Effect of ZnO layer thickness upon optoelectrical properties of NiO/ ZnO heterojunction prepared at room temperature

In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector.     

Structural,optical, and photocatalytic investigation of nickel oxide@graphene oxide nanocomposite thin films by RF magnetron sputtering

Despite the recent advancement in graphene oxide (GO) as a host material in energy and environmental sectors, its composite thin films with metal oxides such as nickel oxide (NiO) and its optical, structural, chemical state, and photocatalytic activities have been poorly explored. Herein, we have reported the GO/NiO thin films preparation by a combination of chemical and physical deposition techniques (i.e. spin coating followed by DC/RF sputtering). The as-prepared composites thin films were characterised using Raman spectroscopy, X-ray diffraction/photoelectron spectroscopy scanning electron microscopy, and atomic force microscopy. The surface topography confirmed the uniform deposition of NiO over thin films of GO. The XPS results showed the formation of NiC along with the partial reduction in GO into graphene with their existing four constituents, i.e. NiO, NiC, GO, in the thin film composites. The classical plasmon, Wemple and Didomenico model, was first time applied for GO/NiO to compute energy loss functions, and dispersion energy parameters. The theoretical calculated values for the deposited GO/NiO thin films were found to be in very close agreement to the standard classical plasmon values. The change in spin orbital movement of Ni is considered due to the interaction between its nanoparticles and basal planes of GO. Thin films applied for the photodegradation of recalcitrant organic pollutant 2-chlorophenol (2-CP) revealed the dependence of photocatalytic efficiency on particle size and also on the interaction of GO with NiO rather than the ratio of NiO and GO in the films.     

Influence of substrate temperature and solution molarity on CuO thin films' properties prepared by spray pyrolysis

Journal of Materials Science: Materials in Electronics - In the present work, we have investigated the influence of substrate temperature and solution concentration on copper oxide (CuO) thin film...     

Lubricant Additives Based on Carbon Nanotubes Produced from Carbon-Rich Fly Ash

Carbon-rich fly ash has been reported to be a suitable precursor and catalyst for carbon nanotube (CNT) growth. In this work, CNTs grown from carbon-rich fly ash were evaluated as a lubricant oil additive to reduce the friction coefficient of metallic surfaces using a ball-on-disk tribometer. Different concentrations of the as-grown CNTs in the range 0.005–0.5 wt% were dispersed in a base sunflower oil. The value of the friction coefficient was also investigated as a function of load. Excellent results were obtained for the value of the friction coefficient, where it drastically decreased to around 58% of its original value without additives. This was achieved at a very low concentration of CNTs; that is, 0.1 wt%. The obtained result was compared with that of a commercial multiwalled CNT at the same concentration and found to be superior. This superiority of CNTs produced from fly ash could be attributed to the existence of active radical sites on their side wall. Moreover, the friction coefficient value was observed to decrease with increasing load, which might be due to the formation of protective graphitic carbon layers on antagonist surfaces. The viscosity of pure and 0.1 wt% CNTs-impregnated base oil was also studied in the 25–100°C temperature range. No significant changes are observed in the viscosity of the CNTs-impregnated base oil. These results suggest that the low-cost CNTs produced from fly ash are excellent nanomaterials as additives for lubricant oil.     

Sunlight-enhanced catalytic degradation over Ag–CuO nanoparticles thin films prepared by DC/RF sputtering technique

Herein, we report sunlight-activated photo-catalysis response of direct current radio frequency (DC/RF)-sputtered Ag–CuO nanoparticles thin films. We have adopted this approach for facile removal and easy recovery of thin films after use. Ag was incorporated at 2.5 and 5.4 wt% with reference to pure CuO. Structural analysis through X-ray diffraction showed successful incorporation of Ag into the CuO lattice. Surface morphological observation was carried out using a field emission scanning electron microscope, which showed a uniform deposition of the subjected thin films. The surface composition and change in the chemical state of pure and incorporated thin films were studied by X-ray photoelectron spectroscopy. In addition to structural and surface analysis, optical band gap evolution was also studied through UV–visible spectroscopy. The obtained results reflected that optical band gap decreased from 1.84 to 1.77 and 1.61 eV for 0, 2.5 and 5.4 wt% Ag, respectively. Methylene blue dye was used to investigate the photo-catalytic degradation response of deposited thin films in sunlight. Furthermore, the effect of pH and dye concentration was also taken into account. The degradation results indicate the acceleration of degradation process with the Ag incorporation into CuO lattice. Moreover, the pH also contributes positively to the degradation progression. This research study could provide a platform to understand and develop metal oxide thin films with an efficient photo-catalytic response in sunlight.