were heated and diamond synthesis was started, so this method can be considered as a closed system. The temperature of a graphite rod top was 1800–2400 ◦ C measured with the two-coloured pyrometer (model IR-AQ 2CS, CHINO corporation, Japan) through a silica glass window on the chamber wall. Substrate temperature was under 500 ◦ C measured with a K-type thermocouple attached to the substrate. Synthesizing time was within 2 s, the distance between the substrate and graphite rod top was 5 mm, and supplied electric power was about 200 W. Substrates were silicon single crystal with p-type (100) with 10 × 3 mm2 in size. The experimental apparatus we used for this study was shown and explained elsewhere [5]. 3. Results and discussion We synthesized at various temperatures by using several types of graphite rod tops. At first, the starting temperature was 1800 ◦ C, up to every 100 ◦ C, whence Si substrate was unchanged.
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T. Hirai et al. / Superlattices and Microstructures 40 (2006) 526–529
Fig. 1. Reaction chamber.
Fig. 2. Particles synthesized at 2000 ◦ C ((a) × 1500, (b) × 15 000).
Fig. 3. Particles synthesized at 2200 ◦ C ((a) × 1500, (b) × 15 000).
Diamond and graphite particles were not synthesized below 1900 ◦ C. Figs. 2–4 show SEM photographs of particles synthesized at 2000 ◦ C, 2200 ◦ C, and at 2400 ◦ C kept in 2 s, respectively. In the vicinity of 2000 ◦ C, graphite particles were generated and small submicron diamond particles (under about 0.3 µm) were produced at 2200 ◦ C. Many diamond particles being 1–2 µm in size were synthesized extensively by keeping temperature at 2400 ◦ C in 2 s.
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Fig. 4. Particles synthesized at 2400 ◦ C kept in 2 s ((a) × 1500, (b) × 15 000).
Fig. 5. Raman spectra (top to bottom; 1–2 µm particle, submicron particle).
3.1. Raman spectra Two types of Raman spectra were observed and shown in Fig. 5. In the case of 1–2 µm particles, the symbolic peak was 1330 cm−1 , and FWHM (full width at half maximum) was 9.4 cm−1 . On the other hand, the peak top of submicron particles was 1327 cm−1 , and FWHM was 11.3 cm−1 . 4. Conclusions We successfully synthesized the diamond particles on Si substrate within a shorter experimental time at lower substrate temperature with lower energy consumption than conventional methods. The diamond particles were synthesized at high speed. With this method, we could perform the highest growth rate of CVD methods. However, a small amount of diamond particles only were synthesized. As a next stage, we have to synthesize the diamond film by this method. References [1] Y. Gurbuz, O. Esame, I. Tekin, W.P. Kang, J.L. Davidson, Solid State Electronics 49 (2005) 1055. [2] J. Isberg, J. Hammersberg, D.J. Twitchen, A.J. Whitehead, Diamond and Related Materials 13 (2004) 320. [3] T. Hirai, Y. Takagi, O. Shimizu, Y. Suda, T.V. Semikina, Proc. 15th European Conference on Diamond, Diamond-like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide, 2004, p. 5.1.15. [4] T.V. Semikina, Y. Takagi, T. Hirai, T. Kawai, O. Shimizu, Y. Suda, Proc. 16th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes and Nitrides, 2005, p. 5.2.13. [5] K. Gyoda, Y. Tanaka, Y. Takagi, Mat. Res. Soc. Symp. Proc., vol. 749, Materials Research Society, 2003.