Well-integrated ZnO nanorod arrays on conductive textiles by electrochemical synthesis and their physical properties
© Ko et al.; licensee Springer. 2013
Received: 27 November 2012
Accepted: 4 January 2013
Published: 15 January 2013
We reported well-integrated zinc oxide (ZnO) nanorod arrays (NRAs) on conductive textiles (CTs) and their structural and optical properties. The integrated ZnO NRAs were synthesized by cathodic electrochemical deposition on the ZnO seed layer-coated CT substrate in ultrasonic bath. The ZnO NRAs were regularly and densely grown as well as vertically aligned on the overall surface of CT substrate, in comparison with the grown ZnO NRAs without ZnO seed layer or ultrasonication. Additionally, their morphologies and sizes can be efficiently controlled by changing the external cathodic voltage between the ZnO seed-coated CT substrate and the counter electrode. At an external cathodic voltage of −2 V, the photoluminescence property of ZnO NRAs was optimized with good crystallinity and high density.
Vertically aligned one-dimensional (1D) zinc oxide (ZnO) nanostructures, such as nanorod and nanowire arrays, have attracted much interest in various application fields including field-emission devices, light-emitting diodes, piezoelectric devices, dye-sensitized solar cells, chemical sensors, and photodetectors due to their superior structural and optical properties compared to the bulk structure [1–7]. Over the past decade, there have been many efforts for controlling the structural and morphological properties of the 1D ZnO nanostructures with high density and uniformity because their size, shape, distribution, and crystallinity are closely related to the physical properties [8–10]. Furthermore, the hierarchical architectures built by the 1D ZnO nanostructures with 2D or 3D templates, which look like flowers or urchins, have potentially exhibited the improvements of device performance due to the highly extended surface area and density [11–14]. Nowadays, some vigorous attempts begin to be focused on the growth and deposition of the 1D ZnO nanostructures on various functional material substrates, for example, indium tin oxide-coated polyethylene terephthalate (i.e., ITO/PET) films, metal foils, graphenes, and cellulose fibers, thus leading to the merits of flexible and bendable feasibility with light weight and low cost [15–18].
On the other hand, the fabrication technique of conductive textiles (CTs) has been considerably developed by utilizing an electroless metallization of polymer fibers, and thus they have been used for electromagnetic interference shielding fabrics and flexible electrodes [19, 20]. In addition, the CTs can be a promising candidate as substrate for integrating the 1D ZnO nanostructures by employing the electrochemical deposition (ED) method. When electrons are supplied into the conductive surface in growth solution, ZnO nanorods can be readily synthesized and controlled at a low temperature by varying the external cathodic voltage [15, 21]. Therefore, the ED process with CT substrate can be a powerful and convenient fabrication method for preparing the vertically aligned 1D ZnO nanostructures on a conductive and flexible substrate. In this paper, we synthesized and controlled the integrated ZnO nanorod arrays (NRAs) on nickel (Ni)-coated PET fiber CTs by ED method with different external cathodic voltages. For more regular and dense ZnO NRAs, the CTs were coated by the ZnO seed solution, and the samples were treated by ultrasonic agitation during ED process.
All chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA), which were of analytical grade. To synthesize the ZnO NRAs on CT substrates, we used the commercially available CT substrates which consisted of woven Ni-plated PET (i.e., Ni/PET) fibers. For preparing the working substrate, the CT substrate of 3 × 3 cm2 was cleaned by ethanol and deionized (DI) water in ultrasonic bath for 10 min, respectively, at room temperature. The seed solution was made by dissolving the 10 mM of zinc acetate dehydrate (Zn(CH3COO)2 2H2O) in 50 ml of ethanol and by adding 1.5 wt.% of sodium dodecyl sulfate solution (CH3(CH2)11OSO3Na). After that, the CF substrates were dipped into the seed solution and pulled up slowly. To achieve good adhesion between the coated seed layer and the surface of CT, the samples were placed in the oven at 130°C for 2 h. Meanwhile, the aqueous growth solution was prepared by dissolving the 10 mM of zinc nitrate hexahydrate (Zn(NO3)2 6H2O) and 10 mM of hexamethylenetetramine ((CH2)6 N4) in 900 ml of DI water at 74 to 76°C under magnetic stirring. For growing the ZnO NRAs via the ED process, we used a simple two-electrode system containing the working electrode (i.e., deposited sample) and counter electrode (i.e., platinum mesh) since it is convenient and cost-effective for the synthesis of metal oxides nanostructures [22, 23]. For providing reliable information on the growth condition in ED process, the time-dependent applied current densities were recorded at different external cathodic voltages. In order to investigate the effect of external cathodic voltage on the growth property of ZnO NRAs, the samples were fabricated at various cathodic voltages from −1.6 to −2.8 V for 1 h. Herein, the pH value of growth solution was measured in the range of approximately 6.25 to 6.5 during the ED process. The morphologies and structural properties were observed by using a field-emission scanning electron microscope (FE-SEM; LEO SUPRA 55, Carl Zeiss, Reutlingen, Germany) and a transmission electron microscope (TEM; JEM 200CX, JEOL, Tokyo, Japan). The crystallinity and optical property were analyzed by the X-ray diffraction (XRD; M18XHF-SRA, Mac Science Ltd., Yokohama, Japan) patterns and the photoluminescence (PL; RPM2000, Accent Optical Technologies, York, UK) spectra, respectively.
Results and discussion
The ZnO NRAs were successfully integrated on the CT substrate (i.e., woven by Ni/PET fibers) by the ED process using the seed layer and ultrasonic agitation under a proper external cathodic voltage of −2 V for 1 h. The sizes/heights of ZnO NRAs were distributed to be approximately 65 to 80 nm/600 to 800 nm, and they could be clearly coated over the whole surface of the CT substrate with the seed layer and ultrasonic agitation. In a comparative investigation, it is clearly observed that the seed layer and ultrasonic agitation played key roles in providing a uniform organization of the ZnO NRAs with good nuclei sites as well as removing the adhesive ZnO microrods. Additionally, the well-integrated ZnO NRAs exhibited a narrow and strong PL NBE emission with good crystallinity. This optimal ED process for the well-integrated ZnO NRAs on CT substrates can be an essential growth technique for producing flexible and wearable functional materials in ZnO-based optoelectronic and electrochemical devices.
This research was supported by the basic science research program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (no. 2011-0026393).
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