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

Synthesis of zinc oxide nanostructures on graphene/glass substrate by electrochemical deposition: effects of current density and temperature

The electrochemical growth of zinc oxide (ZnO) nanostructures on graphene on glass using zinc nitrate hexahydrate was studied. The effects of current densities and temperatures on the morphological, structural, and optical properties of the ZnO structures were studied. Vertically aligned nanorods were obtained at a low temperature of 75°C, and the diameters increased with current density. Growth temperature seems to have a strong effect in generating well-defined hexagonal-shape nanorods with a smooth top edge surface. A film-like structure was observed for high current densities above -1.0 mA/cm2 and temperatures above 80°C due to the coalescence between the neighboring nanorods with large diameter. The nanorods grown at a temperature of 75°C with a low current density of -0.1 mA/cm2 exhibited the highest density of 1.45 × 109 cm-2. X-ray diffraction measurements revealed that the grown ZnO crystallites were highly oriented along the c-axis. The intensity ratio of the ultraviolet (UV) region emission to the visible region emission, IUV/IVIS, showed a decrement with the current densities for all grown samples. The samples grown at the current density below -0.5 mA/cm2 showed high IUV/IVIS values closer to or higher than 1.0, suggesting their fewer structural defects. For all the ZnO/ graphene structures, the high transmittance up to 65% was obtained at the light wavelength of 550 nm. Structural and optical properties of the grown ZnO structures seem to be effectively controlled by the current density rather than the growth temperature. ZnO nanorod/graphene hybrid structure on glass is expected to be a promising structure for solar cell which is a conceivable candidate to address the global need for an inexpensive alternative energy source

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

Effect of Growth Pressure on Structural Properties of SiC Film Grown on Insulator by Utilizing Graphene as a Buffer Layer

Heteroepitaxial growth of silicon carbide (SiC) on graphene/SiO2/Si substrates was carried out using a home-made hot-mesh chemical vapor deposition (HM-CVD) apparatus. Monomethylsilane (MMS) was used as single source gas while hydrogen (H2) as carrier gas. The substrate temperature, tungsten mesh temperature, H2 flow rate and distance between mesh and substrate were fixed at 750 °C, 1700 °C, 100 sccm and 30 mm, respectively. The growth pressures were set to 1.2, 1.8 and 2.4 Torr. The growth of 3C-SiC (111) on graphene/SiO2/Si were confirmed by the observation of θ-2θ diffraction peak at 35.68°. The diffraction peak of thin film on graphene/SiO2/Si substrate at pressure growth is 1.8 Torr is relatively more intense and sharper than thin film grown at pressure growth 1.2 and 2.4 Torr, thus indicates that the quality of grown film at 1.8 Torr is better. The sharp and strong peak at 33° was observed on the all film grown, that peak was attributed Si(200) nanocrystal. The reason why Si (200) nanocrystal layer is formed is not understood. In principle, it can’t be denied that the low quality of the grown thin film is influenced by the capability of our home-made apparatus. However, we believe that the quality can be further increased by the improvement of apparatus design. As a conclusion, the growth pressures around 1.8 Torr seems to be the best pressures for the growth of heteroepitaxial 3C-SiC thin film

Properties of amorphous carbon microspheres synthesised by palm oil-CVD method

Amorphous carbon microspheres were synthesized using a dual‐furnace chemical vapour deposition method at 800–1000° C. Palm oil‐based cooking oil (PO) and zinc nitrate solution was used as a carbon source and catalyst precursor, respectively with PO to zinc nitrate ratio of 30:20 (v/v) and a silicon wafer as the sample target. Regular microsphere shape of the amorphous carbons was obtained and a uniform microsphere structure improved as the carbonization temperature increased from 800 to 1000° C. At 800° C, no regular microspheres were formed but more uniform structure is observed at 900° C. Generally the microspheres size is uniform when the heating temperature was increased to 1000° C, but the presence of mixed sizes can still be observed. X‐ray diffraction patterns show the presence of oxide of carbon, ZnO phase together with Zn oxalate phase. Raman spectra show two broad peaks characteristic to amorphous carbon at 1344 and 1582 cm−1 for the D and G bands, respectively. These bands become more prominent as the preparation temperature increased from 800 to 1000° C. This is in agreement with the formation of amorphous carbon microspheres as shown by the FESEM study and other Zn‐based phases as a result of the oxidation process of the palm oil as the carbon source and the zinc nitrate as the catalyst precursor, respectively

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

The properties of sonicated immersion grown hematite films at various annealing temperatures

In this research, hematite (α-Fe2O3) film was synthesized to study the effect of annealing temperature on its crystallinity, optical and electrical properties. Through a sonicated solution immersion technique, hematite films were deposited on a fluorine-doped tin oxide (FTO) glass substrate. In the synthesis process, 0.2 M ferric chloride (FeCl3·6H2O) was used as a precursor, 0.2 M urea (NH2CONH2) as the stabilizer, and de-ionized (DI) water as a solvent to produce 200 ml of aqueous solution. During the annealing treatment, we varied the temperatures at 350 ºC, 450 ºC and 500 ºC. The X-ray diffraction (XRD) pattern revealed the presence of peaks of 2θ angles between 20° to 90°, corresponding to (104), (110), (214), (125) and (128) planes, which exhibited crystalline structures of rhombohedral with diffraction peaks of hematite phase (α-Fe2O3). Optical characterizations showed that the transmittances of all samples were close to 100% in the high wavelength level of the visible light region, which is close to the infrared spectrum. Absorption of hematite samples was found to be more than 0.6 a.u. in the low wavelength level of the visible light region close to the ultraviolet spectrum and close to 0 in the high wavelength level of the visible light region close to the infrared spectrum. A sample with an annealing temperature of 500 °C has the lowest transmission and the highest absorbance in the visible region due to dim pigments in the hematite film

Fabrication of single chamber microbial fuel cell (SMFC) using soil as a substrate

This paper presents a Single-chamber Microbial Fuel Cell (SMFC) design by utilizing soil as a substrate with two sets of electrode combinations, which are graphite-activated carbon and copper-zinc of different sizes. It was found that graphite and activated carbon produced greater power density compared to copper and zinc. Moreover, it was observed that the graphite-activated carbon cloth electrode with a bigger surface area of 51cm2 resulted in a higher power density of 904mW/m2. To further improve the voltage production of this model, four SMFCs were stacked in series and connected to a DC-DC boost converter to increase the voltage to 1.482 V for the copper-zinc electrode and 1.722 V for the graphite-activated carbon electrode, respectively, which was sufficient to light up an LED light