Electronic Structure Of ZnO Research Articles

A combined theoretical and experimental study on vertically aligned ZnO and ZnO: Sn

Vertically aligned ZnO and Sn (5, 10 v/v%) doped ZnO microrods were produced using chemical bath deposition technique on ZnO seed layers fabricated on glass substrates by spin coating method. The thickness of the seed layer is 365 nm and the length of the ZnO and ZnO:Sn rods are in the range of 1–5 μm. The length of the rods decreases with increasing Sn concentration. The structural, morphological, elemental compound, electrical and optical properties of ZnO and ZnO:Sn films were investigated using x-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, two probe method and UV–Vis absorption spectroscopy, respectively. The electronic structure of ZnO and Sn doped ZnO is calculated depending Density Functional Theory thanks to the WIEN2k program. Based on experimental and theoretical calculations, the band gap energy decreases with increasing Sn concentration. The band gap energy of seed layer, pure ZnO, Sn (5%) and Sn (10%) doped ZnO films was estimated as 3.27 eV, 3.18 eV, 3.14 eV and 3.12 eV, respectively. The band gap energy of Sn (1 atom) and Sn (2 atom) doped ZnO calculated theoretically was found as 0.392 eV and 0.245 eV, respectively. The Fermi Energy shifting towards the conduction band was observed upon Sn doping. Sn (5%) doped ZnO film shows the highest electrical conductivity although its band gap energy is higher than that of Sn (10%). The highest conductivity is attributed to the lowest dislocation density and less oxygen vacancies in the structure.

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.

Structure and Photocatalytic Activity of Copper and Carbon-Doped Metallic Zn Phase-Rich ZnO Oxide Films

ZnO is one of the most important industrial metal oxide semiconductors. However, in order to fully realise its potential, the electronic structure of ZnO has to be modified to better fit the needs of specific fields. Recent studies demonstrated that reactive magnetron sputtering under Zn-rich conditions promotes the formation of intrinsic ZnO defects and allows the deposition of metallic Zn phase-rich ZnO films. In photocatalytic efficiency tests these films were superior to traditional ZnO oxide, therefore, the purposeful formation of intrinsic ZnO defects, namely Zn interstitials and oxygen vacancies, can be considered as advantageous self-doping. Considering that such self-doped ZnO remains a semiconductor, the natural question is if it is possible to further improve its properties by adding extrinsic dopants. Accordingly, in the current study, the metallic Zn phase-rich ZnO oxide film formation process (reactive magnetron sputtering) was supplemented by simultaneous sputtering of copper or carbon. Effects of the selected dopants on the structure of self-doped ZnO were investigated by X-ray diffractometer, scanning electron microscope, X-ray photoelectron spectroscope and photoluminescence techniques. Meanwhile, its effect on photocatalytic activity was estimated by visible light activated bleaching of Methylene Blue. It was observed that both dopants modify the microstructure of the films, but only carbon has a positive effect on photocatalytic efficiency.

First principles study of IIIA atoms adsorbed on ZnO (0001) surface and the applications in optoelectronic devices

First principles method is used to study the adsorption behavior, formation energy and electronic structure of IIIA (B, Al, Ga, In) atoms adsorbed on Top, T4 and H3 sites of ZnO (0001) surface. The date shows that the formation energy of B, Al, Ga and In atoms adsorbed on Top site is highest, then followed by T4 site, and H3 is a more stable adsorption site. With the periodic increase of B, Al, Ga and In atoms, the formation energy of corresponding models decreases gradually, and the binding ability with O atoms also decreases gradually. The electronic structure of ZnO (0001) surface is sensitive to the adsorption sites. When these atoms are adsorbed on Top sites, the electronic structures of B-Top, Al-Top, Ga-Top and In-Top models have a little change compared with ZnO (0001) surface. However, when these atoms are adsorbed on T4 and H3 sites, the impurity states appear on the VBM, which narrowing the band gap of the corresponding models.

Core-double shell ZnO@In2O3@ZnO hollow microspheres for superior ethanol gas sensing

• ZnO@In 2 O 3 @ZnO hollow microspheres have been prepared. • The heterojunctions were created at the interface of In 2 O 3 and both inner and outer ZnO. • The sensor exhibits enhanced gas-sensing properties toward ethanol. • The sensing mechanism is appropriately speculated. Core-double shell-structured ZnO@In 2 O 3 @ZnO microspheres consisting of ZnO hollow microspheres, an In 2 O 3 interlayer, and a ZnO outer layer were synthesized by decorating In 2 O 3 and ZnO on the surface of ZnO hollow microspheres. The ZnO hollow microspheres with a size of 1.4 μm provided a good matrix for the adhesion of In 2 O 3 and ZnO. Both In 2 O 3 and the ZnO shells have a loose microstructure, which provided numerous gas diffusion channels and active sites for gas diffusion and gas sensing reaction. The surface defects and electronic structure of ZnO and ZnO@In 2 O 3 @ZnO were examined by photoluminescence (PL) and ultraviolet photoelectron spectroscopy (UPS). The gas sensing properties of the ZnO hollow microspheres, ZnO@In 2 O 3 core-shell microspheres, and ZnO@In 2 O 3 @ZnO core-double shell microspheres were compared using ethanol as the target gas. The response of ZnO@In 2 O 3 @ZnO toward 100 ppm ethanol was 453.2 at the optimum operating temperature of 200 °C, which was 2 and 30 times higher than that of ZnO@In 2 O 3 and ZnO. Even at a concentration of 1 ppm, the response of ZnO@In 2 O 3 @ZnO reached 53.2, indicating its excellent gas-sensing performance at low concentrations. The superior gas sensing properties of ZnO@In 2 O 3 @ZnO were attributed to its high specific surface area, abundant surface defects, and radial electronic modulation mechanism.

Properties and Configurations of B-N Co-Doped ZnO Nanorods Fabricated on ITO/PET Substrate

Based on flexible materials, optoelectronic devices with optoelectronic technology as the core and flexible electronic devices as the platform are facing new challenges in their applications, including material requirements based on functional electronic devices such as lightness, thinness, and impact resistance. However, there is still a big gap between the current preparation technology of flexible materials and practical applications. At present, the main factors restricting the more commercial development of flexible materials include preparation conditions and performance. In this work, B-N co-doped ZnO nanorod arrays (NRAs) were successfully synthesized on the polyethylene terephthalate (PET) substrate coated with indium tin oxide (ITO) by the hydrothermal method. Based on the density functional theory, the effect of B-N co-doping on the electronic structure of ZnO was calculated; the incorporation of B and N led to an increase in the lattice constant of ZnO. The B-N co-doped ZnO has obvious rectification characteristics with the positive conduction voltage of 2 V in the I–V curve.

Effect of Al doping on optical properties of ZnO thin films: theory and experiment

The structural, electronic, and optical properties of zinc oxide thin films with Al-doping have been investigated experimentally and with density functional theory (DFT) calculations. Changes in properties of doped thin films, which are deposited on a glass substrate by a high-frequency magnetron sputtering method, are monitored using X-ray diffraction data and UV measurements. Our theoretical calculations show that the electronic structure of ZnO: Al can be well described by the DFT+U method. The XRD measurements demonstrated the formation of a pure single ZnO phase and Al atoms is well incorporated in the ZnO lattice. Also, we determine the optical constants such as optical dielectric function, refractive index, optical band gap values, extinction coefficient, and optical conductivity of the doping films through transmittance spectra. The calculated results show the change of lattice parameters Al-doped ZnO. The optical band gap of ZnO: Al is increased compared with pure ZnO. Besides, around the Fermi level of Al-doped ZnO was emerged the shallow donor states from mainly 3s-Al states. Our DFT calculations of optical properties Al-doped ZnO agree satisfactorily with the experimentally measured transmittance values.

A Highly Efficient and Stable Photocatalyst; N-Doped ZnO/CNT Composite Thin Film Synthesized via Simple Sol-Gel Drop Coating Method.

The thin film of N-doped ZnO/CNT nanocomposite was successfully fabricated on soda lime glass substrate by a simple sol-gel drop-coating method. The structural, morphological, chemical, and optical properties of as prepared samples were characterized by a variety of tools such as X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared spectroscopy (FT-IR), and UV-visible spectroscopy. The hexagonal crystalline structure was confirmed from XRD measurement without any other impurity phase detection in samples. The N-doped ZnO/CNT composite showed excellent photo-catalytic activity towards cationic methylene blue (MB) dye degradation with 100% removal rate under UV light irradiation as compared to N-doped ZnO (65%) and pure ZnO (47.36%). The convincing performance has also been observed for the case of visible light irradiation. The enhancement of that photocatalytic activity might be due to narrowing the band gap as well as the reduction of electron–hole pair recombination in ZnO matrix with the incorporation of dopant nitrogen and CNT. It is assumed from the obtained results that N-doped ZnO/CNT nanocomposite thin film can be employed as an economically achievable and ecofriendly method to degrade dye with UV and visible light irradiation. Additionally, density functional theory (DFT) calculations were applied to explore the effect of N-doping on electronic structure of ZnO. The computational study has supported the experimental results of significant band gap contraction, which leads to the maximum absorption towards higher wavelength and no appreciable change of lattice parameters after doping. A conceivable photocatalytic mechanism of N-doped ZnO/CNT nanocomposite has been proposed as well.

Direct sunlight-active Na-doped ZnO photocatalyst for the mineralization of organic pollutants at different pH mediums

This work reports the preparation of Na-doped ZnO (Na-ZnO) as a promising photocatalyst under sunlight through a very simple precipitation method. The crystal and electronic structures of the prepared Na-ZnO were characterized by experimental techniques and Density Functional Theory (DFT) calculations. Where the DFT calculations revealed that the effect of Na-doping on the ZnO electronic structure is consistent with the experimental observations and the bandgap value found to be decreasing. Under direct sunlight, the as-prepared Na-ZnO decolorized more than 99.5% of the methylene blue dye (MB) after 1.5 h and led to mineralization of 98.3% of it after 3 h. While pure ZnO decolorized only 35% of MB dye at the same conditions. The prepared Na-ZnO has a promising photocatalytic activity at different pH's and high photostability reaching to 7 recycle with the same efficiency. Finally, the primary active species produced during the photocatalytic reaction were determined and the photocatalytic mechanism was elucidated.

Effect of intrinsic point defects on ZnO electronic structure and absorption spectra

The effect of intrinsic point defects on the electronic structure and absorption spectra of ZnO was investigated by first-principle calculation. Among the intrinsic point defects in ZnO, oxygen vacancies [Formula: see text] and interstitial zinc [Formula: see text] have the lower formation energy and the more stable structure under zinc(Zn)-rich condition, whereas zinc vacancies [Formula: see text] and interstitial oxygen [Formula: see text] have the lower formation energy and the more stable structure under oxygen(O)-rich condition. The band gap of [Formula: see text] becomes narrow and the absorption spectrum has a redshift. In the visible region, the photo-excited electron transition of [Formula: see text] is graded from the valence band top to the impurity level and then to the conduction band bottom, showing the redshift of absorption spectrum of [Formula: see text] and explaining the reason of [Formula: see text] forming a deep impurity levels in ZnO. Moreover, the impurity energy level of [Formula: see text] coincides with the Fermi level, indicating the significant trap effect and the slow recombination of electrons and holes, which are conducive to the design and preparation of novel ZnO photocatalysts. The band gap of [Formula: see text] and [Formula: see text] broadened and the absorption spectrum showed blueshift, explaining the different values of the ZnO band gap width.

An experimental and theoretical study of the effect of Ce doping in ZnO/CNT composite thin film with enhanced visible light photo-catalysis

Ce-doped ZnO/CNT composite thin film was fabricated successfully on soda-lime-silica glass substrate by sol-gel drop coating method. The structure and morphology of nanocrystalline Ce-doped ZnO/CNT thin film were characterized by X-ray Diffraction (XRD), X-ray photo-electron spectroscopy (XPS), Field Emission Scanning Electron Microscope (FESEM) and UV–Visible spectroscopy. The photocatalytic activity of Ce-doped ZnO/CNT thin film was evaluated by photocatalytic degradation of methylene blue (MB) in aqueous solution as a model pollutant under visible light irradiation. The synthesized Ce-doped ZnO/CNT composite thin film showed 76.71% photocatalytic efficiency whereas bare ZnO thin film showed that of only 25.30%. It has been reported that improved photocatalytic efficiency of composite is due to the synergistic effect of Ce doping and insertion of CNTs into ZnO matrix. The experimental photodegradation data were well fitted to first-order kinetics. The photocatalytic activity of the prepared thin film can be regenerated, which implies that the photocatalytic degradation process could be operated at a relatively low cost. The results suggest that Ce-doped ZnO/CNT composite thin film prepared by sol-gel drop coating method can be developed as an economically feasible and environmentally friendly method to degrade dye containing wastewater using visible light. Furthermore, atomic models for Ce doping in ZnO cluster was used to investigate the effect of doping on electronic structure of ZnO through density functional theory calculations. The computational study suggested a significant narrowing of the band gap and change of the maximum absorption bands towards higher wavelength. These all support the experimental results.

Modeling of ZnO electronic structure from first principles by applying advanced functionals

Modeling of ZnO electronic structure from first principles by applying advanced functionals

Mechanochemical synthesis of zincite doped with cadmium in various amounts

Abstract This work investigates the limit of Cd doping in ZnO derived by means of mechanochemical synthesis using CdCl2, ZnCl2 and Na2CO3 as precursors and NaCl as diluent. The prepared samples were characterized using X-ray diffraction (XRD), Fourier transformed infrared attenuated total reflectance (FTIR ATR) spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS),N2 adsorption-desorption isotherms, scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS), while photocatalytic efficiency has been evaluated for methylene blue degradation process. Zn for Cd replacement limits in the crystal lattice of ZnO derived via mechanochemical synthesis were found to be only 2%. For Cd present in a larger portion, CdO and CdCO3 phases appear. Cd doping limits in ZnO were not affected by the milling interval. However, it was observed that Cd doping impairs the nanocrystallinity of ZnO. The morphology and the electronic structure of ZnO and thus photocatalytic activity was inappreciably affected by the Cd doping.

Cu-Doped ZnO Electronic Structure and Optical Properties Studied by First-Principles Calculations and Experiments.

The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. For the Zn1-xCuxO (x = 0, x = 0.0278, x = 0.0417) original structure, geometric optimization and energy calculations were performed and compared with experimental results. With increasing Cu concentration, the band gap of the Zn1-xCuxO decreased due to the shift of the conduction band. Since the impurity level was introduced after Cu doping, the conduction band was moved downwards. Additionally, it was shown that the insertion of a Cu atom leads to a red shift of the optical absorption edge, which was consistent with the experimental results.

Effect of in, ga and al heavy doping on electronic structure of zno: first principle calculation

Effect of in, ga and al heavy doping on electronic structure of zno: first principle calculation

Ionicity of ZnO —A key system for transparent conductive oxides

The electronic structure of ZnO is dominated by coexisting electron and ionic states/bonds caused by charge polarization and self-trapping phenomena of the valence charges. Their interplay manifests itself in intrinsic electronic defects which have different degree of spatial localization and electronic correlation. The relative abundance of intrinsic defects can be determined by the ionicity factor and its value can be derived from three independent experimental procedures in a consistent way. This approach also explains the complex satellite features in the XPS and XAS data. Ionicity and satellite formation are two experimental findings which can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects.

Electronic and magneto-optical properties of ZnO:Co

High-quality ZnO:Co thin films were synthesized on the sapphire (0001) substrates by pulsed laser deposition. XRD result reveals that the Zn1-xCoxO films are of wurtzite-type crystal structure with x up to x = 0.35. The structural, optical and magnetic properties of ZnO:Co thin films are studied by experiments and theoretical calculations. Electronic structure of ZnO:Co with native defects are studied by the first-principles density functional theory. The experimental data and theoretical data have demonstrated quite good agreement. The optical and magneto-optical properties, namely, on-and off-diagonal conductivity tensor and the transversal Kerr effect (TKE), are calculated for comparison with available experimental data. The origin of observed TKE peaks is discussed..

Visible-light-active ZnO via oxygen vacancy manipulation for efficient formaldehyde photodegradation

We developed a facile method for the synthesis of visible light responsive ZnO through the introduction of different concentrations of oxygen vacancy for efficient formaldehyde photodegradation under visible light irradiation. The visible light active ZnO was prepared using ZnO2 instead of traditional Zn(OH)2 as a precursor. According to the results of Raman and XPS, the concentrations of oxygen vacancy decreased with the increase of annealing temperatures. The effects of different concentrations of oxygen vacancy on the electronic structure of ZnO were investigated by density functional theory (DFT) simulation and the results were confirmed by UV–VIS spectra, which showed the oxygen vacancy narrowed the band gap of ZnO. ZnO with stable concentration of oxygen vacancy was used for formaldehyde photodegradation. The results of photocatalytic experiments reflected that oxygen vacancy can not only act as impurity levels in the band structure of ZnO but can also work as electron traps to accept the photogenerated electrons. The oxygen vacancy in ZnO effectively prohibited the recombination of electron–hole pairs, enhancing the photocatalytic activity of ZnO. The results of our study provide us useful information for the understanding of the mechanisms of the photocatalytic process of ZnO with oxygen vacancy.

Theoretical Study of the Electronic Structures of Na-Doped ZnO

The first-principles with pseudopotentials method based on the density functional theory was applied to calculate the formation energy of impurities and the electronic structure of ZnO doped with Na. In Na-doped ZnO, NaOis the most unstable than the other cases. Simultaneously, NaZnis more stable than Naiaccording to that NaZnhave smaller formation energy. Furthermore, the electronic structure of Na-doped ZnO indicates that that NaZnbehaves as an acceptor, while Naibehaves as a donor.

Metallic filament formation by aligned oxygen vacancies in ZnO-based resistive switches

The electronic structure of ZnO with defects of oxygen vacancies were investigated by using first-principles methods. Some structure models were constructed in order to investigate the effects of the distribution of oxygen vacancies on the electronic properties of ZnO. By analyzing the calculated results, we found that only the aligned oxygen vacancies can form the conducting channel in ZnO, and the transformation of the oxygen vacancy from charged state to neutral state is consistent with the energetics rule of the forming aligned oxygen vacancies. As for the heterojunction of Pt/ZnO/Pt, the oxygen vacancies near the interface of Pt/ZnO depress the local Schottky barrier effectively, and the aligned oxygen vacancies in ZnO form a conducting filament connecting two Pt electrodes. The metallic filament formation in Pt/ZnO/Pt resistive switching cells should be closely related to the carrier injection from Pt electrode into ZnO and the arrangement of oxygen vacancies in ZnO slab.