Chueh-Jung Huang

Improvement of dielectric properties of Ba0.6Sr0.4TiO3 thin films by MgO doping

MgO-doped Ba0.6Sr0.4TiO3 (BST) thin films were synthesized by rf magnetron sputtering at substrate temperature of 750°C using single-phase targets with different MgO contents ranging from 0to5mol%. Microstructure, dielectric constant, and leakage current density of the MgO-doped BST films were characterized to understand the influence of the MgO dopant on film properties. Polycrystalline and perovskite phase solid solution films with a dense microstructure were obtained in all deposition conditions. The thickness of the 0,2,and5mol% MgO-doped BST films was measured to be 190, 140, and 150nm, respectively. The electrical and dielectric properties of the BST-containing capacitors are both found to be improved significantly by doping MgO in the BST films. The voltage-dependent capacitance C-V increases with increasing MgO doping up to 5mol%. The evidence for the asymmetric distribution of charge carriers in the MgO–BST film is derived from the interfacial layer. The leakage current density of the 5mol% MgO-d...

Effect of Hygroscopic Platinum/Titanium Dioxide Particles in the Anode Catalyst Layer on the PEMFC Performance

This study investigates the feasibility of adding platinum (Pt)/titanium dioxide (TiO 2 ) particles into the anode catalyst layer to improve the performance of proton exchange membrane fuel cells. The effects of adding Pt/TiO 2 in the catalyst layer on three critical factors, namely, the wettability, the electrical resistance, and the loading of Pt/TiO 2 particles, were also evaluated. It was observed that the water contact angles of these catalyst layers were decreased as the weight percentage of Pt/TiO 2 particles increased. Similarly, the electrochemically active surface areas prepared by these catalyst inks were decreased with the increase in Pt/TiO 2 addition. Single cell performance with various amounts of Pt/TiO 2 particles in the anode catalyst layer was investigated under different temperatures of anode humidifier. The cell with 5% Pt/TiO 2 particle addition in the anode catalyst layer revealed the best performance at anode humidifier temperatures ranging from 25 to 75°C.

Effect of Annealing on the Sn-Doped TiO2 Films Prepared by DC/RF Cosputtering

Nb-doped titanium oxide (TiO 2 ) thin films were deposited on glass by dc/radio-frequency (dc/rf) magnetron cosputtering, in which dc and rf were utilized for Ti and Nb targets, respectively. The coated samples were postannealed at temperatures ranging from 473 to 773 K for 1 h in ambient air. Glancing incidence X-ray diffraction revealed a polycrystalline phase for the Nb-doped films postannealed at 523 K, in contrast to the undoped one that has to be annealed at 723 K, indicating that Nb dopant can enhance the crystallization of amorphous TiO 2 . Furthermore, the as-deposited Nb-doped film postannealed at 673 K was found to have an anatase-dominated phase with a fine-grain microstructure observed by transmission electron microscopy. Heat-treatment also induces a change in the surface morphology of the TiO 2 films examined by field-emission scanning electron microscopy. The optical properties of the TiO 2 films were characterized by UV/visible spectrophotometry. The average transmittance of the films is higher than 85%, and a small absorbance zone occurs in the visible region. Under visible light irradiation, all the Nb-doped TiO 2 films exhibit better photocatalytic activity than that of undoped ones. Among them, the Nb-doped TiO 2 film annealed at 673 K shows the best photocatalytic performance.

Formation Mechanism and Characterization of Ag-Metal Chelate Polymer Prepared by a Wet Chemical Process

In this study, a metal chelate polymer (MCP) contained Ag(0) was prepared from commercial polyvinyl acetate (PVAc) and silver nitrate (AgNO3) by a wet chemical method using concentrate formic acid (HCOOH) as solvent. The characterization of these MCP materials, and the formation mechanism that involved in the MCP system, were studied by the analyses of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). The Ag(I) cations of silver nitrate (AgNO3) were found coordinated with polymer functional groups to form polymer–Ag(I) complexes. The XRD analysis revealed that these complexed Ag(I) ions were in-situ reduced to generate Ag(0) metal by HCOOH solvent in MCP system. The results of FTIR and NMR analyses demonstrated that there are hydrolyzed hydroxyl groups present in the MCP chains. The XPS analysis showed that the oxygen ligands that interacted with the Ag(0) were mostly contributed from the OH groups. The interaction between the reduced Ag(0) metal and the polymer chains was confirmed by transmission electron microscopy (TEM) investigation on the MCP materials.

Investigation of the Characteristics of Undoped and Sn-Doped ZnO Films Prepared by an Acidic Sol

Transparent conducting thin films of undoped and Sn-doped zinc oxide films were prepared on glass substrate by a dip-coating method using an acidic sol. The effect of metal sources, zinc chloride (ZnCl 2 ) and zinc acetate dihydrate [Zn(OAC) 2 ·2H 2 O], on the crystalline structure and properties of the films was investigated in detail. X-ray diffraction analysis reveals that the acidic sol leads to ZnO crystals with a hexagonal wurtzite structure after annealing treatment. Transmission electron microscopy results evidence that the Sn-doped ZnO thin films are a mixed phase of wurtzite ZnO and tetragonal SnO 2 nanocrystals. Field-emission scanning electron microscopy shows that the morphology of the films is largely affected by the zinc metal sources, and optical and electrical properties of the films are closely related to their microstructure. The undoped films prepared with the zinc chloride source exhibit a lower transmittance in the visible wavelength between 600 and 800 nm, compared with that using the zinc acetate dihydrate source. The electrical resistivity of the undoped films is high (p > 2.0 X 10 4 Ω cm) but can be reduced by a Sn doping treatment. The optimum electrical resistivity of the Sn-doped films can reach to about 1.5 X 10 1 Ω cm.

Preparation and Electrical Properties of Metallized Polyvinyl Acetate-Silver Nitrate/Polyethylene Terephthalate Films

An electrically conductive metal chelate polymer (MCP) was prepared by adding silver nitrate (AgNO3) metal salt to polyvinyl acetate (PVAc) polymer, and subsequently coated onto polyethylene terephthalate (PET) substrates. The MCP films were then treated with a sodium borohydride (NaBH4) aqueous solution to form reduced metal chelate polymer (RMCP) films. Characterization of the films was carried out by UV/VIS spectrometry, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Both SEM and XRD results show the presence of crystalline Ag particles in the MCP and RMCP films. The electric conductivity of the PVAc polymer was improved significantly by the addition of AgNO3 metal salt to form the PVAc–AgNO3 chelate polymer. It was found that the sheet resistance (Rs) of both MCP and RMCP films decreased with increasing AgNO3 content. For the same AgNO3 concentration, the electric conductivity of the RMCP films is at least 4 orders of magnitude higher than that of the MCP films. Because of this high electric conductivity, the electromagnetic interference shielding effectiveness (EMI/SE) of the RMCP films is also evaluated.

Anisotropic Relaxation Behavior of Compressive Residual Stress in Delafossite CuAlO2

The anisotropic relaxation behavior of the compressive residual stress of delafossite CuAlO 2 film was identified to take place on silicon substrate, on which the film was grown. Experimental results suggest that in order to release the internal compressive residual stress of the CuAlO 2 film, CuO hillocks would be favored to grow on the film surface. It was also proposed that because of the structural anisotropic nature associated with the delafossite CuAlO 2 , the compressive residual stress was released first by breaking the O-Cu-O bonds of the dumbbell layers and subsequently by the diffusion of Cu and O atoms along the a-axis direction on the close-packed Cu layers, suggesting that the c-axis direction across the AlO 6 octahedral layers has a greater resistance to compressive residual stress.

Characteristics of ZnO Thin Films Prepared by Acidic Sol Method

Zinc oxide (ZnO) thin films are grown using an acidic sol by dip coating. The acidic sol is prepared from a methanolic solution of zinc chloride using formic acid (HCOOH) as the stabilizer and poly(vinyl acetate) (PVAc) as the tackifier. Crystalline ZnO thin films are obtained following annealing at 480 °C for 1 h. The effects of dip-coating conditions on the microstructure and optical properties of the ZnO thin films are investigated using a variety of analytical tools. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) show that fine ZnO crystallites comprise the bottom layer of the films, and large crystallites emerge on the surface of the fine crystallite layer. Selected area diffraction (SAD) patterns indicate that both the fine and large crystallites exhibit a hexagonal wurtzite crystal structure. The particle size distribution of the bottom fine crystallites is below 20 nm, while that of the large crystallites varies from 500 to 800 nm, depending on the number of dip-coating times. The ZnO films have an absorption edge that starts at approximately 370 nm and cuts off at 290 nm. As calculated from the absorption edge, the ZnO films have optical gaps of about 4.02–4.11 eV.