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Effect of laser parameters on the property of DLC films grown by pulsed laser deposition
Surface and Coatings Technology 115 (1999) 266–269 www.elsevier.nl/locate/surfcoat
Effect of laser parameters on the property of DLC films grown by pulsed laser deposition k S.S. Pang a, S.Y. Lee a, *, H.S. Jung b, H.H. Park b a Department of Electrical Engineering, Yonsei University, Seoul 120-749, South Korea b Department of Ceramic Engineering, Yonsei University, Seoul 120-749, South Korea Received 27 April 1998; accepted 7 May 1999
Abstract Diamond-like carbon (DLC ) films have been fabricated by pulsed laser deposition (PLD). The effect of the laser fluence and the substrate temperature on the properties of DLC films was systematically investigated. The substrate temperatures in the range of room temperature to 600°C were varied systematically to observe the effect of substrate temperature on the property of DLC films. Also, film depositions at laser fluences from 6 to 17 J cm−2 were investigated. High-quality DLC films were obtained with the deposition parameters of substrate temperature of 300°C and laser fluence of 12 J cm−2. © 1999 Elsevier Science S.A. All rights reserved. Keywords: DLC; FED; Laser fluence; PL; PLD; Raman spectroscopy; SEM; Thin film
1. Introduction The fabrication of diamond-like carbon (DLC ) films by pulsed laser deposition (PLD) has been widely studied for potential applications involving electronic devices, tool coatings, optical windows and semiconductors [1]. DLC has marvelous characteristics, such as a large thermal conductivity, high hardness and chemical inertness. DLC films have been shown to have a negative electron affinity (NEA) (i.e. the conduction band is above the vacuum level ) and a low work function of around 0.2~0.3 eV [2]. Therefore, DLC films have advantages related to their field emission characteristics. At the atomic level, DLC presently refers to a group of carbon materials with strong sp2 and sp3 arrangements of atoms incorporated into an amorphous structure [3]. There are many techniques for depositing DLC material. The PLD technique was adopted to grow DLC film since films deposited by this method contained a higher proportion of sp3 bonds desirable in field emission applications [4]. These days, PLD has emerged as a useful deposition k Presented at the ICMCTF ’98 Conference, San Diego, CA, USA, April 1998. * Corresponding author. Tel.: +82-2-361-2776; fax: +82-2-364-9770. E-mail address: [email protected] (S.Y. Lee)
technique [5]. In comparison to sputtering, ion beam evaporation, electron beam evaporation and plasmaassisted chemical vapor deposition, PLD allows the use of reactive gases with a range of pressure selections without affecting the deposition process [6 ]. Pulsed laser deposition techniques can produce films without hydrogen and with a high degree of diamond-like properties. In general, the characterization of DLC thin films depends on the deposition parameters. The laser fluence and the substrate temperature play a vital role in the resulting film properties [7]. In this study, the effect of the laser fluence and the substrate temperature on the properties of DLC films was investigated.
2. Experimental A Nd:YAG laser was used to fabricate DLC thin films on p-type Si (100) substrates. The schematic diagram of PLD system is shown in Fig. 1. A pulsed laser with a wavelength of 355 nm was fired at an energy in the range of 1~2 J cm−2 and at a frequency of 5 Hz. The pulsed laser was focused on the target surface with a 45° beam incident angle from the normal to the target surface. Prior to deposition, Si substrates with dimensions of 1.2 cm×1.2 cm were ultrasonically degreased in acetone
0257-8972/99/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S0 2 5 7- 8 9 7 2 ( 9 9 ) 0 0 24 7 - 9
S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
267
Fig. 1. Schematic diagram of a pulsed laser deposition system.
and methanol. Graphite targets were fixed on target holders using silver paste after polishing the target surface. The laser beam was focused onto a solid graphite target rotating linearly to avoid any deep craters that may eject macroscopic graphite particles. The properties of DLC thin films were studied using SEM, Raman spectroscopy, photoluminescence (PL) and XPS.
3. Results and discussion Fig. 2 shows the results of Raman spectroscopy of DLC thin films deposited at a laser fluence of
12 J cm−2, for two deposition temperatures, 200 and 300°C. The two peaks of film grown at 200°C appear exactly at the position of the graphite line (1580 cm−1) and the disordering line (1350 cm−1) as observed in Fig. 2(a) [8]. As shown in Fig. 2(b), we found strong DLC peak at 1560 cm−1 in the laser-ablated thin film grown at 300°C [9]. Films deposited at substrate temperatures higher than 300°C showed graphite peaks. Raman spectroscopy of two films deposited at a substrate temperature of 300°C is shown in Fig. 3. The laser fluence varies from 10 to 14 J cm−2. Fig. 3(b) and (c) show a relatively weak but reliable diamond peak (1560 cm−1), and Fig. 3(a) and (d ) indicate the graphite
Fig. 2. Raman spectroscopy on DLC thin films at substrate temperature: (a) 200°C and (b) 300°C.
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S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
Fig. 3. Raman spectroscopy on DLC thin films at 300°C with laser fluence at: (a) 14 J cm−2; (b) 13 J cm−2; (c) 11 J cm−2; and (d ) 10 J cm−2.
phase in laser-ablated films. High-quality DLC films were obtained at a laser fluence of 12 J cm−2 and a substrate temperature of 300°C based on these experimental results as shown in Fig. 2(b). Good DLC films were obtained at 300°C , a relatively high temperature compared to that in previous studies. The films had smooth surfaces with some particles on the surface; a typical result is shown in Fig. 4. The
film thickness was found, using cross-sectional SEM, to be about 400~600 nm. A photoluminescence (PL) analysis was performed using an argon laser (488 nm) to examine the optical band gap of DLC thin films. The PL peak appeared at 643.2 nm, as shown in Fig. 5. The optical band gap of the film in Fig. 2(b) is estimated to be about 1.9 eV based on this PL observation.
Fig. 4. Cross-section SEM image of a thin film deposited at a laser fluence of 12 J cm−2 and a temperature of 300°C.
Fig. 5. PL analysis of a DLC thin film of deposited at a laser fluence of 12 J cm−2 and a temperature of 300°C.
S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
269
4. Conclusions
References
Good DLC films were fabricated at the substrate temperature of 300°C and for the case when the laser fluence was 12 J cm−2. The strong DLC peak of the film deposited at these conditions has been confirmed from Raman spectroscopy. SEM revealed that the film surface was uniform and smooth. Based on a PL analysis, the optical band gap was determined to be about 1.9 eV. Laser-ablated DLC thin films grown at a substrate temperature of 300°C and a laser fluence of 12 J cm−2 showed good characteristics for use in field emission devices.
[1] A.A. Voevodin, M.S. Donley, Surf. Coat. Technol. 82 (1996) 199. [2] F.Y. Chuang, C.Y. Sun, H.F. Cheng, W.C. Wang, I.N. Lin, Appl. Surf. Sci. 113–114 (1997) 259. [3] Rusli, G.A.J. Amaratunga, S.R.P. Silvia, Thin Solid Films 270 (1995) 160. [4] M.A. Capano, N.T. McDevitt, R.K. Singh, F. Qian, J. Vac. Sci. Technol. 14 (2) (1996) 431. [5] J.H. Park, Y.S. Jeong, S.Y. Lee, Thin Solid Film 318 (1998) 243. [6 ] F.-X. Rong, Appl. Phys. Lett. 67 (7) (1995) 1022. [7] F. Xiaong, Y.Y. Wang, V. Leppert, R.P.H. Chang, J. Mater. Res. 8 (9) (1993) 2265. [8] J.S. Lee, K.S. Liu, I.N. Lin, Appl. Phys. Lett. 71 (4) (1997) 554. [9] A.A. Voevodin, S.J.P. Laube, S.D. Walck, J.S. Donley, J.S. Zabinski, J. Appl. Phys. 78 (6) (1995) 4123.
Acknowledgement This study is supported by Nondirected Research Fund, Korea Research Foundation.
Effect of laser parameters on the property of DLC films grown by pulsed laser deposition k S.S. Pang a, S.Y. Lee a, *, H.S. Jung b, H.H. Park b a Department of Electrical Engineering, Yonsei University, Seoul 120-749, South Korea b Department of Ceramic Engineering, Yonsei University, Seoul 120-749, South Korea Received 27 April 1998; accepted 7 May 1999
Abstract Diamond-like carbon (DLC ) films have been fabricated by pulsed laser deposition (PLD). The effect of the laser fluence and the substrate temperature on the properties of DLC films was systematically investigated. The substrate temperatures in the range of room temperature to 600°C were varied systematically to observe the effect of substrate temperature on the property of DLC films. Also, film depositions at laser fluences from 6 to 17 J cm−2 were investigated. High-quality DLC films were obtained with the deposition parameters of substrate temperature of 300°C and laser fluence of 12 J cm−2. © 1999 Elsevier Science S.A. All rights reserved. Keywords: DLC; FED; Laser fluence; PL; PLD; Raman spectroscopy; SEM; Thin film
1. Introduction The fabrication of diamond-like carbon (DLC ) films by pulsed laser deposition (PLD) has been widely studied for potential applications involving electronic devices, tool coatings, optical windows and semiconductors [1]. DLC has marvelous characteristics, such as a large thermal conductivity, high hardness and chemical inertness. DLC films have been shown to have a negative electron affinity (NEA) (i.e. the conduction band is above the vacuum level ) and a low work function of around 0.2~0.3 eV [2]. Therefore, DLC films have advantages related to their field emission characteristics. At the atomic level, DLC presently refers to a group of carbon materials with strong sp2 and sp3 arrangements of atoms incorporated into an amorphous structure [3]. There are many techniques for depositing DLC material. The PLD technique was adopted to grow DLC film since films deposited by this method contained a higher proportion of sp3 bonds desirable in field emission applications [4]. These days, PLD has emerged as a useful deposition k Presented at the ICMCTF ’98 Conference, San Diego, CA, USA, April 1998. * Corresponding author. Tel.: +82-2-361-2776; fax: +82-2-364-9770. E-mail address: [email protected] (S.Y. Lee)
technique [5]. In comparison to sputtering, ion beam evaporation, electron beam evaporation and plasmaassisted chemical vapor deposition, PLD allows the use of reactive gases with a range of pressure selections without affecting the deposition process [6 ]. Pulsed laser deposition techniques can produce films without hydrogen and with a high degree of diamond-like properties. In general, the characterization of DLC thin films depends on the deposition parameters. The laser fluence and the substrate temperature play a vital role in the resulting film properties [7]. In this study, the effect of the laser fluence and the substrate temperature on the properties of DLC films was investigated.
2. Experimental A Nd:YAG laser was used to fabricate DLC thin films on p-type Si (100) substrates. The schematic diagram of PLD system is shown in Fig. 1. A pulsed laser with a wavelength of 355 nm was fired at an energy in the range of 1~2 J cm−2 and at a frequency of 5 Hz. The pulsed laser was focused on the target surface with a 45° beam incident angle from the normal to the target surface. Prior to deposition, Si substrates with dimensions of 1.2 cm×1.2 cm were ultrasonically degreased in acetone
0257-8972/99/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S0 2 5 7- 8 9 7 2 ( 9 9 ) 0 0 24 7 - 9
S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
267
Fig. 1. Schematic diagram of a pulsed laser deposition system.
and methanol. Graphite targets were fixed on target holders using silver paste after polishing the target surface. The laser beam was focused onto a solid graphite target rotating linearly to avoid any deep craters that may eject macroscopic graphite particles. The properties of DLC thin films were studied using SEM, Raman spectroscopy, photoluminescence (PL) and XPS.
3. Results and discussion Fig. 2 shows the results of Raman spectroscopy of DLC thin films deposited at a laser fluence of
12 J cm−2, for two deposition temperatures, 200 and 300°C. The two peaks of film grown at 200°C appear exactly at the position of the graphite line (1580 cm−1) and the disordering line (1350 cm−1) as observed in Fig. 2(a) [8]. As shown in Fig. 2(b), we found strong DLC peak at 1560 cm−1 in the laser-ablated thin film grown at 300°C [9]. Films deposited at substrate temperatures higher than 300°C showed graphite peaks. Raman spectroscopy of two films deposited at a substrate temperature of 300°C is shown in Fig. 3. The laser fluence varies from 10 to 14 J cm−2. Fig. 3(b) and (c) show a relatively weak but reliable diamond peak (1560 cm−1), and Fig. 3(a) and (d ) indicate the graphite
Fig. 2. Raman spectroscopy on DLC thin films at substrate temperature: (a) 200°C and (b) 300°C.
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S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
Fig. 3. Raman spectroscopy on DLC thin films at 300°C with laser fluence at: (a) 14 J cm−2; (b) 13 J cm−2; (c) 11 J cm−2; and (d ) 10 J cm−2.
phase in laser-ablated films. High-quality DLC films were obtained at a laser fluence of 12 J cm−2 and a substrate temperature of 300°C based on these experimental results as shown in Fig. 2(b). Good DLC films were obtained at 300°C , a relatively high temperature compared to that in previous studies. The films had smooth surfaces with some particles on the surface; a typical result is shown in Fig. 4. The
film thickness was found, using cross-sectional SEM, to be about 400~600 nm. A photoluminescence (PL) analysis was performed using an argon laser (488 nm) to examine the optical band gap of DLC thin films. The PL peak appeared at 643.2 nm, as shown in Fig. 5. The optical band gap of the film in Fig. 2(b) is estimated to be about 1.9 eV based on this PL observation.
Fig. 4. Cross-section SEM image of a thin film deposited at a laser fluence of 12 J cm−2 and a temperature of 300°C.
Fig. 5. PL analysis of a DLC thin film of deposited at a laser fluence of 12 J cm−2 and a temperature of 300°C.
S.S. Pang et al. / Surface and Coatings Technology 115 (1999) 266–269
269
4. Conclusions
References
Good DLC films were fabricated at the substrate temperature of 300°C and for the case when the laser fluence was 12 J cm−2. The strong DLC peak of the film deposited at these conditions has been confirmed from Raman spectroscopy. SEM revealed that the film surface was uniform and smooth. Based on a PL analysis, the optical band gap was determined to be about 1.9 eV. Laser-ablated DLC thin films grown at a substrate temperature of 300°C and a laser fluence of 12 J cm−2 showed good characteristics for use in field emission devices.
[1] A.A. Voevodin, M.S. Donley, Surf. Coat. Technol. 82 (1996) 199. [2] F.Y. Chuang, C.Y. Sun, H.F. Cheng, W.C. Wang, I.N. Lin, Appl. Surf. Sci. 113–114 (1997) 259. [3] Rusli, G.A.J. Amaratunga, S.R.P. Silvia, Thin Solid Films 270 (1995) 160. [4] M.A. Capano, N.T. McDevitt, R.K. Singh, F. Qian, J. Vac. Sci. Technol. 14 (2) (1996) 431. [5] J.H. Park, Y.S. Jeong, S.Y. Lee, Thin Solid Film 318 (1998) 243. [6 ] F.-X. Rong, Appl. Phys. Lett. 67 (7) (1995) 1022. [7] F. Xiaong, Y.Y. Wang, V. Leppert, R.P.H. Chang, J. Mater. Res. 8 (9) (1993) 2265. [8] J.S. Lee, K.S. Liu, I.N. Lin, Appl. Phys. Lett. 71 (4) (1997) 554. [9] A.A. Voevodin, S.J.P. Laube, S.D. Walck, J.S. Donley, J.S. Zabinski, J. Appl. Phys. 78 (6) (1995) 4123.
Acknowledgement This study is supported by Nondirected Research Fund, Korea Research Foundation.