SYNTESIS OF CARBON NANOSTRUCTURES NEAR ROOM ...
SYNTESIS OF CARBON NANOSTRUCTURES NEAR ROOM TEMPERATURE USING PECVD ASSISTED BY MICROWAVE F. Carvalho1 , A. A. Vaz2, M. A. Bica de Moraes3, S. Moshkalev2, R. V. Gelamo1* 1
Universidade Federal do Triângulo Mineiro, Uberaba, MG, Brazil; 2Centro de Componentes Semicondutores, Unicamp, Campinas, SP, Brazil; 3Instituto de Física Gleb Wataghin, Unicamp, Campinas, SP, Brazil. e-mail: [email protected] Carbon nanostructures (nanofibers, nanosponges and nanospheres) were synthesized onto Si (001) substrates using plasma enhanced chemical vapor deposition (PECVD) from C2H2-Ar mixtures. The plasma was activated by a microwave generator and the nanostructures were grown at low substrate temperatures (about 120 ºC) on top of previously deposited catalytic Ni and Cu films of 3 nm thick. No films treatment was made prior to the deposition of the carbon nanostructures. Nanoholes, nanospheres and nanofibers were obtained, depending on acetylene partial pressure used during depositions. Atomic force microscopy (AFM) and scanning electron spectroscopy (SEM) were employed for the morphological characterization of the catalytic films, in order to investigate carbon nanostructures growth mechanisms. Raman spectroscopy was used to investigate carbon hybridization states. Nanofibers of 300 to 500 nm long were observed for some plasma conditions (pressure and microwave power), while a mixture of sp2 and sp3 hybridizations were revealed by the Raman spectra. The results shown here indicate a promising simple and low cost technique for the production of conductive carbon nanofibers connected to Si wafers.
Keywords: carbon nanofiber, PECVD, microwave plasma
Introduction The deposition of carbon nanostructures, nanotubes and nanofibres mainly using plasma processes, have shown to be promising especially with respect to lower deposition temperatures compared to CVD techniques and arc discharge. The type and shape of the catalyst nanoparticle also deserve more research to reach carbon structures with fewer defects to facilitate their integration in Si-based devices. Herein we report an investigation on the growth of nanoholes, nanospheres and nanofibers, using an inhouse microwave PECVD system. All nanostructures were formed onto Si (001) substrates coated with Ni or Cu catalytic films. Depositions were performed close to room temperatures (120 ºC at most); no pretreatment of the catalytic film was made. The morphology of the structures was characterized by SEM and AFM as a function of the acetylene partial pressure and metal catalysts, while chemical binding was investigated by Raman spectroscopy. Experimental part Carbon nanostructures were deposited by PECVD microwave assisted using Ar and Acetylene mixtures onto Si (001) substrates recovered by Cu and Ni films (10 nm thick) deposited by DC sputtering system. Acetylene pressure used in the depositions were 34, 64,70, 79 and 100 mTorr. All depositions were made at 210 mTorr using Ar to reach this final pressure. To analyze the substrate and films surface morphology were used AFM and SEM techniques and Raman spectroscopy to estimate the chemical binding of the carbon nanostructures.
Results and discussion
Various different carbon nanostructures were obtained depending on acetylene pressure used. Nanofibers, nanosponges and nanospheres were visible in SEM images. At 79 mTorr acetylene pressure carbon nanofibers of 500 nm long were deposited in relatively low temperature (120oC). No pre-treatments of the catalyst film (Cu and Ni) were necessary to get the nanostructures observed.
G Intensity (arb. units)
D
1000
1200
1400
1600
1800
2000
-1
Wavenumber (cm )
Fig. 1 – SEM image of structures deposited with 79 mTorr of acetylene upon 3nm Cu catalyst film.
Fig. 2 – Raman spectrum of nanofibers deposited with 79 mTorr of acetylene upon 3nm Ni catalyst film.
Conclusions
In this work we have shown that the use of microwave-assisted PECVD can be a successful technique for the synthesis of carbon nanotubes. The various acetylene partial pressures used facilitate the observation of the carbon nanoholes and nanofibers in their first stages of growth.
References [1] Boskovic, B. O., Stolojan, V., Khan, R. U. a, Haq, S. & Silva, S. R. P. Large-area synthesis of carbon nanofibres at room temperature. Nature materials 1, 165–8 (2002).
Acknowledgement: We thank CNPq and Fapemig for their financial support.
Universidade Federal do Triângulo Mineiro, Uberaba, MG, Brazil; 2Centro de Componentes Semicondutores, Unicamp, Campinas, SP, Brazil; 3Instituto de Física Gleb Wataghin, Unicamp, Campinas, SP, Brazil. e-mail: [email protected] Carbon nanostructures (nanofibers, nanosponges and nanospheres) were synthesized onto Si (001) substrates using plasma enhanced chemical vapor deposition (PECVD) from C2H2-Ar mixtures. The plasma was activated by a microwave generator and the nanostructures were grown at low substrate temperatures (about 120 ºC) on top of previously deposited catalytic Ni and Cu films of 3 nm thick. No films treatment was made prior to the deposition of the carbon nanostructures. Nanoholes, nanospheres and nanofibers were obtained, depending on acetylene partial pressure used during depositions. Atomic force microscopy (AFM) and scanning electron spectroscopy (SEM) were employed for the morphological characterization of the catalytic films, in order to investigate carbon nanostructures growth mechanisms. Raman spectroscopy was used to investigate carbon hybridization states. Nanofibers of 300 to 500 nm long were observed for some plasma conditions (pressure and microwave power), while a mixture of sp2 and sp3 hybridizations were revealed by the Raman spectra. The results shown here indicate a promising simple and low cost technique for the production of conductive carbon nanofibers connected to Si wafers.
Keywords: carbon nanofiber, PECVD, microwave plasma
Introduction The deposition of carbon nanostructures, nanotubes and nanofibres mainly using plasma processes, have shown to be promising especially with respect to lower deposition temperatures compared to CVD techniques and arc discharge. The type and shape of the catalyst nanoparticle also deserve more research to reach carbon structures with fewer defects to facilitate their integration in Si-based devices. Herein we report an investigation on the growth of nanoholes, nanospheres and nanofibers, using an inhouse microwave PECVD system. All nanostructures were formed onto Si (001) substrates coated with Ni or Cu catalytic films. Depositions were performed close to room temperatures (120 ºC at most); no pretreatment of the catalytic film was made. The morphology of the structures was characterized by SEM and AFM as a function of the acetylene partial pressure and metal catalysts, while chemical binding was investigated by Raman spectroscopy. Experimental part Carbon nanostructures were deposited by PECVD microwave assisted using Ar and Acetylene mixtures onto Si (001) substrates recovered by Cu and Ni films (10 nm thick) deposited by DC sputtering system. Acetylene pressure used in the depositions were 34, 64,70, 79 and 100 mTorr. All depositions were made at 210 mTorr using Ar to reach this final pressure. To analyze the substrate and films surface morphology were used AFM and SEM techniques and Raman spectroscopy to estimate the chemical binding of the carbon nanostructures.
Results and discussion
Various different carbon nanostructures were obtained depending on acetylene pressure used. Nanofibers, nanosponges and nanospheres were visible in SEM images. At 79 mTorr acetylene pressure carbon nanofibers of 500 nm long were deposited in relatively low temperature (120oC). No pre-treatments of the catalyst film (Cu and Ni) were necessary to get the nanostructures observed.
G Intensity (arb. units)
D
1000
1200
1400
1600
1800
2000
-1
Wavenumber (cm )
Fig. 1 – SEM image of structures deposited with 79 mTorr of acetylene upon 3nm Cu catalyst film.
Fig. 2 – Raman spectrum of nanofibers deposited with 79 mTorr of acetylene upon 3nm Ni catalyst film.
Conclusions
In this work we have shown that the use of microwave-assisted PECVD can be a successful technique for the synthesis of carbon nanotubes. The various acetylene partial pressures used facilitate the observation of the carbon nanoholes and nanofibers in their first stages of growth.
References [1] Boskovic, B. O., Stolojan, V., Khan, R. U. a, Haq, S. & Silva, S. R. P. Large-area synthesis of carbon nanofibres at room temperature. Nature materials 1, 165–8 (2002).
Acknowledgement: We thank CNPq and Fapemig for their financial support.
