Structural and optical properties of
Structural and optical properties of Mg-doped ZnO nanowires
synthesized by electrodeposition
Fang Xuan a, Li Jin Hua*a, Zhao Dong Xu b, Wang Xiao Hua a, Wei Zhi Peng a, Jin Guang Yong a
a School of Science, Changchun University of Science and Technology, Changchun, China, 130022;
b Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and
Physics, Chinese Academy of Sciences, Changchun, China, 130022
ABSTRACT
In this paper, we report that Mg-doped ZnO nanowires were synthesized on ITO substrate by electrodeposition using a mixture of an aqueous solution of zinc acetate, hexamethylenetetramine, and magnesium acetate for the first time. SEM, EDS and XRD were used to investigate the structural properties and chemical composition. and PL spectrum was measured for optical characterism. Compared with undoped ZnO nanowires, the band edge emission shifts from 380 nm to 375 nm.
Keywords: ZnO nanowires; Mg doped; optical properties; electrodeposition
1. INTRODUCTION
In recent years, one-dimensional (1D) nanostructures have been studied extensively for their unique properties and potential applications in nanodevices such as high surface-to-volume ratio, high crystalline quality, and quantum confinement effects, which are suitable for various electronics and optoelectronics applications[1]. Among these nanostructures, ZnO have drawn considerable interests in ultraviolet light-emitting material and photodetectors etc[2,3] due to their wide bandgap (3.37eV at room temperature) and a large exciton binding energy (60meV). For practical device applications, the realization of band-gap engineering in the ZnO system is of great importance[4]. The band-gap energy of ZnO can be widened by the incorporation of magnesium[4], and they have many application in photoelectron devices[5,6]. By now, several approaches for the fabrication of ZnMgO 1D nanostructures have been reported, such as MBE[6], MOCVD[7], PLD [8]. However, those are expensive and energy-consuming processes since they are operated under extreme conditions. Nevertheless, a solution technique such as electrodeposition not only appears as a low temperature alternative, but it is also well suited for cheap large-scale production[9]. And for Mg-doped ZnO nanowires synthesized by electrodeposition method, there were no reports can be found to the best of our knowledge.
In this paper, we report that Mg-doped ZnO nanowires can be synthesized on ITO substrate by a very simple electrodeposition under mild conditions (90°C) for the first time. The structure and optical properties of the synthesized Mg-doped ZnO nanowires were investigated.
2. EXPERIMENTAL
Mg-doped ZnO nanorods were synthesized in a typical three electrode electrochemical cell[9], the electrolyte was an aqueous solution of zinc acetate, hexamethylenetetramine, and required amount magnesium acetate. All the reactants were dissolved in de-ionized water and then heated to 90°C to grow the doped nanowires. A negative potential of ?1 V is relative to a reference electrode. At the end of the growth time (typically 1h), the sample was taken out of the solution and rinsed with de-ionized water, and dried in air at 60°C for several hours.
The sample was investigated by field-emission scanning electron microscopy (FESEM, Hitachis-4800), energy-dispersive X-ray spectroscopy (EDS, GENE SIS 2000 XMS 60S, EDAX, Inc.) attached to the SEM, and a D/max-RA X-ray spectrometer (Rigaku). Photoluminescence (PL) measurements were performed using a He–Cd laser line of 325 nm as the excitation source.
*lijinhua2000@https://www.360docs.net/doc/705328076.html,; phone 137********
International Symposium on Photoelectronic Detection and Imaging 2009: Material and Device Technology for Sensors,
edited by Xu-yuan Chen, Yue-lin Wang, Zhi-ping Zhou, Qing-kang Wang, Proc. of SPIE Vol. 7381, 73810P · ? 2009 SPIE
CCC code: 0277-786X/09/$18 · doi: 10.1117/12.829951
3. RESULTS AND DISCUSSION
The morphologies of the as-grown Mg-doped ZnO nanowires was investigated using FESEM. As shown in Fig.1(a), the nanowires with diameter around 100–200 nm and length about a few micrometers. The composition analysis of the nanowires is shown in Fig.1(b). Besides the peaks from ITO substrate (Si, Ca, Sn, In), the peak from Zn, O and Mg can also be observed in the EDX spectrum, the intensity ratios among the Zn, O and Mg peaks suggest that the Mg content in the nanowires was approximately 7 atom%, revealing the possibility of incorporation of magnesium entering into the ZnO nanowires.
Fig.1.(a) SEM image of magnesium doped ZnO nanowires (b)EDX spetrum of magnesium doped ZnO nanowires.
In addition, in order to confirm Mg whether entered into the crystal lattice, we used XRD to measure the structure change of samples. Fig.2 shows the X-ray diffraction (XRD) pattern of Mg-doped ZnO nanowires and undoped ZnO nanowires. For each sample, all the observed diffraction peaks can be indexed to a ZnO wurtzite structure. As compared to the undoped ZnO nanowires, the Mg doping in ZnO causes significant change in lattice constants, resulting in measurable higher angle shift, which is possibly related to the smaller ionic radius of Mg2+ than Zn2+. Just like the results
in Mg-doped ZnO nanorods[10]. So XRD results show that Mg has successfully entered the ZnO crystal lattice, which is in agreement with the EDX analysis.
Fig.2. XRD pattern of the Mg-doped ZnO nanowires and undoped ZnO nanowires.
Figure.3. displays the room-temperature photoluminescence spectra taken on both Mg-doped and undoped ZnO nanowires. Undoped ZnO nanowires have a peak at 380 nm due to the near-band-edge emission[11]. The band around 510 nm is the emission associated with the oxygen vacancies or defects in ZnO[11]. The Mg-doped ZnO nanowires exhibit an emission peak at 375nm, the authors believe that such a blue shift is related to the Mg substituted Zn which caused the band gap became larger. And compared to undoped ZnO nanowires, the deep level emission was disappeared, which also indicated the Mg-doped ZnO nanowires exhibit better emission properties than undoped ZnO nanowires.
Fig.3. PL spetrum of the Mg-doped ZnO nanowires at room temperature.
4. SUMMARY
In summary, Mg-doped ZnO nanowires were synthesized on ITO substrate by electrodeposition for the first time. The results of EDS and XRD confirmed Mg has successfully entered the ZnO crystal lattice. Room temperature PL spetrum indicated that the band gap of ZnO nanowires became larger, and the band edge emission shifts from 380 to 375. Furthermore, the Mg-doped ZnO nanowires exhibit better emission properties than undoped ZnO nanowires.
ACKNOWLEDGEMENT
This work is supported by the National Natural Science Foundation of China (10647105, 60670659), Key Project of the National Natural Science Foundation of China under Grant Nos. 60336020 and 50532050, the “973” program under Grant No.2006CB604906, the Innovation Project of Chinese Academy of Sciences, the National Natural Science Foundation of China under Grant Nos. 60429403, 60506014, 50402016, 10674133, the Project of Science Development Planing of Jilin Province (20070519), and Program for New Century Excellent Talents in University (NCET-07-022). We thank Mr. Haifeng ZHAO, the technician of Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, for the assistance in using the S-4800 Scanning Electron Microscope.
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