Papers by Author: Hong Qiu

Abstract: Ni/HCl-PANI composites were formed by depositing Ni films on HCl-doped polyaniline (HCl-PANI) substrates. A simple parallel resistor model is used to analyze the resistance-temperature (R-T) characteristic of the composite within 30-300 K. The theoretical analysis reveals that the composite exhibits a metal-semiconductor transition within a certain thickness of the Ni film or the HCl-PANI substrate. The composite shows a semiconducting behavior at temperatures over the transition temperature and a metallic conduction behavior at temperatures below the transition temperature. The transition temperature increases with increasing Ni film thickness whereas it decreases with increasing HCl-PANI substrate thickness. When the Ni film thickness exceeds its upper limit or the HCl-PANI substrate thickness is below its lower limit, the composite only shows the metallic R-T characteristic. When the HCl-PANI substrate thickness exceeds its upper limit, the composite only exhibits the semicoducting R-T characteristic.

Abstract: 80nm-thick network Ni films were sputter-deposited on anodic aluminium oxide (AAO) substrates at 300 K and 573 K. The network films are formed by granule connection. The granule consists of many fine grains. Both granule size and grain size are independent of the deposition temperature. A temperature dependence of the resistance within 1.6-300 K reveals that the network Ni film grown at 300 K exhibits a minimal resistance at about 25 K while that grown at 573 K does not show a minimal resistance. A temperature coefficient of resistance of the network film grown at 573 K is larger than that of the film grown at 300 K.

Abstract: About 300nm-thick Ni₈₀Fe₂₀ films were deposited on SiO₂/Si (100) substrates at 300 K and 673 K in 1.2 Pa and 0.8 Pa Ar gas by a direct current (DC) magnetron sputtering system with the oblique target. The films grown at 300 K have a predominate [11 crystal orientation in the growth direction whereas those deposited at 673 K grow mainly with a [11 crystalline orientation in the growth direction. All the films have a columnar structure. The grain size increases with increasing deposition temperature. The films grown at 673 K are dense compared with those grown at 300 K. The film deposited at 673 K in 0.8 Pa Ar has the lowest resistivity.

Abstract: HCl-doped polyaniline (HCl-PANI) powder is synthesized by using a chemical polymerization procedure. Then Ag nanoparticles are deposited on the HCl-PANI at room temperature by RF sputtering. After this process, the nanocomposite is obtained by the chemical and physical combinative method. The nominal Ag content in the nanocomposite ranges from 1.0 wt% to 3.3 wt%. For all the nanocomposites, the Ag nanoparticles convert to AgCl nanoparticles. Namely, the HCl-PANI-AgCl nanocomposites are obtained. A content of the AgCl in the nanocomposite increases with increasing Ag content. The AgCl nanoparticle consists of many grains. An average grain size of AgCl is about 40 nm and is independent of the Ag content. A conductivity of the nanocomposite decreases with increasing Ag content.

Abstract: 180nm-thick Ni33Fe67 and Ni21Fe79 films were deposited on SiO2/Si(100) substrates at 633 K by DC magnetron co-sputtering. Structural, electrical and magnetic properties of the films were investigated using X-ray diffraction, field emission scanning electron microscopy, a four-point probe technique and an alternating gradient magnetometer. The Ni21Fe79 film has a single bcc structure whereas the Ni33Fe67 film is a fcc-bcc mixed phase. The films grow with granular grains. The grain shape of the Ni21Fe79 film is triangular and rectangular. The Ni33Fe67 film consists of irregular shaped grains and a few large triangular grains. The grain size of the Ni21Fe79 film is larger than that of the Ni33Fe67 film. The resistivities of the Ni21Fe79 and Ni33Fe67 films are 1.82×10-63m and 1.09×10-63m. The saturation magnetization of the Ni21Fe79 and Ni33Fe67 films are 1.09×106 A/m and 1.02×106 A/m. The coercivity of the Ni21Fe79 and Ni33Fe67 films are 2.06×104 A/m and 8.84×103 A/m , respectively.

Abstract: Sr(Bi1-xSmx)8Ti7O27 ceramics were prepared by Sm2O3-substitution for Bi2O3 through solid-state reaction route. The dielectric properties of the sintered bodies such as er, Q and tf were investigated. The ceramics were characterized by SEM, XRD, DTA and TG, which behaved high dielectric constant of 128 ~154 at the frequency of 10 GHz.

Abstract: Dielectric constant of Ba2Ti9O20 ceramics are theoretically calculated based on the chemical structure of the oxides and the mixing rule of dielectric material in this paper. Meanwhile, the microwave properties (εr, Q and τf) of practical Ba2Ti9O20 ceramics are experimentally measured at microwave frequencies. Some of useful suggestions are therefore provided for material optimization of practical ceramics.

Abstract: 185 nm-thick Ni76Fe24 films were deposited on SiO2/Si(100) substrates at room temperature by DC magnetron co-sputtering and they were annealed in a vacuum of 5×10-4 Pa at 300 , 400 and 480 °C for 1 hour, respectively. The as-deposited film grows with thin columnar grains and has void networks in the grain boundaries. As the annealing temperature increases, the grain size gradually increases and the void networks decrease. Besides, the void networks shorten and widen with annealing temperature. The resistivity of the film decreases with increasing annealing temperature. The magnetic hysteresis loop of the as-deposited film shows a hard magnetization requiring a saturation field of 1050 Oe while that of the film annealed at 480 °C represents an easy magnetization. For the film annealed at 480 °C the coercivity is 78 Oe and the ratio of remanent magnetization to saturation magnetization is 0.72. The as-deposited and annealed films have an isotropic magnetization characteristic.