High curie temperature for La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on glass substrates

The manganite LSMO films were successfully grown on glass substrates without any additional buffer layer by pulsed laser deposition. The films have been investigated by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), electrical and magnetic measurements. From the XRD pattern the film is found to be polycrystalline single-phase’s character. The LSMO thin films growth on glass substrate, follows the island growth model with average grain size of 44.46nm. The metal-insulator transition (TMI) temperature was above room temperature and electrical conduction mechanism of LSMO films below phase transition temperature (TP) is due to the electron-electron (major) and electron-magnon scattering processes. The Curie temperature of LSMO films is around 352 K, which is one of the high TC in all LSMO films and as our knowledge, is the highest value that is reported in literature for low cost amorphous substrates such as glass. The low resistivity, high TMI and high TC makes these LSMO films very useful for room temperature magnetic devices

Silver nanoparticle fabrication by laser ablation in polyvinyl alcohol solutions

A laser ablation technique is applied for synthesis of silver nanoparticles in different concentrations of polyvinyl alcohol (PVA) aqueous solution. The ablation of high pure silver plate in the solution is carried out by a nanosecond Q-switched Nd:YAG pulsed laser. X-ray diffraction and transmission electron microscopy are implemented to explore the particles sizes. The effects of PVA concentrations on the absorbance of the silver nanoparticles are studied as well, by using a UV-vis spectrophotometer. The preparation process is carried out for deionized water as a reference sample. The comparison of the obtained results with the reference sample shows that the formation efficiency of nanoparticles in PVA is much higher and the sizes of particles are also smaller

Effect of magnetism in electrical transportation between two superconducting layers

To investigate the interplay between superconducting and magnetic material, a multilayer consisting of two superconducting YBa2Cu3O7 (YBCO) layers and sandwiched with magnetic Ni as a mediator was fabricated. The thin film of YBCO/Ni/YBCO on MgO substrate was prepared by pulsed laser deposition (PLD). The multilayer was initially characterized by XRD and then the morphology of surface was investigated by FESEM. Variation of resistivity via temperature was measured by DC electrical method with four point probe

Growth and characterization of ZnO multipods on functional surfaces with different sizes and shapes of Ag particles

Three-dimensional ZnO multipods are successfully synthesized on functional substrates using the vapor transport method in a quartz tube. The functional surfaces, which include two different distributions of Ag nanoparticles and a layer of commercial Ag nanowires, are coated onto silicon substrates before the growth of ZnO nanostructures. The structures and morphologies of the ZnO/Ag heterostructures are investigated using X-ray diffraction and field emission scanning electron microscopy. The sizes and shapes of the Ag particles affect the growth rates and initial nucleations of the ZnO structures, resulting in different numbers and shapes of multipods. They also influence the orientation and growth quality of the rods. The optical properties are studied by photoluminescence, UV-vis, and Raman spectroscopy. The results indicate that the surface plasmon resonance strongly depends on the sizes and shapes of the Ag particles

Electrical properties and conduction mechanisms in La2/3Ca1/3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La2/3Ca1/3MnO3 thin films were directly grown on MgO(100), Si(100) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found to be polycrystalline, single-phase orthorhombic. The metal-insulator transition temperature is 209 K for LCMO/MgO, 266 K for LCMO/Si and 231 K for film deposited on the glass substrate. The conduction mechanism in these films is investigated in different temperature regimes. Low-temperature resistivity data below the phase transition temperature (T P) have been fitted with the relation ρ = ρ0 + ρ 2T2 + ρ 4.5T4.5, indicating that the electron-electron scattering affects the conduction of these materials. The high-temperature resistivity data (T > T P) were explained using variable-range hopping (VRH) and small-polaron hopping (SPH) models. Debye temperature values are 548 K for LCMO/Cg, 568 K for LCMO/Si and 508 K for LCMO/MgO thin films. In all thin films, the best fitting in the range of VRH is found for 3D dimension. The density of states near the Fermi level N (E F) for LCMO/MgO is lower due to the prominent role of the grain boundary in LCMO/MgO and increase in bending of Mn-O-Mn bond angle, which decreases the double exchange coupling of Mn 3+-O2-Mn4+ and in turn makes the LCMO/MgO sample less conducting as compared to the other films

Characterization and conduction mechanism of La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on different substrates

The La5/8Sr3/8MnO3 (LSMO) thin films were directly grown on MgO and Si wafer substrates by Pulsed Laser Deposition (PLD) technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM). The electrical and magnetic properties of films are studied. From the XRD patterns, the films are found polycrystalline single-phases. The highest magnetoresistance (MR) value obtained was −17.21% for LSMO/MgO film followed by −15.65% for LSMO/Si film at 80K in a 1T magnetic field. Transition temperature (TP) is 224K for LSMO/MgO and 200K for LSMO/Si film. The films exhibit a ferromagnetic transition at temperature (TC) around 363K for LSMO/MgO and 307K for LSMO/Si film. For LSMO/MgO, the high Curie temperature such as 363K is one of the high TC in all LSMO thin films and as our knowledge, is the highest value that is reported in literature for MgO substrates with high lattice mismatch parameter. The conduction mechanisms for both films have been extensively investigated. In the metallic regime, resistivity seems to emanate from the electron–electron (major) and electron-magnon (phonon) scattering processes. For both films in the range of T >TP, the resistivity data were well fitted by both variable range hopping (VRH) and small polaron hopping (SPH) models giving higher density state, and lower activation energy and Mott temperature T0 for LSMO/Si film than those for LSMO/MgO film. The high TC such as 363K makes these LSMO/MgO films very useful for room temperature magnetic devices

Physical and optical properties of zinc oxide micro and nanostructures deposited on various substrates

This thesis attempts to investigate some unknown properties of ZnO microand nanostructures as one of the most promising materials in this decade. Additionally, the interaction between the components consisting of ZnO,buffer layers and substrates can produce new physical properties which may provide some important utilization in electronic and optoelectronic devices. The aim of this work is to study the effect of various substrates with metal or metal oxide layers including Au, Ag, Cu and Au+Cu alloy on the structural,morphological and optical properties of ZnO micro- and nanostructures. In addition, the relevant growth mechanisms are also proposed. The experiments are carried out in a quartz tube using a vapor phase transport of a carbon-zinc oxide mixture at different temperatures (900-1000˚C). The main thesis work involves six distinct studies. Firstly, the conditions to grow ZnO micro- and nanostructures deposited on various substrates such as Si, GaN and corning glass without metal buffer layers are studied and optimum conditions for each morphology are identified. The results indicate that a gas pressure in range of 70 and 90 standard cubic centimeters per minute and 15 cm distance between the source and substrates are necessary for formation of nanostructures with diameters less than 100 nm. ZnO microsphere structure with a radius of around 1.5 μm was obtained under 80 standard cubic centimeters per minute (sccm) gas pressure rate and 30 cm distance from the source. The multipods composed of nanowires and nanorods have been grown on different distributions of Ag nanoparticles on silicon substrates. A low distribution of Ag particles on the substates results in formation of multipod structure with pods ranged from 50-100 nm in diameter, and several micrometers in length. The diameters of the pods are increased (400 nm- 500 nm) while the substrate with more concentration of Ag particles is used. ZnO flower-like multisheets were grown on silicon and corning glass substrates with Cu and Cu+Au alloy buffer layers. Comparison with the clean silicon substrate, the PL spectrum of the flower grown on the Cu/Si shows a higher intensity UV emission peak and the lower intensity visible emission peak. The spectrum also exhibits a higher intensity of the visible emission for ZnO crystalline on the Au+Cu/Si and Cu/Si than the ZnO grown on Si substrate. Shift of the E2 mode in Raman spectrum indicates that the nanowires or nanosheets grown on metal buffer layers are under more in-plane stress. ZnO peach-like morphology was grown on MgO (111) substrate with copper oxide buffer. The sizes of the peaches are not uniform and the diameters of the peaches are ranged from 2 to 5 micrometers. The photoluminescence spectrum demonstrates a strong peak in the ultraviolet (UV) region at around 380 nm, originated from the exciton related recombination. The peak positions at 495 and 520 nm can be assigned to oxygen and zinc vacancies, respectively. The high intensity of E2 (high) mode in the Raman spectrum indicates a good crystallization of the prepared sample. Two different quartz tubes were used to study the effect of different vapor super-saturation on the samples. The XRD patterns have indicated that the crystalline quality of the samples grown using one closed end tube was better than those with both opened ends. Based on the field emission scanning electron microscope images, larger ZnO nanostructures were obtained from one closed end tube due to the O2-rich atmosphere

Synthesis of ZnO/Cu micro and nanostructures via a vapor phase transport method using different tube systems

ZnO micro and nanostructures were grown on copper coated silicon substrates using two different systems: an opened system (both ends opened tube) and a closed system (one closed end tube). The thermodynamic conditions of the systems made a significant difference in boundary layer and super-saturation between the systems. The results indicate that diffusion of the gaseous species through the boundary layers at low and high pressures controls the final formation of the morphologies. The ZnO nanostructures which have been grown in a restricted place have larger diameters and lengths. The structure of the products was analyzed by X-ray diffractometer (XRD) and it was found that the good crystalline quality of the samples was obtained in a closed system. To study the optical properties, photoluminescence (PL) and ultra violet–visible (UV–vis) spectroscopy were employed. It was observed that a decrease in the growth temperature of the opened system caused a broad and dominant visible emission covering the blue and green emission in the PL spectra

Facile synthesis of porous-structured nickel oxide thin film by pulsed laser deposition

Porous-structured nickel oxide (PsNiO) was obtained through the oxidization of a nickel thin film. The nickel thin film was deposited using the pulsed laser deposition (PLD) method on a nickel foil as a substrate. The results show uniform PsNiO after the oxidization of the nickel thin film at 750 degrees C for 1 h. X-ray diffraction (XRD) indicates formation of the NiO crystalline structure. Field emission scanning electron microscopy (FESEM) reveals different morphology on the surface of the nickel foil (sample A) and on the nickel thin film (sample B). Comparison of the FESEM results after oxidization shows that the PsNiO on the nickel thin film was more regular and controllable than the NiO layer on the nickel foil. The FESEM images also show that the thickness of the nickel thin film affected the PsNiO size obtained after oxidization. This resulted from the growth of the porous structure at grain boundaries and from the grain sizes. The electrochemical properties of the PsNiO as an electrode are investigated by cyclic voltammetry (CV). These results show the effect of PsNiO size on the current of anodic peak