Short communicationFabrication and spectroscopic investigation of sandwich-like ZnO:rGO:ZnO:rGO:ZnO structure by layer-by-layer approach
Graphical abstract
Introduction
Transparent conducting materials (TCMs) have attracted enormous interest in recent years across the globe due to their potential use in optoelectronic devices [1], photovoltaics [2], sensors [3], and novel display devices [4], [5]. The prime requirement for the TCMs is more than 90% of optical transparency in the visible regime and very low resistivity of 10-4 Ω.cm [6]. Tin-doped indium oxide (ITO) materials have been fulfilled with these prime requirements and it’s been widely used in the optoelectronic industries. However, due to its brittle in nature, high production cost and future unavailability, there is an extensive demand for the search of novel materials and fabrication technologies [7], [8]. The doped zinc oxide (ZnO) materials are widely used as TCMs and to improve the conductivity of ZnO, various materials have been introduced which include, doping of group III elements (Al and Ga) [9], [10] silver:ZnO nanocomposites [11] and introduction of two-dimensional (2D) materials [12], [13].
Among various two-dimensional (2D) structured materials, graphene has drawn significant consideration because of its extraordinary electrical conductivity (2x105 cm2V-1s−1) [14], thermal (5000 W.m-1K−1) [15], mechanical properties [16] and also exhibits high optical transmittance in the visible regime [17]. Wu et al [18] have synthesized sandwich-like graphene/ZnO (5 nm diameter) nanocomposite materials and identified that the stacking of graphene sheets could be well controlled through decoration of densely packed ZnO nanostructured particles. Li et al [19] have fabricated 3D sandwich-structured ZnO/rGO/ZnO nanocomposites using rapid thermal reduction routes. The sandwich structured materials exhibited maximum capacitance (275F g−1) with anomalous rate capability and cycling stability in comparison with their parent materials. Teh et al [20] fabricated the rGO-hybridized ZnO sandwich thin films using facile electrodeposition route through layer-by-layer technique. Results revealed that the ordering of layer is highly influenced in the charge transfer properties which ultimately improves the efficiency of photocatalytic electrochemical water splitting. Boukhoubza et al [21] have prepared the sandwich structure of GO/ZnO nanorods/GO and evaluated their emission characteristics. The results showed that the decoration of GO layers leads quenching of PL emission intensity attributed to the charge transfer process. To date, a limited studies have been performed for the fabrication and understanding of ZnO/rGO sandwich structures and yet to be explored in details.
Considering the importance of ZnO/rGO sandwich structures in various energy and opto-electronics industries, in this report a simple layer-by-layer approach using spin coating technique has been adopted to prepare ZnO:rGO:ZnO:rGO:ZnO and rGO:ZnO:rGO:ZnO:rGO sandwich structures. The effect of layer ordering of sandwich structures on the microstructural and optical emission characteristics was investigated. Furthermore, the optical transparency of sandwich structures is analysed in a detailed manner.
Section snippets
Experimental
All the required chemicals such as zinc acetate dihydrate (Zn(CH3COO).2H2O), monoethanalamine (C2H7NO), and 2-methoxyethanol (C3H8O2) are analytical grade (Sigma-Aldrich) and used as received.
Results and discussion
The XRD patterns of pure ZnO, sandwich structures of various combinations of the layer ordering of ZnO and rGO are presented in Fig. 2. The peaks located at an angle (2θ) of 31.58, 34.33, 36.26, 47.50, 56.49, 62.57, 67.86 and 72.52° are corresponding to (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (1 1 2) and (0 0 4), respectively which confirmed the fabricated ZnO are in the hexagonal wurtzite structure.
There is no signature of impurities of Zn and graphite precursors identified in the recorded
Conclusion
In conclusion, ZnO:rGO:ZnO:rGO:ZnO and rGO:ZnO:rGO:ZnO:rGO sandwich structures were successfully fabricated through layer-by-layer approach using spin coating technique. The formation, various microstructural parameters, optical transparency, and emission characteristics were analysed by the different spectroscopic techniques. The unit cell volume, bond length, micro-strain and residual stress were considerable altered for the sandwich structures. The significant improvement of electronic
CRediT authorship contribution statement
Thangaraj Pandiyarajan: Conceptualization, Methodology, Investigation, Writing – original draft. Ramalinga Viswanathan Mangalaraja: Supervision, Writing – review & editing. Balasubramanian Karthikeyan: Supervision. Arunachalam Arulraj: Resources. M.A. Gracia-Pinilla: Investigation, Resources.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
T Pandiyarajan gratefully acknowledges the Indian Institute of Information Technology Design and Manufacturing Kurnool for sanctioning Research Seed Money for financial assistance.
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