- Nano Express
- Open Access
Influence of Y-doped induced defects on the optical and magnetic properties of ZnO nanorod arrays prepared by low-temperature hydrothermal process
- Chung-Yuan Kung†1Email author,
- San-Lin Young†2Email author,
- Hone-Zern Chen2,
- Ming-Cheng Kao2,
- Lance Horng3,
- Yu-Tai Shih3,
- Chen-Cheng Lin1,
- Teng-Tsai Lin1 and
- Chung-Jen Ou4
© Lin et al.; licensee Springer. 2012
- Received: 29 November 2011
- Accepted: 22 June 2012
- Published: 7 July 2012
One-dimensional pure zinc oxide (ZnO) and Y-doped ZnO nanorod arrays have been successfully fabricated on the silicon substrate for comparison by a simple hydrothermal process at the low temperature of 90°C. The Y-doped nanorods exhibit the same c-axis-oriented wurtzite hexagonal structure as pure ZnO nanorods. Based on the results of photoluminescence, an enhancement of defect-induced green-yellow visible emission is observed for the Y-doped ZnO nanorods. The decrease of E2(H) mode intensity and increase of E1(LO) mode intensity examined by the Raman spectrum also indicate the increase of defects for the Y-doped ZnO nanorods. As compared to pure ZnO nanorods, Y-doped ZnO nanorods show a remarked increase of saturation magnetization. The combination of visible photoluminescence and ferromagnetism measurement results indicates the increase of oxygen defects due to the Y doping which plays a crucial role in the optical and magnetic performances of the ZnO nanorods.
- Y-doped ZnO nanorods
- Saturation magnetization
The II-VI semiconductor zinc oxide (ZnO) with a direct wide bandgap (3.37 eV) and a large exciton binding energy (60 meV) has attracted substantial attention in the research community [1–3]. Although ZnO had been researched for the past decades, the renewed interests are focused on the low-dimensional nanostructures, such as nanoparticles , nanowires , nanarods , and nanotubes , due to brand new fundamental physical properties and applications of nanodevices. Progressive studies on the performance improvement of these one-dimensional nanostructured ZnOs for optoelectronic device applications have been performed by various growth methods, such as hydrothermal methods , vapor–liquid–solid , metal organic vapor-phase epitaxy , and pulsed laser deposition  and doped with impurities, such as Ag , Li , and P . Besides, effective mass production process of ZnO nanowires by a modified carbothermal reduction method has been also reported . Recent researches further denoted that nanostructured ZnO with large effective surface area is suitable for ultraviolet devices and photovoltaic applications, such as light-emitting diodes , nanolasers , photodetectors , field emitters , chemical sensors , and photo-electrodes in dye-sensitized solar cells .
Recently, the observation of ferromagnetism with high Curie temperature in III-V and II-VI semiconductors has also attracted a great deal of attentions [22–24]. Room temperature ferromagnetism of ZnO doped with transition metals has been also theoretically predicted and experimentally confirmed for spintronics applications [25, 26]. In order to form diluted magnetic semiconductors, ZnO nanostructures have been doped with magnetic metal elements, such as Mn, Co, or Ni . Recently, some researches declared that ferromagnetism had been obtained from undoped nanostructured ZnO and suggested to be induced by defects . Non-magnetic elements, such Bi  or Li , have been doped into ZnO and room temperature ferromagnetism has been also observed. Therefore, ferromagnetism would not originate from the non-magnetic dopants since they do not contribute to ferromagnetism.
Based on the previous reports [1–30], one of the effective ways to approach the optical and magnetic properties of these nanostructured materials is the doping with selective elements. By choosing suitable rare-earth dopant, modification of the properties can be anticipated. In this present study, we will focus on the doping effect of larger non-magnetic element Y on the structural property of Y-doped ZnO (ZnO:Y) nanorods. In addition, the defect-related origin of optical and magnetic properties will be also discussed.
The ZnO and ZnO:Y nanorod arrays were fabricated by hydrothermal method on the ZnO-seeded silicon substrate. Pure ZnO seed layers for both nanorod compositions were firstly deposited on silicon substrate by spin coating technique. Then, the source solutions for ZnO and ZnO:Y nanorods growth were prepared using the precursors, zinc acetate dihydrate Zn(C2H3O2)22H2O and yttrium acetate hydrate Y(C2H3O2)34H2O, in stoichiometric proportions within a blending solvent of de-ionized water and HMTA ((CH2)6 N4). Then, the seeded substrate was placed upside down into the solution contained in a closed vial at 90°C for 3 h to grow the nanorods. Finally, the samples were rinsed with de-ionized water and dried in air for characterization.
The crystal structure was determined by X-ray diffraction (XRD) spectrum using a Rigaku D/max 2200 X-ray diffractometer (Rigaku Corporation, Tokyo, Japan) with Cu-Kα radiation. Morphological characterization was observed using a field emission scanning electron microscope (FE-SEM, JEOL JSM-6700 F, JEOL Ltd., Akishima, Tokyo, Japan) at 3.0 kV. Secondary ion mass spectrometry (SIMS) was utilized to identify the elemental distribution. Room temperature photoluminescence (RTPL) spectroscope was used to measure optical emissions from 350 to 645 nm using the He-Cd laser with wavelength of 325 nm. Raman spectra of the samples were measured with an excitation wavelength of 532 nm from argon laser. Finally, the magnetization measurements were performed using a MicroMag™ 2900 alternative gradient magnetometer (AGM) (Princeton Measurements Corp., Princeton, NJ, USA) at room temperature to investigate the magnetic properties of ZnO and ZnO:Y nanorods.
Under the hydrothermal conditions, HMTA will hydrolyze and release NH3 to provide (OH)−. Finally, the reaction of Zn2+ and (OH)− brings the products, ZnO and H2O. It is obvious that HMTA plays a key role to form Zn-O bonds. The (002) plane of wurtzite-structured ZnO is terminated with Zn2+, resulting in polar top surfaces with positive charge. In the chemical solution, non-polar HMTA will precedently chelate the non-polar facets except the polar (002) plane for epitaxial method. Therefore, a preferential growth along (002) is reasonably observed. Meanwhile, substitution of Y for Zn during the growth of nanorods can be obtained, which is similar to the synthesized process of Ce-doped ZnO nanorods . Compared with ZnO nanorods, the XRD spectrum of ZnO:Y nanorods exhibits obvious single diffraction peak of (002) and two slight peaks of (101) and (100) as shown in the inset of Figure 1. The obvious decrease of (002) diffraction peak intensity for ZnO:Y nanorods shows the restrain of the crystallization compared with ZnO samples. The result also indicates the suppression of growth rate along (002) crystal plane and slight enhancement of growth rate along (101) and (100) crystal planes. Besides, the decrease of a-axle lattice constants from 3.2526 to 3.2576 Å and c-axle lattice constant from 5.1849 to 5.1904 Å is obtained from the 2θ angles of diffraction peaks measured from ZnO and ZnO:Y nanorods. The reason is that the radius of Y3+ ion (0.92 Å) is larger than that of Zn2+ ion (0.74 Å), and the doping of Y into ZnO nanorods should lead the increase of a- and c-axis lattice constants and, correspondingly, the shift of all diffraction peaks towards lower 2θ angle.
ZnO and ZnO:Y nanorods have been successfully synthesized at a low temperature by hydrothermal method. The correlation between the Y-doped induced defects in the ZnO:Y nanorods and their structural, optical, and magnetic properties was studied in details. It was found that the doping of Y results in the increase of defects which also affects the corresponding structural, optical, and magnetic properties of the nanorods. The XRD spectra show that crystallization is suppressed by the doping of Y in the nanorods. The increase of visible emission in RTPL spectra and E1(LO) intensity in Raman spectra demonstrates that the doping of Y will increase the doping-induced defects in the nanorods. Magnetization curve measurements show the room temperature ferromagnetism of both nanorods. Finally, the combination of the optical and magnetic measurement results reveals that the oxygen defects play a crucial role in introducing ferromagnetism which can be enhanced by the doping of Y in the ZnO nanorods.
C-YK is a professor of the Department of Electrical Engineering, National Chung Hsing University. S-LY, H-ZC, and M-CK are professors of the Department of Electronic Engineering, Hsiuping University of Science and Technology. LH and Y-TS are professors of the Department of Physics, National Changhua University of Education. C-CL and T-TL are Ph.D. students. C-JO is a professor of the Department of Electrical Engineering, Hsiuping University of Science and Technology.
This work was sponsored by the National Science Council of the Republic of China under the grant numbers NSC 101-2221-E-164-004 and NSC 99-2221-E-005-103.
- Özgür Ü, Alivov YI, Liu C, Teke A, Reshchikov MA, Doğan S, Avrutin V, Cho SJ, Morkoç H: A comprehensive review of ZnO materials and devices. J Appl Phys 2005, 98: 041301. 10.1063/1.1992666View ArticleGoogle Scholar
- Lim JH, Kang CK, Kim KK, Park IK, Park SJ: UV electroluminescence emission from ZnO light-emitting diodes grown by high-temperature radio frequency sputtering. Adv Mater 2006, 18: 2720. 10.1002/adma.200502633View ArticleGoogle Scholar
- Norton DP, Heo YW, Ivill MP, Ip KA, Pearton SJ, Chisholm MF, Steiner T: ZnO: growth, doping & processing. Mater Today 2004, 7: 34.View ArticleGoogle Scholar
- Segets D, Marczak R, Schafer S, Paula C, Gnichwitz JF, Hirsch A, Peukert W: Experimental and theoretical studies of the colloidal stability of nanoparticles − a general interpretation based on stability maps. ACS Nano 2011, 5: 4658. 10.1021/nn200465bView ArticleGoogle Scholar
- Wei Y, Wu W, Guo R, Yuan D, Das S, Wang ZL: Wafer-scale high-throughput ordered growth of vertically aligned ZnO nanowire arrays. Nano Lett 2010, 10: 3414. 10.1021/nl1014298View ArticleGoogle Scholar
- Zhang BP, Binh NT, Wakatsuki K, Segawa Y, Kashiwaba Y, Haga K: Synthesis and optical properties of single crystal ZnO nanorods. Nanotechnology 2004, 15: S382. 10.1088/0957-4484/15/6/012View ArticleGoogle Scholar
- Li Q, Kumar V, Li Y, Zhang H, Marks TJ, Chang RPH: Fabrication of ZnO nanorods and nanotubes in aqueous solutions. Chem Mater 2005, 17: 1001. 10.1021/cm048144qView ArticleGoogle Scholar
- Solís-Pomar F, Martínez E, Meléndrez MF, Pérez-Tijerina E: Growth of vertically aligned ZnO nanorods using textured ZnO films. Nanoscale Res Lett 2011, 6: 524. 10.1186/1556-276X-6-524View ArticleGoogle Scholar
- Yang L, Yang J, Wang D, Zhang Y, Wang Y, Liu H, Fan H, Lang J: Photoluminescence and Raman analysis of ZnO nanowires deposited on Si(1 0 0) via vapor–liquid–solid process. Physica E 2008, 40: 920. 10.1016/j.physe.2007.11.025View ArticleGoogle Scholar
- Wu CC, Wuu DS, Lin PR, Chen TN, Horng RH: Effects of growth conditions on structural properties of ZnO nanostructures on sapphire substrate by metal–organic chemical vapor deposition. Nanoscale Res Lett 2009, 4: 377. 10.1007/s11671-009-9257-2View ArticleGoogle Scholar
- Son HJ, Jeon KA, Kim CE, Kim JH, Yoo KH, Lee SY: Synthesis of ZnO nanowires by pulsed laser deposition in furnace. Appl Surf Sci 2007, 253: 7848. 10.1016/j.apsusc.2007.02.098View ArticleGoogle Scholar
- Kim K, Debnath PC, Lee DH, Kim S, Lee SY: Effects of silver impurity on the structural, electrical, and optical properties of ZnO nanowires. Nanoscale Res Lett 2011, 6: 552. 10.1186/1556-276X-6-552View ArticleGoogle Scholar
- Lin CC, Young SL, Kung CY, Chen HZ, Kao MC, Horng L, Shih YT: Structural dependence of photoluminescence and room-temperature ferromagnetism in lightly Cu-doped ZnO nanorods. IEEE Trans Magn 2011, 647: 3366.View ArticleGoogle Scholar
- Limpijumnong S, Gordon L, Miao M, Janotti A, Van de Walle CG: Alternative sources of p-type conduction in acceptor-doped ZnO. Appl Phys Lett 2010, 97: 072112. 10.1063/1.3481069View ArticleGoogle Scholar
- Zhou Z, Zhan C, Wang Y, Su Y, Yang Z, Zhang Y: Rapid mass production of ZnO nanowires by a modified carbothermal reduction method. Mater Lett 2011, 65: 832. 10.1016/j.matlet.2010.12.032View ArticleGoogle Scholar
- Sadaf JR, Israr MQ, Kishwar S, Nur O, Willander M: White electroluminescence using ZnO nanotubes/GaN heterostructure light-emitting diode. Nanoscale Res Lett 2010, 5: 957. 10.1007/s11671-010-9588-zView ArticleGoogle Scholar
- Zhang C, Zhang F, Xia T, Kumar N, Hahm JI, Liu J, Wang ZL, Xu J: Low-threshold two-photon pumped ZnO nanowire lasers. Opt Express 2009, 17: 7893. 10.1364/OE.17.007893View ArticleGoogle Scholar
- Dhara S, Giri PK: Enhanced UV photosensitivity from rapid thermal annealed vertically aligned ZnO nanowires. Nanoscale Res Lett 2011, 6: 504. 10.1186/1556-276X-6-504View ArticleGoogle Scholar
- Li C, Fang GJ, Liu NH, Li J, Liao L, Su FH, Li GH, Wu XG, Zhao XZ: Structural, photoluminescence, and field emission properties of vertically well-aligned ZnO nanorod arrays. J Phys Chem C 2007, 111: 12566. 10.1021/jp0737808View ArticleGoogle Scholar
- Park JY, Choi SW, Kim SS: Fabrication of a highly sensitive chemical sensor based on ZnO nanorod arrays. Nanoscale Res Lett 2010, 5: 353. 10.1007/s11671-009-9487-3View ArticleGoogle Scholar
- Baxter JB, Aydil ES: Nanowire-based dye-sensitized solar cells. Appl Phys Lett 2009, 86: 053114.View ArticleGoogle Scholar
- Coey JMD, Venkatesan M, Fitzgerald CB: Donor impurity band exchange in dilute ferromagnetic oxides. Nature Mater 2005, 4: 173. 10.1038/nmat1310View ArticleGoogle Scholar
- Liu C, Yun F, Morkoc H: Ferromagnetism of ZnO and GaN: a review. J Mater Sci Mater Electron 2005, 16: 555. 10.1007/s10854-005-3232-1View ArticleGoogle Scholar
- Mishra DK, Kumar P, Sharma MK, Das J, Singh SK, Roul BK, Varma S, Chatterjee R, Srinivasu VV, Kanjilal D: Ferromagnetism in ZnO single crystal. Phys B: Condens Matter 2010, 405: 2659. 10.1016/j.physb.2010.03.047View ArticleGoogle Scholar
- Xu H, Rosa AL, Frauenheim T, Zhang RQ: N-doped ZnO nanowires: surface segregation, the effect of hydrogen passivation and applications in spintronics. Phys Status Solidi (b) 2010, 247: 2195. 10.1002/pssb.201046059View ArticleGoogle Scholar
- Ahmad M, Zhu J: ZnO based advanced functional nanostructures: synthesis, properties and applications. J Mater Chem 2011, 21: 599. 10.1039/c0jm01645dView ArticleGoogle Scholar
- Pearton SJ, Norton DP, Ivill MP, Hebard AF, Zavada JM, Chen WM, Buyanova IA: ZnO doped with transition metal ions. IEEE Trans Electron Devices 2007, 54: 1040.View ArticleGoogle Scholar
- Seshadri R: Zinc oxide-based diluted magnetic semiconductors. Curr Opin Solid State Mater Sci 2006, 9: 1.View ArticleGoogle Scholar
- Xu C, Chun J, Kim D, Chon B, Joo T: Structural characterization and low temperature growth of ferromagnetic Bi-Cu codoped ZnO bicrystal nanowires. Appl Phys Lett 2007, 91: 153104. 10.1063/1.2791005View ArticleGoogle Scholar
- Yi JB, Lim CC, Xing GZ, Fan HM, Van LH, Huang SL, Yang KS, Huang XL, Qin XB, Wang BY, Wu T, Wang L, Zhang HT, Gao XY, Liu T, Wee ATS, Feng YP, Ding J: Ferromagnetism in dilute magnetic semiconductors through defect engineering: Li-doped ZnO. Phys Rev Lett 2010, 104: 137201.View ArticleGoogle Scholar
- Sugunan A, Warad HC, Boman M, Dutta J: Zinc oxide nanowires in chemical bath on seeded substrates: role of hexamine. J Sol–gel Sci Tech 2006, 39: 49. 10.1007/s10971-006-6969-yView ArticleGoogle Scholar
- Jung YI, Noh BY, Lee YS, Baek SH, Kim JH, Park IK: Visible emission from Ce-doped ZnO nanorods grown by hydrothermal method without a post thermal annealing process. Nanoscale Res Lett 2012, 7: 43. 10.1186/1556-276X-7-43View ArticleGoogle Scholar
- Selim FA, Weber MH, Solodovnikov D, Lynn KG: Nature of native defects in ZnO. Phys Rev Lett 2007, 99: 085502.View ArticleGoogle Scholar
- Zhao X, Shen D, Zhanf D, Li J, Wang X, Fan X: ZnO nanorod arrays grown under different pressures and their photoluminescence properties. J Lumin 2007, 122–123: 766.Google Scholar
- Li D, Leung YH, Djurisic AB, Liu ZT, Xie MH, Shi SL, Xu SJ, Chan WK: Different origins of visible luminescence in ZnO nanostructures fabricated by the chemical and evaporation methods. Appl Phys Lett 2004, 85: 1601. 10.1063/1.1786375View ArticleGoogle Scholar
- Li GR, Lu XH, Wang ZL, Yu XL, Tong YX: Controllable electrochemical synthesis of La3+/ZnO hierarchical nanostructures and their optical and magnetic properties. Electrochim Acta 2010, 55: 3687. 10.1016/j.electacta.2010.01.111View ArticleGoogle Scholar
- Liu W, Li W, Hu Z, Tang Z, Tang X: Effect of oxygen defects on ferromagnetic of undoped ZnO. J Appl Phys 2011, 110: 013901. 10.1063/1.3601107View ArticleGoogle Scholar
- Cheng HM, Hsu HC, Chen SL, Wu WT, Kao CC, Lin LJ, Hsieh WF: Efficient UV photoluminescence from monodispersed secondary ZnO colloidal spheres synthesized by sol–gel method. J Crystal Growth 2005, 277: 192. 10.1016/j.jcrysgro.2004.12.133View ArticleGoogle Scholar
- Kenanakis G, Androulidaki M, Vernardou D, Katsarakis N, Koudoumas E: Photoluminescence study of ZnO structures grown by aqueous chemical growth. Thin Solid Films 2011, 520: 1353. 10.1016/j.tsf.2011.04.123View ArticleGoogle Scholar
- Zhao Y, Jiang Y: Investigation of room temperature UV emission of ZnO films with different defect densities induced by laser irradiation. Spectrochim Acta A 2010, 76: 336. 10.1016/j.saa.2010.03.015View ArticleGoogle Scholar
- Yatsui T, Shimizu T, Yamamoto Y, Kourogi M, Ohtsu M, Lee GH: Near-field ultraviolet photoluminescence spectroscopy for evaluating the crystallinity of polycrystalline zinc oxide. Appl Phys Lett 2001, 79: 2369. 10.1063/1.1410357View ArticleGoogle Scholar
- McCluskey MD, Jokela SJ: Defects in ZnO. J Appl Phy 2009, 106: 071101. 10.1063/1.3216464View ArticleGoogle Scholar
- Alim KA, Fonoberov VA, Shamsa M, Balandina AA: Micro-Raman investigation of optical phonons in ZnO nanocrystals. J Appl Phys 2005, 97: 124313. 10.1063/1.1944222View ArticleGoogle Scholar
- Calleja JM, Cardona M: Resonant Raman scattering in ZnO. Phys Rev B 1977, 16: 3753. 10.1103/PhysRevB.16.3753View ArticleGoogle Scholar
- Rajalakshmi M, Arora AK, Bendre BS, Shailaja M: Optical phonon confinement in zinc oxide nanoparticles. J Appl Phys 2000, 87: 2445. 10.1063/1.372199View ArticleGoogle Scholar
- Sharma SK, Exarhos GJ: Raman spectroscopic investigation of ZnO and doped ZnO films, nanoparticles and bulk material at ambient and high pressures. Solid State Phenom 1997, 55: 32.View ArticleGoogle Scholar
- Wang X, Li Q, Liu Z, Zhang J, Liu Z, Wang R: Low-temperature growth and properties of ZnO nanowires. Appl Phys Lett 2004, 84: 4941. 10.1063/1.1760594View ArticleGoogle Scholar
- Wu JJ, Liu SC: Catalyst-free growth and characterization of ZnO nanorods. J Phys Chem B 2002, 106: 9546. 10.1021/jp025969jView ArticleGoogle Scholar
- Iqbal J, Liu X, Zhu H, Pan C, Zhang Y, Yu D, Yu R: Trapping of Ce electrons in band gap and room temperature ferromagnetism of Ce4+ doped nanowires. J Appl Phys 2009, 106: 083515. 10.1063/1.3245325View ArticleGoogle Scholar
- Coey JMD, Venkatesan M, Fitzgerald CB: Donor impurity band exchange in dilute ferromagnetic oxides. Nat Mater 2005, 4: 173. 10.1038/nmat1310View 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 cited.