Screen printed novel ZnO/MWCNTs nanocomposite thick films

Zinc oxide and multiwall carbon nanotubes (ZnO/MWCNT) nanocomposites thick films were prepared via sol-gel screen printing procedure and followed by sintering at 550 °C. Thus, the prepared films were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Ultraviolet–visible (UV–vis), Photoluminescence (PL), Fourier transform infrared (FTIR), Raman spectroscopy and Two-probe method. XRD analysis revealed (101) orientation for both ZnO and ZnO/MWCNT thick films with wurtzite structure. SEM studies confirmed the porous nature of ZnO film while ZnO/MWCNT films showed ZnO particles trapped in the porous MWCNT network and free from cracks. Reflectance spectroscopy showed direct transition with decreasing band gap whereas refractive index and absorption index showed appreciable variation within the band gap regime related to the change in crystallite size. FTIR profile approved the Zn–O stretching and presence of carboxylic CDC group. The PL spectrum of ZnO and ZnO/MWCNT thick films shows red shift and exhibits UV, blue and green emissions confirmed from CIE diagram. Raman spectrum shows that Raman phonons are shifted and dominated due to doping of MWCNT in ZnO matrix. Electrical properties were investigated using 2-probe method and showed a reduction in resistance on MWCNT incorporation. The novelty of current-work is the fabrication of ZnO/MWCNT through a low-cost screen printing process for the first time and the results exhibits that the bandgap of the deposited film is decreased, which in turn, play a significant role in enhancement of conductivity and colour emission for fabrication of low cost optoelectronics devices (LEDs) as compared with the pure ZnO film.     

Optoelectronic properties of In-doped SnS thin films

Nanostructured un- and In-doped SnS thin films were deposited on fluorine-doped tin oxide (FTO) substrates via an electrochemical deposition technique. The deposited thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectroscopy and UV–visible spectroscopy. The XRD patterns demonstrated that all deposited thin films are made of polycrystalline SnS particles. The AFM images illustrated a distinct change in the surface topography of the SnS thin films due to In-doping. The PL spectra showed two blue emission peaks and a green emission peak for all samples. Also, they highlighted a PL peak for the In-doped thin films. The incorporation of In-dopant leads to enhance in the optical absorption of SnS lattice. The optical energy band gap (E_g) of the deposited thin films was estimated using UV–vis spectroscopy, which indicated that In-doping decreases the E_g value of SnS thin films by creating defect levels. The photocurrent results demonstrated a higher photocurrent response and photocurrent amplitude for the In-doped SnS samples relative to the un-doped SnS thin film. The Mott–Schottky analysis revealed p-type conductivity for all samples. In addition, the carrier concentration of SnS was increased after In doping. The EIS spectra declared that In-doping improves the rate of charge transfer for SnS thin films. The charge transfer resistance of In-doped SnS decreased compared to the undoped SnS thin film. Finally, according to the J-V characteristics, the conversion efficiency of the In-doped SnS thin films was higher than that of the un-doped SnS sample. Therefore, the optical and electrical performance of SnS thin films were improved due to In-doping.     

双离子束溅射非晶SiOxNy薄膜的光致发光研究

采用双离子束溅射法制备了SiOxNy薄膜,用X射线衍射分析(XRD),透射电子显微镜(TEM),X射线光电子能谱(XPS),傅立叶变换红外(FTIR)等对薄膜的结构进行了表征,分析了样品的光致发光(PL)特性。X射线衍射(XRD),透射电子显微镜(TEM)结果表明该薄膜具有非晶结构。XPS测试表明N1s的特征峰位于398eV,对应于N-Si键。在光吸收谱中,与Si-SiO2薄膜相比,SiOxNy的光学带隙得到展宽。在225nm的激光激发下,样品在室温下可发射可见光,峰位位于590nm,与N的缺陷有关。     

Microstructural and optical properties of Ta-doped ZnO films prepared by radio frequency magnetron sputtering

Ta-doped ZnO films with different doping levels (0–5.02 at%) were prepared by radio frequency magnetron sputtering. The effects of the doping amount on the microstructure and the optical properties of the films were investigated. The grain size and surface roughness first significantly decrease and then slowly increase with the increase of Ta doping concentration. Both the grain size and the root mean square (RMS) roughness reach their minimum values at the doping content of 3.32 at%. X-ray Diffraction (XRD) patterns confirmed that the prepared Ta-doped ZnO films are polycrystalline with hexagonal wurtzite structure and a preferred orientation along the (002) plane. X-ray photoelectron spectroscopy (XPS) analysis reveals that Ta exists in the ZnO film in the Ta⁵⁺ and Ta⁴⁺ states. The average optical transmission values of the Ta-doped ZnO films are higher than those of the un-doped ZnO film in the visible region. The band gap energy extracted from the absorption edge of transmission spectra becomes large and the near band edge (NBE) emission energy obtained from PL spectra blueshifts to high energy when the Ta doping content grows from 0 at% to 5.02 at%, which can be explained by the Burstein–Moss shift.     

Electrochemical synthesis and surface characterization of hexagonal Cu–ZnO nano-funnel tube films

An electrochemical deposition technique was used to synthesis hexagonal nano-funnel tube films on zinc foil, utilizing an electrolyte of ZnCl₂+H₂O₂ under ambient conditions. The structures, morphologies, chemical compositions, and optical properties of the synthesized films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectrometry (UV-vis-DRS), photoluminescence (PL) spectrometry, and energy-dispersive X-ray spectrometry (EDS) techniques. The XRD pattern showed a set of diffraction peaks that were indexed to the ZnO, Zn(OH)₂, and Cu phases. The SEM observations revealed a cauliflower-like morphology consisting of branches in the form of nano-funnel tubes. The TEM results demonstrated that the synthesized film was comprised of several branches. The EDS studies confirmed the presence of only Cu, Zn, and O atoms. The UV-vis-DRS spectrum showed the onset of the band gap absorption peak at ～375 nm. The PL studies evaluated various emission bands that originated from different defect mechanisms. In addition, the hexagonal nano-funnel tube film showed a good superhydrophobicity, with a water contact angle of ～153°.     

Stability scheme of ZnO-thin film resistive switching memory: influence of defects by controllable oxygen pressure ratio

We report a stability scheme of resistive switching devices based on ZnO films deposited by radio frequency (RF) sputtering process at different oxygen pressure ratios. I-V measurements and statistical results indicate that the operating stability of ZnO resistive random access memory (ReRAM) devices is highly dependent on oxygen conditions. Data indicates that the ZnO film ReRAM device fabricated at 10% O₂ pressure ratio exhibits the best performance. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) of ZnO at different O₂ pressure ratios were investigated to reflect influence of structure to the stable switching behaviors. In addition, PL and XPS results were measured to investigate the different charge states triggered in ZnO by oxygen vacancies, which affect the stability of the switching behavior.     

Synthesis and characterization of ZnO:Ni thin films grown by spray-deposition

In the present study, nickel-doped zinc oxide thin films (ZnO:Ni) at different percentages (0–10%) were deposited on glass substrates by using a chemical spray technique. The effect of Ni concentration on the structural and optical properties of the ZnO:Ni thin films was investigated. The effect of Ni contents on the crystalline structure and optical properties of the films was systematically investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), UV–vis, Photoluminescence spectra PL, and Raman spectrometry. The XRD analysis showed that both the undoped and Ni-doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The XRD analysis also showed that the films were well crystallized in würtzite phase with the crystallites preferentially oriented towards (002) direction parallel to the c-axis. SEM study reveals the surface of NiZnO to be made of nanocrystalline particles. The SEM images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The band gap decreased up to the 7 at% Ni doping level, but the band gap increased after 10 at% Ni doping level. All thin films exhibited approximately 80% and above transmittance in the visible region. PL spectra of undoped and Ni-doped ZnO thin films showed some marked peaks at 376, 389, 494, and 515 nm. The obtained results revealed that the structures and optical properties of the films were greatly affected by doping levels. These films are useful as conducting layers in electro chromic and photovoltaic devices. Finally, all results were discussed in terms of the nickel doping concentration.     

Effect of Au ion beam on structural,surface, optical and electrical properties of ZnO thin films prepared by RF sputtering

In the present work, ZnO thin films were irradiated with 700?keV Au⁺ ions at different fluence (1?× 10¹³, 1?× 10¹⁴, 2?× 10¹⁴ and 5?× 10¹⁴ ions/cm²). The structural, morphological, optical and electrical properties of pristine and irradiated ZnO thin films were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), spectroscopy ellipsometry (SE) and four point probe technique respectively. XRD results showed that the crystallite size decreased from pristine value at the fluence 1?×?10¹³ ions/cm², with further increase of ion fluence the crystallite size also increased due to which the crystallinity of thin films improved. SEM micrographs showed acicular structures appeared on the ZnO thin film surface at high fluence of 5?×?10¹⁴ ions/cm². FTIR showed absorption band splitting due to the growth of ZnO nanostructures. The optical study revealed that the optical band gap of ZnO thin films changed from 3.08?eV (pristine) to 2.94?eV at the high fluence (5?× 10¹⁴ ions/cm²). The electrical resistivity of ZnO thin film decreases with increasing ion fluence. All the results can be attributed to localized heating effect by ions irradiation of thin films and well correlated with each other.     

Chemical solution deposition of ZnO nanostructure films: Morphology and substrate angle dependency

A chemical solution deposition method was used to synthesize ZnO films on zinc foil utilizing an electrolyte of ZnCl₂ + H₂O₂ under ambient conditions. The structures, morphologies, and chemical compositions of the films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. The XRD patterns showed that the substrate angle had significant influences on the formation of Zn(OH)₂ and the transition to ZnO. The SEM observations revealed that the cauliflower-like and rod-like morphologies were altered to one that was disk-like by changing the substrate angle from 90° to 0°. The XPS and EDS results indicated the presence of Cl atoms with a substrate angle of 0°. The XPS data confirmed the chemical purity of the ZnO film on the substrate with 90°. Photoluminescence (PL) studies found different visible emissions originating from different defect mechanisms. The growth mechanism responsible for the variation in the morphology is discussed. The observed results showed that the variation of pH in the vicinity of the surface substrates can be considered as reason for changing of morphology with the variation of angle. This method may have a potential in the fabrication of other metal oxides at low cost for technological applications.     

Fabrication of spray derived nanostructured n-ZnO/p-Si heterojunction diode and investigation of its response to dark and light

Fluorine doped ZnO thin films were grown by chemical spray pyrolysis technique of zinc acetate and ammonium fluoride, and the effect of fluorine content on structural, optical and electrical properties were evaluated. The structural, morphological, optical properties of ZnO films were investigated by XRD (X-ray diffraction), AFM (Atomic force microscopy), SEM (Scanning electron microscop) and UV–Vis spectroscopy, respectively. According to results, it was observed that all films had polycrystalline texture with hexagonal wurtzite crystal structure and film surface were made up of nano-scale grains, varied by fluorine content. Optical properties showed that optical band gap energy of ZnO changed from 3.28 to 3.24 eV with F content. Shrinkage effect was assessed as the cause in the variation of optical band gap values. Finally, current-voltage (I-V) analysis was performed in Au/ZnO:F/p-Si device in dark and light conditions and certain diode parameters such as ideality factor, barrier height and series resistance were calculated and discussed in detail.     

Aliovalent Ho3+ ion doped BaZrO3 thin films; Structural,optical and photoluminescence properties

Ho doped BaZrO3 thin film phosphors with varying Ho content (1, 2, 3 and 4?at%) were prepared via pulsed laser deposition technique. To understand the effect of doping on structural, morphological, optical and emission properties of thin films, X-ray Diffractrometer (XRD), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and Photoluminescence (PL) Spectroscopy have been used, respectively. Polycrystalline nature with single phase cubic crystalline structure of the films has been obtained. The optical band gap energy, as estimated by SE, has been found to increase with increase in the Ho content. The PL spectra of the synthesized phosphor exhibit green and yellow-orange as prominent emission bands in response to 328?nm as excitation wavelength.     

Fabrication of Mg-doped ZnO nanofibers with high purities and tailored band gaps

The tailored doping levels towards the band gap tunability are one of the challenges to push forward the potential application of one-dimensional (1D) ZnO nanostructures in the opto/electric nanodevices. In present work, we reported the exploration of Mg-doped ZnO nanofibers via electrospinning of polyvinylpyrrolidone (PVP), Zn(CH₃COO)₂ (ZnAc) and Mg(CH₃COO)₂ (MgAc), followed by calcination in air. The resultant products were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), and X-ray photoelectron spectroscopy (XPS). The optical measurements (UV–vis) of the Mg-doped ZnO nanofibers suggested that the optical band gaps of the ZnO nanofibers could be tuned from 3.33 to 3.40 eV as a function of the Mg doing levels. This tunability of the band gap of ZnO nanofibers with an intentional impurity could eventually be useful for optoelectronic applications.     

Microstructure,Surface Morphology and Photoluminescence Properties of Al-Doped ZnO Thin Films Prepared by Plasma Focus Method

Al-doped ZnO (AZO), as one of the most promising transparent conducting oxide (TCO) materials, has now been widely utilized in thin film solar cells. In this research the optimization process of AZO thin films deposited by plasma focus device was carried out by investigation of its physical properties under different deposition conditions for its utilize as a front contact for the Cadmium Telluride (CdTe) based thin film solar cell applications. The effects of number of focus shots and angular position of substrate on the microstructure, surface morphology and photoluminescence properties of the thin films have been systematically studied. X-ray diffraction (XRD) study confirmed the polycrystalline nature of the all deposited AZO thin films. XRD analysis also revealed that crystal structure characteristics of obtained samples strongly depend on deposition conditions (number of shots and angular position). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed the structure growth and enhancement of surface roughness, with increasing of focus shots or decreasing of angular position. From Photoluminescence (PL) emission spectra, the variations of structural defects and band gap energy for all the AZO thin films prepared under different deposition conditions were also discussed.     

Tailoring of polar and nonpolar ZnO planes on MgO (001) substrates through molecular beam epitaxy

ABSTRACT: Polar and nonpolar ZnO thin films were deposited on MgO (001) substrates under different deposition parameters using oxygen plasma-assisted molecular beam epitaxy (MBE). The orientations of ZnO thin films were investigated by in situ reflection high-energy electron diffraction and ex situ X-ray diffraction (XRD). The film roughness measured by atomic force microscopy evolved as a function of substrate temperature and was correlated with the grain sizes determined by XRD. Synchrotron-based X-ray absorption spectroscopy (XAS) was performed to study the conduction band structures of the ZnO films. The fine structures of the XAS spectra, which were consistent with the results of density functional theory calculation, indicated that the polar and nonpolar ZnO films had different electronic structures. Our work suggests that it is possible to vary ZnO film structures from polar to nonpolar using the MBE growth technique and hence tailoring the electronic structures of the ZnO films.PACS: 81; 81.05.Dz; 81.15.Hi.     

Tuning PL emission energy and bandgap with Ni dopant of MgO thin films

In this study, for the first time, the effect of Nickel (Ni) additive on Magnesium oxide (MgO) thin films produced by using successive ionic layer adsorption and reaction technique (SILAR) was investigated. Absorption, photoluminescence (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) measurements were executed to examine how the optical, structural and morphological properties of the samples were affected by the addition of Ni. In the absorption analysis, it was noted that the band gaps of the MgO samples decreased from 4 eV to 3.5 eV with the increase of Ni dopant concentrations. Also, the transmittance values of MgO nanostructures decreases with the increase of Ni contribution, and in the same way, the reflection measurements show that the reflection of MgO decreases with the increase of Ni doping. PL measurements revealed that the fabricated structures radiate around 410 nm and 730 nm. According to XRD measurements, besides the cubic structure of the samples, NiO formations were detected inside the MgO thin film samples due to the increase in Ni dopant. XPS measurements have proven the presence of Ni doping in MgO. SEM measurements showed that all samples exhibited nanowall structure. All these results demonstrate that Ni doping on MgO thin films can be achieved by using SILAR deposition technique.     

Controlled synthesis of (CuO-Cu2O)Cu/ZnO multi oxide nanocomposites by facile combustion route: A potential photocatalytic,antimicrobial and anticancer activity

Photocatalytic activity of (CuO-Cu₂O)Cu/ZnO hetero-junction nanocomposites along with their luminescent, biological applications in the progress of anticancer and antibacterial agents is investigated. The Cu and Zn bi-components modified (CuO-Cu₂O)Cu/ZnO nanocomposites were synthesized via facile combustion route in the presence of controlled fuel to oxidizer ratio and were characterized by X-Ray Diffraction (XRD) patterns, Transmission electron microscopy (TEM), High resolution Transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray photoelectron Spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and energy dispersive X-ray (EDX) analysis. The PL and UV–Visible diffused reflectance spectral (UV–Vis-DRS) techniques were used to measure the optical sensitivity and tuning of band gap in the samples. The excellent photocatalytic degradation of Methylene Blue and industrial waste water under Sunlight irradiation depends on the mass ratios of Cu/Zn. The findings show that the addition of a certain proportion of CuO, Cu₂O, ZnO, and Cu can promote efficiency in Sunlight harvesting and separation of charge carriers. Process parameters namely catalyst quantity, dye concentration and a proposal for the mechanism of degradation pathway, experiments for trapping and enhancer are investigated. The study of photoluminescence, CIE and CCT calculations suggests that the present nanocomposite may find applications as phosphor material in warm white LEDs. The second segment of this study deals with the investigation of antibacterial performance of composites upon Gram-negative and Gram-positive bacteria. The results indicate that nanocomposites can be used in antibacterial control systems and as an important growth inhibitor in various microorganisms. The cytotoxic effect of the (CuO-Cu₂O)Cu/ZnO (CCCZ11) nanocomposite was determined by colorimetric and flow cytometric cell cycle analysis. Our experimental results show that the nanocomposite can induce apoptosis and suppress the proliferation of HeLa cells. The applications of nanocomposites based on Cu, an abundant and inexpensive metal has created much interest in various multifunctional applications.     

Structural,optical and photocatalytic properties of hafnium doped zinc oxide nanophotocatalyst

A series of novel hafnium (Hf) doped ZnO nanophotocatalyst were synthesized using a simple sol–gel method with a doping content of up to 6 mol%. The structure, morphology and optical characteristics of the photocatalysts were characterized by XRD, SEM, TEM, FTIR, XPS, DRS and PL spectroscopy. The successful synthesis and chemical composition of pure and doped ZnO photocatalysts were confirmed by XRD and XPS. DRS confirmed that the spectral responses of the photocatalysts were shifted towards the visible light region and showed a reduction in band gap energy from 3.26 to 3.17 eV. Fluorescence emission spectra indicated that doped ZnO samples possess better charge separation capability than pure ZnO. The photocatalytic activity of Hf-doped ZnO was evaluated by the methylene blue (MB) degradation in aqueous solution under sunlight irradiation. Parameters such as irradiation time and doping content were found effective on the photoactivity of pure ZnO and Hf-doped ZnO. The photocatalysis experiments demonstrated that 2 mol% Hf-ZnO exhibited higher photocatalytic activity as compared to ZnO, ZnO commercial and other hafnium doped ZnO photocatalysts and also revealed that MB was effectively degraded by more than 85% within 120 min. The enhanced photoactivity might be attributed to effective charge separation and enhanced visible light absorption. It was concluded that the presence of hafnium within ZnO lattice could enhance the photocatalytic oxidation over pure ZnO.     

Zinc oxide thin films prepared by thermal evaporation deposition and its photocatalytic activity

Thin zinc oxide (ZnO) films have been grown on silicon substrates by thermal physical vapor deposition approach. X-ray diffraction (XRD) analyses reveal that the deposited films are polycrystalline ZnO phase. Atomic force microscopy images (AFM) show needle-like shape highly oriented ZnO crystals. Thin film thickness ranges from 10 to 80 nm. X-ray photoelectron spectroscopy (XPS) results declare that the films compose mainly of Zn and O. Nevertheless, Si is not detected in the films and consequently no possibility of any silicide formation as is confirmed by XRD analysis. Photocatalytic decomposition of azo-reactive dye on ZnO films is tested. The results show that the dye decomposition efficiency increases with decreasing pH. Maximum photodecomposition, 99.6% is obtained at pH 2 with 10 mg/l dye concentration.     

The evolution behavior of microstructures and optical properties of ZnO films using a Ti buffer layer

ZnO thin films without and with Ti buffer layer were prepared on Si and glass substrates by radio frequency (RF) magnetron sputtering. The effects of Ti buffer layer with different sputtering time on the microstructure and optical properties of ZnO thin films had been investigated by means of X-ray diffraction (XRD), energy dispersive spectrometer, X-fluorescence spectrophotometer and ultraviolet–visible spectrophotometer. The XRD results showed that the full-width at half-maximum (FWHM) for the ZnO (002) diffraction peak gradually decreased with the increase of sputtering time of Ti buffer layer, indicating that the crystalline quality of ZnO thin films was improved. The UV peak located at 390 nm, two blue peaks located at about 435 and 487 nm, two green peaks located at about 525 and 560 nm were observed from PL spectra. The PL spectra showed that the strongest blue light emission of ZnO films was obtained from Ti buffer layer with the sputtering time of 10 min. Meanwhile, the origins of the emission peaks were discussed through the Gaussian deconvolution. We also studied the optical band gaps.     

High thermoelectric performance of high-mobility Ga-doped ZnO films via homogenous interface design

Ga-doped ZnO (GZO) thin films grown on sapphire substrates have been widely investigated as a promising transparent thermoelectric (TE) material. However, due to the large lattice mismatch and thermal expansion between the sapphire substrate and GZO film, strain-induced lattice distortion impedes the transport of electrons, leading to low carrier mobility. In this study, ZnO homo-buffer layers with different thicknesses were inserted between sapphire substrates and GZO films, and their effect on the TE properties was investigated. A thin ZnO interlayer (10 nm) effectively reduced the lattice mismatch of the GZO film and improved the carrier mobility, which contributed to the large enhancement in the electrical conductivity. Simultaneously, energy filtering occurred at the interface between GZO and ZnO, resulting in a relatively high density of states (DOS) effective mass and maintaining a high Seebeck coefficient compared to that of the unbuffered GZO films. Consequently, the GZO film with a 10 nm thick ZnO buffer layer possessed a high power factor value of 449 μW m⁻¹ K⁻² at 623 K. This study provides a facile and effective method for optimizing the TE performance of oxide thin films by synergistically improving their carrier mobility and enhancing their effective mass.