- Nano Express
- Open Access
Field emission properties and growth mechanism of In2O3 nanostructures
© Wang et al.; licensee Springer. 2014
- Received: 27 November 2013
- Accepted: 18 February 2014
- Published: 10 March 2014
Four kinds of nanostructures, nanoneedles, nanohooks, nanorods, and nanotowers of In2O3, have been grown by the vapor transport process with Au catalysts or without any catalysts. The morphology and structure of the prepared nanostructures are determined on the basis of field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The growth direction of the In2O3 nanoneedles is along the , and those of the other three nanostructures are along the . The growth mechanism of the nanoneedles is the vapor-liquid–solid (VLS), and those of the other three nanostructures are the vapor-solid (VS) processes. The field emission properties of four kinds of In2O3 nanostructures have been investigated. Among them, the nanoneedles have the best field emission properties with the lowest turn-on field of 4.9 V/μm and the threshold field of 12 V/μm due to possessing the smallest emitter tip radius and the weakest screening effect.
- Thermal evaporation
- Field emission
- Crystal growth
- Growth mechanism
Recent reports show that reducing the size of In2O3 to a nanoscale gives it various morphologies, such as wires/belts, cubes, octahedrons, and bamboos [3–7]. Recently, the nanostructures of In2O3 have also been paid considerable attention due to their esthetic morphologies , novel characteristics, and important potential applications in various nanodevices [8–13]. It is well known that the properties of nanostructures strongly depend on their morphologies. In previous reports, most of the efforts were focused on the synthesis and properties of single morphology nanostructures. Research on the complex nanostructure was limited, while investigation of the synthesis and properties of complex nanostructures represented developing directions of nanoscience and nanotechnology, which have important potential applications in realizing the multiple functions of nanodevices .
Field emission is one of the most fascinating properties of nanomaterials, such as carbon nanotube, ZnO nanoneedles, and SnO2 nanograss [15–19], and has been extensively studied due to its diverse technological applications in flat-panel displays, microwave-generation devices, and vacuum micro/nanoelectronic devices . In2O3 can be one of the most attractive conductive oxides for field emission because of its relatively low electron affinity, convenience of n-type doping, high chemical inertness, and sputter resistance .
In this paper, four kinds of In2O3 structures, nanoneedles, nanohooks, nanorods, and nanotowers have been grown by the vapor transport process. The morphology and structure of the prepared nanostructures are determined on the basis of field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The field emission properties of the four kinds of In2O3 nanostructures have been investigated, and the In2O3 nanoneedles have preferable characteristics among the four nanostructures due to possessing the smallest emitter tip radius and the weakest screening effect. The growth mechanism is discussed, and the analysis is helpful to understand the relationship between the kinetic factors and the complex structures. It is valuable to realize the controlled synthesis of complex nanostructures.
The synthesis of these In2O3 nanostructures is by the vapor transport process. The fabrication of the In2O3 nanoneedles is as follows: the Au layer (about 10 nm in thickness) is deposited on one single crystal silicon (001) substrate with area of 5 mm2 by sputtering. The active carbon and In2O3 powders (both 99.99%) are mixed in a 1:1 weight ratio and placed into a small quartz tube. One Si substrate covered by Au is put near the mixture of carbon and In2O3 inside the small quartz tube. Then the small quartz tube is pulled into a large quartz tube, and the large quartz tube is put in an electric furnace. The whole system is evacuated by a vacuum pump for 20 min, then the argon gas is guided into the system at 200 sccm, and the pressure is kept at 300 Torr. Afterwards, the system is rapidly heated up to 1,000°C from the room temperature and kept at the temperature for 1 h. Finally, the system is cooled down to the room temperature in several hours. When the substrate is taken out, we can see yellow products on the substrate.
The fabrication process of the In2O3 nanohooks, In2O3 nanorods, and In2O3 nanotowers is basically same with that of In2O3 nanoneedles besides the following contents: Three Si substrates without any catalysts are put far away from the mixture of carbon and In2O3 inside the small quartz tube, and the distance between every two Si substrates is about 2 cm. The argon gas is guided into the system at 250 sccm, the pressure is kept at 350 Torr, and the system is rapidly heated up to 1,050°C from the room temperature.
FESEM, XRD, and TEM are employed to identify the morphology and structure of the synthesized productions. Note that we can easily repeat the experimental results, suggesting that our method is flexible and reproducible.
The growth mechanism of the In2O3 nanoneedles can be explained on the basis of the 1-D growth along the  crystalline direction controlled by vapor-liquid–solid (VLS) initiated due to the existence of Au catalysts [22–24]. In addition, the formation mechanism of the layered nanohooks, layered nanorods, and nanotowers is mainly led by the bottom growth of vapor-solid (VS) without a catalyst droplet [25–27]. The formation mechanism of the layered nanorods with octahedral tops is explained by the periodical 1-D growth along the  direction and the continuous 0-D growth along the  direction [14, 28, 29]. Beside the formation of the hook-shaped top rather than the octahedral top, the formation mechanism of the layered nanohooks is the same with the stages of the layered nanorods [14, 28, 29]. The formation mechanism of the nanotowers is due to a periodical 1-D growth along the  direction and 0-D growth along the  direction .
where A = 1.54 × 10-6 A eV V-2, B = 6.83 × 103 eV-3/2 V μm-1, β is the field enhancement factor, and Φ is the work function of an emitting material. The nonlinearity of the FN plots of the samples in Figure 4b may attribute to the space charge effects, which results from collision and ionization of residual gas molecules by the emitted electrons . In addition, it has demonstrated that the different crystal facets of the emitter tip possess the different work functions . According to the TEM results above, the crystal facets in the emitter tip of four kinds of In2O3 nanostructures are (001) or (100) planes, which indicates that the values of their work function are same. Assuming the work function of the In2O3 is 5.0 eV , β values of the In2O3 nanoneedles, nanohooks, nanorods, and nanotowers are estimated to be 3,695, 1,770, 1,374, and 458, respectively. Comparing with the other three kinds of In2O3 nanostructures, the In2O3 nanoneedles have the threshold field, the lowest turn-on field, and highest β, which demonstrates the In2O3 nanoneedles have the best field emission properties among all of the samples. The corresponding reasons can be described as follows.
It is known that the field enhancement factor β is a key parameter, which reflects the enhanced electron emission due to the localized electronic states by the geometrical configuration of the emitters. In theoretical case, β can be expressed as h/r, where h is the height of emitter and r is the average radius of the emitter tips . In this paper, the In2O3 nanostructures in Figure 1 are in random alignment so that the height of emitter is difficult to measure. Based on the length of the four kinds of In2O3 nanostructures in Figure 1 being all close to 2 μm, their height of emitter can be regarded as being approximately equal. In this case, the field enhancement factor β is mainly depending on 1/r. According to the FE mechanism, the field emission current is mainly produced from the tip of the materials so as to deduce that the field emission current is mainly produced from the tip of the nanostructures. Among the four kinds of In2O3 nanostructures in this paper, the In2O3 nanoneedles had the sharpest tip with the size of 50 nm so as to possess the highest β value. Therefore, the emitter tip radius and the emitter height are two factors that can affect the field emission properties of the In2O3 nanostructures.
Field emission parameters and morphological sizes of the synthesized In 2 O 3 nanostructures
In addition, different electrical properties, i.e., work function (different facet) and substrate-nanostructure electrical contact can affect the field emission properties of the In2O3 nanostructures too. According to the TEM results in Figure 3, the four kinds of In2O3 nanostructures possess the same work function due to the crystal facets in their emitter tip being (001) or (100) planes, which has been discussed above. In addition, nanostructures grown on different substrates can result in different conductivity . In this paper, all of the substrates are single crystal silicon (001) substrates, so the effects of substrate-nanostructure electrical contact for the four kinds of In2O3 nanostructures are same, which may not cause the difference to their field emission properties.
From the TEM results shown in Figure 3, it is observed that the Au nanoparticles are only present at the tip of In2O3 nanoneedles. The presence of these Au nanoparticles at the tip of the nanoneedles could influence the field emission results. As the work function of Au is 5.1 eV, which is quite similar to that of In2O3. Therefore, the effect of the catalyst in the field emission properties is negligible .
In summary, four kinds of In2O3 nanostructures, nanoneedles, layered nanohooks, layered nanorods, and nanotowers, have been grown on single silicon substrates with Au catalysts- or without any catalysts-assisted carbothermal evaporation of In2O3 and active carbon powders. The growth direction of the In2O3 nanoneedles is along the , and those of the other three nanostructures are along the . The growth mechanism of the nanoneedles is the VLS, and those of the other three nanostructures are the VS processes. The field emission measurements demonstrated that the In2O3 nanoneedles have relatively excellent performance among the four kinds of In2O3 nanostructures mainly due to possessing the smallest emitter tip radius and the weakest screening effect.
This work was supported by National Natural Science Foundation of China (50902097), Three Industry Basic Research Emphasis Project of Shenzhen (JC201104210013A), Guangdong Natural Science Foundation of China (9451806001002303), Project of Department of Education of Guangdong Province (2013KJCX0165), Outstanding Young Teacher Training Project in the institutions of higher learning of Guangdong Province (Yq2013145), and open project of Shenzhen Key Laboratory of Micro-Nano Photonic Information Technology (MN201107).
- Dixit A, Sudakar C, Naik R, Naik VM, Lawes G: Undoped vacuum annealed In2O3 thin films as a transparent conducting oxide. Appl Phys Lett 2009, 95: 192105. 10.1063/1.3262963View ArticleGoogle Scholar
- Zhang KHL, Walsh A, Catlow CRA, Lazarov VK, Egdell RG: Surface energies control the self-organization of oriented In2O3 nanostructures on cubic zirconia. Nano Lett 2010, 10: 3740–3746. 10.1021/nl102403tView ArticleGoogle Scholar
- Jong SJ, Jeong YL: Formation mechanism and photoluminescence of necklace-like In2O3 nanowires. Mater Lett 2011, 65: 1693–1695. 10.1016/j.matlet.2011.02.083View ArticleGoogle Scholar
- Jeong JS, Lee JY, Lee CJ, An SJ, Yi GC: Synthesis and characterization of high-quality In2O3 nanobelts via catalyst-free growth using a simple physical vapor deposition at low temperature. Chem Phys Lett 2004, 384: 246–250. 10.1016/j.cplett.2003.12.027View ArticleGoogle Scholar
- Li C, Zhang D, Han S, Liu X, Tang T, Zhou C: Diameter-controlled growth of single-crystalline In2O3 nanowires and their electronic properties. Adv Mater 2003, 15: 143–146. 10.1002/adma.200390029View ArticleGoogle Scholar
- Shi MR, Xu F, Yu K, Zhu Z, Fang J: Controllable synthesis of In2O3 nanocubes, truncated nanocubes, and symmetric multipods. J Phys Chem C 2007, 111: 16267–16271. 10.1021/jp074445mView ArticleGoogle Scholar
- Jeong JS, Lee JY: The synthesis and growth mechanism of bamboo-like In2O3 nanowires. Nanotechnology 2010, 21: 405601. 10.1088/0957-4484/21/40/405601View ArticleGoogle Scholar
- Zheng W, Lu XF, Wang W, Li ZY, Zhang HN, Wang Y, Wang ZJ, Wang C: A highly sensitive and fast-responding sensor based on electrospun In2O3 nanofibers. Sensor Actuator B Chem 2009, 142: 61–65. 10.1016/j.snb.2009.07.031View ArticleGoogle Scholar
- Kar S, Chakrabarti S, Chaudhuri S: Morphology dependent field emission from In2O3 nanostructures. Nanotechnology 2006, 17: 3058. 10.1088/0957-4484/17/12/041View ArticleGoogle Scholar
- Li SQ, Liang YX, Wang TH: Nonlinear characteristics of the Fowler–Nordheim plot for field emission from In2O3 nanowires grown on InAs substrate. Appl Phys Lett 2006, 88: 053107. 10.1063/1.2159092View ArticleGoogle Scholar
- Li SQ, Liang YX, Wang TH: Electric-field-aligned vertical growth and field emission properties of In2O3 nanowires. Appl Phys Lett 2005, 87: 143104. 10.1063/1.2076438View ArticleGoogle Scholar
- Nguyen P, Ng HT, Yamada T, Smith MK, Li J, Han J, Meyyanppan M: Metallic photonic crystals based on solution-processible gold nanoparticles. Nano Lett 2004, 4: 651–655. 10.1021/nl0498536View ArticleGoogle Scholar
- Huang YJ, Yun K, Xu Z, Zhu ZQ: Novel In2O3 nanostructures fabricated by controlling the kinetics factor for field emission display. Phys E 2011, 43: 1502–1508. 10.1016/j.physe.2011.04.017View ArticleGoogle Scholar
- Yan YG, Zhang Y, Zeng HB, Zhang LD: In2O3 nanotowers: controlled synthesis and mechanism analysis. Cryst Growth Des 2007, 7: 940–943. 10.1021/cg0607194View ArticleGoogle Scholar
- Pan ZW, Dai ZR, Wang ZL: Nanobelts of semiconducting oxides. Science 1947–1949, 2001: 291.Google Scholar
- Wang HF, Li ZH, Ghosh K, Maruyama T, Inoue S, Ando Y: Synthesis of double-walled carbon nanotube films and their field emission properties. Carbon 2010, 48: 2882–2889. 10.1016/j.carbon.2010.04.020View ArticleGoogle Scholar
- Yu K, Zhang YS, Xu RL, Ouyang SX, Li DM, Luo LQ, Zhu ZQ, Ma J, Xie SJ, Han SG, Geng HR: Efficient field emission from tetrapod-like zinc oxide nanoneedles. Mater Lett 1866–1870, 2005: 59.Google Scholar
- Marathe S, Koinkar P, Ashtaputre S, Sathe V, More MA, Kulkarni SK: Enhanced field emission from ZnO nanoneedles on chemical vapour deposited diamond films. Thin Solid Films 2010, 518: 3743–3747. 10.1016/j.tsf.2009.10.118View ArticleGoogle Scholar
- Wang B, Yang YH, Wang CX, Xu NS, Yang GW: Field emission and photoluminescence of SnO2 nanograss. J Appl Phys 2005, 98: 124303. 10.1063/1.2142076View ArticleGoogle Scholar
- Satio Y, Uemura S: Field emission from carbon nanotubes and its application to electron sources. Carbon 2000, 38: 169–182. 10.1016/S0008-6223(99)00139-6View ArticleGoogle Scholar
- Klein A: Electronic properties of In2O3 surfaces. Appl Phys Lett 2009, 2000: 77.Google Scholar
- Wang B, Jin X, Ouyang ZB, Xu P: Photoluminescence and field emission of 1D ZnO nanorods fabricated by thermal evaporation. Appl Phys A 2012, 108: 195–200. 10.1007/s00339-012-6870-1View ArticleGoogle Scholar
- Wang B, Jin X, Wu HY, Zheng ZQ: Whispering gallery and Fabry–Perot modes enhanced luminescence from individual ZnO micromushroom. J Appl Phys 2013, 113: 034313. 10.1063/1.4780226View ArticleGoogle Scholar
- Wang B, Li L, Xu P, Xing LW: Fabrication and photoluminescence of the SnO2 plate-shape nanostructures and chrysanthemum-shape nanostructures. Rev Adv Mater Sci 2013, 33: 14.Google Scholar
- Wang B, Jin X, Ouyang ZB: Synthesis, characterization and cathodoluminescence of self-assembled 1D ZnO/In2O3 nano-heterostructures. CrystEngComm 2012, 14: 6888–6903. 10.1039/c2ce26011eView ArticleGoogle Scholar
- Wang B, Jin X, Ouyang ZB, Xu P: Field emission properties originated from 2D electronics gas successively tunneling for 1D heterostructures of ZnO nanobelts decorated with In2O3 nanoteeth. J Nano Res 2012, 14: 1008.View ArticleGoogle Scholar
- Wang B, Jin X, Wu HY, Zheng ZQ, Yang YH: Field emission and photoluminescence of ZnO nanocombs. Appl Phys A 2013, 113: 549–556. 10.1007/s00339-013-7867-0View ArticleGoogle Scholar
- Yan YG, Zhang Y, Zeng HB, Zhang JD, Cao X, Zhang L: Tunable synthesis of In2O3 nanowires, nanoarrows and nanorods. Nanotechnology 2007, 18: 175601. 10.1088/0957-4484/18/17/175601View ArticleGoogle Scholar
- Singh ND, Zhang T, Lee PS: The temperature-controlled growth of In2O3 nanowires, nanotowers and ultra-long layered nanorods. Nanotechnology 2009, 20: 195605. 10.1088/0957-4484/20/19/195605View ArticleGoogle Scholar
- Wang QY, Yu K, Xu F, Wu J, Xu Y, Zhu ZQ: Synthesis and field-emission properties of In2O3 nanostructures. Mater Lett 2008, 62: 2710–2713. 10.1016/j.matlet.2008.01.022View ArticleGoogle Scholar
- Lin J, Huang Y, Bando Y, Tang CC, Li C, Golberg D: Ga2O3 nanobelt heterostructures and their electrical and field emission properties. ACS Nano 2010, 4: 2452. 10.1021/nn100254fView ArticleGoogle Scholar
- Chen Y, Deng SZ, Xu NS, Chen J, Ma XC, Wang EG: Physical origin of non-linearity in Fowler–Nordheim plots of aligned large area multi-walled nitrogen-containing carbon nanotubes. Mater Sci Eng A 2002, 327: 16–19. 10.1016/S0921-5093(01)01871-8View ArticleGoogle Scholar
- Zhang H, Tang J, Yuan JS, Ma J, Shinya N, Nakajima K, Murakami H, Ohkubo T, Qin LC: Nanostructured LaB6 field emitter with lowest apical work function. Nano Lett 2010, 10: 3539–3544. 10.1021/nl101752zView ArticleGoogle Scholar
- Wang ZL, Wang Q, Li HJ, Li JJ, Xu P, Luo Q, Jin AZ, Yang HF, Gu CZ: The field emission properties of high aspect ratio diamond nanocone arrays fabricated by focused ion beam milling. Sci Tech Adv Mater 2005, 6: 799–803. 10.1016/j.stam.2005.06.018View ArticleGoogle Scholar
- Pan N, Xue HZ, Yu MH, Cui XF, Wang XP, Hou JG, Huang JX, Deng SZ: Tip-morphology-dependent field emission from ZnO nanorod arrays. Nanotechnology 2010, 21: 225707. 10.1088/0957-4484/21/22/225707View ArticleGoogle Scholar
- Filip V, Nicolaescu D, Tanemura M, Okuyama F: Modeling the electron field emission from carbon nanotubes films. Ultramicroscopy 2001, 89: 39–49. 10.1016/S0304-3991(01)00107-3View ArticleGoogle Scholar
- Shen Y, Deng SZ, Zhang Y, Liu F, Chen J, Xu NS: Highly conductive vertically aligned molybdenum nanowalls and their field emission property. Nano Res Lett 2012, 7: 463. 10.1186/1556-276X-7-463View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.