Papers by Keyword: Pulsed Laser Deposition (PLD)

Abstract: Using experiment method, ZnO films are prepared at various substrate temperatures, annealing temperatures and oxygen pressures. The films are examined by X-ray diffraction, atomic force microscope. Through researching the structural and optical properties of ZnO films, optimized conditions for growing ZnO films are obtained. The results suggest that high quality ZnO films with high c-axis orientation can be prepared by pulse laser deposition.

Abstract: Niobium nitride (NbN) films were deposited on Nb using pulsed laser deposition (PLD), and the effect of substrate deposition temperature on the preferred orientation, phase, and surface properties of NbN films were explored by x-ray diffraction (XRD) and atomic force microscopy (AFM). It was found that the substrate deposition temperature has a significant influence on properties of the NbN films, leading to a pronounced change in the preferred orientation of the crystal structure and the phase. We find that substrate temperature is a critical factor in determining the phase of the NbN films. For a substrate temperature of 650 °C 850 °C, the NbN film formed in the cubic δ-NbN phase mixed with the β-Nb₂N hexagonal phase. With an increase in substrate temperature, NbN layers became β-Nb₂N single phase. Essentially, films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperatures above 850 °C. Surface roughness and crystallite sizes of the β-Nb₂N hexagonal phase increased as the deposition temperatures increased.

Abstract: Thin films of zirconium oxide have been deposited using pulsed laser deposition on Zr-base alloy substrates, held at 300 K, 573 K and 873 K, in order to understand the effect of substrate temperature on the deposited film. In this study, a KrF excimer laser having 30 ns pulse width and 600 mJ energy at source has been used for depositing the films from a sintered ZrO₂ target using a laser fluence of 5 J.cm^-2. After visual observation, deposited thin films were examined using Raman Spectroscopy (RS) and X-ray Photo-electron Spectroscopy (XPS). It has been found that the oxide deposited at 300 K temperature does not show good adherence with the substrate. The oxide films deposited at 573 K and 873 K are found to be adherent with the substrate and lustrous black in appearance. Thin films of zirconia, deposited using pulsed laser on the Zr-base metallic substrate are initially in amorphous state and possibly little deficient in oxygen. The substrate temperature and the duration of holding at high temperature are responsible for the evolution of nanocrystals in the deposited thin films. The stoichiometry of the amorphous oxide film supports its crystallization, below 573 K, into monoclinic and tetragonal phases and not into cubic phase.

Abstract: Thin films of manganese oxides have been prepared by pulsed laser deposition (PLD) process on silicon and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of temperature and oxygen pressure during the PLD process, pure phases of Mn₂O₃, Mn₃O₄ as well as an amorphous phase of MnO_x were successfully fabricated and characterized by X-ray diffraction. The pseudo-capacitance behaviors of those manganese oxides of different phases have also been evaluated by the electrochemical cyclic voltammetry in 0.1 M Na₂SO₄ aqueous electrolyte. Their specific current and capacitance determined at different scan rates were calculated and compared. The results show that polycrystalline Mn₂O₃ phase has the highest specific current and capacitance, while the values for polycrystalline Mn₃O₄ films are the lowest. The amorphous phase MnO_x films have the values sitting in between those of Mn₂O₃ and Mn₃O₄. The specific capacitance of Mn₂O₃ films reaches 200 F/g at 1 mV/sec scan with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for supercapacitor material research due to its excellent flexibility and capability of controlling microstructures and phases of various materials.

Abstract: The titanium dioxide target (99.7%) of 1 cm in dia was ablated in vacuum by laser pulses (6 ns) at 266 nm and at repetition rate of 10 Hz. During deposition the laser fluence between 1 and 3.5 J/cm² and the O₂ pressure from the range of 10^-2 – 1 Pa were applied. The thin TiO₂ films were deposited on glass substrate (1 × 1 cm²) heated up to 500 °C. The chemical composition of the film and samples produced by annealing were investigated by spectroscopic techniques (μ-Raman, EDX) and the structure, porosity and surface morphology were analysed by means of SEM and x-ray diffraction (XRD). The SEM inspection of the TiO₂ thin film samples indicates that the obtained material is mostly crystalline. After annealing in O₂ at 500 °C the structure characterized by the presence of both anatase and rutile phases is observed in the Raman spectra and confirmed by the XRD data. The phase content ratio depends on the O₂ pressure applied. Results confirm that nanostructures produced in this way represent densely packed columns and promote deep penetration of guest particles such as CO₂.The resulting large active surface is advantageous from the point of view of photocatalytic applications.

Abstract: Highly c-axis oriented ZnO thin films were deposited on n-Si (111) substrate at various oxygen partial pressures by pulsed laser deposition (PLD). X-ray diffraction (XRD), Atomic force microscopy (AFM) were used to analyze the influence of the oxygen partial pressure on the crystallization and morphology of the ZnO thin films. X-ray photoelectron spectroscopy (XPS) was used to analyze relationships between chemical shifts of XPS energy spectra and stoichiometric ratios of ZnO thin films, and quantitative relationships between content of Zn, O and oxygen partial pressures. An optimal crystallized and stoichiometric ZnO thin film was observed at the oxygen partial pressure of 6.5Pa.

Abstract: ZnO thin films were deposited on n-Si (111) substrates at various oxygen partial pressures by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM) were used to analyze the influence of the oxygen partial pressure on the crystallization and morphology of the ZnO thin films. An optimal crystallized ZnO thin film was observed at the oxygen partial pressure of 6.5Pa. X-ray photoelectron spectroscopy (XPS) was used to analyze the surface components and distribution status of various elments in ZnO thin films. It was found that ZnO thin films were grown in Zn-rich state.

Abstract: Quantum dots applied in solar cells will be of great importance to enhance the quantum tunneling efficiency and improve the photogenerated current transport. In this study, a new easy-to-operate technology was developed to fabricate germanium-silicon quantum dots in a SiOx matrix. The quantum dots were formed by first deposited germanium-rich SiO on quartz substrate using pulsed laser deposition technique and then annealed under a comparatively high temperature. We have demonstrated a stable and low-cost fabrication process which is much cheaper than the epitaxy method to provide for the fabrication of high density germanium-silicon quantum dots. Quantum dots with diameters of 3~4 nm embedded in the amorphous SiOx layer were clearly observed. The morphological features of the thin film were characterized. The optical properties were performed by Raman spectroscopy, photoluminescence spectrum and XRD test respectively to verify the crystallization of quantum dots in the SiOx matrix. Reflectance spectrum displayed a high light absorption rate in a spectra region from 300 nm to 1200 nm, evidencing that germanium-silicon quantum dots have promising features to be used as absorber for photovoltaic application.

Abstract: Before a tooth erupts, the ameloblasts are lost, which means that the tooth enamel does not regenerate itself after tooth eruption. In the present study, we attempt to regenerate the tooth enamel artificially using a flexible hydroxyapatite (HAp) sheet. First, a HAp film was deposited on a soluble substrate by pulsed laser deposition (PLD) using an ArF excimer laser. Next, the HAp film was collected as a freestanding sheet by dissolving the substrate using a solvent. The HAp sheet was adhered to the extracted human teeth using a calcium phosphate solution. The variation of the crystal structure of the HAp sheet with time was investigated by X-ray diffraction analysis. Furthermore, the variation in the mechanical characteristics with time between the HAp sheet and dental enamel were evaluated using tensile and scratch tests. The results suggest that the HAp sheet became fused to the tooth enamel within approximately one week.

Abstract: A pulsed laser/plasma hybrid deposition method has been developed to produce the diamond-like carbon (DLC) film at atmospheric pressure in this work. A plasma torch was used to heat up the carbon particles which were simultaneously ablated by a pulsed laser, thus the kinetic energy of the carbon particle can be increased to form the carbon atoms with amorphous bonding structure of the DLC film. The influences of the plasma flow have been examined at various inlet pressures. According to the experimental results of the carbon film inspected by the Raman spectroscopy, it reveals that the intensity ratio of the D-band to G-band of the carbon film can be reduced to 0.5 by the implementation of plasma flow. Therefore the DLC film was solidly formed. The adhesive strength of the DLC film was also characterized by the scratch test, it can be found that the critical loading of the film on the iron substrate is up to 19 N.