Ejh Lee

Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay

Nanocrystalline SnO2 quantum dots were synthesized at room temperature by hydrolysis reaction of SnCl2. The addition of tetrabutyl ammonium hydroxide and the use of hydrothermal treatment enabled one to obtain tin dioxide colloidal suspensions with mean particle radii ranging from 1.5 to 4.3 nm. The photoluminescent properties of the suspensions were studied. The particle size distribution was estimated by transmission electron microscopy. Assuming that the maximum intensity photon energy of the photoluminescence spectra is related to the band gap energy of the system, the size dependence of the band gap energies of the quantum-confined SnO2 particles was studied. This dependence was observed to agree very well with the weak confinement regime predicted by the effective mass model. This might be an indication that photoluminescence occurs as a result of a free exciton decay process.

Photoluminescence of disordered ABO3 perovskites

Intense photoluminescence in highly disordered (amorphous) BaTiO3, PbTiO3, and SrTiO3 prepared by the polymeric precursor method was observed at room temperature. The emission band maxima from the three materials are in the visible region and depend on the exciting wavelength. The origin of the photoluminescence was not exactly identified. However, the line shape indicates that confinement effects are not probable. The experimental results indicate that it could be related to the disordered perovskite structure.

Amorphous lead titanate: a new wide-band gap semiconductor with photoluminescence at room temperature

This paper describes a new amorphous wide-band gap semiconductor with photoluminescence (PL) at room temperature. The amorphous PbTiO3 was prepared by a sol–gel-like process in powder and thin film form. The optical property and the PL behaviour showed a direct relation to the amorphous structure. The PL peak energy can be controlled by the change of the exciting surge energy. Copyright

High dielectric constant of SrTiO3 thin films prepared by chemical process

SrTiO3 thin films were prepared by the polymeric precursor method and deposited by spin-coating onto Pt/Ti/SiO2/Si(100) substrates. The spin-coated films heat treated at 700°C were crack-free, dense, and homogeneous. Microstructural and morphological evaluations were followed by grazing incident X-ray, scanning electron microscopy and atomic force microscopy. Dielectric studies indicated a dielectric constant of about 475, which is higher than that of ceramic SrTiO3, and a factor dissipation of about 0.050 at 100 kHz. SrTiO3 thin films were found to have paraelectric properties with C-V characteristics.

Dielectric properties and microstructure of SrTiO3/BaTiO3 multilayer thin films prepared by a chemical route

Ž. Multilayer thin films with perovskite structures were produced by the polymeric precursor method. SrTiO BaTiO STOBTO 33 Ž. Ž . multilayers were deposited on Pt 111 TiSiO Si 100 substrates by the spin-coating technique and heated in air at 700C. The 2 microstructure and crystalline phase of the multilayered thin films were examined by field-emission scanning electron microscopy Ž. Ž . Ž . FE-SEM , transmission electron microscopy TEM , resolution-high transmission electron microscopy HRTEM , atomic force Ž. microscopy AFM and X-ray diffraction. The SrTiO BaTiO multilayer thin films consisted of grainy structures with an 33 approximate grain size of 60 nm. The multilayered thin films showed a very clear interface between the components. The SrTiO BaTiO multilayer thin films revealed dielectric constants of approximately 527 and loss tangents of 0.03 at 100 kHz. The 33

Preparation, microstructural and electrical characterization of SrTiO3 thin films prepared by chemical route

Abstract Polycrystalline SrTiO3 thin films having a cubic perovskite structure were prepared at different temperatures by the polymeric precursor method on platinum-coated silicon substrate. Crystalline films with uniform composition and thickness were prepared by spin-coating and the post-deposition heat treatment was carried out at different temperatures. The film showed good structural, dielectric, and insulating properties. Scanning electron microscopy (SEM) micrographs showed no occurrence of interdiffusion between the bottom electrode (platinum) and the film during post-annealing, indicating a stable interface between the SrTiO3 and the bottom electrode. The dielectric constant and dissipation factor at a frequency of 100 kHz were 250 and 0.01, respectively, for a 360 nm thick film annealed at 600°C. The capacitance versus applied voltage characteristics showed that the capacitance was almost independent of the applied voltage. The I–V characteristics were ohmic in low fields and a Schottky emission and/or Poole-Frenkel emission were postulated in high fields. Room temperature leakage current density was found to be in the order of 10−7 A/cm2 for a 360 nm thick film in an applied electric field of about 100 kV/cm. The charge storage density of 36 fC/μm2 was obtained in an applied electric field of about 100 kV/cm.

Preparation and properties of ferroelectric BaTiO3 thin films produced by the polymeric precursor method

Pb1 − xCaxTiO3 thin films with x = 0.24 composition were prepared by the polymeric precursor method on Pt/Ti/SiO2/Si substrates. The surface morphology and crystal structure, and the ferroelectric and dielectric properties of the films were investigated. X-ray diffraction patterns of the films revealed their polycrystalline nature. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses showed the surface of these thin films to be smooth, dense and crack-free with low surface roughness. The multilayer Pb1 − xCaxTO3 thin films were granular in structure with a grain size of approximately 60–70 nm. The dielectric constant and dissipation factor were, respectively, 174 and 0.04 at a 1 kHz frequency. The 600-nm thick film showed a current density leakage in the order of 10−7 A/cm2 in an electric field of about 51 kV/cm. The C-V characteristics of perovskite thin films showed normal ferroelectric behavior. The remanent polarization and coercive field for the deposited films were 15 μC/cm2 and 150 kV/cm, respectively.

Influence of the growth parameters of TiO2 thin films deposited by the MOCVD method

The synthesis of TiO2 thin films was carried out by the Organometallic Chemical Vapor Deposition (MOCVD) method. The influence of deposition parameters used during growth on the final structural characteristics was studied. A combination of the following experimental parameters was studied: temperature of the organometallic bath, deposition time, and temperature and substrate type. The high influence of those parameters on the final thin film microstructure was analyzed by scanning electron microscopy with electron dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction.