Co-doped ZnO Research Articles

The Effect of Co and Cu Co-Doping Zno Thin Films on Structural and Optical Properties

Abstract Using a spray pneumatic technique, cobalt (Co) and copper (Cu) co-doped zinc oxide thin films were effectively deposited on a glass substrate. The goal of this work was to create a semiconductor with good optical and electrical properties by co-doping ZnO thin films with Cu and Co. The ZnO thin films obtained from the Co and Cu co-doping exhibit patterns of x-ray diffraction spectra that suggest they are hexagonal ZnO (wurtzite, JCPDS 36-1451). The thin film elaborated with 2 % Co and 7 % Cu has the lowest value of crystallite size (D = 14.67 nm). The transmission spectra demonstrate that all films have good optical transparency in the visible spectrum, with 7 % Cu achieving the highest transmission. Increasing Cu contents raised the band gap energy. The value at the minimum was 3.31 eV. The optical band gap’s broadening is a significant characteristic of advanced materials and may be useful in applications involving metal oxide nanostructures for visible light gas sensing.

Wrinkle type nanostructured of Al-Ce co-doped ZnO thin films for photocatalytic applications

ZnO:Al:Ce thin film photocatalysts were prepared by sol-gel spin coating method for the photocatalytic degradation of Methylene Blue (MB). The effect of Al-Ce co-doping on the structural, surface, optical and photocatalytic properties of ZnO films was analyzed. The crystallite size of the films calculated using the Williamson-Hall method decreased with Al-Ce co-doping. The enhanced photocatalytic activities of ZnO:Al:Ce wrinkle type nanostructured films can be associate with the increased surface area due to the crystallite size reduction by the Al-Ce co-doping. In the morphology analyzes of the films, the wrinkle network structure was observed in the pure ZnO and (6 %) Al-Ce co-doped ZnO films. All ZnO:Al:Ce films exhibited high transparency in the visible light (> 90%). Photoluminescence (PL) spectra depict near band edge (NBE), violet, blue, blue-green and green emission in deposited films. The photocatalytic test shows that the presence of Al-Ce enhances MB degradation efficiency up to 94 %. As a result, it has been observed that the co-existence of Al and Ce has significant effects on both the physical and photocatalytic properties of ZnO films.

Correlations between structural, dielectric properties, and ab initio calculations in Co-doped ZnO nanoparticles: effect of Co concentration

Correlations between structural, dielectric properties, and ab initio calculations in Co-doped ZnO nanoparticles: effect of Co concentration

Investigation on the Effect of Cu and Mg Concentration on the Optical and Structural Properties of Doped and Co-doped ZnO Nanoparticles

Investigation on the Effect of Cu and Mg Concentration on the Optical and Structural Properties of Doped and Co-doped ZnO Nanoparticles

Field-Assisted Regulation Induced by Cobalt-Doped ZnO for Dendrite-Free Lithium Metal Anodes.

Lithium metal batteries are deemed as an optimal candidate for the next generation of durable energy storage devices. However, the growth of lithium dendrite and significant volume expansion pose as obstacles that impede the application of lithium metal batteries. In this work, a functional copper current collector was designed by coating it with Co-doped ZnO (Co/ZnO) to enhance the lithiophilicity through local electric fields and built-in magnetic fields induced by the ferromagnetic material. The incorporation of Co not only induces a local electric field and thus accelerating electron transfer, but also imparts the ferromagnetic behavior to ZnO, resulting in an internal magnetic field to regulate the dynamic trajectory. Profiting from the above advantages, the symmetric cells have excellent cycle stability in 1 mA cm-2 and 1 mAh cm-2 , maintaining ultra-low voltage for over 2000 h. This study provides a realizable pathway for next-generation current collector of copper modification.

Cube-shaped Cobalt-doped zinc oxide nanoparticles with increased visible-light-driven photocatalytic activity achieved by green co-precipitation synthesis

From the perspective of environmental protection, the highly efficient degradation of antibiotics and organic dyes in wastewater needs to be tackled as soon as possible. In this study, an ecofriendly and green cube-shaped cobalt-doped zinc oxide nanoparticles (Co–ZnO NPs) photocatalyst using Pterocladia Capillacea (P. Capillacea) water extract loaded with 5, 10, and 15% cobalt ions were formed via co-precipitation process to degrade antibiotics. The prepared Co–ZnO NPs were tested as a photocatalyst for the photodegradation of ciprofloxacin (CIPF) in the presence of a visible LED-light source. Co–ZnO NPs have been obtained through the co-precipitation method in the presence of P. Capillacea extract as a green capping agent and reducing agent, for the first time. Several characterization techniques including FTIR, XRD, BET, XPS, TEM, EDX, SEM, TGA and DRS UV–Vis spectroscopy were applied to study the prepared Co–ZnO NPs. XRD results suggested that the average size of these NPs ranged between 42.82 and 46.02 nm with a hexagonal wurtzite structure. Tauc plot shows that the optical energy bandgap of ZnO NPs (3.19 eV) gradually decreases to 2.92 eV by Co doping. Examinations showed that 5% Co–ZnO NPs was the highest efficient catalyst for the CIPF photodegradation when compared with ZnO NPs and other 10 and 15% Co–ZnO NPs. A 10 mg/L solution of CIPF was photo-degraded (100%) within the first 15 min irradiation. The kinetics showed that the first-order model is suitable for displaying the rate of reaction and amount of CIPF elimination with R2 = 0.952. Moreover, central composite design optimization of the 5% Co-doped ZnO NPs was also investigated.

Enhancing the optical, electrical, dielectric properties and antimicrobial activity of chitosan/gelatin incorporated with Co-doped ZnO nanoparticles: Nanocomposites for use in energy storage and food packaging

The solution casting method was utilized to produce a brand of new nanocomposites made of chitosan (Cs), gelatin (Ge), and co-doped ZnO nanoparticles (NPs). The physicochemical characteristics of these nanocomposites were examined using a variety of methods. The doped samples' XRD patterns clearly demonstrated changes in the structural features of the Cs/Ge host polymer, with the widening of the peak at 2θ = 20.31 becoming more prominent as Co-doped ZnO NPs concentration increased. Tauc's relation was utilized to describe the direct and indirect bandgap energies using UV–Vis analysis. By including 3.5 wt% of Co-doped ZnO NPs, the optical energy gap direct and indirect of pure Cs/Ge was reduced from 5.22 to 4.92 eV to 4.90 and 4.42 eV, respectively. Co-doped ZnO NPs reinforcing has a significant impact on the in ac conductivity, dielectric constant and loss tangent values. An ionic conductivity of 1.089 × 10−7 S/cm at Cs/Ge-3.5 wt% Co-doped ZnO NPs was observed. The nanocomposites' antimicrobial effect on bacteria and fungi was tested. The adding of 3.5 %Co-doped ZnO NPs improved the activity against S. aureus (22 mm), E. coli (13 mm), A. niger (29 mm), and C. albicans (27 mm) despite the fact that the investigated pure mix had no effect on the microbiological strains. The current research's remarkable findings in terms of optical, dielectric, electrical, and antimicrobial effects indicate that Cs/Ge-coated ZnO film will have significant uses in both food packaging and energy storage devices.

Feasibility analysis of synthesized polyaniline nanocomposites loaded by Co-doped ZnO nanorods for aqueous pollutants oxidation

Polyaniline (PANI) nanocomposites (NCs) based on cobalt (Co)-doped ZnO nanorods were fabricated (PANI-NCs) using chemical oxidation polymerization technique. Co-doped ZnO nanorods were synthesized using hydrothermal route. Microstructure characterization and UV–Visible absorption measurement confirm the formation of wurtzite ZnO nanostructured crystals. Introducing effect of Co-doped ZnO nanorods into PANI matrix on microstructural, optical, surface morphology and electrical properties of the investigated NCs were studied. The characterization of the fabricated NCs was examined using X-ray diffraction (XRD), Fourier transform infrared (FTIR), high-resolution transmission electron microscopy (HR-TEM) and four-probe DC electrical conductivity. Also, the photocatalytic activity of the fabricated NCs was examined using UV irradiation for Procion Blue dye wastewater oxidation. The photocatalytic experimental parameters were studied and the results revealed high photocatalytic activity reached to complete dye removal within 60 min of irradiation time (at pH 7.0 and room temperature). Finally, the data fitted with first-order kinetic model.

Combustion-mediated sol–gel preparation of cobalt-doped ZnO nanohybrids for the degradation of acid red and antibacterial performance

Abstract The present study explores the combustion-mediated sol–gel preparation of the cobalt-doped ZnO (Co/ZnO) nanohybrids. The characterization results of as-prepared samples were investigated using analytical instruments like FTIR, XRD, XPS, SEM, UV-Vis DRS, BET, and TGA. The doping of cobalt into ZnO was achieved at a lower particle size (21.3 nm) than the pure ZnO (29.6 nm). We observed that the Co-doped ZnO grain size seems to be in abundance and diversity than that of the undoped ZnO. Further examination was carried out with photocatalytic degradation of acid red (AR) dye under visible light illumination and antibacterial performance over Spingomonous pausimobilis and Streptococcus pyrogenes to assess the catalytic performance of the prepared Co/ZnO nanohybrid. The photocatalytic degradation results from the optimum reaction conditions are 150 mg of catalyst loading, pH 2, and 10 ppm of initial AR dye concentration, and the complete degradation of AR dye in 120 min. The antibacterial performance of the Co/ZnO nanohybrid was measured and was found to be 25 and 16 mm for S. pausimobilis and S. pyrogenes, respectively, with respect to the control chloramphenicol.

First-principles study on the electromagnetic properties of Co-doped ZnO surface structures controlled by electric field

This work studies the electric-field control and control mechanism of the electrical and magnetic properties of the (1̅00) surface of Co-doped and oxygen-vacancy (VO)-doped ZnO (ZnO:Co(1̅00)-Vo) based on first-principles calculations. When there is no external electric field, the total magnetic moment is 5.74μB, and the magnetism originates from the double-exchange interaction between Co atoms. When the external electric field is equal to −0.9 eV/Å, the total magnetic moment of the system decreases to 3.28μB. When the external electric field is equal to −0.7 or 0.9 eV/Å, the total magnetic moment of the system tends to zero, and antiferromagnetism emerges. The magnetism is caused by bound polarons. At the same time, as the external electric field increases, the Fermi level increases. When the external electric field is 0.5 eV/Å, the effective mass of ZnO:Co(1̅00)-VO in the Γ–X direction decreases, and the mobility increases from 5.68 to 11.63 cm2/(V s). These findings will have a reference value for the design of magnetic memories.

Structural, optical and photocatalytic properties under UV-A and visible lights of Co–, Ni- and Cu-doped ZnO nanomaterials. Comparative study

In this investigation, Co–, Ni- and Cu-doped ZnO nanoparticles were prepared using precipitation methods. The characterization of the as-prepared nanomaterials was carried out using XRD, FT-IR, DRS, XPS and SEM. The XRD analysis showed that the insertion of foreign metal ions into the matrix of ZnO caused a slight shift of the positions of (100), (002) and (101) diffraction peaks of ZnO towards the lower 2θ, by comparison with pure ZnO. The DRS results showed that Co-doped ZnO nanoparticles absorb wavelengths higher than 400 nm. The estimated band gaps (eV) were 2.48, 3.17 and 3.14 for 10 %Co-ZnO, 10 %Ni-ZnO and 10 %Cu-ZnO respectively. The XPS results showed the existence of two valence states for Co and Ni (Co2+/Co3+ and Ni2+/Ni3+) while Cu exists in the form of Cu2+. The photocatalytic efficiency was evaluated under UV and visible irradiations in aqueous solution using methyl orange (MO) as an organic pollutant probe molecule. The results showed that, under visible light, the MO degradation increased significantly by doping ZnO (10 %Co-ZnO: 33.2 %; 10 %Ni-ZnO: 19.8 % and 10 %Cu-ZnO: 52.5 %) by comparison with undoped ZnO (9.3 %). The important increase in photocatalytic activity observed for the doped ZnO by comparison with pure ZnO, particularly for 10 %Cu-ZnO, has been linked to a synergistic effect of both the band gap narrowing and the increase in the lifetime of photogenerated charge carriers.

Analysis of Hazy Ga- and Zr-Co-Doped Zinc Oxide Films Prepared with Atmospheric Pressure Plasma Jet Systems.

Co-doped ZnO thin films have attracted much attention in the field of transparent conductive oxides (TCOs) in solar cells, displays, and other transparent electronics. Unlike conventional single-doped ZnO, co-doped ZnO utilizes two different dopant elements, offering enhanced electrical properties and more controllable optical properties, including transmittance and haze; however, most previous studies focused on the electrical properties, with less attention paid to obtaining high haze using co-doping. Here, we prepare high-haze Ga- and Zr-co-doped ZnO (GZO:Zr or ZGZO) using atmospheric pressure plasma jet (APPJ) systems. We conduct a detailed analysis to examine the interplay between Zr concentrations and film properties. UV-Vis spectroscopy shows a remarkable haze factor increase of 7.19% to 34.8% (+384%) for the films prepared with 2 at% Zr and 8 at% Ga precursor concentrations. EDS analysis reveals Zr accumulation on larger and smaller particles, while SIMS links particle abundance to impurity uptake and altered electrical properties. XPS identifies Zr mainly as ZrO2 because of lattice stress from Zr doping, forming clusters at lattice boundaries and corroborating the SEM findings. Our work presents a new way to fabricate Ga- and Zr-co-doped ZnO for applications that require low electrical resistivity, high visible transparency, and high haze.

Cation-cation co-doped ZnO thin films for transparent conductive oxide applications

This paper presents a recent study on the structural and transparent conductive properties of sol–gel spin-coated ZnO films, focusing on the effects of cation-cation co-doping. The co-doping combinations investigated include (Sn-Ga), (Ga-Co), and (Ga-Mg). All the films exhibit a ZnO hexagonal wurtzite crystal structure with varying crystallite sizes. Interestingly, the films deposited on glass substrates show a high degree of texture along the (002) lattice plane. Among the (Ga-Sn) co-doped ZnO films deposited on glass substrates, the film with 1 at% Sn-Ga co-doping demonstrates the most promising results in terms of both transparency and electrical conductivity. On quartz substrates, the (Ga-Co) co-doped ZnO films with a composition of 3 at% Ga and 1 at% Co exhibit significantly enhanced optical transmittance and high electrical conductivity, making them promising candidates for optoelectronic applications. Furthermore, the (Ga-Mg) co-doping results in improved optical transmittance and high electrical conductivity for the ZnO films deposited on glass substrates with a composition of 1 at% Ga and 3 at% Mg. The observed results on cation-cation co-doped ZnO films represent an exciting and novel advancement in the field of TCO materials. The findings contribute significantly to the ongoing progress and understanding of co-doped ZnO films as efficient TCO materials for various optoelectronic applications.

Effect of annealing onto physical properties of Co:ZnO thin films prepared by spray pyrolysis technique

In this work, the effect of annealing on the physical properties of Co-doped ZnO thin films has been explored. The Co doping level was fixed at 10 weight (wt) % and deposition has been performed using spray pyrolysis techniques. The deposited film was annealed at temperatures of 400, 450, and 500 °C under an air stream of 5 L min−1. The effect of annealing on the physical properties of the deposited film was investigated using x-ray diffraction (XRD), scanning electron microscope(SEM), x-ray dispersive spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and optical spectroscopy. XRD results revealed the formation of a single-phase ZnO thin film with no other phases even after annealing. The estimated crystallite size was found to be 34 nm for the un-annealed film which was reduced to 31 nm for film annealed at 400 °C. The SEM images show the formation of large grains which respond differently to the annealing process. Upon annealing the band gap value shows a reduction and the plasma fRequency shows an increase. The performance of all films as UV sensors shows the reduction in the response time for film annealed at 400 °C and the decay time, at the same voltage, for film annealed at 450 °C.

Influence of buffer layer on optoelectronic properties of B-Mg co-doped ZnO ultrathin film for high-performance transparent conductor application

In order to develop transparent conductors for optoelectronic devices, B-Mg co-doped ZnO (BMZO) thin films and ZnO/BMZO bilayer films were prepared by using a magnetron sputtering system in this work. The properties of the films with varying operating pressure and buffer layer thickness were measured and investigated systematically. It is found that all films have high transparency, which are almost independent of the buffer layer thickness and the working pressure. Working pressure affects the chance of collision between sputtered particles and gas molecules, which impacts on the average free range of sputtered particles and the energy of the particles. Thus, the BMZO films with high crystallinity and low resistivity can be obtained at appropriate working pressure. The introduction of ZnO buffer layer makes the BMZO films more suitable for TCO applications compared to monolayer BMZO. The results showed that the thickness of the buffer layer with the introduction of ZnO buffer layer decreased the surface roughness and internal stress of the films, which increased the electrical and optical properties of the film. In particular, the ZnO/BMZO film prepared at a working pressure of 3 Pa, exhibits the optimized optoelectrical properties when the buffer layer thickness is 12 nm.

On the vibrational properties of transition metal doped ZnO: Surface, defect, and bandgap engineering

We present a comprehensive study on the structure and optical properties of Mn-and Co-doped ZnO samples prepared via solid-state reaction method with different dopant concentrations and atmospheres. The samples were structural and chemically characterized via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray excited photoelectron spectroscopy. The optical characterization was performed via Raman, photoluminescence, and diffuse photoreflectance spectroscopies. Emphasis was done on the studies of their vibrational properties. The structural data confirm the incorporation of Mn and Co ions into the wurtzite ZnO lattice. It is demonstrated that the usual observed additional bands in the Raman spectrum of transitional metal (TM) doped ZnO are related to structural damage, deriving from the doping process, and surface effects. The promoted surface optical phonons (SOP) are of Fröhlich character and, together with the longitudinal optical (LO) polar phonons, are directly dependent on the ZnO electronic structure. The enhancement of SOP and LO modes with TM-doping is explained in terms of nonhomogeneous doping, with the dopants concentrating mainly on the surface of grains, and a resonance effect due to the decrease of the ZnO bandgap promoted by the introduction of the 3d TM levels within the ZnO bandgap. We also discuss the origin of the controversial vibrational mode commonly observed in the Mn-doped ZnO system. It is stated that the observation of the analyzed vibrational properties is a signature of substitutional doping of the ZnO structure with tuning of ZnO optical absorption into the visible range of the electromagnetic spectrum.

Effects of lattice distortion and amount of d electrons on the pressure-driven structural phase transition in ZnO: A comparative study of V-, Mn-, and Co-doped ZnO

The pressure-driven phase transition from fourfold würtzite (B4) to sixfold coordinated rock salt (B1) structure in ZnO, in particular in transition metal (TM) doped ones, exhibited very scattered results and remained as an outstanding issue. The in situ angle-dispersive x-ray diffraction revealed that TM doping can result in significant reduction on the onset pressure at which the pressure-driven B4-to-B1 phase transition starts to emerge, albeit the transition path appeared to be very much dependent on the doping transition metal element. Systematic comparisons on a series of V-, Mn-, and Co-doped ZnO materials indicated that, in addition to ionic sized difference-induced lattice distortion, the amount of the 3d electrons carried by the doped TM atom may also play a prominent role in the underlying mechanism of the pressure-driven phase transition. Specifically, the existence of 3d electrons may have resulted in increased screening of the Coulomb forces between the cations at increasing pressure, leading to significant softening of the c44 and c66 elastic constants, which, in turn, lowers the onset pressure in triggering the B4-to-B1 phase transition in ZnO. Our results also indicate that the initial lattice distortion induced by the ionic size difference may change the landscape of energy barrier and alter the phase transition path.

Minimization of the threshold voltage parameter of the co-doped ZnO doped liquid crystals by machine learning algorithms

This study aims to examine the influence of the co-doped semiconductor nanostructure (Al-Cu):ZnO on the electro-optical properties of the E7 coded pure nematic liquid crystal structures and minimize the threshold voltage of pure E7 liquid crystal. To determine the ideal concentration ratios of the materials for the minimum threshold voltage, we employed different machine learning algorithms. In this context, we first produced twelve composite structures through lab experimentation with different concentrations and created an experimental dataset for the machine learning algorithms. Next, the ideal concentration ratios were estimated using the AdaBoost algorithm, which has an R^2 of 96% on the experimental dataset. Finally, additional composite structures having the estimated concentration ratios were produced. The results show that, with the help of the employed machine learning algorithms, the threshold voltage of pure E7 liquid crystal was reduced by 19% via the (Al-Cu):ZnO doping.

Fabrication and photocatalytic properties of Co doped ZnO nanomaterials

Co-doped ZnO nanocomposites have been prepared on polyethylene terephthalate-indium tin oxide (PET-ITO) flexible substrates using hydrothermal method. The effects of crystal structure, doping mechanism, as well as photocatalytic properties have been intensive investigated. Compared with pure ZnO, Co-ZnO has distinct photocatalytic activity with the degradation rate of 71.36% for methylene blue (MB) solution. The stable electronic structures and the possible electronic sites for Co elements in combination have been discussed with theoretical calculations. Meanwhile, the mechanism to enhance the photocatalytic activity of ZnO has been discussed.

Improvement of Luminescence and Photocatalytic Performance of ZnO:Eu3+ Nanocrystals Activated by Na+ Ions

Undoped and codoped (Eu/Na) ZnO nanocrystals (NCs) were successfully manufactured through an economical sol-gel method. X-ray diffraction (XRD) analysis demonstrated pure hexagonal wurtzite structure without secondary phases for all the samples. The size of the NCs was found to decrease with codoping by Eu3+/Na+ which is related to the existence of strain and stress in the lattice. The dominance of the E2(high) mode in Raman spectra indicates the good crystallinity of the samples. The study from the X-ray photoelectron spectroscopy (XPS) shows the successful insertion of both Eu3+ and Na+ ions into the ZnO lattice and the generation of the zinc and oxygen vacancies (Vo) defects. The band gap energy was reduced and the Urbach energy increased with Na+ content, proving the distortion of the lattice. From the photoluminescence (PL) study, the activation of the Eu3+ ions by Na+ ones was evidenced. Longer PL lifetimes were obtained from Eu3+ ions when they were sensitized by Na+, which may be beneficial to several applications. A process of excitation transfer from both the ZnO host and Na+ sensitizers to the Eu3+ ions was evidenced and discussed. As an application, we tested the performances of the prepared NCs as photocatalysts for Rhodamine B photodegradation under sunlight irradiation. The ZnO NCs codoped with 1% Eu/4% Na displayed the best photodegradation rate with a good stability and a high kinetic rate constant k of 0.021 min−1. The photocatalytic mechanism is discussed in terms of longer radiative recombination from Eu3+ and the generated oxygen vacancies.