Fabrication, structural, optical, electrical, and humidity sensing characteristics of hierarchical NiO nanosheet/nanoball fower like structure flms

In this work, nickel oxide (NiO) nanosheet/nanoball-fower-like structures (NSBS) were directly grown on a NiO seed-coated glass substrate using a low-temperature immersion method at 75 ºC. The thickness, or density, of the nanoball-fower-like structures difered based on the following samples order: NSBS1< NSBS2< NSBS3. The synthesised NSBS flms were investigated in terms of structural, optical, electrical, and humidity sensing characteristics. The X-ray difraction (XRD) analysis revealed that the NSBS samples corresponded to the face-centred cubic NiO with fve difraction patterns indexed to the (111), (200), (220), (311), and (222) planes. The interplanar spacing, lattice parameter, unit cell volume, strain, and stress were also determined from the XRD results. The transmittance spectra showed that the NSBS samples had a transparency of more than 30% in the visible region. The optical bandgap values for the NSBS samples were estimated in the range between 3.72 and 3.75 eV, which is directly related to their lattice expansion and defect characteristics. The current–voltage and Hall efect measurement results revealed that the NSBS2 displayed good electrical properties with the resistance, hole concentration, and hole mobility values of 7.84 MΩ, 8.71×1015 hole/cm−3, and 1.88×102 cm2 /V s, respectively. The NSBS samples performed well for humidity sensing with the highest sensitivity value of 169 being obtained for the NSBS2. These humidity sensing results correlated well with their structural, optical, and electrical characteristics

Heterojunction of SnO2 nanosheet/arrayed ZnO nanorods for humidity sensing

For the first time, a rutile phased tin oxide (SnO2) nanosheet was assembled onto a zinc oxide (ZnO) nanorod array to form SnO2 nanosheet/ZnO nanorod array heterostructure films (TSZR) using a two-step solution immersion method. This study offers a facile and effective path to grow a SnO2 nanosheet assembled layer on ZnO nanorod arrays with a varied density using a tin (II) chloride dihydrate precursor to achieve an optimum humidity sensing response through the SnO2 growth time from 1 to 5 h. The structural characteristics, electrical properties, and humidity sensing response of the heterostructure films were investigated using various characterization techniques, such as field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, X-ray diffraction, atomic force microscopy, Raman spectroscopy, a two-probe current-voltage measurement, and a humidity sensing response measurement system. The synthesized ZnO nanorods have an average diameter of 90 nm, while the grown SnO2 nanosheets have an average width of 20 nm. The humidity response performance of the films demonstrates a remarkable dependence on the SnO2 nanosheet assembled layer on the ZnO nanorod array film with the best humidity sensitivity of 754.4 at room temperature obtained for the 2 h-grown SnO2 nanosheet-based 2TSZR heterostructure sample. The 2TSZR sample also exhibited good stability over a four-cycle measurement and magnified current value of the humidity sensing response at a high operating temperature up to 60 °C. These investigations reveal that the TSZR heterostructure films are promising for humidity sensing devices with high sensitivity

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

Influence of doping concentration on the zinc doped nickel oxide nanostructures: morphological, structural, and optical properties

The zinc doped nickel oxide (Zn:NiO) nanostructures with 0 at.% (UD), 1 at.% (1ZNO), and 2 at.% (2ZNO) of Zn concentrations were successfully deposited on the NiO seed-coated glass substrates. The films were successfully produced from two synthesis techniques: the sol-gel spin coating for NiO seed-coated and the solution immersion for the Zn:NiO nanostructures. The films were then pre-baked at 150 °C and subsequently annealed at 500 °C. The Zn doping concentrations affecting NiO in terms of morphological, structural, and optical properties were investigated. The surface morphologies and cross-sectional images of the Zn:NiO nanostructures were observed by field emission scanning microscopy. The observation showed that the groups of nanoflower (NF), which were grown above the nanosheet (NS) array were gradually decreased with the increasing percentage of the Zn doping. The thickness of the NS also drastically decreases as the Zn dopant is increased. The thicknesses measured are 910 nm, 410 nm, and 100 nm for UD, 1ZNO, and 2ZNO, respectively. The X-ray diffraction analysis showed the Zn:NiO peak intensities were affected and decreased as the Zn doping is increased. Take into account the significant differences in the (200) plane, the crystal parameters were calculated. The dislocation density, interplanar spacing, lattice parameter, and unit cell volume increased as the Zn doping increased. Meanwhile, the average crystallite size reduces when the percentage of Zn doping is increased. This condition makes the Zn:NiO nanostructures are promising for sensing applications due to enhanced surface area. The strain and stress values of the Zn:NiO showed the tensile strain and compressive stress, respectively. The transmittance spectra showed the transparencies in the visible region within 400 to 800 nm wavelength increases when the percentage of Zn doping is increased. The average transmittance percentages are 32.1 %, 62.8 %, and 67.0 % for UD, 1ZNO, and 2ZNO, respectively. The optical bandgap increases sharply as the Zn doping increased from 3.55 to 4.75 eV

Physical properties of novel a-Fe2O3/NiO heterostructures through immersion/ Sol–Gel spin coating method: Different deposition numbers of NiO layer

The novel hematite (α-Fe2O3)/nickel oxide (NiO) heterostructures were grown on fluorine-doped tin oxide (FTO) coated glass substrates at various deposited NiO of 3, 5, and 7 layers. The heterostructures were successfully synthesized using the immersion and sol–gel spin coating methods for α-Fe2O3 and NiO films, respectively. The field emission scanning electron microscopy analysis showed that each sample of α-Fe2O3/NiO heterostructures has a unique surface morphology when deposited with different NiO layers. The X-ray diffraction pattern shows that the number of NiO layers affected the diffraction peaks. The NiO diffraction peak intensity at (111) plane increased when the deposition number of NiO layer was increased. The crystallite sizes of NiO were 35.4, 33.6, and 38.0 nm for 3-, 5-, and 7-layer NiO, respectively. The interplanar spacing, lattice parameter, and unit cell volume indicate NiO with 3-layer as the highest, while 5- and 7-layer had the same values. Meanwhile, the strain and stress values show the compressive strain and tensile stress, respectively. The optical properties reveal that the highest transmittance and the lowest absorbance percentages were recorded for a 3-layer NiO sample. In contrast, the lowest transmittance and the highest absorbance percentages were obtained for the sample with 5-layer NiO. Different thicknesses and morphologies of heterostructures explained these situations. In addition, each unique heterostructure of α-Fe2O3/NiO with high visible light absorption nature is perceived to reduce the bandgap energy and has the potential to be used in sensor and solar cell applications