Fabrication and electrical characterization of transparent NiO/ZnO p–n junction by the sol–gel spin coating method

Sol–gel spin technique was used to fabricate transparent p–n junction between NiO and ZnO semiconductors. Atomic force microscopy studies indicated that ZnO film had a fibrous structure, while NiO film showed very smooth surface morphology. The optical transmittance of these films was about 75 %. The optical band gaps of ZnO and NiO films were obtained to be 3.25 and 3.89 eV, respectively. The current–voltage characteristics of NiO/ZnO junction showed a good rectifying behavior. The junction parameters such as ideality factor and barrier height were calculated using thermionic emission model. The barrier height and ideality factor values of the diode were obtained to be 0.48 and 2.91 eV, respectively. The variation of photocurrent with wavelength indicates that this device had high efficiency in wavelength range of 450–475 nm.     

Nanocrystalline Zn1−x−yBexMgyO thin films synthesized by the sol–gel method: structural and near infrared photoluminescence properties

In this paper, we reports on the structural and optical properties of Zn_1?x?yBe_xMg_yO thin films prepared by sol–gel method, which are new materials for optoelectronic and ultraviolet-light-emitting devices. The crystal structure and core level spectra of these films are studied by X-ray diffraction and X-ray photoelectron spectroscopy. Surface morphology of the films is analyzed by scanning electron microscope images and the surface is composed of spherical shaped grains. Micro-photoluminescence shows a near edge band emission and the peak values tuned from 3.26 eV for the undoped to 3.4 eV for the doped ZnO film. Near infrared emission is observed in the region 1.64–1.67 eV for pure and co-doped ZnO films. In micro-Raman spectra, multiple-order Raman bands originating from ZnO-like longitudinal optical (LO) phonons are observed. A Raman shift of about 5–18 cm^?1 is observed for the first-order LO phonon. A comparative study was made on Raman band for BeZnO, MgZnO and BeMgZnO nanocrystals with the LO phonon band of bulk ZnO. The ultraviolet resonant Raman excitation at room temperature shows multi-phonon LO modes up to the fourth order. Deformation energy of all the films is calculated and BeMgZnO film has the minimum deformation energy.     

Studying structural,morphological and optical properties of nanocrystalline ZnO:Ag films prepared by sol–gel method for antimicrobial activity

Pure and Ag-doped zinc oxide sol–gel thin films were prepared by spin-coating process. Pure and Ag–ZnO films, containing 2–8% Ag, were annealed at 500?°C for 2?h. All thin films were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–visible spectroscopy. X-ray diffraction studies show the polycrystalline nature with hexagonal wurtzite structure of ZnO and Ag:ZnO thin films. The crystallite size of the prepared samples reduced with increasing Ag doping concentrations. AFM and SEM results indicated that the average crystallite size decreased as Ag doping concentration increased. The transmittance spectra were then recorded at wavelengths ranging from 300 to 1000?nm. The films produced yielded high transmission at visible regions. The optical band gap energy of spin-coated films also decreased as Ag doping concentration increased. In particular, their optical band gap energies were 3.75, 3.55, 3.4, 3.3, and 3.23?eV at 0%, 2%, 4%, 6%, and 8%, respectively. Antibacterial activity of pure and Ag-doped zinc oxide against Escherichia coli and Staphylococcus aureus was evaluated by international recognized test (JIS Z 2801). The results showed that pure and Ag-doped ZnO thin film has an antibacterial inhibition zone against E. coli and S. aureus. Gram-positive bacteria seemed to be more resistant to pure and Ag-doped ZnO thin film than gram-negative bacteria. The test shows incrementally increasing in antibacterial activity of the thin films when dopant ratio increased under UV light.

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Growth and morphological studies of NiO/CuO/ZnO based nanostructured thin films for photovoltaic applications

At present, inorganic semiconducting materials are the most economical and viable source for the renewable energy industry. The present work deals with the morphological and optical characterization of copper oxide (CuO) and zinc oxide (ZnO) thin films fabricated by layer by layer deposition on nickel oxide (NiO) coated indium tin oxide (ITO) glass by solution processing methods, mainly chemical bath deposition (CBD) and hydrothermal deposition (HTD) processes at room temperature. As a whole, the above inorganic composite materials (NiO/CuO/ZnO) can be applied in photovoltaic cells. An attempt has been made to study structural, morphological and absorption characteristics of NiO/CuO/ZnO heterojunction using state of the art techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV spectroscopy. The energy band gaps of CuO and ZnO have also been calculated and discussed based on the UV spectroscopy measurements.     

Three‐Dimensional Structures of Nanoporous NiO/ZnO Nanoarray Films for Enhanced Electrochromic Performance

An electrochromic device with the as‐obtained nanoporous NiO /ZnO nanoarray as a working electrode was constructed and assembled. The nanoporous NiO/ZnO nanoarray film with a three‐dimensional structure was prepared on indium tin oxide (ITO) glass substrate through a two‐step route that combined chemical bath deposition method with a hydrothermal method. The nanoporous NiO/ZnO nanoarray electrode reveals a noticeable improvement in electrochromism compared with that of nanoporous NiO alone, including higher optical modulation (81 %), higher coloration efficiency (78.5 cm² C^?1), faster response times (2.6 and 9.7 s for coloring and bleaching, respectively), and favorable durability performance. Such enhancements are mainly attributed to the three‐dimensional structures of nanoporous NiO coated on ZnO nanoarray, namely, 1) the uniform hexagonal ZnO nanoarray loads more nanoporous NiO, 2) nanoporous NiO cross‐linked with ZnO nanorods provides a loose interspace morphology, 3) stronger adhesion between ZnO nanorods and ITO covered with ZnO seed, 4) core–shell and cross‐linked structures promote electrolyte infiltration, and 5) appropriate band gaps improve charge transfer.     

Microwave-assisted sol-gel synthesis of CeO2–NiO nanocomposite based NO2 gas sensor for selective detection at lower operating temperature

The progress in the development of gas sensors has considerably grown using some novel nanomaterials of metal, metal oxide and composite. In the current study, we intended and evaluated the properties of nanomaterials like CeO₂, NiO, and CeO₂–NiO composite and its application as NO₂ gas sensor. Sensing of low concentration of NO₂ gas at optimum functional temperature was succeeded using CeO₂–NiO nanocomposites (NCs) film. The working temperature ranges in between 100 and 225 ?°C. Highly crystalline nanomaterials (CeO₂, NiO and CeO₂–NiO) have been prepared by applying microwave-assisted sol-gel route. The as-prepared nanomaterials are characterized for their structure, size, morphology and constitution by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. XRD studies of nanoparticles reveal the formation of nanoscale CeO₂ and NiO with crystallite size 26, 23 ?nm, respectively. Both are having a face centered cubic structure. The nanocomposite (NC) Ce:Ni ?= ?60:40 has crystallite size of 13 ?nm. XRD study of NCs shows assimilation of Ni metal into the ceria and proves physical similarities of two phases. It can be observed from SEM that prepared NC has a porous surface which enables more surface active sites for adsorbing oxygen. The optical properties are measured with the help of UV–Vis. Spectroscopy. Optical band gaps of 3.19, 3.41 and 2.9 ?eV were observed for CeO_2, NiO nanoparticles (NPs) and CeO₂–NiO NC, respectively. Gas sensing properties state that the NC material shows a higher gas response % of 67.34% for NO₂ gas (25 ?ppm) at comparatively low operating temperature (125 ?°C). It gives response time as (～28 ?s) and the recovery (～54 ?s). NiO incorporation in CeO₂ results in a decline of operating temperature of NC and improves the sensing features.     

Evolution of surface topography and optical band gap of ZnO film deposited on NiO/Si(100)

Evolution of surface features and optical band gap of ZnO thin films deposited on different NiO/Si(100) are reported. In order to create different initial microstructure, we first deposited NiO film on Si(100) at 3 different temperatures (400°C, 650°C, and 700°C) by pulsed laser deposition. These NiO/Si(100) films are used as substrate for the deposition of ZnO films. Combining the results obtained from grazing incidence X‐ray diffraction, atomic force microscope, and UV‐Visible characterization, our study indicated that the microstructure of the substrate takes the important role in dictating properties of the film. Our study also indicated that one needs to choose appropriate synthesis condition to achieve good quality ZnO films.     

Preparation of New Magnetic Nanocatalysts Based on TiO2 and ZnO and Their Application in Improved Photocatalytic Degradation of Dye Pollutant Under Visible Light

Photocatalytic degradation of methyl orange (MO) as a model of an organic pollution was accomplished with magnetic and porous TiO₂/ZnO/Fe₃O₄/PANI and ZnO/Fe₃O₄/PANI nanocomposites under visible light irradiation. The structures of nanocomposites were characterized by various techniques including UV–Vis absorption spectroscopy, XRD, SEM, EDS, BET and TGA. Optical absorption investigations show two λ_max at 450 and 590 nm for TiO₂/ZnO/Fe₃O₄/PANI nanocomposites respectively possessing optical band gaps about 2.75 and 2.1 eV smaller than that of the neat TiO₂ and ZnO nanoparticles. Due to these optical absorptions, the nanocomposites can be considered promising candidates as visible light photocatalysts to produce more electron‐hole pairs. The degradation of MO, extremely increased using polymeric photocatalysts and decolorization in the presence of visible light achieved up to 90% in less than 20 min in comparison with the neat nanoparticles (about 10%). All these advantages promise a bright future for these composites as useful photocatalysts. The degradation efficiency of MO using stable nanocomposites was still over 70% after ten times reusing. The highest decolorizing efficiencies were achieved with 0.75 g L^?1 of catalyst and 10 mg L^?1 of MO at natural pH under visible light irradiation in less than 20 min.     

Structural and optical properties of ZnO thin films by the spin coating Sol-Gel method

ZnO thin films were deposited onto glass subsrates by a Sol-gel spin coating method. The structural and optical properties of ZnO thin films were investigated. The molar ratios of the zinc acetate dihydrate to Monoethanolamine were maintained 1:1. The as-grown film was sintered 250 °C for 10 min, then annealed in air at 500 °C for 30 min. The XRD results indicate that ZnO films were strongly oriented to the c-axis of the hexagonal nature. Absorption measurements were carried out as a function of temperature with 10 K steps in the range 10–320 K. The band gap energy was measured 3.275 and 3.267 eV for 0.5 and 1.0 molarity (M) ZnO thin films at 300 K. The steepness parameters were observed between 10 and 320 K and their extrapolations converged at (E₀, α₀) = 3.65 eV, 172,819 cm⁻¹ and 3.70 eV, 653,436 cm⁻¹ for 0.5 and 1.0 M ZnO thin films, respectively.     

Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide(rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical(PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO(rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300 °C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency(ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of verticallyaligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO(3.56 eV) to 3.63 eV for rGO/ZnO sample,which may be attributed to the Burstein–Moss effect. Photoluminescence(PL) spectra disclosed that rGOhybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8 m A/cm~2 for ZnO and rGO/ZnO at+0.7 V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.     

Influence of Substrate-Target Distance on Structural and Optical Properties of Ga and (Al + Ga)-doped ZnO Thin Films Deposited by Radio Frequency Sputtering

Ga-doped ZnO and (Ga?+?Al) co-doped ZnO thin films were deposited on glass substrates by radio frequency magnetron sputtering for three distances d between a substrate–target. The influence of the distance between substrate–target upon structure, microstructure, vibrational properties, and optical band gap of the thin films was analyzed by X-ray diffraction, atomic force microscopy (AFM), Raman spectroscopy, and optical transmission measurements. The diffraction patterns revealed that the ZnO film crystallites are preferentially oriented with the (002) planes parallel to the substrate surface. AFM images show a smooth and uniform surface as well as a high compact structure. The Raman results reveal that the co-doping with Al?+?Ga introduces 2B₁(low) band and leads to the increase of intensity for longitudinal-optic’s band. In the visible region, the average value of the transmittance was above 80%.     

Structural,morphological, optical and third order nonlinear optical response of spin-coated NiO thin films: An effect of N doping

The present work deals with the deposition of NiO and Nitrogen (N)-doped NiO thin films by sol-gel spin coating technique. Structural, morphological, linear and non-linear optical characteristics of undoped and N-doped (1–15 wt%) NiO films were studied. From XRD measurements, it is evident that single phase nano crystalline NiO is formed for all doping concentrations. Surface morphology study shows that higher concentration of N doped NiO thin films were of high quality and EDX mapping confirmed the doping of Nitrogen in films. The Raman spectra of the studied films were analyzed over the range of 1400-200 cm⁻¹. The optical studies confirm that as doping increases, transparency of the film decreases (except at 10% N doping) and the band gap narrows. Nonlinear parameters such as refractive index and susceptibilities also depend on N dopant concentration. Z-scan studies viz., absorption index, nonlinear refractive index were carried out on undoped and N doped NiO samples and the results were matched with theoretical calculated values.     

Effect of electron radiation on electrical parameters of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes

In this study, RF-magnetron sputtered ZnO thin film as an interlayer was used to improve radiation tolerance of the Schottky diodes. The structural and optical measurements showed that the ZnO thin films have hexagonal crystal structure with preferential c-axis orientation, 20.39 nm grain sizes and 3.15 eV bandgap. The electrical parameters such as ideality factor, barrier height and series resistance of Zn/n-Si/Au–Sb and Zn/ZnO/n-Si/Au–Sb diodes were calculated before and after electron radiation at 25, 50 and 75 gray doses. Deviation values of the parameters showed that the ZnO as an interlayer caused to improved radiation tolerance of the diodes.

     

Influence of Mn incorporation on the structural and optical properties of sol gel derived ZnO film

Undoped and manganese doped ZnO (ZnO:Mn) films were prepared by sol gel method using spin coating technique. The effect of Mn incorporation on the structural and optical properties of the ZnO film has been investigated. The crystalline structure and orientation of the films have been investigated by using their X-ray diffraction spectra. The films exhibit a polycrystalline structure. Mn incorporation led to substantial changes in the structural characteristics of the ZnO film. The scanning electron microscopy (SEM) images of the films showed that the surface morphology of the ZnO film was affected by the Mn incorporation. The transparency of the ZnO film decreased with the Mn incorporation. The optical band gap and Urbach energy values of the ZnO and ZnO:Mn films were found to be 3.22, 3.19 eV and 0.10, 0.23 eV, respectively. The optical constants of these films, such as refractive index, extinction coefficient and optical dielectric constants were determined using transmittance and reflectance spectra. The refractive index dispersion curve of the films obeys the single oscillator model with dispersion parameters. The oscillator energy, E _o , and dispersion energy, E _d, of the films were determined 5.30 and 16.26 eV for ZnO film and 5.80 and 12.14 eV for ZnO:Mn film, respectively.     

Impact of thiourea concentration on the properties of sol–gel derived Zn(O,S) thin films and Cu(In,Ga)Se<Subscript>2</Subscript> solar cells

A novel approach based on sol–gel spin coating method to deposit Zn(O,S) thin film using thiourea(TU) as a sulfur source replacing CdS as buffer layer was developed and the influence of TU concentration on the properties of Zn(O,S) thin films and Cu(In,Ga)Se₂(CIGS) solar cells were investigated in this paper. It was found by X-ray diffraction and X-ray photoelectron spectroscopy that sol–gel derived Zn(O,S) thin films were amorphous and composed of ZnS, ZnO as well as Zn(OH)₂. The variation of the optical band gap as a function of the S/(S+O) ratio was determined by energy-dispersive spectroscopy and UV-VIS-NIR. The results indicated that the minimum value for band gap of approximate 3.72?eV was obtained when the S/(S+O)?=?0.44. Efficiency of up to 7.28% was achieved for a CIGS solar cell with Zn(O,S) buffer layer from 0.2M TU, which was attributed to the optimized conduction band offset (CBO) of +0.45?eV at the CIGS/Zn(O,S) interface.

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Zn(O,S) thin films prepared in sol–gel route was used to replace traditional CdS buffer layer deposited by chemical bath deposition method in Cu(In,Ga)Se₂ solar cells. The best efficiency was achieved for CIGS/Zn(O,S)/i-ZnO/ITO heterostructure solar cell with S/(S+O)?=?0.18, which was attributed to the optimized conduction band offset (CBO) of +0.45?eV at the CIGS/Zn(O,S) interface.

     

Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films

Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.     

Microwave assisted novel MoBi2S5 nanoflowers: Synthesis,characterization, photoelectrochemical performance

In the present article, we have studied the effect of post annealing treatment on microstructural, optical and photoelectrochemical (PEC) properties of MoBi₂S₅ thin films synthesized by microwave assisted technique. The synthesized thin films are vacuum annealed for 4 h at 473 K temperature. The X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and UV–Vis–NIR spectrophotometer techniques were used for characterization of the as deposited and annealed MoBi₂S₅ thin films. The XRD patterns confirm the synthesized and annealed thin films have nanocrystalline nature with rhombohedral-orthorhombic crystal structure. SEM micrographs indicate that, nanoflowers exhibit sharper end after annealing. The optical absorption study illustrates that the optical band gap energy has been decrease from 2.0 eV to 1.75 eV with annealing. Finally, applicability of synthesized thin films has been checked for PEC property. The J-V curves revealed that synthesized thin film photoanodes are suitable for PEC cell application. As well, used simple, economical method has great potential for synthesis of various thin film materials.     

介孔TiO2-ZnO复合薄膜的制备与表征

以三嵌段聚合物P123为模板剂, 以钛酸异丙酯和二水乙酸锌为无机前驱体, 利用溶胶-凝胶法和旋涂法成功地制备了不同ZnO含量的介孔TiO2-ZnO复合薄膜. 在ZnO前驱体摩尔分数为0~50％范围内获得薄膜质量较高的介孔TiO2-ZnO复合薄膜. 用小角XRD、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、能谱仪(EDS)、紫外-可见吸收光谱(UV-Vis)及X射线光电子能谱(XPS)对所得的复合薄膜进行了表征和分析. EDS和XPS等研究证明介孔薄膜为TiO2和ZnO的复合体系, 且ZnO前驱体含量的增加仍能保持TiO2-ZnO复合薄膜的均匀性. UV-Vis研究结果表明, 介孔复合薄膜的光学带隙宽度为3.45-3.58 eV, 随着ZnO含量的增加, 复合薄膜的紫外吸收蓝移.     

Double bandpass filter and dual band gap study for NiO doped into P2O5–ZnO–Na2O glassy system

Abstract

Glass compositions 42?P₂O₅–40ZnO–(18-x)Na₂O: xNiO in which x varies from 0 to 6?mol.% with step of 1?mol.%, are prepared by using the conventional melt annealing method. The effect of nickel ions in the investigated glass system appears in the combined structural and optical properties. Some structural and optical parameters such as molar volume, interionic distance, optical band gap, and Urbach energy are deduced. The variations in the spectroscopic data, which is affected by the deviations in composition and coordination state of nickel ions, are studied in relation to the structural evolution. The analysis of FTIR of the proposed structure shows that the local network structure is based mainly on Q ¹ and Q ² tetrahedron units connected by P–O–P linkages. Also, the optical properties show that the nickel ions occupy both tetrahedral and octahedral sites in the glass network.     

Optical,structural, and photoelectrochemical properties of nanostructured ln-doped ZnO via electrodepositing method

Indium-doped zinc oxide nanorods were electrochemically deposited at low temperature on ITO substrates. The synthesized ZnO-arrayed layers were investigated by using X-ray diffraction, scanning electron microscopy, UV–vis transmittance, electrochemical impedance spectroscopy, and photocurrent spectroscopy. X-ray diffraction analysis demonstrates that the electrodeposited films are crystalline and present the hexagonal Würtzite ZnO phase with preferential (002) orientation. The ZnO films obtained forms aligned hexagonal nanorods, and depending on the increasing In concentration, the surface morphologies of the films are changed. The ln-doped ZnO nanorods (NRs) are well-aligned with the c-axis being perpendicular to the substrates when the ln concentration was between 0 and 2 at.%. of In, the grown films with In contents up to 4 at.%, changes in the optical band gap from 3.31 to 3.39 eV, and the blue shift in the band gap energy was attributed to the Burstein–Moss effect. The effect of In concentration on the photocurrent generated by films shows that the obtained thin films can be used as a photovoltaic material. Changes in the photocurrent response and the electronic disorder were also discussed in the light of In doping. It was found that the carrier density of IZO thin films varied between 1.06?×?10¹⁸ and 1.88?×?10¹⁸ cm^?3 when the In concentration was between 0 and 4 at.%.

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Graphical Abstract Photocurrent response of IZO samples