One-dimensional CuO nanowire: synthesis, electrical, and optoelectronic devices application
© Luo et al.; licensee Springer. 2014
Received: 27 October 2014
Accepted: 17 November 2014
Published: 26 November 2014
In this work, we presented a surface mechanical attrition treatment (SMAT)-assisted approach to the synthesis of one-dimensional copper oxide nanowires (CuO NWs) for nanodevices applications. The as-prepared CuO NWs have diameter and the length of 50 ~ 200 nm and 5 ~ 20 μm, respectively, with a preferential growth orientation along [1 0] direction. Interestingly, nanofield-effect transistor (nanoFET) based on individual CuO NW exhibited typical p-type electrical conduction, with a hole mobility of 0.129 cm2V-1 s-1 and hole concentration of 1.34 × 1018 cm-3, respectively. According to first-principle calculations, such a p-type electrical conduction behavior was related to the oxygen vacancies in CuO NWs. What is more, the CuO NW device was sensitive to visible light illumination with peak sensitivity at 600 nm. The responsitivity, conductive gain, and detectivity are estimated to be 2.0 × 102 A W-1, 3.95 × 102 and 6.38 × 1011 cm Hz1/2 W-1, respectively, which are better than the devices composed of other materials. Further study showed that nanophotodetectors assembled on flexible polyethylene terephthalate (PET) substrate can work under different bending conditions with good reproducibility. The totality of the above results suggests that the present CuO NWs are potential building blocks for assembling high-performance optoelectronic devices.
Metal oxide semiconductors (e.g. ZnO,  TiO2,  NiO,  SnO2, and CuO ) are one of the most common, most diverse and probably the richest class of materials among the various groups of semiconductors. In the past decade, a number of methods including laser ablation [6, 7], thermal oxidation [8, 9], solution-phase growth , and template-assisted synthesis  have been employed to fabricate various one-dimensional metal oxide semiconductor nanostructures, such as nanowires, nanotubes, and nanoribbons . Due to the high surface-volume ratio and quantum-size effect, the resultant nanostructures with improved physical, optical, and electronic properties  have been used as building blocks to construct a number of optoelectronic and electronic devices including solar cells [14, 15], photodetectors [16, 17], gas sensors , non-volatile memory devices , and so on.
Copper oxide (CuO), as one of the most important metal oxide semiconductors, has been widely used because of its abundance in resources and low cost in synthesis. Low-dimensional CuO nanostructures (zero-dimensional and one-dimensional nanostructures) are used, in particular via simple thermal evaporation method , wet chemical method , and metal-assisted growth method . It has been found that the CuO NWs obtained from the above methods normally have good crystallinity and high aspect ratio, which renders them attractive and promising building blocks for fabricating high-performance electronic devices systems . For example, Chang et al. reported the growth of CuO NWs on an oxidized Cu wire at 500°C for infrared (IR) photodetection application. The as-obtained high density of CuO NWs on the Cu wire was highly sensitive to IR light illumination (wavelength: 808 nm), with rise-time and fall-time of 15 and 17 s, respectively . Zhou et al. presented a vertically aligned CuO NWs array-based ultrasensitive sensors for H2S detection with a detection limit as low as 500 ppb. It was revealed that the high sensitivity was due to the formation of highly conductive CuS layer when H2S gas was introduced into the detection chamber . Zheng et al. developed a simple and effective catalyst system comprised of CuO NWs for CO oxidation. They found that CO oxidation percentage was as high as 85% after Ar or H2 plasma treatment . In addition to these device applications, it has been observed that highly-aligned CuO NW arrays are good candidates for field emission due to their low turn-on voltages, high current output .
Despite of the above research progresses, there is a sparsity of research activity dealing with the transport and optoelectronic property of individual CuO nanostructures , which constitutes the basic building blocks of various optoelectronic and electronic devices. Exploration along this direction is highly desirable as it is not only helpful for understanding the electrical property of individual CuO NWs, but also beneficial to the development of high-performance optoelectronic and electronic devices. Herein, we report the synthesis of CuO NWs by heating surface mechanical attrition treatment (SMAT) processed copper foil in tube furnace. The CuO NW is of single crystal with a growth direction of [1 0]. Individual CuO NW-based field-effect transistor displays weak p-type electrical conduction behavior, which was probably due to the O defects, according to the theoretical simulation based on first-principle calculation. Further optoelectronic characterization shows that the CuO NW is sensitive to incident light of 600 nm, with high producibility and stability. It is also observed that the photodetector fabricated on flexible polyethylene terephthalate (PET) substrate showed good reproducibility under different bending conditions. The above result suggests that our CuO NWs will have promising potential in future devices applications.
Synthesis and structural characterization of the CuO NWs
In this study, the CuO NWs were fabricated via SMAT-assisted thermal oxidation method. Briefly, copper plates (99.99%) with size of 20 × 20 × 5 mm were cleaned by alcohol to remove surface impurities including grease and other organics. The copper plates were then treated by an SMAT process in which millimeter-size steel balls were acoustically driven to bombard the Cu surface randomly and in all directions to generate nanocrystalline Cu . After drying in N2 atmosphere, the clean samples were heated in a horizontal tube at 500°C in pure O2 atmosphere (375 Torr) for 2.5 h. The morphologies and structure of the as-prepared CuO NWs were characterized by scanning electron microscopy (SEM, FEI Quanta 200 FEG, FEI, Hillsboro, OR, USA), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2010 at 200 kV, JEOL, Akishima-shi, Tokyo, Japan), X-ray diffraction (XRD, Rigaku D/Max-γB, with Cu Kα radiation, Rigaku Corporation, Tokyo, Japan) and X-ray photoelectron spectroscopy (XPS, ThermoESCALAB250, Thermo Fisher Scientific, Waltham, MA, USA).
Device fabrication and characterization
To evaluate the electrical properties of the CuO NWs, back-gate field-effect transistor (FET) was constructed based on individual CuO NW. Firstly, the as-synthesized CuO NW was dispersed on a SiO2/p + -Si substrate by a contact print technique , then Cu (4 nm)/Au (50 nm) source and drain electrodes were defined by photolithography and e-beam evaporation. In order to achieve ohmic contact between the NW and electrodes, the as-fabricated devices were annealed at 200°C for 10 min in argon atmosphere at a pressure of 0.33 Torr. In this work, flexible photodetectors on PET substrate were constructed by the same process. Both the electrical and optoelectronic characterization of CuO NW-based devices were carried out by using a semiconductor characterization system (Keithley 4200-SCS, Keithley, Cleveland, OH, USA).
The first-principle calculation of [ 0] CuO NW were based on the density functional theory (DFT) implemented in the Vienna ab initio simulation package method [30, 31]. The projector-augmented wave (PAW)  and the Perdew-Burke-Ernzerhof GGA (PBE)  functionals were employed for the total energy calculations. The cutoff energy was 450 eV and the criteria of the forces were set to be 0.01 eV/Å for all atoms. An 11 × 11 × 11 k-grid mesh was used for the bulk CuO and a 7× 1 × 1 mesh for the < 0 > CuO NW, where the vacuum distance was set to be 10 Å to avoid cell-to-cell interactions. To improve the calculations of electronic properties, we used the GGA + U extension to the DFT calculation [34, 35], dealing with the Cu 3d electrons for a better description, where U = 7.5 eV and J = 1.0 eV were adopted.
Results and discussion
Where h, d, and l represent the thickness of oxide layer (300 nm), the NW diameter (125 nm), and the channel length (5 μm), respectively. is the dielectric constant of the SiO2 dielectric layer (approximately 3.9), ϵ0 is the permittivity at vacuum, σ is the conductivity of the NW, and q is the charge of an electron. Based on the equation (Equation 1), the hole mobility is estimated to be 0.134 cm2V-1 s-1. Such a value is larger than the CuO thin film , and CuO NWs synthesized by direct evaporating Cu substrates in oxygen ambient without SMAT process , suggesting that the present SMAT-assisted thermal evaporation is an ideal approach to the synthesis of CuO NWs. Furthermore, the hole concentration is calculated to be 1.29 × 1018 cm-3 according to Equation 2. To obtain a statistical distribution of the CuO NWs, totally ten FETs were analyzed. As displayed in Figure 3d, the hole mobilities of most CuO NWs are in the range of 0.1 to 1.0 cm2V-1 s-1 with an average value of 0.58 cm2V-1 s-1. Meanwhile, the hole concentration is in the range of 0.8 × 1018 to 1.4 × 1018 cm-3 with an average value of 1.13 × 1018 cm-3.
Summary of the device performances of the CuO-based PD with other PDs based on pure materials
In summary, we have fabricated one-dimensional CuO NW by heating SMAT copper plate in oxygen atmosphere. Electrical field-effect transistor device based on the as-prepared individual CuO NW exhibited typical p-type electrical conduction characteristic, with hole mobility and concentration of 0.134 cm2V-1 s-1 and 1.29 × 1018 cm-3, respectively. It is also revealed that the as-synthesized CuO NW was highly sensitive to light irradiation of 600 nm, with a high responsitivity and photoconductive gain of 2.0 × 102 AW-1 and 3.95 × 102, respectively. Further optoelectronic study shows that the photodetector on flexible PET substrate is also highly sensitive to 600-nm wavelength light at different bending conditions. The generality of this study proves that CuO NW obtained via SMAT-assisted thermal evaporation method will have great potential for future high-performance optoelectronic devices application.
LBL, XHW, CX, and RL carried out the experiments. ZJL and XBY conducted the theoretical simulation. JL conceived the idea and supervised the whole work. LBL, XBY, and JL drafted the paper. All authors read and approved the final manuscript.
This work was supported by the National Key Basic Research Program of the Chinese Ministry of Science and Technology (Grant 2012CB932203), the Natural Science Foundation of China (NSFC, Nos. 51202206, 21101051, 11104080, 61106010), the Croucher Foundation (CityU9500006), and the Fundamental Research Funds for the Central Universities (2012HGCX0003, 2013HGCH0012, 2014HGCH0005).
- Wang ZL, Song JH: Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science 2006, 312: 242–246. 10.1126/science.1124005View ArticleGoogle Scholar
- Kwon DH, Kim KM, Jang JH, Jeon JM, Lee MH, Kim GH, Li XS, Park GS, Lee B, Han SW, Kim MY, Hwang CS: Atomic structure of conducting nanofilaments in TiO2 resistive switching memory. Nat Nanotechnol 2010, 5: 148–153. 10.1038/nnano.2009.456View ArticleGoogle Scholar
- Dar FI, Moonooswamy KR, Es-Souni M: Morphology and property control of NiO nanostructures for supercapacitor applications. Nanoscale Res Lett 2013, 8: 363. 10.1186/1556-276X-8-363View ArticleGoogle Scholar
- Choi SW, Katoch A, Sun GJ, Wu P, Kim SS: NO2-sensing performance of SnO2 microrods by functionalization of Ag nanoparticles. J Mater Chem C 2013, 1: 2834–2841. 10.1039/c3tc00602fView ArticleGoogle Scholar
- Feng YZ, Zheng XL: Plasma-enhanced catalytic CuO nanowires for CO oxidation. Nano Lett 2010, 10: 4762–4766. 10.1021/nl1034545View ArticleGoogle Scholar
- Zeng HB, Du XW, Singh SC, Kulinich SA, Yang SK, He JP, Cai WP: Nanomaterials via laser ablation/irradiation in liquid. Adv Funct Mater 2012, 22: 1333–1353. 10.1002/adfm.201102295View ArticleGoogle Scholar
- Niu KY, Yang J, Kulinich SA, Sun J, Du XW: Hollow nanoparticles of metal oxides and sulfides: fast preparation via laser ablation in liquid. Langmuir 2010, 26: 16652–16657. 10.1021/la1033146View ArticleGoogle Scholar
- Nie B, Hu JG, Luo LB, Xie C, Zeng LH, Lv P, Li FZ, Jie JS, Feng M, Wu CY, Yu YQ, Yu SH: Monolayer graphene film on ZnO nanorod array for high-performance Schottky junction ultraviolet photodetectors. Small 2013, 9: 2872–2879. 10.1002/smll.201203188View ArticleGoogle Scholar
- Luo LB, Liang FX, Jie JS: Sn-catalyzed synthesis of SnO2 nanowires and their optoelectronic characteristics. Nanotechnology 2011, 22: 485701. 10.1088/0957-4484/22/48/485701View ArticleGoogle Scholar
- Nguyen P, Ng HT, Yamada T, Smith MK, Li J, Han J, Meyyappan M: Direct integration of metal oxide nanowire in vertical field-effect transistor. Nano Lett 2004, 4: 651–657. 10.1021/nl0498536View ArticleGoogle Scholar
- Fan HJ, Lee W, Hauschild R, Alexe M, Rhun GL, Scholz R, Dadgar A, Nielsch K, Kalt H, Krost A, Zacharias M, Gösele U: Template-assisted large-scale ordered arrays of ZnO pillars for optical and piezoelectric applications. Small 2006, 2: 561–568. 10.1002/smll.200500331View ArticleGoogle Scholar
- Jie JS, Zhang WJ, Jiang Y, Meng XM, Li YQ, Lee ST: Photoconductive characteristics of single-crystal CdS nanoribbons. Nano Lett 2006, 6: 1887–1892. 10.1021/nl060867gView ArticleGoogle Scholar
- Miao JS, Hu WD, Guo N, Lu ZY, Zou XM, Liao L, Shi SX, Chen PP, Fan FY, Ho JC: Single InAs nanowire room-temperature near-infrared photodetector. ACS Nano 2014, 8: 3628–3635. 10.1021/nn500201gView ArticleGoogle Scholar
- Gubbala S, Chakrapani V, Kumar V, Sunkara MK: Band-edge engineered hybrid structures for dye-sensitized solar cells based on SnO2 nanowires. Adv Funct Mater 2008, 18: 2411–2418. 10.1002/adfm.200800099View ArticleGoogle Scholar
- Martinson ABF, Elam JW, Hupp JT, Pellin MJ: ZnO nanotube based dye-sensitized solar cells. Nano Lett 2007, 7: 2183–2187. 10.1021/nl070160+View ArticleGoogle Scholar
- Law JBK, Thong JTL: Simple fabrication of a ZnO nanowire photodetector with a fast photoresponse time. Appl Phys Lett 2006, 88: 133114. 10.1063/1.2190459View ArticleGoogle Scholar
- Wang MZ, Liang FX, Nie B, Zeng LH, Zheng LX, Lv P, Xie C, Li YY, Luo LB: TiO2 nanotube array/monolayer graphene film Schottky junction ultraviolet light photodetectors. Part Part System Ch 2013, 30: 630–636. 10.1002/ppsc.201300040View ArticleGoogle Scholar
- Chen J, Xu L, Li WY, Gou XL: α-Fe2O3 nanotubes in gas sensor and lithium-ion battery application. Adv Mater 2005, 17: 582–586. 10.1002/adma.200401101View ArticleGoogle Scholar
- Wu CY, Wu YL, Wang WJ, Mao D, Yu YQ, Wang L, Xu J, Hu JG, Luo LB: High performance nonvolatile memory devices based on Cu2-xSe nanowires. Appl Phys Lett 2013, 103: 193501. 10.1063/1.4828881View ArticleGoogle Scholar
- Jiang XC, Herricks T, Xia YN: CuO nanowires can be synthesized by heating copper substrates in air. Nano Lett 2002, 2: 1333–1338. 10.1021/nl0257519View ArticleGoogle Scholar
- Ethiraj AS, Kang DJ: Synthesis and characterization of CuO nanowires by a simple wet chemical method. Nanoscale Res Lett 2012, 7: 70–74. 10.1186/1556-276X-7-70View ArticleGoogle Scholar
- Tsai CM, Chen GD, Tseng TC, Lee CY, Huang CT, Tsai WY, Yang WC, Yeh MS, Yew TR: CuO nanowire synthesis catalyzed by a CoWP nanofilter. Acta Mater 2009, 57: 1570–1576. 10.1016/j.actamat.2008.12.003View ArticleGoogle Scholar
- Zhu YW, Yu T, Cheong FC, Xu XJ, Lim CT, Tan VBC, Thong JTL, Sow CH: Large-scale synthesis and field emission properties of vertically oriented CuO nanowire films. Nanotechnology 2005, 16: 88–92. 10.1088/0957-4484/16/1/018View ArticleGoogle Scholar
- Wang SB, Hsiao CH, Cha Zhu YW, Sow CH, Thong JTL: Enhanced field emission from CuO nanowire arrays by in situ laser irradiation. J Appl Phys 2007, 102: 114302. 10.1063/1.2818096View ArticleGoogle Scholar
- Chen JJ, Wang K, Hartman L, Zhou WL: H2S detection by vertically aligned CuO nanowire array sensors. J Phys Chem C 2008, 112: 16017–16021. 10.1021/jp805919tView ArticleGoogle Scholar
- Zhu YW, Sow CH, Thong JTL: Enhanced field emission from CuO nanowire arrays by in situ laser irradiation. J Appl Phys 2007, 102: 114302. 10.1063/1.2818096View ArticleGoogle Scholar
- Hansen BJ, Kouklin N, Lu G, Lin IK, Chen JH, Zhang X: Transport, analyte detection, and opto-electronic response of p-type CuO nanowires. J Phys Chem C 2010, 114: 2440–2447. 10.1021/jp908850jView ArticleGoogle Scholar
- Hansen BJ, Chan HL, Lu J, Lu GH, Chen JH: Short-circuit diffusion growth of long bi-crystal CuO nanowires. Chem Phys Lett 2011, 504: 41–45. 10.1016/j.cplett.2011.01.040View ArticleGoogle Scholar
- Wang L, Lu M, Wang XG, Yu YQ, Zhao XZ, Lv P, Song HW, Zhang XW, Luo LB, Wu CY, Zhang Y, Jie JS: Tuning the p-type conductivity of ZnSe nanowires via silver doping for rectifying and photovoltaic device applications. J Mater Chem A 2013, 1: 1148–1154. 10.1039/c2ta00471bView ArticleGoogle Scholar
- Kresse G, Furthmüller J: Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. J Phys Rev B 1996, 54: 11169–11186. 10.1103/PhysRevB.54.11169View ArticleGoogle Scholar
- Kresse G, Joubert D: From ultrasoft pseudopotentials to the projector augmented-wave method. Phys Rev B 1999, 59: 1758–1775.View ArticleGoogle Scholar
- Blöchl PE: Projector augmented-wave method. Phys Rev B 1994, 50: 17953–17979. 10.1103/PhysRevB.50.17953View ArticleGoogle Scholar
- Perdew JP, Burke K, Ernzerhof M: Generalized gradient approximation made simple. Phys Rev Lett 1997, 78: 1396–1396.View ArticleGoogle Scholar
- Liechtenstein AI, Anisimov VI, Zaanen J: Density-functional theory and strong interactions: orbital ordering in Mott-Hubbard insulators. Phys Rev B 1995, 52: R5467-R5470. 10.1103/PhysRevB.52.R5467View ArticleGoogle Scholar
- Loschen C, Carrasco J, Neyman KM, Illas F: First-principles LDA + U and GGA + U study of cerium oxides: dependence on the effective U parameter. Phys Rev B 2007, 75: 035115.View ArticleGoogle Scholar
- Gonçalves AMB, Campos LC, Ferlauto AS, Lacerda RG: On the growth and electrical characterization of CuO nanowires by thermal oxidation. J Appl Phys 2009, 106: 034303. 10.1063/1.3187833View ArticleGoogle Scholar
- Sanal KC, Vikas LS, Jayaraj MK: Room temperature deposited transparent p-channel CuO thin film transistors. Appl Surf Sci 2014, 297: 153–157.View ArticleGoogle Scholar
- Hu J, Li D, Lu JG, Wu R: Effects on electronic properties of molecule adsorption on CuO surfaces and nanowires. J Phys Chem C 2010, 114: 17120–17126.View ArticleGoogle Scholar
- Luo LB, Huang XL, Wang MZ, Xie C, Wu CY, Hu JG, Wang L, Huang JA: The effect of plasmonic nanoparticles on the optoelectronic characteristics of CdTe nanowires. Small 2014, 10: 2645–2652. 10.1002/smll.201303388View ArticleGoogle Scholar
- Kung SC, Veer WE, Yang F, Donavan KC, Penner RM: 20 micros photocurrent response from lithographically patterned nanocrystalline cadmium selenide nanowires. Nano Lett 2010, 10: 1481–1485. 10.1021/nl100483vView ArticleGoogle Scholar
- Chang SP, Lu CY, Chang SJ, Chiou YZ, Hsueh TJ, Hsu CL: Electrical and optical characteristics of UV photodetector with interlaced ZnO nanowires. IEEE J Sel Top Quant Electron 2011, 17: 990–995.View ArticleGoogle Scholar
- Luo LB, Yang XB, Liang FX, Jie JS, Li Q, Zhu ZF, Wu CY, Yu YQ, Wang L: Transparent and flexible selenium nanobelt-based visible light photodetector. CrystEngComm 2012, 14: 1942–1948. 10.1039/c2ce06420kView 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/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.