Deposited Zinc Oxide Thin Films Research Articles

Effect of Al doping on structural and optical properties of atomic layer deposited ZnO thin films

In this work, zinc oxide (ZnO) and aluminum-doped ZnO (AZO) thin films with varying Al contents were grown via atomic layer deposition on Si and glass substrates. The structural and optical properties of ZnO and AZO thin films were investigated using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), photoluminescence (PL), and ultraviolet-visible spectroscopy. While undoped ZnO had a wurtzite crystal structure, Al2O3 layers altered the crystal structure depending on the Al content. With the increasing number of Al2O3 monolayers, the γ- Al2O3 structure became more prominent, and ZnO peaks were completely suppressed when the Zn ratio reached 10:1 and beyond. SEM images revealed that the thin films homogeneously covered the entire substrate surface. EDS mapping showed a uniform distribution of Zn, Al, and O in the structure. According to the XPS results, the thin films displayed significant peak intensities corresponding to the main components Zn, O, and Al. Zinc atoms were present only in their oxidized state, not as interstitial atoms. The O 1 s peak could be deconvoluted into three components: the oxygen-zinc bond, the oxygen-aluminum bond, and chemisorbed or OH species. In the AZO samples, a direct correlation was observed between the intensity of the Al 2p peak and the number of Al2O3 layers. Additionally, the calculated elemental ratio of Al increased from 2.582 to 23.955 at.% with more Al2O3 layers. Optical measurements revealed that ZnO and AZO thin films exhibit high transmittance in the visible region. Moreover, introducing Al2O3 layers into the supercycle led to an increasing trend in transmittance. Another improvement in the optical properties was observed as a blue shift in the absorption edge with Al doping, indicating band gap widening. The optical band gap of the ZnO thin films increased from 3.2 to 3.5 eV with Al doping. The origin and concentration of defects were evaluated by deconvoluting the PL spectra. A comparative investigation of the PL spectrum and XPS results revealed variations in defect concentration with deposition parameters and defect formation mechanism was discussed.

Control of NLO and photocatalysis properties based on the use of Sn-doped ZnO thin films for optoelectronics applications

Thin films of zinc oxide (ZnO) have unique properties that make them suitable for various applications. In this study, we used a spray pyrolysis process to develop undoped ZnO and ZnO doped with Sn thin films on a glass substrate. We aimed to investigate the effect of Sn concentration on the optical, nonlinear optical, and structural properties of ZnO:Sn thin films. X-ray diffraction analysis revealed that all the deposited ZnO thin films exhibit polycrystalline hexagonal structures well-oriented along the c-axis. The obtained films were transparent in the visible range, with a transmittance between 70% and 80%. The optical energy bandgap values for the films varied from 3.16 eV to 3.29 eV. We also determined the second- and third-order nonlinear susceptibilities, which decreased with increasing Sn concentration. We investigated the photocatalytic activity of the ZnO-doped Sn thin films using methylene blue dye under visible light. Sn doping enhanced the photocatalytic activity of ZnO thin films, with constant rate values of 0.00046 and 0.00074 min[Formula: see text] for ZnO and ZnO:Sn thin films, respectively.

Effect of Capping Agent on Structure, Composition, and Optical Properties of Low-Cost Chemically Deposited Zinc Oxide Thin Films and Their Antibacterial Activities

In the present report, pure zinc oxide and albumen-capped zinc oxide thin films were deposited on a glass substrate by a simple chemical method. The growth rate of the deposited film increases by means of number of dipping linearly. The films deposited were subjected to XRD, SEM, EDX, and UV-visible spectroscopy to analyze the crystal structure, morphology, composition, and optical properties. Structural feature reported that the deposited films were found to be a wurtzite structure. The degree of crystallinity depends on film thickness with deposition time per cycles. The parameters related to film structure, such as stress, strain, dislocation density, lattice constant, and bond length, were determined. The values of the fundamental absorption edge were at 3.28 and 3.06 eV for the deposited films of pure zinc oxide and albumen-capped zinc oxide, respectively. Photoluminescence measurements indicated that the peaks of emission were found to be 375 and 340 nm for zinc oxide and albumen-capped zinc oxide. The effects of an antibacterial activity against different positive and negative bacteria sources were determined.

Photocurrent performance and enhancement of opto-electronic properties of spray pyrolysis deposited ZnO thin films via V-doping

This study reports on the deposition of highly transparent conducting n-type zinc oxide (ZnO) thin films on FTO substrates, via an optimized doping process. Our work is focused on doping zinc oxide with vanadium (V) using spray pyrolysis technique and ensure the synthesis of nanoparticles-shaped ZnO, with an improved optical, microstructural and electrical properties for solar cells applications, as optical window material. Undoped and V-doped ZnO thin films, with careful optimized amounts (2, 4, 6 and 8 at.%), were grown at maintained 550∘C pre-heated substrate during the deposition process, which enables us to obtain nano-sized ZnO particles. We proved that 4 at.% is the optimum V content that enhances the crystallinity of the grown thin film noticeably. With an average transmittance of 80%, the deposited thin films revealed high transparency in the visible domain with a slight decrease in optical transmission which might result from additional scattering. UV-Visible analysis showed that increasing V amounts, a resulting decrease in the energy bandgap ([Formula: see text]) is obtained from 3.26[Formula: see text]eV to 3.17[Formula: see text]eV for 4 at.% of V content. Moreover, deep level defects in zinc oxide can be reduced with vanadium doping and consequently strengthen the UV emission. The UV emission peak intensity rises with increasing V-doping amount then decreases slightly at 8% of V content. The electrical properties measurements showed a decrease in resistivity from 2.8 10[Formula: see text][Formula: see text][Formula: see text][Formula: see text]⋅[Formula: see text]cm to 0.9 10[Formula: see text][Formula: see text][Formula: see text][Formula: see text]⋅[Formula: see text]cm when doping with 4 at.% of V. The crucial effect of the V-doping of ZnO was also demonstrated via the enhancement of carrier mobility that attains 38.5[Formula: see text]cm2/V[Formula: see text]⋅[Formula: see text]s at the optimum vanadium content. The photocurrent analysis revealed much higher visible light absorption in the V-doped zinc oxide thin films than that of undoped film. The photocatalytic activity enhancements are attributed to the lower recombination rate of the photogenerated electron-hole pairs, the narrowed bandgap, yielding a higher photocatalytic performance.

Atomic layer deposited zinc oxide thin film on pencil graphite for DNA sensor applications

Atomic Layer Deposition (ALD) enables precise thin-film deposition on electrode substrates for electrochemical sensors. In this work, we present the first example of ALD grown zinc oxide (ZnO) deposition on pencil graphite surfaces for deoxyribonucleic acid (DNA) sensory applications, including its detection and DNA damage investigation. For DNA sensing studies, the use of highly productive materials is essential. In this context, the ZnO modified pencil graphite electrodes (ZnO/PGEs) exhibited good electrochemical properties that make them a suitable substrate. ZnO films were characterized using scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The DNA recognition capability of the thin film coated electrodes was tested by using differential pulse voltammetry (DPV), which showed a linear response ranging from 1 mg L−1 to 200 mg L−1 based on the oxidation of guanine (G) with a limit of detection value (LOD) of 0.53 mg L−1 (n = 3). In addition to this, impedimetric monitoring of oxidative DNA damage was performed in the presence of copper(II)/hydrogen peroxide (Cu(II)/H2O2) reagents, and protection studies were conducted in the presence of ascorbic acid. ZnO thin film-based electrodes exhibited good sensor performance in terms of sensitivity, stability, and reproducibility.

TeO2–ZnO (tellurium oxide – Zinc oxide) thin film deposition by the thermionic vacuum arc plasma

In this study, 75TeO2–25ZnO and 70TeO2–30ZnO (mol %) (TZ) glasses were synthesized by using a traditional melt-quenching method. The synthesized TZ glasses were deposited as a thin film using the thermionic vacuum arc (TVA) system. The structure of the deposited TZ thin films and the synthesized TZ bulk glass samples were compared. The structural properties of the TZ thin films and bulk glass samples were determined by using X-ray diffraction (XRD) analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy (FT-IR). The morphological properties of the TZ thin films were obtained by using field emission scanning electron microscopy (FE-SEM) images and atomic force microscopy (AFM). The optical properties of bulk glass samples are obtained with ultraviolet–visible spectrophotometry in the range of 350–1000 nm. Lastly, the electrical properties were obtained by using dielectric spectroscopy. XRD and Raman analysis showed that the TZ thin films had an amorphous structure similar to the synthesized bulk glasses with limited crystallization. The results show homogenous and amorphous thin film structures with few polycrystalline formations.

Optical and structural properties of CdS-ZnO thick film

In the present work, we report the fabrication and characterization of undoped ZnO and Cadmium Sulfide (CdS) and Zinc Oxide (ZnO) thick films. The structural properties of ZnO films are characterized by X-ray Diffraction (XRD). It is evident from XRD that, the crystallite size of fabricated ZnO and CdS-ZnO films are 45 nm and 38 nm respectively. Optical properties have been investigated by U-V absorption. It is observed from U-V Spectroscopy that the band gap decreases with CdS doping. We found that all deposited ZnO thin films are to be polycrystalline structures of wurtzite, and the crystallite size of ZnO is in the nanometric range which further decreases with CdS doping.

Study of birefringence inside nanocrystalline Zinc Oxide thin films using terahertz spectroscopy

We present experimental characterizations of nanocrystalline Zinc Oxide (ZnO) thin films in far-infrared (terahertz) frequency region using terahertz time-domain spectroscopy. A time dependent profile, frequency dependent transmission coefficient, refractive index, absorption coefficient and optical density of ZnO thin films are measured in the terahertz regime. A birefringence is observed as a result of TO–LO phonon splitting took place in the ZnO deposited at 400 °C substrate temperature, while at low substrate temperature of 200 °C there is no sign of birefringence. Thus, it can be clearly evidenced that the presence of birefringence in ZnO is correlated with crystallinity exists inside of the thin films. Absorption behaviour of ZnO nano-crystalline thin films shows the potential use of it for future THz photonics devices. RF magnetron sputtering is the key for the deposition of nanocrystalline ZnO thin films on Si (100) substrate at different temperatures. The X-ray diffraction pattern of ZnO thin films were confirmed the formation of wurtzite hexagonal structure and nanocrystalline nature of the deposited ZnO thin films.

Electrochemical deposition of ZnO thin films in aprotic ionic liquids: Effect of the cationic alkyl-chain-length

Zinc oxide (ZnO) is a semiconductor with various physicochemical properties allowing its use in a wide range of technological applications. The aim of this work is to study nanocrystalline ZnO thin-film deposited using zinc salt which is dissolved in pure ionic liquids (ILs). The latter play a dual role: solvent and supporting electrolyte. Most of ILs have a large electrochemical window and sufficient ionic conductivity. In this work, four hydrophobic ILs, based on 1-alkyl-3-methylimidazoliums bis(trifluoromethylsulfonyl)imide were synthetized and characterized to highlight the effect of the length of the cationic alkyl chain on the morphological, structural and optical properties of nanocrystalline ZnO deposits. Grain growth and its arrangement are affected by the length of the cation alkyl chain of ILs, that act as model agents during electroplating. The electrochemical properties of the produced thin layers were also studied.

Boron induced c-axis growth and ammonia sensing signatures of spray pyrolysis deposited ZnO thin films – Relation between crystallinity and sensing

Boron (B) doping in zinc oxide (ZnO) using spray pyrolysis has always led to deterioration of host crystal structure. Unlikely, here, we report the optimized spray pyrolysis deposition parameters for the development of c-axis oriented boron-doped ZnO thin films. As the B concentration increases from 2 to 10 mol%, the hexagonal crystal structure exhibited a highly oriented (002) plane with an increased texture co-efficient. In particular, 2 mol% B dopants promoted the growth of the (101) and (100) planes and increased the crystallite size. Tensile stress in the c-axis plane of 10 mol% B-doped ZnO films leads to the red shift in the band gap (from wide to narrow). Furthermore, 10 mol% B dopants resulted in the enhanced ammonia sensing performance at room temperature. The sensing performance of all the deposited B-doped ZnO films revealed that influence of enhanced planes of host structure energetically favoured the ammonia adsorption.

Enhanced LPG Sensing Properties of Nanograined ZnO Films: Effect of Pd Sensitization

AbstractNanograined zinc oxide (ZnO) thin films are synthesized by successive ionic layer adsorption and reaction (SILAR) method. The structural analysis reveals synthesized films show phase pure ZnO with wurtzite crystal structure. The deposited ZnO thin films show interconnected nanograins with porous morphology. The ZnO films exposes liquefied petroleum gas (LPG) and shows gas response of 18% under the exposure of 2600 ppm LPG at 673 K. The palladium (Pd) sensitization significantly improves the LPG sensing properties. The Pd sensitization improves gas response up to 80% under exposure of 5200 ppm at 498 K. The response and recovery time are 60 and 50 s, respectively.

Influence of zinc ion concentration on structure, morphology and optical properties of spray deposited ZnO thin films

<p>Zinc Oxide (ZnO) thin films were deposited for five different molarity (M) of Zinc acetate hydrated (0.075, 0.1, 0.125, 0.15, 0.175 M) using simple spray technique to study the effect of zinc ion concentration on structure, morphology and optical properties. The XRD patterns of deposited ZnO thin films show hexagonal crystal structure with wurtzite symmetry. The effect of molarity on morphology was studied using scanning electron microscopy (SEM). The elemental analysis was studied by using energy dispersive X-ray analysis (EDX). The optical absorption was recorded by using systronics double beam spectrophotometer (2201). Crystallite size estimated from XRD data was in nanometre (nm) range; however, films deposited for 0.15 M zinc acetate show maximum crystallite size (66 nm) as compared to other samples. All the films show low absorption in wide range (340-999 nm) of electromagnetic spectrum. However, ZnO film deposited for 0.15 zinc acetate hydrated shows maximum blue shifting of absorption edge and higher band gap (3.8 eV) as compared to other samples.</p>

Effect of Oxygen Flow Rate on the Characteristics of RF Sputtered ZnO Thin Films

Zinc Oxide (ZnO) thin films were deposited on glass substrate by radio frequency (RF)reactive magnetron sputtering technique at variable Oxygen flow rates while Argon flow rates waskept constant. The effect of oxygen flow rate on structural, electrical, optical properties of nanostructured ZnO thin films were investigated by X-ray diffractometer, scanning eletron microscopy(SEM), Hall effect measurements and UV-Visible spectrophotometer. X-ray diffraction (XRD) datareveals films are polycrystalline hexagonal structure with (002) peak as a preferred orientation andcrystallite size was found to be in range12 nm-16 nm.The electrical resistivity of films decreasesfrom 10-1 Ω-cm to 10-2 Ω-cm. All deposited ZnO thin films shows high transmittance above 95% inthe visible range 360 nm-800 nm. The optical band gap and refractive indices have been calculatedusing UV-Vis transmission spectra. Oxygen gas flow rates found to have large impact onoptoelectronic properties of ZnO films.

Influence of cobalt doping on the structural, optical, topographical and sensing properties of spray deposited zinc oxide thin films

Structural, optical and gas sensing properties of spray deposited undoped and cobalt doped ZnO thin films have been carried out and reported. Hexagonal wurtzite structure of the investigated thin films is confirmed using X-ray diffraction technique. Interestingly, crystallite sizes are found to decrease with increasing Co concentration with 0.003 M having least size of 40 nm. The growth orientation plane of ZnO thin films are found to vary with Co doping. Atomic force micrographs reveal spherical grains with compact structure for both the films. The optical band gap values at higher doping concentrations were found to be increased. The Co doped (0.003 M) film gained less band gap (3.36 eV) which is beneficial for ammonia sensing application. The sensing characteristics of doped (Co-0.003 M) ZnO (0.1 M) film at various ammonia vapour concentrations at room temperature were studied.

Effect of oxygen pressure and post-annealing on the properties of reactively sputtered zinc oxide thin films

• ZnO thin films are grown at room temperature on glass using radio-frequency sputtering. • As-grown ZnO films have wurtzite crystalline structure and direct bandgap behavior. • ZnO grown in O-rich and O-deficient plasmas shows annealing-sensitive crystallinity. • Bandgap energy evolution with deposition duration and post-annealing is investigated. • ZnO films with stable morphology and optical behavior are grown under some conditions. Using radio-frequency sputtering in the reactive regime at a fixed radio-frequency power of 200 W, we deposited zinc oxide thin films at room temperature on glass substrates in argon-oxygen sputtering atmospheres with different sputtering durations, and various oxygen contents from 20% to 70%. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmittance spectrophotometry were used to probe structural, morphological, chemical and optical properties of as-grown and post-annealed thin films in air at medium temperatures (up to 500 °C). The as-grown samples were found to present a hexagonal crystalline structure with a major (0 0 2) orientation and direct bandgap energies ranging from 3.27 to 3.3 eV. The post-annealing results in the improvement of crystallinity of ZnO thin films deposited at low oxygen contents and in the deterioration then the recrystallization of films deposited in oxygen-rich plasma. The optimal properties and thermal stability were obtained for 30% of oxygen in the sputtering environment, with an annealing-induced shrinkage of the bandgap smaller than 100 meV.

Enhanced optical transmittance of spray deposited zinc oxide thin films for optoelectronic applications

Transparent zinc oxide thin films (undoped and Mo doped) were coated on glass substrates at the substrate temperature of 400°C using spray pyrolysis set up. The various Mo doping concentrations for the Mo doped thin films are 0.25wt.%, 0.5wt.%, 0.75wt.% and 1wt.%. Prepared thin films were characterized by X and UV-Vis Spectroscopy techniques. Thicknesses of the prepared films were determined using gravimetric method. XRD of the films shows that ZnO belongs to the hexagonal wurtzite structure. Preferred growth orientation for undoped and Mo doped ZnO thin films is along (002) direction, except for the 0.5wt.%Mo:ZnO thin film where the (101) peak becomes prominent. The XRD intensity of the (002) peak decreases with increasing Mo doping concentration for 0.25wt.% and 0.5wt.%, after which it increases for 0.75wt.% and 1wt.%. Crystallite sizes and lattice parameters for the ZnO and Mo:ZnO thin films were also evaluated. Optical studies of the prepared films show an average visible transmittance (AVT) of about 88% recorded in the 380nm to 800nm wavelength region. Optical bandgap for all the films were also reported. Slight increase in the bandgap of ZnO is observed with increasing Mo doping concentration.
 Keywords: average visible transmittan optical bandgap.

Mechanisms behind slow photoresponse character of Pulsed Electron Deposited ZnO thin films

Semiconducting Zinc Oxide (ZnO) is ideal candidate for ultraviolet (UV) photodetector due to its promising optoelectronic properties. Photoconductive type ZnO photodetectors, which is fabricated in metal-semiconductor-metal configuration, show mostly very high photoconductivity under UV light, but they are plagued by slow photoresponse time as slow as several tens of hours, even more. Most of the studies claimed that atmospheric adsorbates such as water and oxygen create charge traps states on the surface and remarkably increase both the photoconductivity and response time. There are also limited studies, which claim that the defect states acting as hole trap centers prolong response time significantly. However, the underlying physical mechanism is still unclear. Here we study the effects of both adsorbates and defect-related states on the photoresponse character of Pulsed Electron Deposited ZnO thin films. In order to distinguish between these two mechanisms, we have compared the time-dependent photoresponse measurements of bare-ZnO and SiO2 encapsulated-ZnO thin film samples taken under UV light and high vacuum. We show that the dominant mechanism of photoresponse in ZnO is the adsorption/desorption of oxygen and water molecules even when the measurement is performed in high vacuum. After the encapsulation of sample surface by a thin SiO2 layer, the adsorption/desorption rates can significantly improve, and the effects of these molecules partially removed.

Influence of stress on the photocatalytic properties of sprayed ZnO thin films

Zinc oxide (ZnO) thin films grown on glass substrates are prepared by means of the Ion Layer Gas Reaction process. The XRD pattern revealed that the ZnO lattice parameters decrease continuously, with the increasing of the film thickness, indicating a continuous variation in the compressive strain. The influence of the thickness on the optical, morphological and structural properties of deposited ZnO thin films was investigated. The UV–Vis absorption spectra of deposited thin films were shown to exhibit a blue-shift, resulting in an increase in the optical band gap from 3.13 eV to 3.24 eV. Structural parameters such as crystallite size, lattice parameters, Zn–O bond length, and residual stress have been determined, and the compressive strain (tensile stress) is found to increase with the increasing of spray time and in turn deposited thin film thickness. The PL spectra of deposited ZnO films, show stronger PL intensity with increasing deposited thin film thickness, which confirm the influence of deposited film thickness on the recombination process of charge carriers and thus on its optical properties. These results, were confirmed by the photo-electrochemical experiments. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure, which shows that structural defects and surface morphology of deposited thin films were also demonstrated to have a direct impact on deposited films’ optical properties. Furthermore, to further confirm these experimental optical results, theoretical first principle calculations were conducted. In addition, a wettability alteration and shift from hydrophobic to hydrophilic surface is observed under UV light exposure.

Development and characterization of ZnO piezoelectric thin films on polymeric substrates for tissue repair.

Currently available scaffolds for tissue repair have shown very limited success, so many efforts have being put in the development of novel functional materials capable of regulating cell behavior and enhance the tissue healing rate. Piezoelectric materials, as zinc oxide (ZnO), can be a very interesting solution for scaffold development, as they can deliver electrical signals to cells upon mechanical solicitation, allowing the development of suitable microenvironments for tissue repair. This way, it is reported the deposition of ZnO thin films on a polymer by direct current magnetron sputtering, under different conditions, in order to obtain a piezoelectric ZnO thin film with potential for tissue repair applications. The obtained ZnO thin films were characterized in terms of morphology, crystallography, electrical conductivity, transmittance, piezoelectricity, and adhesion quality. The deposition process resulted in uniform films, with a very good adhesion to the substrate. The different deposition conditions influenced the evolution of the crystalline domains and preferential growths and consequently, the electrical properties of the films. One of the conditions resulted in a thin film with a high piezoelectric coefficient and a conductor behavior, being considered the most promising to act as a bioactive coating.

Investigating Zinc Ketoiminates as a New Class of Precursors for Solution Deposition of ZnO Thin Films.

Zinc oxide (ZnO) has been recognized as one of the most promising metal oxide semiconductor material for processing low-cost thin film transistors (TFTs). Within the scope of this work, we demonstrate a simple, stabilizer free and very efficient chemical solution deposition (CSD) route to grow high quality ZnO layers. The identification of a highly soluble zinc ketoiminate precursor that undergoes hydrolysis under ambient conditions with the facile cleavage of the ligands was the key to develop a simple and straightforward process for ZnO thin films under mild process conditions. Upon heat treatment at moderate temperatures, the precursor decomposes cleanly yielding polycrystalline ZnO thin films, which was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The composition was investigated employing complementary techniques such as X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) which revealed high purity ZnO layers. The functional properties in terms of transparency and optical band gap were determined by ultraviolet-visible (UV-Vis) spectroscopy. The transparent ZnO semiconductor thin films serve as active channel layer of thin film transistors (TFT) which was demonstrated by spin coating of the precursor. Subsequent curing in ambient air, yields a 10 nm film that is sufficient to fabricate working TFTs test structures.