Assembling SnO Nanosheets into Microhydrangeas: Gas Phase Synthesis and Their Optical Property

www.nmletters.org Assembling SnO Nanosheets into Microhydrangeas: Gas Phase Synthesis and Their Optical Property Zhenglin Zhang1,2 , Jing Wang1 , Zhou Yu1 , Fengyu Qu1 , Xiang Wu1,2,∗ (Received 25 September 2012; accepted 4 November 2012; published online 10 November 2012.) Abstract: Large scale SnO microhydrangeas are obtained successfully through thermally evaporating of SnO2 powder wrapped by a filter paper at 1050℃ and using gold coated Si wafer as the substrate. The as-obtained SnO microhydrangeas are consisted of many thin nanosheets with the thicknesses of 30-60 nm and the diameters of 500-600 nm. A vapor-liquid-solid (VLS) growth mechanism for the as-synthesized SnO microhydrangeas was proposed based on experimental results. Photoluminescence spectrum (PL) shows that there is a strong sharp ultraviolet emission peak at 390 nm, revealing that these three-dimensional SnO microhydrangeas may have potential applications in optoelectronic fields. Keywords: SnO; microhydrangeas; Photoluminescence; VLS Citation: Zhenglin Zhang, Jing Wang, Zhou Yu, Fengyu Qu and Xiang Wu, “Assembling SnO Nanosheets into Microhydrangeas: Gas Phase Synthesis and Their Optical Property”, Nano-Micro Lett. 4 (4), 215-219 (2012). http://dx.doi.org/10.3786/nml.v4i4.p215-219 To design rationally the desired nanostructures with the controlled size and shape is a key step toward the future nanotechnological applications. SnO and SnO2 are two important wide band gap semiconductors. Tin dioxide (SnO2 , Eg = 3.62 eV, at 300 K) has been widely studied due to its promising applications in gas sensors [1-3], solar cells [4], optical devices [5-6], lithium ion batteries [7-8], and photocatalysts [9-11]. In contrast, the investigation of SnO materials has fallen behind, perhaps because it decomposes easily at elevated temperature and the divalent tin ion can be oxidized to the tetravalent one. However, as is known, SnO is technologically important as a p-type semiconductor, which is a key functional material that has been widely studied for various potential applications [12]. In the past few decades, many SnO crystals with uniform nanostructures are obtained including sheets [13], wires [14], diskettes [15], and nanoribbons [16]. Those materials have been widely explored for rechargeable lithium batteries [17-18], and storage of solar energy [19]. However, synthesis of hydrangealike SnO structure with thin nanosheet assemblies is rarely reported [20]. In the present work, we present a simply Thermally vapor deposition approach for the controlled growth of SnO microhydrangeas. Morphologies and optical property of the as-synthesized products are investigated by different characterization techniques. The growth mechanism was also proposed. SnO microhydrangeas were synthesized using a facile chemical vapor deposition (CVD) method in a conventional horizontal tube furnace (inner diameter 40 mm, length 70 cm, see Fig. 1(c)). The Si substrates were covered with a layer of Au film of about 5 nm. First, the substrates were immersed into acetone and ethanol in succession, washed ultrasonically for 15 minutes and 1 Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education and College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin, 150025, P. R. China 2 Key Laboratory of Colloid and Interface Chemistry, Ministry of Education and College of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, Shandong, P. R. China. *Corresponding author. E-mail: Nano-Micro Lett. 4 (4), 215-219 (2012)/ http://dx.doi.org/10.3786/nml.v4i4.p215-219 Nano-Micro Lett. 4 (4), 215-219 (2012)/ http://dx.doi.org/10.3786/nml.v4i4.p215-219 (a) (b) Tube furnace Gas Source Substrate (c) Fig. 1 (a-b) Digital photographs of the filter paper wrapped SnO2 power and the boat. (c) Schematic illustration of experimental setup to synthesize the SnO nanostructures. (a) (b) 60 nm 2 μm (c) (d) 101 100 nm 0 5 Energy (KeV) 10 20 30 40 50 2θ/(°) 211 202 Si 200 112 Sn O 002 Sn 110 Intensity (a.u.) Intensity (a.u.) Sn 60 70 Fig. 2 Morphology of the as-synthesized SnO microhydrangeas. (a-b) SEM images at different magnifications. (c) Energydispersive spectrum (EDS) recorded from SnO microhydrangeas. (d) XRD pattern of the as-obtained SnO nanostructures. kept at 10 Torr. Finally, the furnace was cooled down room temperature. The substrates were taken out from the tube. The as-synthesized products were characterized by X-ray diffraction instrument (Rigaku Dmax-rB, CuKα radiation, λ = 0.1542 nm, 40 KV, 100 mA), scanning electron microscope (SEM, Hitachi-4800), microRaman spectrometer (HR800) and Photoluminescence spectrum (HORIBA JY-Fluoro Max 4). Morphology of the as-synthesized product is characterized firstly by SEM. A typical low magnification SEM image is shown in Fig. 2(a), revealing large quan- rinsed with deionized water, then dried by a drier. The substrates were placed downstream, which are 21 cm away from the source material. 1 g SnO2 (99.98% purity) was tightly wrapped by a filter paper (Fig. 1(a)(b)), and was put into an alumina boat. Then, the boat was taken into the horizontal tube furnace. Subsequently, the whole system was evacuated for 30 min by a vacuum pump. The temperature was rapidly increased from room temperature up to 1050℃ and kept 1 h at this temperature. Carrier of argon flowed into the tube at the rate of 100 sccm, and the pressure was 216 Nano-Micro Lett. 4 (4), 215-219 (2012)/ http://dx.doi.org/10.3786/nml.v4i4.p215-219 small quantity of nanosheets were observed for 1 min. Adding time to 30 min (in Fig. 4(b)), it was found that large quantities of nanosheets with a relative smooth surfaces deposited on the substrate. However, it is not assembled to microhydrangeas. When increasing to 1 h at the temperature, many hydrangealike structures appeared, as shown in Fig. 4(c). tities of hydrangealike structures with average diameters of 2-3 μm. Figure 2(b) shows a high magnification SEM image of the as-synthesized products, which are consisted of some nanosheets with smooth surfaces with the average thicknesses of 60 nm. The energy dispersive X-ray spectrum (EDS) of the as-synthesized nanostructure is shown in Fig. 2(c), EDS quantitative analysis gives an average Sn/O ratio of 40.88:59.12 within the accuracy of the technique. The peaks for Sn and O are originated from the source material. Si element is from the substrate. Figure 2d shows XRD pattern of the assynthesized products. All of the diffraction peaks can be indexed to a tetragonal SnO structure (JCPDS Card No.06-0395), with lattice constants of a=3.796 Å and c=4.816 Å. The sharp and strong diffraction peaks indicate that the as-synthesized SnO hydrangealike nanostructures are highly crystalline. Raman spectrograph is utilized to further study the microstructure of the as-synthesized product. Figure 3 shows a Raman scattering spectrum of the asobtained hydrangealike microstructur (...truncated)