可调谐法布里-珀罗滤波器的高精度大范围实时定标

将乙炔(C2H2)气体的吸收光谱作为标准波长参考,对可调谐光纤法布里-珀罗滤波器进行波长实时定标,使解调系统的测量精度提高到1 pm.根据可调谐光纤法布里-珀罗滤波器谐振波长的周期性,提出了大波长范围的波长定标方法,从而可以在1525～1615 nm的范围内对可调谐光纤法布里-珀罗进行精确定标,实现了高精度大波长范围的信号探测.相比于传统的以光纤光栅作为波长参考的定标方法,该方法的测量精度、测量范围、系统运行可靠性都大为改善.     

具有Frétchet树枝结构的新型酞菁锌(Ⅱ)配合物:四-{3,5-二-[3,5-二-(4-羧基苯甲氧基)苯甲氧基]-苯甲氧基}酞菁锌(Ⅱ)的合成与表征

报道了一种新型Frétchet树枝配体取代酞菁锌(II)配合物:四-{3,5-二-[3,5-二-(4-羧基苯甲氧基)苯甲氧基]-苯甲氧基}酞菁锌(II)的合成与表征.首先将对氰基苄溴与3,5-二羟基苯甲醇通过Frétchet反应合成3,5-[二-(4-氰基苯甲氧基)]苯甲醇(1),1与四溴化碳和三苯基膦在四氢呋喃中反应合成3,5-二-(4-氰基苯甲氧基)苄溴(2),2与3,5-二羟基苯甲醇反应合成3,5-二-[3,5-二-(4-氰基苯甲氧基)苯甲氧基]苯甲醇(3),接着,3与4-硝基邻苯二甲腈合成"前驱物"四-{3,5-[二-(4-氰基苯甲氧基)]}苯甲氧基邻苯二甲腈(4),然后以1,8-二氮杂双环[5.4.0]十一碳-7-烯(DBU)为催化剂,醋酸锌为模板剂,4通过缩聚反应合成氰基端基的Frétchet树枝配体取代酞菁锌四-{3,5-二-[3,5-二-(4-氰基苯甲氧基)苯甲氧基]-苯甲氧基}锌酞菁配合物5,最后,5的氰基端基在NaOH溶液中水解为相应的以羧基端基Frétchet树枝配体取代酞菁锌:四-{3,5-二-[3,5-二-(4-羧基苯甲氧基)苯甲氧基]-苯甲氧基}酞菁锌(II)(6).采用元素分析,IR,1H NMR,ESI-MS和MALDI-TOF-MS表征所有化合物的结构,通过UV/Vis,稳态和瞬态荧光光谱法研究了5和6的光物理性质.5和6是一类性能较好的树枝状酞菁光敏剂.     

Exchange coupling in multilayers with semiconductors

Intrinsic and heat-induced exchange coupling exists between ferromagnetic films separated by non-magnetic semiconducting spacer layers. Magnetic coupling across thin amorphous layers of Si, SiO, Ge and Ge/Si heterostructures is described. Antiferromagnetic coupling occurs in a limited thickness range for Si and Si/Ge heterostructures, and ferromagnetic coupling is found for SiO, Ge, and certain thicknesses of Si and Si/Ge heterostructures. The coupling strength is very weak, of the order of a few 10^–6 J/m². It exhibits a pronounced temperature dependence with a positive temperature coefficient for both ferro- and antiferromagnetic couplings. The observations indicate that resonant tunneling through defect states in the spacer material mediates the exchange coupling.     

Influence of material design parameters on radiative recombination in GaAs doping superlattices grown by MBE

The specific luminescence process in GaAs doping superlattices arises from recombination of electrons populating low-index conduction subbands with holes in the acceptor impurity band across the indirect gap in real space. The luminescence peak energy thus directly reflects the actual value of the tunable gap for the photoexcited state of the superlattice. We have studied the tunability of the effective gap, the recombination rate, and the relative quantum efficiency on superlattice specimen of different material design parameters by means of low-temperature photoluminescence measurements. For optimized design parameters the ratio between luminescence and excitation intensity remains nearly constant over the entire tunability range of the effective gap.     

CLASSICAL SOLUTION OF VERIGIN PROBLEM WITH SURFACE TENSION

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Electrochromic device based on tungsten oxide and on Nnfion-H as polymeric electrolyte

We describe the preparation, electrical and optical characterization of a prototype of a nearly solid-state electrochromic device. It is fabricated with Nafion-H, a polymeric electrolyte, and involves cathodically coloring tungsten trioxide doped with molybdenum. The device switches rapidly with the applied potential ranging from –2.4 up to 0.8V, between blue and transparent state. The corresponding integrated photopic (T _p) and solar (T _s transmittance is T _p (bleached) = 70.7%, T _s (bleached) = 59.6%, T _p (colored) = 15.5%, and T _s (colored) = 12.2%.     

Universal amplitudes and profiles for critical adsorption

The analysis of published experimental data for seven different binary liquid mixtures allows us to test the concept of universality for critical phenomena at interfaces and to compare the values of three independent universal surface amplitudes with theoretical predictions. In spite of uncomfortable large experimental error bars in the case of one surface amplitude we find agreement for five different systems and disagreement for two. For the other two surface amplitudes we obtain a marginal agreement between theory and experiment which is impeded by the lack of experimental error bars. We also test the scaling functions for critical adsorption. In view of the complexity of the data analysis the agreement between theory and experiment is satisfactory and encouraging. Experimental improvements are suggested in order to obtain more stringent tests.Dedicated to H. Wagner on the occasion of his 60th birthday     

Non-exponential dark capacitance transients from red-emitting GaP LED's — Field and edge effects on the 0.75 eV centre

The origin of the non-exponential behaviour of the previously reported [2] dark capacitance transients from red-emitting GaP LED's has been investigated in detail. In particular, the effects of the electric field and the junction edge-region on hole-emission from the 0.75 eV level has been studied. A small apparent electric-field enhancement of the emission rate has been shown to be caused predominantly by junction edge effects.     

Dislocation-related photoluminescence in silicon

Photoluminescence is studied in silicon, deformed in a well-defined and reproducible way. Usual deformation conditions (high temperature, low stress) result in sharp spectra of the D1 through D4 lines as recently described in the literature. New lines D5 and D6 emerge for predeformation as above and subsequent low-temperature, high-stress deformation. Another new sharp line, D12, is observed when both the familiar and the novel lines appear simultaneously. Annealing for 1 h atT _A 300 °C causes all new lines to disappear and the D1–D4 spectra to reappear. Quantitative annealing and TEM micrographs suggest that D5 is related to straight dislocations and D6 to stacking faults, whereas D1–D4 are due to relaxed dislocations. Photoluminescence under uniaxial stress shows that D1/D2 originate in tetragonal defects with random orientation relative to 100 directions, whereas D6 stems from triclinic centers, preferentially oriented — as are the D3/D4 centers. We conclude that the D3/D4 and the D5 and D6 defects are closely related, whereas the independent D1/D2 centers might be deformation-produced point defects in the strain region of dislocations.     

New oxygen donors in silicon

Oxygen donor traps and oxygen-related precipitates are investigated by deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). The so-called New Donors (ND's) occur after thermal treatments in the temperature range of 650 °–800 ° C. They have a continuous distribution of trap states with respect to energy in the band gap of Si. The concentration of the trap states increases towards the conduction band edge. The precipitates observed are mainly platelets and ribbon-like defects. The formation and annihilation kinetics of ND traps and oxygen-related precipitates are correlated. An SiO _x Interface Model is proposed to explain the origin and the donor-like behavior of the ND traps. The ND trap spectrum is composed of two different types of trap states: interface states at the surface of precipitates and bound states in the Coulombic wells of a fixed positive charge which is located in the SiO _x precipitates.