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Production of fluorinated fullerene film by a CF4 RF plasma
Thin Solid Films 386 Ž2001. 286᎐290
Production of fluorinated fullerene film by a CF4 RF plasma Sung-Chae Yang a,U , Tetsu Mieno b a
Satellite Venture Business Laboratory, Shizuoka Uni¨ ersity, 3-5-1 Johoku, Hamamatsu 432-8561, Japan b Department of Physics, Shizuoka Uni¨ ersity, 836 Ooya, Shizuoka 422-8529, Japan Received 17 June 1999; received in revised form 6 March 2000; accepted 6 June 2000
Abstract In order to prepare highly fluorinated fullerene, C 60 Fx , film and to realize the perfluorination of fullerene film as C 60 F60 , RF CF4 plasma is used. From the experimental results, it is found that the best condition for preparation of highly fluorinated fullerene is to restrain the rising temperature of the substrate during the fluorination of fullerene film by using the cooling system and to use ions with lower energy by using the lower input power and symmetric structure of electrodes. In this study, fluorinated fullerene films with double shaped distribution as two peaks at C 60 F14 and C 60 F43 was obtained, and the strong intensity at around C 60 F60 is also detected by using RF CF4 plasma with cooling system. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Fluorinated fullerene; RF plasma; Substrate temperature
1. Introduction Since the discovery and production of the fullerenes C 60 and C 70 , there has been considerable interest in the chemical alteration of this new allotropes carbon. Recent theoretical and experimental studies have considered the possible perfluorination of C 60 ; however, the results are inconclusive as to whether C 60 F60 is stable. For example, Selig and co-workers w1x were the first to carry out reactions between F2 gas and solid C 60 and C 70 . Mass spectrometry and infrared spectroscopy indicated broad distributions of fluorofullerenes C 60 Fx and C 70 Fx with F atoms covalently attached to the available carbon atoms. The positive ion mass spectrum of C 60 Fx gave a distribution of mass peaks extending from C 60 F30 to C 60 F44 with the maximum intensity occurring at C 60 F38 . Only ions containing an even number of fluorine atoms were observed. The corresponding C 70 Fx spectra showed even-numbered fluoU
Corresponding author. Tel.: q81-9040880209; fax: q81542381680. E-mail address: [email protected] ŽS. Yang..
rine compounds from C 70 F36 to C 70 F46 with the maximum intensity at C 70 F40 . However, the former methods, to prepare fluorinated fullerenes, have some problems such as a special gas operation technique is necessary for safe operation, because the operating temperature is very high and the operating time is very long because the chemical reaction is slow w2,3x. And also much more work will be necessary to improve our understanding and to solve the chemical reaction process of fluorinated fullerenes. In order to improve the fluorination process of fullerene thin film and to perform the safety method for the preparation of fluorinated fullerenes in a relatively shorter operation time, we have investigated the production of fluorinated fullerene thin film by using a cold cathode DC discharge of CF4 gas. From these experimental results, it is found that the surface of fullerene thin film becomes fullerene fluoride such as C 60 Fx Ž x s 15᎐51. with the maximum intensity at C 60 F33 by the measurement of a laser-desorption time-of-flight mass spectrometer ŽTOF-MS; ShimadsurKratos, Kompact Maldi III. w4x. The aim of this study is to obtain the more intense
0040-6090r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 0 . 0 1 6 7 5 - 8
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
287
peak at the region of higher fluorinated fullerene. Therefore, we have carried out the experiments for the various experimental conditions, i.e. various pressures, input powers and discharge times. In this paper, the dependence of the higher fluorofullerenes on input power and surface temperature of fullerene films is reported mainly by using the measurements of TOFMS. 2. Experimental apparatus and methods A preparation of fullerene film and its fluorination are carried out in the different chambers. To prepare the fullerene thin film, a cylindrical vacuum chamber made of metal, 250 mm high and 8 inch in diameter, is used. In this experiment, Cu and Ni substrates are placed at a distance of 200 mm above a tantalum oven 30 mm in diameter. Approximately 0.5 g of fullerene, C 60 , powder is placed in the oven. By heating the oven at 500᎐700⬚C for approximately 5 h at a pressure of 10y5 torr, the fullerene inside the oven is sublimated and deposited on the substrates. In this experiment, the film thickness is approximately 5 m and the film appears flat under scanning electron microscope observation, described in detail elsewhere w4x. In order to fluorinate fullerene film, the experiments were performed in a conventional parallel plate reactor, as shown in Fig. 1. A cylindrical vacuum chamber made of quartz is 100 mm in length and 100 mm in diameter. Plane electrodes of 80 mm in diameter and 25 mm in spacing is prepared. A CF4 gas is used in the experiments. CF4 plasma is generated by a RF power generator under the conditions of gas pressure Ps 0.1᎐0.5 torr, input power Pin s 30᎐100 W and discharge time Td s 0.5᎐2 h, respectively. The samples of fullerene film, which were prepared by evaporation of C 60 , are mounted on each electrode
Fig. 1. Experimental apparatus.
ŽRF and ground electrodes.. The fluorinated fullerene films are analyzed by using a TOF-MS. The fluorinated fullerene films are kept in a desiccator for further measurements. The fluorination of fullerene is carried out with or without a cooling system because of the heating effect of the fullerene films mounted on electrode by the collision of charged particles should be examined. 3. Experimental results and discussions In this study, after the deposition of fullerene films on Cu and Ni substrates by sublimation of fullerene powder in vacuum, they are reacted with RF CF4 plasma under varying pressure, input power and discharge time, respectively. However, in this paper, it is reported mainly for the conditions of pressure Ps 0.2 torr, discharge time Td s 2 h and lower input power because good results have been obtained at these experimental conditions. At the other experimental conditions, i.e. higher input power as 70 or 100 W, fullerene films are damaged such that the color is changed andror removed by the bombardment of charged particles.
Fig. 2. Mass spectrum of C 60 Fx on the surface of fluorinated fullerene film from TOF-MS, which is prepared under the conditions of pressure Ps 0.2 torr, input power Pin s 50 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode Žnegative ion detection, 100 shots averaged, maximum intensity is 13 mV for 22% transmittance of applied laser..
288
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
The conventional result of the mass spectrum analysis of the fluorinated fullerene film under the operating conditions: pressure Ps 0.2 torr, input power Pin s 50 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode Žnegative ion detection, 100 shots averaged. is presented in Fig. 2. This figure shows that fullerene, C 60 , has been fluorinated to give C 60 Fx Ž xs 22, 26, 36 etc.., with the maximum intensity occurring at C 60 F22 . From this figure, it is also found that the peak of the perfluorinated fullerene, C 60 F60 , is obtained even if the intensity is weak. However, the intensity of the fluorinated fullerene spectrum decreases with increasing the coefficient x of fluorinated fullerene, C 60 Fx . The aim of this study is to obtain the more intense peak at the region of higher fluorinated fullerene. Therefore, we have carried out the experiments for the various experimental conditions. Consequently, it is found out that fullerene films are damaged such that the color is changed andror removed by the bombardment of charged particles at higher input power or longer discharge time. Therefore, we have measured temporal variation of the surface temperature of fullerene films for the discharge time. Fig. 3 shows the temporal variation of the surface temperature of RF electrode for the discharge time according to each experimental condition. From this figure, it is found that the surface temperature of substrate increases to more than 100⬚C for the discharge time Td s 2 h. Therefore, it is considered that this temperate variation greatly affects the sublimation of fluorinated fullerene ŽC 60 Fx . at the surface of the fullerene film. This effect of temperate variation is more effective at the region of highly fluorinated fullerene than lower one. As a result, it is considered
Fig. 3. Temporal variation of the surface temperature of RF electrode for the discharge time.
that the intensity of TOF-MS at the region of higher fluorinated fullerene is weak. Therefore, in order to obtain the higher fluorofullerene and to realize the perfluorination of fullerene film as C 60 F60 , RF CF4 plasma with cooling system is used. The result of TOF-MS for the conditions of pressure Ps 0.2 torr, input power Pin s 30 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode is shown in Fig. 4. The surface temperature of the substrate after 2 h of treatment is 36⬚C and the same conditions as that of Fig. 2 are used at the analysis of TOF-MS. From this figure, it is found that there are many peaks of fluorinated fullerene, with double shaped distribution as two strong peaks at C 60 F14 Žfirst peak. and C 60 F43 Žsecond peak.. The strong intensity at around C 60 F60 is also obtained. These results are clearly different from the results of Fig. 2. These results are explained as follows.
Fig. 4. Mass spectrum of C 60 Fx on the surface of fluorinated fullerene film from TOF-MS, which is prepared under the conditions of pressure Ps 0.2 torr, input power Pin s 30 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode with cooling system Žnegative ion detection, 100 shots averaged, maximum intensity is 3 mV for 25% transmittance of applied laser..
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
In the former experiments Žwithout a cooling system., fluorinated fullerene is emitted from the fullerene film with increasing the substrate temperature, and this effect is more effective at the region of higher fluorinated fullerene. However, using the cooling system of the RF electrode, it is possible to restrain the rising temperature of the substrate during the fluorination of fullerene film. Consequently, it is considered that the intense peak at the region of around second peak can be obtained. Fig. 5a shows the intensity of TOF-MS for the coefficient x of fluorinated fullerene, C 60 Fx , concerning the substrate type and position under the conditions of pressure Ps 0.2 torr, input power Pin s 30 W and discharge time Td s 2 h. From this figure, it is well known that higher fluorinated fullerene is obtained at this experimental condition. It is also found that the spectrum profile has two peaks at the coefficient xs 14 and 43 and it is independent of the substrate type and
289
position. Fig. 5b shows the intensity of TOF-MS for the coefficient x under the condition of input power Pin s 50 W. From this figure, it is known that the intensity of fluorinated fullerene decreases with increasing x of C 60 Fx and the second peak is not shown. These experimental results are clearly different, even if the substrate temperatures are not so different, i.e. 36⬚C and 48⬚C after plasma treatment for 2 h, respectively. This result means that the input power is one of important parameter to obtain more highly fluorinated fullerene. It is considered that if higher input power is applied, then not only increasing of the substrate temperature but also increasing of the input ion energy to the substrate. Using the cooling system of the electrode, increasing of the substrate temperature can be depressed, but input ion energy can not be controlled. It is considered that the intensity of higher fluorinated fullerene decreases with increasing the input power because using the high input power is possible to break the binding of fluorinated fullerene. On the other hand, in order to obtain more active reaction between the CF4 plasma and fullerene film we have studied also by using an asymmetric structure of electrodes, RF electrode of 50 mm in diameter and ground electrode of 80 mm in diameter. However, in these experiments, it is very difficult to obtain the fluorinated fullerene because the input ion energy is higher than that of using a symmetric structure of electrodes according to higher space potential. From this result, it is also found out that lower ion energy is needed to prepare highly fluorinated fullerene film. 4. Conclusion In order to obtain the higher fluorofullerenes, C 60 Fx , than that of DC plasma and to realize the perfluorination of fullerene film as C 60 F60 , fluorination of fullerene film by RF CF4 plasma is carried out. Consequently, from the measurement of TOF-MS, fluorinated fullerene films with double shaped distribution as two peaks at C 60 F14 and C 60 F43 were obtained by using RF CF4 plasma with cooling system. Furthermore, the strong intensity at around C 60 F60 is also obtained. From these results, it is considered that RF plasma is more useful than DC plasma, and the surface temperature of substrate and inputted ion energy are important parameters to achieve highly fluorinated fullerene films. Acknowledgements
Fig. 5. Dependence of TOF-MS intensity on the coefficient x of fluorinated fullerene, C 60 Fx , for the substrate type and position under the conditions: Ža. pressure Ps 0.2 torr, input power Pin s 30 W and discharge time Td s 2 h; and Žb. Ps 0.2 torr, Pin s 50 W and Td s 2 h.
It is a pleasure to thank Mr R. Ikeya of Shizuoka University for his technical assistance. References w1x H. Selig, C. Lifshitz, T. Perez, J.E. Fischer, A.R. McGhie, W.J.
290
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
Romanow, J.P. McCauley, A.B. Smith III, J. Am. Chem. Soc. 113 Ž1991. 5475. w2x A.A. Tuinman, P. Mukherjee, J.L. Adcock, R.L. Hettich, R.N. Compton, J. Phys. Chem. 96 Ž1992. 7584.
w3x K. Kniaz, J.E. Fischer, H. Selig, G.B.M. Vaughan, W.J. Romanow, D.M. Cox, S.K. Chowdhury, J.P. McCauley, R.M. Strongin, A.B. Smith III, J. Am. Chem. Soc. 115 Ž1993. 6060. w4x T. Mieno, A. Sakurai, Jpn. J. Appl. Phys. 34 Ž1995. L458.
Production of fluorinated fullerene film by a CF4 RF plasma Sung-Chae Yang a,U , Tetsu Mieno b a
Satellite Venture Business Laboratory, Shizuoka Uni¨ ersity, 3-5-1 Johoku, Hamamatsu 432-8561, Japan b Department of Physics, Shizuoka Uni¨ ersity, 836 Ooya, Shizuoka 422-8529, Japan Received 17 June 1999; received in revised form 6 March 2000; accepted 6 June 2000
Abstract In order to prepare highly fluorinated fullerene, C 60 Fx , film and to realize the perfluorination of fullerene film as C 60 F60 , RF CF4 plasma is used. From the experimental results, it is found that the best condition for preparation of highly fluorinated fullerene is to restrain the rising temperature of the substrate during the fluorination of fullerene film by using the cooling system and to use ions with lower energy by using the lower input power and symmetric structure of electrodes. In this study, fluorinated fullerene films with double shaped distribution as two peaks at C 60 F14 and C 60 F43 was obtained, and the strong intensity at around C 60 F60 is also detected by using RF CF4 plasma with cooling system. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Fluorinated fullerene; RF plasma; Substrate temperature
1. Introduction Since the discovery and production of the fullerenes C 60 and C 70 , there has been considerable interest in the chemical alteration of this new allotropes carbon. Recent theoretical and experimental studies have considered the possible perfluorination of C 60 ; however, the results are inconclusive as to whether C 60 F60 is stable. For example, Selig and co-workers w1x were the first to carry out reactions between F2 gas and solid C 60 and C 70 . Mass spectrometry and infrared spectroscopy indicated broad distributions of fluorofullerenes C 60 Fx and C 70 Fx with F atoms covalently attached to the available carbon atoms. The positive ion mass spectrum of C 60 Fx gave a distribution of mass peaks extending from C 60 F30 to C 60 F44 with the maximum intensity occurring at C 60 F38 . Only ions containing an even number of fluorine atoms were observed. The corresponding C 70 Fx spectra showed even-numbered fluoU
Corresponding author. Tel.: q81-9040880209; fax: q81542381680. E-mail address: [email protected] ŽS. Yang..
rine compounds from C 70 F36 to C 70 F46 with the maximum intensity at C 70 F40 . However, the former methods, to prepare fluorinated fullerenes, have some problems such as a special gas operation technique is necessary for safe operation, because the operating temperature is very high and the operating time is very long because the chemical reaction is slow w2,3x. And also much more work will be necessary to improve our understanding and to solve the chemical reaction process of fluorinated fullerenes. In order to improve the fluorination process of fullerene thin film and to perform the safety method for the preparation of fluorinated fullerenes in a relatively shorter operation time, we have investigated the production of fluorinated fullerene thin film by using a cold cathode DC discharge of CF4 gas. From these experimental results, it is found that the surface of fullerene thin film becomes fullerene fluoride such as C 60 Fx Ž x s 15᎐51. with the maximum intensity at C 60 F33 by the measurement of a laser-desorption time-of-flight mass spectrometer ŽTOF-MS; ShimadsurKratos, Kompact Maldi III. w4x. The aim of this study is to obtain the more intense
0040-6090r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 0 - 6 0 9 0 Ž 0 0 . 0 1 6 7 5 - 8
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
287
peak at the region of higher fluorinated fullerene. Therefore, we have carried out the experiments for the various experimental conditions, i.e. various pressures, input powers and discharge times. In this paper, the dependence of the higher fluorofullerenes on input power and surface temperature of fullerene films is reported mainly by using the measurements of TOFMS. 2. Experimental apparatus and methods A preparation of fullerene film and its fluorination are carried out in the different chambers. To prepare the fullerene thin film, a cylindrical vacuum chamber made of metal, 250 mm high and 8 inch in diameter, is used. In this experiment, Cu and Ni substrates are placed at a distance of 200 mm above a tantalum oven 30 mm in diameter. Approximately 0.5 g of fullerene, C 60 , powder is placed in the oven. By heating the oven at 500᎐700⬚C for approximately 5 h at a pressure of 10y5 torr, the fullerene inside the oven is sublimated and deposited on the substrates. In this experiment, the film thickness is approximately 5 m and the film appears flat under scanning electron microscope observation, described in detail elsewhere w4x. In order to fluorinate fullerene film, the experiments were performed in a conventional parallel plate reactor, as shown in Fig. 1. A cylindrical vacuum chamber made of quartz is 100 mm in length and 100 mm in diameter. Plane electrodes of 80 mm in diameter and 25 mm in spacing is prepared. A CF4 gas is used in the experiments. CF4 plasma is generated by a RF power generator under the conditions of gas pressure Ps 0.1᎐0.5 torr, input power Pin s 30᎐100 W and discharge time Td s 0.5᎐2 h, respectively. The samples of fullerene film, which were prepared by evaporation of C 60 , are mounted on each electrode
Fig. 1. Experimental apparatus.
ŽRF and ground electrodes.. The fluorinated fullerene films are analyzed by using a TOF-MS. The fluorinated fullerene films are kept in a desiccator for further measurements. The fluorination of fullerene is carried out with or without a cooling system because of the heating effect of the fullerene films mounted on electrode by the collision of charged particles should be examined. 3. Experimental results and discussions In this study, after the deposition of fullerene films on Cu and Ni substrates by sublimation of fullerene powder in vacuum, they are reacted with RF CF4 plasma under varying pressure, input power and discharge time, respectively. However, in this paper, it is reported mainly for the conditions of pressure Ps 0.2 torr, discharge time Td s 2 h and lower input power because good results have been obtained at these experimental conditions. At the other experimental conditions, i.e. higher input power as 70 or 100 W, fullerene films are damaged such that the color is changed andror removed by the bombardment of charged particles.
Fig. 2. Mass spectrum of C 60 Fx on the surface of fluorinated fullerene film from TOF-MS, which is prepared under the conditions of pressure Ps 0.2 torr, input power Pin s 50 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode Žnegative ion detection, 100 shots averaged, maximum intensity is 13 mV for 22% transmittance of applied laser..
288
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
The conventional result of the mass spectrum analysis of the fluorinated fullerene film under the operating conditions: pressure Ps 0.2 torr, input power Pin s 50 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode Žnegative ion detection, 100 shots averaged. is presented in Fig. 2. This figure shows that fullerene, C 60 , has been fluorinated to give C 60 Fx Ž xs 22, 26, 36 etc.., with the maximum intensity occurring at C 60 F22 . From this figure, it is also found that the peak of the perfluorinated fullerene, C 60 F60 , is obtained even if the intensity is weak. However, the intensity of the fluorinated fullerene spectrum decreases with increasing the coefficient x of fluorinated fullerene, C 60 Fx . The aim of this study is to obtain the more intense peak at the region of higher fluorinated fullerene. Therefore, we have carried out the experiments for the various experimental conditions. Consequently, it is found out that fullerene films are damaged such that the color is changed andror removed by the bombardment of charged particles at higher input power or longer discharge time. Therefore, we have measured temporal variation of the surface temperature of fullerene films for the discharge time. Fig. 3 shows the temporal variation of the surface temperature of RF electrode for the discharge time according to each experimental condition. From this figure, it is found that the surface temperature of substrate increases to more than 100⬚C for the discharge time Td s 2 h. Therefore, it is considered that this temperate variation greatly affects the sublimation of fluorinated fullerene ŽC 60 Fx . at the surface of the fullerene film. This effect of temperate variation is more effective at the region of highly fluorinated fullerene than lower one. As a result, it is considered
Fig. 3. Temporal variation of the surface temperature of RF electrode for the discharge time.
that the intensity of TOF-MS at the region of higher fluorinated fullerene is weak. Therefore, in order to obtain the higher fluorofullerene and to realize the perfluorination of fullerene film as C 60 F60 , RF CF4 plasma with cooling system is used. The result of TOF-MS for the conditions of pressure Ps 0.2 torr, input power Pin s 30 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode is shown in Fig. 4. The surface temperature of the substrate after 2 h of treatment is 36⬚C and the same conditions as that of Fig. 2 are used at the analysis of TOF-MS. From this figure, it is found that there are many peaks of fluorinated fullerene, with double shaped distribution as two strong peaks at C 60 F14 Žfirst peak. and C 60 F43 Žsecond peak.. The strong intensity at around C 60 F60 is also obtained. These results are clearly different from the results of Fig. 2. These results are explained as follows.
Fig. 4. Mass spectrum of C 60 Fx on the surface of fluorinated fullerene film from TOF-MS, which is prepared under the conditions of pressure Ps 0.2 torr, input power Pin s 30 W, discharge time Td s 2 h and Cu substrate mounted on RF electrode with cooling system Žnegative ion detection, 100 shots averaged, maximum intensity is 3 mV for 25% transmittance of applied laser..
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
In the former experiments Žwithout a cooling system., fluorinated fullerene is emitted from the fullerene film with increasing the substrate temperature, and this effect is more effective at the region of higher fluorinated fullerene. However, using the cooling system of the RF electrode, it is possible to restrain the rising temperature of the substrate during the fluorination of fullerene film. Consequently, it is considered that the intense peak at the region of around second peak can be obtained. Fig. 5a shows the intensity of TOF-MS for the coefficient x of fluorinated fullerene, C 60 Fx , concerning the substrate type and position under the conditions of pressure Ps 0.2 torr, input power Pin s 30 W and discharge time Td s 2 h. From this figure, it is well known that higher fluorinated fullerene is obtained at this experimental condition. It is also found that the spectrum profile has two peaks at the coefficient xs 14 and 43 and it is independent of the substrate type and
289
position. Fig. 5b shows the intensity of TOF-MS for the coefficient x under the condition of input power Pin s 50 W. From this figure, it is known that the intensity of fluorinated fullerene decreases with increasing x of C 60 Fx and the second peak is not shown. These experimental results are clearly different, even if the substrate temperatures are not so different, i.e. 36⬚C and 48⬚C after plasma treatment for 2 h, respectively. This result means that the input power is one of important parameter to obtain more highly fluorinated fullerene. It is considered that if higher input power is applied, then not only increasing of the substrate temperature but also increasing of the input ion energy to the substrate. Using the cooling system of the electrode, increasing of the substrate temperature can be depressed, but input ion energy can not be controlled. It is considered that the intensity of higher fluorinated fullerene decreases with increasing the input power because using the high input power is possible to break the binding of fluorinated fullerene. On the other hand, in order to obtain more active reaction between the CF4 plasma and fullerene film we have studied also by using an asymmetric structure of electrodes, RF electrode of 50 mm in diameter and ground electrode of 80 mm in diameter. However, in these experiments, it is very difficult to obtain the fluorinated fullerene because the input ion energy is higher than that of using a symmetric structure of electrodes according to higher space potential. From this result, it is also found out that lower ion energy is needed to prepare highly fluorinated fullerene film. 4. Conclusion In order to obtain the higher fluorofullerenes, C 60 Fx , than that of DC plasma and to realize the perfluorination of fullerene film as C 60 F60 , fluorination of fullerene film by RF CF4 plasma is carried out. Consequently, from the measurement of TOF-MS, fluorinated fullerene films with double shaped distribution as two peaks at C 60 F14 and C 60 F43 were obtained by using RF CF4 plasma with cooling system. Furthermore, the strong intensity at around C 60 F60 is also obtained. From these results, it is considered that RF plasma is more useful than DC plasma, and the surface temperature of substrate and inputted ion energy are important parameters to achieve highly fluorinated fullerene films. Acknowledgements
Fig. 5. Dependence of TOF-MS intensity on the coefficient x of fluorinated fullerene, C 60 Fx , for the substrate type and position under the conditions: Ža. pressure Ps 0.2 torr, input power Pin s 30 W and discharge time Td s 2 h; and Žb. Ps 0.2 torr, Pin s 50 W and Td s 2 h.
It is a pleasure to thank Mr R. Ikeya of Shizuoka University for his technical assistance. References w1x H. Selig, C. Lifshitz, T. Perez, J.E. Fischer, A.R. McGhie, W.J.
290
S. Yang, T. Mieno r Thin Solid Films 386 (2001) 286᎐290
Romanow, J.P. McCauley, A.B. Smith III, J. Am. Chem. Soc. 113 Ž1991. 5475. w2x A.A. Tuinman, P. Mukherjee, J.L. Adcock, R.L. Hettich, R.N. Compton, J. Phys. Chem. 96 Ž1992. 7584.
w3x K. Kniaz, J.E. Fischer, H. Selig, G.B.M. Vaughan, W.J. Romanow, D.M. Cox, S.K. Chowdhury, J.P. McCauley, R.M. Strongin, A.B. Smith III, J. Am. Chem. Soc. 115 Ž1993. 6060. w4x T. Mieno, A. Sakurai, Jpn. J. Appl. Phys. 34 Ž1995. L458.