Porous Zinc Oxide Films Research Articles

Nanostructured ZnO/Ag Film Prepared by Magnetron Sputtering Method for Fast Response of Ammonia Gas Detection.

Possessing a large surface-to-volume ratio is significant to the sensitive gas detection of semiconductor nanostructures. Here, we propose a fast-response ammonia gas sensor based on porous nanostructured zinc oxide (ZnO) film, which is fabricated through physical vapor deposition and subsequent thermal annealing. In general, an extremely thin silver (Ag) layer (1, 3, 5 nm) and a 100 nm ZnO film are sequentially deposited on the SiO2/Si substrate by a magnetron sputtering method. The porous nanostructure of ZnO film is formed after thermal annealing contributed by the diffusion of Ag among ZnO crystal grains and the expansion of the ZnO film. Different thicknesses of the Ag layer help the formation of different sizes and quantities of hollows uniformly distributed in the ZnO film, which is demonstrated to hold superior gas sensing abilities than the compact ZnO film. The responses of the different porous ZnO films were also investigated in the ammonia concentration range of 10 to 300 ppm. Experimental results demonstrate that the ZnO/Ag(3 nm) sensor possesses a good electrical resistance variation of 85.74% after exposing the sample to 300 ppm ammonia gas for 310 s. Interestingly, a fast response of 61.18% in 60 s for 300 ppm ammonia gas has been achieved from the ZnO/Ag(5 nm) sensor, which costs only 6 s for the response increase to 10%. Therefore, this controllable, porous, nanostructured ZnO film maintaining a sensitive gas response, fabricated by the physical deposition approach, will be of great interest to the gas-sensing community.

Light-soaking tests of zinc oxide photoanodes sensitized with an indoline dye on different transparent conductive substrates

Dye-sensitized solar cells (DSCs) were prepared using porous zinc oxide (ZnO) films on aluminum-doped zinc oxide (AZO) and fluorine-doped tin oxide (FTO) transparent conductive glass substrates. X-ray diffraction measurements revealed that, the porous ZnO films were crystallographically oriented differently on the two transparent substrates. The two DSCs were prepared using metal-free indoline dye as the sensitizer and a liquid electrolyte as the hole conductor. Measurements of the power conversion efficiency of the two DSCs over a period of time showed deterioration in the conversion efficiency of the DSCs with the deterioration being faster in ZnO/FTO than ZnO/AZO. The deterioration is attributed mainly to the decrease in light-harvesting ability of the sensitizer and recombination of photo-excited electrons resulting in the decrease in the short-circuit photocurrent densities and the open-circuit voltages in both DSCs during the light-soaking process.

Low-temperature Growth of Porous and Dense ZnO Films for Perovskite Solar Cells on ITO Substrate

A novel precursor with zinc oxide (ZnO) structure was synthesized for ZnO film deposition using diethylzinc in some solvents. Non-doped ZnO films on a glass substrate were successfully grown by con...

A sensitive film structure improvement of reduced graphene oxide based resistive gas sensors

This study was focused on how to improve the gas sensing properties of resistive gas sensors based on reduced graphene oxide. Sol-airbrush technology was utilized to prepare reduced graphene oxide films using porous zinc oxide films as supporting materials mainly for carbon dioxide sensing applications. The proposed film structure improved the sensitivity and the response/recovery speed of the sensors compared to those of the conventional ones and alleviated the restrictions of sensors' performance to the film thickness. In addition, the fabrication technology is relatively simple and has potential for mass production in industry. The improvement in the sensitivity and the response/recovery speed is helpful for fast detection of toxic gases or vapors in environmental and industrial applications.

Gas Sensors Fabricated by Aerosol Deposition

Zinc oxide (ZnO) is a low toxicity and environmentally friendly material, and it is applied on devices, sensors or actuators for trending towards green-life. A porous ZnO film deposited by a rapid process of aerosol deposition (AD) was employed as the gas-sensitive material in a CO gas sensor for reducing the manufacturing cost and time, further extending the AD application. A relative resistance change (R / R) of the ZnO gas sensor was used for CO gas measurement. The sensitivity of the fabricated ZnO gas sensors had a more outstanding performance about 49%, compared to the literature data reported by Joshi.

Effectiveness of ZnO/carbon-based material as a catalyst for photodegradation of acrolein

Acrolein (ACR) is a metabolite of cyclophosphamide (CYP) and induces hemorrhagic cystitis (HC). Here, we investigated the effectiveness of ZnO/carbon fiber (CF) composites as catalysts for removing ACR through photodegradation. Specimens composed of CF and zinc oxide (ZnO) were prepared and annealed at 200–400°C in air. For the ZnO/CF specimen annealed at 200°C (CZ200), a continuous and porous ZnO film was formed on the CF surface. Field-emission scanning electron microscopy and physisorption analysis indicated that this composite had a high specific surface area. X-ray diffraction analysis and photoluminescence spectroscopy showed that the ZnO film was amorphous, exhibiting a broad emission spectrum. An ultraviolet (UV) radiation-based degradation system and methylene blue (MB) solution were used to evaluate the feasibility of using the composites as photodegradation catalysts. CZ200 exhibited the highest MB photodegradation rate (95%). The photodegradation of ACR (75ppm) under 4W UV light was investigated using an untreated CF sample, an active carbon fiber (ACF) fabric sample, and the CZ200 specimen. CZ200 (45%) exhibited higher ACR degradation rate than CF (8%) and ACF (28%). Hence, we confirmed that ZnO/CF composites can be used to photodegrade ACR and have potential for use in preventing CYP-induced HC in chemotherapy patients.

Optical and structural properties of porous zinc oxide fabricated via electrochemical etching method

Abstract We investigated the optical and structural properties of porous zinc oxide (ZnO) thin film fabricated by ultraviolet light-assisted electrochemical etching. This fabrication process used 10 wt% potassium hydroxide solution as an electrolyte. Hillock-like porous ZnO films were successfully fabricated according to the field emission scanning electron microscopy results. The cross-sectional study of the sample indicated that anisotropic-dominated etching process occurred. However, the atomic force microscopic results showed an increase in surface roughness of the sample after electrochemical etching. A resonance hump induced by the porous structure was observed in the infrared reflectance spectrum. Using theoretical modeling technique, ZnO porosification was verified, and the porosity of the sample was determined.

Preparation of Porous ZnO Film by Zinc Oxalate Recurrence Method

This paper presents a method called zinc oxalate (ZnC2O4) recurrence method to prepare porous zinc oxide (ZnO) films via templating with polystyrene (PS) spheres. Effects of calcination time and temperature, concentration of ZnC2O4 in precursor solution on ZnO films were studied. Optimal synthetic conditions and structural features of ZnO films were investigated by DTA, XRD and SEM. Experimental results show that porous ZnO films can be easily prepared by zinc oxalate recurrence methods.

Porous zinc oxide films: Controlled synthesis, cytotoxicity and photocatalytic activity

The anodic oxidation technique was successfully carried out to fabricate porous ZnO films. Energy dispersive X-ray and scanning electron microscope indicated that the anodic oxidation time was the key factor to control surface pore density, which varied from 0.2 ± 0.01% to 59.8 ± 5.4%. The cytotoxicity study indicated that porous ZnO films displayed the pore density-dependent cytotoxicity on the metabolism and spread of NIH 3T3 fibroblasts. The photocatalytic activity of porous ZnO films was investigated by employing methyl orange as the model compound and it was pore density-dependent. In view of the relatively facile separation property and subsequently the decrease of toxic side effects to the environment of film-form ZnO products compared to powder products, this study suggested the superior potential of the former as the photocatalyst.

Effects of potential and temperature on the electrodeposited porous zinc oxide films

Porous ZnO films were prepared by electrodeposition method in zinc nitrate aqueous solution using ITO glass covered with polystyrene sphere (PS) colloidal crystal arrays as substrates. The preparation procedure includes two parts: deposition of ZnO in the interstices of the colloidal crystals and subsequent removal of the PS templates. The influences of deposition potential and temperature on the ZnO films were investigated. The ordered, uniform porous ZnO films with optical transmittance of approximately 63.6% at 600 nm could be obtained when the deposition potential and temperature were −1.1 V and 70 °C, respectively. The optical band gap energy increased along with the absolute deposition potential and temperature, ranging from 3.33 to 3.43 eV and from 3.35 to 3.42 eV, respectively.

Comparison of ZnO thin films grown on a polycrystalline 3C–SiC buffer layer by RF magnetron sputtering and a sol–gel method

Zinc oxide (ZnO) thin films were deposited on a polycrystalline (poly) 3C–SiC buffer layer using RF magnetron sputtering and a sol–gel method. The post-deposition annealing was performed on ZnO thin films prepared using both methods. The formation of ZnO piezoelectric thin films with less residual stress was due to a close lattice mismatch of the ZnO and SiC layers as obtained by the sputtering method. Nanocrystalline, porous ZnO film prepared using the sol–gel method showed strong ultraviolet UV emission at a wavelength of 380nm. The 3C–SiC buffer layer improved the optical and piezoelectric properties of the ZnO film produced by the two deposition methods. Moreover, the different structures of the ZnO films on the 3C–SiC intermediate layer caused by the different deposition techniques were also considered and discussed.

Selective real-time nitric oxide detection by functionalized zinc oxide

Ferriprotoporphyrin IX chloride (haemin)-functionalized Al-doped zinc oxide (ZnO) is used for nitric oxide (NO) sensing at room temperature. The devices show high selectivity to NO against CO2 and O2. There is no such selectivity without haemin. Porous ZnO film made by a polystyrene sphere template is used to provide a high surface area. In comparison with non-porous ZnO film with low surface area, both the sensitivity and the response speed of the sensor made by porous ZnO are clearly improved. NO concentration down to 1 ppm can be detected. The response time is 20 s. The sensor is reversible after purging with pure nitrogen for about 100 s. Such a device is able to detect real-time variation of NO which is a vital physiological signalling molecule.

Study of sol-gel derived porous ZnO photoelectrode for the application of dye-sensitized solar cells

In this study, the porous zinc oxide (ZnO) films were deposited on SnO2:F coated glass substrate by sol-gel technique with zinc acetate as precursor, ethanol as solvent, and diethanolamine as chelating agent. Two sets of ZnO films with equal number of coatings and the same film thicknesses were deposited with various zinc acetate concentrations. The surface morphology of the porous ZnO film strongly depends on the zinc acetate concentration. It was also revealed from the optical study that the dye absorption increases with an increase in the zinc acetate concentration. The ZnO film with 1.0mol∕l zinc acetate concentration has shown the best porous structure and maximum rms roughness value (187nm). The maximum photoelectric conversion efficiencies, 0.64% and 0.8%, were achieved for ZnO films with 1.0mol∕l of zinc acetate concentration in both sets of samples: equal number of coatings and the same film thicknesses, respectively.

アノード酸化により作製したポーラス酸化亜鉛の構造と光触媒特性

Formation of anodic porous zinc oxide (ZnO) films with high specific surface area was investigated in various electrolytes such as oxalic acid, ammonium borate, and sodium hydroxide solutions. Composition of the anodic film formed in oxalic acid, which was composed of an outer rock-like structure and an inner granular structure, was mainly Zn(OH)2 containing a small amount of ZnO. In contract, crystalline porous ZnO film with a straight cellular structure was formed in a sodium hydroxide solution. At low anodizing voltage of 9 V, formation of thicker films of more than 30 μm was achieved through suppression of extensive gas evolution. Photocatalytic activity of the ZnO films assessed using photodegradation of methylene blue under UV irradiation was comparable with that of TiO2 nanoparticle film (P25).

Electrodeposition zinc-oxide inverse opal and its application in hybrid photovoltaics

This article reports the preparation of three-dimensional (3D) mesoporous zinc oxide (ZnO) films and their application in solar cells. The films were obtained through electrochemical deposition in DMSO solutions by using PS colloidal crystal as templates. The ZnO films with inverse opal (IO) structure were obtained after removing the templates by thermolysis. The ordered porous ZnO films were used to prepare hybrid solar cells by infiltrating the films with poly(3-hexylthiophene) (P3HT) or P3HT:ZnO nanocomposite. Results showed that the interpenetrating network of both ZnO(IO) and P3HT can form continuous pathways for electron and hole transport. By infiltrating a P3HT:ZnO nanocomposite into the porous ZnO films, the photocurrent of the solar cell can be dramatically improved. The cell shows the V oc and I sc of 462 mV and 444.3 μA/cm 2, respectively. By using a 420 nm cutoff filter, the cell retains about 80% and 50% of its original V oc and I sc after continuous white-light illumination (100 mW/cm 2) for 10 h. Stability of the device under above conditions was estimated to be 51 h.

One-step Preparation and Photosensitivity of Size-quantized Cadmium Chalcogenide Nanoparticles Deposited on Porous Zinc Oxide Film Electrodes

Abstract Size-quantized cadmium chalcogenide nanoparticles were effectively deposited on a porous zinc oxide particulate film electrode by a one-step hydrothermal method in which an increase in the concentration of 3-mercaptopropionic acid reduced the size of deposited nanoparticles. The photoelectrochemical properties of the resulting electrodes varied depending on the kind of metal chalcogenide nanoparticles deposited and their size.

Fabrication of 2D and 3D ordered porous ZnO films using 3D opal templates by electrodeposition

Both two- and three-dimensional ordered porous zinc oxide films were fabricated by electrodeposition using three-dimensional polystyrene opal templates. Scanning electron microscope measurements showed that the dimensions (monolayer or multilayer) of porous zinc oxide films can be controlled by selecting zinc nitrate in different solvents (water or mixed ethanol–water solvents). Optical measurements showed that the porous structures generated in mixed ethanol–water solutions exhibited the photonic stopband, indicating large-scale crystalline order in the samples. It was found that the position of stopband center and the surface morphologies in the three-dimensional zinc oxide porous films were dependent on the ethanol content in the electrolyte. The influence of ethanol content on the porous films was discussed.

Fabrication of 2D Ordered Porous ZnO Films Using 3D Opal Templates by Electrodeposition

Abstract The fabrication of two-dimensionally ordered porous zinc oxide films using three-dimensional colloidal crystal templates by electrodeposition is reported. The hydrophilicity of the substrate and the hydrophobicity of the template are utilized to control the generated structures.

Growth of layered basic zinc acetate in methanolic solutions and its pyrolytic transformation into porous zinc oxide films

Layered basic zinc acetate (LBZA), Zn 5(OH) 8(CH 3COO) 2·2H 2O, was deposited on glass substrates by a chemical bath deposition (CBD) method using methanolic solutions of zinc acetate dihydrate. The substrates were put into bottles filled with the solutions and sealed up and were kept at 60 °C in a drying oven. Immersion time necessary for the deposition of LBZA films was typically more than 28 h. This was a key to inducing heterogeneous nucleation of LBZA through control over a degree of supersaturation in the evolution of a unique, nest-like morphology. Hydration water contained by zinc acetate dihydrate was quantitatively enough to promote hydrolysis of zinc acetate. The LBZA films were transformed into nanocrystalline, porous ZnO films without morphological deformation by heating at 150 °C in air. A mechanism of the formation of the nest-like morphology was discussed based on nonaqueous solution reactions, nucleation, and crystal growth during the CBD process.