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Synthesis and growth mechanism of BCN nanowires
Materials Letters 65 (2011) 2476–2478
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
Synthesis and growth mechanism of BCN nanowires Yanchun Yin a, b, Yongjun Chen b,⁎ a b
Guangxi Vocational and Technical College of Health, Nanning 530023, China School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
a r t i c l e
i n f o
Article history: Received 15 April 2011 Accepted 6 May 2011 Available online 12 May 2011 Keywords: Nanocrystalline materials Chemical vapor deposition Growth mechanism
a b s t r a c t The synthesis of ternary boron carbonitride (BCN) nanowires was reported in this study through a simple approach, by the reactions among a novel precursor boron triiodide (BI3), ammonia and water-free alcohol at 1100 °C. The product was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectrometer (EDS) and electron energy loss spectroscopy (EELS), respectively. The results show that the BCN nanowires are structurally disordered and possess a uniform diameter of about 30 nm. The elemental mapping shows that B and N elements are distributed homogeneously within the nanowires, while C element is enriched in the outer layer of the nanowires. The formation of these nanowires is believed to be governed by a vapor–solid (VS) growth model. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Ternary boron carbonitride (BCN) nanotubes have recently attracted much attentions because of their excellent mechanical properties, electrical properties and anti-oxidant capacities [1,2]. In addition, theoretical studies have revealed that the band gap of BCN nanotubes can be tailored over a wide range by simply varying the chemical composition rather than by geometrical structure [3–7], which is superior to their carbon and boron nitride (BN) counterparts. This gives BCN nanotubes potential application in electronics and electrical conductors [8]. Since the discovery of BCN nanotubes in 1994 [9], hollow BCN nanotubes have been synthesized by methods such as arc-discharge [10], laser ablation [11], chemical vapor deposition (CVD) [12,13], template route and pyrolysis techniques [14,15]. The author's group developed recently a novel vapor-phase method for the synthesis of BCN nanotubes [16], by reacting B2O2 vapor with water-free alcohol, N2 and H2. More recently, another socalled solid-state reaction approach was also explored by the same group to synthesize BCN nanotubes [17]. However, very few works were reported on solid BCN nanowires [15,18–20]. Furthermore, the precursors involved in the synthesis of BCN nanowires are generally dangerous/hazardous, or the nanowire product is of low purity. For examples, BCN nanofibers were obtained from a mixture of N2, H2, CH4 and B2H6 [19], or prepared by pyrolyzing BH3 with N(CH3)3 (1:1) and pyridine over cobalt powder [15]. Thus, it is of great significance to explore novel and simple precursors to synthesize BCN nanowires. Inspired by the previous work using
⁎ Corresponding author. Tel./fax: + 86 771 3233718. E-mail address: [email protected] (Y. Chen). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.05.026
water-free alcohol as the carbon source to synthesize BCN nanotubes [16] and using a novel precursor boron triiodide (BI3) to prepare BN nanowires [21], we report here a simple and effective approach to synthesize BCN nanowires by reacting BI3 with ammonia and waterfree alcohol at elevated temperatures. The synthesized nanowires were well characterized and the growth mechanism was discussed.
2. Experimental The experimental is very similar to that of BN nanowire synthesis [21]. Firstly, an alumina boat loading with BI3 powder (98% purity) and a polished silicon substrate was inserted into an alumina tube, which was then fixed in a conventional tube furnace. The starting material of BI3 was located at the center of the furnace and the Si substrate was put in a downstream direction with a distance of about 3 cm. Prior to heating, the furnace chamber was flushed with N2 flow (about 500 mL min − 1) to eliminate the residual air. Then the furnace was quickly heated to 1100 °C at a rate of 40 °C min − 1 under N2 flow (50 mL min − 1). NH3 gas flow at a rate of 10 mL min − 1 instead was introduced into the chamber when the temperature reaches at 1100 °C. Meanwhile, water-free alcohol (AR grade) carried by Ar flow (10 mL min − 1) was also introduced. The growth was stopped 30 min later by pulling the boat out of the hot zone of the furnace. Then the furnace was cooled naturally to ambient temperature under N2 flow. Upon completion of the experiment, no BI3 powder was left in the boat and a thin layer of gray deposition was observed on the Si substrate. The product was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S4500), transmission electron microscopy (TEM; JEM-2010 F), X-ray energy dispersive spectrometer (EDS) and electron energy loss spectroscopy (EELS), respectively.
Y. Yin, Y. Chen / Materials Letters 65 (2011) 2476–2478
2477
Fig. 1. Low-magnification (a) and high-magnification (b) SEM images of the product.
3. Results and discussion Fig. 1 shows the SEM images of the deposition. It can be seen that large quantity of nanowires with length of several micrometers are produced (Fig. 1a). High-magnification image (Fig. 1b) reveals that
the nanowires have a uniform and thin diameter of about 30 nm. At the ends of nanowires, no metal or other particles can be observed. Consisting with the SEM observation, TEM image (Fig. 2a) also shows the large production of nanowires and no particle or nanotube is found. Fig. 2b shows a typical HRTEM image of a nanowire. BCN
Fig. 2. (a) TEM image of BCN nanowires. (b) High-resolution TEM image of one nanowire, consisting of disordered structure with some crystalline nanodomains. (c) EDS result under SEM taken from a group of nanowires. (d) EELS spectrum taken from one nanowire.
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Y. Yin, Y. Chen / Materials Letters 65 (2011) 2476–2478
Fig. 3. Elemental maps of several nanowires.
basal (002) planes in random orientations and some quasi-crystalline nanodomains are demonstrated, which are very different from those of BCN nanotubes with well crystallized hexagonal structures. EDS analysis (under SEM) also reveals the presence of O and Si at low contents in the nanowires (Fig. 2c). The Si signal should come from the Si substrate, while O comes from the slight oxidation of the nanowires. Quantitative analysis indicates that the atomic contents of B, C, N, O and Si elements are about 43.3%, 7.3%, 39.1%, 9.9% and 0.4%, respectively, revealing the carbon insufficient compared with those normal B-C-N compounds such as BCN, BC2N and BC4N. Fig. 2d shows a representive EELS spectrum taken from one nanowire. It demonstrates the distinct absorption peaks of B, C and N characteristic Kedges at 188, 287 and 399 eV, respectively. This result further verifies the nanowire composition of B, C and N. The elemental mapping taken on several nanowires also reveals the composition of B, C and N (Fig. 3). However, C element is relatively concentrated in the outer layers of the nanowires, which is consistent with the EDS results discussed above. Therefore, it can be concluded that B-C-N nanowires are synthesized in our work. No catalyst particles are found inside or at the ends of nanowires and the nanowire tips have almost the same size as the body. Therefore, these BCN nanowires are not formed via a conventional vapor–liquid– solid (VLS) mechanism [22]. According to the experimental details, the following formation process is proposed. First, when the temperature reached the vaporization temperature of BI3 (about 210 °C), BI3 vapor started to rise. Then reactions among vapors of BI3, NH3 and C2H5OH (alcohol) took place at 1100 °C. Possibly, nanosized BCN particles were formed on the substrate, which might act as the seeds for the further growth of BCN crystal. Some possible defects (e.g. dislocations) in the seeds may absorb the surrounding vapor species, allowing the growth of BCN nanowires. Continuous reactions among vapors provided more BCN species for the continuous growth of the nanowires. In our work, a very low rate of NH3 flow was used so that most of BI3 vapor could be involved in the reactions instead of being flushed out of the chamber. Therefore, the whole growth process of the nanowires appeared to be governed by a vapor–solid (VS) mechanism [23]. In addition, the fast reactions among vapors and a relatively low experimental temperature might also be responsible for the formation of poor crystallized nanowires with some crystalline nanodomains. However, the detailed growth process needs further investigation. The possible reactions are expressed as follows: BI3 ðsÞ→BI3 ðgÞ
ð1Þ
BI3 ðgÞ + NH3 ðgÞ + C2 H5 OHðgÞ→BCNðnanowiresÞ + HIðgÞ + H2 OðgÞ: ð2Þ
4. Conclusions High-purity BCN nanowires were successfully synthesized by heating a novel precursor BI3 at 1100 °C in the presence of NH3 and water-free alcohol. The nanowires have lengths of several micrometers and uniform diameters of 30 nm. VS mechanism is responsible for the growth of the nanowires. Because of the fast reactions among vapors of BI3, NH3 and C2H5OH and a relatively low experimental temperature, the nanowires possess a disordered structure with local crystalline nanodomains. These uniquely structured BCN nanowires may find some interesting properties and applications in comparison with those nanowires possessing well crystallized hexagonal structure.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
Liu AY, Wentzcovitch RM, Cohen ML. Phys Rev B 1989;39:1760. Dorozhkin P, Golberg D, Bando Y, Dong ZC. Appl Phys Lett 2002;81:1083. Kim SY, Park J, Choi HC, Ahn JP, Hou JQ, Kang HS. J Am Chem Soc 2007;129:1705. Liao L, Liu KH, Wang WL, Bai XD, Wang EG, Liu YL, et al. J Am Chem Soc 2007;129:9562. Miyamoto Y, Rubio A, Cohen ML, Louie SG. Phys Rev B 1994;50:4976. Enyashin AM, Makurin YN, Ivanovskii AL. Carbon 2004;42:2081. Blase X, Charlier JC, Vita AD, Car R. Appl Phys Lett 1997;70:197. Kawaguchi M. Adv Mater 1997;9:8. Stephan O, Ajayan PM, Colliex C, Redlich P, Lambert JM, Bernier P, et al. Science 1994;266:1683. Suenaga K, Colliex C, Demoncy N, Loiseau A, Pascard H, Willaime F. Science 1997;278:653. Redlich P, Loeffler J, Ajayan PM, Bill J, Aldinger F, Rühle M. Chem Phys Lett 1996;260:465. Bai XD, Guo JD, Yu J, Wang EG, Yuan J, Zhou WZ. Appl Phys Lett 2000;76:2624. Yin LW, Bando Y, Golberg D, Gloter A, Li MS, Yuan X, et al. J Am Chem Soc 2005;27: 16354. Terrones M, Golberg D, Grobert N, Seeger T, Reyes-Reyes M, Mayne M, et al. Adv Mater 2003;15:1899. Sen R, Satishkumar BC, Govindaraj A, Harikumar KR, Gargi R, Zhang JP, et al. Chem Phys Lett 1998;287:671. Luo LJ, Mo LB, Tong ZF, Chen YJ. Nanoscale Res Lett 2009;4:834. Mo LB, Chen YJ, Luo LJ. Appl Phys A Mater Sci Proc 2010;100:129. Bai XD, Guo JD, Yu J, Wang EG, Yuan J, Zhou WZ. Appl Phys Lett 2000;76:2624. Bai XD, Yu J, Liu S, Wang EG. Chem Phys Lett 2000;325:485. Yu J, Ahn J, Yoon SF, Zhang Q, Gan RB, Chew K, et al. Appl Phys Lett 2000;77:1949. Chen YJ, Zhang HZ, Chen Y. Nanotechnology 2006;17:786. Morales AM, Lieber CM. Science 1998;279:208. Chen YJ, Li JB, Han YS, Yang XZ, Dai JH. J Crystal Growth 2002;245:163.
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
Synthesis and growth mechanism of BCN nanowires Yanchun Yin a, b, Yongjun Chen b,⁎ a b
Guangxi Vocational and Technical College of Health, Nanning 530023, China School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
a r t i c l e
i n f o
Article history: Received 15 April 2011 Accepted 6 May 2011 Available online 12 May 2011 Keywords: Nanocrystalline materials Chemical vapor deposition Growth mechanism
a b s t r a c t The synthesis of ternary boron carbonitride (BCN) nanowires was reported in this study through a simple approach, by the reactions among a novel precursor boron triiodide (BI3), ammonia and water-free alcohol at 1100 °C. The product was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectrometer (EDS) and electron energy loss spectroscopy (EELS), respectively. The results show that the BCN nanowires are structurally disordered and possess a uniform diameter of about 30 nm. The elemental mapping shows that B and N elements are distributed homogeneously within the nanowires, while C element is enriched in the outer layer of the nanowires. The formation of these nanowires is believed to be governed by a vapor–solid (VS) growth model. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Ternary boron carbonitride (BCN) nanotubes have recently attracted much attentions because of their excellent mechanical properties, electrical properties and anti-oxidant capacities [1,2]. In addition, theoretical studies have revealed that the band gap of BCN nanotubes can be tailored over a wide range by simply varying the chemical composition rather than by geometrical structure [3–7], which is superior to their carbon and boron nitride (BN) counterparts. This gives BCN nanotubes potential application in electronics and electrical conductors [8]. Since the discovery of BCN nanotubes in 1994 [9], hollow BCN nanotubes have been synthesized by methods such as arc-discharge [10], laser ablation [11], chemical vapor deposition (CVD) [12,13], template route and pyrolysis techniques [14,15]. The author's group developed recently a novel vapor-phase method for the synthesis of BCN nanotubes [16], by reacting B2O2 vapor with water-free alcohol, N2 and H2. More recently, another socalled solid-state reaction approach was also explored by the same group to synthesize BCN nanotubes [17]. However, very few works were reported on solid BCN nanowires [15,18–20]. Furthermore, the precursors involved in the synthesis of BCN nanowires are generally dangerous/hazardous, or the nanowire product is of low purity. For examples, BCN nanofibers were obtained from a mixture of N2, H2, CH4 and B2H6 [19], or prepared by pyrolyzing BH3 with N(CH3)3 (1:1) and pyridine over cobalt powder [15]. Thus, it is of great significance to explore novel and simple precursors to synthesize BCN nanowires. Inspired by the previous work using
⁎ Corresponding author. Tel./fax: + 86 771 3233718. E-mail address: [email protected] (Y. Chen). 0167-577X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2011.05.026
water-free alcohol as the carbon source to synthesize BCN nanotubes [16] and using a novel precursor boron triiodide (BI3) to prepare BN nanowires [21], we report here a simple and effective approach to synthesize BCN nanowires by reacting BI3 with ammonia and waterfree alcohol at elevated temperatures. The synthesized nanowires were well characterized and the growth mechanism was discussed.
2. Experimental The experimental is very similar to that of BN nanowire synthesis [21]. Firstly, an alumina boat loading with BI3 powder (98% purity) and a polished silicon substrate was inserted into an alumina tube, which was then fixed in a conventional tube furnace. The starting material of BI3 was located at the center of the furnace and the Si substrate was put in a downstream direction with a distance of about 3 cm. Prior to heating, the furnace chamber was flushed with N2 flow (about 500 mL min − 1) to eliminate the residual air. Then the furnace was quickly heated to 1100 °C at a rate of 40 °C min − 1 under N2 flow (50 mL min − 1). NH3 gas flow at a rate of 10 mL min − 1 instead was introduced into the chamber when the temperature reaches at 1100 °C. Meanwhile, water-free alcohol (AR grade) carried by Ar flow (10 mL min − 1) was also introduced. The growth was stopped 30 min later by pulling the boat out of the hot zone of the furnace. Then the furnace was cooled naturally to ambient temperature under N2 flow. Upon completion of the experiment, no BI3 powder was left in the boat and a thin layer of gray deposition was observed on the Si substrate. The product was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S4500), transmission electron microscopy (TEM; JEM-2010 F), X-ray energy dispersive spectrometer (EDS) and electron energy loss spectroscopy (EELS), respectively.
Y. Yin, Y. Chen / Materials Letters 65 (2011) 2476–2478
2477
Fig. 1. Low-magnification (a) and high-magnification (b) SEM images of the product.
3. Results and discussion Fig. 1 shows the SEM images of the deposition. It can be seen that large quantity of nanowires with length of several micrometers are produced (Fig. 1a). High-magnification image (Fig. 1b) reveals that
the nanowires have a uniform and thin diameter of about 30 nm. At the ends of nanowires, no metal or other particles can be observed. Consisting with the SEM observation, TEM image (Fig. 2a) also shows the large production of nanowires and no particle or nanotube is found. Fig. 2b shows a typical HRTEM image of a nanowire. BCN
Fig. 2. (a) TEM image of BCN nanowires. (b) High-resolution TEM image of one nanowire, consisting of disordered structure with some crystalline nanodomains. (c) EDS result under SEM taken from a group of nanowires. (d) EELS spectrum taken from one nanowire.
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Y. Yin, Y. Chen / Materials Letters 65 (2011) 2476–2478
Fig. 3. Elemental maps of several nanowires.
basal (002) planes in random orientations and some quasi-crystalline nanodomains are demonstrated, which are very different from those of BCN nanotubes with well crystallized hexagonal structures. EDS analysis (under SEM) also reveals the presence of O and Si at low contents in the nanowires (Fig. 2c). The Si signal should come from the Si substrate, while O comes from the slight oxidation of the nanowires. Quantitative analysis indicates that the atomic contents of B, C, N, O and Si elements are about 43.3%, 7.3%, 39.1%, 9.9% and 0.4%, respectively, revealing the carbon insufficient compared with those normal B-C-N compounds such as BCN, BC2N and BC4N. Fig. 2d shows a representive EELS spectrum taken from one nanowire. It demonstrates the distinct absorption peaks of B, C and N characteristic Kedges at 188, 287 and 399 eV, respectively. This result further verifies the nanowire composition of B, C and N. The elemental mapping taken on several nanowires also reveals the composition of B, C and N (Fig. 3). However, C element is relatively concentrated in the outer layers of the nanowires, which is consistent with the EDS results discussed above. Therefore, it can be concluded that B-C-N nanowires are synthesized in our work. No catalyst particles are found inside or at the ends of nanowires and the nanowire tips have almost the same size as the body. Therefore, these BCN nanowires are not formed via a conventional vapor–liquid– solid (VLS) mechanism [22]. According to the experimental details, the following formation process is proposed. First, when the temperature reached the vaporization temperature of BI3 (about 210 °C), BI3 vapor started to rise. Then reactions among vapors of BI3, NH3 and C2H5OH (alcohol) took place at 1100 °C. Possibly, nanosized BCN particles were formed on the substrate, which might act as the seeds for the further growth of BCN crystal. Some possible defects (e.g. dislocations) in the seeds may absorb the surrounding vapor species, allowing the growth of BCN nanowires. Continuous reactions among vapors provided more BCN species for the continuous growth of the nanowires. In our work, a very low rate of NH3 flow was used so that most of BI3 vapor could be involved in the reactions instead of being flushed out of the chamber. Therefore, the whole growth process of the nanowires appeared to be governed by a vapor–solid (VS) mechanism [23]. In addition, the fast reactions among vapors and a relatively low experimental temperature might also be responsible for the formation of poor crystallized nanowires with some crystalline nanodomains. However, the detailed growth process needs further investigation. The possible reactions are expressed as follows: BI3 ðsÞ→BI3 ðgÞ
ð1Þ
BI3 ðgÞ + NH3 ðgÞ + C2 H5 OHðgÞ→BCNðnanowiresÞ + HIðgÞ + H2 OðgÞ: ð2Þ
4. Conclusions High-purity BCN nanowires were successfully synthesized by heating a novel precursor BI3 at 1100 °C in the presence of NH3 and water-free alcohol. The nanowires have lengths of several micrometers and uniform diameters of 30 nm. VS mechanism is responsible for the growth of the nanowires. Because of the fast reactions among vapors of BI3, NH3 and C2H5OH and a relatively low experimental temperature, the nanowires possess a disordered structure with local crystalline nanodomains. These uniquely structured BCN nanowires may find some interesting properties and applications in comparison with those nanowires possessing well crystallized hexagonal structure.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
Liu AY, Wentzcovitch RM, Cohen ML. Phys Rev B 1989;39:1760. Dorozhkin P, Golberg D, Bando Y, Dong ZC. Appl Phys Lett 2002;81:1083. Kim SY, Park J, Choi HC, Ahn JP, Hou JQ, Kang HS. J Am Chem Soc 2007;129:1705. Liao L, Liu KH, Wang WL, Bai XD, Wang EG, Liu YL, et al. J Am Chem Soc 2007;129:9562. Miyamoto Y, Rubio A, Cohen ML, Louie SG. Phys Rev B 1994;50:4976. Enyashin AM, Makurin YN, Ivanovskii AL. Carbon 2004;42:2081. Blase X, Charlier JC, Vita AD, Car R. Appl Phys Lett 1997;70:197. Kawaguchi M. Adv Mater 1997;9:8. Stephan O, Ajayan PM, Colliex C, Redlich P, Lambert JM, Bernier P, et al. Science 1994;266:1683. Suenaga K, Colliex C, Demoncy N, Loiseau A, Pascard H, Willaime F. Science 1997;278:653. Redlich P, Loeffler J, Ajayan PM, Bill J, Aldinger F, Rühle M. Chem Phys Lett 1996;260:465. Bai XD, Guo JD, Yu J, Wang EG, Yuan J, Zhou WZ. Appl Phys Lett 2000;76:2624. Yin LW, Bando Y, Golberg D, Gloter A, Li MS, Yuan X, et al. J Am Chem Soc 2005;27: 16354. Terrones M, Golberg D, Grobert N, Seeger T, Reyes-Reyes M, Mayne M, et al. Adv Mater 2003;15:1899. Sen R, Satishkumar BC, Govindaraj A, Harikumar KR, Gargi R, Zhang JP, et al. Chem Phys Lett 1998;287:671. Luo LJ, Mo LB, Tong ZF, Chen YJ. Nanoscale Res Lett 2009;4:834. Mo LB, Chen YJ, Luo LJ. Appl Phys A Mater Sci Proc 2010;100:129. Bai XD, Guo JD, Yu J, Wang EG, Yuan J, Zhou WZ. Appl Phys Lett 2000;76:2624. Bai XD, Yu J, Liu S, Wang EG. Chem Phys Lett 2000;325:485. Yu J, Ahn J, Yoon SF, Zhang Q, Gan RB, Chew K, et al. Appl Phys Lett 2000;77:1949. Chen YJ, Zhang HZ, Chen Y. Nanotechnology 2006;17:786. Morales AM, Lieber CM. Science 1998;279:208. Chen YJ, Li JB, Han YS, Yang XZ, Dai JH. J Crystal Growth 2002;245:163.