- Email: [email protected]
Boron Nitride Nanowires Produced on Commercial Stainless Steel foil
Chinese Journal of Chemical Engineering, 16(3) 485ü487 (2008)
RESEARCH NOTES
Boron Nitride Nanowires Produced on Commercial Stainless Steel foil CHEN Yongjun (чࢋ)*, TONG Zhangfa (ව֥) and LUO Lijie (৭ुࠍ) School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China Abstract Chemical vapor deposition growth of one-dimensional nanomaterials usually demands substrates that have been coated with a layer of catalyst film. In this study, a green process to synthesize boron nitride (BN) nanowires directly on commercial stainless steel foils was proposed by heating boron and zinc oxide powders under a mixture gas flow of N2 and 15% H2 at 1100ºC, and a large quantities of pure h-BN nanowires have been produced directly on commercial stainless steel foil. The stainless steel foils not only acted as the substrate but also the catalyst for the nanowire growth. The synthesized BN nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopes, X-ray energy dispersive spectrometer and photoluminescence spectroscopy. The nanowires also possess strong PL emission bands at 515, 535, and 728 nm. Keywords boron nitride nanowires, chemical vapor deposition, stainless steel foil
1
INTRODUCTION
One-dimensional (1D) nanostructured materials, such as nanotubes (NTs) and nanowires (NWs), have attracted great interest over the past decade due to their unique physical and chemical properties and potential application in the fabrication of nanoscale electronic, photonic and sensing devices [1, 2]. Boron nitride (BN) is an important wide-gap semiconductor with outstanding thermal and electrical properties [3]. It also has a relatively high melting point, mechanical strength, hardness, excellent corrosion and oxidation resistance. Since the first report in 1995 [4], many methods have been demonstrated for the synthesis of hollow BN nanotubes [58]. However, very little has been reported on the synthesis of solid BN nanowires [913]. Here, we report a simple chemical vapor deposition (CVD) method to grow BN nanowires directly on commercial stainless-steel foils by heating a mixture of B and zinc oxide (ZnO) powder at 1100°C under a mixture gas of nitrogen and hydrogen (N2+H2). In this process, the stainless steel foil was not only used as a substrate to deposit the product but also as a catalyst source for the growth of BN nanowires. It is a green process because no rare metal was consumed to catalyze the growth of nanowires and BN nanowires was simply produced from several inorganic materials rather than poisonous organic precursors that other researchers normally used. This method showed the advantages of higher purity and yield of BN nanowires, while previously reported methods have normally resulted in a mixture product of BN nanowires and particles [10, 11]. Furthermore, photoluminescence (PL) property of the BN nanowires was also measured. 2
EXPERIMENTAL
Hexagonal ZnO and amorphous B powder were mixed with a ZnOΉB molar ratio of 1.5Ή1, and milled for 24 h under N2 atmosphere (300 kPa) in a vertical planetary ball mill. Approximately 0.5 g of the milled powder was loaded into a ceramic combustion
boat, which was then placed into a quartz tube. A 0.05 mm thick liner made of commercial stainless steel foil (Cr0.19Fe0.70Ni0.11), with the same length of the quartz tube, was inserted inside the quartz tube, serving as a deposition substrate. The quartz tube was then inserted into a conventional tube furnace such that the ceramic boat was located in the center of the furnace. Prior to heating, the furnace tube was vacuumed and flushed several times with high-purity N2 to eliminate the residual air in the chamber. Under a mixture gas flow of ˉ N2+15%H2 (200 mlǜmin 1), the furnace was heated to ˉ 1100ºC at a rate of 10ºCǜmin 1 and held at that temperature for 1.5 h. Finally, the furnace was cooled ˉ down to ambient temperature at a rate of 10ºCǜmin 1 under N2 flow. Upon completion of the experiment, no starting material was left in the combustion boat and a̚1.5 cm width white deposition film in the form of girdle was found on the stainless-steel foil. The temperature of this zone was measured to be 9501000°C. The synthesized nanowires were characterized by X-ray diffraction (XRD) with cobalt KĮ radiation (Ȝ 0.178897 nm), field-emission scanning electron microscopy (FE-SEM, Hitachi S4500), transmission electron microscopy (TEM, JEM-2010F), X-ray energy dispersive spectrometer (EDS), Raman spectroscopy (Renishaw 2000, 782 nm diode laser excitation) and photoluminescence (PL) spectroscopy (Hitachi F-4500, 488 nm excitation) at room temperature. 3
RESULTS AND DISCUSSION
Figure 1 shows the XRD results for the clean stainless-steel substrate [trace (a)] and the product ˉ nanowires, which were synthesized under 200 mlǜmin 1 of N2+15%H2 [trace (b)]. The diffraction peaks for the clean substrate can be attributed to the cubic phase of Cr0.19Fe0.70Ni0.11 (JCPDS No. 33-0397). Following the growth of nanowires, hexagonal BN (h-BN) (JCPDS No. 85-1068) and cubic Fe3O4 (JCPDS No. 85-1436) phases are observed in addition to the substrate phase of Cr0.19Fe0.70Ni0.11. The presence of Fe3O4 may result from the surface oxidation of the substrate at high
Received 2007-09-24, accepted 2008-01-14. * To whom correspondence should be addressed. E-mail: [email protected]
486
Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008
Figure 1 X-ray diffraction patterns of (a) the clean stainless steel substrate before nanowire growth and (b) BN nanowires ͩ h-BN;ƺCr0.19Fe0.70Ni0.11;ƾFe3O4
temperature. The XRD results prove the product composition of h-BN. The SEM images of the product are shown in Fig. 2. Fig. 2 (a) reveals that the product consists of a large number of nanowires. The EDS result [inset in Fig. 2 (a)] reveals the predominant composition of B and N with a very small amount of O, Fe, Ni and Si. The presence of Fe, Ni and Si can be attributed to the substrate, while O may be due to surface oxidation of the substrate (i.e. Fe3O4 as is verified by XRD results). The enlarged view [Fig. 2 (b)] indicates that the diameters of these nanowires are 3080 nm. Careful observation suggests that some nanowires are capped with nanoparticles (indicated by black arrows), which could be regarded as the symbol of vapor-liquid-solid (VLS) model and will be discussed later in the paper.
Figure 3 (a) TEM image of the BN nanowires with an inset of EDX spectrum of the nanowires; (b) ED pattern of a cluster of nanowires; (c) HRTEM image of a nanowire
particles and O would come from the slight surface oxidation of the nanowires. The Cu peaks are caused by the copper TEM grid. The electron diffraction (ED) rings of a cluster of nanowires, as shown in Fig. 3 (b), displays the reflection planes of h-BN. Fig. 3 (c) shows the high-resolution TEM (HRTEM) image of a single nanowire. The interplane spacing is about 0.335 nm, which corresponds to the (002) plane of the hexagonal system of BN, and further confirms the nanowire composition of h-BN. Figure 4 shows the PL spectrum of the synthesized BN nanowires. There are three main emission bands at 515, 535, and 728 nm. Since the band gap of h-BN is about 3.67.1 eV [14], the corresponding PL bands should be located in the range of 175345 nm. Hence, these PL bands should be caused by the electron transitions from the conduction band to the local levels in the band gap or from the local levels to the valence band, rather than the direct transitions from the conduction band to the valence band. The defects in the nanowires formed in this study would result in the formation of such local levels. Compared with the PL emission bands at 519 nm and 538 nm observed in mesographite BN (m-BN) samples [15] and at 520 nm for BN nanoparticles in NaY zeolite [16], slight blue shifts are observed for the nanowires in this study. These blue shifts can be attributed to the quantum size effects that result from size-dependent widening of the
Figure 2 (a) SEM image of the BN nanowires (The inset is the EDS spectrum of the nanowires); (b) Enlarged SEM image of the nanowires (The black arrows show a particle attached at nanowire ends)
The TEM image of the nanowires [Fig. 3 (a)] reveals that the nanowires have clean surfaces and a diameter range similar to that observed by SEM. The inset is the EDS result of a cluster of nanowires, which shows the predominant nanowire composition of B and N with a low level of O, Si and Fe. The presence of Si and Fe should be caused by the catalyst
Figure 4 Photoluminescence (PL) spectrum of the BN nanowires
Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008
energy gap [17, 18]. There have been no previous reports on the observation of the PL emission band at 728 nm for h-BN. However, Zhu et al. observed a PL emission peak at 700 nm for BN whiskers interweaved with nanofiber-like structures [19]. Therefore we also believed that the defect-trapped states (vacancy-type defect) in the BN nanowires result in the emission band at 728 nm in this study. As described above, the growth mechanism of the BN nanowires is believed to be within the framework of the conventional catalyzed VLS model given that the ends of the nanowires are capped with particles, as is mentioned above. We suggested that the nanowires form via a process as follows. Firstly, B reacts with ZnO at high temperature (1100°C) to generate Zn and B2O2 vapor [reaction (1)]. The produced B2O2 vapor is then transported by the N2 and H2 flow to the lower temperature zone (9501000ºC). The surface of the stainless-steel substrate probably partially melts at this temperature and liquid Fe-Cr-Ni alloy droplets are formed on the surface. The liquid droplets adsorb the growth species from the surrounding vapors of B2O2, N2 and H2. Once the concentrations of species are greater than the saturation threshold, BN crystals precipitate from the liquid droplets. Reaction (2) describes the reaction. A continuous supply of growth species enables the finally formation of 1D BN nanowires. The overall reaction for the process is speculated in reaction (3). Zn vapor is transported by the carrier gas to a much lower-temperature zone (below the melting point of Zn) where it is deposited on the substrate in the form of Zn particles or nanowires, which will be discussed elsewhere. This ensures that the produced BN nanowires are not contaminated by Zn products.
2B(s) 2ZnO(s) o 2Zn(g) B2 O 2 (g)
(1)
2
3 4
5
6
7
8
9
10
11
12 13
14
15
B2 O2 (g) + N 2 (g) 2H 2 (g) o 2BN(s) 2H 2 O(g) (2) 2B(s) + 2ZnO(s) + N 2 (g) 2H 2 (g) o 2BN(s) 2H 2 O(g) 2Zn(g)
16
(3) 17
ACKNOWLEDGEMENTS 18
The first author (CHEN Yongjun) thanks Dr. CHI Bo and CHEN Ying for the fruitful discussions. REFERENCES 1
Cui, Y., Wei, Q.Q., Park, H.K., Lieber, C.M., “Nanowire nanosen-
19
487
sors for highly sensitive and selective detection of biological and chemical species”, Science, 293, 12891292 (2001). Favier, F., Walter, E.C., Zach, M.P., Benter, T., Penner, R.M., “Hydrogen sensors and switches from electrodeposited palladium mesowire Arrays”, Science, 293, 22272231 (2001). Paine, R.T., Narula, C.K., “Synthetic routes to boron nitride”, Chem. Rev., 90, 7391 (1990). Chopra, N.G., Luyken, R.J., Cherrey, K., Crespi, V.H., Cohen, M.L., Louie, S.G., Zettl, A., “Boron nitride nanotubes”, Science, 269, 966967 (1995). Lourie, O.R., Jones, C.R., Bartlett, B.M., Gibbons, P.C., Ruoff, R.S., Buhro, W.E., “CVD growth of boron nitride nanotubes”, Chem. Mater., 12, 18081810 (2000). Fan, L.T., Song, J.C., Yutani, N., “Long ropes of boron nitride nanotubes grown by a continuous laser heating”, Appl. Phys. Lett., 76, 32393241 (2000). Han, W.Q., Bando, Y., Kurashima, K., Sato, Y., “Synthesis of boron nitride nanotubes from carbon nanotubes by a substitution reaction”, Appl. Phys. Lett., 73, 30853089 (1998). Velazquez-Salazar, J.J., Munoz-Sandoval, E., Romo-Herrera, J.M., Lupo, F., Ruhle, M., Terrones, H., Terrones, M., “Synthesis and state of art characterization of BN bamboo-like nanotubes: Evidence of a root growth mechanism catalyzed by Fe”, Chem. Phys. Lett., 416, 342348 (2005). Huo, K.F, Hu, Z., Chen, F., Fu, J.J., Chen, Y., Liu, B.H., Ding, J., Dong, Z.L., White, T., “Synthesis of boron nitride nanowires”, Appl. Phys. Lett., 80, 36113613 (2002). Deepak, F.L., Vinod, C.P., Mukhopadhyay, K., Govindaraj, A., Rao, C.N.R., “Boron nitride nanotubes and nanowires”, Chem. Phys. Lett., 353, 345352 (2002). Sekiguchi, T., Liu, Q., Tanaka, T., Hu, J., Zhu, Y., Bando, Y., “Cathodoluminescence study of widegap-semiconductor. Nanowires”, Eur. J. Appl. Phys., 27, 107109 (2004). Chen, Y.J., Zhang, H.Z., Chen, Y., “Pure boron nitride nanowires produced from boron triiodide”, Nanotech., 17, 786789 (2006). Chen, Y.J., Chi, B., Mahon, D.C., Chen, Y., “An effective approach to grow boron nitride nanowires directly on stainless-steel substrates”, Nanotech., 17, 29422946 (2006). Solozhenko, V.L., Lazarenko, A.G., Petitet, J.P., Kanaev, A.V., “Bandgap energy of graphite-like hexagonal boron nitride”, J. Phys. Chem. Solid., 62, 13311334 (2001). Yao, B., Liu, L., Su, W.H., Shen, Z.X., Liu, L., Sun, W.X., Ding, J., “Effects of degree of three-dimensional order and Fe impurities on photoluminescence of boron nitride”, J. Appl. Phys., 96, 19471952 (2004). Li, X.T., Shao, C.L., Qiu, S.L., Xiao, F.S., Zheng, W.T., Terasaki, Q., “BN and Si nanostructures: Preparation and visible photoluminescence properties”, Mater. Lett., 44, 341346 (2000). Brus, L.E., “The origin of the extensive interest is that the absorption spectrum of the clusters is a strong function of their radii”, J. Phys. Chem., 80, 44034409 (1984). Wirth, K.E., “Nanometer size semiconductor clusters: Materials synthesis, quantum size effect and photophysica properties”, J. Phys. Chem., 95, 525532 (1991). Zhu, Y.C., Bando, Y., Xue, D.F., Sekiguchi, T., Golberg, D., Xu, F.F., Liu, Q.L., “New boron nitride whiskers: Showing strong ultraviolet and visible light luminescence”, J. Phys. Chem. B, 108, 61936196 (2004).
RESEARCH NOTES
Boron Nitride Nanowires Produced on Commercial Stainless Steel foil CHEN Yongjun (чࢋ)*, TONG Zhangfa (ව֥) and LUO Lijie (৭ुࠍ) School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China Abstract Chemical vapor deposition growth of one-dimensional nanomaterials usually demands substrates that have been coated with a layer of catalyst film. In this study, a green process to synthesize boron nitride (BN) nanowires directly on commercial stainless steel foils was proposed by heating boron and zinc oxide powders under a mixture gas flow of N2 and 15% H2 at 1100ºC, and a large quantities of pure h-BN nanowires have been produced directly on commercial stainless steel foil. The stainless steel foils not only acted as the substrate but also the catalyst for the nanowire growth. The synthesized BN nanowires were characterized by X-ray diffraction, scanning and transmission electron microscopes, X-ray energy dispersive spectrometer and photoluminescence spectroscopy. The nanowires also possess strong PL emission bands at 515, 535, and 728 nm. Keywords boron nitride nanowires, chemical vapor deposition, stainless steel foil
1
INTRODUCTION
One-dimensional (1D) nanostructured materials, such as nanotubes (NTs) and nanowires (NWs), have attracted great interest over the past decade due to their unique physical and chemical properties and potential application in the fabrication of nanoscale electronic, photonic and sensing devices [1, 2]. Boron nitride (BN) is an important wide-gap semiconductor with outstanding thermal and electrical properties [3]. It also has a relatively high melting point, mechanical strength, hardness, excellent corrosion and oxidation resistance. Since the first report in 1995 [4], many methods have been demonstrated for the synthesis of hollow BN nanotubes [58]. However, very little has been reported on the synthesis of solid BN nanowires [913]. Here, we report a simple chemical vapor deposition (CVD) method to grow BN nanowires directly on commercial stainless-steel foils by heating a mixture of B and zinc oxide (ZnO) powder at 1100°C under a mixture gas of nitrogen and hydrogen (N2+H2). In this process, the stainless steel foil was not only used as a substrate to deposit the product but also as a catalyst source for the growth of BN nanowires. It is a green process because no rare metal was consumed to catalyze the growth of nanowires and BN nanowires was simply produced from several inorganic materials rather than poisonous organic precursors that other researchers normally used. This method showed the advantages of higher purity and yield of BN nanowires, while previously reported methods have normally resulted in a mixture product of BN nanowires and particles [10, 11]. Furthermore, photoluminescence (PL) property of the BN nanowires was also measured. 2
EXPERIMENTAL
Hexagonal ZnO and amorphous B powder were mixed with a ZnOΉB molar ratio of 1.5Ή1, and milled for 24 h under N2 atmosphere (300 kPa) in a vertical planetary ball mill. Approximately 0.5 g of the milled powder was loaded into a ceramic combustion
boat, which was then placed into a quartz tube. A 0.05 mm thick liner made of commercial stainless steel foil (Cr0.19Fe0.70Ni0.11), with the same length of the quartz tube, was inserted inside the quartz tube, serving as a deposition substrate. The quartz tube was then inserted into a conventional tube furnace such that the ceramic boat was located in the center of the furnace. Prior to heating, the furnace tube was vacuumed and flushed several times with high-purity N2 to eliminate the residual air in the chamber. Under a mixture gas flow of ˉ N2+15%H2 (200 mlǜmin 1), the furnace was heated to ˉ 1100ºC at a rate of 10ºCǜmin 1 and held at that temperature for 1.5 h. Finally, the furnace was cooled ˉ down to ambient temperature at a rate of 10ºCǜmin 1 under N2 flow. Upon completion of the experiment, no starting material was left in the combustion boat and a̚1.5 cm width white deposition film in the form of girdle was found on the stainless-steel foil. The temperature of this zone was measured to be 9501000°C. The synthesized nanowires were characterized by X-ray diffraction (XRD) with cobalt KĮ radiation (Ȝ 0.178897 nm), field-emission scanning electron microscopy (FE-SEM, Hitachi S4500), transmission electron microscopy (TEM, JEM-2010F), X-ray energy dispersive spectrometer (EDS), Raman spectroscopy (Renishaw 2000, 782 nm diode laser excitation) and photoluminescence (PL) spectroscopy (Hitachi F-4500, 488 nm excitation) at room temperature. 3
RESULTS AND DISCUSSION
Figure 1 shows the XRD results for the clean stainless-steel substrate [trace (a)] and the product ˉ nanowires, which were synthesized under 200 mlǜmin 1 of N2+15%H2 [trace (b)]. The diffraction peaks for the clean substrate can be attributed to the cubic phase of Cr0.19Fe0.70Ni0.11 (JCPDS No. 33-0397). Following the growth of nanowires, hexagonal BN (h-BN) (JCPDS No. 85-1068) and cubic Fe3O4 (JCPDS No. 85-1436) phases are observed in addition to the substrate phase of Cr0.19Fe0.70Ni0.11. The presence of Fe3O4 may result from the surface oxidation of the substrate at high
Received 2007-09-24, accepted 2008-01-14. * To whom correspondence should be addressed. E-mail: [email protected]
486
Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008
Figure 1 X-ray diffraction patterns of (a) the clean stainless steel substrate before nanowire growth and (b) BN nanowires ͩ h-BN;ƺCr0.19Fe0.70Ni0.11;ƾFe3O4
temperature. The XRD results prove the product composition of h-BN. The SEM images of the product are shown in Fig. 2. Fig. 2 (a) reveals that the product consists of a large number of nanowires. The EDS result [inset in Fig. 2 (a)] reveals the predominant composition of B and N with a very small amount of O, Fe, Ni and Si. The presence of Fe, Ni and Si can be attributed to the substrate, while O may be due to surface oxidation of the substrate (i.e. Fe3O4 as is verified by XRD results). The enlarged view [Fig. 2 (b)] indicates that the diameters of these nanowires are 3080 nm. Careful observation suggests that some nanowires are capped with nanoparticles (indicated by black arrows), which could be regarded as the symbol of vapor-liquid-solid (VLS) model and will be discussed later in the paper.
Figure 3 (a) TEM image of the BN nanowires with an inset of EDX spectrum of the nanowires; (b) ED pattern of a cluster of nanowires; (c) HRTEM image of a nanowire
particles and O would come from the slight surface oxidation of the nanowires. The Cu peaks are caused by the copper TEM grid. The electron diffraction (ED) rings of a cluster of nanowires, as shown in Fig. 3 (b), displays the reflection planes of h-BN. Fig. 3 (c) shows the high-resolution TEM (HRTEM) image of a single nanowire. The interplane spacing is about 0.335 nm, which corresponds to the (002) plane of the hexagonal system of BN, and further confirms the nanowire composition of h-BN. Figure 4 shows the PL spectrum of the synthesized BN nanowires. There are three main emission bands at 515, 535, and 728 nm. Since the band gap of h-BN is about 3.67.1 eV [14], the corresponding PL bands should be located in the range of 175345 nm. Hence, these PL bands should be caused by the electron transitions from the conduction band to the local levels in the band gap or from the local levels to the valence band, rather than the direct transitions from the conduction band to the valence band. The defects in the nanowires formed in this study would result in the formation of such local levels. Compared with the PL emission bands at 519 nm and 538 nm observed in mesographite BN (m-BN) samples [15] and at 520 nm for BN nanoparticles in NaY zeolite [16], slight blue shifts are observed for the nanowires in this study. These blue shifts can be attributed to the quantum size effects that result from size-dependent widening of the
Figure 2 (a) SEM image of the BN nanowires (The inset is the EDS spectrum of the nanowires); (b) Enlarged SEM image of the nanowires (The black arrows show a particle attached at nanowire ends)
The TEM image of the nanowires [Fig. 3 (a)] reveals that the nanowires have clean surfaces and a diameter range similar to that observed by SEM. The inset is the EDS result of a cluster of nanowires, which shows the predominant nanowire composition of B and N with a low level of O, Si and Fe. The presence of Si and Fe should be caused by the catalyst
Figure 4 Photoluminescence (PL) spectrum of the BN nanowires
Chin. J. Chem. Eng., Vol. 16, No. 3, June 2008
energy gap [17, 18]. There have been no previous reports on the observation of the PL emission band at 728 nm for h-BN. However, Zhu et al. observed a PL emission peak at 700 nm for BN whiskers interweaved with nanofiber-like structures [19]. Therefore we also believed that the defect-trapped states (vacancy-type defect) in the BN nanowires result in the emission band at 728 nm in this study. As described above, the growth mechanism of the BN nanowires is believed to be within the framework of the conventional catalyzed VLS model given that the ends of the nanowires are capped with particles, as is mentioned above. We suggested that the nanowires form via a process as follows. Firstly, B reacts with ZnO at high temperature (1100°C) to generate Zn and B2O2 vapor [reaction (1)]. The produced B2O2 vapor is then transported by the N2 and H2 flow to the lower temperature zone (9501000ºC). The surface of the stainless-steel substrate probably partially melts at this temperature and liquid Fe-Cr-Ni alloy droplets are formed on the surface. The liquid droplets adsorb the growth species from the surrounding vapors of B2O2, N2 and H2. Once the concentrations of species are greater than the saturation threshold, BN crystals precipitate from the liquid droplets. Reaction (2) describes the reaction. A continuous supply of growth species enables the finally formation of 1D BN nanowires. The overall reaction for the process is speculated in reaction (3). Zn vapor is transported by the carrier gas to a much lower-temperature zone (below the melting point of Zn) where it is deposited on the substrate in the form of Zn particles or nanowires, which will be discussed elsewhere. This ensures that the produced BN nanowires are not contaminated by Zn products.
2B(s) 2ZnO(s) o 2Zn(g) B2 O 2 (g)
(1)
2
3 4
5
6
7
8
9
10
11
12 13
14
15
B2 O2 (g) + N 2 (g) 2H 2 (g) o 2BN(s) 2H 2 O(g) (2) 2B(s) + 2ZnO(s) + N 2 (g) 2H 2 (g) o 2BN(s) 2H 2 O(g) 2Zn(g)
16
(3) 17
ACKNOWLEDGEMENTS 18
The first author (CHEN Yongjun) thanks Dr. CHI Bo and CHEN Ying for the fruitful discussions. REFERENCES 1
Cui, Y., Wei, Q.Q., Park, H.K., Lieber, C.M., “Nanowire nanosen-
19
487
sors for highly sensitive and selective detection of biological and chemical species”, Science, 293, 12891292 (2001). Favier, F., Walter, E.C., Zach, M.P., Benter, T., Penner, R.M., “Hydrogen sensors and switches from electrodeposited palladium mesowire Arrays”, Science, 293, 22272231 (2001). Paine, R.T., Narula, C.K., “Synthetic routes to boron nitride”, Chem. Rev., 90, 7391 (1990). Chopra, N.G., Luyken, R.J., Cherrey, K., Crespi, V.H., Cohen, M.L., Louie, S.G., Zettl, A., “Boron nitride nanotubes”, Science, 269, 966967 (1995). Lourie, O.R., Jones, C.R., Bartlett, B.M., Gibbons, P.C., Ruoff, R.S., Buhro, W.E., “CVD growth of boron nitride nanotubes”, Chem. Mater., 12, 18081810 (2000). Fan, L.T., Song, J.C., Yutani, N., “Long ropes of boron nitride nanotubes grown by a continuous laser heating”, Appl. Phys. Lett., 76, 32393241 (2000). Han, W.Q., Bando, Y., Kurashima, K., Sato, Y., “Synthesis of boron nitride nanotubes from carbon nanotubes by a substitution reaction”, Appl. Phys. Lett., 73, 30853089 (1998). Velazquez-Salazar, J.J., Munoz-Sandoval, E., Romo-Herrera, J.M., Lupo, F., Ruhle, M., Terrones, H., Terrones, M., “Synthesis and state of art characterization of BN bamboo-like nanotubes: Evidence of a root growth mechanism catalyzed by Fe”, Chem. Phys. Lett., 416, 342348 (2005). Huo, K.F, Hu, Z., Chen, F., Fu, J.J., Chen, Y., Liu, B.H., Ding, J., Dong, Z.L., White, T., “Synthesis of boron nitride nanowires”, Appl. Phys. Lett., 80, 36113613 (2002). Deepak, F.L., Vinod, C.P., Mukhopadhyay, K., Govindaraj, A., Rao, C.N.R., “Boron nitride nanotubes and nanowires”, Chem. Phys. Lett., 353, 345352 (2002). Sekiguchi, T., Liu, Q., Tanaka, T., Hu, J., Zhu, Y., Bando, Y., “Cathodoluminescence study of widegap-semiconductor. Nanowires”, Eur. J. Appl. Phys., 27, 107109 (2004). Chen, Y.J., Zhang, H.Z., Chen, Y., “Pure boron nitride nanowires produced from boron triiodide”, Nanotech., 17, 786789 (2006). Chen, Y.J., Chi, B., Mahon, D.C., Chen, Y., “An effective approach to grow boron nitride nanowires directly on stainless-steel substrates”, Nanotech., 17, 29422946 (2006). Solozhenko, V.L., Lazarenko, A.G., Petitet, J.P., Kanaev, A.V., “Bandgap energy of graphite-like hexagonal boron nitride”, J. Phys. Chem. Solid., 62, 13311334 (2001). Yao, B., Liu, L., Su, W.H., Shen, Z.X., Liu, L., Sun, W.X., Ding, J., “Effects of degree of three-dimensional order and Fe impurities on photoluminescence of boron nitride”, J. Appl. Phys., 96, 19471952 (2004). Li, X.T., Shao, C.L., Qiu, S.L., Xiao, F.S., Zheng, W.T., Terasaki, Q., “BN and Si nanostructures: Preparation and visible photoluminescence properties”, Mater. Lett., 44, 341346 (2000). Brus, L.E., “The origin of the extensive interest is that the absorption spectrum of the clusters is a strong function of their radii”, J. Phys. Chem., 80, 44034409 (1984). Wirth, K.E., “Nanometer size semiconductor clusters: Materials synthesis, quantum size effect and photophysica properties”, J. Phys. Chem., 95, 525532 (1991). Zhu, Y.C., Bando, Y., Xue, D.F., Sekiguchi, T., Golberg, D., Xu, F.F., Liu, Q.L., “New boron nitride whiskers: Showing strong ultraviolet and visible light luminescence”, J. Phys. Chem. B, 108, 61936196 (2004).