Papers by Keyword: Wet Chemical Synthesis

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: Transparent conducting oxides (TCOs) are wide band gap semiconductors having found their use in optoelectronics, flexible electronics, flat panel displays, electrochromic windows, transparent heater windows, and many more. Aluminum (Al) doped zinc oxide (AZO) is an important TCO material which is being widely investigated for such applications. Its optoelectronic properties can be tuned by adjusting the Al content. In this work we study the variation patterns of the electrical conductivity and the optical transparency of AZO thin films with altering the Al content between 0 and 8 at%. The AZO thin films were prepared by wet chemical synthesis from its stabilized sol of zinc acetate dihydrate and aluminum nitrate nonahydrate dissolved in an ethanol and methanol mix. The morphological, electrical, and optical characteristics of these films were explored employing optical microscopy, Hall effect measurements, and UV-Vis-NIR spectrophotometry, respectively. We found out that annealing induces cracks into the AZO thin films and can severely degrade its electrical conductivity. Therefore, it’s imperative to control the Al content as well as the film morphology and structure. Before studying the effects of the Al content, the cracks were mitigated by optimizing the deposition and annealing conditions. The films were spin coated from its sol at 3000 RPM for 30 seconds. The films were dried at 100 °C and were subsequently annealed at 450°C. Since annealing induced cracks, therefore three coats were applied and annealed each time to mitigate the number of transverse cracks across the thickness of the film. The crack minimization was also confirmed by the enhancement in electrical conductivity. For the uniform crack-free AZO films, the Al doping was found to significantly modify the electronic behavior of the films. We expect an initial increase in the conductivity up to around 2 at% Al doping beyond which a decrease in conductivity is expected due to Al₂O₃ formation.

Abstract: High temperature Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_δ of low density has been synthesized via co-precipitation method and its electrical and structural properties have been studied. The optimum porosity of the samples was obtained using variety amount of sucrose C₁₂H₂₂O₁₁ which is used as supplementary filler. The electrical properties of superconductor such as critical temperature, T_c and critical current density, J_c were determined using the four-probe method. X-ray diffraction (XRD) was used to analyze the structural properties of the samples. The density of samples was measured using densitometer. The obtained results have revealed a significant influence of the pore presence in superconducting samples on the electrical properties. The T_c for low density Bi-2223 with 0.1g sugar sucrose is much higher compared to 0.05g, 0.15g and standard sample which is T_{c zero} is 98 K. The J_c for low density Bi-2223 with 0.1g sugar sucrose is 6 A/cm² at 60 K which is higher than high density samples. The crystallographic structure remains in the tetragonal form where a=b≠c for all samples.

Abstract: In this work, synthesis of ZnO nanoparticle by solution method and its application in non-volatile memory is reported. Nanocrystalline ZnO particles were prepared by a novel chemical route using the combination of zinc nitrate [Zn (NO₃)₂ 6H₂O] and sodium hydroxide [NaOH] at low temperature. The effects of temperature and bath concentration for the synthesis of ZnO powder have been studied. Synthesized powder was characterized by X-ray diffraction (XRD), UV-Vis spectrometer, transmission electron microscopy (TEM) and photoluminescence. Using the prepared ZnO nanoparticles with organic PMMA; non-volatile memory cells were prepared and studied its switching property.

Abstract: This study presents wet chemical reaction synthesis of nano Hydroxyapatite (HA) powder from seashells and the use of HA powder for the preparation of a composite coating with polysulfone (PSU), a biocompatible polymer which is electrospun on to Ti-6Al-4V alloy. The XRD/EDX patterns obtained for the synthesized powder showed phase pure hydoxyapatite and the HR-SEM analysis revealed that the HA particles have rod-shaped morphology. The HA powder was reinforced with Polysulfone (PSU) under different concentrations and coated by electro spinning over 2 mm thick sheets of Ti-6Al-4V alloy. The coated titanium sheets were also characterized by HR-SEM.

Abstract: The synthesis of intermetallic Ni-Al nanoparticles by co-reduction approach of several organometallic precursors with sodium naphthelide in non-aqueous solution was studied. The state of the art in nanoparticles synthesisation is the selection of suitable precursors and the adaption of colloid chemistry to non-aqueous media at the room temperature under inert atmosphere. The reduction of an organometallic precursor, nickel (II) acetylacetonate, Ni(Acac)₂ as a source of Ni element of the intermetallic, and aluminum trichloride, AlCl₃ in tetrahydrofuran (THF) solution gave a black particles. The powder X-ray diffraction spectroscopy (pXRD) result shows an expansion of lattice parameter for FCC-Ni indicating the cooperation of Al atoms in Ni structures. The estimation value of Al concentration using Scherrer’s equation is 10 at%. The particles were investigated in more detail by hard X-ray photoemission spectroscopy (HX-PES). The HX-PES spectrums confirmed that the black particles has binding energy consistent to standard materials of Ni₃Al. The absence of organic residues shown by the Fourier-transform infrared, FTIR spectrometer indicates that the as prepared Ni-Al nanoparticles are free from by-products.

Abstract: High-T_c superconductivity has been an emerging field for researchers since its discovery. Bismith based superconductors commonly called BSCCO have great importance among the superconducting family. It is divided into three phases among them 2223 phase is highly studied in order to investigate its superconducting properties by substitution of different elements. We have studied the substitution of cerium (Ce) on calcium site of bismuth based Bi (Pb)Sr (Ba)-2223 high-T_c superconductor. The nominal compositions of Bi_1.6Pb_0.4Sr_1.6Ba_0.4(Ca_1-xCe_x)₂Cu₃O_x ceramic superconductor were prepared by wet chemical method. Stoichiometric amounts of Bi₂O₃, PbO, Sr (NO₃)₂, BaCO₃, CaCO₃, CuO and CeO₂ were used as starting materials. Structural analysis was done by X-ray diffraction (XRD) at room temperature and different parameters were calculated. DC resistivity measurements for the transition temperature of synthesized superconducting samples were taken by the standard four-probe method, apparatus for which was developed in our laboratory. It is observed that with the substitution of cerium on calcium site the single high-T_c 2223 phase is obtained.

Abstract: Wet-chemical syntheses have been applied to the production of ceramic powders, with the aim of tailoring compositional and micro/nanostructural features, as an imperative requirement toward the elaboration of ceramic components with improved functional or even structural properties. Three syntheses are here presented and discussed, respectively concerning a purephased, nanostructured YAG powder, a biphasic Al2O3-YAG composite and three-phased Al2O3- YAG-ZrO2 material. In particular, this paper is aimed to illustrate the path followed from the set-up of the easier synthesis of the mono-phased system to the definition of the advanced procedures for the production of more and more complex compositions.

Abstract: The present chapter deals with the difficult task of giving a brief survey of the synthetic routes employed to prepare materials with characteristic features on the nanometer scale. Definitions and general concepts regarding nanostructured and nanometer-sized materials are shortly tackled in the introductory part, which is followed by an overview of the most important approaches developed to synthesize such materials. No attempt is made to create a comprehensive and detailed synopsis of the experimental methods currently available. Rather, attention is focused on a selected number of general methodologies, the choice of which can be usually motivated by a mix of historical perspective, scientific significance and technological potential. So-called “top-down” approaches are discussed first, whereas the second part of the chapter is devoted to “bottom-up” ones. The former group includes mechanical processing, melt quenching, and de-vitrification methods. Sonochemistry, pulsed laser ablation, wet chemical synthesis, sol-gel processing, microwave processing, spray pyrolysis, flame synthesis, inert gas condensation, vapor deposition, and vapor-liquid-solid growth form instead the latter group.

Abstract: The chalcogenide CdSe quantum dots (QDs) were obtained by wet chemical synthesis route, using cadmium oxide and pure selenium as precursors, hexadecylamine (HDA), tetradecylphosphine oxide (TDPO) and tri-n-octylphosphine oxide (TOPO) as complexing agents in tri-n-butylphosphine (TBP) solvent in the reactor with an argon protection atmosphere. This study aims at manipulating the size of QDs for the potential in vivo medical applications. The CdSe nanoparticles were analyzed by particle size analyzer, photoluminescence (PL) spectroscopy, FE-SEM, TEM, and XPS. The desired particle size and photoluminescence response of CdSe QDs can be achieved by adjusting proper molar ratios of HDA/TOPO and CdO/Se, along with the synthesis temperature and reaction time. Our results show that the obtained CdSe quantum dots have the average particle size of 1~10 nm within a size variation of 1.5 nm. The resultant CdSe QDs provide stable PL responses as excited by light sources of 388~550 nm wavelengths.