Zn-doped Films Research Articles

The nano-sheet structure adjustment and long-term stability of Zn-doped NiO electrochromic films

NiO is a typical anode electrochromic material based on its excellent electrochemical performance. However excellent cycle stability has always been the most important goal pursued by researchers. This study successfully prepared the complex multi-channel self-assembled nanosheet structure of low concentration and different Zn content doped NiO films with outstanding cycle stability on FTO by the low-temperature hydrothermal method. This excellent cycle stability provides a basis for applying NiO as a complementary layer in electrochromic devices. Zn doping influences the surface microstructure and electrochromic properties of NiO films. It is worth noting that all samples show large modulation amplitude, high coloring efficiency, and fast response time at the wavelength of 550 nm. The samples doped with 1% Zn exhibited more outstanding electrochromic properties than the samples without Zn doping, including fast switching speed (6.4 s and 3.8 s), significantly high coloration efficiency (52.49 cm2·C−1), transmittance modulation (68.57 % at 550 nm), and especially outstanding cycle stability (99.47 % after 5000 cycles). Zn doping affects the microstructure of the film surface, which greatly improves the cycle stability of the film by combining doping and structure control. We consider that the 1 % Zn-doped sample has the best cyclic stability because of the lower interface barrier between the 1 % Zn-doped sample and the FTO, the Zn-doped film forms a complex multi-channel structure, and the coupling effect makes the sample more conducive to the charge entry and exit.

Study on the Optical and Gas-Sensing Performance of Zn-doped CuO Films

The pure copper oxide thin film was deposited on glass substrates by SILAR method with 30 cycles. To examine the doping effect, Zn-doped films at different doping ratios were prepared under the same conditions as the undoped film. The XRD, SEM and Raman measurements were performed to investigate the morphological and structural properties of the samples. Analysis showed increasing aggregation and amorphous structure with doping. The optical parameters were characterized by spectrophotometer measurement and relevant formulas. The band gap energies were determined to increase from 2.50 to 2.79 eV with the increasing Zn rate. The Hervé and Vandamme, Moss and Ravindra relations were used to determine the refractive index. The room temperature gas-sensing performance for the undoped and doped samples were reported and the responses for 5 ppm gas were calculated as 249 %, 800 %, 189 % and 15 % for the CuO, 1Zn:CuO, 3Zn:CuO and 5Zn:CuO, respectively. The response of CuO thin films changed with doping, and 1% Zn doping rate was determined as the optimal rate in this study.

Boosting of CO2 sensitivity in Zn-doped SnO2 thin film: Analysis based on structural, optical and dielectric characterization

Zn-incorporated SnO2 thin films are deposited by spray pyrolysis technique from an ethanolic solution of SnCl4·5H2O at 310 °C. The structural analysis shows that both undoped and Zn-doped films are tetragonal rutile structures with crystallite sizes ranging from 44 to 35 nm. Morphological analysis shows that the particles are spherical in shape and uniformly distributed. The UV–Vis absorbance spectra of the samples are recorded and the band gap energies are estimated. The CO2 sensing properties are investigated in detail. The dielectric constant is found to vary with frequency that is attributed to the multi-relaxation time constant of the energy states responsible for the conduction mechanism. The AC conductivity has been found to obey a power law, indicating a multi-hopping conduction mechanism in the samples. These results are discussed in relation to the sensing characteristics of the sample.

Zinc doping effects on the microstructural, electrical and optical properties of nanostructured ZnxBi2-xS3 ([formula omitted]) thin films grown by ultrasonic spray pyrolysis

Zinc-doped bismuth sulfide (Bi2-xZnxS3) nanocrystalline thin films were deposited on glass substrates by using an ultrasonic spray pyrolysis (USP) technique and their structural, morphological, electrical and optical properties experimentally addressed. X-ray diffraction (XRD) and micro-Raman spectroscopy have confirmed the generation of a single-phase polycrystalline orthorhombic material. The crystallite size and micro-deformation of the films was found to depend on the dopant concentration. The surface appears condensed and dense with a uniform spatial grain distribution, as revealed by scanning electron microscopy (SEM) images. Energy dispersive X-ray spectroscopy (EDS) studies revealed a certain Bi deficiency in both undoped and Zn-doped films. When the nominal Zn doping concentration increases from x = 0 to x = 0.09, the crystallite size decreases from 30 to 21 nm. The optical band gap of the films increased from 1.62 to 1.65 eV with Zn content increasing up to x = 0.06, then reducing to 1.58 eV for the maximum Zn content. Optical measurements showed a high absorption coefficient (α > 104 cm−1) in the visible and near-infrared ranges. The Urbach energy followed a similar behavior as a function of doping concentration. The electrical conductivity as well as the sheet carrier mobility of the Bi2-xZnxS3 films increase sharply by increasing the Zn content up to x = 0.06. For this doping concentration, mobility reaches 1.37 × 105 cm2/Vs while keeping carrier concentration above 1017 cm−3. Our experimental results provide strong evidence that Zn-doping is a suitable method to increase Bi2S3 light-harvesting efficiency in solar cell devices.

Impact of zinc on the physical and morphological properties of sputtered copper oxide thin films

In this study, thin films of pure and zinc (Zn) doped copper oxides were successfully deposited on a glass substrate via reactive magnetron sputtering at varying Zn concentrations. The effects of oxygen/argon ratio and dopant dosage on the structure, morphology, and topography of films were analyzed by the X-ray diffraction technique (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray fluorescence (XRF), Raman, and atomic force microscopy (AFM). The investigations through XRD and Raman revealed the formation of CuO, and Cu2O phases during the copper oxide deposition at 20% oxygen partial pressure, while an increase in the oxygen partial pressure up to 50% resulted in the formation of single-phase CuO. XRD spectra of the Zn-doped films indicated the monoclinic structure of CuO with a gradual increase in the cell volume from 91 A3˙ in the undoped sample to 123 A3˙ in the sample with a high dopant concentration. By increasing the applied RF power from 10 to 40 W, the cationic ratio (Zn/Zn + Cu) increased from 0.007 to 0.039. AFM analysis figured out the decrease of surface roughness from 11.04 nm in the undoped sample to 3.57 nm in the highly Zn-doped sample. In FESEM images, semi-spherical particles with uniform distribution were observed. By increasing the oxygen partial pressure from 20% to 40% in undoped samples, the average grain size was reduced from 110 to 68 nm, but doping by Zn did not affect the grain size significantly.

Switching of majority charge carriers by Zn doping in NdNiO3 thin films

We have studied the effects of Zn doping on the structural and electronic properties of epitaxial NdNiO3 thin films grown on single-crystal LaAlO3 (001) (LAO) substrates by pulsed laser deposition. The films are deposited in two sets, one with variation in Zn doping, and another with variation in thickness for undoped and 2% Zn doping. The experimental investigations show that Zn occupies Ni-site and that the films are grown with an in-plane compressive strain on LAO. All the films show metal-to-insulator transitions with a thermal hysteresis in the temperature-dependent resistivity curves except 5% Zn-doped film, which remains metallic. The theoretical fits show non-Fermi liquid behaviour, which gets influenced by Zn doping. The Hall resistance measurements clearly show that Zn doping causes injection of holes in the system which affects the electronic properties as follows: i) the metallic conduction increases by two factors just by 0.5% Zn doping whereas, 5% doping completely suppresses the insulating state, ii) a reversal of the sign of Hall coefficient of resistance is observed at low temperature.

Comparative study of Ag, Sn or Zn doped TiO2 thin films for photocatalytic degradation of methylene blue and methyl orange

Nanocrystalline titania (TiO2) films with high optical transmittance and appropriate type and level of metal dopants offer promise for use in photocatalysis and environmental remediation purposes. In this study, a facile, cost-efficient sol-gel reflux synthesis route was devised to obtain smooth, nanocrystalline anatase TiO2 thin films doped with silver (Ag), tin (Sn) or zinc (Zn) with up to 5 mole percent. The microstructure, surface morphology and phase composition were determined using scanning electron microscope, atomic force microscope and x-ray diffraction techniques. The films were found to be nanocrystalline with average crystallite size of the order of ∼11 nm. Upon Ag or Sn doping, the films became superhydrophilic due to generation of surface defects and enhanced absorption via incident light scattering. The low extinction coefficient confirmed low surface roughness and uniform dispersion of the metal dopants into the TiO2 lattice. There was a decrease in the refractive index values of the Zn-doped films. The band gap values, as computed using Tauc plots, indicated a maximum reduction from 3.66 eV for the updoped TiO2 to 3.25 eV for Ag-doped TiO2 film. When assessed for photocatalytic degradation of methylene blue (MB) and methyl orange (MO), all the films were found to follow pseudo first-order kinetics in accordance with the Langmuir-Hinshelwood model. The apparent rate constant values were found to increase by 2 to 3 fold (4.30 × 10−3 s–1 for MB; 5.34 × 10−3 s–1 for MO) upon doping with 5 mole percent ZnO, presumably due to dual role of Zn as a reductant causing Ti3+ formation and a stabilizer of the oxygen vacancies.

Role of metallic dopants on the properties of copper (1) iodide nanopod-like structures

The addition of impurities as dopants to any material affects the properties of the material where the dopant modulates the optical and structural properties of the material. Copper (1) iodide films which were successfully doped with Al, Pband Zn (as metallic dopants) were synthesized by the successive ionic layer adsorption and reaction (SILAR) technique while the morphological, structural, optical and electrochemical properties were investigated using the scanning electron microscope (SEM), X-ray diffraction (XRD), UV–Vis spectrophotometer and potentiostat respectively. The SEM image revealed a nanopod-like structure for the deposited CuI films while the XRD results confirmed the crystalline nature of the films with a face centered cubic structure. The optical results showed a progressive decrease of the absorbance values at increasing wavelengths while the optical bandgap energy of the undoped CuI film reduced from 2.47eV to 1.90eV, 1.75eV and 1.8eV for the Al-doped, Pb-doped and Zn-doped CuI films respectively. The undopedCuI film also showed a higher extinction coefficient value than the metallic-doped CuI films. The Zn-doped film had the maximum specific capacitance of 116 F g−1at 2 mV/s.

Hydrothermal synthesis of Zn-doped Ni–Mn–Al–O thin films toward high-performance negative temperature coefficient thermistor

In this study, Zn-doped Ni–Mn–Al–O negative temperature coefficient thermistor (NTC) film with high electrical performance has been demonstrated. XRD, XPS, SEM and electrical measurements were carried out to explore the impact of Zn-doping. The XRD analysis of NiMn1.8−xAl0.2ZnxO4 films confirmed the cubic spinel crystal phase regardless of x. The SEM image illustrated that the morphology of NiMn1.8−xAl0.2ZnxO4 is closely related to the Zn doping amount. The XPS showed that the relative molar content of Mn3+ and Mn4+ increased with the increase of Zn doping concentration. Remarkably, the Zn-doped Ni–Mn–Al–O film presented the typical NTC characteristics, and the room temperature resistance (R25) increased with the improvement in Zn doping concentration. Moreover, the thermistor constant B25/50 remained reasonably high from 4088 to 4272 K. Meanwhile, the aging test showed that the Zn-doped films were more stable, even aging at 150 °C for 500 h.

Optoelectronic, magnetic and antifungal properties of CdS thin films co-doped with zinc and bromine

This paper reports the results obtained on the optical, electrical, magnetic and antifungal properties of CdS thin films co-doped with zinc and bromine. XRD studies reveal that all the films exhibit hexagonal crystal structure of pure CdS. The undoped, Zn-doped and (Zn, Br) co-doped CdS thin films have a strong (0 0 2) preferential growth. Nanosized grains are evinced from the SEM images of all the samples. Optical transparency of undoped CdS increases from 76 to 81% for the Zn-doped film and to 90% for the co-doped films. Decreased electrical resistivity is observed for the co-doped films. Room temperature ferromagnetic orderings in the form of S-shaped loops are observed for all the films. Antifungal activity was performed against A. niger fungus strain and from the zones of inhibition developed around the samples it was observed that the Zn-doped and (Zn, Br) co-doped CdS thin films exhibit better antifungal efficiency.

Influence of Ti and Zn Dopants on Structural Properties and Electrochromic Performance of Sol-Gel Derived WO3 Thin Films

The influence of different transition metals doping (Ti and Zn) on structural properties and electrochromic adjustment and performance of sol-gel derived WO3 thin films was conducted and investigated. Ti-doped WO3 and Zn-doped WO3 thin films were deposited onto F-doped tin oxide (FTO) substrates using spin coating technique. Tungsten powder, Titanium butoxide and zinc acetate dehydrate were used as starting precursors. The as-deposited films were annealed at 500°C for 2h. The effect of Ti and Zn doping on structural, surface morphologies, optical properties of the films were examined using X-ray diffractometer, scanning electron microscope and UV-VIS spectrophotometer. The XRD analyses suggest that the crystalline of WO3 can be identified as a monoclinic WO3 structure. XRD results additionally indicate the existence of ZnWO4 structure in the Zn-doped films, which is clearly observed by SEM. The optical measurement of all films indicate good transparency in the visible region and near infrared region with more than 60% in transmittance. In addition, It was found that the electrochromic performance of WO3 can be enhanced by small doping concentration of titanium due to structural modification of the films caused by close ionic radius of Ti to W rather than that of Zn.

Zinc-Doping in TiO<sub>2 </sub>Films to Enhance Photovoltaic Performance of Dye-Sensitized Solar Cells

Dye-sensitized solar cells based on Zn-doped TiO2 thin film prepared by the hydrothermal method show a photovoltaic efficiency of 7.68%, which is higher than that of the undoped TiO2 thin film (6.16%). The Zn-doped films exhibit an elevated electron Fermi level,which may enhance band bending to lower the density of empty trap states.Because of this Zn-doping,the consequent Dsscs can alleviate the decay of light to electric energy conversion efficiency due to light intensity reduction. Intensity-modulated photocurrent spectroscopic analysis reveals that enhanced transport of photogenerated electrons as a result of the trap density minimization is responsible for the high photovoltaic performance.

Zinc-doping in TiO2 films to enhance electron transport in dye-sensitized solar cells under low-intensity illumination

A nanocrystalline TiO(2) film with highly dispersed Zn-doping shows its capability for efficient electron transport in dye-sensitized solar cells (DSSCs). The Zn-doping is conducted via Zn(2+) introduction into a layered titanate followed by hydrothermal treatment and calcination. The Zn-doped films exhibit an elevated electron Fermi level, which may enhance band bending to lower the density of empty trap states. Because of this Zn-doping, the consequent DSSCs can alleviate the decay of light-to-electric energy conversion efficiency due to light intensity reduction. Intensity-modulated spectroscopic analysis reveals that enhanced transport of photogenerated electrons as a result of the trap density minimization is responsible for the high cell performance under low-intensity illumination. A Zn-doping content of ca. 0.4 at% Zn/Ti can enhance the light conversion efficiency by 23% at a solar light intensity as low as 11 mW cm(-2). This technique can significantly extend the indoor application of DSSCs.

Microstructures of High-${\rm T}_{\rm C}$ Superconducting Films Introduced Zero-Dimensional and One-Dimensional Artificial Pinning Centers

Artificial pinning centers have been introduced into high-TC superconducting films in order to improve the JC at 77 K and magnetic fields. The dimensionality of artificial pinning centers has an important role in improving JC against the magnetic field direction. The one-dimensional artificial pinning centers, such as dislocations and nanorods, are much effective on the B//c-axis. However, pinning centers with magnetic angular independences are much important for practical use. Then, a new concept of zero-dimensional artificial pinning centers is applied to high-TC superconducting films, which is local superconductivity disappearance resulting in the substitution of 3d-transition elements such as Zn or Co for Cu. We have no clear evidence of element substitution from microstructural observations. However, the magnetic field angular independences in a wide region except the B//a-axis are revealed in a Zn-doped film, which probably results form zero-dimensional pinning centers. Unexpected magnetic field angular dependences are also revealed, indicating the existence of other pinning centers except zero-dimensional pinning centers. It is found that unexpected defects, such as c-axis-correlated defects or stacking faults, are induced by 3d-transition element substitution.

Fabrication of Zn-doped RE123 LPE films for persistent current switch materials

We have studied fabrication of a Zn-doped REBa 2Cu 3O y (RE123) film prepared by the liquid phase epitaxy (LPE) to control critical temperature ( T c) and critical current density ( J c), as a persistent current switch (PCS) material. Through the investigation of the relationship between the Zn concentrations in liquid and solid, it was found that the effective distribution coefficient ( k e) was almost constant for the liquid compositions within the range of this study. This means that we could control T c, corresponding to the Zn concentration in the film, of the Zn-doped Y123 LPE film due to changing Zn concentration in the solution. Concerning required properties for PCS, the product of J c (at 20 K, 3 T) and normal resistivity of the Zn-doped LPE film was almost the same as that of the non-doped films. This means that Zn-doped film has an additional advantage of the controlled T c of about 40 K, which is the capability of the quick response for switching.

Superconductivity and transport properties of epitaxial YBa2(Cu1-xZnx)3O7-thin films

The influence of Zn-doping on the superconducting properties of epitaxial c-axis oriented YBa2(Cu1-xZnx)3O7-film was investigated. The authors find a depression of the superconducting Tc of -10.5 K/(at.% Zn). In the range of small doping concentrations x<or=0.005 the Zn-atoms act as effective pinning centers. This becomes evident by an enhancement of both the depinning field and the average activation energy for flux creep. The absolute values of the critical current density are not depressed for these concentrations. Measurements of the angular dependence of the critical transport current density jcab( phi ) in the ab-plane on the angle of an applied magnetic field show for Zn-doped films more structures than for undoped films. For explanation of jcab( phi ) a model based on intrinsic pinning in combination with the pinning effectivity of the Zn-impurities is discussed.

Structure of photodoped and thermally Zn-doped glassy arsenic sulfide films.

The structure of photodoped and thermally Zn-doped arsenic sulfide amorphous films has been investigated. X-ray-diffraction and electron-diffraction studies indicate that, after Zn doping, the ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ films remain amorphous, although the amount of dissolved zinc is about 55 at. %. An extended x-ray-absorption fine-structure (EXAFS) study has been made at both sulfur and zinc K edges. EXAFS analysis indicates that the structure of photodoped and thermally Zn-doped films is similar. Zinc was shown to be surrounded by S and As atoms, while sulfur is bonded to zinc and arsenic. The interatomic distances obtained correlate with those found in c-ZnS and c-${\mathrm{Zn}}_{3}$${\mathrm{As}}_{2}$. The x-ray-absorption edge (Zn K edge) for doped films is situated in between those for c-ZnS and metallic zinc. Infrared absorption measurements also show the formation of Zn-S bonds. Despite the similarity in structure, photodoped and thermally doped films give electron spin resonance signals with different g factors. Different models for zinc dissolution in chalcogenide glasses are proposed and discussed on the basis of the experimental data.

ＥＣＲプラズマ励起ＭＯＶＰＥ法によるＧａＮ単結晶膜の低温成長

A low-temperature-growth technique for GaN single crystal films has been developed using electron cyclotron resonance (ECR) plasma excitation. GaN films were grown on sapphire substrates utilizing reaction of trimethylgallium (TMGa) with highly activated nitrogen produced by ECR excitation of ammonia. Growth conditions to obtain single crystals were studied. Single crystal growth of Zn-doped films can be obtained. Zn-doped films exhibit a luminescence band peaking at 430550 nm. Surface morphologies of both undoped and Zn-doped films are very smooth.