Morphology Of ZnO Thin Films Research Articles

Fabrication and analysis of ZnO and Al-doped ZnO films using the SILAR technique

In this study, undoped ZnO and Al-doped ZnO thin films were successfully deposited on ITO substrates at various concentrations using the SILAR method. The deposited thin films underwent characterization via SEM/EDS, XRD, and UV-Vis spectroscopy. XRD analysis revealed that the thin films crystallized at the nanoscale, with crystallization quality varying based on the concentration of Al dopant. SEM/EDS analysis indicated a notable influence of Al doping concentration on the morphology of ZnO thin films. UV-Vis analysis highlighted significant differences in both the optical band gap values and transmittance of the thin films depending on the dopant used.

Lithium doping effect on microstructural and electrical properties of zinc oxide thin film grown by metal-organic chemical vapor deposition

In this study, the undoped and Li-doped ZnO thin films were grown on Si(100) substrate using metal-organic chemical vapor deposition (MOCVD). Zinc acetylacetonate hydrate and lithium acetylacetonate solution were used as ZnO thin film precursor and Li dopant source. The effect of lithium doping on microstructural was characterized using a scanning electron microscope (SEM) and X-ray diffractometer (XRD). XRD diffractogram analysis shows that undoped and Li-doped ZnO thin films have polycrystalline hexagonal wurtzite structures with preferred peak crystal orientation (103). Li doping slightly changes the lattice parameters and cell volume of ZnO thin films through the increase of crystallite size and slightly affects the surface morphology of ZnO thin films. Current-voltage (I-V) measurement and four-point probe method were used to measure the electrical properties of lithium doped ZnO thin films. The electrical conductivity of ZnO thin films increases as Li doping is given compared to undoped films. These results are also supported by the I-V curve of Li-doped ZnO thin films by having a higher slope, indicating improvement in electrical properties.

Effect of gamma ray irradiation on structural and surface properties of c-axis oriented ZnO thin films

The changes in structure and surface morphology of ZnO thin films due to gamma ray irradiation at high doses are reported. Raman spectroscopy measurements indicate improvement in wurtzite ZnO phase by a higher amount with initial dose of 66 kGy (kGy) and by a lower amount for doses of 132 kGy and 200 kGy. Improvement in c-axis orientation was confirmed by X-ray diffraction measurements. X-ray diffraction measurements also showed a decrease in average crystallite size of ZnO. This is attributed to dissociation of Zn-O bonds by gamma rays which was identified using spectroscopy measurements. Gamma ray irradiation induced surface rearrangement and change in surface roughness with dose were identified using atomic force microscopy measurements. The observed results are explained on the basis of displacement damage and partial annealing effects caused by energetic gamma rays in ZnO thin films.

Effect of Mn doping on defect-related photoluminescence and nanostructure of dense 3-D nano-root network of ZnO

In this paper, we investigate the effect of Mn doping on an interesting morphology of ZnO thin films prepared by sol-gel spin coating technique. The tunability of morphology, structural and optical properties by doping has been reported. X-ray diffraction (XRD) patterns of the samples annealed at 400 °C confirm the formation of hexagonal wurtzite ZnO without any Mn related phases. On introduction of Mn in ZnO lattice, the crystallite size decreases. Field emission scanning electron microscope (FESEM) studies of the samples confirmed the formation of 3-D nanostructured thin films with morphology similar to a dense network of roots. The nano-root network comprises nanoparticles and as the Mn content is increased, the nanoparticles agglomerate. Energy-dispersive X-ray spectroscopy-based color mapping technique was employed to observe the distribution of Zn, Mn, and O elements. On increasing the doping concentration of Mn, there is a blue-shift in the absorption edge in the absorption spectra recorded by UV–Vis spectroscopy. The optical bandgap increases linearly from 3.26 eV to 3.32 eV on increasing the Mn content from 0 at% to 5 at%. Photoluminescence spectroscopy was used to characterize the deep level emissions. A broad deep level emission band arising due to defects was observed which ranges from violet to red region in the undoped ZnO and is significantly suppressed after Mn-doping. Owing to its dense 3-D intertwined nanoroot network, the proposed study is expected to find potential application in gas sensing, photodetection and catalysis.

The Effect of Pre-heating Temperature on Structural and Optical Properties ZnO Thin Film Synthesized using Sol-Gel spin Coating Method

The synthesis of ZnO thin film has been successfully carried out using the sol-gel spin coating method. The production of ZnO thin film was grown on a glass substrate with a rotation speed of 5000 rpm and calcined with pre-heating temperature variations of 250, 300 and 350°C and post-heating at a temperature of 550°C. The results of the characterization of ZnO thin films with XRD showed that all crystal structures in the form of hexagonal wurtzite with the largest crystal size for 350°C pre-heating temperature were 35.3 nm. Morphology of ZnO thin films resulting from SEM characterization in the form of crystallite granules and most of them are round and almost uniform and compact. The results of the characterization of ZnO thin film with UV-Vis showed the highest transmittance value for 350°C pre-heating temperature was 53.9%. The highest absorbance value for 250°C pre-heating temperature is 1,192. The biggest energy band gap value for 350°C pre-heating temperature is 3.15 eV.

Morphology Evolution Of ZnO Thin Films Deposited By Nitrogen Mediated Crystallization Method

We study the surface morphology of ZnO thin films deposited by nitrogen mediated crystallization method utilizing atomic force microscopy as a function of nitrogen flow rates. Initially, the surface morphology of ZnO thin film deposited without nitrogen exhibits a bumpy surface with spiky grains where the skewness and kurtosis values were found to be 0.48 and 4.80, respectively. By addition of small amount of nitrogen, the skewness and kurtosis values of the films significantly decrease associated with a flatter topography. Further increase in nitrogen flow rate to 16 sccm has roughened the surface shown mainly by the increase in kurtosis value to be 3.30. These results indicate that the addition of small amount of nitrogen during deposition process has enhanced the adatoms migration on the surface resulting in a superior film with a larger grain size. Two-dimensional power spectral density analysis reveals that all the films have self-affine fractal geometry with total fractal values in the range of 2.14 to above 3.00.

(0 0 2)-oriented growth and morphologies of ZnO thin films prepared by sol-gel method

AbstractZinc acetate was used as a starting material to prepare Zn-solutions from solvents and ligands with different boiling temperature. The ZnO thin films were prepared on Si(1 0 0) substrates by spin-coating method. The effect of baking temperature and boiling temperature of the solvents and ligands on their morphologies and orientation was investigated. The solvents and ligands with high boiling temperature were favorable for relaxation of mechanical stress to form the smooth ZnO thin films. As the solvents and ligands with low boiling temperature were used to prepare Zn-solutions, the prepared ZnO thin films showed (0 0 2) preferred orientation. As n-propanol, 2-methoxyethanol, 2-(methylamino)ethanol and monoethanolamine were used to prepare Zn-solutions, highly (0 0 2)-oriented ZnO thin films were formed by adjusting the baking temperature.

Ultraviolet photodetection characteristics of Zinc oxide thin films and nanostructures

ZnO thin films were deposited by using RF sputtering technique at 150W and 4×10-3 mbar pressure. Post-deposition rapid thermal annealing of ZnO thin films were carried out at 1000°C for 600sec. ZnO nanostructures (nanowires/nanorods) were hydrothermally grown by using equimolar solution of Zinc nitrate and hexamethyltetramine. Morphology of ZnO thin films and nanostructures were investigated using scanning electron microscope. A comparative study on the ultraviolet photodetection behaviour of ZnO thin films and nanostructures were carried out by adopting current-voltage measurement technique at room temperature. ZnO annealed films have shown relatively lower transient photocurrent decay as compared to as- deposited film, which may be due to the faster evacuation of the charge carries. However, in case of ZnO nanorods transient photocurrent decay is relatively slow than that of nanowires, which is attributed to delayed readsorption of oxygen molecules onto the nanorods surface due to its larger width.

Synthesis of ZnO films in different solvents and their photocatalytic activities

ZnO thin films have been successfully synthesized via the chemical bath deposition (CBD) method without using any catalysts or templates. The effects of solvents (such as water, ethanol and n‐propanol) on structure and morphology of ZnO thin films have been studied. XRD analysis showed that all ZnO thin films with wurtzite crystal structure were obtained via various solvents. SEM images showed that ZnO thin films prepared in different solvents have different sizes and morphologies. TEM images showed that crystalline ZnO samples prepared in different solvents have different growth habits. Photoluminescence and photocatalysis properties have been investigated at room temperature. ZnO thin films prepared in water showed superior photocatalytic activity in the degradation of rhodamine B (RhB) compared to other samples.

Effect of electrodeposition duration on the morphological and structural modification of the flower-like nanostructured ZnO

Flower-like morphology of ZnO thin films were successfully electrodeposited via a one-step route only by changing electrodeposition duration and potential at a fixed concentration on n-Si (100) in 78.10−4 M Zn (NO3)2, 6H2O and 0.1 M KNO3 solution at 70 °C without using any catalyst, additives or seed layer. The as electrodeposited products were characterized by X-ray diffraction, scanning electronic microscopy and photoluminescence. The effects of the electrodeposition potential and duration on the morphology, structure and photoluminescence properties were studied. The results show that the product morphology changes with a change in the applied voltage and electrodeposition duration. Well defined shape of flower-like ZnO morphology was generated under the limited conditions of −1.2 V for 60 min, with (002) preferred orientation. Strong UV emission is obtained in the case of ZnO flower like morphology electrodeposited at −1.2 V for 60 min. The band-gap energy value of ZnO flower-like, determined from optical reflectance spectra, is 3.37 eV.

Impedance spectroscopy and sensors under ethanol vapors application of sprayed vanadium-doped ZnO compounds

Thin films of vanadium-doped zinc oxide with different vanadium-doping levels (0, 1, 2 and 3at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using at relatively low substrate temperature (460°C). The effect of V doping on the structural, morphological and optical properties of the films was investigated by Mhamdi et al. (2013). The X-ray diffraction analysis shows that the films were well crystallized in würtzite phase with the crystallites preferentially oriented toward (002) direction parallel c-axis. As also that the average particle size along the surface of the films decreases with increasing of concentration of vanadium. In this work we study the AC and DC conductivity and gas sensor application on ZnO:V thin films. The dielectric properties of ZnO:V thin films were studied by means of complex impedance spectroscopy and frequency dependence of conductivity measured from the impedance data at a range of frequency intervals between 10Hz and 13MHz with a temperature between 355 and 445°C. The frequency dependence of the dielectric constant ɛ′, dielectric loss ɛ″, loss tangent (tanδ) and AC electrical conductivity (σAC) of the layers was subsequently investigated. In literature, we have shown in previous papers that structural and surface morphology of ZnO thin films, prepared by spray, plays an important role in the gas detection mechanism. In this article, we have studied the response evolution of ZnO:V sensors ethanol versus time and working temperature, relative doping and the concentration of the ethanol vapor.

Growth evolution of self-textured ZnO films deposited by magnetron sputtering at low temperatures

In this work, the evolution of the surface morphology of ZnO thin films deposited by reactive RF magnetron sputtering has been investigated using atomic force microscopy (AFM) and X-ray diffraction (XRD). All AFM images of the films were analyzed using scaling concepts. To study the growth evolution, different ZnO films with thicknesses of up to 1270nm were deposited at temperatures of 100 and 250°C. For the films grown at 100°C, AFM data show that the lateral length ξ evolves continuously while the temporal evolution of the root mean square roughness σ presents two distinct regimes. Early during the depositions, the morphology of the ZnO films is mainly characterized by granular structures. Beyond thickness of about 600nm, pyramid-like structures with {214} crystallographic facets start to develop. For the films grown at 250°C, however, only one growth regime was observed and for the thicker films, the surface morphology consisted of polygonal structures. For the films grown at 100°C, the growth exponents, β, and the exponent defining the evolution of the characteristic wavelength of the surface, p, were β1=0.70±0.02 and β2=0.26±0.2; and p=0.2±0.04. For the films grown at 250°C, the exponent values were β=0.78±0.02 and p=0.32±0.05. These values of the exponents indicate the occurrence of surface mechanisms, such as shadowing and surface diffusion, as well as facet stabilization at 100°C. For the films grown at 250°C, however, structural misorientation during growth also plays an important role.

Effect of methanol ratio in mixed solvents on optical properties and wettability of ZnO films by cathodic electrodeposition

ZnO thin films were prepared in the electrolyte with different methanol ratio by cathodic electrodeposition method. Microstructure, surface morphology, optical properties and wettability of the thin films were investigated by X-ray diffractometer, field-emission scanning electron microscope, ultraviolet–visible spectroscope, fluorescence spectrometer and water contact angle apparatus. Increase of methanol ratio in the solvents may restrain the (002) plane preferential orientation in some extent. Change of current density curves with the ratio of methanol in the solution play a vital role on electrochemical reaction kinetics, microstructure and/or surface morphology of ZnO thin films. With the methanol ratio increase from 0 to 0.8, the surface morphology changes from nanorods to net-like nanostructure. The adsorbed NO3− ions on the polar planes hinder the crystal growth along the c-axis and redirect the growth direction along the nonpolar planes. The maximum and minimum band gaps have been obtained in the ZnO thin films with the methanol ratio of 0.4 and 0.6, respectively. Change of contact angle before UV irradiation may be related to surface morphology and oxygen vacancies. The maximum light-induced water contact angle change has been observed in the sample with the methanol ratio of 0.8. The results may be attributed to the higher surface roughness and net-like morphology.

Scanning fluorescence-based ultrasensitive detection of dengue viral DNA on ZnO thin films

In this article, ZnO thin film acts as a matrix to bind with a sequence specific probe strand, which is employed as a recognition element and is involved in sensing the complementary DNA of dengue virus specific serotypes. ZnO thin films possess high surface area, high catalytic efficiency with an isoelectric point of ∼9.5, thus leading to strong electrostatic attraction and strong adsorption capability towards negatively charged DNA having an isoelectric point of 4. ZnO thin film deposition is carried out by ultrasonic spray pyrolysis (USP) at the temperature of 450°C using dry air as the carrier gas along with 0.1M of zinc acetate as the precursor to obtain transparent films with a thickness of around 150–200nm. X-ray diffraction data show the dominant peak corresponding to (100). The morphology of ZnO thin films was analyzed using field emission-scanning electron microscope (FE-SEM) and atomic force microscope (AFM). The optical characteristics of thin films were studied using UV-spectroscopic analysis, which confirms the band gap of the film to be 3.3eV. Further, sequence specific DNA immobilization is carried out for the bio-functionalization of ZnO thin films to detect 4 DENV serotypes, thus enabling simultaneous detection in an array having sensitivity in the range of 1×10−15 moles of DNA.

Modification of ZnO thin films induced by high-density electronic excitation of femtosecond KrF laser

The effect of laser irradiation on nanoscale morphology of ZnO thin films has been studied in the regime of high-density electronic excitation. A femtosecond KrF laser (248 nm, 450 fs) was used to irradiate the films prepared by solgel (SG) and pulsed laser deposition (PLD) methods with fluences below ablation threshold and above that of Mott density. This regime corresponds to electron-hole plasma (EHP) creation, resulting in a specific nanostructuring of monocrystalline ZnO surfaces. A strong nanoscale modification of thin films in the domain of laser fluences 105  mJ/cm2<E<180  mJ/cm2 has been evidenced. While PLD films maintain a smooth surface with nanoholes arranged in straight and zig–zag lines (similar to ZnO monocrystals) surrounded by domains of ∼100  nm size, SG films show the flake-like structure with an open porosity. This behavior can be related to the density of the prepared films.

Influence of Sb doping on the structural, optical and electrical properties of p-ZnO thin films prepared on n-GaN/Al2O3 substrates by a simple CVD method

ZnO thin films with different Sb doping concentrations were prepared on n-GaN/Al2O3 substrates by simple chemical vapor deposition. Field-emission scanning electron microscopy (FE-SEM) showed that the morphologies of ZnO thin films were rougher and the size of the crystal grains reduced with increasing Sb concentration. The X-ray diffraction measurements indicated that the (002) diffraction peak positions of samples shifted gradually towards the lower angle side, which explained the substitution of Sb3+ into the Zn site by Sb doping. In addition, Hall measurement results indicated that Sb doped ZnO thin films had p-type conductivity, and the optimal Sb2O3/ZnO mass ratio for p-type ZnO thin film was approximately 1:4. Optical absorption spectrum measurement indicated that the energy gaps of the samples were evidently narrowed with increasing Sb doping concentration.

Structure and Electrical Characteristics of Zinc Oxide Thin Films Grown on Si (111) by Metal-organic Chemical Vapor Deposition

ZnO thin films were grown on Si (111) substrates by low-pressure metal-organic chemical vapor deposition. The crystal structures and electrical properties of as-grown sample were investigated by scanning electron microscopy (SEM) and conductive atomic force microscopy (C-AFM). It can be seen that with increasing growth temperature, the surface morphology of ZnO thin films changed from flake-like to cobblestones-like structure. The current maps were simultaneously recorded with the topography, which was gained by C-AFM contact mode. Conductivity for the off-axis facet planes presented on ZnO grains enhanced. Measurement results indicate that the off-axis facet planes were more electrically active than the c-plane of ZnO flakes or particles probably due to lower Schottky barrier height of the off-axis facet planes.

Effect of Seed Layer Structure on Surface Morphology and Photoluminescence Property of ZnO Nanorods Grown on LiNbO3 Substrate

ZnO nanorods were synthesized on the ZnO seed layers with various surface morphologies. The ZnO thin film was deposited on a 64° Y−cut LiNbO3 substrate by radio frequency magnetron sputtering and ZnO nanorod arrays were then synthesized on the thin films via the hydrothermal method. The surface morphology of ZnO thin films were controlled by the ratios of oxygen to argon. The crystalline structure, surface morphology, and photoluminescence characteristics of the films and nanorod arrays were examined by X-ray diffraction, scanning electron microscopy, and photoluminescence spectrometry. The surface morphology of ZnO seed layers affects the growth of ZnO nanorod arrays obviously.

Low temperature electrochemical deposition of nanoporous ZnO thin films as novel NO2 sensors

The nanoporous ZnO thin films were prepared on Ti substrate by the low temperature, one-step electrochemical deposition for a novel NO2 sensor. The porous structure of the prepared thin films can be controlled by the added amounts of eosin Y in the deposition bath. The crystalline structure and morphologies of ZnO thin films were characterized. The effect of the surface structure and defects of ZnO thin films on the adsorption of oxygen and the gas sensing performance were investigated. The sensing test results indicate that the ZnO porous thin films have high sensitivity toward NO2. On the other hand, the response to NO2 is higher than that to CH4 and CO at relative low temperature indicating its good sensing selectivity. The intrinsic sensing characterization is attributed to the native defects in ZnO because the relative content of donors is more than that of the acceptors, which was confirmed by the photoluminescence analysis. This work presents a new possibility and usefulness of such electrochemically prepared ZnO porous thin film and can give rise to interesting option for developing other novel sensors.

Room temperature radio-frequency plasma-enhanced pulsed laser deposition of ZnO thin films

In this study, we compared the crystalline structures, optical properties, and surface morphologies of ZnO thin films deposited on silicon and glass substrates by conventional pulsed laser deposition (PLD) and radio-frequency (RF) plasma-enhanced PLD (RF-PEPLD). The depositions were performed at room temperature under 30–100mTorr pressure conditions. The RF-PEPLD process was found to have deposited a ZnO structure with preferred (002) c-axis orientation at a higher deposition rate; however, the RF-PEPLD process generated more defects in the thin films. The application of oxygen pressure to the RF-PEPLD process reduced defects effectively and also increased the deposition rate.