Magnetic properties of silicon doped with gadolinium

The magnetic semiconductor GdxSi1-x was prepared by low-energy dual ion-beam epitaxy. GdxSi1-x shows excellent magnetic properties at room temperature. A high magnetic moment of 10 mu(B) per Gd atom is observed. The high atomic magnetic moment is interpreted as being a result of the RKKY mechanism. The indirect exchange interaction between ions is strong at large distances due to the low state density of the carriers in the magnetic semiconductor.

High energy ion implantation enhanced intermixed quantum well structures and their absorption characteristics in passive optical waveguides

We have shown that high energy ion implantation enhanced intermixing (HE-IIEI) technology for quantum well (QW) structures is a powerful technique which can be used to blue shift the band gap energy of a QW structure and therefore decrease its band gap absorption. Room temperature (RT) photoluminescence (PL) and guided-wave transmission measurements have been employed to investigate the amount of blue shift of the band gap energy of an intermixed QW structure and the reduction of band gap absorption, Record large blue shifts in PL peaks of 132 nm for a 4-QW InGaAs/InGaAsP/InP structure have been demonstrated in the intermixed regions of the QW wafers, on whose non-intermixed regions, a shift as small as 5 nm is observed. This feature makes this technology very attractive for selective intermixing in selected areas of an MQW structure. The dramatical reduction in band gap absorption for the InP based MQW structure has been investigated experimentally. It is found that the intensity attenuation for the blue shifted structure is decreased by 242.8 dB/cm for the TE mode and 119 dB/cm for the TM mode with respect to the control samples. Electro-absorption characteristics have also been clearly observed in the intermixed structure. Current-Voltage characteristics were employed to investigate the degradation of the p-n junction in the intermixed region. We have achieved a successful fabrication and operation of Y-junction optical switches (JOS) based on MQW semiconductor optical amplifiers using HE-IIEI technology to fabricate the low loss passive waveguide. (C) 1997 Published by Elsevier Science B.V.

钐原子激发态光谱的研究

稀土元素钐(Sm)的基态构型包括7个能级4f~66s~2 ~7F_(Ji) (Ji = 0,1……6)。2个6s外层电子和4f内层电子都有可能激发，产生复杂的光谱。给研究工作带来一定的困难。本文首先在原子束装置中，采用脉冲染料激光器。对钐原子进行一步共振激发。结合Boxcar技术测量了钐原子激发态的荧光衰减曲线。得到八个钐原子低能级的自然辐射寿命。不但对有争议的4f~66s6p ~7D_1~0态寿命值过行了复测，而且其中五个能级~5G_4~0(18503.49cm~(-1)), ~7D_2~0(16681.74cm~(-1)), ~7D_3~0(17243.55cm~(-1)), ~7D_4~0(17959.27cm~(-1))和 ~5G_5~0(18811.11cm~(-1))的寿命值是我们首次测得。另，本文还在原子束中采用激光二步共振激发，记录荧光光谱的方法对钐原子的高激发态新能级进行了测量。实验中选择十四条不同的激发路线，其第一步跃迁波长λ_1分别为：590.260nm, 590.605nm, 590.904nm, 591.636nm, 592.789nm, 597.938nm, 598.968nm, 599.509nm, 600.418nm, 604.500nm, 607.006nm, 608.412nm, 609.990nm及611.779nm。它们将钐原子从基组态~7F激发到4f~66s6p或4f~55d6s~2 构型的奇宇称中间态。第二步激光波长λ_2的扫描范围为556.0-576.0nm，λ_2将钐原子从上述中间态激发到位于34150-37732cm~(-1)能量区间的偶宇称高激发态。我们测定了在此能量范围内的122个偶宇称能级，其中117个能级为我们首次测得。本论文完善了钐原子的能级、寿命的光谱数据，对进一步研究钐原子有重要意义。

蹄蝠科的核型进化：比较染色体涂色、G带和C带分析

：与其姐妹科(菊头蝠科)相比，蹄蝠科的细胞遗传学研究较少。迄今为止，仅少数蹄蝠科几个物种有高分辨率的G带核型报道，且有关该科核型进化的大多数结论都是基于常规Giemsa染色研究而得。该研究利用三叶小蹄蝠的染色体特异探针，通过比较染色体涂色、G和C显带，建立了5种蹄蝠的染色体同源性图谱，并探讨了它们同源染色体间的G和C带异同。结果表明：罗伯逊易位、臂内倒位以及异染色质的扩增可能是蹄蝠科物种核型进化的主要机制。通过对这5种蹄蝠物种及其外群物种之间的同源染色体片段的比较分析，作者推测蹄蝠科的祖先核型并不像先前认为的全由端着丝粒染色体组成, 而应该含有中着丝粒染色体。

低碳含量a-Si_（1-x）C_x∶H薄膜的化学键结构

利用两种不同激发波长进行Raman测量，研究了低碳含量a-Si_(1-x)C_x:H(～<20at.%)薄膜的结构特征。采用647.1nm激发时，由于激发光能量接近于各样品的光学带隙，因而在样品中具有较大的穿透深度；而采用488nm激发时，激发光被样品表面强烈吸收，探测深度的变化造成了两种激发下Raman谱出现较大的差异。实验结果表明样品体内存在硅团簇结构，样品的自由表面存在一层浓度的缺陷层。这两种空间的不均匀性造成了高能激发时Raman谱的TO模频率和半高宽比低能激发时有大的红移和展宽。以上结果证明不同激发波长将造成Raman测量结果的差异。

Effect of SiO2 encapsulation on the nitrogen reorganization in GaNAs/GaAs single quantum well

Effects of SiO2, encapsulation and rapid thermal annealing (RTA) on the optical properties of GaNAs/GaAs single quantum well (SQW) were studied by low temperature photoluminescence (PL). A blueshift of the PL peak energy for both the SiO2-capped region and the bare region was observed. The results were attributed to the nitrogen reorganization in the GaNAs/GaAs SQW. It was also shown that the nitrogen reorganization was obviously enhanced by SiO2 cap-layer. A simple model [1] was used to describe the SiO2-enhanced blueshift of the low temperature PL peak energy.

Low power design in 100 MHz embedded SRAM

Low power design method is used in a 100MHz embedded SRAM. The embedded SRAM used in a FFT chip is divided into 16 blocks. Two-level decoders are used and only one block can be selected at one time by tristate control circuits, while other blocks are set stand-by. The SRAM cell has been optimized and the cell area has been minimized at the same time.