Papers by Keyword: Thin Film

Abstract: An embedded system-based spin coating machine has been developed to grow thin films. Pure zinc oxide (ZnO) and magnesium-doped zinc oxide (ZnO: Mg) thin films with different doped samples have been prepared using the spin coating technique for LPG gas sensing application. The spin coating machine is fully controlled by a PIC microcontroller (PIC16f877A), which can drive a driver circuit to drive a spinning motor, and ZnO: Mg thin films are deposited using this machine. XRD results indicated that the movie has a hexagonal wurtzite structure with a preferred orientation, and the crystallite size increases with the increasing doping concentration of Mg. The surface morphology investigation shows that grains are irregular in shape, and doping concentrations do not influence the surface morphology. From the TEM image, particle sizes observed ranged between 23 and 28 nm, with an average value of ~25.8 nm. The maximum visible average transmittance was 96% for an optimum Mg doping concentration of 10 wt% %. The investigated DC electrical conductivity of Mg-doped ZnO thin films shows enhanced electrical conductivity compared to pure ZnO, and the AC conductivity is decreased with increasing Mg doping concentrations from 5 to 10 wt%. The operation and sensing mechanism of Pure ZnO and ZnO: Mg thin films behind their impressive results has been studied in depth.

Abstract: Herein we report a simple and cost-effective way for synthesis and application of ZnO-PVA nanocomposite using the spin coating technique in which an aqueous solution containing sources of above was deposited on a glass substrate using spin coating technique and further annealed at 120°C. The structural, optical and morphological properties investigated reveals polycrystalline nature of uniformly coated ZnO-PVA composite thin film with a band gap of 3.26 eV. Photo-detector device is made by patterning silver electrodes at two ends of thin film by keeping an electrode gap of ~ 1 mm. Current-voltage measurements are performed under dark and UV illumination. A linear rise in photocurrent under UV illumination (100 μW/cm²) indicate reliable photodetection properties of the device with ~ 6 μA photocurrent, 120 A/W responsivity, 5.8 x 10⁴external quantum efficiency, 6 x 10⁴ sensitivity and 0.6ms rise time, which is highly applicable for fabricating UV photodetectors going to be used for advance application in defence and space.

Abstract: Photoconductive amorphous selenium (a-Se) layers are utilized in flat panel X-ray imaging detectors as a direct conversion medium, converting X-ray photons directly into electric charge. Commercial a-Se direct conversion Active Matrix Flat Panel Imagers (AMFPIs) have demonstrated superior image quality in mammography, showcasing the potential of this X-ray imaging technology [1-2]. The use of a-Se is limited, however, by its low Z, resulting in low stopping of high energy X-rays [2]. This limitation is not shared by PbO thin films. Earlier PbO films consisted of small poly-crystalline platelets with low film density and suffered from the presence of both oxygen vacancies and impurity phases (PbO₂). Recent advances [3-4] have yielded dense amorphous PbO (a-PbO) films with apparently uniform stoichiometry, as confirmed by X-ray photoelectron spectroscopy (XPS). More careful analysis [5] using X-ray absorption spectroscopy (XAS) indicated some tailing of the conduction band, which was attributed to suspected O-vacancies. An annealing study on a-PbO [3] indicated a transition to β-PbO around 500 C. X-ray diffraction (XRD) data of the β-PbO (annealed a-PbO) film matched that of a β-PbO reference, while XAS data did not. This was attributed to the different depths of the sample volumes probed by the two techniques. Doppler-broadened positron annihilation spectroscopy (DBPAS) was conducted on several a-PbO samples synthesized under different conditions using the McMaster Variable-Energy Positron Beam (MVEPB) and the results were modelled using VEPFIT [6]. All samples were found to have a three-layer structure, with the bulk S-parameters between 0.4725 and 0.4753. The two other layers were contained within the first 300nm of the film and varied in thickness, diffusion length and S-parameter value. This confirms the suitability of DBPAS, as a sensitive probe of vacancy-type defects and the layer structure of thin films, to guide the optimization of a-PbO synthesis for photoconductive detectors. Work is underway to produce a series of samples which vary systematically in their synthesis conditions to establish synthesis-structure relationships.

Abstract: In this recent study, thin films of pure tin oxide (SnO₂) denoted by TO and tin oxide doped with nickel (Ni) and zinc (Zn) at varying concentrations of 5 wt.%, 10 wt.%, and 15 wt.% were developed and characterized on ordinary glass substrates. The deposition of the films was conducted using the sol-gel technique (Dip-coating). These films are referred to as (Ni-Zn) co-doped tin oxide (NZTO) films that can be used in diverse applications such as gas and UV sensors. The effect of Ni/Zn co-doping on the structural, morphological, optical, and electrical properties of undoped SnO₂ was investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy. The electrical properties were further examined using the quadruple method. XRD analysis revealed that all samples were polycrystalline with a rutile-type tetragonal crystal structure, predominantly oriented along the (110) plane, but changed to (100) and (200) orientations with high doping contents. The grain size values exhibited a decreasing tendency with increasing co-doping content. The SEM images indicated that the films possessed a porous surface and were made up of well-defined and homogenously dispersed spherical and polyhedron-shaped nanoparticles, which were influenced by doping with Ni and Zn. The FTIR study showed that all the films exhibit the Sn-O-Sn, Sn-O, Sn-OH, and H-O vibration peaks. The NZTO films enhanced the crystal structure and raised the optical energy gap from 4.03 eV for TO to 4.09 eV for NZTO. The thickness also increased from d = 353.44 nm for pure TO films to d = 448.43 nm for films doped with 15% NZTO. The highest transmittance value was observed to be 93% for TO within the visible range. Hall effect measurements indicated that TO exhibited n-type conductivity and p-type conductivity when doped with 5%, 10%, or 15% NZTO. This allows photodetectors based on TO to show great sensitivity to UV light.

Abstract: X-ray Absorption Spectroscopy (XAS) experiments are usually performed at synchrotron facilities utilizing high-intensity X-ray sources produced by particle accelerators. However, this study showcases an in-house XAS experiment carried out using an X-ray Diffractometer (XRD) system that is typically available in material laboratories. The Rigaku SmartLab XRD was employed and configured for the Bragg-Brentano (BB) measurement mode. 20 keV electron energy is used to energize a molybdenum (Mo) target and produce high-intensity white X-rays via the Bremsstrahlung effect. Several crystals were tested as crystal analyzers for white X-ray dispersion to obtain optimal X-ray intensity and resolution. The detector energy filter is optimized to increase the peak-to-background ratio then the energy dispersion and resolution over the θ/2θ scanning range is determined and evaluated. The performance of the in-house XAS experiment is compared to theoretical calculations and synchrotron data from previous studies by observing resolution and spectrum shape and peak features of deposited Copper (Cu) and Copper Oxide (CuO) samples. Our findings showed that the absorption edges were clearly observed despite the peak broadening and shifting above absorption edge. Furthermore, some peaks were also observed in the XAS spectrum which originated from X-ray fluorescence of elements from both the samples and hardware components.

Abstract: This study investigates the modeling and optimization of a single solar cell structure, utilizing the inorganic double perovskite Cs₂AuBiCl₆. This material features an A₂BB'X₆ composition and possesses a bandgap energy of 1.12 eV. The fundamental structure of the solar cell has been described, and the physical parameters of its primary layers have been outlined. A simulation model was developed to calculate the current-voltage characteristics and photovoltaic parameters, taking into account recombination rates due to defects within the absorber and at the interfaces with the electron transport layer (ETL) and hole transport layer (HTL). The influence of various parameters was analyzed, including bulk and interface density of defects, layer thicknesses, back contact work function and operating temperature. Additionally, the performance of structures with alternative transport materials for the ETL and HTL layers was evaluated. The impact of energy bandgap offsets with the absorbing perovskite layer was considered to identify materials that enhance the collection of photogenerated carriers and ultimately improve efficiency. The simulations revealed an optimized structure that demonstrated enhanced performance compared to the initial design. The optimized solar cell achieved a yield of 18.4 %, representing an increase of 5.4 % over the basic structure, with key performance metrics including, short-circuit current density Jsc = 36.75 mA/cm², fill factor FF = 76.76 %, open-circuit voltage V_oc = 0.5879 V. Given its narrow bandgap value, the optimized structure was further examined in a tandem cell configuration, showcasing its potential for high-efficiency devices with a yield reaching 33 %. This work significantly contributes to the development of efficient, stable, and non-toxic perovskite solar cells for photovoltaic applications, paving the way for advancements in sustainable energy technologies.

Abstract: Ni-YSZ cermet remains to be the most used anode material for solid oxide fuel cells (SOFCs), and metal-supported solid oxide fuel cells are considered as the third generation SOFCs which can possibly address the overpotential and ohmic losses due to thicker components of electrolyte-and anode-supported cells. This study investigates the low-temperature deposition of crystalline NiO-YSZ thin film anodic layers on stainless steel (SS316L) substrates via screen-printing and hot pressing. Results revealed that screen-printing and hot pressing of NiO-YSZ on SS316L substrates at only 700°C (100 MPa) successfully deposited a ~40-μm thin film with a cubic crystalline structure. The thin film can also be fully reduced to Ni-YSZ with a cubic crystalline structure for both Ni and YSZ. In addition, EDS mapping revealed a relatively homogenous distribution of the Ni-YSZ components.

Abstract: Inorganic thermoelectric (TE) materials have gained significant attention because of their salient properties. However, they possess some significant drawbacks, including high production costs, high heat loss, and fragility. Recently, Organic conducting polymers presented a promising platform as an alternative TE material because of their great mechanical flexibility, high stretchability, and environmental friendliness. In this work, we report for the first time on the TE properties of n-PEDOT:PSS film prepared using spray coating technique. The structural, optical and TE properties of the obtained n-PEDOT:PSS thin film was investigated using X-ray diffraction spectroscopy, UV-vis spectroscopy and Seebeck coefficient measurement systems, respectively. The n-PEDOT:PSS layer showed excellent optical properties with a band gap ranges from 3.91 to 3.78. In addition, the Seebeck coefficient and power factor (PF) were obtained to be 1096.77 µVK^-1 and 298.59 µWm^-1K^-2 respectively, making n-PEDOT:P PSS to be regarded as efficient TE material.

Abstract: Cd_1-0.06Mn_0.06Te epitaxial thin films were synthesis on glass substrates by the Molecular Beam Condensation (MBC) method in the vacuum evaporation equipment УВН-71-ПЗ with steam-oil pumping and nitrogen trap at working pressure of residual gas (1÷2)x10^-4 Pa. By using additional source of Te vapor and controlling temperature, it has been determined the optimum conditions for obtaining Cd_1-0.06Mn_0.06Te epitaxial films with a perfect structure, clean and smooth surface, without of second phase inclusions. XRD investigations showed that Cd_1-0.06Mn_0.06Te epitaxial films grow on glass substrates on the (111) plane of the face-centered cubic lattice with the lattice parameter of a = 6.481 Å. Effect of γ-irradiation on XRD spectra of Cd_1-0.06Mn_0.06Te epitaxial films reveals that, XRD patterns of initial and γ-irradiated samples did not show any phase transformations, however there is a variation in relative intensities of diffraction peaks. It has been found that Cd_1-0.06Mn_0.06Te epitaxial films with a film thickness of d=15 µm, absorb light up to a wavelength of λ=765 nm and at λ>765 nm the absorption begins to gradually decrease and then the material becomes transparent. The obtained results indicate that Cd_1-0.06Mn_0.06Te epitaxial films absorb light quanta in the visible and infrared spectral regions. Iirradiation of Cd_1-0.06Mn_0.06Te epitaxial films with γ rays at low irradiation doses leads to a change in the optical parameters, the profile of the spectrum curves and the intrinsic absorption edge. In additions to experimental studies, a theoretical ab initio calculations of band structure (BS) of ideal and defective semiconductors of Cd_1-0.06Mn_0.06Te has been also carried out by using Density Functional Theory (DFT) method via Atomistix ToolKit computer program. The band gap energy has been calculated as E_g = 1.6 eV for ferromagnetic (FM) and E_g = 1.7 eV for antiferromagnetic (AFM) state of Cd_1-0.06Mn_0.06Te compound. The results of theoretical calculations on the band gap energy of ideal and defective Cd_1-0.06Mn_0.06Te semiconductors are in a good agreement with experimental findings.

Abstract: The determination of the dependencies of the electrical resistivity of the thin film to temperature is of great importance both for understanding the conduction mechanism and for numerous technical applications of these films. In this work, to characterize, the electrical properties of thin films, a GM cryocooler-based automatic board temperature range electrical properties measurement system has been constructed. The system can measure multiple samples simultaneously. The cooling process was simulated using the time-discrete differencing to validate the optimized device design parameters and minimize heat losses. Furthermore, the temperature-dependent sheet resistance results were compared with the results from the physical property measurement system.