- Email: [email protected]
Facile fabrication of aligned SnO2 nanotube arrays and their field-emission property
Materials Letters 118 (2014) 43–46
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile fabrication of aligned SnO2 nanotube arrays and their field-emission property Jvjun Yuan a,b,c, Hongdong Li b,n, Qiliang Wang b, Xianke Zhang a, Shaoheng Cheng b, Huajun Yu a, Xiurong Zhu a, Yingmao Xie a a
College of Physics and Electronics, Gannan Normal University, Ganzhou 341000, PR China State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, PR China c Institute of Optoelectronic Materials and Technology, Gannan Normal University, Ganzhou 341000, PR China b
art ic l e i nf o
a b s t r a c t
Article history: Received 22 September 2013 Accepted 10 December 2013 Available online 17 December 2013
The aligned SnO2 nanotube arrays on Si substrate have been prepared via liquid-phase deposition with the solution system of SnF2 utilizing ZnO nanorod arrays as sacrificial template. The SnO2 nanotubes are distributed uniformly and grown perpendicularly to the substrate. The SnO2 nanotubes are rutile phase with the outside diameter of 190–310 nm and the wall thickness of 45 nm. The template-related growth mechanism for the formation of SnO2 nanotube is investigated. Experimentally, the SnO2 nanotube array shows an efficient field-emission property, which is favorable for realizing high performance cold cathode electron emitters. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nanocrystalline materials Crystal growth Liquid-phase deposition ZnO template SnO2 nanonanotube Field-emission property
1. Introduction Tin unintentionally doped tin dioxide (SnO2) is intrinsically an n-type semiconductor with a wide band gap (Eg ¼ 3.6 eV at 300 K), and well-known for its potential applications in gas sensors, lithium-ion batteries, transparent conducting electrodes, and electron field emitters [1–4]. Recently, SnO2-based low-dimensional nanostructures have received growing interests because of their unique properties and enormous potential as building blocks for nanodevices [5–7]. Among these nanostructures, the SnO2 nanotubes (SnNTs) with high surface-to-volume raios are suggested to be ideal objects for the nanodevices used in photoelectronic fields. A variety of efficient synthetic strategies have been reported to fabricate SnO2 nanotubes, such as chemical vapor deposition [8], solid–vapor growth [9] and template-assisted synthesis [10–14]. The template-directed synthesis is generally performed due to its low energy consumption and relatively simple procedure. To date, most SnO2 nanotubes were obtained via sol–gel or electrophoretic processing combined with various porous membranes including anodic aluminium oxide, polycarbonate and mesoporous silica [10– 14]. However, the SnO2 nanotubes prepared by the abovementioned methods were normally freestanding, which are difficult for directly using in nanodevices because they cannot arrange in an
n
Corresponding author. Tel./fax: þ 864 315 168 095. E-mail address: [email protected] (H. Li).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.12.036
ordered fashion on the solid surface after the removal of the templates. Therefore, finding a facile synthetic method to obtain aligned SnNT arrays on some substrates are quietly desirable. The SnNTs were fabricated by two-step method using ZnO nanorod arrays as the sacrificial templates [15,16]. In the two-step method, a layer of SnO2 shell was first deposited on ZnO nanorod arrays and subsequently ZnO/SnO2 core–shell nanostructure arrays were converted into corresponding SnNTs by means of acid etching. Wang et al. reported a onestep method for synthesizing vertically aligned SnNTs using ZnO nanowire array template [17]. The ZnO nanowires were converted into SnO2 nanotubes via liquid-phase deposition (LPD) with the solution systems of (NH4)2 TiF6 and H3BO3, and simultaneous ZnO dissolution. It is evident that the LPD method is favorable for fabricating vertically aligned SnNTs based on the highly orientated ZnO nanorod template. Herein, we report a facile synthetic strategy for aligned SnNTs on Si substrate via LPD with the solution system of SnF2 utilizing ZnO nanorod arrays as the sacrificial templates. The growth mechanism for the formation of SnNTs is investigated. Furthermore, the SnNTs show an efficient field-emission (FE) property.
2. Experimental The Si substrate covered with a 10 nm-thickness ZnO seed layer (deposited by magnetron sputtering) were placed in Teflon lined
44
J. Yuan et al. / Materials Letters 118 (2014) 43–46
Fig. 1. (a) Plain-view and (b) cross-section SEM images of ZnO nanorod arrays templates, (c) plain-view and (d) cross-section SEM images of SnNTs on Si substrate, (e) EDX spectrum of SnNTs, (f) XRD patterns of SnNTs (up) and ZnO nanorods (bottom) on Si substrate.
Fig. 2. TEM images of (a) a ZnO nanorod, (b) SnO2 nanotubes. The insets are the associated selected area electron diffraction patterns.
J. Yuan et al. / Materials Letters 118 (2014) 43–46
stainless steel autoclaves along with an equimolar (0.025 M) aqueous solution of zinc acetate dihydrate and hexamethylenetetramine. After hydrothermal reaction at 95 1C for 4 h, the ZnO nanorod arrays were formed on Si substrate. For the synthesis of SnNTs, the templates of Si substrate with ZnO nanorods were immersed in the (0.0075 M) aqueous solution of SnF2 at room temperature for 4 h. Finally, the products of SnNTs on Si substrate were washed with deionized water and calcined at 600 1C for 2 h in air. The structure and morphologies of the samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The element signatures of the samples were characterized by energy-dispersive X-ray (EDX). The UV–vis transmission optical properties were texted by UV-3150 double-beam spectrophotometer. The field emission (FE) measurement using an anode probe technique were carried out at a pressure of 4 10 5 Pa with the distance of 260 μm between the anode and cathode (SnNTs samples)
45
( 1.3 μm) of SnNTs becomes shorter than that of the original ZnO nanorods (length: 1.5 μm). UV–vis absorption (recorded by reflection mode) was carried out to evaluate the optical properties of the SnNTs on Si substrate. Fig. 4a shows the absorption spectrum for the SnNTs sample. In the direct transition semiconductor, the optical absorption coefficient (α) and the band gap energy (Eg) are related by αhυ¼ D (hυ Eg)1/2, where h is Planck's constant, υ is the frequency of the incident photon, Eg is the optical band gap and D is constant. The variations of (αhυ)2 versus the photon energy hυ in the fundamental absorption region are plotted in the inset of Fig. 4a. The Eg
3. Results and discussion Fig. 1a and b shows the SEM images of ZnO nanorod arrays grown on Si substrate. The highly aligned and dense ZnO nanorod arrays were grown on Si substrate. These nanorods have nearly uniform lengths of 1.5 μm with a diameter region of 150– 280 nm. After LDP process, the end-capped SnNTs are found with an average length of 1.3 μm and outside diameters of 190– 310 nm (Fig. 1c and d). Fig. 1e shows the EDX profile of SnNTs, and the signals of Sn and O atoms are evidently presented. As expected that ZnO nanorod arrays templates have been completely removed by LPD process. From XRD pattern of SnNTs (Fig. 1f), the diffraction peaks can be indexed to pure rutile SnO2 (JCPDS 1-657). No evident ZnO diffraction peaks (compared with the pattern taken from the ZnO template in Fig. 1f) are found in the final product, further suggesting the absence of ZnO removed in the SnNT formation process. Analyzed from the TEM images and and the associated selected area electron diffraction (SAED), the ZnO nanorods are single crystal growing along the (0 0 0 1) axis (Fig. 2a), and the SnO2 samples (i.e., SnNTs) have a tubular and end-closed structure with a wall thickness of 45 nm. The SnNTs consist of nano-sized gains, and the corresponding SAED shows ring feature (the up-left inset of Fig. 2b). The average grain size is 6.5 nm for SnO2 nanotubes, estimated from the (1 1 0) peak by Scherrer formula: d¼0.89λ/Dcosθ, where λ is 1.54016 Å, θ is the diffraction angle, and D is the full width at half maximum (FWHM) of the (1 1 0) peak. The above results reveal that the SnNTs on Si substrate using a simple one-step solution approach have been successfully prepared. Fig. 3 illustrates schematically the steps for the formation of an end-closed SnNTs. The process started with growing vertically aligned ZnO nanorods on Si substrate by hydrothermal method, and followed by converting ZnO nanorods into SnO2 nanotubes by placing the ZnO nanorod array in an aqueous solution of SnF2. The reactions are summarized as the following [18,19] SnF2 þ H2Oþ 1/2O22SnO2 þ2H þ þ2F
(1)
ZnOþ2H þ -Zn2 þ þH2O
(2)
In the synthesis system, the SnO2 is formed by a hydrolysis of SnF2 (Eq. (1)). The dissolution of ZnO under the acidic condition follows Eq. (2), which occurs simultaneously with SnO2 formation. In general, the dissolution rate of ZnO is higher than that of the SnO2 formation in the initial stage, and consequently, the length
Fig. 3. Schematic of the steps for forming the end-closed SnO2 nanotube.
Fig. 4. (a) UV–vis absorption spectrum of the SnNTs on Si substrate. The inset is the corresponding plot of (hv)2 versus photon energy. (b) Field-emission (FE) current density of SnNTs on Si substrate as a function of the applied electronic field. The inset shows the corresponding F–N plot.
46
J. Yuan et al. / Materials Letters 118 (2014) 43–46
value of the SnNTs is estimated to be 3.85 70.05 eV by extrapolating the linear portion to the photon energy axis in that figure, which is slightly larger than that of bulk SnO2 (3.6 eV). This can be attributed to the larger average size of the grains of SnNTs ( 6.5 nm) than the exciton Bohr radius of 2.7 nm for SnO2 [20]. Fig. 4b shows the FE current densities J versus electric field E plot of SnNTs on Si substrate. The corresponding Fowler–Nordheim (F–N) plot is presented in the inset of Fig. 4b. The F–N plot is approximately linear at high-applied fields, indicating that the emitting electrons mainly result from barrier tunneling electrons extracted by the electric field [21,22]. The turn-on electric field (defined as the E corresponding to the J of 0.75 μA cm 2) is estimated to be 5.4 V cm 1. Meanwhile, the needed electric fields for the current density of 0.38 mA of SnNTs is 11 V cm 1. The FE property is superior to those of the reported SnO2 nanorods and nanowires [23,24] The reason for the efficient FE property is mainly due to aligned structure, good electrical contact with the conducting substrate, and weaker field-screening effect [25]. 4. Conclusion We have reported a facile synthetic strategy for aligned SnNTs on Si substrate via liquid-phase deposition with the solution system of SnF2 utilizing ZnO nanorod arrays as a sacrificial template. This strategy simplifies the approach to obtain aligned SnNTs. It is demonstrated that the SnNTs show an efficient FE property favorable for fabricating high performance cold cathode electron emitters. Acknowledgments This work was financially supported by theNational Natural Science Foundation of China (NSFC) with No. 51072066 and 11247305, the Ph.D. Programs Foundation of Ministry of Education of China with No.20100061110083, the Open Project of State Key
Laboratory of Superhard Materials (Jilin University) with No. 201213 and the Youth Fund of Science and Technology Department of Jiangxi Province with No. 20131522040044.
References [1] Juttukonda V, Paddock RL, Raymond JE, Denomme D, Richardson AE, Slusher LE, et al. J Am Chem Soc 2006;128:420–1. [2] Lei DL, Zhang M, Hao QY, Chen LB, Li QH, Zhang ED, et al. Mater Lett 2011;65:1154–6. [3] Liu ZQ, Zhang DH, Han S, Li C, Tang T, Jin W, et al. Adv Mater 2003;15:1754–7. [4] Wang X, Liu W, Yang H, Li X, Li N, Shi R, et al. Acta Mater 2011;59:1291–9. [5] Wang CF, Xie SY, Lin SC, Cheng X, Zhang XH, Huang RB, et al. Chem Commun 2004:1766–7. [6] Wang YL, Guo M, Zhang M, Wang XD. CrystEngComm 2010;12:4024–7. [7] Li XB, Wang XW, Shen Q, Zheng J, Liu WH, Zhao H, et al. Appl Mater Interfaces 2013;5:3033–41. [8] Ying B, Liu M. Adv Funct Mater 2005;15:57–62. [9] Duan J, Cao Q, Yang S, Huang H, Zhao X, Zhang R, et al. J Cryst Growth 2006;289:164–7. [10] Kim H, Cho J. J Mater Chem 2008;18:771–5. [11] Lee WJ, Park MH, Wang Y, Lee JY, Cho J. Chem Commun 2010;46:622–4. [12] Park NG, Kang MG, Ryu KS, Kim KM, Chang SH. J Photochem Photobiol, A 2004;161:105–10. [13] Zhu W, Wang WZ, Xu HL, Shi JL. Mater Chem Phys 2006;99:127–30. [14] Shi LN, Xu YM, Li Q. Nanoscale 2010;2:2104–8. [15] Kuang Q, Xu T, Xie ZX, Lin SC, Huang RB, Zheng LS. J Mater Chem 2009;19:1019–23. [16] Wang JZ, Du N, Zhang H, Yu JX, Yang S. J Phys Chem C 2011;115:11302–5. [17] Desai UV, Xu CK, Wu JM, Gao D. J Phys Chem C 2013;117:3232–9. [18] Tsukuma K, Akiyama T, Imai H. J Non-Cryst Solids 1997;210:48–54. [19] Matsushima Y, Satoh R, Kawai T, Maeda K, Suzuki T. J Ceram Soc Jpn 2010;118:206–12. [20] Lee EJH, Ribeiro C, Giraldi TR, Longo E, Leite ER, Varela JA. Appl Phys Lett 2004:841745–7. [21] Li LJ, Zong FJ, Cui XD, Ma HL, Wu XH, Zhang QD, et al. Mater Lett 2007;61:4152–5. [22] Ma LA, Yea Y, Hua LQ, Zheng KL, Guo TL. Physica E 2008;40:3127–30. [23] Deshpande AC, Koinkar PM, Ashtaputre SS, More MA, Gosavi SW, Godbole PD, et al. Thin Solid Films 2006;515:1450–4. [24] Wu JM. Thin Solid Films 2008;517:1289–93. [25] Li ZJ, Wang HY, Liu P, Zhao B, Zhang YF. Appl Surf Sci 2009;255:4470–3.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Facile fabrication of aligned SnO2 nanotube arrays and their field-emission property Jvjun Yuan a,b,c, Hongdong Li b,n, Qiliang Wang b, Xianke Zhang a, Shaoheng Cheng b, Huajun Yu a, Xiurong Zhu a, Yingmao Xie a a
College of Physics and Electronics, Gannan Normal University, Ganzhou 341000, PR China State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, PR China c Institute of Optoelectronic Materials and Technology, Gannan Normal University, Ganzhou 341000, PR China b
art ic l e i nf o
a b s t r a c t
Article history: Received 22 September 2013 Accepted 10 December 2013 Available online 17 December 2013
The aligned SnO2 nanotube arrays on Si substrate have been prepared via liquid-phase deposition with the solution system of SnF2 utilizing ZnO nanorod arrays as sacrificial template. The SnO2 nanotubes are distributed uniformly and grown perpendicularly to the substrate. The SnO2 nanotubes are rutile phase with the outside diameter of 190–310 nm and the wall thickness of 45 nm. The template-related growth mechanism for the formation of SnO2 nanotube is investigated. Experimentally, the SnO2 nanotube array shows an efficient field-emission property, which is favorable for realizing high performance cold cathode electron emitters. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nanocrystalline materials Crystal growth Liquid-phase deposition ZnO template SnO2 nanonanotube Field-emission property
1. Introduction Tin unintentionally doped tin dioxide (SnO2) is intrinsically an n-type semiconductor with a wide band gap (Eg ¼ 3.6 eV at 300 K), and well-known for its potential applications in gas sensors, lithium-ion batteries, transparent conducting electrodes, and electron field emitters [1–4]. Recently, SnO2-based low-dimensional nanostructures have received growing interests because of their unique properties and enormous potential as building blocks for nanodevices [5–7]. Among these nanostructures, the SnO2 nanotubes (SnNTs) with high surface-to-volume raios are suggested to be ideal objects for the nanodevices used in photoelectronic fields. A variety of efficient synthetic strategies have been reported to fabricate SnO2 nanotubes, such as chemical vapor deposition [8], solid–vapor growth [9] and template-assisted synthesis [10–14]. The template-directed synthesis is generally performed due to its low energy consumption and relatively simple procedure. To date, most SnO2 nanotubes were obtained via sol–gel or electrophoretic processing combined with various porous membranes including anodic aluminium oxide, polycarbonate and mesoporous silica [10– 14]. However, the SnO2 nanotubes prepared by the abovementioned methods were normally freestanding, which are difficult for directly using in nanodevices because they cannot arrange in an
n
Corresponding author. Tel./fax: þ 864 315 168 095. E-mail address: [email protected] (H. Li).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.12.036
ordered fashion on the solid surface after the removal of the templates. Therefore, finding a facile synthetic method to obtain aligned SnNT arrays on some substrates are quietly desirable. The SnNTs were fabricated by two-step method using ZnO nanorod arrays as the sacrificial templates [15,16]. In the two-step method, a layer of SnO2 shell was first deposited on ZnO nanorod arrays and subsequently ZnO/SnO2 core–shell nanostructure arrays were converted into corresponding SnNTs by means of acid etching. Wang et al. reported a onestep method for synthesizing vertically aligned SnNTs using ZnO nanowire array template [17]. The ZnO nanowires were converted into SnO2 nanotubes via liquid-phase deposition (LPD) with the solution systems of (NH4)2 TiF6 and H3BO3, and simultaneous ZnO dissolution. It is evident that the LPD method is favorable for fabricating vertically aligned SnNTs based on the highly orientated ZnO nanorod template. Herein, we report a facile synthetic strategy for aligned SnNTs on Si substrate via LPD with the solution system of SnF2 utilizing ZnO nanorod arrays as the sacrificial templates. The growth mechanism for the formation of SnNTs is investigated. Furthermore, the SnNTs show an efficient field-emission (FE) property.
2. Experimental The Si substrate covered with a 10 nm-thickness ZnO seed layer (deposited by magnetron sputtering) were placed in Teflon lined
44
J. Yuan et al. / Materials Letters 118 (2014) 43–46
Fig. 1. (a) Plain-view and (b) cross-section SEM images of ZnO nanorod arrays templates, (c) plain-view and (d) cross-section SEM images of SnNTs on Si substrate, (e) EDX spectrum of SnNTs, (f) XRD patterns of SnNTs (up) and ZnO nanorods (bottom) on Si substrate.
Fig. 2. TEM images of (a) a ZnO nanorod, (b) SnO2 nanotubes. The insets are the associated selected area electron diffraction patterns.
J. Yuan et al. / Materials Letters 118 (2014) 43–46
stainless steel autoclaves along with an equimolar (0.025 M) aqueous solution of zinc acetate dihydrate and hexamethylenetetramine. After hydrothermal reaction at 95 1C for 4 h, the ZnO nanorod arrays were formed on Si substrate. For the synthesis of SnNTs, the templates of Si substrate with ZnO nanorods were immersed in the (0.0075 M) aqueous solution of SnF2 at room temperature for 4 h. Finally, the products of SnNTs on Si substrate were washed with deionized water and calcined at 600 1C for 2 h in air. The structure and morphologies of the samples were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The element signatures of the samples were characterized by energy-dispersive X-ray (EDX). The UV–vis transmission optical properties were texted by UV-3150 double-beam spectrophotometer. The field emission (FE) measurement using an anode probe technique were carried out at a pressure of 4 10 5 Pa with the distance of 260 μm between the anode and cathode (SnNTs samples)
45
( 1.3 μm) of SnNTs becomes shorter than that of the original ZnO nanorods (length: 1.5 μm). UV–vis absorption (recorded by reflection mode) was carried out to evaluate the optical properties of the SnNTs on Si substrate. Fig. 4a shows the absorption spectrum for the SnNTs sample. In the direct transition semiconductor, the optical absorption coefficient (α) and the band gap energy (Eg) are related by αhυ¼ D (hυ Eg)1/2, where h is Planck's constant, υ is the frequency of the incident photon, Eg is the optical band gap and D is constant. The variations of (αhυ)2 versus the photon energy hυ in the fundamental absorption region are plotted in the inset of Fig. 4a. The Eg
3. Results and discussion Fig. 1a and b shows the SEM images of ZnO nanorod arrays grown on Si substrate. The highly aligned and dense ZnO nanorod arrays were grown on Si substrate. These nanorods have nearly uniform lengths of 1.5 μm with a diameter region of 150– 280 nm. After LDP process, the end-capped SnNTs are found with an average length of 1.3 μm and outside diameters of 190– 310 nm (Fig. 1c and d). Fig. 1e shows the EDX profile of SnNTs, and the signals of Sn and O atoms are evidently presented. As expected that ZnO nanorod arrays templates have been completely removed by LPD process. From XRD pattern of SnNTs (Fig. 1f), the diffraction peaks can be indexed to pure rutile SnO2 (JCPDS 1-657). No evident ZnO diffraction peaks (compared with the pattern taken from the ZnO template in Fig. 1f) are found in the final product, further suggesting the absence of ZnO removed in the SnNT formation process. Analyzed from the TEM images and and the associated selected area electron diffraction (SAED), the ZnO nanorods are single crystal growing along the (0 0 0 1) axis (Fig. 2a), and the SnO2 samples (i.e., SnNTs) have a tubular and end-closed structure with a wall thickness of 45 nm. The SnNTs consist of nano-sized gains, and the corresponding SAED shows ring feature (the up-left inset of Fig. 2b). The average grain size is 6.5 nm for SnO2 nanotubes, estimated from the (1 1 0) peak by Scherrer formula: d¼0.89λ/Dcosθ, where λ is 1.54016 Å, θ is the diffraction angle, and D is the full width at half maximum (FWHM) of the (1 1 0) peak. The above results reveal that the SnNTs on Si substrate using a simple one-step solution approach have been successfully prepared. Fig. 3 illustrates schematically the steps for the formation of an end-closed SnNTs. The process started with growing vertically aligned ZnO nanorods on Si substrate by hydrothermal method, and followed by converting ZnO nanorods into SnO2 nanotubes by placing the ZnO nanorod array in an aqueous solution of SnF2. The reactions are summarized as the following [18,19] SnF2 þ H2Oþ 1/2O22SnO2 þ2H þ þ2F
(1)
ZnOþ2H þ -Zn2 þ þH2O
(2)
In the synthesis system, the SnO2 is formed by a hydrolysis of SnF2 (Eq. (1)). The dissolution of ZnO under the acidic condition follows Eq. (2), which occurs simultaneously with SnO2 formation. In general, the dissolution rate of ZnO is higher than that of the SnO2 formation in the initial stage, and consequently, the length
Fig. 3. Schematic of the steps for forming the end-closed SnO2 nanotube.
Fig. 4. (a) UV–vis absorption spectrum of the SnNTs on Si substrate. The inset is the corresponding plot of (hv)2 versus photon energy. (b) Field-emission (FE) current density of SnNTs on Si substrate as a function of the applied electronic field. The inset shows the corresponding F–N plot.
46
J. Yuan et al. / Materials Letters 118 (2014) 43–46
value of the SnNTs is estimated to be 3.85 70.05 eV by extrapolating the linear portion to the photon energy axis in that figure, which is slightly larger than that of bulk SnO2 (3.6 eV). This can be attributed to the larger average size of the grains of SnNTs ( 6.5 nm) than the exciton Bohr radius of 2.7 nm for SnO2 [20]. Fig. 4b shows the FE current densities J versus electric field E plot of SnNTs on Si substrate. The corresponding Fowler–Nordheim (F–N) plot is presented in the inset of Fig. 4b. The F–N plot is approximately linear at high-applied fields, indicating that the emitting electrons mainly result from barrier tunneling electrons extracted by the electric field [21,22]. The turn-on electric field (defined as the E corresponding to the J of 0.75 μA cm 2) is estimated to be 5.4 V cm 1. Meanwhile, the needed electric fields for the current density of 0.38 mA of SnNTs is 11 V cm 1. The FE property is superior to those of the reported SnO2 nanorods and nanowires [23,24] The reason for the efficient FE property is mainly due to aligned structure, good electrical contact with the conducting substrate, and weaker field-screening effect [25]. 4. Conclusion We have reported a facile synthetic strategy for aligned SnNTs on Si substrate via liquid-phase deposition with the solution system of SnF2 utilizing ZnO nanorod arrays as a sacrificial template. This strategy simplifies the approach to obtain aligned SnNTs. It is demonstrated that the SnNTs show an efficient FE property favorable for fabricating high performance cold cathode electron emitters. Acknowledgments This work was financially supported by theNational Natural Science Foundation of China (NSFC) with No. 51072066 and 11247305, the Ph.D. Programs Foundation of Ministry of Education of China with No.20100061110083, the Open Project of State Key
Laboratory of Superhard Materials (Jilin University) with No. 201213 and the Youth Fund of Science and Technology Department of Jiangxi Province with No. 20131522040044.
References [1] Juttukonda V, Paddock RL, Raymond JE, Denomme D, Richardson AE, Slusher LE, et al. J Am Chem Soc 2006;128:420–1. [2] Lei DL, Zhang M, Hao QY, Chen LB, Li QH, Zhang ED, et al. Mater Lett 2011;65:1154–6. [3] Liu ZQ, Zhang DH, Han S, Li C, Tang T, Jin W, et al. Adv Mater 2003;15:1754–7. [4] Wang X, Liu W, Yang H, Li X, Li N, Shi R, et al. Acta Mater 2011;59:1291–9. [5] Wang CF, Xie SY, Lin SC, Cheng X, Zhang XH, Huang RB, et al. Chem Commun 2004:1766–7. [6] Wang YL, Guo M, Zhang M, Wang XD. CrystEngComm 2010;12:4024–7. [7] Li XB, Wang XW, Shen Q, Zheng J, Liu WH, Zhao H, et al. Appl Mater Interfaces 2013;5:3033–41. [8] Ying B, Liu M. Adv Funct Mater 2005;15:57–62. [9] Duan J, Cao Q, Yang S, Huang H, Zhao X, Zhang R, et al. J Cryst Growth 2006;289:164–7. [10] Kim H, Cho J. J Mater Chem 2008;18:771–5. [11] Lee WJ, Park MH, Wang Y, Lee JY, Cho J. Chem Commun 2010;46:622–4. [12] Park NG, Kang MG, Ryu KS, Kim KM, Chang SH. J Photochem Photobiol, A 2004;161:105–10. [13] Zhu W, Wang WZ, Xu HL, Shi JL. Mater Chem Phys 2006;99:127–30. [14] Shi LN, Xu YM, Li Q. Nanoscale 2010;2:2104–8. [15] Kuang Q, Xu T, Xie ZX, Lin SC, Huang RB, Zheng LS. J Mater Chem 2009;19:1019–23. [16] Wang JZ, Du N, Zhang H, Yu JX, Yang S. J Phys Chem C 2011;115:11302–5. [17] Desai UV, Xu CK, Wu JM, Gao D. J Phys Chem C 2013;117:3232–9. [18] Tsukuma K, Akiyama T, Imai H. J Non-Cryst Solids 1997;210:48–54. [19] Matsushima Y, Satoh R, Kawai T, Maeda K, Suzuki T. J Ceram Soc Jpn 2010;118:206–12. [20] Lee EJH, Ribeiro C, Giraldi TR, Longo E, Leite ER, Varela JA. Appl Phys Lett 2004:841745–7. [21] Li LJ, Zong FJ, Cui XD, Ma HL, Wu XH, Zhang QD, et al. Mater Lett 2007;61:4152–5. [22] Ma LA, Yea Y, Hua LQ, Zheng KL, Guo TL. Physica E 2008;40:3127–30. [23] Deshpande AC, Koinkar PM, Ashtaputre SS, More MA, Gosavi SW, Godbole PD, et al. Thin Solid Films 2006;515:1450–4. [24] Wu JM. Thin Solid Films 2008;517:1289–93. [25] Li ZJ, Wang HY, Liu P, Zhao B, Zhang YF. Appl Surf Sci 2009;255:4470–3.