Co-doped Zinc Oxide Research Articles

Photoluminescence, ellipsometric, optical and morphological studies of sprayed Co-doped ZnO films

In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350[Formula: see text]C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV–Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co[Formula: see text] ions substitute Zn[Formula: see text] ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

First-principles study on the electronic and optical properties of Si and Al co-doped zinc oxide for solar cell devices

Electronic and optical properties of co-doped zinc oxide ZnO with silicon (Si) and aluminum (Al), in Zn1−2x Si x Al x O (0 ≤ x ≤ 0.0625) original structure forms, are investigated by the first-principles calculations based on the density functional theory (DFT). The optical constants and dielectric functions are investigated with the full-potential linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation (GGA) by WIEN2k package. The complex dielectric functions, refractive index and band gap of the pure as well as doped and co-doped ZnO were investigated, which are in good agreement with the available experimental results for the undoped ZnO. Thus, the maximum optical transmittance of the co-doped ZnO of about 95 % was achieved; it is higher than that of pure ZnO. Thus, we showed for the Si–Al co-doped ZnO with x = 0.0315 that the optical transmittance can cover a larger range in the visible light region. In addition, an occurrence of important energy levels around Fermi levels was showed, which is mainly due to doping atoms that lead to an overlap between valence and conduction bands, and consequently to the significant conductor behavior of the Si–Al co-doped ZnO. The original Zn1−2x Si x Al x O structure reveals promising optical and electronic properties, and it can be investigated as good candidates for practical uses as transparent and conducting electrodes in solar cell devices.

P-55: Ga and In Co-Doped Zinc Oxide Films Deposited on Flexible High Gas Barrier Films for Transparent Conductive Electrode

We developed the highly moisture resistance Zinc Oxide films on flexible high gas barrier PEN substrates. After the damp test, changing ratio of sheet resistance were 1.02, this value can be applied the flexible device electrode. We studied the structural, optical and electrical properties of Zinc Oxide films in detail. After a damp test at 60 °C, 95%RH for 1000 h, sheet resistance of 200 nm thickness GIZO film on deposited plastic high gas barrier substrate was 30 ohm/sq., and changing ratio of sheet resistance, before and after damp test value was 1.02.

Al-Sn doped ZnO thin film nanosensor for monitoring NO2 concentration

The metal oxide semiconductor gas sensor technology is robust and has quick response times. In this work, aluminium and tin co-doped zinc oxide (ASZO) thin films were synthesized by a sol–gel dip-coating process as sensors for the greenhouse gas nitrogen dioxide (NO2). The prepared ASZO thin films were characterized using such techniques as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and photoluminescence (PL) emission studies in order to analyze the elemental confirmation, particle size, surface roughness and optical emission properties, respectively. The XRD data reveals the hexagonal structure of ASZO and that the preferential orientation is along 2θ=36.19°. SEM images of the ASZO thin film exhibit rod-like formations of ASZO on the substrate. The ASZO films show enhanced sensing behaviour, sensing NO2 gas even at 2ppm at an operating temperature of 170°C. The response and recovery times were determined to be 30 and 20s, respectively.

Application of Aliumium and Lanthanum Co-doped Zinc Oxide Infrared Stealth Coating on Tent Fabrics

Application of Aliumium and Lanthanum Co-doped Zinc Oxide Infrared Stealth Coating on Tent Fabrics

Effect of substrate temperature on transparent conducting Al and F co-doped ZnO thin films prepared by rf magnetron sputtering

ZnO is a wide bandgap semiconductor that has many potential applications such as solar cells, thin film transistors, light emitting diodes, and gas/biological sensors. In this study, a composite ceramic ZnO target containing 1wt% Al2O3 and 1.5wt% ZnF2 was prepared and used to deposit transparent conducting Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering. The effect of substrate temperatures ranging from room temperature (RT) to 200°C on structural, morphological, electrical, chemical, and optical properties of the deposited thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Hall effect measurement, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and UV–vis spectrophotometer. The XRD results showed that all the AFZO thin films had a (002) diffraction peak, indicating a typical wurtzite structure with a preferential orientation of the c-axis perpendicular to the substrate. The FE-SEM and AFM analyses indicated that the crystallinity and grain size of the films were enhanced while the surface roughness decreased as the substrate temperature increased. Results of Hall effect measurement showed that Al and F co-doping decreased the resistivity more effectively than single-doping (either Al or F doping) in ZnO thin films. The resistivity of the AFZO thin films decreased from 5.48×10−4 to 2.88×10−4Ω-cm as the substrate temperature increased from RT to 200°C due to the increased carrier concentration and Hall mobility. The optical transmittances of all the AFZO thin films were over 92% in the wavelength range of 400–800nm regardless of substrate temperature. The blue-shift of absorption edge accompanied the rise of the optical band gap, which conformed to the Burstein-Moss effect. The developed AFZO thin films are suitable as transparent conducting electrodes for various optoelectronic applications.

Physical study on Cobalt–Indium Co-doped ZnO nanofilms as hydrophobic surfaces

The present work reports some physical investigations on (Co,In) codoped zinc oxide nanofilms deposited on glass substrates at 460 °C by the spray pyrolysis technique. The effect of Co and In concentration on the structural, morphological, optical and surface wettability properties have been investigated using X-ray diffraction (XRD) patterns, Raman spectroscopy, SEM, optical measurement, photoluminescence spectroscopy as well as the measurement of hydrophobicity in terms of water contact angle. It is found that all films crystallized in würtzite ZnO phase, with a preferentially orientation towards (002) direction parallel to c-axis. The Raman spectra of the samples exhibit the presence of E2high characteristic mode of würtzite structure with high crystallinity as well as two dominant bands 1LO and 2LO. Also, no additional modes introduced by codopoing have been found. SEM micrographs show the uniform deposition of fine grains on surface films. Thicknesses of films are less than 100 nm. In addition, optical investigations indicate that the band gap narrowing of (Co,In) codoped ZnO thin films is due to the increase in the band tail width. Indeed, PL study indicates that (Co,In) codoped ZnO nanofilms exhibit a large decrease of the UV luminescence, which is assigned to the trapping of photo-generated electrons by both In3+ and Co2+ ions as well as an improvement of charge separation in the ZnO thin films. Finally, the (Co,In) codoping influences the surface wettability property and transform the ZnO character from hydrophilic (θ<90°) for pure ZnO nanofilm to hydrophobic (θ>90°) for (Co,In) codoped ZnO ones.

Synthesis, structural and optical properties of nanoparticles (Al, V) co-doped zinc oxide

The synthesis by the sol–gel method, structural and optical properties of ZnO, Zn0.99Al0.01O (AlZ), Zn0.9V0.1O (VZ) and Zn0.89Al0.01V0.1O (AlVZ) nanoparticles was reported. The approach was slow release of water for hydrolysis by esterification reaction followed by a supercritical drying in ethyl alcohol. After thermal treatment at 500∘C in air, the obtained nanopowders were characterized by various techniques such as transmission electron microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. The structural properties showed that the ZnO nanoparticles with an average particle size of 25 nm exhibit hexagonal wurtzite structure. From the optical studies, it was found that the optical band gap was located between 2.97 and 3.17 eV. The obtained electrical properties showed the potential application of the samples in optoelectronic devices. The powder of AlVZ presented a strong luminescence band in the visible range. The PL band energy position presented a small blue shift with the increase of measurement temperature. Different possible attributions of this emission band will be discussed.

Effect of Co-Ag doping on structural and optical properties of zinc oxide nanoparticles

Co-Ag co-doped Zinc oxide nanoparticles were synthesized by chemical co-precipitation method. The synthesized nanoparticles were subjected to X-ray diffraction technique and the average crystallite size was found to be around 29–31 nm. The crystallite size increased as the cobalt concentration increased. The optical properties were characterized by UV-Vis and PL spectral analysis. The FT-IR spectra of the samples were recorded and the characteristic absorption bands shifted to lower values as the cobalt concentration increased. The SEM analysis showed sphere shaped particles distributed uniformly. These co-doped (Co,Ag) ZnO nanoparticles may be used in optoelectronics, spintronics, as antibacterial reagents to treat diseases caused by bacteria and fungi and in waste water treatment

Sintering Effect on Clamping Characteristics and Pulse Aging Behavior of ESD-Sensitive V2O5/Mn3O4/Nb2O5Codoped Zinc Oxide Varistors

V₂O₅/Mn₃O₄/Nb₂O₅ codoped zinc oxide varistor ceramics were sintered at a temperature range as low as 875~950&#x2103;. The voltage clamping characteristics of V₂O₅/Mn₃O₄/Nb₂O₅ codoped zinc oxide varistor ceramics were investigated at a pulse current range of 1~50 A. The sintering temperature had a significant effect on clamp voltage ratio, which exhibits surge protection capabilities. The varistor ceramics sintered at 875&#x2103; exhibited the best clamping characteristics, in which the clamp voltage ratio was 2.69 at a pulse current of 50 A. The varistor ceramics sintered at 900&#x2103; exhibited the highest electrical stability, where = 3,824 V/cm (initial 3,909 V/cm), and E_{1 mA/cm²} = 27 (initial 39) after application of a pulse current of 100 A.

Structural, linear and nonlinear optical properties of co-doped ZnO thin films

Different compositions of Co-doped zinc oxide [(Zn(1−x)Co x O) (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple–DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy (E o), the dispersion energy (E d), and the static refractive index (n 0), were determined. The nonlinear refractive index of the Zn(1−x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

Structural and optical properties of sol–gel derived Zn0·8−xNaxMg0·2O thin films

Na/Mg co-doped zinc oxide nominally named Zn0·8−xNaxMg0·2O films were prepared on pyrex glass substrates by sol–gel spin-coating method. Effects of Na doping concentration as well as annealing temperature on structural and optical properties of the films were investigated in detail by X-ray diffraction, scanning electron microscopy and photoluminescence spectra. Compared with Zn0·8Mg0·2O films, Na/Mg co-doped zinc oxide films have better c-axis preferred orientation and surface morphology, but these structural properties become worse with increasing x values. There is an optimum annealing temperature for preparation of Zn0·8−xNaxMg0·2O films with excellent characteristics. Under the experimental conditions, Zn0·78Na0·02Mg0·2O films annealed at 560°C have the best c-axis preferred orientation, the most neat and uniform surface morphology as well as the best ultraviolet luminescent property to produce a kind of purple luminescent materials and ultraviolet detector.

Structural characterization and optoelectrical properties of Ti–Ga co-doped ZnO thin films prepared by magnetron sputtering

The Ti–Ga co-doped zinc oxide (TGZO) thin films were deposited on glass substrates by radio frequency magnetron sputtering technique in an argon atmosphere. The effect of working pressure on the crystallinity, microstructure, morphology and optoelectrical properties of thin films was investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, four-point probe and spectrophotometer. It is observed that all the deposited films are polycrystalline with a hexagonal wurtzite structure and highly textured along the c-axis perpendicular to the substrate surface. As the working pressure increases, the dislocation density, stress and resistivity decrease initially and then increase, while the crystallite size, average visible transmittance and figure of merit exhibit the reverse variation trend. The TGZO thin film deposited at the working pressure of 0.4 Pa possesses the best optoelectronic properties, with the largest crystallite size of 85.66 nm, the lowest dislocation density of 1.363 × 1014 lines m−2, the minimum compressive stress of 0.232 GPa, the lowest resistivity of 6.715 × 10−4 Ω cm, the highest average visible transmittance of 88.24 % and the maximum figure of merit of 1.314 × 103 Ω−1 cm−1. The optical energy-gaps of thin films were estimated by Tauc’s law and observed to be in the range of 3.515–3.548 eV which are hardly affected by the working pressure. Furthermore, the optical parameters such as refractive index, extinction coefficient, dielectric constant and nonlinear optical susceptibility were determined by the method of optical spectrum fitting, and the dispersion behavior of refractive index was studied in terms of the Sellmeier’s dispersion model. The results show that the microstructure and optoelectrical properties of the TGZO thin films are subjected to the working pressure.

Fabrication and characterization of optical and electrical properties of Al–Ti Co-doped ZnO nano-structured thin film

Al and Ti Co-doped zinc oxide (ATZO) nano-structured thin films with 1 at % Al and 0.1 at % Ti were deposited on glass substrate via sol–gel technique. X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) methods were used to investigate the structure, morphology and surface roughness of the thin films. The optical properties were investigated by spectroscopic ellipsometry (SE) and UV-VIS spectrophotometer. The resistivity measurement was performed using a LCR-meter. XRD analysis confirmed the zinc oxide hexagonal wurtzite structure for the thin films. It was found that Ti doping reduces the roughness and grain size values to 8.2 nm and 50 nm, respectively. The optical band gap energy was concluded to be 3.23 eV for ZnO film and it increases to 3.26 eV for ATZO films. Refractive index decreased upon Ti doping as a consequence of increase in charge carrier concentration. All the thin films exhibit high transmittance over 85% in the visible wavelength region. Ti replacement causes to decrease in resistivity and minimum resistivity value of 13 × 106 Ωcm was measured for ATZO thin film.

Sputtered Al–N codoped p-type transparent ZnO thin films suitable for optoelectronic devices

Aluminum–nitrogen (Al–N) codoped zinc oxide (ZnO) thin films were grown on glass substrate by radio frequency (RF) reactive magnetron sputtering using aluminum doped zinc oxide (AZO, 2.5wt% Al2O3) target and N2 as reactive gas. The structural, morphology, optical and electrical properties were also investigated with different flow rate of N2 gas. X-ray diffraction results shows that codoped ZnO thin films have similar wurtzite structure like undoped ZnO film. Al–N thin films have high transparency 78% in visible region as the nitrogen flow rate increases the transparency and band gap decreases. The best p-type codoped sample shows a resistivity and hole concentration of 0.554Ωcm and 8.3×1019cm−3 at room temperature, respectively. Current–voltage (I–V) characteristics of p-type codoped ZnO thin films are also discussed.

Effect of hydrogen doping on the properties of Al and F co-doped ZnO films for thin film silicon solar cell applications

Aluminum and fluorine co-doped zinc oxide (AFZO) thin films were prepared in Ar+H2 atmospheres by rf magnetron sputtering at room temperature. The structural, electrical, and optical properties of the prepared films were investigated using X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall-effect measurement, X-ray photoelectron spectroscopy, and ultraviolet–visible spectrometry, and their dependence on deposition atmosphere (i.e. H2/(H2+Ar) ratio) was studied. The resulting films showed a (0 0 2) diffraction peak, indicating a typical wurtzite structure, and the optimal film crystallinity was obtained with the H2/(H2+Ar) ratio of 3%. The electrical resistivity of AFZO films decreased to 9.16×10−4Ω-cm, which was lower than ZnO:Al and ZnO:F films due to double doping effect of Al and F. The resistivity further decreased to below 5×10−4Ω-cm for the AFZO film with the H2/(H2+Ar) ratio of 3%–5%. All the films regardless of hydrogen content displayed high transmittances (>92%) in the visible wavelength range. Applying the developed AFZO films as front transparent electrodes, amorphous Si thin film solar cells were fabricated and the open-circuit voltage, fill factor, and efficiency of the cell with the hydrogenated AFZO film were improved in contrast to those without the hydrogenated film.

Nitrogen and cobalt co-doped zinc oxide nanowires – Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting has been considered as a promising and environmentally benign approach for efficient and economic hydrogen generation by utilization of solar energy. Development of semiconductor materials with low band gap, high photoelectrochemical activity and stability has been of particular interest for a viable PEC water splitting system. In this study, Co doped ZnO, .i.e., (Zn0.95Co0.05)O nanowires (NWs) was selected as the composition for further co-doping with nitrogen by comparing solar to hydrogen efficiency (SHE) of ZnO NWs with that of various compositions of (Zn1−xCox)O NWs (x = 0, 0.05, 0.1). Furthermore, nanostructured vertically aligned Co and N-doped ZnO, .i.e., (Zn1−xCox)O:N NWs (x = 0.05) have been studied as photoanodes for PEC water splitting. An optimal SHE of 1.39% the highest reported so far to the best of our knowledge for ZnO based photoanodes was obtained for the co-doped NWs, (Zn0.95Co0.05)O:N - 600 NWs generated at 600 °C in ammonia atmosphere. Further, (Zn0.95Co0.05)O:N-600 NWs exhibited excellent photoelectrochemical stability under illumination compared to pure ZnO NWs. These promising results suggest the potential of (Zn0.95Co0.05)O:N-600 NWs as a viable photoanode in PEC water splitting cell. Additionally, theoretical first principles study conducted explains the beneficial effects of Co and N co-doping on both, the electronic structure and the band gap of ZnO.

Zinc oxide-praseodymia semiconducting varistors having a powerful surge suppression capability

We introduced the varistor having more powerful surge suppression capability. This research focuses on the effect of sintering time on electrical properties and pulse current degradation of Pr/Co/Cr/Y/Mg co-doped zinc oxide varistors for surge suppression. With increasing sintering time, the breakdown field decreased from 2768 to 1680V/cm, and the nonlinear coefficient decreased from 57.7 to 29.3. Considering pulse current, a higher nonlinear coefficient led to the lower clamp voltage ratio. Therefore, the sample sintered for 1h exhibited the best clamp characteristics, in which the clamp voltage ratio was in the range of K=1.52–1.77 for pulse currents of 1–10A and K=2.04–3.43 for pulse currents of 400–2500A. Considering pulse absorption capability, the sample sintered for 3h exhibited the strongest electrical stability; −3.9% in ∆E1mA/cm2/E1mA/cm2 and −6.9% ∆α1/α1 after application of a pulse current of 2500A.

Cr-N co-doped ZnO nanoparticles: synthesis, characterization and photocatalytic activity for degradation of thymol blue

Here we report the synthesis of CrN co-doped ZnO for the first time. Zinc oxide (ZnO) nanoparticles were synthesized by direct precipitation method via the reaction between zinc nitrate [Zn(NO 3 ) 2 .6H 2 O] and ammonium carbonate [(NH 4 ) 2 CO 3 ] in aqueous solutions with proper concentration. Modified photocatalysts were synthesized by the incipient wetness impregnation method (chromium-doped ZnO) and by solid state reactions using ZnO and urea as precursors (nitrogen-doped ZnO). Chromium-nitrogen co-doped ZnO nanomaterials were prepared from the already prepared N-doped ZnO nanomaterials via one step impregnation method. The as-synthesized photocatalysts were investigated by XRD, BET, SEM-EDX, FTIR, and UV–Vis techniques. Photocatalytic degradation of thymol blue using as-synthesized photocatalysts was studied under visible as well as UV irradiations. Highest photocatalytic degradation efficiency of chromium-nitrogen co-doped zinc oxide could be attributed to the lower rate of recombination of the photo-generated electrons and holes as well as to its lower band gap energy as the result of the co-doping. Photocatalytic degradation is found to follow pseudo first order kinetics. KEY WORDS : Photocatalysts, Precipitation method, Impregnation method, Co-doping, Zinc oxide, Thymol blue Bull. Chem. Soc. Ethiop. 2015 , 29(2), 247-258 DOI: http://dx.doi.org/10.4314/bcse.v29i2.8

Production and Photoelectric Activity of P and Al Co‐Doped ZnO Nanomaterials

Materials that have both conductivity and photocatalytic activity are widely applied in electrical devices and as environmental pollution handles. Based on such requirements, phosphorus and aluminium co-doped conductive zinc oxide nanocrystals (PAZO NCs) with novel visible-light catalytic activities have been mass produced by the combustion method. The PAZO NCs have diameters of 30–100 nm and BET specific surface areas of 15.27–18.99 m2 g–1. These PAZO NCs exhibited novel photocatalytic activity and good conductivity [the powder conductivity was (0.98–1.76) ×10–4 S cm–1], the reason being mainly attributed to the increase in carrier concentration and defects through P and Al co-doping. In addition, we found that the 3PAZO NCs, in which the molar ratio of Zn to P atoms is 100:3, had the best visible-light catalytic efficiency of the PAZO NCs, and the size of PAZO NCs decreased with increasing doping of phosphorus and aluminium. This study is useful as a reference for the mass production of modified ZnO NCs and its applications, such as in environmental management, photocatalysis, and anti-static electricity.