聚合物载体茂金属催化剂的制备及其烯烃聚合

本文采用苯乙烯、4-乙烯吡啶为单体，自由基聚合得到交联的苯乙烯-4-乙烯吡啶 共聚物。用上述共聚物为载体，表面处理后来负载均相茂锆Cp_2ZrCl_2形成聚合物载体茂锆催化剂。探讨了不同合成路线、合成条件对最终催化剂性能的影响。制备路线、表面处理及载体自身条件（含N量、交联度、粒度）是影响载体催化剂性能的重要因素。对这种新型的聚合物载体茂金属催化剂进行了深入的表征。XPS 及红外光谱分析推断形成了阳离子活性中心，并由此推出活性中心形成过程的假设。采用上述合成的聚合物载体茂金属催化剂催化乙烯均聚及乙烯/α-烯烃共聚合。探讨了不同聚合条件对催化活性、聚合物的性能的影响。该催化剂在高温下稳定，产品的堆密度随反应温度的升高而降低，分子量在50℃左右出现极大值，故采用50～60℃。Al/Zr 在500-800活性基本接近最大值，故Al/Zr取600-800。催化剂效率对催化剂浓度在4 * 10~（-5）M-20 * 10~（-5）M范围内不敏感。其聚合反应动力学曲线表明其聚合要比均相催化剂稳定得多。对乙烯均聚物的表征明所得PE含有一定支链（或侧链）；且分了量分布窄，分子量高。长链α-烯烃的加入，在一定范围内会对乙烯聚合有促进作用，α-烯烃深度继续增大，催化活性减小；聚合产物中α-烯烃单元的含量一直增加，聚合物粒子形态先逐渐长实，后疏松开裂，最后到无颗粒的弹性体状。共聚温度升高，使共聚单元含量有提高；不同α-烯烃对共聚反应不同，该载体催化剂顺序为1-辛烯＞1-己烯＞1-癸烯。对乙烯/1-己烯共聚物的~（13）C-NMR研究和溶剂萃取分级实验表明，共聚物中1-己烯分布均匀，几乎不存在聚集在一起的HHH片段，1-己烯单元几乎全部被以E-H-E序到的方式分隔开。

海南长臂猿(Nomascus hainanus)生境变化与潜在适宜生境研究

海南长臂猿(Nomascus hainanus)是世界上最濒危的灵长类之一，曾经广泛分 布于海南岛的低海拔地区，但现已濒临灭绝；生境变化被认为是它的主要致危因 素之一。为了探讨过去十多年中它们的生境变化原因和变化趋势，并在整个海南 岛内寻找它们的潜在生境，为制订保护计划提供帮助，我们利用遥感和地理信息 系统技术对海南长臂猿的生境状况进行了分析。海南长臂猿的高质量生境是成熟 的山地雨林和沟谷雨林，根据卫星遥感影像的识别能力，我们把成熟林定义为海 南长臂猿的适宜生境，通过对1991 年和2001 年拍摄的Landsat 卫星影像的解译， 我们分析比较了海南岛林地在这十年内的变化情况；通过这两个时期成熟林不同 大小斑块数量与面积的比较，以及成熟林平均斑块面积、斑块密度、斑块之间的 最近距离平均值、最大斑块所占面积等四个破碎化参数的计算，分析了海南长臂 猿高质量生境十年来的生境破碎化趋势；还对不同海拔带的人工林、天然林以及 成熟林的变化情况进行了比较；进而通过海南岛林地变化与社会和经济因素相关 性分析对海南长臂猿生境变化的原因进行了探讨。 结果显示，海南岛的成熟林面积由1991 年的157,927 hm2 减少到2001 年的 107,597 hm2，降低了32％；大小分别为10 hm2、25 hm2、50 hm2、100 hm2、200 hm2 的成熟林斑块的面积和数量都有所下降，并且自然保护区外的下降程度比自 然保护区内严重，省级自然保护区的下降程度比国家级自然保护区的严重。海南 岛现存最大的成熟林斑块位于鹦哥岭省级自然保护区。在这十年中，成熟林破碎 化程度加重，具体表现为平均斑块面积减少、斑块密度增加、斑块之间最近距离 平均值减小、最大斑块所占面积减少。在0-800 m 海拔带上，成熟林的下降比率 达到了36％，在这个海拔带上的人工林面积已远远大于天然林，在800-1400 m 海拔带上，成熟林的下降比率为23％，天然林的面积大于人工林。统计分析显 示当地的农业人口和农业总产值与成熟林的面积呈显著负相关(R =-0.534 P＜ 0.01；R =-0.512 P＜0.01)，同时农业人口与人工林和耕地面积呈显著正相关(R =0.611 P＜0.05；R =0.759, P＜0.05)，这说明成熟林下降与人口增长带来的耕地 扩张以及为了追求经济增长而大量种植人工林密切相关。而海南长臂猿曾经广泛分布在低海拔地区，这一带上大面积的生境丧失使它们的种群在短期内濒临灭 绝。 为了对未来海南长臂猿的生境保护和种群恢复提供帮助，我们利用地理信息 系统Arcgis 软件分析了海南长臂猿2001 年的生境空间分布格局，以成熟林的面 积和距离为指标预测了海南长臂猿的潜在适宜生境。结果显示，至2001 年，海 南岛除了白马岭、南高岭、抱龙、俄贤岭四个地方外，长臂猿的适宜生境多半分 布于自然保护区内；海南长臂猿目前唯一的分布地位于昌江县和白沙县交界的坝 王岭自然保护区，并且只活动于核心区内的一小块地区，此处有两段公路在使用 中，对海南长臂猿的保护不利。 根据上述研究结果，我们建议政府采取措施严格控制海南长臂猿潜在适宜生 境分布地的人口增长，切实执行天然林保护法，并设法恢复低海拔地带的天然植 被。建议在白马岭、南高岭、抱龙、俄贤岭建立四个新的自然保护区，把鹦哥岭 自然保护区从省级提升到国家级。在坝王岭自然保护区的低海拔地带种植本土速 生树种，将海南长臂猿活动区周围的小斑块与大斑块连接到一起，并设法消除该 保护区内两段公路对海南长臂猿的较大负面影响，提高海南长臂猿的生境质量并 扩大其活动范围。同时在自然保护区周边社区大力开展环境保护教育，努力使当 地人可以从生态系统保护中受益。

RECRYSTALLIZATION, IMPURITY MIGRATION AND OPTICAL ACTIVATION OF YB-IMPLANTED SILICON INDUCED BY RAPID THERMAL ANNEALING

The rapid thermal annealing temperature dependence of the recrystallization, Yb migration and its optical activation were studied for Yb-implanted silicon. For the annealing regime 800-1000-degrees-C, the Yb segregates both at the crystal/amorphous interface and at the surface, which is different from the usual segregation of Er at the crystal/amorphous interface, and the efficiency of optical activation also increases with annealing temperature. However, the amorphous layer regrows completely and no photoluminescence is observed after the annealing at 1200-degrees-C.

RADIATIVE RECOMBINATION IN N-TYPE AND P-TYPE GAAS COMPENSATED WITH LI

We report fundamental changes of the radiative recombination in a wide range of n-type and p-type GaAs after diffusion with the group-I element Li. These optical properties are found to be a bulk property and closely related to the electrical conductivity of the samples. In the Li-doped samples the radiative recombination is characterized by emissions with excitation-dependent peak positions which shift to lower energies with increasing degree of compensation and concentration of Li. These properties are shown to be in qualitative agreement with fluctuations of the electrostatic potential in strongly compensated systems. For Li-diffusion temperatures above 700-800-degrees-C semi-insulating conditions with electrical resistivity exceeding 10(7) OMEGA cm are obtained for all conducting starting materials. In this heavy Li-doping regime, the simple model of fluctuating potentials is shown to be inadequate for explaining the. experimental observations unless the number of charged impurities is reduced through complexing with Li. For samples doped with low concentrations of Li, on the other hand, the photoluminescence properties are found to be characteristic of impurity-related emissions.

WELL WIDTH DEPENDENCE OF THE EXCITON LIFETIME IN NARROW GAAS/GAALAS QUANTUM-WELLS

We have studied the radiative excitonic lifetime as a function of the well width in GaAs/GaAlAs quantum wells. An increasing lifetime with decreasing well width has been observed in very narrow and high quality GaAs/GaAlAs quantum wells, and attributed to the reduced overlap of the electron and hole wave functions and the increase of the exciton effective volume. This is the first observation of its kind in the conventional GaAs/GaAlAs quantum wells.

INVESTIGATION OF THE GROWN DIAMOND (100) SURFACE USING HIGH-RESOLUTION ELECTRON-ENERGY LOSS SPECTROSCOPY

The diamond (100) facets deposited at initial 1.0% CH4 have been investigated using high resolution electron energy loss spectroscopy (HREELS). The diamond (100) facets grown at 800-degrees-C are terminated by CH2 radicals, and there is no detectable frequency shift compared with the characteristic frequencies of molecular subgroup CH2. Beside the CH2 vibration loss, CH bend loss (at 140 meV) of locally monohydrogenated dimer is detected for the diamond (100) facets grown at 1000-degrees-C. Dosing the (100) facets grown at 800-degrees-C with atomic hydrogen at 1*10(-6) mbar, the loss peak at 140 meV appears. It is suggested that there are enough separately vacant sites and uniformly dispersed monohydrogenated dimers on (100) facets. This structure relaxes the steric repulsion between the adjacent hydrogen atoms during the diamond (100) surface growth.

A DUAL ION-BEAM EPITAXY SYSTEM

The design and characteristics of a dual ion beam epitaxy system (DIBE) are discussed. This system is composed of two beam lines, each providing a mass-separated ion beam converging finally with the other into the target chamber. The ions are decelerated and deposited on a substrate which can be heated to a temperature of 800-degrees-C. Currents of a few hundred microamperes are available for both beams and the deposit energies are in the range from tens to 1000 eV. The pressure of the target chamber during processing is about 7 x 10(-6) Pa. Preliminary experiments have proved that compound semiconductor materials such as GaN can be synthesized using the DIBE system.

DIRECT ION-BEAM DEPOSITION OF CARBON-FILMS ON SILICON IN THE ION ENERGY-RANGE OF 15-500 EV

Direct ion beam deposition of carbon films on silicon in the ion energy range of 15-500 eV and temperature range of 25-800-degrees-C has been studied. The work was carried out using mass-separated C+ and CH3+ ions under ultrahigh vacuum. The films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and transmission electron diffraction analysis. In the initial stage of the deposition, carbon implanted into silicon induced the formation of silicon carbide, even at room temperature. Further carbon ion bombardment then led to the formation of a carbon film. The film properties were sensitive to the deposition temperature but not to the ion energy. Films deposited at room temperature consisted mainly of amorphous carbon. Deposition at a higher temperature, or post-deposition annealing, led to the formation of microcrystalline graphite. A deposition temperature above 800-degrees-C favored the formation of microcrystalline graphite with a preferred orientation in the (0001) direction. No evidence of diamond formation in these films was observed.

CONSTRUCTION AND APPLICATIONS OF A DUAL MASS-SELECTED LOW-ENERGY ION-BEAM SYSTEM

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass-resolved low-energy ion beams which merge at the target with an incident energy range 50-25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100-mu-A/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3-0.5 x 2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1 x 10(-7) Pa and a typical pressure of 5 x 10(-6) Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the target can be heated to 800-degrees-C and scanned mechanically with an electronic scanning control unit. The dual beam system has been used to grow GaN using a Ga+ and a N+ beam, and to study the oxygen and hydrogen ion beam bombardment effects during carbon ion beam deposition. The results showed that the simultaneous arrival of two beams at the target is particularly useful in compound formation and in elucidation of growth mechanisms.

Aggregation and precipitation in high dose as ion implanted Ge0.5Si0.5 alloy

Thermally stimulated redistribution and precipitation of excess arsenic in Ge0.5Si0.5 alloy has been studied by X-ray photoelectron spectroscopy (XPS), cross sectional transmission electron microscopy (XTEM) and X-ray energy disperse spectrometry (EDS). Samples were prepared by the implantation of 6 X 10(6) As+ cm(-2) and 100 keV with subsequent thermal processing at 800 degrees C and 1000 degrees C for 1 h. The XPS depth profiles from the implanted samples before and after the thermal annealing indicate that there is marked redistribution of the elements in heavily arsenic-implanted Ge0.5Si0.5 alloys during the annealing, including: (1) diffusion of As from the implanted region to the surface; (2) aggregation of Ge in the vicinity of the surface. A high density of precipitates was observed near the surface which were by XTEM and EDS identified as an arsenide. It is suggested that most of the implanted As in Ge0.5Si0.5 alloy exists in the form of GeAs.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

Diamond growth by carbon ion implantation of diamond

Medium energy (5-25 keV) C-13(+) ion implantation into diamond (100) to a fluence ranging from 10(16) cm(-2) to 10(18) cm(-2) was performed for the study of diamond growth via the approach of ion beam implantation. The samples were characterized with Rutherford backscattering/channelling spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and Auger electron spectroscopy. Extended defects are formed in the cascade collision volume during bombardment at high temperatures. Carbon incorporation indeed induces a volume growth but the diamond (100) samples receiving a fluence of 4 x 10(17) to 2 x 10(18) at. cm(-2) (with a dose rate of 5 x 10(15) at. cm(-2) s(-1) at 5 to 25 keV and 800 degrees C) showed no He-ion channelling. Common to these samples is that the top surface layer of a few nanometers has a substantial amount of graphite which can be removed by chemical etching. The rest of the grown layer is polycrystalline diamond with a very high density of extended defects.

Stress and resistivity controls on in situ boron doped LPCVD polysilicon films for high-Q MEMS applications

The simultaneous control of residual stress and resistivity of polysilicon thin films by adjusting the deposition parameters and annealing conditions is studied. In situ boron doped polysilicon thin films deposited at 520 ℃ by low pressure chemical vapor deposition (LPCVD) are amorphous with relatively large compressive residual stress and high resistivity. Annealing the amorphous films in a temperature range of 600-800 ℃ gives polysilicon films nearly zero-stress and relatively low resistivity. The low residual stress and low resistivity make the polysilicon films attractive for potential applications in micro-electro-mechanical-systems (MEMS) devices, especially in high resonance frequency (high-f) and high quality factor (high-Q MEMS resonators. In addition, polysilicon thin films deposited at 570 ℃ and those without the post annealing process have low resistivities of 2-5 mΩ·cm. These reported approaches avoid the high temperature annealing process (> 1000℃), and the promising properties of these films make them suitable for high-Q and high-f MEMS devices.

GaAs基MOEMS波长可调谐滤波器的设计和理论模拟

采用传输矩阵理论和结合悬臂梁的电学一机械模型对GaAs基1.55 μm微光电机械系统(MOEMS)波长可调谐滤波器的光学和电学特性进行了深入的对比分析和研究.结果表明,采用800 nm厚的空气腔可以实现滤波器波长的调谐范围为100 nm,所需最大反向偏压为4 V,波长的调谐速率可以达到1.83 MHZ.