卟啉类L—B膜分子间相互作用的光谱研究

以无取代的meso-四-(4-N)-吡啶基卟啉及其过渡族金属(主要Cu~(2+)、Zn~(2+))络合物制备L-B膜,以近紫外-可见吸收光谱和荧光光谱为手段,研究叶啉类分子在氯仿溶液中,L-B膜状态下以及固态状态下的相互作用。探讨分子聚集体的存在对光谱性质的影响。 为了研究叶咻类分子间的相互作用及其对光谱性质的影响,我们首先分析了叶啉在CHCl_3溶液中及固态状态下的近紫外-可见吸收光谱和荧光光谱。并将其与叶啉类分子的L-B膜作比较。结果表明,卟啉类的Soret吸收带带宽及峰位置在三种状态下均不相同,L-B膜的情况介于溶液中的和固体下的情况之间,说明了在L-B膜中,卟啉分子存在着某种形式的聚集体,且在这种聚集体中分子间的相互作用程度比固体弱,可以认为L-B膜上的分子呈准晶体状态。     

Change of light holes valence band in lead-tin telluride films by isovalent substitution of chalcogen atoms

Rotational weak-field magnetoresistance measurements at 78 K were used to determine the parameters of the valence band of light holes for Pb_0.8Sn_0.2Te and Pb_0.8Sn_0.2Te_0.98S_0.02 epitaxial films grown on (111)-oriented BaF₂. It was shown that an isovalent substitution of 2% of tellurium atoms by sulphur atoms in solid solution films of lead telluride-tin telluride leads to the decrease of the energy splitting value of valence band valleys Δσ_v from 18 meV to 2 meV. The physical reasons for this phenomenon were analysed. Obtained experimental data were compared with the results of other experiments on photoluminescence and concentration dependencies of thermoEMP coefficient.     

用正电子湮没技术研究新型高临界温度T_c超导材料Ba-Y-Cu氧化物

本文介绍用正电子湮没技术研究了具有高临界温度下T_c的新型超导材料Ba-Y-Cu氧化物。实验发现,在起始转变温度以下,正电子寿命减少与电阻随温度的变化曲线符合。在临界温度T_c处,出现了正电子寿命峰。     

Space and time resolved surface temperature distributions in Si power diodes operating under self-heating conditions

In order to optimize and improve the design of power devices with improved surge current safe operating area it is necessary to obtain a good correlation between measured and simulated space and time resolved temperature distributions. Therefore, an IR microscope capable of measuring the space and time resolved surface temperature distributions in Si power diodes operating under self-heating conditions has been developed. The minimum detectable spot size is 15 μm, while the signal rise time is detector limited to about 1 μs. The lower temperature detectivity limit is about 10°C over room temperature.

Using this instrument dynamic thermal phenomena in fast recovery 3.3 kV Si power diodes having radiation-induced recombination centers [Proceedings of the 7th EPE, Trondheim, 1997] subjected to 1.2 ms 400–2000 A/cm² and 0.3–2 ms 2000 A/cm² current pulses have been studied. The experimental results have been compared to results from 2D device simulations including surface recombination and carrier lifetime temperature dependence. The agreement between experimental and device simulation results (i.e. dynamic IV characteristics and time and space resolved temperature distributions) is very good up to a peak current density of 1500 A/cm², and a reasonable good one for peak current densities up to 2000 A/cm² (1.2 ms current pulses).     

Zinc-phthalocyaninetetraphosphonic acid as a novel transparent-conducting-oxide passivation for organic photovoltaic devices

A novel monolayer chemical passivation improving the surface electronic properties of indium-tin oxide (ITO), used as an electrode in organic solar cells (OSC), is reported. Deposition of zinc-phthalocyaninetetraphosphonic acid on ITO substrates, from a water solution, creates a chemically bound organic monolayer passivation, which improves the charge transfer through the ITO/zinc-phthalocyanine (ZnPc) interface in ZnPc/C₆₀ OSC. Current–voltage measurements on devices produced on such substrates show improved serial and parallel resistances as well as fill factor, compared to OSC on non-passivated substrates. The use of this novel passivation for electrodes allows to dispose off the additional conventional PEDOT:PSS buffer layer.     

FBG反射谱展宽效应在轨道传感器中的应用研究

实验验证了光纤Bragg光栅(FBG)在非均匀应力下的反射谱展宽效应,并将这种展宽效应应用于轨道列车轮重、位置和轴数的监测。将FBG传感器置于铁轨特定位置,当受非均匀应力时,列车轮重的增加会引起FBG反射谱展宽,反映为检测光强增大。利用模型验证了FBG反射谱分别在温度、均匀应力及非均匀应力下的变化,根据有限元分析模拟铁轨模型的应变分布,进而通过模型实验和实际测试验证了这种方案的可行性。     

HfAlOx high-k gate dielectric on SiGe: Interfacial reaction, energy-band alignment, and charge trapping properties

Ultra thin HfAlO_x high-k gate dielectric has been deposited directly on Si_1−xGe_x by RF sputter deposition. The interfacial chemical structure and energy-band discontinuities were studied by using X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (TOF-SIMS) and electrical measurements. It is found that the sputtered deposited HfAlO_x gate dielectric on SiGe exhibits excellent electrical properties with low interface state density, hysteresis voltage, and frequency dispersion. The effective valence and conduction band offsets between HfAlO_x (E_g = 6.2 eV) and Si_1−xGe_x (E_g = 1.04 eV) were found to be 3.11 eV and 2.05 eV, respectively. In addition, the charge trapping properties of HfAlO_x/SiGe gate stacks were characterized by constant voltage stressing (CVS).     

Effects of annealing temperature on the phase formation,optical, photoluminescence and magnetic properties of sol-gel YFeO3 films

YFeO₃ (YFO) thin films were deposited onto quartz substrates via sol-gel spin-coating technique and annealed at different temperature ranged between 650 and 900 °C. The impact of annealing temperature on the phase formation, microstructural, optical, photoluminescence (PL) and magnetic properties of the films were systematically investigated. X-ray diffraction analysis revealed an amorphous structure in film annealed at 650 °C and formation of hexagonal-YFO (h-YFO) phase in films annealed at 750–800 °C. The films annealed at 850–900 °C exhibited an orthorhombic-YFO (o-YFO) structure. Atomic force microscopy images of h-YFO films showed homogeneous surface with uniform particles size and shape. The particle size increased and had irregular shape in o-YFO films. The average particle size was 44 and 117 nm, while the root square roughness was 1.38 and 2.55 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The optical band gap (E_g) was 2.53 and 2.86 eV for h- and o-YFO films annealed at 750 and 850 °C, respectively. The PL spectra of h-YFO films were red-shifted compared with that of o-YFO films. The PL emission related to near band edge was observed at 459.0 and 441.9 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The magnetization was enhanced with the increasing of annealing temperature and has the value of 4.8 and 12.5 emu/cm³ at 5000 Oe for h- and o-YFO films annealed at 750 and 850 °C, respectively.