CO2 Sensing Property of CuO-BaTiO3 Mixed Oxide Film Prepared by Self-Assembled Multibilayer Film as a Precursor

Preparation of CuO-BaTiO₃ mixed oxide thin film by the decomposition of a self-assembled multibilayer film as a molecular template was investigated in this study. Furthermore, CO₂ sensing property of the resultant thin film was investigated as a capacitive type sensor. The self-assembled bilayer film of few 1000 layers thickness can be obtained easily by casting an aqueous suspension consisting of dimethyldihexadecylammoiun bromide (DC1-16), Cu(ClO₄)₂, Ba(TiO(C₂H₄)₂), 2,6-dimetyle-3,5heptadione (DHP), and polyvinyl alcohol. Divalent copper ion (Cu²⁺)) which is associated with 2 DHP molecules was incorporated into the molecular bilayer film and BaTiO₃ precursor exists at the interspace of molecular bilayer film by coordinating with polyvinyl alcohol. Upquenching the organic-inorganic film at 1173 K leads to the uniform film of CuO-BaTiO₃ oxide mixture. Although operating temperature shifted to higher temperature, the resultant film exhibits the capacitance change upon exposure to CO₂. Consequently, it is concluded that the mixed oxide film of CuO-BaTiO₃ prepared by the decomposition of multibilayer film was also an appropriate capacitive type CO₂ sensor.     

I−V relations in semiconductors with ionic motion

Semiconductors with mobile donors and acceptors are mixed-ionic-electronic-conductors, MIECs, which exhibit peculiar electronic (electron/hole), I _e , current-voltage relations. This is a result of the redistribution of the ions under the applied electrical potential. MIECs are usually ionic materials which exhibit relative low electron/hole mobilities as compared to the materials used in the semiconductor industry. However, thin layers of MIECs exhibit a low resistance and fast response and become of increasing interest. The I _e −V relations are discussed for a few typical examples. It is shown that they depend on the energy band gap as when it is large, the semiconductor is either p-type or n-type. The I _e −V relations depend also on the nature of the electrodes, whether blocking for ion exchange or not. Experimental results for Cu₂O are presented and analyzed using one of the models discussed. ICE-2005, KIST, Seoul, Korea, (Invited)     

Structure and dielectric properties of Cu and (K,Na) doped SrBi2Nb2O9 ferroelectric ceramics

Ferroelectric ceramics, SrBi₂Nb₂O₉ (SBN), Sr_0.8Cu_0.2Bi₂Nb₂O₉ (SCBN) and Sr_0.8K_0.1Na_0.1Bi₂Nb₂O₉ (SKNBN) were prepared by a solid state reaction process. X-ray diffraction analysis shows that the alkali and Cu almost diffuse into the SBN lattice to form a solid solution during sintering and some slight secondary phases was detected. The effect of alkali and Cu on dielectric properties of the SBN ceramics was discussed. The dielectric loss factor of (K,Na) doped SBN ceramics degraded considerably to 0.01 and their frequency and temperature stabilities were enhanced. The dielectric constant was enhanced by approximately 60% and the Curie temperature (Tc) was also improved for Cu doped SrBi₂Nb₂O₉ ceramics.     

YBa2Cu3O7-x/SrTiO3//LaAlO3 heterostructures obtained by injection MOCVD

Abstract

YBa₂Cu₃O_7-x /Ba_xSr_1-xTiO₃ /LaAlO₃ heterostructures can be used as a basis for devices with voltage control in microwave circuits.

Ba_xSr_1-xTiO₃ (x=0–0.1) (BST) thin films have been epitaxially grown on LaAlO₃ substrates using injection MOCVD. The excellent crystalline quality of the obtained BST films can be proven by a FWHM of <0,2° for the rocking curve of the (002) BST reflection. An AFM study revealed flat surfaces, showing a surface roughness R_s as low as 1nm. YBa₂Cu₃O_7-x/Ba_xSr_1-x TiO₃//LaAlO₃ heterostructures were than optimised. The YBa₂Cu₃O_7-x (YBCO) layers obtained on Ba_xSr_1-xTiO₃ films are epitaxial with a FWHM of 0.45° for the (005) YBCO rocking curve and display very promising superconducting properties of T_c=92K.

Finally the microwave properties of the superconducting films were studied. For YBa₂Cu₃O_7-x layers directly deposited on LaAlO₃, surface resistance values of 0,32mΩ were obtained, while for YBa₂Cu₃O_7-x /SrTiO₃//LaAlO₃ heterostructures, higher values of 1mΩ at 8.5GHz were measured.     

Growth and electrical properties of (211) BaTiO3 thin films on Pt-coated Si(100) substrates

Abstract

Barium titanate (BaTiO₃) thin films with high (211) orientation have been prepared on Pt(111)/Si(100) substrates by R. F. magnetron sputtering at a substrate temperature between 550°C and 580°C in an Ar/O₂ atmosphere. The I-V curve of a thin film capacitor (Ag-BaTiO_3-Pt) has been measured and the C-V curves are obtained for frequencies between 100Hz and 1MHz. Neither the I-V curve nor the C-V curves are symmetrical and a very large change in the slope of all curves is found to occur at ～+0.5v.     

NO2 sensing characteristics of ZnO nanorods prepared by hydrothermal method

ZnO nanorods were prepared via a hydrothermal reaction in a solution containing Zn(NO₃)₂⋅6H₂O, NaOH, cyclohexylamine, ethanol and water, and their NO₂ and CO sensing behaviors were investigated. The morphology and agglomeration of ZnO nanorods could be manipulated by controlling the amount of water in the solution, which was explained by the variation in the [OH⁻] due to an interaction between the water and cyclohexylamine. Sea-urchin-like and well-dispersed ZnO nanorods were prepared at low and high water content, respectively. Well-dispersed ZnO nanorods showed 1.8 fold change in resistance at 1 ppm NO₂ while there was no significant change in resistance at 50 ppm CO. The present ZnO nanorods can be used in automated car ventilation systems to detect NO₂ in the presence of CO. Presenting author in conference: PYEONG-SEOK CHO     

Influence of the processing rates and sintering temperatures on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

The stoichiometric CaCu₃Ti₄O₁₂ pellets were prepared by the solid state synthesis. X-ray diffraction data revealed the tenorite CuO and cuprite Cu₂O secondary phases on the unpolished CaCu₃Ti₄O₁₂ samples regardless of the heating rates. Also, the dielectric constant marked the highest for the CaCu₃Ti₄O₁₂ sample sintered at the lowest heating rate (1°C/min), which was explained by the increased grain conductivity due to the cation reactions. On the other hand, Cu₂O phase was found only on the unpolished CaCu₃Ti₄O₁₂ sample sintered over 1100°C and those are considered as the remains reduced from the CuO phase. The higher sintering temperature showed the increased dielectric constant and the loss tangent of the CaCu₃Ti₄O₁₂ samples, and this result could be interpreted by the impedance measurement data. The relationship between the processing condition and the dielectric properties was discussed in terms of the cation non-stoichiometry and the defect chemistry in CaCu₃Ti₄O₁₂.     

Dielectric behavior of Bi2/3Cu3Ti4O12 ceramic and thick films

The paper reports on synthesis, sintering and microstructure of Bi_2/3Cu₃Ti₄O₁₂, a lead-free, high-permittivity material with internal barrier layer capacitor behavior. Complex impedance and capacitance of the ceramic and thick films were studied as a function of frequency (10 Hz–2 MHz) and temperature (−170 to 400°C). Dc electrical conductivity of the samples was measured in the temperature range 20–400°C. Broad and high maxima of dielectric permittivity versus temperature plots were observed reaching 60,000 for ceramic and 5,000 for thick films. The maxima decrease and shift to higher temperatures with increasing frequency. Two arcs ascribed to grains and grain boundaries were found in the plots of imaginary part versus real part of impedance. Analysis of the impedance spectra indicates that Bi_2/3Cu₃Ti₄O₁₂ ceramic could be regarded as electrically heterogeneous system composed of semiconducting grains and less conducting grain boundaries. The developed thick film capacitors with dielectric layers based on Bi_2/3Cu₃Ti₄O₁₂ exhibit dense microstructure, good cooperation with Ag electrodes, high permittivity up to 5,000 and relatively low temperature coefficient of capacitance in the temperature range 100–300°C. Broad maxima in the dielectric permittivity versus temperature curves may be attributed to Maxwell–Wagner relaxation.     

Novel diffusion control process using ultra thin buffer layer for MFIS memory

Abstract

MFIS structures having excellent clear interfaces and well-crystallized ferroelectric layer were successfully fabricated by a newly developed ultra thin metal buffer layer process on SiO₂/Si. We examined the effect of sputtered Zr or ZrO₂ ultra thin films as a buffer layer for Pb_xLa_1?xTiO₃ (PLT) growth. TEM observation revealed that the buffer layer formation process in which Zr oxidized after the metal deposition had advantages to produce MFIS structures. This method is also superior for the crystallization and the control of the orientation of PLT thin film on amorphous SiO₂. Especially, for buffer layer thicknesses below 10 nm, preferred c-axis oriented PLT thin films were grown. The I-V characteristics of MFIS-FET fabricated by the proposed method showed a clear memory window due to the remanent polarization of the ferroelectric thin film. This process is the most attractive candidate for realizing MFIS structure memory.     

Photoemission study on natural oxidation of Cu3Au with synchrotron radiation

We report the results of a study of the natural oxidation of Cu₃Au(110) with high‐resolution X‐ray photoemission spectroscopy in conjunction with synchrotron radiation. The clean surface of Cu₃Au(110) is terminated with 50% Au and 50% Cu atoms. After natural oxidation in the air, Cu atoms segregate on the surface and produce Cu‐oxide. As a result, Au atoms move into the bulk. Au atoms below the oxide reduce the diffusion of O atoms farther into bulk and limit the oxide thickness. The face dependence of natural oxidation indicates that the diffusion of Cu atoms also contributes to oxide formation. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 43–47, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21149     

The <00l>-oriented growth of Cu2S films and its switching properties

Cu₂S films have been deposited on Pt/TiO₂/SiO₂/Si(111) substrates, and annealed at different temperatures in a vacuum chamber. They were characterized by using X-ray diffraction and scanning electron microscopy. It was observed that the Cu₂S films deposited at room temperature are well crystallized and the grains are oriented along different directions. With the increase of the annealing temperature, the grains of Cu₂S films prefer the <00l>-orientations, and the average size of Cu₂S films decreases. After annealed at 400°C, the films are completely <00l>-oriented, and the grain boundaries of Cu₂S films become undistinguishable due to the possible movements of the ions at high temperature. The resistive ratio of the ‘off’ state to the ‘on’ state is about 10⁷ for the memory unit of Cu/Cu₂S/Pt structure with the Cu₂S films annealed at 400°C, about 6 orders of magnitude higher than that for the memory unit with the Cu₂S films deposited at room temperature.     

CO2 Sensing Property of CuO-BaTiO3 Mixed Oxide Film Prepared by Self-Assembled Multibilayer Film as a Precursor

Preparation of CuO-BaTiO₃ mixed oxide thin film by the decomposition of a self-assembled multibilayer film as a molecular template was investigated in this study. Furthermore, CO₂ sensing property of the resultant thin film was investigated as a capacitive type sensor. The self-assembled bilayer film of few 1000 layers thickness can be obtained easily by casting an aqueous suspension consisting of dimethyldihexadecylammoiun bromide (DC1-16), Cu(ClO₄)₂, Ba(TiO(C₂H₄)₂), 2,6-dimetyle-3,5heptadione (DHP), and polyvinyl alcohol. Divalent copper ion (Cu²⁺)) which is associated with 2 DHP molecules was incorporated into the molecular bilayer film and BaTiO₃ precursor exists at the interspace of molecular bilayer film by coordinating with polyvinyl alcohol. Upquenching the organic-inorganic film at 1173 K leads to the uniform film of CuO-BaTiO₃ oxide mixture. Although operating temperature shifted to higher temperature, the resultant film exhibits the capacitance change upon exposure to CO₂. Consequently, it is concluded that the mixed oxide film of CuO-BaTiO₃ prepared by the decomposition of multibilayer film was also an appropriate capacitive type CO₂ sensor.     

Microstructure and electroluminescence of ZnS:Cu,Cl phosphor powders prepared by firing with CuS nanocrystallites

This paper presents the microstructure and electroluminescent performance of ZnS:Cu,Cl phosphor powders prepared by firing micrometer-sized ZnS with NaCl and CuS nanocrystallites at 900^∘C in the reducing atmosphere. A series of samples with Cu addition ranging from 40 to 5000 ppm were studied. XRD analysis showed that ZnS:Cu,Cl samples with Cu addition of ≥400 ppm exhibited a transformation from hexagonal to cubic structure. The whole series of ZnS:Cu,Cl samples showed significant photoluminescent (PL) intensity; however, only samples with Cu addition of ≥400 ppm revealed measurable electroluminescent (EL) intensity. This difference was supposed to be a result of nano-sized Cu_xS precipitation in ZnS during firing treatment, where Cu_xS acted as electron emission source to enhance the EL intensity. Furthermore, ZnS:Cu,Cl powder sections were analyzed using X-ray mapping (XRM) of a scanning transmission electron microscope, revealing that Cu_xS precipitates of 50–80 nm in size were observed only in the samples with EL emission, i.e. Cu addition ≥400 ppm. The variation of EL intensity was interpreted in terms of the concentration of Cu activators as well as the phase and the amount of Cu_xS in ZnS.     

Sintering Behavior and Interfacial Analysis of Ni/Cu Electrode with BaTiO<Subscript>3</Subscript> Particulates

The sintering behavior of Ni electrode alloyed with Cu and the interfacial structure between Ni/Cu to BaTiO₃ (BT) have been investigated. The quantitative properties, which include thermal shrinkage, thermal expansion, wetting behaviors of Ni/Cu alloys on BT sheet, and composition distribution were measured by several thermal analysis techniques (TGA/DTA/TMA) and microstructural techniques (SEM/TEM/ HRTEM) with energy-dispersive spectroscopy (EDS). The shrinkage of the Ni/Cu/ BaTiO₃ composite tested in 5%H₂/N₂ atmosphere showed strong influence by the addition of Cu, and retarded slightly due to the addition of the BT particulates. The Cu alloyed with Ni improves the continuity of the electrode and does not trigger mutual reaction between Ni and BT.     

基于MgB2高温超导材料的吉瓦级远程直流输电研究

本文主要探究以具有成本效益和环保特性的新型高温超导材料(MgB_2)作为直流输电电缆,以液氢作为冷却剂,实现吉瓦级远程直流输电的可能性。首先分析超导直流输电的必要性及其优势,说明超导直流输电的基本模型,然后介绍MgB_2超导电缆和液氢制冷系统,接着阐述基于十二脉动换流器的直流输电控制策略。最后使用PSCAD软件完成超导直流输电系统仿真,在相同传输条件下进行MgB_2高温超导电缆和传统电缆的线路功率损耗比较,证明了超导直流输电系统具有线路损耗低,容量不受限制的优点,为MgB_2高温超导材料在超导直流输电领域的开发设计提供初步依据。     

Influence of Heat Treatment at 550–810°C on Inter- and Intragrain Critical Currents of Bi,Pb-2223 Ceramics

The degradation of the superconducting phase Bi_1.65Pb_0.35Sr_1.8Ca_2.2Cu₃O_y and its characteristics: electrical resistivity R, critical temperature T_c (R=0), critical current density j_c, and volume fraction of Meissner phase Cm, have been investigated at 550–810°C and P_O2=2·10¹·1·10⁵ Pa by X-ray diffraction, resistance, inductance and magnetic methods. It was established that at P_O210³ Pa degradation of the ceramic samples runs through the solid solutions decomposition. As a result, the intergrain critical current is decreased 10–20 times while the intragrain one is increased 1.5–2 times. At P_O2=10¹–10² Pa the inter- and intragrain critical currents are decreased by 5–10 times and by 1.5–2 times respectively as a result of oxygen extraction without visible destruction of the Bi,Pb-2223 structure.     

Study on Cu/ZrW2O8 composite layers prepared by co-electrodeposition

ABSTRACT

To obtain composite materials with a low coefficient of thermal expansion (CTE), Cu/ZrW₂O₈ composite layers were prepared by co-electrodeposition. The influence of the co-electrodeposition parameters on the particle content in the composite layers and the effects of particle content on the thermal expansion and microhardness of the layers were studied. In general, the addition of ZrW₂O₈ particles significantly enhanced the microhardness and reduced the CTE of the Cu/ZrW₂O₈ composite materials. The surface morphology changed with the current density and ZrW₂O₈ particle loading. Finally, the CTE of the Cu/ZrW₂O₈ composite materials was much lower than that of pure Cu.     

Spinel-structured Ni-free Zn0.9Cu x Mn2.1-x O4 (0.1 ≤ x ≤ 0.5) thermistors of negative temperature coefficient

Most spinel-structured materials of negative temperature coefficient (NTC) contain Ni, which have high cost. In this work, Ni-free Zn_0.9Cu _x Mn_2.1-x O₄ (0.1?≤?x?≤?0.5) NTC material system is developed. X-ray diffraction (XRD) spectra show that Zn_0.9Cu _x Mn_2.1-x O_\intered at 1100 °C crystallizes in a tetrahedral spinel structure, which is caused by the Jahn-Teller effect of the Mn³⁺ ions at the B sites. Cu2p_3/2 X-ray photoelectron spectra (XPS) demonstrate that most of Cu ions located at B sites are at the valance of 2+. The resistivity of Zn_0.9Cu _x Mn_2.1-x O₄ varies from 1,340 Ω cm to 51,489 Ω cm, and B value from 3,357 K to 4,276 K. The resistivity drift after annealing at 150 °C in air for 1,000 h is less than 3 % which is stable enough for practical application.     

Luminescence Enhancement of ZnS:Cu Nanocrystals by Zinc Sulfide Coating with Core/Shell Structure

Via wet chemical method with organic assistant, ZnS:Cu/ZnS core/shell structure was prepared. X-ray diffraction measurements showed that ZnS:Cu was formed with zinc blende structure, and ZnS shell growth on the surface was indicated through a red-shift in the UV-Vis absorption spectra with increasing particle size. The emission peak at about 510 nm was observed, which should be assigned to recombination of an electron from the shallow delocalized donor levels at the t₂ level of Cu²⁺ centers. As passivation layer, effect of ZnS shell on luminescence intensity and lifetime of ZnS:Cu were investigated. Comparing with uncoated ZnS:Cu, ZnS shell really enhanced the luminescence intensity and lifetime significantly, which resulted from the reduction of nonradiative recombination sites.     

Study of magnetic entropy change in La0.65Sr0.35Cu0.1Mn0.9O3 complex perovskite

The magnetocaloric properties of new complex magnetic material La_0.65Sr_0.35Cu_0.1Mn_0.9O₃, suitable for the Ericsson cycle, have been investigated. For this material, the effect of Cu doping can be attributed to a combination of doping disorder, Cu-Mn super exchange interactions and a site-percolation mechanism, which suppress the metallic conduction and Curie temperature. The Curie temperature decreases to 355 K. The magnetocaloric study exposes a comparable value of the magnetic entropy change for La_0.65Sr_0.35Cu_0.1Mn_0.9O₃ sample, the value of the maximum entropy change, increases from 1.132 J/kgK to 3.11 J/kgK as magnetic field increases from 1 T to 4 T. A large relative cooling power (RCP) has been observed for La_0.65Sr_0.35Cu_0.1Mn_0.9O_3. As a result, the studied sample can be considered as potential material for magnetic refrigeration.