Advances in Science and Technology Vol. 119

Abstract: This research study utilises Essential Macleod software to optimize beam splitter for efficient hybrid photovoltaic application. The spectral splitting was carried out by alternating multilayer coating designs having Na₃AlF₆ as low index material, Y₂O₃ as middle index material and TiO₂ as high index material. The wavelength range of optimized design was selected from 400 nm to 1000 nm with reference wavelength 510 nm at an incident angle of 45. The beam splitter model comprises 56 alternating layers based on the formula [LMHM]¹⁴. The Optimac refinement approach is used to enhance the modelled structure. Different built-in analysis techniques in the essential Macleod package are also used to analyze our design, like density, total absorptance and admittance diagram. It is concluded that the modelled beam splitter transmits about 90% light in the visible spectrum range and reflects 90% light in the infrared region, which is very useful for an application like solar cells and the thermoelectric generator.

Abstract: Well dispersed Aluminum Nitride (AlN) nanopowder and AlN thin film were compared to observe their structural and luminescence properties. AlN thin films were deposited on silicon and copper substrates by RF magnetron sputtering. PL peaks analysis indicated the same pattern of emission peaks over different excitation wavelengths ranging from 200 nm to 300 nm for both the AlN nanopowder and thin film, nearly 100 -1000 times PL increment observed in AlN nanopowder. It is suggested that the reason for PL of AlN material is due to surface defects and impurities like oxygen-related point defects (O⁺_N), nitrogen vacancies (V_N), the transition from the donor level of V_N (nitrogen-vacancy) to the acceptor level of AlN (antisites defects), and various defect complexes (V^3-_Al – 3 O⁺_N) are responsible for the enhanced observed emission peaks. With well-defined emission curves, AlN Nanopowder and thin films are observed to be good substrate and insulator material for microelectronic circuits, Light Emitting Diodes, Laser Diodes, and in biomedical applications such as bioimaging and biosensors.

Abstract: Chromium doped aluminum nitride (AlN: Cr) thin films were grown on silicon, glass and copper substrates by DC and RF magnetron sputtering co-deposition. After growth, thin films on silicon substrates were annealed at 1373 K for 30 min in N₂ atmosphere. The AlN: Cr thin films were characterized by x-ray diffraction for structural analysis, by FS5 spectrofluorometer for the study of photoluminescence, absorption, transmission, and chromaticity. As-deposited and annealed silicon substrate and as-deposited glass substrate thin films of AlN: Cr exhibited intense photoluminescence emission in the range of 400 to 679.5 nm. Spectral evidence demonstrated conclusively that the AlN: Cr thin films on as-deposited glass substrate and annealed silicon substrate have excellent photoluminescence emission which is due to both AlN (host) and Cr³⁺ ions. The reasons of photoluminescence of AlN in the visible region are surface defects and impurities. Impurities become the cause to produce different types of defects and vacancies just like oxygen point defects (O⁺_N), nitrogen vacancies (V_N) and various defect complexes (V^3-_Al – 3 O⁺_N). It may also be due to the recombination of photogenerated hole with the electron occupied by the nitrogen vacancies and due to the transition between deep level of (V^3-_Al – 3 O⁺_N) defect complexes and shallow level of V_N and the reason behind the photoluminescence of Cr³⁺ ions is due to vibrational energy levels ⁴T₁ and ⁴T₂ and due to ⁴T₁→⁴A₂ and ⁴T₂→⁴A₂ transitions. AlN: Cr thin films can give better results in the applications like light emitting diodes (LEDs), laser diodes (LDs), field emission displays, microelectromechanical system (MEMS), optical MEMS and biomedical applications. Key words: III-V Semiconductor Material, Thin films, Photoluminescence Mechanism

Abstract: Titania (TiO₂) is an important material having found its use in many technological applications. Due to its large surface-to-volume ratio, TiO₂ nanofibers (NFs) are drawing increased attention in 3^rd generation photovoltaics. The electro-optical response of TiO₂ can be tuned by metal doping and structural control at the nano level. In this research, NFs of copper (Cu) doped Titania (TiO₂) were fabricated by using electrospinning. To do away with Polyvinylpyrrolidone (PVP), the NFs were calcined and annealed in air at 500°C for 2 hours. The Energy-Dispersive X-ray Spectroscopy (EDS) results confirmed the doping of copper inside the titania after calcination. Scanning Electron Microscopy (SEM) results show NFs of varying diameters mostly in the 80 nm to 200 nm regime. SEM of the post-annealed samples shows relatively rougher fibers of reduced size compared to the uncalcined samples. The increase in roughness and reduction in the NFs diameter means an increase in the overall surface area and more efficient charge transport as Hall effect measurement results depicted that after doping of copper in nanofibers, the conductivity improved by 2 times as compared to undoped nanofibers of titania. Moreover, Ultraviolet-visible Spectroscopy (UV-Vis) showed Cu doping shifted the absorption of the spectrum.

Abstract: Ferrites materials with Spinel structure have been broadly studied in recent years because of numerous technological applications. Lanthanum substituted Co-ferrites nanoparticles (CoLa_0.075Fe_1.925O₄) were synthesized via chemical co-precipitation method. X-ray Diffraction study revealed that prepared nanoparticales are single-phased spinel ferrites. Lattice constant, crystallite size, theoretical densities were estimated from XRD data. Electrical properties have been investigated with frequency ranging from 20Hz to 3MHz at room temperature. Dielectric constant and dielectric loss factor shows decreasing trend with increasing frequency. Ac conductivity exhibit increasing behavior with increasing frequency. The contribution of grains and intergrain boundaries in conduction process was estimated from impedance study. Nyquist plot shows dominant contribution of grain boundary resistance than the grain resistance in conduction mechanism.

Abstract: The storage of large amount of data is a global challenge. Nonvolatile memory devices have been the recent focus of researchers because data is retained after removing power supply in these devices. Resistive random-access memory device has large storage density and it works on high operation speed, so this has motivated me to work on resistive switching device. The nanocrystalline material of general formula Gd₂O₃ has been synthesized by simplified sol-gel process and CoFe_1.9Ce_0.1O₄ has been synthesized by coprecipitation process. Gd₂O₃ samples were calcinated at 500 °C for 2 hours and CoFe_1.9Ce_0.1O₄ samples were calcinated at 600 °C for 2 hours and the pellets were sintered at 630 °C for 3 hours. The nanocomposite of general formula (x)Gd₂O₃ +(1-x) CoFe_1.9Ce_0.1O₄ with x=0,0.3 has been synthesized by wet chemical method. X-ray diffraction technique has been done for structural analysis which confirms the cubic structure of CoFe_1.9Ce_0.1O₄ material. AC conductivity has increased with increased frequency of this sample. This sample with 0.1 concentration of Cerium has good resistive switching properties. (x)Gd₂O₃ +(1-x) CoFe_1.9Ce_0.1O₄ sample shows increased conductivity hence switching mechanism further enhances from CoFe_1.9Ce_0.1O₄ sample so it is a potential candidate for resistive switching device application.

Abstract: Transparent conducting oxides (TCO) are semiconducting materials that are electrically conductive as well as optically transparent thus making them suitable for application in photovoltaics, transparent heat transfer windows, electrochromic windows, flexible display, and transparent electronics. One of the methods to enhance the conductivity of metal oxides is doping, however, it can adversely affect the optical transparency of metal oxide. Aluminum (Al) doped zinc (Zn) oxide (AZO) is an important TCO material whose optoelectronic properties heavily rely on the Al doping level. There are various methods to develop AZO thin films. However, since Al and Zn are high vapor pressure materials, and their precise content control isn’t that easy, that’s why we dedicated this study to devise a facile method of Al doping into the ZnO structure. We report a twostep synthesis route to develop AZO thin films over glass substrates. Sub stoichiometric zinc oxide (ZnOx) thin films were sputter deposited over glass employing RF magnetron sputtering at 70W and 9 x 10-3 Torr Ar pressure. To mitigate Zn losses during annealing at 450 °C, the films were first oxidized up to 200 °C in air so as to convert ZnOx into stoichiometric ZnO. To incorporate Al into the ZnO structure, Al was spin coated on top of ZnO from its stabilized sol of 0.07 molar aluminum nitrate nonahydrate in ethanol. The samples were subsequently annealed at 450 °C for 2h in air with a controlled heating ramp of 3 °C/min. The film morphology, microstructure, electronic, and optical characteristics were explored employing scanning electron microscopy, energy dispersive x-ray spectroscopy, Hall effect measurements, and UV-Vis-NIR spectrophotometry, respectively. We found that both the Al and oxygen (O) content affect the optoelectronic behavior of AZO. Even without Al doping, O deficient samples were found to be sufficiently conductive, however, the ZnOx is less transparent relative to O rich stoichiometric ZnO. Furthermore, if ZnOx is annealed at higher temperatures, it causes Zn losses, since Zn is a relatively high vapor pressure material. It degrades the film morphology as well. Once we have ZnO we can confidently treat it at 450 °C to allow Al diffusion into the interiors of the ZnO film. We found that AZO produced via this method is sufficiently conductive as well as transparent.

Abstract: In comparison to other Periodic Table elements, rare earth elements demonstrate long-term stability and strong conductivity. Ceria nanomaterial has found many applications in numerous technologies. Doped ceria was prepared by many wet chemical methods. In this paper, we examine the electrical properties of the ceria after adding three dopants, two of which are rare earth elements (Gd and Nd) and one metal (Ca). The compositions, Ce_0.75Gd_0.05Nd_0.2O₂ and Ce_0.75Gd_0.05Nd_0.14Ca_0.06O₂, were formed using the WOWS (without water and surfactant) Sol-Gel method. The X-ray diffraction (XRD) technique was used to investigate the crystallinity of nanostructures. The structure of both samples was cubic. For the electrical measurements, the Precision Analyzer was used for doped Ceria as a function of temperature. With the variation in composition, the electrical properties changes.

Abstract: Perpex circular piece along with SV-40 epoxy was served as a viewing window of a glove-box over the period of 4 years. While in periodic pressurized operation, leakage occurred at 2 bar. For investigation, a fresh piece of the same Perpex glass and epoxy were used as reference. Visual observation, optical microscopy, hardness testing and Fourier transform infrared spectroscopy (FTIR) were utilized as characterization techniques. The FTIR spectrum revealed variation in transmission peaks in old epoxy as compared to new epoxy, which was due to secession and crosslinking within old epoxy over the lifespan. It could be inferred that the shrinkage of the epoxy effected interfacial bonding of Perpex and epoxy, therefore the assembly failed during pressured condition of the glove box.