Developing high-sensitivity UV sensors based on ZnO nanorods grown on TiO2 seed layer films using solution immersion method

https://doi.org/10.1016/j.sna.2019.111827Get rights and content

Highlights

  • At the surface, the effective surface energy is lower, thus reduces the energy barriers and facilitating nucleation.

  • TiO2:ZnO nanorods thin film showed the highest intensity of absorbance values at UV and visible region compared to others.

  • The photoresponse of the TiO2:ZnO nanorods device was improved compared with the bare TiO2 and bare ZnO.

Abstract

TiO2:ZnO nanorods thin film has the great properties of packed ZnO nanorods with good crystallinity and improved UV absorption properties which are suitable for optoelectronic device applications. ZnO nanorods array was fabricated by using a seeding method with TiO2 as seed layer. As a result, well aligned of ZnO rods with good distribution can grow. Different samples of TiO2, ZnO and TiO2:ZnO nanorods thin film were used as based material in UV sensor devices. The responsivities of the sensors are 1.70 × 10−1A/W, 7.76 × 10−5 A/W and 2.22 × 10−7 A/W for TiO2:ZnO nanorods, TiO2 seed layer and ZnO rods based UV sensors respectively. Results indicate that the TiO2:ZnO nanorods UV sensor exhibits rapid and high response to UV light compared with TiO2 and ZnO sensor because of its small size of nanorods and seed layer acting as an absorbance assisted and capacitive layer on the glass surface.

Introduction

Recently, wide band gap semiconductors based ultraviolet (UV) sensor has been widely utilized compared to low band gap semiconductor like silicon and GaAs based UV sensors which has problem on lack of wave band sensitivity [1], fast degradation under UV illumination and withstand from cross-sensitivity with visible and near infrared radiations [2]. In a comparison to those devices, UV sensors based on wide band gap semiconductors are highly sensitive to UV light compared to visible and infrared light. Moreover, it is durable and stable when exposed to UV radiation attributed to their strong chemical bonds. Direct wide band gap semiconductor such as ZnO is a potentially strong UV sensing material as it has high UV photosensitivity. This strong sensing property is most important for good UV photodetection [3]. Besides that, UV sensor based on ZnO nanostructures provide high surface area that enables them to transport electrons rapidly and efficiently [4]. Narrow band gap semiconductors like Si or GaAs has widely used as sensing element in UV sensor development. However, those devices has problems on low sensitivity in the UV region [1], fast degradation under UV illumination and suffer from cross-sensitivity with visible and near infrared radiations [2]. Since those devices also respond to the visible and infrared light, filters are needed to cut off the radiation of long wavelength [5,6]. This problem leads to the higher fabrication cost. Thus, to avoid the use of filters and to achieve visible-blind detection, UV sensor based on wide band gap semiconductors have been studied. They are highly sensitive to UV light compared to visible and infrared light.

UV sensors based on ZnO nanostructures are also easy to fabricate and provide large surface area that enables them to transport electrons rapidly and efficiently. Thus, they demonstrate high responsivity and photo current gain [4,6]. Besides of these advantages, the performance of ZnO based UV sensors still slow due to longer photo response time [6] and the response cover region of the devices is still too broad to meet the requirement in some particular applications [5]. There are several factors that influence the performance of these devices such as the morphology, structure and dimension of ZnO nanostructures [7]. One of the efforts that lead to the surface modification of ZnO is by utilizing the catalytic seed layer. Typically, this seed layer is used in improving the performance of UV photoconductive sensor since it can provide continuous transport pathway for electron movement in the film. Thus, seed layer is often used in improving the performance of UV sensor [8]. Table 1 shows the sensing performances of previous works which used various ZnO structures for UV detections. Various combination materials with ZnO were studied, like GaN, Al, TiO2 and ZnO itself. Most of them got the responsivity around 10−3 A/W.

Then, TiO2 can behaves as a catalytic promoter during the involved reaction in a chemical process [16] and it can greatly modify the physical and optical properties of the thin films [17,18] when introduced to the ZnO matrices. TiO2 is a good potential of semiconductors owing to its superior properties and important applications including has wide band gap (3.2 eV) nearly identical to that ZnO, high chemical stability, high melting point, non-toxic, strong oxidized ability [19] and long thermal photostability [20]. TiO2 can be widely found in many applications such as sensors, photocatalysts, dye-sensitized solar cells (DSSCs), lithium ion batteries, splitting of water, and direct methanol fuel cells (DMFCs) [21].

In this study, different samples of TiO2, ZnO and TiO2:ZnO nanorods thin film were used as based material in ultraviolet (UV) sensor devices. TiO2 seed layer coated-glass substrate was used in this work, as a template to grow ZnO nanorods. Hence, TiO2:ZnO nanorods thin film was fabricated using sol-gel spin-coating and solution-immersion method, respectively as UV photoconductive sensor application. Solution-immersion method was used to synthesize ZnO nanorods where the precursor solution of Zn2+ used is aqueous solution of Zn(NO3)2.6H2O and stabilizer C6H12N4 with molar ratio of 1:1. The characterizations of the samples were carried out by FESEM, XRD and UV–vis spectroscopy, respectively. UV sensor based on TiO2:ZnO nanostructures thin films was fabricated and tested using UV measurement system.

Section snippets

TiO2 by sol-gel spin coating method

In the preparation of TiO2 solution, titanium (IV) butoxide was dissolved in ethanol, GAA, deionized water and a drop of triton-x-100. This mixture undergoes hydrolysis and polycondensation reactions to form a colloid. Then, the process of spin-coating was carried out to deposit TiO2 seed layer on a glass substrate with the dimension size of approximately 2.0 × 2.5 cm. The precursor solution of TiO2 was dropped on a glass substrate using three different steps spin coating, 2000 rpm for 10 s,

Field emission scanning electron microscope

Fig. 2(a) shows surface morphologies for synthesized TiO2 seed layer-coated glass substrate prepared via sol-gel spin-coating technique. The images disclose that the seed layer composed of small compact particles with porous nature. Fig. 2(b) indicates typical 3D atomic force microscope (AFM) images and corresponding surface profiles of TiO2 seed layer. It shows that the irregular and randomly distributed nano-pillar and voids over the entire surface. The black and white region on the surface

Conclusion

In summary, we have presented bare TiO2, bare ZnO rods and TiO2:ZnO nanorods UV sensors synthesized by spin coating and the thermal immersion method to detect UV light. The thin film of TiO2:ZnO nanorods showed dual abilities of absorption properties in UV and visible region compared to the seed layer. The small size of the ZnO nanorods and the existence of TiO2 seed layer improve the absorbance of light for the sensing process. The hetero-junction also forms on TiO2 seed layer and ZnO surface

Author’s declaration

I declare that the work in this thesis was carried out in accordance with the regulations of Universiti Teknologi MARA. It is original and is the result of my own work, unless otherwise indicated or acknowledged as referenced work. This thesis has not been submitted to any other academic publisher or non-academic publisher for any other publication.

In the event that my paper is found to violate the conditions mentioned above, I voluntarily waive the right of conferment of my paper.

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.

Acknowledgements

We would like to express our gratitude to Ministry of Education Malaysia, Research Management Institute (RMI) and Universiti Teknologi MARA (UiTM), Shah Alam, Selangor, Malaysia for financial support.

Nur Amierah Mohd Asib received her Bachelor of Science (Physics) with Honours (2012) degrees from Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. She is currently undertaking her candidature for a PhD in Science also at Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. Her research interests include synthesis and characterization of nanostructured metal oxides (e.g. ZnO, TiO2) and ultraviolet sensors.

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Nur Amierah Mohd Asib received her Bachelor of Science (Physics) with Honours (2012) degrees from Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. She is currently undertaking her candidature for a PhD in Science also at Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. Her research interests include synthesis and characterization of nanostructured metal oxides (e.g. ZnO, TiO2) and ultraviolet sensors.

Mohd Husairi graduated with honors in bachelor in (Hons) Industry Physics from the Universiti Teknologi Mara (UiTM) Shah Alam, Malaysia with vice canselor award. He obtained his PhD at NANO-SciTech Centre from UiTM Shah Alam in semiconductor fabrication (Thin films, Epitaxy & Nanostructures). Now, he works at UiTM Shah Alam under Physics and Material department, Faculty of Applied Sciences as a Senior Lecturer. He also one of the associate members in NANO-SciTech Centre, Institute of Science at UiTM Shah Alam. Involved in many activities in research and writing field like present the paper in conference, as a panel for defend and evaluation of project and write some article and paper.

Kevin Alvin Eswar is a member of Nano Scitech Centre, Institute of Science of UniversitiTeknologi Mara (UiTM) Shah Alam, Malaysia since 2011. He graduated with honors in Bac. Sc. (Hons) Physics, earned a Master’s degree from the UniversitiTeknologi Mara (UiTM) Shah Alam, Malaysia. Currently, he is working in UiTM Sabah Tawau Campus as an academician since 2014. His interest including nanomaterials, semiconductor and sensors.

Nurul Afaah Abdullah received her Bachelor of Science (Physics) with Honours (2012) degrees from Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. In 2017, she received his Master in Science from the same university. She is currently pursuing her PhD in Science also at Universiti Teknologi MARA (UiTM) Shah Alam, Malaysia. Her research interests include synthesis and characterization of nanostructured metal oxides (e.g. ZnO) and carbon based nanomaterial (e.g. graphene).

Mohamad Hafiz Mamat received his Bachelor of Engineering (Electrical & Electronic Eng. and Information Eng.) from Nagoya University, Japan (2005) and Master of Electrical Engineering from Universiti Teknologi MARA (UiTM), Shah Alam, Selangor (2009). In 2013, he received his PhD in Electrical Engineering also from the same university (UiTM Shah Alam, Malaysia). He is currently an academic staff and an active researcher at NANO-Electronic Centre, Faculty of Electrical Engineering, UiTM Shah Alam, Malaysia. His research interests include synthesis and characterization of nanomaterials (e.g: ZnO, TiO2, etc.), as well as fabrication of thin film-based devices and sensors (UV, chemical and gas sensors).

Mohamad Rusop Mahmood received his Bachelor of Engineering from Nagoya University, Japan in 1989 and Master of Engineering from Nagoya Institute of Technology, Japan (1998). In 2003, he received his PhD of Engineering (Opto-Electronic Devices and Nanotechnology) also from the Nagoya Institute of Technology, Japan. He is currently an academic staff and a Professor since 2005 at Faculty of Engineering, Universiti Teknologi MARA (UiTM), Shah Alam, Malaysia. He was the head and an active researcher at NANO-SciTech Centre, Institute of Science, UiTM Shah Alam, Malaysia. His research interests include synthesis and characterization of oxide-based nanomaterials, Porous Silicon, SQDN, Lead Zirconium Titanate, Silicon Nitride, etc. As well as carbon-based nanomaterials including CNTs, a-C, a-C:H, a-C:N, CNx, Carbon Nano-Blade, Fullerence, Nano-Diamond and Nano-Composite Polymer for various application in nanotechnology field.

Zuraida Khusaimi received her Bachelor of Science from University of Aberdeen, Scotland, United Kingdom (1993), Master in Analytical Chemistry from Universiti of Malaya, Kuala Lumpur (2002). She successfully obtained her PhD in 2012 at UiTM Shah Alam, Malaysia. She currently holds the position of a Senior Lecturer at the School of Chemistry and Environment, Faculty of Applied Science. She is a research fellow at NANO-SciTech Centre, Institute of Science, UiTM. Her research interests include synthesis (solution-based methods) and characterization of metal oxide based-nanomaterials (e.g: ZnO, TiO2, etc.).

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