单晶硅衬底上Ge填埋层低温应力诱导重结晶制备多晶硅薄膜

本文采用电子束蒸发法,室温下在Si(400)的基片上生长含锗(Ge)填埋层的非晶硅薄膜,其结构为a-Si/Ge/Sisubstrate,并在真空中进行后续退火.采用Raman散射(Raman Scattering)、X射线衍射(X-ray Diffraction)、高分辨电子扫描显微镜(HRSEM)、光学显微镜和热重差热分析(DSC)等手段,研究退火后样品晶化特性和晶化机理.结果表明,室温下生长的含有250 nm Ge填埋层的生长态样品在400℃退火5h,薄膜基本全部实现晶化,并表现出明显的Si (111)择优取向.样品分别在400℃、500℃、600℃和700℃退火后薄膜的横向光学波的波峰均在519cm-1附近,半高宽大约为6.1 cm-1,且均在Si(111)方向高度择优生长.退火温度为600℃的样品对应的晶粒尺寸约为20 μm.然而,在相同的薄膜结构(a-Si/Ge/Si substrate)的前提下,当把生长温度提高到300℃时,温度高达到700℃退火时间5h后,薄膜依然是非晶硅状态.差热分析表明,室温生长的样品,在后续退火过程中伴随界面应力的释放,从而诱导非晶硅薄膜重结晶成多晶硅薄膜.     

SiNX覆盖层厚度对非晶In-Ga-Zn-O薄膜退火晶化的影响研究

采用射频磁控溅射在二氧化硅衬底上沉积一层厚度200 nm的非晶In-Ga-Zn-O(IGZO)薄膜,并在IGZO膜层上沉积厚度分别为20 nm、50 nm、60 nm、70 nm、90 nm的SiNX薄膜覆盖层,于350℃条件下N2气氛中退火1 h.采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、能量色散谱仪(EDS)对IGZO薄膜的微观结构及成分进行研究.研究结果表明,退火后无覆盖层的IGZO膜层仍为非晶状态,70 nm以上SiNX覆盖层下的IGZO薄膜不发生晶化.与此不同,20～60 nm的SiNX覆盖层下IGZO膜层与SiNX覆盖层的界面处存在纳米凸起柱,使IGZO薄膜与SiNX覆盖层的接触界面脱离,此厚度的SiNX覆盖层具有诱导非晶IGZO薄膜晶化的作用,IGZO膜层内部的晶粒直径约10 nm.成分分析结果表明,结晶处In原子含量增加,IGZO薄膜中In原子的局域团聚是IGZO薄膜发生晶化的原因.     

退火温度对Co掺杂CeO2稀磁氧化物薄膜的结构和铁磁性能的影响

采用溶胶-凝胶法,在Si(100)和石英玻璃衬底上制备了3;Co掺杂CeO2稀磁氧化物薄膜,研究了不同退火温度(500 ℃, 600 ℃和700 ℃)对薄膜结构和铁磁性能的影响.XRD 和拉曼光谱结果表明,随着退火温度的升高,薄膜晶化度明显提高.不同退火温度下的3;Co掺杂CeO2薄膜为多晶薄膜,且未破坏CeO2原有的结构.随着退火温度的升高, 晶粒尺寸逐渐增大.另外,3;Co掺杂CeO2薄膜在可见光范围内都有很好的透射率,其室温下的光学带隙Eg随退火温度增加而减小.超导量子干涉磁强计(SQUID)测量表明所有样品都表现出室温铁磁性,随着退火温度的升高,饱和磁化强度和矫顽力增大,700 ℃退火的薄膜具有最大的饱和磁化强度和最大的矫顽力.不同退火温度导致样品的磁性有了明显的变化,这源于磁性产生的不同机理.可见薄膜的结构最终影响了其铁磁性能.     

铝层厚度对铝诱导非晶硅薄膜晶化过程的影响

基于铝诱导非晶硅薄膜固相晶化方法,利用直流磁控溅射离子镀技术制备了Al/Si/…Al/Si/glass周期性结构的薄膜.采用真空退火炉对Al/Si多层薄膜进行了500℃退火实验,通过透射电子显微镜(TEM)分析了退火前、后Al/Si多层薄膜截面形貌的变化规律,并结合扩散过程探讨了铝层厚度对铝诱导非晶硅薄膜晶化过程的本质影响机理.研究结果表明:在铝诱导非晶硅薄膜固相晶化过程中,随退火过程的进行,Al、Si原子会沿Al/si层间界面进行互扩散运动且在Si层中达到临界浓度Cs的Al原子所在区域整体呈线形平行于Al/Si界面逐渐向铝原子扩散距离增大的方向推进;随着Al层厚度的增加,Al在Si层中达到临界浓度Cs的区域整体向前推进速度加快,已扩散区域产生硅初始晶核的数量也随之增大;随Al/Si层厚比的增大,虽因铝诱导而晶化的硅薄膜均为多晶态,但非晶硅薄膜在晶化过程中的生长晶面数量增多,同时硅晶粒的尺寸有所减小.     

退火时间对铝诱导非晶硅薄膜晶化过程的影响

基于铝诱导非晶硅薄膜固相晶化方法,利用直流磁控溅射离子镀技术制备了Al/ Si…Al/ Si/ glass周期性结构的薄膜.采用真空退火炉对Al/ Si多层薄膜进行了500℃退火实验,通过透射电子显微镜(TEM)分析了不同退火时间下Al/ Si多层薄膜截面形貌的变化规律,并结合扩散过程探讨了退火时间对铝诱导非晶硅薄膜晶化过程的影响机理.研究结果表明:在铝诱导非晶硅薄膜固相晶化过程中,在退火过程的初期,晶态硅薄膜的生长主要来源于因Al的存在而形成的硅初始品核数量增加的贡献.随退火时间的延长,晶态硅薄膜的生长主要是依靠临界浓度线已推进区域中未参与形核的硅原子扩散至初始品核位置并进行外延生长来实现的.经500℃退火1 h后,Al/ Si薄膜的截面形貌巾出现了沿Si(111)晶面生长的栾品组织.     

铝诱导非晶硅薄膜晶化动力学研究

为探讨其晶化过程及动力学机理,本文采用磁控溅射技术制备Al/Si薄膜,并利用快速光热退火制备微晶硅.通过采用不同的衬底温度及对铝膜进行退火处理,探究其晶化动力学过程.利用拉曼散射光谱(Raman)仪和X射线衍射(XRD)仪对薄膜进行性能表征.结果表明:退火及衬底加热均能在界面形成非共融的硅铝化合物;延长退火时间能使Al/Si界面充分扩散,达到成核条件.较大的铝晶粒及其择优取向,能有效改善铝诱导晶化效果.     

激光退火实现非晶Si晶化的成核势垒研究

采用脉冲激光烧蚀技术,在真空条件下沉积了一系列非晶Si薄膜,并对薄膜样品进行不同能量密度的激光退火处理.通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、Raman散射仪(Raman)等手段对退火后的薄膜进行形貌、晶态成分表征,确定了非晶Si薄膜晶化的激光能量密度阈值(85 mJ/cm2).结合激光晶化机理进行定量计算.结果显示:形成一个18 nm的Si晶粒所需要的能量,即成核势垒大小约为1.4×10-9 mJ.     

电场辅助铝诱导晶化非晶硅薄膜

以氢气稀释的硅烷和氢气为反应气体,利用PECVD法先在玻璃衬底上生长非晶硅薄膜,然后利用磁控溅射法在非晶硅薄膜上镀制铝膜,最后将镀有铝膜的非晶硅薄膜样品置于快速热处理炉中,在外加电场辅助条件下,在氮气气氛下对薄膜样品进行退火制备多晶硅薄膜.本论文研究了不同外加电场强度和退火时间对非晶硅薄膜晶化的影响.利用XRD、SEM和Raman等测试方法对薄膜样品的晶相结构、表面形貌和晶化程度进行了表征.实验结果表明,在外加横向电场辅助铝诱导晶化的条件下,非晶硅薄膜在500 ℃低温下成功地转化成多晶硅薄膜,并且随着横向电场强度的增大以及退火时间的延长,薄膜的晶化程度增强,晶粒尺寸增大.     

氧化锡纳米晶的合成与生长

采用水热法制备了氧化锡纳米晶,通过X射线衍射仪(XRD)和高分辨透射电镜(HRTEM)对氧化锡纳米晶样品的晶体结构、晶粒形貌进行了表征,并研究了氧化锡纳米晶生长和位错的产生机制.结果表明:在退火温度低于500 ℃时,晶粒生长依靠着周围的非晶成分而长大,纳米晶内部无晶格缺陷;退火温度高于500 ℃时,晶粒通过相互粘结的方式而长大.晶粒之间的不完全取向粘结导致了缺陷与位错的产生.     

PECVD沉积硅薄膜退火性质的分析

利用等离子体增强化学气相沉积(PECVD)制备硅薄膜,对硅薄膜进行退火处理.通过X射线衍射谱,拉曼光谱以及傅里叶变换红外吸收光谱,研究了退火温度在550～ 700℃范围内,硅薄膜退火过程中的生长特性.实验表明:多晶硅的晶粒尺寸并不随着退火温度的提高而持续增大,当退火温度在550～650℃范围内,硅薄膜始终表现出(111)方向的择优生长取向.当退火温度高于650℃时,氧原子活性增强,硅-氧键增加.对于存在应变、已结晶的薄膜,由于内部应力的累积,薄膜更容易随着退火温度的升高而脱落.     

Drawning-out Crystallization

Equations for the modelling of a continuous perfectly agitated crystallizer with drowning-out reaction are presented. Because the supersaturation of the solution is usually limited by the materials balance resulting from the technology used and the crystal growth rate is thus rather low, an agglomeration mechanism is considered in order to obtain larger particles. The results are demonstrated on an example of drawning-out of KCl by NaCl.     

药物结晶中的经典与非经典结晶路径

晶体的结晶路径分为经典结晶路径和非经典结晶路径。经典结晶路径往往涉及一些简单的化学结构,晶体的成核、生长是通过单体的依次添加实现的,经过长期研究,目前研究人员已对其有了较为深刻的理解并形成了一套相对完善的理论体系;但对于非经典的结晶路径,由于涉及复杂中间态粒子的形成和多步结晶过程,尚未获得全面、统一的理论支持。在药物结晶领域,有机分子构象自由度的引入增加了体系的复杂性,分子间弱的相互作用使得固态药物分子存在多晶型现象。由于药物的理化性质及生物利用度与其晶型息息相关,同时,药物结晶过程中出现的一些复杂中间态粒子往往会改变最终得到的药物晶型,因此迫切需要加强对药物晶体成核和生长路径的研究,以期发展能实现对药物晶体成核和生长过程主动控制的方法。本文简要综述了目前药物在溶液或熔体中结晶的经典与非经典结晶路径,包括奥斯特瓦尔德阶段定律、独立成核、交叉成核。从溶液化学的角度看,分子在浓溶液中会通过自组装形成结构合成子,成核与溶液中的生长单元、结构合成子密切相关。从分子水平上探索溶液中有关分子运动的信息、分析各体系下晶核与结构合成子之间的关系是区分两种结晶路径的关键所在,非经典结晶在药物结晶领域是机遇也是挑战。     

Crystallization tests bench

A model of an air-cooled tube (“air-heat saw”) installed in a laboratory tube furnace is presented. The setup (“crystallization tests bench”) allows easy regulation and simultaneous crystallization tests of a series of different crystallization parameters in crucible columns, enabling fast studies of obtaining crystals from materials with unknown crystallization parameters. The relationships between the crystallization rate and parameters of air-cooled tube are given and numerically analyzed. This method can also be applied in crucible or chamber furnaces.     

Crystallization of gel-derived glasses

The crystallization behaviors of gels, gel-derived glasses and melted glasses are reviewed, and comparisons are effected among the observed behaviors. These comparisons are related to the behavior expected on the basis of models for the nucleation frequency and crystal growth rate, as well as the anticipated differences in material characteristics among gels and the two types of glasses. Different temperature regimes are identified where different comparisons between melted and gel-derived materials are expected. It is concluded that a need exists for more definitive, detailed data on the crystallization behavior of gel-derived materials.     

Crystallization of copper sulphate

Results of the studies of copper sulphate pentahydrate batch crystallization in the temperature range from 70 down to 30 °C are presented. In some of the experiments, free sulphuric acid has been added. The metastable zone width, nucleation and growth kinetic parameters, as well as the system kinetic constant were determined and compared with the data published in the literature.     

Crystallization of Silver-Germanium Alloys under Microgravity I. Eutectic Crystallization in Hypoeutectic Alloy

The results of a study on eutectic crystallisation in the hypoeutectic alloy under different convection conditions are presented. Buoyancy driven convection was suppressed by processing the samples under microgravity conditions. The effect of convection level on the eutectic crystallisation is shown to be significant: In the absence of convection, the non-equilibrium level of the process is enhanced. The characteristic dependence of the particle size on the distance from the surface of a sample, observed on the minor phase of the eutectic, is discussed.     

Rapid Crystallization of L-Alanine on Engineered Surfaces using Metal-Assisted and Microwave-Accelerated Evaporative Crystallization

This study demonstrates the application of metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique to rapid crystallization of L-alanine on surface engineered silver nanostructures. In this regard, silver island films (SIFs) were modified with hexamethylenediamine (HMA), 1-undecanethiol (UDET), and 11-mercaptoundecanoic acid (MUDA), which introduced -NH(2), -CH(3) and -COOH functional groups to SIFs, respectively. L-Alanine was crystallized on these engineered surfaces and blank SIFs at room temperature and using MA-MAEC technique. Significant improvements in crystal size, shape, and quality were observed on HMA-, MUDA- and UDET-modified SIFs at room temperature (crystallization time = 144, 40 and 147 min, respectively) as compared to those crystals grown on blank SIFs. Using the MA-MAEC technique, the crystallization time of L-alanine on engineered surfaces were reduced to 17 sec for microwave power level 10 (i.e., duty cycle 100%) and 7 min for microwave power level 1 (duty cycle 10%). Raman spectroscopy and powder x-ray diffraction (XRD) measurements showed that L-Alanine crystals grown on engineered surfaces using MA-MAEC technique had identical characteristic peaks of L-alanine crystals grown using traditional evaporative crystallization.     

Crystallization of Silver — Germanium Alloys under Microgravity II. Primary Crystallization

Results of a study on primary crystallization in hypoeutectic and hypereutectic alloys under different convection conditions during solidification are presented. The conditions of suppressed buoyancy driven convection are assumed in the microgravity samples. The intensity of convection was shown to affect the resulting microstructures significantly. The number and the size of primary dendrites in both hypoeutectic samples was found to be comparable. In the microgravity processed hypoeutectic sample the primary dendrites exhibit a greater tendency to branch compared with the ground-based sample. In eutectic samples, a small amount of primary solid solution, due to the existence of an asymmetric coupled zone, was observed. In hypereutectic samples the number of primary germanium crystals is higher in the space sample. The influence of convection on the nucleation of primary crystals thus depends on the composition of such samples. In the case of the primary solid solution the effect of convection on the growth stage of crystallization appears. On the other hand, in the case of primary germanium the intensity of convection affects mainly the nucleation stage of crystallization. The influence of convection on the growth is only secondary. The reasons for such a difference are based on the transport requirements during the nucleation stage.     

Crystallization Kinetics of Sodium Perborate

Some basic physicochemical properties of aqueous sodium perborate solutions, essential in designing an effective control, were measured. The kinetics of primary nucleation was determined by the measurement of the metastable zone width. The differential method was applied for the determination of the crystal growth rate equation. It was found that the solubility and the nucleation rate constants are in very good agreement with the literature data whereas the parameters of the growth rate equation show an influence of the experimental conditions.     

Crystallization of recombinant cyclo-oxygenase-2

The integral membrane protein, prostaglandin H₂ synthase, or cyclo-oxygenase (COX), catalyses the first step in the conversion of arachidonic acid to prostaglandins (PGs) and is the target of nonsteroidal anti-inflammatory drugs (NSAIDs). Two isoforms are known. The constitutive enzyme, COX-1, is present in most tissues and is responsible for the physiological production of PGs. The isoform responsible for the elevated production of PGs during inflammation is COX-2 which is induced specifically at inflammatory sites. Three-dimensional structures of inhibitor complexes of COX-2, and of site variants of COX-2 which mimic COX-1, provide insight into the structural basis for selective inhibition of COX-2. Additionally, structures of COX-2 mutants and complexes with the substrate can provide a clearer understanding of the catalytic mechanism of the reaction. A crystallization protocol has been developed for COX-2 which reproducibly yields diffraction quality crystals. Polyethyleneglycol 550 monomethylether (MMP550) and MgCl₂ were systematically varied and used in conjunction with the detergent β-D-octylglucopyranoside (β-OG). As a result of many crystallization trials, we determined that the initial β-OG concentration should be held constant, allowing the salt concentration to modulate the critical micelle concentration (CMC) of the detergent. Over 25 crystal structures have been solved using crystals generated from this system. Most crystals belong to the space group P2₁2₁2, with lattice constants of a=180, b=134, c=120 Å in a pseudo body-centered lattice.