Fabrication and characterisation of aligned zinc oxide nanorod array- based ultraviolet photoconductive sensors / Mohamad Hafiz Mamat

Ultraviolet (UV) photoconductive sensors have been fabricated using undoped and aluminium (Al)- doped zinc oxide (ZnO) nanorod arrays and novel nanostructures, such as nanohole-enhanced, aligned Al-doped ZnO nanorod arrays and Al-doped ZnO nanorod-nanoflake network thin-film structures. These nanostructures were deposited using a novel technique known as the sonicated sol-gel immersion method. The use of Al-doped nanostructures in UV photoconductive sensor applications has not been widely discussed in the literature. The nanorod array properties and the fabricated sensor performances were analysed using field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, atomic force microscopy, micro-Raman spectroscopy, photoluminescence spectrometry, ultraviolet– visible–near-infrared spectrophotometry, atomic force microscopy, thickness profilometry, two-probe current-voltage measurement system, and UV photocurrent measurement system under a 365- nm UV lamp. In this study, several parameters were studied regarding the growth of ZnO nanorod arrays for use in UV photoconductive sensor applications, including the doping process (undoped and Al-doped), the precursor volumes (50-1,000 ml), the annealing temperatures (300-500°C), the ambient annealing environment (air, vacuum, and oxygen environments), the immersion times (10-300 min), the sonication times (0-50 min), and the coating processes (intrinsic ZnO and poly(vinyl alcohol)). Additionally, the effects of the metal contact gap and the bias voltage on the UV sensor performance were also investigated. For each experimental parameter, the UV photoconductive sensor responsivity, sensitivity, rise time constant, and decay time constant were thoroughly studied. Based on this investigation, it can be concluded that the performance of the sensors was closely related to the nanorod dimensions (i.e., the diameter and length), crystallinity, surface condition, stress, impurities, resistance, bias voltage, and gap between the metal contacts. Notably, a significant responsivity of 1,350.84 A/W was achieved for the UV photoconductive sensor using the nanohole-enhanced, aligned Al-doped ZnO nanorod arrays prepared with a 50-min immersion time, which had a small thickness of approximately 600 nm. Additionally, the sensitivity of the device was improved by lowering the dark current value of the sensor. This condition was achieved by lowering the annealing temperature, by carrying out the annealing process in an oxygen environment, or by growing the Al-doped ZnO nanorod arrays in a precursor solution that had been sonicated for a long period of time. Notably, growing the Al-doped ZnO nanorod arrays in the precursor solution that had been sonicated for the longest amount of time for the UV photoconductive sensor application yielded better results as both the dark current and the time constants of the sensor were reduced. The fabrication of UV photoconductive sensors using a novel sensor configuration of the Al-doped ZnO nanorod-nanoflake network thin film was also performed in this study. The sensors exhibited a responsivity of 46.4 mA/W, a sensitivity of 17.5, a rise time constant of 10 s, and a decay time constant of 84 s. Throughout this study, it was found that the performance of the fabricated ZnO nanorod array-based UV photoconductive sensor was very promising and demonstrated high responsivity, sensitivity, and fast response

Properties of nano-structured zinc oxide thin films for ultraviolet photoconductive sensor applications / Mohamad Hafiz Mamat

Nanostructured zinc oxide (ZnO) materials in thin film structure have been synthesized using the sol-gel method. The thin film depositions have been carried out by spin-coating technique and hydrothermal aqueous chemical growth method on silicon and glass substrates. The thin films were annealed for 1 hour before characterization process. The surface morphologies of prepared ZnO thin films were observed using Field Emission Scanning Electron Microscopy (FESEM) and Scanning Electron Microscopy (SEM) to investigate the evolution of ZnO particle and surface morphology. The structural properties of ZnO thin films were characterized using X-Ray Diffraction (XRD) for purity and crystallinity of ZnO thin films and particle size estimation. The optical properties of ZnO thin films were examined using UV-Vis-NIR spectrophotometer for transmittance, absorption coefficient, band gap energy, carrier concentration, porosity and Urbach energy study. The optical properties of ZnO thin films also were studied using Photoluminescence (PL) spectrophotometer to investigate the luminescence properties, crystallinity and defects state of ZnO materials. The electrical properties were investigated using current-voltage (I-V) measurement to study the conductance behavior of the thin films. ZnO thin film-based ultraviolet (UV) sensors have been prepared by sol-gel spin-coating method. The sensors have been characterized using I-V measurement system under UV lamp irradiation to investigate the response of ZnO thin films to the UV light

Aluminum- and Iron-Doped Zinc Oxide Nanorod Arrays for Humidity Sensor Applications

Metal-doped zinc oxide (ZnO) nanorod arrays have attracted much attention due to improvement in their electrical, structural, and optical properties upon doping. In this chapter, we discuss the effects of aluminum (Al)- and iron (Fe)-doping on ZnO nanorod arrays properties particularly for humidity sensor applications. Compared to Fe, Al shows more promising characteristics as doping element for ZnO nanorod arrays. The Al-doped ZnO nanorod arrays showed dense arrays, small nanorods diameter, and high porous surface. The I-V characteristics showed that Al-doped sample possesses higher conductivity. From the humidity sensing performance of the samples, Al-doped ZnO nanorod arrays possess the superior sensitivity, more than two times higher than that of the undoped ZnO nanorod arrays sample, demonstrating great potential of Al-doped ZnO nanorod arrays in humidity sensor applications

Synthesis of Titanium Dioxide Nanorod Arrays Using a Facile Aqueous Sol-Gel Route for Ultraviolet Photosensor Applications

In this chapter, we review the state of the art of aqueous sol-gel route for ultraviolet (UV) photosensor applications based on the nanostructured TiO2. The performance of UV photosensor is associated with the high surface-to-volume ratio, porosity, surface defects, light trapping, and the intensity of the UV radiation. One-dimensional (1D) growth of TiO2 nanorod arrays (TNAs) offers an enhance charge carrier mobility to overcome the photocurrent loss due to the existence of multiple grain boundaries in granular-like and porous nanostructures. Photoelectrochemical cell (PEC)-based device structure is preferred in TNA-based UV photosensor due to its low cost, facile fabrication process, high contact area, low recombination of the excitonic charge carriers, high photocurrent gain, and fast response and recovery times. It also could work in applied bias mode, as well as in “self-powered” mode. Our study has introduced a new one-step method to deposit a thin film TNA on an FTO-coated glass substrate at low temperature and a rapid process using a facile glass container. The fabricated PEC-based UV photosensor using the deposited TNAs has successfully shown its potential in the application of UV photosensor

THE STRUCTURAL PROPERTIES OF ZnO/TiO2 BILAYER THIN FILM AS PHOTOANODE

   The ZnO/TiO2 bilayer was fabricated on the fluorine-doped tin oxide (FTO) substrate. The ZnO nanorods and TiO2 nanoparticles were developed as photoanode material that were fabricated by using sol-gel immersion and squeegee method. The structure of ZnO/TiO2 bilayer showed a good properties for photoanode in DSSCs application. The ZnO/TiO2 bilayer has large surface area that could increase a dye loading and performance of photoanode. Meanwhile, the micro-Raman spectra of ZnO/TiO2 bilayer indicated a good crystallinity. Therefore, the ZnO/TiO2 bilayer showed a good structure for photoanode in DSSCs application.Key words: ZnO nanorods, TiO2 nanoparticles, ZnO/TiO2 bilayer, Photoanode ABSTRAKLapisan ZnO/TiO2 difabrikasi di atas substrat oksida timah yang di doping florin (FTO). Batang nano ZnO dan partikel nano TiO2 dikembangkan sebagai material fotoanoda yang difabrikasi menggunakan metode pencelupan sol-gel dan squeegee. Struktur lapisan ZnO/TiO2menunjukkan sifat fotoanoda yang baik dalam aplikasi DSSCs. Lapisan ZnO/TiO2memiliki luas permukaan yang besar yang bisa meningkatkan muatan dye dan performa fotoanoda. Sedangkan spktrum mikro-Raman lapisan ZnO/TiO2mengindikasikan kristalinitas yang bagus. Oleh karena itu, lapisan ZnO/TiO2menunjukkan struktur yang baik untuk fotoanoda di dalam aplikasi DSSCs.Kata Kunci: batang nano ZnO, partikel nano TiO2, lapisan ZnO/TiO2, fotoanod

HYDROTHERMAL GROWTH AND SQUEEGEE METHOD IN THE FABRICATION OF MIXED-PHASE TiO2 NANOSTRUCTURES

In this work, the modification of TiO2 nanostructures based on its morphology and crystallinity phase were fabricated using a simple method. Hydrothermal growth method was used to synthesize nanorods and nanoflowers, while nanoparticles was applied using squeegee method. The average length and diameter of the as-grown nanorods were 3.5 and 46-215 nm, respectively. Meanwhile, the average total thickness and band gap value of mixed-phase TiO2 nanostructures were 15.98-24.54 nm and 2.84 eV, respectively. Based on its structural and electrical properties, the fabricated film has great potential to be applied as photoanode semiconductor layer for dye-sensitized solar cells application. Key words: TiO2, Nanostructures, Mixed-phase, Hydrothermal, Squeege

THE USE OF TRIPLE-TAILS CUSTOM-MADE SURFACTANT IN THE PRODUCTION OF GRAPHENE OXIDE THIN FILM AS TRANSPARENT CONDUCTIVE ELECTRODE

In this work, graphene oxide (GO) and reduced GO (rGO) thin films were fabricated from GO and rGO using the custom-made and commercial surfactants, which were sodium 1,4-bis (neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate and sodium dodecyl sulphate, respectively. The GO solution was synthesized using electrochemical exfoliation method followed by reduction process utilizing hydrazine hydrate to produce rGO solution. The GO and rGO transfer process were done using spraying deposition method on fluorine-doped tin oxide substrate. The fabricated GO and rGO thin films consists of several layers resulted in high transparency over 85% with maximum transmittance of 93.69%. Based on several characterizations, the fabricated GO and rGO thin films have potential to be applied as transparent conductive electrode.Key words: Custom-made, Surfactant, Electrochemical, Spraying, Electrode. ABSTRAKDalam penelitian ini, film tipis grafin oksida (GO) dan grafin oksida yang direduksi (rGO) difabrikasi dari GO dan rGO menggunakan surfaktan yang dibuat khusus dan surfaktan komersial yaitu secara berurutan adalah sodium 1,4-bis (neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulphonate dan sodium dodecyl sulphate. Larutan GO disintesis menggunakan metode eksfoliasi elektrokimia diikuti dengan proses reduksi menggunakan hidrazin hidrat untuk menghasilkan larutan rGO. Proses transfer GO dan RGO dilakukan dengan menggunakan metode deposisi penyemprotan diatas substrat oksida timah oksida dengan doping florin. Film tipis GO dan rGO yang difabrikasi terdiri dari beberapa lapis dengan transparansi tinggi mencapai 85% dengan transmitansi maksimum sebesar 93,69%. Berdasarkan beberapa karakterisasi, film tipis GO dan rGO ini memiliki potensi untuk diaplikasikan sebagai elektroda konduktif transparan.Kata Kunci: dibuat khusus, surfaktan, elektrokimia, penyemprotan, elektrod

Palm oil as the carbon source for the synthesis of carbon nanotubes using floating catalyst - chemical vapour deposition method

CNTs were synthesized using floating catalyst by dual‐furnace thermal chemical vapour deposition method at 800–1000° C. Cooking oil made of palm oil was used as the carbon precursor. Ferrocene in the presence of 0.05 M zinc nitrate and a p‐type silicon wafer was used as a catalyst precursor and a sample target, respectively. The deposition temperature was varied from 800–1000° C. Nitrogen gas was used as a gas carrier with a constant flow rate of 150 sccm/min. Field emission scanning electron micrographs show the formation of CNTs together with other carbons formed on the silicon substrate. Raman spectroscopy studies were also supported the formation of CNTs

Heterogeneous SnO2/ZnO nanoparticulate film: Facile synthesis and humidity sensing capability

Highly sensitive and extremely thin tin oxide/zinc oxide (SnO2/ZnO) heterojunction films were prepared via a two-step solution-based method for humidity-sensing application. The average diameters of the ZnO and SnO2 nanoparticles were 26 and 6 nm, respectively. The deposition of SnO2 for 3 min reduced film resistance from 6.74 MΩ to 0.40 MΩ. Remarkably, the humidity-sensing performance of the heterojunction sensors was critically dependent on deposition time, and sensors subjected to 3 min deposition exhibited the highest sensitivity (90.56) to humidity, which was significantly higher than that of bare ZnO. This study indicates that the use of SnO2/ZnO heterojunction has a great potential in humidity sensing applications