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Controllable growth of ZnO nanorod-carbon nanotube heterojunction arrays by low-temperature wet chemical bath deposition method for using in dye solar cell

F. Dehghan Nayeria, E. Asl Soleimania, S. Darbaria, J. Sabbaghzadehb, S. Mohajerzadeha
Tehran of University, IR

Keywords: ZnO NR-MWCNTarrays, chemical bath deposition, nanothorns

Abstract:

In this paper, we describe a cost-effective and efficient approach for the large-scale synthesis of heterojunctions between ZnO NRs and MWCNTs. Our work represents a new type of heterostructure with many benefits. The wet chemical base deposition (CBD) method have many advantages such as scalability, low-cost, environmental friendliness and easy of handling. Additionally, wet chemical base deposition methods allow for a greater choice of substrates, including both inorganic and organic substrates, since solution phase reactions occur at relatively low temperatures and larg scales on each layer compared to those in other method. Fig.1 shows the schematic diagrams (a-c) and corresponding SEM images (d-f) that illustrate the growth process we propose for our heterostructure formation. The vertically aligned MWCT arrays were grown on ~10 nm Ni thin film deposited on the Si by using plasma enhanced chemical vapor deposition at 650˚C. (step 1, Fig.1 1a,c). Then, the MWCTs were coated by ZnO seed layer through the RF sputtering deposition process at room temperature. The as-formed nuclei deposit on CNT sites and act as sites for further nucleation leading to¬¬¬¬ the formation of clustered particles (step2). The aqueous solutions composed of zinc nitrate(Zn(NO3)2-6H2O, 98%) and hexamethylenetetramine (HMT)(C6H12N4, 99%) were used as a precursor source for the growth of ZnO NR. the length of the sprouts increases, producing ZnO nanothorns (step 3). Fig.2 shows the SEM images of ZnO NR-MWCNT array with precursor concentration vary from 6 mM to 24 mM. The growth temperature and time were 85˚C and 4h, respectively, Fig.2 shows that ZnO NR don’t formed on carbon nanotube when precursor concentration was 6 mM. The average diameter and lenght of ZnO NR increased 20 nm to 70 nm and 150nm to 800nm respectively when the precursor concentration increased. Fig.3 shows the SEM images of ZnO NR-MWCNT as a function of growth time from 4 h to 8 h. The precursor concentration and growth temperature were 12 mM and 80˚C, respectively. All the ZnO NR show hexagonal prism shape independent of the growth time. The average diameter and length of ZnO nanorods increased from ~20 nm to ~70 nm and from 150 nm to 800 nm, respectively. The growth temperature has a strong impact on the diameter. Fig. 4 shows the length of ZnO NR increased with the increase of growth temperature. Fig. 5 shows X-ray diffraction (XRD) profiles of the CNT-ZnO NR heterojunction arrays, respectively. the diffraction peak at 26.0˚ corresponded to d spacing of the (002) plane of graphite still exists in the XRD pattern of CNT-ZnO NR heterojunction arrays, which further indicates that CNT patterns are not destroyed. The other peak positions show good agreement with those of the zinc oxide with hexagonal wurtzite phase. In summary, ZnO NR arrays were self-assembled onto the surfaces of MWCNTs by a facile solution method at low temperature, forming ZnO NR -MWCNT heterojunction nanostructures. The ZnO NR surface density on CNTs could be easily controlled by manipulating time and temperature an precursor concentration solution
 
 
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