Synthesis and characterization of twinned flower–like ZnO structures grown by hydrothermal methods
Introduction
Owing to its large direct band gap of 3.37 eV and high exciton binding energy of 60 meV [1], Zinc oxide (ZnO) is thought to be a promising material for applications in the fields of optoelectric and photovoltaic devices [2]. Despite the difficulties faced by thin film studies, growth and applications of ZnO nano- and micro- structures become a promising research field, because of the high quality and substrate universality [3], [4]. Different methods have been used to grow the micro- and nano-sized ZnO structures, which includes the chemical vapor deposition (CVD) [5], hydrothermal method [6], [7], pulse laser deposition (PLD) [8], thermal evaporation [9], etc. For its controllable morphology, lesser material cost, lower growth temperature and high product yields, hydrothermal method is widely applied to form the ZnO with different morphologies [10], [11], [12], which prompt the research of ZnO in nano- and micro- scales. In this paper, we present low-temperature growth of twinned flower-like structures of ZnO. The size of the synthesized ZnO is in the micrometer scale, while the size of flakes is in the nanometer scale, which ensure the high intensity of near bandgap emissions. XRD and SEM results show mixed hexagonal structures of synthesized ZnO structures. The cathodoluminescence (CL) spectra on a single twinned flower-like structure shows an excellent optical property.
Section snippets
Experimental procedure
ZnO samples were fabricated by one-step CTAB (Cetyltrimethyl Ammonium Bromide)-assisted hydrothermal method. All reagents were analytic grade and used without further purification. 0.60 g hexamethylene tetramine and 0.90 g Zn(Ac)2·2H2O were dissolved in ethanol solution at room temperature for the growth of ZnO. The ethanol solution was formed by adding ethanol into distilled water with the ethanol volume fraction of 0.85. 0.9 g CTAB was added into the solution by stirring at room temperature to
Results and discussion
Fig. 1(a) shows the XRD patterns of the as-grown ZnO samples. The pattern consists of 11 diffraction peaks and can be indexed to the wurtzite hexagonal structure of ZnO (JCPDS no. 75-0576 and 36-1451). Data of the standard JCPDS cards are also shown as a reference in the inset of figure. From the pattern, we can conclude that the as-grown sample is pure ZnO with hexagonal structures. However, some discussions must be made on the results. As we can see from the insets, standard reference data of
Conclusion
In summary, twinned flower-like ZnO structure was successfully synthesized by CTAB assisted hydrothermal method at a low-temperature. Temperature-dependent PL results indicate that the main emission peak is related to the recombination of the bound exciton recombination of the acceptor, which shows a good crystal quality of samples. Although the PL and area CL spectra give the defect-related emission in visible emission range, the CL spectra measured on a single twinned flower-like ZnO
Acknowledgment
This work is supported by National Natural Science Foundation of China (Grant no: 11174241), foundations from Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (Grant number: 12CS03). Parts of experimental tests have been done at Nanofabrication Facility and Platform for Characterization & Test, SINANO.
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