Growth-Parameter Spaces and Optical Properties of Cubic Boron Nitride Films on Si(001)

Cubic boron nitride (c-BN) films were deposited on Si(001) substrates in an ion beam assisted deposition (IBAD) system under various conditions, and the growth parameter spaces and optical properties of c-BN films have been investigated systematically. The results indicate that suitable ion bombardment is necessary for the growth of c-BN films, and a well defined parameter space can be established by using the P/a-parameter. The refractive index of BN films keeps a constant of 1.8 for the c-BN content lower than 50%, while for c-BN films with higher cubic phase the refractive index increases with the c-BN content from 1.8 at chi(c) = 50% to 2.1 at chi(c) = 90%. Furthermore, the relationship between n and rho for BN films can be described by the Anderson-Schreiber equation, and the overlap field parameter gamma is determined to be 2.05.

Comparison and combination of several stress relief methods for cubic boron nitride films deposited by ion beam assisted deposition

Cubic boron nitride (c-BN) films were prepared by ion beam assisted deposition (IBAD) technique, and the stresses were primary estimated by measuring the frequency shifts in the infrared-absorption peaks of c-BN samples. To test the possible effects of other factors, dependencies of the c-BN transversal optical mode position on film thickness and c-BN content were investigated. Several methods for reducing the stress of c-BN films including annealing, high temperature deposition, two-stage process, and the addition of a small amount of Si were studied, in which the c-BN films with similar thickness and cubic phase content were used to evaluate the effects of the various stress relief methods. It was shown that all the methods can reduce the stress in c-BN films to various extents. Especially, the incorporation of a small amount of Si (2.3 at.%) can result in a remarkable stress relief from 8.4 to similar to 3.6 GPa whereas the c-BN content is nearly unaffected, although a slight degradation of the c-BN crystallinity is observed. The stress can be further reduced down below I GPa by combination of the addition of Si with the two-stage deposition process. (c) 2008 Elsevier B.V. All rights reserved.

Effects of crystalline quality on the phase stability of cubic boron nitride thin films under medium-energy ion irradiation

To investigate the effect of radiation damage on the stability and the compressive stress of cubic boron nitride (c-BN) thin films, c-BN films with various crystalline qualities prepared by dual beam ion assisted deposition were irradiated at room temperature with 300 keV Ar+ ions over a large fluence range up to 2 x 10(16) cm(-2). Fourier transform infrared spectroscopy (FTIR) data were taken before and after each irradiation step. The results show that the c-BN films with high crystallinity are significantly more resistant against medium-energy bombardment than those of lower crystalline quality. However, even for pure c-BN films without any sp(2)-bonded BN, there is a mechanism present, which causes the transformation from pure c-BN to h-BN or to an amorphous BN phase. Additional high resolution transmission electron microscopy (HRTEM) results support the conclusion from the FTIR data. For c-BN films with thickness smaller than the projected range of the bombarding Ar ions, complete stress relaxation was found for ion fluences approaching 4 x 10(15) cm(-2). This relaxation is accompanied, however, by a significant increase of the width of c-BN FTIR TO-line. This observation points to a build-up of disorder and/or a decreasing average grain size due to the bombardment. (c) 2005 Elsevier B.V. All rights reserved.

Investigation of Mn-implanted n-Si by low-energy ion beam deposition

Mn ions were implanted to n-type Si(0 0 1) single crystal by low-energy ion beam deposition technique with an energy of 1000 eV and a dose of 7.5 x 10(17) cm(-2). The samples were held at room temperature and at 300degreesC during implantation. Auger electron spectroscopy depth profiles of samples indicate that the Mn ions reach deeper in the sample implanted at 300degreesC than in the sample implanted at room temperature. X-ray diffraction measurements show that the structure of the sample implanted at room temperature is amorphous while that of the sample implanted at 300degreesC is crystallized. There are no new phases found except silicon both in the two samples. Atomic force microscopy images of samples indicate that the sample implanted at 300degreesC has island-like humps that cover the sample surface while there is no such kind of characteristic in the sample implanted at room temperature. The magnetic properties of samples were investigated by alternating gradient magnetometer (AGM). The sample implanted at 300degreesC shows ferromagnetic behavior at room temperature. (C) 2004 Elsevier BN. All rights reserved.

Recent advances in synthesis and properties of cubic boron nitride films

Cubic boron nitride (c-BN) attracts widespread interest as a promising material for many potential applications because of its unique physical and chemical properties. Since the 1980's the research in c-BN thin films has been carried out, which reached its summit in the mid of 1990's, then turned into a downward period. In the past few years, however, important progress was achieved in synthesis and properties of cubic boron nitride films, such as obtaining > 1 mu m thick c-BN films, epitaxial growth of single crystalline c-BN films, and advances in mechanics properties and microstructures of the interlayer of c-BN films. The present article reviews the current status of the synthesis and properties of c-BN thin films.

Study of GaN thin films grown on intermediate-temperature buffer layers by molecular beam epitaxy

A detailed characterisation study of GaN thin films grown by rf-plasma molecular beam epitaxy on intermediate-temperature buffer layers (ITBL) was carried out with Hall, photoluminescence (PL) and deep-level transient Fourier spectroscopy (DLTFS) techniques. The unique feature of our GaN thin films is that the GaN epitaxial layers are grown on top of a double layer that consists of an ITBL, which is grown at 690 degreesC, and a conventional low-temperature buffer layer deposited at 500 degreesC. It is observed that the electron mobility increases steadily with the thickness of the ITBL, which peaks at 377 cm(2)V(-1)S(-1) for an ITBL thickness of 800 nm. The PL also demonstrated systematic improvements with the thickness of the ITBL. The DLTFS results suggest a three-order-of-magnitude reduction in the deep level at E-c-0.40 eV in the device fabricated with the GaN films grown on an ITBL thickness of 1.25 mum in comparison with the control device without an ITBL. Our analyses indicate that the utilization of an ITBL in addition to the conventional low-temperature buffer layer leads to the relaxation of residual strain within the material, resulting in an improvement in the optoelectronic properties of the films. (C) 2002 Elsevier Science BN. All rights reserved.

RBAC实施中国墙策略及其变种的研究

中国墙策略的目的是防止在有竞争关系的企业间访问信息导致的利益冲突.著名的中国策略模型包括Brewer等人提出的BN模型和Sandhu提出的基于格访问控制模型实施的中国墙模型.然而这些模型都存在严重的缺陷:灵活性不够或者实施不方便.RBAC是目前主流的访问控制模型,该模型的特点是策略中立.基于RBAC模型全面研究了实施中国墙策略及其各种变种策略的方法,利用角色体系和RBAC的约束机制,给出了具体的构造方法,讨论了这些构造中约束的形式化描述方法.与传统的中国墙模型相比,更加灵活,并可在支持RBAC的系统中直接实施.

PBT/HIPS枘混体系的结构与性能及生物隆解聚合物结晶性能的研究

以过氧化二异丙苯(DCP)为引发剂，甲基丙烯酸缩水甘油醋(GMA)为活性单体对HIPS进行熔融接枝，制得了功能化的高抗冲苯乙烯(HIPS－g－GMA）。比较HIPS－g－GMA和纯的HIPS的红外谱图，可以看到在HIPS－g－GMA的谱图上出现了一个新的吸收峰，即1730cm~(-1)处的C=O的伸缩振动吸收峰，它为接枝的GMA中的醋基基团的特征峰，因此可以确定GMA己经接枝到HIPS上。能谱分析也提供了相似的结论。同时研究了单体浓度和DCP用量对产物接枝率的影响。用化学滴定方法测定了接枝物的接枝率。随着GMA量的增加，接枝率也随之增加，当GMA用量超过14％时，接枝率趋于平缓；接枝率随DCP量增加而增加。采用DSC、SEM, WAXD, DMA及力学性能等方法和手段研究PBTIHIPS和PBT/HIPS-g-GMA二元共混体系的结晶、形态结构、动态力学性能及力学性能随组成的变化。当PBT为分散相，在增容体系中的PBT出现了分级结晶现象，结晶温度降低，这是由于分散相更为精细的结果。DMA结果表明，在PBTIHIP S-g-GMA体系中由于发生了化学反应，有接枝共聚物生成，体系中两个聚合物的Tg松弛均出现了较明显的降低，增容后体系的力学性能有显著提高。采用DSC, SEM, DMA及力学性能等方法和手段研究PBT/HIPS/HIPS-g-GMA三元共混体系的结构与性能。结果表明PBT无论是分散相还是连续相，HIPS-g-GMA的作用表现为：（1）对PBTIHIPS体系的熔融和结晶行为产生了明显的影响，使PBT的结晶速率变慢，结晶度降低，结晶尺寸分布变宽，结晶完善性变差；（2）改善了共混体系的相容性。未增容体系的形态结构为锐型界面，分散相粒子同基材相连接处清晰缝隙表明两组分间界面粘接很差，为典型的不相容两相形态结构；而加入功能化接枝物的体系的分散相粒子明显变小且分布均匀，甚至难以分辨两相结构的界面；（3）提高了体系的力学性能。在多官能团单体存在下，辐照对PBTIHIPS产生影响。（1）对共混体系的熔融和结晶行为产生影响，使共混体系中的PBT的熔点降低，熔程变宽，结品度下降，结晶速率变慢，结晶尺寸分布变宽，结晶完善性变差；（2）辐射引发多官能团单体反应，使体系的两个Tg松弛发生内移，表明体系的相容性得到改善；（3）当PBT为连续相时，辐射引发的多官能团单体反应对体系的形态结构影响不如化学增溶剂HIPS-g-GMA的效果显著，含有TMPTA的体系的形态结构要好于TAIL o当PBT为分散相，体系的形态结构变化很大，分散相尺寸明显变下小，且分布均匀；（4）辐射改性能提高PBT为分散相的共混体系的力学性能。利用DSC研究了不同成核剂对生物降解聚合物PHBV的结晶性能的彩响。结果表明：（1)添加的成核剂均能影响PHBV的结晶和熔融行为，提高PHBV的结晶速率和使PHBV的结晶更加完美；（2）所有的成核剂均能降低PHBV的结晶自由能；（3）成核剂对PHBV的影响依次为BN, talc, Tb_2O_3和La_2O_3。

碱土金属与不对称变色酸多卤代双偶氮氯膦类试剂的新显色反应的研究及反应机理的探讨

本文研究了碱土金属锶、钙与新型显色剂2-(4-氯－2－苯膦酸)－7－(2, 6-二溴－4－氯苯基)－1，8－二羟基－3，6－萘二磺酸(简称DBC－偶氮氯膦)的显色反应及其在分析上的应用。研究结果提出了两种高选择性的测定锶、钙的新方法。本文研究出的新分析方法在实际样品的分析中收到了令人满意的结果。本文还研究了碱土金属元素与五种多卤代偶氮氯膦类试剂的显色反应性能，对反应的机理和配合物的结构方面的问题作了一些研究及探讨。通过对几种多卤代偶氮氯膦类试剂与碱土金属显色反应的研究。筛选出较好的显色剂，并对寻求更好的碱土元素显色剂提出了一些建议。本论文分五个部分，现分述如下：1. 一种新的测定锶的高选择性光度法的研究：本文利用武汉大学化学系最近合成的新显色剂DBC－偶氮氯膦进行了锶显色反应及其在分析上应用的研究。研究结果表明：锶与DBC－偶氮氯膦在酸性条件下可形成一种十分稳定的兰色配合物，该配合物在630nm波长处有最大吸收。摩尔吸光系数为ε＝6.0*10~4l·mol~(-1)·cm~(-1)配合物中Sr:DBC－偶氮氯膦=1:2。在丙酮、Na_2SO_4、EDTA等存在下，并采用双波等分光光度，有效地消除了钡、钙的干扰及在此条件下其他共存的三十余种离子的干扰。本文还进行了显色酸度，配合物稳定性的试验，利用本方法进行了海水，氧化镁试剂和硅铁锶合金中锶的直接测定，结果较为满意，与其他方法进行对照，结果相符，加入试验的回收率一般为99－102％。方法灵敏，简便，选择性好，快速和不需要任何分离过程。2. DBC－偶氮氯膦与钙显色反应的研究及其在高纯氧化钇中钙的测定的应用：本文利用DBC－偶氮氯膦进行了钙显色反应的研究。并将此显色反应于高纯氧化钇(Y_2O_3>99.99％～99.999％)中的ppm级的钙的测定。本文进行了钙与DBC－偶氮氯膦生成的配合物的吸收光谱，显色反应酸度范围，显色剂的用量，配合物的稳定性，配合物的组成及干扰组分的消除等方面的研究。研究结果表明：钙在弱碱性条件下可与DBC－偶氮氯膦形成一种兰色的配合物，该配合在625nm处有最大吸收。表观摩尔吸光系ε＝2.8*10~4l·mol~(-1)·cm~(-1)。配合物的组成是Ca:DBC－偶氮氯膦＝1:1。在DTPA－Zn存在下较大量的氧化钇和铁等三十余种离子不干扰测定。方法线性范围较宽。配合使用偶氮氧化BN－TBP(磷酸三丁酯)－环乙烷体系进行一次简单的粗分离后，成功地测定了高纯氧化钇中的微量钙，此方法是目前已见报导的分光光度法中，在测定高纯氧化钇中微量钙方面最简便的方法。用此方法测定的削钢中微量钙，也得到满意的结果，加入试验回收率较好。方法灵敏、简易、选择性较好。3. 新型显色剂DBC－偶氮氯膦的提纯和鉴定：本文提出了一种分离提纯新型稀土显色剂DBC-偶氮氯膦的方法。通过利用国产离心薄层层析仪。在硅胶G和CaSO_4做的薄板上，以甲醇和二氯甲烷作展开剂，分离了杂质。然后用PMBP环乙烷萃取了其中引入的钙，提纯后的试剂经过分析鉴定，纯度在94％以上，其中钙量低于空白值(原子吸收法测定)。方法产率在90％以上，用提纯后的试剂进行了红外光谱，元素分析，热失重分析，得到了试剂组成及结构，与试剂合成单位所提出的一样，并用层析法，光度法检查了纯度，比较了粗品与纯品的吸收曲线和对碱土的灵敏度。4. 碱土金属与多卤代偶氮氯膦类试剂的显色反应的研究：本文研究了钙、锶、钡分别与五种多卤代偶氮氯膦类试剂(2，6－二溴－4－氯偶氮氯膦，2，4，6－三溴偶氮氯膦，2，6－二溴－4－磺酸偶氮氯膦。2，4，6－三氯偶氮氯膦，2，6－二溴－4－硝基偶氮氯膦)显色反应。记录了各显色反应的吸收光谱。试验了各元素与各种试剂显色的酸度范围，测定了各种配合物的组成，进行了各种试剂对碱土元素的选择性的试验。比较了几种试剂对碱土的灵敏度。研究结果表明：TB－偶氮氯膦和DBC－偶氮氯膦是较好的碱土试剂，从灵敏度，选择性和显色酸度来看，这两个试剂都优于其他几种试剂。DBN－偶氮氯膦性能较差。研究还指出，钙只有在碱性条件下才能与这几种试剂较好地显色。酸性条件下碱土元素与几种试剂都形成1:2配合物。钙在碱性条件下与试剂形成的是1:1配合物。本文对试剂结构与其性能方面的关系进行了讨论。对进一步合成新的碱土试剂提出了一些看法。5.碱土金属与DBC－偶氮氯膦显色反应机理及配合物结构的探讨：本文研究了DBC－偶氮氯膦在不同酸度下的存在形式，质子化情况及反应中的质子释放情况。测定了钙、锶、钡与其形成的配合物的稳定常数。利用红外光谱、激光拉曼光谱、核磁共振谱等对所生成配合物的结构进行了研究。根据实验结果和有关的分子轨道理论。配位场理论对配合物的结构进行了讨论。提出配合物的结构式及空间构型。本文还对显色反应机理和配合物成键情况进行了初探。本文的研究工作。为进一步开展水溶液中配合物结构的研究和显色反应机理的研究起了抛砖引玉的作用。

立方氮化硼薄膜制备与性质研究新进展

立方氮化硼（c-BN）具有优异的物理和化学性质,在力学、光学和电子学等方面有着广泛的应用前景.自上世纪80年代开始,低压沉积c-BN薄膜的研究迅速发展,到90年代中期达到高潮,随后进展缓慢,c-BN薄膜研究转入低潮.近年来,c-BN薄膜研究在几方面取得了突破,如获得与衬底粘附良好、厚度超过1μm的c-BN厚膜;成功实现了c-BN单晶薄膜的异质外延生长;此外,在c-BN薄膜力学性质和过渡层微结构研究方面也取得了进展.本文主要评述最近几年c-BN薄膜研究在以上几方面取得的最新进展.

升华法生长AlN体单晶初探

研究了高温升华法（PVT）生长AlN体单晶的技术和材料的性质.使用陶瓷BN坩埚,加热温度约在1900℃左右,生长结果为AlN晶须或致密多晶,难以生长出较大的AlN晶粒.用钨坩埚加热生长温度达到2200℃左右时,在AlN陶瓷片和6H-SiC片上生长了直径22mm的AlN晶体,最大的晶粒尺寸长10mm、直径5mm.利用X射线粉末衍射分析了几种不同AlN样品的结构和组成.讨论了PVT法生长AlN晶体所涉及的化学热力学过程和现象.

异质外延立方氮化硼薄膜的微结构研究

利用离子束辅助沉积技术在金刚石薄膜衬底上制备立方氮化硼薄膜,傅立叶变换红外谱的结果表明,在高度(001)织构金刚石薄膜衬底上沉积的立方氮化硼薄膜是纯的立方相,而在多晶金刚石薄膜衬底上制备的立方氮化硼薄膜中还含少量的六角氮化硼.高分辨透射电镜的分析表明,在金刚石晶粒上异质外延的c-BN直接成核于金刚石衬底,界面没有六角氮化硼过渡层;而在含有大量缺陷的晶粒边界,存在六角氮化硼的成核与生长.

Effects of silicon incorporation on composition, structure and electric conductivity of cubic boron nitride thin films

We have achieved in-situ Si incorporation into cubic boron nitride (c-BN) thin films during ion beam assisted deposition. The effects of silicon incorporation on the composition, structure and electric conductivity of c-BN thin films were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrical measurements. The results suggest that the content of the cubic phase remains stable on the whole with the incorporation of Si up to a concentration of 3.3 at.%, and the higher Si concentrations lead to a gradual change from c-BN to hexagonal boron nitride. It is found that the introduced Si atoms only replace B atoms and combine with N atoms to form Si-N bonds, and no evidence of the existence of Si-B bonds is observed. The resistance of the Si-doped c-BN films gradually decreases with increasing Si concentration, and the resistivity of the c-BN film with 3.3 at.% Si is lowered by two orders of magnitude as compared to undoped samples.

维生素 C 二步发酵中伴生菌的研究

在维生素 C 二步发酵中，第二步发酵为混菌发酵。氧化葡萄糖酸杆菌为产酸菌，巨大芽孢杆菌为伴生菌。巨大芽孢杆菌和氧化葡萄糖酸杆菌纯化培养的生物学特性不同于其在混菌培养中的生物学特性。种子液的组成和生物量影响 2－酮基－L－古龙酸的合成。在发酵过程中，采采取适宜的调控措施有利于产酸。Na~+和 H~+可诱导对数生长期的巨大芽孢杆菌发生自溶，Na~+诱导的自溶作用可被 Ca~++抑制。200mM Na~+ 可抑制 2－酮基－L－古龙酸的合成。H~+可抑制稳定期的巨大芽孢杆菌衰亡。本文建立了简便易行的巨大芽孢杆菌的筛选模型，并获得两株耐低 pH 和 2－酮基－L－古龙酸的突变株 Bn 和 B5，与氧化葡萄糖酸杆菌混合培养，发酵转化率可分别提高 4.1%和 3.8%。Bn和 B5 生长的最适 pH 值为 6.0～8.0，可促进氧化葡萄糖酸杆菌的生长，表现为延迟期缩短，稳定期延长。苏云金芽孢杆菌 B529 作为伴生菌与氧化葡萄糖酸杆菌组成的新混合菌系，具有抗污染、稳定高产的特性。B529 和巨大芽孢杆菌释放的分子量在 30～50kDa 和 >100kDa 的组份均可促进氧化葡萄糖酸杆菌产酸，其中 30～50kDa 的组份是促进产酸的关键物质。二菌所释放的活性物质经 Sephadex G-150 柱层析呈现不同的洗脱图谱，说明二菌释放的活性物质成分可能不同。B529 的培养上清液可增强氧化葡萄糖酸杆菌的细胞酶活力和 L－山梨糖胶氢酶的活性。新混全菌系的最适发酵条件被确定，在4M~3 发酵罐中连续被批发酵，平均糖酸转化率提高了 6.4%，发酵周期缩短 7.3h。