1Materials Science Laboratory, Physics Department, College of Science và Mathematics, Mindanao State University-Iligan Institute of Technology, A. Bonifacio Avenue, Tibanga, 9200 Iligan, Philippines


The influence of varying OH− ion concentration on the surface morphology of chemically deposited ZnO-SiO2 nanostructures on glass substrate was investigated. The morphological features, phase structure, và infrared characteristics were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), respectively. Results revealed that silica significantly changes the hexagonal morphology of bare ZnO rod lớn “pointed tips” when using low initial OH− precursor concentration. Increasing OH− ion concentration resulted in a “flower-like” formation of ZnO-SiO2 & a remarkable change from “pointed tips” lớn “hemispherical tips” at the vị trí cao nhất surface of the rods. The surface capping of SiO2 lớn ZnO leads khổng lồ the formation of these “hemispherical tips.” The infrared spectroscopic analysis showed the characteristics peaks of ZnO and SiO2 as well as the Si-O-Zn band which confirms the formation of ZnO-SiO2. Phase analysis manifested that the formed ZnO-SiO2 is of wurtzite structure. Furthermore, a possible growth mechanism is proposed based on the obtained results.

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1. Introduction

Zinc oxide (ZnO) is a widely known -type semiconductor that attracted research interest due khổng lồ its properties like wide energy band gap of 3.37 eV và high exciton binding energy of 60 meV <1> which makes it suitable for many applications like in solar cells <2>, photodetectors <3>, & gas sensors <4>. Another interesting aspect of ZnO growth is its ability lớn be engineered khổng lồ different structural features by changing some parameters during synthesis. Tailoring the morphology, shape, and size of ZnO could be a way of expanding its potential especially in solar cell & sensor technologies where reaction at the surface is very crucial. Works have been reported for controlling form size and shape of ZnO nanostructures lượt thích varying the initial zinc & hydroxyl ion concentrations <5, 6> và also by introducing silica (SiO2) lớn ZnO as a concept of composite material <7, 8>. With good mechanical resistance and high dielectric strength, SiO2 is likely lớn be an ideal component to lớn enhance the properties of ZnO. ZnO-SiO2 is seen to have significant potential application as an antibacterial coating <9>, luminescent material <10, 11>, photocatalyst <12>, và also as gas sensor <13> because of the good sensing capability of ZnO which could be enhanced more with the presence of SiO2 for kích cỡ and shape control that could lead to lớn better chemical activity at the surface. However, understanding the mechanism for the growth of ZnO-SiO2 nanostructures is still a formidable task particularly on controlling its surface morphology. Aside from these, most works related to ZnO synthesis use complex processes & sophisticated equipment lượt thích PLD <14>, CVD <15, 16>, và vapor phase transport process <17–19> among others which is not practical & economical in nature.

Recently, we reported preliminary investigations on the synthesis of ZnO-SiO2 both in powder form <20> and deposited on glass substrates <21> by using simple wet chemical deposition process. It is also worth mentioning that the SiO2 from rice husk ash, a naturally occurring material, was used as an alternative khổng lồ the expensive liquid tetraethyl orthosilicate (TEOS). We found out that SiO2 modifies the surface of ZnO from hexagonal into pointed tips and confirms the attachment of SiO2 to ZnO through FTIR spectroscopy. In this current contribution, the influence of initial OH− ion concentration on the surface morphology of ZnO-SiO2 is presented. Moreover, a proposed mechanism for the growth of ZnO-SiO2 on glass substrates is also presented based on the evolution of morphology of ZnO-SiO2 with varying initial OH− ion concentration. Results of this work would pave the way for the control of the morphology of the nanostructures & for its possible use as methane gas detector.

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2. Experimental Procedure2.1. Wet Chemical Deposition Process

ZnO-SiO2 nanostructures were synthesized through low temperature chemical deposition process using zinc sulphate (ZnSO4) và ammonium hydroxide (NH4OH). First, 0.03 M ZnSO4 aqueous solution & varied ammonium hydroxide (NH4OH) concentrations (1.0 M, 2.0 M, and 3.0 M) were prepared separately in a beaker. The ammonium hydroxide was then added dropwise lớn the ZnSO4 solution & magnetically stirred while subsequently placing the precleaned glass substrates. After 30 minutes’ stirring of the mixed precursors, 0.1 grams of laboratory (in-house) prepared amorphous silica powder was then added and then the solution was continuously stirred for 3 hours while maintaining the bath temperature at 70°C. After 3 hours of constant stirring and heating, the substrates were washed with distilled water in order khổng lồ remove loosely attached residues present và were allowed to dry at ambient room temperature. Table 1 shows the parameters considered for the synthesis of ZnO-SiO2 where fixed concentration of ZnSO4 was used at varying NH4OH concentrations. The amount of amorphous silica powder used was the same for all samples.