Surface topography, structural, optical and dc electrical behaviors of pristine and Co-doped ZnS thin films

The prime goal of the present research is to synthesize pristine zinc sulfide (PZS) and cobalt (Co)-doped zinc sulfide (CDZS) thin films with different doping concentrations (DC) via chemical bath deposition (CBD) method. The effect of Co-doping on the surface topography, structural, optical and dc-electrical behaviors of PZS thin films has been ascertained. Scanning electron microscopy images exhibited nearly sphere-shaped agglomerates of grains dispersed throughout the surface with cracks in PZS thin film whereas cracks were absent in CDZS. Atomic force microscopy image displayed smooth surface of CDZS thin film with evenly dispersed small grains. The hexagonal wurtzite structure of PZS and CDZS thin films with varied X-ray diffraction (XRD) parameters was confirmed via XRD analysis. Optical investigation revealed that the optical direct band gap energy increased with decreasing DC from 12 % to 4 %. Alteration of other optical parameters namely absorption coefficient, extinction coefficient, refractive index, real and imaginary parts of dielectric constant, etc. with DC was also discussed. Direct current electrical investigation revealed that the current-voltage characteristics are linear for all thin films signifying that the electrical conduction in CDZS is ohmic in nature.

Engineering Mn-Doped CdS Thin Films Through Chemical Bath Deposition for High-Performance Photoelectrochemical Water Splitting

Doping conventional materials with a second element is an exciting strategy for enhancing catalytic performance via electronic structure modifications. Herein, Mn-doped CdS thin films were successfully synthesized with the aid of the chemical bath deposition (CBD) by varying the pH value (8, 10, and 12) and the surfactant amount (20, 40, 60 mg). Different morphologies like nano-cubes, nanoflakes, nano-worms, and nanosheets were obtained under different deposition conditions. The optimized Mn-doped CdS synthesized at pH=8 exhibited better photoelectrochemical (PEC) performance for oxygen evolution reaction (OER) than pure CdS films, with a maximum photocurrent density of 300 μA/cm2 at an external potential of 0.5 V, under sunlight illumination. The observed performance is attributed to the successful Mn doping, porosity, high surface area, and nanosphere morphology.

Investigation and optimization of In-Vitro behaviour of Perovskite barium titanate as a scaffold and protective coatings

The piezoelectric effect is widely known to have a significant physiological function in bone development, remodeling, and fracture repair. As a well-known piezoelectric material, barium titanate is particularly appealing as a scaffold layer to improve bone tissue engineering applications. Currently, the chemical bath deposition method is used to prepare green synthesized barium titanate coatings to improve mechanical and biological characteristics. Molarity of the solutions, an essential parameter in chemical synthesis, is changed at room temperature (0.1-1.2 Molar) to prepare coatings. The XRD spectra for as deposited coatings indicate amorphous behavior, while polycrystalline nature of coatings is observed after annealing (300 °C). Coatings prepared with solutions of relatively low molarities, i.e. from 0.1 to 0.8 M, exhibit mixed tetragonal - cubic phases. However, the tetragonal phase of Perovskite barium titanate is observed using solution molarities of 1.0 M and 1.2 M. Relatively high value of transmission, i.e. ∼80%, is observed for the coatings prepared with high molarities. Band gap of annealed coatings varies between 3.47 and 3.70 eV. For 1.2 M sample, the maximum spontaneous polarization (Ps) is 0.327x10-3 (μC/cm2) and the residual polarization (Pr) is 0.072x10-3 (μC/cm2). For 1.2M solution, a high hardness value (1510 HV) is recorded, with a fracture toughness of 28.80 MPam-1/2. Low values of weight loss, after dipping the coatings in simulated body fluid, is observed. The antibacterial activity of BaTiO3 is tested against E. coli and Bacillus subtilis. Drug encapsulation capability is also tested for different time intervals. As a result, CBD-based coatings are a promising nominee for use as scaffold and protective coatings.

Improved osteointegration response using high strength perovskite BaTiO3 coatings prepared by chemical bath deposition

A wide range of bioactive materials have been investigated for tissue engineering and regeneration. Barium titanate is a promising smart material to be used as scaffold for bone tissue engineering. Barium titanate coatings are prepared in the present study using chemical bath deposition technique. Coatings are prepared at room temperature with the variation in solution molarity from 0.1 to 1.2 M. Perovskite tetragonal phase is observed after annealing the samples at 300 °C using 1.0-1.2 M solutions. Normal-anomalous dielectric response is observed for annealed coatings. Maximum transmission of ∼55% and ∼82% is observed under as-prepared and annealed coatings, respectivly. Variation in direct band gap, i.e. 3.45-3.64 eV, is observed with varying molarity. High hardness of the coatings (∼1180 HV) is observed at 1.2M with fracture toughness of ∼22 MPam^-1/2. Biodegradation studies show smaller values of weight loss even after immersion in simulated body fluid (SBF) after 26 weeks. Barium titanate coatings also show high antioxidant activity. BaTiO₃'s antibacterial reaction is evaluated against microorganisms such as Escherichia coli (E. coli) and Staphylococcus aureus. Antibacterial activity shows highest zone of inhibition (∼31 mm) against Staphylococcus aureus bacteria. Quantitative real-time PCR is used to assess the gene expression profile in cultivated cells. Thus, coatings produced without the use of hazardous solvents/reagents utilizing CBD technique are a potential material for biomedical applications.

Lossy mode resonance fiber-optic sensor based on ZnO particles fabricated by chemical bath deposition

We present a lossy mode resonance (LMR) sensor fabricated by chemical bath deposition (CBD) using a U-shaped optical fiber with an exposed core. The ZnO particles that generate LMR were prepared by a very costly method in three steps via permanganate activation and the deposition of ZnO on the fiber core using CBD. The process of deposition was monitored in real time through the optical fiber, and a clear absorption spectrum with an LMR peak was obtained. The surface of the sensor with absorbance reaching 1.0 was covered with nano- to submicron particles of ZnO. The refractive index (RI) sensitivity of the sensor was measured using sucrose solution and was found to increase as the amounts of ZnO on the sensor increased, reaching 23 Abs/RI unit (RIU). The RI resolutions of the sensors with absorbance reaching 0.40, 0.65, and 1.0 during CBD were determined as ΔRI = 0.000060, 0.00017, and 0.00018, respectively, with a 99.7% confidence interval for the RI. Pretreatment during CBD was found to dramatically affect the fabrication of LMR sensors owing to their size and occupancy of deposited ZnO particles, the effects of which can be observed in real time using fiber optics.

Synthesis and characterization of copper zinc iron sulphide (CZFS) thin films

In an aqueous bath, quaternary thin films (TFs) of copper zinc iron sulphide (CZFS) were deposited on glass (soda-lime) substrates. The present study aimed to analyse the effect of deposition periods on the properties of the prepared CZFS TFs using Chemical bath deposition (CBD). The precursor and films were examined by Fourier Transform Infrared (FTIR) spectroscopy to check for the chemical formation present. Rutherford backscattering spectroscopy (RBS) was used to determine the elemental compositions and stoichiometry of the deposited films. The optical characteristics were observed by a UV-Vis Spectrophotometer and a four-point probe (FPP) for the electrical properties. The optical characterization revealed a direct transition band-gap energy that decreased from 1.96 to 1.50 eV with an increase in deposition period. The optical constants were studied with respect to the wavelength within the range of 300–900 nm. The films exhibited high resistive properties with a conductivity that varied with an increase in deposition period. The effect of deposition periods on the optical properties of refractive index, extinction coefficient, and real and imaginary parts of dielectric constants has been reported. All these parameters were found to increase with deposition period except for the film deposited for 18 h (C3). These results confirm that the aqueous deposited CZFS films can be tuned for various optoelectronic applications.

Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning

Different ZnO nanostructures can be grown using low-cost chemical bath deposition. Although this technique is cost-efficient and flexible, the final structures are usually randomly oriented and hardly controllable in terms of homogeneity and surface density. In this work, we use colloidal lithography to pattern (100) silicon substrates to fully control the nanorods' morphology and density. Moreover, a sol-gel prepared ZnO seed layer was employed to compensate for the lattice mismatch between the silicon substrate and ZnO nanorods. The results show a successful growth of vertically aligned ZnO nanorods with controllable diameter and density in the designated openings in the patterned resist mask deposited on the seed layer. Our method can be used to fabricate optimized devices where vertically ordered ZnO nanorods of high crystalline quality are crucial for the device performance.

Effects of growth conditions on properties of CBD synthesized ZnO nanorods grown on ultrasonic spray pyrolysis deposited ZnO seed layers

ZnO nanorods were synthesized on a seed layer coated glass substrate using chemical bath deposition (CBD). Prior to growth, a seed layer had been prepared via ultrasonic spray pyrolysis method. The aim was to explore the influence of varying the chemical bath deposition conditions namely: growth time, bath temperature and concentration levels of the precursor on the orientation, structural, optical and vibrational properties of the subsequently grown nanorods. The presence of ZnO nanorods resembling the hexagonal-wurtzite structure having preference of orientation along the c-axis and varying crystallinity under different growth parameters was confirmed by X-ray diffraction (XRD). Scanning Electron Microscopy (SEM) acquired images of uniformly arranged and vertically oriented ZnO nanorods grown at a relatively higher bath temperature of 90 °C and shorter growth period of 2 h. UV/Vis/NIR spectrophotometer measurements revealed an optical transmittance of between 50 – 70 % for the nanorods. Raman spectroscopy results confirmed the presence of Raman active E_2(low) and E_2(high) modes corresponding to 98 cm⁻¹ and 478 cm⁻¹ belonging to the hexagonal ZnO phase. This work shows that the orientation, structural, optical and vibrational properties of the grown nanorod structures are controlled via alteration of the growth parameters.

Effect of electron beam irradiation on chemically synthesized nanoflake-like CdS electrodes for photoelectrochemical applications

In this paper, we chemically synthesized interconnected nanoflake-like CdS thin films for photoelectrochemical solar cell applications and subsequently irradiated them with electron beam irradiation at various doses of irradiation. The as-synthesized and irradiated samples were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and electrochemical measurements. XRD and XPS results confirmed the formation of CdS with a hexagonal crystal structure. FE-SEM and HR-TEM studies confirmed the photoelectrochemical performance, which was dependent on the surface morphology. The calculated values for efficiency demonstrated an outstanding photoelectrochemical performance with a fill factor of 0.38 and efficiency of 3.06% at 30 kGy. The high photoelectrochemical performance may be due to the interconnected nanoflake-like nanostructure and higher active surface area of the CdS samples. These results show that the electron beam irradiation is capable as an electrode for photoelectrochemical solar cells.

Semiconducting Hybrid Layer Fabrication Scaffolded by Virus Shells

The formation of virus-based semiconducting hybrid thin films is a two-step process, which involves assembly of virus particles as a template layer and subsequent selective mineralization of the virus surface with inorganic nanoparticles to build a semiconducting organic-inorganic hybrid film. Here, we present the use of the convective assembly technique to obtain homogeneous and dense template monolayers of wild-type tobacco mosaic virus (wt-TMV) and the TMV mutant E50Q, of which most particles do not have detectable amounts of RNA in the protein tube. On the top of the aligned virus layer, zinc oxide (ZnO) is deposited to prepare virus-ZnO semiconducting hybrid films with controllable thickness under mild conditions of the chemical bath deposition (CBD).

Role of annealing on the structural and optical properties of nanostructured diaceto bis-benzimidazole Mn(II) complex thin films

A coordination complex, manganese incorporated benzimidazole, thin films were prepared by chemical bath deposition method. Structural characterization of the deposited films, carried out by Fourier transform infrared spectroscopy, Raman and electron paramagnetic resonance spectral analyses, reveals the distorted tetrahedral environment of the metal ion with bis-benzimidazole ligand. Further the molecular composition of the deposited metal complex was estimated by energy-dispersive X-ray spectroscopy. The prepared thin films were thermally treated to study the effect of annealing temperature on the surface morphology and the results showed that the surface homogeneity of the films increased for thermally treated films up to 150°C. But distortion and voids were observed for the films annealed at 200°C. The Raman analysis reveals the molecular hydrogen bond distortion which leads to the evaporation of the metal complex from the thin film surface with respect to annealing temperature. The linear and nonlinear optical properties of the as prepared and annealed films were studied using ultraviolet-visible transmittance spectroscopy, second harmonic generation and Z-scan analyses. Films annealed at 150°C show a better linear transmittance in the visible region and larger SHG efficiency and third order nonlinear susceptibility when compared with the other samples. Further, the film annealed at 150°C was subjected to optical switching analysis and demonstrated to have an inverted switching behavior.

Enhanced electrochemical performance of monoclinic WO3 thin film with redox additive aqueous electrolyte

To achieve the highest electrochemical performance for supercapacitor, it is very essential to find out a suitable pair of an active electrode material and an electrolyte. In the present work, a simple approach is employed to enhance the supercapacitor performance of WO3 thin film. The WO3 thin film is prepared by a simple and cost effective chemical bath deposition method and its electrochemical performance is tested in conventional (H2SO4) and redox additive [H2SO4+hydroquinone (HQ)] electrolytes. Two-fold increment in electrochemical performance for WO3 thin film is observed in redox additive aqueous electrolyte compared to conventional electrolyte. WO3 thin film showed maximum specific capacitance of 725Fg(-1), energy density of 25.18Whkg(-1) at current density of 7mAcm(-2) with better cycling stability in redox electrolyte. This strategy provides the versatile way for designing the high performance energy storage devices.

Ternary CuBiS2 nanoparticles as a sensitizer for quantum dot solar cells

This work investigates the synthesis and application in solar cells of a novel solar absorber material CuBiS2. Ternary copper chalcogenide CuBiS2 nanoparticles were grown on a mesoporous TiO2 electrode by the chemical bath deposition (CBD) method. The synthesized CuBiS2 nanoparticles, size 5-10nm, have an energy gap Eg of 2.1eV. Liquid-junction quantum dot-sensitized solar cells were fabricated from the CuBiS2-sensitized electrode using a polysulfide electrolyte. Three types of counter electrodes (CEs) - Pt, Au and Cu2S - were tested. The photovoltaic performance depends on the CBD reaction time and the CE. The best cell, obtained with the Cu2S CE, exhibited the photovoltaic performance of a short-circuit current density Jsc of 6.87mA/cm(2), an open-circuit voltage Voc of 0.25V, a fill factor FF of 36% and a power conversion efficiency η of 0.62%. The present work demonstrates the feasibility of CuBiS2 as a solar energy material.

Superhydrophobic ZnO networks with high water adhesion

ZnO structures were deposited using a simple chemical bath deposition technique onto interdigitated electrodes fabricated by a conventional photolithography method on SiO2/Si substrates. The X-ray diffraction studies show that the ZnO samples have a hexagonal wurtzite crystalline structure. The scanning electron microscopy observations prove that the substrates are uniformly covered by ZnO networks formed by monodisperse rods. The ZnO rod average diameter and length were tuned by controlling reactants' concentration and reaction time. Optical spectroscopy measurements demonstrate that all the samples display bandgap values and emission bands typical for ZnO. The electrical measurements reveal percolating networks which are highly sensitive when the samples are exposed to ammonia vapors, a variation in their resistance with the exposure time being evidenced. Other important characteristics are that the ZnO rod networks exhibit superhydrophobicity, with water contact angles exceeding 150° and a high water droplet adhesion. Reproducible, easily scalable, and low-cost chemical bath deposition and photolithography techniques could provide a facile approach to fabricate such ZnO networks and devices based on them for a wide range of applications where multifunctionality, i.e., sensing and superhydrophobicity, properties are required.

PACS

81.07.-b; 81.05.Dz; 68.08.Bc.