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The growth of carbon nanotubes on large areas of silicon substrate using commercial iron oxide nanoparticles as a catalyst
Materials Letters 64 (2010) 2188–2190
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
The growth of carbon nanotubes on large areas of silicon substrate using commercial iron oxide nanoparticles as a catalyst Marcos Felisberto a, Leandro Sacco a, Iñaki Mondragon b, Gerardo H. Rubiolo a,c, Roberto J. Candal d, Silvia Goyanes a,⁎ a
LP&MC, Dept. de Física, FCEyN-UBA, and IFIBA-CONICET, Pab1, Ciudad Universitaria 1428 Bs. As., Argentina Dept. Ing. Química y M. Ambiente, Escuela Politécnica, University of the Basque Country, Pza. Europa 1, 20018 Donostia-San Sebastián, Spain Dept. de Materiales (GIDAT-CAC), Comisión Nacional de Energía Atómica, Avda General Paz 1499, B1650KNA San Martín, Pcia. Bs. As., Argentina d INQUIMAE-CONICET, Ciudad Universitaria 1428 Bs. As., Argentina & Escuela de Ciencia y Tecnologia, UNSAM, Campus Miguelete, San Martín, Bs. As., Argentina b c
a r t i c l e
i n f o
Article history: Received 17 May 2010 Accepted 4 July 2010 Available online 13 July 2010 Keywords: Chemical vapour deposition Nanomaterials Carbon nanotubes Commercial nanoparticles Iron oxide Synthesis
a b s t r a c t A new approach to chemical vapour deposition (CVD) growth of carbon nanotubes (CNTs) using commercial magnetite nanoparticles, avoiding its in situ synthesis, is reported. Commercial magnetite nanoparticles were used as catalyst material to growth multiwalled carbon nanotubes by chemical vapour deposition onto a silicon substrate of several square centimeters in area. It is shown that the application of an alternating electric field during the deposition of catalytical nanoparticles is an effective technique to avoid their agglomeration allowing nanotube growth. Scanning electron microscopy showed that the nanotubes grow perpendicularly to the substrate and formed an aligned nanotubes array. The array density can be controlled by modifying the deposited nanoparticle concentration. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Problems associated with carbon nanotube growth onto large areas and at low temperatures constitute one of the main obstacles for the development of all their potential applications. Chemical vapour deposition is the main method to provide large scale production of nanotubes [1] using substrate with the catalyst nanoparticles (NPs) deposited by different methods, which involve several technologies. High vacuum technologies, as sputtering, electron beam evaporation between others have been used with success but only in small surfaces [2]. Block copolymers have been used to generate patterns of catalytic NPs. These methods can be applied on surfaces of bigger areas, but its implementation requires several difficult steps [2]. Thermal decomposition of metal precursor salts [3], and the synthesis of NPs included in oxide or ceramic matrices also require the use of high temperatures for the formation of oxide NPs, and its application to large surfaces in unlikely [4]. The utilization of commercial nanoparticles has several advantages when compared with the techniques mentioned above. First of all, the use of commercial NPs avoid the need to synthesize the NPs in situ, using high temperatures that may damage the support; secondly the NPs can be spread over surfaces as large as needed in a way cheaper
⁎ Corresponding author. Tel.: + 54 11 45763300x255; fax: + 54 11 45763300. E-mail address: [email protected] (S. Goyanes). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.07.016
than the methods described before. Finally, the use of plasma enhance chemical vapour deposition allows the reduction of iron oxide NPs and CNTs growth at temperatures as low as 250 °C, leading to the use of thermal sensible supports [5]. Nowadays it is possible to obtain commercial iron oxide nanoparticles, which can be suspended in liquids and deposited on surfaces as large as several square meters. As far as we known, there are no references on the synthesis of carbon nanotubes using commercial nanoparticles as catalyst precursor. In this work, we report a new method that allows depositing commercial iron oxide nanoparticles on large areas at temperatures lower than 50 °C. We also show that these nanoparticles are able for CNTs growing by CVD. In our novel approach, the commercial nanoparticles are electrically charged using acid condition prior the application of an alternating electric field during their deposition onto a silicon substrate. This allowed them to remain unaggregated on substrate surface before CNT growing by CVD. We also can control the surface density of nanoparticles, what allowed the growth of carbon nanotubes in bundles without the use of expensive techniques to create patterns on the substrate as photolithography. 2. Material and methods Magnetite nanoparticles (MNPs) with an average particle size of 9 nm were purchased from Integran Tecnologies Inc. (Canada). Polished, 111 oriented, p-doped, RCA standard cleaned [6] silicon
M. Felisberto et al. / Materials Letters 64 (2010) 2188–2190
2189
wafers were used as supports. Magnetite particles were used as supplied by the manufacturer. The surface of the particles was not functionalized. Particles dispersion was stabilized by incorporating nitric acid to the magnetite isopropanolic suspension. In such a way, the particles acquired positive charge leading to particle stabilization. A 2.4 mg/L magnetite suspension was prepared by incorporating the powder (as received from the company) into 1 mM nitric acid in isopropanol solution under stirring. The contact angle of the solution on a freshly cleaned silicon substrate was 0°, measured with an equipment with resolution of 0.1° (ramé-hart advanced goniometer). The suspension was sonicated using a high intensity ultrasonic processor (500 W, 25 kHz) at 288 K during 40 min, in order to break MNP aggregates. The sonication time was selected to obtain the lower particle effective diameter in suspension, measured by dynamic light scattering (Brokhaven 90 plus). Further application of ultrasound did not modified the effective particle diameter. The used MNP concentrations were chosen after estimation of the amount of nanoparticles needed to form a monolayer on the substrate (1.25 × 10 12 nanoparticles/cm 2 ). Samples were prepared with 9 × 1011 nanoparticles/cm2 and 6 × 1012 nanoparticles/cm2, with the appropriated amount of drops to achieve films with density of 1.8 and 12 μg/cm2, respectively. In both cases, the suspension drops were of 25 μL and they were deposited onto silicon wafers of 3 cm2 in area. Each one of the drops was dried by Joule effect by applying an alternating electric field. Voltages of 150 V were applied with 40 mA circulating current on the substrate. The substrate temperature is homogeneous in all deposition area and was kept, in all the cases, lower than 50 °C. Multiwalled carbon nanotubes (MWCNTs) were grown by CVD technique. Magnetite nanoparticles were reduced (to metallic iron)
under 200 sccm of H2:N2 (10:90) mixture gas flow, during 60 min at 180 Torr and 800 °C (temperature determined by temperature program reduction, TPR, analysis in a Shimadzu TGA-51). After reduction, a 2 sccm of acetylene and 100 sccm of H2:N2 flow was introduced into the reactor with the temperature kept at 800 °C. Synthesis of MWCNTs was carried out during 50 min. Morphological characterization of MWCNTs was performed by field emission scanning electron microscopy (FESEM Zeiss LEO 982 GEMINI) and transmission electron microscopy (TEM-EM Philips 301).
Fig. 1. Schematic representation of the system used to deposition of MNPs solution drops.
Fig. 2. FE-SEM micrographs of MWCNTs grown on: a) high and b) low magnetite nanoparticle surface density silicon substrate.
3. Results and discussion A schematic representation of the system used to deposite the MNPs is shown on Fig. 1. The silicon substrate was placed between two aluminium electrodes where the alternating field was applied. Fig. 2 a–b shows micrographs of MWCNTs grown on the high and low NPs surface density substrates, respectively. In both cases the nanotubes were grown perpendicular to the substrate. For the high MNP surface density, Fig. 2a, the substrate was completely covered by MWCNTs while in the low density case, Fig. 2b, the MWCNTs were grown in cylindrical bundles of 1–4 μm of diameter. In both cases the MWCNTs had 20–40 nm and 6–9 nm outer and inner diameter, respectively, as measured by transmission electron microscopy. In the case shown in Fig. 2b, the amount of nanoparticles by cm2 is lower than the necessary to form a monolayer of MNPs on the substrate, while in the high density case (Fig. 2a) the substrate surface is completely covered with, at least, 4 monolayers. This leads to the differences observed in the growing patterns of the MWCNTs. When nanoparticles cover the entire surface forming a MNP film, the nanotubes grow as a continuous carpet. When the MNPs are not enough to completely cover the substrate surface, the MNPs form
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M. Felisberto et al. / Materials Letters 64 (2010) 2188–2190
Fig. 3. FE-SEM micrographs and EDS analysis of low density case substrate showing the catalyst distribution.
islands on which the nanotubes grow, leading to the MWCNT bundles (Fig. 3). FESEM analysis of the substrate with the MNPs before the carbon nanotube synthesis shows that, under low covering conditions, the MNP forms zones of 1–2 μm, as can be seen in Fig. 3. These zones are separated by areas without or with low iron concentrations, as determined by EDS (inset in Fig. 3). Should be noted, that these zones are formed by an assembly of single MNP very close to each other but not aggregated together as a single particle. The consolidation of the MNPs in fused aggregates did not lead to the growth of CNTs [7]. In the high density case, as the substrate is covered with at least 4 monolayers of MNPs, the distance between neighboring particles is very small and the FESEM microscopy has no resolution to discern one nanoparticle to each other. Aggregation of MNPs during the drying of suspension drops constitutes a problem for the synthesis of CNTs. Attempts to dry the drops by thermal treatment did not lead to the growth of nanotubes but fibers and other carbonaceous species. Drying the drops using an alternating electric field, we were able to minimize the aggregation of the nanoparticles, probably as a consequence of the oscillatory movement imposed to them by the field. 4. Conclusions Well dispersed liquid suspension of commercial MNPs can be effectively used for the synthesis of MWCNTs on relatively large surfaces. A key control parameter is the drying of the suspension drops. By applying an alternating electric field to dry the drops of the suspension it is possible to control the MNP aggregation, leading to vertically aligned CNT. The method also allows the control of the
surface density of NPs leading to the growth of carbon nanotubes in different spatial arrangements. This methodology, applied together with plasma enhanced chemical vapour deposition, could provide a way to large scale growth of carbon nanotubes at low temperatures. Acknowledgments The authors are thankful for funds of Buenos Aires University (UBACyT X094), CONICET PIP 2010–2012, Project 11220090100699, Basque Country Government (Grupos Consolidados -IT-365-07) and ETORTEK/inanoGUNE projects. SG, GHR and RJC are CONICET members. MF is thankful for the PhD fellowship from CONICET. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007– 2013) under grant agreement no. 213939. References [1] Harri PJF. Carbon nanotube science: synthesis, properties and applications. Cambridge: Cambridge University Press; 2009. [2] Meyyappan M, Delzeit L, Cassell A, Hash D. Carbon nanotube growth by PECVD: a review. Plasma Sources Sci Technol 2003;12:205–16. [3] Qi X, Zhong W, Deng Y, Au C, Du Y. Synthesis of helical carbon nanotubes, wormlike carbon nanotubes and nanocoils at 450 °C and their magnetic properties. Carbon 2010;48:365–76. [4] Monte F, Morales MP, Levy D, Fernandez A, Ocaña M, Roig A, et al. Formation of γ-Fe2O3 isolated nanoparticles in silica matrix. Langmuir 1997;13:3627–34. [5] Chang S-C, Lin T-C, Li T-S, Huang S-H. Carbon nanotubes grown from nickel catalyst pretreated with H2/N2 plasma. Microelectron J 2008;39:1572–5. [6] Kern W, Puotinen DA. Cleaning solutions based on hydrogen peroxide for use in silicon semiconductor technology. RCA Rev 1970;31:187–206. [7] Kukovitsky EF, L'vov SG, Sainov NA, Shustov VA, Chernozatonskii LA. Correlation between metal catalyst particle size and carbon nanotube growth. Chem Phys Lett 2002;355:497–503.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
The growth of carbon nanotubes on large areas of silicon substrate using commercial iron oxide nanoparticles as a catalyst Marcos Felisberto a, Leandro Sacco a, Iñaki Mondragon b, Gerardo H. Rubiolo a,c, Roberto J. Candal d, Silvia Goyanes a,⁎ a
LP&MC, Dept. de Física, FCEyN-UBA, and IFIBA-CONICET, Pab1, Ciudad Universitaria 1428 Bs. As., Argentina Dept. Ing. Química y M. Ambiente, Escuela Politécnica, University of the Basque Country, Pza. Europa 1, 20018 Donostia-San Sebastián, Spain Dept. de Materiales (GIDAT-CAC), Comisión Nacional de Energía Atómica, Avda General Paz 1499, B1650KNA San Martín, Pcia. Bs. As., Argentina d INQUIMAE-CONICET, Ciudad Universitaria 1428 Bs. As., Argentina & Escuela de Ciencia y Tecnologia, UNSAM, Campus Miguelete, San Martín, Bs. As., Argentina b c
a r t i c l e
i n f o
Article history: Received 17 May 2010 Accepted 4 July 2010 Available online 13 July 2010 Keywords: Chemical vapour deposition Nanomaterials Carbon nanotubes Commercial nanoparticles Iron oxide Synthesis
a b s t r a c t A new approach to chemical vapour deposition (CVD) growth of carbon nanotubes (CNTs) using commercial magnetite nanoparticles, avoiding its in situ synthesis, is reported. Commercial magnetite nanoparticles were used as catalyst material to growth multiwalled carbon nanotubes by chemical vapour deposition onto a silicon substrate of several square centimeters in area. It is shown that the application of an alternating electric field during the deposition of catalytical nanoparticles is an effective technique to avoid their agglomeration allowing nanotube growth. Scanning electron microscopy showed that the nanotubes grow perpendicularly to the substrate and formed an aligned nanotubes array. The array density can be controlled by modifying the deposited nanoparticle concentration. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Problems associated with carbon nanotube growth onto large areas and at low temperatures constitute one of the main obstacles for the development of all their potential applications. Chemical vapour deposition is the main method to provide large scale production of nanotubes [1] using substrate with the catalyst nanoparticles (NPs) deposited by different methods, which involve several technologies. High vacuum technologies, as sputtering, electron beam evaporation between others have been used with success but only in small surfaces [2]. Block copolymers have been used to generate patterns of catalytic NPs. These methods can be applied on surfaces of bigger areas, but its implementation requires several difficult steps [2]. Thermal decomposition of metal precursor salts [3], and the synthesis of NPs included in oxide or ceramic matrices also require the use of high temperatures for the formation of oxide NPs, and its application to large surfaces in unlikely [4]. The utilization of commercial nanoparticles has several advantages when compared with the techniques mentioned above. First of all, the use of commercial NPs avoid the need to synthesize the NPs in situ, using high temperatures that may damage the support; secondly the NPs can be spread over surfaces as large as needed in a way cheaper
⁎ Corresponding author. Tel.: + 54 11 45763300x255; fax: + 54 11 45763300. E-mail address: [email protected] (S. Goyanes). 0167-577X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2010.07.016
than the methods described before. Finally, the use of plasma enhance chemical vapour deposition allows the reduction of iron oxide NPs and CNTs growth at temperatures as low as 250 °C, leading to the use of thermal sensible supports [5]. Nowadays it is possible to obtain commercial iron oxide nanoparticles, which can be suspended in liquids and deposited on surfaces as large as several square meters. As far as we known, there are no references on the synthesis of carbon nanotubes using commercial nanoparticles as catalyst precursor. In this work, we report a new method that allows depositing commercial iron oxide nanoparticles on large areas at temperatures lower than 50 °C. We also show that these nanoparticles are able for CNTs growing by CVD. In our novel approach, the commercial nanoparticles are electrically charged using acid condition prior the application of an alternating electric field during their deposition onto a silicon substrate. This allowed them to remain unaggregated on substrate surface before CNT growing by CVD. We also can control the surface density of nanoparticles, what allowed the growth of carbon nanotubes in bundles without the use of expensive techniques to create patterns on the substrate as photolithography. 2. Material and methods Magnetite nanoparticles (MNPs) with an average particle size of 9 nm were purchased from Integran Tecnologies Inc. (Canada). Polished, 111 oriented, p-doped, RCA standard cleaned [6] silicon
M. Felisberto et al. / Materials Letters 64 (2010) 2188–2190
2189
wafers were used as supports. Magnetite particles were used as supplied by the manufacturer. The surface of the particles was not functionalized. Particles dispersion was stabilized by incorporating nitric acid to the magnetite isopropanolic suspension. In such a way, the particles acquired positive charge leading to particle stabilization. A 2.4 mg/L magnetite suspension was prepared by incorporating the powder (as received from the company) into 1 mM nitric acid in isopropanol solution under stirring. The contact angle of the solution on a freshly cleaned silicon substrate was 0°, measured with an equipment with resolution of 0.1° (ramé-hart advanced goniometer). The suspension was sonicated using a high intensity ultrasonic processor (500 W, 25 kHz) at 288 K during 40 min, in order to break MNP aggregates. The sonication time was selected to obtain the lower particle effective diameter in suspension, measured by dynamic light scattering (Brokhaven 90 plus). Further application of ultrasound did not modified the effective particle diameter. The used MNP concentrations were chosen after estimation of the amount of nanoparticles needed to form a monolayer on the substrate (1.25 × 10 12 nanoparticles/cm 2 ). Samples were prepared with 9 × 1011 nanoparticles/cm2 and 6 × 1012 nanoparticles/cm2, with the appropriated amount of drops to achieve films with density of 1.8 and 12 μg/cm2, respectively. In both cases, the suspension drops were of 25 μL and they were deposited onto silicon wafers of 3 cm2 in area. Each one of the drops was dried by Joule effect by applying an alternating electric field. Voltages of 150 V were applied with 40 mA circulating current on the substrate. The substrate temperature is homogeneous in all deposition area and was kept, in all the cases, lower than 50 °C. Multiwalled carbon nanotubes (MWCNTs) were grown by CVD technique. Magnetite nanoparticles were reduced (to metallic iron)
under 200 sccm of H2:N2 (10:90) mixture gas flow, during 60 min at 180 Torr and 800 °C (temperature determined by temperature program reduction, TPR, analysis in a Shimadzu TGA-51). After reduction, a 2 sccm of acetylene and 100 sccm of H2:N2 flow was introduced into the reactor with the temperature kept at 800 °C. Synthesis of MWCNTs was carried out during 50 min. Morphological characterization of MWCNTs was performed by field emission scanning electron microscopy (FESEM Zeiss LEO 982 GEMINI) and transmission electron microscopy (TEM-EM Philips 301).
Fig. 1. Schematic representation of the system used to deposition of MNPs solution drops.
Fig. 2. FE-SEM micrographs of MWCNTs grown on: a) high and b) low magnetite nanoparticle surface density silicon substrate.
3. Results and discussion A schematic representation of the system used to deposite the MNPs is shown on Fig. 1. The silicon substrate was placed between two aluminium electrodes where the alternating field was applied. Fig. 2 a–b shows micrographs of MWCNTs grown on the high and low NPs surface density substrates, respectively. In both cases the nanotubes were grown perpendicular to the substrate. For the high MNP surface density, Fig. 2a, the substrate was completely covered by MWCNTs while in the low density case, Fig. 2b, the MWCNTs were grown in cylindrical bundles of 1–4 μm of diameter. In both cases the MWCNTs had 20–40 nm and 6–9 nm outer and inner diameter, respectively, as measured by transmission electron microscopy. In the case shown in Fig. 2b, the amount of nanoparticles by cm2 is lower than the necessary to form a monolayer of MNPs on the substrate, while in the high density case (Fig. 2a) the substrate surface is completely covered with, at least, 4 monolayers. This leads to the differences observed in the growing patterns of the MWCNTs. When nanoparticles cover the entire surface forming a MNP film, the nanotubes grow as a continuous carpet. When the MNPs are not enough to completely cover the substrate surface, the MNPs form
2190
M. Felisberto et al. / Materials Letters 64 (2010) 2188–2190
Fig. 3. FE-SEM micrographs and EDS analysis of low density case substrate showing the catalyst distribution.
islands on which the nanotubes grow, leading to the MWCNT bundles (Fig. 3). FESEM analysis of the substrate with the MNPs before the carbon nanotube synthesis shows that, under low covering conditions, the MNP forms zones of 1–2 μm, as can be seen in Fig. 3. These zones are separated by areas without or with low iron concentrations, as determined by EDS (inset in Fig. 3). Should be noted, that these zones are formed by an assembly of single MNP very close to each other but not aggregated together as a single particle. The consolidation of the MNPs in fused aggregates did not lead to the growth of CNTs [7]. In the high density case, as the substrate is covered with at least 4 monolayers of MNPs, the distance between neighboring particles is very small and the FESEM microscopy has no resolution to discern one nanoparticle to each other. Aggregation of MNPs during the drying of suspension drops constitutes a problem for the synthesis of CNTs. Attempts to dry the drops by thermal treatment did not lead to the growth of nanotubes but fibers and other carbonaceous species. Drying the drops using an alternating electric field, we were able to minimize the aggregation of the nanoparticles, probably as a consequence of the oscillatory movement imposed to them by the field. 4. Conclusions Well dispersed liquid suspension of commercial MNPs can be effectively used for the synthesis of MWCNTs on relatively large surfaces. A key control parameter is the drying of the suspension drops. By applying an alternating electric field to dry the drops of the suspension it is possible to control the MNP aggregation, leading to vertically aligned CNT. The method also allows the control of the
surface density of NPs leading to the growth of carbon nanotubes in different spatial arrangements. This methodology, applied together with plasma enhanced chemical vapour deposition, could provide a way to large scale growth of carbon nanotubes at low temperatures. Acknowledgments The authors are thankful for funds of Buenos Aires University (UBACyT X094), CONICET PIP 2010–2012, Project 11220090100699, Basque Country Government (Grupos Consolidados -IT-365-07) and ETORTEK/inanoGUNE projects. SG, GHR and RJC are CONICET members. MF is thankful for the PhD fellowship from CONICET. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007– 2013) under grant agreement no. 213939. References [1] Harri PJF. Carbon nanotube science: synthesis, properties and applications. Cambridge: Cambridge University Press; 2009. [2] Meyyappan M, Delzeit L, Cassell A, Hash D. Carbon nanotube growth by PECVD: a review. Plasma Sources Sci Technol 2003;12:205–16. [3] Qi X, Zhong W, Deng Y, Au C, Du Y. Synthesis of helical carbon nanotubes, wormlike carbon nanotubes and nanocoils at 450 °C and their magnetic properties. Carbon 2010;48:365–76. [4] Monte F, Morales MP, Levy D, Fernandez A, Ocaña M, Roig A, et al. Formation of γ-Fe2O3 isolated nanoparticles in silica matrix. Langmuir 1997;13:3627–34. [5] Chang S-C, Lin T-C, Li T-S, Huang S-H. Carbon nanotubes grown from nickel catalyst pretreated with H2/N2 plasma. Microelectron J 2008;39:1572–5. [6] Kern W, Puotinen DA. Cleaning solutions based on hydrogen peroxide for use in silicon semiconductor technology. RCA Rev 1970;31:187–206. [7] Kukovitsky EF, L'vov SG, Sainov NA, Shustov VA, Chernozatonskii LA. Correlation between metal catalyst particle size and carbon nanotube growth. Chem Phys Lett 2002;355:497–503.