一种半晶性联苯酯侧基聚酰亚胺

A novel polyimide(PI) containing pendent biphenyl ester groups was synthesized from 3,5-diaminobenzoic-4′-biphenyl ester (DABBE)and 3,3′,4,4′-oxydiphthalic dianhydride(ODPA) by a one-step high-temperature polycondensation in m-cresol.This PI is a semicrystalline polymer.Lots of short fine fibric crystals with length and diameter about 20、μm and 1、μm respectively disperse randomly in the PI film. The optical textures and the X-ray diffraction patterns of the PI solution and film show that the PI main chains are in the extended conformation and pack parallel to each other, and the pendent biphenyl ester groups occupy the space between the main chain layers,more or less perpendicular to the main chains.At the same time, mechanical and thermally stable properties of the PI film were investigated. The excellent mechanical properties of general polyimide films are reasonably maintained, the polyimide film with pendent groups showes higher tensile strength and modulus and lower T g. TGA study showes a typical two-step weight loss behavior corresponding to the pyrolysis of pendent groups and main chains of the PI,respectively.

Identification and characterization of single crystal Bi_(2)Te_(3-x)Se_(x) alloy

The results of experimental investigation of n-type semiconductor based on Bi2Te3 alloy were presented. This material is used in manufacture of thermoelectric coolers and electrical power generation devices. BizTe2.88Se0.12 solid solution single crystal has been grown using the Czochralski method. Monitoring of structure changes of the sample was carried out by electron microscope. The elemental composition of the studied alloy was obtained by energy dispersive spectrometry （EDS） analysis and empirical formula of the compound was established. X-ray diffraction analysis confirmed that the Bi2Te2.88Se0.12 sample was a single phase with rhombohedral structure. The behavior upon heating was studied using differential thermal analysis （DTA） technique. Changes in physical and chemical properties of materials were measured as a function of increasing temperature by thermogravimetric analysis （TGA）. The lattice parameters values obtained by X-ray powder diffraction analyses of Bi2Te2.88Se0.12 are very similar to BizTe3 lattice constants, indicating that a small portion of tellurium is replaced with selenium. The obtained values for specific electrical and thermal conductivities are in correlation with available literature data. The Vickers microhardness values are in range between HV 187 and HV 39.02 and decrease with load increasing. It is shown that very complex process of infrared thermography can be applied for characterization of thermoelectric elements and modules.

MnQ_2(Q=S,Se,Te)and Te_4 Structures and Their Semiconductor Properties

The solvo―thermal technique is used for the synthesis of [Mn(en)_3]Te_4 (I).The crystal structure has been determined by single crystal X―ray diffraction techniques. Thecrystal belongs to the monoclinic, space group p2_1/c with unit cell:a = 0. 846 1(1), b=1.5653(2),c=1.426 9(2) nm, α = 90°, β=91. 37(1) (3)°, γ=90°, V=1. 889 3(4) nm^3, and Z=4. The resultsshow that the structure contains a linear chain Zintl anion, [Te_4 ]^(2-) and a complex cation,[Mn(en)_3l^(2+). Optical studies have been performed on the powder sample of I, suggesting that thecompound is a semiconductor with a band gap of 0. 73 eV. The semiconductor properties for MnQ_2(Q=S, Se, Te) and [Mn(en)_3]Te_4 have been discussed by molecular orbital theory.

Strain Relaxation Related Photoluminescence Bands in Ge/Si Short Period Superlattices

Pure-Ge/Si short period superlattice (SPS) grown by gas source MBE (GSMBE) is studied by photoluminescence spectroscopy and Raman scattering spectroscopy. An abnormal band in photoluminescence is found in an intermediate range of Lsi between 1.9 nm-2.9 nm for samples with LGe fixed at 1.5 ml. In contrast to a pure-Ge/Si quantum well, the energy of the band shows red-shift as Lsi increases. Raman scattering shows that Si-Si vibration related Raman shift reaches a minimum for samples with strongest PL intensity of the abnormal band. It is therefore concluded that the abnormal band is related with strain relaxation process.

RESEARCH OF BJMOSFET FREQUENCY CHARACTERISTICS

The parasitic capacitance effect and its influence to the performance have been investigated in Bi-polar Junction Metal-Oxide-Semiconductor Field-Effect Transistor (BJMOSFET). The frequency characteristic equivalent circuit and high frequency response model of BJMOSFET have been presented. The frequency characteristic of BJMOSFET is simulated using the multi-transient analytical method and PSPICE9 simulator. The conclusions that BJMOSFET owns less total capacitance, wider frequency band, better transient charac-teristic and better frequency responses are reached by comparing with the traditional MOSFET at the same structure parameters and bias conditions. BJMOSFET, as a novel promising high frequency device, would be desired to find application in future integrated circuit.

Magnetic-field enhanced high-thermoelectric performance in topological Dirac semimetal Cd3As2 crystal

Thermoelectric materials can be used to convert heat to electric power through the Seebeck effect. We study magneto-thermoelectric figure of merit （ZT） in three-dimensional Dirac semimetal Cd3A 5 2 crystal. It is found that enhancement of power factor and reduction of thermal conductivity can be realized at the same time through magnetic field although magnetoresistivity is greatly increased. ZT can be highly enhanced from 0.17 to 1.1 by more than six times around 350 K under a perpendicular magnetic field of 7 T. The huge enhancement of ZT by magnetic field arises from the linear Dirac band with large Fermi velocity and the large electric thermal conductivity in CdsA 5 2. Our work paves a new way to greatly enhance the thermoelectric performance in the quantum topological materials.