Zn Thin Films Research Articles

An investigation of thin Zn films on 4H-SiC(0001)[sbnd]graphene

In this work, the growth of thin Zn films on 4H-SiC(0001)graphene and the effects of system annealing at various temperatures are presented. Metal growth on graphene is interesting to understand the grown morphology and metal intercalation, to use it to tune graphene properties. The properties such as chemical composition and surface structure were studied for deposited films and after annealing from 640 K to 1080 K. Using X-ray Photoelectron Spectroscopy and Low Energy Electron Diffraction techniques it was found that zinc interacts weakly with the substrate and does not change the XPS spectra bond energies but it intercalates, as seen from the extinction of the 6 × 6 diffraction spots. Moreover, in order to obtain complementary results, Density Functional Theory calculations were performed. The theoretical results for adsorption energy of Zn at various types of SiC surfaces can explain the preferred adsorption sites and the decrease of adsorption energy with Zn coverage presented in the experimental results.

Analysis of vertical phase distribution in reactively sputtered zinc oxysulfide thin films

Zinc oxysulfide (Zn(O,S)) is widely used for photovoltaic and optoelectronic devices because its electronic properties are tunable with adjustments to the S-to-O composition ratio. Zn(O,S) thin films used in devices are typically assumed to have constant S-to-O composition ratios across their thicknesses. However, S-to-O composition ratio gradients, and thus electronic property variations along the vertical direction, can be naturally induced. Such gradients can enhance device performance. In this work, we analyzed the S-to-O composition ratios along the thickness directions of Zn(O,S) thin films deposited at a fixed O2 gas flux. Natural O enrichment was observed near the bottom of the film, attributed to the highly reactive nature of the sputtering process. By increasing O2 gas flux during sputtering, more compositionally uniform thin films were obtained. We suggest that non-uniform phase distribution in the depth direction could be considered for achieving desired composition ratios when depositing Zn(O,S) thin films using reactive sputtering.

Morphological evolution of ZnO nanostructures with hydrothermal oxidation time and their electrochemical glucose sensing properties

In this work, zinc oxide (ZnO) nanostructures have been grown from electrodeposited Zn thin film followed by hydrothermal oxidation. The Zn layer was grown on copper (Cu) substrate at room temperature and then oxidized hydrothermally at 95 °C for different time duration. X-ray diffraction (XRD) patterns depicted that Zn thin film transformation to ZnO started after 1 h of oxidation and almost completed after 24 h. SEM results show the morphological transformation from Zn thin film to ZnO nanostructures by varying hydrothermal oxidation time duration. The influence of this morphological transformation on the photoluminescence (PL) spectra and non-enzymatic glucose sensing has been investigated. The full width half maximum (FWHM) of the UV emission peak in PL spectra became narrow with an increase in oxidation time. The electrochemical glucose sensing measurements show that the current density rises with an increase in oxidation time. The maximum current density has been observed for ZnO nanostructure oxidized for 24 h.

The Properties of Zn-Doped AlSb Thin Films Prepared by Pulsed Laser Deposition

Aluminum antimony (AlSb) is a promising photovoltaic material with a band gap of about 1.62 eV. However, AlSb is highly deliquescent and not stable, which has brought great difficulties to the applications. Based on the above situation, there are two purposes for preparing our Zn-doped AlSb (AlSb:Zn) thin films: One is to make P-type AlSb and the other is to find a way to suppress the deliquescence of AlSb. The AlSb:Zn thin films were prepared on glass substrates at different substrate temperatures by using the pulsed laser deposition (PLD) method. The structural, surface morphological, optical, and electrical properties of AlSb:Zn films were investigated. The crystallization of AlSb:Zn thin films was enhanced and the electrical resistivity decreased as the substrate temperature increased. The scanning electron microscopy (SEM) images indicated that the grain sizes became bigger as the substrate temperatures increased. The Raman vibration mode AlSb:Zn films were located at ~107 and ~142 cm−1 and the intensity of Raman peaks was stronger at higher substrate temperatures. In the experiment, a reduced band gap (1.4 eV) of the AlSb:Zn thin film was observed compared to the undoped AlSb films, which were more suitable for thin-film solar cells. Zn doping could reduce the deliquescent speed of AlSb thin films. The fabricated heterojunction device showed the good rectification behavior, which indicated the PN junction formation. The obvious photovoltaic effect has been observed in an FTO/ZnS/AlSb:Zn/Au device.

Effects of substrate orientation and solution movement in chemical bath deposition on Zn(O,S) buffer layer and Cu(In,Ga)Se2 thin film solar cells

With a colloid aggregation process, chemical bath deposited (CBD) Zn(O,S) thin films always consist of many particles or clusters on the surface and their removal is a long-standing problem. In this work, by varying the substrate orientations and solution movements, their effects on the quality of the Zn(O,S) layers, the formed junctions, and the performance of the Zn(O,S)-Cu(In,Ga)Se2 (CIGS) solar cells have been systematically investigated. Unlike CBD-CdS growth for which stirring or rocking the solution is a common and useful practice for improved quality, surprisingly, for CBD-Zn(O,S) growth, solution movement plays a primary role and substrate orientation plays a secondary role to influence the film quality and the device performance. Equally surprising, the above effects strongly depend on the recipes and chemicals used for the CBD process. It has been identified that, independent of recipes, depositing Zn(O,S) films with the substrate inclined in a static solution can minimize the formation of particles/clusters, generate homogeneous and high quality buffer layers on CIGS with the best device performance. Disturbing the CBD solution would in general introduce large particles/clusters to adsorb on the Zn(O,S) films, leading to degraded junction quality, strong light soaking effect, and poor device performance.

Structural and Optical Properties of (110) Plane Textured SnO2:Zn Thin Films

SnO2:xZn thin films (x = 0, 1, 3, 5, 10, 15 wt%) were deposited onto a glass substrate by ultrasonic spray pyrolysis at 350°C and characterized by XRD, UV–VIS spectra, AFM imaging, and texture analysis. All deposited thin films exhibited preferential orientation along the (110) plane. The films were highly transparent (about 80%) in the visible. Upon an increase in x, the band gap energy of the films decreased from 3.7 eV to 3.3 eV.

Effects of Ammonia‐Induced Surface Modification of Cu(In,Ga)Se2 on High‐Efficiency Zn(O,S)‐Based Cu(In,Ga)Se2 Solar Cells

Post‐treatment of Cu(In,Ga)Se2 (CIGS) surfaces, as an efficient way to improve the performance of CIGS solar cells, has received increasing attention in recent years. To alleviate the limitations of the as‐grown CIGS thin films, such as oxidation, Na accumulation, and microstructure of CIGS surface, ammonia (NH3) etching solution was introduced to post‐treat the CIGS surface to improve its quality in this study. To investigate the mechanisms of NH3 etching effects on the CIGS surfaces and the resulted devices, a series of NH3 solution treatments, of different concentrations, on CIGS films is carried out and the resulted surfaces and devices are carefully examined. It is demonstrated that proper concentration of NH3 solution could not only result in a new microstructure between CIGS and Zn(O,S) thin films but also improve the performance of the Zn(O,S) based CIGS solar cells, especially in terms of the device fill factor. As a result, a Zn(O, S) based CIGS solar cell with a conversion efficiency of over 20% is obtained with application of NH3 treatment together with MgF2 anti‐reflective coating. Furthermore, it is found that NH3 treatment could effectively reduce the undesired light soaking effect, which often appears in the Zn(O,S) based CIGS solar cells.

Fabrication of Zn(O,S) thin films by ozone assisted photochemical deposition and its potential applications as buffer layers in kesterite-based thin film solar cells

Zn(O,S) thin films have attracted intensive attention for their potential application as Cd-free buffer layers in kesterite-based solar cells due to their desirable band alignment with Cu2ZnSnS4 (CZTS) or Cu2ZnSnSxSe4-x (CZTSSe) materials. In this work, Zn(O,S) thin films with controllable content of oxygen have been designed via ozone-assisted photochemical deposition processes. Results showed that the deposited Zn(O,S) thin films using various ozone flow rate are flat, compact and uniform with a thickness of ~ 40 nm, consisting of nanoparticles with a diameter of 30–50 nm. The introduction of ozone into synthesis processes can hardly impose any effect on the morphologies, but significantly modify and tune the oxygen contents in the deposited thin films. Moreover, optical absorption spectra indicate that the optical band-gap of Zn(O,S) films can be readily tuned from 3.3 to 3.7 eV by changing the ozone flow rates. Furthermore, it is confirmed that the solar cells with Zn(O,S)/CZTS structure has a higher conversion efficiency of 3.0% and a higher open circuit voltage of 0.516 V compared to those with ZnS/CZTS structure. Our research would open an easy and promising approach to prepare Cd-free buffer layer materials for kesterite-based thin film solar cells.

Effect of sulfurization temperature on optical and compositional properties of sputtered Zn(O, S) thin films

Zinc oxysulfide or Zn(O,S) is emerging as an alternate n-type buffer layer for kesterite, chalcogenides and CdTe based thin film solar cell due to it is being made from non-toxic elements and tunable bandgap, its suitable optical and electrical properties required for a buffer layer. Generally, buffer layers of these solar cells are deposited using chemical bath deposition (CBD) techniques, but these require breaking of vacuum and again inserting the sample in vacuum during solar cell fabrication, which is not economical and is cumbersome. Sputtering is considered to be industrial process and therefore, here we have deposited Zn(O,S) thin film by sputtering technique and effect of sulfurization temperature on bandgap and composition of Zn(O,S) films have been studied. The bandgap of deposited films changed from 3.36 eV to 3.15 eV by changing the sulfurization temperatures. By changing the sulfurization temperature, the composition of films also changed. Crystallite size (D) of Zn(O,S) films increased from 12.1 nm to 22.3 nm by varying the sulfur content for samples S1-S4, respectively. Optical, morphological, compositional and structural properties have been studied using UV-Vis-NIR spectroscopy, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray diffractometer (XRD), respectively.

PH-controlled surface engineering of nanostructured ZnO films generated via a sustainable low-temperature H2O oxidation process

Developing a consistent and sustainable protocol for fabricating predetermined ZnO nanostructures is of significant interest in materials science and industry, owing to the emergence of ZnO-based devices and applications. Herein, the design of novel nanostructured ZnO films via a green, sustainable and low-temperature H2O oxidation technique is presented. Surface engineering was achieved by controlling the pH value of H2O during oxidation of Zn thin films. Diverse ZnO nanostructures of high structural and optical qualities including nanoparticles, microparticles composed of smaller rods, columnar nanorods and nanotubes having different growth orientations emerged. The morphology, chemical composition, structure, surface chemistry and optical properties of the nanomaterials were comprehensively characterized as a function of pH value. The experimental results and proposed growth mechanism for each nanostructure were presented and thoroughly discussed to have a deeper understanding on the physical insights governing the pH-controlled development of the nanostructures. This in-depth examination could pave the way to pioneering properties and functionalities that could sustainably fulfill the requirements of next generation optoelectronic devices.

Genetic programming modelling for the electrical resistivity of Cu–Zn thin films

Electrical resistivity measurement is an exact way to find defects in metals and alloys. Defects contribute to the residual resistivity, and determining their number is very important. Defining the inner electrical structure of an alloy is difficult, and especially it is unpredictable in alloys. This article offers a genetic programming formulation to learn how deposition conditions and alloy constituents affect the electrical resistivity of Cu–Zn alloy. Input parameters selected were: measurement temperature (K), Cu and Zn% content in the deposition bath and thin films, bath temperature, deposition potential, and the grain size of the samples. Electrical resistivity values were the output parameters. A total of 130 training and testing sets were selected. The comparative results prove the superior performance in predicting electrical resistivity of the films. The produced model proposes a close relationship for all the input parameters with the electrical resistivity property.

Quaternary Zn-Ni-MoO2-NbO2 intermetallic composite deposits on mild steel via electrodeposition route

In majority of industrial applications zinc electrodeposition has been widely used for the corrosion resistant coating on steel due to its unique properties, low cost and sacrificial nature. Steel remains the most widely used material in most applications due to its excellent properties but its faults cannot be over emphasis in term of deterioration. A thin film of Zn on steel substrates was prepared by electrodeposition technique using incorporated rare earth metallic composites to form an optimised bath plating solution. Quaternary Zn-Ni-MoO2-NbO2 alloy coatings, as a potential replacement for Zn-Ni coatings were deposited from an acid sulphate solution. The mechanical wear and corrosion behaviours of Zn-Ni-MoO2-NbO2 Coated Mild Steel in 3.65% NaCl are described; these were studied by means of MTR-300 dry abrasive wear and polarization measurements respectively. The crystal particles present were observed by X-ray diffraction pattern (XRD) and energy dispersive X-ray diffraction spectrometer (EDS). The microhardness of deposited plate were investigated by means of Vickers microhardness. Scanning electron microscope and was used to study the surface morphology, and synergistic influence content in bath on surface morphology revealed that morphological changes observed in presence of additives exhibits synergistic influence on improving corrosion resistance and hardness of the deposit.

Cu(In,Ga)Se2 solar cell with Zn(S,O) as the buffer layer fabricated by a chemical bath deposition method

Zn(S,O) polycrystalline thin films were prepared using chemical bath deposition. The Zn(S,O) thin film with high-crystalline quality fully covered the substrate by controlling concentrations of starting materials, temperature of the substrate, and reaction time. The obtained Zn(S,O) thin films were characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy. The optical transmittance of the Zn(S,O) thin film with a thickness of 106.84 nm exceeded 90% in the wavelength range of 350–1400 nm. The obtained Zn(S,O) films were applied as buffer layers in the CuIn1−xGaxSe2 (CIGS) solar cells. By optimizing the thickness and quality of the buffer layer and using light soaking, a 11.65%-efficiency CIGS solar cell was obtained without an anti-reflective coating layer. The short-circuit current density increased compared with that of CIGS solar cell with cadmium sulfide buffer layer due to the higher band gap of Zn(S,O) than that of CdS. The increase of the efficiency with the light-soaking time was mainly due to the fill factor increase. The CIGS solar cell showed good weak light effect and high stability. The dominant recombination mechanisms in the CIGS solar cell with Zn(S,O) buffer layer were the tunneling-enhanced recombination in the space charge region and the interface recombination at the Zn(S,O)/CIGS interface.

Plasma-enhanced atomic layer deposition of highly transparent zinc oxy-sulfide thin films

The potential of Plasma Enhanced Atomic Layer Deposition (PEALD) for the synthesis of zinc oxy-sulfide Zn(O,S) thin films was explored for the first time, using a supercycle strategy and DEZ, Ar/O2 plasma and H2S as precursors. The growth and the properties of the material were studied by varying the pulse ratio on the full range of composition and the process temperature from Tdep = 120 °C to 220 °C. PEALD-Zn(O,S) films could be grown from pure ZnO to pure ZnS compositions by varying the H2S/(O2 plasma + H2S) pulse ratio. Three distinct growth modes were identified depending on the nature of exchange mechanisms at the film surface during the growth. Films globally have an amorphous structure, except for the extremely sulfur-rich or sulfur-poor ones. High transmission values (up to 85% for Zn(O,S) for 500 < λ < 2500 nm) and optical band gaps (3.3–3.8 eV) have been obtained. The PEALD-Zn(O,S) process and the thin film properties were compared with ALD-Zn(O,S) to highlight the specificities, disadvantages and benefits of plasma enhancement for the synthesis of multi-element materials.

Nano-structural variations of ZnO:N thin films as a function of deposition angle and annealing conditions: XRD, AFM, FESEM and EDS analyses

In this work the influence of the variation of the stoichiometry of the annealing gas as a mixture of oxygen and nitrogen on the morphology, shape and crystallography (chemical composition) of Zn thin films produced by the use of electron beam evaporation technique at different oblique angle depositions (OAD) is investigated. The different stoichiometry of annealing gas together with the void fraction resulting from the OAD provided conditions as a new route for formation of different shaped ZnO:N nanostructures (nano-columns, pyramids, nano-rods and particularly nano-bowls). Results, in particular show the formation of nano-bowl structure for high concentration of nitrogen in the annealing gas (80% of grains show formation of nano-bowls on the surface) while introduction of low flow of oxygen in the gas mixture prevents the formation of both zinc nitride and zinc oxide. However, further increase of oxygen in the gas mixture leads to formation of both of these structures in form of nano-bowls and hexagonal nano-columns of different shapes, respectively. This is the first report on the formation of ZnO:N nano-bowls. When, only oxygen is used for the annealing process only ZnO in nano-nail (conical hexagonal structure) shape is produced. Detailed morphological, chemical and structural investigations are carried out on all samples by field emission electron microscopy (FESEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and X-ray diffraction (XRD) methods.

Determination and analysis of optical constants and dispersion energy parameters of Zn(S,O) thin films

Zn(S,O) thin films was elaborated by annealing in air and sulfur atmospheres the zinc films deposited by thermal evaporation method. The samples were analyzed for their optical properties by using Ultraviolet–Visible-near Infrared spectroscopy. The optical constants and the dispersion parameters of the films were calculated from the analysis of the transmittance and reflectance data in the spectral range 300–1800 nm. The band gap energy varied from 3.27 to 3.08 eV depending on the sulfur content. The bowing parameter was calculated as 2.45 eV. Swanepoel model was employed to study the wavelength dependence of the refractive index. The lattice dielectric constant εL, the plasma frequency ωp and the ratio of the carrier density to the carrier effective mass N/m* were calculated from the examination of the refractive index. Wemple-Di Domenico single oscillator model was applied to determine the dispersion parameters of the samples such as the high-frequency dielectric constant ε∞, the oscillator energy E0 and the dispersion energy Ed.

Impact of thiourea concentration on the properties of sol–gel derived Zn(O,S) thin films and Cu(In,Ga)Se2 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.

Fabrication and in vitro properties of zinc-based superhydrophilic bioceramic coatings on zirconium

In this study, as the first step, the bioceramic coatings were fabricated on Zr (commercial pure zirconium) in calcium acetate and β‑calcium glycerophosphate salt-based electrolyte by MAO (micro arc oxidation). And then, as the second step, the Zn (zinc) thin film layer measured an average thickness of 5 nm was coated on the MAO surface by TE (thermal evaporation). The phase composition, surface and cross sectional morphology, elemental composition and wettability of the MAO and Zn-based MAO coatings were analyzed by powder-XRD and TF-XRD, SEM, EDS-mapping and contact angle goniometer, respectively. The phases of cubic-ZrO2, perovskite-CaZrO3 and HA (hydroxyapatite) were observed on the surfaces by powder and TF-XRD analyses. The morphology of the MAO surface was not changed by TE although the chemistry of it was different from the MAO surface. The surfaces of both coatings were porous and rough. The Zn was uniformly deposited through the whole surface. After TE process, the wettability of the surface decreased and the Zn-based surface exhibited superhydrophilicity compared to MAO surface. In vitro bioactivity test of both coatings were investigated by immersion test in SBF (simulated body fluid) up to 10 days. The bone like apatite layer (secondary apatite) on the Zn-based bioceramic surface was compact and uniform compared the one on the MAO surface although it was completely propagated through both surfaces. In vitro anti-bacterial test of both coatings were carried out by microbial adhesion for Gram positive and Gram negative bacteria. It was observed that the microbial adhesions of the Zn-based bioceramic surfaces were lower than ones of the MAO bioceramic surfaces for all Gram-positive and Gram-negative bacteria.

Effect of substrate on texture and mechanical properties of Mg–Cu–Zn thin films

In this work, thin films of Mg–Cu–Zn with 60 nm thicknesses have been deposited on the Si(100), Al, stainless steel, and Cu substrates using DC magnetron sputtering. FESEM images displayed uniformity of Mg–Cu–Zn particles on the different substrates. AFM micrograph revealed the roughness of thin film changes due to the different kinds of the substrates. XRD measurements showed the existence of strong Mg (002) reflections and weak Mg (101) peaks. Residual stress and adhesion force have been measured as the mechanical properties of the Mg–Cu–Zn thin films. The residual stresses of thin films which have been investigated by X-ray diffraction method revealed that the thin films sputtered on the Si and Cu substrates endure minimum and maximum stresses, respectively, during the deposition process. However, the force spectroscopy analysis indicated that the films grew on the Si and Cu experienced maximum and minimum adhesion force. The texture analysis has been done using XRD instrument to make pole figures of Mg (002) and Mg (101) reflections. ODFs have been calculated to evaluate the distribution of the orientations within the thin films. It was found that the texture and stress have an inverse relation, while the texture and the adhesion force of the Mg–Cu–Zn thin films have direct relation. A thin film that sustains the lowest residual stresses and highest adhesive force had the strongest {001} basal fiber texture.

Influence of Oxygen Vacancies on the Magnetic Properties of Zn1 – xCo x O y Films

Thin films of Zn1 – xCo x O y (х = 0–0.3) with a temperature of the ferromagnetic transition of ТС > 300 K are obtained from ZnO–Co3O4 ceramic targets. The electron concentration in the films is found to decrease exponentially with increasing cobalt content. It is revealed that the magnetization of the films obtained under oxygen deficiency conditions varies in a nonmonotonous way as the cobalt concentration increases. This is caused by the oxidation of metallic nanoclusters of cobalt due to an increase in the oxygen content in the targets. Investigation of the transmission spectra of Zn1 – xCo x O y films revealed extrema in the visible region of the spectrum and near the edge of the fundamental absorption band, associated with electron states introduced by cobalt.