Hexagonal Wurtzite ZnO Research Articles

Boosting highly transparent and conducting indium zinc oxide thin films through solution combustion synthesis: influence of rapid thermal annealing

IZO thin films with In:Zn ratio of 7:3 and 3:7 were prepared by solution combustion synthesis of metal oxide nitrates and influence of post-deposition rapid thermal annealing (RTA) was studied. Individual 0.5 M indium and zinc oxide precursor solutions were mixed in 7:3 and 3:7 compositions. XRD analysis showed IZO 7:3 composition has only cubic bixbyite In2O3 structure while IZO 3:7 composition showed both hexagonal wurtzite ZnO and cubic bixbyite In2O3 phases. SEM and AFM analysis showed low roughness for IZO 7:3, rms < 2 nm whereas for IZO 3:7 composition surface roughness was >22 nm due to phase segregation. UV/ViS/NIR analysis showed transparency range desirable of transparent conductors for both compositions. Post-deposition RTA treatment resulted in high conductivity single phase IZO 7:3 films. Segregation of phases enhanced carrier scattering resulting in decreased mobility for IZO 3:7 films. Best performing IZO films demonstrated low resistivity 7.66 × 10−3 Ohm cm and high carrier concentration 5.09 × 1019/cm3 after 10 min RTA at 600 °C. These results demonstrate combustion synthesis and RTA are successful for development of films with enhanced conductivity and transparency through low cost vacuum-free synthesis reducing indium content for applications in photovoltaic devices, flat panel displays and transparent electronics.

Decomposition of organic pollutant in waste water using magnetic catalyst nanocomposite

In this study, magnetic recyclable catalyst Fe3O4/CuO/ZnO/nanographene platelets (Fe3O4/CuO/ZnO/NGP) and Fe3O4/CuO/TiO2/nanographene platelets (Fe3O4/CuO/TiO2/NGP) composites were synthesized by simple hydrothermal method. Methylene blue was used as a model of textile dye to evaluate their catalytic activities. A range of analytical techniques including X-ray diffraction, energy-dispersive X-ray spectroscopy and vibrating sample magnetometer were employed to reveal the crystal structure, composition and property of the nanocomposites. The catalytic performance was evaluated by degradation of methylene blue in aqueous solution under UV light and ultrasonic irradiation simultaneously. X-ray diffraction results revealed that cubic spinel Fe3O4, monoclinic CuO, hexagonal wurtzite ZnO and graphene platelets exist in Fe3O4/CuO/ZnO/NGP, while in Fe3O4/CuO/TiO2/NGP nanocomposites instead of hexagonal wurtzite ZnO, anatase TiO2 is observed. These results confirmed that the nanocomposites were the desired materials. In addition, all samples exhibited ferromagnetic behavior at room temperature and could be rapidly separated from aqueous solution for repeated use under external magnetic field. From the degradation of methylene blue, it is found that the as-prepared nanocomposites exhibited excellent catalytic activity compared with nanocomposite synthesized without nanographene platelets. The nanocomposites still retain the 100% of the initial activity after it has been used four times repeatedly.

Magnetically Separable and Reusable Fe3O4/ZnO/Nanographene Platelets Photocatalyst for the Removal of Dye

In this study, we report the sol-gel synthesis of nanocomposite Fe3O4/ZnO with nanographene platelets (NGP)and characterized by suitable techniques, including field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), UV-visible diffuse reflectance spectroscopy and vibrating sample magnetometer. The as-synthesized Fe3O4/ZnO/NGP nanocomposites materials were used for photocatalyst under UV as well as visible light irradiation to remove methylene blue as a model of organic polutan. The XRD spectra reveal peaks that can be attributed to cubic spinel Fe3O4, hexagonal wurtzite ZnO and nanographene platelets structure. The FESEM images show Fe3O4/ZnO uniformly decorating NGP sheets. EDX analysis signifies the formation of Fe3O4/ZnO/NGP. The photocatalytic activity was found to be ZnO loading dependent. Higher ZnO loading lead to higher rate of photocatalytic activity under UV light irradiation, while the opposite trend observed under visible light irradiation. The addition of NGP effectively enhanced the photocatalytic performance of Fe3O4/ZnO nanocomposites. Separation of Fe3O4/ZnO/NGP nanocomposites from the solution could be achieved by applying an external magnetic field, demonstrating the magnetic properties of the nanocomposites.

Synthesis of ZnO and Nd doped ZnO polyscales for removal of rhodamine 6G dye under UV light irradiation

Herein we report, a simple strategy for the synthesis of hexagonal wurtzite ZnO and Nd doped ZnO (Nd/ZnO) using sonochemically assisted chemical co-precipitation method. The samples were characterized by standard analytical techniques, such as Fourier transform infrared and UV–vis spectroscopy (FTIR), x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX) analysis, Photoluminescence (PL) and specific surface area analysis (BET). The XRD results showed that the synthesized ZnO and Nd/ZnO samples were crystalline and accumulated as interleaving polyscales with flower like structure. A redshift is observed in Nd/ZnO samples in comparison with ZnO with increased visible light absorption ability. The band gap energy of Nd doped samples is observed to decrease from 3.21 for pristine ZnO to 3.17 eV with an increase in Nd content. The photocatalytic studies over Rhodamine 6G revealed that the Nd/ZnO samples exhibited excellent photocatalytic activity compared to pristine ZnO. 5% Nd/ZnO showed highest (97.39%) photocatalytic performance for dye removal which is attributable to high surface area 23.949 m2 g−1 together with the efficient increase in the rate of separation of photogenerated electron-hole pairs and capability of hydroxyl radical’s generation as evidenced by UV–Vis absorbance spectra.

Modifications in structural, morphological, optical and photocatalytic properties of ZnO:Mn nanoparticles by sol-gel protocol

ZnO:Mn nanoparticles with different Mn concentrations (0, 1 and 3 at%) have been produced by sol-gel wet chemical route. The effect of manganese doping on the structural, micro-structural, optical and photocatalytic properties of zinc oxide nanoparticles (ZnO NPs) has been investigated. X-ray diffraction and Raman investigations confirmed high quality monophase wurtzite hexagonal structure of pure and Mn-doped ZnO NPs; and no separate phase of dopant has been found. The chemical composition of Mn-doped ZnO NPs has been confirmed by X-ray photoelectron spectroscopic measurements. Additionally, the presence of Mn 2p3/2 peak at 640 eV in XPS spectra confirmed the addition of Mn in ZnO host matrix. TEM micrograph showed spherical shaped NPs with an average size in the range of 21–35 nm. The high resolution TEM images exhibit the highly crystalline nature and the inter-planar distances of hexagonal wurtzite ZnO:Mn nanoparticles. Raman study also confirmed the hexagonal wurtzite structure of ZnO:Mn (0, 1 and 3 at%) NPs. Optical absorption spectra showed a red shift in the absorbance band edge with increasing Mn doping in ZnO. The increasing doping level of Mn in ZnO resulted in the narrowing of bandgap and the increasing of visible light absorption. For photocatalytic behavior, the methylene blue (MB) decolorization efficiency in the very presence of synthesized pure and Mn-doped ZnO NPs has been studied under visible light irradiation. Photoluminescence measurements showed that the band edges of ultraviolet and green emissions are slightly red shifted; and PL intensity decreases with the increasing concentration of Mn in ZnO NPs. The significantly enhanced photocatalytic activity of Mn doped ZnO NPs is because of the increase in light absorption and the effective separation between photogenerated electron-hole pairs.

Photocatalytic degradation of methylene blue in aqueous solution by using ZnO-SnO2 nanocomposites

ZnO–SnO2 (ZS) nanocomposites with different compositions were prepared using a simple coprecipitation method with zinc chloride, stannic chloride pentahydrate, and ammonium hydroxide as raw materials. The morphology and structure of the samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Results showed that the synthesized ZS nanocomposites consisted of hexagonal wurtzite ZnO and tetragonal rutile SnO2. The particle size of ZS decreased evidently with increasing content of SnO2 in the sample. The photocatalytic activity of ZS was explored by analyzing the degradation of methylene blue (MB). After 60 min of UV irradiation, the degradation rate of MB with ZS0.25 reached 96.53%, which was 28.75% higher than that with pure ZnO. Catalytic activity remained at 87.90% after three recycles. A plausible MB degradation mechanism was proposed by testing using UV–vis absorption spectra, Fourier-transform infrared spectra, total organic carbon, high-performance liquid chromatography, and electrospray ionization mass spectrometry.

The efficiency of ZnO/platinum octaethylporphyrin (PtOEP) nanocomposite photoanode at dye-sensitized solar cells

In the present work, we have been studied the applications of ZnO/platinum octaethylporphyrin (PtOEP) nanocomposites as photoanodes for dye-sensitized solar cells (DSSC). The structural properties of ZnO:PtOEP nanocomposites were examined by X-ray diffraction and Raman spectroscopy analysis which confirm the hexagonal wurtzite ZnO structure. Also, the simultaneous existence of PtOEP and ZnO in XRD and Raman mode was confirmed the formation of nanocomposite. Scanning electron microscopy image of the surface morphology confirms the presence of PtOEP particle in the film. The variation in the weight ratios of ZnO:PtOEP is taken to optimize the performance of the DSSC. The photovoltaic and electrochemical impedance spectroscopy (EIS) data indicate that the optimum performance can be achieved at ZnO:PtOEP(1:0.009). Also, the (EIS) measurement of ZnO:PtOEP(1:0.009) photoanode shows displayed faster electron transport, significantly increased electron lifetime, and higher charge collection efficiency than those of pure ZnO.

Dual effect of lignin amine on fabrication of magnetic Fe3O4/C/ZnO nanocomposite in situ and photocatalytic property

The Fe3O4/C/ZnO ternary composite has been synthesized by a facile one-pot method, in which lignin amine (LA) was used as carbon source as well as bridging ligand. Its structure, morphology and composition have been intensively characterized. The composite is found to be composed by cubic spinel Fe3O4, amorphous carbon and hexagonal wurtzite ZnO. Its morphology features as particles in the mean sizes of about 20 nm, which is larger than those of Fe3O4 and Fe3O4/ZnO. This case may be caused by the special construction of the resulting composite. Fe3O4 is covered by carbon, together forming particles; simultaneously, they interconnect with ZnO particles, leading to an increase in the particle size. With these peculiar structural characteristics, the synergistic effect is unraveled to enhance catalytic property of the composite while being applied in water treatment. Fe3O4/C/ZnO under both ultraviolet and visible light irradiation is found to show high degradation efficiencies. More importantly, the catalytic performance is very stable, maintaining 94% even after 5-cycle re-using test. Moreover, our composite materials also display excellent photocatalytic activities on degrading norfloxacin (NF) that is widely used as antibody. Due to easy recovery, good performance and facile synthetic route, our Fe3O4/C/ZnO is anticipated to have a good practical prospect in applications of water treatment.

Effect of Sn doping on electrical and antibacterial performance of Zn0.96-xMn0.04O nanoparticles by bio-synthesis method

Zn0.96-xMn0.04SnxO (x = 0, 0.02, 0.04) were synthesized using Phyllanthus Niruri leaf extract mediated co-precipitation method. The x-ray diffraction pattern demonstrates that doping of Mn and Sn did not show any variations in the ZnO hexagonal wurtzite structure. The reduced crystallite size by Sn doping is because of lattice distortion that altogether prevented the growth. The variations in lattice parameters, average crystallite size, peak position and peak intensity from XRD in addition to EDX, FTIR and optical studies supports the substitution of Sn2+ into Zn-Mn-O lattice. The presence of chemical bonding was studied by FTIR spectroscopy. The optical absorption and band gap alterations with respect to Sn doping were investigated by UV-Visible spectroscopy. The widening of band gap by Sn doping is attributable to both size and compositional effects. The dielectric properties, conductivity and antibacterial properties are boosted up with the addition of the Co-dopant Sn to 4%.

Tuning the properties of ZnO thin film on ITO substrates with Ga dopant for dye sensitized solar cell applications

The performance of pristine and Ga doped ZnO thin films spray deposited on ITO as photoanode in dye-sensitized solar cell (DSSC) was investigated. X-ray diffraction analysis confirmed the hexagonal ZnO wurtzite phase, with preferential grains orientation along (002) plane for lower Ga concentration. Field emission scanning electron microscopy observations revealed homogeneous surface covering the entire substrate with a porous nature. Atomic force microscopy surface topography analysis indicated the deterioration of grain growth along c-axis for higher Ga doping levels. Transmission electron microscopy analysis revealed the formation of hexagonal and prismatic-shaped grains in the range 34–18 nm. Higher transmittance in the range of 85% in the visible region was obtained for 1.5 at.% Ga doped ZnO film, meanwhile the energy band gap increased with Ga doping reaching 3.46 eV. DSSC fabricated with 1.5 at.% Ga doped ZnO as photoanode and pomegranate dye as sensitizer exhibited a power conversion efficiency of 1.21%.

Effect of post-annealing on the properties of Co-doped ZnO thin films deposited by channel-spark ablation

In this study, we report on the effect of post-annealing treatment on the structure and morphology of Co-doped ZnO (CZO) thin film nano-composites deposited on Si (100) by channel-spark pulsed electron beam ablation (PEBA) from a single target, CoxZn1-xO (x = 0.20). The as-grown CZO films have been deposited within the temperature range 350 °C–450 °C, at electron beam acceleration voltages of 15 kV and 16 kV, and a beam frequency of 4 Hz. The films have been subjected to thermal annealing at either 400 °C or 600 °C for one hour. The effect of post-growth annealing on film properties has been discussed in terms of surface morphology, chemical composition, chemical state, and crystal structure. Experimental results show that, overall, post-annealing treatment significantly affects the structural and morphological properties of the films. Films annealed at 400 °C have higher average particle size and degree of crystallinity of ZnO hexagonal wurtzite structure relatively to the films annealed at 600 °C. Films annealed at 400 °C exhibit larger content in hexagonal close-packed (hcp) metallic Co (Co°) compared to the films annealed at 600 °C and to as-grown films. Both x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) indicate that enhanced growth of Coо is achieved at the annealing temperature of 400° C.

Zinc interstitial threshold in Al-doped ZnO film: Effect on microstructure and optoelectronic properties

In order to know the threshold quantity of the zinc interstitials that contributes to an increase in carrier concentration in the Al-doped ZnO (AZO) films and their effect on the overall microstructure and optoelectronic properties of these films, in this work, Zn-rich-AZO and ZnO thin films are fabricated by adding excess zinc (from a zinc metallic target) during their deposition in RF magnetron sputtering and are then investigated using a wide range of experimental techniques. All these films are found to grow in a ZnO hexagonal wurtzite crystal structure with strong (002) orientation of the crystallites, with no indication of Al2O3, metallic Zn, and Al. The excessively introduced zinc in these AZO and/or ZnO films is found to increase the shallow donor level defects (i.e., zinc interstitials and oxygen-related electronic defect states), which is found to significantly increase the carrier concentration in these films. Additionally, aluminum is seen to enhance the creation of these electronic defect states in these films, thereby contributing more to the overall carrier concentration of these films. However, carrier mobility is found to decrease when the carrier concentration values are higher than 4 × 1020 cm−3, because of the electron-electron scattering. Whereas the optical band gap of the ZnO films is found to increase with increasing carrier concentration because of the Burstein-Moss shift, these decrease for the AZO films due to the band gap narrowing effect caused by excess carrier concentration.

Effect of dilute concentrations of Sm on the temperature‐dependent electrical and dielectric properties of ZnO

AbstractCompounds of undoped and samarium (Sm) doped ZnO have been prepared by standard solid‐state reaction method. X‐ray diffraction (XRD), Williamson‐Hall (W‐H) analysis, Transmission Electron Microscopy (TEM), temperature‐dependent electrical and dielectric studies have been done to characterize these materials. Inclusion of Sm as dopant in hexagonal wurtzite ZnO changes the lattice parameters to a small extent with some Sm aggregation at higher concentration. Also, the mean particle sizes of ZnO:Sm compounds showed an inter‐correlation with the Scherrer method, W‐H analysis as well as with TEM results. The electrical resistivity depicts an exponential decay and metal‐semiconductor transition (MST) at ~300 K for the pristine sample whereas there is large decrement in the resistivity with Sm doping. The analysis of σac of ZnO suggests that the power law is obeyed and indicated an increase in the ac conductivity with Sm content. The mechanism behind this type of conductivity is elucidated by small polaron tunneling (SPT) model of conductivity. The dependence of ln dc on the temperature inverse shows that the traps of electrons are thermally activated such that low and high temperature activation energies confirm the presence of vacancies and interstitials of both O and Zn ions. Thus, a high value of dielectric constant makes these materials suitable for high frequency and charge storage device applications.

Dye sensitized solar cells using catalytically active CuO-ZnO nanocomposite synthesized by single step method

In the present paper we report a low cost, single step preparation method for the synthesis of CuO-ZnO nanocomposite through simple co-precipitation technique using oxalic acid. To have a better idea about the deviations brought about by the inclusion of CuO in ZnO lattice, pure ZnO nanoparticles synthesized from 0.1M solutions were also investigated. X-ray diffraction studies showed that the composite contains only hexagonal wurtzite ZnO and monoclinic CuO structures. The magnetic studies of CuO-ZnO heterostructures were also conducted in order to elucidate the source of the ferromagnetism observed at room temperature. The catalytic efficiency of the as prepared nanocomposite was estimated by the degradation of methylene blue and eosin yellowish which also shows its suitability as a promising candidate in waste water treatment. The effect of chenodeoxycholic acid as a co-adsorbent in the performance of dye sensitized solar cells fabricated using the synthesized ZnO and the nanocomposite was also studied and significant improvement in photovoltaic performance has been obtained for nanocomposite based solar cell.

Synthesis of porous zinc-based/zinc oxide composites via sol\u2013gel and ambient pressure drying routes

Porous Zn-based and ZnO composites are successfully fabricated via the sol–gel process and ambient pressure drying method using hexane as the drying solvent for the reduction in capillary force during drying process. Various highly porous Zn-based phases (Zn1-based and Zn5-based) that are studied by X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy show that they contribute through heat treatment (at 200 °C) to the development of ambient pressure dried nanoporous wurtzite (hexagonal) ZnO. A macroporous flower-like structure consisting of nanosheets is observed in porous Zn-based composites, and nanoporous structure is observed within platelets of ZnO nanoparticles. Possible routes for preparing highly porous Zn-based/ZnO composites are discovered by detailing the process for ambient pressure drying synthesis of porous wurzite ZnO.

The optoelectronic properties and role of Cu concentration on the structural and electrical properties of Cu doped ZnO nanoparticles

In the current study, we synthesized a Cu-doped ZnO (CZO) nanoparticles material using a sol-gel method with different doping concentrations of Cu (0, 2, 3 and 4 at.%). The control of the Cu concentration on structural, electrical and optical properties of CZO nanoparticles was investigated in detail. The XRD analysis of the CZO nanoparticles reveals the formation of ZnO hexagonal wurtzite structure for all samples which confirm the incorporation of Cu2+ ions into the ZnO lattice by substitution. Furthermore, CZO nanoparticles showed a small red shift of absorption band with the incorporation of Cu from 0 to 4 at.%; i.e. a decreased band gap value from 3.34 eV to 3.27 eV with increasing of Cu doping content. The frequency dispersion of the electric conductivity were studied using the Jonscher universal power law, according to relation σ(ω) = σDC + A ωs(T). Alternative current conductivity increases with increasing Cu content in spite of the decrease the activation energy with copper loading. It was found that the conductivity reached its maximum value for critical Cu concentration of 3 at.%. The frequency relaxation phenomenon was also investigated and all results were discussed in term of the copper doping concentration.

Effective photocatalytic removal of different dye stuffs using green synthesized zinc oxide nanogranules

Zinc oxide nanoparticles (ZnO-NPs) obtained by a green synthetic strategy using lemon juice and ethylene glycol. The material was characterized using the techniques UV–vis spectroscopy, FTIR spectroscopy, X-ray diffraction analysis, FESEM, EDAX and HRTEM. Diffraction patterns and TEM micrographs confess the formation of hexagonal wurtzite ZnO nanaogranules with some honed faces and having an average size of 49.16 nm. The developed ZnO-NPs was tested for the photocatalytic degradation of Methylene Blue, Congo Red and Rhodamine B target dyes under UV irradiation and found to have remarkable activity.

Synthesis, characterization and ferromagnetic properties of Zn1-xMnxO (x ≤ 0.05) nanoparticles

Zn1-xMnxO (x ≤ 0.05) nanoparticles were synthesized by a combination of room temperature precipitation and high temperature calcination. Pure hexagonal wurtzite ZnO nanoparticles with the size of ≤100 nm and a dominant vibrational peak at 437 cm−1 of E2H non-polar optical phonon mode were detected. The present research was succeeded in doping of ZnO lattice by Mn2+ ions, including the detection of an additional peak at 528 cm−1 associated with lattice defects. Magnetic properties of Zn1-xMnxO (x ≤ 0.05) nanoparticles were controlled by correlated spin of Mn–O–Mn exchange couple and lattice disorder. The saturation magnetization of ferromagnetic Zn0.97Mn0.03O was the highest at 51.49 × 10−3 emu/g.

Effect of sintering temperature on the microstructure, electrical and magnetic properties of Zn0.98 Mn0.02O material

Zn0.98Mn0.02O material was synthesized from ZnO and MnO2 powders using solid state reaction method. The microstructure, electrical and magnetic properties of Zn0.98Mn0.02O were studied as a function of sintering temperature. The X-ray diffraction analysis indicates that the main phase of synthesized sample is composed of hexagonal wurtzite ZnO phase. While the secondary phase of ZnMnO3 were found at the sintering temperature of 700°C and 900°C. The electrical properties measurement of Zn0.98Mn0.02O sample revealed that the resistivity and the dielectric constant of samples increase with the increase of sintering temperature. The ferromagnetic properties at room temperature were observed in the Zn0.98Mn0.02O samples sintered at 500°C and 700°C. It also found that the increase in sintering temperature leads to a tendency toward the changes in the magnetic properties into paramagnetic. The presence of ZnMnO3 secondary phases in Zn0.98Mn0.02O system is believed to be a factor that affects the decrease of the electrical and magnetic properties of the sample.

ZnO core–shell pn homojunction photodetector and its fast UV sensing properties

In this article, we report the fabrication and characterization of ZnO core–shell p–n homojunction photodetector (PD) based on p-ZnO (ZnO:Na) nanorods and n-ZnO (ZnO:Al) film. Hexagonal wurtzite ZnO:Na nanorods in single crystalline has been demonstrated by XRD and TEM analysis. Hall measurement shows that ZnO:Na nanorods exhibit p-type conduction with a hole concentration in the order of 1017 cm−3. Low temperature PL analysis confirms the shallow acceptor level of 128 ± 3 meV of p-ZnO:Na nanorods. And the ZnO homojunction exhibits good rectifying behavior. Under the irradiation of UV light, the ZnO homojunction PD exhibits fast on/off response with a rising and recovery time of smaller than ~ 82 ms. This work not only demonstrates the realization of p-ZnO:Na by a simple CVD method, but also sheds the light on constructing ZnO p–n homojunction based UV PDs and LEDs.