Advanced Materials Research Vol. 710

Abstract: By combination of electromagnetic levitation and copper-plate quenching, deep undercooling and non-equilibrium solidification of Si melts were realized. Several different morphologies of Si solidified at different undercoolings were found on the quenched surfaces, including spherical non-faceted morphology, faceted dendritic morphology, octahedral morphology and other polyhedral morphology. The mixed microstructures consisting of non-faceted and faceted morphologies in one single sample provide direct evidence for the growth mode transition from a continuous form to a lateral form.

Abstract: In this paper, we use Bruggeman model to calculate refractive index of nanoporous silicon, which was fabricated by electrochemical etching. The calculated result shows that the refractive index of the nanoporous silicon decreases linearly with increasing porosity and etching current density. In addition, the refractive index of nanoporous silicon was also measured by spectroscopic ellipsometry in the visible light spectrum range. The measured refractive index and extinction coefficient were in agreement with the calculated data, after being modified by the refractive index modified model of heavily doped silicon. In particular, we estimate the refractive index at the optical wavelengths in visible and near-infrared spectrum ranges, which may be widely used in various types of optical sensors and optoelectronic devices for optical communication systems.

Abstract: Shape memory alloy (SMA) as an effective alternative to steel has received much attention. The constitutive model of SMA has raped developed for nearly 10 years, such as Boyd and Lagoudas model, Auricchio model, etc. However, a number of constitutive models were more complex, and not easily applied to engineering. In order to study SMA concrete pullout test using numerical simulation software, the tensile property of superelastic SMA was studied in this paper, different units (SOLID185 and LINK8) were simulated at the same time. Through the comparative analysis of results of different constitutive models, an easier used constitutive model of SMA was obtained. Combining with the numerical case, it shows that link8 is more convenient and accurate to simulates SMA.

Abstract: A series of novel polyfluorenes derivatives containing different ratio of phenanthro -[9,10-imidazole (PI) group on backbone are designed, synthesized and well characterized. Comparing with the class blue polymer PF, they all exhibit deep blue emission in solution and film with high PL efficiency, and show better film forming ability because of the insert of bulky substituent on PI unit by the AFM measurement. The CV results of all compounds deliver balanced carriers injection ability, and the decreased LUMO levels and improved HOMO levels are observed, which is befit of the preparation of high performance deep blue OLED.

Abstract: According to the profile section of transport equipment, the wide and hollow AZ31 magnesium alloy profiles was self-designed. Extrusion molding performance of the profiles, the law of microstructure and mechanical properties were studied when billets pretreatment and extrusion temperature were changed. The conclusions are as follows: (1) The grains of AZ31 profiles extruded by pre-extrusion billet are smaller and the strength is better, its maximum tensile strength is 280MPa. (2) Other processes being equal, the grains of AZ31 profiles are smaller and strength is higher, but the plastic is bad, when the extrusion temperature is 300°C. However, both strength and ductility of AZ31 profiles are better, when the extrusion temperature is 350°C. (3) Wide and Hollow AZ31 profiles perform significant heterogeneity and anisotropic characteristics on mechanical properties.

Abstract: Vanadium dioxide (VO₂) films were grown on c-and m-plane sapphire substrates by pulsed laser deposition (PLD) technique with VO₂ ceramic target. The VO₂ films with preferred growth orientation and uniform dense distribution have been achieved on both substrates, as confirmed by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The terahertz (THz) transmission properties of VO₂ thin films were studied by terahertz time-domain spectroscopy (THz-TDS). The results indicate that the THz transmission properties of VO₂ films are strongly influenced by the sapphire substrate orientation, suggesting that VO₂ films are ideal material candidates for THz modulation.

Abstract: In this paper, a novel ZnO-based graphite-insulator-semiconductor (GIS) diode was fabricated on graphite substrate by radio frequency (rf) magnetron sputtering. A SiO₂ thin film was used as the insulator layer grown by electron beam evaporation technique. The measurement of current-voltage of the ZnO-based GIS diode showed a Schottky rectifying diode characteristic with a threshold voltage of 5.2 V and a poor leakage current of ~10^-3 A under a reverse bias condition. An interesting negative capacitance phenomenon was also observed from the GIS diode. The successful fabrication of ZnO-based GIS diode on graphite substrate offers the significant opportunity to be readily transferred onto any rigid or flexible foreign substrates, since the graphite substrate consists of weakly bonded layer structure.

Abstract: In order to accelerate the commercialization of SOFCs technology, the key is the development of high performance cathode materials operated at intermediate temperature. Sr and Cu doped rare earth oxide La_1-xSr_xFe_1-yCu_.yO_3-δ (x=0.1, 0.3 ; y=0.1, 0.2, denoted as LSFCu-11, LSFCu-31 and LSFCu-32 ) were synthesized by solid state reaction method (SSR). The formation process, phase structure and microstructure of the synthesized samples were characterized using TG/DSC, XRD and SEM. The thermal expansion coefficients (TEC) of the samples were analyzed by thermal dilatometry. The electrical conductivities of the samples were measured with DC four-terminal method from 25 to 950 °C. The results indicate that the samples exhibit a single phase with orthorhombic and hexagonal perovskite structure after sintered at 1200 °C for 4h. The electrical conductivity of the samples increases with temperature up to a maximum value, and then decreases gradually. The small polaron hopping is regarded as the conducting mechanism for synthesized samples at T 550 °C. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. LSFCu-32 has higher mixed conductivity (> 100 S·cm^-1) at intermediate temperature and can meet the demand of cathode material for IT-SOFC. In addition, the average TECs of LSFCu-11, LSFCu-31 and LSFCu-32 are 1.22 × 10^-6 K^-1 , 1.30 × 10^-6 K^-1 and 1.34 × 10^-6 K^-1 respectively.

Abstract: Ti₂AlN ceramic have been prepared by self-propagating high-temperature synthesis method using Ti, Al and TiN mixture as raw materials under different N₂ pressures. X-ray diffraction (XRD) and scanning electron microscope (SEM) have been used to determine the phase composition and micro morphology of the products. XRD analysis indicates that the main phase of the products is layered ternary compound Ti₂AlN, but there are TiN and AlTi₃ impurities in the products. With increasing N₂ pressure, the relative content of TiN and AlTi₃ decreases. SEM imagines exhibits that the grains of the products become larger with increasing N₂ pressures.