Materials science communicationZnO nanorods/polyaniline heterojunctions for low-power flexible light sensors
Graphical abstract
Introduction
Flexible sensors are playing an increasingly paramount role in optoelectronics applications [1]. While the most sizably voluminous market is currently for glucose sensors utilized by diabetics, other types of flexible sensors are emerging [1]. IDTechEx forecasts that the market for flexible sensors will have incremented by more than $1 billion by 2020 [2]. To this end, several types of flexible polymeric materials, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), are currently considered due to their exceptional dielectric properties, corrosion resistance, high processing temperature between 196 and 260 C, low coefficient of friction, and low cost among other credentials. In particular, PET is more advantageous over indium-doped tin oxide (ITO) and fluorine-doped tin oxide (FTO) due to its high transparency, good flexibility, availability on industrial scale, and low cost [3].
On the other hand, ZnO nanorods have recently attracted consequential attention due to their unique shape and structure resulting in remarkable piezoelectric, magnetic, and optoelectronic properties. Specifically, the high optical gain of ZnO [4] makes it the material of focus in optoelectronics and sensing applications. However, the difficulty of doping ZnO to p-type polarity has led the researchers to seek to create heterojunctions with other p-type semiconductors to enable the use of ZnO in a plethora of electronic devices [1]. In particular, the combination of ZnO with polymers is a current hot research focus [1]. In this regard, most of ZnO NRs/polymer-based heterostructures are synthesized through surface coating of the polymer layer, with very limited reports on the direct growth of ZnO NRs on conducting polymeric substrates. To this end, aqueous chemical growth method has been greatly employed to assemble ZnO nanorods on a variety of substrates including amorphous, polycrystalline, single crystalline, and flexible substrates [2], [3], [4], [5], [6].
Herein, we report the successful fabrication of high quality, vertically aligned ZnO nanorods/polyaniline heterojunctions on PET flexible substrates and investigate their applicability as flexible light sensors. FESEM, XRD, PL and Raman characteristics of the fabricated heterojunctions are discussed.
Section snippets
Materials and methods
PET substrates were cleaned using 2-propanol and acetone to remove any contamination on the surface. Polyaniline emeraldine salt powder (Sigma Aldrich) was dissolved in formic acid under stirring for 30 min. Then, thin PAni films were fabricated by coating polyaniline solution onto the PET substrates, and kept in air for 1 h at room temperature. In the second stage, a radio frequency (RF) magnetron system with a ZnO target (99.999% purity) was used to deposit ZnO seed layer onto the PAni thin
Results and discussion
Fig. 2 shows the morphology of the fabricated ZnO nanorods grown on the ZnO seed layer/PAni substrates. Vertically oriented, high-density, hexagonal ZnO nanorods with diameters ranging from 73 nm to 87 nm and lengths of 1.4 ± 0.1 μm were successfully obtained. No delimitation was observed, highlighting the importance of the ZnO seed layer. In order to grow the best ZnO (NRs) by chemical bath deposition method, ZnO seeds were needed as nuclei sites for the growth of the ZnO (NRs) [7], [8], [9].
Conclusion
Low cost, high quality ZnO nanorods were grown on p-type Anipolymeric films via chemical bath deposition and coating methods. Phase analysis studies showed that ZnO nanorods/PAni exhibited a strong (002) diffraction peak, confirming the preferential growth along the c-axis. The high PL intensity of the peak appeared in the UV region revealed the high quality of ZnO NRs on PAni, as also confirmed by Raman spectroscopy. The ZnO NRs/PAni-based photodetectors offered excellent stability over time.
Acknowledgments
The authors would like to thank the Nano-Optoelectronics Research and Technology (N.O.R.) of the School of Physics, Universiti Sains Malaysia.
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2022, PolymerCitation Excerpt :Significant reasons behind the importance of the mentioned parameters are their effect on the production, non-recombination, movement through junction, and external circuit of the generated carriers. Since, the preparation of the PZU and ZPU is dependent on the used synthesis and deposition methods with mainly spontaneous processes; hence the formation of identical surface morphology of the layers is to be expected, unless the synthesis and deposition conditions change [3,10,15,16,36,37,44]. Therefore, the test results of the same prepared samples in the six months are evidence of the stable behavior of the organized layers by the mentioned synthesis and deposition methods.
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Permanent address: Polymer Research Center, University of Basra, Iraq.