Nano ZnO Thin Films Research Articles

Synergistically enhanced NH3 gas sensing of graphene oxide-decorated Nano-ZnO thin films

This study focuses on enhancing nanostructured ZnO thin films ammonia (NH3) sensing capabilities at room temperature by integrating graphene-oxide (GO) via the drop-casting technique, thereby exploring the possibilities of tailoring NH3 sensing measurements. Structural investigations indicated the hexagonal-wurtzite structure of the sputtered ZnO and GO-decorated thin films. The Raman spectroscopy results validate the electrochemically exfoliated GO, and the X-ray photoelectron spectroscopy characterization revealed the Zn2+ state and oxygen vacancies. The NH3 gas sensing measurements for GO/ZnO revealed a remarkable increase in sensitivity, with a limit of detection (LOD) of 0.1 ppm. This exhibited a response 50 times superior to bare ZnO for 5 ppm of NH3 at room temperature (RT). As a result of decorating GO increased active sites and surface area. This significant enhancement in sensor response underscores the synergistic effect of GO-decoration, and ZnO leading to substantially improved gas-detecting capabilities.

Structural and Optical Performance of The doped ZnO Nano-thin Films by (CSP)

In this study, were investigated structural, optical properties and morphological ofZnO and Te-doped ZnO Nano-thin films deposited by Chemical spray pyrolysis(CSP) method. The structural properties of films were studied as pure and Te dopant ZnO at concentration 2 and 4%. The films were characterized by XRD to study the structure of films. It was observed that the hexagonal wurtzite structure of ZnO for all samples. The films exhibited wurtzite (102) preferential growth in pure and the dopant ratios. Grain size values calculated fromScherrer’s formula of the films were varied in range of (79-113) nm. The band gap energy values were calculated respectively for undoped ZnO and 2% 4% Te doped ZnO samples.

Effect of Oxygen Sputter Pressure on the Structural, Morphological and Optical Properties of ZnO Thin Films for Gas Sensing Application

ZnO thin films were prepared on glass substrates at low (5 × 10−4 mbar) and high (3 × 10−3 mbar) sputter pressure using dc reactive magnetron sputtering. The structural, morphological, compositional and optical properties of the thin films were investigated. XRD patterns of both films confirmed the polycrystalline nature of the films with hexagonal Wurtzite structure. SEM study indicates that the surface of the film formed at high sputter pressure was more uniform, compact and porous in nature. From the EDAX analysis, no other characteristic peaks of other impurities were observed and the formation of single phase of ZnO was confirmed. From the study of photoluminescence, three peaks were observed, one strong near band-edge emission at 390 nm followed by weak and broad visible emissions around 420–480 nm. Room temperature ammonia sensing characteristics of ZnO nanothin films formed at higher sputter pressure were studied for different ammonia vapour concentration levels. The response of the Ammonia sensor at room temperature (30 °C) operation was observed to be of high sensitivity with quick response and recovery times.

The structural and optical properties of Y (Y = Al, B, Si and Ti)-doped ZnO nano thin films from the first principles calculations

Based on the density functional theory, the structural stability and optical properties of undoped and Y (Y = Al, B, Si and Ti)-doped ZnO nano thin films are investigated. The good stability of the films based on the ZnO (0 0 0 1) can be obtained when the layer is larger than 12. Moreover, the dielectric function, refractive index, absorption, and reflectivity of doped ZnO nano thin films have been analyzed in detail. In the visible light range, the values of ZnO films from 12 to 24 layers are all smaller than those of the bulk. And with the augment of the layers, the values keep increasing. All the results signify that the nano film of 12 layers possesses the lowest reflectivity and weakest absorption. In addition, there is an evident impact of some doped element on the properties of nano films. The absorption and reflectivity of Ti, Si-doped ZnO nano thin films are higher than those of the clean films, while Al, B-doped are lower, especially B-doped. Moreover, the conductivity of the doped structure is better than that of the bulk. Thus, the B-doped ZnO nano thin films could be potential candidate materials of transparent conductive films.

Microstructural and electrical characterizations of transparent Er-doped ZnO nano thin films prepared by sol–gel process

In this study, rare earth element (Er) doped ZnO nano thin films which have dual structure of (Zn1−xErx)O (x = 0.0, 0.01, 0.02, 0.03, 0.04 and 0.05) are prepared by using sol–gel method. The microstructure and electrical properties of prepared nano thin films are investigated. Nano thin films are coated on the glass substrate by using the dip coating method. The films are annealed at 600 °C for 30 min. The X-ray diffractometer (XRD), scanning electron microscopy and atomic force microscopy are used to determine the structural properties such as crystal structures, grain sizes, surface morphology; Hall effect measurements system is used to investigate the electrical properties of materials. XRD results showed that all Er doped nano thin films have a hexagonal structure and (002) orientation. Surface morphologies of ZnErO thin films are denser and more uniform than the undoped ZnO thin film. According to the Hall effect measurements, the resistivity of the films decreased with increasing Er concentration from $$0$$ to $$4\%$$ and then slightly increased at $$5\% Er$$ .

Nano ZnO thin films synthesis by sol–gel spin coating method as a transparent layer for solar cell applications

Zinc oxide nano-structured thin films have been synthesized by low-temperature and cost-effective sol–gel spin coating method. Zinc oxide films with good adherence have been deposited on soda lime glass substrates with two thicknesses 250.15 and 311.32 nm. High transmission (>95%) zinc oxide films with proper interference fringes in the visible and near infrared region have been obtained. Film thickness, optical constants and dispersion parameters have been calculated accurately by using Swanepoel method, which basely depends on the interference fringes of the transmission spectra. Zinc oxide films have direct optical band gap, its values slightly change with the annealing temperatures and film thickness. The X-ray diffraction studies indicated the hexagonal wurtzite structure for zinc oxide films with preferred orientation along (002) plane. Raman spectroscopy confirmed the hexagonal structure for the films. The average particle size is in the nano-scale and the crystallinity level increases with the annealing temperatures and film thickness.

Microtron Irradiation Induced Tuning of Band Gap and Photoresponse of Al-ZnO Thin Films Synthesized by mSILAR

Al-doped polycrystalline nano ZnO (Al-ZnO) thin films with different doping concentrations were successfully prepared by the microwave-assisted successive ionic layer adsorption and reaction (mSILAR) technique. The structural analysis along with the orientation of the prepared films was examined by powder x-ray diffraction (PXRD) patterns. The deposited film is polycrystalline and the (002) orientation enhanced upon doping. Additional investigations were carried out to study the effect of electron beam irradiation (e−-irradiation) on the band gap and photoconductivity of both irradiated and unirradiated samples. Both the Al doping and e−-irradiation led to the enhancement of the photoconductivity of prepared materials. This property enables us to tune the properties of materials for various applications by controlling dopant concentrations and e−-irradiation. The dependence of photocurrent on e−-irradiation of Al-ZnO thin films was not reported previously. Therefore, Al-doped polycrystalline nano-ZnO thin film is a promising material for band gap engineering and for the development of solar cells.

Effect of Post-Annealing on the Properties of Eu Doped ZnO Nano Thin Films

Europium (Eu) doped nanostructure ZnO thin films are prepared by using spray pyrolysis technique. The ZnO:Eu thin films are deposited at a substrate temperature of 623K on glass substrates, using europium nitrate as a Eu source. The as-prepared ZnO:Eu films are annealed in air at 673K and 723K for 1h. The effect of post-annealing on the structural, electrical and optical properties of the films has been studied. XRD measurements show that all the films are nanocrystallized in the hexagonal wurtzite structure and exhibit a preferential orientation along (002) plane, the intensity of preferentially oriented (002) peak is apparently improved. The resistivity of annealed film is larger than the as-deposited. ZnO:Eu film annealing at 723K for 60min exhibits lowest resistivity of 3.62×10-4Ω cm. In addition, the ZnO:Eu film shows good optical transmittance of 94%.

Experimental and Numerical Evaluation on Optical Properties of Al‐Doped ZnO Film Materials

The aim of this article is to provide a systematic method to perform numerical and experimental evaluation on the optical properties of Al‐doped ZnO nano thin films. Some different doping density samples are deposited for testing the transmittance. The results show that the transmittance of Al‐doped ZnO has a nonlinear relation with the optical constants and Al‐doped quantity. The optical band gap of the Al‐doped ZnO decreases with the Al doping quantity increasing. Meanwhile, the Maxwell‐Garnett (MG) theory is used to investigate the optical properties of Al‐doped ZnO nano thin films in visible range. The comparison can illustrate the validity of both test and design method. It implies a potential design and evaluation method for developing a new type of ceramic nano thin film in engineering.

Nano-ZnO film preparation at low temperature and the optical indices calculation

The refractive indices of thin films based on Kramers-Kronig theory are corrected. And the correction theory is used to determine the optical indices of nano-ZnO thin films prepared by low temperature sol-gel method. The calculated results indicate that in the visible (Vis) range, the refractive indices of nano-ZnO thin films exhibit a slight abnormal dispersion, while in the ultraviolet (UV) region, the refractive indices increase with wavelengths increasing (normal dispersion). But the refractive indices show complex change near the absorption edge. The maximum refractive index (1.95) of nano-ZnO thin films within UV range at low temperature annealing is much lower than that of the films annealed at high temperature. The absorption and refractive indices are closely related to the defects in nano-ZnO thin films.

Effect of the Growth Parameters on Nonlinear Optical Properties of Al‐Doped ZnO Nano Films

The objective of this research work is to provide a systematic method to perform test and evaluation on the nonlinear optical properties of Al‐doped ZnO nano thin film structure for designing a high‐performance optical‐electronic structure. Some different kinds of samples can be manufactured for testing. The samples are designed by changing technical parameters such as sputtering power of Al and ZnO, pressure and sputtering time and each parameter has three levels. The test results show that the main factor is the sputtering power of Al, which means the doping density of Al. In the meantime, the Maxwell–Garnett theory is used to investigate the optical prosperities of Al‐doped ZnO nano thin films in the visible range. The optical band gap of Al‐doped ZnO nano thin films increases with the increasing of Al doping density, but it becomes slowly when the doping density is more than 16.0%. The results and the investigation method are useful for designing and manufacturing for nano thin films.

Investigation on the electronic and optical properties of Al-doped ZnO nanostructures

In order to investigate the electronic structures and optical properties of Al-doped ZnO materials, the characteristics such as band structure, density of states, complex dielectric constant of pure ZnO nanowires and Al-doped ZnO were studied by using first-principle method based on the density function theory (DFT). With the Al doping increasing, the band gap of Al-doped ZnO narrows, which is different from that of Al-doped ZnO nano-thin films. It supplies the theoretical reference value for the modulation of the band gap and optical properties of Al-doped ZnO.

A photoconductor based on heavily Al-doped nano-ZnO thin film and its application to a chaos generator

Nano-ZnO thin film with heavy Al doping was deposited on Si substrate by RF magnetron sputtering, and a photoconductor was fabricated on the nano-ZnO thin film using Au as contact metal, producing with a metal–semiconductor–metal structure. The photoconductor was then applied to Chua's circuit through element replacement. Simulation results demonstrated that a triple-scroll optoelectronic chaotic attractor can be generated in the modified Chua's circuit.

Photoluminescence and defect evolution of nano-ZnO thin films at low temperature annealing

Nano-ZnO thin films composed of nanoparticles with sizes of 10–16 nm on silicon substrates at low temperature were prepared by sol-gel method. By placing the nano-ZnO thin films at room temperature or annealing at 100°C in air for 10 h intermittently, within a total 70 h annealing time, the evolution of PL spectra of the nano-ZnO thin films were studied in detail. As the annealing time increases, the PL peaks shift from violet to blue and green bands. The PL peaks at violet and blue bands decrease with the annealing time, but the PL peaks at green band are opposite. The PL spectra are related to the defects in the nano-ZnO thin films. The PL peaks positioned at 430 nm are mainly related to defects of zinc interstatials (Zni), oxygen vacancies and (Vo); the ones at 420 nm to oxygen interstitials (Oi), Zinc vacancies (Vzn), Zni; and the ones at 468 nm to Vzn, Zni, and charged oxygen interstatials(Vo+). The green luminescence is related to Oi, Vo and Zni. The evolutions of PL spectra and the defects are also related to the concentrations of Zn in the thin films, the thicknesses of the films and the annealing time. For the films with 0.5 M and 1.0 M Zn concentrations, after 20 h and 30 h annealing in air at 100°C, respectively, either placing them in air at room temperature or continuing anneal in air at 100°C, the PL spectra are stable. Under the low temperature annealing, Zni decreases with the annealing time, and Oi increases. Sufficient Oi favors to keep the nano-ZnO thin films stable. This result is important to nano-ZnO thin films as electron transport layers in inverted or tandem organic solar cells.

Influence of Mn doping on structural and optical properties of ZnO nano thin films synthesized by sol–gel technique

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10 at%) were synthesized by a dip-coating sol–gel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5 at% of Mn doping level, the c-axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO–Mn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The surface quality of the ZnO–Mn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the transparency of all the samples is greater than 85 %. We note, also, that a small doping (1 %) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5 %, practically the same values of index and gap as pure ZnO are found.

Field Electron Emission from Hydrogen Plasma Treated Nano-ZnO Thin Films

A nano-Zno films are deposited on the Mo film/ceramic substrates by using the electron beam vapor deposition technique. Then a hydrogen plasma treated method is used to improve the characteristics of ZnO thin films by microwave plasma chemical vapor deposition system. Effects of process parameters on morphologies and structures of the ZnO thin films are detected and analysed by field emission scanning electron microscopy, X-ray diffraction spectrum and energy dispersive spectrum. The experimental result indicates that the hydrogen plasma treated techniques can essentially reduce the surface resistance and improve the field emission current density of the nano-ZnO thin films. For the hydrogen plasma treated sample, its field emission current density can increased more than three times at 2.2 V/microm electric field condition.

Synthesis of nano ZnO thin film on Al foil by rf glow discharge plasma and its effect on E. coli and P. aeruginosa

Nano ZnO thin films were deposited on thin Al foils by a rf glow discharge plasma method in which sublimed zinc acetate vapor (precursor) reacted with oxygen plasma inside a low-pressure reactor. The films were microstructurally characterized using XRD, TEM, FESEM, optical reflectance and micro-Raman spectroscopy methods. In view of the good scope of ZnO coating in food packaging, the antibacterial activity in the ZnO thin films was studied by exposing the films to E. coli and P. aeruginosa for up to 8 h. Bacterial cell inhibition of up to 98–99 % was observed in the thin films.

Spectral properties of aluminium doped zinc oxide thin films prepared by SILAR method

The spectral properties of undoped and Al doped ZnO nano thin films prepared using double dip method otherwise called SILAR method (Successive Immersion Layer Adsorption Reaction) are reported. The thin films were having polycrystalline hexagonal structure. The optical properties of these films are studied and reported. The optical constants like the band gap (E g ), refractive indices (n, k), dielectric constant (e), optical conductivity (σ), were estimated using an approximation algorithm developed from established procedures using transmittance spectrum of the thin films. The average excitation energy (E 0), oscillator strength (E d ), effective mass (m*), plasma frequency (ω p ), static dielectric constant (e∞) and carrier concentration (N) are also estimated and reported. The highly transparent thin films showed nanowires protruding from stacked nanorods on SEM inspection that signifies the suitability of these thin films for gas sensors.

Influence of drying conditions on the optical and structural properties of sol–gel-derived ZnO nanocrystalline films

Zinc oxide nanothin films were prepared on glass substrate by sol–gel dip-coating method using zinc acetate dihydrate, methanol, and monoethanolamine as precursor, solvent, and stabilizer, respectively. The relationship between drying conditions and the characteristics of ZnO nanocrystalline films (c-axis orientation, grain size, roughness and optical properties) was studied. The films were dried in an oven at different temperatures and by IR radiation. Then, the films were annealed at 500°C in a furnace. The chemical composition, transmission spectra, structure, and morphology of the samples were studied using infrared (IR) and UV–visible spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM), respectively. The XRD results show that the drying conditions affect the orientation of crystallization along the (0 0 2) plane. AFM images show that the thicknesses of the films decrease from 128 to 93 nm by changing the drying conditions. The photoluminescence (PL) of ZnO nanothin films shows the UV emission at near band edge and broad green radiation at about 465 nm wavelength.

纳米氧化锌薄膜发光管的研究 Study of Nano-ZnO Thin Film Lighting Tube

目的：本文是为研制一种新型节能的纳米氧化锌薄膜发光管进行了研究。方法：采用低成本的丝网印刷方法制备纳米氧化锌薄膜，然后经过热烧结和退火等工艺进行处理。结果：实验结果表明经过热烧结和退火处理等工艺后，氧化锌薄膜具有良好的场致发射特性，且发射电流比较均匀稳定。结论：场致发射条件下的阳极发光亮度均匀稳定，说明热烧结和退火处理工艺得到的纳米氧化锌薄膜可用于制作发光管，并且是毫瓦级功耗的节能发光管。 Objective: The new energy-saving Nano-ZnO thin film lighting tube was innovated in this paper. Method: There are many ways to fabricate Nano-ZnO thin film, but it is difficult to produce the uniform thin film. Nano-ZnO thin film was fabricated by lower cost screen-printed, then, processed thin film with thermal sinter and anneal post-treatment. Result: Through thermal sinter and anneal post-treatment, the field emission was intentionally improved and made the stability and uniformity of emission became better. The fluorescence powder which at least one color was used at the anode electric film of lighting tube. Conclusion: After some measures, under the field emission, the uniformity of anode luminescent was stability. It indicated that the thermal sinter and anneal post-treatment intentionally improve field emission of Nano-ZnO thin film, it can be used in fabricate Nano-ZnO film cathode of field emission lighting tube. The result of the lighting tube research could be used in the fields of LED monitor and lighting equipment and so on, and it also could afford some theory evidence. The innovation is that the power consume of this new energy-saving Nano-ZnO thin film lighting tube was mW grade, it could save plenty of energy source.